A 2.8 arc-min beamwidth antenna: Lunar eclipse observations at 3.2 mm

This paper describes the principal electrical and mechanical features of a millimeter-wave antenna facility. The basic instrumentation consists of a 15-foot (4.57 meter) diameter parabolic antenna, a servo control system, an on-line general purpose computer, and radiometric receiving equipment. In the zenith attitude position of the antenna reflector, the measured contour accuracy, with respect to a true parabola, is 0.0018-inch rms. At horizon attitudes, the rms value degrades to 0.0036 inch. These contour accuracy measurements include the effects of partial solar heating and wind velocities up to 20 mph. Although the reflector is not unusually large physically, it is extremely large in terms of electrical aperture; i.e.,
D/\lambda = 1436
at 94 Gc/s and 3660 at 240 Gc/s. The measured pointing accuracy is 20 arc-sec (0. 1 mrad) for the overall system. The tracking rate ranges from
0.001\deg
/s to
3\deg
/s. The facility features automatic program control. Ephemeris data existing on magnetic tape or in computer memory provide real-time attitude control of the antenna. High-resolution measurement of the lunar surface during the total eclipse of December 30, 1963, at a wavelength of 3.2 mm (94 Gc/s) is described. Specific areas of the lunar surface were monitored before, during, and after the eclipse. A summary of the relative brightness temperatures and the cooling rates of the observed areas is included. A typical high-resolution radiometric contour map of the moon is also shown.