Spatial Adaptive Processing for Passive Bistatic Radar

Abstract

Abstract —This paper presents work done on the application of Spatial Adaptive Processing (SAP) to Passive Bistatic Radar (PBR) systems. Specifically, the main goal is to analyse SAP performances in terms of interference spatial filtering and the estimation of the target’s Direction of Arrival (DoA) when using PBR systems. Multiple solutions are provided and compared in order to identify the best multichannel processing architecture. Results are shown by using real multichannel PBR data. I. I NTRODUCTION Passive Bistatic Radar (PBR) is gradually making progress both in terms of signal processing and system development (demonstrators and prototypes). The most simple PBR system is composed of two highly directive dedicated antennas used for the acquisition of the surveillance and the reference signals. A typical solution, adopted to overcome the problem of suppressing interference components, is based on the employment of highly directive antennas followed by temporal adaptive filtering techniques [1]. A wide variety of temporal adaptive processing techniques has been developed for the removal of the interference before the signal is matched filtered [2]. The main drawbacks of this architecture can be summarized as follows: • a single directive antenna cannot simultaneously look into different directions • the spatial filtering effectiveness is strictly related to its physical and geometrical properties and, therefore, it cannot adapt to environment changes. When the interference signal is particularly strong, the filtering effectiveness of this architecture is often unsatisfactory. An alternative approach is based on the use of antenna arrays and Spatial Adaptive Processing (SAP). Using a phased array antenna combined with SAP techniques, it is possible to electronically steer multiple beams. This allows for: • the reference and surveillance signals to be collected at the same time • strong interferences to be more effectively removed • the target’s localization accuracy to be improved (which represents another main issue in PBR). The most simple method used to estimate the target’s Direction of Arrival (DoA) is based on an interferometric approach, which exploits the signal phase difference between the two receiving channels. Using more complex antenna arrays and the implementation of SAP techniques (high-resolution DoA estimators) allows for the target DoA estimation to be improved. The application of SAP techniques to a passive phased array radar is the main concern of this study. In particular, SAP techniques are investigated from two points of view: • spatial filtering for interference reduction and target detection, • high-resolution DoA estimation algorithms for target DoA estimation. Two possible approaches are analysed. In the first one, SAP algorithms are applied directly to the received array snapshot. In the second one, SAP techniques are applied after the matched filter and the formation of the range-Doppler maps. The main drawbacks and advantages of these solutions are investigated and tested on real data. The paper is organized as follows. In Section 2, the main theoretical aspects of SAP theory are briefly recalled. In Section 3, we analyze how SAP techniques, in terms of both spatial filtering and DoA estimation, can be employed within a common PBR processing architecture. In section 4, we will present a case study where real data are used to evaluate the performance of the proposed algorithms. II. A