| 摘要 |
<p>ANTENNA WITH ECHO CANCELLING ELEMENTS In a Cassegrainian antenna, radiation transmitted from the feed system is reflected back as an echo to the feed from the subreflector. In the prior art, a flat plate has been located near the subreflector to return an echo cancelling reflection to the feed in one frequency range. In this disclosure, operation of an echo cancelling device which may be mounted externally on the feed side of the subreflector is extended to two frequency ranges by adding a reflective outwardly-flared wall-like ring around the perimeter of the flat plate. The ring may include two conical segments sized to adjust the relative reflection amplitudes to obtain substantially complete cancellations over broad bandwidths at both frequency ranges. The ring may also be stepped, or serrated, in cross section to avoid unwanted specular reflections and resonances. The dimensions and location of the ring and plate are adjusted by an iterative experimental procedure to obtain optimum dual band cancellations for a given subreflector shape and illumination. The ring and plate may be integral with the subreflector.</p> |
