When selecting an antenna, what factors should you consider? The appropriate antenna is crucial for everything from fleet management and smart highway systems to cellular infrastructure and FirstNet rollouts. However, how can you know which antenna is right for you? When picking an antenna, there are a few factors to think about.
1. Antenna Frequency:
An antenna's bandwidth and frequency range are related words. The range of frequencies over which an antenna satisfies a particular parameter specification is referred to as the antenna's bandwidth. Gain, radiation pattern, VSWR, and other characteristics are commonly given. The most typical parameter for bandwidth concerns is the VSWR, and this bandwidth is referred to as the impedance bandwidth.
2. VSWR Specification
The Voltage Standing Wave Ratio (VSWR) is a measurement of the mismatch between an antenna and its feed line. The VSWR value ranges from 1 to infinity. A VSWR of less than 2 is considered acceptable for most antenna applications. A 2:1 VSWR specification is commonly employed, which means that the operating bandwidth is chosen from a range of frequencies with a VSWR less than 2.
3. Antenna Gain
The directivity of an antenna determines its gain. Directivity refers to an antenna's ability to focus energy in a single direction rather than spreading it out equally over a wide range of angles. The gain of an antenna is the directivity minus the antenna's loss. The radiation efficiency is a measure that indicates the antenna's loss and has a value between 0 and 1.
4. Directional or Omni-directional:
An omnidirectional antenna is one that broadcasts and absorbs energy equally well in all horizontal directions. An antenna may also focus energy in a certain direction, indicating that it is directional. Omni-directional antennas are ideal for applications that require complete coverage. For certain applications, having the ability to concentrate the available energy radiated by the antenna in a specific direction is either not needed or desired. This will influence antenna selection.
Line-of-sight, height and distance between antennas, and the curvature of the earth must all be considered when determining the best antenna site. Due to the limited line-of-sight range of VHF broadcasts, antennas must be set as high as feasible. Your antennas should always be in the same plane (vertical-to-vertical/horizontal-to-horizontal) or as near to it as possible.