Remarks on Signal Processing in HF Radars Using FMCW Modulation

Besides the well known microwave radar systems mainly used in navigation, surveillance, and control applications, High-Frequency (HF) radars gain increased attention during the last decades. These HF radars are operated in the 3-30 MHz frequency range and due to ground-wave or sky-wave propagation provide over-the-horizon (OTH) capabilities. Many of these OTH radars apply frequency modulated continuous wave (FMCW) modulation for range resolution, which enables them to operate with a relatively low transmit power of a few watts only. Sometimes these types of radars are referred to as “silent radar”. This paper discusses the signal processing chain from deramping the received signal down to processing of range-Doppler-azimuth spectra. Some steps which are critical for the overall system performance are discussed in detail and a new technique to derive the structure of radio frequency interference (RFI), which is superposed to the radar echoes, is described.