CN113589078B - High-frequency performance prediction method for medium degradation connector in humid environment - Google Patents
High-frequency performance prediction method for medium degradation connector in humid environment Download PDFInfo
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Abstract
The invention discloses a high-frequency performance prediction method of a dielectric degradation connector in a humid environment. The invention includes: measuring the high-frequency transmission performance of the undegraded coaxial connector, and establishing an equivalent circuit model of the undegraded coaxial connector; establishing an equivalent circuit model of the degraded coaxial connector, and predicting high-frequency parameters of the connector with different degradation degrees; carrying out an acceleration test in a high humidity environment to obtain connector samples with different degradation degrees, and measuring the degraded connector samples to obtain high-frequency parameters; and comparing the measured value of the degradation sample with the equivalent circuit simulation result to obtain the degradation grade and the actual water film thickness corresponding to the degradation connector. The method combines theoretical analysis and experimental test, fully researches the high-frequency performance prediction method of the medium degradation connector in a humid environment, and provides theoretical support for guiding engineering application. The method is suitable for analyzing all coaxial connectors with similar structures.
Description
Technical Field
The invention relates to a high-frequency performance prediction method of a medium degradation connector in a humid environment, which applies comprehensive analysis methods such as theoretical modeling, experimental testing and the like and belongs to the field of communication circuits.
Background
The relevant information of the American aviation company clearly shows the relationship between product failure and environmental stress, and in the influence of environmental stress such as temperature, humidity, salt spray, pressure and the like, the product failure caused by humidity accounts for about 42 percent of all the environmental stress-induced failures.
The radio frequency coaxial connector is a transmission system which takes an inner conductor and an outer conductor with the same axis as a central line and takes an insulating medium as a support between the inner conductor and the outer conductor, and the radio frequency coaxial connector plays a role in transmitting various radio frequency electromagnetic field signals. Coaxial connectors are widely used in various complex environments as important components for signal transmission in communication systems. When the connector is operated in a high humidity environment for a long time, moisture in the environment is likely to intrude into the interior of the connector, causing contact portions and insulation of the connectorThe rim portion and the mechanical connection fail. After water molecules enter the connector through the micropores of the contact piece, electrochemical corrosion occurs under the action of potential difference, so that the thickness of an oxide film at the contact part of the inner conductor of the electric connector is increased continuously, the contact resistance of the electric connector is increased continuously, and finally contact failure is caused. In addition, moisture can enter the interior of the connector causing moisture absorption, and diffusion problems in the dielectric. Moisture enters the insulator to form a conductive path, which causes a decrease in the insulation resistance of the insulator of the electrical connector and a decrease in the electrical performance of the connector. Taking PBT insulator as an example, the insulation resistance is 5 multiplied by 10 when the air temperature is 25 ℃ and the humidity is 40 percent 6 M.OMEGA., and when the relative humidity increased to 80%, the insulation resistance decreased to 2X 10 6 M omega. In addition, many insulating materials swell after absorbing moisture, causing low mass strength and other major mechanical properties to degrade, ultimately leading to failure of the connector mechanical connection. Therefore, the connector is highly regarded when working in high temperature and high humidity areas.
Current research on connector degradation focuses more on the effect of degradation of the contact portions of the conductors within the connector on signal transmission. Related research contents comprise establishment of a connector electrical contact impedance network model under a severe environment, a degradation rule of electrical contact impedance characteristics and research on wear degradation of contact parts in the connector. Modeling simulation of connector medium degradation in a severe environment and related research on influence of the medium degradation on high-frequency signal transmission are less. In order to solve the problems, the invention provides a high-frequency performance prediction method of a connector with medium degradation in a humid environment to more comprehensively understand the influence of the medium degradation of the connector on signal transmission.
Disclosure of Invention
In view of the drawbacks in the above studies, the present invention provides a method for predicting high frequency performance of a connector with dielectric degradation in a humid environment, comprising the steps of:
and measuring the high-frequency parameters of the undegraded coaxial connector, establishing an equivalent circuit model of the undegraded coaxial connector, and simulating to obtain the high-frequency parameters. The specific implementation steps are as follows: prior to measuring the high frequency parameters of the coaxial connector, the vector network analyzer needs to be subjected to SOLT calibration to eliminate most errors of the instrument. And then connecting the nondegraded coaxial connector with a vector network analyzer to obtain the high-frequency parameters of the piece to be tested. When the equivalent circuit model of the nondegraded coaxial connector is established, the conductor resistance of the connector is very small, the insulation resistance is very large, and the conductor loss and the dielectric loss of the connector are very small, so that the coaxial connector is simplified into a lossless transmission line, the equivalent circuit is modeled into a cascade connection form of a plurality of groups of capacitance and inductance lumped units, the capacitance and inductance value in the circuit is calculated based on a coaxial line capacitance and inductance formula, and other parasitic parameters are obtained by fitting a circuit model simulation result of the nondegraded connector and a last step of actual measurement result.
And (3) establishing an equivalent circuit model of the degraded coaxial connector, and predicting high-frequency performance parameters of the connector with different degradation levels. The method comprises the following specific steps: the medium layer of the coaxial connector with degraded medium in a humid environment is composed of insulating material polytetrafluoroethylene and a water film attached to the surface of the insulating material polytetrafluoroethylene. The inductance value in the connector equivalent circuit model is related only to the size of the connector and the conductor permeability, and therefore the inductance values in the circuit models before and after degradation are equal. The capacitance value in the equivalent circuit model is related to the size of the connector and the dielectric constant of the medium between the inner conductor and the outer conductor, and the equivalent dielectric constant of the medium layer is changed due to the degradation of the medium of the coaxial connector in a humid environment, so that the capacitance value of the equivalent circuit model is changed. In addition, the resistivity of water is lower than that of insulating material polytetrafluoroethylene, and the loss tangent of water is higher than that of insulating material polytetrafluoroethylene, so that the equivalent insulation resistance value between the inner and outer conductors of the connector is reduced due to the deterioration of the medium, and the medium loss is increased. The influence of the connector medium degradation on the insulation resistance, loss tangent and equivalent dielectric constant was quantitatively calculated and analyzed. The calculation formula of the insulation resistance per unit length of the nondegraded coaxial connector is as follows:
dielectric layer of coaxial connector degraded in humid environmentEdge resistance R De Loss tangent tan. Delta De The calculation formula of (2) is as follows:
equivalent dielectric constant epsilon of degraded dielectric layer of coaxial connector in humid environment e And an equivalent capacitance value C i The calculation formula of (c) is:
wherein: rho m Resistivity, rho, of polytetrafluoroethylene, which is the insulating material of coaxial connectors Wa_sur Is the surface resistivity of water. r is ai And r bi Respectively the outer diameter of the inner conductor and the inner diameter of the outer conductor of each section of the coaxial connector. R is P Representing the insulation resistance per unit length, R, when the connector dielectric material is polytetrafluoroethylene W The resistance value per unit length when the dielectric material is a water film is represented. W a Is the thickness of the water film attached to the teflon surface of the insulating material and is also used to characterize the degradation grade of the connector. tan delta m And tan delta W Respectively, the loss tangent of polytetrafluoroethylene and water. C m ＝2πε 0 ε m /ln[(r bi -W a )/r ai ]And C W ＝2πε 0 ε W /ln[r bi /(r bi -W a )]Respectively represents the capacitance per unit length of the coaxial connector, epsilon, when the dielectric layers are made of insulating materials such as polytetrafluoroethylene and a water film m And ε W Respectively represents the relative dielectric constants, epsilon, of polytetrafluoroethylene and water 0 Is the dielectric constant in vacuum. And calculating and comparing the insulation resistance value and the loss tangent value before and after the coaxial connector medium is degraded, wherein the result shows that: the change of the insulation resistance and the loss tangent before and after the dielectric degradation is small, and the dielectric loss generated by the dielectric degradation is known to be small, so that the influence on the signal transmission is negligible. Therefore, the capacitance value of the equivalent circuit model is changed due to the change of the equivalent dielectric constant of the degraded connector dielectric layer, which is a main factor affecting the transmission of high-frequency signals. Based on a transmission line theory and a capacitance calculation formula of a coaxial cable with concentric annular non-uniform media, solving equivalent capacitance values of degraded coaxial connector media in wet environments when different water film thicknesses are attached to the surfaces of the degraded coaxial connector media, and replacing the capacitance values in an equivalent circuit model of an undegraded coaxial connector with the capacitance values to obtain equivalent circuit models of coaxial connectors with different degradation degrees. And (3) changing the thickness of the water film, correspondingly changing the equivalent capacitance, and predicting the high-frequency performance parameters of the connector with different degradation levels according to the circuit simulation result.
And carrying out an accelerated test on the coaxial connector in a high-humidity environment to obtain a degraded connector experiment sample, and measuring the high-frequency performance parameters of the degraded sample. The specific implementation steps are as follows: placing a plurality of groups of connectors in a high-humidity environment for degradation to obtain connector experiment samples with different degradation levels, calibrating a vector network analyzer, connecting the degraded connectors with the vector network analyzer, and measuring high-frequency performance parameters of the connectors with different degradation levels.
And comparing the measurement result of the degraded connector with the equivalent circuit simulation result to obtain the corresponding degradation grade of the connector and the actual water film thickness. The specific operation steps are as follows: and changing the thickness of the water film in the equivalent circuit model of the degraded connector to enable the simulation result to be equal to the actual measurement result, thereby obtaining the degradation grade of the degraded connector and the corresponding water film thickness.
Compared with the prior art, the invention has the following advantages:
(1) The method for establishing the equivalent circuit model of the medium degradation connector in the humid environment is provided, and the high-frequency performance parameters of the connector with different degradation levels are predicted.
(2) And a calculation formula of equivalent insulation resistance, loss tangent and dielectric constant of the degradation medium of the coaxial connector in a humid environment is provided, and the influence of the degradation of the connector medium on the parameters is quantitatively analyzed, so that which parameter is the main reason for reducing the transmission quality of the high-frequency signal is judged.
(3) With the actual coaxial connector as the object of study, the high frequency performance parameters of the connectors of different degradation levels in a high humidity environment were measured.
(4) And comparing the measured value of the degraded coaxial connector with the circuit simulation result to obtain the actual water film thickness corresponding to the degraded coaxial connector.
Drawings
FIG. 1 is an overall technical roadmap for the present invention.
Fig. 2 is a schematic diagram of the construction of a media degrading connector in a wet environment of the present invention.
Fig. 3 is an equivalent circuit model of a media-degraded connector in a wet environment of the present invention.
Detailed Description
The invention is explained in detail below with reference to the figures and examples.
This example describes a specific process of the scheme of the present invention with reference to fig. 1 to 3, where the method includes:
step 101: high frequency performance parameters of the undegraded coaxial connector were measured. The vector network analyzer needs to be calibrated before measuring the high-frequency parameters.
Step 102: and establishing an equivalent circuit model of the nondegraded coaxial connector. The specific implementation steps are as follows: an equivalent circuit model of an undegraded coaxial connector is modeled as a cascade of sets of capacitive-inductive lumped cells.
Step 103: and respectively calculating and comparing the equivalent insulation resistance value, the loss tangent and the dielectric constant of the dielectric layers of the coaxial connectors before and after degradation. The method comprises the following specific steps: the dielectric layer of the coaxial connector degraded in a humid environment is formed by polytetrafluoroethylene serving as an insulating material and a water film attached to the surface of the polytetrafluoroethylene, as shown in fig. 2, and an equivalent circuit model of the coaxial connector degraded in a humid environment is shown in fig. 3. Based on a calculation formula of the conductance capacitance of the coaxial cable with the concentric annular non-uniform medium, the insulation resistance value, the loss tangent value and the dielectric constant of the connector before and after medium degradation are solved and compared, and the result shows that the influence of the medium degradation on the insulation resistance and the loss tangent is very small, and the influence of the medium degradation on high-frequency signal transmission can be ignored. The change in the equivalent dielectric constant of the degraded connector dielectric layer resulting in a change in the capacitance value of the equivalent circuit model is a major factor causing the high frequency signal transmission to be affected.
Step 104: and establishing an equivalent circuit model of the degraded coaxial connector. On the basis of the equivalent circuit model of the undegraded coaxial connector, an equivalent circuit model of the dielectric-degraded coaxial connector is established, as shown in fig. 3. The capacitance value in the circuit is solved based on a capacitance formula of the coaxial cable with the concentric annular non-uniform medium, the capacitance value is an expression related to the thickness of the water film, and the capacitance values of the connectors with different degradation degrees are obtained by changing the thickness of the water film. And replacing the capacitance value in the equivalent circuit model of the undegraded coaxial connector by the capacitance value, and obtaining the equivalent circuit models of the coaxial connectors with different degradation degrees by keeping other parameter values unchanged. And changing the thickness of a water film in the circuit model for simulation, and predicting the high-frequency performance parameters of the connector with different degradation levels.
Step 105: and (3) placing a plurality of groups of experimental samples in a high-humidity environment for accelerated test to obtain connector samples with different degradation grades.
Step 106: coaxial connectors that degrade in a wet environment were measured. And after calibration, measuring the high-frequency performance parameters of the degraded connector by using a vector network analyzer.
Step 107: and changing the thickness of the water film in the circuit model of the degraded connector to ensure that the simulation result is the same as the actual measurement result, and obtaining the degradation grade of the connector and the corresponding thickness of the water film.
Claims (5)
1. A method for predicting high frequency performance of a media degrading connector in a humid environment, comprising the steps of:
measuring the nondegraded coaxial connector to obtain high-frequency performance parameters, establishing an equivalent circuit model of the nondegraded coaxial connector, and simulating to obtain the high-frequency performance parameters;
solving the equivalent insulation resistance, loss tangent and dielectric constant of the dielectric layer of the degraded coaxial connector, establishing an equivalent circuit model of the degraded coaxial connector, and predicting high-frequency performance parameters corresponding to different degradation levels;
performing an accelerated test in a high humidity environment to obtain connector samples with different degradation degrees, and measuring high-frequency performance parameters of the coaxial connector with medium degradation in the high humidity environment;
and comparing the measured value of the degraded connector with the equivalent circuit simulation result to obtain the corresponding degradation grade of the connector and the actual water film thickness.
2. The method for predicting the high-frequency performance of the medium degradation connector in the humid environment according to claim 1, wherein a vector network analyzer is calibrated by SOLT, and then the coaxial connector which is not degraded is connected with the vector network analyzer to measure the high-frequency performance parameters of the coaxial connector; then, based on a transmission line theory, an equivalent circuit model of the nondegradable coaxial connector is modeled into cascade connection of a plurality of groups of capacitance and inductance lumped units, capacitance and inductance values in the circuit model are calculated based on a coaxial line capacitance and inductance formula, and other parasitic parameters are obtained by fitting a circuit simulation result and an actual measurement result of the nondegradable coaxial connector.
3. The method for predicting the high-frequency performance of a connector degraded by media in a humid environment according to claim 1, wherein the media layer of the coaxial connector degraded by the humid environment is composed of polytetrafluoroethylene, which is an insulating material of the connector, and a water film attached to the surface thereof; solving the insulation resistance, loss tangent and equivalent dielectric constant of the coaxial connector degradation dielectric layer in unit length under a humid environment based on a calculation formula of the conductance capacitance of the coaxial cable with the concentric annular non-uniform dielectric; insulation resistance per unit length R of degraded coaxial connector dielectric layer De The calculation formula of (c) is:
loss tangent tan delta of degraded coaxial connector dielectric layer De The calculation formula of (c) is:
equivalent dielectric constant epsilon of degraded dielectric layer of coaxial connector e The calculation formula of (c) is:
wherein: r P Represents the insulation resistance per unit length, R, when the dielectric material of the connector is polytetrafluoroethylene W Represents the resistance value per unit length, ρ, when the dielectric material is a water film m Is the resistivity, rho, of the insulating material PTFE of coaxial connectors Wa_sur Is the surface resistivity of water, r ai And r bi Respectively the outer diameter of the inner conductor and the inner diameter of the outer conductor, W, of each section of the coaxial connector a Is the thickness of water film, tan delta, attached to the surface of polytetrafluoroethylene, which is an insulating material m And tan delta W Loss tangent, C, of polytetrafluoroethylene and water, respectively m ＝2πε 0 ε m /ln[(r bi -W a )/r ai ]And C W ＝2πε 0 ε W /ln[r bi /(r bi -W a )]Respectively represents the capacitance per unit length, epsilon, of the coaxial connector when the dielectric layers are made of insulating materials such as polytetrafluoroethylene and water films m And epsilon W Respectively represents the relative dielectric constants, epsilon, of polytetrafluoroethylene and water 0 Is the vacuum dielectric constant; the numerical change of the insulation resistance and the loss tangent before and after the connector medium is degraded is very small, and the capacitance value in the equivalent circuit can be influenced only by the dielectric constant of the degraded medium, so that the inductance value and the parasitic parameter are not kept on the basis of an equivalent circuit model of a non-degraded connectorInstead, only the capacitance value of the parallel part of the circuit is changed, so that the equivalent circuit model of the degraded connector and the high-frequency performance parameters of the connectors with different degradation degrees can be obtained.
4. The method for predicting the high-frequency performance of the medium degradation connector in the humid environment according to claim 1, wherein the coaxial connector is placed in a high-humidity environment, connector samples with different degradation degrees are obtained by changing degradation time, and corresponding high-frequency performance parameters are measured by using a vector network analyzer.
5. The method for predicting the high-frequency performance of the connector with the medium degraded under the humid environment according to claim 1, wherein the degradation grade of the connector is characterized by the thickness of a water film in an equivalent circuit, and the degradation grade of the medium of the coaxial connector can be obtained by changing the thickness of the water film to enable a circuit simulation result to be the same as a high-frequency performance parameter curve of the connector with different degradation degrees measured by experiments.
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