Sparse Array Optimization and Radar Interference Analysis for Adaptive Beamforming

Abstract

This thesis investigates non-uniform array antenna optimization for wideband frequency invariant beam- forming and radar interference analysis for adaptive beamforming systems.

In the first part, non-uniform array optimization methods are proposed to achieve frequency invariant beamforming over a wide frequency band while reducing the number of antenna elements. Thinned and sparse array optimization approaches are developed to preserve frequency invariant beamwidth charac- teristics across frequency. For thinned arrays, a joint genetic algorithm based optimization framework is proposed to simultaneously optimize the array thinning pattern and frequency-dependent complex exci- tation weights. Based on the optimized thinned array results, a design rule relating the target beamwidth, operating frequency band, and required aperture size is identified and applied to sparse array optimiza- tion. A target pattern optimization is further performed to reduce the peak sidelobe level while satisfying frequency invariant constraints. The proposed methods are validated over a 2–18 GHz band with beam steering angles up to 50 deg, achieving beamwidth deviations within ±2 deg and approximately 65% reduction in antenna elements compared with conventional approaches. Experimental results using a fabricated LPDA antenna confirm the effectiveness of the proposed methods in the presence of mutual coupling.

In the second part, an efficient analysis method for radar-to-radar interference in adaptive beamform- ing systems is proposed. To reduce computational complexity, the transmitting radar antenna is modeled using an equivalent near-field source, while the receiving radar array is represented by complex-valued fields or received currents depending on the operating frequency difference. An array manifold is con- structed to evaluate interference strength as a function of direction. The proposed method is validated under both line-of-sight and non-line-of-sight conditions, and radar face interference is analyzed in the presence of onboard structures. The results demonstrate that the proposed approach effectively identi- fies dominant interference directions and magnitudes and can be extended to multi-radar interference analysis in practical systems.