If you find that your newly purchased 2.4GHz or 5.8GHz device does not provide the wireless coverage you expected, it does not necessarily mean that there is a problem with the device, or that you have placed the device in the wrong place. More than 90% of the reasons are that you do not have Equip the device with a suitable antenna; even if your WiFi client can access the Internet through your home wireless router, have you checked the actual wireless signal strength, if the signal-to-noise ratio (SNR) is too low, the wireless transmission speed will not reach 54Mbps or higher, of course, wireless interference will also affect the transmission speed, but even the basic wireless signal is not good, so don't expect high-speed Internet access. So which type of antenna should we buy? This can’t be explained in a few words. Choosing the right antenna is actually a matter of knowledge. We must start by understanding the basic knowledge of the antenna. The following article will introduce the principle of the antenna and some antenna parameters. I believe that it can help you select and install the appropriate antenna to enhance the effective coverage and performance of your wireless system.

Antenna is a passive body, that is, it does not need to provide electricity or other energy. It is not a power amplifier and will not amplify the input wireless signal. On the contrary, due to the signal attenuation caused by the feeder and the connector, the released wireless energy will be It is less than the energy input to the antenna contact. In fact, the antenna only plays the role of a directional amplifier, so that the sending and receiving energy is concentrated in a specific area of ​​the space, and changing the energy distribution area to the place where it is needed is the only purpose of the antenna. It is a waste to distribute energy to some places without wireless devices, or to distribute energy excessively to a certain area. According to the law of constant energy, if the energy is distributed to a situation where the signal coverage is seen, the energy is only distributed at the same level, and the signal is not distributed. Does not radiate to the sky or the ground.

Gain

Gain is a general representation method of antenna characteristics. It refers to the strength gain in a certain area relative to the following two ideal standard transceiver modes. The ideal standard transceiver mode is based on the energy of the radiator emitted from an isotropic antenna ( As shown in the figure below), it is an isotropic radiator, radiating in any direction in space, and all directions are 0dB. According to this standard as a reference, the calculated gain unit is dBi. Another ideal standard transceiver mode is based on The energy emitted by a free-space half-wavelength dipole is used as a reference, and the calculated gain unit is dBd. Obviously, the latter radiator has a gain relative to the former radiator, and the calculated result is 2.16, that is, 1 dBd = 2.16 dBi, most antennas use dBi as the calculation unit, the typical gain of 2.4GHz or 5.8GHz is from 2 dBi to 26 dBi

Radiation Pattern

Gain can only be used as a reference for selecting an antenna. It can only display the gain in the direction with the strongest energy, and does not provide any distribution of energy. The radiation pattern can accurately display the distribution of energy in free space. There are two types of horizontal radiation pattern (horizontal / azimuth sweep plane) and vertical radiation pattern (vertical / elevaTIon sweep plane). The right picture is the horizontal and vertical radiation pattern of the 8dB omnidirectional gain antenna OP2408 produced by a company. The red line (H plane) is horizontal distribution, imagine that you can see the signal coverage from the vertex of the antenna, you will find that the energy of the 8dB omnidirectional gain antenna is distributed around 360 degrees with the antenna as the center; the blue line (E plane) is vertical distribution, Imagine that you see the signal coverage from the side of the antenna, the energy is only emitted at the same level, and the signal does not radiate to the sky or the ground.