Describe
Antenna gain is a very important part of the antenna knowledge structure, and of course it is also one of the important parameters for selecting an antenna. Antenna gain also plays an important role in the operation quality of the communication system. Generally speaking, the improvement of gain mainly depends on reducing the beam width of the vertical radiation, while maintaining the omnidirectional radiation performance in the horizontal plane.
- The definition of antenna gain: The ratio of the radiated power flux density of the antenna in a specified direction to the maximum radiated power flux density of the reference antenna at the same input power. → Pay attention to the following points: (1) Unless otherwise specified, the antenna gain refers to the gain in the maximum radiation direction; (2) Under the same conditions, the higher the gain, the better the directivity, and the farther the distance of radio wave propagation, that is, the increased distance covered. However, the width of the wave velocity will not be compressed, and the narrower the wave lobe, the worse the uniformity of coverage. (3) The antenna is a passive device and cannot generate energy. Antenna gain is simply the ability to efficiently concentrate energy to radiate or receive electromagnetic waves in a particular direction.
- Calculation formula of antenna gain We can know from the definition of antenna gain that the antenna gain is closely related to the antenna pattern. The narrower the main lobe and the smaller the side lobe, the higher the gain. 2.4GHz22dBi bipolar/cross-polarized MIMO parabolic antenna (1) For a parabolic antenna, the following formula can be used to approximate its gain: G(dBi)=10Lg{4.5×(D/λ0)^2} *Notice: D: Paraboloid diameter λ0: central working wavelength 4.5: Statistical empirical data 2.4GHz13dBi Bipolar Omnidirectional MIMO Antenna-N Type Female Connector (2) For vertical omnidirectional antennas, the following formula can also be used for approximate calculation: G (dBi)=10Lg{2L/λ0} *Notice: L: Antenna length λ0: central working wavelength
- Gain and transmit power The radio frequency signal output by the radio transmitter is sent to the antenna through the feeder (cable), and is radiated by the antenna in the form of electromagnetic waves. After the electromagnetic wave reaches the receiving location, it is received by the antenna (only a small part of the power is received), and sent to the radio receiver through the feeder. Therefore, in wireless network engineering, it is very important to calculate the transmitting power of the transmitting device and the radiation capability of the antenna. The transmitted power of radio waves refers to the energy within a given frequency range, and there are usually two measurement or measurement standards: Power (W): Relative to the linear level of 1 watt (Watts). Gain (dBm): relative to the proportional level of 1 milliwatt (Milliwatt). →The two expressions can be converted to each other: dBm=10xlog [power mW] mW=10^[gain dBm/10dBm] In wireless systems, antennas are used to convert current waves into electromagnetic waves. During the conversion process, the transmitted and received signals can also be “amplified”. The measure of this energy amplification is called “Gain”. Antenna gain is measured in “dBi”. Since the electromagnetic wave energy in the wireless system is generated by the amplification and superposition of the transmitting energy of the transmitting device and the antenna, it is best to measure the transmitting energy with the same measurement-gain (dB), for example, the power of the transmitting device is 100mW, or 20dBm; the antenna The gain is 10dBi, then: Transmitting total energy = transmitting power (dBm) + antenna gain (dBi) ＝20dBm＋10dBi ＝30dBm Or: = 1000mW = 1W [3dB rule] →In the “low power” system, every dB is very important, especially remember the “3dB rule”. Every increase or decrease of 3dB means that the power is doubled or reduced by half: -3dB=1/2 power -6dB=1/4 power +3dB=2x power +6dB=4x power For example, the wireless transmission power of 100mW is 20dBm, the wireless transmission power of 50mW is 17dBm, and the transmission power of 200mW is 23dBm.
