Passive intermodulation prediction method for coaxial connector under different communication frequency bands
Technical Field
The invention relates to a passive intermodulation prediction method for coaxial connectors under different communication frequency bands, and a passive intermodulation power prediction model for the coaxial connectors under different frequency bands is obtained based on methods such as theoretical modeling, finite element simulation analysis and experimental test, and belongs to the crossing field of an electrical contact theory and a communication technology.
Background
Passive Intermodulation (PIM) interference refers to a phenomenon that a linear combination product, which is generated by inter-modulating signals with two or more frequencies in a Passive device and has a frequency different from a fundamental frequency signal, falls into a receiving frequency band to form interference, and has a non-negligible influence on the transmission quality of a radio frequency communication system. The passive intermodulation is due to the slight nonlinear effects present in the passive devices. Coaxial connectors are the most diverse and most used important components in the entire mobile communication system. Coaxial connectors complete the connection by means of metal contacts, which are generally considered to be linear, but will exhibit slight nonlinear effects in the case of high power passing.
The passive intermodulation is a key index for measuring the quality of mobile communication equipment, the mobile communication has different frequency bands of 900MHz, 1800MHz and the like, and with the development of 5G or even 6G of the mobile communication, the research on the passive intermodulation characteristics under different frequency bands becomes an important problem, so that the research on the passive intermodulation characteristics under different frequency bands and the modeling analysis of the passive intermodulation characteristics have great significance for obtaining the relation between the power of a passive intermodulation product and the frequency and the power of an input signal.
At present, modeling analysis of passive intermodulation of a coaxial connector under a single frequency band is basically mature, mostly, a polynomial model is adopted to model nonlinearity of the coaxial connector, and then a prediction model of the passive intermodulation power of the coaxial connector is obtained. The passive intermodulation analysis of the coaxial connector under multiple frequency bands and the analysis of the influence of the frequency on the passive intermodulation performance of the coaxial connector are rare, and the method has very important practical value and application prospect for the research of the passive intermodulation power prediction of the coaxial connector under different communication frequency bands.
Disclosure of Invention
Aiming at the one-sidedness and limitation of passive intermodulation performance analysis and prediction of the coaxial connectors under different frequency bands in the prior art, the invention aims to analyze and establish the passive intermodulation power prediction model of the coaxial connectors under different frequency bands on the basis of the combination of theoretical analysis, finite element simulation analysis and experimental test.
To achieve the above object, the present invention provides the following analysis scheme, comprising the steps of:
(1) passive intermodulation test of the multi-band coaxial connector:
three pairs of connector pairs consisting of brand-new DIN revolution N male connectors and N female revolution DIN connectors were selected as test samples. The base material of the inner conductor and the outer conductor of the connector is brass, the middle plating layer is nickel, the surface plating layer is gold, and the plating thicknesses of the three groups of samples are basically the same. The three groups of samples are subjected to a double-tone passive intermodulation test under different communication frequency bands, the frequency bands are selected to be 800MHz, 900MHz, 1800MHz, 1900MHz and 2000MHz, the input power of the two carriers is the same, and the two carriers are set to step from 35dBm to 44dBm at intervals of 1 dB. All the double-tone passive intermodulation tests are carried out at room temperature, the DIN heads at the two ends of the connector are respectively connected to the output end of the passive intermodulation tester and a standard low intermodulation load by using a torque wrench, the connection fastening is ensured, and the connection state stability of the test instrument, the test sample and the load in the test process is ensured. The time of each passive intermodulation test lasts for 15 seconds, and the maximum value of the third-order passive intermodulation of the test result within 15 seconds is taken as the final result.
(2) Establishing a passive intermodulation power prediction model of the coaxial connector under different communication frequency bands:
passive intermodulation is mainly caused by the non-linear characteristics of the coaxial connector. The passive intermodulation analysis method analyzes the passive intermodulation from the nonlinear angle of the material. The magnetic material in the coaxial connector plating is believed to be a non-linear source of passive intermodulation interference, and the amount of current flowing through the region of magnetic material and the equivalent resistance of the region of magnetic material are key to analyzing the passive intermodulation of the coaxial connector.
The method is based on the skin effect theory, and the influence of frequency on the current density distribution of the coaxial connector is analyzed. And then analyzing the influence of the frequency on the equivalent resistance of the nickel layer of the coaxial connector based on the magneto-resistance effect theory. And then establishing a finite element simulation model of the cross section of the inner conductor of the connector according to the actual structure and the size of the piece to be tested, setting and testing corresponding frequency and power parameters to perform finite element simulation, and obtaining the data of the nickel layer current amount and the nickel layer average magnetization intensity amplitude under different signal frequencies and input power settings through the finite element simulation. By combining theoretical analysis and finite element simulation analysis, the influence of frequency on the current density distribution of the coaxial connector and the influence of frequency on the equivalent resistance of the nickel layer of the coaxial connector are comprehensively considered, a passive intermodulation power prediction model of the coaxial connector under different communication frequency bands can be established, the model is related to input power and signal frequency at the same time, and can be expressed as follows:
wherein P is
IM3Is the third order intermodulation power, I
IM3Is a third order intermodulation current, r
eq,NiIs the equivalent resistance of the nickel layer, a
3,a
5,a
7Is a coefficient of a polynomial model, I
NiThe amount of nickel current, which is related to the input power and signal frequency,
is the average magnetization amplitude of the nickel layer, which is related to the signal frequency.
Is the average magnetization amplitude of the nickel layer at a signal frequency of 900 MHz.
According to the passive intermodulation prediction method of the coaxial connector under different communication frequency bands, passive intermodulation tests are carried out on a coaxial connector sample under a plurality of communication frequency bands, theoretical analysis and finite element simulation analysis are combined, and a passive intermodulation power prediction model of the coaxial connector under different communication frequency bands is established under the condition that the influence of frequency on the current density distribution of the coaxial connector and the influence of frequency on the equivalent resistance of a nickel layer of the coaxial connector are considered. Theoretical support is provided for analyzing the influence of signal frequency on the passive intermodulation performance of the coaxial connector and predicting the passive intermodulation performance of the coaxial connector under different communication frequency bands. Compared with a passive intermodulation analysis method of a coaxial connector under a single frequency band, the passive intermodulation analysis method mainly has the following advantages:
1) the influence of the signal frequency on the passive intermodulation performance of the coaxial connector is analyzed.
2) And carrying out passive intermodulation test under multiple frequency bands on the coaxial connector through the passive intermodulation test system with the multiple frequency bands. 3) A prediction model of the third-order passive intermodulation power of the coaxial connector under different signal frequencies and input powers is quantitatively provided.
Drawings
FIG. 1 is a general schematic diagram of the technical route of the method.
Detailed Description
The present invention is described in further detail below with reference to the attached drawing figures. In the following description, a connector pair composed of a DIN-revolution N-male connector and an N-revolution N-female connector is taken as an example for analysis, but the present embodiment is not limited to the present invention, and the passive intermodulation power prediction of coaxial connectors in different communication frequency bands can be performed by using the analysis method of the present invention when coaxial connectors with similar structures of the present invention are used as analysis objects.
The general schematic diagram of the technical route is shown in fig. 1, and a connector pair consisting of a DIN revolution N revolution connector and an N revolution DIN revolution connector is selected as a test sample; carrying out passive intermodulation test on the test sample under different communication frequency bands; under the condition of considering the influence of frequency on the current density distribution of the coaxial connector and the influence of frequency on the equivalent resistance of a nickel layer of the coaxial connector, theoretical analysis and finite element simulation analysis are carried out, and a prediction model of third-order passive intermodulation power of the coaxial connector under different signal frequencies and input power is quantitatively provided. The analysis method of the present invention comprises the steps of:
step 101-102: passive intermodulation test of the multi-band coaxial connector;
three pairs of connectors consisting of brand-new DIN revolution N male connectors and N female revolution DIN male connectors are selected as test samples, the three groups of samples are produced by the same manufacturer in the same batch, DIN heads at two ends of the samples can be directly connected with a passive intermodulation test instrument, and interference caused by intermodulation of a test cable or unstable connection of the test cable and other factors is avoided. The thickness of the plating layer of the sample is tested by using an X-ray fluorescence thickness gauge, and the thicknesses of the middle plating layer and the surface plating layer of the three groups of samples are basically the same. In addition, through intermodulation test, the three groups of samples have similar third-order intermodulation power under the frequency band of 900MHz, and the error among the samples does not exceed 2 dB.
And carrying out standard double-tone passive intermodulation test on the three groups of connector samples under different communication frequency bands, wherein the communication frequency bands of the intermodulation test are selected to be 800MHz, 900MHz, 1800MHz, 1900MHz and 2000MHz, the input power of two carriers in the test process is the same, the input power is set to be stepped from 35dBm to 44dBm by taking 1dB as an interval, and a third-order intermodulation value is selected as a test result. In addition, all the double-tone passive intermodulation tests are carried out at room temperature, the DIN heads at the two ends of the connector are respectively connected to the output end of the passive intermodulation tester and the standard low intermodulation load by using a torque wrench, the connection fastening is ensured, the connection state stability of the test instrument, the test sample and the load in the test process is ensured, and the stability and the accuracy of the test result obtained in the test process are ensured.
In the process of the double-tone passive intermodulation test, for each group of samples, in each communication frequency band, each test time under each input power lasts for 15 seconds, and if the test result is relatively stable within 15 seconds, the maximum value of the test result within 15 seconds is taken as a final result; and if the test result is not stable enough within 15 seconds, the test for 15 seconds is carried out again until the stable test result within 15 seconds can be obtained, and the maximum value of the test result within 15 seconds in the stable test process is taken as the final result. And recording all test results obtained in the test process, and performing next-step sorting and analysis.
Step 103-106: establishing a passive intermodulation power prediction model of the coaxial connector under different communication frequency bands;
and establishing a passive intermodulation power prediction model of the coaxial connector under different communication frequency bands. The passive intermodulation is mainly caused by the nonlinear characteristic of the coaxial connector, and the passive intermodulation is analyzed from the material nonlinearity. The magnetic material in the coaxial connector plating is believed to be a non-linear source of passive intermodulation interference, and the amount of current flowing through the region of magnetic material and the equivalent resistance of the region of magnetic material are key to analyzing the passive intermodulation of the coaxial connector.
The method is based on the skin effect theory, and the influence of frequency on the current density distribution of the coaxial connector is analyzed. And then analyzing the influence of the frequency on the equivalent resistance of the magnetic coating region of the coaxial connector based on the magneto-resistance effect theory. And then establishing a finite element simulation model of the cross section of the inner conductor of the connector according to the actual structure and the size of the piece to be tested, setting and testing corresponding signal frequency and input power parameters to perform finite element simulation, and obtaining the data of the nickel layer current magnitude and the nickel layer average magnetization intensity amplitude under different signal frequency and input power settings through the finite element simulation. By combining theoretical analysis and finite element simulation analysis, the influence of frequency on the current density distribution of the coaxial connector and the influence of frequency on the equivalent resistance of the nickel layer of the coaxial connector are comprehensively considered, a passive intermodulation power prediction model of the coaxial connector under different communication frequency bands can be established, the model is related to input power and signal frequency at the same time, and can be expressed as follows:
wherein P is
IM3Is the third order intermodulation power, I
IM3Is a third order intermodulation current, r
eq,NiIs the equivalent resistance of the nickel layer, a
3,a
5,a
7Is a coefficient of a polynomial model, I
NiThe amount of current flowing to the nickel layerWhich is related to the input power and the signal frequency,
is the average magnetization amplitude of the nickel layer, which is related to the signal frequency.
Is the average magnetization amplitude of the nickel layer at a signal frequency of 900 MHz.