Restoring the Orthogonality of Two Polarizations in Radio Communication Systems, I

Making use of two orthogonal polarizations simultaneously can double the capacity of a radio communication system. 1 The requirement of maintaining orthogonality is easily fulfilled when the transmitting and receiving antennas are aligned in the beam maximum of each other. Sometimes this alignment is not possible; for example, in some satellite communication systems the ground stations are distributed across the beamwidth of the satellite antenna. Then any polarization variation within the antenna beamwidth will give rise to cross-polarization coupling. Rain attenuation may also introduce significant depolarization at the higher microwave frequencies.2 In practice the two orthogonal polarizations leaving the transmitter are either two orthogonal linearly polarized waves or two opposite circularly polarized waves. Whatever be the cause of polarization distortion, the failure to maintain orthogonality will produce two nonorthogonal elliptically polarized waves at the receiving terminal. The purpose of this paper is to present a method of recovering orthogonality by transforming the two nonorthogonal elliptically polarized waves into two orthogonal linear polarizations. The transformation employs a differential phase shifter and a differential attenuator. 3063