Experimental Results Using Satellite Illuminator for Passive Bistatic Radar

Passive, bistatic radar offers an attractive method for remotely detecting and imaging targets without the requirement of a dedicated transmitter. Passive radar systems are usually cheaper than their active counterparts, which easily allows for multi-sensor networks. Furthermore, passive radar systems are difficult to detect and jam. With these advantages come several challenges, however. Bistatic ranging is often a more difficult problem than monostatic ranging since the bistatic range depends on the position of the target relative to the transmitter and the receiver(s). Also, passive radars have no control over the transmitted waveform and are forced to utilize signals of opportunity. These non-cooperative signals of opportunity are typically communications signals which do not usually offer the high transmit power or wide bandwidth of a conventional monostatic radar. This study describes a new passive radar system utilizing a non-cooperative, satellite-based illuminator. Capabilities of this new system are initially demonstrated with Doppler imaging results from land-, sea-, and air-based targets. 1.0 INTRODUCTION Passive radar using terrestrial transmitters has been studied for the past several decades. Given their significantly lower cost, passive radar technology has been proposed for a wide variety of applications, including airport security and harbor surveillance [1,2]. When compared to the number of studies involving the use of terrestrial emitters, relatively few studies have explored the use of satellite-based illuminators for passive radar [3,4]. Furthermore, existing studies of reflections from satellite-based transmitters typically focus either on specular scattering or scattering within the plane of incidence. Recent literature suggests that moving to out-of-plane geometries offers better flexibility and fosters the development of multi-static and bistatic multipleinput/multiple-output (MIMO) networks [3]. The system described herein utilizes signals transmitted by the XM/Sirius satellite radio constellation as a network of illuminators-of-opportunity. Reflections of XM/Sirius signals from various targets are processed into range-Doppler maps for several different targets, ranges, and bistatic geomeries. 2.0 OVERVIEW OF BISTATIC RADAR Bistatic radar presents the opportunity to view targets at unique angles which are not achievable with monostatic systems. This section seeks to clarify the viewing geometries available to a bistatic radar system, as well as the benefits and drawbacks of various bistatic configurations. Figure 2-1 shows a basic illustration of the bistatic radar geometry, including one reference and one surveillance channel. A reduction in the bistatic angle β between the transmitter and receiver in the illustration demonstrates a geometry towards an “over-the-shoulder” configuration, which mimics the behavior of a continuous-wave monostatic radar. Such a configuration is often ideal in that self-interference from the direct signal is limited and the bistatic Doppler can be maximized. Figure 2-1 illustrates the relationship between the bistatic geometry and the Doppler shift of the reflection from the target. Note that this Doppler shift can change significantly if the STO-MP-SET-241 2B-2 1 PUBLIC RELEASE