Method and device for measuring dielectric constant of material by two-channel superheterodyne free space method

Abstract

The invention provides a two-channel superheterodyne free space method material dielectric constant measurement method and device, which are used for accurately measuring the dielectric constant of a low-loss wave-transparent material. According to the embodiment, a dual-channel superheterodyne circuit structure is used, and two related waveguide channels with different frequencies are adopted to generate a medium / low-frequency measurement signal and a synchronization signal respectively; a measurement signal is fed into the lock-in amplifier after being input into the inductive voltage divider, and a synchronizing signal is input into the lock-in amplifier; a channel transmission coefficient module value is calculated according to a voltage division ratio of an inductive voltage divider before a measured material is placed in a measuring position and a voltage division ratio after voltage compensation after the measured material is placed in, and a channel transmission coefficient phase shift is calculated according to a phase difference between a measuring signal and a synchronizing signal before and after the measured material is placed in a lock-in amplifier. And then performing phase correction on the channel transmission coefficient to obtain an end surface transmission coefficient of the tested material, and performing inversion calculation on a dielectric constant real part and a loss angle tangent value of the tested material according to a free space method.

Description

Technical Field

[0001] The present application relates to the technical field of material dielectric constant measurement, and in particular, to a dual-channel superheterodyne free-space method for measuring material dielectric constant and a device therefor. Background Art

[0002] Accurately measuring the electromagnetic intrinsic parameters of materials, especially the complex dielectric constant, is crucial for the design and development of microwave and millimeter-wave devices or radio frequency systems in various fields. For example, in the research and development of quasi-optical components (such as dielectric lenses and quasi-optical filters), it is necessary to accurately master the complex dielectric constant of materials at the design stage to achieve the expected simulation performance. In the cryogenic receiver system in the field of radio astronomy, accurately characterizing the complex dielectric constant of materials plays a key role in selecting the material with the lowest loss to achieve the performance of the receiver. In the millimeter-wave radar in the field of automotive assisted driving, accurately measuring the complex dielectric properties of materials such as radar PCB substrates, radar radomes, and bumpers is extremely important for the design and performance evaluation of vehicle-mounted radars and components.

[0003] There are mainly three measurement methods for measuring the complex dielectric constant of materials in the millimeter-wave band: The first method is the measurement method using terahertz time-domain spectroscopy (THz-TDS). This type of method extracts the dielectric parameters of materials through the time-domain or frequency-domain response after a pulsed wave penetrates the material. The measurement frequency range is extremely wide, but its frequency resolution is not high. In addition, the measurement accuracy is limited, especially it cannot accurately measure the dielectric loss of materials.

[0004] The second method is the resonance cavity method based on various resonance principles, including closed resonance cavities, split resonance cavities, quasi-optical open resonance cavities, etc. The measurement accuracy of this type of method is very high, especially suitable for the measurement of low-loss materials (loss tangent less than 0.01), but it can only work at discrete resonance frequencies.

[0005] The third method is the continuous wave measurement method based on a vector network analyzer (referred to as a network analyzer). This type of method can be divided into free-space method, coaxial line method, and waveguide method according to different transmission forms. Compared with other methods, the free-space method measurement device has more advantages. Because it is not restricted by the processing and preparation of samples, it can realize non-destructive testing of material dielectric parameters in a relatively wide frequency range, and can more conveniently be compatible with various high and low temperature complex test environments.

[0006] In a classical free-space method measurement system, the transmission and reflection signals of a material are generally measured by a vector network analyzer, and then the dielectric parameters are inversely calculated. From theoretical analysis, it can be known that the measurement accuracy of the real part of the dielectric constant of a material mainly depends on the measurement accuracy of the phase of the transmission coefficient, while the measurement accuracy of the tangent value of the loss angle of a material mainly depends on the measurement accuracy of the modulus value of the transmission coefficient. For low-loss wave-transparent materials, the modulus value and phase repeatability of the transmission coefficient of the material measured by traditional methods such as free-space test devices based on vector network analyzers are poor, and the measurement uncertainty is large, which cannot meet the requirements of high-precision measurement. In the millimeter-wave band, the technical index of the measurement uncertainty of the transmission coefficient given by commercial vector network analyzer manufacturers can only ensure the measurement accuracy when measuring high-loss materials (tangent of loss angle not less than 0.01), and is not applicable to the accurate measurement of low-loss wave-transparent materials.

[0007] In summary, there are still challenges in the measurement and characterization of the broadband dielectric properties of low-loss dielectric materials in the millimeter-wave band. Due to the large measurement uncertainties of the modulus value and phase angle of the transmission coefficient, the classical free-space method based on commercial vector network analyzers is difficult to solve the problem of accurate measurement of low-loss wave-transparent materials. Summary of the Invention

[0008] An embodiment of the present application provides a dual-channel superheterodyne free-space method for measuring the dielectric constant of a material and a device thereof, which is used for the measurement accuracy of the dielectric constant of low-loss wave-transparent materials.

[0009] To achieve the above object, the present application adopts the following technical solutions: Based on one aspect of the embodiments of the present invention, the present invention provides a dual-channel superheterodyne free-space method device for measuring the dielectric constant of a material, and the device includes: A first superheterodyne circuit, located in a first waveguide channel, for generating a medium / low-frequency measurement signal, which includes a first-band transmitting antenna and a first-band receiving antenna; A second superheterodyne circuit, located in a second waveguide channel, for generating a medium / low-frequency synchronous reference signal; The first superheterodyne circuit and the second superheterodyne circuit use the same signal source; A second frequency synthesizer, for converting the synchronous reference signal into a medium / low-frequency synchronous signal with the same frequency as the measurement signal; An induction voltage divider, for measuring and distributing the voltage of the measurement signal, and one output port thereof is connected to a lock-in amplifier to feed the measurement signal into the lock-in amplifier; A lock-in amplifier, for measuring the phase difference between the fed measurement signal and the synchronous signal, and measuring the voltage of the fed measurement signal; A compensation module, configured to obtain a first voltage division ratio (D1) from an inductive voltage divider and a first voltage (V1) of a measurement signal from a lock-in amplifier before a material under test is placed at a measurement position between a first-band transmitting antenna and a first-band receiving antenna; and after the material under test is placed at the measurement position, obtain a second voltage (V2) of the measurement signal from the lock-in amplifier, adjust the voltage division ratio of the inductive voltage divider according to the difference between the first voltage and the second voltage, so that the voltage of the measurement signal measured by the lock-in amplifier returns to the first voltage to compensate for the reduced voltage; after compensation, the voltage division ratio of the inductive voltage divider is a second voltage division ratio (D2); A calculation module, configured to calculate the modulus value of the channel transfer coefficient according to the first voltage division ratio and the second voltage division ratio, and calculate the phase shift of the channel transfer coefficient according to the phase difference between the measurement signal and the synchronization signal before and after the material under test is placed; perform phase correction on the channel transfer coefficient according to the modulus value of the channel transfer coefficient and the phase shift of the channel transfer coefficient to obtain the end-face transfer coefficient of the material under test; and inversely calculate the real part of the dielectric constant and the tangent value of the loss angle of the material under test by using the free space method.

[0010] Further, the first superheterodyne circuit and the second superheterodyne circuit use frequency multipliers with different multiples to perform mixing on two waveguide channels at different frequencies respectively; The first superheterodyne circuit and the second superheterodyne circuit share the same local oscillator source, and the local oscillator source generates a local oscillator signal based on a reference signal provided by the signal source.

[0011] Further, the first superheterodyne circuit includes a first frequency multiplier and a third frequency multiplier with the same frequency multiplication multiple N; the second superheterodyne circuit includes a second frequency multiplier and a fourth frequency multiplier with the same frequency multiplication multiple M; where N is not equal to M, and both N and M are positive integers greater than 0; The first-band transmitting antenna and the first-band receiving antenna in the first superheterodyne circuit are connected between the first frequency multiplier and the first mixer; one path of the local oscillator signal output by the local oscillator source is frequency-multiplied by the third frequency multiplier and then mixed with the signal output by the first-band receiving antenna to generate the measurement signal; The other path of the local oscillator signal output by the local oscillator source is frequency-multiplied by the fourth frequency multiplier and then mixed with the signal output by the second frequency multiplier to generate the synchronization reference signal.

[0012] Further, when one of the first waveguide channel and the second waveguide channel is used as a measurement channel, the other channel is used as a synchronization channel; The device further includes: The switch selection circuit consists of a first switch (K1), a second switch (K2), a third switch (K3), and a fourth switch (K4); the first switch and the second switch are used to select the measurement channel and send the medium / low-frequency measurement signal of the measurement channel to the induction voltage divider; the third switch and the fourth switch are used to select the synchronization channel and send the medium / low-frequency synchronization signal of the synchronization channel to the phase-locked amplifier; The first frequency synthesizer is used to convert the synchronization reference signal output by the first mixer into a medium / low-frequency synchronization signal with the same frequency as the measurement signal when the first waveguide channel is used as the synchronization channel; the first frequency synthesizer and the second frequency synthesizer are only connected to the circuit and function when the channel where they are located is the synchronization channel; When the first waveguide channel is the measurement channel, the first-band transmitting antenna and the first-band receiving antenna are actually connected between the first frequency multiplier and the first mixer in the first superheterodyne circuit, and at the same time, the second frequency multiplier is directly connected to the second mixer; When the second waveguide channel is the measurement channel, the second-band transmitting antenna and the second-band receiving antenna are actually connected between the second frequency multiplier and the second mixer in the second superheterodyne circuit, and at the same time, the first frequency multiplier is directly connected to the first mixer.

[0013] Further, the first-band transmitting antenna and the first-band receiving antenna, and the second-band transmitting antenna and the second-band receiving antenna are standard gain horn antennas or point-focusing lens horn antennas, and the gain of the antennas is greater than 20 dB.

[0014] Further, the first waveguide channel is a W-band (75 GHz - 110 GHz) waveguide channel, and the second waveguide channel is a V-band (50 GHz - 75 GHz) waveguide channel.

[0015] Further, the signal output by the signal source can be respectively input into the first frequency multiplier and the second frequency multiplier through the first directional coupler; the signal output by the local oscillator source is respectively input into the third frequency multiplier and the fourth frequency multiplier through the second directional coupler.

[0016] Based on another aspect of the embodiments of the present invention, the present invention also provides a dual-channel superheterodyne free-space method for measuring the dielectric constant of materials. This method is applied to the aforementioned device, and this method includes the steps: Before the material to be measured is placed at the measurement position between the transmitting antenna and the receiving antenna of the corresponding band in the measurement channel, obtain the first voltage of the measurement signal measured by the phase-locked amplifier, the first phase difference between the measurement signal and the synchronization signal, and obtain the first voltage division ratio measured by the induction voltage divider; After the material to be measured is placed, obtain the second voltage of the measurement signal from the phase-locked amplifier, and adjust the voltage division ratio of the induction voltage divider according to the difference between the first voltage and the second voltage, so that the voltage of the measurement signal measured by the phase-locked amplifier returns to the first voltage to compensate for the reduced voltage; After compensation, obtain the second phase difference between the measurement signal measured by the lock-in amplifier and the synchronization signal, and the second voltage division ratio measured by the inductive voltage divider. Calculate the magnitude of the channel transmission coefficient according to the first voltage division ratio and the second voltage division ratio, and calculate the phase shift of the channel transmission coefficient according to the first phase difference and the second phase difference before and after the material under test is placed. After phase correction of the channel transmission coefficient according to the magnitude of the channel transmission coefficient and the phase shift of the channel transmission coefficient, obtain the end-face transmission coefficient of the material under test; Set the signal source to other frequency points, and measure the end-face transmission coefficient of the material under test at other frequency points again, so as to establish the frequency response function of the phase of the end-face transmission coefficient of the material under test, and calculate the initial iteration value of the real part of the dielectric constant of the material under test according to the slope of the frequency response function; Adopt the free space method, use the non-linear iterative algorithm, and based on the initial iteration value of the real part of the dielectric constant of the material under test, inversely calculate the real part of the dielectric constant and the tangent value of the loss angle of the material under test.

[0017] It should be understood that the above general description and the following detailed description are only exemplary and explanatory, and cannot limit this specification. Brief Description of the Drawings

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments of the present invention or the prior art. Obviously, the drawings in the following description are only some embodiments recorded in the present invention. For those of ordinary skill in the art, other drawings can also be obtained according to these drawings of the embodiments of the present invention.

[0019] Figure 1 It is a schematic structural diagram of a dual-channel superheterodyne free space method material dielectric constant measurement device provided by an embodiment of the present application; Figure 2 It is a schematic structural diagram of a dual-channel superheterodyne free space method material dielectric constant measurement device in which both channels can be used as measurement channels provided by an embodiment of the present invention; Figure 3 It is a schematic structural diagram of a dielectric constant measurement device in the case of using the second waveguide channel in the V band as the measurement channel in an embodiment of the present invention; Figure 4 It is a schematic step flow diagram of a dual-channel superheterodyne free space method material dielectric constant measurement method provided by an embodiment of the present invention. Detailed Embodiments

[0020] Exemplary embodiments will be described in detail below. When the following description refers to the accompanying drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this specification. They are merely exemplary embodiments of devices and methods consistent with some aspects of this specification.

[0021] The terms used in this specification are for the purpose of describing specific embodiments only and are not intended to limit this specification. The singular forms "a", "the", and "said" used in this specification are also intended to include the plural forms unless the context clearly indicates otherwise.

[0022] It should be understood that in this specification, terms such as "first", "second", "third", etc. may be used to describe various information or structural modules. The purpose is to more clearly describe the solution and should not be construed as indicating or implying relative importance or implicitly indicating the quantity, order, or position of the indicated technical features, etc. Thus, features defined with "first", "second", "third", etc. may explicitly or implicitly include one or more of such features. In the description of this specification, unless otherwise specified, the meaning of "a plurality" is two or more; "if" may be interpreted as "when", "while", or "in response to a determination".

[0023] In this specification, orientation terms such as "upper", "lower", "left", "right", "north", "south", "west", "east", etc. may include but are not limited to being defined relative to the schematic placement of components in the accompanying drawings. It should be understood that these directional terms may be relative concepts. They are used for relative description and clarification and may change accordingly as the orientation of the components in the accompanying drawings changes.

[0024] In this specification, unless otherwise clearly specified and limited, the term "connection" should be understood in a broad sense. For example, "connection" may be a fixed connection, a detachable connection, or an integral one; it may be directly connected or indirectly connected through an intermediate medium. In addition, the term "coupled" may be a direct electrical connection or an indirect electrical connection through an intermediate medium. The term "contact" may be direct contact or indirect contact through an intermediate medium.

[0025] In this specification, "and / or" describes the association relationship of associated objects and indicates that three relationships may exist. For example, A and / or B may represent: A exists alone, A and B exist simultaneously, or B exists alone, where A and B may be singular or plural. The character " / " generally represents an "or" relationship between the associated objects before and after.

[0026] In the traditional method of using a vector network analyzer (VNA) to measure the reflection and transmission characteristics of materials to electromagnetic waves using the free space method, the VNA is used as the core instrument, and the VNA is connected to a transmitting antenna and a receiving antenna (such as a horn antenna). The material to be tested is placed flat between the transmitting antennas to ensure that the electromagnetic wave is incident vertically. The VNA transmits a swept-frequency microwave signal, which penetrates the material and is captured by the receiving end. After obtaining the S parameters of the material to be tested (including the S11 reflection coefficient and the S21 transmission coefficient) by measurement, the Nicolson-Ross-Weir (NRW) algorithm is used to invert the dielectric constant of the material to be tested.

[0027] However, the above-mentioned traditional method of using VNA self-space method to measure the reflection and transmission characteristics of electromagnetic waves of materials has at least the following technical problems when applied to the measurement of the dielectric constant of low-loss wave-transmitting materials: (1) When the microwave signal of the VNA penetrates a low-loss wave-transmitting material, the electromagnetic wave attenuation is minimal and the amplitude of the transmission coefficient is close to 1 (the ideal lossless material has |S21|=1). In actual measurement, the slight change of |S21| needs to be accurately captured to calculate the loss tangent. However, the amplitude measurement accuracy of commercial VNA is usually ±0.1dB. For low-loss wave-transmitting materials, this error will be magnified, resulting in drastic fluctuations in the calculated value of tanδ.

[0028] (2) The measurement accuracy of the dielectric constant of low-loss wave-transmitting materials depends on the measurement accuracy of the transmission coefficient S21 phase. The phase jitter of the VNA local oscillator source will be directly transmitted to the phase measurement result, resulting in more significant phase noise in the millimeter wave frequency band (such as above 30 GHz).

[0029] (3) The NRW formula directly combines the complex equations of the reflection coefficient S11 and the transmission coefficient S21 to solve the dielectric constant. ε r , when there is a small error in the S parameter measurement, the inversion result will exponentially amplify the error (especially when the transmission coefficient S21 is close to 1).

[0030] (4) The wavelength of millimeter waves is extremely short. The dynamic range and phase noise indicators of commercial VNAs in the millimeter wave band are degraded (e.g., phase noise>-90 dB / Hz), making it difficult to distinguish weak signal changes in low-loss materials. VNA technical specifications are usually calibrated based on medium- and high-loss materials (tanδ≥0.01), and there is no error compensation mechanism for low-loss materials.

[0031] Based on spending a great deal of time researching and analyzing the technical problems and the causes of the technical problems existing in the above-mentioned traditional scheme for measuring the dielectric constant of materials using a commercial vector network analyzer and the free space method, the inventor proposes a dual-channel superheterodyne free space method for measuring the dielectric constant of materials. This scheme is different from the above-mentioned traditional scheme for measuring the dielectric constant of materials using a commercial vector network analyzer. This scheme uses a dual-channel superheterodyne circuit structure, and two related but different-frequency waveguide channels are used to generate medium / low-frequency measurement signals and synchronization signals respectively; a low-loss wave-transmitting material under test is placed between the transmitting antenna and the receiving antenna in the corresponding channel band; the measurement signal is input to an inductive voltage divider and then fed into a lock-in amplifier, and the synchronization signal is input to the synchronization terminal of the lock-in amplifier; according to the voltage division ratio of the inductive voltage divider before the material under test is placed in the measurement position and the voltage division ratio after voltage compensation after it is placed, the modulus value of the channel transmission coefficient is calculated, and according to the phase difference between the measurement signal and the synchronization signal measured by the lock-in amplifier before and after placement, the phase shift of the channel transmission coefficient is calculated, and more accurate measurements of both the modulus value and the phase shift of the channel transmission coefficient are achieved simultaneously. Then, after phase correction of the channel transmission coefficient, the transmission coefficient of the end face of the material under test is obtained, and then the real part of the dielectric constant and the tangent value of the loss angle of the material under test are inversely calculated according to the free space method. The measurable range of the attenuation dynamic of this scheme can reach about 90 dB, and the technical indicators of the measurement uncertainty of attenuation and phase shift are much better than the measurement scheme using a traditional commercial network analyzer, which can greatly improve the measurement accuracy of the dielectric constant of low-loss wave-transmitting materials.

[0032] Figure 1 FIG. is a schematic structural diagram of a dual-channel superheterodyne free space method device for measuring the dielectric constant of materials provided in an embodiment of the present application. In the measuring device in this embodiment, there are a first waveguide channel and a second waveguide channel. The channel used for measurement can also be called a measurement channel, and the channel used for synchronization can also be called a synchronization channel. The measuring device includes: A first superheterodyne circuit, located in the first waveguide channel, for generating medium / low-frequency measurement signals ( f test ), which includes a first-band transmitting antenna and a first-band receiving antenna.

[0033] A second superheterodyne circuit, located in the second waveguide channel, for generating medium / low-frequency synchronization reference signals.

[0034] The first superheterodyne circuit and the second superheterodyne circuit use the same signal source, so that the measurement signal and the synchronization signal are cross-correlated.

[0035] A second frequency synthesizer, for converting the synchronization reference signal into a medium / low-frequency synchronization signal ( f sync ) having the same frequency as the measurement signal.

[0036] An inductive voltage divider for measuring and distributing the voltage of a measurement signal, one of its output ports is connected to a lock-in amplifier to feed the measurement signal into the lock-in amplifier; the voltage division ratio between the measurement signal voltage input at the input port and the measurement signal voltage distributed to the lock-in amplifier can be obtained through the inductive voltage divider.

[0037] A lock-in amplifier for measuring the phase difference between the fed measurement signal ( f test ) and the synchronization signal ( f sync ), and measuring the voltage of the fed measurement signal; the phase difference before the test material is placed is the first phase difference ( ), and the phase difference after the test material is placed is the second phase difference ( ).

[0038] A compensation module for obtaining the first voltage division ratio (D1) from the inductive voltage divider and the first voltage (V1) of the fed measurement signal from the lock-in amplifier before the test material is placed at the measurement position between the first-band transmitting antenna and the first-band receiving antenna; and after the test material is placed at the measurement position, obtaining the second voltage (V2) of the fed measurement signal from the lock-in amplifier, adjusting the voltage division ratio of the inductive voltage divider according to the difference between the first voltage and the second voltage to make the measurement signal voltage measured by the lock-in amplifier return to the first voltage to compensate for the reduced voltage; after compensation, the voltage division ratio measured by the inductive voltage divider is the second voltage division ratio (D2). Preferably, the compensation module can mainly consist of a control circuit, a data acquisition circuit, and an embedded computing unit, and can realize automatic voltage acquisition, balance indication of the measured voltage, and automatic compensation.

[0039] A calculation module for obtaining the first voltage division ratio and the second voltage division ratio from the inductive voltage divider (IVD) and calculating the modulus of the channel transmission coefficient ( ), obtaining the first phase difference and the second phase difference from the lock-in amplifier and calculating the phase shift of the channel transmission coefficient ( ), and performing phase correction on the channel transmission coefficient ( ) according to the modulus of the channel transmission coefficient and the phase shift of the channel transmission coefficient to obtain the end-face transmission coefficient of the test material ( ); preferably, the calculation module can automatically read the voltage division ratio signal from the inductive voltage divider and the phase difference signal from the lock-in amplifier through computer programming, and obtain the end-face transmission coefficient of the test material through data processing and calculation. The calculation module can be implemented by an embedded computing unit or a general-purpose computer, and can form an algorithm library for the dielectric constant calculation process, which is called and executed by the calculation module.

[0040] The calculation module is also used to inversely calculate the real part of the dielectric constant and the tangent value of the loss angle of the test material by the free space method. During the inverse calculation, according to the end-face transmission coefficient of the test material and the single reflection coefficient ( ), and the relationship between the single - pass transmission coefficient ( T ) is calculated through a non - linear iterative algorithm to obtain the real part and the imaginary part of the dielectric constant of the measured material, and then the tangent value of the loss angle is calculated.

[0041] Preferably, the first super - heterodyne circuit and the second super - heterodyne circuit use frequency multipliers with different multiples to mix the two waveguide channels at different frequencies respectively, so as to reduce the mutual interference between the two super - heterodyne circuits.

[0042] Preferably, the first super - heterodyne circuit and the second super - heterodyne circuit share the same local oscillator source, and the local oscillator source generates a local oscillator signal based on the reference signal provided by the same signal source. In other embodiments of the present invention, each super - heterodyne circuit can also use its own local oscillator source and generate its own local oscillator signal using the reference signal provided by the same signal source, but this increases the cost.

[0043] Preferably, the first super - heterodyne circuit includes a first frequency multiplier and a third frequency multiplier with the same frequency multiplication factor N, and the second super - heterodyne circuit includes a second frequency multiplier and a fourth frequency multiplier with the same frequency multiplication factor M; where N is not equal to M, and both N and M are positive integers greater than 0.

[0044] The first - band transmitting antenna and the first - band receiving antenna in the first super - heterodyne circuit are connected between the first frequency multiplier and the first mixer; The first frequency multiplier in the first super - heterodyne circuit and the second frequency multiplier in the second super - heterodyne circuit generate a first radio - frequency signal ( f 1 ) and a second radio - frequency signal ( Nf 1 ) with different frequencies respectively based on the radio - frequency signal ( Mf 1 ) output by the same signal source; The local oscillator source outputs a local oscillator signal based on the reference signal provided by the signal source, and the local oscillator signal is output as a third radio - frequency signal ( Nf 1 + f m1 , where f m1 is an intermediate - frequency / low - frequency signal) and a fourth radio - frequency signal ( Mf 1 + f m2 , where f m2 is an intermediate - frequency / low - frequency signal) through the third frequency multiplier and the fourth frequency multiplier respectively; In the first superheterodyne circuit, a first-band transmitting antenna and a first-band receiving antenna are provided. The first-band transmitting antenna and the first-band receiving antenna in the first superheterodyne circuit are connected between a first frequency multiplier and a first mixer. A space for placing the material to be measured is reserved between the first-band transmitting antenna and the first-band receiving antenna as the measurement position. The first radio frequency signal ( Nf 1 ), output by the first frequency multiplier, after passing through the first-band transmitting antenna and the first-band receiving antenna, is mixed with the third radio frequency signal ( Nf 1 + f m1 ), output by the third frequency multiplier, in the first mixer and then outputs an intermediate / low-frequency measurement signal ( f test ); In the second superheterodyne circuit, the second radio frequency signal ( Mf 1 ), is mixed with the fourth radio frequency signal ( Mf 1 + f m2 ), in the second mixer and then outputs a synchronous reference signal ( f m2 ). The synchronous reference signal outputs an intermediate / low-frequency synchronous signal ( f sync ) after passing through the second frequency synthesizer. The function of the second frequency synthesizer is to convert the synchronous reference signal ( f m2 ) into an intermediate / low-frequency synchronous signal ( f test ) that has the same frequency as and is correlated with the intermediate / low-frequency measurement signal ( f sync ); The intermediate / low-frequency measurement signal ( f test ) is input into an induction voltage divider (IVD) and then fed into the input terminal of a lock-in amplifier. The intermediate / low-frequency synchronous signal ( f sync ) is input into the synchronous port of the lock-in amplifier; Based on the above device, according to the voltage division ratio obtained from the induction voltage divider and the phase change measured from the lock-in amplifier before and after the material to be measured is placed in the measurement position, the accurate measurement of the modulus value of the transmission coefficient and the phase shift of the material to be measured in the measurement channel can be realized simultaneously. Furthermore, based on the free space method, the dielectric constant of the material to be measured can be inversely calculated.

[0045] In an embodiment of the present invention, the first waveguide channel and the second waveguide channel respectively correspond to two different electromagnetic wave frequency bands. For example, the first waveguide channel is a waveguide channel in the W band (75 GHz to 110 GHz), and the second waveguide channel is a waveguide channel in the V band (50 GHz to 75 GHz). The present invention does not specifically limit the electromagnetic wave frequency band ranges of the two waveguide channels. Preferably, the two frequency band ranges do not overlap, and the two frequency bands can be millimeter wave frequency bands, microwave frequency bands, etc.

[0046] In an embodiment of the present invention, in order to implement various functions such as signal monitoring, power distribution, and isolation protection, the signal output by the signal source can be respectively input into the first frequency multiplier and the second frequency multiplier through the first directional coupler; the signal output by the local oscillator source is respectively input into the third frequency multiplier and the fourth frequency multiplier through the second directional coupler. The present invention does not specifically limit the manner in which the output signals of the signal source and the local oscillator source are connected to the frequency multipliers, and methods such as directional couplers, direct connections, waveguides, coaxial cables, etc. can be selected according to the requirements of the waveguide frequency band and the measurement scenario.

[0047] Figure 2 It is a structural schematic diagram of a heterodyne free space method material dielectric constant measurement device in which both channels of the present invention can be used as measurement channels. In order to meet the requirements for measuring the dielectric constant of the material to be measured at different frequency bands and improve the flexibility and practicability of the measurement device, a switch selection circuit is added in this embodiment, and a first frequency synthesizer, a second band transmitting antenna, and a second band receiving antenna are newly added. Through the cooperation of the switch selection circuit and the two frequency synthesizers, the flexible switching of the channel roles is realized, so that any one of the two channels can be used as the measurement channel while the other channel is used as the synchronization channel.

[0048] In this embodiment, the switch selection circuit includes a first switch (K1), a second switch (K2), a third switch (K3), and a fourth switch (K4). K1 and K2 can use bidirectional switches, and K3 and K4 can use unidirectional switches. K1 and K2 are used to select the measurement channel and directly send the medium / low frequency measurement signal in the measurement channel to the induction voltage divider. K3 and K4 are used to select the synchronization channel and send the medium / low frequency synchronization signal processed by the frequency synthesizer in the synchronization channel to the lock-in amplifier.

[0049] In this embodiment, when one waveguide channel is used as the measurement channel, the other waveguide channel is used as the synchronization channel; the first frequency synthesizer and the second frequency synthesizer are only connected to the circuit and play a role when the channel they are in is the synchronization channel, and are used to convert the synchronization reference signal into a medium / low frequency synchronization signal with the same frequency as the measurement signal; When the first waveguide channel is used as the measurement channel, the first-band transmitting antenna and the first-band receiving antenna are actually connected between the first frequency multiplier and the first mixer in the first superheterodyne circuit. At the same time, in the second waveguide channel, the second frequency multiplier and the second mixer need to be directly connected, and the second-band transmitting antenna and the second-band receiving antenna are bypassed. At the same time, it is also necessary to directly input the measurement signal output by the first mixer into the induction voltage divider by controlling four switches, input the signal output by the second mixer into the second frequency synthesizer, and input the synchronous signal output by the second frequency synthesizer into the lock-in amplifier. That is, K1 is placed on one side of the induction voltage divider and disconnected from the side of the first frequency synthesizer; K2 is placed on one side of the second frequency synthesizer and disconnected from the side of the IVD; K3 is disconnected from the first frequency synthesizer, and at the same time K4 is closed and connected to the second frequency synthesizer.

[0050] When the second waveguide channel is used as the measurement channel, the second-band transmitting antenna and the second-band receiving antenna are actually connected between the second frequency multiplier and the second mixer in the second superheterodyne circuit. At the same time, in the first waveguide channel, the first frequency multiplier and the first mixer need to be directly connected, and the first-band transmitting antenna and the first-band receiving antenna are bypassed. At the same time, it is also necessary to directly input the measurement signal output by the second mixer into the induction voltage divider by controlling four switches, input the signal output by the first mixer into the first frequency synthesizer, and input the synchronous signal output by the first frequency synthesizer into the lock-in amplifier. That is, K1 is placed on one side of the first frequency synthesizer and disconnected from the side of the induction voltage divider; K2 is placed on one side of the induction voltage divider and disconnected from the side of the second frequency synthesizer; K3 is closed and connected to the first frequency synthesizer, and at the same time K4 is disconnected from the second frequency synthesizer.

[0051] In the embodiment of the present invention, the transmitting antenna and the receiving antenna in the measurement channel can be a standard gain horn antenna or a point-focusing lens horn antenna. Preferably, the gain of the antenna should be greater than 20 dB.

[0052] Figure 3 FIG. is a schematic structural diagram of a dielectric constant measuring device in the case of using the second waveguide channel in the V band as the measurement channel in an embodiment of the present invention. In this embodiment, the second waveguide channel is a V-band waveguide channel, and the V-band waveguide channel is used as the measurement channel to measure the dielectric constant of the material to be measured through the V-band waveguide channel. The first waveguide channel is a W-band waveguide channel, and the W-band waveguide channel is a synchronous channel.

[0053] The signal source outputs a signal (frequency f 1 ), which is fed into the V-band waveguide channel (measurement channel) through the first directional coupler, and a frequency of 2 in the range of 50 GHz to 75 GHz is generated by the ×2 frequency multiplier (second frequency multiplier) f 1The signal; the other path is fed into the W-band waveguide channel (synchronization channel), and through a ×3 frequency multiplier (the first frequency multiplier), a signal with a frequency in the range of 75 GHz to 110 GHz is generated as 3 f 1 of the signal.

[0054] The local oscillator generates a stable local oscillator signal with a frequency of f 1 +5KHz based on the reference signal provided by the signal source. The local oscillator signal is divided into two paths by the second directional coupler. One path passes through a ×2 frequency multiplier (the fourth frequency multiplier) to generate 2 f 1 +10kHz millimeter-wave signal. This signal is heterodyned with the signal in the V-band waveguide channel in the second mixer to output a 10kHz intermediate-frequency measurement signal; the other path of the local oscillator signal passes through a ×3 frequency multiplier (the third frequency multiplier) to generate 3 f 1 +15kHz millimeter-wave signal. This signal is mixed with the W-band waveguide channel in the first mixer to output a 15kHz intermediate-frequency synchronization reference signal.

[0055] By controlling the switch K1 to be thrown to the first frequency synthesizer, K2 to be thrown to the side of the induction voltage divider, K3 to be closed, and K4 to be opened, the 15kHz intermediate-frequency synchronization reference signal passes through the first frequency synthesizer, that is, the frequency synthesizer of ×2÷3, and then a 10kHz intermediate-frequency synchronization signal with the same frequency as the intermediate-frequency measurement signal is obtained. The synchronization signal is input into the lock-in amplifier. The 10kHz intermediate-frequency measurement signal output by the second mixer is input into the induction voltage divider.

[0056] Similarly, when measuring the dielectric constant of the material in the W-band, the W-band waveguide channel is used as the measurement channel, and the V-band waveguide channel is used as the synchronization channel. It is necessary to bypass the V-band transmitting antenna and receiving antenna in the V-band waveguide channel, directly connect the ×2 frequency multiplier to the second mixer, and connect the W-band transmitting antenna and receiving antenna between the ×3 frequency multiplier and the first mixer in the W-band waveguide channel. By controlling the switch K1 to be thrown to the side of the induction voltage divider, K2 to be thrown to the side of the second frequency synthesizer, K3 to be opened, and K4 to be closed, the 15kHz intermediate-frequency measurement signal is input into the induction voltage divider; the 10kHz synchronization reference signal output by the second mixer passes through the second frequency synthesizer, that is, the frequency synthesizer of ×3÷2, and then a 15kHz intermediate-frequency synchronization signal with the same frequency as the intermediate-frequency measurement signal is obtained. The synchronization signal is input into the lock-in amplifier.

[0057] The dual-channel superheterodyne free-space method material dielectric constant measurement device provided by this embodiment simultaneously includes a V-band waveguide channel and a W-band waveguide channel, and can simultaneously achieve broadband measurement of the dielectric constant of the material to be measured in the frequency band of 50 GHz - 110 GHz for both the V-band and the W-band in one set of device, having better broadband measurement characteristics, better practicability and flexibility.

[0058] The dual-channel superheterodyne free-space method material permittivity measurement device provided by this embodiment includes two waveguide section channels, and each waveguide section channel is a complete single-channel superheterodyne circuit system. The two channels are reference to each other. Since the RF signal frequencies in the two channels are different, signal cross-leakage crosstalk between channels can be well eliminated, and it has better anti-crosstalk performance.

[0059] In the measurement device provided by the embodiment of the present invention, since the RF signals of the two-band waveguide channels come from the same signal source, their RF signal frequencies are correlated, and the intermediate / low-frequency signals obtained after mixing are also completely correlated. Therefore, the stability of the measurement data of the lock-in amplifier can be ensured, and more accurate measurement results can be obtained.

[0060] Although the V band and the W band are respectively used for the two channels in the above embodiment, those skilled in the art can understand that the measurement device and method provided by the embodiment of the present invention can also be extended to other waveguide frequency bands. If other electromagnetic wave frequency bands are used, only the waveguide devices and transceiver antennas used in the two-band channels need to be correspondingly replaced to meet the measurement requirements of the corresponding frequency bands.

[0061] Figure 4 It is a schematic flow chart of the steps of the dual-channel superheterodyne free-space method material permittivity measurement method provided by an embodiment of the present invention. This method is applied to the measurement device provided by the embodiment of the present invention. According to the voltage divider ratio and the phase difference between the measurement signal and the synchronization signal measured by the inductive voltage divider and the lock-in amplifier, the attenuation and phase shift of the channel transmission coefficient are calculated. After phase correction, the complex form of the end-face transmission coefficient of the material to be measured is obtained, and then the real part of the permittivity and the tangent value of the loss angle of the material to be measured are inversely calculated based on the free-space transmission and reflection theory. Since the technical indicators of the measurement uncertainty of the attenuation and phase shift measured by this method are far better than those of commercial network analyzers, this method can solve the problem of accurate measurement of low-loss materials (tangent value of loss angle less than 0.01), and can achieve high-precision measurement of the permittivity of low-loss wave-transparent materials in the millimeter-wave band.

[0062] Figure 4 The method steps of the example are based on the scenario where the measurement channel (such as the V-band channel) and the synchronization channel (such as the W-band channel) have been determined, and the switching circuit has completed the routing operation. Before starting the measurement step, first set the output frequency ( f 1 ) and power level of the signal source, and correspondingly adjust the output frequency and power level of the local oscillator source to enable the lock-in amplifier to synchronize normally and have a stable output reading.

[0063] This method includes the following steps: Step 401: Before placing the material under test in the measurement position between the corresponding band transmitting antenna and receiving antenna in the measurement channel, (by the compensation module) obtain the first voltage (V1) of the measurement signal measured by the lock-in amplifier, (by the calculation module) obtain the first phase difference between the measurement signal measured by the lock-in amplifier and the synchronization signal ( ) and obtain the first voltage division ratio (D1) measured by the inductive voltage divider.

[0064] Step 402: After placing the material under test in the measurement position, (by the compensation module) obtain the second voltage (V2) of the measurement signal from the lock-in amplifier, adjust the voltage division ratio of the inductive voltage divider according to the difference between the first voltage and the second voltage, so that the voltage of the measurement signal measured by the lock-in amplifier returns to the first voltage (V1) to compensate for the reduced voltage; The measurement device and method provided by the embodiments of the present invention are applicable to non-destructive measurement of the material under test of flat media. The measurement position of the material under test is located at the central position between the transmitting antenna and the receiving antenna. After placing the material under test, both the transmitting antenna and the receiving antenna need to be aligned with the material under test. Preferably, the size of the material under test should be 3 to 4 times the beam diameter of the antenna at the position where the material under test is located.

[0065] Step 403: After compensation, (by the calculation module) obtain the second phase difference between the measurement signal measured by the lock-in amplifier and the synchronization signal ( ) and the second voltage division ratio (D2) measured by the inductive voltage divider, calculate the modulus value of the channel transmission coefficient of the measurement channel according to the first voltage division ratio and the second voltage division ratio, and calculate the phase shift of the channel transmission coefficient according to the phase difference between the measurement signal and the synchronization signal before and after placing the material under test; After performing phase correction on the channel transmission coefficient according to the modulus value of the channel transmission coefficient and the phase shift of the channel transmission coefficient, obtain the end-face transmission coefficient of the material under test ( ) The method for calculating the modulus value of the channel transmission coefficient ( ) according to the first voltage division ratio (D1) and the second voltage division ratio (D2) measured by the inductive voltage divider is: (Equation 1) The method for calculating the phase shift of the channel transmission coefficient ( ) and the second phase difference ( ) according to the first phase difference between the measurement signal measured by the lock-in amplifier and the synchronization signal ( ) is: (Equation 2) After performing phase correction on the channel transmission coefficient according to the modulus value of the channel transmission coefficient ( ) and the phase shift of the channel transmission coefficient ( ), obtain the end-face transmission coefficient of the material under test ( ) is as follows: (Equation 3) where k0 is the free space propagation wave number, , f is the electromagnetic wave frequency, and are the vacuum permittivity and permeability respectively, d is the sample thickness. To improve the measurement accuracy, the thickness of the material under test d can be averaged after multiple measurements.

[0066] The reason for correcting the channel transmission coefficient ( ) with is to express the phase delay caused by the electromagnetic wave passing through air with the same thickness as the material under test.

[0067] Step 404: Set the signal source to other frequency points ( f i ), and measure the end-face transmission coefficient of the material under test at other frequency points ( f i ) again, so as to establish the frequency response function of the phase of the end-face transmission coefficient ( ) of the material under test, and calculate the initial iteration value of the real part of the dielectric constant of the material under test according to the slope of the frequency response function; Let the expression of the frequency response function of the phase of the end-face transmission coefficient ( ) of the material under test be: y = a f + b (Equation 4) where, f represents the measurement frequency (the frequency of the output signal of the first harmonic source or the second harmonic source), y represents the phase of the end-face transmission coefficient of the material under test. a is the slope, b is the offset, both a and b are constants, and the values of a and b can be determined according to the frequency response function characterized by the straight line determined by the two points (f1, y1) and (f i , y i ) measured successively.

[0068] The initial iteration value of the real part of the dielectric constant of the material under test is obtained by the following Equation 5: (Equation 5) where, a is the slope obtained from the phase frequency response function of the end-face transmission coefficient of the material under test, is the vacuum permittivity, is the vacuum permeability, d is the thickness of the material under test.

[0069] Step 405: adopting the free space method and using a nonlinear iterative algorithm, based on the iterative initial value of the real part of the dielectric constant of the material being measured, inversely calculate the real part of the dielectric constant and the loss tangent value of the material being measured.

[0070] The single reflection coefficient of air and the end surface of the material being tested is , the single transmission coefficient between the two end surfaces of the material being tested is T According to the multiple transmission and reflection analysis of the electromagnetic wave by the measured material, the measured end surface transmission coefficient of the measured material in formula (3) can be obtained ( )and and T With the following relationship: (Formula 6) Among them, the reflection coefficient ( ) is calculated as: , (Formula 7) in, is the dielectric constant of the material being measured in plural form, and are the real and imaginary parts of the dielectric constant of the material under test, respectively. (Equation 6) describes the measured transmission coefficient of the end face of the material under test ( ) (including the comprehensive results of multiple reflection transmission) and the single transmission coefficient of the material being tested ( T ) and reflection coefficient ( ) are quantitatively related.

[0071] Single transmission coefficient of the material being tested ( T ) has the following relationship with the real and imaginary parts of the dielectric constant of the material being measured: (Formula 8) (Formula 9) in, is the speed of light in vacuum, d is the thickness of the material being measured, f is the frequency of electromagnetic waves.

[0072] By combining (Equation 6), (Equation 8) and (Equation 9), a nonlinear equation iteration algorithm is used to calculate the real part and imaginary part of the dielectric constant of the material under test based on the initial value of the real part of the dielectric constant of the material under test obtained in step 404, and then the loss tangent value is obtained. .

[0073] The above description of the exemplary embodiments of this specification should be understood that in some cases, the modules described in this specification may be divided in a different manner from that in the embodiments, and the recorded actions or steps may also be executed in a different order from that in the embodiments, and the desired results can still be achieved. In addition, the processes depicted in the drawings do not necessarily require the specific order or continuous order shown to achieve the desired results. In certain embodiments, multitasking and parallel processing are also possible or may be advantageous.

[0074] Those skilled in the art will readily conceive of other embodiments of this specification after considering the specification and practicing the invention herein. This specification is intended to cover any variations, uses, or adaptations of this specification, which follow the general principles of this specification and include the common general knowledge or conventional technical means in the technical field not exemplified in this specification.

[0075] The above is only the preferred embodiment of this specification and is not intended to limit this specification. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of this specification shall be included within the scope of protection of this specification.

Claims

1. A dual-channel superheterodyne free-space method material dielectric constant measurement device, characterized in that The device includes: A first superheterodyne circuit, located in the first waveguide channel, for generating a medium / low-frequency measurement signal, which includes a first-band transmitting antenna and a first-band receiving antenna; A second superheterodyne circuit, located in the second waveguide channel, for generating a medium / low-frequency synchronous reference signal; The first superheterodyne circuit and the second superheterodyne circuit use the same signal source; A second frequency synthesizer, for converting the synchronous reference signal into a medium / low-frequency synchronous signal with the same frequency as the measurement signal; An inductive voltage divider, for measuring and distributing the voltage of the measurement signal, and one of its output ports is connected to a lock-in amplifier to feed the measurement signal into the lock-in amplifier; A lock-in amplifier, for measuring the phase difference between the fed measurement signal and the synchronous signal, and measuring the voltage of the fed measurement signal; A compensation module, for obtaining a first voltage division ratio from the inductive voltage divider and a first voltage of the measurement signal from the lock-in amplifier before the material under test is placed at the measurement position between the first-band transmitting antenna and the first-band receiving antenna; and after the material under test is placed at the measurement position, obtaining a second voltage of the measurement signal from the lock-in amplifier, adjusting the voltage division ratio of the inductive voltage divider according to the difference between the first voltage and the second voltage, so that the voltage of the measurement signal measured by the lock-in amplifier returns to the first voltage to compensate for the reduced voltage; after compensation, the voltage division ratio of the inductive voltage divider is the second voltage division ratio; A calculation module, for calculating the modulus value of the channel transmission coefficient according to the first voltage division ratio and the second voltage division ratio, and calculating the phase shift of the channel transmission coefficient according to the phase difference between the measurement signal and the synchronous signal before and after the material under test is placed; performing phase correction on the channel transmission coefficient according to the modulus value of the channel transmission coefficient and the phase shift of the channel transmission coefficient to obtain the end-face transmission coefficient of the material under test; and inversely calculating the real part of the dielectric constant and the tangent value of the loss angle of the material under test by using the free space method.

2. The device according to claim 1, wherein The first superheterodyne circuit and the second superheterodyne circuit use frequency multipliers with different multiples to perform mixing on the two waveguide channels at different frequencies respectively; The first superheterodyne circuit and the second superheterodyne circuit share the same local oscillator source, and the local oscillator source generates a local oscillator signal based on the reference signal provided by the signal source.

3. The device according to claim 2, wherein The first superheterodyne circuit includes a first frequency multiplier and a third frequency multiplier with the same frequency multiplication factor N; the second superheterodyne circuit includes a second frequency multiplier and a fourth frequency multiplier with the same frequency multiplication factor M; where N is not equal to M, and both N and M are positive integers greater than 0; The first-band transmitting antenna and the first-band receiving antenna in the first superheterodyne circuit are connected between the first frequency multiplier and the first mixer; one path of the local oscillator signal output by the local oscillator source is multiplied by the third frequency multiplier and then mixed with the signal output by the first-band receiving antenna to generate the measurement signal; The other path of the local oscillator signal output by the local oscillator source is multiplied by the fourth frequency multiplier and then mixed with the signal output by the second frequency multiplier to generate the synchronous reference signal.

4. The device according to claim 3, wherein When one of the first waveguide channel and the second waveguide channel is used as the measurement channel, the other channel is used as the synchronous channel; The device further includes: The switch selection circuit consists of a first switch, a second switch, a third switch, and a fourth switch; the first switch and the second switch are used to select the measurement channel and send the medium / low-frequency measurement signal of the measurement channel to the induction voltage divider; the third switch and the fourth switch are used to select the synchronization channel and send the medium / low-frequency synchronization signal of the synchronization channel to the phase-locked amplifier; The first frequency synthesizer is used to convert the synchronization reference signal output by the first mixer into a medium / low-frequency synchronization signal with the same frequency as the measurement signal when the first waveguide channel is used as the synchronization channel; the first frequency synthesizer and the second frequency synthesizer are only connected to the circuit and function when the channel they are in is the synchronization channel; When the first waveguide channel is the measurement channel, the first-band transmitting antenna and the first-band receiving antenna are actually connected between the first frequency multiplier and the first mixer in the first superheterodyne circuit, and at the same time, the second frequency multiplier is directly connected to the second mixer; When the second waveguide channel is the measurement channel, the second-band transmitting antenna and the second-band receiving antenna are actually connected between the second frequency multiplier and the second mixer in the second superheterodyne circuit, and at the same time, the first frequency multiplier is directly connected to the first mixer.

5. The device according to claim 4, wherein The first-band transmitting antenna and the first-band receiving antenna, and the second-band transmitting antenna and the second-band receiving antenna are standard gain horn antennas or point-focusing lens horn antennas, and the gain of the antenna is greater than 20 dB.

6. The device according to claim 4, wherein The first waveguide channel is a W-band (75 GHz to 110 GHz) waveguide channel, and the second waveguide channel is a V-band (50 GHz to 75 GHz) waveguide channel.

7. The device according to claim 4, wherein The signal output by the signal source can be respectively input into the first frequency multiplier and the second frequency multiplier through the first directional coupler; the signal output by the local oscillator source is respectively input into the third frequency multiplier and the fourth frequency multiplier through the second directional coupler.

8. A dual-channel superheterodyne free-space method for measuring the dielectric constant of materials, characterized in that, This method is applied to the device according to any one of claims 1 to 7, and the method includes the steps of: Before the material to be measured is placed at the measurement position between the corresponding-band transmitting antenna and the receiving antenna in the measurement channel, obtain the first voltage of the measurement signal measured by the phase-locked amplifier, the first phase difference between the measurement signal and the synchronization signal, and obtain the first voltage division ratio measured by the induction voltage divider; After the material to be measured is placed, obtain the second voltage of the measurement signal from the phase-locked amplifier, and adjust the voltage division ratio of the induction voltage divider according to the difference between the first voltage and the second voltage, so that the voltage of the measurement signal measured by the phase-locked amplifier returns to the first voltage to compensate for the reduced voltage; After compensation, obtain the second phase difference between the measurement signal and the synchronization signal measured by the phase-locked amplifier and the second voltage division ratio measured by the induction voltage divider, calculate the modulus value of the channel transmission coefficient according to the first voltage division ratio and the second voltage division ratio, and calculate the phase shift of the channel transmission coefficient according to the first phase difference and the second phase difference before and after the material to be measured is placed; After performing phase correction on the channel transmission coefficient according to the modulus value of the channel transmission coefficient and the phase shift of the channel transmission coefficient, obtain the end-face transmission coefficient of the material to be measured; Set the signal source to other frequency points, and measure the end-face transmission coefficient of the material under test at other frequency points again, so as to establish the frequency response function of the phase of the end-face transmission coefficient of the material under test, and calculate the initial iteration value of the real part of the dielectric constant of the material under test according to the slope of the frequency response function; Adopt the free space method, use the nonlinear iterative algorithm, and based on the initial iteration value of the real part of the dielectric constant of the material under test, inversely calculate the real part of the dielectric constant and the tangent value of the loss angle of the material under test.

9. The method according to claim 8, wherein The method for calculating the modulus of the channel transmission coefficient ( ) according to the first pressure ratio (D1) and the second pressure ratio (D2) is as follows: The method for calculating the phase shift of the channel transmission coefficient based on the first phase difference ( ) and the second phase difference ( ) before and after placing the material under test is as follows: ​ The method of obtaining the transmission coefficient of the end face of the material under test after phase correction of the channel transmission coefficient according to the modulus value of the channel transmission coefficient ( ), and the phase shift of the channel transmission coefficient ( ) is as follows: ) where \(k_0\) is the free-space propagation wave number, d and \(d\) is the sample thickness.

10. The method according to claim 9, wherein The method of adopting the free space method, using the nonlinear iterative algorithm, and based on the initial iteration value of the real part of the dielectric constant of the material under test, inversely calculating the real part of the dielectric constant and the tangent value of the loss angle of the material under test is as follows: The end-face transmission coefficient of the material under test ( ), the single reflection coefficient between air and the end face of the material under test ( ), and the single transmission coefficient between the two end faces of the material under test ( T ) are related as follows: Single - transmission coefficient of the material under test ( T ), and the relationship with the real part ( ) and the imaginary part ( ) of the dielectric constant of the material under test is as follows: wherein, is the speed of light in vacuum, d is the thickness of the material to be measured, f is the electromagnetic wave frequency; Based on the above relationship, adopt the nonlinear equation iterative algorithm. After inversely calculating the real part and the imaginary part of the dielectric constant of the material under test based on the initial iteration value of the real part of the dielectric constant of the material under test, further calculate to obtain the tangent value of the loss angle.

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