GB2382927A

GB2382927A - Adaptive radio antennas

Info

Publication number: GB2382927A
Application number: GB0225487A
Authority: GB
Inventors: Colin Nigel Ribton
Original assignee: Antenova Ltd
Current assignee: Antenova Ltd
Priority date: 2001-11-01
Filing date: 2002-11-01
Publication date: 2003-06-11
Anticipated expiration: 2022-11-01
Also published as: GB0225487D0; GB2382927B; GB0126256D0; WO2003038949A1

Abstract

A compound radio antenna 1 comprising a plurality of directional antenna elements a-f and provided with control circuitry 2,3,4 adapted selectively to enable one or more of the elements a-f in direct response to detected characteristics of received radio signals. The antenna 1 is able to make use of angular and/or polarisation diversity, and is able intelligently to steer from a substantially omni-directional mode of operation to a highly directional mode in response to the received radio signals, thereby helping to improve sensitivity and gain while reducing interference.

Description

AI)APTIVE RAI)IO ANTENNAS

The present invention relates to modes of operation and control of a number of small directional antennas, including but not limited to dielectric resonator antennas, used at a radio terminal (for example a mobile telephone).

The direction of arrival of radio signals varies depending upon the environment surrounding the terminal. This effect has been examined by a large number of workers in the field of microwave propagation, in particular for mobile telephony and

similar applications. This work has shown that the angular spread of direction of :- arrival is greatest in urban areas and least in rural areas. As a radio terminal moves from one radio environment to another the optimum form of the antenna will change.

A high gain antenna is desirable for spatially filtering radio signals (e. g. looking towards the optimum direction and away from interferers). However passive gain is achieved by making antennas directional, and such directionality necessitates pointing the antenna correctly in order to obtain improved performance. Moreover, in some radio environments, it is desirable to receive from a wide distribution of directions of arrival, and to transmit in a broad beam; whereas in other radio environments best communication will be achieved by receiving from only a narrow angle and transmitting a narrow beam.

: It is known that: À A number of directional antennas arranged in an array pointing in different directions can be combined to form an antenna with a near omni-directional pattern À Two or more of such antennas can be combined to form a broad beam

By selectively combining antenna elements (bar one or two) a null can be produced in the antenna gain pattern À An antenna may consist of 2 polarisations - these polarizations may be combined to increase the gain of the antenna Using suitable control electronics the null in the combined antenna gain pattern can be made deeper and more effective by shifting the relative phase between the antenna elements À The present applicant has built on these known findings to provide an adaptive radio antenna with several novel features and advantages.

According to a first aspect of the present invention, there is provided a compound radio antenna comprising a plurality of directional antenna elements and provided with control circuitry adapted selectively to enable one or more of the elements in direct response to detected characteristics of received radio signals.

According to a second aspect of the present invention, there is provided a method of controlling a compound radio antenna comprising a plurality of directional antenna elements, wherein a control algorithm is used selectively to enable one or more of the elements in direct response to detected characteristics of received radio signals.

Although preferred embodiments of the present invention utilise dielectric resonator antennas (DRAB) as the antenna elements, it will be appreciated that any other appropriate small directional antenna elements may be used.

The control circuitry preferably includes electronic control means adapted selectively to activate one or more antenna elements individually and/or in various combinations. There may be provided steering control means, a protocol stack and RF switching/combining circuitry as described in more detail hereinbelow.

Control to adapt form of antenna gain pattern A number of antenna elements may be selectively combined so that the antenna gain pattern can change its form to optimise signal reception and transmission for the environment. A number of small directional antennas (for example a cluster of DRA segments as described in the present applicant's International patent application WO 01/69721, the full disclosure of which is hereby incorporated into the present

application by reference) can each be connected independently to a receiver and/or a transmitter. ) ,. Alternatively each element can be switched to a combining circuit through independent selection switches. This circuit can combine the signals from the selected antennas and route them to the receiver. It can also equally distribute the signal to each of the selected antennas from the transmitter amplifier.

When the direction of arrival of signals is undetermined, the antenna elements may be combined to form a substantially omni-directional pattern, see Fig 1(a). This enables the system to receive signals from all directions.

As the direction of arrival of signals is determined further by the control system (by monitoring of the signals from each of the antenna elements) the form of the antenna . gain pattern can be automatically and progressively changed from an omni-

directional pattern to one where the pattern has a null in the direction of unwanted signals. The antenna gain pattern can then be progressively adapted further by the control system to produce a more directed antenna gain pattern that gives the maximum signal gain and rejection of unwanted signals. Such adaptation may be effected by switching in of appropriate antenna elements; alternatively or in addition, this may be effected by changing the effective phase path length to each of the elements (for

example by switching in or our predetermined lengths of transmission cable or the like). In many protocols, and for example in WCDMA, the antenna may be required to point in two directions simultaneously, see Fig. l(c). This can be achieved by selecting two segments which point in the correct directions. In this case each segment may be controlled independently to optimise gain for one of the two radio paths. This manner of control can be extended to multiple radio channels being independently optimised by selecting antenna elements pointing in the optimum direction. Null steering Mobile user equipment can be enabled with a number of small directional antennas, a control algorithm and RF switching and/or combining networks to steer a null in the combined antenna gain pattern towards a source of interference, and thereby to reduce the level of the received interference. This may be achieved by a number of means. The phase length of the path to each of the antenna elements can be varied to steer a null in the antenna pattern. Alternatively or in addition, individual elements may be de-energised to create a null in the antenna pattern. The null can be directed towards a source of interference. The null can also be directed such that signals transmitted by the antenna do not interfere with equipment nearby and, or alternatively, the gain pattern of the antenna can be appropriately directed for good or substantially optimal propagation of the signal from the terminal to the receiving station. In both cases, the control system operates by receiving information from either the equipment being interfered with or by receiving information from the receiving station.

Control algorithm Two or more small directional antennas in a radio terminal can be controlled so as intelligently to steer toward a desired signal as described hereinbefore, but alternatively may be controlled to switch from one antenna element to another. Such switching may be carried out at set intervals rather than being determined by the strength or other characteristics of the received signals. This method will increase the average amplitude of the received signal, and provides a method of avoiding fast fades in high multipath environments. For particular protocols, where data is interleaved over several radio blocks for example, this method will increase the diversity of the antenna and may thereby improve the radio link. Alternatively, the control system may switch from one antenna element to another when the radio link integrity falls below a preset or predetermined level and thereby switch the direction of the gain of the antenna system from one direction to another.

Selection and phasing of signals from elements The control system may select the antenna element giving the best signal in such an array, or may combine antenna elements to produce an optimum or a best-available signal, or may introduce a relative phase shift between the signals from the elements to optimise or at least improve the signal and reduce interference caused by multipath effects. Arrangement of antenna elements The antennas may be arranged so as to provide À angular diversity À polarization diversity or a combination of these two forms of antenna diversity.

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- > Alternatively or in addition to the above, the antennas may be sited at sufficient distances from each other so as to avoid all being obstructed by a user, for example by being covered by a user9s hand.

Combinations of these diverse elements can be explored by the control system in order to optimise or at least improce the radio link for the given environment.

Table 1 below shows a comparison of the benefits provided by different modes of an antenna of embodiments of the present invention.

J Benefi t Suppress Eletter Improved Increase Decrease inter-op battery life data rate at network network interference range capacity back haul traffic Antenna mode directional 3G (single GSM GSM GSM segment), with scanning _. . _

single 3G 3G 3G 3G segment GSM GSM GSM with polling _ null steering 3G 3G 3(; GSM GSM GSM

twin 3G 3C] 3G d rechons rid, )

. multi- 3G 3G 3G 3G 3G segment GSM GSM GSM adaptation Table 1 Benefits of different modes of the antenna For a better understanding of the present invention and to show how it may be carried into effect, reference shall now be made by way of example to the accompanying drawings, in which: FIGURE 1 shows various modes of operation of a compound antenna embodying the present invention, FIGURE 2 shows a control system for an antenna embodying the present invention; and FIGURE 3 shows a control circuit configuration for an antenna embodying the present invention.

Figure l(a) shows a compound antenna 1 formed of six sectored DRA elements a, b, c, d, e and f, which is this case are all excited so as to provide an omni-directional mode of operation.

In Figure 1(b), two elements, a and b, are switched off to produce a null in a radiation pattern generated by excited elements c, d, e and f.

In Figure l(c), two elements, c and e, are excited and the remaining elements are switched off. This generates a radiation pattern having beams in two separate directions.

In Figure l(d), two adjacent elements, d and e, are both excited and combined to give a relatively broad directional beam.

In Figure l(e), a single element, e, is excited to give a highly directional relatively narrow beam.

Figure 2 shows a sectored DRA 1 of the type shown in Figure 1. Each element a, b, c, d, e and f is connected by way of RF switching/combining circuitry 2 and a steering control unit 3 to a protocol stack 4, which may form part of an integrated circuit or computer device (not shown). The control system depicted in Figure 2 is able to provide selective activation of the various antenna elements a to e, either individually or in combination, in response to detected signal strengths and/or other signal characteristics so as to enable intelligent steering and other control of the compound antenna.

The control system may include a control algorithm which may consist of a process where the direction of arrival of the incoming signal is determined by measuring the signal strength on each of the antenna elements a to f. Using this information, the control algorithm will set up an RF switch network that will determine the direction of transmission of the radio signal. In protocols where the radio link is reciprocal (i.e. where the uplink and downlink propagation paths are identical or can be approximated to be identical) it may be assumed that within a short period of time the optimum uplink direction will be the direction of arrival of the downlink direction.

Alternatively, or in addition to the above process, the network basestation may provide feedback information to the handset on the received signal strength. Under these conditions, the terminal will select the optimum direction of transmission by sampling a number of directions of transmission. The basestation will provide a metric to the terminal of the relative efficiency of each direction of transmission and this information can be used to select the antenna elements to be used for the transmission from the terminal. These elements may be different from the elements used for the reception of the signal. The optimization routine may be a continuous

i process with an update period commensurate with the duration of a typical multipath channel lifetime.

The RE switching control circuitry 2,3 is designed such that the elements selected for the transmission and reception of the signal may be selected individually as necessary. In TDMA systems this can be effected by rapid switching between the optimum uplink and downlink configurations. In CDMA systems the configuration difference between the uplink and the downlink configurations is effected by the use of biased diode elements to make the signal forward and reverse paths different.

The short duration of multipath experienced in cellular networks, for example, requires that the control algorithm processing is performed in the lower layers of the protocol stack, and most likely as part of a digital signal processing operation. In other situations where the lifetime of multipath is longer, the control algorithms may be executed at higher layers of the protocol stack 4 and will be less time critical.

The diagram shown in Figure 3 illustrates a possible configuration of the control circuit. The antenna elements are each connected to a diplexer and this is used to separate the transmit and receive parts. Each transmit and receive of each element may be individually or severally selected to allow the appropriate antenna segments to be selected. This is achieved by connection of a configuration of elements 11 each with a different gain pattern (either directionally different, of different polarization or -. spatially dispersed) to diplexers 12 and then to separate receive and transmit selection switches, 13 and 14, respectively. The receive channel signal 15 may then be single or a combination of elements and therefore correspond to a signal arriving within a certain angle and/or polarization and with an optimum or at least improved fade profile relative to the handset. The receive and transmit selection switches are controlled by a control system 17.

The preferred features of the invention are applicable to all aspects of the invention and may be used in any possible combination.

- Throughout the description and claims of this specification, the words "comprise"

and "contain" and variations of the words, for example "comprising" and "comprises", mean "including but not limited to", and are not intended to (and do not) exclude other components, integers, moieties, additives or steps.

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Claims

CLAIMS:

1. A compound radio antenna comprising a plurality of directional antenna elements and provided with control circuitry adapted selectively to enable one or more of the elements in direct response to detected characteristics of received radio signals.

2. An antenna as claimed in claim 1, wherein the control circuitry includes electronic control means adapted selectively to activate one or more antenna elements individually and/or in predetermined combinations.

i.,

3. An antenna as claimed in claim 1 or 2, wherein the control circuitry includes steering control means.

4. An antenna as claimed in any preceding claim, wherein the control circuitry includes a protocol stack.

5. An antenna as claimed in any preceding claim, wherein the control circuitry includes RF switching/combining circuitry.

6. An antenna as claimed in any preceding claim, wherein the elements are arranged so as to provide angular diversity.

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7. An antenna as claimed in any preceding claim, wherein the elements are arranged so as to provide polarization diversity.

8. An antenna as claimed in any preceding claim, wherein the elements are disposed sufficiently far apart from each other so as to avoid all being obstructed by a user's hand.

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9. An antenna as claimed in any preceding claim, wherein the control circuitry is adapted to modify a radiation pattern of the antenna from substantially omni-

directional to substantially directional in response to received radio signal characteristics.

10. An antenna as claimed in any preceding claim, wherein non-adjacent elements are selectively and simultaneously activatable so as to produce a radiation pattern with peaks in two different directions.

11. An antenna as claimed in any preceding claim, wherein the elements are I-- dielectric resonator antenna elements.

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12. A method of controlling a compound radio antenna comprising a plurality of directional antenna elements, wherein a control algorithm is used selectively to enable one or more of the elements in direct response to detected characteristics of received radio signals.

13. A method according to claim 12, wherein the control circuitry includes electronic control means that selectively activates one or more antenna elements individually and/or in predetermined combinations.

14. A method according to claim 12 or 13, wherein the elements are arranged so as to provide angular diversity.

1S. A method according to claim 12, 13 or 14, wherein the elements are arranged so as to provide polarization diversity.

16. A method according to any one of claims 12 to 15, wherein the control circuitry modifies a radiation pattern of the antenna from substantially omni-

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17. A method according to any one of claims 12 to 16, wherein nonadjacent elements are selectively and simultaneously activated so as to produce a radiation pattern with peaks in two different directions.

18. A method according to any one of claims 12 to 17, wherein the elements are dielectric resonator antenna elements.

19. A compound radio antenna substantially as hereinbefore described with reference to the accompanying drawings.

20. A method of controlling a compound radio antenna substantially as hereinbefore described with reference to the accompanying drawings.

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