Ricerc@Sapienza

The exploitation of the Global Navigation Satellite Systems (GNSS) as transmitters of opportunity in passive radar systems for maritime surveillance is particularly attractive because of the main advantages consisting in a global coverage (even in open sea) and in the availability of multiple sources (different satellites and constellations). The main drawback stays in the restricted power budget provided by navigation satellites.

This paper investigates the possibility to localize small aircrafts and drones in three-dimensions by exploiting a passive radar based on WiFi transmissions. Specifically, following the latest results of the authors, where the effectiveness of the WiFi-based passive radar has been demonstrated for the detection and 2D localization of small aircrafts, the advanced capability to estimate their height is demonstrated in this paper. In addition, the new capability is explored to detect and localize small commercial drones and UAVs in 3D.

This paper addresses the problem of a passive radar system mounted on a moving platform with the purpose of Ground Moving Target Indication (GMTI). When exploiting digital communication signals for passive radar, the signal structures result in ambiguities and grating-lobes which may overlap echo signals of targets, which are then difficult to detect. Echo signals of targets can also be covered by Doppler-shift induced from the receiver’s motion. We suggest to apply a reciprocal filter for ambiguities removal and the Displaced-Phase Centre- Antenna (DPCA) technique for clutter removal.

Passive Bistatic Radar (PBR) systems use noncooperative illuminators of opportunity to detect, localise and track targets. The aim of this paper is to investigate the potential of PBR target detection in the presence of non-random signals emitted by non-cooperative transmitters of opportunity, such as radar systems, and without the use of a reference channel. An experiment to detect a moving target was carried out at the Defence Academy of the United Kingdom to demonstrate target detection capabilities using a low cost off-the-shelf receiver.

The potentialities of passive radar (PR) will be illustrated in this chapter with reference to the surveillance of areas of limited extent. Despite the exploitation of the PR principle in short range applications could appear as a simple task, it is shown that it brings a number of challenging issues that must be solved to benefit from its potential advantages. In addition the requirements on such sensors could be much more demanding to enable advanced capabilities.

In this paper, we consider the possibility to jointly exploit multiple frequency channels emitted by the same transmitter to improve target detection capability in a DVB-T based passive radar. In particular, appropriate multi-frequency techniques are presented for target detection to be effective in the considered application. The proposed approaches are validated and compared with reference to several experimental data for maritime surveillance applications.

Suitable methods to jointly exploit the diversity of information conveyed by different polarimetric channels in Passive Coherent Location (PCL) systems are a topic of current research. Possible signal processing strategies were devised for FM radio based PCL with the purpose of enhancing the target detection capability and their benefits were largely demonstrated. This paper presents the results from a preliminary investigation carried out considering a multi-channel PCL system exploiting DVB-T signals.

In this paper we present a robust approach for target direction of arrival (DoA) estimation in passive radar that jointly exploits spatial and frequency diversity. Specifically we refer to a DVB-T based passive radar receiver equipped with a linear array of few antenna elements non-uniformly spaced in the horizontal dimension, able to collect multiple DVB-T channels simultaneously. We resort to a maximum likelihood (ML) approach to jointly exploit the target echoes collected across the antenna elements at multiple carrier frequencies.

Suitable strategies to exploit polarimetric diversity have been proved to be able to enhance the target detection capability of passive radar (or passive coherent location - PCL) systems. In this work, the authors describe a novel polarimetric adaptive detection scheme, based on a two-dimensional autoregressive model for the disturbance. The effectiveness of the proposed strategy is shown against experimental data collected by means of a FM radio based multi-channel PCL prototype.

Long coherent integration times can be exploited in passive radar systems in order to broaden their coverage and to improve their target detection capability. However, proper strategies must be considered to compensate for the target migration effects that could limit the system performance when long coherent processing intervals are used.