A simple NULA design strategy for target detection and DoA estimation in mobile passive radar

This paper explores the advantages of Non-Uniform Linear Array (NULA) configurations for target detection and Direction of Arrival (DoA) estimation in mobile passive radar space-time adaptive processing (STAP). The limited number of receiving channels and the low directivity of antennas, typical of passive radar systems, may limit the moving target detection and angular localization capabilities. Therefore, the use of non-uniform distributions of antennas is encouraged, aimed at making the most of the available channels, by leveraging on spatial diversity. However, selecting a suitable NULA configuration represents a difficult task, being characterized by competing requirements. On the one hand, maximizing the array total length shrinks the clutter notch and reduces the DoA estimation error. On the other hand, increasing the inter-element spacings may lead to the appearance of statistical ambiguities, associated to sidelobes of the array beampattern, resulting in large estimation errors, as well as detection performance degradations. We propose a simple strategy for the selection of suitable NULA configurations, based on a requirement on the maximum peak-to-sidelobe ratio, which guarantee satisfactory performances in terms of both target detection and DoA estimation. The resulting array configuration are tested, via numerical analysis, addressing the case of a mobile passive radar exploiting DVB-T as a signal of opportunity.