An Algorithm for Signal Synthesis and Acquisition of CAPS Based on Dual-Linear Polarization Antennas

Aiming at solving polarization loss caused by a circular polarization antenna receiving linear polarization signals in the China Area Positioning System (CAPS), this paper proposes a signal synthesis and acquisition algorithm of CAPS based on dual-linear polarization antennas. Because in CAPS commercial communication satellites serve as navigation satellites, a variety of antennas have to be used for transponders. These include horizontally polarized antennas and vertically polarized antennas. Since the signal polarization needs to fit the antenna polarization, CAPS navigation signals have two types of polarization-horizontal polarization and vertical polarization. Using a circular polarization antenna can receive these two types of signals, but will introduce a polarization loss of 3dB. Our new algorithm uses two linear polarization antennas to receive signals individually and carries out some signal processing to reduce the polarization loss. The algorithm first performs signal acquisition with the dual-linear polarization antennas. According to the acquisition result the algorithm then synchronizes the signals. After the synchronization, it sums the signals from the two channels using the maximal-SNR (signal-to-noise ratio) combining which reduces the energy loss caused by polarization mismatching. The algorithm has already been applied to an experimental receiving system. By analyzing the data acquired by the experimental system, we find the SNR of the synthesized signal increases 1.5dB over the one-channel signals.