A Novel Df-gsc-based Algorithm for Active Cancellation of Hostile Probing Sources

Adaptive arrays are of immense interest due to their ability to automatically steer nulls towards undesired interference sources, thereby reducing the output noise and enhancing the detection of desired signal. In active phased arrays, each antenna element is weighted for beamforming. These weights are estimated iteratively using different algorithms. Generalized sidelobe cancellers (GSC) are amongst the conventional adaptive beamformers that nullify the hostile probing signals (e.g. of radar) while simultaneously maintaining high output signal-to-interference-noise ratio (SINR) towards the desired one. However, GSC is quite sensitive to the direction-of-arrival mismatch. Further, the input signal is present in the stochastic gradient, which makes the gradient large, thereby requiring a very small step size. This further reduces the speed of convergence. In order to avoid such problems recently a modified scheme has been proposed in which the decision feedback filter is included in the conventional GSC scheme. This improves the robustness against various mismatch errors. Such designs are identified as decision feedback generalized sidelobe cancellers (DF-GSC). In this paper, an efficient receiver signal model is employed to investigate the capabilities of DF-GSC for two distinct narrowband radar sources probing the receiving antenna. Using the modified expression for eigenvalues of array correlation matrix and the optimum weight vectors, the performance parameters, viz. output SINR and mean square error are determined. First-order derivative constraints are included along with the point constraints in the LMS algorithm to improve the performance of sidelobe canceller schemes. The role of power level of the hostile sources in the generation of the adapted pattern is also investigated. It is demonstrated that the DF-GSC scheme can be considered as an efficient method for active phased arrays for nullifying the hostile probes while maintaining sufficient gain towards the desired signal. The interference suppression capabilities of DF-GSC scheme of phased arrays can be exploited for active RCS reduction. 1. INRODUCTION Adaptive arrays are of immense interest due to their ability to automatically steer nulls onto undesired sources of interference, thereby reducing the output noise and enhancing the detection of desired signal. These have their roots in different fields including retrodirective antennas, self-phasing arrays, and sidelobe cancellers . In active phased arrays, each antenna element is weighted for beamforming. These weights are estimated iteratively using different algorithms. Least mean square (LMS) algorithms are iterative algorithms that are most popular because of their simplicity in implementation and superior performance. Generalized sidelobe cancellers (GSC) are amongst the conventional adaptive beamformers that nullify the hostile probes (e.g. radar) while simultaneously maintaining high output signal-to-interference-noise ratio (SINR) towards the desired one. However, GSC is quite sensitive to the direction of arrival (DOA) mismatch. Further, the input signal is present in the stochastic gradient, which makes the gradient large, thereby requiring a very small step size. This further reduces the speed of convergence . In order to avoid such problems, Lee and Wu [2] proposed the modified scheme in which the decision feedback filter is included in the conventional GSC scheme. This improves the robustness against various mismatch errors. Such designs are identified as decision feedback generalized sidelobe cancellers (DF-GSC). In this paper, an efficient receiver signal model proposed by Godara [1] is employed to investigate the capabilities of DF-GSC for two distinct narrowband radar sources probing the receiving antenna. Using the modified expression for eigenvalues of array correlation matrix (ACM) and the optimum weight vectors, the performance parameters, viz. output SINR and mean square error (MSE) are determined Proceedings of the International Conference on Aerospace Science and Technology 26 28 June 2008, Bangalore, India