An Experimental Broadband Imaging Feed

The successful performance of an offset dual-reflector antenna often depends upon illumination by a broadband feed with a narrow feed pattern. 1 For example, a broadband corrugated horn with the required pattern could be used, but it would be excessively long for most practical applications. Good illumination can also be achieved by a narrowband offset launcher,2 which is essentially an offset reflector fed by a relatively short feed horn. Excellent 19/28.5 GHz dual-frequency performance was demonstrated by the Crawford Hill 7-meter antenna using a quasi-optical frequency diplexer to combine two narrowband offset launchers.1 However, this approach is not usually cost effective, especially for lower frequency systems. In this paper we present design * Now at AT&T Long Lines.