GB2242574A

GB2242574A - Adaptive beamformer

Info

Publication number: GB2242574A
Application number: GB9007286A
Authority: GB
Inventors: Robin Paul Rickard
Original assignee: STC PLC
Current assignee: STC PLC
Priority date: 1990-03-31
Filing date: 1990-03-31
Publication date: 1991-10-02
Anticipated expiration: 2010-03-31
Also published as: GB2242574B; GB9007286D0

Abstract

In a beamformer arrangement element signals are fed via respective weighting networks W1-Wn to a summing network and the weighting networks are adjustable to achieve minimisation of the power output of the summing network SIGMA 1. The arrangement includes means T2-Tn and SW1 for sampling element signals prior to the weighting means, means SP1 for sampling the power output of the summing means, adjustable weighting means Ws for weighting the samples of the element signals, means SIGMA 2 for combining the weighted samples and the power output samples, means PROC for measuring the power output of the combining means, means for perturbing the weighting of the sampled element signals and means for adjusting the weighting networks in response to the power output measurements to achieve the minimisation of the power output of the summing network. In a modification (Fig 2) two weighting networks (Ws' and WS'') are used instead of Ws to determine the effect of upward and downward weight perturbation. <IMAGE>

Description

PERTURBATION PROCESSOR BEAMFORMER This invention relates to a perturbation processor beamformer used in adaptive beamforming arrays.

The application of orthogonal perturbation sequences to adaptive beamforming is known. See for example A. Cantoni, "Application of Orthogonal Perturbation Sequences to Adaptive Beamforming", IEEE Transactions on Antennas and Probation, Vol. AP-28, No. 2, March 1980, pp. 191-202.

In a known perturbation processor beamformer each element weighting is perturbed to alternately increase and decrease the weight while performing a measurement of the beamformer output power in order to determine the optimum weight required to achieve minimisation of the output power, i.e. to form a null in the beamformer pattern. However, temporarily perturbing the weight to enable measurement of the output power causes an unwanted modulation of the signal at the beamformer output.

It is an object of the present invention to provide a perturbation processor beamformer which is not subject to modulation of the output signal as a result of the perturbation process.

According to the invention there is provided a beamformer arrangement wherein element signals are fed via respective weighting-networks to a summing network, the weighting networks being adjustable to achieve minimisation of the power output of the summing network, the arrangement including means for sampling element signals prior to the weighting means, means for sampling the power output of the summing means, adjustable weighting means for weighting the samples of the element signals, means for combining the weighted samples and the power output samples, means for measuring the power output of the combining means, means for perturbing the weighting of the sampled element signals and means for adjusting the weighting networks in response to the power output measurements to achieve the minimisation of the power output of the summing network.

Embodiments of the invention are now described with reference to the accompanying drawings in which: Fig. 1 is a block schematic of a beamforming arrangement, Fig. 2 is an alternative beamforming arrangement, and Fig. 3 shows a modification of the arrangement of Fig. 1.

In the arrangement illustrated a plurality of elements El - En, e.g. antenna elements in an adaptive array, feed signals via respective adjustable weighting networks Wl - Wn to a summing network

The adjustments of the weights applied by the weighting networks are controlled by a perturbation processor PROC. Samples of the signals from elements E2 - En are taken via sampling taps T2 - Tn and are selected by switch SW1 to be applied sequentially to a further weighting network Ws. As eac sample is presented to weighting network Ws the processor performs a perturbation operation on weights applied to the sample. Splitter SP1 splits off a portion of the output signal from summing network

and this is fed to a second summing network

together with the output from weighting network Ws.The output of summing network

is then applied to the processor. The processor effects a power measurement in the output of

2 while the weights in W2 are perturbed and determines the optimum weight to be applied to the element signal from which the sample is taken. This optimum weight is then set in the relevant weighting network W2 - Wn and the process is repeated for the next sample selected by switch SW1.

In this way the optimum weights to be applied to the element signals can be regularly calculated using perturbation techniques without imposing any undesirable modulation on the output signal resulting from the perturbations.

In the alternative arrangement of Fig. 2 the output of switch SW1 is fed via a second splitter SP2 to two weighting networks Ws' and was". Ws' is used to determine the effect of upward weight perturbation and Ws" is used to determine the effect of downward perturbation. The sample of the beamformer SP1 is further split in splitter SP3 and fed to summing networks

together with the respective outputs of Ws' and Ws". The processor PROC can then perform upward and downward weight perturbations smultaneously to determine the optimum weight adjustment to be applied to the relevant weighting network W2 - Wn. This arrangement allowing simultaneous upward and downward perturbatIon of the weight overcomes the effect of noise in the perturbation loop. In the arrangement of Fig. 1 because the effects of upward and downward perturbation of a gIven weight are performed t different times, instead of simultaneously as in Fig. 2, nose is introduced into the power measurement and will affect the calculation of the optimum weight. This in turn restricts the speed at which the weight update loop can operate. In the arrangement of Fig. 2 the simultaneous calculation of the effects of upward and downward perturbations eliminates the delay error and resultant noise inherent in the arrangement of Fig. 1.

In the arrangement of Fig. 3 the use of a sum and difference hybrid 31 provides an alternative method of performing an upwards and downwards perturbation simultaneously.

Claims

1. A beamformer arrangement wherein element signals are fed via respective weighting networks to a summing network, the weighting networks being adjustable to achieve minimisation of the power output of the summing network, the arrangement including means for sampling element signals prior to the weighting means, means for sampling the power output of the summing means, adjustable weighting means for weighting the samples of the element signals, means for combining the weighted samples and the power output samples, means for measuring the power output of the combining means, means for perturbing the weighting of the sampled element signals and means for adjusting the weighting networks in response to the power output measurements to achieve the minimisation of the power output of the summing network.

2. An arrangement according to claim 1 wherein the element sampling means includes switching means to select the samples sequentially for application to the adjustable sample weighting means in time shared operation.

3. An arrangement according to claim 2 wherein the weighting of each sample is perturbed alternately upwardly and downwardly.

4. An arrangement according to claim 1 or 2 having two separate adjustable weighting means to which eacn sample is simultaneously applied, wherein the weighting for each sample is perturbed upwardly in one weighting means and downwardly in the other weighting means simultaneously, the arrangement further having two separate combining means to which samples of the power output are applied, the output of the two weighting means being applied each to a respective one of the combining means.

5. An arrangement according to claim 1 or 2 wherein the means for combining the weighted samples and the power output samples comprises a sum and difference hybrid network whereby simultaneous upward and downward perturbation effects are contrived.

6. A beamformer arrangement substantially as described with reference to the accompanying drawings.