Range compression strategies for passive radar on airborne platforms

This paper focuses on range compression aspects to be considered in the signal processing of passive radars. In particular it focuses on passive radar systems mounted on moving platforms for ground moving target indication on the one hand and on synthetic-aperture radar on the other hand. As the signals of opportunity are not created for radar purposes, the underlying signal structure can lead to ambiguities and sidelobes and thus impede target detection or decrease the signal-to-noise ratio. Careful signal processing algorithms must be applied on the range compression stage in order to deal with these issues. Here we provide an overview of possible range compression techniques and give a suggestion which technique is the most appropriate depending on the type of application.

I. Introduction

Research on passive radar or Passive Coherent Location (PCL) has been focusing over the last years on the development of systems onboard of moving (typically airborne) platforms. The goal is to replicate, or emulate, in a passive radar context all typical active airborne radar applications, such as Synthetic Aperture Radar (SAR) and Ground Moving Target Indication (GMTI). By aiming at this, issues and challenges arise due to: (i) the bistatic geometry, and (ii) the uncontrolled nature of the transmitted waveform of opportunity. While the first aforementioned point has been already addressed in past research when dealing with general bistatic geometries, the latter aspect is more peculiar of passive radar and it requires dedicated analysis. Among numerous illuminators of opportunity nowadays available for passive radar design, the digital broadcast television signals (namely DVB-T(2) and ATSC) offer interesting characteristics in terms of signal power density and signal bandwidth. Specifically, the DVB-T(2) transmitting infrastructure is: (i) illuminating the ground, which is the area of interest for SAR and GMTI applications; (ii) transmitting a digital modulated signal, which enables the implementation of the demodulation/remodulation (demod/remod) scheme for passive radar processing [8]; and (iii) operating at Very High Frequency (VHF)/Ultra High Frequency (UHF) frequencies, which allow the design of relatively small receivers based on the Software Defined Radio (SDR) principle.