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Maximum Power Transmission Between Two Reflector Antennas in the Fresnel Zone

01 April 1971

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Maximum Power Transmission Between Two Reflector Antennas in the Fresnel Zone By T. S. CHU (Manuscript received August 11, 1970) Power transfer between two ellipsoidal reflector antennas with common focal -points and dual-mode feeds has been investigated. Assuming a circularly symmetric feed pattern, the II-plane pattern of an openend circular waveguide excited by the TEU mode, the maximum transmission coefficient between reflector apertures is found to be within 0.5 percent of the value computed for transmission between two circular apertures with optimum illumination described by the generalized prolate spheroidal function. Transmission loss between tiro reflector antennas versus illumination taper is computed for various values of the parameter p = (ka^a.,)/R]. The minimum transmission loss is obtained as a compromise between feed spill-over and aperture transmission efficiency. In view of the inconvenience of building different ellipsoidal reflectors for different antenna spacings in order to achieve maximum power transfer, we examine the feasibility of using a defocused ellipsoid to simulate ellipsoids of different focal lengths. The deviation of the aperture phase distribution of a defocused ellipsoid from a required spherical phase front is approximately given by an explicit expression. A simple upper bound of the transmission loss due to small phase deviation is obtained for a given maximum phase deviation. 1. I N T R O D U C T I O N Millimeter waves have never been used in long-haul radio transmission systems because of rain attenuation.