Method for measuring gain of differential probe through four-port vector network analyzer

Abstract

The invention discloses a method for measuring the gain of a differential probe through a four-port vector network analyzer. The method comprises the steps of calibrating a reference plane, measuring an S parameter, obtaining a T parameter through a de-embedding method, and obtaining a differential voltage gain and a common-mode voltage gain through calculation. According to the method, the balance state is established between the positive and negative pole inputs of the differential probe, so that the influence of common-mode voltage can be effectively inhibited, the differential gain is measured more accurately, and balance measurement is realized; a measurement system is modeled through a de-embedding technology, so that the influence of a parasitic effect can be removed from a measurement result, and the measurement precision is further improved; meanwhile, the differential gain and the common-mode gain can be measured respectively, so that the common-mode rejection ratio can be calculated more accurately.

Description

Technical Field

[0001] The invention relates to the field of differential probe gain measurement, and in particular to a method for measuring the differential probe gain through a four-port vector network analyzer. Background Art

[0002] As the speed and bandwidth of baseband signals in all types of electronic systems today continue to increase, differential probe pairs have shown significant advantages over single-ended signal lines. Their immunity to strong noise and environmental coupling, broadband characteristics brought by the two-conductor TEM configuration, and low radiated emissions make them the preferred option for high-speed SerDes and fast signal transmission.

[0003] Although the traditional differential probe measurement method is suitable for some test circuits, it is an unbalanced method. There are both differential voltage and common-mode voltage between the positive and negative inputs, that is, the differential probe obtains output when both differential and common-mode inputs are present. This cannot restore the differential gain and common-mode gain of the differential probe in a balanced state, and it is even more impossible to obtain the common-mode rejection ratio of the differential probe. At the same time, the deviation between the measurement plane and the reference plane will inevitably result in a part of the transmission network not being embedded in the calibration process of the vector network analyzer, which will lead to the mixing of the measurement data, and the voltage gain will inevitably have a phase error. Summary of the invention

[0004] In view of the above-mentioned deficiencies in the prior art, the present invention provides a method for measuring differential probe gain using a four-port vector network analyzer, which eliminates the problem of measurement phase error caused by the offset between the measurement plane and the reference plane in the traditional differential probe test method.

[0005] In order to achieve the above-mentioned object of the invention, the technical solution adopted by the present invention is:

[0006] A method for measuring differential probe gain by a four-port vector network analyzer is provided, comprising the following steps:

[0007] S1. Calibrate the four-port vector network analyzer;

[0008] S2. Construct a four-port test fixture; the four-port test fixture includes a first interface, a second interface, a third interface and a fourth interface, the first interface and the third interface are connected through a microstrip line, the second interface and the fourth interface are connected through a microstrip line, and the two microstrip lines are symmetrical about the horizontal axis to form a coupling line;

[0009] S3. Connect the two probes of the differential probe to the midpoint of the coupling line, and connect a 50-ohm load to the output end of the differential probe; connect the four ports of the four-port vector network analyzer to the four interfaces of the four-port test fixture, record the current S parameters and save them as an S4P file;

[0010] S4. Reconnect the third port of the four-port vector network analyzer to the output end of the differential probe, and disconnect the 50-ohm load connected to the output end of the differential probe; disconnect the second port and the fourth port of the test fixture from the vector network analyzer, and connect the vacant port of the test fixture to the 50-ohm load; leave the fourth port of the four-port vector network analyzer vacant, record the current S parameters and save them as an S3P file;

[0011] S5, mirroring the four-port test fixture to form a through calibration piece; replacing the four-port test fixture with the through calibration piece, using the same connection method as step S4 to obtain the current S parameters and save them as an S3P1 file;

[0012] S6. Add a microstrip line in the middle of the through calibration piece to form a line calibration piece; replace the four-port test fixture with the line calibration piece, use the same connection method as step S4 to obtain the current S parameters and save them as an S3P2 file;

[0013] S7. Calculate the half-side transmission parameters of the four-port test fixture according to the S3P1 file and the S3P2 file, and then obtain the voltage ratio between point C and point B, and record it as G CB ;

[0014] S8. Obtain the voltage ratio between point C and point A in differential mode according to the S4P file and record it as SDD 21 ;According to the S3P file, obtain the voltage ratio between point D and point A in differential mode and record it as SD 21 ; SD 21 *G CB / SDD 21 The result is taken as the differential mode gain of the differential probe;

[0015] S9. Obtain the voltage ratio between point C and point A in the common mode according to the S4P file and record it as SCC 21 ;According to the S3P file, obtain the voltage ratio between point D and point A in the common mode and record it as SC 21 SC 21 *G CB / SCC 21 The result is taken as the common-mode gain of the differential probe;

[0016] Among them, point A is the contact point between the differential line equivalent to the first interface and the second interface in the four-port test fixture and the four-port vector network analyzer; point B is the contact point between the differential probe and the four-port test fixture; point C is the contact point between the differential line equivalent to the third interface and the fourth interface in the four-port test fixture and the four-port vector network analyzer; point D is the output endpoint of the differential probe.

[0017] Furthermore, the specific method of step S7 includes the following sub-steps:

[0018] S7-1. Obtain the transmission parameter T of the through calibration component from the S3P1 file and the S3P2 file respectively. Mt Transmission parameter T of the line calibration piece Ml ;

[0019] S7-2, according to the formula:

[0020] T Mt =T A T Nt T B

[0021] T Ml =T A T Nl T B

[0022] Get the half-side transmission parameters T of the four-port test fixture A ; where T Nt is the unit matrix; T Nl is the transmission matrix of an ideal transmission line with a single length of l; T B is the transmission parameter of the other half of the four-port test fixture,

[0023] S7-3. Half-side transmission parameters T through the four-port test fixture A Get the voltage ratio between point C and point B and record it as G CB .

[0024] Furthermore, SDD 21 The calculation expression is:

[0025]

[0026] in is the voltage ratio between the third port and the second port of the four-port vector network analyzer in the S4P file; is the voltage ratio between the second port and the third port of the four-port vector network analyzer in the S4P file; is the voltage ratio between the fourth port and the first port of the four-port vector network analyzer in the S4P file; It is the voltage ratio between the fourth port and the second port of the four-port vector network analyzer in the S4P file.

[0027] Furthermore, SD 21 The calculation expression is:

[0028]

[0029] in The voltage ratio between the third port and the first port of the four-port vector network analyzer in the S3P file; It is the voltage ratio between the third port and the second port of the four-port vector network analyzer in the S3P file.

[0030] Furthermore, SCC 21 The calculation expression is:

[0031]

[0032] in is the voltage ratio between the third port and the first port of the four-port vector network analyzer in the S4P file; is the voltage ratio between the third port and the second port of the four-port vector network analyzer in the S4P file; is the voltage ratio between the fourth port and the first port of the four-port vector network analyzer in the S4P file; It is the voltage ratio between the fourth port and the second port of the four-port vector network analyzer in the S4P file.

[0033] Furthermore, SC 21 The calculation expression is:

[0034]

[0035] in is the voltage ratio between the third port and the first port of the four-port vector network analyzer in the S4P file; It is the voltage ratio between the third port and the second port of the four-port vector network analyzer in the S4P file.

[0036] The beneficial effects of the present invention are:

[0037] 1. This method can effectively suppress the influence of common-mode voltage by establishing a balanced state between the positive and negative inputs of the differential probe, thereby more accurately measuring the differential gain and achieving balanced measurement; and by modeling the measurement system through de-embedding technology, the influence of parasitic effects can be removed from the measurement results, further improving the measurement accuracy; at the same time, this method can measure the differential gain and common-mode gain separately, thereby more accurately calculating the common-mode rejection ratio.

[0038] 2. The measurement of differential gain and common-mode gain are performed separately on the same set of boards. There is no need to change the test fixture, the number of measurements is relatively reduced, and the measurement error can be reduced.

[0039] 3. This method does not require a balun when measuring differential gain. The test fixture is only a component-free PCB board printed with microstrip differential lines, which greatly reduces the cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 is a schematic diagram of the process of this method;

[0041] Figure 2 is the equivalent circuit diagram of this method;

[0042] Figure 3 To measure differential gain Figure 2 Equivalent diagram of ;

[0043] Figure 4 This is the simulation schematic diagram of this method;

[0044] Figure 5 This is the simulation result diagram of the two-port transmission coefficient in the four-port differential mode;

[0045] Figure 6 This is the simulation result diagram of the two-port transmission coefficient in the four-port common mode;

[0046] Figure 7 This is the simulation result diagram of the two-port transmission coefficient in the three-port differential mode;

[0047] Figure 8 This is the simulation result diagram of the two-port transmission coefficient in the three-port common mode;

[0048] Fig. 9 This is the half-side simulation schematic diagram of the four-port test fixture;

[0049] Fig.10 This is a comparison chart of the amplitude between the test and the actual value in four-port differential mode;

[0050] Fig.11 This is the phase comparison diagram between the test and the actual phase in four-port differential mode;

[0051] Fig.12 This is a comparison chart of the amplitude between the test and the actual under four-port common mode;

[0052] Fig.13 This is the phase comparison diagram between the test and the actual phase in the four-port common mode;

[0053] Fig.14 Schematic diagram of the simulation of line calibration and through calibration. DETAILED DESCRIPTION

[0054] The specific implementation modes of the present invention are described below so that those skilled in the art can understand the present invention. However, it should be clear that the present invention is not limited to the scope of the specific implementation modes. For those of ordinary skill in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the attached claims, these changes are obvious, and all inventions and creations utilizing the concept of the present invention are protected.

[0055] like Figure 1 As shown, the method for measuring the differential probe gain by a four-port vector network analyzer includes the following steps:

[0056] S1. Calibrate the four-port vector network analyzer;

[0057] S2. Construct a four-port test fixture; the four-port test fixture includes a first interface, a second interface, a third interface and a fourth interface, the first interface and the third interface are connected through a microstrip line, the second interface and the fourth interface are connected through a microstrip line, and the two microstrip lines are symmetrical about the horizontal axis to form a coupling line;

[0058] S3. Connect the two probes of the differential probe to the midpoint of the coupling line, and connect a 50-ohm load to the output end of the differential probe; connect the four ports of the four-port vector network analyzer to the four interfaces of the four-port test fixture, record the current S parameters and save them as an S4P file;

[0059] S4. Reconnect the third port of the four-port vector network analyzer to the output end of the differential probe, and disconnect the 50-ohm load connected to the output end of the differential probe; disconnect the second port and the fourth port of the test fixture from the vector network analyzer, and connect the vacant port of the test fixture to the 50-ohm load; leave the fourth port of the four-port vector network analyzer vacant, record the current S parameters and save them as an S3P file;

[0060] S5, mirroring the four-port test fixture to form a through calibration piece; replacing the four-port test fixture with the through calibration piece, using the same connection method as step S4 to obtain the current S parameters and save them as an S3P1 file;

[0061] S6. Add a microstrip line in the middle of the through calibration piece to form a line calibration piece; replace the four-port test fixture with the line calibration piece, use the same connection method as step S4 to obtain the current S parameters and save them as an S3P2 file;

[0062] S7. Calculate the half-side transmission parameters of the four-port test fixture according to the S3P1 file and the S3P2 file, and then obtain the voltage ratio between point C and point B, and record it as G CB ;

[0063] S8. Obtain the voltage ratio between point C and point A in differential mode according to the S4P file and record it as SDD 21 ;According to the S3P file, obtain the voltage ratio between point D and point A in differential mode and record it as SD 21 ; SD 21 *G CB / SDD 21 The result is taken as the differential mode gain of the differential probe;

[0064] S9. Obtain the voltage ratio between point C and point A in the common mode according to the S4P file and record it as SCC 21 ;According to the S3P file, obtain the voltage ratio between point D and point A in the common mode and record it as SC 21 SC 21 *G CB / SCC 21 The result is taken as the common-mode gain of the differential probe;

[0065] Among them, point A is the contact point between the differential line equivalent to the first interface and the second interface in the four-port test fixture and the four-port vector network analyzer; point B is the contact point between the differential probe and the four-port test fixture; point C is the contact point between the differential line equivalent to the third interface and the fourth interface in the four-port test fixture and the four-port vector network analyzer; point D is the output endpoint of the differential probe.

[0066] In the specific implementation process, the purpose of calibrating the four-port vector network analyzer is to eliminate the systematic errors of each port of the four-port vector network analyzer, including impedance mismatch, transmission loss and phase delay. This process can be performed using a four-port calibration piece or a single-port calibration piece. Using a four-port calibration piece is the most convenient calibration method. Connect the four-port calibration piece to the four ports of the four-port vector network analyzer, and then calibrate according to the instrument prompts. If there is no four-port calibration piece, you can also use a single-port calibration piece to calibrate each port one by one. First, connect a cable with a 500hm characteristic impedance to the port of the four-port vector network analyzer, and then connect the single-port calibration piece to the other end of the cable. After completing the calibration according to the instrument prompts, remove the calibration piece and repeat the same operation for the other ports. After completing the port calibration, the four ports of the four-port vector network analyzer need to be connected to the four-port test fixture, which is used to connect the device under test and ensure the stability of signal transmission.

[0067] In the specific implementation process, the simulation schematic diagram of the line calibration component and the through calibration component is as follows Fig.14 As shown in the figure, the four ports P01, P02, P03, P04 on the left and the microstrip line form a line calibration component; the four ports P05, P06, P07, P08 on the right and the microstrip line form a through calibration component. The two ports on the same side of the calibration component are differential input or output ports. If P03 and P04 are differential input ports, then P01 and P02 are differential output ports of the line calibration component. The same applies to the through calibration component.

[0068] like Figure 2As shown in the figure, when measuring S4P, the four ports of the test fixture, Port 1, Port 2, Port 3, and Port 4, are connected to the four ports of the four-port vector network analyzer respectively. At this time, the front-end probe of the differential probe is connected to the coupling line of the four-port test fixture, and the output end of the differential probe is connected to a 50Ohm load. When measuring S3P, the front-end probe of the differential probe is connected to the coupling line, and the ports connecting the four-port test fixture to the four-port vector network analyzer become Port 1, Port 2, and Port 5. Figure 2 Here, 50Ohm represents the equivalent impedance of the load and the four-port vector network analyzer.

[0069] The four-port test fixture is a simple differential microstrip line, and is a symmetrical structure about the horizontal axis on the PCB like the connector. The contact point of the differential probe is located on the vertical axis, that is, the midpoint of the two microstrip lines. In differential signal transmission testing, it is crucial to accurately measure the characteristics of the signal. However, due to its inherent three-port structure, the traditional differential probe will introduce imbalance problems and affect the accuracy of the test results, so the present embodiment adopts a de-embedding method. Since conventional de-embedding methods are difficult to support high bandwidth, the present embodiment adopts TRL de-embedding. It is an option to equate the four-port test fixture to a cascade of two symmetrical four-port transmission networks, because the T matrix of the four-port transmission network must have an inverse matrix that can be used for de-embedding.

[0070] Since the four-port test fixture is symmetrical about the horizontal axis, the even-odd mode analysis can prove that the original four-port S parameters have the following properties:

[0071] S 11 =S 22 ,S 33 =S 44

[0072] S 12 =S 21 ,S 34 =S 43

[0073] S 13 =S 24 ,S 31 =S 42

[0074] S 14 =S 31 ,S 41 =S 32

[0075] That is, it can be considered that ports 1 and 2 are exactly the same, and ports 3 and 4 are exactly the same. Therefore, the original four-port S parameter matrix becomes:

[0076]

[0077] Transform it into a differential mixed S-parameter matrix:

[0078]

[0079] in:

[0080] The conversion parameters for both differential and common modes are zero, and the parameters for different pure modes are separate. This means that the differential and common mode parameters are independent of each other. Since the four-port test fixture has horizontal symmetry, the mode conversion parameters can be omitted by assuming horizontal symmetry, simplifying the propagation mode to pure differential mode and pure common mode. This means that in a horizontally symmetrical test, if only the differential S parameters are de-embedded, this symmetry can reduce each 4×4 matrix to a 2×2 matrix and simplify the 4-port network to a two-port network, which can be de-embedded by TRL to obtain the complete half-side S parameters. The same is true when de-embedding the common mode S parameters.

[0081] Therefore, the four-port network can be equivalent to a two-port network in differential mode and common mode, and the attached Figure 1 Simplify and eliminate the influence of the four-port test fixture. This embodiment introduces the measurement equivalent two-port network in differential mode and common mode respectively:

[0082] To test the S parameters of the fixture, the four-port test fixture is mirrored and symmetrical, and a test circuit board that can be directly measured is made including the adapter (that is, the through calibration piece). At the same time, a set of line calibration pieces are processed within the working frequency band (that is, a microstrip line is added in the middle of the through calibration piece, which is regarded as an ideal transmission line with known transmission parameters). The connection method of the test fixture is the same as the connection method of measuring the S3P file. As a result, the following two sets of measurement parameters are obtained:

[0083] T Mt =T A T Nt T B

[0084] T Ml =T A T Nl T B

[0085] Where T A is the half-side transmission parameter of the four-port test fixture; T Nt is the unit matrix; T Mt is the transmission parameter of the thru calibration component; T Ml is the transmission parameter of the line calibration component; T Nl is the transmission matrix of an ideal transmission line with a single length of l; TB is the transmission parameter of the other half of the four-port test fixture,

[0086] When measuring differential gain, Figure 2 Can be equivalent to Figure 3 . Figure 3 Port D1 in Figure 2 Port 1 and port 2 are equivalent to the differential port, port D2 is the differential port equivalent to port 3 and port 4, and the other ports are the same. In order to achieve the de-embedding of the test fixture, Figure 2 The four-port test fixture in the example is equivalent to two half-side test fixtures, using the T D (i.e. T A ) matrix representation, (i.e. T B ) is its generalized reverse transmission matrix. In this way, the differential probe connected to point B can be regarded as a pure test result without being affected by the test fixture. For example, the load of the subsequent stage has been determined, and the voltage division ratio has also been determined, so the voltage ratio between point C and point B can be obtained and recorded as G CB .

[0087] exist Figure 3 In the figure, since the four-port analysis needs to be simplified to a two-port analysis, point A is the connection point between the differential line equivalent to Port 1 and Port 2 and the 50Ohm load, point B is the contact point between the differential probe and the test fixture, point C is the connection point between the differential line equivalent to Port 3 and Port 4 and the 50Ohm load, and point D is the connection point between the differential probe and the 50Ohm load. Figure 3 Except for point D, the voltages at points A, B, and C are all in differential form. Therefore, you only need to find the voltage ratio between point C and point A, the voltage ratio between point D and point A, and the voltage ratio between point C and point B in order to get the voltage ratio between point D and point B, that is, the differential voltage gain of the differential probe.

[0088] When measuring the S4P file, the voltage ratio between point C and point A is actually S 21 , that is, SDD 21 , by converting the four-port S parameters in the S4P file to obtain the S parameters in the differential mode, the conversion formula is as follows:

[0089]

[0090] in is the voltage ratio between the third port and the second port of the four-port vector network analyzer in the S4P file; is the voltage ratio between the second port and the third port of the four-port vector network analyzer in the S4P file; is the voltage ratio between the fourth port and the first port of the four-port vector network analyzer in the S4P file; It is the voltage ratio between the fourth port and the second port of the four-port vector network analyzer in the S4P file.

[0091] When measuring the S3P file, the voltage ratio between point D and point A is actually the S 21 , namely SD 21 , by converting the four-port S parameters of the S3P file to obtain the S parameters in the differential mode, the conversion formula is as follows:

[0092]

[0093] in The voltage ratio between the third port and the first port of the four-port vector network analyzer in the S3P file; It is the voltage ratio between the third port and the second port of the four-port vector network analyzer in the S3P file.

[0094] Therefore, the voltage ratios of point C to point A and point D to point A have been measured, and only need to be obtained by TRL de-embedding. The voltage ratio between point C and point B can be obtained through mathematical conversion, and then the differential mode gain can be obtained.

[0095] The calculation of common-mode gain can be obtained in the same way. The test fixture used is also the same. In the common-mode mode, the calculation expression of the voltage ratio between point C and point A is:

[0096]

[0097] in is the voltage ratio between the third port and the first port of the four-port vector network analyzer in the S4P file; is the voltage ratio between the third port and the second port of the four-port vector network analyzer in the S4P file; is the voltage ratio between the fourth port and the first port of the four-port vector network analyzer in the S4P file; It is the voltage ratio between the fourth port and the second port of the four-port vector network analyzer in the S4P file.

[0098] In common mode, the voltage ratio between point D and point A is calculated as:

[0099]

[0100] in is the voltage ratio between the third port and the first port of the four-port vector network analyzer in the S4P file; It is the voltage ratio between the third port and the second port of the four-port vector network analyzer in the S4P file.

[0101] In one embodiment of the present invention, the simulation principle diagram of the method is as follows Figure 4 As shown in the figure, two sections of differential microstrip lines are used to simulate the four-port test fixture, and parallel capacitors are added to simulate the transmission line with high characteristic capacitive reactance, while ensuring frequency selectivity. The differential probe simulation uses a cascade network of 25k ideal resistors and fully differential amplifier ADL5580, just like the two-port, and its output is connected to Term5, which is equivalent to the fifth port of vector network analysis. Ports 1, 2, 3, and 4 form a four-port network, corresponding to the S4P file measured in the measurement of step 3, which are converted into two-port transmission coefficients in differential and common mode of the four-port network respectively; ports 1, 2, and 5 form a three-port network, corresponding to the S3P file measured in the measurement of step 5, which are converted into two-port transmission coefficients under differential input and common mode input of the three-port network respectively.

[0102] Through Figure 4 The circuit shown is simulated by S parameters to obtain the two-port transmission coefficients of the four-port network in differential mode and common mode. Figure 5 This is the simulation result diagram of the two-port transmission coefficient in the four-port differential mode. Figure 6 This is the simulation result diagram of the two-port transmission coefficient in the four-port common mode. Figure 7 This is the simulation result diagram of the two-port transmission coefficient in the three-port differential mode. Figure 8 This is the simulation result diagram of the two-port transmission coefficient in the three-port common mode.

[0103] In this embodiment, the half-side simulation schematic diagram of the four-port test fixture for solving the voltage ratio between point C and point B is as follows: Fig. 9 As shown in the figure, the comparison between the actual amplitude and phase of this method in differential mode and common mode is as follows: Fig.10 , Fig.11 , Fig.12 and Fig.13 As shown in the figure, it can be seen that the test value obtained by this method coincides with the curve of the actual value, and there is no phase error, which verifies the feasibility of this method.

Claims

1. A method for measuring differential probe gain using a four-port vector network analyzer, characterized in that: The following steps are involved: S1. Calibrate the four-port vector network analyzer; S2. Construct a four-port test fixture; the four-port test fixture includes a first interface, a second interface, a third interface and a fourth interface, the first interface and the third interface are connected through a microstrip line, the second interface and the fourth interface are connected through a microstrip line, and the two microstrip lines are symmetrical about the horizontal axis to form a coupling line; S3. Connect the two probes of the differential probe to the midpoint of the coupling line, and connect a 50-ohm load to the output end of the differential probe; connect the four ports of the four-port vector network analyzer to the four interfaces of the four-port test fixture, record the current S parameters and save them as an S4P file; S4. Reconnect the third port of the four-port vector network analyzer to the output end of the differential probe, and disconnect the 50-ohm load connected to the output end of the differential probe; disconnect the second port and the fourth port of the test fixture from the vector network analyzer, and connect the vacant port of the test fixture to the 50-ohm load; leave the fourth port of the four-port vector network analyzer vacant, record the current S parameters and save them as an S3P file; S5, mirroring the four-port test fixture to form a through calibration piece; replacing the four-port test fixture with the through calibration piece, using the same connection method as step S4 to obtain the current S parameters and save them as an S3P1 file; S6. Add a microstrip line in the middle of the through calibration piece to form a line calibration piece; replace the four-port test fixture with the line calibration piece, use the same connection method as step S4 to obtain the current S parameters and save them as an S3P2 file; S7. Calculate the half-side transmission parameters of the four-port test fixture according to the S3P1 file and the S3P2 file, and then obtain the voltage ratio between point C and point B, and record it as G CB ; S8. Obtain the voltage ratio between point C and point A in differential mode according to the S4P file and record it as SDD 21 ;According to the S3P file, obtain the voltage ratio between point D and point A in differential mode and record it as SD 21 ; SD 21 *G CB / SDD 21 The result is taken as the differential mode gain of the differential probe; S9. Obtain the voltage ratio between point C and point A in the common mode according to the S4P file and record it as SCC 21 ;According to the S3P file, obtain the voltage ratio between point D and point A in the common mode and record it as SC 21 SC 21 *G CB / SCC 21 The result is taken as the common-mode gain of the differential probe; Among them, point A is the contact point between the differential line equivalent to the first interface and the second interface in the four-port test fixture and the four-port vector network analyzer; point B is the contact point between the differential probe and the four-port test fixture; point C is the contact point between the differential line equivalent to the third interface and the fourth interface in the four-port test fixture and the four-port vector network analyzer; point D is the output endpoint of the differential probe.

2. The method for measuring differential probe gain by a four-port vector network analyzer according to claim 1, characterized in that: The specific method of step S7 includes the following sub-steps: S7-1. Obtain the transmission parameter T of the through calibration component from the S3P1 file and the S3P2 file respectively. Mt Transmission parameter T of the line calibration piece Ml ; S7-2, according to the formula: T Mt =T A T Nt T B T Ml =T A T Nl T B Get the half-side transmission parameters T of the four-port test fixture A ; where T Nt is the unit matrix; T Nl is the transmission matrix of an ideal transmission line with a single length of l; T B is the transmission parameter of the other half of the four-port test fixture, S7-3. Half-side transmission parameters T through the four-port test fixture A Get the voltage ratio between point C and point B and record it as G CB .

3. The method for measuring differential probe gain by a four-port vector network analyzer according to claim 1, characterized in that: SDD 21 The calculation expression is: in is the voltage ratio between the third port and the second port of the four-port vector network analyzer in the S4P file; is the voltage ratio between the second port and the third port of the four-port vector network analyzer in the S4P file; is the voltage ratio between the fourth port and the first port of the four-port vector network analyzer in the S4P file; It is the voltage ratio between the fourth port and the second port of the four-port vector network analyzer in the S4P file.

4. The method for measuring differential probe gain by a four-port vector network analyzer according to claim 1, characterized in that: SD 21 The calculation expression is: in The voltage ratio between the third port and the first port of the four-port vector network analyzer in the S3P file; It is the voltage ratio between the third port and the second port of the four-port vector network analyzer in the S3P file.

5. The method for measuring differential probe gain by a four-port vector network analyzer according to claim 1, characterized in that: SCC 21 The calculation expression is: in is the voltage ratio between the third port and the first port of the four-port vector network analyzer in the S4P file; is the voltage ratio between the third port and the second port of the four-port vector network analyzer in the S4P file; is the voltage ratio between the fourth port and the first port of the four-port vector network analyzer in the S4P file; It is the voltage ratio between the fourth port and the second port of the four-port vector network analyzer in the S4P file.

6. The method for measuring differential probe gain by a four-port vector network analyzer according to claim 1, characterized in that: SC 21 The calculation expression is: in is the voltage ratio between the third port and the first port of the four-port vector network analyzer in the S4P file; It is the voltage ratio between the third port and the second port of the four-port vector network analyzer in the S4P file.

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