Passive radar detection of drones with staring illuminators of opportunity

Passive Bistatic Radars (PBRs) use non-cooperative illuminators of opportunity to detect, localise and track targets. They have attracted considerable research interest in recent years because they can be operated and deployed at a relatively low cost, are difficult to detect and hence allow covert operations in hostile environments and do not require the allocation of an increasingly more congested frequency spectrum. Various analogue and digital communication systems (such as television (TV) and radio broadcast systems) have been studied and exploited as illuminators of opportunity. However, despite the extensive work carried out on PBRs that exploit random communication signals, there has been limited research investigating the use of existing non-cooperative radar systems as illuminators of opportunity. The exploitation of radar signals to achieve passive bistatic detection is attracting attention as it may offer significant advantages. Because common radar waveforms are deterministic, a reference channel is essentially not required to detect a target. Prior intelligence or live estimations of the deterministic waveform design parameters allow the passive receiver to be matched with the illuminator of opportunity and thus generate a range–Doppler map. Radar signals are also designed for detection and provide Doppler tolerance, large bandwidths (which provide good range resolutions) and good compression ratios. This chapter presents a PBR solution that exploits non-random signals transmitted by a non-cooperative staring radar system to detect drones. Staring radars offer a constant illumination of the volume under surveillance and, unlike radar systems that deploy a rotating antenna, offers a continuous signal of opportunity. They are very attractive illuminators in particular for short-range applications to detect low Radar Cross Section (RCS) and slow moving targets.