Aharon A. Ksienski

A Decision Theoretic Approach to the Angular Resolution and Parameter Estimation Problem for Multiple Targets

The problem of multiple-target resolution and parameter estimation is formulated in a decision theoretic context. The estimation portion of the problem is explicitly solved and experimentally implemented. The results show that it is possible to obtain accurate parameter estimates for targets separated as close as a quarter of a 3-dB beamwidth. This resolution was obtained for reasonable SNRs and with a system that utilized only commercially available components.

Dependence of adaptive array performance on conventional array design

A direct relationship between conventional array design and the array performance in an adaptive mode is given. It is shown that the basic goals of conventional array design such as low sidelobes and narrow beamwidth have a direct effect on the adaptive array performance and should not be ignored. Expressions are obtained showing that the output signal-to-interference-plus-noise ratio (SINR) of an adaptive array is related to the conventional pattern of the array. These expressions allow the prediction of the performance of an array in its adaptive mode given its conventional electromagnetic characteristics. Thus, they are an important design tool for adaptive arrays. The relations between the conventional and adaptive array are illustrated for linear and circular arrays.

SMI adaptive antenna arrays for weak interfering signals

The performance of adaptive antenna arrays in the presence of weak interfering signals (below noise level) is studied. It is shown that conventional adaptive arrays are unable to suppress such interfering signals. To overcome this problem, the feedback loops controlling the array weights are modified. In the modified feedback loops, the noise level in the feedback loops is reduced by reducing the correlation between the noise components of the two inputs to the loop correlator. Two techniques to decorrelate these noise components are discussed. It is shown that adaptive arrays with the modified feedback loops provide the desired interference suppression. An expression is given for the amount of noise decorrelation required to achieve a specified interference suppression.

Optimum Frequencies for Aircraft Classification

The selection of the optimum features for aircraft classification from radar returns was studied. A constraint was imposed that a minimum number of simultaneous frequencies be used. The results indicate that a high reliability of classification is achievable with only two frequencies, and even a single frequency can provide over 95 percent reliability if both phase and amplitude at two orthogonal polarizations are used. The data set tested involved eight military aircraft whose sizes varied over a three-to-one range.

An experimental adaptive array to suppress weak interfering signals

An experimental adaptive antenna system to suppress weak interfering signals is described. It is a sidelobe canceller with two auxiliary elements. Modified feedback loops are used to control the array weights. The received signals are simulated in hardware for parameter control. Digital processing is used for algorithm implementation and performance evaluation. The experimental results are presented. They show that interfering signals as much as 10 dB below the thermal noise level in the main channel are suppressed by 20-30 dB. Such a system has potential application in suppressing the interference encountered in direct broadcast satellite communication systems. >

Prediction of Adaptive Array Performance

A direct relationship between the conventional properties of an array and the array performance in an adaptive mode is given. Expressions are provided to obtain the output signal-to-interference-plus-noise ratio (SINR) of an adaptive array in terms of its conventinal pattern and the locations of the desired signal and jammers. These expressions permit one to evaluate the performance of an adaptive array without an exhaustive search for all possible scenarios and parametric values to ascertain that the required performance levels be met. In fact, one can predict the jammer locations for which the array will provide its best and worst performance by observing the conventional pattern. Several examples are provided to demonstrate the relationship between the conventional pattern and the adaptive array performance. The examples include both linear and planar arrays.