User's Manual

Hardware Installation Guide Radio Site Planning
02030311-10 Airspan Networks Inc. 5-13
5.9.2. 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.
5.9.3. Operating in 900 MHz
The performance of ASWipLL 900 operating in the 900 MHz band may vary
dramatically depending on the polarization of antennas, i.e. vertical or horizontal.
Therefore, it is recommended that the operator, during installation, compare the
performance between horizontal and vertical polarization of external antennas, and
implement the polarization providing the best performance. Some third-party
antennas that can be optionally supplied by Airspan for the 900 MHz band support
both horizontal and vertical polarization.