This paper mainly introduces some passive components on the communication link, and introduces the appearance, function, type, main technical index definition and scope of components.
1 power divider
1) The function of power divider is to evenly divide the power signal into several parts for different coverage areas.
2) Type: power divider generally has three types: two power divider, three power divider and four power divider.
The power divider is generally divided into two types: microstrip and cavity. Inside the cavity power divider is a copper rod whose diameter is composed of multiple steps from coarse to fine range, so as to realize impedance transformation. The two microstrip lines are composed of several microstrip lines and several resistors, so as to realize impedance transformation
3) Main indicators: including distribution loss, insertion loss, isolation, input / output standing wave ratio, power tolerance, frequency range and in band flatness.
The indicators are described below:
Distribution loss: refers to the amount of signal power reduced compared with the original input signal after ideal power distribution. This value is the theoretical value. For example, the two power division is 3dB, the three power division is 4.8dB, and the four power division is 6dB. (because the output impedance of the power divider is different, a network analyzer with port impedance matching shall be used to measure the distribution loss close to the theoretical value)
Theoretical calculation method of distribution loss: for example, if there is a 30dBm signal, the converted milliwatt is 1000MW. If the signal is divided into three parts through the ideal 3 power divider, each power = 1000 ÷ 3 = 333.33mw, and 333.33mw is converted into DBM = 10lg333 33 = 25.2dbm, then the ideal distribution loss = input signal - output power = 30-25.2 = 4.8dB. It can also be calculated that the 2 power division is 3dB and the 4 power division is 6dbl insertion loss: it refers to the amount reduced by the output power of the signal power after passing through the actual power divider compared with the original input signal, and then subtract the actual value of the distribution loss, (in some places, it refers to the reduction of the output power after the signal power passes through the actual power divider compared with the original input signal). The value range of insertion loss is generally below 0.1dB; The of microstrip varies according to the two, three and four power dividers, about 0.4 ~ 0.2db, 0.5 ~ 0.3dB and 0.7 ~ 0.4db.
Calculation method of insertion loss: the loss from input a to output B, C and D can be measured through the network analyzer. Assuming that the 3 power division is 5.3db, then the insertion loss = actual loss - theoretical distribution loss = 5.3db-4.8db = 0.5dB
The insertion loss of microstrip power divider is slightly larger than that of cavity power divider, which is generally about 0.5dB, and that of cavity is generally about 0.1dB. Since the insertion loss cannot be measured directly by the network analyzer, it is generally expressed by the loss on the whole path (i.e. distribution loss + insertion loss): 3.5db/5.5db/6.5db, etc. to represent the insertion loss of the two / three / four power dividers.
Isolation: refers to the isolation between the output ports of the power divider. It usually varies according to the second, third and fourth power dividers, about 18 ~ 22dB, 19 ~ 23dB and 20 ~ 25dB.
The isolation can be measured by the network analyzer to directly measure the loss between each output port, as shown in the light blue curve above, the loss between BC and CD.
L input / output standing wave ratio: refers to the matching of input / output ports. Since the output port of the cavity power divider is not 50 ohms, there are no standing wave requirements for the output port of the cavity power divider, and the requirements for the input port are generally 1.3 ~ 1.4 or even 1.15; Microstrip power divider has requirements for each port. The general range is input: 1.2 ~ 1.3, output: 1.3 ~ 1.4.
L power tolerance: refers to the maximum working power tolerance that can pass through this power divider for a long time (without damage). Generally, the average power of microstrip power divider is 30 ~ 70W, and that of cavity is 100 ~ 500W.
L frequency range: generally, the nominal frequency range is 800 ~ 2200MHz. In fact, the required frequency band is 824-960MHz plus 1710 ~ 2200MHz. The intermediate frequency band is not available. Some power dividers also have 800 ~ 2000MHz and 800 ~ 2500mhz frequency bands
L in band Flatness: refers to the difference between the maximum and minimum values of interpolation loss including allocation loss in the whole available frequency band, generally 0.2 ~ 0.5dB.
2 coupler
1) The function of the coupler is to divide the signal unevenly into two parts (called trunk end and coupling end, and some are also called through end and coupling end)
2) Type: there are many coupler models, such as 5 dB, 10 dB, 15 dB, 20 dB, 25 dB, 30 dB, etc.
From the structure, it is generally divided into microstrip and cavity. Inside the cavity coupler is a primary coupling composed of two metal rods
Inside the microstrip coupler are two microstrip lines, which form a network similar to multistage coupling
3 main indicators: coupling degree, isolation degree, directivity, insertion loss, input-output standing wave ratio, power tolerance, frequency band range and in band flatness.
The indicators are described below:
Coupling degree: the direct difference between the output power from the coupling port and the input signal power when the signal power passes through the coupler. (generally theoretical values, such as 6dB, 10dB, 30dB, etc.)
Calculation method of coupling degree: it is the value of signal power c-a. For example, if the input signal a is 30dBm and the output signal C at the coupling end is 24dbm, the coupling degree = C-A = 30-24 = 6dB, so this coupler is 6dB coupler. Because the coupling degree is actually not so ideal, it generally has a fluctuation range. For example, for a coupler with a nominal 6dB, the actual coupling degree may fluctuate between 5.5 and 6.5.
Isolation degree: refers to the isolation between the output port and the coupling port; Generally, this index is only used to measure microstrip coupler. And it varies according to the coupling degree: for example, 5-10db is 18 ~ 23dB, 15dB is 20 ~ 25dB, and 20dB (including above) is 25 ~ 30dB; The isolation of cavity coupler is very good, so there is no requirement for this index.
Calculation method: as shown in the figure above, it refers to the loss on the light blue curve in the figure. Use the network analyzer to input the signal from B, and the amount reduced at C is the isolation.
Directivity: refers to the value of the isolation between the output port and the coupling port minus the value of the coupling degree. Since the directivity of the microstrip decreases gradually with the increase of the coupling degree, there is basically no directivity above 30dB, so there is no such index requirement for the microstrip coupler. The directivity of the cavity coupler is generally 17 ~ 19dB at 1700 ~ 2200MHz, 824 ～ 960MHz: 18 ～ 22dB.
Calculation method: directivity = isolation - coupling
For example, if the 6dB isolation is 38dB and the measured coupling is 6.5db, then directivity = isolation coupling = 38-6.5 = 31.5db.
Insertion loss: refers to the value obtained by subtracting the value of distribution loss from the reduced signal power from the signal power through the coupler to the output. Generally, the insertion loss of microstrip coupler varies according to the coupling degree. Generally, it is 0.35 ~ 0.5dB for less than 10dB and 0.2 ~ 0.5dB for more than 10dB.
Calculation method: as the inner conductor of the coupler is actually lossy, as shown in the figure above, taking 6dB coupler as an example, in the actual test, it is assumed that the input a is 30dBm, the measured coupling degree is 6.5db, the ideal value of the output end is 28.349dbm (calculated according to the measured input signal and coupling degree), and then the measured signal of the output end is assumed to be 27.849dbm, Then insertion loss = theoretical output power measured output power = 28.349-27.849 = 0.5dB;
Input / output standing wave ratio: refers to the matching of input / output ports, and the requirements of each port are generally 1.2 ~ 1.4;
Power tolerance: refers to the maximum working power tolerance that can pass through this coupler for a long time (without damage). Generally, the average power of microstrip coupler is 30 ~ 70W, and that of cavity is 100 ~ 200W.
Frequency range: generally, the nominal frequency is 800 ~ 2200MHz. In fact, the required frequency band is 824-960MHz plus 1710 ~ 2200MHz. The intermediate frequency band is not available. Some power dividers also have 800 ~ 2000MHz and 800 ~ 2500mhz frequency bands
In band Flatness: refers to the difference between the maximum and minimum coupling degree in the whole available frequency band. Microstrip is generally 0.5 ~ 0.2db. Cavity: since the coupling degree is a curve, there is no such requirement.
Coupling loss: the ideal coupler input signal is a, and if a part is coupled to B, the output port C must be reduced. The coupler and power divider are passive components. They do not use power supply (i.e. do not consume energy) and have no power supplement, because the energy is conserved and the sum of input signals and multiple output signals is equal (excluding insertion loss).
The calculation method is as follows: firstly, convert the "DBM" power of all ports into "milliwatts". For example, the power of input a was originally 30dBm, converted into "milliwatts" was 1000MW, and the output of coupling end was 25.5dbm (assuming that 6dB coupler is used, and the actual coupling degree of 6dB coupler is 6.5db), and the conversion of 25.5dbm into milliwatts is 316.23mw. Assuming that there is no other loss in the coupler, the remaining power should be 1000-316.23 = 683.77 MW, which is output by the output terminal. If 683.77 MW is converted to "DBM" = 28.349, the coupling loss of the coupler is equal to the power at the input (DBM) - the power at the output (DBM) = 30dbm-28.349dbm = 1.651db. This value refers to the coupling loss without additional loss (device loss) of the coupler.
Flatness of microstrip coupler: generally 0.5dB below 10dB, 1.5dB for 10 ~ 20dB and 2.0db for 20 ~ 30
Flatness of cavity coupler: because the coupling degree of cavity coupler is a curve similar to parabola, the flatness is very poor It is difficult to express in actual use. Please refer to the following table:
3 combiner and Bridge
1) Function: the main function of combiner is to synthesize several signals.
2) Type: combiner is divided into two types: dual frequency combiner and Bridge combiner. Dual frequency combiner is divided into GSM / CDMA two network combiner and GSM / DCS two network combiner.
3) Description of working mechanism: the working principle of dual frequency combiner is similar to that of duplexer, but it is required that the synthesized signals are not within the same frequency band, such as G network and C network, G network and D network. Duplex combiner can be used only when there is a combination between C network and D network. Moreover, dual frequency combiner has the characteristics of low insertion loss (some are only a few tenths of DB) and large isolation (greater than 70 ~ 90dB). Since the second harmonic of network C falls in network D, the isolation between network C and network D is about 10 dB less than that of other types.
When the combined signal is in the same frequency band, the bridge combiner can only be used The bridge combiner has a combiner loss. For example, 2-in-1 has a combiner loss of 3dB, and the isolation of the bridge combiner is much lower than that of the duplex combiner, which is generally only about 20dB.
