Radar altimeter nearest return tracking

摘要

An FMCW distance measuring device is disclosed which enables increased accuracy by detecting the nearest return. A portion of the transmitted wave in an FMCW altimeter is mixed with the received signal indicating distance to ground to produce a beat frequency between the transmitted wave and the received wave. The beat frequency is a spectrum of frequencies, the lowest of which indicates the nearest return in a target area. The beat frequency spectrum is coupled for sampling by an analog-to-digital converter and then coupled to an apparatus for performing a Fast Fourier Transform to isolate the nearest return. In an altimeter, the Fast Fourier Transform of the return spectrum enables the FMCW radar to have an accuracy approaching that of pulsed radars without the associated disadvantages.