WO2008136003A2

WO2008136003A2 - Method and devices for phased array beam scanning

Info

Publication number: WO2008136003A2
Application number: PCT/IL2008/000636
Authority: WO
Inventors: Gil Levi; Alexander Toshev
Original assignee: Bon Networks Inc.
Priority date: 2007-05-08
Filing date: 2008-05-07
Publication date: 2008-11-13
Also published as: WO2008136003A3

Abstract

Methods and devices allow omni-directional performance with high gain from a scanning phased array antenna (PAA). In some embodiments, the PAA includes at least 4 radiating antenna elements, each element fed one of only two phases separated by 180 degrees. In other embodiments, the PAA includes at least 4 radiating antenna elements, each element fed one of only four phases separated by 90 degrees. The two or four phases are controlled by a phase control device and obtained without use of phase shifters. The PAA is scanned to obtain an essentially omni-directional beam that provides a gain of at least a 6db. The PAA can be miniaturized and used in a cellular phone and other portable electronic devices.

Description

Method and devices for phased array beam scanning

FIELD OF THE INVENTION

The present invention relates in general to phased array antennas (PAAs), in particular to miniaturized PAAs and to RF semiconductor chips used to control such PAAs, and most particularly to incorporation of such miniaturized PAAs in portable electronic devices such as laptops, cellular phones and PDAs.

BACKGROUND OF THE INVENTION

Low cost terrestrial wireless applications and mobile applications require omni-directional antenna radiation patterns. This means that there is no preferred direction for reception/transmission of the signal. For example, the antenna and RF part of a WLAN system include an omni-directional antenna such as a dipole or PIFA antenna and a transceiver. Omni-directional antennas have low gain (around 0 decibels (dB)).

Due to the limited bandwidth of a WLAN channel, different techniques have been investigated for enhancement of channel capacity and improvement of bit error rate (BER) of the system. One of these techniques involves multiple-input-multiple- output (MIMO) schemes, in which transmission and reception are performed simultaneously from several omni-directional antennas. The MIMO approach normally implements space or polarization diversity. Both cases require de- correlation between radiating antennas. Another technique for decreasing the BER of a WLAN system involves increase of the gains of transmit-receive antennas. Increase of antenna gain requires usage of directional antennas, such as PAAs. Due to requirement for coverage of the full space around the antenna, beam scanning of the phased array is also required. Scanning PAAs are often used in radar and military applications. The prior art of such antennas involves scanning of their main beam by applying phase control on the radiating elements of the array. The term "main beam" assumes that there is only one peak in the PAA pattern. The phase difference between adjacent elements in existing PAAs typically never reaches or approaches 180° (180 degrees), because a phase difference close to this value splits the PAA beam into several main peaks. This split is the phenomenon most unwanted in existing applications of scanning PAAs, because only one preferred direction of reception/transmission connected with only one main beam of the antenna is desired. Therefore, phase differences close to 180° have never been considered as relevant in existing PAAs.

Most commonly used beam scanning techniques use phase shifters after each radiating antenna element in the phased array. The drawback of this approach is in the very expensive antenna hardware implementation, arising from the large number of phase shifters required. Also, this approach cannot be implemented in cellular (mobile) phones and other portable electronic devices, where low cost and low power are key requirements. Moreover, due to the small footprint area available in cellular phones, only a small antenna array utilizing a small number of radiating elements can practically be integrated in such a phone. A low number of radiating elements reduces the array gain and therefore the antenna gain. Also, the insertion losses introduced by utilizing a phase shifter in-line with every radiating element decrease the effectiveness of the directional antenna by significantly reducing the antenna gain. This is especially true in applications such as mobile phones, where typically the small array gain, due to the low number of radiating elements able to fit in the very small footprint, would be compensated by the phase shifter insertion losses when implemented in-line with all radiating elements. This would make the antenna gain similar to that of an omni-directional antenna, negating the purpose of a more complicated scanning directional phased array antenna.

In various applications, there is therefore a need for, and it would be advantageous to have, essentially omni-directional antennas with increased gain. SUMMARY OF THE INVENTION

We disclose a scanning phased array antenna with essentially omni-directional properties and relatively high (>6dB) gain. We disclose a method for scanning of a PAA without use of phase shifters, as well as phase control devices used to enable the scanning. Since phase shifters are eliminated, the architecture of the PAA is modified, allowing its miniaturization and efficient use in cellular phones and other portable electronic devices. The method provides high antenna gain (compared with omnidirectional antennas) and capability for steering the antenna beam, thus allowing essentially omni-directional coverage. The proposed PAA includes at least 4 radiating elements.

In various embodiments of the method, a limited number of phase settings (also referred to herein as "phase states" or just "phases") are used for scanning of the antenna beam. These phases are characterized by a number of phase shifts that are different for each radiating element of the PAA. For every beam of the scanning PAA, a set of phase shifts must be applied to each of the radiating elements to create the specific beam. This limited number of phase states constitutes a "phase set". The particular phase required by each radiating element for steering of the array beam is selected from the phase set according to one of two procedures: rounding of the phase value (optimal vs. available) or using a pattern optimization criterion (like beam position, beam shape etc.). By "rounding of the phase value" we mean that if the optimal phase shift needed for a certain radiating element of the antenna in order to create a certain desired beam is 135°, then we round this number to 180° which is the closest available phase value in the phase set of 0° and 180°. By "using a pattern optimization criterion" we mean if we have 4 radiating elements in the PAA and our phase set includes 2 phases of 0° and 180°, then we simulate all possible beams formed by these two phases using 4 radiating elements (in theory, 16 different possible beams to check). Then we select the minimum number of beams from the possible 16 to create a total hemisphere or space pattern coverage with the needed antenna gain. The selection procedure is performed in the antenna design stage. During operation, the phase control device applies the phases selected in the design stage to the appropriate radiating elements to create each and every PAA beam according to a desired real-time performance. Phase shifters normally positioned after the radiating elements are now discarded and replaced by a combination of switches and splitters which switch the proper phase from the phase set.

In one embodiment, the phase set includes only two phases, 0° and 180°, and each radiating element is assigned one of these phases for every beam used in the scanning antenna. These two phases are typically already produced by existing differential amplifies (a power amplifier on the transmit path and a low noise amplifier on the receive path). The optimization criterion for selection of the phases from this phase set is according to one of the methods disclosed herein.

In another embodiment, the phase set includes four phases and each radiating element is assigned one of these phases for every beam used in the scanning antenna. This embodiment uses a quadrature filter, commonly implemented by a polyphase filter. Polyphase filters are an efficient solution for high accuracy quadrature generation in radio frequency CMOS design. They typically generate four phases - 0°, 90°, 180° and 270°, which are assigned as described exemplarily in FIG. 2b and FIG. 8. Note that in FIG. 2b only three of the four phases (0°, 90° and 270°) are used to generate 7 beams. As in the two phase state embodiment, in this embodiment too phase shifters are not needed and not used in-line with the radiating elements.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is herein described, by way of example only, with reference to the accompanying drawings, wherein:

FIG. 1 shows geometries and parameters that used in the calculation, of the ideal phase difference Aφ between two adjacent elements;

FIGS. 2a, b show an exemplary implementation of a 4 element phased array antenna and the phases set to each antenna element in order to create different antenna beams (a) two phase implementation; (b) 4 phase implementation of which only 3 phases are used in the beam patterns creation;

FIGS. 3a-d show the simulated beam patterns created with the four different phase setting in FIG. 2a; FIG. 4 shows a simulated combined beam pattern obtained by combining the 4 beam patterns in FIG. 3;

FIG. 5 shows one embodiment of a system that includes a phase control device for scanning of a PAA using only two phase states for each radiating element;

FIG. 6 shows another embodiment of a system that includes a phase control device for scanning of a PAA using only two phase states for each radiating element;

FIG. 7 shows yet another embodiment of a system that includes a phase control device for scanning of a PAA using only two phase states for each radiating element;

FIG. 8 shows one embodiment of a system that includes a phase control device for scanning of a PAA using only four phase states for each radiating element;

FIG. 9 shows an exemplary embodiment of the phase distribution module used to apply the proper phase to each of the antennas.

FIG 10 shows in (A) a known mobile (e.g. cellular) phone and in (B) an embodiment of a mobile phone that incorporates a 4 element scanning phased array antenna of the invention and its control system.

In the following description like elements in different figures are marked with identical numbers.

DETAILED DESCRIPTION OF THE INVENTION

We have discovered that, in contrast with accepted practice, the application of phase control of at least 4 radiating elements employing a phase difference of 180° (or in some embodiments 90°) provides a solution to the problems described in the Background section. This phase control steers the beam at the largest angle from boresight and at the same time splits it. In contrast with accepted opinion and practice, the splitting of the main PAA beam is now a desired phenomenon, used to increase the coverage capabilities of an antenna. Exemplary (and by no means limiting) applications that benefit particularly from this discovery are cellular phones and other portable electronic devices, as well as wireless LAN clients and access points.

There are two approaches for the calculation of the phases (or "phase settings") needed for each radiating element. The first approach is suitable for arrays with a relatively low number of radiating elements N, for example in a mobile phone application with only 4 radiating elements in the PAA. When only two phases (0° and 180 ) are used as potential input phases for each radiating element, the total number of possible combinations of phases for the PAA (i.e. the total number of possible antenna beams P) is:

P = 2^N (1)

If N is not very large, a run through all the beams may be performed and selection of the best beams that cover the needed space may be obtained. The same may be done for phase sets of more than 2 phases, e.g. for a 4 phase set implemented with a quadrature filter instead of a 2 phase set implemented using differential amplifiers. However, if N is too large, the total number of possible antenna beams may become too high, and the simulation of the antenna beam for every possibility may become impractical, making such an approach unsuitable. The second approach borrows the conventional approach for calculation of the phase difference between adjacent radiating elements used in array theory (when only one peak of the antenna beam is desired). The conventional equations are modified to account for only the required two phases (0/180°) or four phases (obtained by truncation or rounding to the nearest available phase of the phase set). Thus, the resulting radiation pattern of the antenna beams produced may not always have a single peak. FIG. 1 shows geometries and parameters used in the calculation of the ideal phase difference Δφ between two adjacent elements.

The phases between radiating elements are calculated from:

Aφ (2)

where Aφ is the phase difference between radiating elements, λ is wavelength, d is distance between radiating elements, θ is the desired slant angle of the antenna beam,

and TruncationL \ .) /mod . = ,1„8„0 is the truncation with modulus 180°. If d = — 2 and θ - 90°,

Aφ is 180°, see expression (3):

Aφ = Truncation! ~-sin(90° j) = 180° (3)

\ Λ- 2 / mod=₁80

Simulations using expressions (1) and (2) show that only 4 different antenna beams are needed to sufficiently cover the entire hemisphere or space.

FIGS. 2a and 2b show an exemplary implementation of a 4 element PAA and the phases set to each antenna element in order to create respectively 4 and 7 different antenna beams. The antennas in FIGS. 2a and 2b include each four radiating elements 1- 4 marked and arranged in the pattern shown. Each of the radiating elements in (a) is fed a signal having a relative phase shift of either 0 or 180° as shown in both the attached table and inside the elements identified in each phase setting configuration (BEAM #1 - BEAM#4). In (b), the antenna elements are fed a signal having a relative phase shift of either 0°, 90° or 270° (the 180° phase is not used here, but may be used in other embodiments). FIGS. 3a-d show the simulated beam patterns created with the four different phase setting configurations of FIG. 2a. Similar simulations (not shown) have been run for the 4-phase setting configurations of FIG. 2b. All patterns have contours marked by numbers representing relative intensities in decibels (dB), "1" indicating smallest intensity and 2, 3, 4, 5... etc., indicating increasing intensities. The beam pattern in FIG. 3a, with numbered contours 1 (smallest intensity) to 10 (highest intensity), represents a boresight beam, where the antenna receives (transmits) primarily from (to) directions close to its boresight. The beam pattern in FIG. 3b represents an H-plane differential beam, where the antenna receives (transmits) primarily from (to) two directions symmetrically situated in the relative H-plane of the antenna. The beam pattern in FIG. 3 c represents a V-plane differential beam, where the antenna receives (transmits) primarily from (to) two directions symmetrically situated in the relative V-plane of the antenna. The beam pattern in FIG. 3d represents a 45° plane differential beam where the antenna receives (transmits) primarily from (to) 4 directions symmetrically situated in 45° planes of the antenna.

As shown in FIG. 4, the four beams can be combined into one single beam that provides essentially full coverage of the entire hemisphere around the antenna with a relatively high antenna gain (the latter in comparison with the gain of an omni- directional antenna). Note that this full coverage is obtained by using only the same two phases (with a 180° difference) as inputs to each antenna element.

In order to control the antenna and steer the beams accordingly, a driving mechanism is needed to allocate the required phase to each element to obtain the desired beam. This goal is achieved with a phase switching RF phase control device (such as 550 in FIG. 5). The phase control device has typically four functions: (a) to produce the phases (unless already produced by external differential amplifiers, quadrature filters or similar means); (b) to optimally provide respective phase sets to the antenna elements, (c) to support functions (a) and (b) in both transmit and receive modes; and (d) to amplify the signal in the transmit or receive modes (unless already amplified by external amplifiers). The phases are exemplarily produced via a set of differential amplifiers, a power amplifier (PA) in the transmit path and a low noise amplifier (LNA) in the receive path (respectively 528 and 530 in FIG. 5). A differential amplifier produces two signals at its outputs. The signals have the same amplitude, with one signal phase being 0° while the other being 180°. A phase set of 0° and 180° phases is generated using the outputs of at least one differential amplifier. The phase set drives a phase switching device that provides the different antenna elements with the required phase set per beam. The phase switching device may be designed to serve both the antenna phase requirements of the 0° and 180°, as well as a Transmit/Receive switch (TRs w). In transmit mode, the TRs w connects the phase set to the PA, while in receive mode the phase bank is connected to the LNA.

FIG. 5 shows one embodiment of a system that includes a phase control device 550 for scanning of a PAA using only two phase states for each radiating element. Device 550 includes a transmit module 100 and a receive module 101. On the transmit path, a differential "RF OUT" signal 102 from differential amplifier 528 enters transmit module 100, advancing through two parallel lines 104 and 106 the respective phases of 0 and 180°. The two lines enter a first phase distribution module 108 which then distributes the correct phases according to (or in response to) commands from a CONTROL command interface 126. Phase distribution module 108 then outputs the signal with the correct phase accordingly into feed lines 110. The feed lines, which are of the same phase delay, guide the signals into phased array antenna elements 112 for wireless transmission. On the receive path, signals received by phased array antenna elements 124 are carried to receive module 101 via feed lines 122. The feed lines, which are of the same phase delay, enter receive module 101 and direct the signal into a second phase distribution module 120. Phase distribution module 120 then chooses the right phase path to each of the corresponding signals arriving from antenna elements 124 in response to commands from CONTROL command interface 126 and sends the signals via phase 0 and phase 180° outputs (116 and 118 respectively) out of receive module 101 and into a differential "RF IN" signal 114 of the low noise amplifier/s 530.

FIG. 6 shows another embodiment of a system that includes a phase control device 650 for scanning of a PAA using only two phase states for each radiating element. Device 650 includes the elements of device 550 but also integrates a differential power amplifier 604 and a differential low noise amplifier 618. Device 650 performs just like 550, except that it allows a smaller footprint and lower cost implementation when implemented in a single semiconductor (preferably but not limited to CMOS) chip. This also allows signals RF OUT 602 and RF IN 616 to either be differential or regular (single input-single output).

FIG. 7 shows yet another embodiment of a system that includes a phase control device 750 for scanning of a PAA using only two phase states for each radiating element. Device 750 includes the elements of device 650 but also integrates a transmit and receive (TfR) switch that allows the same antenna to be used for both transmission and reception. A phase distribution module 710 is used in the transmit path to allocate and apply the needed phase from two phases 706 and 708 to every antenna. In the receive path, module 710 connects feed lines 712 to two phases 720 and 722, which in turn are fed to a low noise amplifier 718. The device performs just like devices 550 and 650 in cases where the same antennas are used for transmission and reception (a common scenario in mobile wireless communications), except that this embodiment allows a smaller footprint and lower cost implementation when implemented in a single semiconductor (preferably but not limited to CMOS) chip. In an alternative option, device 650 may be used in a similar scenario where the same antennas are used for transmission and reception. In this case, an additional T/R switch is needed for every antenna used.

FIG. 8 shows yet another embodiment of a system that includes a phase control device 850 for scanning of a PAA using only three or four phase states for each radiating element. Device 850 is similar to device 550, with one major difference - the number of phases in the phase set. Device 850 uses up to 4 phases in the phase set, obtained through quadrature filters (804 and 822 respectively) in both the transmit and receive paths, whereas device 550 uses 2 phases implemented using external differential amplifiers 528 and 530. hi the transmit path, quadrature filter 804 takes a single RF OUT input 802 and splits it to 4 outputs of phase 0°, 90°, 180° and 270° (marked 808, 806, 810 and 812 respectively). Note that in some embodiments (e.g. as shown in FIG. 2b), not all 4 phases are used for beam scanning. Filter 804 then distributes the 4 phases to the appropriate antennas 818 through a feed line 816, all of which have the same phase delay (or typically the same length). In the receive path, quadrature filter 822 combines 4 phases fed from antennas 836 (marked 824, 826, 828 and 830 respectively) via feed lines 834 through a Phase Distribution Module 832 and outputs a RF IN signal 820.

An exemplary embodiment of the phase distribution module (for example a two-phase module 508) is shown in FIG 9. Module 508 receives 2 phases 902 (phase 0°) and 904 (phase 180°). The phase 0° signal is then routed to a 1 : 4 switching splitter 906, which splits the signal into a number of signals matching the number of antennas that need to use this phase. The same is done to the phase 180° signal, which is routed to a 1:4 switching splitter 908, which splits the signal into a number of signals matching the number of antennas that need to use this phase. An appropriate 2x1 selection switch 910 then selects the appropriate phase 0° or 180° for each antenna output. FIG 10 shows in (a) a known mobile (e.g. cellular) phone having a regular antenna 1014 and in (b) a mobile phone that incorporates a 4 element scanning phased array antenna 1014' of the invention and its control system. The mobile phone in (a) has the RF OUT 702 and RF IN 716 signals connected respectively to amplifiers 1002 and 1004. A T/R switch 1006 is used to switch signals transmitted and received via antenna 1014. In the mobile phone in (b), the RF OUT 702 and RF IN 716 signals are exemplarily connected to device 700 which is in turn connected to PAA 1014'. An antenna control 724 connects device 700 to the phone's control software/hardware.

In operation, the scanning PAA steers the beams to compensate for the movement of the mobile phone vs. the base station it is transmitting to and receiving from. This way, at each specific time, the antenna control instructs the phase distribution module in the phase control device to apply the needed phases out of the phase set in order to create a beam which points in the right direction for the transmission and reception to be optimal. The antenna can thus deliver high gain, in contrast with mobile phones in known art, which use omni-directional antennas and do not benefit from a high gain.

To summarize, some advantages of the method for scanning of the phased array antenna and the various phase control devices disclosed herein are as follows:

• Increased antennas gain vs. omni-directional antennas • Elimination of the phase shifters used to produce the phases vs. other phased array antennas

• Larger frequency bandwidth

• Excellent phase accuracy

• Smaller real-estate area which leads to smaller chip level implementation with less package pin count and fewer external components

• Lower cost implementation of a PAA vs. conventional implementation using multiple phase shifters

• Reduced power consumption, since the same device (amplifier) provides two functions (phase and amplification) for the same current. • Improved power efficiency, since the path loss between the amplifier and the antenna elements is lower because the phase shifters are eliminated. • Simplified PAA implementation: because in an exemplary case where the phase control device drives four antenna elements, each amplifier in the transmit path handles a quarter of the transmitted output power. The 6dB reduced power requirement simplifies the PAA implementation, as well its noise contribution on the chip level.

The advantages of the antenna control mechanism described above lead to significant simplification of the antenna architecture and allow low cost implementation of the transceiver phase control device in a semiconductor chip.

While the invention has been described with respect to a limited number of embodiments, it will be appreciated that many variations, modifications and other applications of the invention may be made. What has been described above is merely illustrative of the application of the principles of the present invention. Those skilled in the art can implement other arrangements and methods without departing from the spirit and scope of the present invention.

Claims

WHAT IS CLAIMED IS

1. A method for operating a scanning phased array antenna having radiating elements with corresponding antenna beams, the method comprising the steps of: a) providing a respective phase set for each radiating element, each respective phase set having only two phases; and b) scanning each antenna beam using a phase selected from the respective phase set.

2. The method of claim 1, wherein the step of providing a respective phase set having only two phases includes providing two phases separated by 180 degrees.

3. The method of claim 1, wherein the step of scanning each antenna beam using a phase selected from the respective phase set includes scanning each antenna beam using a phase selected according to an optimization criterion.

4. The method of claim 3, wherein the optimization criterion is selected from the group consisting of rounding of an ideal phase and optimization of an antenna beam pattern shape.

5. The method of claim 1, wherein the respective phase state sets of all radiating elements are identical.

6. The method of claim 1, further comprising the step of using the phased array antenna as a cellular phone antenna.

7. A method for operating a scanning phased array antenna having radiating elements with corresponding antenna beams, the method comprising the steps of: a) providing a respective phase set for each radiating element, each respective phase set having only four phases separated therebetween by 90 degrees; and b) scanning each antenna beam using a phase selected from the respective phase set.

8. The method of claim 7, wherein the step of scanning each antenna beam using a phase selected from the respective phase set includes scanning each antenna beam using a phase selected according to an optimization criterion.

9. The method of claim 8, wherein the optimization criterion is selected from the group consisting of rounding of an ideal phase and optimization of an antenna beam pattern shape.

10. The method of claim 7, wherein the respective phase state sets of all radiating elements are identical.

11. The method of claim 7, further comprising the step of using the phased array antenna as a mobile phone antenna.

12. A method for operating a scanning phased array antenna comprising the steps of: a) forming a phased array antenna beam without using any phase shifting elements; and b) scanning the phased array antenna beam.

13. The method of claim 12, wherein the step of forming a phased array antenna without using any phase shifting elements includes using a phase control device to form a beam using only two phases separated by 180 degrees.

14. The method of claim 12, wherein the step of forming a phased array antenna without using any phase shifting elements includes using a phase control device to form a beam using only four phases separated therebetween by 90 degrees.

15. The method of claim 13, wherein the using a phase control device to form a beam using only two phases separated by 180 degrees includes obtaining the two phases from differential amplifier outputs in antenna transmit and/or receive paths.

16 The method of claim 14, wherein the using a phase control device to form a beam using only two phases separated therebetween by 90 degrees includes obtaining the four phases from a quadrature filter.

17 The method of claim 16, wherein the quadrature filter is implemented by a polyphase filter.

18. The method of claim 12, further comprising the step of using the phased array antenna as a mobile phone antenna.

19. A scanning phased array antenna comprising: a) a number of radiating antenna elements; and b) a phase control device for providing a phase chosen from a set of only two phases separated by 180 degrees to each radiating element, wherein the antenna transmits and receives an essentially omni-directional beam without use of phase shifters.

20. The antenna of claim 19, wherein the a number of radiating antenna elements is at least 4.

21. The antenna of claim 19, incorporated in a portable electronic device.

22. The antenna of claim 21, wherein the portable electronic device includes a mobile phone.

23. A scanning phased array antenna comprising: a) a number of radiating antenna elements; and b) a phase control device for providing a phase chosen from a set of four phases separated by 90 degrees to each radiating element, wherein the antenna transmits and receives an essentially omni-directional beam without use of phase shifters.

24. The antenna of claim 23, wherein the a number of radiating antenna elements is at least 4.

25. The antenna of claim 23, incorporated in a portable electronic device.

26. The antenna of claim 25, wherein the portable electronic device includes a mobile phone.