A primary horn is adapted to attach two probes to a common circuit board to easily ensure a good receiving performance and reduce a manufacturing cost. The primary horn 11 includes a first probe 13 disposed at an open end 12a side of a waveguide 12 for detecting a first linearly polarized wave and a second probe 15 disposed at a termination short-circuit surface 12b side of the waveguide 12 for detecting a second linearly polarized wave orthogonal to the first linearly polarized wave. Both probes protrude parallel to each other. A reflector 14 for reflecting the first linearly polarized wave is interposed in the middle between both probes 13 and 15. A phase converter 17 forming a phase-adjusting aperture 16 is disposed in a plane comprising the second probe 15. Therefore, the second linearly polarized wave passes through the phase-adjusting aperture 16, so that the plane of polarization of the second linearly polarized wave is changed to be oriented in the same direction as the plane of polarization of the first linearly polarized wave.
展开▼
