FM/CW sweep linearizer and method therefor

A sweep linearization network for an FM/CW radar system wherein the transmitter sweep rate is subject to variation as a function of range, said network comprising:

• (a) a sweep slope circuit providing an adjustable sweep slope signal for controlling the sweep rate of the interrogation signal of an FM/CW radar transmitter;
• (b) a random access memory having N address locations wherein individual sweep slope coefficients are stored corresponding to individual segments of a single sweep of transmitter frequency;
• (c) a multiplying digital-to-analog converter receiving said sweep slope signal and, sequentially said sweep slope coefficients for generating a driving signal, the characteristics of which are controlled by said sweep slope signal and composite of said sweep slope coefficients;
• (d) integrator means for generating a driving ramp signal in response to said driving signal;
• (e) an oscillator having a swept FM output signal, responsive to said driving ramp signal;
• (f) sampling means monitoring said output signal for providing a transmitter characteristic signal;
• (g) mixer means receiving said transmitter characteristic signal and a delayed transmitter characteristic signal having a phase shift of 360.degree. at a specified frequency, for developing an equal frequency excursion segmented sampling signal;
• (h) a voltage comparator for detecting the period of the individual segments of said sampling signal based upon a reference amplitude thereof to yield a measured time segment signal;
• (i) timing means for timing said individual segments and measuring the periods thereof in response to the output of said voltage comparator;
• (j) register means for storing the timed values for a selected one of said segments of the measured time signal and at least one comparison interval having a relative period of 1/N;
• (k) processor means for computing a time error signal as a ratio of the time period for said selected one of said segments of the measured time signal to said at least one comparison interval;
• (l) an add/subtract circuit receiving the sweep coefficient for a given sweep segment N.sub.i and said error signal in respect thereof, for developing a modified coefficient as an input to said digital-to-analog converter and updating that coefficient stored in said random access memory;
• and,
• (m) a voltage to frequency converter receiving said sweep slope signal for generating timing command pulses establishing N segments for each of said sweeps.

A method for linearizing the sweep of the interrogation signal of an FM/CW radar system, wherein the sweep rate of said interrogation signal is subject to variation as a function of range, comprising the steps of:

• (a) developing a sweep slope signal for controlling the sweep rate of the interrogation signal of an FM/CW radar;
• (b) storing in an updatable memory a plurality of N sweep slope coefficients corresponding to N discrete segments of an individual sweep of said interrogation signal;
• (c) applying said slope signal and, sequentially, said sweep slope coefficients as inputs to a driver for developing a ramp signal establishing the slope characteristics of said interrogation signal;
• (d) sampling said interrogation signal to develop a transmitter characteric signal;
• (e) discriminating said transmitter characteristic signal into a plurality of measured time periods t.sub.i for equal frequency excursions, where i is an integer from 1 to N;
• (f) generating a comparison time signal of clock pulses t.sub.r having an equitemporal period 1/N;
• (g) comparing a selected one of said measured time periods with at least one interval of said comparison time signal to develop an error signal proportional to and indicative of any slope error in said sweep;
• and,
• (h) applying said error signal to said memory to update the sweep slope coefficient corresponding to said selected one of said measured time periods.