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

Abstract

The present application relates to the technical field of microwave measurement and reverberation chamber, and particularly relates to a theoretical model of a reverberation chamber test of an equivalent absorption cross section of a wave-absorbing material based on a mirror principle and application, comprising: establishing a mirror model, and obtaining the number of mirror objects after multiple reflections and the total surface area of the mirror model; obtaining a time constant in an unloaded state; obtaining a time constant in a loaded state; and constructing a theoretical model of a reverberation chamber test of an equivalent absorption cross section of a wave-absorbing material. The present application applies the mirror principle to the field of microwave measurement based on a reverberation chamber, and realizes a fast and accurate reverberation chamber test of an equivalent absorption cross section.

Description

Technical Field

[0001] This invention relates to the fields of microwave measurement and reverberation chamber technology, specifically to a theoretical model and application of reverberation chamber testing based on the equivalent absorption cross section of absorbing materials according to the mirror principle. Background Technology

[0002] A microwave reverberation chamber is a large metal resonant cavity that uses various stirring techniques to alter the distribution of electromagnetic modes within the chamber, thereby generating a statistically uniform, isotropic, and uniformly polarized electromagnetic field within the working area. Compared to traditional microwave measurement techniques, reverberation chambers can generate a high-intensity electromagnetic field environment with relatively low power input, and are therefore 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 massive numbers of wireless devices has presented new requirements and challenges for wireless testing technology. Reverberation chamber technology, with its advantages of low construction cost, large testing area, and high efficiency, provides an economical and efficient solution for the air interface testing of wireless devices, and has thus gained attention and favor from the industry.

[0003] In actual testing, the reverberation chamber is constantly under load due to the presence of equipment such as antennas, the device under test (DUT), supports, and cables. Different DUTs correspond to different loading states. Existing research generally suggests that loading deteriorates the field uniformity of the reverberation chamber; therefore, most reverberation chamber tests require a lower loading state. However, in some active tests, it is necessary to adjust the coherence bandwidth of the reverberation chamber through loading to achieve flat fading of the wireless channel, thereby ensuring test accuracy. It can be seen that different reverberation chamber tests have different requirements for the loading state of the reverberation chamber; therefore, determining the loading state of the reverberation chamber is crucial.

[0004] The adjustment of the reverberation chamber's loading state is primarily achieved by controlling the loading amount of the absorbing material, and the loading performance of the absorbing material can be measured by its absorption cross-section. The absorption cross-section is defined as the ratio of the absorbed power to the incident wave power density under plane wave illumination. Given the statistical homogeneity of the electromagnetic field in a reverberation chamber, the absorption cross-section under a single incident wave state cannot effectively measure the performance of the absorbing material in a high-reverberation environment. Therefore, the concept of the equivalent absorption cross-section is commonly used in the field of reverberation chambers. The equivalent absorption cross-section is defined as the average value of the absorption cross-sections for all incident directions and polarization states. It is worth noting that the equivalent absorption cross-section not only measures the loading state of the reverberation chamber but also has a clear mathematical relationship with many characteristic parameters of the reverberation chamber and wireless channels (such as quality factor, channel transfer function, coherence bandwidth, etc.). 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] Currently, the equivalent absorption cross-section of microwave absorbing materials is mainly determined using the quality factor method. This method, based on the energy loss mechanism within a reverberation chamber, establishes a mathematical relationship between the equivalent absorption cross-section of the absorbing material and the corresponding quality factor. Based on this, the equivalent absorption cross-section is calculated using formulas by measuring the quality factor of the reverberation chamber under both unloaded and loaded conditions. Furthermore, some studies have established a theoretical model of the equivalent absorption cross-section under uniform wave conditions, based on the original definition of the equivalent absorption cross-section. This method derives the transmission and reflection coefficients of electromagnetic waves at the surface of the absorbing material under different incident directions and polarization states, thereby establishing a mathematical relationship between the equivalent absorption cross-section of the absorbing material, the geometric surface area of ​​the absorbing material, and the relative permittivity.

[0006] However, existing methods for testing the equivalent absorption cross-section in reverberation chambers have 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 electromagnetic waves by the absorbing material, making it difficult to guide the loading optimization of the reverberation chamber. The mathematical model based on the original definition of the equivalent absorption cross-section requires the characteristic parameters of the absorbing material (such as relative permittivity, conductivity, and surface area) to be given in advance; otherwise, the equivalent absorption cross-section of the absorbing material cannot be accurately calculated. Furthermore, this method has stringent requirements on the shape and size of the object under test: the 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 absorbing materials based on the mirror principle in a reverberation chamber to solve the above problems. Summary of the Invention

[0008] This invention provides a theoretical model and application for reverberation chamber testing of the equivalent absorption cross-section of absorbing materials based on the mirror principle. According to different reverberation chamber testing environments and the characteristics of absorbing materials, a theoretical model for reverberation chamber testing of the equivalent absorption cross-section of absorbing materials is determined, thereby achieving accurate measurement of the equivalent absorption cross-section. This addresses existing problems.

[0009] The theoretical model for reverberation chamber testing of the equivalent absorption cross section of absorbing materials based on the mirror principle of the present invention is as follows:

[0010] Based on the mirror principle, a mirror model of the reverberation chamber test system under no-load conditions is established, and the number of mirror objects and the total surface area of ​​the mirror model after multiple reflections are obtained.

[0011] The losses in the reverberation chamber system under no-load conditions are all equivalent to the losses of the reverberation chamber cavity wall, and the electric field intensity of the electromagnetic wave after multiple reflections is obtained based on the initial electric field intensity.

[0012] Under no-load conditions, the first electric field energy in the reverberation chamber after multiple reflections of electromagnetic waves is obtained based on the electric field intensity 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.

[0013] The time constant under no-load conditions is obtained based on the energy of the first electric field.

[0014] Under loading conditions, the probability that electromagnetic waves are not absorbed by the absorbing material after multiple reflections is obtained.

[0015] Under 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, the initial electric field energy, the number of mirror objects after multiple reflections, and the total surface area of ​​the mirror model, the second electric field energy in the reverberation chamber after multiple reflections of the electromagnetic wave is obtained.

[0016] The time constant under the loading state is obtained based on the energy of the second electric field.

[0017] Based on the typical distance, the internal surface area of ​​the reverberation chamber, and the time constants under no-load and loaded conditions, a theoretical model for testing the reverberation chamber with the equivalent absorption cross-section of the absorbing material is constructed. The typical distance is the average propagation distance between reflection points during the entire reflection process of the electromagnetic wave.

[0018] Preferably, under no-load conditions, the expression for the electric field strength of the electromagnetic wave after multiple reflections is:

[0019]

[0020] In the formula, Indicates the passage of electromagnetic waves Electric field strength after secondary reflection; Indicates the initial electric field strength; This represents the average reflection coefficient under all incident directions and polarization states.

[0021] Preferably, under no-load conditions, the expression for the energy of the first electric field in the reverberation chamber after multiple reflections of the electromagnetic wave is:

[0022]

[0023] In the formula, This indicates that under no-load conditions, the electromagnetic wave passes through [a certain point] within a propagation time t. The energy of the first electric field in the reverberation chamber after the second reflection; This represents the initial electric field energy; Represents the speed of light; This represents the typical distance, which is the average propagation distance between reflection points during the entire reflection process of the electromagnetic wave; Represents the natural logarithm operation; Indicates the passage of electromagnetic waves The propagation time of the second reflection; This represents the average reflection coefficient under all incident directions and polarization states; Indicates the initial electric field strength; Indicates the process Number of mirrored objects after secondary reflection; Indicates the process The total surface area of ​​the mirror model after secondary reflection.

[0024] Preferably, the time constant under no-load conditions satisfies the expression:

[0025]

[0026] In the formula, Represents the time constant under no-load conditions; This indicates that under no-load conditions, electromagnetic waves pass through The energy of the first electric field in the reverberation chamber after the second reflection; This represents the initial electric field energy; Indicates the passage of electromagnetic waves The propagation time of the second reflection.

[0027] Preferably, under loaded conditions, the expression for the probability that an electromagnetic wave is not absorbed by the absorbing material after multiple reflections is:

[0028]

[0029] In the formula, This indicates that under load, electromagnetic waves pass through The probability that the wave-absorbing material does not absorb the wave after the second reflection; This represents the probability that an electromagnetic wave is absorbed by the absorbing material after zero reflections. Indicates the electromagnetic wave passing through the first The probability of being absorbed by the absorbing material after secondary reflection; This represents the equivalent absorption cross section of the absorbing material; This indicates the surface area inside the reverberation chamber.

[0030] Preferably, under loaded conditions, the expression for the energy of the second electric field in the reverberation chamber after multiple reflections of the electromagnetic wave is:

[0031]

[0032] In the formula, This indicates the propagation time of electromagnetic waves under loaded conditions. Internal Path The energy of the second electric field in the reverberation chamber after the second reflection; This represents the initial electric field energy; Represents the speed of light; This represents the typical distance, which is the average propagation distance between reflection points during the entire reflection process of the electromagnetic wave; This represents the equivalent absorption cross section of the absorbing material; This indicates the internal surface area of ​​the reverberation chamber; This represents the average reflection coefficient under all incident directions and polarization states; Indicates the passage of electromagnetic waves The propagation time of the second reflection; Indicates the process Number of mirrored objects after secondary reflection; Indicates the process The total surface area of ​​the mirror model after secondary reflection.

[0033] Preferably, the time constant under loading state satisfies the expression:

[0034]

[0035] In the formula, This represents the time constant under loading conditions; Indicates that under loaded conditions, electromagnetic waves pass through The energy of the second electric field in the reverberation chamber after the second reflection; This represents the initial electric field energy; Indicates the passage of electromagnetic waves The propagation time of the second reflection.

[0036] Preferably, the expression of the theoretical model is:

[0037]

[0038] In the formula, This represents the time constant under loading conditions; Represents the time constant under no-load conditions; This indicates the internal surface area of ​​the reverberation chamber; Represents the speed of light; Indicates a typical distance.

[0039] Preferably, the unloaded state is when there is no microwave absorbing material in the reverberation chamber; the loaded state is when the reverberation chamber contains microwave absorbing material.

[0040] The technical solution adopted in 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 cavity surface area, typical distance, and time constants corresponding to the no-load and loaded states of the reverberation chamber into the theoretical model of the present invention to obtain the equivalent absorption cross section of the absorbing material under test, wherein the typical distance is determined by Monte Carlo simulation; and the transmission coefficient between the transmitting antenna and the receiving antenna is measured at all stirring positions, and the time constant is obtained based on the transmission coefficient.

[0041] The beneficial effects of this invention are:

[0042] By obtaining the time constants under both unloaded and loaded conditions, a theoretical model for reverberation chamber testing of the equivalent absorption cross-section of the absorbing material based on the mirror principle is constructed. This theoretical model is then used to obtain the equivalent absorption cross-section of the absorbing material under test. The entire process intuitively and clearly demonstrates the path of electromagnetic waves being (or not being) absorbed by the absorbing material. This helps to analyze the relative positions of the excitation source and the absorbing material under specific requirements, provides guidance for loading optimization, and enables rapid and accurate measurement of the equivalent absorption cross-section of the absorbing material. It is also unaffected by the characteristics of the absorbing material and the size of the cavity, making it easy for engineering applications.

[0043] Secondly, this invention applies the mirror principle to the field of microwave measurement based on reverberation chambers, realizing rapid and accurate testing of reverberation chambers with equivalent absorption cross sections. This expands the analytical theory in the field of reverberation chamber measurement and helps promote the application and popularization of the mirror principle in other reverberation chamber tests, thereby improving their testing performance. Attached Figure Description

[0044] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0045] Figure 1 This is a flowchart illustrating the construction of a theoretical model for testing the equivalent absorption cross section of an absorbing material based on the mirror principle in a reverberation chamber according to the present invention.

[0046] Figure 2 This is a schematic plan view of a mirror model of the reverberation chamber used in an embodiment of the present invention;

[0047] Figure 3 This is a schematic diagram of the reverberation chamber scene 1 for measuring the equivalent absorption cross section of the absorbing material in an embodiment of the present invention;

[0048] Figure 4This is a schematic diagram of the reverberation chamber scene 2 for measuring the equivalent absorption cross section of the absorbing material in an embodiment of the present invention;

[0049] Figure 5 A schematic diagram of Monte Carlo simulation results for a typical distance of the reverberation chamber used in the embodiments of the present invention;

[0050] Figure 6 The power delay spectrum at 3.2 GHz of the reverberation chamber used in the embodiments of the present invention under three loading states;

[0051] Figure 7 This is a schematic diagram showing the measurement results of the time constant of the reverberation chamber used in the embodiments of the present invention under three loading states;

[0052] Figure 8 This is a schematic diagram showing the measurement results of the equivalent absorption cross section of the absorbing material based on the mirror principle and traditional methods in reverberation chamber scenario 1 and reverberation chamber scenario 2, according to an embodiment of the present invention. Detailed Implementation

[0053] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0054] An embodiment of the theoretical model for reverberation chamber testing of the equivalent absorption cross section of absorbing materials based on the mirror principle of the present invention, such as... Figure 1 As shown, it includes:

[0055] S1. Establish a mirror model and obtain the number of mirrored objects and the total surface area of ​​the mirror model after multiple reflections.

[0056] Specifically, based on the mirror principle, a mirror model of the reverberation chamber test system under no-load conditions is established, and the number of mirror objects and the total surface area of ​​the mirror model after multiple reflections are obtained.

[0057] S2. Obtain the time constant under no-load conditions;

[0058] Specifically, the losses within the reverberation chamber system under no-load conditions are all equivalent to the losses of the reverberation chamber walls, and the electric field intensity of the electromagnetic wave after multiple reflections is obtained based on the initial electric field intensity. Under no-load conditions, the first electric field energy in the reverberation chamber after multiple reflections is obtained based on the electric field intensity of the electromagnetic wave after multiple reflections, the initial electric field energy, the number of mirror objects after multiple reflections, and the total surface area of ​​the mirror model. The time constant under no-load conditions is obtained based on the first electric field energy. Here, the no-load condition means that there is no absorbing material in the reverberation chamber.

[0059] For example, the expression for the electric field strength of an electromagnetic wave after multiple reflections is as follows:

[0060] (1)

[0061] In the formula, Indicates the passage of electromagnetic waves Electric field strength after secondary reflection; Indicates the initial electric field strength; This represents the average reflection coefficient under all incident directions and polarization states.

[0062] For example, in this embodiment, under no-load conditions, the expression for the energy of the first electric field in the reverberation chamber after multiple reflections of the electromagnetic wave is:

[0063] (2)

[0064] (3)

[0065] According to equations (1) and (2), we have:

[0066] (4)

[0067] In the formula, Represents the propagation time under no-load conditions. Internal electromagnetic waves pass through The energy of the first electric field in the reverberation chamber after the second reflection; This represents the initial electric field energy; Represents the speed of light; This represents the typical distance, which is the average propagation distance between reflection points during the entire reflection process of the electromagnetic wave; Represents the natural logarithm operation; Indicates the passage of electromagnetic waves The propagation time of the second reflection; This represents the average reflection coefficient under all incident directions and polarization states; This represents the initial electric field strength, which is a preset electric field strength. Indicates the process Number of mirrored objects after secondary reflection; Indicates the process The total surface area of ​​the mirror model after secondary reflection.

[0068] For example, in this embodiment, the time constant under no-load conditions satisfies the expression:

[0069] (5)

[0070] In the formula, Represents the time constant under no-load conditions; Represents the propagation time under no-load conditions. Internal electromagnetic waves pass through The energy of the first electric field in the reverberation chamber after the second reflection; This represents the initial electric field energy, which is a preset electric field energy. Indicates the passage of electromagnetic waves The propagation time of the second reflection.

[0071] S3. Obtain the time constant under loading status;

[0072] Specifically, under the loading state, based on the probability that the electromagnetic wave is not absorbed by the absorbing material after multiple reflections, the electric field strength, initial electric field energy, number of mirror objects after multiple reflections, and total surface area of ​​the mirror model, the second electric field energy in the reverberation chamber after multiple reflections of the electromagnetic wave is obtained; the time constant under the loading state is obtained based on the second electric field energy; wherein, the loading state is that the reverberation chamber contains absorbing material.

[0073] For example, under loaded conditions, the expression for the probability that an electromagnetic wave is not absorbed by the absorbing material after multiple reflections is:

[0074] (6)

[0075] In the formula, This indicates that under load, electromagnetic waves pass through The probability that the wave-absorbing material does not absorb the wave after the second reflection; This represents the probability that an electromagnetic wave is absorbed by the absorbing material after zero reflections. Indicates the electromagnetic wave passing through the first The probability of being absorbed by the absorbing material after secondary reflection; This represents the equivalent absorption cross section of the absorbing material; This indicates the surface area inside the reverberation chamber.

[0076] For example, under loaded conditions, the expression for the energy of the second electric field in the reverberation chamber after multiple reflections of the electromagnetic wave is:

[0077] (7)

[0078] In the formula, This indicates the propagation time of electromagnetic waves under loaded conditions. Internal Path The energy of the second electric field in the reverberation chamber after the second reflection; This represents the initial electric field energy; Represents the speed of light; This represents the typical distance, which is the average propagation distance between reflection points during the entire reflection process of the electromagnetic wave; This represents the equivalent absorption cross section of the absorbing material; This indicates the internal surface area of ​​the reverberation chamber; This represents the average reflection coefficient under all incident directions and polarization states; Indicates the passage of electromagnetic waves The propagation time of the second reflection; Indicates the process Number of mirrored objects after secondary reflection; Indicates the process The total surface area of ​​the mirror model after secondary reflection.

[0079] For example, the time constant in the loading state satisfies the expression:

[0080] (8)

[0081] In the formula, This represents the time constant under loading conditions; Indicates that under loaded conditions, electromagnetic waves pass through The energy of the second electric field in the reverberation chamber after the second reflection; This represents the initial electric field energy; Indicates the passage of electromagnetic waves The propagation time of the second reflection.

[0082] S4. Construct a theoretical model for reverberation chamber testing of the equivalent absorption cross section of the absorbing material;

[0083] Based on the typical distance, the internal surface area of ​​the reverberation chamber, and the time constants under no-load and loaded conditions, a theoretical model for testing the reverberation chamber with the equivalent absorption cross-section of the absorbing material is constructed. The typical distance is the average propagation distance between reflection points during the entire reflection process of the electromagnetic wave.

[0084] For example, the expression for the theoretical model is:

[0085] (9)

[0086] In the formula, This represents the time constant under loading conditions; Represents the time constant under no-load conditions; This indicates the internal surface area of ​​the reverberation chamber; Represents the speed of light; Indicates a typical distance.

[0087] The application of a theoretical model for testing an equivalent absorption cross-section reverberation chamber based on the mirror principle according to the present invention includes: inputting the cavity surface area, typical distance, and time constants corresponding to the unloaded and loaded states of the reverberation chamber into the theoretical model to obtain the equivalent absorption cross-section of the absorbing material under test, wherein the typical distance is determined by Monte Carlo simulation; and obtaining the time constant by measuring the transmission coefficient between the transmitting antenna and the receiving antenna at all stirring positions.

[0088] For example, in this embodiment, the steps for obtaining the typical distance are as follows: The internal surface area of ​​the reverberation chamber is determined based on its dimensions, and the typical distance is determined through Monte Carlo simulation, namely: 1. Setting simulation parameters, including the number of excitation sources, the number of propagation directions, and the number of reflections; 2. Setting the boundary conditions for the simulation based on the dimensions of the reverberation chamber; 3. Randomly setting the first... i indivual( 4. The coordinate position of the excitation source; i The incentive source is randomly set. j indivual( 5. Initial propagation direction; Simulation in the 1st... i The incentive source is from the first j 6. Under the initial incident conditions, determine the propagation distance, reflection point, and direction of the reflected wave; 7. Set the reflection point determined in step 5 as the new excitation source position, and set the reflected wave direction determined in step 5 as the new propagation direction. Repeat step 5 until the number of reflections in the simulation reaches the number of reflections set in step 1; 8. Repeat steps 4-6 until the number of propagation directions in the simulation reaches the number of propagation directions set in step 1; 9. Repeat steps 3-7 until the number of excitation sources in the simulation reaches the number of excitation sources set in step 1; 10. Calculate the typical distance based on the simulation data.

[0089] For example, the steps for obtaining the time constants under the unloaded and loaded states are as follows: Under the unloaded state (i.e., no absorbing material is deployed), measure the transmission coefficient between the transmitting antenna and the receiving antenna in the reverberation chamber, and calculate the time constant of the unloaded reverberation chamber; under the loaded state (the 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. The steps for calculating the time constants of the unloaded and loaded reverberation chambers are as follows: connect the transmitting antenna and the receiving antenna to the two ports of a vector network analyzer, respectively, and obtain the transmission coefficient between the transmitting antenna and the receiving antenna through the vector network analyzer. The power delay spectrum (i.e., the first electric field energy spectrum) of the unloaded reverberation chamber is plotted based on the transmission coefficient corresponding to the unloaded reverberation chamber. The time constant of the unloaded reverberation chamber is obtained by extracting the decay rate of the power delay spectrum of the unloaded reverberation chamber. The power delay spectrum (i.e., the second electric field energy spectrum) of the loaded reverberation chamber is plotted based on the transmission coefficient corresponding to the loaded reverberation chamber. The time constant of the loaded reverberation chamber is obtained by extracting the decay rate of the power delay spectrum of the loaded reverberation chamber.

[0090] The following is in conjunction with the appendix Figures 2 to 8 This embodiment will be described in detail below:

[0091] like Figure 2 As shown, in this embodiment, the mirror model planar schematic diagram includes multiple rectangles (reverberation chambers), and the subscripts in the rectangles are... ( This indicates that the rectangle represents the point through which the electromagnetic wave passes. The image produced during secondary reflection. Furthermore, Figure 2 Examples of electromagnetic wave propagation paths that are (or not) absorbed by absorbing materials in practice are shown, along with their equivalent propagation paths in a mirror model.

[0092] like Figure 3 and 4 As shown, the reverberation chamber measures 1.50m × 1.44m × 0.92m and includes two mechanical stirrers and a mechanical turntable with a height-adjustable antenna bracket. Both the transmitting and receiving antennas are standard horn antennas. The transmitting antenna is mounted on a bracket on the bottom of the reverberation chamber, with its main radiation direction pointing towards the horizontal stirrer. The receiving antenna is mounted on a bracket on the turntable, offset 20 cm from the center of the turntable (turntable diameter 60 cm). The transmitting and receiving antennas are connected to two ports of a network analyzer, respectively. The test frequency band of this embodiment is 2.4GHz-4GHz. The stirrers and turntable rotate independently, with 20 positions per revolution, resulting in 400 stirring positions in a single test. The position of the transmitting antenna remains constant throughout the entire test.

[0093] This embodiment measures the equivalent absorption cross-section of the absorbing material under two different reverberation chamber loading conditions. Reverberation chamber test scenario 1 is as follows: Figure 3 As shown, scenario 1 consists of three identical pieces of absorbing material stacked in the corner of the reverberation chamber. Scenario 2 of the reverberation chamber test is as follows... Figure 4 As shown, Scene 2 consists of three identical absorbing materials laid flat on the wall of the reverberation chamber at a certain interval. The dimensions of the absorbing materials are 16cm × 5cm × 48cm, and the spacing is 10cm.

[0094] The feasibility and effectiveness of the theoretical model for reverberation chamber testing based on the equivalent absorption cross-section of absorbing materials according to the mirror principle are verified. The verification steps are as follows:

[0095] Step 1. Perform Monte Carlo simulations on typical distances of the reverberation chamber to determine the values ​​of typical distances;

[0096] Step 2. Conduct tests under no-load conditions in the reverberation chamber, obtaining 400 sets of results. (Transmission coefficient) parameter;

[0097] Step 3. In reverberation chamber test scenario 1 and reverberation chamber test scenario 2, the absorbing material was deployed in the reverberation chamber and tested, obtaining 400 sets of samples for each scenario. parameter;

[0098] Step 4. Based on the measurements obtained in Step 2 and Step 3 Parameters were used to calculate the time constant of the reverberation chamber in three different states.

[0099] Step 5. Using the typical distance obtained in Step 1 and the time constant obtained in Step 4, calculate the equivalent absorption cross section based on the mirror principle. At the same time, using the time constant obtained in Step 4, calculate the equivalent absorption cross section based on the traditional method. Compare and verify the equivalent absorption cross sections obtained by the two methods.

[0100] The power delay profile (PDP) of the reverberation chamber can be calculated using the following equation (10). Based on this, the time constant of the reverberation chamber can be calculated using the following equation (11). When the loading state of the reverberation chamber is constant, the time constant is constant. This parameter reflects the dissipation rate of the energy stored in the reverberation chamber. The smaller the value, the faster the energy dissipation rate.

[0101] (10)

[0102] according to get:

[0103] (11)

[0104] In the formula, This is the first time the network analyzer has recorded this. f frequency points S 21 The parameter IFFT stands for Inverse Fast Fourier Transform algorithm. Expressing the request N The statistical average of the samples, in this embodiment ln represents the natural logarithm operation. slope The calculation is solved by curve fitting. The slope of the linear portion.

[0105] The equivalent absorption cross section of the absorbing material based on the mirror principle can be calculated using the following equation (12):

[0106] (12)

[0107] In the formula, S It is the internal surface area of ​​the reverberation chamber; L This is a typical distance; c It's the speed of light; This represents the time constant under loading conditions; This represents the time constant under no-load conditions.

[0108] The equivalent absorption cross section of the absorbing material based on the traditional method can be calculated by the following formula (13):

[0109] (13)

[0110] In the formula, It is the equivalent absorption cross section of the absorbing material using traditional methods; V It is the internal volume of the reverberation chamber; This represents the time constant under loading conditions; Represents the time constant under no-load conditions; c It's the speed of light.

[0111] In this embodiment, the simulated typical distance variation curves under different propagation direction numbers and different reflection numbers are as follows: Figure 5 As shown. From Figure 5 It can be seen that the simulated typical distance gradually stabilizes with the increase of the number of reflections and the number of propagation directions, which is the true value of the typical distance. When the number of reflections reaches 60 and the number of propagation directions reaches 200, the simulated typical distance almost stops changing. In summary, simulation can determine the typical distance of the reverberation chamber used in this embodiment to be 0.808 m. In practice, appropriate simulation parameters can be set to determine the typical distance of the reverberation chamber used, depending on the requirements of calculation time and accuracy.

[0112] The power delay spectrum at 3.2 GHz in the reverberation chamber under no-load, loaded state 1 (loaded state of scenario 1), and loaded state 2 (loaded state of scenario 2) is as follows: Figure 6 As shown. The inverse Fourier transform bandwidth used in this embodiment is 600MHz. The PDP curves of the reverberation chamber in all three states exhibit typical exponential decay characteristics. It can be seen that the energy decay rate in the loaded reverberation chamber is faster than that in the unloaded state. This is because the loaded absorbing material absorbs part of the energy fed into the reverberation chamber, accelerating energy dissipation. 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 area of ​​the absorbing material is different in the two scenarios: the exposed surface area of ​​the absorbing material in scenario 2 is larger than that in scenario 1 (see...). Figure 3 and Figure 4 Therefore, the absorbing material will absorb more electromagnetic energy in scenario 2. In general, the rate of energy decay within the reverberation chamber increases with the increase of the exposed surface area of ​​the absorbing material.

[0113] The measurement results of the time constant of the reverberation chamber under no-load, loaded state 1 (loaded state of scenario 1), and loaded state 2 (loaded state of scenario 2) are as follows: Figure 7 As shown. In this embodiment of the invention, the inverse Fourier transform bandwidth is 600MHz, therefore the time constant is plotted in the range of 2.7 GHz - 3.7 GHz. (From...) Figure 7 It can be seen that under specific loading conditions, the time constant of the reverberation chamber does not change significantly with frequency. Furthermore, the time constant decreases significantly with increasing exposed surface area of ​​the absorbing material, meaning that the energy decay rate within the reverberation chamber increases with increasing exposed surface area of ​​the absorbing material, which is consistent with the results obtained from the PDP curve.

[0114] In this embodiment, the measurement results of the equivalent absorption cross-section of the absorbing material based on the mirror principle and traditional methods are as follows in two reverberation chamber scenarios: Figure 8 As shown. By 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 consistent, and are independent of the test frequency and test scenario. This result fully demonstrates the effectiveness, feasibility, and stability of the reverberation chamber test of the equivalent absorption cross section based on the mirror principle proposed in this invention.

[0115] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

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

2. The theoretical model for testing the equivalent absorption cross section of absorbing materials based on the mirror principle in a reverberation chamber according to claim 1, characterized in that, Under no-load conditions, the expression for the electric field strength of an electromagnetic wave after multiple reflections is: In the formula, Indicates the passage of electromagnetic waves Electric field strength after secondary reflection; Indicates the initial electric field strength; This represents the average reflection coefficient under all incident directions and polarization states.

3. The theoretical model for testing the reverberation chamber based on the equivalent absorption cross-section of absorbing materials according to the mirror principle as described in claim 2, characterized in that, Under no-load conditions, the expression for the energy of the first electric field in the reverberation chamber after multiple reflections of the electromagnetic wave is: In the formula, Represents the propagation time under no-load conditions. Internal electromagnetic waves pass through The energy of the first electric field in the reverberation chamber after the second reflection; This represents the initial electric field energy; Represents the speed of light; This represents the typical distance, which is the average propagation distance between reflection points during the entire reflection process of the electromagnetic wave; Represents the natural logarithm operation; Indicates the passage of electromagnetic waves The propagation time of the second reflection; This represents the average reflection coefficient under all incident directions and polarization states; Indicates the initial electric field strength; Indicates the process Number of mirrored objects after secondary reflection; Indicates the process The total surface area of ​​the mirror model after secondary reflection.

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

5. The theoretical model for testing the equivalent absorption cross section of absorbing materials based on the mirror principle in a reverberation chamber according to claim 1, characterized in that, Under loaded conditions, the expression for the probability that an electromagnetic wave is not absorbed by the absorbing material after multiple reflections is: In the formula, This indicates that under load, electromagnetic waves pass through The probability that the wave-absorbing material does not absorb the wave after the second reflection; This represents the probability that an electromagnetic wave is absorbed by the absorbing material after zero reflections. Indicates the electromagnetic wave passing through the first The probability of being absorbed by the absorbing material after secondary reflection; This represents the equivalent absorption cross section of the absorbing material; This indicates the surface area inside the reverberation chamber.

6. The theoretical model for testing the equivalent absorption cross section of absorbing materials based on the mirror principle in a reverberation chamber according to claim 5, characterized in that, Under loaded conditions, the expression for the energy of the second electric field in the reverberation chamber after multiple reflections of the electromagnetic wave is: In the formula, This indicates the propagation time of electromagnetic waves under loaded conditions. Internal Path The energy of the second electric field in the reverberation chamber after the second reflection; This represents the initial electric field energy; Represents the speed of light; This represents the typical distance, which is the average propagation distance between reflection points during the entire reflection process of the electromagnetic wave; This represents the equivalent absorption cross section of the absorbing material; This indicates the internal surface area of ​​the reverberation chamber; This represents the average reflection coefficient under all incident directions and polarization states; Indicates the passage of electromagnetic waves The propagation time of the second reflection; Indicates the process Number of mirrored objects after secondary reflection; Indicates the process The total surface area of ​​the mirror model after secondary reflection; Indicates that under loaded conditions, electromagnetic waves pass through The electric field strength after secondary reflection.

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

8. The theoretical model for testing the reverberation chamber based on the equivalent absorption cross section of absorbing materials according to the mirror principle as described in claim 1, characterized in that, The theoretical model is expressed as follows: In the formula, This represents the time constant under loading conditions; Represents the time constant under no-load conditions; This indicates the internal surface area of ​​the reverberation chamber; Represents the speed of light; Indicates a typical distance.

9. The theoretical model for testing the reverberation chamber based on the equivalent absorption cross section of absorbing materials according to the mirror principle as described in claim 1, characterized in that, The unloaded state is when there is no microwave absorbing material in the reverberation chamber; the loaded state is when there is microwave absorbing material in the reverberation chamber.

10. An application of a theoretical model for testing a reverberation chamber with an equivalent absorption cross-section based on the mirror principle, characterized in that... include: The internal surface area of ​​the reverberation chamber, typical distance, and time constants corresponding to the no-load and loaded states are input into the theoretical model described in any one of claims 1-9 to obtain the equivalent absorption cross section of the absorbing material under test. The typical distance was determined through Monte Carlo simulation; the transmission coefficient between the transmitting and receiving antennas was measured at all stirring positions, and the time constant was obtained based on the transmission coefficient.

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