In this paper, the ergodic capacity (EC) of a land mobile satellite (LMS) system using dual-polarized antennas for transmit diversity is analysed. Three key channel parameters, i.e. cross-polarization discrimination (XPD), transmit and receive correlation coefficients and Ricean K-factor are included in channel modeling and their effects on the EC are investigated. In particular, we derive the estimated expression and approximation at high SNR of EC for Rayleigh fading and fairly tight upper bound for Ricean fading. Simulation results corroborate the theoretic analyses. About 1.5dB power gain is estimated to be obtained in high SNR regime by using dual-polarized antennas, compared with non-polarized antennas. It is found that the EC benefits from poorer XPD but degrades with higher transmit and receive correlation coefficients. Besides, the EC grows logarithmically with K-factor, which indicates that more fixed part of channel will enhance the communication performance.
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