A low loss, dual polarized switch for polarization state selection

The development of satellite communications presents opportunities for user antennas capable of operating with several different systems. From a user perspective, an antenna that can operate sequentially with several systems is desirable. While a variety of antenna designs exist for multiple frequency operation, an additional challenge exists for systems that use polarization reuse to extend the system capacity. The orthogonal polarization states in polarization reuse systems have stringent purity requirements to avoid cochannel interference. However, since some satellite programs use linear polarization while others use circular polarization, antennas for multiple program applications must be able to select either linear or circular polarization states as appropriate to the satellite system being used at the moment, while maintaining the required polarization isolation for each state. The conventional way to transform one polarization state into another uses hybrid circuitry. Linear polarization can be converted into circular polarization with quadrature hybrids, and circular polarization can be converted into linear polarization by 0-180/spl deg/ hybrids. The switch design described in this paper addresses these inherent limitations of conventional polarization state transformations.