Bistatic radar systems have been studied and built since the earliest days of radar They have the advantages that the receivers are passive, and hence undetectable The receiving systems are also potentially simple and cheap Bistatic radar may have a counter-stealth capability, since target shaping to reduce monostatic RCS will in general not reduce the bistatic RCS In spite of those advantages, rather few bistatic radar systems have got past the 'technology demonstrator' phase It has also been remarked that activity in bistatic radar tends to vary on a period of approximately fifteen years, and that currently we are at a peak of that cycle; there is particular current interest in passive coherent location (PCL) techniques, using broadcast and communications signals as 'illuminators of opportunity' This paper presents a review of some of the history, and the properties and current developments in the subject, and conjectures whether or not the present interest is just another peak in the cycle

From a different perspective: principles, practice and potential of bistatic radar

Bistatic Radar - Principles And Practice

Bistatic radar has long been recognised as an interesting variant of radar, with a number of potential advantages for air defence. Space-based radar is seen by the US Department of Defense as a key technique for future AMTI and GMTI applications, and the DISCOVERER II programme is indicative of current thinking, aiming ultimately at a network of several tens of satellites. This system would also involve bistatic receivers to give near-continuous surveillance. The purpose of this paper is to present a system concept for a bistatic radar using a satellite-based illuminator of opportunity and a static ground-based receiver. The paper presents system design and performance calculations, and describes experiments to be performed.

Bistatic radar using satellite-borne illuminators

It has been remarked that interest in the subject of bistatic radar has varied cyclically, with a period of about fifteen years. The very first radars were bistatic, until T/R switches were invented. Interest was revived in the 1950s/1960s, with semi-active homing missiles and the SPASUR system, then died away. The second resurgence was in the mid-1970s to mid-1980s, with systems such as SANCTUARY and the first experiments in Passive Bistatic Radar. And the third resurgence started in the mid-1990s, and is still continuing. There are good reasons to believe that this time it is for real. The consequences of Moore’s law mean that digital processing power, which is essential to realise practical systems, increases inexorably. The advent of GPS solves many of the problems of timing and synchronization which were previously very difficult. Bistatic systems may be able to address new military and security operational requirements such as the detection and tracking of low-signature targets, and the increasing use of unmanned air vehicle (UAV) platforms is also well-suited to bistatic and multistatic configurations. There has been particular interest in bistatic radar exploiting broadcast, communications or radionavigation signals as illuminators - so-called passive bistatic radar (PBR).

New directions in bistatic radar

: This tutorial describes the basis of passive bistatic radar (PBR) systems, and in particular the nature of the waveforms of illuminators of opportunity that they exploit. It shows that there is a wide variety of such waveforms, from broadcast, communications and radionavigation transmissions, and that in general they are not optimum for radar purposes. In addition, they usually vary significantly as a function of time, with the imposed modulation. It is therefore necessary to understand the effect of the waveform on the performance of the passive bistatic radar, so as to be able to choose the most appropriate illuminator, and to use the waveform in the optimal way, and it is in this sense that PBR forms a part of the subject of waveform diversity. The tutorial presents a short summary of the properties of bistatic radar, then goes on to consider the specific case of passive bistatic radar. Next, two brief sections provide a review of the radar equation for bistatic radar and of the ambiguity function for bistatic radar, before considering the properties of a variety of different waveforms that may be used for passive bistatic radar purposes and how best to exploit them. Finally, a description is given of some practical passive bistatic radar systems and examples of results.

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Passive Bistatic Radar and Waveform Diversity

The paper describes a technique for implementing moving target indication (m.t.i.) in an independent bistatic radar receiver. Conventional techniques for m.t.i., and the particular features and advantages of the bistatic radar configuration are also reviewed.The technique of phase priming by clutter echoes is suggested as a means for providing a coherent reference at the receiver, without need for any link between radar transmitter and receiver. An oscillator at the receiver is primed at the instant of switch-on at the beginning of each p.r.i. with a small sample of echo signal from close-in stable clutter, such that its phase is determined by that of the clutter echo. This enables m.t.i. processing to be obtained, just as with a conventional monostatic radar system.An experimental system using this principle is described, and results demonstrated and discussed.

S.M. Carter

Papers

Provision of moving target indication in an independent bistatic radar receiver