A method for measuring anisotropic materials using a strip air line

Abstract

The present invention discloses a method for measuring anisotropic materials using a strip air line. The strip air line is used as a measuring device, and during the measurement, samples to be measured are placed both above and below the conductive strip of the strip air line, so that the TEM mode exists in the area of the samples to be measured, thus ensuring the accuracy of the measurement results. The multireflect-thru calibration technique is used to calibrate the measurement system, and the entire calibration process is completed using only one metal short circuit plate based on the air strip air line. The present invention uses a linear combination method to solve the permittivity and permeability of anisotropic materials, avoiding the influence of field components in different directions of the electromagnetic field on the measurement results. Thus, accurate measurement of the permittivity and permeability of anisotropic materials using a strip air line at low frequencies is achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of microwave measurement, and particularly relates to a method for measuring anisotropic materials using a strip air line. Background Art

[0002] Anisotropic materials are currently widely used in fields such as electromagnetic stealth and materials science, and the relative permittivity and relative permeability are the most important electromagnetic parameters of anisotropic materials. Due to the different values of electromagnetic parameters of anisotropic materials in different principal axis directions, the measurement of electromagnetic parameters of anisotropic materials is a difficult point.

[0003] Traditional methods for measuring anisotropic electromagnetic parameters include the resonant cavity method, the free space method, and the microstrip line method. However, both the resonant cavity method and the free space method require that the size of the sample to be measured be large enough at low frequencies. Therefore, they are generally not used to measure the electromagnetic parameters of materials at low frequencies. The microstrip line method can measure the electromagnetic parameters of materials at low frequencies. As described in the literature ([1] M.I. Hossain, N. Nguyen-Trong and A.M. Abbosh, "Calibrated Parallel-Plate Waveguide Technique for Low-Frequency and Broadband Absorptivity Measurement," in IEEE Antennas and Wireless Propagation Letters, vol. 19, no. 9, pp. 1541-1545, Sept. 2020, doi: 10.1109 / LAWP.2020.3008889) and ([2] Y. Han and W. Che, "Low-Profile Broadband Absorbers Based on Capacitive Surfaces," in IEEE Antennas and Wireless Propagation Letters, vol. 16, pp. 74-78, 2017.), the microstrip line is used to measure anisotropic materials. However, during the measurement process, due to placing the material to be measured only under the conductor strip of the microstrip line and the characteristics of the microstrip line itself, the quasi-TEM mode rather than the TEM mode is transmitted in the area to be measured. In this way, it is impossible to ensure that the polarization direction of the electromagnetic field is consistent with the principal axis direction of the anisotropic material throughout the measurement frequency band. Therefore, it is difficult to accurately measure anisotropic materials using a microstrip line.

[0004] In traditional microstrip line measurement systems, time-domain gating technology and TRL calibration are used as calibration methods. In the time-domain gating calibration method, the calibration error is large because the time-domain gate cannot completely separate the useful signal from the interference signal. For TRL calibration, transmission lines of different lengths need to be fabricated. At low frequencies, the required equipment length is long, which increases the manufacturing cost.

[0005] Therefore, a new technical solution is needed for the measurement of anisotropic materials at low frequencies. Summary of the Invention

[0006] To overcome the deficiencies of the prior art, the present invention provides a method for measuring anisotropic materials using a strip air line. The strip air line is used as the measurement device. During the measurement process, samples to be measured are placed above and below the conductive strip of the strip air line, so that the TEM mode exists in the area of the samples to be measured, thus ensuring the accuracy of the measurement results. The multireflect-thru calibration technology is used to calibrate the measurement system. The entire calibration process is completed using only one metal short circuit plate based on the air strip air line. The present invention uses a linear combination method to solve the permittivity and permeability of anisotropic materials, avoiding the influence of field components in different directions of the electromagnetic field on the measurement results. Thus, accurate measurement of the permittivity and permeability of anisotropic materials using a strip air line at low frequencies is achieved.

[0007] The technical solution adopted by the present invention to solve its technical problems includes the following steps:

[0008] Step 1: The strip air line is composed of a conductive strip and two ground plates above and below. Plastic studs are used to support between the conductive strip and the upper and lower ground plates. Step-type transition bands are provided at both ends of the conductive strip to achieve impedance matching. Coaxial lines are used to excite both ends of the conductive strip; when using the strip air line to measure anisotropic materials, the TEM mode exists in the area of the material to be measured;

[0009] Step 2: Perform multireflect-thru calibration on the strip air line measurement system;

[0010] The calibration of the system is completed using four reflection standards and one thru standard; the lateral middle position of the strip air line is defined as the measurement reference plane, and the strip air line itself serves as the thru standard; a metal short circuit plate is placed between the conductive strip and the ground plate, and four different reflection standards are achieved by moving the metal short circuit plate to four different positions;

[0011] Step 2-1: Connect the strip air line using a vector network analyzer. The A port and B port of the vector network analyzer are respectively connected to the coaxial connectors at the left and right ends of the conductive strip; the metal short circuit plate is respectively placed at four different positions in the strip air line, and the S-parameters of the four reflection standards in the forward and reverse directions in the frequency band of 0.3 - 1 GHz are measured as They respectively represent the measured values of the i-th reflection standard, with the superscript "~". The matrix form of the S parameter is

[0012] For ports A and B, the lengths of the reflection standards from the measurement reference plane are denoted as l Ai and l Bi , and the four reflection standards have the same propagation constant γ A and γ B , and the same reflection coefficient Γ T ; E A and E B are the calibration parameters used to represent the error matrix during the calibration process, and their specific expressions are shown in (4) and (5);

[0013] For port A, the following equations exist for the four reflection standards:

[0014]

[0015] where E′ iA = E iA Γ T ,

[0016] Using the Newton iteration method to solve the equation detP(γ A ) = 0, the propagation constant γ A is obtained; where P(γ A ) is the coefficient matrix of equation (1);

[0017] Furthermore, from:

[0018]

[0019] E′ 1A , E 2A and E′ 3A are obtained;

[0020] For port B, E′ 1B , E 2B and E′ 3B are similarly obtained. During the process of solving for port B i.e., is the reflection coefficient of port B;

[0021] Step 2-2: Use a vector network analyzer to measure the forward and reverse S parameters of the empty ribbon air line, i.e., the through standard The reflection coefficient Γ T of the reflection standard is obtained as:

[0022]

[0023] Combined with E′ iA = E iA Γ T The calibration parameters are obtained:

[0024]

[0025]

[0026] and

[0027]

[0028] Step 3: Two anisotropic materials of the same size are combined to form the first group of samples. The two anisotropic materials are respectively placed above and below the conductor strip of the strip air line. The S-parameters of the first group of samples are measured using a vector network analyzer. The ξ and η axes of the first group of samples are aligned with the x-axis and y-axis of the strip air line;

[0029] Then the transmission matrix of the strip air line when placing the first group of samples is obtained from the following formula:

[0030]

[0031] where

[0032] The transmission matrix T with the two ends of the first group of samples as the reference planes is as follows:

[0033]

[0034] The S-matrix S of the first group of samples is obtained m ;

[0035]

[0036] Step 4: Using the NWR algorithm, calculate its dielectric constant ε m and permeability μ r1 from the S r1 matrix of the first group of samples;

[0037] Denote:

[0038]

[0039] Then the reflection coefficient is expressed as:

[0040]

[0041] The propagation factor is expressed as:

[0042]

[0043] Dielectric constant ε r1 and magnetic permeability μ r1 are obtained from the following two equations:

[0044]

[0045]

[0046] where λ 0 is the wavelength in free space, λ c = ∞ is the cut-off wavelength of the TEM mode, and l is the thickness of the first group of samples along the electromagnetic wave propagation direction;

[0047] Step 5: Rotate the two anisotropic materials of the first group of samples to be the second group of samples. The ξ-axis and η-axis of the second group of samples are kept the same as the y-axis and x-axis directions of the strip air line respectively during the measurement process; Repeat the processes of Step 3 and Step 4 to calculate the dielectric constant ε r2 and magnetic permeability μ r2 ;

[0048] Step 6: The dielectric constants ε rξ and ε rη along the ξ-axis and η-axis of the anisotropic material, as well as the magnetic permeabilities μ rξ and μ rη are obtained from the following system of equations:

[0049] aε rξ +bε rη = ε r1 (15)

[0050] aε rη +bε rξ = ε r2 (16)

[0051] bμr ξ +aμ rη = μ r1 (17)

[0052] bμ rη +aμ rξ = μ r2 (18)

[0053] where a and b are constants, which reflect the relationship between the x-direction and y-direction components of the electromagnetic field in the strip air line.

[0054] Preferably, the upper and lower ground plates and the conductive strip are all metal plates with a thickness of 1 mm. The length of the conductive strip is 938 mm and the width is 85 mm; the length of the conductive strip step is 11 mm and the width is 49 mm; the upper and lower ground plates are of the same size, with a length of 964 mm and a width of 400 mm; the distances between the conductive strip and the upper and lower ground plates are both 30 mm.

[0055] Preferably, the metal short - circuit plate is composed of two upper and lower parts, and the dimensions are both 400 mm×30 mm×20 mm.

[0056] Preferably, the two pieces of anisotropic materials of the same size have dimensions of 300 mm×30 mm×30 mm.

[0057] Preferably, the metal short - circuit plate is moved to four different positions, which are 15 mm to the left of the measurement reference plane, 23 mm, 60 mm, and 98 mm to the right of the measurement reference plane respectively.

[0058] Preferably, a = 0.13 and b = 0.87.

[0059] The beneficial effects of the present invention are as follows:

[0060] 1. Compared with the existing microstrip line measurement technology, the present invention uses an air - strip line and places anisotropic materials to be measured above and below the conductive strip, ensuring that the TEM mode is transmitted in the strip line and the polarization direction of the electromagnetic wave is consistent with the principal axis direction of the anisotropic material throughout the frequency band. Therefore, the dielectric constant and magnetic permeability of the anisotropic material can be accurately measured in principle.

[0061] 2. The present invention uses a linear combination method to improve the accuracy of solving the electromagnetic parameters in each principal axis direction of the anisotropic material. In the strip line, most of the electric field components are perpendicular to the conductive strip, that is, in the y - direction, and most of the magnetic field components are parallel to the conductive strip, that is, in the x - direction. Therefore, when the accuracy requirement is not high and only the dielectric constant and magnetic permeability in a certain principal axis direction of the anisotropic material need to be measured, the measurement result can be obtained through only one measurement. However, considering the influence of a small amount of electric field components in the direction parallel to the conductive strip and a small amount of magnetic field components in the direction perpendicular to the conductive strip on the result, the present invention uses a linear combination method to obtain the accurate values of ε rξ and ε rη as well as μ rξ and μ rη in two principal axis directions through two measurements.

[0062] 3. To simplify the calibration process while ensuring calibration accuracy, the present invention adopts the multireflect-thru calibration technology. During the calibration process, the measurement of four reflection standards can be conveniently completed by simply moving the position of a metal shorting plate, achieving the accurate measurement of the dielectric constant and magnetic permeability of anisotropic materials by the strip air line measurement system. Description of the Drawings

[0063] Figure 1 is a schematic diagram of the strip air line of the present invention.

[0064] Figure 2 is a top view of the strip air line of the present invention.

[0065] Figure 3 is a schematic diagram of the strip air line measuring the reflection standard of the present invention.

[0066] Figure 4 is a schematic diagram of the strip air line measuring anisotropic materials of the present invention.

[0067] In the figure: 1 - conductive strip, 2 - stepped transition strip, 3 - ground plane. Detailed Embodiment

[0068] The present invention will be further described below in conjunction with the drawings and embodiments.

[0069] To avoid the problem that the resonant cavity method and the free space method cannot measure materials at low frequencies, as well as the errors and inconveniences of the traditional calibration method when measuring anisotropic materials using the quasi-TEM mode in the microstrip line measurement system, the present invention proposes a technique for measuring anisotropic materials using a strip air line. A strip air line is adopted, and the multireflect-thru calibration technology is used to measure the dielectric constant and magnetic permeability of anisotropic materials in the frequency band of 0.3 - 1 GHz.

[0070] A method for measuring anisotropic materials using a strip air line includes the following steps:

[0071] Step 1: The strip air line is composed of a conductive strip and upper and lower ground planes. Plastic studs are used to support between the conductive strip and the upper and lower ground planes. Stepped transition strips are provided at both ends of the conductive strip to achieve impedance matching, and coaxial cables are used to excite both ends of the conductive strip; when using the strip air line to measure anisotropic materials, the TEM mode exists in the area of the material to be measured.

[0072] Step 2: Perform multireflect-thru calibration on the strip air line measurement system.

[0073] The calibration of the system is completed using four reflection standards and one through standard; the lateral middle position of the strip air line is defined as the measurement reference plane, and the strip air line itself serves as the through standard; a metal shorting plate is placed between the conductive strip and the ground plane, and four reflection standards are achieved by moving the metal shorting plate to four different positions.

[0074] Step 2-1: Connect the strip air line using a vector network analyzer, with the A port and B port of the vector network analyzer connected to the coaxial cables at the left and right ends of the conductive strip respectively; place the metal shorting plate at four different positions in the strip air line, and measure the S-parameters of the four reflection standards in both the forward and reverse directions in the frequency band of 0.3 - 1 GHz as respectively representing the i-th reflection standard, with the superscript "~" indicating the measured value, where the form of the S matrix is

[0075] For the A port and B port, the lengths of the reflection standards from the measurement reference plane are denoted as l Ai and l Bi , and the four reflection standards have the same propagation constant γ A and γ B , the same reflection coefficient Γ T . E A and E B are specifically expressed as shown in (4) and (5) and are calibration parameters used to represent the error matrix during the calibration process;

[0076] For the A port, the following equations exist for the four reflection standards:

[0077]

[0078] where E′ iA = E iA Γ T ,

[0079] Use Newton's iterative method to solve the equation detP(γ A ) = 0 to obtain the propagation constant γ A ;

[0080] Furthermore, from:

[0081]

[0082] obtain E′ 1A , E 2A and E′ 3A ;

[0083] For the B port, similarly obtain E′ 1B , E 2B and E′3B During the process of solving for Port B That is is the reflection coefficient of Port B;

[0084] Step 2-2: Measure the S-parameters of the empty strip air line, i.e., the through standard, using a vector network analyzer Obtain the reflection coefficient Γ of the reflection standard T which is:

[0085]

[0086] Combined with E′ i = E i Γ T and the results in Step 1, the calibration parameters can be obtained:

[0087]

[0088]

[0089] and

[0090]

[0091] Step 3: Form the first group of samples by combining two anisotropic materials of the same size. Place the two anisotropic materials above and below the conductive strip of the strip air line respectively, and measure the S-parameters of the first group of samples using a vector network analyzer. The ξ and η axes of the first group of samples are aligned with the x and y axes of the strip air line;

[0092] Then the transmission matrix of the strip air line when placing the first group of samples is obtained from the following formula.

[0093]

[0094] Wherein,

[0095] The transmission matrix T with the two ends of the first group of samples as reference planes is as follows:

[0096]

[0097] Obtain the S m matrix of the first group of samples;

[0098]

[0099] Step 4: Use the NWR algorithm to calculate its dielectric constant ε m and magnetic permeability μ r1 using the S r1 matrix of the first group of samples;

[0100] Note:

[0101]

[0102] Then the reflection coefficient is expressed as:

[0103]

[0104] The propagation factor is expressed as:

[0105]

[0106] The permittivity ε r1 and the permeability μ r1 are obtained from the following two equations:

[0107]

[0108]

[0109] where λ 0 is the wavelength in free space, λ c = ∞ is the cut-off wavelength of the TEM mode, and l is the thickness of the first group of samples along the direction of electromagnetic wave propagation;

[0110] Step 5: Rotate the two anisotropic materials of the first group of samples to be the second group of samples. The ξ-axis and η-axis of the second group of samples are kept the same as the y-axis and x-axis directions of the strip air line respectively during the measurement process; Repeat the processes of Step 3 and Step 4 to calculate the permittivity ε r2 and the permeability μ r2 ;

[0111] Step 6: The permittivities ε rξ and ε rη of the anisotropic material along the ξ-axis and η-axis, as well as the permeabilities μ rξ and μ rη are obtained from the following system of equations:

[0112] aε rξ +bε rη = ε r1 (15)

[0113] aε rη +bε rξ = ε r2 (16)

[0114] bμ rξ +aμ rη = μ r1 (17)

[0115] bμ rη +aμrξ = μ r2 (18)

[0116] where a and b are constants obtained through simulation experiments, reflecting the relationship between the x - direction and y - direction components of the electromagnetic field in the strip air line. Specific embodiments:

[0118] The present invention proposes a strip air line measurement system for measuring anisotropic materials. The strip air line is composed of a conductive strip and upper and lower ground planes, and is excited by coaxial plugs and coaxial lines at both ends. Step - shaped transition strips are used at both ends of the conductive strip to achieve impedance matching. Twelve plastic pillars are used to support between the conductive strip and the upper and lower ground planes.

[0119] Both the upper and lower ground planes and the conductive strip are metal plates with a thickness of 1 mm. The upper and lower ground planes are 964 mm long and 400 mm wide. The middle part of the conductive strip is 938 mm long and 85 mm wide. The transition parts at both ends of the conductive strip are 11 mm long and 49 mm wide. The size of a pair of metal short - circuit plates is 400 mm×20 mm×30 mm. The specific dimensions are shown in Figure 2 .

[0120] The method for measuring metallic anisotropic materials using the strip air line in the present invention is as follows:

[0121] 1. Connect the strip air line with a vector network analyzer, and place the left - hand surface of the metal short - circuit plate at positions - 15 mm, 23 mm, 60 mm, and 98 mm relative to the center of the strip air line respectively. Negative numbers indicate on the left side of the center of the strip air line, and measure the S - parameters of four reflection standards respectively. As Figure 3 shown.

[0122] 2. Denote the two ports of the vector network analyzer as A and B. For ports A and B, the lengths of the reflection standards from the reference plane (the middle position of the strip air line) are denoted as l Ai and l Bi , where i = 0, 1, 2, 3 represents the i - th reflection standard in each group, and the propagation constants are γ A and γ B . For example, for the first reflection standard, the lengths for ports A and B are l A1 = - 0.015 m, l B1 = 0.015 - 0.02 = - 0.005 m, where 0.02 m is the width of the reflection standard. For the second reflection standard, the lengths for ports A and B are l A2 = 0.023 m, l B2 = - 0.023 - 0.02 = - 0.043 m. The reflection coefficient of the reflection standard is Γ T , and for port A, the following equations exist for the four reflection standards:

[0123]

[0124] Wherein E′ i = E i Γ T , In the formula, the "~" at the top of the parameter represents the measured value. Substitute the in the S matrix measured by the four reflection standards and the length of the reflection standard into the above formula, and use the Newton iteration method to solve the equation detP(γ A ) = 0 to obtain the propagation constant γ A .

[0125]

[0126] Substitute the propagation constant γ A and the S-parameter measurement results into the above formula to solve for E′ 1A , E 2A and E′ 3A . The same method can be used to find E′ 1B , E 2B and E′ 3B .

[0127] 3. Use a vector network analyzer to measure the through standard S-parameters of the air-filled ribbon line, denoted as The reflection coefficient of the reflection standard can be obtained from the following formula:

[0128]

[0129] Obtain:

[0130]

[0131]

[0132] and

[0133]

[0134] As Figure 4 shown, place the first set of materials in the air-filled ribbon line. The ξ and η axes of the first set of materials are the same as the x and y of the air-filled ribbon line. Use a vector network analyzer to measure the S-parameters of the air-filled ribbon line when the sample to be measured is placed. Then the transmission matrix of the air-filled ribbon line when the sample to be measured is placed can be obtained from the following formula.

[0135]

[0136] The transmission matrix T with the two end surfaces of the sample to be measured as the reference surfaces can be obtained as follows:

[0137]

[0138] Obtain S of the sample to be measured m matrix:

[0139]

[0140] That is, the calibration process of the entire system is completed, and the obtained matrix S uses the two side surfaces of the sample to be measured as the reference surfaces.

[0141] 4. Calculate the permittivity and permeability of the sample to be measured from the S matrix according to the NRW algorithm. Denote

[0142]

[0143] Then the reflection coefficient can be expressed as:

[0144]

[0145] The propagation factor can be expressed as:

[0146]

[0147] The permittivity and permeability are obtained from the following two equations:

[0148]

[0149]

[0150] where λ 0 is the wavelength in free space, and λ c = ∞ is the cut-off wavelength of the TEM mode. l is the thickness of the material to be measured along the electromagnetic wave propagation direction.

[0151] 5. Repeat the above process to measure the relative permittivity and relative permeability of the second group of samples, and solve for ε rξ and ε rη as well as μ rξ and μ rη .

[0152] As Figure 1 and Figure 2 shown, the thickness of the first conduction band is 1 mm, the length L s is 938 mm, the width W s is 85 mm, the transition thickness of the second conduction band step is 1 mm, the length L t is 11 mm, the width W t is 49 mm, and the upper and lower ground planes 3 have a thickness of 1 mm, the length L g is 964 mm, the width W gIt is 400 mm. The distances between the guiding tape and the upper and lower ground plates are both 30 mm. The metal shorting plate used as the reflection standard consists of upper and lower parts, and the dimensions of both are 400 mm × 30 mm × 20 mm. The dimensions of the two groups of anisotropic samples are both 300 mm × 30 mm × 30 mm. For the first group of materials, the ξ and η axes are the same as the x and y axes of the strip air line during the measurement process. For the second group of materials, the ξ and η axes are the same as the y and x axes of the strip air line during the measurement process.

[0153] First, the S-parameters of the four reflection standards are measured using a vector network analyzer to obtain E′ 1A , E 2A and E′ 3A . Using the same method, E′ 1B , E 2B and E′ 3B can be obtained.

[0154] Then, the S-parameters of the through standard are obtained by measuring the empty strip air line using a vector network analyzer, and the calibration parameters E A , E B and E t are obtained.

[0155] Finally, the two groups of anisotropic samples are respectively placed in the strip air line, and the two groups of S-parameters are measured using a vector network analyzer. The dielectric constants ε r1 , ε r2 and the permeabilities μ r1 , μ r2 of the two groups of samples are respectively obtained. Substitute ε r1 , ε r2 and μ r1 , μ r2 into (15)-(18) to solve for ε rξ and ε rη as well as μ rξ and μ rη . Using the same method, and can be obtained. Thus far, the dielectric constants and permeabilities of the anisotropic materials are obtained using the strip air line.

Claims

1. A method for measuring anisotropic materials using a strip air line, characterized in that, it includes the following steps: Step 1: The strip air line is composed of a conductive strip and upper and lower ground plates. Plastic studs are used to support between the conductive strip and the upper and lower ground plates. Step-type transition zones are provided at both ends of the conductive strip to achieve impedance matching, and coaxial cables are used to excite both ends of the conductive strip; when using the strip air line to measure anisotropic materials, it is in TEM mode in the area of the material to be measured; Step 2: Perform multireflect-thru calibration on the strip air line measurement system; Use four reflection standards and one thru standard to complete the calibration of the system; Define the lateral middle position of the strip air line as the measurement reference plane, and the strip air line itself serves as the thru standard; Place a metal shorting plate between the conductive strip and the ground plate, and realize four reflection standards by moving the metal shorting plate to four different positions; Step 2-1: Connect the strip air line using a vector network analyzer. The A port and B port of the vector network analyzer are respectively connected to the coaxial connectors at the left end and right end of the conductive strip. Place metal shorting plates at four different positions in the strip air line respectively, and measure the S-parameters of the four reflection standards in the forward and reverse directions in the frequency band of 0.3 - 1 GHz as the four reflection standards, denoted as respectively represent the i-th reflection standard, and the superscript "~" represents the measured value. The matrix form of the S-parameters is For ports A and B, the lengths of the reflection standard distance measurement reference planes are denoted as l Ai and l Bi , and the four reflection standards have the same propagation constant γ A and γ B , the same reflection coefficient Γ T ; E A and E B The specific representations of are the calibration parameters used to represent the error matrix during the calibration process as shown in (4) and (5); For port A, the following equations exist for the four reflection standards: wherein E’ iA = E iA Γ T , Use the Newton iteration method to solve the equation detP(γ A ) = 0 to obtain the propagation constant γ A ; where P(γ A ) is the coefficient matrix of Equation (1); Further from: Obtain E’ 1A , E 2A and E’ 3A ; For port B, E’ is also obtained 1B , E 2B and E’ 3B . During the process of solving for port B i.e., is the reflection coefficient of port B; Step 2-2: Measure the forward and reverse two-way S-parameters of the empty ribbon air line, i.e., the through standard, using a vector network analyzer Obtain the reflection coefficient Γ of the reflection standard T It is: Combined with E’ iA = E iA Γ T The calibration parameters are obtained as follows: and Step 3: Combine two anisotropic materials of the same size to form the first group of samples. The two anisotropic materials are respectively placed above and below the conductive strip of the strip air line, and use a vector network analyzer to measure the S parameters of the first group of samples. The ξ and η axes of the first group of samples are kept consistent with the x and y axes of the strip air line; The transmission matrix of the strip air line when placing the first group of samples is obtained by the following formula: Among them, The transmission matrix T with the two end surfaces of the first group of samples as reference planes is as follows: Obtain the S matrix S of the first set of samples m ; Step 4: Use the NWR algorithm to calculate its permittivity ε m and permeability μ r1 through the S r1 matrix of the first set of samples; Denote: Then the reflection coefficient is expressed as: The propagation factor is expressed as: Dielectric constant ε r1 and magnetic permeability μ r1 are obtained from the following two equations: where λ 0 is the wavelength in free space, λ c = ∞ is the cut-off wavelength of the TEM mode, and l is the thickness of the first group of samples along the electromagnetic wave propagation direction; Step 5: Rotate the two pieces of anisotropic material of the first group of samples to be the second group of samples. During the measurement process, the ξ-axis and η-axis of the second group of samples are respectively kept the same as the y-axis and x-axis directions of the strip air line; repeat the processes of Step 3 and Step 4 to calculate the permittivity ε r2 and permeability μ r2 ; Step 6: The dielectric constants ε rξ and ε rη along the ξ-axis and η-axis of the anisotropic material, as well as the magnetic permeabilities μ rξ and μ rη are obtained from the following system of equations: aε rξ +bε rη =ε r1 (15) aε rη +bε rξ =ε r2 (16) bμ rξ +aμ rη =μ r1 (17) bμ rη +aμ rξ =μ r2 (18) where a and b are constants, which reflect the relationship between the x-direction and y-direction components of the electromagnetic field in the strip air line.

2. The method for measuring anisotropic materials using a strip air line according to claim 1, characterized in that, the upper and lower ground plates and the conductive strip are all metal plates with a thickness of 1 mm. The length of the conductive strip is 938 mm and the width is 85 mm; the step length of the conductive strip is 11 mm and the width is 49 mm; the upper and lower ground plates are of the same size, with a length of 964 mm and a width of 400 mm; the distance between the conductive strip and the upper and lower ground plates is both 30 mm.

3. The method for measuring anisotropic materials using a strip air line according to claim 1, characterized in that, the metal shorting plate is composed of upper and lower parts, and the dimensions are both 400 mm×30 mm×20 mm.

4. The method for measuring anisotropic materials using a strip air line according to claim 1, characterized in that, the two anisotropic materials of the same size have dimensions of 300 mm×30 mm×30 mm.

5. The method for measuring anisotropic materials using a strip air line according to claim 1, characterized in that, the positions where the metal shorting plate is moved to four different positions are respectively 15 mm to the left of the measurement reference plane, 23 mm to the right of the measurement reference plane, 60 mm, and 98 mm from the measurement reference plane.

6. The method for measuring anisotropic materials using a strip air line according to claim 1, characterized in that, a = 0.13, b = 0.87.

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