Over-the-horizon radar continuous-wave interference suppression using harmonic least-squares fitting

High Frequency (HF) skywave over-the-horizon (OTH) radar is routinely affected by radio frequency interference (RFI) from natural sources (e.g. lightning), and transmissions from other users, such as continuous-wave (CW) signals. Although adaptive processing effectively mitigates interference and noise, it can impact negatively upon target detection in some cases. This paper describes a simple filtering technique, harmonic least-squares fitting (HLSF), which has potential for application throughout the OTH radar signal processing chain. In this paper we illustrate HLSF application for clutter suppression, transient detection, and CW interference suppression. In each instance HLSF application demonstrates advantages over commonly used techniques.