WO2009108121A1

WO2009108121A1 - Patch antenna array for wireless communication

Info

Publication number: WO2009108121A1
Application number: PCT/SG2008/000067
Authority: WO
Inventors: Monai Krairiksh; Akkarat Boonpoogna; Phaophark Sirisuk; Mitchai Chongcheawchamnan; Chuwong Phongcharoenpenich; Jukkrit Tagapanij
Original assignee: The Thailand Research Fund; King Mongkurt's Institute Of Technology Ladkrabang; Axis Ip Holding Pte Ltd
Priority date: 2008-02-28
Filing date: 2008-02-28
Publication date: 2009-09-03

Abstract

An antenna system for wireless communication applications is disclosed. The antenna system comprises a radiating element having two feed points for transmitting and receiving signals. The antenna system also has a switch coupled to the radiating element at the two feed points and a signal processor coupled to the switch for switching between the two feed points for signal coupling the radiating element with the signal processor and for modifying the radiation pattern of the radiating element. The signal processor is for processing signals received from the radiating element. The antenna system further has a power detector coupled to the switch for determining power level of the signals received by the signal processor. In particular, when the antenna system is in use, the signal processor modifies the radiation pattern and that the power level of the signals is influenced by the radiation pattern, whereby modifying the radiation pattern optimizes the power level of the signals received by the signal processor from the radiating element.

Description

PATCH ANTENNA ARRAY FOR WIRELESS COMMUNICATION

Field of Invention The invention relates generally to antennas. In particular, it relates to an array of patch antennas for wireless communication.

Background

The use of wide-band technology is becoming increasingly popular in mobile communication systems. This allows high-speed communication to be established between mobile devices for achieving faster data transfer. As a result, antenna systems that employ wide-band technology have a propensity to be affected by interference and the effects of multipath fading during communication with other wide-band antenna systems.

A conventional way of mitigating the problem of interference in wide-band antenna systems is through the use of Constant Modulus Algorithm (CMA). With proper initiation conditions, the CMA is capable of mitigating the forgoing interference effectively.

However, the CMA tends to converge slowly, which undesirably reduces the operational speed of the wide-band antenna systems. Additionally, the CMA has a tendency to develop errors that potentially results in the wide-band antenna systems receiving interference signals instead of desired signals. This makes conventional wide-band antenna systems using CMA unsuitable for supporting high-speed mobile communication, such as at an operating frequency of 5.8GHz.

There is therefore a need for an antenna system which is resistive to interference and capable of operating at high speed for supporting mobile communication. Summary

Embodiments of the invention are disclosed hereinafter for an antenna system which is resistive to interference and capable of operating at high speed for supporting mobile communication.

In accordance with a first embodiment of the invention, there is disclosed an antenna system for wireless communication applications. The antenna system comprises a radiating element having two feed points for transmitting and receiving signals. The antenna system also has a switch coupled to the radiating element at the two feed points and a signal processor coupled to the switch for switching between the two feed points for signal coupling the radiating element with the signal processor and for modifying the radiation pattern of the radiating element. The signal processor is for processing signals received from the radiating element. The antenna system further has a power detector coupled to the switch for determining power level of the signals received by the signal processor. In particular, when the antenna system is in use, the signal processor modifies the radiation pattern and that the power level of the signals is influenced by the radiation pattern, whereby modifying the radiation pattern optimizes the power level of the signals received by the signal processor from the radiating element.

In accordance with a second embodiment of the invention, there is disclosed a method for configuring an antenna system for wireless communication applications. The method involves an initial step of providing a radiating element having two feed points for transmitting and receiving signals and a switch coupled to the radiating element at the two feed points. The method also involves providing a signal processor coupled to the switch for switching between the two feed points for signal coupling the radiating element with the signal processor and for modifying the radiation pattern of the radiating element. The signal processor is for processing signals received from the radiating element. The method further involves providing a power detector coupled to the switch for determining power level of the signals received by the signal processor. In particular, when the antenna system is in use, the signal processor modifies the radiation pattern and that the power level of the signals is influenced by the radiation pattern, whereby modifying the radiation pattern optimizes the power level of the signals received by the signal processor from the radiating element.

In accordance with a third embodiment of the invention, there is disclosed an antenna system for wireless communication applications. The antenna system comprises a plurality of radiating elements, each of the plurality of radiating elements having two feed points for transmitting and receiving signals. The antenna system also has a switch coupled to each of the plurality of radiating elements at the two feed points and a signal processor coupled to the switch for switching between the two feed points for signal coupling each of the plurality of radiating elements with the signal processor and for modifying the radiation pattern of each of the plurality of radiating elements. The signal processor is for processing signals received from each of the plurality of radiating elements. The antemia system further has a power detector coupled to the switch for determining power level of the signals received by the signal processor. In particular, when the antenna system is in use, the signal processor modifies the radiation pattern and that the power level of the signals is influenced by the radiation pattern, whereby modifying the radiation pattern optimizes the power level of the signals received by the signal processor from the plurality of radiating elements.

Brief Description of Drawings

Embodiments of the invention are described in detail hereinafter with reference to the drawings, in which:

Fig. 1 is an isometric view of a radiating element according to an embodiment of the invention;

Fig. 2 is a bottom view of the radiating element of Fig. 1;

Fig. 3 shows a schematic diagram of the antenna system according to an embodiment of the invention;

Fig. 4 shows propagation of electromagnetic waves along x and y axes when a first feeding probe of the radiating element of Fig. 1 receives signals; Fig. 5 shows propagation of electromagnetic waves along x and y axes when a second feeding probe of the radiating element of Fig. 1 receives signals;

Fig. 6 is a graph showing measured radiation patterns generated by the antenna system of Figs. 4 and 5 across the x-y plane;

Fig. 7 is a graph showing radiation patterns generated by the radiating element of Fig. 1 along predetermined directions during operation of the antenna system of Fig. 3; and

Fig. 8 shows a table of radiation patterns of the antenna system of Fig. 3 during operation thereof.

Detailed Description With reference to the drawings, an antenna system that is dimensionally small for high frequency code division multiple access (CDMA) applications according to embodiments of the invention is disclosed.

Various conventional antenna systems have been previously proposed. Some of these conventional antenna systems have insufficient operating speed and are therefore not suitable for use in high frequency CDMA applications. Other conventional antenna systems have fixed radiation patterns, which inevitably limits the operational flexibility of the antenna systems.

For purposes of brevity and clarity, the description of the invention is limited hereinafter to CDMA applications. This, however, does not preclude embodiments of the invention from other applications that require similar operating performance as the CDMA applications. The functional principles fundamental to the embodiments of the invention remain the same throughout the various embodiments.

Embodiments of the invention relates to an antenna system. The antenna system is preferably dimensionally small and is used for high frequency CDMA applications that require a compact design. The antenna system preferably comprises an array of radiating elements that includes a predetermined number of radiating elements.

The embodiments of the invention are described in greater detail in accordance with Figs. 1 to 8 of the drawings hereinafter, wherein like elements are identified with like reference numerals.

The invention relates to an antenna system according to a first embodiment of the invention. The antenna system is dimensionally small and is used for high frequency CDMA applications that require a compact design. The antenna system preferably comprises a radiating element array that includes a predetermined number of radiating elements.

Fig. 1 is an isometric view of each radiating element 104 of a radiating element array 102. The radiating element 104 is formed on a surface of a substrate 106, such as a printed circuit board (PCB). The radiating element 104 is used for transmitting and receiving signals to and from other antenna systems.

The radiating element 104 is geometrically shaped and preferably plate-like. In the first embodiment of the invention as shown in Fig. 1, the radiating element 104 is a patch antenna that is preferably square-shaped and has a planar surface. The length of each side of the radiating element 104 is preferably equal to one operating wavelength λ₀ of the antenna system 100.

The substrate 106 preferably has a dielectric constant ε_rof 10.2 and a lost tangent of 0.0013. The substrate 106 preferably has a thickness of 0.25mm. One exemplary dimension of the radiating element 102 is 15.5mm by 15.5mm. This advantageously allows the antenna system 100 to adopt a compact design for installation in wireless communication handsets.

The following description of the radiating element 104 is made with reference to an x- axis, a y-axis and a z-axis. The three axes are perpendicular to each other and intersect at an origin O. The x and y axes extend along the radiating element 104 and are coincident therewith.

With reference to Fig. 1, the radiating element 104 has a first feed point 108 and a second feed point 110. The first feed point 108 is located along the x-axis and at a distance x/ from the origin O. The second feed point 110 is located along the y-axis and at a distance y/ from the origin O.

As shown in Fig. 1, the first and second feed points 108, 110 are connected to a first and second feeding probes 112, 114, respectively. The first and second feed points 108, 110 are further connected via the first and second feeding probes 112, 114 to a radio frequency (RF) switch 116. The RF switch 116 preferably functionally switches between the first and second feeding probes 112, 114 such that only one of the first 112 and the second 114 feeding probes is in use at any one time.

Fig. 2 shows a bottom view of the radiating element 104. With reference to Fig. 2, the RF switch 116 is formed on one side of the substrate 106 opposite the radiating element 104. The RF switch 116 is preferably a single pole double throw (SPDT) switch.

Fig. 3 shows a schematic diagram of the antenna system 100. The radiating element array 102 has four radiating elements 104. The four radiating elements 102 are arranged such that the origin O of each radiating element 104 coincides with the circumference of a circle 117 of radius r_a. The origin O of each radiating element 104 is also preferably located at 90° from each other along the circumference of the circle 117. One exemplary value of the radius r_a of the radiating element array 102 is 15.5mm.

^■ With reference to Fig. 3, each of the radiating elements 104 is connected to a phase shifter 118 via the RF switch 116. The phase shifter 118 is preferably a one-bit phase shifter and is further connected to a signal processor 120 and a power divider 122.

The signal processor 120 is connected to each radiating element 104 and preferably operationally processes signals received directly from the phase shifter 118. The power divider 122 preferably functionally divides power output from each phase shifter 118.

Additionally, the power divider 122 is separately connected to a down converter 124 and a power combiner 126. The power combiner 126 preferably functionally combines the power received from the power divider 122. The power divider 122 and the power combiner 126 forms a summing module 128 for summing the signals received from each radiating element 104. The down converter 124 is connected to the signal processor 120 via a first analog-to-digital converter 130. The down converter 124 preferably functionally down converts the frequency of the output received from the power divider 122.

The power combiner 126 is further connected to a power detector 132. The power detector 132 is comiected to the signal processor 120 via a second analog-to-digital converter 134. The signal processor 120 is further connected to the RF switch 116 of the radiating element 104.

The power detector 132 preferably functionally monitors the power of signals received by the antenna system 100. The signal processor 120 subsequently selects a signal with the highest power for initializing a Constant Modulus Algorithm (CMA) to improve signal-to-interference plus noise ratio (SINR) of the antenna system 100.

In this way, the antenna system 100 is advantageously capable of initializing the CMA algorithm efficiently. This desirably enables the antenna system 100 to perform high-speed signal processing and consume less power.

With reference to Fig. 4, electromagnetic waves propagate along the y-axis when the first feeding probe 112 receives signals from the signal processor 120. More specifically, electric field propagating in opposite directions along each of the y-axis and x-axis are in phase.

The electric field distribution preferably follows a traverse magnetic TM₀₂₀ mode, in which the electric field is uniformly distributed along the x-axis and has a two half- cycle distribution pattern along the y-axis. The resultant magnetic field is vertically polarized and propagates in opposite directions along the y-axis.

Similarly, as shown in Fig. 5, electromagnetic waves propagate along the x-axis when the second feeding probe 114 receives signals from the signal processor 120. In this case, the electric field distribution follows a TM₂₀0 mode, in which the electric field is uniformly distributed along the y-axis and has a two half-cycle distribution pattern along the x-axis. The resultant magnetic field is vertically polarized and propagates in opposite directions along the x-axis.

Figs. 6 shows measured radiation patterns of the antenna of Fig. 4 and 5 across the x-y plane. The radiation patterns measured across the x-y plane show desirable characteristics at distances Jt/and y/, where both x/ and y/ are equal to 4mm.

Fig. 7 shows radiation patterns generated by the antenna system 100 along predetermined directions during operation of the antenna system 100. More specifically, the direction of propagation is measured across the x-y plane, and between the x and y axes where propagation angles φ are 0° and 180° respectively.

With reference to Fig. 7, the radiation patterns are generated with three different values of r_a and in the direction where φ is equal to 45°. The signal processor 120 controls the phase shifters 118 so that transmission signals generated by the antenna system 100 is directed at a desired direction.

The radiating element array 102 is capable of providing a radiating beam directed at a predetermined direction. The direction of the radiating beam is dependable on the phase shift value α of each of the phase shifters 118, and is further dependable on the radius r_a of the circumference of the circle 117. Table 1 below shows phase shift values, αi to α₄, corresponding to each of the radiating elements 102 for different radii r_a of the radiating element array 102.

Table 1

Fig. 8 shows radiation patterns of the antenna system 100 during operation. The signal processor 120 controls each of the phase shifters 118 to vary the phase shift values, a_\ to α₄, of each corresponding radiating elements 104. The signal processor 120 therefore modifies the radiation patterns such that the power levels of the signals in various directions are influenced by the radiation patterns.

In doing so, the signal processor 120 modifies the radiation patterns to thereby optimize the power level of the signals that the signal processor 120 receives in various directions from the radiating elements 104. This advantageously allows fast convergence and initialization of the CMA to be established. The convergence and initialization of the CMA is desirably four times faster than conventional antenna systems that use omni-directional radiating elements. This also allows the antenna system 100 to operate at high speed for supporting mobile communication, such as at an operating frequency of 5.8GHz.

In the foregoing manner, an antenna system that is dimensionally small for high frequency CDMA applications is disclosed. Although embodiments of the invention are disclosed, it becomes apparent to one skilled in the art in view of this disclosure that numerous changes and/or modifications can be made without departing from the scope and spirit of the invention. For example, as shown in Fig. 3, the number of radiating elements may be increased to achieve other alternative radiating patterns for the antenna system.

Claims

1. An antenna system for wireless communication applications, the antenna system comprising: a radiating element having two feed points for transmitting and receiving signals; a switch coupled to the radiating element at the two feed points; a signal processor coupled to the switch for switching between the two feed points for signal coupling the radiating element with the signal processor and for modifying the radiation pattern of the radiating element, the signal processor for processing signals received from the radiating element; and a power detector coupled to the switch for determining power level of the signals received by the signal processor, wherein when in use the signal processor modifies the radiation pattern and the power level of the signals is influenced by the radiation pattern, whereby modifying the radiation pattern optimizes the power level of the signals received by the signal processor from the radiating element.

2. The antenna system of claim 1, further comprising additional radiating elements for forming an array of radiating elements, the geometrical centre of each of the array of radiating elements being arranged along the circumference of a circle.

3. The antenna system of claim 1, wherein the radiating element is a patch antenna formed on a substrate.

4. The antenna system of claim 3, wherein the patch antenna is substantially planar.

5. The antenna system of claim 1, wherein the switch is a single pole double throw radio frequency switch.

6. The antenna system of claim 1, further comprising a phase shifter coupled to the radiating element for phase shifting the signals received by the radiating element.

7. The antenna system of claim 6, wherein the power detector is coupled to a power combiner and further to a power divider, the power combiner being coupled to a down converter via the phase shifter and further to a first analog-to-digital converter, the first analog-to-digital converter being coupled to the signal processor.

8. The antenna system of claim 7, wherein the power combiner is coupled to the power detector and further to a second analog-to-digital converter, the second analog- to-digital converter being coupled to the signal processor.

9. The antenna system of claim 1, wherein a first feeding probe and a second feeding probe are coupled to one of the two feed points and the other of the two feed points, respectively.

10. The antenna system of claim 9, wherein the first feeding probe and the second feeding probe are coupled to the switch.

11. A method for configuring antenna system for wireless communication applications, the method comprising the steps of: providing a radiating element having two feed points for transmitting and receiving signals; providing a switch coupled to the radiating element at the two feed points; providing a signal processor coupled to the switch for switching between the two feed points for signal coupling the radiating element with the signal processor and for modifying the radiation pattern of the radiating element, the signal processor for processing signals received from the radiating element; and providing a power detector coupled to the switch for determining power level of the signals received by the signal processor; wherein when in use the signal processor modifies the radiation pattern and the power level of the signals is influenced by the radiation pattern, whereby modifying the radiation pattern optimizes the power level of the signals received by the signal processor from the radiating element.

12. The method of claim 11, further comprises the step of: arranging the geometrical centre of the at least one radiating element in a circle

13. The method of claim 11, wherein the step of providing at least one radiating element further comprises the step of: providing the at least one radiating element as a patch antenna formed on a substrate.

14. The method of claim 13 , wherein the patch antenna is substantially planar.

15. The method of claim 11, wherein the step of providing a switch further comprises the step of: providing the switch as a single pole double throw radio frequency switch.

16. The method of claim 11, wherein the method further comprising the step of: providing a phase shifter coupled to the at least one radiating element for phase shifting the signals received by the at least one radiating element.

17. The method of claim 11, wherein the step of providing summing module further comprises the step of: coupling a power detector to a power combiner and further to a power divider, the power combiner being coupled to a down converter via the phase shifter and further to a first analog-to-digital converter, the first analog-to-digital converter being coupled to the signal processor.

18. The method of claim 17, wherein the step of coupling a power detector to a power combiner and further to a power divider further comprises the step of: coupling the power combiner to the power detector and further to a second analog-to-digital converter, the second analog-to-digital converter being coupled to the signal processor.

19. The method of claim 11, wherein the step of providing at least one radiating element having two feed points further comprises the step of: coupling a first feeding probe and a second feeding probe to one of the two feed points and the other of the two feed points, respectively.

20. The method of claim 19, wherein the step of coupling a first feeding probe and a second feeding probe to the first feed point and the second feed point, respectively, further comprises the step of: coupling the first feeding probe and the second feeding probe to the switch.

21. An antenna system for wireless communication applications, the antenna system comprising: a plurality of radiating elements, each of the plurality of radiating elements having two feed points for transmitting and receiving signals; a switch coupled to each of he plurality of radiating element at the two feed points; a signal processor coupled to the switch for switching between the two feed points for signal coupling each of the plurality of radiating elements with the signal processor and for modifying the radiation pattern of each of the plurality of radiating elements, the signal processor for processing signals received from each of the plurality of radiating elements; and a power detector coupled to the switch for determining power level of the signals received by the signal processor, wherein when in use the signal processor modifies the radiation pattern and the power level of the signals is influenced by the radiation pattern, whereby modifying the radiation pattern optimizes the power level of the signals received by the signal processor from the plurality of radiating elements.

22. The antemia system of claim 21, wherein the geometrical centre of each of the plurality of radiating elements is arranged along the circumference of a circle.

23. The antenna system of claim 21, wherein each of the plurality of radiating elements is a patch antenna formed on a substrate.

24. The antenna system of claim 23, wherein the patch antenna is substantially planar.

25. The antenna system of claim 21, wherein the switch is a single pole double throw radio frequency switch.

26. The antenna system of claim 21, further comprises a phase shifter coupled to each of the plurality of radiating elements for phase shifting the signals received by each of the plurality of radiating elements .

27. The antenna system of claim 26, wherein the power detector is coupled to a power combiner and further to a power divider, the power combiner being coupled to a down converter via the phase shifter and further to a first analog-to-digital converter, the first analog-to-digital converter being coupled to the signal processor.

28. The antenna system of claim 27, wherein the power combiner is coupled to the power detector and further to a second analog-to-digital converter, the second analog- to-digital converter being coupled to the signal processor.

29. The antenna system of claim 21, wherein a first feeding probe and a second feeding probe are coupled to one of the two feed points and the other of the two feed points, respectively.

30. The antenna system of claim 29, wherein the first feeding probe and the second feeding probe are coupled to the switch.