New microwave communication services have raised interest in base station antennas capable of radiating an omnidirectional pattern in the azimuthal plane, as is the case for cellular communications. Those antennas usually comprise linear dipole or slot arrays and, at higher frequencies, printed antenna arrays. Although such arrays may produce adequate radiation patterns, the main disadvantages of their use rest on reduced bandwidths and increasing losses with frequency due to phase and power control circuits. Alternatively, at microwave or millimetric ranges, one may employ reflector antenna configurations for base stations, comprising reflector surfaces shaped in order to radiate uniformly in the horizontal plane while taking into account free-space attenuation via cosecant squared-like power patterns in vertical planes, with radiated energy concentrated below the horizon line for reduced interference. The main characteristics of two such configurations are reviewed.
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