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There is increasing interest in multiband antenna installations where the same antenna and feeder are used for radio-relay systems simultaneously operating in the 4-, 6-, and ll-GHz common-carrier bands. At 11 GHz the circular waveguide feeder can support many unwanted modes. Delay distortion is caused in part by higher order mode conversion-reconversion in such an oversized-waveguide feeder. An investigation of the antenna system has revealed that two major sources of delay distortion result at 11 GHz from mode conversion in the system combining networks. This paper discusses the results of this investigation and the steps taken to reduce the mode conversion-reconversion and resulting delay distortion.
Date of Publication: February 1970