Reverberation chamber testing method for equivalent absorption cross section of wave-absorbing material based on mirror image principle and application of reverberation chamber testing method

Abstract

The invention relates to the technical field of microwave measurement and reverberation chambers, in particular to a theoretical model for reverberation chamber testing of an equivalent absorption cross section of a wave-absorbing material based on the mirror image principle and application, and the method comprises the steps: building a mirror image model, and obtaining the number of mirror image objects after multiple reflections and the total surface area of the mirror image model; acquiring a time constant in a no-load state; acquiring a time constant in a loading state; and constructing a theoretical model for testing the reverberation chamber of the equivalent absorption cross section of the wave-absorbing material. The mirror image principle is applied to the field of microwave measurement based on the reverberation chamber, and rapid and accurate equivalent absorption cross section reverberation chamber testing is achieved.

Description

Technical Field

[0001] The present invention relates to the technical fields of microwave measurement and reverberation chamber technology, and particularly relates to a theoretical model and application of reverberation chamber testing for the equivalent absorption cross-section of an absorbing material based on the mirror principle. Background Art

[0002] A microwave reverberation chamber is a large metal resonant cavity. By using different stirring techniques, the distribution of electromagnetic modes in the reverberation chamber is changed, thereby generating a statistically uniform, isotropic, and polarization-uniform electromagnetic field in the working area. Compared with traditional microwave measurement techniques, the reverberation chamber can generate a high-intensity electromagnetic field environment with a lower input power, so it is widely used in the field of electromagnetic compatibility testing. In recent years, with the continuous development and in-depth application of wireless communication technology, the research and development of a large number of wireless devices have put forward new requirements and challenges for wireless testing technology. With its advantages such as low construction cost, large test area, and high efficiency, the reverberation chamber technology provides an economical and efficient solution for the over-the-air testing of wireless devices, and thus has received the attention and favor of the industrial community.

[0003] In actual tests, due to the presence of devices such as antennas, DUTs, brackets, and cables, the reverberation chamber is always in a loaded environment, and different DUTs correspond to different loading states. Existing research generally believes that loading will lead to the deterioration of the field uniformity in the reverberation chamber. Therefore, most reverberation chamber tests require the loading state of the reverberation chamber to be as low as possible. However, in some active tests, it is necessary to adjust the coherence bandwidth of the reverberation chamber by loading to achieve flat fading of the wireless channel, thereby ensuring the accuracy of the test. It can be seen that different reverberation chamber tests have different requirements for the loading state of the reverberation chamber. Therefore, it is crucial to determine the loading state of the reverberation chamber.

[0004] The adjustment of the loading state of the reverberation chamber is mainly achieved by controlling the loading amount of the absorbing material, and the loading performance of the absorbing material can be measured by the absorption cross-section. The absorption cross-section is defined as the ratio of the absorbed power of an object under plane-wave illumination to the incident-wave power density. Given the statistical uniformity of the electromagnetic field in the reverberation chamber, the absorption cross-section under a single-state incident wave cannot effectively measure the performance of the absorbing material in a high-reverberation environment. Therefore, the concept of equivalent absorption cross-section is usually adopted in the field of reverberation chambers. The equivalent absorption cross-section is defined as the average value of the absorption cross-sections in all incident directions and polarization states. It is worth pointing out that the equivalent absorption cross-section can not only measure the loading state of the reverberation chamber, but also has a clear mathematical relationship with many characteristic parameters (such as quality factor, channel transfer function, coherence bandwidth, etc.) that characterize the reverberation chamber and the wireless channel. It can be seen that as long as the equivalent absorption cross-section of the absorbing material can be determined, the loading state of the reverberation chamber and the characteristics of the wireless channel can be determined.

[0005] At present, the equivalent absorption cross-section of microwave absorbing materials is mainly determined by the quality factor method. This method is based on the energy loss mechanism in a reverberation chamber, and establishes a mathematical relationship between the equivalent absorption cross-section of the microwave absorbing material and the quality factor corresponding to its loss. On this basis, by measuring the quality factors of the reverberation chamber in the unloaded and loaded states, the equivalent absorption cross-section is calculated using a formula. In addition, some research has established a theoretical model of the equivalent absorption cross-section based on the original definition of the equivalent absorption cross-section under the condition of uniform incoming waves. This method derives the transmission coefficient and reflection coefficient of electromagnetic waves at the surface of the microwave absorbing material under different incident directions and different polarization states, and then establishes a mathematical relationship between the equivalent absorption cross-section of the microwave absorbing material, the geometric surface area of the microwave absorbing material, and the relative permittivity.

[0006] However, the existing reverberation chamber method for testing the equivalent absorption cross-section has the following problems: The quality factor method can only reflect the dissipation mechanism of electromagnetic field energy, and cannot intuitively reflect the propagation mechanism of electromagnetic waves in the reverberation chamber and the absorption mechanism of the microwave absorbing material for electromagnetic waves, making it difficult to guide the loading optimization work of the reverberation chamber. The mathematical model established based on the original definition of the equivalent absorption cross-section requires the characteristic parameters of the microwave absorbing material (such as relative permittivity, conductivity, surface area) to be given in advance, otherwise the equivalent absorption cross-section of the microwave absorbing material cannot be accurately calculated. In addition, this method has relatively strict requirements for the shape and size of the test object: the test object should have a regular geometric shape, and its skin depth should be much larger (or much smaller) than the cross-sectional size, otherwise more complex derivations and calculations are required.

[0007] Therefore, it is necessary to provide a theoretical model and application for testing the equivalent absorption cross-section of microwave absorbing materials based on the mirror principle in a reverberation chamber to solve the above problems. Summary of the Invention

[0008] The present invention provides a theoretical model and application for testing the equivalent absorption cross-section of microwave absorbing materials based on the mirror principle in a reverberation chamber. According to different reverberation chamber test environments and microwave absorbing material characteristics, a theoretical model for testing the equivalent absorption cross-section of microwave absorbing materials in a reverberation chamber is determined, and then accurate measurement of the equivalent absorption cross-section is achieved. To solve the existing problems.

[0009] The following technical solutions are provided for a theoretical model of testing the equivalent absorption cross-section of microwave absorbing materials based on the mirror principle in a reverberation chamber of the present invention, including: According to the mirror principle, establish a mirror model of the reverberation chamber test system in the unloaded state, and obtain the number of mirror objects after multiple reflections and the total surface area of the mirror model; Equivalent all the losses in the reverberation chamber system in the unloaded state to the losses of the reverberation chamber cavity wall, and obtain the electric field strength of the electromagnetic wave after multiple reflections based on the initial electric field strength; In the no-load state, based on the electric field strength after multiple reflections of electromagnetic waves, the initial electric field energy, the number of mirror objects after multiple reflections, and the total surface area of the mirror model, obtain the first electric field energy in the reverberation chamber after multiple reflections of electromagnetic waves; Obtain the time constant in the no-load state according to the first electric field energy; In the loaded state, obtain the probability that the electromagnetic wave is not absorbed by the absorbing material after multiple reflections; In the loaded state, based on the probability that the electromagnetic wave is not absorbed by the absorbing material after multiple reflections, the electric field strength after multiple reflections of the electromagnetic wave, the initial electric field energy, the number of mirror objects after multiple reflections, and the total surface area of the mirror model, obtain the second electric field energy in the reverberation chamber after multiple reflections of the electromagnetic wave; Obtain the time constant in the loaded state according to the second electric field energy; According to the typical distance, the inner surface area of the reverberation chamber, and the time constants corresponding to the no-load state and the loaded state, construct a theoretical model for the reverberation chamber test of the equivalent absorption cross-section of the absorbing material, where the typical distance is the average propagation distance between the reflection points during the entire reflection process of the electromagnetic wave.

[0010] Preferably, in the no-load state, the expression for the electric field strength after multiple reflections of the electromagnetic wave is:

[0011] In the formula, represents the electric field strength after times of reflections of the electromagnetic wave; represents the initial electric field strength; represents the average reflection coefficient for all incident directions and polarization states.

[0012] Preferably, in the no-load state, the expression for the first electric field energy in the reverberation chamber after multiple reflections of the electromagnetic wave is:

[0013] In the formula, represents the first electric field energy in the reverberation chamber after times of reflections of the electromagnetic wave within the propagation time t in the no-load state; represents the initial electric field energy; represents the speed of light; represents the typical distance, that is, the average propagation distance between the reflection points during the entire reflection process of the electromagnetic wave; represents the natural logarithm operation; represents the propagation time after times of reflections of the electromagnetic wave; represents the average reflection coefficient for all incident directions and polarization states; represents the initial electric field strength; represents after the number of mirror objects after reflections; represents the total surface area of the mirror model after

[0014] Preferably, the time constant in the no-load state satisfies the expression:

[0015] wherein, represents the time constant in the no-load state; represents in the no-load state, the first electric field energy in the reverberation chamber after the electromagnetic wave passes through reflections; represents the initial electric field energy; represents the propagation time of the electromagnetic wave after passing through reflections.

[0016] Preferably, in the loaded state, the expression for the probability that the electromagnetic wave is not absorbed by the absorbing material after multiple reflections is:

[0017] wherein, represents in the loaded state, the probability that the electromagnetic wave is not absorbed by the absorbing material after passing through reflections; represents the probability that the electromagnetic wave is absorbed by the absorbing material after 0 reflections; represents the probability that the electromagnetic wave is absorbed by the absorbing material after the th reflection; represents the equivalent absorption cross-section of the absorbing material; represents the inner surface area of the reverberation chamber.

[0018] Preferably, in the loaded state, the expression for the second electric field energy in the reverberation chamber after the electromagnetic wave passes through multiple reflections is:

[0019] wherein, represents the second electric field energy in the reverberation chamber after the electromagnetic wave passes through reflections within the propagation time in the loaded state; represents the initial electric field energy; represents the speed of light; represents the typical distance, i.e., the average propagation distance between reflection points during the entire reflection process of the electromagnetic wave; represents the equivalent absorption cross-section of the absorbing material; represents the inner surface area of the reverberation chamber; represents the average reflection coefficient under all incident directions and polarization states; represents the propagation time of the electromagnetic wave after reflections; represents after reflections, the number of mirror objects; represents after reflections, the total surface area of the mirror model.

[0020] Preferably, the time constant in the loaded state satisfies the expression:

[0021] wherein, represents the time constant in the loaded state; represents that in the loaded state, after the electromagnetic wave passes through reflections, the second electric field energy in the reverberation chamber; represents the initial electric field energy; represents that the electromagnetic wave passes through reflections, the propagation time.

[0022] Preferably, the expression of the theoretical model is:

[0023] wherein, represents the time constant in the loaded state; represents the time constant in the unloaded state; represents the inner surface area of the reverberation chamber; represents the speed of light; represents the typical distance.

[0024] Preferably, the unloaded state means there is no absorbing material in the reverberation chamber; the loaded state means there is an absorbing material in the reverberation chamber.

[0025] The technical solution adopted by the application of the theoretical model for testing the equivalent absorption cross-section reverberation chamber based on the mirror principle of the present invention includes: inputting the inner surface area of the reverberation chamber, the typical distance, and the corresponding time constants in the unloaded state and the loaded state into the theoretical model of the present invention to obtain the equivalent absorption cross-section of the absorbing material to be tested, wherein the typical distance is determined by Monte Carlo simulation; the transmission coefficient between the transmitting antenna and the receiving antenna is measured at all stirring positions, and the time constant is obtained according to the transmission coefficient.

[0026] The beneficial effects of the present invention are: By obtaining the time constants in the no-load state and the loaded state respectively, and then constructing a theoretical model for reverberation chamber testing of the equivalent absorption cross-section of microwave absorbing materials based on the mirror principle based on the time constants corresponding to the no-load state and the loaded state, so as to obtain the equivalent absorption cross-section of the microwave absorbing material to be measured by using the theoretical model. The whole process intuitively and clearly shows the path of electromagnetic waves being (or not being) absorbed by the microwave absorbing material, which helps to analyze the relative positions of the excitation source and the microwave absorbing material under specific requirements, has a certain guiding role in the optimization of loading, can quickly and accurately measure the equivalent absorption cross-section of the microwave absorbing material, and is not affected by the characteristics of the microwave absorbing material and the cavity size factors, and is easy to be applied in engineering.

[0027] Secondly, the present invention applies the mirror principle to the field of microwave measurement based on the reverberation chamber, realizes the reverberation chamber testing of the equivalent absorption cross-section quickly and accurately, expands the analysis theory in the field of reverberation chamber measurement, and helps to promote the application and popularization of the mirror principle in other reverberation chamber tests to improve their test performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained according to these drawings.

[0029] Figure 1 It is a flowchart for constructing a theoretical model for reverberation chamber testing of the equivalent absorption cross-section of microwave absorbing materials based on the mirror principle of the present invention; Figure 2 It is a schematic plan view of the mirror model of the reverberation chamber used in the embodiment of the present invention; Figure 3 It is a schematic structural view of reverberation chamber scene 1 for measuring the equivalent absorption cross-section of microwave absorbing materials in the embodiment of the present invention; Figure 4 It is a schematic structural view of reverberation chamber scene 2 for measuring the equivalent absorption cross-section of microwave absorbing materials in the embodiment of the present invention; Figure 5 It is a schematic diagram of the Monte Carlo simulation results of the typical distances of the reverberation chamber used in the embodiment of the present invention; Figure 6 It is a power delay spectrum diagram at 3.2 GHz of the reverberation chamber used in the embodiment of the present invention under three loading states; Figure 7 It is a schematic diagram of the measurement results of the time constants of the reverberation chamber used in the embodiment of the present invention under three loading states; Figure 8Schematic diagram of the measurement results of the equivalent absorption cross-section of the absorbing material based on the mirror principle and the traditional method in reverberation chamber scenario 1 and reverberation chamber scenario 2 of the embodiments of the present invention. Detailed implementation manners

[0030] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0031] An embodiment of the theoretical model for the reverberation chamber test of the equivalent absorption cross-section of an absorbing material based on the mirror principle of the present invention, as Figure 1 shown, includes: S1. Establish a mirror model and obtain the number of mirror objects after multiple reflections and the total surface area of the mirror model; Specifically, according to the mirror principle, establish a mirror model of the reverberation chamber test system in the no-load state, and obtain the number of mirror objects after multiple reflections and the total surface area of the mirror model.

[0032] S2. Obtain the time constant in the no-load state; Specifically, all the losses in the reverberation chamber system in the no-load state are equivalently regarded as the losses of the reverberation chamber cavity wall, and the electric field strength after multiple reflections of the electromagnetic wave is obtained based on the initial electric field strength; in the no-load state, based on the electric field strength after multiple reflections of the electromagnetic wave, the initial electric field energy, the number of mirror objects after multiple reflections, and the total surface area of the mirror model, obtain the first electric field energy in the reverberation chamber after multiple reflections of the electromagnetic wave; obtain the time constant in the no-load state according to the first electric field energy; where the no-load state means that there is no absorbing material in the reverberation chamber.

[0033] Exemplarily, the expression of the electric field strength after multiple reflections of the electromagnetic wave is: (1) In the formula, represents the electric field strength after n times of reflections of the electromagnetic wave; represents the initial electric field strength; represents the average reflection coefficient in all incident directions and polarization states.

[0034] Exemplarily, in this embodiment, in the no-load state, the expression of the first electric field energy in the reverberation chamber after multiple reflections of the electromagnetic wave is: (2) (3) According to Equations (1) and (2), we have: (4) wherein, represents the propagation time under the no-load state for the electromagnetic wave passing through the first electric field energy in the reverberation chamber after reflections; represents the initial electric field energy; represents the speed of light; represents the natural logarithm operation; represents the propagation time for the electromagnetic wave passing through reflections; represents the average reflection coefficient under all incident directions and polarization states; represents the initial electric field strength, and the initial electric field strength is a preset electric field strength; represents the number of mirror objects after reflections; represents the total surface area of the mirror model after reflections.

[0035] Exemplarily, in this embodiment, the time constant under the no-load state satisfies the expression: (5) wherein, represents the time constant under the no-load state; represents the propagation time under the no-load state for the electromagnetic wave passing through the first electric field energy in the reverberation chamber after reflections; represents the initial electric field energy, and the initial electric field energy is a preset electric field energy; represents the propagation time for the electromagnetic wave passing through

[0036] S3. Obtain the time constant under the loaded state; Specifically, under the loaded state, according to the probability that the electromagnetic wave is not absorbed by the absorbing material after multiple reflections, the electric field strength, the initial electric field energy, the number of mirror objects, and the total surface area of the mirror model after multiple reflections of the electromagnetic wave, obtain the second electric field energy in the reverberation chamber after multiple reflections of the electromagnetic wave; obtain the time constant under the loaded state according to the second electric field energy; wherein, the loaded state means that the reverberation chamber contains an absorbing material.

[0037] Exemplarily, under the loaded state, the expression for the probability that the electromagnetic wave is not absorbed by the absorbing material after multiple reflections is: (6) In the formula, represents the probability that the electromagnetic wave is not absorbed by the wave - absorbing material after reflections under the loading state; represents the probability that the electromagnetic wave is absorbed by the wave - absorbing material after 0 reflections; represents the probability that the electromagnetic wave is absorbed by the wave - absorbing material after the th reflection; represents the equivalent absorption cross - section of the wave - absorbing material; represents the inner surface area of the reverberation chamber.

[0038] Exemplarily, under the loading state, the expression of the second - electric - field energy in the reverberation chamber after multiple reflections of the electromagnetic wave is: (7) In the formula, represents the second - electric - field energy in the reverberation chamber after the electromagnetic wave undergoes reflections within the propagation time under the loading state; represents the initial electric - field energy; represents the speed of light; represents the typical distance, that is, the average propagation distance between the reflection points during the entire reflection process of the electromagnetic wave; represents the equivalent absorption cross - section of the wave - absorbing material; represents the inner surface area of the reverberation chamber; represents the average reflection coefficient under all incident directions and polarization states; represents the propagation time when the electromagnetic wave undergoes reflections; represents after reflections, the number of mirror objects; represents after reflections, the total surface area of the mirror model.

[0039] Exemplarily, the time constant under the loading state satisfies the expression: (8) In the formula, represents the time constant under the loading state; represents the second - electric - field energy in the reverberation chamber after the electromagnetic wave undergoes reflections under the loading state; represents the initial electric - field energy; represents the propagation time when the electromagnetic wave undergoes reflections.

[0040] S4. Construct a theoretical model for reverberation chamber testing of the equivalent absorption cross-section of the absorbing material; Construct a theoretical model for reverberation chamber testing of the equivalent absorption cross-section of the absorbing material according to the typical distance, the inner surface area of the reverberation chamber, and the time constants corresponding to the no-load state and the loaded state, where the typical distance is the average propagation distance between reflection points during the entire reflection process of the electromagnetic wave.

[0041] Exemplarily, the expression of the theoretical model is: (9) In the formula, represents the time constant in the loaded state; represents the time constant in the no-load state; represents the inner surface area of the reverberation chamber; represents the speed of light; represents the typical distance.

[0042] An application of the theoretical model for reverberation chamber testing of the equivalent absorption cross-section based on the mirror principle of the present invention includes: inputting the inner surface area of the reverberation chamber, the typical distance, and the time constants corresponding to the no-load state and the loaded state into the theoretical model to obtain the equivalent absorption cross-section of the absorbing material to be tested, where the typical distance is determined by Monte Carlo simulation; the time constant is obtained by measuring the transmission coefficient between the transmitting antenna and the receiving antenna at all stirring positions and according to the transmission coefficient.

[0043] Exemplarily, in this embodiment, the steps for obtaining the typical distance are: determine the inner surface area of the reverberation chamber according to the size of the reverberation chamber for the test, and at the same time determine the typical distance by Monte Carlo simulation, that is: 1. Set the simulation parameters, and the simulation parameters include the number of excitation sources, the number of propagation directions, and the number of reflections; 2. Set the boundary conditions of the simulation according to the size of the reverberation chamber; 3. Randomly set the coordinate position of the i th ( ) excitation source in the reverberation chamber; 4. For the i th excitation source, randomly set the j th ( ) initial propagation direction; 5. Simulate the reflection under the condition that the i th excitation source is incident from the j th initial direction, and determine the propagation distance, reflection point, and reflection wave direction of the reflected wave; 6. Set the reflection point determined in step 5 as the new excitation source position, and at the same time set the reflection wave direction determined in step 5 as the new propagation direction, and repeat step 5 until the number of reflections in the simulation reaches the number of reflections set in step 1; 7. Repeat steps 4-6 until the number of propagation directions in the simulation reaches the number of propagation directions set in step 1; 8. Repeat steps 3-7 until the number of excitation sources in the simulation reaches the number of excitation sources set in step 1; 9. Calculate the typical distance according to the simulation data.

[0044] Exemplarily, the steps of obtaining the time constants corresponding to the no-load state and the loaded state are as follows: In the no-load state (i.e., without deploying the microwave absorbing material), measure the transmission coefficient between the transmitting antenna and the receiving antenna in the reverberation chamber, and calculate the time constant of the no-load reverberation chamber; in the loaded state (the microwave absorbing material to be tested is deployed in the reverberation chamber), measure the transmission coefficient between the transmitting antenna and the receiving antenna in the reverberation chamber, and calculate the time constant of the loaded reverberation chamber. Among them, the steps of calculating the time constant of the no-load reverberation chamber and the time constant of the loaded reverberation chamber are: Connect the transmitting antenna and the receiving antenna to the two ports of the vector network analyzer respectively, and obtain the transmission coefficient between the transmitting antenna and the receiving antenna through the vector network analyzer ( ), draw the power delay spectrum (i.e., the first electric field energy spectrum) of the no-load reverberation chamber according to the transmission coefficient corresponding to the no-load reverberation chamber, obtain the time constant of the no-load reverberation chamber by extracting the attenuation rate of the power delay spectrum of the no-load reverberation chamber, draw the power delay spectrum (i.e., the second electric field energy spectrum) of the loaded reverberation chamber through the transmission coefficient corresponding to the loaded reverberation chamber, and obtain the time constant of the loaded reverberation chamber by extracting the attenuation rate of the power delay spectrum of the loaded reverberation chamber.

[0045] The following specifically describes this embodiment with reference to the attached Figures 2 to 8 drawings: As Figure 2 shown, in this embodiment, the schematic diagram of the mirror model plane includes multiple rectangles (reverberation chambers), and the subscripts in the rectangles () indicate that the rectangle is the mirror image generated when the electromagnetic wave undergoes the th reflection. In addition, Figure 2 shows an example of the propagation path of the electromagnetic wave actually absorbed (or not absorbed) by the microwave absorbing material and its equivalent propagation path in the mirror model.

[0046] As Figure 3 and 4 shown, the size of the reverberation chamber is 1.50 m × 1.44 m × 0.92 m, in which two mechanical stirrers and a mechanical turntable are installed, and an antenna bracket with adjustable height is equipped on the turntable. Both the transmitting antenna and the receiving antenna are standard horn antennas. The transmitting antenna is installed on the bracket at the bottom of the reverberation chamber, and its main radiation direction points to the horizontal stirrer. The receiving antenna is installed on the bracket of the turntable and is 20 cm away from the center of the turntable (the diameter of the turntable is 60 cm). The transmitting antenna and the receiving antenna are respectively connected to the two ports of the network analyzer. The test frequency band of the embodiment of the present invention is 2.4 GHz - 4 GHz, the stirrers and the turntable rotate independently, and each has 20 positions in one rotation, so there are 400 stirring positions in one test. During the whole test process, the position of the transmitting antenna remains unchanged.

[0047] In this embodiment, the equivalent absorption cross-section of the absorbing material is measured under two reverberation chamber loading conditions. The reverberation chamber test scenario 1 is as shown in Figure 3 Figure 1. In scenario 1, three absorbing materials of the same size are stacked in the corner of the reverberation chamber. The reverberation chamber test scenario 2 is as shown in Figure 4 Figure 2. In scenario 2, three absorbing materials of the same size are laid flat on the cavity wall of the reverberation chamber at a certain spacing. The size of the absorbing materials of the same size is 16 cm × 5 cm × 48 cm, and the spacing is 10 cm.

[0048] To verify the feasibility and effectiveness of the application of the theoretical model for the reverberation chamber test of the equivalent absorption cross-section of the absorbing material based on the mirror principle, the verification steps are as follows: Step 1. Perform Monte Carlo simulation on the typical distances of the used reverberation chamber to determine the values of the typical distances; Step 2. Conduct tests in the unloaded state of the reverberation chamber to obtain 400 groups of (transmission coefficient) parameters; Step 3. In reverberation chamber test scenario 1 and reverberation chamber test scenario 2, deploy the absorbing materials in the reverberation chamber respectively and conduct tests to obtain 400 groups of parameters in each scenario; Step 4. According to the parameters measured in Step 2 and Step 3, calculate the time constants of the reverberation chamber in three states respectively; Step 5. Use the typical distance obtained in Step 1 and the time constant obtained in Step 4 to calculate the equivalent absorption cross-section based on the mirror principle. At the same time, use the time constant obtained in Step 4 to calculate the equivalent absorption cross-section based on the traditional method, and compare and verify the equivalent absorption cross-sections obtained by the two methods.

[0049] The power delay profile (PDP) of the reverberation chamber can be calculated by the following formula (10). On this basis, the time constant of the reverberation chamber can be calculated by the following formula (11). When the loading state of the reverberation chamber is certain, the time constant is constant. This parameter reflects the dissipation rate of the stored energy in the reverberation chamber. The smaller its value, the faster the energy dissipation rate. (10) According to we get: (11) In the formula, is the f parameter of the S 21 recorded by the network analyzer at the th frequency point. IFFT represents the inverse fast Fourier transform algorithm, NThe statistical average of the samples, in this embodiment . ln represents the natural logarithm operation, slope The operation is solved by curve fitting The slope of the linear part.

[0050] The equivalent absorption cross-section of the microwave absorbing material based on the mirror principle can be calculated by the following formula (12): (12) In the formula, S is the inner surface area of the reverberation chamber; L is the typical distance; c is the speed of light; represents the time constant under the loaded state; represents the time constant under the unloaded state.

[0051] The equivalent absorption cross-section of the microwave absorbing material based on the traditional method can be calculated by the following formula (13): (13) In the formula, is the equivalent absorption cross-section of the microwave absorbing material by the traditional method; V is the inner volume of the reverberation chamber; represents the time constant under the loaded state; represents the time constant under the unloaded state; c is the speed of light.

[0052] In this embodiment, under the conditions of different numbers of propagation directions and different numbers of reflections, the variation curve of the typical distance obtained by simulation is as Figure 5 shown. It can be seen from Figure 5 that the simulated value of the typical distance gradually approaches the stable value, that is, the true value of the typical distance, as the number of reflections and the number of propagation directions increase. When the number of reflections reaches 60 and the number of propagation directions reaches 200, the simulated value of the typical distance hardly changes any more. Generally speaking, through simulation, the typical distance of the reverberation chamber used in this embodiment can be determined to be 0.808 m. In practice, the appropriate simulation parameters can be set according to the requirements such as the calculated time and accuracy to determine the typical distance of the used reverberation chamber.

[0053] The power delay spectra at 3.2 GHz of the reverberation chamber under the unloaded state, the loaded state 1 (the loaded state of scenario 1), and the loaded state 2 (the loaded state of scenario 2) are as Figure 6As shown. In this embodiment, the inverse Fourier transform bandwidth used is 600 MHz. The PDP curves of the reverberation chamber in three states all exhibit typical exponential decay characteristics. It can be seen that: compared with the reverberation chamber in the unloaded state, the energy decay rate in the loaded reverberation chamber is faster. This is because the loaded absorbing material absorbs part of the energy fed into the reverberation chamber, accelerating the dissipation of energy. At the same time, the energy decay rate in Scenario 2 is significantly greater than that in Scenario 1. This is because the exposed surface areas of the absorbing material in the two scenarios are different: the exposed surface area of the absorbing material in Scenario 2 is larger than that in Scenario 1 (see Figure 3 and Figure 4 ), so the absorbing material will absorb more electromagnetic energy in Scenario 2. Generally speaking, the energy decay rate in the reverberation chamber increases with the increase in the exposed surface area of the absorbing material.

[0054] The measurement results of the time constant of the reverberation chamber in the unloaded state, Loading State 1 (the loading state of Scenario 1), and Loading State 2 (the loading state of Scenario 2) are as Figure 7 shown. In the embodiment of the present invention, the inverse Fourier transform bandwidth used is 600 MHz, so the drawing range of the time constant is 2.7 GHz - 3.7 GHz. From Figure 7 it can be seen that under a specific loading state, the change of the time constant of the reverberation chamber with frequency is not significant. In addition, the time constant decreases significantly with the increase in the exposed surface area of the absorbing material, that is, the energy decay rate in the reverberation chamber increases with the increase in the exposed surface area of the absorbing material, which is consistent with the result obtained from the PDP curve.

[0055] In this embodiment, under two reverberation chamber scenarios, the measurement results of the equivalent absorption cross-section of the absorbing material based on the mirror principle and the traditional method are as Figure 8 shown. From Figure 8 it can be seen that: the calculation results of the equivalent absorption cross-section of the absorbing material based on the mirror principle and the traditional method are basically the same, and are independent of the test frequency and test scenario. This result fully proves the effectiveness, feasibility, and stability of the reverberation chamber test of the equivalent absorption cross-section based on the mirror principle proposed by the present invention.

[0056] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A theoretical model for reverberation chamber testing of equivalent absorption cross-section of absorbing materials based on the mirror principle, characterized in that: include: According to the mirror principle, a mirror model of the reverberation chamber test system under no-load condition is established, and the number of mirror objects after multiple reflections and the total surface area of ​​the mirror model are obtained; All losses in the reverberation chamber system under no-load condition are equivalent to the losses of the reverberation chamber wall, and the electric field strength of the electromagnetic wave after multiple reflections is obtained based on the initial electric field strength; In a no-load state, the first electric field energy in the reverberation chamber after multiple reflections of the electromagnetic wave is obtained based on the electric field intensity after multiple reflections of the electromagnetic wave, the initial electric field energy, the number of mirrored objects after multiple reflections, and the total surface area of ​​the mirrored model; Acquire a time constant in a no-load state according to the first electric field energy; Under the loading state, obtain the probability that the electromagnetic wave is not absorbed by the absorbing material after multiple reflections; Under the loading state, the second electric field energy in the reverberation chamber after multiple reflections of the electromagnetic wave is obtained according to the probability that the electromagnetic wave is not absorbed by the absorbing material after multiple reflections, the electric field strength of the electromagnetic wave after multiple reflections, the initial electric field energy, the number of mirrored objects after multiple reflections, and the total surface area of ​​the mirrored model; Acquire a time constant in a loaded state according to the energy of the second electric field; According to the typical distance, the inner surface area of ​​the reverberation chamber, and the corresponding time constants under no-load and loaded conditions, a theoretical model for reverberation chamber testing of the equivalent absorption cross section of absorbing materials is constructed, wherein the typical distance is the average propagation distance between reflection points of the electromagnetic wave during the entire reflection process.

2. According to claim 1, the theoretical model for reverberation chamber testing of equivalent absorption cross-section of absorbing materials based on the mirror principle is characterized in that: In the no-load state, the expression of the electric field strength of the electromagnetic wave after multiple reflections is: In the formula, Indicates that electromagnetic waves pass through The electric field strength after the second reflection; represents the initial electric field strength; represents the average reflection coefficient for all incident directions and polarization states.

3. The theoretical model for reverberation chamber testing of equivalent absorption cross-section of absorbing materials based on the mirror principle according to claim 1 is characterized in that: Under no-load conditions, the expression of the first electric field energy in the reverberation chamber after multiple reflections of the electromagnetic wave is: In the formula, Indicates the propagation time in no-load state Electromagnetic waves passing through The first electric field energy in the reverberation chamber after the second reflection; represents the initial electric field energy; represents the speed of light; It represents the typical distance, that is, the average propagation distance between reflection points of the electromagnetic wave during the entire reflection process; represents the natural logarithm operation; Indicates that electromagnetic waves pass through The propagation time of the secondary reflection; represents the average reflection coefficient for all incident directions and polarization states; represents the initial electric field strength; Indicates passing The number of mirrored objects after reflection; Indicates passing The total surface area of ​​the mirror model after secondary reflection.

4. The theoretical model for reverberation chamber testing of equivalent absorption cross-section of absorbing materials based on the mirror principle according to claim 1 is characterized in that: The time constant under no-load condition satisfies the expression: In the formula, Indicates the time constant under no-load condition; Indicates the propagation time in no-load state Electromagnetic waves passing through The first electric field energy in the reverberation chamber after the second reflection; represents the initial electric field energy; Indicates that electromagnetic waves pass through The propagation time of the second reflection.

5. The theoretical model for reverberation chamber testing of equivalent absorption cross-section of absorbing materials based on the mirror principle according to claim 1 is characterized in that: Under the loading state, the probability that the electromagnetic wave is not absorbed by the absorbing material after multiple reflections is expressed as: In the formula, Indicates that under loading condition, electromagnetic waves pass through The probability of not being absorbed by the absorbing material after the second reflection; It indicates the probability that the electromagnetic wave is absorbed by the absorbing material after 0 reflections; Indicates that electromagnetic waves pass through The probability of being absorbed by the absorbing material after the secondary reflection; It represents the equivalent absorption cross section of the absorbing material; Represents the internal surface area of ​​the reverberation chamber.

6. The theoretical model for reverberation chamber testing of equivalent absorption cross-section of absorbing materials based on the mirror principle according to claim 1 is characterized in that: Under the loading state, the expression of the second electric field energy in the reverberation chamber after multiple reflections of the electromagnetic wave is: In the formula, Indicates the propagation time of electromagnetic waves under loading condition Passing through The second electric field energy in the reverberation chamber after the secondary reflection; represents the initial electric field energy; represents the speed of light; It represents the typical distance, that is, the average propagation distance between reflection points of the electromagnetic wave during the entire reflection process; It represents the equivalent absorption cross section of the absorbing material; Represents the inner surface area of ​​the reverberation chamber; represents the average reflection coefficient for all incident directions and polarization states; Indicates that electromagnetic waves pass through The propagation time of the secondary reflection; Indicates passing The number of mirrored objects after reflection; Indicates passing The total surface area of ​​the mirror model after secondary reflection.

7. The theoretical model for reverberation chamber testing of equivalent absorption cross-section of absorbing materials based on the mirror principle according to claim 1 is characterized in that: The time constant under loading condition satisfies the expression: In the formula, Indicates the time constant under loading state; Indicates that under loading condition, electromagnetic waves pass through The second electric field energy in the reverberation chamber after the secondary reflection; represents the initial electric field energy; Indicates that electromagnetic waves pass through The propagation time of the second reflection.

8. The theoretical model for reverberation chamber testing of equivalent absorption cross-section of absorbing materials based on the mirror principle according to claim 1 is characterized in that: The expression of the theoretical model is: In the formula, Indicates the time constant under loading state; Indicates the time constant under no-load condition; Represents the inner surface area of ​​the reverberation chamber; represents the speed of light; Indicates typical distance.

9. The theoretical model for reverberation chamber testing of equivalent absorption cross-section of absorbing materials based on the mirror principle according to claim 1 is characterized in that: The no-load state means that there is no absorbing material in the reverberation chamber; the loaded state means that there is absorbing material in the reverberation chamber.

10. An application of a theoretical model for equivalent absorption cross-section reverberation chamber testing based on the mirror principle, characterized in that: include: Inputting the inner surface area, typical distance, and corresponding time constants under no-load state and loaded state of the reverberation chamber into the theoretical model described in any one of claims 1 to 9 to obtain the equivalent absorption cross section of the absorbing material to be tested; The typical distance is determined by Monte Carlo simulation; the transmission coefficient between the transmitting antenna and the receiving antenna is measured at all stirring positions, and the time constant is obtained according to the transmission coefficient.

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