A waveguide transmission line structure-based nonlinear characterization method for wave-absorbing sheet material and related device

Abstract

The application provides a waveguide transmission line structure-based nonlinear characterization method for wave-absorbing sheet materials and a related device, and belongs to the technical field of radio frequency passive intermodulation testing. The application repeatedly performs an assembling step and a testing step until testing of all to-be-tested wave-absorbing sheets is completed; whether the reflection PIM of more than a set number of wave-absorbing sheets is lower than the sensitivity of a receiving system is judged; if yes, the input power is increased by a step in a set range until the PIM amplitude of the wave-absorbing sheet is located in a PIM testing system testing threshold value; the wave-absorbing sheets without testing results are retested, the assembling step and the testing step are repeatedly performed, and all to-be-tested wave-absorbing sheets are distinguished until the intermodulation level is obtained. The application solves the problem that the accuracy of nonlinear characterization of wave-absorbing sheet materials is not high.

Description

Technical Field

[0001] This invention belongs to the field of radio frequency passive intermodulation testing technology, specifically relating to a nonlinear characterization method and related apparatus for absorbing sheet materials based on waveguide transmission line structures. Background Technology

[0002] Passive intermodulation (PIM) is a common nonlinear problem in modern communication systems. When radio frequency devices or materials exhibit nonlinear responses under high-power multicarrier signals, they generate interference signals in the receiving frequency band, severely affecting the system's sensitivity and communication quality. With the rapid development of fifth-generation mobile communication, satellite communication, and radar systems, higher requirements are being placed on the low intermodulation performance of materials and devices.

[0003] As a crucial component of electromagnetic compatibility and stealth technology, microwave absorbing sheets are widely used in radomes, radar systems, and microwave anechoic chambers. Their primary function is to absorb incident electromagnetic waves, reducing reflection and scattering. However, traditional absorbing materials may introduce passive intermodulation effects in practical applications, leading to a degradation in system performance. Therefore, effectively characterizing and evaluating the passive intermodulation properties of absorbing sheet materials has become a pressing technical problem to be solved.

[0004] Existing passive intermodulation testing methods mainly include coaxial cable structure testing and free space testing. The following section introduces these two methods: Coaxial line structure testing method: This method is based on a coaxial transmission line to build a test system, which has the advantages of mature structure, strong anti-interference ability, and stable test results, making it suitable for routine intermodulation characterization of devices or connectors. However, the test frequency range of this method is limited by the operating bandwidth of the coaxial line, and the incident waveform is in transmission line mode, making it difficult to simulate the plane wave incident conditions in actual applications. Furthermore, this method is not suitable for large-sized or sheet-like materials; samples must be processed into specific shapes to be placed in the coaxial structure, thus destroying the original state of the material.

[0005] Free-space testing methods: This method allows for direct testing under free-space conditions, with incident waves more closely resembling real-world application scenarios. It is suitable for large-size or sheet-like materials, requires no special sample processing, and offers a wide testing frequency range, covering microwave to millimeter-wave bands. However, this method involves complex testing systems, requiring high-power sources, precision antennas, and anechoic chamber environments, resulting in high costs. Test results are easily affected by environmental factors, leading to poor repeatability. Furthermore, it demands stringent system calibration and experimental conditions, making it difficult to achieve rapid and standardized material intermodulation characterization.

[0006] In summary, existing testing methods have certain limitations in characterizing passive intermodulation of absorbing sheet materials, and it is difficult to balance the simplicity of experimental conditions, the accuracy of test results, and the relevance to application scenarios.

[0007] Therefore, there is an urgent need to propose a new testing method to achieve efficient and accurate characterization of the passive intermodulation effect of absorbing sheet materials under laboratory conditions. Summary of the Invention

[0008] The purpose of this invention is to provide a nonlinear characterization method and related apparatus for absorbing sheet materials based on waveguide transmission line structures, in order to solve the problem of low accuracy in the nonlinear characterization of absorbing sheet materials in the prior art.

[0009] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a nonlinear characterization method for absorbing sheet materials based on waveguide transmission line structures, comprising the following steps: Calibration steps: The waveguide transmission line structure is calibrated to obtain the calibrated waveguide transmission line structure; Assembly steps: Assemble the absorber to be tested onto the calibrated waveguide transmission line structure to obtain the waveguide transmission line structure with the absorber. Test procedure: Test the waveguide transmission line structure equipped with the absorbing sheet to obtain the return loss index of the absorbing sheet under test. If the return loss index of the absorbing sheet under test is less than the first set threshold in the test frequency band, perform PIM test and obtain the PIM test result; if the return loss index of the absorbing sheet under test is greater than or equal to the first set threshold in the test frequency band, do not perform PIM test. Repeat the assembly and testing steps until all the absorbers under test have been tested. Inspection steps: Determine whether there are more than a set number of absorbers whose reflected PIM is lower than the sensitivity of the receiving system. If so, increase the input power in steps within a set range until the PIM amplitude of the absorber is within the test threshold of the PIM test system. Retest the absorbers that have no test results. Repeat the assembly and testing steps until the intermodulation level of all absorbers under test can be distinguished.

[0010] A further improvement of this invention is that the calibration of the waveguide transmission line structure to obtain the calibrated waveguide transmission line structure specifically involves: The waveguide transmission line structure is calibrated for electrical parameters. After the electrical parameters are calibrated, the waveguide transmission line structure is calibrated for noise by the PIM test system itself to obtain the calibrated waveguide transmission line structure.

[0011] A further improvement of this invention is that, after the electrical parameter calibration, the noise of the waveguide transmission line structure is calibrated using the PIM test system itself, specifically as follows: After electrical parameter calibration, the noise of the PIM test system itself is measured when the dual-carrier input power is at the set power. If the noise of the PIM test system itself is less than the second set threshold, keep the PIM test system powered on and let it stand still for the set time, and then measure the noise of the PIM test system itself again. If the deviation between the two measurement results does not exceed the third set threshold, the calibration is deemed effective. Otherwise, continue to let the PIM test system stand still until the PIM test system is thermally stable and then retest.

[0012] A further improvement of the present invention is that, before assembling the absorber to be tested onto the calibrated waveguide transmission line structure to obtain the waveguide transmission line structure with the absorber, the fill rate is determined, and based on the fill rate, it is determined whether there is an obvious air gap between the absorber and the inner cavity of the waveguide transmission line structure.

[0013] A further improvement of this invention is that the formula for calculating the fill rate is: .

[0014] A further improvement of this invention is that when the return loss index of the absorber under test is less than a first set threshold within the test frequency band, a PIM test is performed, specifically as follows: When the return loss index of the absorber under test is less than the first set threshold in the test frequency band, a joint test of forward transmission PIM and reverse reflection PIM is performed.

[0015] A further improvement of this invention is that, after obtaining the PIM test results, a reflection PIM curve is plotted based on the PIM test results.

[0016] Secondly, the present invention provides a nonlinear characterization system for absorbing sheet materials based on waveguide transmission line structures, comprising: The calibration module is used to calibrate the waveguide transmission line structure to obtain the calibrated waveguide transmission line structure. The assembly module is used to assemble the absorber under test onto the calibrated waveguide transmission line structure to obtain a waveguide transmission line structure with the absorber assembled. The test module is used to test the waveguide transmission line structure equipped with an absorbing sheet to obtain the return loss index of the absorbing sheet under test. When the return loss index of the absorbing sheet under test is less than a first set threshold in the test frequency band, a PIM test is performed to obtain the PIM test result; when the return loss index of the absorbing sheet under test is greater than or equal to the first set threshold in the test frequency band, a PIM test is not performed. Repeat the assembly and test modules until all the absorbers under test have been tested. The testing module is used to determine whether there are more than a set number of absorbing sheets whose reflected PIM is lower than the sensitivity of the receiving system. If so, the input power is increased in steps within a set range until the PIM amplitude of the absorbing sheet is within the test threshold of the PIM test system. The absorbing sheets with no test results are retested. The assembly module and the test module are used repeatedly until the intermodulation level of all the absorbing sheets under test is distinguished.

[0017] Thirdly, the present invention provides an electronic device, including a memory and a processor, wherein the memory stores a computer program, and the processor executes the computer program to implement the steps of the nonlinear characterization method for absorbing sheet materials based on waveguide transmission line structures described above.

[0018] Fourthly, the present invention provides a storage medium storing a computer program thereon, wherein the computer program, when executed by a processor, implements the steps of the nonlinear characterization method for absorbing sheet materials based on waveguide transmission line structures described above.

[0019] Compared with the prior art, the present invention has the following beneficial effects: The proposed nonlinear characterization method for absorbing sheet materials based on waveguide transmission line structures involves two aspects. First, calibrating the waveguide transmission line structure to obtain a calibrated structure significantly improves the accuracy of nonlinear characterization and effectively eliminates the interference of thermal drift on test results. Second, determining whether more than a set number of absorbing sheets have a reflected PIM lower than the sensitivity of the receiving system. If so, increasing the input power in steps within a set range until the PIM amplitude of the absorbing sheet is within the test threshold of the PIM test system, retesting the absorbing sheets without test results, and repeating the assembly and testing steps until the intermodulation levels of all the absorbing sheets under test are distinguished. This operation not only effectively avoids misjudgments and missed tests caused by the reflected PIM of the absorbing sheet being lower than the sensitivity of the receiving system, but also improves the stability and reliability of the test results, thereby improving the accuracy of nonlinear characterization of absorbing sheet materials.

[0020] Furthermore, the present invention discloses a method for assembling the absorber under test onto a calibrated waveguide transmission line structure. Before obtaining the waveguide transmission line structure with the absorber, the fill ratio is determined, and based on the fill ratio, it is determined whether there is a significant air gap between the absorber and the inner cavity of the waveguide transmission line structure. This operation can ensure that the contact state is consistent each time the absorber under test is replaced, effectively eliminating systematic errors caused by assembly differences and improving test repeatability and reliability.

[0021] Furthermore, this invention discloses a method for conducting joint forward transmission PIM and reverse reflection PIM tests when the return loss index of the absorber under test is less than a first set threshold in the test frequency band. This operation can significantly improve the material characterization dimensions and information content.

[0022] Furthermore, this invention discloses that after obtaining the PIM test results, a reflection PIM curve is plotted based on the PIM test results. This operation realizes a quantitative description of the nonlinear characteristics of the absorbing sheet material, which facilitates the lateral comparison between different absorbing sheet materials and the establishment of a database. Attached Figure Description

[0023] Figure 1 This is a flowchart of the nonlinear characterization method for absorbing sheet materials based on waveguide transmission line structure according to the present invention; Figure 2 This is a schematic diagram of the nonlinear characterization system for absorbing sheet materials based on waveguide transmission line structure according to the present invention; Figure 3 This is a block diagram illustrating the PIM test principle of the waveguide transmission line of the present invention. Figure 4 This is an exploded view of the rectangular waveguide assembly absorber structure of the present invention; Figure 5 This is an assembly diagram of the rectangular waveguide of the present invention; Figure 6 This is a flowchart of the reflection PIM test based on the waveguide transmission line structure of the present invention; Figure 7 Comparison of return loss before and after assembling the absorbing plate in the 1.8GHz rectangular waveguide transmission line of this invention; Figure 8 The PIM test results of the reflection of the 1.8GHz rectangular waveguide of this invention with different absorbing sheets; Figure 9 Comparison of calculated and measured PIM values ​​for the 1.8GHz rectangular waveguide assembled with polyurethane absorbing sheet of the present invention; Figure 10 Comparison of calculated and measured PIM values ​​for the 1.8GHz rectangular waveguide assembled with a polyurethane coated absorber according to the present invention; Figure 11 Comparison of calculated and measured PIM values ​​for the 1.8GHz rectangular waveguide equipped with SABPIM absorbing sheet of the present invention; Figure 12 This is a schematic diagram of the structure of the electronic device of the present invention; In the diagram: 1. First L29 connector; 2. Second L29 connector; 3. First waveguide converter; 4. Second waveguide converter; 5. First waveguide section; 6. Second waveguide section; 7. Absorbing plate. Detailed Implementation

[0024] To further understand the content of this invention, the invention will be described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the embodiments are merely illustrative and not limiting of the invention.

[0025] Example 1: The flowchart of the nonlinear characterization method for absorbing sheet materials based on waveguide transmission line structure of this invention is as follows: Figure 1 As shown, the nonlinear characterization method for absorbing sheet materials based on waveguide transmission line structures of the present invention includes the following steps: S1. Calibration steps: Calibrate the waveguide transmission line structure to obtain the calibrated waveguide transmission line structure; S2. Assembly steps: Assemble the absorber to be tested onto the calibrated waveguide transmission line structure to obtain the waveguide transmission line structure with the absorber. S3. Test Procedure: Test the waveguide transmission line structure equipped with the absorbing sheet to obtain the return loss index of the absorbing sheet under test. If the return loss index of the absorbing sheet under test is less than the first set threshold in the test frequency band, perform PIM test and obtain the PIM test result; if the return loss index of the absorbing sheet under test is greater than or equal to the first set threshold in the test frequency band, do not perform PIM test. S4. Repeat the assembly and testing steps until all the absorbers under test have been tested. S5. Inspection steps: Determine whether there are more than a set number of absorbers whose reflected PIM is lower than the sensitivity of the receiving system. If so, increase the input power in steps within the set range until the PIM amplitude of the absorber is within the test threshold of the PIM test system. Retest the absorbers that have no test results. Repeat the assembly steps and test steps until the intermodulation level of all absorbers under test can be distinguished.

[0026] Example 2: A schematic diagram of the nonlinear characterization system for absorbing sheet materials based on waveguide transmission line structure of this invention is shown below. Figure 2 As shown, the nonlinear characterization system for absorbing sheet materials based on waveguide transmission line structures of the present invention includes: The calibration module is used to calibrate the waveguide transmission line structure to obtain the calibrated waveguide transmission line structure. The assembly module is used to assemble the absorber under test onto the calibrated waveguide transmission line structure to obtain a waveguide transmission line structure with the absorber assembled. The test module is used to test the waveguide transmission line structure equipped with an absorbing sheet to obtain the return loss index of the absorbing sheet under test. When the return loss index of the absorbing sheet under test is less than a first set threshold in the test frequency band, a PIM test is performed to obtain the PIM test result; when the return loss index of the absorbing sheet under test is greater than or equal to the first set threshold in the test frequency band, a PIM test is not performed. Repeat the assembly and test modules until all the absorbers under test have been tested. The testing module is used to determine whether there are more than a set number of absorbing sheets whose reflected PIM is lower than the sensitivity of the receiving system. If so, the input power is increased in steps within a set range until the PIM amplitude of the absorbing sheet is within the test threshold of the PIM test system. The absorbing sheets with no test results are retested. The assembly module and the test module are used repeatedly until the intermodulation level of all the absorbing sheets under test is distinguished.

[0027] Example 3: The nonlinear characterization method for absorbing sheet materials based on waveguide transmission line structures of the present invention includes the following steps: S1. Calibration steps: The waveguide transmission line structure is calibrated to obtain the calibrated waveguide transmission line structure.

[0028] This step involves calibrating the waveguide transmission line structure to obtain the calibrated waveguide transmission line structure, specifically as follows: The waveguide transmission line structure is calibrated for electrical parameters. After the electrical parameters are calibrated, the waveguide transmission line structure is calibrated for noise by the PIM test system itself to obtain the calibrated waveguide transmission line structure.

[0029] In this step, after the electrical parameters are calibrated, the noise of the PIM test system itself is calibrated for the waveguide transmission line structure. Specifically: After electrical parameter calibration, the noise of the PIM test system itself is measured when the dual-carrier input power is at the set power. If the noise of the PIM test system itself is less than the second set threshold, keep the PIM test system powered on and let it stand still for the set time, and then measure the noise of the PIM test system itself again. If the deviation between the two measurement results does not exceed the third set threshold, the calibration is deemed effective. Otherwise, continue to let the PIM test system stand still until the PIM test system is thermally stable and then retest.

[0030] The following is a detailed explanation of this step: The waveguide transmission line structure is connected to the test system via a low intermodulation L29 connector and an RG141 low intermodulation cable, and calibration is performed in the following two sub-steps: A. Two-port electrical parameter calibration A vector network analyzer is used to simultaneously test the return loss S11 and insertion loss S21 of the waveguide transmission line structure. The return loss S11 must be less than -10 dB and the insertion loss S21 less than 1 dB within the test frequency band. If the insertion loss S21 exceeds 1 dB, it indicates additional loss in the waveguide transmission line structure, requiring inspection of the connector connections or the fabrication quality of the transmission line's internal cavity before retesting.

[0031] B. Noise calibration of the PIM testing system itself After dual-port electrical parameter calibration, the noise of the PIM test system itself was measured when the dual-carrier input power was set to the power (33dBm). If the noise of the PIM test system itself is less than the second set threshold (-130dBm), keep the PIM test system powered on and let it stand still for the set time (5 minutes) before measuring the noise of the PIM test system itself again; if the deviation between the two measurement results does not exceed the third set threshold (2dBm), the calibration is deemed effective; otherwise, continue to let the PIM test system stand still until the PIM test system is thermally stable and then retest.

[0032] S2. Assembly steps: Assemble the absorber to be tested onto the calibrated waveguide transmission line structure to obtain the waveguide transmission line structure with the absorber.

[0033] In this step, the absorber to be tested is assembled on the calibrated waveguide transmission line structure (specifically, it is assembled in the middle of the calibrated waveguide transmission line structure). Before obtaining the waveguide transmission line structure with the absorber, the fill rate is determined, and based on the fill rate, it is determined whether there is a significant air gap between the absorber and the inner cavity of the waveguide transmission line structure. (If the fill rate is less than 90%, it indicates that there is a significant air gap between the absorber and the inner cavity of the waveguide transmission line structure, and it is necessary to re-cut or select an absorber of a more suitable size. If the fill rate is in the range of 90% to 100%, it indicates that there is no significant air gap between the absorber and the inner cavity of the waveguide transmission line structure.)

[0034] The formula for calculating the fill rate in this step is:

[0035] When assembling the absorber under test onto the calibrated waveguide transmission line structure, the absorber is secured using an adjustable clamping screw mechanism. A torque wrench is used to uniformly control the clamping torque to 1 N·m. This clamping operation must be repeated each time the material under test is changed to ensure consistent assembly contact for each material and avoid introducing additional systematic errors due to differences in tightness.

[0036] After assembling the absorber under test onto the calibrated waveguide transmission line structure, visually inspect both ends of the waveguide transmission line structure to confirm that the absorber has no obvious warping, offset or visible air gap before proceeding to step S3.

[0037] S3. Test Procedure: Test the waveguide transmission line structure equipped with the absorbing plate to obtain the return loss index of the absorbing plate under test. If the return loss index of the absorbing plate under test is less than the first set threshold in the test frequency band, perform PIM test and obtain the PIM test result; if the return loss index of the absorbing plate under test is greater than or equal to the first set threshold in the test frequency band, do not perform PIM test.

[0038] Test Procedure: A vector network analyzer is used to test the waveguide transmission line structure equipped with an absorbing sheet to obtain the return loss index of the absorbing sheet under test. If the return loss index of the absorbing sheet under test is less than the first set threshold (-10dB) in the test frequency band, a PIM test is performed to obtain the PIM test result. If the return loss index of the absorbing sheet under test is greater than or equal to the first set threshold (-10dB) in the test frequency band, a PIM test is not performed (indicating that the absorption rate of the absorbing sheet is too high and the thickness needs to be reduced).

[0039] In this step, if the return loss index of the absorber under test is less than the first set threshold within the test frequency band, a PIM test is performed, specifically as follows: When the return loss index of the absorber under test is less than the first set threshold in the test frequency band, a joint test of forward transmission PIM and reverse reflection PIM is performed.

[0040] The following is a detailed explanation of the joint test of forward transmission PIM and reverse reflection PIM: A PIM receiving channel is connected to each end of the waveguide transmission line structure. Under dual 33dBm carrier excitation, forward-propagating PIM (intermodulation signal transmitted from the excitation end towards the low intermodulation load direction) and reverse-reflected PIM (intermodulation signal reflected back to the PIM test system) are simultaneously acquired. Based on the theory that the intermodulation signal propagates equally to both sides after generation at the absorber, the amplitude difference between the forward-propagating PIM and the reverse-reflected PIM should approach 0dB in an ideal homogeneous material. If the measured deviation exceeds 3dB, it reflects the asymmetric nonlinear characteristics of the absorber in the electromagnetic propagation direction, which can be used as an auxiliary basis for judging the uniformity of the material's internal structure or filler distribution. The PIM test results of both channels are read and recorded, with the carrier excitation set to 33dBm.

[0041] After obtaining the PIM test results in this step, a reflection PIM curve is plotted based on the PIM test results.

[0042] S4. Repeat the assembly and testing steps until all the absorbers under test have been tested.

[0043] S5. Inspection steps: Determine whether there are more than a set number of absorbers whose reflected PIM is lower than the sensitivity of the receiving system. If so, increase the input power in steps within the set range until the PIM amplitude of the absorber is within the test threshold of the PIM test system. Retest the absorbers that have no test results. Repeat the assembly steps and test steps until the intermodulation level of all absorbers under test can be distinguished.

[0044] Inspection steps: Determine whether there are more than a set number of absorbers whose reflected PIM is lower than the sensitivity of the receiving system (specifically the spectrum analyzer). If so, increase the input power in steps of the set range (1dB) until the PIM amplitude of the absorber is within the test threshold of the PIM test system. Retest the absorbers that have no test results. Repeat the assembly and testing steps until the intermodulation level of all the absorbers under test can be distinguished.

[0045] The waveguide transmission line structure in this embodiment is not limited; a rectangular waveguide or a circular waveguide can be used.

[0046] In this embodiment, the waveguide transmission line structure is designed with silver-plated aluminum alloy, which can greatly suppress PIM.

[0047] In this embodiment, the waveguide transmission line structure is a wave-to-same conversion structure, which can be connected to cables using a low-PIM L29 connector.

[0048] In this embodiment, the waveguide transmission line structure is designed as a detachable assembly structure, which allows for free adjustment of the length of the waveguide transmission line structure, and the absorbing sheet is assembled in the middle.

[0049] The method of this invention can change the test frequency band simply by changing the dimensions of the waveguide transmission line structure.

[0050] Example 4: The method of the present invention will be described in detail below: Figure 3 This is a block diagram illustrating the PIM (Positioning Indicator Model) test principle for waveguide transmission lines (also known as waveguide transmission structures, or simply waveguides), with dual carrier waves (in...). Figure 3 (represented by signal source 1 and signal source 2) is fed into the power amplifier (in Figure 3 In the process of power amplifiers 1 and 2 (represented by power amplifier 1), the signal is further processed by a combiner and a duplexer (in... Figure 3 The PIM signal (represented by duplexer 1) is fed into the waveguide transmission line. A portion of the excited PIM signal propagates forward within the waveguide transmission line, while the portion is fed by a low intermodulation load (in...). Figure 3 The portion absorbed by the waveguide transmission line (represented by load 1) is reflected back to duplexer 1 and displayed by the spectrum analyzer. Generally, waveguide transmission lines can be tested in open free space or in a low intermodulation anechoic chamber. This embodiment uses a low intermodulation anechoic chamber for PIM testing.

[0051] When performing PIM testing after assembling an absorber on a waveguide transmission line, the carrier wave is transmitted through the waveguide transmission line and generates an intermodulation signal through the absorber. If the intermodulation frequency is within the transmission frequency of the waveguide transmission line, it can be assumed that half of the PIM on the absorber propagates in the forward direction and is absorbed by a low PIM load, while the other half is reflected back into the PIM testing system and received by the spectrum analyzer via a duplexer.

[0052] When the PIM is generated at the absorbing plate and propagates in the waveguide, in the far field, the electromagnetic field becomes TE. 10 The mode, therefore, the nonlinear current source d i The formulas for calculating the electric and magnetic fields generated in the far field are: (1) in, a and b These represent the width and height of the rectangular waveguide, respectively. dA 10 for H z The peak value of the directional magnetic field. β Let be the propagation constant. φ For current source d i The initial phase, ω Angular frequency, μ Let be the permeability. Meanwhile, the total electric and magnetic fields of the rectangular waveguide are respectively: (2) It can be deduced that the total PIM is: (3) From a single current source d i The generated PIM is: (4) in, C For radiation resistance, J nl,l For unit nonlinear current density, and J nl,l ≈ J nl, b, we can obtain: (5) The nonlinear current density of third-order intermodulation can be written as: (6) in, ε 3 is the third-order nonlinear permittivity. P c This refers to the input carrier power.

[0053] Substituting formulas (5) and (6) into formula (3) yields the expression for the third-order reflection PIM: (7) Figure 4 and Figure 5 The images show exploded views and assembly diagrams of the waveguide transmission line used in this invention. The waveguide transmission line structure consists of two L29 connectors (in...). Figure 4 and Figure 5(represented by labels 1 and 2), two waves are converted (in) Figure 4 and Figure 5 (represented by numerals 3 and 4), two waveguide sections (in) Figure 4 and Figure 5 (represented by numerals 5 and 6) and absorbing sheet (in Figure 4 and Figure 5 The absorber consists of seven parts (represented by the number 7). The material of the absorber in this embodiment can be polyurethane, polyurethane coated, or low-intermodulation SABPIM (a type of absorber). In application, the type of absorber can be added or removed according to specific needs. During testing, the replacement process is completed simply by re-inserting the absorber into the waveguide transmission line.

[0054] Figure 6 This is a flowchart of the reflection PIM test based on a waveguide transmission line structure. The main steps include rectangular waveguide assembly, electrical parameter and PIM noise floor (also known as the noise of the PIM test system itself) testing, absorbing sheet assembly and replacement, and absorbing sheet electrical parameter and PIM testing. Different waveguide transmission lines can test the reflection PIM of absorbing sheets in different frequency bands; the specific relationship between dimensions and frequency bands is shown in Table 1.

[0055] Table 1. Relationship between waveguide dimensions and frequency bands

[0056] Figure 7 The comparison results show the return loss of a 1.8GHz rectangular waveguide transmission line before and after assembling the absorber. Figure 7 As can be seen, the return loss of all three types of absorbing sheets used remained below -10dB in the intermodulation test frequency band.

[0057] Figure 8 The PIM test results of three types of absorbing sheets under a 1.8GHz rectangular waveguide transmission line clearly show that the PIM values ​​of the different absorbing sheets vary considerably, with a maximum resolution close to 45dB. Furthermore, as the input power increases, the PIM values ​​of all three types of absorbing sheets increase with a slope close to 3, which is in line with expectations. Based on formula (7), the third-order nonlinear coefficients of the three types of absorbing sheets at this frequency can be derived. g 3. Thus, the reflection PIM value of the absorber under different input powers can be calculated. Figure 9 , Figure 10 and Figure 11 The comparison results show the calculated and measured values ​​(also known as actual measured values) of the reflected PIM (polyurethane image quality) of polyurethane absorbing sheets, polyurethane coated absorbing sheets, SABPIM-1 absorbing sheets, and SABPIM-2 absorbing sheets under different input powers. Figure 9 , Figure 10 and Figure 11The comparison results show that: A. The calculated values ​​and measured values ​​are in high agreement, verifying the accuracy of the method. Figure 9 , Figure 10 and Figure 11 The calculated value obtained by substituting the third-order nonlinear dielectric constant g3 (derived from formula (7)) extracted by the method of the present invention into the theoretical model was compared with the actual measured value, and the two showed a high degree of agreement. This fully demonstrates that the method of the present invention can accurately and truly reflect the nonlinear characteristics of the absorbing sheet material and has high characterization accuracy.

[0058] B. The reflected PIM increases systematically with input power, which is consistent with theoretical expectations. Figure 9 , Figure 10 and Figure 11 The curves clearly show that as the input power increases, the reflection PIM value of each absorbing sheet increases monotonically with a slope close to 3 (dB / dB), which is completely consistent with the prediction of the third-order intermodulation theory (it can be seen from formula (7) that the slope of the third-order PIM power is 3), further proving the theoretical self-consistency and reliability of the method of the present invention.

[0059] C. Quantitatively distinguishes microwave absorbing sheets made of different materials, and has the ability to make lateral comparisons. pass Figure 9 , Figure 10 and Figure 11 The comparison clearly shows that there are significant differences in the reflection PIM levels among the three types of absorbers: polyurethane, polyurethane coating, and SABPIM. Figure 8 The maximum resolution is close to 45 dB, indicating that the method of the present invention can effectively distinguish the material intermodulation performance of different absorbing sheets, realize the quantitative description of the nonlinear characteristics of absorbing sheets, and facilitate the establishment of a database and horizontal comparison between absorbing sheets of different materials.

[0060] The method of the present invention has the following advantages: 1. By setting clear two-port electrical parameter calibration conditions and temperature stability PIM noise floor calibration, the accuracy of nonlinear characterization of absorbing sheet materials is significantly improved, and the interference of thermal drift on test results is effectively eliminated.

[0061] 2. It adopts a modular silver-plated aluminum alloy waveguide transmission line, which completely encloses the electromagnetic field within the waveguide, providing strong shielding and minimal environmental interference.

[0062] 3. Absorbing sheets can be directly assembled with simple cutting, maintaining the original shape of the material. This overcomes the limitation of the coaxial line method, which requires special processing of the sample, and is especially suitable for large-size or sheet-shaped absorbing materials.

[0063] 4. Simultaneously acquiring forward transmission PIM and reverse reflection PIM, and using the amplitude difference between the two (ideally, homogeneous materials approach 0 dB, and a deviation >3 dB reflects asymmetric nonlinearity) to assist in judging the homogeneity of the internal structure of the material, significantly improving the material characterization dimensions and information content.

[0064] 5. By introducing a fill rate index (90%~100%) and a standard torque wrench tightening (1 N·m), the contact state is ensured to be consistent each time the absorber under test is replaced, effectively eliminating systematic errors caused by assembly differences and improving test repeatability and reliability.

[0065] 6. The thickness of the absorbing sheet is dynamically determined and adjusted by the return loss S11, providing an adaptive test optimization process for materials with different absorption capabilities, and realizing the fine differentiation of different materials.

[0066] 7. By plotting the complete curve of reflected PIM as a function of input power, and combining it with theoretical formulas, the (TE) is derived. 10 The third-order nonlinear dielectric constant g3 is extracted from the third-order PIM expression in the model, realizing a quantitative description of the nonlinear characteristics of the absorbing sheet material, which facilitates the horizontal comparison between absorbing sheets of different materials and the establishment of a database.

[0067] 8. By simply changing the physical dimensions of the waveguide transmission line, the test frequency band can be covered from 0.8 GHz to 2.6 GHz (rectangular waveguide width from 292.1 mm to 72.14 mm, and circular waveguide inner diameter from 251.84 mm to 83.62 mm), providing wideband expansion capability.

[0068] 9. The silver-plated aluminum alloy waveguide, combined with the L29 low intermodulation connector and RG141 low intermodulation cable, suppresses the system's PIM noise floor to a minimum. Below 130 dBm, far lower than typical testing platforms, effectively ensuring the authenticity of test results.

[0069] 10. Compared with free space testing methods, this invention does not require a complex anechoic chamber antenna system, the experimental conditions are simpler, the testing process is easier to standardize and promote, and the testing threshold and cost are reduced.

[0070] Example 5: Please see Figure 12 As shown, the present invention also provides an electronic device 100 based on a nonlinear characterization method for absorbing sheet materials with waveguide transmission line structure; the electronic device 100 includes a memory 101, at least one processor 102, a computer program 103 stored in the memory 101 and executable on the at least one processor 102, and at least one communication bus 104.

[0071] The memory 101 can be used to store the computer program 103. The processor 102 implements the steps of the nonlinear characterization method for absorbing sheet materials based on waveguide transmission line structures described in Embodiment 1 by running or executing the computer program stored in the memory 101 and calling the data stored in the memory 101. The memory 101 may mainly include a program storage area and a data storage area. The program storage area may store the operating system, application programs required for at least one function (such as sound playback function, image playback function, etc.), etc.; the data storage area may store data created according to the use of the electronic device 100 (such as audio data), etc. In addition, the memory 101 may include non-volatile memory, such as hard disk, memory, plug-in hard disk, smart media card (SMC), secure digital (SD) card, flash card, at least one disk storage device, flash memory device, or other non-volatile solid-state storage device.

[0072] The at least one processor 102 may be a Central Processing Unit (CPU), or other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. The processor 102 may be a microprocessor or any conventional processor. The processor 102 is the control center of the electronic device 100, connecting various parts of the electronic device 100 via various interfaces and lines.

[0073] The memory 101 in the electronic device 100 stores multiple instructions to implement a nonlinear characterization method for absorbing sheet materials based on waveguide transmission line structures, and the processor 102 can execute the multiple instructions to achieve the following: Calibration steps: The waveguide transmission line structure is calibrated to obtain the calibrated waveguide transmission line structure; Assembly steps: Assemble the absorber to be tested onto the calibrated waveguide transmission line structure to obtain the waveguide transmission line structure with the absorber. Test procedure: Test the waveguide transmission line structure equipped with the absorbing sheet to obtain the return loss index of the absorbing sheet under test. If the return loss index of the absorbing sheet under test is less than the first set threshold in the test frequency band, perform PIM test and obtain the PIM test result; if the return loss index of the absorbing sheet under test is greater than or equal to the first set threshold in the test frequency band, do not perform PIM test. Repeat the assembly and testing steps until all the absorbers under test have been tested. Inspection steps: Determine whether there are more than a set number of absorbers whose reflected PIM is lower than the sensitivity of the receiving system. If so, increase the input power in steps within a set range until the PIM amplitude of the absorber is within the test threshold of the PIM test system. Retest the absorbers that have no test results. Repeat the assembly and testing steps until the intermodulation level of all absorbers under test can be distinguished.

[0074] Example 6: If the modules / units integrated in the electronic device 100 are implemented as software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, all or part of the processes in the methods of the above embodiments can also be implemented by a computer program instructing related hardware. The computer program can be stored in a computer-readable storage medium, and when executed by a processor, it can implement the steps of the various method embodiments described above. The computer program includes computer program code, which can be in the form of source code, object code, executable files, or certain intermediate forms. The computer-readable medium can include: any entity or device capable of carrying the computer program code, a recording medium, a USB flash drive, a portable hard drive, a magnetic disk, an optical disk, a computer memory, and a read-only memory (ROM).

[0075] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0076] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0077] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0078] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0079] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method for nonlinear characterization of a wave-absorbing sheet material based on a waveguide transmission line structure, characterized in that, Includes the following steps: Calibration steps: The waveguide transmission line structure is calibrated to obtain the calibrated waveguide transmission line structure; Assembly steps: Assemble the absorber to be tested onto the calibrated waveguide transmission line structure to obtain the waveguide transmission line structure with the absorber. Test procedure: Test the waveguide transmission line structure equipped with the absorbing sheet to obtain the return loss index of the absorbing sheet under test. If the return loss index of the absorbing sheet under test is less than the first set threshold in the test frequency band, perform PIM test and obtain the PIM test result; if the return loss index of the absorbing sheet under test is greater than or equal to the first set threshold in the test frequency band, do not perform PIM test. Repeat the assembly and testing steps until all the absorbers under test have been tested. Inspection steps: Determine whether there are more than a set number of absorbers whose reflected PIM is lower than the sensitivity of the receiving system. If so, increase the input power in steps within a set range until the PIM amplitude of the absorber is within the test threshold of the PIM test system. Retest the absorbers that have no test results. Repeat the assembly and testing steps until the intermodulation level of all absorbers under test can be distinguished.

2. The nonlinear characterization method for absorbing sheet materials based on waveguide transmission line structures according to claim 1, characterized in that, The calibration of the waveguide transmission line structure to obtain the calibrated waveguide transmission line structure is specifically as follows: The waveguide transmission line structure is calibrated for electrical parameters. After the electrical parameters are calibrated, the waveguide transmission line structure is calibrated for noise by the PIM test system itself to obtain the calibrated waveguide transmission line structure.

3. The nonlinear characterization method for absorbing sheet materials based on waveguide transmission line structures according to claim 2, characterized in that, After the electrical parameters are calibrated, the noise of the PIM test system itself is calibrated on the waveguide transmission line structure, specifically as follows: After electrical parameter calibration, the noise of the PIM test system itself is measured when the dual-carrier input power is at the set power. If the noise of the PIM test system itself is less than the second set threshold, keep the PIM test system powered on and let it stand still for the set time, and then measure the noise of the PIM test system itself again. If the deviation between the two measurement results does not exceed the third set threshold, the calibration is deemed effective. Otherwise, continue to let the PIM test system stand still until the PIM test system is thermally stable and then retest.

4. The nonlinear characterization method for absorbing sheet materials based on waveguide transmission line structures according to claim 1, characterized in that, Before assembling the absorber under test onto the calibrated waveguide transmission line structure to obtain the waveguide transmission line structure with the absorber, the fill ratio is determined, and based on the fill ratio, it is determined whether there is an obvious air gap between the absorber and the inner cavity of the waveguide transmission line structure.

5. The nonlinear characterization method for absorbing sheet materials based on waveguide transmission line structures according to claim 4, characterized in that, The formula for calculating the fill rate is: 。 6. The nonlinear characterization method for absorbing sheet materials based on waveguide transmission line structures according to claim 1, characterized in that, When the return loss index of the absorber under test is less than a first preset threshold within the test frequency band, a PIM test is performed, specifically as follows: When the return loss index of the absorber under test is less than the first set threshold in the test frequency band, a joint test of forward transmission PIM and reverse reflection PIM is performed.

7. The nonlinear characterization method for absorbing sheet materials based on waveguide transmission line structures according to claim 1, characterized in that, After obtaining the PIM test results, the reflection PIM curve is plotted based on the PIM test results.

8. A nonlinear characterization system for absorbing sheet materials based on waveguide transmission line structures, characterized in that, include: The calibration module is used to calibrate the waveguide transmission line structure to obtain the calibrated waveguide transmission line structure. The assembly module is used to assemble the absorber under test onto the calibrated waveguide transmission line structure to obtain a waveguide transmission line structure with the absorber assembled. The test module is used to test the waveguide transmission line structure equipped with an absorbing sheet to obtain the return loss index of the absorbing sheet under test. When the return loss index of the absorbing sheet under test is less than a first set threshold in the test frequency band, a PIM test is performed to obtain the PIM test result; when the return loss index of the absorbing sheet under test is greater than or equal to the first set threshold in the test frequency band, a PIM test is not performed. Repeat the assembly and test modules until all the absorbers under test have been tested. The testing module is used to determine whether there are more than a set number of absorbing sheets whose reflected PIM is lower than the sensitivity of the receiving system. If so, the input power is increased in steps within a set range until the PIM amplitude of the absorbing sheet is within the test threshold of the PIM test system. The absorbing sheets with no test results are retested. The assembly module and the test module are used repeatedly until the intermodulation level of all the absorbing sheets under test is distinguished.

9. An electronic device comprising a memory and a processor, wherein the memory stores a computer program, characterized in that, When the processor executes the computer program, it implements the steps of the nonlinear characterization method for absorbing sheet materials based on waveguide transmission line structures as described in any one of claims 1 to 7.

10. A storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, it implements the steps of the nonlinear characterization method for absorbing sheet materials based on waveguide transmission line structures as described in any one of claims 1 to 7.

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