Development of a wide-band quadrature junction for simultaneous C-band and Ku-band satellite communication applications

In satellite communications, single frequency band systems with narrow bandwidth have gradually evolved into multi-band antenna systems with ever increasing bandwidth. Additional characteristics for earth stations are dual polarization, CP/LP switching, and TE₂₁ monopulse tracking, all integrated behind a common horn aperture. In the course of designing a multi-band feed system, a common wide-band orthomode transducer (OMT) followed by a series of diplexers or triplexers is often considered. However, such a design fails to work if the total operating frequency band goes beyond the bandwidth capabilities of the common OMT. A different approach is to separate polarization and frequency at the same time using a quadrature junction. The paper describes a feed for an 18.3 m Cassegrain antenna operating simultaneously at C-Band and Ku-Band. The system is able to switch between circular and linear polarization and, furthermore, to adjust the linear polarization angle independently in each band. Measured feed test results and calculated reflector performance are reported.