Field of the Invention

The present invention relates to a folded loop antenna with a switch circuit for establishing connection between the antenna structure and the ground or any other sub circuit of an electronic apparatus. Background of the Invention

Different small embedded antennas are used in wireless communication devices such as in radio telephones, personal base stations, portable handsets, personal digital assistants, MP3 players, video players and other small, compact and lightweight communication terminals. The number of antennas in each device is increasing as well as the number of available wireless services such as Global System for Mobile Communications (GSM), Distributed Control System (DCS), Personal Communications Service (PCS), UW, Digital Video Broadcasting-Terrestrial/Handheld (DVB-T/H), Wireless Fidelity (Wifi), Bt, Worldwide Interoperability for Microwave Access (Wimax), Long Term Evolution (LTE), Global Positioning System (GPS) etc. Thus, embedded antennas need to be small and to have high performance. Different folded antennas are available for wireless communication devices. However, Specific Absorption Rate (SAR) and Hearing Aid Compatibility (HAC) level and high performances are challenging for the available antennas. Further the available antennas have to, in many cases, make a compromise between the size of the antenna and the performances of the antenna.

One of these available antennas is a small folded loop antenna designed to provide the capability to create several resonances, in low band (< 1 GHz) and up to six resonances in high bands (1 ,5 GHz to 3 GHz bands). This folded loop antenna has drawbacks, for example, a narrow bandwidth of the low band resonance. There is a need for antennas with very wide frequency band in low band (<1 GHZ), because of increasing number of protocols, such as LTE. Typically, for example, a 2G/3G/LTE antenna needs to cover from 698 MHZ to 964 MHz, from 1710 MHz to 2170 MHz and from 2500MHz to 2690 MHz. The very wide low frequency band (698MHZ to 964MHz) may not be coverable with good Return Loss (RL) <-6dB and high efficiency by the low band resonance of the folded loop antenna. In addition, another drawback is that only one of the different resonances of the folded loop antenna located in the high band (1710 MHZ to 2170 MHZ) is coming from a balanced (non-radiating) mode. Therefore only one resonance (and so one limited portion of the high band) may benefit of the advantages of the balanced mode, for example, lower losses from the head when the phone is in "beside head" position, lower HAC and SAR values. There is, therefore, a need for a small high performance antenna providing high efficiency, higher immunity to the losses created by the head effect when the device is used beside the head, wide bandwidths, low Specific Absorption Rate (SAR) and low Hearing Aid Compatibility (HAC).

Summary of the Invention

Now there has been invented an improved antenna structure by which the above problems are alleviated. Various aspects of the invention include an antenna structure which is characterized by what is stated in the independent claim. Various embodiments of the invention are disclosed in the dependent claims.

The invention relates to an antenna structure comprising at least one folded loop antenna element, a radiator, and at least one active switch circuit for establishing a connection between the antenna structure and the ground or other sub circuit of an electronic apparatus, wherein the antenna structure is a high performance antenna providing high efficiency, higher immunity to the losses created by the head effect when the device is used beside the head, wide bandwidths, low Specific Absorption Rate (SAR) and low Hearing Aid Compatibility (HAC). According to a first aspect of the invention, there is provided an antenna structure for a wireless communication device comprising a folded loop antenna radiator comprising a signal feeding point at the first end of the loop antenna and at least one contact point at the second end of the loop antenna. At least one switch circuit is electrically connected to the contact point of the loop antenna. The switch circuit comprises at least a first switch path with a load and a second switch path with a load, wherein the load of the first switch path is different from the load of the second switch path. The folded loop antenna radiator is connectable to a ground plane or a sub circuit of an electronic device through one of the switch paths.

According to an example embodiment, the switch circuit is a switch, a diode, a varactor, a capacitor bank, a Micro Electrical Mechanical System (MEMS). According to an example embodiment, there is a low pass or high pass filter between the folded loop antenna radiator and said at least one switch circuit. According to an example embodiment, the load is a simple load. According to an example embodiment, the simple load is a resistor, inductor, capacitor, short end or open end. According to an example embodiment the load is a complex load. According to an example embodiment, the complex load is a combination of the simple loads, wherein the simple loads are connected in parallel or in series.

Description of the Drawings

In the following, various embodiments of the invention will be described in more detail with reference to the appended drawings, in which

Fig. 1 shows a block diagram of an antenna structure according to an example embodiment;

Fig. 2 shows a plane view of an antenna structure according to an example embodiment; and shows a block diagram of a switch of an antenna structure according to an example embodiment.

Detailed Description of the Embodiments

In the following, several embodiments of the invention will be described in the context an antenna structure comprising at least one antenna element, radiator, and at least one switch circuit. It is to be noted, however, that the invention is not limited to a number of antenna radiators or type or number of switch circuits. In fact, the different embodiments have applications widely in any environment where antenna structures are required.

Fig. 1 shows an antenna structure 1 00 according to an embodiment of the invention. The antenna structure 1 00 comprises an antenna element i.e. an antenna radiator 1 01 and a switch circuit 1 02. The antenna radiator 1 01 has a signal feeding point 1 03 and a contact point. The feeding point 1 03 is located at the beginning (first end) of the loop of the radiator 1 01 while the contact point is located near the end (second end) of the radiator 1 01 . There may also be more than one feeding points and switch circuits (and respectively more than one contact points), for example, two, three, four or five. The end of the radiator 1 01 , the contact point, is electrically connected to the circuit 1 02. The circuit 1 02 comprises at least two switch paths comprising at least one simple load. The simple load may be, for example, a resistor 1 05, an inductor 1 06, a capacitor 1 07, a short end 1 08 or an open end 1 09. However, the switch path may also comprise any complex load, wherein the complex load may be any combination of the simple loads 1 05, 1 06, 1 07, 1 08, 1 09 or it may also comprise more than one same kind of simple loads or a combination of simple loads, wherein there are more than one same kind of simple loads. Two or more simple loads may be connected in parallel or in series. Loads of each switch path are different or at least a load of at least one switch path is different from the load of at least one other switch path of a switch circuit. Via the switch path the end of the radiator 101 can be electrically connected to a ground plane 1 04 of an electronic device instead of connecting the end of the radiator 101 directly to the ground plane 104 of an electronic device. However, it is also possible to connect the end of the radiator 101 via the switch path to, for example, a sub circuit of the electronic device.

The circuit 102 connected at the end of the radiator 101 may be, for example, a switch, a diode, a varactor, a capacitor bank, a Micro Electrical Mechanical System (MEMS) or any other circuit which can provide a tunable impedance load at the end of the loop antenna radiator 101 . The switch may be realized in any type of technology such as gallium arsenide (GaAs), Complementary Metal-Oxide Semiconductor (CMOS), Silicon On Sapphire (SOS) or Micro-Electro- Mechanical Systems (MEMS). It may be Single-Port N-throw (SPnT) type, meaning that the number of states is n, wherein the n may be 1 ,2,3 or more.

With the different kinds of switch paths with at least one load the impedance and electrical length of the loop of the radiator 101 can be controlled and tuned. This offers a possibility for the antenna structure 100 to have different configurations i.e. tuning states in order to cover the low band or the high band with a more optimum matching for each band. Several tuning states may also be used to cover different part of the low band or high band in order to achieve optimum performance on specific portions of each band. The typical bands covered by the antenna are, for example, GSM frequency bands: 850, 900, 1800 or 1900 MHz, Wideband Code Division Multiple Access (WCDMA) bands: 21 10 to 2170 MHz (Bands I), 1930 to 1990 MHz (Band II), 869 to 894 MHz (Band V), or 925 to 960 MHz (Band VIII), and Long Term Evolution (LTE) bands: 4, 17 1 , 3, 7, 8, or 20.

By adjusting the electrical length of the loop of the radiator 101 it may be possible to tune the resonance of the high band higher or lower, which resonance of the high band is coming from the balanced mode. Therefore, the benefits of the balanced mode resonance can be available in different portions of the band. It should also be noted that when compared to a conventional folded loop antenna, the antenna structure 100 may be smaller with same level of performances or the antenna structure 100 may provide better performances within a given volume.

Fig. 2 shows a plane view of an antenna structure 200 according to an example embodiment. The antenna structure 200 comprises a folded loop antenna radiator 201 and a switch circuit 202. The switch circuit 202 is electrically connected to the end of the antenna radiator 201 , to a connection point. Signal is applied to the antenna structure 200 at its feed point 204. The antenna radiator 201 is realized in flex foil technology. However, it is also possible to realize the antenna radiator using Metal sheet technology, LDS technology, Two shot molding MID technology, or any other method.

Fig. 3 shows a block diagram of an example of a switch circuit 300 of an antenna structure according to an example embodiment. The switch circuit 300 is a switch circuit with a Single-Pole Four-Throw (SP4T) switch 301 . The switch circuit 300 has an LC filter comprising an inductor 302 and a capacitor 303 at the input, which acts as an ESD protection for the active device. Inductance and capacitance values for this filter may be, for example, L = 15nH and C = 8pF. Impedance loads of the four switch paths 304, 305, 306, 307 may be, for example, short-circuit, open end, inductance, capacitance, or any other complex reactive circuit, as series LC or parallel LC. Again the switch paths 304, 305, 306, 307 have different kinds of loads. However, it is also possible that only one switch path has a different kind of load in comparison to the other switch paths.

Either a folded loop antenna radiator or a switch circuit or both may be designed to avoid undesired switching in one band. For example, if the antenna itself covers high-band, for example, 1710-2170MHz or 1710- 2600MHz, and no resonance switching is need, a low-pass filter may be added at the input of the switch circuit. The low pass filter prevents a high-band signal from passing through the switch circuit and thus the high-band will remain unchanged. An antenna structure according to this invention may have any shape necessary to comply with the dimensional requirements of the wireless communication device in which the antenna structure is adapted for use. The antenna radiator and the switch circuit may also have any shape necessary to comply with the functional and electrical requirements of the wireless communication device in which the antenna structure is suitable for use.

It is obvious that the present invention is not limited solely to the above- presented embodiments, but it can be modified within the scope of the appended claims.