Orthogonal polarizations in RF transmissions from a broadcast antenna provide increased channel capacity and improved channel performance. In the same channel frequency band, two independent signals may be transmitted and received with isolation provided by dual-linear or dual-circular polarizations. This technique has wide application in communications: satellite communications, terrestrial microwave, cellular phone networks, and broadcasting. Transmitting antennas that provide polarization isolation for channel combining are analyzed and found to be successful and efficient in applications such as the IBOC FM scheme and DTV simulcast applications. However, the UHF and VHF broadcast propagation channel may not preserve the polarization sense and purity of the transmitted signal, in some cases degrading reception. The possibility of overcoming these problems and application of the multiple-input multiple-output (MIMO) channel is discussed. The use of orthogonal polarizations to increase channel capacity for VHF and UHF broadcasting is analyzed. Dual-polarized receive antennas have been found to dramatically increase mobile signal reception and virtually eliminate disconnects from the base station, and the application to broadcast DTV and IBOC transmission is made. The application of dual-polarized channels in Distributed Transmission networks and low power broadcast repeater networks is also described.
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