Downconverter for the combined reception of linear and circular polarization signals from collocated satellites

A microwave downconverter apparatus and scheme is hereby presented for the simultaneous reception of both linearly and circularly polarized signals from collocated satellites. A single antenna and waveguide feed is used for reception from two collocated satellites, wherein one satellite employs both right and left hand circular polarizations and the other employs both vertical and horizontal linear polarizations. The vertical and horizontal components of the linearly polarized signals and the vertical and horizontal components of the circularly polarized signals are separated by the antenna feed apparatus and applied to the input of the downconverter of this invention. Following a stage of RF amplification, both the horizontal and vertical components are further separated into two distinct paths by means of a diplexer. Since the linearly and circularly polarized signals are displaced one from the other by means of frequency, the diplexer provides a means of separating the two polarization techniques. The vertical and horizontal components of the linearly polarized signals are then downconverted to an intermediate frequency by means of a local oscillator and mixers. The vertical and horizontal components of the circularly polarized signals are likewise downconverted to an intermediate frequency. However, in the case of the circularly polarized signals, a 90-degree combiner with two output ports is employed prior to downconversion to enable vertical and horizontal components to be combined in phase such that the right hand circularly polarized signal appears at one port and the left hand circularly polarized signal appears at the other port.