A method for measuring differential probe gain using a four-port vector network analyzer

Abstract

The present invention discloses a method for measuring differential probe gain using a four-port vector network analyzer. The method includes reference plane calibration, S-parameter measurement, T-parameter de-embedding, and differential voltage gain and common-mode voltage gain calculation. By establishing a balanced state between the positive and negative inputs of the differential probe, the method effectively suppresses the influence of common-mode voltage, enabling more accurate differential gain measurement and balanced measurement. Furthermore, by modeling the measurement system using de-embedding technology, the influence of parasitic effects can be removed from the measurement results, further improving measurement accuracy. Furthermore, the method can measure differential gain and common-mode gain separately, enabling more accurate calculation of the common-mode rejection ratio.

Description

Technical Field

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

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

[0003] While the traditional differential probe measurement method is suitable for some circuit testing scenarios, it is an unbalanced method. Both differential and common-mode voltages exist between the positive and negative inputs. This means the differential probe generates an output with both differential and common-mode inputs. This makes it impossible to restore the differential gain and common-mode gain of a balanced differential probe, and even less so, to determine the common-mode rejection ratio (CMRR). Furthermore, the deviation between the measurement plane and the reference plane inevitably results in portions of the transmission network not being de-embedded during the vector network analyzer's calibration process, leading to scrambling of the measurement data and unavoidable phase errors in the voltage gain. 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 measurement phase error problem caused by the offset between the measurement plane and the reference plane in traditional differential probe testing methods.

[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 using 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, wherein the first interface and the third interface are connected by a microstrip line, and the second interface and the fourth interface are connected by 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 coupled line and connect a 50-ohm load to the output 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 of the differential probe and disconnect the 50-ohm load connected to the output of the differential probe. Disconnect the second and fourth ports of the test fixture from the vector network analyzer and connect the unused ports of the test fixture to a 50-ohm load. Leave the fourth port of the four-port vector network analyzer unused, record the current S parameters, and save them as an S3P file.

[0011] S5. Mirror the four-port test fixture to form a through calibration piece. Replace the four-port test fixture with the through calibration piece, use 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 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 common mode and record it as SC 21 SC 21 *G CB / SCC 21 The result is 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 and second interfaces 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 and fourth interfaces 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 parameters of the through calibration component from the S3P1 file and the S3P2 file respectively. Transmission parameters of the calibration kit ;

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

[0020]

[0021]

[0022] Obtaining half-side transmission parameters of a four-port test fixture ;in is the identity matrix; The length of the single l The transmission matrix of an ideal transmission line; is the transmission parameter of the other half of the four-port test fixture, ;

[0023] S7-3, Half-side transmission parameters through a four-port test fixture 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; 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; 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; 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 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.

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

[0037] 1. This method effectively suppresses 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 differential gain and achieving balanced measurement. Furthermore, by modeling the measurement system through de-embedding technology, the influence of parasitic effects can be removed from the measurement results, further improving measurement accuracy. Furthermore, this method can measure 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 with printed microstrip differential lines, which greatly reduces costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 Schematic diagram of the process of this method;

[0041] Figure 2 This 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 principle 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 under the four-port common mode 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 under the three-port common mode mode;

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

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

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

[0051] Figure 12 This is a comparison chart of the amplitudes tested and actually achieved in four-port common-mode mode.

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

[0053] Figure 14 This is a simulation diagram of the line calibration component and the through calibration component. DETAILED DESCRIPTION

[0054] The specific embodiments of the present invention are described below to facilitate understanding of the present invention by those skilled in the art. However, it should be clear that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the appended claims, these changes are obvious, and all inventions and creations utilizing the concepts of the present invention are protected.

[0055] like Figure 1As shown in FIG, the method for measuring the gain of a differential probe using 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, wherein the first interface and the third interface are connected by a microstrip line, and the second interface and the fourth interface are connected by 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 coupled line and connect a 50-ohm load to the output 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 of the differential probe and disconnect the 50-ohm load connected to the output of the differential probe. Disconnect the second and fourth ports of the test fixture from the vector network analyzer and connect the unused ports of the test fixture to a 50-ohm load. Leave the fourth port of the four-port vector network analyzer unused, record the current S parameters, and save them as an S3P file.

[0060] S5. Mirror the four-port test fixture to form a through calibration piece. Replace the four-port test fixture with the through calibration piece, use 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 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 and second interfaces 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 and fourth interfaces 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 practice, the purpose of calibrating a four-port vector network analyzer is to eliminate systematic errors at each port, including impedance mismatch, transmission loss, and phase delay. This process can be performed using either a four-port calibration kit or a single-port calibration kit. Using a four-port calibration kit is the most convenient calibration method. Connect the four-port calibration kit to the four ports of the four-port vector network analyzer and perform calibration according to the instrument prompts. If a four-port calibration kit is not available, a single-port calibration kit can be used to calibrate each port one by one. First, connect a cable with a 500 ohm characteristic impedance to one port of the four-port vector network analyzer, then connect the single-port calibration kit to the other end of the cable. After completing the calibration according to the instrument prompts, remove the calibration kit and repeat the same steps for the remaining ports. After completing the port calibration, the four ports of the four-port vector network analyzer need to be connected to a four-port test fixture. The four-port test fixture is used to connect the device under test and ensure stable signal transmission.

[0067] In the specific implementation process, the simulation diagram of the line calibration component and the through calibration component is as follows Figure 14 As shown in the figure, the four ports on the left, P01, P02, P03, and P04, and the microstrip line constitute the line calibration component; the four ports on the right, P05, P06, P07, and P08, and the microstrip line constitute the 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 the 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. The front-end probes of the differential probe are connected to the coupled lines of the four-port test fixture, and the output of the differential probe is connected to a 50 Ohm load. When measuring S3P, the front-end probes of the differential probe are connected to the coupled lines, and the ports of the four-port test fixture connected to the four-port vector network analyzer become Port 1, Port 2, and Port 5. Figure 2 The 50Ohm here 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 its structure is symmetrical about the horizontal axis on the PCB, just like the connector. The contact point of the differential probe is located on the vertical axis, which 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, affecting the accuracy of the test results, so this embodiment adopts a de-embedding method. Since conventional de-embedding methods are difficult to support high bandwidth, this 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, even-odd mode analysis can prove that the original four-port S parameters have the following properties:

[0071]

[0072] 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:

[0073]

[0074] Transform it into a differential mixed S-parameter matrix:

[0075]

[0076] in: ;

[0077] The conversion parameters for both differential and common modes are zero, and the parameters for the different pure modes are separate. This demonstrates that the differential and common-mode parameters are independent of each other. Due to the horizontal symmetry of the four-port test fixture, the assumption of horizontal symmetry allows the mode conversion parameters to be omitted, simplifying the propagation modes to pure differential and pure common modes. This means that in horizontally symmetric testing, if only differential S-parameters are de-embedded, this symmetry reduces each 4×4 matrix to a 2×2 matrix, simplifying the four-port network to a two-port network. The two-port network can then be de-embedded using TRL to obtain the full half-side S-parameters. The same applies when de-embedding common-mode S-parameters.

[0078] 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:

[0079] To measure the S parameters of the test fixture, we mirrored the four-port test fixture and fabricated a test circuit board (the through calibration component) that can be directly measured, including the adapter. We also fabricated a set of line calibration components within the operating frequency band (adding a microstrip line to the through calibration component, treating it as an ideal transmission line with known transmission parameters). The test fixture connections were the same as those used to measure the S3P file. This yielded the following two sets of measurement parameters:

[0080]

[0081]

[0082] in is the half-side transmission parameter of the four-port test fixture; is the identity matrix; is the transmission parameter of the thru calibration piece; is the transmission parameter of the line calibration piece; The length of the single l The transmission matrix of an ideal transmission line; is the transmission parameter of the other half of the four-port test fixture, .

[0083] 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 2The four-port test fixture in the test is equivalent to two half-side test fixtures, using the half-side transmission network (Right now ) matrix representation, (Right now ) 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 its voltage division ratio has also been determined, so the voltage ratio of point C to point B can be obtained and recorded as G CB .

[0084] 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 differential. Therefore, by sequentially calculating the voltage ratios at points C and A, D and A, and C and B, we can find the voltage ratio between D and B, and thus the differential voltage gain of the differential probe.

[0085] When measuring the S4P file, the voltage ratio between point C and point A is actually the voltage ratio in differential mode. ,Right now , by converting the four-port S parameters in the S4P file to obtain the S parameters in differential mode, the conversion formula is as follows:

[0086]

[0087] in is the voltage ratio between the third port and the second port of the four-port vector network analyzer in the S4P file; 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; is the voltage ratio between the fourth port and the second port of the four-port vector network analyzer in the S4P file.

[0088] When measuring the S3P file, the voltage ratio between point D and point A is actually the voltage ratio of the differential input mode. ,Right now , by converting the four-port S parameters of the S3P file to obtain the S parameters in differential mode, the conversion formula is as follows:

[0089]

[0090] 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.

[0091] 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.

[0092] The common-mode gain can be calculated similarly, using the same test fixture. In common-mode mode, the voltage ratio between point C and point A is calculated as:

[0093]

[0094] 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; is the voltage ratio between the fourth port and the second port of the four-port vector network analyzer in the S4P file.

[0095] In common mode, the voltage ratio between point D and point A is calculated as:

[0096]

[0097] 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.

[0098] In one embodiment of the present invention, the simulation principle diagram of the method is as follows: Figure 4As shown, two differential microstrip lines are used to simulate a four-port test fixture. A shunt capacitor is added to simulate a transmission line with high characteristic capacitive reactance while ensuring frequency selectivity. The differential probe simulation, like the two-port configuration, uses a cascaded network consisting of a 25kΩ ideal resistor and the ADL5580 fully differential amplifier. Its output is connected to Term5, which acts as the fifth port in vector network analysis. Ports 1, 2, 3, and 4 form a four-port network. These correspond to the S4P file measured in step 3, which is converted into the two-port transmission coefficients for the four-port network in differential and common-mode modes, respectively. Ports 1, 2, and 5 form a three-port network. These correspond to the S3P file measured in step 5, which is converted into the two-port transmission coefficients for the three-port network in differential and common-mode input modes, respectively.

[0099] Through Figure 4 The circuit shown is simulated with 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 of the two-port transmission coefficient in the four-port differential mode. Figure 6 This is the simulation result of the two-port transmission coefficient in the four-port common mode. Figure 7 This is the simulation result of the two-port transmission coefficient in the three-port differential mode. Figure 8 This is the simulation result of the two-port transmission coefficient in the three-port common mode.

[0100] In this embodiment, the schematic diagram of the half-side simulation of the four-port test fixture for solving the voltage ratio between point C and point B is as follows: Figure 9 As shown in the figure, the amplitude and phase comparison between this method and the actual one in differential mode and common mode are as follows: Figure 10 、 Figure 11 、 Figure 12 and Figure 13 As shown in the figure, the test value obtained by this method coincides with the actual value curve, 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, wherein the first interface and the third interface are connected by a microstrip line, and the second interface and the fourth interface are connected by 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 coupled line and connect a 50-ohm load to the output 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 of the differential probe and disconnect the 50-ohm load connected to the output of the differential probe. Disconnect the second and fourth ports of the test fixture from the vector network analyzer and connect the unused ports of the test fixture to a 50-ohm load. Leave the fourth port of the four-port vector network analyzer unused, record the current S parameters, and save them as an S3P file. S5. Mirror the four-port test fixture to form a through calibration piece. Replace the four-port test fixture with the through calibration piece, use 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 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 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 and second interfaces 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 and fourth interfaces 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 using a four-port vector network analyzer according to claim 1, wherein: The specific method of step S7 includes the following sub-steps: S7-1. Obtain the transmission parameters of the through calibration component from the S3P1 file and the S3P2 file respectively. Transmission parameters of the calibration kit ; S7-2, according to the formula: Obtaining half-side transmission parameters of a four-port test fixture ;in is the identity matrix; The length of a single l The transmission matrix of an ideal transmission line; is the transmission parameter of the other half of the four-port test fixture, ; S7-3, Half-side transmission parameters through a four-port test fixture Get the voltage ratio between point C and point B and record it as G CB .

3. The method for measuring differential probe gain using a four-port vector network analyzer according to claim 1, wherein: 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; 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; 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 using a four-port vector network analyzer according to claim 1, wherein: 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 using a four-port vector network analyzer according to claim 1, wherein: 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; 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 using a four-port vector network analyzer according to claim 1, wherein: SC 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.

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