The following article serves to build an understanding about the antenna parameter known as Electrical Tilt. Tilting antennas is an important concept for applications like cellular and multipoint base stations that require targeting of their transmission to obtain greater control over each antennas coverage area.
There are two general types of tilting mechanisms, electrical, and mechanical. While at first glance the two seem similar there are significant differences. Conventional mechanical downtilting involves a rudimentary arm bracket to tilt the antenna body forward to focus the antenna boresight into the ground below. This process has the effect of localising coverage to the target area, but has the unintentional effect of uptilting rear and sidelobes. Coverage and field density may also deviate from the radio planning model.
To counter these unplanned side effects, electrical tilting is more commonly used as it provides a consistent horizontal radiation pattern with the added benefit of downtilting side and back lobes. A combination of mechanical uptilt and electrical downtilt is occasionally used in problematic areas to provide a conventional main beam but with downtilted side and back lobes.
|No Tilt||Mechanical Tilt||Electrical Tilt|
Definition of Electrical Tilt
An antennas electrical tilt is defined as the angular shift in elevation of the direction of maximum gain of the antenna by a specific electrical design of the antenna. Electrical tilt can be fixed or variable.
When disclosing electrical tilt on test reports and datasheets, Halberd Bastion follow the BASTA reporting recommendations. BASTA define the reporting of inter-port isolation per the following (adapted) specification. Halberd Bastion has expanded the draft BASTA specification to improve clarity.
- Electrical tilt type is fixed or variable.
- For a fixed electrical tilt antenna, the nominal value in degrees.
- For a variable electrical tilt antenna, the nominal range of values in degrees.
- Tolerance in degrees.
The below specification represents a single-band, single beam, dual-polarised ±45° antenna (two ports).
Testing & Reporting
Testing for inter-port isolation is performed in the same manner as many other S-parameter tests, using a two port vector network analyser (VNA) or similar instrument. An example measurement between two antenna ports is shown below.
- NGMN, "Recommendations on Base Station Antenna Standards", NGMN Alliance, N-P-BASTA v9.6, Jan. 2013.