BEAM AND NULL STEERING IN FDA RADARS AND OTHER CHARACTERISTICS WITH DIFFERENT GEOMETRIES

Abstract

Frequency diverse array (FDA) radars have gained exceptional attention from the researchers during the past decade, due to their unique range-angle and time modulated beampatterns. This range–angle dependent beampattern provides additional degrees of freedom in the spatial domain as compared to a conventional phased array radar that offers only an angle dependent beampattern. The range-angle- time dependent beampattern with the aid of advanced signal processing algorithms, has been exploited for interference suppression, beamforming, direction of arrival estimation, target tracking, and localization in radar environments. In this dissertation, utilizing the extra degrees of freedom in FDA, new beamforming schemes have been proposed. In linear frequency diverse array radars (LFDA), null steering in cognitive radar system has been proposed. This work is a ‘near to implementable form’ of cognitive radar system that offers a null steering solution both in range and angle dimensions. Similarly frequency offset selection based 3D adaptive transmit beamforming has been proposed for planar frequency diverse array radars (PFDA). The proposed scheme outsmarts other existing techniques in terms of concentrated maxima, deeper nulls and enhanced system signal to interference plus noise ratio (SINR). Previous researches have focused largely on evaluating FDA system performance in uniform linear array (ULA) and uniform rectangular arrays. Despite the advantages and implementation convenience of other array geometries, they have not been extensively investigated. In this thesis, new geometries like “circular” and “elliptical” have also been explored in the domain of frequency diversity. Normally, 3D localization of targets can be achieved with PFDA, but investigation in this dissertation validates that uniform circular frequency diverse array (UCFDA) offers much sharper localization, improved directivity and better adaptive beamforming performance as compared to PFDA. Despite the fact that UCFDA offers much improved beamforming performance and signal to interference plus noise ratio than PFDA, circular geometry is a high side lobe geometry. Investigation into elliptical frequency diverse arrays (EFDA) reveals that, much better range selectivity and reduced side lobe levels can be achieved. Extending the domain of frequency diversity further, the thesis also focuses on UCFDA and EFDA with non-uniform frequency offset. The non-uniform function selected for this purpose is tangent hyperbolic function. The proposed systems not only offers a highly configurable type array system but also outsmarts the existing non-uniform frequency offset scheme in terms of significantly reduced side lobe levels.