What polarization is required?
Most communication systems use either vertical, horizontal or elliptical (RHC-right hand circular or LHC-left hand circular) polarization, with vertical dominating commercial VHF/UHF applications. In some instances, the selection is determined by the installation site, with the antenna oriented to provide the best performance. If this is anticipated, your antenna should provide mounting for either polarization.
Selecting the proper polarization for the system can enhance the overall performance by minimizing the interference from adjoining systems. For example, by installing you system orthogonal to other systems in the area, you can provide up to 20 dB of isolation. This will result in up to a 99% power reduction of the interfering system! Elliptical polarization can sometimes decrease fading.
Many systems are challenged because they must interface with handheld transmitters. These units move around a room or warehouse, with the antenna often pointing many degrees off-axis. To accommodate these application, the fixed antennas often use circular or elliptical polarization with a hemispherically shaped pattern trading off high gain for reasonable gain in all directions.
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This information should be used as a guideline only to help you in the appropriate selection of an antenna.
