  Unmanned aerial vehicle (UAV) can provide superior flexibility and
cost-efficiency for modern radar imaging systems, which is an ideal platform
for advanced remote sensing applications using synthetic aperture radar (SAR)
technology. In this paper, an energy-efficient passive UAV radar imaging system
using illuminators of opportunity is first proposed and investigated. Equipped
with a SAR receiver, the UAV platform passively reuses the backscattered signal
of the target scene from an external illuminator, such as SAR satellite, GNSS
or ground-based stationary commercial illuminators, and achieves bi-static SAR
imaging and data communication. The system can provide instant accessibility to
the radar image of the interested targets with enhanced platform concealment,
which is an essential tool for stealth observation and scene monitoring. The
mission concept and system block diagram are first presented with
justifications on the advantages of the system. Then, a set of mission
performance evaluators is established to quantitatively assess the capability
of the system in a comprehensive manner, including UAV navigation, passive SAR
imaging and communication. Finally, the validity of the proposed performance
evaluators are verified by numerical simulations.
