Cellular base station sites are typically designed and deployed with three sectors arranged to serve different azimuth bearings, for example each sector serving a 120 degree range of angle from a cell site location. Each sector includes an antenna with an azimuthal radiation pattern which defines the sector coverage footprint. The half-power beamwidth (HPBW) of the azimuth radiation pattern of a base station sector antenna is generally optimal at around 65 degrees as this provides sufficient gain and efficient tri-sector site tessellation of multiple sites in a network or cluster of sites serving a cellular network area.
Most mobile data cellular network access technologies including High Speed Packet Access (HSPA) and Long Term Evolution (LTE) employ 1:1 or full spectrum re-use schemes in order to maximise spectral efficiency and capacity. This aggressive spectral re-use means that inter-sector and inter-cell interference needs to be minimised so that spectral efficiency can be maximised. Antenna tilting, normally delivered by electrical phased array beam tilt provides a network optimisation freedom to address inter-cell interference, but few options exist to optimise inter-sector interference. The Front-to-Back (FTB), Front-to-Side (FTS) and Sector Power Ratio (SPR) of an antenna pattern are parameters which indicate the amount of inter-sector interference; the larger the FTB and FTS and the lower the SPR value, the lower the inter-sector interference.
One way to improve network performance is by effective control of the azimuth beamwidth of the base station antenna. This azimuth beamwidth is typically measured at the minus 3 dB position for HPBW, and minus 10 dB for FSR. In most cellular deployment, the HPBW is typically required at 65 degrees, while the FSR beamwidth is set at 120 degrees to ensure that power does not spill over to adjacent cells, therefore maintaining a good carrier-to-interference (C/I) ratio.
Reducing the 3 dB azimuth beamwidth to 60 degrees or even 55 degrees typically improves the SPR, but may also impact cellular network tessellation efficiency for basic service coverage, and necessarily requires a wider antenna to achieve the narrower beamwidth which then places additional pressure on the site in terms of zoning, wind-loading and rentals. For instance, base station antennas with variable azimuth beamwidths are available which can be used to provide better load balancing between sectors and to adjust sector to sector overlap. However, such solutions may not be suitable for accommodating multiple arrays and hence supporting multiple spectrum bands which is a desirable requirement for base station antennas. In addition, such variable beamwidth antennas can be large (the size being governed by the minimum achievable beamwidth) with some solutions requiring mechanical and active electronics and hence potentially costly to deploy and maintain.
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