When many people buy a wireless router, they will see such a parameter as "antenna gain". Merchants tell you that this will make the wireless signal stronger, and it seems that the higher the better. In fact, the gain of the antenna is not really a signal enhancement, but through the shaping of the signal, the signal in some areas is weakened, and the signal in the other part of the area is enhanced.
Antenna gain is theoretically the ratio of the signal power density generated by the actual antenna and the ideal point source antenna at a certain location in space with the same input power. The concept of a point source antenna is mentioned here, what is it? In fact, it is an antenna that people imagine uniformly transmitting signals, and its signal radiation pattern is a uniformly diffused spherical shape. In fact, the antenna has a radiation gain direction (hereinafter referred to as the radiation surface), and the signal on the radiation surface will be stronger than the radiation value of the theoretical point source antenna, while the signal radiation in other directions is weakened. The ratio of the actual value to the theoretical value here is the antenna gain.
It is worth noting that the passive antenna common to ordinary people will not only not enhance the transmit power in essence, but will also consume the transmit power. The reason why it is also considered to have a gain is because it sacrifices other directions, concentrates on enhancing the radiation direction, and improves signal utilization.
Antenna gain actually indicates the degree to which wireless power is concentrated, so it is closely related to the antenna radiation pattern. The general understanding is that the narrower the main lobe and the smaller the secondary lobe on the antenna radiation pattern, the higher the gain. So how do you calculate the antenna gain? For general antennas, the gain can be estimated using the formula g(dbi) = 10lg{32000/(2θ3db, e×2θ3db, h)}. In the formula, 2θ3db, e and 2θ3db, h are the lobe widths of the antenna in the two main planes, respectively; 32000 is the empirical data calculated.
So what would it mean if a 100mw wireless transmitter had an antenna with a gain of +3dbi? First, the transmit power is converted into a signal gain dbm to represent. The calculation method is:
100mw=10lg100=20dbm
The total transmit power is then calculated, which is equal to the sum of the transmit power and the antenna gain. The calculation method is as follows:
20dbm+3dbi=23dbm
Finally, the equivalent transmit power is recalculated as follows:
10^(23/10)≈200mw
。
The antennas of our common wireless routers are omnidirectional antennas. Its radiation surface is perpendicular to the level of the antenna, where the radiation gain is the greatest, and the radiation above and below the top and bottom end of the antenna is greatly weakened. It's a bit like flattening a signal racket a bit.
There is also a common plate antenna, which is usually a directional antenna. Its radiant surface is in the sector directly in front of the plate, and the signal in other areas is weakened. It's a bit like adding a spotlight cover to a light bulb.
In short, high-gain antennas have the advantages of longer range and better signal quality, but they must sacrifice radiation in individual directions (generally wasted directions). Low-gain antennas are usually over a large directional range but have a shorter range. When the wireless product is shipped, the manufacturer will generally be equipped according to the use scenario. Ordinary people don't have to worry, professionals can delve into it.