Antenna design and development are their own science. We could do a deep dive into antennas and their role in wireless network design and not come up for air for weeks.
But the more useful approach for the wireless user is a basic understanding of the major types of antennas and the terminology used. Antennas can be grouped into two major categories:
- Omni-Directional Antenna – These antennas radiate radio frequency (RF) energy in (more or less) a sphere. This 360-degree coverage from the antenna allows the RF power to be distributed equally in all directions. This type of antenna is used at locations that need to communicate to multiple other sites such as a master location or repeater location.
- Directional Antenna – As the name would imply, this type of antenna focuses the RF energy in one direction to both transmit and receive power. A directional antenna can be made in many different types such as parabolic dish, Yagi or corner reflector, but each will increase the signal in a single direction to maximize the energy to and from a single location. This type of antenna is best used at remote, fixed locations.
With a basic understanding of where best to use a specific type of antenna, there are additional terms involved in selecting an antenna for operation:
Antenna Gain – This term is used to define how much increase in signal an antenna will provide. This increase in signal will apply to both the transmit power and the receive signal. The unit of measure for this term is decibel (dB), which is a logarithmic increase. The easiest way to remember how gain affects the signal is that every 3dB gain will double the RF energy. This logarithmic increase is easy to see when you consider that an antenna with a 9dB gain will actually increase the RF energy eight (x8) times (2x2x2=8).
Beamwidth – This is the most commonly misunderstood antenna characteristic. The beamwidth is the defined area around an antenna where most of the energy is radiated. It can be listed as a vertical beamwidth (up and down) or horizonal beamwidth (side to side). But, from a user’s perspective, the only item of importance is whether the remote site where the radio is sending the signal is within the antenna’s beamwidth. This value is part of the antenna specifications and not something that requires measurement.
Polarization – The polarization of an antenna describes how it is mounted in reference to the earth’s surface. If mounted perpendicular to the ground, it is vertically polarized, while an antenna mounted parallel to the ground is horizontally polarized. Most wireless applications use vertical polarization, but the critical factor is that all antennas in the same wireless network must be polarized the same.
As a rule when installing an antenna, keep it in open air, not near any surface of metal or mounting structure. Anything that is close to or in the beamwidth of the antenna can change how the antenna operates. If you have any questions on how an antenna works, please feel free to contact us at ESTeem.