Stabilized Linear FM Generator

A technique for generating high-linearity chirp (linear FM) signals is presented. It uses a delay line and mixer to sense the slope of the output of a swept oscillator, and the difference from desired slope is fed back to correct the oscillator frequency. The technique also improves the coherence of the oscillator. An analysis is performed of the amount of linearization that can be achieved for three possible loop configurations. Experimental results are presented of tests run on a backward wave oscillator (BWO) operating over a bandwidth of 240 MHz with time duration of 120 ¿s. The results indicate a linearity corresponding to a phase error (from parabolic) of 30 degrees (peak) and coherence within 5 degrees.