Cellular communications systems are well known in the art. In a typical cellular communications system, a geographic area is divided into a series of regions that are referred to as “cells,” and each cell is served by one or more base stations. A base station may include baseband equipment, radios and antennas that are configured to provide two-way radio frequency (“RF”) communications with mobile subscribers that are geographically positioned within the cell. A common cellular communications system network plan involves a base station serving a cell using three base station antennas, wherein each base station antenna serves a 120 degree “sector” of the cell in the azimuth plane. The base station antennas are often mounted on a tower or other raised structure, with the radiation pattern (“antenna beam”) that is generated by each base station antenna directed outwardly to serve the respective sector. Typically, a base station antenna is implemented as a phase-controlled array of radiating elements, with the radiating elements arranged in one or more vertical columns. Herein, “vertical” refers to a direction that is perpendicular relative to the plane defined by the horizon.
As demand has grown for cellular communications systems to support increased capacity and provide enhanced capabilities, a variety of new cellular services have been introduced. These new services typically operate in different frequency bands from existing services to avoid interference. When new services are introduced, the existing “legacy” services typically must be maintained to support legacy mobile devices. Thus, as new services are introduced, either new cellular base stations must be deployed or existing cellular base stations must be upgraded to support the new services in the new frequency bands. In order to reduce cost and the total number of base station antennas deployed, base station antennas are now available that include at least two different arrays of radiating elements, where each array of radiating elements supports a different type of cellular service in a different frequency band. Such antennas are typically referred to as multi-band antennas.