Abstract: The input probe of an LNB for commonly receiving clockwise and counterclockwise circularly polarized waves includes a rectangular microstrip patch, with the length of one edge of it being .lambda..sub.g /4, which is installed at the center of an annular strip shaped ground pattern, with a feed horn being disposed at the side opposite to a substrate. Four input probes are installed adjacently to the respective edges of the rectangular microstrip patch. The two pair of the input probes which are installed adjacently to the respective edges of the rectangular microstrip patch are respectively commonly connected to first and second feed lines. With this arrangement, the length of one input probe relative to that of the other one shows a difference of .lambda..sub.g /4.