Principles and Analysis of Power Dividers, Couplers, and Bridges

作者： 沃锌科技 时间：2023-11-28 15:57:43 阅读：15

This article mainly introduces some passive components on the communication link, including their appearance, function, types, main technical specifications, definitions, and scope.

1 power divider

1) The function of a power divider is to evenly divide the power signal into several parts for use in different coverage areas.

2) Types: There are generally three types of power dividers: two power dividers, three power dividers, and four power dividers.

2 types. The interior of the cavity power divider is composed of a copper rod with multiple stepwise decreasing diameters from coarse to fine, which realizes impedance transformation. The two microstrip lines are composed of several microstrip lines and several resistors, which realizes impedance transformation

3) Main indicators: including allocation loss, insertion loss, isolation, input-output standing wave ratio, power margin, frequency range, and in band flatness.

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It refers to the amount by which the signal power is reduced compared to the original input signal after ideal power allocation. This value is a theoretical value, such as 3dB for two power division, 4.8dB for three power division, and 6dB for four power division. (Due to the different impedance at the output end of the power divider, a network analyzer with port impedance matching should be used to measure the distribution loss that is close to the theoretical value.)

For example, if there is a 30dBm signal that is converted to milliwatts, it is 1000 milliwatts. If this signal is divided into three parts through an ideal 3-power divider, and each part has a power of 1000 ÷ 3=333.33 milliwatts, then converting 333.33 milliwatts to dBm=10lg333.33=25.2dBm, the ideal allocation loss=input signal output power=30-25.2=4.8dB, and the 2-power divider can also be calculated to be 3dB, 4 power divider is 6dBl insertion loss: it refers to the amount by which the signal power decreases compared to the original input signal after passing through the actual power divider, minus the actual value of the allocation loss. (In some places, it also refers to the amount by which the signal power decreases compared to the original input signal after passing through the actual power divider.). The range of insertion loss values is generally below 0.1dB for cavities; The microstrip voltage varies according to the different power dividers, which are approximately 0.4~0.2dB, 0.5~0.3dB, and 0.7~0.4dB.

The loss from A to output terminals B, C, and D is assumed to be 5.3dB. Therefore, the insertion loss=actual loss - theoretical allocation loss=5.3dB-4.8dB=0.5dB

It is generally around 0.5dB, and the cavity is generally around 0.1dB. Due to the fact that insertion loss cannot be directly measured using a network analyzer, it is generally represented by the loss along the entire path (i.e. allocation loss+insertion loss): 3.5dB/5.5dB/6.5dB, etc. to represent the insertion loss of the second/third/fourth power divider.

Isolation degree: 18-22dB, 19-23dB, 20-25dB.

Loss between BC and CD.

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 is no standing wave requirement for the output port of the cavity power divider. The input port requirements are generally 1.3~1.4 or even 1.15; The microstrip power divider has requirements for each port, generally ranging from input: 1.2~1.3 to output: 1.3~1.4.

Power margin: refers to the maximum operating power margin that can be passed through this power divider for a long time (without damage). Generally, microstrip power dividers have an average power of 30-70W, while cavities have an average power of 100-500W.

Frequency range: Generally, the nominal frequency range is 800-2200MHz, but in reality, the required frequency band is 824-960MHz plus 1710-2200MHz, and the intermediate frequency band is not available. Some power dividers still have frequency bands of 800-2000MHz and 800-2500MHz

In band flatness: refers to the difference between the maximum and minimum values of insertion loss and allocation loss within the entire available frequency band, generally ranging from 0.2 to 0.5dB.

2 Couplers

1) The function of a coupler is to unevenly divide the signal into two parts (referred to as the backbone end and coupling end, or some as the through end and coupling end)

2) Types: There are many types of couplers, such as 5 dB, 10 dB, 15 dB, 20 dB, 25 dB, 30 dB, etc.

2 types. The interior of the cavity coupler consists of two metal rods, forming a primary coupling

Two microstrip lines form a network similar to multi-level coupling

3 main indicators: coupling degree, isolation degree, directionality, insertion loss, input-output standing wave ratio, power tolerance, frequency range, and in band flatness.

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Coupling degree: 6dB, 10dB, 30dB, etc.)

The value of 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 a 6dB coupler. Because the coupling degree is not actually as ideal, there is usually a fluctuation range, such as a coupler with a nominal 6dB, and the actual coupling degree may fluctuate between 5.5 and 6.5.

Isolation degree: 18-23dB for 5-10dB, 20-25dB for 15dB, and 25-30dB for 20dB (including above); The isolation degree of the cavity coupler is very good, so there is no requirement for this indicator.

Input B, measure the decrease at point C, which is the isolation degree.

Directionality: There is basically no directionality above 30dB, so microstrip couplers do not have this indicator requirement. The directionality of cavity couplers is generally 17-19dB at 1700-2200MHz, and 18-22dB at 824-960MHz.

Calculation method: directionality=isolation degree - coupling degree

The isolation degree of 6dB is 38dB, and the measured coupling degree is 6.5dB. Therefore, directionality=isolation degree - coupling degree=38-6.5=31.5dB.

Insertion loss: 0.35-0.5dB below 10dB, 0.2-0.5dB above 10dB.

Taking the 6dB coupler as an example, in actual testing, assuming that the input A is 30dBm, the measured coupling degree is 6.5dB, and the ideal output value is 28.349dBm (calculated based on the measured input signal and coupling degree), and then measuring the output signal, assuming it is 27.849dBm, then the insertion loss=theoretical output power - measured output power=28.349-27.849=0.5dB;

Input/output standing wave ratio:/matching of output ports, with requirements for each port generally ranging from 1.2 to 1.4;

Power tolerance: 30-70W average power, while for the cavity, it is 100-200W average power.

Frequency range: 800-2200MHz, the actual required frequency band is 824-960MHz plus 1710-2200MHz, and the intermediate frequency band is not available. Some power dividers still have frequency bands of 800-2000MHz and 800-2500MHz

Flatness within the band: 0.5~0.2dB. Chamber: Since the coupling degree is a curve, there is no such requirement.

Coupling loss: A, coupling a part to B, then the output port C must be reduced. Couplers and power dividers are both passive components that do not use a power source (i.e. do not consume energy) during operation, and do not have power replenishment because energy is conserved, and the sum of input signals and multiple output signals is equal (excluding insertion loss).

The power of "dBm" is expressed in units of "milliwatts". For example, if the input power of A was originally 30dBm, converting it to "milliwatts" would result in 1000 milliwatts, while the output of the coupling end would be 25.5dBm (assuming a 6dB coupler is used, and the actual coupling degree of the 6dB coupler is 6.5dB), converting 25.5dBm to milliwatts would be 316.23 milliwatts. Assuming there are no other losses in this coupler, the remaining power should be 1000-316.23=683.77 milliwatts, all output from the output terminal. Converting 683.77 milliwatts to "dBm"=28.349, the coupling loss of this coupler is equal to the input power (dBm) - output power (dBm)=30 dBm -28.349 dBm=1.651 dB. This value refers to the coupling loss of the coupler without additional losses (device losses).

Below 10dB, it is generally 0.5dB, 10-20dB is generally 1.5dB, and 20-30dB is generally 2.0dB

Due to the coupling degree of the cavity coupler being a parabolic curve, the flatness is very poor. It is difficult to represent in practical use, as shown in the table below:

3-combiner and bridge

1) Function: The main function of a combiner is to combine several signals.

2) Types: Combiners are divided into two types: dual frequency combiners and bridge combiners. Dual frequency combiners are divided into GSM/CDMA dual network combiners and GSM/DCS dual network combiners.

3) Working mechanism explanation: The working principle of a dual frequency combiner is similar to that of a duplexer, but it requires that the synthesized signal is not within the same frequency band range, such as G and C networks, G and D networks, and the combination between C and D networks can only be used with a dual frequency combiner. Moreover, dual frequency combiners have the characteristics of low insertion loss (some only have a few tenths of dB) and high isolation (greater than 70-90dB). Due to the second harmonic of the C network falling within the D network, the isolation degree between the C network and the D network is about 10 dB lower than other types.

Bridge combiners have combiner losses, such as 3dB for 2-in-1 combiners, and the isolation degree of bridge combiners is much lower than that of duplex combiners, usually only about 20dB.