Experimental verification of an integral equation solution for a thin-walled dichroic plate with cross-shaped holes

In order to add the capability of an X-band up-link onto the NASA/JPL Deep Space Network (DSN) 70-m antenna, a new dichroic plate is needed to replace the Pyle-guide shaped dichroic plate currently in use. The replacement dichroic plate must exhibit an additional pass band at the new up-link frequency of 7.165 GHz, while maintaining a pass band at the existing down-link frequency of 8.425 GHz. Because of the wide frequency separation of these two pass bands, conventionally designed air-filled dichroic plates exhibit grating lobe problems. A new method of solving this problem using a dichroic plate with cross-shaped holes is presented and verified experimentally. Two checks of the integral equation solution are described here. One is the comparison to a modal analysis for the limiting cross shape of a square hole. As a final check a prototype dichroic plate with cross-shaped holes was built and measured