A frequency-modulated radar is a radar in which a continuous-wave transmission is frequency modulated in a known manner in order to obtain range information. When the frequency modulation is linear with time, the difference between the frequency of the received signal and the transmitted signal is directly proportional to the target range. The difference frequency is given by (2R/c) (df/dt), R being the range to the target, c the velocity of electromagnetic waves and df/dt the slope of the sawtooth frequency modulation. Therefore, the difference frequency is proportional to both range and the slope of the modulated waveform. In an Ideal sawtooth frequency-modulated waveform, the slope would be a constant; however, the device to be used in the portable PM-CW radar, a varactor-tuned Gunn oscillator, exhibits a non-linear frequency sweep. If the frequency sweep is non-linear, the return from a. target at fixed range is frequency modulated. As a result the bandwidth of the echo signal is increased, and range resolution is impaired. Work on this thesis will be directed towards linearization of this FM sweep and, accordingly, to optimize range resolution.

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http://archive.org/details/linearizationoff1094517105

Lieutenant, United States Navy