The general meaning of gain is simply the magnification.stayelectronicsIt is usually the ratio of signal output to signal input of a system, such asAntenna gainThe parameter representing the radiation concentration degree of the directional antenna is the ratio of the square of the electric field intensity generated by the directional antenna and the non directional antenna in the predetermined direction.Amplifier gain, which refers to the amplifier power magnification, expressed in the common logarithm of the ratio of output power to input power, etc.
Gain generally refers to the gain of componentsCircuitThe increase degree of current, voltage or power of equipment or system is specified in decibels (dB), that is, the unit of gain is generally decibels (dB), which is a relative value.Commonly used in electronicslogarithmThe gain is measured in units and is expressed in bels:
Gain = logten(Ptwo/Pone) bel
P1 and P2 are the input and output power respectively.
Since the value of gain is usually large, it is generally usedDecibel(dB, 1/10 of Beige)
Gain = 10×logten(Ptwo/Pone) dB
This is the relationship between the absolute value of the gain and the relative value in decibels.
Common gain
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Antenna gain
antennaGain refers to the signal generated by the actual antenna and the ideal radiation unit at the same point in space under the condition of equal input powerpower density Ratio.Antenna gain is an extremely important standard for network access test, which represents antenna directivity and signal energy concentration.The size of the gain affects the coverage and strength of the antenna transmission signal.The narrower the main lobe and the smaller the side lobe, the more concentrated the energy will be, and the higher the antenna gain will be.[1]In general, the improvement of gain mainly depends on reducing the lobe width of radiation in the vertical plane, while maintaining omnidirectional radiation performance in the horizontal plane.Antenna gain pairMobile communication systemThe operational quality of is extremely important because it determines the signal level at the cell edge.Increasing the gain can increase the network coverage in a certain direction, or increase the gain margin in a certain range.Any cellular system is a two-way process. Increasing the antenna gain can simultaneously reduce the gain budget margin of the two-way system.Generally, there are two units of antenna gain: dBi and dBd, where dBi is the reference of the ideal point source antenna, and the radiation in all directions is uniform;DBd refers to the gain dBi=dBd+2.15 relative to the symmetrical array antenna with the antenna of the half wave array (dipole) as the reference.Under the same conditions, the higher the gain, the farther the radio wave travels.Generally, the antenna gain of the GSM directional base station is 18dBi, and that of the omnidirectional base station is 11dBi.For the same antenna gain, dBi is 2.15 dB larger than dBd in value.
Amplifier gain
Amplifier gain is the logarithm of the ratio of output power and input power of the amplifier to indicate the degree of power amplification.Also referred to as voltage orelectric currentThe magnification of.Similarly, the decibel is the unit of amplifier gain.The ratio of output and input of the amplifier is the amplification factor, and the unit is "times", such as 10 times amplifier and 100 times amplifier.When "decibel" is used as the unit, the magnification is called gain, which is two terms of a concept.In electricity, the conversion relationship between decibel and magnification is: AV (I) (dB)=20lg [Vo/Vi (Io/II)];When Ap (dB)=10lg (Po/Pi) decibel is defined, the formulas of voltage (current) gain and power gain are different, but we all know that the relationship between power and voltage, current is P=V ^ 2/R=I ^ 2R.After using this formula, the gain values of the two are the same: 10lg [Po/Pi]=10lg (V2o/R)/(V2i/R)=20lg (Vo/Vi).Using decibels as a unit has great advantages.
The total magnification of the electronic system is often thousands, tens of thousands or even hundreds of thousands. A radio needs to amplify a total of about 20000 times from the signal received by the antenna to the loudspeaker playback output.If you take a logarithm in decibels, the value will be much smaller.When amplifiers are cascaded, the total amplification is the multiplication of all levels.In decibels, the total gain is the sum.If the front stage of a power amplifier is 100 times (20dB) and the rear stage is 20 times (13dB), then the total power magnification is 100 × 20=2000 times, and the total gain is 20dB+13dB=33dB.
Power gain
Power gain refers to the ratio of output power and input power in a circuit.Unlike other signal gains, such as voltage gain and current gain, power gain is sometimes confused due to the relatively vague definition of "input power" and "output power".Three important power gains include: operating power gain, converter power gain, and available power gain.It is worth noting that the above three definitions of gain are based on the average effect of power rather than instantaneous power, but the word "average" is often omitted, which may cause confusion in some cases.
Loop gain
Loop gain is a term used in electronics and control engineering. It refers to the total gain in a feedback loop, usually expressed in proportion or decibels.Loop gain is often used in the circuits of amplifiers and electronic oscillators, and later expanded to control factories and equipmentindustrial control system Medium.The concept of loop gain is also used in biology.In the feedback loop, in order to control the output, the output of the equipment and program will be measured. After sampling, the input signal will be affected by this to make the output control more ideal.The loop gain and loop phase shift determine the characteristics of the device, and also determine whether the output is stable or unstable (oscillation).Heinrich Buckhausen first discovered the importance of loop gain in the analysis of the characteristics of electronic feedback amplifiers in 1921. Later in the 1930s, it was developed by Hendrik Wade Bode and Harry Nyquist of Bell Laboratories.
In communication, loop gain can refer to carrier terminal or two-wireRepeaterAvailable power gain on.The maximum available gain is determined by the total loss of the closed loop, and the available gain cannot be greater than the total loss.
Other terms
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Out of band
Out of band: refers to the amplification ability of the measured compensator (transmitter) to signals outside the working band.When the equipment reaches full power output, set the equipment gain to the maximum, test the signal power in the working band at this time, set the frequency of the signal source as required, and measure the output power at this time. The level value between the two is out of band suppression;The measured gain of the device is the out of band gain of the device.Out of band suppression and out of band gain can be converted mutually (if the gain of the equipment is Gp, the out of band suppression measured at 1MHz away from the operating band is ∆ K, then the out of band gain measured at 1MHz away from the operating band is Go, then GO=GP - ∆ K).
Optical communication
Gain is an important parameter to evaluate EDFA. It represents the amplification capacity of the amplifier and is defined as the ratio of output power to input power.
G=（Pout-Pase）/Pin
Where Pase isSignal bandwidthSpontaneity of internal EDFARadiant power, Pout and Pin are the output and input power of the signal respectively.
