WIFI is a passive subject, that is, it does not need to provide power or other energy. It is not a power amplifier, nor does it amplify incoming wireless signals. On the contrary, due to the signal attenuation caused by the feeder and the connector, the released wireless energy will be higher than the input. The antenna contacts have almost no energy. In fact, the antenna is only used as a directional amplifier, so the transmission and reception energy is concentrated in a specific area of  space. Changing the energy distribution area to the desired location is the sole purpose of the antenna. It is wasteful if energy is distributed to places where there are no wireless devices, or over-distributed to certain areas. According to the law of constant energy, increasing energy in one direction means reducing energy in other areas.

Gain
Gain is a general expression of wireless characteristics. It refers to the intensity gain in a specific area relative to the following two ideal standard transceiver modes. The ideal standard transceiver mode is that the energy of the radiator is emitted from an isotropic antenna. It is an isotropic radiator that emits in any direction in space, and all directions are 0dB. The gain unit calculated according to this standard as a reference is dBi. Another ideal standard transceiver mode is based on free space half-wavelength dual The energy of the polar radiation is used as a reference. The calculated revenue unit is dBd. Obviously, the latter radiator has a gain relative to the previous radiator. The calculated value is 2.16, that is, 1 dBd = 2.16 dBi. Currently, most antennas use dBi as the calculation unit, and the typical gain of 2.4GHz or 5.8GHz is 2 dBi to 26 dBi.