SHIELDING OF SINGLE-REFLECTOR AND DOUBLE-REFLECTOR EARTH STATION ANTENNAS - A NEAR-FIELD AND FAR-FIELD APPROACH

The paper describes the off-axis radiation pattern calculation of a Ca ssegrain antenna system with prescribed geometrical parameters, in the absence and presence of a (hypothetical) half-plane obstacle located either in the near or far field of the antenna. The attenuation caused by the obstacle as a function of antenna orientation and position is calculated and presented. The results for the halfplane shielding of t he double-reflector system are compared with those obtained for a sing le-reflector antenna system shielded by the same obstacle. Three diffe rent, but related, approaches for calculating the additional propagati on loss are presented and compared. It is found that the proposed near -field approach gives the best overall results.