RESEARCH PAPER Adaptive Target Detection in Passive Bistatic Radars: A Theoretical Analysis Mohammad Zamani 1 • Abbas Sheikhi 1 Received: 2 January 2016 / Accepted: 10 December 2016 Ó Shiraz University 2017 Abstract This paper provides a theoretical analysis to consolidate the theory of ‘‘adaptive’’ target detection in the surveillance channel of passive bistatic radars where noise, strong returns of clutter and target returns are present. It is known in the literature that by generating the mixing pro- duct for each bistatic sample delay in the surveillance channel using the preprocessed and multipath-free refer- ence channel signal, adaptivity can be realized. However, the theoretical background of this idea is not strong. In this paper, the statistical characteristics and the distribution of the mixing product are analyzed leading to the hypothesis test applicable to the ‘‘adaptive’’ detection problem. We investigate the iid requirements of secondary data, and a suitable scheme for secondary data generation in which these requirements are approximately satisfied is proposed. Several adaptive target detectors from active pulse radars’ literature based on the derived hypothesis test are gener- alized for use in passive radars and their performances are assessed by simulations and theoretical analysis. The simulation results indicate that these detectors are generally preferred compared to the conventional cross ambiguity function processing. It is also shown that the simulation- based and theoretical detection performances validate each other. Keywords Passive bistatic radar  Adaptive detection  Mixing product  Ambiguity function 1 Introduction Passive bistatic radars (PBRs) are known by some char- acteristics and benefits that make them unsubstitutable in some applications. They do not require dedicated trans- mitters and so are inexpensive, invulnerable to jamming, covert and without frequency allocation requirements. Moreover, frequency and space diversity are provided. But as the transmitter’s location and the transmission properties cannot be controlled by the radar designer, processing, synchronization and system challenges are increased (Ch- erniakov 2008). The general geometry of a PBR is shown in Fig. 1. The transmitter of opportunity is assumed to have a wide beam antenna in azimuth, propagating the transmitting signal in a wide sector. The receiver’s antenna is an array antenna with several directional surveillance beams produced by a suitable beamforming method and a separate beam toward the transmitter (reference beam) for the reception of directly transmitted signal. So, the PBR depicted in Fig. 1 has M surveillance channels and one reference channel. The surveillance channels collect the target echoes. Unfortunately, the strong unwanted returns of direct signal and clutter/multipath are also received in the surveillance channels which degrade or deny the capability to detect the targets (Cherniakov 2008; Colone et al. 2009a; Radmard and Nayebi 2015). For each surveillance channel, time- domain signal processing and target detection are done independently. The algorithms to allow for the detection of targets can be categorized into ‘‘adaptive’’ and ‘‘non- adaptive’’. For PBRs, the non-adaptive approach has been researched vastly, while the theory of adaptive approach is still immature. The analytical discussion of PBR ‘‘adap- tive’’ detection problem is the main subject of this paper. Before introducing the works which have already been & Abbas Sheikhi sheikhi@shirazu.ac.ir 1 Department of Communications and Electronics, School of Electrical and Computer Engineering, Shiraz University, Shiraz, Iran 123 Iran J Sci Technol Trans Electr Eng DOI 10.1007/s40998-017-0015-7