Method and apparatus for maintaining linearity and frequency accuracy of an FM chirp waveform

摘要

A homodyne radar apparatus and method for performing radar cross- section surement by maintaining the linearity and compensating for frequency drift of an FM chirp waveform produced by a YIG tuned oscillator. A digital computer uses a predetermined data look-up table of each YIG oscillator frequency characteristic in conjunction with a digital to analog converter to provide a compensating sweep signal to linearize the frequency output of the oscillator. The computer uses an analog to digital converter in conjunction with a reference circuit output to compare the actual YIG signal nulls resulting from the reference circuit to the nulls in a signal produced by a lab standard oscillator in the reference circuit to adjust start sample delay of the ADC and to correct any frequency drift evidenced by the difference in the null of the signal.