BEM Reference Signal Estimation for an Airborne Passive Radar Antenna Array

In this paper, we consider an airborne passive radar using digital video broadcasting-terrestrial OFDM signals. In such an application, the channel composite nature and the mobility of the receiver deeply alter the signal and, therefore, degrade the decoding processing. Classic methods experience difficulties in dealing with such channel impacts. In order to reconstruct a proper reference signal, we propose here a channel estimation method that exploits both antenna diversity and a basis expansion model modeling the channel time variations. The application of this method to experimental in-flight recorded data demonstrates the performance improvement provided by the proposed method over the classic demodulation and other methods developed to cope with intercarrier interferences.

I. Introduction

Passive radars have attracted a lot of attention and concern during the past decade. Signal processing methods have been developed for all available transmitters of opportunity such as FM [1], digital audio broadcasting (DAB) [2], digital video broadcasting–terrestrial (DVB-T) [3]– [5], and even global system for mobile or Wi-Fi [6]. This topic has nowadays reached a certain maturity. Systems have been designed and tested for different applications: At first air surveillance [7], but also ground moving target identification and sea surveillance [8], [9]. Besides passive radar characteristics, such as low weight, low power consumption, and stealthyness, they are good candidates to airborne applications. As a consequence, analyses have been recently drawn so as to study the applicability of passive airborne radars. Kulpa et al. [10] describe the overall concept, whereas Tan et al. [11] provide an insight of the necessary system performance, and Tan et al. [12] simulate the received signal and analyses the ambiguity function. The first experiments have allowed to examine ground clutter [13], and to consider the detection capabilities of such a system [14] –[16] based on FM signal. Moreover, Ulander et al. [17], [18] show the benefits of a suitable bistatic geometry to face ground clutter echoes for DVB-T SAR imagery.