Synthetic-Aperture Radar Based on Nonsinusoidal Functions: V-Look-Down Radar

The use of radar signals without a sinusoidal carrier permits one to design all-weather radars that operate below a frequency of about 10 GHz, but still use a bandwidth of almost 10 GHz. This statement implies that one obtains about two orders of magnitude more information than with a radar that operates with the same restriction on the highest used frequency, but uses a sinusoidal carrier. The increase in information shows up primarily in a better time resolution, but time resolution can be translated into range resolution, angular resolution, and Doppler resolution. This paper investigates the exploitation of the Doppler resolution for a look-down radar. The radar is assumed to be at an altitude of 30 km, and to look down to the Earth to find low-flying aircrafts or cruise missiles flying with subsonic velocity at an altitude of 20 to 40 m. The problem for such a radar is the cancellation of the enormous ground-clutter signal which masks the weak signal returned by the target.