The crosspolarisation properties of symmetric front-fed paraboloids with random surface errors are investigated. Average crosspolar far-field patterns and crosspolarisation discriminations are computed for different RMS surface errors. The influence of the correlation interval and phase-error model used is indicated.

A general overview of current technology in the field of communication satellite antennas is presented. Among the topics discussed are: the design of multiple beam systems; frequency reuse; and polarization control of antenna measurements. Consideration is also given to: contour beam synthesis; dual shaped reflector synthesis; beam shaping; and offset reflector design. The applications of the above technologies to present and future generations of communications satellites is considered, with emphasis given to such systems as: the Intelsats; the Defense Satellite Communications System, (DSCS-III); Satellite Business System (SBS), and Comstar.

Possible geometrical configurations of Schwarzschild antenna systems are investigated. Input parameters to a rapid design procedure are the subreflector subtended angle and the blocking ratio Ds/D. To allow comparison with Cassegrain antennas, simple formulas are developed for the aperture field, the gain factor, co-and crosspolar components of the radiation pattern and the polarisation efficiency of the antenna using geometrical optics (GO). The scan properties are investigated for both lateral feed displacement (as assumed by Schwarzschild) and displacement of the feed over the special locus minimising the weighted phase error in the aperture plane. Comparison with the focused and defocused properties of the Cassegrain antenna leads to the conclusion that, even without leaving the framework of geometrical optics, there appears to be no reason to prefer the more complicated Schwarzschild antenna system.

A theoretical investigation of the defocused Schwarzschild antenna system is described. Scan properties have been compared with those of the Cassegrain antenna system. It is shown that both the focused and defocused radiation patterns of the two systems are almost identical.

From the end of July 1975 until August 1976 the reception of signals from the geostationary satellite ATS-6was possible since at that time the satellite was brought into a position above Victoria Lake at 35° East. The copolar signal showed attenuation which varies strongly with the amount of rain. The rain was measured by a rain gauge located close to the 3 meter precision Cassegrain antenna. The attenuation measured at the satellite link did not always correspond with the attenuation measured at the nearby line of sight link at 34 GHz. For example during heavy thunderstorms the attenuation might have reach values as high as 20 dB or more. For smaller attenuations comparison is possible with a radiometer experiment at 30.1 GHz. In general this comparison shows good results for attenuations less than 10 dB. The crosspolar signal measured showed values of — 55 dB to about — 20 dB relative to the copolar depending upon several reasons. First of all the rain showed mostly a strong increase in the crosspolar signal but satellite movements and errors in the antenna pointing will also increased this level. Various examples are shown. It appears that the copolar — cross-polar isolation reached the lowest value at attenuations of 3–6 dB. Although the time that the satellite was available for measurements was limited, some statistic results can be given despite the fact the signal transmitted from the satellite was not always constant.