Passive radar in the high frequency band

Passive radar systems using emitters of opportunity for target detection and tracking have received significant interest recently, especially those which exploit frequency modulated (FM) radio stations and TV transmitters as signal sources. This paper is concerned with passive radar systems that utilize signal sources in the high frequency (HF) band (3-30 MHz), where due to long-distance ionospheric propagation, the transmitter may be located beyond the line-of-sight (i.e. over-the-horizon). To investigate this application, a two-dimensional (L-shaped) antenna array with a digital receiver per element was tuned to simultaneously record cooperative and non-cooperative HF signal sources within the receiver bandwidth. This data was processed by conventional and adaptive methods to determine the detection performance of the system for a dedicated aircraft target. GPS data from the cooperative aircraft provided accurate ground truth of the target flight path and velocity, enabling its bi-static range/Doppler and direction of arrival (azimuth/elevation) versus time profiles to be calculated and compared with radar measurements. The experimental system and data processed in the paper is exclusively from the DSTO HF radar program.