[The thing about the walkie-talkie] What you must know about the antenna gain of the radio antenna feeder system!

In the practical application of wireless communication, in order to effectively improve the communication effect and reduce the input power of the antenna, the antenna will be made into various structures with radiation directivity to concentrate the radiation power, which leads to the concept of "antenna gain". Simply put, the antenna gain refers to the degree to which an antenna radiates the input RF power. Obviously, the gain of the antenna has a great relationship with its pattern. The narrower the main lobe and the smaller the side lobe, the higher the gain of the antenna. Antennas with different structures have great differences in their directional patterns.

In the field of communication technology, the antenna gain is also expressed by the simplified method of relative comparison and logarithm, which is the same as other parameters such as power and level. The specific calculation method is: produce the same radiation in a certain direction to a certain position When the field strength is high, take the logarithm of the ratio of the input power of the lossless ideal reference antenna to the input power of the antenna to be considered and then multiply it by 10 (G=10lg (reference Pin/considered Pin)), that is, the antenna is called in this field. Gain in point direction. Commonly used units for measuring antenna gain are dBi and dBd. For dBi, the benchmark is an ideal point source antenna, that is, a real "point" to compare the antenna gain. The radiation of an ideal point source antenna is omnidirectional, and its pattern is an ideal sphere. The radiation intensity of electromagnetic waves at all points on the same sphere is the same; for dBd, the reference is an ideal dipole antenna. Since the dipole antenna is directional, the two have a fixed constant difference of 2.15, that is, 0dBd="2".15dBi.

It should be noted that the so-called "omnidirectional antenna" is not a strict term. The omnidirectional antenna should refer to the omnidirectional direction in the three-dimensional space. Antennas are called omnidirectional antennas, such as whip antennas, which have a circular main lobe in the radial direction, but still have axial side lobes.

Common antenna gain: whip antenna 6-9dBi, GSM base station Yagi antenna 15-17dBi, parabolic directional antenna can easily achieve 24dBi.

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 site, 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 the engineering of wireless network, it is very important to calculate the transmitting power of the transmitting device and the radiation capability of the antenna.

Tx is short for Transmits. The transmitted power of radio waves refers to the energy in a given frequency band, and there are usually two measures or measures:

1. Power (W): Linear level relative to 1 watt (Watts). For example, the transmit power of a WiFi wireless network card is usually 0.036W, or 36mW

2. Gain (dBm): relative to the proportional level of 1 milliwatt (milliwatt). For example, the transmit gain of a WiFi wireless network card is 15.56dBm.

The two expressions can be converted to each other:

1. dBm = 10 x log [power mW]

2. mW = 10 [Gain dBm / 10 dBm]

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 transmitting energy of the transmitting device and the amplification and superposition of the antenna, it is best to measure the transmitting energy with the same measure - gain (dB), for example, the power of the transmitting device is 100mW, or 20dBm; The gain is 10dBi, then:

Total transmit energy = transmit power (dBm) + antenna gain (dBi)

                =20dBm +10dBi

                =30dBm

      Or: =1000mW

                =1W

In "low power" systems (such as wireless local area network equipment) every dB counts, especially remembering the "3 dB rule". Every 3 dB increase or decrease means doubling or halving the power:

-3 dB = 1/2 power

‍‍‍‍‍-6 dB = 1/4 power

+3 dB = 2x power

+6 dB = 4x power

For example, the wireless transmit power of 100mW is 20dBm, while the wireless transmit power of 50mW is 17dBm, and the transmit power of 200mW is 23dBm.

 14:46:04

Power/Level (dBm): The output capability of the amplifier, generally in units of W, mW, dBm. dBm is the absolute power level expressed in decibels by taking 1mW as the reference value.

Conversion formula:

Level (dBm)=10lgW

5W→10lg5000 = 37dBm

10W→10lg10000 = 40dBm

20W→10lg20000 = 43dBm

It is not difficult to see from the above that each time the power is doubled, the level value increases by 3dBm