Antenna gain calculation method

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Antenna gain calculation method [Copy link]

Gain refers to the ratio of the power density of the signal generated by the actual antenna and the ideal radiating unit at the same point in space under the condition of equal input power. It quantitatively describes the degree to which an antenna concentrates the input power for radiation. Gain is obviously closely related to the antenna pattern. The narrower the main lobe of the pattern and the smaller the side lobe, the higher the gain. The physical meaning of gain can be understood in this way: to generate a signal of a certain size at a certain point at a certain distance, if an ideal non-directional point source is used as the transmitting antenna, an input power of 100W is required, while when a directional antenna with a gain of G = 13 dB = 20 is used as the transmitting antenna, the input power only needs 100 / 20 = 5W. In other words, the gain of an antenna is the multiple of the input power amplified compared with an ideal non-directional point source in terms of the radiation effect in the direction of maximum radiation. The gain of a half-wave symmetrical oscillator is G=2.15dBi. Four half-wave symmetrical oscillators are arranged up and down along a vertical line to form a vertical four-element array, and its gain is about G=8.15dBi (the unit of dBi indicates that the comparison object is an ideal point source with uniform radiation in all directions). If a half-wave symmetrical oscillator is used as a comparison object, the unit of its gain is dBd. The gain of a half-wave symmetrical oscillator is G=0dBd (because it is compared with itself, the ratio is 1, and the logarithm is zero.) The gain of a vertical four-element array is about G=8.15 – 2.15=6dBd. Several calculation formulas for antenna gain 1. The narrower the antenna main lobe width, the higher the gain. For a general antenna, its gain can be estimated by the following 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 obtained by statistics. 2. For parabolic antennas, the gain can be approximately calculated using the following formula: G(dBi)=10Lg{4.5×(D/λ0)2} In the formula, D is the diameter of the parabola; λ0 is the central operating wavelength; 4.5 is statistical empirical data. 3. For upright omnidirectional antennas, there is an approximate calculation formula G(dBi)=10Lg{2L/λ0} In the formula, L is the antenna length; λ0 is the central working wavelength; About the units of antennas such as db, dBi, dBd, etc. Some friends tend to confuse these units easily. dB is based on logarithmic values. 1. dB is simply a relative value, that is, the logarithm of the value of A compared to B. It is often used to say how many dB higher or lower A is than B, but it is unreasonable to say how many dB the gain of A is, because we don't know what B is. It's just that many of our friends sometimes say dB for simplicity, but this is not accurate enough. However, we often make the mistake and understand it as dBi by default. Otherwise, you can ask for clarification. 2. dBd, this has a standard reference value, that is, B is defined as a half-wave dipole antenna in free space, so that there is a unified reference for comparing the values of A and B. If you tell your friends that this antenna is 10dBd, they will understand that your antenna can gather 10 times more energy in the main radiation direction than a half-wave dipole antenna, that is, it is 10 times better. 3. dBi, the meaning of this unit is relatively complicated, but it is the ratio unit that best expresses the actual environment. Here, the reference object B is a point source oscillator (this object does not actually exist, it can be regarded as a small section of the oscillator with a relatively short wavelength, or called a micro-segment). In the standard definition, this point source oscillator should be an ideal spherical omnidirectional radiation. At this time, there is a certain mathematical relationship with dBd, that is, 1dBd=2.14dBi. However, in reality, most antennas are affected by the installation height, the most important of which is the ground. Due to the mirror effect of the ground, the beam shape is often changed, and it is often 2-5dB higher in some directions. You should understand 19dBi by now. Many regular antenna manufacturers often like to use dBi to mark the gain value of the antenna. They usually indicate the installation height or the calculation method of the marked value, or they produce the installation environment that everyone knows, such as the roof-mounted antenna, and often omit the description. Transmitting power and gain The radio frequency signal output by the radio transmitter is transmitted to the antenna through the feeder (cable) and 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 very small part of the power is received) and sent to the radio receiver through the feeder. Therefore, in the wireless network project, it is very important to calculate the transmission power of the transmitter and the radiation capacity of the antenna. Tx is the abbreviation of Transmits. The transmission power of radio waves refers to the energy within a given frequency band. There are usually two measurement standards: Power (W) - linear level relative to 1 watt (Watts). Gain (dBm) - proportional level relative to 1 milliwatt (Milliwatt). The two expressions can be converted to each other: dBm = 10 x log[Power in mW] mW = 10 [Gain in dBm / 10 dBm] In wireless systems, antennas are used to convert current waves into electromagnetic waves. In the conversion process, they can also "amplify" the transmitted and received signals. The measure of this energy amplification is called "Gain". The unit of measurement for antenna gain is "dBi". Since the electromagnetic wave energy in the wireless system is generated by the transmission energy of the transmitting device and the amplification of the antenna, the best metric for measuring the transmission energy is gain (dB). For example, the power of the transmitting device is 100mW, or 20dBm; the gain of the antenna is 10dBi, then: Total transmission energy = transmission power (dBm) + antenna gain (dBi) = 20dBm + 10dBi = 30dBm Or: = 1000mW = 1W In "low power" systems every dB is very important, especially remember the "3dB rule". Every 3dB 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, a 100mW wireless transmitter has a power of 20dBm, a 50mW wireless transmitter has a power of 17dBm, and a 200mW transmitter has a power of 23dBm.

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What are the indicators that need to be measured for antennas? Gain, S1, S12, etc. There are many. Which indicators do we need to set? What kind of instruments are needed for testing?