Digital beamforming in a compact 20-32 MHz radar

Most current research and development programs in the field of digital beamforming are concerned with systems that operate in the traditional microwave frequency bands or higher. This paper discusses digital beamforming in a novel high frequency (HF) radar that operates from 20 to 32 MHz. Under the STEEL TRAP sensor program of the Department of Defense, we developed a semi-portable HF radar to measure the scattering properties of air targets. Earlier semi-portable HF radars, as well as most skywave HF radars, have used analog beamforming and frequency-modulated continuous wave (FMCW) waveforms. The STEEL TRAP HF radar (STHFR) radiates a pulsed waveform and has an eight-element receiving array that forms beams digitally. This paper describes the beamforming approach and the technique used for determining target angular position, and presents examples taken from a series of scattering measurements of a sounding rocket