Millimeter wave dielectric testing system and method for wave-absorbing material under low-frequency microwave electric field

Abstract

The application aims to provide a millimeter wave dielectric test system and method of wave-absorbing material under low-frequency microwave electric field, belonging to the technical field of microwave and millimeter wave test. The test system innovatively combines the rectangular resonant cavity and the free space method test technology, controls the electric field intensity of the material to be tested through the rectangular resonant cavity, sets the double-pass quartz test tube through the opening of the resonant cavity, sets the ellipsoidal reflector at both ends of the rectangular resonant cavity to realize the free space method test of the millimeter wave dielectric performance of the material to be tested, uses the rectangular resonant cavity to provide the low-frequency microwave electric field, avoids the mode interference between the excitation signal and the test signal mode, the large frequency span of the vector network analyzer during the test and other problems, and greatly improves the test accuracy. Meanwhile, the dielectric test system designed by the application has the characteristics of high test precision, good test stability, low use and maintenance cost.

Description

Technical Field

[0001] This invention belongs to the field of microwave and millimeter-wave testing technology, specifically relating to a millimeter-wave dielectric testing system and method for absorbing materials under the action of a low-frequency microwave electric field. Background Technology

[0002] Microwave-absorbing materials have wide applications in both military and civilian fields. In the military, they serve as important stealth materials, reducing or eliminating the detection of aircraft, tanks, and ships by electromagnetic waves generated by radar and infrared radiation. In the civilian field, they are used for electromagnetic information leakage protection, electromagnetic radiation protection, and building absorption. The dielectric constant determines the absorption capacity of a microwave-absorbing material. Since microwave devices, such as radar, operate in the millimeter-wave band, studying the millimeter-wave dielectric properties of microwave-absorbing materials is crucial. Furthermore, with the rapid development of mobile communication systems, the electromagnetic energy of space electromagnetic radiation is increasing year by year. Therefore, it is particularly important to test the dielectric properties of microwave-absorbing materials in the millimeter-wave band under a low-frequency microwave electric field environment equivalent to external space.

[0003] Traditional dielectric property measurement techniques include the resonant cavity method and the network parameter method. The former is simple to operate, has a wide range of applications, and requires simple equipment, but its measurement range is limited to materials with medium and low dielectric constants and low loss materials, and it is not suitable for testing microwave absorbing materials. The latter treats the material under test and the entire system as an equivalent single-port or two-port network, and then uses electromagnetic wave transmission and reflection to measure the scattering parameters of the network, and calculates the electromagnetic parameters of the material under test accordingly. It is suitable for measuring the dielectric parameters of microwave absorbing materials, but this method cannot provide a stable low-frequency electric field environment.

[0004] For millimeter-wave dielectric testing of absorbing materials under low-frequency microwave electric fields, the team led by Li En at the University of Electronic Science and Technology of China (Gao Yong. Research on Microwave Dielectric Properties of Typical Materials under High Power [D]. University of Electronic Science and Technology of China, 2019.) has conducted some research. They used two different modes of the same resonant cavity to test the excitation signal of the excitation microwave electric field environment and the test signal of the dielectric properties of the material, and obtained the evolution law of the dielectric properties of some materials in the low-frequency band with the change of microwave electric field intensity. However, this method has certain defects for testing the dielectric properties of absorbing materials in the millimeter-wave band under low-frequency microwave electric field environment. For example, a single resonant cavity can only generate excitation signals of the same frequency or with a small frequency span; in addition, even if it can barely achieve simultaneous coverage from the low-frequency microwave band to the millimeter-wave band, the impact of various clutter mode interferences on the test accuracy cannot be ignored, that is, it is easy to cause mode interference problems. Summary of the Invention

[0005] To address the problems existing in the background technology, the present invention aims to provide a millimeter-wave dielectric testing system and method for absorbing materials under the action of a low-frequency microwave electric field. This testing system innovatively combines rectangular resonant cavity and free-space method testing techniques to achieve the measurement of the dielectric constant of absorbing materials in the millimeter-wave band under the action of a low-frequency microwave electric field. This avoids problems such as the large frequency band span during single-resonant cavity testing and interference between the excitation signal of the low-frequency microwave electric field environment and the test signal mode for the dielectric properties of the material under test in the millimeter-wave band, greatly improving the accuracy of the test.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows:

[0007] A millimeter-wave dielectric testing system for absorbing materials under low-frequency microwave electric field includes a first vector network analyzer 1, a second vector network analyzer 2, a first band-stop filter 3, a second band-stop filter 4, a first horn antenna 5, a second horn antenna 6, a first ellipsoidal reflector 7, a second ellipsoidal reflector 8, a rectangular resonant cavity 9, a quartz test tube 10, a first isolator 12, a power amplifier 13, a second isolator 14, a directional coupler 15, a matching load 20, and a microwave probe 21.

[0008] In this configuration, one end of the first band-stop filter 3 is connected to one port of the first vector network analyzer 1, and the other end of the first band-stop filter 3 is connected to the first horn antenna 5; one end of the second band-stop filter 4 is connected to the other port of the first vector network analyzer 1, and the other end of the second band-stop filter 4 is connected to the second horn antenna 6; one port of the second vector network analyzer 2 is connected to one end of the first isolator 12, and the other port of the second vector network analyzer 2 is connected to the coupling port 19 of the directional coupler; the other end of the first isolator 12 is connected in sequence to the output terminal 16 of the power amplifier 13, the second isolator 14, and the directional coupler 15; the input terminal 17 of the directional coupler 15 is connected to the microwave probe 21, and the isolation terminal 18 of the directional coupler is connected to the matched load 20;

[0009] The microwave probe 21 is disposed at one end of the rectangular resonant cavity 9. A quartz test tube 10 is disposed at the center of the rectangular resonant cavity 9. The two ends of the quartz test tube 10 are open and the height is the same as the height of the rectangular resonant cavity 9. The absorbing material to be tested is disposed on the central wall of the quartz test tube 10.

[0010] The major axis of the ellipsoid of the first ellipsoidal reflector 7 forms a 45-degree angle with the axis of the first horn antenna 5, and the phase center of the first horn antenna 5 is located at the first focal point of the first ellipsoidal reflector 7; the major axis of the ellipsoid of the second ellipsoidal reflector 8 forms a 45-degree angle with the axis of the second horn antenna 6, and the phase center of the second horn antenna 6 is located at the first focal point of the second ellipsoidal reflector 8; the center of the quartz test tube 10 is located at the second focal point of both the first ellipsoidal reflector 7 and the second focal point of the second ellipsoidal reflector 8.

[0011] Furthermore, the aperture field of the first horn antenna 5 and the second horn antenna 6 is uniformly distributed, and the sidelobe level is more than 20dB lower than the main lobe level.

[0012] Furthermore, the horn antennas 5 and 6 are dual-mode horn antennas or corrugated horn antennas.

[0013] Furthermore, both the first ellipsoidal reflector 7 and the second ellipsoidal reflector 8 are made of brass.

[0014] This invention also provides a method for dielectric testing of absorbing materials based on the above-described testing system, comprising the following steps:

[0015] Step 1. Without placing the material to be tested, perform response calibration on the first vector network analyzer 1;

[0016] Step 2. After calibration, place the test material 11 inside the quartz test tube 10, and use the first vector network analyzer 1 to test the return loss coefficient S of the test material 11 at the required microwave electric field intensity point. 11 and transmission coefficient S 21 ;

[0017] Step 3. Based on the return loss coefficient S obtained in Step 2 when loading the material under test. 11 and transmission coefficient S 21 Using the calibration data from step 1, the relative complex permittivity of the material under test is calculated. The specific calculation process is as follows:

[0018]

[0019] in:

[0020]

[0021] z is the normalized characteristic impedance of the material under test, γ is the propagation constant of the material under test, d is the thickness of the material under test, Γ is the surface reflection coefficient of the sample under test, and T is the surface transmission coefficient of the sample under test.

[0022]

[0023] Where γ is the propagation constant of the material under test, γ0 is the propagation constant in free space, λ0 is the wavelength in free space, and ε r Let μ be the dielectric constant of the material to be tested. r The magnetic permeability of the material to be tested;

[0024] From equation (1), Γ and Τ can be written as:

[0025]

[0026] Where K is an intermediate variable;

[0027] According to equation (2), the propagation constant γ of the material to be measured can be written as:

[0028]

[0029] From equations (2) and (3), we have:

[0030]

[0031] We can obtain the following through equations (4), (5), and (6):

[0032]

[0033] Furthermore, in step 2, the microwave electric field strength can be changed by adjusting the input power. The specific relationship between the microwave electric field strength and the input power is as follows:

[0034] Adjust the excitation signal frequency so that the rectangular resonant cavity operates at TE. 101 Mode, for rectangular resonator TE 101 The electromagnetic field distribution within the cavity is as follows:

[0035]

[0036] Where E0 is the amplitude of the electric field intensity, Z TE For TE 101 The wave impedance of the mode, η is the free space wave impedance, a is the length of the rectangular resonant cavity, and d is the height of the rectangular resonant cavity;

[0037] If the rectangular resonant cavity only experiences conductivity loss due to the cavity wall, then the cavity loss P c for:

[0038]

[0039] Among them, H t Let R be the tangential magnetic field component of the cavity wall surface, b be the width of the rectangular resonant cavity, and R be the tangential magnetic field component of the cavity wall surface. s η is the surface resistance of the rectangular resonant cavity, λ is the operating wavelength of the rectangular resonant cavity at resonance, and η is the wave impedance.

[0040] The quality factor Q of a rectangular resonant cavity under no-load conditions c for:

[0041]

[0042] Where k is the wave number at resonance, and ω0 is the resonant angular frequency;

[0043] When the rectangular resonant cavity is in a resonant state, its electric field stores energy W. e Equal to magnetic field energy storage W m ,

[0044]

[0045] Where ε is the dielectric constant within the rectangular resonant cavity. For E y The conjugate of , where V is the volume inside the rectangular resonant cavity;

[0046] Assume the microwave input power P of the excitation resonant cavity TE101 All of the material is injected into the resonant cavity, considering only the cavity wall metal loss P. c By definition of the quality factor:

[0047]

[0048] Combining equations (8), (9), (10), (11), and (12), the maximum electric field strength inside the rectangular resonant cavity and at the material under test is obtained as follows:

[0049]

[0050] The mechanism of this invention is as follows: This invention uses two vector network analyzers to separate the test signal and the electric field excitation signal within a single rectangular resonant cavity. One vector network analyzer excites a low-frequency microwave electric field within the rectangular resonant cavity, while the other vector network analyzer provides the test signal. The free-space method is then used to perform millimeter-wave dielectric measurements on the material under test. In free space, the electromagnetic waves and the low-frequency electric field within the rectangular resonant cavity do not interfere with each other, thus avoiding the problems of large frequency band spans and mode interference caused by simultaneously exciting a low-frequency electric field and performing millimeter-wave measurements within a single resonant cavity.

[0051] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0052] This invention innovatively combines the rectangular resonant cavity free-space method with the rectangular resonant cavity to provide a low-frequency microwave electric field, thereby controlling the electric field strength at the material under test. By opening the resonant cavity and installing a double-pass quartz test tube, and simultaneously placing ellipsoidal reflectors at both ends of the rectangular resonant cavity, the free-space method is used to test the millimeter-wave dielectric properties of the material under test. This avoids problems such as mode interference between the excitation signal and the test signal, and the large frequency band span of the vector network analyzer during testing, greatly improving the accuracy of the test. Furthermore, the dielectric testing system designed in this invention features high testing accuracy, good testing stability, and low usage and maintenance costs. Attached Figure Description

[0053] Figure 1 This is a schematic diagram of the millimeter-wave dielectric testing system for absorbing materials under the action of a low-frequency microwave electric field, as described in this invention.

[0054] Figure 2 This is a schematic diagram of the rectangular resonant cavity in the dielectric testing system of the present invention.

[0055] Wherein, 1 is the first vector network analyzer, 2 is the second vector network analyzer, 3 is the first band-stop filter, 4 is the second band-stop filter, 5 is the first horn antenna, 6 is the second horn antenna, 7 is the first ellipsoidal reflector, 8 is the second ellipsoidal reflector, 9 is the rectangular resonant cavity, 10 is the quartz test tube, 11 is the material under test, 12 is the first isolator, 13 is the power amplifier, 14 is the second isolator, 15 is the directional coupler, 16 is the output port of the directional coupler, 17 is the input port of the directional coupler, 18 is the isolation port of the directional coupler, 19 is the coupling port of the directional coupler, 20 is the matched load, and 21 is the microwave electric probe. Detailed Implementation

[0056] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings.

[0057] This invention provides a millimeter-wave dielectric testing system for absorbing materials under low-frequency microwave electric fields. A schematic diagram of the overall structure of the system is shown below. Figure 1 As shown, it includes a first vector network analyzer 1, a second vector network analyzer 2, a first band-stop filter 3, a second band-stop filter 4, a first horn antenna 5, a second horn antenna 6, a first ellipsoidal reflector 7, a second ellipsoidal reflector 8, a rectangular resonant cavity 9, a quartz test tube 10, a first isolator 12, a power amplifier 13, a second isolator 14, a directional coupler 15, a matching load 20, and a microwave probe 21;

[0058] In this configuration, one end of the first band-stop filter 3 is connected to one port of the first vector network analyzer 1, and the other end of the first band-stop filter 3 is connected to the first horn antenna 5; one end of the second band-stop filter 4 is connected to the other port of the first vector network analyzer 1, and the other end of the second band-stop filter 4 is connected to the second horn antenna 6; one port of the second vector network analyzer 2 is connected to one end of the first isolator 12, and the other port of the second vector network analyzer 2 is connected to the coupling port 19 of the directional coupler; the other end of the first isolator 12 is connected in sequence to the output terminal 16 of the power amplifier 13, the second isolator 14, and the directional coupler 15; the input terminal 17 of the directional coupler 15 is connected to the microwave probe 21, and the isolation terminal 18 of the directional coupler is connected to the matched load 20;

[0059] The microwave probe 21 is disposed at one end of the rectangular resonant cavity 9. A quartz test tube 10 is disposed at the center of the rectangular resonant cavity 9. The quartz test tube 10 is cylindrical with openings at both ends. The height from the upper surface to the lower surface of the quartz test tube 10 is the same as the height of the rectangular resonant cavity 9. The absorbing material 11 to be tested is placed horizontally at the center of the height of the quartz test tube 10, and its diameter is the same as the diameter of the upper surface of the quartz test tube. The structural schematic diagram of the rectangular resonant cavity is shown below. Figure 2 As shown;

[0060] The major axis of the ellipsoid of the first ellipsoidal reflector 7 forms a 45-degree angle with the axis of the first horn antenna 5, and the phase center of the first horn antenna 5 is located at the first focal point of the first ellipsoidal reflector 7; the major axis of the ellipsoid of the second ellipsoidal reflector 8 forms a 45-degree angle with the axis of the second horn antenna 6, and the phase center of the second horn antenna 6 is located at the first focal point of the second ellipsoidal reflector 8; the center of the quartz test tube 10 is located at the second focal point of both the first ellipsoidal reflector 7 and the second focal point of the second ellipsoidal reflector 8.

[0061] Example 1

[0062] A method for dielectric testing of microwave absorbing materials based on the above-mentioned testing system includes the following steps:

[0063] Step 1. Without placing the material to be tested, perform response calibration on the first vector network analyzer 1;

[0064] Step 2. After calibration, place the test material 11 inside the quartz test tube 10, and use the first vector network analyzer 1 to test the return loss coefficient S of the test material 11 under the required microwave electric field strength. 11 and transmission coefficient S 21 ;

[0065] The microwave electric field strength can be changed by adjusting the input power. The specific relationship between the microwave electric field strength and the input power is as follows:

[0066] Adjust the excitation signal frequency so that the rectangular resonant cavity operates at TE. 101 Mode, for rectangular resonator TE 101 The electromagnetic field distribution within the cavity is as follows:

[0067]

[0068] Where E0 is the amplitude of the electric field intensity, Z TE For TE 101 The wave impedance of the mode, η is the free space wave impedance, a is the length of the rectangular resonant cavity, and d is the height of the rectangular resonant cavity;

[0069] If the rectangular resonant cavity only experiences conductivity loss due to the cavity wall, then the cavity loss P c for:

[0070]

[0071] Among them, H t Let R be the tangential magnetic field component of the cavity wall surface, b be the width of the rectangular resonant cavity, and R be the tangential magnetic field component of the cavity wall surface. s η is the surface resistance of the rectangular resonant cavity, λ is the operating wavelength of the rectangular resonant cavity at resonance, and η is the wave impedance.

[0072] The quality factor Q of a rectangular resonant cavity under no-load conditions c for:

[0073]

[0074] Where k is the wave number at resonance, and ω0 is the resonant angular frequency;

[0075] When the rectangular resonant cavity is in a resonant state, its electric field stores energy W. e Equal to magnetic field energy storage W m ,

[0076]

[0077] Where ε is the dielectric constant within the rectangular resonant cavity. For E y The conjugate of , where V is the volume inside the rectangular resonant cavity;

[0078] Assume the microwave input power P of the excitation resonant cavity TE101 All of the material is injected into the resonant cavity, considering only the cavity wall metal loss P. c By definition of the quality factor:

[0079]

[0080] Combining equations (14), (15), (16) and (17) and (18), the maximum electric field strength inside the rectangular resonant cavity and at the material under test is obtained as follows:

[0081]

[0082] Step 3. Based on the return loss coefficient S obtained in Step 2 when loading the material under test. 11 and transmission coefficient S 21 Using the calibration data from step 1, the relative complex permittivity of the material under test is calculated. The specific calculation process is as follows:

[0083]

[0084] in:

[0085]

[0086] z is the normalized characteristic impedance of the material under test, γ is the propagation constant of the material under test, d is the thickness of the material under test, Γ is the surface reflection coefficient of the sample under test, and T is the surface transmission coefficient of the sample under test.

[0087]

[0088] Where γ is the complex propagation constant of the material under test, γ0 is the complex propagation constant in free space, λ0 is the wavelength in free space, and ε r Let μ be the dielectric constant of the material to be tested. r The magnetic permeability of the material to be tested;

[0089] From equation (20), Γ and Τ can be written as:

[0090]

[0091] Where K is an intermediate variable;

[0092] According to equation (21), the complex propagation constant γ of the material to be measured can be written as:

[0093]

[0094] From equations (21) and (22), we have:

[0095]

[0096] We can obtain the following from equations (23), (24), and (25):

[0097]

[0098] Step 4. Change the excitation signal power of the second vector network analyzer 2 to obtain different microwave electric field intensities in the region of the material under test. Repeat steps 2 to 3 to obtain the millimeter-wave dielectric properties of the absorbing material under different microwave electric fields.

[0099] The above description is merely a specific embodiment of the present invention. Any feature disclosed in this specification may be replaced by other equivalent or similar features unless otherwise specified. All disclosed features, or steps in all methods or processes, may be combined in any way except for mutually exclusive features and / or steps.

Claims

1. A millimeter-wave dielectric testing system for absorbing materials under low-frequency microwave electric field, characterized in that, It includes a first vector network analyzer (1), a second vector network analyzer (2), a first band-stop filter (3), a second band-stop filter (4), a first horn antenna (5), a second horn antenna (6), a first ellipsoidal reflector (7), a second ellipsoidal reflector (8), a rectangular resonant cavity (9), a quartz test tube (10), a first isolator (12), a power amplifier (13), a second isolator (14), a directional coupler (15), a matching load (20), and a microwave probe (21); Among them, one end of the first band-stop filter (3) is connected to one port of the first vector network analyzer (1), and the other end of the first band-stop filter (3) is connected to the first horn antenna (5); one end of the second band-stop filter (4) is connected to the other port of the first vector network analyzer (1), and the other end of the second band-stop filter (4) is connected to the second horn antenna (6); one port of the second vector network analyzer (2) is connected to one end of the first isolator (12), and the other port of the second vector network analyzer (2) is connected to the coupling end (19) of the directional coupler; the other end of the first isolator (12) is connected in sequence to the output end (16) of the power amplifier (13), the second isolator (14), and the directional coupler (15); the input end (17) of the directional coupler (15) is connected to the microwave probe (21), and the isolation end (18) of the directional coupler is connected to the matched load (20); The microwave probe (21) is set at one end of the rectangular resonant cavity (9). A quartz test tube (10) is set at the center of the rectangular resonant cavity (9). The two ends of the quartz test tube (10) are open and the height is the same as the height of the rectangular resonant cavity (9). The absorbing material to be tested is set on the central wall of the quartz test tube (10). The major axis of the ellipsoid of the first ellipsoidal reflector (7) forms a 45-degree angle with the axis of the first horn antenna (5), and the phase center of the first horn antenna (5) is located at the first focus of the first ellipsoidal reflector (7); the major axis of the ellipsoid of the second ellipsoidal reflector (8) forms a 45-degree angle with the axis of the second horn antenna (6), and the phase center of the second horn antenna (6) is located at the first focus of the second ellipsoidal reflector (8); the center of the quartz test tube (10) is located at the second focus of both the first ellipsoidal reflector (7) and the second focus of the second ellipsoidal reflector (8).

2. The millimeter-wave dielectric testing system for absorbing materials under low-frequency microwave electric field as described in claim 1, characterized in that, The aperture field of the first horn antenna (5) and the second horn antenna (6) is uniformly distributed, and the sidelobe level is more than 20dB lower than the main lobe level.

3. The millimeter-wave dielectric testing system for absorbing materials under low-frequency microwave electric field as described in claim 1, characterized in that, The horn antenna is a dual-mode horn antenna or a corrugated horn antenna.

4. The millimeter-wave dielectric testing system for absorbing materials under low-frequency microwave electric field as described in claim 1, characterized in that, Both the first ellipsoidal reflector (7) and the second ellipsoidal reflector (8) are made of brass.

5. A method for dielectric testing of absorbing materials based on the millimeter-wave dielectric testing system for absorbing materials under the action of a low-frequency microwave electric field as described in any one of claims 1-4, characterized in that, Includes the following steps: Step 1. Without placing the material under test, perform response calibration on the first vector network analyzer; Step 2. After calibration, place the test material in a quartz test tube and use a first vector network analyzer to test the return loss coefficient S of the test material at the required microwave electric field intensity point. 11 and transmission coefficient S 21 ; Step 3. Based on the return loss coefficient S obtained in Step 2 when loading the material under test. 11 and transmission coefficient S 21 Using the calibration data from step 1, the relative complex permittivity of the material under test is calculated. The specific calculation process is as follows: in: z is the normalized characteristic impedance of the material under test, γ is the propagation constant of the material under test, d is the thickness of the material under test, Γ is the surface reflection coefficient of the sample under test, and T is the surface transmission coefficient of the sample under test. Where γ is the complex propagation constant of the material under test, γ0 is the complex propagation constant in free space, λ0 is the wavelength in free space, and ε r Let μ be the dielectric constant of the material to be tested. r The magnetic permeability of the material to be tested; From equation (1), we can obtain that Γ and T are: Where K is an intermediate variable; According to equation (2), the complex propagation constant γ of the material to be tested is: From equations (2) and (3), we have: By solving equations (4), (5), and (6) simultaneously, we can obtain:

6. The method for dielectric testing of absorbing materials as described in claim 5, characterized in that, In step 2, the microwave electric field strength is changed by adjusting the input power. The specific relationship between the microwave electric field strength and the input power is as follows: Adjust the excitation signal frequency so that the rectangular resonant cavity operates at TE. 101 Mode, for rectangular resonator TE 101 The electromagnetic field distribution within the cavity is as follows: Where E0 is the amplitude of the electric field intensity, Z TE For TE 101 The wave impedance of the mode, η is the free space wave impedance, a is the length of the rectangular resonant cavity, and d is the height of the rectangular resonant cavity; If the rectangular resonant cavity only experiences conductivity loss due to the cavity wall, then the cavity loss P c for: Among them, H t Let R be the tangential magnetic field component of the cavity wall surface, b be the width of the rectangular resonant cavity, and R be the tangential magnetic field component of the cavity wall surface. s η is the surface resistance of the rectangular resonant cavity, λ is the operating wavelength of the rectangular resonant cavity at resonance, and η is the wave impedance. The quality factor Q of a rectangular resonant cavity under no-load conditions c for: Where k is the wave number at resonance, and ω0 is the resonant angular frequency; When the rectangular resonant cavity is in a resonant state, its electric field stores energy W. e Equal to magnetic field energy storage W m , Where ε is the dielectric constant within the rectangular resonant cavity. For E y The conjugate of , where V is the volume inside the rectangular resonant cavity; Assume the microwave input power P of the excitation resonant cavity TE101 All of the material is injected into the resonant cavity, considering only the cavity wall metal loss P. c By definition of the quality factor: Combining equations (8), (9), (10), (11), and (12), the maximum electric field strength inside the rectangular resonant cavity and at the material under test is obtained as follows:

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