A technique for microwave ranging and remote phase synchronization

A very precise electrical-distance measurement system that is also capable of supplying a phase-synchronous signal to a remote location is required for a new type of radio telescope, the large adaptive reflector (LAR). The system is based on a round-trip phase synchronization method, and is designed to work over a free-space path of length up to 1 km, the focal distance of the telescope. The electrical length of this path is to be measured with an accuracy of 70 μm and a phase-stable signal is to be provided at the remote end as the basis for a local-oscillator signal of stability equivalent to 5° at 22 GHz. Phase synchronization and distance measurement are accomplished with the same microwave ranging circuit. The distance measurement is derived from phase comparison of high-frequency signals, including a novel use of the Chinese Remainder Theorem (CRT) to resolve the unavoidable wavelength ambiguity. The design of the system is described, and limitations imposed by phase-measurement and frequency-setting accuracy are explored. Errors due to atmospheric dispersion are negligible under most circumstances. Accurate phase synchronization has been demonstrated over a free-space path of ~300 m. The complete system has been simulated under noisy conditions, and its ability to meet the specifications demonstrated