Antenna gain

　　The long-term antenna gain introduces how much power is transmitted in the peak radiation direction relative to the isotropic source. Antenna gain more generally refers to the specification table of antenna. Antenna gain is important because it takes into account the actual loss.
　　With a 3 dB gain antenna, the power received from the antenna is much higher than 3 dB, which will be received from a lossless isotropic antenna with the same input power. 3 dB is equivalent to twice the power supply.
　　Antenna gain is sometimes discussed as a function of direction or angle. However, when a single number specifies the gain, then this number is the peak gain in all directions. The antenna gain of "g" can be compared with the directivity of "d" of the future formula.
[equation 3]
　　The gain of a real antenna can be as high as 50 dB for a very large satellite dish antenna. Directivity can be as low as 1.76 dB for a real antenna (such as a short dipole antenna). The directivity should never be less than 0 dB. However, the gain of the peak antenna can be arbitrarily small. This is because of loss or inefficiency. Electrically small antenna is a relatively small antenna, and the wavelength of antenna operating frequency. Small antennas can be very inefficient. Antenna gain is often less than - 10 dB, even when impedance mismatch is not considered.