Antennas serve as the first receiving point and the last exit point in a satellite transmission system. They can transmit and receive from all directions (these are known as omni antennas) or in a particular direction (like those used in television broadcasting).
An isotropic antenna is a hypothetical antenna. It emits the same radiation in all radiation – uniform radiation in short. A directional antenna can radiate or receive electromagnetic waves from certain directions, with some directions better than the others. Omni antennas can radiate or intercept electromagnetic fields fairly well in horizontal directions.
Although defined as an ideal antenna that can radiate uniformly in all directions, there is no actual physical example of this. It has a three-dimensional radiation pattern, which simply means that it has a 360-degree beam width both in the vertical and horizontal direction. It is also defined as an ideal antenna that can radiate across all directions and has a gain of 1 (0 dB), meaning zero gain and zero loss.
With that, it is used as a reference antenna for antenna gain, one of the characteristics of antennas. The unit used to measure antenna gain is called dBi, which stands for decibels over isotropic. It is calculated by dividing the power in the strongest direction by the power that would be transmitted by the antenna that is emitting the same total power.
An omnidirectional antenna can receive signals of equal quality from all directions, similar to an isotropic antenna. This is in contrast to directional antennas, which are better at receiving signals from a particular direction. Having this kind of quality has its advantages, including the ability to detect signals that are weaker or somewhat distant – something it does better than an omni antenna. However, being able to do so leaves such an antenna unable to pull in signals from other directions.
Although the use of the prefix omni indicates that the antenna can receive signals from any direction, the truth is that such antennas are omnidirectional on just one plane. Put simply, an omni antenna can detect signals from the northern, southern, eastern, and western portions of its location but it can’t do so from above or below.
Given its spherical radiation pattern, omni antennas can be used for a variety of applications. They are widely used for radio broadcasting and in mobile devices that make use of radio. Examples of the latter include cellular phones, cordless phones, FM radios, GPS, walkie-talkies, and wireless computer networks.
Omnidirectional antennas are also used by base stations that need to communicate with mobile radios. Examples of these include dispatchers for the police and taxis, as well as aircraft communications.
Omni antennas are not difficult to install. Since it covers a 360-degree horizontal pattern, this type of antenna can be mounted from a ceiling in an indoor environment in an upside down position.
While omnidirectional antennas certainly have advantages over the directional variety, it’s still best to determine the type to use after a proper site survey.
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