Modification of Cassegrain Earth station antenna for dual band operation

The modification of a C-band Earth station antenna for efficient reception at both C- and Ku-bands is discussed. The original antenna was a 9-meter Cassegrain type, which employed shaped reflectors to receive signals in the 3.7 to 4.2 GHz frequency range. By replacing the original aluminum subreflector with an identically shaped composite incorporating a Frequency Selective Surface (FSS), and placing a feed at the best focal point of the main reflector, the antenna becomes a high gain prime focus type over the Ku-band range of 10.95 to 12.75 GHz. At C-band, Cassegrain operation is maintained with very little loss. This paper details the design procedure which led to the successful frequency selective subreflector, provides measured transmission data on several FSS candidates and subreflector samples, and compares the radiation patterns of the original and revised antenna. Emphasis is placed on the design of the frequency selective composite, particularly those practical aspects of the composite construction, which are not readily available in the literature