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Title:
AN ANTENNA FOR RADIO FREQUENCY IDENTIFICATION SYSTEMS, METHODS OF CONFIGURING SAME, AND A RADIO FREQUENCY IDENTIFICATION READER
Document Type and Number:
WIPO Patent Application WO/2011/015511
Kind Code:
A1
Abstract:
The present invention provides an antenna for an RFID system, including a conductor line (8), wherein the conductor line includes at least two loop parts (80, 82) and at least one connecting part (81). Successive loop parts (80,82) are connected by a connecting part (81). The connecting part is disposed in such a manner as to be separated from said loop. Although the loop circumference is in the order of a wavelength the connecting part (81) ensures the current on the loop parts (80, 82) to flow in the same diretion. Thus, the antenna can attain a sufficient size in a UHF RFID system and satisfy the reading distance requirement for a near-field UHF RFID reader. Alternative solutions for the connecting part are detour lines and phase shifting devices.

Inventors:
YU, Dan (Room 2-6-1403, Furongjie 15Jiamei Fengshang Zhongxin Chaoyang District, Beijing 2, 10010, CN)
YUAN, Yong (Room 202, Unit 5 Building 5 Juzhen Residential,Changping District, Beijing 8, 10220, CN)
HORST, Dieter (Nelkenweg 6a, Cadolzburg, 90556, DE)
Application Number:
EP2010/061038
Publication Date:
February 10, 2011
Filing Date:
July 29, 2010
Export Citation:
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Assignee:
SIEMENS AKTIENGESELLSCHAFT (Wittelsbacherplatz 2, München, 80333, DE)
YU, Dan (Room 2-6-1403, Furongjie 15Jiamei Fengshang Zhongxin Chaoyang District, Beijing 2, 10010, CN)
YUAN, Yong (Room 202, Unit 5 Building 5 Juzhen Residential,Changping District, Beijing 8, 10220, CN)
HORST, Dieter (Nelkenweg 6a, Cadolzburg, 90556, DE)
International Classes:
H01Q7/00; G06K7/00; H01Q1/22; H01Q11/14; H01Q21/20
Domestic Patent References:
2007-07-26
2001-06-14
Foreign References:
US2311872A1943-02-23
GB490383A1938-08-15
JP2009171313A2009-07-30
JPS60208108A1985-10-19
JP2003099730A2003-04-04
EP1672732A12006-06-21
US6147655A2000-11-14
EP2009742A12008-12-31
US20080048867A12008-02-28
Other References:
"Couplers, hybrids and directional couplers" In: Ian Hickman: "Practical Radio-Frequency Handbook" 3 September 1997 (1997-09-03), Newnes , Oxford , XP002606922 ISBN: 9780750634472 , pages 49-57 page 53, line 17 - page 54, line 21 figure 5.4d
Attorney, Agent or Firm:
SIEMENS AKTIENGESELLSCHAFT (Postfach 22 16 34, München, 80506, DE)
Download PDF:
Claims:
CLAIMS

1. An antenna for a radio frequency identification system, comprising a conductor line, the conductor line comprising at least two loop parts and at least one connecting part, wherein: said loop parts, of which there are at least two, are disposed in one loop and are spatially discontinuous;

in every two successive loop parts, the end of the first loop part and the beginning of the second loop part are connected by a connecting part, the connecting part being disposed in such a manner as to be separate from said loop;

when an excitation signal is fed into said conductor line, said loop parts, of which there are at least two, and the connecting parts, of which there is at least one, generate an excitation current, and the excitation current of the loop parts, of which there are at least two, then generates a magnetic field.

2. The antenna as claimed in claim 1, wherein:

said excitation current has opposite phases in every two successive loop parts;

in every two successive loop parts, the direction from the beginning to the end of the first loop part is opposite to the direction from the beginning to the end of the second loop part; said excitation current has the same direction in at least two loop parts.

3. The antenna as claimed in claim 2, wherein:

said excitation current has a phase reversal point in every connecting part.

4. The antenna as claimed in claim 3, wherein:

the phase reversal point is located between the two end points of the connecting part.

5. The antenna as claimed in claim 3, wherein:

the phase reversal point is an end point of the connecting part .

6. The antenna as claimed in claim 3, wherein:

the phase reversal point is one end point of the connecting part or is located between the two end points of the connecting part.

7. The antenna as claimed in claim 2, wherein:

said conductor line comprises an even number of connecting parts;

every connecting part of said even number of connecting parts is folded, and every folded connecting part has at least two sections;

every two folded connecting parts are disposed in parallel for at least one section;

said excitation current has the opposite direction in every pair of sections which are disposed in parallel.

8. The antenna as claimed in claim 1, wherein:

said excitation current has the same phase in every two successive loop parts;

in every two successive loop parts, the direction from the beginning to the end of the first loop part and the direction from the beginning to the end of the second loop part are the same ;

said excitation current has the same direction in at least two loop parts.

9. The antenna as claimed in claim 8, wherein:

said excitation current has two phase reversal points in every connecting part.

10. The antenna as claimed in claim 11, wherein:

said two phase reversal points are the two end points of the connecting part.

11. The antenna as claimed in claim 11, wherein:

said two phase reversal points are located between the two end points of the connecting part.

12. The antenna as claimed in claim 11, wherein:

one of the two phase reversal points is an end point of the connecting part, and the other phase reversal point is located between the two end points of the connecting part.

13. The antenna as claimed in claim 8, wherein:

said connecting parts, of which there is at least one, is folded in every connecting part, and every folded connecting part comprises at least one pair of sections which are disposed in parallel;

said excitation current has the opposite direction in every pair of sections which are disposed in parallel.

14. The antenna as claimed in claim 1, wherein:

the terminal point of said conductor line is open- circuited.

15. The antenna as claimed in claim 14, wherein;

said loop parts, of which there are at least two, and said connecting parts, of which there is at least one, are constructed from one section of conductor, one end point of which is connected to a signal feed-in point for feeding in said excitation signal, the other end point of the section of conductor being open-circuited.

16. The antenna as claimed in claim 14, wherein;

said conductor line comprises four or more loop parts and two or more connecting parts;

said four or more loop parts and said two or more connecting parts are constructed from two sections of conductor, and every section of the conductor comprises two or more loop parts and one or more connecting parts, wherein, one terminal point of every section of the conductor is connected to a signal feed-in point for feeding in the excitation signal.

17. The antenna as claimed in claim 1, wherein:

the terminal point of said conductor line is short- circuited.

18. The antenna as claimed in claim 17, wherein:

said loop parts, of which there are at least two, and said connecting parts, of which there is at least one, are constructed from a section of conductor whose two end points are separately connected to a signal feed-in point for feeding in the excitation signal.

19. The antenna as claimed in claim 17, wherein:

said loop parts, of which there are at least two, and said connecting parts, of which there is at least one, are constructed from a section of conductor, one end point of which is connected to a signal feed-in point for feeding in the excitation signal, the other end point of the connector being grounded.

20. The antenna as claimed in claim 1, wherein:

said loop parts, of which there are at least two, and said connecting parts, of which there is at least one, are disposed on a base plate, and said connecting parts, of which there is at least one, are disposed inside the loop.

21. The antenna as claimed in claim 1, wherein:

said loop parts, of which there are at least two, are disposed on a base plate, and said connecting parts, of which there is at least one, are disposed under said base plate.

22. The antenna as claimed in claim 1, wherein:

said loop parts, of which there are at least two, form a circular loop.

23. The antenna as claimed in claim 1, wherein:

said loop parts, of which there are at least two, form an oval-shaped loop.

24. The antenna as claimed in claim 1, wherein:

said loop parts, of which there are at least two, form a polygonal loop.

25. The antenna as claimed in claim 1, wherein:

said loop parts, of which there are at least two, form a spiral loop.

26. A method of configuring the antenna as claimed in claim 1, comprising:

the lengths of every loop part and every connecting part are determined according to the frequency of said excitation signal, so that when an excitation signal is fed into the conductor line, said loop parts, of which there are at least two, and said connecting parts, of which there is at least one, generate an excitation current, and the excitation current of said loop parts, of which there are at least two, then generates a magnetic field.

27. The configuration method as claimed in claim 26, wherein :

said excitation current has the opposite phase in every two successive loop parts. - A A -

28. The antenna as claimed in claim 27, wherein:

said excitation current has a phase reversal point in every connecting part.

29. The antenna as claimed in claim 28, wherein:

the phase reversal point is one end point of the connecting part.

30. The antenna as claimed in claim 28, wherein:

the phase reversal point is located between the two end points of the connecting part.

31. The configuration method as claimed in claim 26, wherein :

said excitation current has the same phase in every two successive loop parts.

32. The antenna as claimed in claim 31, wherein:

said excitation current has two phase reversal points in every connecting part.

33. The antenna as claimed in claim 32, wherein:

said two phase reversal points are the two end points of the connecting part.

34. The antenna as claimed in claim 32, wherein:

said two phase reversal points are located between the two end points of the connecting part.

35. An antenna for a radio frequency identification system, comprising a conductor line which comprises at least four loop parts and at least three connecting parts, wherein:

said loop parts, of which there are at least four, are disposed in two separate loops in the same plane and are spatially discontinuous, with at least two loop parts being disposed on each loop;

in every two successive loop parts, the end of the first loop part and the beginning of the second loop part are connected by a connecting part, the connecting part being disposed in such a manner as to be separate from said two loops; when an excitation signal is fed into said conductor line, said loop parts, of which there are at least four, and said connecting parts, of which there are at least three, generate an excitation current, and the excitation current in each of said loop parts disposed in each loop then generates a magnetic field, said magnetic fields, of which there are two, being opposite in polarity.

36. The antenna as claimed in claim 35, wherein:

said excitation current in said loop parts has the same direction in each loop;

said excitation current in said loop parts has the opposite direction with respect to said two loops.

37. A configuration method for the antenna as claimed in claim 35, comprising:

the lengths of every loop part and every connecting part are determined according to the frequency of said excitation signal, so that when an excitation signal is fed into said conductor line, said loop parts, of which there are at least four, and said connecting parts, of which there are at least three, generate an excitation current, the excitation current in each of said loop parts disposed in each loop then generating a magnetic field, said magnetic fields, of which there are two, being opposite in polarity.

38. The configuration method as claimed in claim 37, wherein :

said excitation current in said loop parts has the same direction in each loop;

said excitation current in said loop parts has the opposite direction with respect to said two loops.

39. An antenna for a radio frequency identification system, comprising a radiating unit which comprises at least two sections of conductor and at least one phase-shifting device, wherein :

said sections of conductor, of which there are at least two, are disposed in a loop and spatially discontinuous;

in every two successive sections of conductor, the end of the first section of the conductor and the beginning of the second section of the conductor are connected to the input terminal and output terminal, respectively, of a phase-shifting device;

said phase-shifting device comprises a 90 degree phase- shifting component, a first resistance component and a second resistance component, said 90 degree phase-shifting component being connected in series with said first resistance component and then connected in parallel with said second resistance component, the nodes of the two ends of said parallel circuit separately constituting the input terminal and the output terminal of said phase-shifting device;

when an excitation signal is fed into said radiating unit, said sections of conductor, of which there are at least two, and said phase-shifting device, of which there is at least one, generate an excitation current, the excitation current of said sections of conductor, of which there are at least two, then generating a magnetic field.

40. The antenna as claimed in claim 39, wherein:

said excitation current has the same phase in said sections of conductor, of which there are at least two.

41. The antenna as claimed in claim 39, wherein:

said 90 degree phase-shifting component is designed as a transmission line transformer.

42. The antenna as claimed in claim 39, wherein:

said first resistance component and said second resistance component have the structures of resistance components suitable for broadband.

43. A configuration method for the antenna as claimed in claim 39, comprising:

the lengths of every section of the conductor and the resistance values of every first resistance component and every second resistance component are determined according to the frequency of said excitation signal, so that when an excitation signal is fed into said radiating unit, said sections of conductor, of which there are at least two, and said phase- shifting devices, of which there is at least one, generate an excitation current, the excitation current of said sections of conductor, of which there are at least two, then generating a magnetic field.

44. The configuration method as claimed in claim 43, wherein : - A l - said excitation current has the same phase in said sections of conductor, of which there are at least two.

45. An antenna for a radio frequency identification system, comprising a radiating unit which has at least four sections of conductor and at least three phase-shifting devices, wherein: said sections of conductor, of which there are at least four, are disposed in two separate loops in the same plane and are spatially discontinuous, with at least two sections of conductor being disposed on every loop;

in every two successive sections of conductor, the end of the first section of the conductor and the beginning of the second section of the conductor are connected to the input terminal and the output terminal, respectively, of a phase- shifting device;

said phase-shifting device comprises a 90 degree phase- shifting component, a first resistance component and a second resistance component, said 90 degree phase-shifting device being connected in series to the first resistance component and then being connected in parallel to the second resistance component, the nodes of the two ends of the parallel circuit constituting the input terminal and the output terminal, respectively, of the phase-shifting device;

when an excitation signal is fed into said radiating unit, said sections of conductor, of which there are at least four, and said phase-shifting devices, of which there are at least three, generate an excitation current, the excitation current in said conductor which is disposed on each loop then generating a magnetic field from each loop, said magnetic fields, of which there are two, being opposite in polarity.

46. The antenna as claimed in claim 45, wherein:

said excitation current in said conductor has the same direction with respect to each loop of said conductor;

said excitation current in said conductor has the opposite direction with respect to said two loops.

47. A method of configuring the antenna as claimed in claim 45, comprising:

the lengths of every section of conductor and the resistance values of every first resistance component and every second resistance component are determined according to the frequency of the excitation signal, so that when an excitation signal is fed into the radiating unit, said sections of conductor, of which there are at least four, and said phase- shifting devices, of which there are at least three, generate an excitation current, the excitation current in said conductor which is disposed on each loop further generating a magnetic field from each loop, said magnetic fields, of which there are two, being opposite in polarity.

48. The configuration method as claimed in claim 47, wherein :

said excitation current in said conductor has the same direction in every loop;

said excitation current in said conductor has the opposite direction with respect to said two loops.

49. A radio frequency identification reader having the antenna as claimed in any one of claims 1, 35, 39 and 45.

50. The reader as claimed in claim 49, wherein:

said excitation signal is a radio frequency signal sent by said reader, and the frequency range of the radio frequency signal is 800/900MHz.

Description:
DESCRIPTION

An antenna for radio frequency identification systems, methods of configuring same, and a radio frequency identification reader

Technical Field

The present invention relates to radio frequency identification (RFID) technology. Specifically, it relates to an antenna for RFID systems, methods of configuring same, and an RFID reader that has this antenna.

The Background Art

In recent years, ultra high frequency (UHF) RFID technology has received increasing attention. As it can identify hundreds of individual objects per second, UHF RFID has created a large number of opportunities in applications relating to material flows. However, traditional far-field UHF RFID communication systems are frequently influenced by multipath propagation, i.e. transmitted radio signals that reach a receiver through multiple propagation paths. Reflection and refraction in the surrounding environment can lead to multiple, different propagation paths of radio signals, which result in different path delays, phase shifts and signal attenuation. Depending on the specific signal frequencies used, the multipath signal components have an additive effect that can either be reinforcing or offsetting. FIG. 1 shows the distribution of RFID signal strengths within a 5 m 2 room in which three metal reflectors have been installed. If the room walls are made from concrete materials, then the walls, too, can partially reflect the radio signals emitted by the reader. Owing to the alternating reinforcing and offsetting additive effects of multipath components, the signal strengths exhibit a ripple pattern. The reading zones that are to be covered are indicated by white circles/ovals in the figure. From which it can be seen that some points in these zones have obviously low signal strength (where the color is lighter) . The lack of field strength uniformity caused by multipath propagation will greatly reduce the reading reliability of UHF RFID systems and thereby limit the use of far-field UHF RFID technology in many fields of application that demand high levels of reliability. This is particularly true in manufacturing, where the large number of metal reflectors makes control of the signal field strength of far-field UHF RFID technology completely impossible. However, it is generally necessary in manufacturing to assess accurately whether a tag is in the reading zone. When an RFID system is used in manufacturing, the following questions must be answered: When will the tag enter the reading zone? When will the tag be directly in front of the reader? When will the tag leave the reading zone? Once the RFID system is unable to control the reading zone, disastrous consequences may occur. For example, as shown in FIG. 2, as a result of cross-over reading caused by the multipath effect, the operating platform will handle the workpiece tagged 1 according to an incorrect command (contained in tag 2) .

As they are less reliable, the use of far-field UHF RFID systems in manufacturing has come up against considerable resistance. In contrast to UHF RFID systems, high frequency (HF) RFID systems can attain controllable reading field strengths because they employ near-field magnetic field coupling communication technology. Therefore, this technology has been broadly applied in manufacturing. However, with the rapid development of industry, more and more manufacturing operations require low-priced RFID products that can read and write rapidly. Reading and writing speed and price are precisely the weaknesses of current HF RFID systems, yet they are the strengths of UHF RFID systems. If a UHF RFID system were able to attain controllable read zones similar to those of HF RFID systems, it would become a highly competitive alternative to HF RFID systems.

With the development of silicon technology and antenna technology, near-field UHF RFID technology has become an effective solution for raising the reliability of UHF RFID systems. The basic principle of near-field UHF RFID technology is that near-field magnetic coupling is adopted as the form of communication between the UHF RFID reader and the tags. The most important technology behind near-field UHF RFID is antenna technology. The only aspects of traditional far-field UHF RFID technology that need to be improved are the reader antenna and the tag antenna. There is no need to make any improvement to the reader itself or to the tags themselves. Therefore, the majority of reader and tag manufacturers will find it easier to accept near-field technology.

If they are to be used successfully in manufacturing, near-field UHF RFID reader antennas will have to satisfy the requirements below: dimensions similar to those of HF RFID reader antennas so as to obtain an effective reading distance; magnetic field strength uniformity to ensure reliable reading; far-field field strength gain so as to avoid cross-over reading with distant tags; large bandwidth to overcome antenna detuning effects from nearby metal objects.

The design requirements for near-field UHF RFID antennas are very different from those for traditional far-field antennas. Therefore, the original design methods no longer suit near-field UHF RFID antennas, for the design goals differ. Moreover, since the frequencies in the UHF range are very high, the design of UHF near-field antennas will also create new challenges beyond those of HF near-field antenna design. For example, since the signal wavelengths are shorter, it is not possible to obtain desired reading distances and uniform magnetic field strength distributions using a simple conductor loop, as is the case with HF near-field antennas.

To address the challenges in near-field UHF RFID antenna design, US 2008/0048867 Al discloses an RFID reader antenna based on a discontinuous loop. This antenna comprises multiple conductor sections that are not in contact with each other, and these conductor sections are arranged in a loop and are isolated from each other by gaps. When excitation signals are fed into the first and last of these conductor sections, every two successive conductor sections are coupled by means of the - A - gaps between them, with the result that said excitation signals can be transmitted along each conductor section in sequence, thereby establishing an excitation current in each conductor section. This excitation current then generates a magnetic field. The role of the gaps between the conductor sections is similar to that of capacitance. By adjusting gap widths and the lengths of the overlapping conductor portion of the two sides of the gap, one can change the amount of phase shift in the gap, with the result that a same-phase electrical current distribution forms in all conductor sections, which in turn results in a uniform magnetic field. A few variants of the antenna disclosed by US 2008/0048867 Al are shown in FIGS. 3 through 5.

"The RF in RFID, Passive UHF RFID in Practice" (Elsevier Publication, 2007) by Daniel Dobkin et al . presents a near- field UHF antenna design method based on capacitance compensation. Its design principle is shown in FIG. 6. In this method, the antenna conductor loop is divided into several conductor sections by capacitors. The capacitor phase shifts are changed by means of the design capacitance values of the capacitors, with the result that same-phase current distribution is formed on every conductor loop section. This in turn results in a uniform magnetic field.

The above antenna schemes take as their goal conductor loops having same-phase current distributions. However, the parameters for adjusting phase shifts are fixed in these schemes, e.g. gap widths and lengths of conductor overlap portions in the discontinuous loop antenna scheme, and capacitance values in the capacitance compensation antenna scheme. In addition, the phase shifts determined by these parameters are affected by signal frequencies to a considerable degree. It is very difficult for the fixed, unchanging parameters described above to ensure constant phase shifts throughout a broad signal bandwidth. Therefore, the above schemes are very unlikely to achieve same-phase current distributions throughout an entire signal bandwidth. In addition, the discontinuous loop antenna scheme is highly sensitive with respect to gap widths and lengths of conductor overlap portions. This sensitivity will definitely present difficulties in mass production of the antenna.

Contents of the Invention

In addressing the above problems in the current art, the object of the present invention is to provide an antenna for RFID systems, methods of configuring same, and an RFID reader having this antenna. With said antenna and method of configuring same, it is possible to attain a sufficient antenna size in a UHF RFID system and to satisfy the reading distance requirement for a near-field UHF RFID reader.

The above-described object of the present invention is realized through the technical scheme below: an antenna for an RFID system, including a conductor line, wherein the conductor line includes at least two loop parts and at least one connecting part. Said loop parts, of which there are at least two, are disposed in one loop and are spatially discontinuous. In every two successive loop parts, the end of the first loop part and the beginning of the second loop part are connected by a connecting part. The connecting part is disposed in such a manner as to be separate from said loop. When an excitation signal is fed into said conductor line, said loop parts, of which there are at least two, and the connecting parts, of which there is at least one, generate an excitation current, and the excitation current in the loop parts, of which there are at least two, then generates a magnetic field.

The methods of configuring the antenna of the present invention include the following: the lengths of every loop part and every connecting part are determined according to the frequency of said excitation signal, so that when an excitation signal is fed into the conductor line, said loop parts, of which there are at least two, and said connecting parts, of which there is at least one, generate an excitation current, and the excitation current of said loop parts, of which there are at least two, then generates a magnetic field.

In configuring and implementing the antenna of the present invention, one can, by making the conductor line include loop parts and connecting parts in the quantities required by the UHF RFID system, achieve sufficiently large antenna dimensions and thereby satisfy the reading distance requirements of a near-field UHF RFID reader. In a preferred embodiment, it is possible to cause the excitation current to have opposite phases in every two successive loop parts and, in every two successive loop parts, cause the direction from the beginning to the end of the first loop part to be opposite to the direction from the beginning to the end of the second loop part; or cause the excitation current to have the same phase in every two loop parts, and, in every two successive loop parts, cause the direction from the beginning to the end of the first loop part and the direction from the beginning to the end of the second loop part to be the same, thereby causing the excitation current to have the same direction in every loop part. Of even greater benefit is the fact that the connecting parts can be ingeniously folded in many patterns, thus reducing the size of the connecting parts without changing the size of the loop parts. In this way, it is possible to reduce the overall dimensions of the antenna without changing the reading distance. Moreover, by folding the connecting parts, one can form in the connecting parts multiple pairs of sections that are basically parallel. The current in each pair of parallel sections has opposite directions, with the result that the current in the connecting parts does not have a substantive effect on the magnetic field generated by the current in the loop parts.

One variant of the antenna of the present invention is as follows: an antenna for an RFID system, comprising a conductor line which comprises at least four loop parts and at least three connecting parts. Said loop parts, of which there are at least four, are disposed in two separate loops in the same plane and are spatially discontinuous, with at least two loop parts being disposed on each loop. In every two successive loop parts, the end of the first loop part and the beginning of the second loop part are connected by a connecting part, and the connecting part is disposed in such a manner as to be separate from said two loops. When an excitation signal is fed into said conductor line, said loop parts, of which there are at least four, and said connecting parts, of which there are at least three, generate an excitation current, and the excitation current in said loop parts disposed in each loop then generates a magnetic field. Said magnetic fields, of which there are two, are opposite in polarity.

In said variant, the magnetic fields generated by the currents in the loop parts disposed in the two loops have opposite polarities. These two magnetic fields with opposite polarities will form a new magnetic field. This new magnetic field is orthogonal relative to the magnetic fields generated by the electric currents in the loop parts of the two loops. Thus, using the magnetic fields generated by the electric currents in the loop parts of the two loops, it becomes possible to read an RFID tag passing through a reading zone parallel to the planes where the two loops are located, and using said new magnetic field, it becomes possible to read an RFID tag passing through a reading zone perpendicular to the planes in which the two loops are located.

A method of configuring said variant of the antenna of the present invention includes: the lengths of every loop part and every connecting part are determined according to the frequency of said excitation signal so that when an excitation signal is fed into said conductor line, said loop parts, of which there are at least four, and said connecting parts, of which there are at least three, generate an excitation current. The excitation current in said loop parts disposed in each loop further generates a magnetic field from each loop, and said magnetic fields, of which there are two, are opposite in polarity.

Given the technical concept of generating a magnetic field by means of a spatially discontinuous conductor loop, an alternative solution to the antenna of the present invention is as follows: An antenna for an RFID system, comprising a radiating unit which comprises at least two sections of conductor and at least one phase-shifting device. Said sections of conductor, of which there are at least two, are disposed in a loop and spatially discontinuous. In every two successive sections of conductor, the end of the first section of the conductor and the beginning of the second section of the conductor are connected to the input terminal and output terminal, respectively, of a phase-shifting device. Said phase- shifting device comprises a 90 degree phase-shifting component, a first resistance component and a second resistance component. Said 90 degree phase-shifting component is connected in series with said first resistance component and then connected in parallel with said second resistance component. The nodes of the two ends of said parallel circuit separately constitute the input terminal and the output terminal of said phase-shifting device. When an excitation signal is fed into said radiating unit, said sections of conductor, of which there are at least two, and said phase-shifting device, of which there is at least one, generate an excitation current. The excitation current of said sections of conductor, of which there are at least two, then generates a magnetic field.

By means of said phase-shifting devices, one can achieve any desired phase shift quantity φ. Moreover, the thermal loss effect of the first resistance component and the second resistance component can also eliminate the radiation from said radiating unit and thereby lower the far-field gain of the antenna .

The configuration method of an antenna based on said alternative solution includes: the lengths of every section of the conductor and the resistance values of every first resistance component and every second resistance component are determined according to the frequency of said excitation signal so that when an excitation signal is fed into said radiating unit, said sections of conductor, of which there are at least two, and said phase-shifting devices, of which there is at least one, generate an excitation current. The excitation current of said sections of conductor, of which there are at least two, then generate a magnetic field.

Similar to said variant of an antenna based on the present invention, a variant of said solution includes a radiating unit which has at least four sections of conductor and at least three phase-shifting devices. Said sections of conductor, of which there are at least four, are disposed in two separate loops in the same plane and are spatially discontinuous, with at least two sections of conductor being disposed on every loop. In every two successive sections of conductor, the end of the first section of the conductor and the beginning of the second section of the conductor are connected to the input terminal and the output terminal, respectively, of a phase-shifting device. Said phase-shifting device comprises a 90 degree phase- shifting component, a first resistance component and a second resistance component. Said 90 degree phase-shifting device is connected in series to the first resistance component and then is connected in parallel to the second resistance component. The nodes of the two ends of the parallel circuit constitute the input terminal and the output terminal, respectively, of said phase-shifting device. When an excitation signal is fed into said radiating unit, said sections of conductor, of which there are at least four, and said phase-shifting devices, of which there are at least three, generate an excitation current. The excitation current in said conductor which is disposed on each loop then generates a magnetic field from each loop. Said magnetic fields, of which there are two, are opposite in polarity.

A method of configuring the alternative variant of said solution includes: the lengths of every section of conductor and the resistance values of every first resistance component and every second resistance component are determined according to the frequency of the excitation signal so that when an excitation signal is fed into the radiating unit, said sections of conductor, of which there are at least four, and said phase- shifting devices, of which there are at least three, generate an excitation current. The excitation current in said conductor which is disposed on each loop then generates a magnetic field from each loop. Said magnetic fields, of which there are two, are opposite in polarity. When an antenna based on the present invention, or an alternative solution to an antenna based on the present invention, is used on an RFID reader, the current in said loop parts, of which there are at least two, or said conductor sections, of which there are at least two, can generate a sufficiently large, controllable magnetic field, and this magnetic field can be used to obtain an effective reading distance, thereby satisfying the reading requirement for a near-field UHF RFID reader. Of even greater benefit is the fact that when said variant of an antenna based on the present invention, or a variant of said alternative solution, is used on an RFID reader, then regardless of whether an RFID tag is moving parallel to the plane in which said two loops are located or is moving perpendicular to the plane in which said two loops are located, the RFID reader will be able to read the RFID tag and will thereby be able to satisfy the different requirements of multiple fields of application.

Explanation of the Drawings

The object, features and advantages of the present invention are explained in detail below through specific embodiments in light of the attached drawings. These embodiments are illustrative only and do not impose restrictions .

FIG. 1 is a magnetic field distribution diagram of a far- field UHF RFID antenna.

FIG. 2 is a diagram of the cross-over reading problems that result from the multipath effect in UHF RFID systems.

FIGS 3 through 5 are diagrams of RFID antennas based on continuous loops in the current art.

FIG. 6 is a schematic diagram of a UHF RFID antenna based on capacitance compensation in the current art.

FIG. 7 is a diagram of a waveform of a current standing wave when a conductor line is open-circuited.

FIG. 8 is an embodiment of an antenna based on the present invention .

FIG. 9 is a diagram of a waveform of a current standing wave in the embodiment shown in FIG. 8.

FIG. 10 is another embodiment of an antenna based on the present invention.

FIG. 11 is a diagram of a waveform of a current standing wave in the embodiment shown in FIG. 10.

FIG. 12 is another embodiment of an antenna based on the present invention.

FIG. 13 is a variant of the embodiment shown in FIG. 12.

FIG. 14 is another embodiment of an antenna based on the present invention.

FIG. 15 is another embodiment of an antenna based on the present invention.

FIG. 16 is another embodiment of an antenna based on the present invention.

FIG. 17 is another embodiment of an antenna based on the present invention.

FIG. 18 is an embodiment of a variant of an antenna based on the present invention.

FIG. 19 is a schematic circuit diagram of a phase-shifting device in an alternative solution to an antenna based on the present invention.

Specific Embodiments

The design principles for antennas based on the present invention come from standing wave theory.

According to standing wave theory, if the terminal point of a conductor line is open-circuited or short-circuited or is connected to a purely reactive load, incoming waves will be reflected entirely. The reflected waves will be added to incoming waves and thereby form standing waves on conductor lines. When a conductor line terminal point is open-circuited, the incoming wave current and the reflected wave current will have the same amplitude and opposite phases at the terminal point of the conductor line. The conductor line terminal point is a current wave node. Beginning at this wave node, current wave nodes are located at intervals equal to one-half of a wavelength along the conductor line. Beginning at each current wave node, at a distance along the conductor line equal to one- fourth a wavelength, is a current antinode. The current phase between two current nodes is the same throughout. That is, it is the same, either positive phase or negative phase, at any point in time. The current phases on the two sides of each current phase node are always opposites. That is, at any point in time, one side is positive phase, and the other side is negative phase; or one side is negative phase, and the other side is positive phase. A diagram of the waveform of the current standing wave at a point in time is as shown in FIG. 7. In FIG. 7, the horizontal axis 1 represents the conductor line length from the conductor line terminal point. The vertical axis i represents the amplitude of the current waveform, and λ represents the wavelength. When the terminal point of the conductor line is short-circuited, the current of the incoming waves and the current of the reflected waves have the same amplitude and the same phase at the conductor line terminal point, and the conductor line terminal point is a current wave antinode. Starting at this antinode, current wave antinodes are located at intervals equal to one-half a wavelength along the conductor line. Beginning at each current wave node, current wave nodes are located along the conductor line at distances equal to one-fourth of a wavelength from each current wave antinode. The current phase between two current nodes is the same throughout. The current phases on the two sides of each current phase node are always opposites. If one takes the waveform of the current standing wave shown in FIG. 7 and shifts it left one-fourth of a wavelength along the horizontal axis, the result is the waveform of the current standing wave when the conductor line terminal point is short-circuited. If the waveform of the current standing wave when the conductor line terminal point is open or short-circuited is shifted less than one-fourth of a wavelength to the left, the result is the waveform of a current standing wave when the conductor line terminal point is connected to a purely reactive load.

When the RFID system is operating within the UHF range, e.g. 800/900 MHz or a higher range, the conductor loop circumference can match the frequency signal wavelength or be even longer, e.g. the antenna conductor loop diameter can be 10 cm, in order to achieve a sufficiently large antenna for an effective reading distance. This means that the phases of the current in different sections of the conductor loop may be opposites, thus causing the magnetic fields generated by the current in different sections of the loop to cancel each other. A uniform magnetic field distribution becomes as a consequence impossible .

Therefore, the design principle of the antenna based on the present invention is as follows: when the length of the conductor line matches or is longer than the signal wavelength, only some parts of this conductor line are disposed in a loop in accordance with the above-described characteristics of current standing waves formed on these loop parts. After the magnetic fields generated by the current in these loop parts are added to each other, they can reinforce each other and thereby synthesize a magnetic field with a uniform distribution. The remaining parts of this conductor line are used to regulate the phases of the current in the loop parts. These remaining parts are disposed apart from said loop. That is, they are not disposed in said loop, with the result that the current in said parts does not substantively affect the magnetic fields generated by the current in the loop parts.

Based on the design principles described above, an antenna based on the present invention includes a conductor line, which comprises at least two loop parts and at least one connecting part, wherein said loop parts, of which there are at least two, are disposed in one loop and are spatially discontinuous. In every two successive loop parts, the end of the first loop part and the beginning of the second loop part are connected by a connecting part. The connecting part is disposed in such a manner as to be separate from said loop. When an excitation signal is fed into said conductor line, said loop parts, of which there are at least two, and the connecting parts, of which there is at least one, generate an excitation current, and the excitation current of the loop parts, of which there are at least two, then generates a magnetic field.

An embodiment of an antenna based on the present invention is as shown in FIG. 8. This antenna includes a conductor line 8. The conductor line 8 has two loop parts, 80 and 82, and one connecting part 81. The loop parts 80 and 82 are disposed in an oval loop, forming a spatially discontinuous, oval shaped conductor loop. The connecting part 81 is between the loop parts 80 and 82. It is disposed inside the oval loop, and it connects the end of the loop part 80 to the beginning of the loop part 82. An excitation signal can be fed in from the beginning of the loop part 80, thereby generating an excitation current in the loop parts 80 and 82 and in the connecting part 81. The terminal point of the conductor line 8, i.e., the end of the loop part 82, is open-circuited. Therefore, the excitation current forms a current standing wave in the conductor line 8, and its waveform diagram at one point in time is as shown in FIG. 9. The horizontal axis 1 in FIG. 9 represents the length of the conductor line from the terminal point of the conductor line 8. The vertical axis i represents the amplitude of the excitation current standing wave. λ represents the wavelength of the excitation signal.

As shown in FIG. 9, the length of the conductor line 8 is one wavelength. Its beginning and end parts are the loop parts 80 and 82. The lengths of the loop parts 80 and 82 are, on the whole, equal, and both are shorter than half a wavelength. The connecting part 81 is between the loop parts 80 and 82. The end of the loop part 82 is a wave node of the current standing wave. Beginning at this wave node, current wave nodes are located at intervals equal to one-half of a wavelength along the conductor line 8. Thus, a current wave node exists in the connecting part 81, and the beginning of the loop part 80 is a current wave node. It is therefore known that the excitation current reverses phase in the connecting part 81 and that the current in loop parts 80 and 82 always has opposite phases. When the current in one of the loop parts has a positive phase, the current in the other loop part will have a negative phase.

Although the current in loop parts 80 and 82 has opposite phases, the direction of loop part 80 from the beginning to the end is clockwise, and the direction of loop part 82 from the beginning to the end is counterclockwise, as shown in FIG. 8. As a result, the direction of the current in loop parts 80 and 82 is the same throughout. That is, at any point in time, the current in both loop parts 80 and 82 will be the same; either it will be clockwise in both or it will be counterclockwise in both. Therefore, the current in loop parts 80 and 82 substantively forms one loop current. This loop current then can generate a uniform magnetic field.

A current wave node exists in the connecting part 81. The lengths of the two sides of the connecting part 81 are basically equal, and the phases of the current are opposite. Thus, the magnetic fields generated on the two sides of this wave node in the connecting part 81 are able to offset each other, with the result that the current in the connecting part 81 does not substantively affect the magnetic field generated by the current in loop parts 80 and 82.

Another embodiment of an antenna based on the present invention is as shown in FIG. 10. This antenna comprises a conductor line 10. The conductor line 10 has two loop parts 100 and 102 and a connecting part 101. The loop parts 100 and 102 are disposed in a circular loop, forming a spatially discontinuous, circular conductor loop. The end of the loop part 100, and the beginning of the loop part 102 are connected to each other through the connecting part 101. The connecting part 101 is disposed in folded form between loop parts 100 and 102. An excitation signal can be fed in from the beginning of the loop part 100 and consequently generate an excitation current in loop parts 100 and 102 and in the connecting part 101. The terminal point of the conductor line 10, i.e., the end of loop part 102, is open-circuited. Therefore, the excitation current forms a current standing wave in the conductor line 10. The diagram of the waveform at a point in time is as shown in FIG. 11. The horizontal axis 1 in FIG. 11 represents the conductor line length from the conductor line 10 terminal point, and the vertical axis i represents the amplitude of the excitation current standing wave, λ represents the wavelength of the excitation signal.

As shown in FIG. 11, the length of the conductor line 10 is three halves of a wavelength. Its beginning and end parts are loop parts 100 and 102. The lengths of loop parts 100 and 102 are basically equal, and both are less than half a wavelength. The connecting part 101 is between loop parts 100 and 102. The end of loop part 102 is a wave node of the current standing wave. Beginning at this wave node, current wave nodes are located at intervals equal to one-half of a wavelength along the conductor line 10. Thus, two current wave nodes exist in the connecting part 101, and the beginning of the loop part 100 is a current wave node. It is therefore known that the excitation current reverses phase twice in the connecting part 101, and that the current in loop parts 100 and 102 have the same phase. Therefore, the current in loop parts 100 and 102 substantively forms one loop current. This loop current then can generate a uniform magnetic field.

The length of the connecting part 101 is greater than half a wavelength. It is disposed between loop parts 100 and 102 in folded form, which reduces the space required by the connecting part 101. In addition, multiple pairs of sections that are basically disposed in parallel can be formed in the connecting part 101. The current in each pair of sections disposed in parallel has opposite directions, and thus the consequent magnetic field offset each other throughout, with the result that the current in the connecting part 101 does not have a substantive effect on the magnetic field generated by the current in loop parts 100 and 102.

In the different embodiments of antennas based on the present invention presented below, it will become apparent that the connecting part can be ingeniously folded in many patterns which reduce the size of the connecting part while keeping the dimensions of the loop parts unchanged. Therefore, it is possible to reduce the overall dimensions of an antenna while the reading distance remains the same. In addition, by folding the connecting part, one can form multiple pairs of sections that are disposed basically parallel to each other within the connecting part, with the result that the current in the connecting part does not have a substantive effect on the magnetic field generated by the current in the loop parts.

It should be noted here that the connecting part does need to be folded in order to implement an antenna based on the present invention. As can be seen in other embodiments of antennas based on the present invention that will be presented below, the connecting part can be separated from the loop parts in other ways that prevent the electric current in the connecting part from having a substantive effect on the magnetic fields generated by the current in the loop parts.

To attain sufficient reading distances according to the different needs of specific applications, one can increase the length of the conductor line, causing the conductor line to include multiple loop parts and two or more connecting parts. These loop parts are disposed in a loop and are spatially discontinuous. In every two successive loop parts, the end of the first loop part and the beginning of the second loop part are connected by a connecting part. The connecting part is disposed in such a manner as to be separate from said loop. When an excitation signal is fed into said conductor line, said multiple loop parts and said two or more connecting parts generate an excitation current, and the excitation current in said multiple loop parts then generates a magnetic field.

According to an analysis of the standing wave waveforms of the excitation current as shown in FIG. 9 or FIG. 11, it is preferable that the excitation current have an opposite phase in every two successive loop parts and that, in every two successive loop parts, the direction from the beginning to the end of the first loop part is opposite to the direction from the beginning to the end of the second loop part, thereby causing the direction of the excitation current to be the same in said multiple loop parts. Or it is preferable that the excitation current have the same phase in every two successive loop parts and that, in every two successive loop parts, the direction from the beginning to the end of the first loop part is the same as the direction from the beginning to the end of the second loop part, thereby causing the direction of the excitation current to be the same in said multiple loop parts. The current in said multiple loop parts substantively forms a loop current, and this loop current can then generate a uniform magnetic field.

When the excitation current has an opposite phase in every two successive loop parts, the excitation current can have a phase reversal point, i.e. a standing wave node, in every connecting part. This wave node can be an end point of every connecting part, or it can be located between the two end points of every connecting part. It can also be located between the two end points of every connecting part for some connecting parts and be an end point of every remaining connecting part.

FIG. 12 presents another embodiment of an antenna based on the present invention. In this embodiment, the antenna based on the present invention comprises a conductor line 12. Said conductor line 12 has four loop parts 120, 122, 120' and 122' and two connecting parts 121 and 121'. These four loop parts and two connecting parts are constructed from two sections of conductor. One section of the conductor is formed into loop parts 120 and 122 and connecting part 121. The other section of the conductor is formed into loop parts 120' and 122' and connecting part 121 ' . The loop parts and connecting parts of the two sections of the conductor have axial symmetry. Loop parts 120, 122, 120' and 122' are disposed in a quadrilateral loop. They form a spatially discontinuous, quadrilateral conductor loop. Each loop part has two loop sections. The end of loop part 120 is connected to the beginning of loop part 122 through the connecting part 121. The end of loop part 120' is connected to the beginning of loop part 122 ' through the connecting part 121'. Each connecting part is folded into two sections. The excitation signal is fed from the beginning of the loop part 120 and from the beginning of the loop part 120 ' . The ends of loop parts 122 and 122' are open-circuited.

In the antenna based on the present invention, every two successive loop parts are, in terms of an electrical circuit, an upstream loop part and an adjacent downstream loop part. In the embodiment shown in FIG. 12, because the ends of loop parts 122 and 122 ' are open-circuited, loop parts 122 and 122 ' do not have an electrical circuit connection. Thus, there is no connecting part between loop parts 122 and 122 ' .

When said excitation signal is fed into the beginnings of loop parts 120 and 120', both excitation currents that are generated in the two sections of conductor form standing waves. In this embodiment, the two current standing waves have one wave node at the end of loop part 122 and one at the end of loop part 122 ' . In addition, the two current standing waves also have one wave node at the beginning of connecting part 121 (i.e., the connection point between connecting part 121 and the end of loop part 120) and one at the beginning of connecting part 121' (i.e., the connection point between connecting part 121' and the end of loop part 120'). Thus, at a point in time, the directions in which the excitation currents flow in loop parts 120, 122, 120' and 122' and in connecting parts 121 and 121' are as shown by the arrows in FIG. 12.

As can be seen by the current directions shown in FIG. 12, although the excitation currents have opposite phases in every two successive loop parts, the excitation current has the same direction in loop parts 120, 122, 120' and 122' because the direction from the beginning to the end of the first loop part is opposite to the direction from the beginning to the end of the second loop part in every two successive loop parts. Thus, the excitation currents in loop parts 120, 122, 120' and 122' substantively form a loop current. This loop current can then generate a uniform magnetic field.

Both connecting parts 121 and 121' are folded so that each forms two sections. As shown in FIG. 12, the folded connecting parts 121 and 121' have a pair of sections that are basically disposed in parallel. The currents in this pair of sections that is disposed in parallel have opposite directions, and the magnetic fields which they generate cancel each other out. Therefore, the current in this pair of sections disposed in parallel does not have a substantive effect on the magnetic field generated by said loop current. The currents in the remaining two sections of connecting parts 121 and 121' have the same direction and will have some effect on the magnetic field generated by said loop current. In the following embodiment, a variant of the embodiment shown in FIG. 12 is given. It can eliminate the effect generated by the current in said two sections.

FIG. 13 presents another embodiment of an antenna based on the present invention. This embodiment is a variant of the embodiment shown in FIG. 12. The conductor line 13 of the antenna shown in FIG. 13 also includes four loop parts 130, 132, 130 ' and 132 ' and two connecting parts 131 and 131 ' . These four loop parts and two connecting parts are constructed from two sections of conductor. It differs from the embodiment shown in FIG. 12 in that a line tail 1321/1321' is formed on each section of conductor in the embodiment shown in FIG. 13. The beginning of each line tail is connected to the end of the last loop part of each section of the conductor. The end of each line tail thereby forms the new terminal point of each section of the conductor. In order to avoid affecting the magnetic field generated by the currents in the loop parts, each line tail is likewise separated from said loop. In the present embodiment, each line tail preferably forms, with a section of folded connecting part, a pair of sections that are basically parallel. Therefore, as shown in FIG. 13, line tails 1321 and 1321', together with connecting parts 131 and 131', form three pairs of basically parallel sections.

As the ends of line tails 1321 and 1321' separately form the new terminal points of the two sections of the conductor, the characteristics of the current standing waves of each section of the conductor will change. Each of the ends of line tails 1321 and 1321' form a current wave node, and the other wave node of each current standing wave is shifted from the beginning of each connecting part to between the two end points of each connecting part. Thus, as shown by the directions indicated by the arrows in FIG. 13, the directions of the excitation currents in loop parts 130, 132, 130' and 132' are the same. As a result, the excitation current in loop parts 130, 132, 130' and 132' substantively form a loop current, and this loop current then generates a uniform magnetic field. In the three pairs of basically parallel sections formed by line tails 1321 and 1321' and connecting parts 131 and 131', the currents in each pair of parallel sections have opposite directions. Thus, the magnetic fields which they generate cancel each other out, thereby eliminating the effect of the currents in each section of connecting parts 131 and 131 ' on the magnetic field generated by said loop current.

Another benefit can be derived from the construction of line tails 1321 and 1321' in the conductor line 13: because the positions of the current standing wave nodes on connecting parts 131 and 131' are adjusted by means of line tails 1321 and 1321', the wave nodes are shifted from the beginning of each connecting part to between the two end points of each connecting part. In this way, the excitation current in each loop part will always be in the antinodal region of the current standing wave, and this can result in stronger excitation currents throughout each loop part, which in turn results in a stronger magnetic field generated by the excitation currents in loop parts 130, 132, 130' and 132'.

FIG. 14 presents another embodiment of an antenna based on the present invention. In this embodiment, the antenna based on the present invention comprises a conductor line 14. The conductor line 14 comprises four loop parts 140, 142, 144 and 146 and three connecting parts 141, 143 and 145. These four loop parts and three connecting parts are constructed from one section of conductor. The terminal point of this section of conductor is open-circuited. The loop parts 140, 142, 144 and 146 are in a circular loop and form a spatially discontinuous, circular conductor ring. In every two successive loop parts, the end of the first loop part is connected to the beginning of the second loop part through a connecting part. The three connecting parts 141, 143 and 145 are disposed inside said circular loop.

As shown in FIG. 14, in loop parts 140, 142, 144 and 146, in every two successive loop parts, the direction from the beginning to the end of the first loop part is opposite to the direction from the beginning to the end of the second loop part. At the same time, every two successive loop parts are disposed on two sides of said circular loop. The connecting parts 141 and 145 are folded inside said circular loop. Each folded connecting part forms two sections, and one of these two sections is basically parallel to the connecting part 143. Thus, loop parts 140, 142, 144 and 146 and connecting parts 141, 143 and 145 are disposed symmetrically about the center.

In the present embodiment, the conductor line 14 further comprises a line head 1401. The beginning of this line head is connected to a signal feed-in point for feeding in said excitation signal. The end of this line head has an electrical circuit connection in conductor line 14 to the beginning of the first loop part 140. Additionally, and similar to the embodiment shown in FIG. 13, the conductor line 14 further comprises a line tail 1461. The beginning of this line tail has an electrical circuit connection to the end of the last loop part 146 of conductor line 14. The end of this line tail forms the terminal point of the conductor line 14. Both the line tail 1461 and the line head 1401 are disposed in such a manner as to be separate from said loop. Preferably, in the present embodiment, the line tail 1461 and one section of folded connecting part together form a pair of basically parallel sections, and the line head 1401 and a section of another folded connecting part together form another pair of basically parallel sections. Thus, as shown in FIG. 14, the line tail 1461 and the line head 1401, together with connecting parts 141, 143 and 145, form four pairs of basically parallel sections.

When said excitation signals are fed in from the signal feed-in point connected to the beginning of line head 1401, the excitation current generated thereby forms a standing wave on conductor line 14. The current standing wave has a node at the end of the line tail 1461. In addition, the current standing wave has one node between the two end points of each of connecting parts 141, 143 and 145. Thus, at a point in time, the directions of the current in line conductor 14 are as shown by the arrows in FIG. 14.

The excitation current has the same direction in loop parts 140, 142, 144 and 146. Therefore, the excitation current in loop parts 140, 142, 144 and 146 substantively form a loop current, and this loop current then generates a uniform magnetic field. In the four pairs of basically parallel sections formed by the line tail 1461, the line head 1401, and connecting parts 141, 143 and 145, the current has opposite directions in each pair of parallel sections. The magnetic fields generated thereby cancel each other out. Therefore, the current in these parallel sections does not have a substantive effective on the magnetic field generated by said loop current.

In the embodiment shown in FIG. 14, there is an odd number of connecting parts in the conductor line 14. As a result, the sections formed from the folding of the connecting parts cannot be entirely arranged in parallel pairs. Under these circumstances, the beginning of the first loop part can have an electrical circuit connection in the conductor line with the line head, and the end of the last loop part can have an electrical circuit connection in the conductor line with the line tail. In this way, each section of each folded connecting part is matched with another section that is basically parallel to it. The current has opposite directions in each pair of basically parallel sections. As a result, the current in these pairs of sections does not have a substantive effect on the magnetic field generated by the current in said loop-shaped part. At the same time, the amplitude of the excitation current standing wave in each loop part can be adjusted by means of the line head and the line tail, with the result that they are basically in the antinodal region of the current standing wave, thereby increasing the strength of the excitation current in each loop part and in turn strengthening the magnetic field generated by the excitation current in the loop parts.

FIG. 15 presents another embodiment of an antenna based on the present invention. In this embodiment, the antenna based on the present invention comprises a conductor line 15. The conductor line 15 comprises five loop parts 150, 152, 154, 156 and 158 and four connecting parts 151, 153, 155 and 157. These five loop parts and four connecting parts are constructed from one section of conductor. Each of the two end points of said conductor is connected to a signal feed-in point for feeding in an excitation signal. That is, this section of conductor forms a short-circuit conductor line. The loop parts 150, 152, 154, 156 and 158 are in a circular loop and form a spatially discontinuous, circular conductor line. The beginning of loop part 150 and the end of loop part 158 form the two end points of said conductor. In every two successive loop parts, the end of the first loop part is connected to the beginning of the second loop part by means of a connecting part. In addition, the direction from the beginning to the end of the first loop part is the opposite of the direction from the beginning to the end of the second loop part. The four connecting parts 151, 153, 155 and 157 are disposed inside said circular loop. Each connecting part is folded into two sections, with the result that each section in each folded connecting part has a matching section that is basically parallel to it.

When said excitation signals are fed into the conductor line 15 from the signal feed-in points connected to the beginning of loop part 150 and to the end of loop part 158, the excitation current generated thereby forms a standing wave in conductor line 15. The current standing wave has a wave node between the two end points of each connecting part and an antinode between the two end points of each loop part. Thus, at one point in time, the directions of the excitation current are as indicated by the arrows in FIG. 15.

The excitation current has the same direction in loop parts 150, 152, 154, 156 and 158. Therefore, the excitation current in loop parts 150, 152, 154, 156 and 158 substantively forms a loop current, and this loop current then generates a uniform magnetic field. The excitation current has an opposite direction in each pair of basically parallel sections formed by connecting parts 151, 153, 155 and 157. The magnetic fields formed thereby cancel each other out. Therefore, the current in these four pairs of parallel sections does not have a substantive effect on the magnetic field generated by said loop current .

In the embodiment described in FIG. 15, the number of connecting parts in the conductor line 15 is even. Under these circumstances, by folding each connecting part, one can arrange the folded connecting parts into pairs where each section is basically parallel within the pair. The current within each basically parallel pair of sections has opposite directions, with the result that the current in the connecting parts does not have a substantive effect on the magnetic field generated by the current in the loop-shaped part.

In the preferred embodiments of antennas based on the present invention that are described above, the excitation current has opposite phases in every two successive loop parts, and in every two successive loop parts, the direction from the beginning to the end of the first loop part is opposite to the direction from the beginning to the end of the second loop part. As a result, the excitation current has the same direction in each loop part. Therefore, the current in each loop part substantively forms a loop current, and this loop current then can generate a uniform magnetic field. The excitation current has a phase reversal point in each connecting part. By folding every or some of the connecting parts through flexible employment of different patterns, and by using the line tail to adjust the position phase reversal point on every connecting part, one can create a stronger excitation current throughout every loop part, while also arranging every section of every folded connecting part so that it is paired with a section basically parallel to it. The current within each parallel pair of sections has opposite directions, with the result that the current in the connecting parts does not have a substantive effect on the magnetic field generated by said loop current.

With reference to the preferred embodiments described above, and employing the analytic method of the excitation current standing waveform shown in FIG. 9, a person skilled in the art can, based on the different requirements of specific fields of application, cause the conductor line to comprise appropriate quantities of loop parts and connecting parts so as to obtain an antenna of sufficient size. However, it should be noted that said folding patterns in the above embodiments are not limiting. A person skilled in the art can, based on the design principles for antennas based on the present invention, and given specific loop part shapes and connecting part quantities, flexibly employ appropriate patterns to fold connecting parts and thereby eliminate the effect of the excitation current in the connecting parts on the magnetic field generated by the excitation current in the loop parts. Furthermore, the folding patterns described in the above embodiments are not necessary. As will be seen in the next embodiment of an antenna based on the present invention, said connecting parts may also be separated from said loop parts according to other patterns that prevent the excitation current in the connecting parts from having a substantive effect on the magnetic field generated by the excitation current in the loop parts .

FIG. 16 presents another embodiment of an antenna based on the present invention. In this embodiment, an antenna based on the present invention comprises a conductor line 16. The conductor line 16 comprises four loop parts 160, 162, 164 and 166 and three connecting parts 161, 163 and 165. These four loop parts and three connecting parts are constructed from one section of conductor. Loop parts 160, 162, 164 and 166 are disposed in a loop pattern on a base plate, forming a spatially discontinuous, circular conductor loop. In every two successive loop parts, the end of the first loop part is connected through a connecting part to the beginning of the second loop part. In addition, the direction from the beginning to the end of the first loop part is the same as the direction from the beginning to the end of the second loop part. The three connecting parts 161, 163 and 165 are disposed under said base plate. Taking the three dimensional coordinates shown in FIG. 16 as the reference system, these three connecting parts are disposed about the negative semi-axis of the z-axis. The conductor line 16 is open-circuited or short-circuited. As a result, when an excitation signal is fed into the conductor line 16, the excitation current that it generates forms a standing wave in the conductor line 16. The excitation current has the same phase in every two successive loop parts, and because the direction from the beginning to the end of the first loop part is the same as the direction from the beginning to the end of the second loop part in every two successive loop parts, the excitation current has the same direction in the four loop parts 160, 162, 164 and 166. Application of the analytic method of the excitation current standing waveform shown in FIG. 11 reveals that the excitation current has at least two wave nodes in every connecting part. In this embodiment, preferably, the excitation current has two wave nodes in every connecting part. These two wave nodes can be the two end points of each connecting part, or they can be between the two end points of each connecting part. It is also possible that one of them could be the end point in each connecting part, while the other one is located between the two end points of each connecting part.

As the excitation current has the same direction in the four loop parts 160, 162, 164 and 166, the excitation current in loop parts 160, 162, 164 and 166 substantively forms a loop current, and this loop current then generates a uniform magnetic field. According to the right-hand rule, this magnetic field will be distributed along the z-axis. In actual applications, the reading zone can be located in the positive semi-axis of the z-axis. Therefore, the connecting parts 161, 163 and 165 disposed about the negative semi-axis of the z-axis will not have a substantive effect on the magnetic field in the reading zone.

In addition, the connecting parts 161, 163 and 165 that are disposed about the negative semi-axis of the z-axis may be folded in a manner similar to the embodiment shown in FIG. 10. This approach can, on the one hand, reduce the space required by the connecting parts 161, 163 and 165. On the other hand, it can form multiple basically parallel sections in every connecting part. The current has opposite directions in every pair of parallel sections. The magnetic fields generated thereby always cancel each other and thus further eliminate the effect of the current in connecting parts 161, 163 and 165 on the magnetic field in the reading zone.

Several embodiments of antennas based on the present invention were described above in the light of the attached drawings. By means of these descriptions, a person skilled in the art should be able to comprehend the design principles of antennas based on the present invention. Moreover, in accordance with the different requirements of specific fields of application, such a person would be able to achieve sufficiently large antennas by including appropriate numbers of loop parts and connecting parts in the conductor lines and thus ensure effective reading distances. By employing the analytic methods of excitation current standing waveforms shown in FIG. 9 or 11, one may, in a preferred embodiment, cause the excitation current in every two successive loop parts to have opposite phases and moreover cause the direction from the beginning to the end of the first loop part in every two successive loop parts to be opposite to the direction from the beginning to the end of the second loop part. Or one could cause the excitation current in every two successive loop parts to have the same phase and moreover cause the direction from the beginning to the end of the first loop part in every two successive loop parts to be the same as the direction from the beginning to the end of the second loop part. As a result, the excitation current would have the same direction in all loop parts. Of even greater benefit is the fact that the connecting parts can be ingeniously folded in many patterns, thus reducing the size of the connecting parts without changing the size of the loop parts. In this way, it is possible to reduce the overall dimensions of the antenna without changing the reading distance. Moreover, by folding the connecting parts, one can form in the connecting parts multiple pairs of sections that are basically parallel. The current in each pair of parallel sections has opposite directions, with the result that the current in the connecting parts does not have a substantive effect on the magnetic field generated by the current in the loop parts.

To form current standing waves in actual applications, an antenna based on the present invention can comprise an open or short-circuited conductor line. When the conductor line is open-circuited, this conductor line can be constructed from one section of conductor. One end point of this section of conductor is connected to a signal feed-in point for feeding in said excitation signal. The other end point of this section of conductor is open-circuited. Or this conductor line can be constructed from two sections of conductor, and one end point of each section of conductor is connected to a signal feed-in point for feeding in said excitation signal. When the conductor line is short-circuited, this conductor line can be constructed from one section of conductor. The two end points of this section of conductor are each connected with a signal feed-in point for feeding in said excitation signals. Or one end point of this section of conductor is connected to a signal feed-in point for feeding in said excitation signal, and the other end point of this section of conductor is grounded.

As described in the above embodiment, when an antenna based on the present invention is specifically implemented, said loop parts can be disposed on a base plate, and said connecting parts can be disposed off said base plate. Optionally, both said loop parts and said connecting parts may also be disposed on one base plate, with said connecting parts disposed either inside or outside of said loop parts so that they become separate from the loop where the loop parts are located. In addition, said loop parts can be formed into an oval loop, a circular loop or a polygonal loop or into a loop of any shape formed on a base plate, concerning which no more needs to be said. It is worth noting that, when said conductor line is constructed from one section of conductor, said loop parts may also be disposed according to a spiral loop pattern, as shown in FIG. 17. For the sake of simplicity, FIG. 17 shows only the loop parts of a conductor line 17 disposed on a base plate, and the connecting parts disposed separately from the spiral loop are not shown. These connecting parts may, for example, be disposed behind the base plate (with the forward direction being the direction in which the base plate faces the reader) . By disposing said loop parts in a spiral loop pattern, one can increase the length of the conductor line 17 while keeping the antenna the same size. Therefore, one can increase the strength of the magnetic field generated by the excitation current in said loop parts.

In an antenna based on the present invention, the current in said loop parts, of which there are at least two, is used to generate a sufficiently large, uniform magnetic field. This magnetic field is used to obtain an effective reading distance and thereby satisfy the reading requirement for a UHF RFID reader. In applications of near-field UHF RFID readers, an antenna based on the present invention can be placed in a metal chamber in order to control the far-field gain of the antenna. This metal chamber concentrates the magnetic field of the antenna in the reading zone, reducing radiation from the antenna in other zones and thereby reducing the antenna' s far- field gain. In addition, the use of said metal chamber can also overcome antenna detuning effects from nearby metal objects and thus make the antenna's magnetic field easier to control.

The present invention also provides a method of configuring an antenna based on the present invention. In this method, the length of every loop part and the length of every connecting part is determined according to the frequency of said excitation signal. As a result, when an excitation signal is fed into said conductor line, said loop parts, of which there are at least two, and said connecting parts, of which there is at least one, generate an excitation current, and the excitation current in said loop parts, of which there are at least two, then generates a magnetic field.

As shown by the current standing waveform diagram of FIG. 7, the characteristics of the excitation current standing wave formed in the conductor line are directly related to the wavelength of the excitation current, and the wavelength of the excitation current is decided by the frequency of the excitation signal. Therefore, when configuring an antenna based on the present invention, the key is to configure the lengths of every loop part and of every connecting part according to the frequency of the excitation signal.

Taking the excitation current standing waveforms shown in FIGS. 9 and 11 as examples, when configuring an antenna based on the present invention, determine the lengths of every loop part and every connecting part in accordance with the excitation signal frequency and thereby cause the excitation current to have opposite phases in every two successive loop parts and every connecting part to have a current wave node. Alternatively, cause the excitation current to have the same phase in every two successive loop parts and every connecting part to have two current wave nodes. Thus, in accordance with the above-described phase characteristics of the excitation current in every loop part and every connecting part, cause in every two succeeding loop parts the direction from the beginning to the end of the first loop part to be opposite to the direction from the beginning to the end of the second loop part. Alternatively, cause in every two successive loop parts the direction from the beginning of the end of the first loop part to be the same as the direction from the beginning to the end of the second loop part, thus causing the excitation current in all the loop parts to have the same direction.

When an antenna based on the present invention is specifically implemented, said loop parts, of which there are at least two, can be disposed on a base plate. In this case, the parameters of said base plate will change the free-space propagation characteristics of the electromagnetic waves and thereby change the wavelengths of the electromagnetic waves. The base plate parameters can, for example, include the thickness of said base plate, the dielectric constant of said base plate, and the dielectric loss factor of said base plate. Therefore, when configuring an antenna based on the present invention, one can further determine the equivalent wavelengths of the excitation current based on the parameters of said base plate and use these equivalent wavelengths to adjust the lengths of every loop part and every connecting part. The use of the equivalent dielectric constant for the propagation medium in determining the equivalent wavelengths of electromagnetic waves when being propagated in a propagation medium is current art within this field. No more will be said on this.

To summarize the above, in configuring and implementing an antenna based on the present invention, the size of said antenna is determined according to different requirements of specific fields of application, and the lengths of every loop part and of every connecting part are determined according to the excitation signal frequency. It is on this basis that the quantities of loop parts and connecting parts needed for the conductor line of the antenna are decided. These loop parts are disposed in a loop pattern, and in every two successive loop parts, the end of the first loop part is connected to the beginning of the second loop part through a connecting part that is separated from said loop pattern, with the result that said loop parts form a spatially discontinuous conductor loop. The current distribution in said loop parts is regulated by means of said connecting parts such that the magnetic fields generated by the current in said loop parts are added to each other and strengthen each other. As a result, this conductor loop can be used to generate a uniform magnetic field. In addition, by separating said connecting parts from said loop pattern, one can prevent the current in said connecting parts from having a substantive effect on the magnetic field generated by the current in said loop parts.

As it regulates the current distribution in said loop parts by means of said connecting parts, an antenna based on the present invention can be adapted to a broad range of excitation signal frequencies. Moreover, in contrast to the gap widths and the lengths of overlapped portions of conductors in US 2008/0048867 Al, the lengths of said connecting parts are not highly sensitive with respect to antennas based on the present invention. Therefore, antennas based on the present invention can easily be manufactured in large batches.

When an antenna based on the present invention is used for reading, the RFID tag must be parallel to the plane in which the loop parts are located when it passes through the reading zone because the magnetic field generated by the current in the loop parts is perpendicular to the plane in which the loop parts are located. In some fields of application, the RFID tag might be parallel to the plane in which the loop parts are located as it passes through the reading zone, but it might also be perpendicular to the plane in which the loop parts are located as it passes through the reading zone. In such cases, it will not be possible to read RFID tags that are perpendicular to the plane in which the loop parts are located as it passes through the reading zone.

A variant of an antenna based on the present invention that enables the RFID tag to be read in both of the situations described above is as follows: an antenna for an RFID system comprises a conductor line. This conductor line comprises at least four loop parts and at least three connecting parts. Said loop parts, of which there are at least four, are disposed in two separate loops in the same plane and are spatially discontinuous, with at least two loop parts being disposed on each loop. In every two successive loop parts, the end of the first loop part and the beginning of the second loop part are connected by a connecting part. This connecting part is disposed in such a manner as to be separate from said two loops. When an excitation signal is fed into said conductor line, said loop parts, of which there are at least four, and said connecting parts, of which there are at least three, generate an excitation current, and the excitation current then generates a magnetic field in each of said loop parts disposed in each loop further. Said magnetic fields, of which there are two, are opposite in polarity.

In said variant of an antenna based on the present invention, because the magnetic fields generated by the current in the loop parts disposed on the two loops are opposite in polarity, these two polar-opposite magnetic fields will form a new magnetic field. This new magnetic field will be orthogonal to the magnetic fields generated by the excitation current in the loop parts on the two loops. Thus, using the magnetic fields generated by the excitation current in the loop parts on the two loops, one can read an RFID tag that is parallel to the plane in which the loop parts are located as it passes through the reading zone, and using said new magnetic field, one can read an RFID tag that is perpendicular to the plane in which the loop parts are located as it passes through the reading zone .

An embodiment of said variant is as shown in FIG. 18. The conductor line 18 of this embodiment comprises four loop parts 180, 182, 184 and 186 and three connecting parts 181, 183 and 185. The loop parts 180 and 186 are disposed in a loop, and the loop parts 182 and 184 are disposed in another loop. The loop in which loop parts 180 and 186 are located is separate from the loop in which loop parts 182 and 184 are located, but are coplanar. As the magnetic field generated by the excitation current in loop parts 180 and 186 is polar-opposite to the magnetic field generated by the current in loop parts 182 and 184, the two polar-oppose magnetic fields will form a new magnetic field. The magnetic lines of force of these three magnetic fields are as shown by the dashed lines in FIG. 18. Thus, an RFID tag, regardless of whether it is moving parallel to the plane in which said loop parts are located or is moving perpendicular to the plane in which said loop parts are located, will in either case cut through magnetic lines of force. This movement which cuts through magnetic lines of force enables the RFID tag to be read when moving in either manner.

A method of configuring said variant of an antenna based on the present invention includes the following: the lengths of every loop part and every connecting part are determined according to the frequency of said excitation signal so that when an excitation signal is fed into said conductor line, said loop parts, of which there are at least four, and said connecting parts, of which there are at least three, generate an excitation current. The excitation current in said loop parts disposed in each loop further generates a magnetic field from each loop, and said magnetic fields, of which there are two, are opposite in polarity.

Detailed descriptions of specific embodiments of antennas based on the present invention and of methods of configuring them have already been provided above, and these specific forms of implementation may be appropriately applied to said variant and to the method of configuring same. Therefore, no more will be said concerning specific embodiments of said variant or of the method of configuring same.

An alternative solution, which is based on the technical concept of using a spatially discontinuous conductor loop to generate a magnetic field, to an antenna based on the present invention is as follows: an antenna for an RFID system comprises a radiating unit, which comprises at least two sections of conductor and at least one phase-shifting device. Said sections of conductor, of which there are at least two, are disposed in a loop and are spatially discontinuous. In every two successive sections of conductor, the end of the first section of the conductor and the beginning of the second section of the conductor are connected to the input terminal and output terminal, respectively, of a phase-shifting device. Said phase-shifting device comprises a 90 degree phase-shifting component, a first resistance component and a second resistance component. Said 90 degree phase-shifting component is connected in series with said first resistance component and then connected in parallel with said second resistance component. The nodes of the two ends of said parallel circuit separately constitute the input terminal and the output terminal of said phase-shifting device. When an excitation signal is fed into said radiating unit, said sections of conductor, of which there are at least two, and said phase-shifting devices, of which there is at least one, generate an excitation current. The excitation current of said sections of conductor, of which there are at least two, then generates a magnetic field.

In said alternative solution, to enable the excitation current in the sections of spatially discontinuous conductor to generate a uniform magnetic field, said phase-shifting device is used to regulate the phases of the excitation current in said sections of conductor. A circuit diagram of said phase- shifting device is as shown in FIG. 19. By means of said phase- shifting device, one can realize any phase shift quantity φ. The phase-shift quantity φ is decided by the ratio of the resistance Ri of the first resistance component to the resistance R2 of the second resistance component. The relationship between φ and Ri and R2 can be expressed using the formula stated below:

= tan(φ)

R,

Moreover, due to the thermal loss effect of the first and second resistance components, it is also possible to eliminate radiation from said radiating unit and thereby lower the antenna's far-field gain.

In a preferred embodiment of said alternative solution, said 90 degree phase-shifting component can be built as a transmission line transformer, and the first and second resistance components can be built as resistance components suitable for broadband, thereby enabling said phase-shifting device to adapt to a wider range of excitation signal frequencies .

A method of configuring an antenna based on said alternative solution includes: determine the lengths of each section of conductor and the resistance values of each first and each second resistance component according to the frequency of said excitation signal so that, when an excitation signal is fed into said radiating unit, an excitation current is generated by said sections of conductor, of which there are at least two, and said phase-shifting devices, of which there is at least one. The excitation current in said sections of conductor, of which there are at least two, then generates a magnetic field.

When using said configuration method to configure an antenna based on the said alternative solution, the dimensions of the antenna are determined according to the different requirements of specific fields of application, and the lengths of each section of conductor are determined according to the frequency of the excitation signal. The quantity of conductors that is required is determined on the basis of the above. Based on the lengths of each section of conductor and the quantities of conductors, one may determine the phase shift quantity that needs to be achieved by each phase-shifting device and determine therefrom the resistance values of each first resistance component and each second resistance component. Thus, one can cause the excitation current to have the same phase in all sections of the conductor and thereby enable the spatially discontinuous conductor loop formed by all sections of the conductor to generate a uniform magnetic field.

Like said variant of an antenna based on the present invention, a variant of said alternative solution comprises a radiating unit which has at least four sections of conductor and at least three phase-shifting devices. Said sections of conductor, of which there are at least four, are disposed in two separate loops in the same plane and are spatially discontinuous, with at least two sections of conductor being disposed on every loop. In every two successive sections of conductor, the end of the first section of the conductor and the beginning of the second section of the conductor are connected to the input terminal and the output terminal, respectively, of a phase-shifting device. Said phase-shifting device comprises a 90 degree phase-shifting component, a first resistance component and a second resistance component. Said 90 degree phase-shifting device is connected in series to the first resistance component and then is connected in parallel to the second resistance component. The nodes of the two ends of said parallel circuit constitute the input terminal and the output terminal, respectively, of said phase-shifting device. When an excitation signal is fed into said radiating unit, said sections of conductor, of which there are at least four, and said phase-shifting devices, of which there are at least three, generate an excitation current. The excitation current in said conductor which is disposed on each loop then generates a magnetic field from each loop. Said magnetic fields, of which there are two, are opposite in polarity.

A method of configuring a variant of said alternative solution includes: determine the lengths of each section of conductor and the resistance values of each first and each second resistance component according to the frequency of said excitation signal so that, when an excitation signal is fed into said radiating unit, an excitation current is generated by said sections of conductor, of which there are at least four, and said phase-shifting devices, of which there are at least three. The excitation current in said conductor, which is disposed in each loop, then generates a magnetic field from each loop. Said magnetic fields, of which there are two, are opposite in polarity.

By configuring the variant of said alternative solution, one can cause the excitation current in the conductor to have the same direction in each loop, but to have opposite directions with respect to the two loops of the conductor, with the result that the excitation current in the two loops of the conductor generates polar-opposite magnetic fields. These two polar-opposite magnetic fields will form a new magnetic field. This new magnetic field will be orthogonal to the magnetic fields generated by the excitation current in the two loops of the conductor. Thus, using the magnetic fields generated by the excitation current in the two loops of the conductor, one can read an RFID tag that is parallel to the plane in which the two loops are located as it passes through the reading zone, and using said new magnetic field, one can read an RFID tag that is perpendicular to the plane in which the two loops are located as it passes through the reading zone.

The above are detailed descriptions of antennas based on the present invention, of alternative solutions and variants, and of methods of configuring same. A person skilled in the art should comprehend that the above descriptions are not at all limiting. Any variant or modification that is made without departing from the substance of the invention shall fall under the protective scope of the present invention. Therefore, the protective scope of the present invention is determined by the attached claims.