Over-the-horizon aircraft detection using skywave AM-radio broadcast signals

We present the preliminary experimental results of a collaborative research project to determine the feasibility of using AM-radio broadcasts of opportunity for aircraft detection at ranges of thousands of kilometers from a terrestrial receiver. This passive over-the-horizon (OTH) radar concept exploits the unique property of high frequency (HF) signals to allow coverage over very long distances by virtue of skywave propagation. In particular, the aim of the project is to develop, test and evaluate the potential of an experimental HF system for passive detection of aircraft in an OTH forward-scatter geometry. This system explicitly utilizes the AM-carrier component for proof-of-concept and takes full advantage of fast and robust processing schemes to enable real-time practical implementation. Remarkably, it is shown that aircraft target detection and angle-Doppler parameter estimation is feasible at ranges of thousands of kilometers using conventional processing schemes and modest antenna apertures.