A cable shielding effectiveness measurement device, method and uncertainty evaluation method

Abstract

The present invention discloses a cable shielding effectiveness measurement device, method and uncertainty assessment method. The working area of ​​the device is provided with a cable to be tested, a matching load and a shielding calibration piece, which clarifies that the DUT is measured in the working area, fully utilizing the advantage of good field uniformity in the working area, so that the volatility of the measurement result is smaller; the matching load is placed outside the reverberation chamber, which reduces one radio frequency connection cable compared to placing the matching load outside the reverberation chamber, and greatly reduces the influence of leakage of the connection cable on the test result. The present invention adopts a comparative method measurement with the calibration piece as a reference. The shielding effectiveness of the calibration piece is stable and close to the shielding attenuation value of the cable to be tested, so that the level range of the spectrum reading is relatively concentrated, and it is easier to obtain relatively accurate measurement results, which has good practicality. The present invention makes the measurement results more reasonable and reliable through uncertainty analysis of the measurement results, which has good practicality.

Description

Technical Field

[0001] The present invention belongs to the technical field of shielding effectiveness testing, and in particular relates to a cable shielding effectiveness measuring device, method and uncertainty evaluation method. Background Art

[0002] Cables are core components for achieving conductive interconnection from the module level to the system level in the RF field, ensuring accurate, low-loss, and efficient signal transmission. Cables are typically composed of conductors and dielectrics, and leakage is inevitable during signal transmission. Measurement systems involving the transmission of electromagnetic waves in space, such as antenna measurement systems and radar cross-section measurement systems, place high demands on the system's noise floor, and thus on the shielding effectiveness of the extensively used connecting cables. Cable shielding effectiveness testing primarily includes the power absorbing clamp method, current probe injection method, shielded room antenna method, reverberation chamber method, and GTEM cell method.

[0003] Among the many cable shielding effectiveness measurement methods, the reverberation chamber method fully utilizes the characteristics of the internal electromagnetic field being statistically uniform in all directions. It does not require high cable layout and positioning, and is a simple and reliable measurement method. In addition, since the excitation signal in the electromagnetic reverberation chamber method can be applied to the cable under test from various angles, positions, and polarizations, its shielding effectiveness evaluation can be more comprehensive. Figure 1 As shown in the figure, the international standard IEC61726-1999 specifically provides a method for measuring the shielding effectiveness of cable accessories, cables, connectors and passive millimeter wave components based on the reverberation chamber method.

[0004] Control the frequency synthesizer (or signal source) to increase the signal power (P INJ ) is fed into the reverberation chamber through the transmitting antenna, and the field strength power at a specific point in the chamber is received by the reference antenna and then received by the spectrum analyzer (P REF ). Feed power (P INJ ) and received power (P REF The ratio of the insertion loss to the cavity is the insertion loss of the cavity. The insertion loss is closely related to the frequency and also depends on the quality factor of the cavity.

[0005] The device under test (DUT) is exposed to an almost uniform isotropic electromagnetic field, and the signal level sensed by the DUT is received by the spectrum analyzer (P DUT ). Shielding attenuation is calculated using the following formula:

[0006]

[0007] or

[0008]

[0009] Among them, P DUTis the power coupled to the DUT, P REF is the power coupled to the reference antenna, P INJ is the power fed into the reverberation chamber cavity, Δ ins is the insertion loss of the reverberation chamber.

[0010] However, the disadvantages of the prior art are as follows:

[0011] ① It is not clear that the DUT test area is in the working area. Usually, only in the working area can the electromagnetic field strength be considered uniform, that is, the electromagnetic waves are uniformly and isotropically distributed; near the boundary of the cavity, the field strength is not uniform; the reference antenna involved in the calculation of the insertion loss of the reverberation chamber also needs to be placed in the working area, which is not clear either.

[0012] ② In the above shielding attenuation calculation formula, the DUT's received power is relatively small (the shielding of coaxial cables is generally above 60dB), and the reference antenna's received power is relatively large. In this way, the spectrum analyzer will measure power within a large dynamic range, and the spectrum analyzer's linearity will have a significant impact on the measurement results.

[0013] ③ When measuring the DUT, the matching load (50Ω) is connected outside the cavity, which requires two connecting cables to connect the two ends of the DUT, increasing the impact of the leakage of the connecting cables on the shielding attenuation measurement.

[0014] ④ No method for uncertainty analysis of shielding attenuation measurement results was provided, and the accuracy and reliability of the measurement results could not be confirmed. Summary of the Invention

[0015] The object of the present invention is to provide a cable shielding effectiveness measurement device, method and uncertainty evaluation method, aiming to solve the above-mentioned problems.

[0016] The present invention is mainly achieved through the following technical solutions:

[0017] A cable shielding effectiveness measuring device includes a control end, a spectrum analyzer, a signal source, and a transmitting antenna, a first stirring paddle, a second stirring paddle, and a working area arranged in a reverberation chamber. The working area is provided with a cable to be tested, a matching load, and a shielding calibration component; a spectrum analyzer and a signal source are provided on one side of the working area, and a first stirring paddle and a transmitting antenna are provided on the other side, and a second stirring paddle is provided below; the signal source is connected to the transmitting antenna through a radio frequency cable, and the transmitting antenna mouth faces away from the working area to avoid direct radiation to the working area; the spectrum analyzer is connected to the working area through a radio frequency cable; the control end is connected to the signal source, the spectrum analyzer, the first stirring paddle, and the second stirring paddle respectively through control lines.

[0018] The present invention is mainly achieved through the following technical solutions:

[0019] A method for measuring the shielding effectiveness of a cable, using the above-mentioned measuring device, comprises the following steps:

[0020] Step S100: Connect the matching load to the spectrum analyzer through the RF cable to complete a frequency point measurement. The measurement result is recorded as P Meas_match ;

[0021] Step S200: Connect one end of the cable to be tested to a matching load, and connect the other end to a spectrum analyzer via a radio frequency cable to complete a frequency point measurement. The measurement result is recorded as {P Meas_DUT,max} f ;

[0022] Step S300: Determine whether P Meas_DUT -P Meas_match ≥10dB, if so, proceed to step S400, otherwise it is necessary to perform special shielding on the receiving RF cable or replace the RF cable at the receiving end;

[0023] Step S400: Connect one end of a shielded calibration piece to a matching load, and connect the other end to a spectrum analyzer via a radio frequency cable to complete a frequency point measurement. The measurement result is recorded as {P Meas_CAL1,max} f ;

[0024] Step S500: Replace the shielded calibration piece, connect one end of the new shielded calibration piece to the matching load, and connect the other end to the spectrum analyzer through a radio frequency cable to complete a frequency point measurement. The measurement result is recorded as {P Meas_CAL2,max} f ;

[0025] Step S600: Calculate the shielding attenuation of the cable to be tested according to the following formula:

[0026] a s_m1 =(P Meas_DUT,max -P Meas_CAL1,max )+a s_CAL1

[0027] a s_m2 =(P Meas_DUT,max -P Meas_CAL2,max )+a s_CAL2

[0028] a s =(a s_m1 +a s_m2 ) / 2

[0029] Among them, a s_CAL1 、a s_CAL2 are the shielding attenuation values ​​of the shielding calibration piece in step S400 and step S500 respectively,

[0030] a s_m1、a s_m2 The shielding attenuation values ​​of the cable to be tested are respectively the shielding calibration components used as references in step S400 and step S500;

[0031] a s is the shielding attenuation value a s_CAL1 、a s_CAL2 The average value of the shielding attenuation is used as the final shielding attenuation value of the cable to be tested.

[0032] In order to better implement the present invention, further, the two shielding calibration parts in step S300 and step S400, the shielding attenuation value of one shielding calibration part is greater than the shielding attenuation value of the cable to be tested, and the shielding attenuation value of the other shielding calibration part is less than the shielding attenuation value of the cable to be tested.

[0033] In order to better implement the present invention, further, the frequency point measurement includes the following steps:

[0034] Step A1: Using a control terminal, the first stirring paddle and the second stirring paddle are moved to a position;

[0035] Step A2: Setting the specific frequency and power of the signal source through the control terminal;

[0036] Step A3: Control the spectrum analyzer through the control terminal to receive the peak level within a sweep bandwidth centered on the frequency set in step A2, which is recorded as P Meas ;

[0037] Step A4: Repeat steps A2-A3 to traverse all the frequency points that need to be measured. Meas} f ;

[0038] Step A5: Repeat steps A1 to A4, traverse all the blade positions of the first stirring paddle and the second stirring paddle that need to be measured, take the maximum value of the measurement results of each frequency point, and obtain {P Mea,max} f , complete a frequency point measurement.

[0039] The present invention is mainly achieved through the following technical solutions:

[0040] An uncertainty assessment method, using the above method, includes the uncertainty components u1, u2, u3, and u4 introduced by the accuracy of the spectrum analyzer cursor level reading, the amplitude stabilization characteristics of the receiving cable, the uniformity of the reverberation chamber working area, and the measurement repeatability; the combined uncertainty is:

[0041]

[0042] Where: c is the sensitivity coefficient;

[0043] The expanded uncertainty is:

[0044] U=k*u c

[0045] Where k=2.

[0046] In order to better implement the present invention, further, the uncertainty component u1 introduced by the accuracy of the spectrum analyzer vernier level reading is:

[0047]

[0048] Where Δ is the maximum permissible error of the level reading within the measured level range of the measurement frequency band;

[0049] Or the uncertainty component u1 introduced by the accuracy of the spectrum analyzer cursor level reading is:

[0050] u1=U sp / 2

[0051] Among them U sp is the reading uncertainty of the spectrum analyzer cursor level.

[0052] In order to better implement the present invention, further, the sensitivity coefficient of the uncertainty introduced by the accuracy of the spectrum analyzer vernier level reading is 1.23.

[0053] In order to better implement the present invention, further, the uncertainty component u2 introduced by the amplitude stabilization characteristic of the receiving cable is:

[0054]

[0055] Where Δ is the maximum change in the measurement frequency band;

[0056] The uncertainty component u3 introduced by the uniformity of the reverberation chamber working area is:

[0057] u3=FU

[0058] Among them, FU is the field uniformity index;

[0059] The uncertainty component u4 introduced by measurement repeatability is:

[0060] Complete at least 8 cable shielding effectiveness measurements to obtain several sets of measurement values ​​{a s}, and take the standard deviation R of the measured value, which is u4.

[0061] In order to better implement the present invention, further, the sensitivity coefficients of the amplitude stabilization characteristics of the receiving cable, the uniformity of the working area of ​​the reverberation chamber, and the uncertainty introduced by the measurement repeatability are all 1.

[0062] The beneficial effects of the present invention are as follows:

[0063] (1) In the cable shielding effectiveness measurement device, it is clear that the DUT is measured in the working area, making full use of the advantage of good field uniformity in the working area, so that the fluctuation of the measurement results is smaller; the matching load is placed inside the reverberation chamber, which reduces one RF connection cable compared to placing the matching load outside the reverberation chamber, greatly reducing the impact of the leakage of the connection cable on the test results;

[0064] (2) In the cable shielding effectiveness measurement device, the reference antenna is removed, which reduces the system complexity and improves the measurement accuracy. On the one hand, if the reference antenna is placed in the working area, it will disturb the electromagnetic field in the working area; on the other hand, the receiving power of the reference antenna is significantly different from that of the DUT, which will span the larger measurement range of the spectrum level measurement and place higher requirements on the linearity of the spectrum.

[0065] (3) The present invention adopts a comparative measurement method with a calibration piece as a reference. The shielding effectiveness of the calibration piece is stable and close to the shielding attenuation value of the cable to be tested, so that the level range of the spectrum reading is relatively concentrated, making it easier to obtain relatively accurate measurement results, and having good practicality;

[0066] (4) The present invention can customize a series of calibration pieces with different shielding attenuation, and select two calibration pieces as references for comparative measurement, so that the shielding attenuation value of the cable to be tested is as close as possible to the shielding attenuation value of the two calibration pieces. The average of the two measurement results is used as the final measurement result, which increases the stability and reliability of the measurement results;

[0067] (5) The present invention makes the measurement results more reasonable and reliable through uncertainty analysis of the measurement results, and has better practicality. BRIEF DESCRIPTION OF THE DRAWINGS

[0068] Figure 1 This is a principle block diagram of an existing reverberation chamber-based shielding effectiveness measurement device;

[0069] Figure 2 It is a structural diagram of an existing shielding effectiveness calibration component;

[0070] Figure 3 This is a principle block diagram of the cable shielding effectiveness measurement device based on a reverberation chamber of the present invention;

[0071] Figure 4 Shielding attenuation curves of calibration components with different apertures d, hole thicknesses t, and hole numbers v;

[0072] Figure 5 Flowchart of the cable shielding effectiveness measurement method of the present invention;

[0073] Figure 6 This is a flow chart of frequency measurement based on reverberation room. DETAILED DESCRIPTION

[0074] Example 1:

[0075] A cable shielding effectiveness measuring device, such as Figure 3 As shown, the connection relationship of the device is as follows:

[0076] ①The signal source is connected to the transmitting antenna through a wall-penetrating RF cable, with the transmitting antenna facing the stirring paddle or wall to avoid direct exposure to the working area;

[0077] ② Place the cable under test (DUT), matching load, and shielded calibration components in the work area and connect them to the spectrum analyzer via a through-wall RF cable.

[0078] ③The computer is connected to the signal source, spectrum analyzer and stirring paddle through control lines.

[0079] like Figure 6 As shown, the cable shielding effectiveness measuring device works as follows:

[0080] 1) The computer controls the stirring paddle to move to a position;

[0081] 2) Computer controls the signal source to set a specific frequency and power;

[0082] 3) The computer controls the spectrum analyzer to receive the peak level within a sweep bandwidth centered on the frequency set in the previous step, which is recorded as P Meas ;

[0083] 4) Repeat steps 2) to 3) to traverse all the frequency points that need to be measured {P Meas} f ;

[0084] 5) Repeat steps 1) to 4) to traverse all blade positions that need to be measured, and take the maximum value of the measurement results at each frequency point. Mea，max} f , complete a test.

[0085] In the cable shielding effectiveness measurement device, the DUT is measured within the workspace, leveraging the workspace's excellent field uniformity to minimize measurement fluctuations. Placing the matching load within the reverberation chamber, compared to placing the matching load outside the reverberation chamber, eliminates one RF connection cable, significantly reducing the impact of cable leakage on test results. Furthermore, the device eliminates the reference antenna, reducing system complexity while improving measurement accuracy and enhancing practicality.

[0086] Example 2:

[0087] A cable shielding effectiveness measurement method is performed using the above-mentioned measuring device, such as Figure 5As shown, the following steps are included:

[0088] 1) First, connect the matching load to the RF cable at the receiving end and complete a measurement of the above “working mode”. The measurement result is recorded as P Meas_match , this measurement is the system noise floor measurement;

[0089] 2) Connect one end of the cable to be tested to the matching load and the other end to the RF cable at the receiving end to complete a measurement of the above "working mode". The measurement result is recorded as {P Meas_DUT,max} f , this measurement is DUT measurement;

[0090] 3) Connect one end of the calibration piece to the matching load and the other end to the RF cable at the receiving end to complete a measurement of the above “working mode”. The measurement result is recorded as {P Meas_CAL1,max} f , this measurement is the calibration piece measurement.

[0091] 4) Replace another calibration piece, connect one end of the calibration piece to the matching load, and the other end to the RF cable of the receiving end, and complete a measurement of the above "working mode". The measurement result is recorded as {P Meas_CAL2,max} f , this measurement is the calibration piece measurement.

[0092] 5) Calculate shielding attenuation according to the following formula:

[0093] a s_m1 =(P Meas_DUT,max -P Meas_CAL1,max )+a s_CAL1

[0094] a s_m2 =(P Meas_DUT,max -P Meas_CAL2,max )+a s_CAL2

[0095] a s =(a s_m1 +a s_m2 ) / 2

[0096] Among them, a s_CAL1 、a s_CAL2 are the calculated shielding attenuation values ​​of the two calibration pieces, a s_m1 、a s_m2 The shielding attenuation values ​​of the cable are measured twice using the calibration kit as a reference; a s It is the average of the two shielding attenuation values, which is used as the final measurement result.

[0097] When selecting calibration components, it's best to select two components with shielding attenuation values ​​close to the cable's own for measurement and calculation. Ideally, one component should have a shielding attenuation greater than the cable's, while the other should have a shielding attenuation less than the cable's. If you don't have prior knowledge of the cable's shielding, you can first perform a rough scan of the cable at a few frequencies to determine the approximate range. Then, select the appropriate calibration component for a more detailed scan and measurement.

[0098] Preferably, it should be noted that P Meas_match Less than P Meas_DUT The error should be at least 10dB to ensure the accuracy and reliability of the measurement results. If it is not satisfied, the receiving RF cable needs to be specially shielded or the RF cable at the receiving end needs to be replaced.

[0099] like Figure 2 As shown in the figure, the calibration piece adopts the air line punching model in the appendix of IEC 61726-1999, and a series of calibration pieces with different shielding attenuation values ​​are customized according to parameters such as hole diameter, hole thickness and number of holes. Figure 4 As shown, two calibration kits with similar parameter configurations can be selected based on the shielding value of the cable under test for comparative measurement. This invention allows for a series of customized calibration kits with different shielding attenuation values. Two calibration kits are then selected as references for comparative measurement, ensuring that the shielding attenuation value of the cable under test is as close as possible to the shielding attenuation values ​​of the two calibration kits. The average of the two measurements is then used as the final result, increasing the stability and reliability of the measurement results.

[0100] The present invention adopts a comparative measurement method with a calibration piece as a reference. The shielding effectiveness of the calibration piece is stable and close to the shielding attenuation value of the cable to be tested, so that the level range of the spectrum reading is relatively concentrated, making it easier to obtain relatively accurate measurement results, and having good practicality.

[0101] Example 3:

[0102] An uncertainty assessment method, such as Figure 5 As shown, based on the above cable shielding effectiveness measurement method, for each frequency point, measuring the shielding attenuation value requires measuring at least three quantities: P Meas_DUT,max 、P Meas_CAL1,max 、P Meas_CAL2,max . Analyzing the measurement system and the calculation formula for shielding attenuation, the main sources of uncertainty include:

[0103] 1) Accuracy of spectrum analyzer cursor level readings;

[0104] 2) The amplitude stabilization characteristics of the receiving cable;

[0105] 3) Uniformity of the reverberation chamber working area;

[0106] 4) Measurement repeatability.

[0107] Analyze the uncertainty introduced by each component:

[0108] a. Uncertainty component u1 introduced by the accuracy of the spectrum analyzer cursor level reading;

[0109] You can query the manufacturer's specifications of the spectrum analyzer to obtain the maximum allowable error ΔdB of the level reading within the measurement frequency band and calculate the uncertainty component according to the uniform distribution.

[0110]

[0111] Alternatively, obtain the spectrum analyzer cursor level reading uncertainty U according to the spectrum analyzer's measurement report. sp (k=2);

[0112] u1=U sp / 2

[0113] Measure three quantities P Meas_DUT,max 、P Meas_CAL1,max 、P Meas_CAL2,max The sensitivity coefficients are

[0114]

[0115]

[0116]

[0117] The overall sensitivity coefficient is

[0118]

[0119] b. The uncertain component u2 introduced by the amplitude stabilization characteristics of the receiving cable;

[0120] During the measurement process, the load, the cable under test, and the calibration device need to be connected and tested, which will change the state of the receiving cable and cause fluctuations in the amplitude. The S21 of the cable is measured using a vector network analyzer. By bending, coiling, and moving the cable, the amplitude changes are observed. The maximum change ΔdB within the measurement frequency band is taken and the uncertainty component is calculated based on the uniform distribution.

[0121]

[0122] c. Uncertain component u3 introduced by the field uniformity in the working area of ​​the reverberation chamber;

[0123] It is necessary to place field strength probes at eight fixed points in the rectangular working area to measure the field strength value that changes with the blades. According to IEC61000-4-21, the field uniformity index is calculated as FUdB.

[0124] u3=FU

[0125] d. Uncertain component u4 introduced by measurement repeatability;

[0126] According to the above-mentioned "working mode" and "measurement method", complete at least 8 complete cable shielding measurements to obtain {a s} value, take the standard deviation R of the measured value, which is u4;

[0127] e. Finally, the combined uncertainty is:

[0128]

[0129] Expanded uncertainty

[0130] U=ku c (k=2)

[0131] Preferably, the components are summarized as shown in Table 1.

[0132] Table 1

[0133]

[0134]

[0135] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any simple modification or equivalent change made to the above embodiment based on the technical essence of the present invention shall fall within the scope of protection of the present invention.

Claims

1. A method for measuring the shielding effectiveness of a cable, using a measuring device to measure the shielding effectiveness of a cable, characterized in that: The measuring device includes a control terminal, a spectrum analyzer, a signal source, a transmitting antenna, a first stirring paddle, a second stirring paddle, and a working area arranged in a reverberation chamber. The working area is provided with a cable to be tested, a matching load, and a shielding calibration component. The spectrum analyzer and signal source are provided on one side of the working area, and the first stirring paddle and the transmitting antenna are provided on the other side, and the second stirring paddle is provided below. The signal source is connected to the transmitting antenna via a radio frequency cable, and the transmitting antenna port faces away from the working area to avoid direct radiation to the working area. The spectrum analyzer is connected to the work area via a radio frequency cable; the control end is connected to the signal source, the spectrum analyzer, the first stirring paddle, and the second stirring paddle respectively via control lines; The measuring method comprises the following steps: Step S100: Connect the matching load to the spectrum analyzer via a radio frequency cable to complete a frequency point measurement. The measurement result is recorded as P Meas_match ; Step S200: Connect one end of the cable to be tested to a matching load, and connect the other end to a spectrum analyzer via a radio frequency cable to complete a frequency point measurement. The measurement result is recorded as { P Meas_DUT,max } f ; Step S300: Determine whether P Meas_DUT - P Meas_match ≥10 dB If so, proceed to step S400, otherwise it is necessary to perform special shielding on the receiving RF cable or replace the RF cable at the receiving end; Step S400: Connect one end of a shielded calibration piece to a matching load, and connect the other end to a spectrum analyzer via a radio frequency cable to complete a frequency point measurement. The measurement result is recorded as { P Meas_CAL1,max } f ; Step S500: Replace the shielded calibration piece, connect one end of the new shielded calibration piece to the matching load, and connect the other end to the spectrum analyzer through a radio frequency cable to complete a frequency point measurement. The measurement result is recorded as { P Meas_CAL2,max } f ; Step S600: Calculate the shielding attenuation of the cable to be tested according to the following formula: a s_m1 =（ P Meas_DUT,max - P Meas_CAL1,max ）+ a s_CAL1 a s_m2 =（ P Meas_DUT,max - P Meas_CAL2,max ）+ a s_CAL2 a s =（ a s_m1 + a s_m2 ） / 2 in, a s_CAL1 、 a s_CAL2 are the shielding attenuation values ​​of the shielding calibration piece in step S400 and step S500 respectively, a s_m1 、 a s_m2 The shielding attenuation values ​​of the cable to be tested are respectively the shielding calibration components used as references in step S400 and step S500; a s is the shielding attenuation value a s_CAL1 、 a s_CAL2 The average value of the shielding attenuation is used as the final shielding attenuation value of the cable to be tested.

2. A cable shielding effectiveness measurement method according to claim 1, characterized in that: In the two shielding calibration pieces in step S300 and step S400, the shielding attenuation value of one shielding calibration piece is greater than the shielding attenuation value of the cable to be tested, and the shielding attenuation value of the other shielding calibration piece is less than the shielding attenuation value of the cable to be tested.

3. A cable shielding effectiveness measurement method according to claim 1 or 2, characterized in that: The frequency point measurement includes the following steps: Step A1: Using a control terminal, the first stirring paddle and the second stirring paddle are moved to a position; Step A2: Setting the specific frequency and power of the signal source through the control terminal; Step A3: The spectrum analyzer is controlled by the control terminal to receive the peak level within a sweep bandwidth centered on the frequency set in step A2, which is recorded as P Meas ; Step A4: Repeat steps A2-A3 to traverse all the frequency points that need to be measured. P Meas } f ; Step A5: Repeat steps A1 to A4, traverse all the blade positions of the first stirring paddle and the second stirring paddle that need to be measured, take the maximum value of the measurement results of each frequency point, and obtain { P Mea , max } f , complete a frequency point measurement.

4. A method for evaluating uncertainty, comprising evaluating uncertainty by the measurement method according to any one of claims 1 to 3, characterized in that: The uncertainty evaluation method includes the accuracy of the spectrum analyzer cursor level reading, the amplitude stabilization characteristics of the receiving cable, the uniformity of the reverberation chamber working area, and the uncertainty components introduced by the measurement repeatability. u 1. u 2. u 3. u 4; The combined uncertainty is: in: c is the sensitivity coefficient; The expanded uncertainty is: U= k*u c in, k =2.

5. The uncertainty assessment method according to claim 4, characterized in that: The uncertainty component introduced by the accuracy of the spectrum analyzer cursor level reading u 1 is: Where Δ is the maximum permissible error of the level reading within the measured level range of the measurement frequency band; Or the uncertainty component introduced by the accuracy of the spectrum analyzer cursor level reading u 1 is: in U sp is the reading uncertainty of the spectrum analyzer cursor level.

6. The uncertainty assessment method according to claim 5, characterized in that: The sensitivity coefficient of the uncertainty introduced by the accuracy of the spectrum analyzer vernier level reading is 1.

23.

7. The uncertainty assessment method according to claim 4, characterized in that: Uncertainty components introduced by the amplitude stabilization characteristics of the receiving cable u 2 is: Where Δ is the maximum change in the measurement frequency band; Uncertainty components introduced by the uniformity of the reverberation room working area u 3 is: in, FU is the field uniformity index; Uncertainty component introduced by measurement repeatability u 4 is: Complete at least 8 cable shielding effectiveness measurements and obtain several sets of measurement values ​​{ a s }, and take the standard deviation of the measured value R , which is u 4.

8. The uncertainty assessment method according to claim 7, characterized in that: The sensitivity coefficients of the uncertainty introduced by the amplitude stabilization characteristics of the receiving cable, the uniformity of the working area of ​​the reverberation chamber, and the measurement repeatability are all 1.

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