摘要:

An array is defined as a set of sensors, for example antennas or acoustic transducers. The outputs from these sensors can be processed in an adaptive manner to respond to an unknown interference environment in an attempt to optimise the performance of the system in some defined manner. The paper is intended as an introduction to, and to some extent a survey of, some of the methods used in adaptive array processing. It has, however, no pretence to be comprehensive. Some of the topics covered include the use of constraints, gradient techniques, including the stochastic steepest-descent algorithm, properties of the covariance matrix, the power inversion algorithm and the use of weight purturbation techniques.

DOI:10.1049/ip-f-1.1983.0002

出版商:IEE    

年代:1983

数据来源: IET

摘要:

The problem of minimising a real scalar quantity (for example array output power, or mean square error) as a function of a complex vector (the set of weights) frequently arises in adaptive array theory. A complex gradient operator is defined in the paper for this purpose and its use justified. Three examples of its application to array theory problems are given.

DOI:10.1049/ip-f-1.1983.0003

出版商:IEE    

年代:1983

数据来源: IET

摘要:

The basic similarities and essential differences between adaptive processing structures in the space and time domains are considered. Attention is focused on the fact that a cascade structure is required to decorrelate the signals received from different elements of an antenna array, while a very different and more efficient lattice filter structure may be used to decorrelate successive samples of a time series. The difference is explained by examining the Levinson-Durbin recursion algorithm, which essentially gives rise to the lattice filter structure. The algorithm is presented in a generalised form which takes into account the effect of non-stationary statistics and shows clearly how the use of recursion in time is fundamentally responsible for its efficiency. The algorithm is clearly not appropriate for antenna array decorrelation or in the spatial domain generally.

DOI:10.1049/ip-f-1.1983.0004

出版商:IEE    

年代:1983

数据来源: IET

摘要:

High-resolution methods of spectral estimation have recently found application in the processing of data received by spatially distributed arrays of sensors. These techniques have been used for estimation of the directional power illuminating the array and have proved useful as a first step in the analysis and classification of possible targets. Several desirable qualities are offered by these spatial spectral analysis techniques: high resolution for short arrays, low sidelobe levels, ability to work with arbitrary array geometries, and tolerance to correlated (multipath) targets being but a few. Spectral estimators based on certain eigenvectors of the data covariance matrix have these properties. The paper discusses the use of filters based on these eigenvectors (called eigenfilters) in adaptive array processing, and two different estimation algorithms are compared. The first algorithm involves a simple gradient descent approach, while the second utilises a decomposition of the array data by a spatial filter which leads to a triangular structured lattice filter. Comparisons are made between these algorithms and with other conventional high-resolution spectral estimators.

DOI:10.1049/ip-f-1.1983.0005

出版商:IEE    

年代:1983

数据来源: IET

摘要:

The performance of current cancellation systems is limited when broadband cancellation is required. The paper covers some of the work performed at Plessey (Roke Manor) to overcome these problems by using an adaptive transversal filter. The paper begins by considering some of the effects which limit broadband performance of current cancellation equipment. Secondly, assuming that each tap weighting of the transversal filter is controlled by a correlation loop, a matrix equation is derived for these weight values. From this the residual signal level can be found. The paper then explains the computer program used to solve the matrix equation for given input signal conditions. This result is then used to find the residual power. These evaluations show the potential improvement of an ATF cancellation system compared with a conventional system. Finally, practical work with a four-tap system is discussed, and an improved cancellation performance is demonstrated using low-cost cancellation loops.

DOI:10.1049/ip-f-1.1983.0006

出版商:IEE    

年代:1983

数据来源: IET

摘要:

Directional interference suppression is based on a recursive estimation procedure of the state of a filter forming the directional interference spectrum. For the stationary filter, this leads to an iterative solution of the Wiener-Hopf matrix equation. It can be shown that the number of samples required for convergence is related to the number of degrees of freedom of the filter. The nonstationary case of a changing interference environment is treated by an appropriate deterministic dynamic process model. Tracking performance and problems of digital implementation are studied by computer simulation.

DOI:10.1049/ip-f-1.1983.0007

出版商:IEE    

年代:1983

数据来源: IET

摘要:

Optimum beamformers with multiple linear constraints are usually designed under the assumptions of plane-wave signals and an ideal propagation medium. In acutal operating conditions these ideal assumptions do not hold; for example, signal suppression can arise from beam steering angle errors if the optimum weights are calculated from the signal-plus-noise cross-spectral matrix. To overcome this, it is desirable to broaden the signal acceptance angle (i.e. the width of the main beam) while preseving the beam-former's ability to reject interference from directions outside this acceptance angle. This can be accomplished by the use of multiple directional constraints or a single directional constraint combined with multiple derivative constraints. The paper compares the performance of these two constraint systems and shows that the signal suppression of a directional constraint system approaches that of a derivative constraint system as the angle between the directional constraints is decreased. The comparison is based upon the analysis of signal suppression effects and the ill conditioning of the equations for the optimum weight vectors. In the examples considered the derivative constraints avoid the ill conditioning problems associated with the use of multiple directional constraints.

DOI:10.1049/ip-f-1.1983.0008

出版商:IEE    

年代:1983

数据来源: IET

摘要:

A computer program has been written for the statistical investigation of the transient response of adaptive arrays of the radar sidelobe cancellation type, using multiple parallel feedback correlation loops. The expressions for the response are derived, the program is described in general terms, and some results are presented for a particular array, giving an indication of the performance available from these systems.

DOI:10.1049/ip-f-1.1983.0009

出版商:IEE    

年代:1983

数据来源: IET

摘要:

The design and operation of a compact processor for small adaptive arrays is described. The control law is based on the minimisation of the array output power subject to a linear weight constraint. This choice enables the processor to be used in a wide range of applications using relatively simple control techniques to avoid cancellation of the wanted signal. Practical results supporting many of the design equations are provided, and several types of application are discussed. The design approach has been chosen to facilitate a future VLSI implementation.

DOI:10.1049/ip-f-1.1983.0010

出版商:IEE    

年代:1983

数据来源: IET

摘要:

There are many applications of adaptive antennas where it is desirable to set an adjustable threshold below which received signals are not nulled by the adaptive process. This may be achieved with a gradient descent adaptive control algorithm by a suitable choice of integration loss and update gain factors. Generally, the gradient estimate is obtained by a correlation process, and the hardware design can be simplified by incorporating some form of signal limiting prior to the correlator. However, it is known that this can also have severe implications on the thresholding performance in the presence of multiple signals. The paper presents a straightforward discussion of the problems associated with the use of limiting and analyses the resultant degradation of the nulling characteristics of the array.

DOI:10.1049/ip-f-1.1983.0011

出版商:IEE    

年代:1983

数据来源: IET