User's Manual

Hardware Installation Guide Radio Site Planning
02030311-07 Airspan Networks Inc. 5-7
5.7.2. Omni-Directional Antennas
In some scenarios, where capacity demand is relatively low, external omni-
directional antenna use at the Base Station may seem attractive. However, it is
recommended to avoid using omni-directional antennas (if possible), due to the
following disadvantages that these antennas pose compared to directional antennas:
! Higher sensitivity to external interferences.
! Higher sensitivity to multipath, resulting in the following:
! The root mean square (RMS) delay spread at the Base Station is substantially
higher.
! Multipath interference at the CPE side (when using omni-directional antenna
at the Base Station) is substantially higher. In fact, when using an omni-
directional antenna, the existence of clear Fresnel zone between BSR and
SPR/IDR is insufficient to eliminate multipath interference, since multipath,
in this case, can be caused by reflections originating from obstacles outside
the Fresnel zone.
! Higher sensitivity to alignment. Since the omni-directional antenna gain is
achieved by narrowing the vertical beam width, a relatively low deviation in the
antenna alignment will result in severe signal attenuation.