When determining a wireless LAN (WLAN) solution within a building or facility, there are many factors to consider. The size and design of the facility determine the number of wireless access points required for this coverage. Another consideration is the selection of suitable wireless antennas to provide the desired coverage.
The wireless antenna is one of the most important components of any wireless access point or wireless client device, as it's the antenna that determines how radio signals are propagated, what radiation patterns they produce and how much profit they produce. The radiation pattern can be isotropic, which means that the antenna transmits the signal uniformly in all directions, and we often refer to these antennas as omni directional. Depending on the location of the antenna, we may need a radiation pattern because it is not isotropic, but it radiates in a pattern that maximizes the radio signal in a certain direction.
A wireless antenna is normally designed to work efficiently in a narrow frequency band, the greater the antenna frequency range, the more antennas are the "wide antenna". Wi-Fi antennas are used in the 2.4Ghz ISM band or in the 5Ghz band, so the antenna has to be designed to work within these specific frequency ranges.
In most countries, there is a limitation on the amount of power that can transmit a wireless antenna, and is usually in the 1-W area with a 6dBi gain for omni directional antennas and somewhere in the area of 23dBi directional antennas. Antenna gain is the measure of how much effective signal power is increased by an antenna for a given input power and is measured in decibel (dB). The 25 milliliter input would produce a power of 50 milliliters. EIRP or effective isotropic radiant power is determined by transmit power and antenna gain, i.e. 15 dBm transmit power with 6 dB would produce a 21 dBm EIRP of.
Let's look at some types of antennas that are available and how they usually perform:
1. Omni-directional antennas:
This type of antenna, as mentioned, usually produces a pattern of isotropic radiation, often referred to as a form of "donut". It is worth remembering that true isotropic antennas are theoretical and other forms of omni directional antennas that compare isotropic designs.
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A vertical omni directional antenna is usually based on a dipole design in which the radiation pattern of a dipole antenna in the horizontal plane is 360 degrees, with the vertical plane varying depending on whether the dipole is vertical or not. A vertically oriented dipole antenna typically has a radiation pattern of 75 degrees. The dipole antenna is usually said to have a profit, on average just over 2Db.
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These antennas are designed to be mounted on the ceiling, over false ceilings or even walls.
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The antennae for cordless rubber ducks were first used in the first walkie talkies, such as a reduced whipping antenna designed in a quarter wave.
2. Directional antennas:
Elements of reflection and radiation are added to the design of the standard diode to focus the energy of the signal in a certain direction. Directional antennas can give a gain compared to the standard isotropic antenna of approximately 3dB to 20Db.
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Yagi antennas are referred to as high performance antennas and have multiple reflective and radiating elements to provide a typical gain between 12 and 20 dB. They are often used as external antennas and have a typical horizontal width of approximately 30 degrees and 15-25 degrees vertical beam width.
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The most common type of wireless dish is the parabolic dish, which uses a curly dish in the form of a parabola to direct the wireless radio waves to a narrow beamwidth. These types of antennas are very sincere and can also have an extremely high gain, up to 40 or 50 dB. Usually used for point-to-point wireless communication. The wireless bridges outdoors usually use a satellite dish.
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The structure is usually a pair of metal plates that actually form the elements of the antenna that form the transmission line. They are usually semi-wavelength design, with a typical gain of approximately 2dB, similar to a conventional dipole antenna.
Of course there are many other variants of the wireless antenna that are not mentioned here, but this article is designed to give the layman a simple explanation of the basic types of wireless antenna.
After a successful wireless site survey, antennas or vertical dipoles usually use mostly in the smallest office environment. Problem areas can best be met by patch or wireless antennas to maximize coverage.