Cross-polarization performance of the RCA Satcom system

To significantly increase the efficiency of the available spectrum and the use of the orbital arc, the RCA Satcom system employs the technique known as 'Spectrum Reuse', whereby two or more separate channels within the same frequency band are transmitted (or received) on two separate orthogonal linearly polarized beams. Since polarization isolation between the orthogonally polarized beams is not perfect due to various depolarization mechanisms, the desired channel will receive some interference from adjacent cross-polarized channels, causing interference to the desired channel which may result in degraded performance. Since this degradation can not be allowed to compromise the system performance, the amount of interference must be determined so that allowances can be made for its effect on system design. This paper describes the loss of polarization isolation that occurs when a signal travels from transmitter to receiver, with emphasis on the depolarization caused by the propagation medium. A statistical estimation (availability) is made of the overall polarization isolation for various earth station locations throughout the United States. Additionally, some examples of how this isolation is translated into signal interference and then allocated relative to the overall interference to the signal are given.