Bistatic radar using satellite-borne illuminators of opportunity

This thesis presents an investigation into the feasibility of using DBS TV satellites as illuminators of opportunity for bistatic radar. A review of studies in bistatic radars, terrestrial illuminators of opportunity and dedicated space-borne transmitters is given and the concept being investigated is explained. A review of bistatic radar and DBS TV satellites is given. It is shown that a radar based on typical domestic DBS TV system parameters and target RCSs derive SNRs from -7dB down to -77dB. Extensive signal processing gains of up to 90dB are required to integrate echo energy to reliable detection thresholds. Iso-range, iso-Doppler and iso-power contours are presented that predict the response of a receiver at UCL to target echoes. DBS TV waveforms are not necessarily favourable for radar purposes. Crosscorrelation is the method identified to process echo signals. Auto-correlation functions and ambiguity functions of sampled DBS TV waveforms are presented. Range resolution and side-lobe levels are examined for some TV modulation standards. It is shown that broadcast 'scrambling' suppresses 64's TV line ambiguities by approximately 15dB. Design and construction of an experimental bistatic radar receiver using modified domestic DBS TV equipment interfaced with a quad-channel digitising oscilloscope is presented. Coherently demodulated reference and echo signals were digitised, correlated and integrated on a PC-compatible. Results of trials that were conducted at UCL with the ASTRA satellite and a transponder to evaluate radar performance are presented. It is shown that signal and noise levels integrate as predicted, and signal energy integrates in proportion to integration time. Extrapolation of radar performance is made to show a 20dBm2 target at 100km would require correlation and integration over 100s of 109 independent samples. It is concluded such a radar is not agile enough for tracking, but is more suited to surveillance. Recommendations in the design of future systems are proposed to reduce integration time required, and thus extend possible applications.