The Use of Solar Radio Emission for the Measurement of Radar Angle Errors

Historically, celestial bodies have been used as primary directional references for optical instruments such as navigational sextants, surveying theodolites, etc. Since celestial bodies are also sources of radio emission, they may be used directly as primary radio directional references. " R a d i o sextants" use the sun and moon as microwave directional references for all-weather marine navigation. 1 Conventional microwave tracking systems can also track these sources. For example, an X-band monopulse radar having an 8-foot antenna and crystal mixer receiver tracks the sun with an accuracy limited only by atmospheric effects. M o o n tracking is of poorer quality because of the lower signal-to-noise ratio, but improvements in noise figure and a larger time-bandwidth product could make moon tracking competitive with present sun tracking. The major limitation in using the sun as a precise reference has been the uncertainty of the position of its "radio center." This uncertainty is caused by regions of enhanced radio emission associated with sunspots. A method and experimental results will be described which overcome this limitation by taking advantage of the apparent rotation of the solar disk. This makes possible highly accurate alignment and zero setting without the usual optical aids. 1799