Antenna pattern measurement of an in-orbit satellite

A two-dimensional antenna pattern of an in-orbit satellite can be measured by tilting the spin axis of a satellite and by offsetting the antenna bias angle. In July 1979, the antenna pattern of Japan's Communication Satellite for Experimental Purposes (CS) was measured. In a comparison of the measured pattern with the pre-launch pattern, poor coincidence was found in the outer region due to the spin modulation. In order to remove the spin modulation effect on an antenna pattern measurement, a new method of data processing named 'spin coherent detection method' is introduced. The pattern obtained by this method had good coincidence with the pre-launch pattern. In addition, the locus of antenna pointing direction due to the spin effect could be obtained.