Antenna beamwidth is measured in degrees between the half power points (3 dB) of the major lobe of the antenna, Beamwidth can be expressed in terms of azimuth (horizontal or H-plane) and elevation (vertical or E-plane).
The predominant type of antenna configuration within urban areas at PCS frequencies will be three sectored. This implies that each sector should utilize an antenna with 120 degree horizontal beamwidth, however, it has been found through simulation that the use of 120 degree antennas provide too much overlap.
As the coverage of any sector within a CDMA system is directly affected by the noise generated by its neighboring sectors and traffic within those sectors, the use of 120 degree can lead to reduced coverage area through the rise in system noise. The excessive overlap of sectors can also lead to increased softer handoff and therefore the reduction of call processing capability.
If narrow horizontal beamwidth antennas are used, for example 60 degrees, simulation has shown that insufficient coverage (i.e. coverage holes) can exist between adjacent sectors. The use of 60 degree high gain antennas can also restrict the vertical beamwidth and can lead to coverage nulls close to the cell site. From current simulation, the optimum horizontal antenna beamwidth for PCS systems has been found to be between 90 and 100 degrees.
This beamwidth has been proven to minimize softer hand off while providing adequate coverage. However, before choosing an antenna of this beamwidth, the system engineer should ensure that all factors outlined within this “Antenna Parameters” subsection have been identified.