Description

Antenna device, antenna system and method of operation

The invention relates to an antenna device, an antenna system and a method of operation.

In US 6,037,911 a high gain antenna is disclosed, especially suitable for applications with very high frequencies, e.g. with wave lengths in the mil- limeter range. The antenna uses a planar printed structure in form of pentagonal dipoles as radiation elements in conjunction with a dedicated flat reflector.

In US 6,940,470 B2 an antenna device is disclosed comprising a dielec- trie substrate board, dipole means formed on the substrate board and a V-shaped or convex reflector member.

It is the technical object underlying the invention to provide for an antenna device, an antenna system and a method of operation which have a high gain and a wide band width and which allow the integration of multiple antenna devices in an antenna system with a small geometrical size.

The invention solves this object by an antenna device having the fea- tures of claim 1 , an antenna system having the features of claim 14 and a method of operation having the features of claim 22.

The antenna device according to the invention comprises a dielectric substrate, e.g. a printed circuit board, having a front dielectric face and a back dielectric face, at least one dipole means or dipole printed on said dielectric substrate comprising a first and a second element for radiating and receiving electromagnetic signals, said first element pointing in a first direction and said second element pointing in a second direction

opposite to said first direction, and a reflector means associated with the dipole means. The printed dipole means defines a symmetry plane perpendicular to the substrate, the reflector means have a generally concave shape symmetric to a symmetry plane of the reflector means, wherein the symmetry plane of the reflector means coincides with the symmetry plane of the dipole means. The specific arrangement of the concave shaped reflector means in conjunction with the dipole means causes a defined horizontal or vertical radiation pattern of about 90 degrees which enables an integration of the antenna device as a 90 de- gree sector antenna within an antenna system, resulting in a small geometrical size of the antenna system.

In a further development said first element is printed on said front dielectric face and said second element is printed on said back dielectric face.

In a further development said first and second elements are each formed of a first segment of a circle or an ellipse, a second segment of a circle or an ellipse, wherein the second segment is arranged axially symmetric to the first segment, and a linking segment linking the first and the sec- ond segment, wherein the first segment, the second segment and the linking segment are each formed of a conductive material printed on said dielectric substrate. This arrangement implements an antenna composed of the first and second elements which works on a higher resonance as compared to elements which have a completely filled surface by using a higher level mode. Consequently a higher gain can be achieved. The size of the surface which is free of the conductive material and which may be close to a feeding point of the elements influences an antenna matching. Therefore an Antenna using such elements achieves higher gain capabilities by a smaller number of first and second ele- ments, however an operation bandwidth may be reduced.

In a further development said first and second elements have an elliptic or a circular shape. Such rounded shapes without edges result in a good radiation pattern of the antenna device.

In a further development said first and second elements are formed of a conductive material printed on said dielectric substrate, wherein the conductive material fills the complete outline of each element. Alternatively regions free of the conductive material are formed within the outline of each element. The conductor free regions inside the elements affect matching, resulting in "notch filter" functionality and the capability to provide steep matching edges in operation bands. This is suitable for providing application related dedicated solutions, where specific frequency regulators for protection bands are required.

In a further development a length and a width of said first and second elements are respectively smaller than 0.5 lambda, whereby lambda is a free space wavelength of a center frequency of a working frequency band of the antenna device.

In a further development a distance between the reflector means in their symmetry plane and the middle of said dielectric substrate is approximately one fourth of a free space wavelength or an electrical wavelength of a working frequency band of the antenna device.

In a further development a width of the dielectric substrate is the same or smaller than a width defined between longitudinal edges of the reflector means. The longitudinal edges of the reflector means may be attached to longitudinal edges of the dielectric substrate. Accordingly the substrate and the reflector means are arranged such that they define a volume together with front and end surfaces of this arrangement. If the width of the dielectric substrate is smaller than the width defined between the longitudinal edges of the reflector means the edges of the reflector means extend vertically above the dielectric substrate. Such an

- A - arrangement causes a suppression of radiation under the dielectric substrate which allows the integration of the antenna device in an antenna system containing more than one such antenna device. Each antenna devices serves as a sector antenna having a vertical radiation of prefer- able 90 degrees.

In a further development the reflector means form a reflective surface without recesses, e.g. holes. Such reflector means are easy to manufacture.

In a further development the antenna device comprises metal strip means for supplying signals to and from said dipole means, said metal strip means comprising a first line printed on said front face and coupled to said first element and a second line printed on said back face and coupled to said second element, wherein said first and second lines respectively comprise a plurality of first and second line portions, said first and second line portions respectively being connected to each other by T-junctions, whereby each of said first and second line portions is tapered between two adjacent T-junctions, so that the width of each line portion increases towards said first and second elements, respectively, and said line portions are tapered corresponding in decreasing or increasing function to provide an impedance transformation in the succeeding T-junction. This results in a wide band high gain signal feeding for the dipole means.

In a further development said first and said second lines and said T- junctions are balanced and arranged parallel and opposite to each other on said front and back dielectric face, respectively.

In a further development the antenna device comprises a transition element coupled to said first and second lines and to third and fourth lines to provide a transition between said first and second lines and said third and fourth lines, respectively, transforming a balanced microstrip struc-

ture of said first and second lines to an unbalanced microstrip structure, wherein one of the third or fourth lines are increasing in the width according to an exponential function with a negative exponent.

The antenna system according to the invention comprises at least two, preferably four, antenna devices according to the invention. The antenna devices are preferably displaced by 90 degree to each other.

In a further development of the antenna system at least one of the an- tenna devices is switched off according to an operation mode of the antenna system. This allows a flexible operation of the antenna system.

In a further development of the antenna system at least one of the antenna devices is mounted rotatable, in order to obtain an optimum transmission quality.

In a further development of the antenna system it comprises at least one radio transmission unit which may be dedicated to one or more of the at least two antenna devices and a body, whereby the antenna devices and the radio transmission unit are integrated in the body. Such an arrangement allows a compact design of a completely functional radio transmission unit including a dedicated antenna system. Preferable a first radio transmission unit is a wireless local area network (WLAN) transceiver or router and/or a second radio transmission unit is a World- wide Interoperability for Microwave Access (WiMAX) transceiver. Preferably the first radio transmission unit and the second radio transmission unit are functionally coupled to implement a router.

The method of operation of a wireless communication system compris- ing at least one antenna system according to the invention comprises the steps: placing the antenna system in an indoor environment, adjusting one of the at least two antenna devices in a direction of a maximum signal strength of a signal originated from a outdoor WiMAX or a Ultra-

wideband (UWB) base station and transmitting data by means of the other of the at least two antenna devices within the indoor environment. The indoor data transmission may e.g. be carried out according to a wireless LAN (WLAN) standard.

The invention is now explained with reference to the accompanying drawings, in which

Fig. 1 shows an antenna device according to a first embodi- ment of the invention with a first polarization direction,

Fig. 2 shows an antenna device according to a second embodiment of the invention with the first polarization direction,

Fig. 3 shows an antenna device according to a third embodiment of the invention with a second polarization direction,

Fig. 4 shows an antenna device according to a fourth embodi- ment of the invention with the second polarization direction,

Fig. 5 shows an antenna device according to a fifth embodiment of the invention with the first polarization direction,

Fig. 6 shows alternative dipole means of an antenna device according to an embodiment of the invention comprising first and second elements each formed of a first segment of a circle, a second segment of a circle and a linking segment between the first and the second segments,

Fig. 7 shows alternative dipole means of an antenna device according to a further embodiment of the invention compris-

ing first and second elements each formed of a conductive material printed on said dielectric substrate, wherein regions free of the conductive material are formed within the outline of each element,

Fig. 8 and 9 show antenna devices with different forms of reflector means, each in cross sectional views,

Fig. 10 to 13 show different BULUN structures for signal feeding,

Fig. 14 shows an antenna system comprising antenna devices with horizontal polarisation,

Fig. 15 shows an antenna system comprising antenna devices with vertical polarisation,

Fig. 16 shows an antenna system comprising antenna devices with vertical polarisation, wherein the antenna devices have dielectric substrates with reduced surfaces,

Figs. 17 to 19 show further embodiments of antenna systems according to the invention, and

Fig. 20 shows an exemplary operation scenario of an antenna system according to the invention.

Fig. 1 shows an antenna device 200 according to a first embodiment of the invention with a linear polarization in x-direction.

The antenna device 200 comprises a dielectric substrate 1 with a front dielectric face 2 and a back dielectric face 3. Two dipole means 4 each comprise a first element 5 printed on the front dielectric face 2 and a second element 6 printed on the back dielectric face 3. The dipole

means 4 radiate and receive electromagnetic signals, wherein the first elements 5 point in a first direction x and the second elements 6 point in a second direction -x opposite to said first direction x. The dipole means 4 are arranged in the longitudinal direction x in the middle of the dielec- trie substrate 1 related to the longitudinal direction x. The elements 5 and 6 have a circular shape with a diameter I. The elements 5 and 6 may have another elliptic or rounded shape, whereby a diameter or length I and a width w of the elements 5 and 6 are respectively smaller than 0.5 lambda, whereby lambda is a free space wavelength of a cen- ter frequency of a working frequency band of the antenna device 200.

The elements 5 and 6 are each formed of a conductive material printed on said dielectric substrate 1 , wherein the conductive material fills the complete outline of the elements 5 and 6, respectively.

A reflector means 10 associated with the dipole means 4 has a functional concave shape with a continuous closed reflective surface. A concave cross section of the reflector means 10 in the direction y extends without changing it's shape in the longitudinal direction x. The reflector means 10 is realized by an plastic body with a metalized surface. The plastic body may be manufactured by extrusion or injection moulding.

The printed dipole means 4 define a symmetry plane 100 in the longitudinal direction x perpendicular to the substrate 1. The symmetry plane 100 of the dipole means 4 coincides with a symmetry plane in the longitudinal direction x of the reflector means 10.

The substrate 1 is placed on top of and aligned with the reflector means 10, whereby a width ws in y-direction of the dielectric substrate 1 is the same as a width defined between edges in x or longitudinal direction of the reflector means 10. Such an arrangement causes a suppression of radiation under the dielectric substrate 1 in -z direction which allows the integration of the antenna device 200 in an antenna system containing

more than one such antenna device 200 with no or little interference between the different antenna devices 200. Each antenna device 200 serves as a sector antenna having a vertical radiation of preferable 90 degrees.

Signals to and from the dipole means 4 are supplied by metal strip means 7. The metal strip means 7 comprise a first line 8 printed on the front face 2 and coupled to the first element 5 and a second line 9 printed on the back face 3 and coupled to the second element 6, wherein the first and second lines 8 and 9 respectively comprise a plurality of first and second line portions 13 and 14, which are respectively connected to each other by T-junctions 15, whereby each of the first and second line portions 13 and 14 is tapered between two adjacent T- junctions 15, so that the width of each line portion 13 and 14 increases towards the first and second elements 5 and 6, respectively, and said line portions 13 and 14 are tapered corresponding in decreasing or increasing function to provide an impedance transformation in the succeeding T-junction 15.

The first and second lines 8 and 9 and the T-junctions 15 are balanced and arranged parallel and opposite to each other on the front and back dielectric face 2 and 3, respectively.

A transition element 12 is coupled to the first and second lines 8 and 9 and to third and fourth lines 16 and 17 to provide a transition between the first and second lines 8 and 9 and the third and fourth lines 16 and

17, respectively, transforming a balanced microstrip structure of the first and second lines 8 and 9 to an unbalanced microstrip structure, wherein the third line 16 is decreasing in the width according to an exponential function with a negative exponent. The transition element 12 is also called BALUN, i.e. a device designed to convert between balanced and unbalanced electrical signals, such as between coaxial cable and ladder

line. BALUNs can be considered as simple forms of transmission line transformers.

The above discussed structure of the metal strip means 7 allows a broadband signal feeding to the dipole means 4.

Fig. 6 shows alternative dipole means 4 of an antenna device according to a further embodiment of the invention comprising a first element 5 and second element 6. The first element 5 is formed of a first segment 5a of a circle, a second segment 5b of a circle, wherein the second segment 5b is arranged axially symmetric with respect to a horizontal axis to the first segment 5a, and a linking segment 5c arranged as a conductive strip between the first and second segments 5a and 5b. The second element 6 is formed of a first segment 6a of a circle, a second segment 6b of a circle, wherein the second segment 6b is arranged axially symmetric with respect to a horizontal axis to the first segment 6a, and a linking segment 6c arranged as a conductive strip between the first and second segments 6a and 6b. The first segments 5a and 6a, the second segments 5b and 6b and the linking segments 5c and 6c are each formed of a conductive material printed on the dielectric substrate 1. The metal strip means 7 supplies signals to the elements 5 and 6, respectively. The linking segments 5c and 6c separate a lower area 5d and 6d from an upper area 5e and 6e, respectively. The lower areas 5d and 6d influence the input impedance of the dipole means 4. The upper areas 5e and 6e influence further radiation parameters of the dipole means 4. The dipole means 4 of Fig. 6 provides a higher order radiation resonance with increased gain.

Fig. 7 shows another alternative dipole means of an antenna device ac- cording to an embodiment of the invention comprising first and second elements 5 and 6 each formed of a conductive or metalized material printed on said dielectric substrate 1 , wherein regions 5f and 6f free of the conductive material are formed within the outline of each element 5

and 6, respectively. A length of the non metalized regions 5f and 6f, their thickness and position in the circular or elliptic elements 5 and 6 influences a frequency position of a notch filter (resonance), realized by the depicted elements 5 and 6. Further a steepness in a corresponding matching diagram and/or a steepness of an edge of a matching at a boarder of operation bands is also controlled by the above parameters.

The elements shown in Figs. 6 and 7 still exhibit an envelope or an outer edge with an elliptic or circular shape, wherein a part of the elliptic or cir- cular shape is erased in different manners. In Fig. 6 non metalized regions or conductor free areas are provided on the right and the left side of the linking segment 5c. In Fig. 7 closed portions of the conductor free areas are provided inside the elements 5 and 6, wherein the conductor free areas do not touch an outer edge or outline of the elements 5 and 6.

Fig. 8 and 9 show antenna devices 200 with different forms of reflector means 10, each in cross sectional views. In Fig. 8 the concave cross section of the reflector means 10 is composed of two straight lines 10a and 10b, wherein the lines 10a and 10b are mirrored at the symmetry plane 100 of the reflector means 10 to form the other half of the reflector means 10. The straight line 10a constitutes an angle α of about 45 degrees with a plane perpendicular to the substrate 1 and the straight line 10b constitutes an angle β of about 60 degrees with the plane perpendicular to the substrate 1. More than two straight lines 10a and 10b with different angles may be used to build the concave form of the reflector means 10. This arrangement allows to group for e.g. four antenna devices as 90 degrees sector antennas within an antenna system, wherein the antenna devices adjoin on longitudinal edges of the substrate 1 and are rotated by 90 degrees with respect to the adjoining antenna device.

A distance h between the reflector means 10 in their symmetry plane and the middle of the dielectric substrate 1 is approximately one fourth of

an electrical wavelength of a working frequency band of the antenna device.

In Fig. 9 the reflector means 10 is composed of a segment of a circle or an ellipse. The distance h may be equal to one half of the width ws of the dielectric substrate 1.

The shown arrangement allows to group for e.g. four antenna devices as 90 degrees sector antennas within an antenna system, wherein the an- tenna devices adjoin on longitudinal edges of the substrate 1 and are rotated by 90 degrees with respect to the adjoining antenna device.

Figs. 2 to 5 show antenna devices 200 according to various embodiments of the invention, each having concave reflector means 10 with a symmetry plane 100 which coincides with the symmetry plane of the printed dipole means 4.

The antenna device 200 of Fig. 2 differs from the antenna device 200 of Fig. 1 by the position and the rating of the transition element or BALUN 12. The transition element 12 of Fig. 2 is placed at a front side of the antenna device 200 whereas the transition element 12 of Fig. 1 is placed at a longitudinal side of the antenna device 200. The transition element 12 of Fig. 1 may be designated for broadband coaxial signal feeding and the transition element 12 of Fig. 2 may be designated for broadband planar signal feeding. The preferred position and rating of the BALUN 12 depends on the use of the antenna device 200 in an antenna system.

Fig. 3 shows an antenna device 200 with a linear polarization in y- direction and a transition element 12 with a tapering for achieving broadband impedance matching with coaxial signal feeding.

Fig. 4 shows an antenna device 200 with a linear polarization in y- direction and a transition element 12 with a tapering for achieving

broadband impedance matching with planar signal feeding. The signals may be fed through the antenna device 200 by metal strip means 7'.

Fig. 5 shows an antenna device 200 similar to that of Fig. 2, wherein the dielectric substrate 1 has a reduced width ws ¹ to reduce the manufacturing cost of the dielectric substrate 1. The arrangement of the dipole means 4 relative to the reflector means 10 is the same as in Fig. 2.

Figs. 10 to 13 show different BULUNs or transition elements 12 for sig- nal feeding used in the antenna devices 200 of Figs. 1 to 5.

The transition element 12 of Fig. 10 is used for example in the antenna device 200 of Fig. 1 to couple a coaxial cable 20 with the printed feeding structure on the dielectric substrate 1. The inner or hot conductor 42 of the coaxial cable 20 is electrically connected to a first BALUN portion 40 printed on the front face of the dielectric substrate 1. The shielding 43 of the coaxial cable 20 is electrically connected to a second BALUN portion 41 printed on the back face of the dielectric substrate 1. The second BALUN portion 41 is decreasing in the width towards the T-junction 15 according to an exponential function with a negative exponent. The transition element 12 of Fig. 11 is similar to that of Fig. 10, wherein the BALUN additionally extends in longitudinal direction.

The transition element 12 of Fig. 12 is used for example in the antenna devices 200 of Figs. 2, 4 and 5 to couple a signal feeding means with the printed feeding structure on the dielectric substrate 1. The transition element 12 of Fig. 13 is used for example in the antenna device 200 of Fig. 3 to couple a signal feeding means in form of the coaxial cable 20 with the printed feeding structure on the dielectric substrate 1.

Fig. 14 shows an antenna system 1000 comprising four antenna devices 200 with horizontal polarisation. The antenna devices may be of the type of the antenna device 200 shown in Fig. 3. The antenna devices 200 ad-

join on longitudinal edges of the substrate 1 and are rotated by 90 degrees with respect to the adjoining antenna device. Therefore the antenna devices 200, a top 300 and a bottom 301 constitute a body in which a radio transmission unit (not shown) may be integrated. The ra- dio transmission unit may be a wireless LAN transceiver or router, a WiMAX transceiver or router, a UWB transceiver or router and/or a Wi- MAX or UWB to WLAN router.

In case of e.g. a WiMAX to WLAN router a WiMAX portion of the router may be allocated to one of the four antenna devices 200 and a WLAN portion of the router may be allocated to another antenna device 200.

Fig. 15 shows an antenna system 1000 comprising four antenna devices 200 with vertical polarisation. The antenna devices 200 may be of the type of the antenna device 200 shown in Fig. 1. Except this difference the antenna system 1000 is similar to that of Fig. 14.

Fig. 16 shows an antenna system 1000 comprising four antenna devices 200 with vertical polarisation, wherein the antenna devices 200 have di- electric substrates 1 with reduced surfaces. The antenna devices 200 may be of the type of the antenna device 200 shown in Fig. 5. Except this difference the antenna system 1000 is similar to that of Fig. 15.

Figs. 17 to 19 show further embodiments of antenna systems 1000 ac- cording to the invention.

The antenna system 1000 of Fig. 17 comprises four antenna devices 200 each having two dipole means with a horizontal and two dipole means 4 with a vertical polarization.

The antenna system 1000 of Fig. 18 comprises four antenna devices 200 each having four dipole means with a vertical polarization. Alternatively the antenna system 1000 of Fig. 18 may e.g. be formed of eight

antenna devices 200 of Fig. 1 , wherein on each side of the antenna system 1000 two such antenna devices 200 are stacked.

Fig. 19 shows an antenna system 1000 with four antenna devices 200 each having eight dipole means with a vertical polarization. The antenna system 1000 may e.g. be formed of 16 antenna devices 200 of Fig. 1 , wherein on each side of the antenna system 1000 four such antenna devices 200 are stacked. The achievable gain increases with the number of dipole means of each antenna device.

Fig. 20 shows an exemplary operation scenario of an antenna system 1000 according to the invention. The antenna system 1000 may be one of the antenna systems 1000 shown in figs. 14 to 19.

The antenna system 1000 is placed in an indoor environment, e.g. in a room near a window 50. At least one of the antenna devices is adjusted in a direction of a maximum signal strength of a signal originated from a outdoor WiMAX or UWB base station 2000. Data within the indoor environment are exchanged or transmitted by means of another antenna de- vice of the antenna system 1000. The antenna system 1000 may comprise additional hardware and/or software (not shown) by which a Wi- MAX or UWB to WLAN router is implemented in conjunction with the antenna devices. The WLAN data received and/or transmitted over one of the antenna devices is then transparently redirected or routed to/from another antenna device.

The above embodiments of an antenna, a corresponding antenna system and a corresponding method of operation are especially dedicated for low cost printed antennas and antenna systems on simple low cost substrates, where manufacturing tolerances are secondary compared to system costs. The invention addresses very wide band frequency operation allowing multi band operation capability and the ability to integrate a front end on the same substrate on which the antenna is printed. The

invention is especially useful for access point solutions for UWB systems, WiMax systems and other wireless WAN systems.