Wi-Fi Antennas: what you need to know before choosing one

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Sometimes the Wi-Fi signal is not strong enough and you must, for example, not go too far from the router/access point, otherwise the connection will be lost or poor quality. How to fix it? One solution is to use a long distance Wi-Fi antenna. It is a practical choice, and completely inexpensive. But let’s try to understand what are the judgment criteria to keep in mind, in choosing the best Wi-Fi antenna for your needs.

Directional and omnidirectional antennas

An omnidirectional antenna radiates electromagnetic waves in all directions, in a spherical shape. In the case of directional antennas, vice versa, the signal is essentially radiated in one direction only.

The gain of the antenna: dB/dBi

The tendency of an antenna to concentrate the signal in a specific direction is known as gain, and is measured in dB (decibels).
The higher the gain value, the better.
A perfect omnidirectional antenna, which radiates the signal in all directions with the same intensity as if dealing with a sphere, will have a gain of 0 dB.
An omnidirectional antenna with a gain of 2 dB would spread the signal following the shape of the planet, that is slightly flattened at the poles; an omnidirectional antenna instead characterized by a gain of 15 dB will radiate the signal as if it were dealing with a dish, therefore in a substantially horizontal way.
If you placed an omnidirectional antenna with 15 dB gain in a building, the signal would remain on the same plane, never reaching the lower and upper floors.
The same considerations apply to directional antennas.
However, in the specifications of a WiFi antenna, the gain values ​​are often indicated in dBi (isotropic decibels) which express the gain in decibels compared to an ideal isotropic antenna. To go from dBi to dBd, that is the real gain, it is sufficient to subtract the value 2.15. For example, in the case of 8 dBi of gain, this would result in 5.85 dBd.

Antenna coverage – the transmissive power: dBm

Concentrating the signal in one direction causes it to be radiated with substantially the same power but, on the other hand, coverage will be lost in the other directions.
To know the coverage of the antenna, it will be necessary to check the corresponding transmission power, expressed in dBm (decibels with reference to one milliwatt). The link that exists between gain and power leads as a consequence that at every 3 dB of gain, the value of the transmitting power is doubled. This effect is caused by the concentration of the signal in one direction.
Values ​​lower than -85 dBm can be considered as limit values, below which it is not possible to establish the link, or for which – in any case – the data exchange will take place in an unstable manner, with a high rate of lost packets.

The two models of radio antennas

Wi-Fi antennas are basically divided into two broad categories:
Isotropic antenna. It is the conceptual abstraction of an antenna that radiates in all directions in a uniform (isotropic) manner operating on a spherical symmetry.
Dipole. It is the antenna generally taken as a reference, since an isotropic antenna is a physically impossible idealization.

How to choose a Wi-Fi antenna

The dipole is the simplest example of an antenna, made up of a pair of straight wires – the antennas mounted on common routers and access points are all dipoles, even if they are protected with an external plastic casing.
When choosing an antenna, therefore, the gain value is expressed in dBi. The higher the gain value in dBi, the more the antenna will radiate the signal in a specific direction.
More relevant is the dBm value relating to the transmission power which can generally be adjusted from the software administration panel. In this regard, however, it is worth noting that many antennas or wireless devices allow for powers of 27 dBm/500 mW or more. The use of these powers is not allowed in our country, since they cannot exceed 20 dBm/100 mW. The transmissive power of the WiFi antenna must therefore be adjusted in such a way as not to exceed the legal limits.
In the case of a normal WiFi router, the antenna is omnidirectional and this is correct, because the signal must be radiated in all directions in order to “cover” all the positions in which the client systems may be. One of the basic tips, when choosing the location of the WiFi router, is to place the device in the center of the building, and therefore not in a decentralized position or behind reinforced concrete walls, subdivisions in plasterboard, geographical maps, cards and cardboard, metal walls… all elements that have a high degree of absorption and represent the most important obstacles for a correct diffusion of the wireless signal.
If you need to exchange data wirelessly over longer distances, you should choose directional antennas instead.

Speed ​​

A quality wi-fi antenna is also distinguished by its high speed, and by the performance it is able to guarantee during the connection. However, the fastest wi-fi antenna is not necessarily the right solution for everyone: for simple navigation or to watch some videos on the internet, a 300 Mbps or 500 Mbps model will suffice, and with a good basic connection it can also be used for online gaming or streaming. If, on the other hand, you really want to play it safe and avoid lag problems during multiplayer games, or streaming movies and TV series, then you will have to aim for a 1,200 Mbps product.

What does it mean that a Wi-Fi antenna works in dual band?

The Wi-Fi you use probably uses the 2.4 GHz band. Since more people use it, for example in multi-storey buildings or many offices, the level of network congestion increases, and with it interference, and transmission errors. A dual band Wi-Fi antenna is capable of transmitting on two bands: that of 2.4 GHz and that of 5 GHz. If you have a Wi-Fi antenna that operates on both networks, you can enjoy greater connection performance, managing to obtain both a wider coverage (2.4 GHz band) and a lower congestion (5 GHz band). In summary:
– 5 GHz band: more power but less range.
– 2.4 GHz band: less power but greater range.

Finally, here is a selection of the best Wi-Fi antennas: check of course that the antenna is compatible with the operating system you use, even if normally most devices are interchangeable.

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