Abstract: A system and method are disclosed for measuring medium range distances, of about 1-10 meters, to a target. A transmission signal is reflected off the target, with the phase difference between the transmitted and received signals taken as an indication of the target distance. The transmitter and receiver are part of a phase-locked loop, with a VCO adjusting the transmission frequency until a predetermined transmission-reception phase difference is reached. A coarse distance measurement is first obtained by comparing the transmitted signal with the received signal, followed by a fine distance measurement in which a multiple of the transmission signal frequency is compared with the received signal. The frequency multiplication in the preferred embodiment is obtained by dividing the VCO output frequency to obtain the transmission frequency. The transmission signal is initialy set at a low frequency prior to the coarse adjustment to avoid phase ambiguities.

Abstract: A digital radio frequency memory (DRFM) system for storing and retrieving radio frequency signals in a digital memory. The system includes a digital memory, digital converters at the input and output of the digital memory, and input and output mixers. The RF signal to be stored is applied to the input mixer along with a modulated local oscillator signal to produce an IF signal which is converted into digital values for storage in the digital memory. When the stored digital values are retrieved from the memory to reproduce the RF signal, they are converted back into an analog IF signal which passes through a low-pass filter before being applied to the output mixer. The local oscillator signal, modulated with the same waveform used in storing the digital values, is also applied to the output mixer to provide the reconstructed RF signal. A pseudo random, discrete digital valued waveform is used to phase modulate the local oscillator signal in the preferred embodiment of the invention.