The design and performance of a digital microwave frequency lock system is described. The system locks a microwave source to a fixed intermediate frequency oscillator by digitally comparing the down‐converted microwave frequency to the IF. The microwave source may be frequency swept at a variable rate whose precision is the same as the reference oscillator, and the microwave source retains the long term stability of thefixedfrequency reference oscillator even when the microwave frequency is being swept. The digital frequency lock system is compared with an analog phase lock system, and it is concluded that the digital frequency lock is superior with respect to capture range and reliability, identical with respect to long term stability, and inferior with respect to spectral purity.
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