Total power radiometers at 12, 20 and 30 GHz used in the OLYMPUS experiment at Virginia Tech

Abstract

This paper discusses the total power radiometers in the propagation experiment at Virginia Tech using the OLYMPUS communications satellite. The experiment is set up to measure the received signal strength of beacons at 12.502, 19.770 and 29.656 GHz on board the OL YMPUS satellite in order to gather space-earth propagation statistics for a period of one year. The radiometers are used to set the clear sky reference levels for the beacon receivers.

The paper begins with an overview of radio signal attenuation mechanisms, and a general discussion of radiometry. A description of the OLYMPUS radiometers follows, with sections on calibration techniques and the methods required to convert radiometer data into derived path attenuation for use in setting the clear air reference levels for the beacon receivers.

Several novel techniques were used in the Virginia Tech radiometers including the use of voltage to frequency converters for integration purposes, and reference load calibration using a waveguide switch to swap the radiometer input from the antenna to a waveguide load of known and stable temperature. The penultimate chapter contains data recorded in the course of the experiment which was selected at random from the month of January 1991. The data is compared to corresponding free space beacon attenuation data and shows conclusively that the total power radiometer can produce highly accurate and stable attenuation measurements for extended periods of time.