Analysis and Suppression of Range-Domain Periodic Interference in High-Frequency FMICW Radar

High-frequency radar (HFR) is widely used to measure ocean surface currents. In archived field data, radar echoes are often contaminated by interference, which usually appears as strips parallel to the range axis in the range-Doppler (RD) spectrum. Recently, a different form of interference has been frequently observed in the RD spectrum collected at one site by an Ocean State Measuring and Analyzing Radar, type S (OSMAR-S), whose strips show different periodicities other than continuity in the range domain. These periodicities cannot be readily explained by existing interference models. In this paper, we first give a theoretical derivation of the range-domain periodic interference (RPI) for frequency-modulated interrupted continuous wave (FMICW) radars, which shows that the periodic interference pattern is most likely formed by a sinusoidal interference modulated by a time shifted version of the radar gating function. Then, to improve the performance of interference suppression, we propose two novel interference suppression methods: Orthogonal projection filtering (OPF) with adaptively selected training range bins (OPF-A) and OPF with fixed training range bins from RD spectrum (OPF-F-RD). Finally, archived field OSMAR-S data are used to test the performance of the RPI suppression methods. The OPF-A and OPF-F-RD outperform OPF with fixed training range bins (OPF-F) in the quality of both the echo signal and the extracted radial current. Therefore, the proposed OPF-A and OPF-F-RD are good choices to suppress different kinds of interference in HFR operations.