A dielectric test device and method based on a microstrip negative group delay circuit

Abstract

The present invention discloses a dielectric testing device and method based on a microstrip negative group delay circuit, which relates to the technical field of microwave engineering. Based on the coupling between a ring resonator and a microstrip transmission line, and a standard circuit formed with known dielectric constant and loss tangent value, a dielectric plate to be measured is covered on the standard circuit to obtain a circuit to be measured, and further the resonant frequency and group delay value of the circuit to be measured are obtained. According to the group delay value of the circuit to be measured and the resonant frequency of the circuit to be measured obtained, an exponential function is selected for fitting, and the dielectric constant and loss tangent of the dielectric plate to be measured are respectively calculated and obtained. Through the technical solution of the present invention, a dielectric electromagnetic parameter plate testing method that can be applied to plates operating in various microwave frequency bands, has the advantages of high flexibility, low cost and simple structure, etc., and can obtain highly accurate test parameters.

Description

Technical Field

[0001] The present invention relates to the technical field of microwave engineering, and particularly to a dielectric testing device and method based on a microstrip negative group delay circuit. Background Art

[0002] In recent years, the rapid development of microwave technology has promoted the continuous expansion of the application fields of microwave dielectric materials and microwave components. At present, the consistency of the performance characteristics of microwave dielectric substrates from different manufacturers or different batches of the same manufacturer has become a common concern of material workers and microwave circuit designers. At the same time, in practical engineering applications, people also need to know accurate material parameters. The consistency of microwave dielectric substrates is of great significance for the setting of design parameters, debugging, production control, and acceptance of purchased equipment. Therefore, it is particularly important to quickly and conveniently measure whether the complex permittivity of microwave dielectric substrate materials is consistent.

[0003] There are many studies on the dielectric constant characteristics of microwave base materials at home and abroad. The main testing methods include the resonant cavity or dielectric resonator method, the transmission line terminal method, and the free space method, etc. These methods have their own characteristics and deficiencies, but through continuous development and improvement, they are all basically mature and widely used. However, the special measuring instruments on the market are relatively expensive and complex to operate, and are not suitable for actual users. Summary of the Invention

[0004] The purpose of the present invention is to provide a dielectric testing device and method based on a microstrip negative group delay circuit to solve the problems in the prior art.

[0005] To achieve the above purpose, the present invention provides the following technical solutions:

[0006] A dielectric testing device based on a microstrip negative group delay circuit uses the negative group delay property of the circuit to test the resonant frequency offset and group delay value of a dielectric plate to be tested operating in each frequency band, and obtains the permittivity and loss tangent of the dielectric plate to be tested. The dielectric testing device includes a dielectric substrate and a ring resonator. A microstrip transmission line is arranged on any side of the ring resonator. The two ends of the microstrip transmission line are respectively connected to an input port and an output port, and the input port and the output port respectively constitute the input end and the output end of the dielectric testing device.

[0007] Further, the aforementioned ring resonator and the microstrip transmission line are coupled to form a standard circuit.

[0008] Another aspect of the present invention proposes a dielectric testing method based on a microstrip negative group delay circuit, including the following steps:

[0009] Step A: Obtain the dielectric constant, loss tangent value of the dielectric substrate (1) used to form the standard circuit, and the resonant frequency of the ring resonator (3). Based on the coupling between the ring resonator (3) and the microstrip transmission line (2), form the standard circuit, and then proceed to Step B;

[0010] Step B: Cover the dielectric plate to be measured on the standard circuit to obtain the circuit to be measured. Further obtain the resonant frequency and group delay value of the circuit to be measured, obtain the resonant frequency offset between the circuit to be measured and the standard circuit, and the group delay of the circuit to be measured. Based on the resonant frequency offset, group delay value, and the dielectric constant of the dielectric plate to be measured itself, obtain the selected fitting exponential function, and then proceed to Step C;

[0011] Step C: For the dielectric plate to be measured, calculate and obtain the dielectric constant and loss tangent of the dielectric plate to be measured according to the obtained selected fitting exponential function, the resonant frequency offset of the circuit to be measured, and the group delay value of the circuit to be measured.

[0012] Furthermore, in the aforementioned Step A, based on the standard circuit formed by the coupling between the ring resonator (3) and the microstrip transmission line (2), and the dielectric constant and loss tangent of the dielectric substrate (1), according to the following formula:

[0013]

[0014] Calculate and obtain the physical size r of the standard circuit, where f0 is the resonant frequency of the ring resonator (3) itself, n is the harmonic number, c is the speed of light, and ε eff is the effective dielectric constant of the dielectric substrate for fabricating the standard circuit;

[0015] Based on the physical size of the standard circuit, the standard circuit is equivalent to an RLC circuit. Correspondingly, the ring resonator (3) is equivalent to a parallel circuit composed of an equivalent capacitance C, an equivalent inductance L, and an equivalent resistance R. According to the following formula:

[0016]

[0017] Obtain the group delay value τ(ω) of the standard circuit, where Q is the quality factor of the ring resonator (3), ω0 is the resonant angular frequency of the ring resonator (3) itself, R is the equivalent resistance, N is the turns ratio of the coupling between the microstrip transmission line (2) and the transformer in the standard circuit, and Z0 is the load at both ends of the microstrip transmission line (2).

[0018] Furthermore, in the aforementioned Step B, when the dielectric plate to be measured is covered on the standard circuit, the circuit to be measured is obtained, and the resonant frequency of the circuit to be measured shifts. According to the following formula:

[0019] Δf = f0 - f1

[0020] Obtain the resonance frequency offset Δf, where f0 is the resonance frequency of the ring resonator (3) itself, and f1 is the resonance frequency after covering the dielectric plate to be measured;

[0021] Correspondingly, under the influence of the loss tangent of the dielectric plate to be measured, the group delay value of the circuit to be measured changes based on the group delay value of the standard circuit.

[0022] Further, in the aforementioned step B, based on the resonance frequency offset, the group delay value, and the dielectric constant and loss tangent of the dielectric plate to be measured itself, obtain a selected fitting exponential function according to the following formula:

[0023]

[0024] Obtain the selected fitting exponential function, where A is a constant to be determined, e is the base of the natural logarithm, t is a constant to be determined, x is the independent variable, and y0 is a constant to be determined.

[0025] Further, for the dielectric plate to be measured, in the aforementioned step C, obtain the circuit to be measured by coupling the dielectric plate to be measured with the standard circuit. Based on the obtained selected fitting exponential function, according to the following formula:

[0026]

[0027]

[0028] Obtain the dielectric constant ε of the dielectric plate to be measured r and the loss tangent tanδ, where A1, t1, and y1 are the constants to be measured corresponding to the dielectric constant of the dielectric plate to be measured, and A2, t2, and y2 are the constants to be measured corresponding to the loss tangent of the dielectric plate to be measured, Δf is the frequency offset, and τ is the group delay value corresponding to the circuit to be measured.

[0029] The dielectric test device and method based on a microstrip negative group delay circuit described in the present invention, compared with the prior art by adopting the above technical solutions, have the following technical effects:

[0030] In the production of microwave dielectric plates, maintaining the consistency and uniformity of the electromagnetic parameters of the dielectric plates is a key production requirement. In order to achieve the purpose of low cost and easy operation when testing the electromagnetic parameters of the plates, this patent proposes a technology for measuring the electromagnetic parameters of plates based on a microstrip negative group delay circuit, which can be applied to plates operating in various microwave frequency bands and has the advantages of high flexibility, low cost, and simple structure; the present invention first proposes a method for measuring the dielectric constant and loss tangent of dielectric plates based on a microstrip negative group delay resonance ring. This method is relatively simple in structure and test mechanism compared with other methods, and is easy to test the consistency and uniformity of the electrical measurement parameters of microwave plates. Brief Description of the Drawings

[0031] Figure 1 Schematic structural diagram of a medium testing device according to an exemplary embodiment of the present invention;

[0032] Figure 2 Schematic size structure diagram of a standard circuit according to an exemplary embodiment of the present invention;

[0033] Fig. 3(a) is an equivalent circuit diagram of a standard circuit according to an exemplary embodiment of the present invention;

[0034] Fig. 3(b) is an equivalent circuit diagram of the coupling between a ring coupler and a microstrip line according to an exemplary embodiment of the present invention;

[0035] Figure 4 Schematic flow diagram of a medium testing method according to an exemplary embodiment of the present invention;

[0036] Fig. 5(a) shows the group delay value of the standard circuit corresponding to an exemplary embodiment of the present invention at a resonant frequency of 1.970 GHz;

[0037] Fig. 5(b) shows the insertion loss value of the standard circuit corresponding to an exemplary embodiment of the present invention at a resonant frequency of 1.970 GHz;

[0038] Fig. 6(a) shows the influence of the change in the average radius of the ring resonator corresponding to an exemplary embodiment of the present invention on the resonant frequency;

[0039] Fig. 6(b) shows the influence of the change in the ring width of the ring resonator corresponding to an exemplary embodiment of the present invention on the resonant frequency;

[0040] Fig. 6(c) shows the influence of the change in the coupling gap between the ring resonator and the microstrip line corresponding to an exemplary embodiment of the present invention on the resonant frequency;

[0041] Fig. 7(a) is a trend diagram of the change in the dielectric constant corresponding to the exemplary circuit under test of the present invention with respect to the resonant frequency offset;

[0042] Fig. 7(b) is a trend diagram of the change in the loss angle corresponding to the exemplary circuit under test of the present invention with respect to the group delay value;

[0043] Fig. 8(a) is a fitting curve graph of the resonant frequency offset and the dielectric constant based on different boards;

[0044] Fig. 8(b) is a fitting curve graph of the group delay and the loss tangent of the angle based on different boards;

[0045] Figure 9 Simulation and actual measurement comparison diagram of S parameters and group delay for testing a type of FR4 board;

[0046] Figure 1Among them, 1 - dielectric substrate; 2 - microstrip transmission line; 3 - ring resonator; 4 - dielectric plate to be measured; 21 - input port; 22 - output port. Detailed implementation manners

[0047] In order to better understand the technical content of the present invention, specific embodiments are given below in conjunction with the accompanying drawings for illustration.

[0048] In the present invention, various aspects of the present invention are described with reference to the accompanying drawings, in which many illustrative embodiments are shown. The embodiments of the present invention are not limited to those shown in the drawings. It should be understood that the present invention can be implemented by any one of the various concepts and embodiments introduced above, as well as the concepts and implementation manners described in detail below, because the concepts and embodiments disclosed in the present invention are not limited to any implementation manner. In addition, some aspects disclosed in the present invention can be used alone, or in any appropriate combination with other aspects disclosed in the present invention.

[0049] Refer to Figures 1-4 , the present invention provides a dielectric test device and method based on a microstrip negative group delay circuit. In combination with Figure 1 , a dielectric test device based on a microstrip negative group delay circuit uses the negative group delay property of the circuit to test the resonance frequency offset and group delay value of the dielectric plate 4 to be measured in different frequency bands, and obtains the dielectric constant and loss tangent of the dielectric plate 4 to be measured. The dielectric electromagnetic parameter test device includes a dielectric substrate 1 and a ring resonator 3. A microstrip transmission line 2 is arranged on any side of the ring resonator 3. The ring resonator 3 and the microstrip transmission line 2 constitute the negative group delay circuit of the present invention. The two ends of the microstrip transmission line 2 are respectively connected to the input port 21 and the output port 22. The input port 21 and the output port 22 respectively constitute the input end and the output end of the dielectric test device. The bottom surface of the dielectric substrate 1 is copper-clad and serves as the ground plane of the circuit. The microstrip transmission line is placed outside the ring resonator to form coupling. The dielectric plate to be measured is covered on the negative group delay circuit. As Figure 2 shown is the specific example dimension diagram of a dielectric electromagnetic parameter test method based on a microstrip negative group delay circuit of the present invention. The actual dimensions of each part are as follows:

[0050]

[0051] Figure 2 Among them, r is the average value of the inner and outer diameters of the resonance ring, w r is the line width of the resonance ring, s is the distance between the coupled microstrip line and the ring, w p is the line width of the microstrip line. At a given resonance frequency, the average circumference of the resonance ring is equal to an integer multiple of the wavelength λ in the medium, that is, the microstrip resonance ring satisfies the following relationship:

[0052] 2πr = nλg n = 1, 2, 3,... (1)

[0053] Wherein, r is the average radius of the resonant ring, n is the harmonic number, and λg is the waveguide wavelength.

[0054] The calculation method of the waveguide wavelength λg of the microstrip resonant ring is shown in Equation (1-2), and λg is a function of the frequency f.

[0055]

[0056] Wherein, c is the speed of light, is the effective dielectric constant, and f is the resonant frequency.

[0057] Therefore, from Equations (1) and (2), the effective dielectric constant of the dielectric substrate can be calculated.

[0058]

[0059] By using a resonator, the dielectric constant corresponding to the resonant frequency can be obtained, and the theoretical calculated value of the resonant frequency can be deduced from Formula (1). In a given resonator structure, the calculation formula of the resonant frequency f can be obtained from Formulas (2) and (3) as follows:

[0060]

[0061] As shown in Fig. 3(a), the ring resonator 3 is coupled with the microstrip transmission line 2 to form a standard circuit. As shown in Fig. 3(b), the ring resonator 3 is equivalent to a parallel circuit composed of an equivalent capacitor C, an equivalent inductor L, and an equivalent resistor R.

[0062] Combined with Figure 4 , a dielectric test method based on a microstrip negative group delay circuit includes the following steps:

[0063] Step A: Obtain the dielectric constant, loss tangent value of the dielectric substrate 1 for forming the standard circuit, and the resonant frequency of the ring resonator 3. Based on the coupling between the ring resonator 3 and the microstrip transmission line 2, and the obtained dielectric constant and loss tangent value, form a standard circuit, and then enter Step B;

[0064] Step B: Cover the dielectric plate to be measured 4 on the standard circuit to obtain the circuit to be measured, further obtain the resonant frequency and group delay value of the circuit to be measured, obtain the resonant frequency offset between the circuit to be measured and the standard circuit, and the group delay value of the standard circuit. Based on the resonant frequency offset and group delay value, select a fitting exponential function, and then enter Step C;

[0065] Step C: For the dielectric plate to be measured 4, according to the selected fitting exponential function, the resonant frequency offset of the circuit to be measured, and the group delay value of the circuit to be measured, calculate and obtain the dielectric constant and loss tangent of the dielectric plate to be measured 4 respectively.

[0066] Embodiment

[0067] Combined with FIGS. 3(a) and 3(b), Figure 4 when the ring resonator is placed near the microstrip line, it will couple with the edge magnetic field of the microstrip line. Let the electrical lengths of the microstrip lines on both sides of the ring resonator be θ1 and θ2 respectively, and the distance between the edge of the ring resonator and the microstrip line be s, that is, the coupling distance s. One end of the microstrip line is connected to the input voltage source and a 50Ω load, the other end of the input voltage source is grounded, the other end of the microstrip line is connected to a 50Ω output load, and the other end of the output load is grounded. The circuit in FIG. 3(a) can be equivalent to the RLC circuit shown in FIG. 3(b). When the ring resonator is coupled, it behaves as a series load on the microstrip line. The ring resonator can be equivalent to a parallel circuit composed of an equivalent inductor L, an equivalent resistor R, and an equivalent capacitor C, and the coupling model with the microstrip line is the turns ratio N of the transformer.

[0068] According to the inherent properties of the ring resonator, the resonant frequency of the ring resonator is:

[0069]

[0070] where ω0 is the resonant angular frequency of the ring resonator itself, L is the equivalent inductor, and R is the equivalent resistor. When the ring resonator has not been loaded onto the microstrip line, its own quality factor Q value is:

[0071]

[0072] where Q is the quality factor of the ring resonator, which characterizes a quality index of the ratio of the stored energy to the energy loss per week in a energy storage device (such as an inductor coil, capacitor, etc.) in a resonant circuit. The larger the Q value of the component, the better the selectivity of the circuit or network composed of the component. The coupling coefficient g of the ring resonator coupled to the microstrip line is defined as the ratio of the Q value when the resonator is not loaded onto the microstrip line to the Qe value when it is loaded onto the microstrip line.

[0073]

[0074] where Z0 is the load at both ends of the microstrip line, Z0 = 50Ω. When the ring resonator is coupled to the microstrip line, the equivalent series impedance Z of the ring resonator R is:

[0075]

[0076] where j is the imaginary unit, and ω is the resonant frequency of the entire circuit after the ring resonator is coupled to the microstrip line. For the equivalent circuit in FIG. 3(b), its S parameters can be written as:

[0077]

[0078]

[0079] The S-parameters are scattering parameters, which are important parameters in microwave transmission. S 12 is the reverse transmission coefficient, that is, isolation. S 21 is the forward transmission coefficient, that is, insertion loss. S 11 is the input reflection coefficient, that is, input return loss, S 22 is the output reflection coefficient, that is, output return loss.

[0080] The above S-parameter matrix does not consider the influence of the microstrip lines θ1 and θ2 on both sides on the S-parameters. When the microstrip lines θ1 and θ2 on both sides are added, we can get:

[0081]

[0082]

[0083]

[0084] Substituting the coupling coefficient g into the S-parameters, the insertion loss S of the equivalent circuit can be obtained 21 is:

[0085]

[0086] where θ = θ1 + θ2. Then the phase of the insertion loss of the equivalent circuit is:

[0087]

[0088] According to the definition of group delay: The group delay function of this circuit can be obtained as:

[0089]

[0090] where, let When ω = ω0:

[0091]

[0092] It can be seen that when the frequency is the resonant frequency of the dielectric resonator, the group delay value of this circuit is negative.

[0093] As mentioned above, Q is the quality factor of the ring resonator, which is a quality index representing the ratio of the stored energy to the energy loss per cycle. It can also be expressed as:

[0094]

[0095] Among them, Q c is the conductor loss, Q d is the dielectric loss, Q r is the radiation loss, and the dielectric loss Q d can be expressed as:

[0096]

[0097] where tanδ is the tangent of the loss angle of the dielectric material, q is the dielectric filling factor, and ε r is the relative permittivity of the dielectric material.

[0098] When tanδ increases, from Equation (13), the dielectric loss Q d decreases, the corresponding quality factor Q decreases, and thus the group delay τ increases. The same conclusion can also be obtained and verified by the simulation data in the HFSS model.

[0099] In this example, the resonant frequency of the resonant ring used is 2 GHz. The dielectric substrate for making the standard circuit is a certain board with a relative permittivity of 3.78 and a tangent of the loss angle of 0.006. The thickness of the dielectric board to be measured is 1.6 mm. However, the solution described in this patent is not limited to a resonant ring with a frequency of 2 GHz, a certain board with a relative permittivity of 3.78 and a tangent of the loss angle of 0.006, and a dielectric board to be measured with a thickness of 1.6 mm. By using resonant rings with other resonant frequencies, standard circuits made of other dielectric substrates, and dielectric boards to be measured with other thicknesses, the measurement effects described in this patent can still be achieved.

[0100] As shown in Figures 5(a) and 5(b), when the microstrip negative group delay circuit has not measured the board, that is, before covering the board to be measured to obtain the circuit to be measured, the resonant frequency obtained from the simulation test is 1.970 GHz, the corresponding group delay value is -2.01 ns, and the insertion loss is -1.58 dB.

[0101] The self-characteristics of the ring resonator 3 mainly affect the resonant frequency. As can be seen from Figure 6(a), when r increases, the resonant frequency will decrease accordingly. As can be seen from Figure 6(b), the ring width mainly affects the resonant frequency. When w increases, the resonant frequency will decrease accordingly. As can be seen from Figure 6(c), the coupling gap mainly affects the group delay value. When s increases, the absolute value of the group delay will decrease accordingly.

[0102] Combined with Figure 7(a), under the condition that the resonant frequency of the known negative group delay circuit (or standard circuit) without measuring the board is 1.970 GHz, when the board is covered above, the resonant frequency will shift. The frequency shift Δf is defined as the difference between the resonant frequency f0 without covering the board and the resonant frequency f1 after covering the board to be measured, that is:

[0103] Δf = f0 - f1 (5)

[0104] Δf has a certain relationship with the dielectric constant of the side plate, as shown in Figure 7(a): when the frequency offset is 101MHz, the dielectric constant is 4.0; when the frequency offset is 106MHz, the dielectric constant is 4.2; when the frequency offset is 109MHz, the dielectric constant is 4.4; when the frequency offset is 115MHz, the dielectric constant is 4.6; when the frequency offset is 117MHz, the dielectric constant is 4.8, etc.

[0105] As shown in Figure 7(b), when the group delay of the negative group delay circuit (or standard circuit) is known to be -2.01ns when the plate is not tested, the group delay will shift when the plate is covered on top. The group delay value has a certain relationship with the loss tangent of the plate on the side, as shown in Figure 7(b): when the group delay value is -1.85ns, the loss tangent is 0.008; when the group delay value is -1.50ns, the loss tangent is 0.026; when the group delay value is -1.30ns, the loss tangent is 0.04; when the group delay value is -0.65s, the loss tangent is 0.99, etc.

[0106] Figure 8(a) is an exponential fit of the simulation test results in Figure 7(a), and the frequency offset Δf and dielectric constant ε are obtained. r The relationship between the frequency offset and the dielectric constant is as follows:

[0107]

[0108] From formula (6), we can get the one-to-one correspondence between the frequency offset and the dielectric constant of the measured plate. Since the accuracy adjustment of the vector network analyzer is different in actual measurement, the following is a comparison table of frequency offset and dielectric constant with a step size of 1 MHz.

[0109]

[0110] FIG8(b) is an exponential fitting of the simulation test results in FIG7(b), and the relationship between the group delay τ and the loss tangent tanδ is obtained. The relationship between the delay value and the loss tangent is as follows:

[0111]

[0112] From formula (7), we can get the one-to-one correspondence between the group delay value and the loss tangent of the measured plate. Since the accuracy adjustment of the vector network analyzer is different in actual measurement, the following is a comparison table of the delay value and the loss tangent with a step size of 0.05ns.

[0113]

[0114] In this test, the dielectric constant of the FR4 board to be measured is 4.4, and the loss angle is 0.02. After testing, the frequency offset is 107 MHz and the group delay is 1.7 ns. As can be seen from Figure 8, the simulation and the measurement are in good agreement, basically conforming to the functional relationships between the resonant frequency f0 and the dielectric constant ε in Equations (6) and (7), r and between the group delay τ and the loss tangent tanδ. The deviation between the simulation and the measurement may be caused by processing errors, the fitting degree between the board to be measured and the microstrip negative group delay circuit, the test accuracy of the vector network analyzer, etc.

[0115] Although the present invention has been disclosed above with the preferred embodiments, it is not intended to limit the present invention. Those with ordinary knowledge in the technical field to which the present invention pertains can make various modifications and refinements without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention shall be subject to what is defined by the claims.

Claims

1. A dielectric testing method for a dielectric testing device based on a microstrip negative group delay circuit, characterized in that: The dielectric test device utilizes the negative group delay characteristic of the circuit to measure the resonance frequency offset and group delay value of the dielectric plate (4) to be tested operating in various frequency bands, and obtains the dielectric constant and loss tangent of the dielectric plate (4) to be tested. It is characterized in that the dielectric test device includes a dielectric substrate (1) and a ring resonator (3). A microstrip transmission line (2) is arranged on any side of the ring resonator (3). The two ends of the microstrip transmission line (2) are respectively connected to an input port (21) and an output port (22). The input port (21) and the output port (22) respectively constitute the input end and the output end of the dielectric test device; The dielectric test method includes the following steps: Step A: Obtain the dielectric constant, loss tangent value of the dielectric substrate (1) used to form the standard circuit, and the resonance frequency of the ring resonator (3). Based on the coupling of the ring resonator (3) and the microstrip transmission line (2) to form a standard circuit, then enter Step B; Step B: Cover the dielectric plate (4) to be tested on the standard circuit to obtain a circuit to be tested, and further obtain the resonance frequency and group delay value of the circuit to be tested. Obtain the resonance frequency offset between the circuit to be tested and the standard circuit and the group delay value of the circuit to be tested. Based on the resonance frequency offset, group delay value, and the dielectric constant of the dielectric plate (4) itself, obtain a selected fitting exponential function, then enter Step C; Step C: For the dielectric plate (4) to be tested, calculate and obtain the dielectric constant and loss tangent of the dielectric plate (4) to be tested according to the selected fitting exponential function, the resonance frequency offset of the circuit to be tested, and the group delay value of the circuit to be tested.

2. The dielectric testing method for a dielectric testing device based on a microstrip negative group delay circuit according to claim 1, characterized in that, In the said Step A, based on the standard circuit formed by the coupling of the ring resonator (3) and the microstrip transmission line (2), and the dielectric constant and loss tangent of the dielectric substrate (1), according to the following formula: Calculate the physical size r of the standard circuit, where f0 is the resonance frequency of the ring resonator (3) itself, n is the harmonic number, c is the speed of light, and ε eff is the effective dielectric constant of the dielectric substrate for fabricating the standard circuit; Based on the physical dimensions of the standard circuit, the standard circuit is equivalent to an RLC circuit. Correspondingly, the ring resonator (3) is equivalent to a parallel circuit composed of an equivalent capacitance C, an equivalent inductance L, and an equivalent resistance R. According to the following formula: Obtain the group delay value τ(ω) of the standard circuit, where Q is the quality factor of the ring resonator (3), ω0 is the resonance angular frequency of the ring resonator (3) itself, R is the equivalent resistance, N is the turns ratio of the coupling of the microstrip transmission line (2) and the transformer in the standard circuit, and Z0 is the load at both ends of the microstrip transmission line (2).

3. The dielectric testing method for a dielectric testing device based on a microstrip negative group delay circuit according to claim 1, characterized in that, In the said Step B, when the dielectric plate (4) to be tested is covered on the standard circuit, a circuit to be tested is obtained, and the resonance frequency of the circuit to be tested shifts. According to the following formula: Δf = f0 - f1 Obtain the resonance frequency offset Δf, where f0 is the resonance frequency of the ring resonator (3) itself, and f1 is the resonance frequency after covering the dielectric plate to be tested; Correspondingly, the group delay value of the circuit to be tested changes based on the group delay value of the standard circuit under the influence of the loss tangent of the dielectric plate (4) itself.

4. The dielectric testing method for a dielectric testing device based on a microstrip negative group delay circuit according to claim 2, characterized in that, In the said Step B, based on the resonance frequency offset, group delay value, and the dielectric constant and loss tangent of the dielectric plate (4) itself, obtain a selected fitting exponential function. According to the following formula: Obtain a selected fitting exponential function, where A is a constant to be determined, e is the base of the natural logarithm, t is a constant to be determined, x is the independent variable, and y0 is a constant to be determined.

5. The dielectric testing method for a dielectric testing device based on a microstrip negative group delay circuit according to claim 3, characterized in that, For the medium plate (4) to be measured, in the step C, a measured circuit is obtained by coupling the medium plate (4) to be measured with a standard circuit. Based on the obtained selected fitting exponential function, according to the following formula: Obtain the dielectric constant ε of the dielectric plate (4) to be measured r and the loss tangent tanδ, where A1, t1, and y1 are the undetermined constants corresponding to the dielectric constant of the dielectric plate (4) to be measured, A2, t2, and y2 are the undetermined constants corresponding to the loss tangent of the dielectric plate (4) to be measured, Δf is the resonance frequency offset, and τ is the group delay value corresponding to the circuit to be measured.

6. The dielectric testing method for a dielectric testing device based on a microstrip negative group delay circuit according to claim 1, characterized in that, The ring resonator (3) is coupled with the microstrip transmission line (2) to form a standard circuit.

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