Measurement System and Method for Reflection Coefficient of Microwave and Millimeter-Wave Equivalent Sources

Abstract

The invention discloses a microwave millimeter wave equivalent source reflection coefficient measurement system and method, wherein the system only includes a vector network analyzer and two single-port devices with different reflection characteristics, and then by connecting the two output ports of the three-port device to be measured to the two test ports of the vector network analyzer, according to the scattering parameter equation of the three-port device, a general expression of the equivalent source reflection coefficient is obtained; by connecting two single-port devices with different reflection characteristics to the input port of the three-port device respectively through the general expression of the equivalent source reflection coefficient, the first and second expressions of the equivalent source reflection coefficient with reflection characteristics A and B can be obtained respectively; thus, by combining the first expression of the equivalent source reflection coefficient and the second expression of the equivalent source reflection coefficient, the final expression of the equivalent source reflection coefficient is obtained. The invention requires less equipment, is simple to operate and calculate, and can simplify the uncertainty evaluation, which is conducive to solving the mismatch and measurement uncertainty evaluation problems in power measurement.

Description

Technical Field

[0001] The present invention relates to the technical field of microwave / millimeter-wave measurement, and specifically provides a measurement system and method for the reflection coefficient of a microwave millimeter-wave equivalent source. Background Art

[0002] At present, with the continuous innovation and progress of integrated circuits, devices are gradually evolving towards miniaturization and microminiaturization, and the operating frequency band is also continuously expanding towards higher frequency bands. Among them, the manufacturing and application in the microwave millimeter-wave frequency band are the most extensive. In the process of power measurement, mismatch is the main part determining the uncertainty of microwave millimeter-wave power measurement. Reducing and accurately evaluating the influence of mismatch is an inevitable requirement for reducing the uncertainty of power measurement. A common method is to introduce a three-port device (generally a directional coupler or a two-resistor power divider, except for a three-resistor power divider) between the signal source and the device under test, and reduce the reflection coefficient corresponding to the signal source end by constructing a stable-amplitude signal source system or using the power ratio method, thereby reducing the mismatch. Among them, the factor corresponding to the signal source reflection coefficient in the mismatch term derived by the power ratio method is the same as the expression of the signal source reflection coefficient in the mismatch term derived by the stable-amplitude signal source system. Therefore, it is called the equivalent source reflection coefficient, denoted as Γ ge .

[0003] At present, some general measurement methods for the equivalent source reflection coefficient can be used to obtain the equivalent source reflection coefficient, which can be divided into the following four categories:

[0004] (1) Method based on obtaining the scattering parameters of the device: This method is currently the most mainstream measurement method for the equivalent source reflection coefficient. The expression of the equivalent source reflection coefficient composed of four specific scattering parameters of the three-port device is directly derived from the scattering parameter equations of the three-port device, and it can be seen that the equivalent source reflection coefficient is only related to the scattering parameters of the three-port device itself. The equivalent source reflection coefficient can be obtained according to a specific calculation formula, and the specific calculation formula is expressed as:

[0005]

[0006] Among them, S 22 , S 21 , S 31 and S 32 are the scattering parameters between the ports in the three-port device, which can be directly measured by a multi-port vector network analyzer or directly measured by combining a two-port vector network analyzer with a matching load. In addition, based on this principle, a measurement method similar to obtaining the equivalent source reflection coefficient by obtaining the scattering parameters has also been derived, such as the Shimaoka K method. The essence of this method is still based on the above specific calculation formula, but uses the derived formula to replace S 32 / S 31This item does not apply to the measurement of the equivalent source reflection coefficient related to the directional coupler. Therefore, the method of obtaining the scattering parameters of the device has various degrees of cumbersome operation processes, and the results depend on the measurement accuracy of the scattering parameters, and the uncertainty evaluation is complex.

[0007] (2) Based on the power ratio method: This method is based on the power transfer standard method and derives the power ratio expression of two output ports in a three-port device as follows:

[0008]

[0009] where P2 and P3 are the powers at the two output ports of the three-port device, K c is a constant coefficient related to the transfer standard, Γ L is the reflection coefficient of the connected load, |1 - Γ ge Γ L | 2 is the mismatch term. For each frequency point, by changing the load reflection coefficient in the mismatch term, an analytical equation system is constructed to obtain the equivalent source reflection coefficient. In addition, by neglecting the higher-order small terms (|Γ ge | 2 |Γ L | 2 ) in the mismatch term, a mismatched load is constructed and the frequency is changed to make the load phase change continuously, and the equivalent source reflection coefficient can also be obtained. However, this type of method requires a large number of devices, complex operations, generally requires redundant measurements, and depends to a large extent on the measurement accuracy, and it is difficult to obtain a rigorous analytical result.

[0010] (3) Based on the port amplitude stabilization method: This method is based on the scattering parameter equation of a three-port device. When a certain output port is determined as the calculation port of the equivalent source reflection coefficient, the power at the other output port is made zero or the power change amount is zero, and the reflection coefficient at its calculation port is directly measured by a reflection coefficient measuring device, which is the equivalent source reflection coefficient. However, the system setup and operation of this method are complex and not conducive to automatic sweep frequency measurement.

[0011] (4) Based on the single-port calibration method of the network analyzer: This method constructs a single-port calibration system for the network analyzer and substitutes the equivalent source reflection coefficient into the calibration result in the form of a source matching error term. By completing the single-port calibration, the obtained source matching error term is the equivalent source reflection coefficient. Although this method belongs to direct measurement, it requires a very good understanding of the calibration principle of the network analyzer, and the network analyzer must have an external internal receiver interface to facilitate the construction of a special single-port calibration system. Summary of the Invention

[0012] In view of the above problems, the present invention proposes a measurement system and method for the reflection coefficient of a microwave and millimeter-wave equivalent source, which requires fewer devices, has simple operations and calculations, and can simplify the uncertainty evaluation, facilitating the solution of the mismatch problem and the measurement uncertainty evaluation problem in power measurement.

[0013] A measurement system for the reflection coefficient of a microwave and millimeter-wave equivalent source according to the present invention includes only a vector network analyzer and two single-port devices with different reflection characteristics. The specific measurement method is as follows:

[0014] Step 1: Build a measurement system for the reflection coefficient of a microwave and millimeter-wave equivalent source;

[0015] Define the two output ports of the three-port device under test as output port 1 and output port 2. Calibrate the vector network analyzer for two ports, and connect output port 1 and output port 2 of the three-port device under test to the two test ports of the vector network analyzer respectively.

[0016] Step 2: According to the scattering equation of the three-port device, the general expression for the equivalent source reflection coefficient is obtained as:

[0017]

[0018] In the formula, Γ ge is the equivalent source reflection coefficient corresponding to a certain output port of the three-port device, which is an unknown quantity; and are the reflection coefficient measured by test port 1 of the vector network analyzer and the transmission coefficient from the signal transmitted by test port 1 to test port 2 measured by test port 2 respectively when the input port of the three-port device is connected to a single-port device with a reflection characteristic Γx; k is a constant coefficient related to the connection state of the three-port device and is not affected by the change of the connected single-port device.

[0019] Step 3: Connect the input port of the three-port device to a single-port device with a reflection characteristic A. According to the general expression for the equivalent source reflection coefficient given in Step 2, the first expression for the equivalent source reflection coefficient is obtained as:

[0020]

[0021] Step 4: Connect the input port of the three-port device to a single-port device with a reflection characteristic B. According to the general expression for the equivalent source reflection coefficient given in Step 2, the second expression for the equivalent source reflection coefficient is obtained as:

[0022]

[0023] Step 5: Combine the first and second expressions of the equivalent source reflection coefficient given in Step 3 and Step 4, eliminate the constant coefficient k, and obtain the final equivalent source reflection coefficient as follows:

[0024]

[0025] The advantages of the present invention are as follows:

[0026] 1. For the measurement system of the equivalent source reflection coefficient proposed by the present invention, only one vector network analyzer with two-port measurement is required, and the network analyzer does not need to have an external internal receiver interface; only two single-port devices with different reflection characteristics are required for the connection components, with few devices and low cost.

[0027] 2. For the measurement method of the equivalent source reflection coefficient proposed by the present invention, based on the separation characteristics of the output ports of the three-port device, different reflection conditions are constructed by sequentially connecting devices with different reflection characteristics to the input port to obtain the equivalent source reflection coefficient, and generally no redundant measurement is required, and the operation and measurement are simple and convenient; the equivalent source reflection coefficients corresponding to two output ports in the three-port device can be directly obtained by one measurement, achieving two goals with one action.

[0028] 3. In the measurement method of the equivalent source reflection coefficient proposed by the present invention, it can be deduced from the final expression of the equivalent source reflection coefficient that the influence quantity of the transmission coefficient-related uncertainty can be partially offset, which is beneficial to weakening the influence of the mismatch term on the power measurement, and further beneficial to the evaluation of the measurement uncertainty of the power result. Description of the Drawings

[0029] Figure 1 It is a schematic diagram of the measurement system of the equivalent source reflection coefficient of microwave and millimeter wave of the present invention.

[0030] Figure 2 It is a flowchart of the measurement method of the equivalent source reflection coefficient of microwave and millimeter wave of the present invention.

[0031] Figure 3(a) is a measurement result diagram of the modulus value of the equivalent source reflection coefficient.

[0032] Figure 3(b) is a measurement result diagram of the phase of the equivalent source reflection coefficient.

[0033] Figure 4(a) is a diagram of the experimental standard deviation result of the modulus value of the equivalent source reflection coefficient.

[0034] Figure 4(b) is a diagram of the experimental standard deviation result of the phase of the equivalent source reflection coefficient. Detailed Embodiments

[0035] The present invention will be further described in detail below with reference to the accompanying drawings.

[0036] The measurement system for the reflection coefficient of the microwave and millimeter-wave equivalent source of the present invention includes a vector network analyzer and two single-port devices with different reflection characteristics, such as Figure 1 shown.

[0037] The vector network analyzer adopts a two-port vector network analyzer or a multi-port vector network analyzer without an external internal receiver interface; the two test ports of the vector network analyzer are used to connect the two output ports of the three-port device.

[0038] For the two single-port devices with different reflection characteristics, it is not necessary to know the accurate value of their reflection coefficients. Just select two single-port devices with different reflection characteristics, and it is recommended that the difference in reflection characteristics is large, such as the combination of a short-circuit device and an open-circuit device in a calibration component; different reflections of the incident signal can be realized through the two single-port devices with different reflection characteristics, so as to change the reflection coefficients and transmission coefficients at the two output ports of the three-port device measured by the vector network analyzer.

[0039] Through the above measurement system, based on the separation characteristics of the output ports of the three-port device, by sequentially connecting two single-port devices with different reflection characteristics to the input port of the three-port device, the amplitude and phase of the equivalent source reflection coefficient corresponding to the two output ports of the three-port device can be obtained simultaneously. The specific detection principle is as follows:

[0040] It can be deduced from the scattering parameter equation of the three-port device that the output voltages (b2, b3) of its two output ports and the output port reflection voltage a2 corresponding to the equivalent source reflection coefficient satisfy the following relationship:

[0041]

[0042] Among them, k is a constant coefficient related to the connection state of the three-port device and is not affected by the change of the connected single-port device. The expression in the brackets is the calculation formula for the equivalent source reflection coefficient based on the method of obtaining the scattering parameters of the device. Through the above formula, it can be obtained:

[0043]

[0044] Since the left side of the equation is the expression of the equivalent source reflection coefficient obtained by the method of acquiring the scattering parameters of the device, the equivalent source reflection coefficient can be obtained by the reflection coefficient of the output port corresponding to the measured equivalent source reflection coefficient on the right side of the equation and the transmission coefficient between the two output ports. And it can be known therefrom that the physical meaning of the equivalent source reflection coefficient can be expressed as the separation degree of the voltages satisfying the proportional coefficient at the two output ports caused by the unit reflection voltage at a certain output port in the three-port device, which is used to characterize the device characteristics. When the output port corresponding to the equivalent source reflection coefficient is connected to a non-reflective load, a2 = 0, that is, the voltages b2 and b3 at the two output ports satisfy the proportional relationship k; when the output port corresponding to the equivalent source reflection coefficient is connected to a load with reflection characteristics, the voltages b2 and b3 at the two output ports do not satisfy the proportional relationship k, but satisfy the following conditions:

[0045]

[0046] Therefore, by measuring the reflection coefficient of the output port corresponding to the equivalent source reflection coefficient and the transmission coefficient between the two output ports, and constructing two different reflection situations at the input port to eliminate the proportional coefficient k, the final expression of the equivalent source reflection coefficient can be obtained.

[0047] The specific steps of the measurement method of the equivalent source reflection coefficient of microwave and millimeter wave in the present invention are as follows:

[0048] S1: Build a measurement system for the equivalent source reflection coefficient of microwave and millimeter wave;

[0049] Define the two output ports of the three-port device under test as output port 1 and output port 2, perform two-port calibration on the vector network analyzer, and connect output port 1 and output port 2 of the three-port device under test to the two test ports of the vector network analyzer respectively.

[0050] S2: Obtain the general expression of the equivalent source reflection coefficient according to the scattering equation of the three-port device;

[0051] The equivalent source reflection coefficient satisfies the following general expression:

[0052]

[0053] In the formula, Γ ge is the equivalent source reflection coefficient corresponding to a certain output port of the three-port device, which is an unknown quantity; and are the reflection coefficient measured by test port 1 of the vector network analyzer and the transmission coefficient from the signal transmitted from test port 1 to test port 2 measured by test port 2 respectively when the input port of the three-port device is connected to a single-port device with reflection characteristics Γx; k is a constant coefficient related to the connection state of the three-port device and is not affected by the change of the connected single-port device.

[0054] S3: Connect the input port of the three-port device to a single-port device with a reflection characteristic A. According to the general expression of the equivalent source reflection coefficient given in Step 2, obtain the first expression of the equivalent source reflection coefficient;

[0055] Taking the single-port device as a short circuit (short) as an example, the first expression of the equivalent source reflection coefficient is:

[0056]

[0057] S4: Connect the input port of the three-port device to a single-port device with a reflection characteristic B. According to the general expression of the equivalent source reflection coefficient given in Step 2, obtain the second expression of the equivalent source reflection coefficient;

[0058] Taking the single-port device as an open circuit (open) as an example, the second expression of the equivalent source reflection coefficient is:

[0059]

[0060] S5: Simultaneously solve the first expression and the second expression of the equivalent source reflection coefficient given in Step S3 and Step S4, and eliminate the constant coefficient k to obtain the final expression of the equivalent source reflection coefficient as:

[0061]

[0062] The equivalent source reflection coefficient obtained through the above steps is the equivalent source reflection coefficient at the output port connected to the first test port of the vector network analyzer in the three-port device; for the equivalent source reflection coefficient at the other output port in the three-port device, on the premise of ensuring that the connection relationship between the three-port device and the vector network analyzer in Step 1 remains unchanged, change S 21 to S 12 , S 11 to S 22 , that is:

[0063]

[0064] Perform direct measurement and calculation to obtain it. Among them, and are the reflection coefficient measured by the test port 2 of the vector network analyzer and the transmission coefficient from the signal transmitted from the test port 2 to the test port 1 measured by the test port 1 respectively when the input port of the three-port device is connected to a single-port device with a reflection characteristic Γx(short, open);

[0065] In summary, when the input ports of a three-port device are respectively connected to two single-port devices with different reflection characteristics, the equivalent source reflection coefficient at the output port can be obtained by measuring the reflection coefficients of the corresponding two output ports and the transmission coefficient between the ports.

[0066] The method for measuring the equivalent source reflection coefficient of the present invention in the microwave and millimeter-wave bands is in the range of 1 GHz - 67 GHz. The two connection device combinations used are a short-circuit device and an open-circuit device, a short-circuit device and a matched load, and an open-circuit device and a matched load. Fig. 3(a) is the measurement result diagram of the modulus of the equivalent source reflection coefficient, and Fig. 3(b) is the measurement result diagram of the phase of the equivalent source reflection coefficient. It can be seen that when the connection reflection device group is changed, the results of the equivalent source reflection coefficient calculated by the method of the present invention are highly consistent, and are also highly consistent with the results of the equivalent source reflection coefficient obtained by the method of obtaining the scattering parameters of the device.

[0067] Figs. 4(a) and 4(b) are the experimental standard deviation result diagrams of the modulus and phase of the equivalent source reflection coefficient for 6 repeated measurements in the embodiment of the present invention (using a short-circuit device + an open-circuit device). Fig. 4(a) is the experimental standard deviation result diagram of the modulus of the equivalent source reflection coefficient, and Fig. 4(b) is the experimental standard deviation result diagram of the phase of the equivalent source reflection coefficient. It can be seen that the experimental standard deviation of the modulus of the equivalent source reflection coefficient by the method of the present invention is below 0.0019, and when the modulus is relatively large (Γ ge ≥0.1), the experimental standard deviation of the phase is below 0.72°, showing good repeatability. In addition, from the mathematical model of the equivalent source reflection coefficient of the present invention, it can be deduced that the influence of the uncertainty of the transmission coefficient can be partially offset, that is, the parameters S 21 / S 12 measured by a network analyzer exist simultaneously in the upper and lower terms on the right side of the final expression, and the influence of the uncertainty of the parameter S 21 / S 12 can be partially offset when evaluating the uncertainty, thereby reducing the uncertainty of the parameter Γ ge , which is beneficial to power result correction and measurement uncertainty evaluation.

Claims

1. A method for measuring the reflection coefficient of a microwave and millimeter-wave equivalent source, characterized in that: The specific steps are as follows: Step 1: Build a measurement system for the reflection coefficient of the microwave and millimeter-wave equivalent source; Define the two output ports of the three-port device under test as Output Port 1 and Output Port 2, and perform two-port calibration on the vector network analyzer. Connect Output Port 1 and Output Port 2 of the three-port device under test to the two test ports of the vector network analyzer respectively; Step 2: According to the scattering equation of the three-port device, the general expression for the equivalent source reflection coefficient is obtained as: where Γ ge is the equivalent source reflection coefficient corresponding to a certain output port of the three-port device, which is an unknown quantity; and are the reflection coefficient measured at test port 1 of the vector network analyzer and the transmission coefficient from the signal transmitted from test port 1 to test port 2 measured at test port 2 respectively when the input port of the three-port device is connected to a one-port device with reflection characteristic Γx; k is a constant coefficient related to the connection state of the three-port device and is not affected by the change of the connected one-port device; Step 3: Connect the input port of the three-port device to a one-port device with reflection characteristic A. According to the general expression for the equivalent source reflection coefficient given in Step 2, the first expression for the equivalent source reflection coefficient is obtained as: Step 4: Connect the input port of the three-port device to a one-port device with reflection characteristic B. According to the general expression for the equivalent source reflection coefficient given in Step 2, the second expression for the equivalent source reflection coefficient is obtained as: Step 5: Combine the first expression and the second expression for the equivalent source reflection coefficient given in Step 3 and Step 4, and eliminate the constant coefficient k to obtain the final equivalent source reflection coefficient as: For the one-port device, there is no need to know the accurate value of its reflection coefficient. Just select two with different reflection characteristics; The obtained equivalent source reflection coefficient is the equivalent source reflection coefficient at the output port connected to the first test port of the vector network analyzer in the three-port device; for the equivalent source reflection coefficient at the other output port in the three-port device, on the premise of ensuring that the connection relationship between the three-port device and the vector network analyzer in step 1 remains unchanged, change S in the obtained equivalent source reflection coefficient expression 21 to S 12 , S 11 to S 22 , that is:

2. The measurement method of the reflection coefficient of the microwave and millimeter-wave equivalent source according to claim 1, wherein: The vector network analyzer uses a two-port vector network analyzer or a multi-port vector network analyzer that does not require an external internal receiver interface; 3. The measurement method of the microwave and millimeter-wave equivalent source reflection coefficient according to claim 1, characterized in that: The one-port device uses a short-circuit breaker and an open-circuit breaker with different reflection characteristics.

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