Abstract: An antenna pointing detection system for use with circularly polarized electromagnetic radiation has a horn, a waveguide and at least one mode switching arm. The horn receives radiation in a primary mode from the radiation source. The waveguide receives radiation from the horn and supports only radiation in a primary mode, e.g. the TE.sub.11 mode and the next higher order TE mode, e.g. the TE.sub.21 mode at one or more rectangular mode switching arms extending from the circular waveguide for stimulating radiation of the-next order TE.sub.21 mode in the waveguide. The arm has a series of switchable pin diodes for changing the effective length of the mode switching arm to cause a phase alteration in the TE.sub.21 mode thereby causing a deflection of the effective pointing direction of the horn. The magnitude of the received signal is detected and compared with different deflections of the horn to operate conventional antenna pointing hardware.

Abstract: A four element antenna turnstile tracking system which outputs an azimuth error signal, an elevation error signal and an independent sum signal. Three tracking antennas are disposed triangularly at the vertices of a triangle and the sum antenna is disposed in a predetermined relationship to the tracking antennas. The three tracking antennas are symmetrically connected to a unique four port turnstile type junction which generates an elliptical wave in accordance with the difference in signals from the three tracking antennas. An orthogonal mode transducer outputs the orthogonal components of this elliptical wave, these components being the azimuth error and the elevation error signals.