Modeling simulation method for predicting conducted interference and radiated interference of PCB

Abstract

The invention relates to a modeling simulation method for predicting conducted interference and radiated interference of a PCB (Printed Circuit Board), which comprises the following steps of: establishing a conducted interference test system model and a trace equivalent model, extracting an excitation source signal, and establishing a parasitic parameter model; establishing a conducted interference model by combining the models; establishing a radiation interference field model, establishing a radiation interference path model based on the conducted interference model, and further establishing a field-path joint model as a radiation interference model; an excitation source is added into the radiation interference model for radiation interference simulation, a radiation interference simulation scheme of actual measurement or simulation excitation source and antenna receiving is adopted for a first frequency band not exceeding the specified frequency, and a radiation interference simulation scheme of simulation excitation source and probe receiving is adopted for a second frequency band exceeding the specified frequency. According to the method, electromagnetic interference coupling among complex traces of the PCB, high-frequency signals and a test environment is comprehensively considered, a simulation result is close to an actual measurement result, and good predictability is achieved.

Description

Technical Field

[0001] The invention relates to the field of PCB, and in particular to a modeling and simulation method for predicting PCB conducted interference and radiated interference. Background Art

[0002] Printed Circuit Board (PCB) is the core component of consumer electronic products. With the continuous reduction of PCB size and the continuous increase of signal frequency, the number of cases of electromagnetic interference (EMI) exceeding the standard is increasing, and the reasons for exceeding the standard are becoming more and more complicated. It can be expected that the dV / dt and dI / dt of high-frequency jumping signals are large, so complex electromagnetic field distribution will be generated, and the smaller PCB size will cause the electromagnetic interference generated to affect the working signals of nearby traces and components.

[0003] For common electronic products in electric vehicles, the PCB generally contains main excitation sources such as high-frequency switching power supplies and high-speed CAN transceivers, and the propagation paths from copper plates and traces to metal shells and ground must also be considered. Part of the rapidly changing voltage and current of the excitation source propagates outward through the wiring harness in the form of conducted interference, and the other part propagates outward through space and wiring harnesses in the form of radiated interference.

[0004] At present, there are relevant standards at home and abroad for the limit values ​​of EMI emissions of vehicles and vehicle components. The domestic standard GB / T 18655-2018 "Limits and measurement methods of radio disturbance characteristics of vehicles, ships and internal combustion engines for protecting vehicle receivers" introduces how to measure the various electromagnetic interferences generated by automobiles and their components during operation (including conducted interference tests and radiated interference tests), and has different amplitude limits for the peak (PK) and average (AVG) values ​​of electromagnetic interference in each frequency band.

[0005] Therefore, if you forget or ignore the EMI of the product during the design phase, it may lead to additional costs and delay the time to market. At the same time, if you can use simulation methods to study the influencing factors of the EMI emission of electronic products and predict the distribution trend and amplitude of electromagnetic interference in the environment required by the test standards, you can save a lot of test costs, labor costs and manufacturing costs.

[0006] Therefore, accurate analysis of the electromagnetic interference generation mechanism of PCB and the construction of accurate conducted interference prediction simulation model and radiated interference prediction simulation model are of great significance to reducing the test cost of automotive electronic products before they are put on the market and reducing the impact of PCB electromagnetic interference on external electronic equipment.

[0007] The Chinese invention patent with the publication number CN115688646A discloses an expert system for predicting EMI radiation on PCB motherboards, which proposes that as long as the component library, PCB layout and wiring data, simulation data and personality file related information of the PCB motherboard are input into the EMC expert system, the system will perform EMC design rule checks on network noise, and finally form an overall estimate of the electromagnetic interference radiated by the detected PCB motherboard. However, this method only qualitatively analyzes the PCB radiation interference situation based on the EMC design rules. Such analysis is too simplistic and does not take into account the electromagnetic interference coupling between the complex traces of the PCB, high-frequency signals and the test environment. Therefore, the obtained electromagnetic interference qualitative analysis results are too simple and cannot predict the national standard test results. Summary of the invention

[0008] In order to solve the above problems, the present invention provides a modeling and simulation method for predicting PCB conducted interference and radiated interference, which comprehensively considers the electromagnetic interference coupling between the complex traces of the PCB, high-frequency signals and the test environment. The simulation results are close to the measured results and have good predictability.

[0009] The present invention is implemented by the following scheme: A modeling and simulation method for predicting PCB conducted interference and radiated interference comprises the steps of:

[0010] Establish a conducted interference test system model and trace equivalent model for the PCB to be predicted, extract the excitation source signal of the PCB to be predicted, and build a parasitic parameter model;

[0011] Establishing a conducted interference model based on the conducted interference test system model, the trace equivalent model, the excitation source signal and the parasitic parameter model;

[0012] Building a radiation interference field model, building a radiation interference path model based on the conducted interference model, and building a field-path joint model using the radiation interference field model and the radiation interference path model;

[0013] The field-circuit joint model is used as a radiation interference model and an excitation source is added to the radiation interference model to perform radiation interference simulation, wherein for a first frequency band not exceeding a specified frequency, a radiation interference simulation scheme using a measured or simulated excitation source and antenna reception is adopted, and for a second frequency band exceeding the specified frequency, a radiation interference simulation scheme using a simulated excitation source and probe reception is adopted.

[0014] The further improvement of the modeling and simulation method for predicting PCB conducted interference and radiated interference of the present invention is that before building a radiated interference path model based on the conducted interference model:

[0015] Using the conducted interference model to perform conducted interference simulation on the PCB to be predicted and obtain a conducted interference simulation result;

[0016] At the same time, a conducted interference test is performed on the PCB to be predicted and a conducted interference test result is obtained;

[0017] Comparing the conducted interference simulation result with the conducted interference test result, and if the error is greater than a preset conducted interference accuracy threshold, adjusting the conducted interference model until the error is less than the preset conducted interference accuracy threshold;

[0018] Then, the radiation interference path model is built based on the adjusted conducted interference model.

[0019] The further improvement of the modeling and simulation method for predicting PCB conducted interference and radiated interference of the present invention is:

[0020] After adding an excitation source to the radiation interference model to perform radiation interference simulation, a radiation interference simulation result is obtained;

[0021] Performing a radiation interference test on the PCB to be predicted and obtaining a radiation interference test result;

[0022] The radiation interference simulation result is compared with the radiation interference test result. If the error is greater than a preset radiation interference accuracy threshold, the radiation interference model is adjusted until the error is less than the preset radiation interference accuracy threshold.

[0023] A further improvement of the modeling and simulation method for predicting PCB conducted interference and radiated interference of the present invention is that the conducted interference test system model is a LISN model, and while establishing the LISN model, a power supply model for simulating the power supply state is established.

[0024] A further improvement of the modeling and simulation method for predicting PCB conducted interference and radiated interference of the present invention is that the step of establishing the trace equivalent model includes: performing S parameter simulation of the trace for the key signal lines of the PCB to be predicted; extracting the equivalent SPICE model of the PCB to be predicted as the trace equivalent model; wherein the key signal lines include clock signal lines and CAN signal lines.

[0025] A further improvement of the modeling and simulation method for predicting PCB conducted interference and radiated interference of the present invention is that the step of extracting the excitation source signal of the PCB to be predicted includes: measuring the key PIN pin signal of the key chip on the PCB to be predicted; converting the measured time domain signal into a frequency domain signal; determining the excitation source signal according to the frequency and amplitude of the frequency domain signal; wherein the key chip includes a switching power supply chip and a CAN transceiver chip, and the key PIN pin signal is a high-frequency PIN pin signal.

[0026] A further improvement of the modeling and simulation method for predicting PCB conducted interference and radiated interference of the present invention is that the parasitic parameter model includes three groups of LC circuits, and the values ​​of the three groups of LC circuits are respectively determined by the parasitic inductance and capacitance calculation formulas between the PCB to be predicted and the metal desktop, the external long wire of the PCB to be predicted and the ground, and the external short wire of the PCB to be predicted and the ground.

[0027] A further improvement of the modeling and simulation method for predicting PCB conducted interference and radiated interference of the present invention is that the specified frequency is determined by the current clamp cutoff frequency.

[0028] A further improvement of the modeling and simulation method for predicting PCB conducted interference and radiated interference of the present invention is that the radiation interference field model includes an antenna model, a test table model and a cable model built based on the GB / T 18655-2018 standard.

[0029] The further improvement of the modeling and simulation method for predicting PCB conducted interference and radiated interference of the present invention is:

[0030] The radiation interference simulation scheme adopted in the first frequency band includes the following steps: obtaining a common mode current as an excitation source by a measurement method; performing a frequency domain product operation on the excitation source and a transfer function of a conducted interference test system in the radiation interference model to obtain a receiving voltage distribution at an antenna port; performing a frequency domain operation on the receiving voltage and an antenna coefficient respectively to obtain a radiation interference frequency domain distribution reflecting the electric field strength and use it as a radiation interference simulation result of the first frequency band;

[0031] The radiation interference simulation scheme adopted in the second frequency band includes the steps of: obtaining common-mode current simulation results through the field-circuit joint model; substituting the simulation results into the radiation interference model as the excitation source and performing time domain simulation to obtain the electric field strength distribution at the receiving probe, and using it as the radiation interference simulation result of the second frequency band.

[0032] The present invention includes but is not limited to the following beneficial effects:

[0033] 1. The conducted interference model is established by combining the conducted interference test system model, the trace equivalent model that can reflect the impedance characteristics of the PCB trace, the excitation source signal, and the parasitic parameter model that can reflect the electromagnetic interference coupling characteristics between the components of the transmission interference test system, so that it has higher accuracy.

[0034] 2. Based on the conducted interference model, a circuit model is established and a field-circuit joint model is built in combination with the field model. A common-mode current excitation source is introduced to simulate the radiation interference. The electromagnetic interference coupling between the complex traces of the PCB, high-frequency signals and the test environment is comprehensively considered to make the model prediction closer to reality. In addition, different adaptation simulation schemes are adopted in different frequency bands to ensure the simulation accuracy of the model in the lower first frequency band and the simulation efficiency in the higher second frequency band.

[0035] 3. Based on the GB / T 18655-2018 standard, a prediction model for PCB conducted interference and radiated interference is built. The simulation results are close to the measured results and have good predictive properties, providing theoretical support and academic basis for predicting electromagnetic interference. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 The figure is a flow chart of a modeling and simulation method for predicting PCB conducted interference in an embodiment of the present invention.

[0037] Figure 2 The figure is a flow chart of a modeling and simulation method for predicting PCB radiation interference in an embodiment of the present invention.

[0038] Figure 3 This is an equivalent SPICE model diagram of the PCB to be predicted in an embodiment of the present invention.

[0039] Figure 4 It is a time domain diagram of the excitation source signal of the PCB to be predicted in an embodiment of the present invention.

[0040] Figure 5 4 is a parasitic parameter model diagram of the PCB to be predicted in an embodiment of the present invention.

[0041] Figure 6 This is a diagram of the conducted interference model of the PCB to be predicted in an embodiment of the present invention.

[0042] Figure 7 This is a model diagram of the radiation interference field of the PCB to be predicted in an embodiment of the present invention. DETAILED DESCRIPTION

[0043] In order to solve the problem that the traditional PCB electromagnetic interference model does not consider the electromagnetic interference coupling between the complex traces, high-frequency signals and the test environment of the PCB, which makes the electromagnetic interference qualitative analysis results too simple and cannot predict the national standard test results, the present invention provides a modeling and simulation method for predicting PCB conducted interference and radiated interference, which comprehensively considers the electromagnetic interference coupling between the complex traces, high-frequency signals and the test environment of the PCB, and the simulation results are close to the measured results, with good predictability. The modeling and simulation method for predicting PCB conducted interference and radiated interference is further explained below with the electronic products of electric vehicles as a specific example and in combination with the accompanying drawings.

[0044] See also Figures 1 to 7 As shown, a modeling and simulation method for predicting PCB conducted interference and radiated interference includes the following steps:

[0045] Step 1: Figure 1 As shown, a conducted interference test system model for test system research and a trace equivalent model for PCB trace research are established for the PCB to be predicted, the excitation source signal of the PCB to be predicted is extracted, and a parasitic parameter model is built.

[0046] Specifically: the conducted interference test system model is a LISN model. While establishing the LISN model, a power supply model for simulating the power supply status of the entire vehicle is established. The power supply model in this embodiment uses a regulated power supply with a regulated voltage of 14V. Both the LISN model and the regulated power supply model are general models, and their modeling methods are not described in detail here.

[0047] The steps of establishing the trace equivalent model include: importing the PCB model file to be predicted in odb format into CST software, performing S parameter simulation of the trace for key signal lines such as the clock signal line and CAN signal line of the PCB to be predicted; then using the Spice Extraction tool in the CST software to perform data conversion, and then extracting the equivalent SPICE model of the PCB to be predicted as the trace equivalent model. The equivalent SPICE model is shown in FIG. Figure 3 shown.

[0048] The steps of extracting the excitation source signal include: using a high-resolution oscilloscope (which can read 20w data per millisecond) to measure the high-frequency PIN pin signals of key chips such as the switching power supply chip and the CAN transceiver chip with a probe when the PCB to be predicted is working normally; Figure 4 As shown, Figure 4 The time domain diagram of the CAN-H signal is shown) converted into a frequency domain signal; the excitation source signal is determined according to the frequency and amplitude of the frequency domain signal.

[0049] The parasitic parameter model is constructed by calculating the theoretical formula and simulating the parasitic parameters of the PCB to be predicted and its conducted interference test system. The parasitic parameter model includes three groups of LC circuits, such as Figure 5 As shown, the values ​​of the three groups of LC circuits are determined by the parasitic inductance and capacitance calculation formulas between the predicted PCB and the metal desktop, the predicted PCB external long wire to the ground, and the predicted PCB external short wire to the ground.

[0050] 1. The calculation formula for the parasitic inductance and capacitance between the PCB to be predicted and the metal desktop includes:

[0051] The capacitance C between the PCB board and the large reference planeCM It can be calculated by closed formula (1):

[0052]

[0053] Where: C P is the plane capacitance and edge capacitance between the PCB board and the reference plane, C i is the intrinsic capacitance of the PCB, S is the surface area of ​​the PCB, h is the height between the PCB and the reference plane, ε0 is the absolute dielectric constant of vacuum, ε r is the relative dielectric constant of the foam between the PCB board and the desktop.

[0054] The inductance L between the rectangular PCB board and the large reference plane CM It can be calculated by formula (2) and formula (3):

[0055]

[0056] L CM =Z c 2 ·C CM (3)

[0057] Where: w is the width of the microstrip line.

[0058] 2. The parasitic inductance calculation formula from the external wire (long or short) of the PCB to be predicted to the ground includes:

[0059]

[0060] Where: d is the distance from the transmission line to the ground, r is the radius of the transmission line, X is the length of the transmission line, and μ0 is the magnetic permeability.

[0061] Step 2: Figure 1 and Figure 6 As shown, a conducted interference model is established based on the conducted interference test system model 1 (such as a LISN model), the trace equivalent model 2 (such as an equivalent SPICE model), the excitation source signal 3 (key PIN foot signal) and the parasitic parameter model 4 (including three groups of LC circuits). The conducted interference model is established by combining the conducted interference test system model, the trace equivalent model that can reflect the impedance characteristics of the PCB trace, the excitation source signal, and the parasitic parameter model that can reflect the electromagnetic interference coupling characteristics between the components of the transmission interference test system, so that it has a higher accuracy.

[0062] Step 3: Figure 2 and Figure 7As shown, a radiation interference field model is built, a radiation interference path model is built based on the conducted interference model, and a field-path joint model is built using the radiation interference field model and the radiation interference path model. Specifically, the radiation interference field model is a three-dimensional field model, which includes an antenna model 5, a test table model, and a cable model 6 built based on the GB / T 18655-2018 standard. The type of the antenna model is not limited to Figure 7 The biconical antenna model shown is specifically divided into four frequency bands (0.15MHz to 30MHz, 30MHz to 300MHz, 300MHz to 2500MHz, 1000MHz to 2500MHz) according to the GB / T18655-2018 standard to establish vertical monopole antenna, biconical antenna, logarithmic antenna and horn antenna models respectively. The radiation interference path model is built based on the aforementioned conducted interference model. Therefore, the field-path joint model comprehensively considers the electromagnetic interference coupling between the complex traces of the PCB, high-frequency signals and the test environment, making the model closer to reality. And the radiation interference field model is built based on the GB / T 18655-2018 standard, so that the radiation interference model can more accurately predict the national standard test results.

[0063] Step 4: Use the field-circuit joint model as a radiation interference model and add an excitation source to the radiation interference model to perform radiation interference simulation, wherein for the first frequency band not exceeding the specified frequency, a radiation interference simulation scheme using a measured or simulated excitation source and antenna reception is adopted, and for the second frequency band exceeding the specified frequency, a radiation interference simulation scheme using a simulated excitation source and probe reception is adopted.

[0064] Specifically, based on actual experience and experimental verification, the current current clamp cutoff frequency of 400MHz is used as the designated frequency point, and the test frequency band is divided into a first frequency band not exceeding 400MHz and a second frequency band exceeding 400MHz. Figure 2 As shown, the radiation interference simulation scheme adopted in the first frequency band includes the steps of: obtaining a common-mode current as an excitation source through a measurement method, and the measurement method is to perform a CE current method test on the predicted PCB with the help of a current clamp and a spectrum analyzer to obtain the common-mode current; performing a frequency domain product operation on the excitation source and the transfer function of the conducted interference test system in the radiation interference model to obtain the receiving voltage distribution at the antenna port; then performing a frequency domain operation on the receiving voltage and the antenna coefficient respectively to obtain the radiation interference frequency domain distribution reflecting the electric field strength and use it as the radiation interference simulation result of the first frequency band; the radiation interference simulation scheme adopted in the second frequency band includes the steps of: obtaining a common-mode current simulation result through the field-circuit joint model; substituting the simulation result as the excitation source into the radiation interference model and performing a time domain simulation to obtain the electric field strength distribution at the receiving probe, and use it as the radiation interference simulation result of the second frequency band.

[0065] As a preferred implementation, in order to make the constructed conducted interference model and the radiated interference model more accurate, the conducted interference model and the radiated interference model need to be optimized.

[0066] The optimization steps for the conducted interference model include:

[0067] 1.1. Use the built conducted interference model to simulate the conducted interference of the PCB to be predicted and obtain the conducted interference simulation results. Specifically, the conducted interference model can be simulated in the time domain and transformed in the FFT frequency domain in the CST simulation software to obtain the conducted interference spectrum, that is, the conducted interference simulation results.

[0068] 1.2. At the same time, the PCB to be predicted is tested for conducted interference and the conducted interference test result is obtained. The specific test method is a conventional method and will not be described in detail here.

[0069] 1.3. Compare the conducted interference simulation result with the conducted interference test result. If the error is greater than a preset conducted interference accuracy threshold, adjust the conducted interference model until the error is less than the preset conducted interference accuracy threshold.

[0070] The optimization steps for the radiation interference model include:

[0071] 2.1. First, optimize and adjust the conducted interference model, and then build the radiation interference model based on the adjusted conducted interference model.

[0072] 2.2. After building the radiation interference model (i.e., the field-circuit joint model), add an excitation source to the radiation interference model to perform radiation interference simulation and obtain the radiation interference simulation results.

[0073] 2.3. Perform a radiation interference test on the PCB to be predicted and obtain the radiation interference test result. The specific test method is a conventional method and will not be described here.

[0074] 2.4. Compare the radiation interference simulation result with the radiation interference test result. If the error is greater than a preset radiation interference accuracy threshold, adjust the radiation interference model until the error is less than the preset radiation interference accuracy threshold.

[0075] Through the above optimization, the simulation results of the conducted interference model and the radiated interference model are close to the measured results, which have good predictability and provide theoretical support and academic basis for predicting electromagnetic interference.

[0076] The present invention is described in detail above in conjunction with the embodiments of the accompanying drawings. A person skilled in the art can make various variations of the present invention according to the above description. Therefore, certain details in the embodiments should not constitute a limitation of the present invention, and the scope of protection of the present invention shall be defined by the scope of the attached claims.

Claims

1. A modeling and simulation method for predicting PCB conducted interference and radiated interference, characterized in that: Includes steps: Establish a conducted interference test system model and trace equivalent model for the PCB to be predicted, extract the excitation source signal of the PCB to be predicted, and build a parasitic parameter model; Establishing a conducted interference model based on the conducted interference test system model, the trace equivalent model, the excitation source signal and the parasitic parameter model; Building a radiation interference field model, building a radiation interference path model based on the conducted interference model, and building a field-path joint model using the radiation interference field model and the radiation interference path model; The field-circuit joint model is used as a radiation interference model and an excitation source is added to the radiation interference model to perform radiation interference simulation, wherein for a first frequency band not exceeding a specified frequency, a radiation interference simulation scheme using a measured or simulated excitation source and antenna reception is adopted, and for a second frequency band exceeding the specified frequency, a radiation interference simulation scheme using a simulated excitation source and probe reception is adopted.

2. The modeling and simulation method for predicting PCB conducted interference and radiated interference as claimed in claim 1, characterized in that: Before building the radiation interference model based on the conducted interference model: Using the conducted interference model to perform conducted interference simulation on the PCB to be predicted and obtain a conducted interference simulation result; At the same time, a conducted interference test is performed on the PCB to be predicted and a conducted interference test result is obtained; Comparing the conducted interference simulation result with the conducted interference test result, and if the error is greater than a preset conducted interference accuracy threshold, adjusting the conducted interference model until the error is less than the preset conducted interference accuracy threshold; Then, the radiation interference path model is built based on the adjusted conducted interference model.

3. The modeling and simulation method for predicting PCB conducted interference and radiated interference as claimed in claim 1, characterized in that: After adding an excitation source to the radiation interference model to perform radiation interference simulation, a radiation interference simulation result is obtained; Performing a radiation interference test on the PCB to be predicted and obtaining a radiation interference test result; The radiation interference simulation result is compared with the radiation interference test result. If the error is greater than a preset radiation interference accuracy threshold, the radiation interference model is adjusted until the error is less than the preset radiation interference accuracy threshold.

4. The modeling and simulation method for predicting PCB conducted interference and radiated interference as claimed in claim 1, characterized in that: The conducted interference test system model is a LISN model. When establishing the LISN model, a power supply model for simulating the power supply state is established.

5. The modeling and simulation method for predicting PCB conducted interference and radiated interference as claimed in claim 1, characterized in that: The step of establishing the trace equivalent model includes: performing S parameter simulation of the trace for the key signal lines of the PCB to be predicted; extracting the equivalent SPICE model of the PCB to be predicted as the trace equivalent model; wherein the key signal lines include clock signal lines and CAN signal lines.

6. The modeling and simulation method for predicting PCB conducted interference and radiated interference as claimed in claim 1, characterized in that: The step of extracting the excitation source signal of the PCB to be predicted includes: measuring the key PIN pin signal of the key chip on the PCB to be predicted; converting the measured time domain signal into a frequency domain signal; determining the excitation source signal according to the frequency and amplitude of the frequency domain signal; wherein the key chip includes a switching power supply chip and a CAN transceiver chip, and the key PIN pin signal is a high-frequency PIN pin signal.

7. The modeling and simulation method for predicting PCB conducted interference and radiated interference as claimed in claim 1, characterized in that: The parasitic parameter model includes three groups of LC circuits, and the values ​​of the three groups of LC circuits are respectively determined by the parasitic inductance and capacitance calculation formulas between the predicted PCB and the metal desktop, the predicted PCB external long wire to the ground, and the predicted PCB external short wire to the ground.

8. The modeling and simulation method for predicting PCB conducted interference and radiated interference as claimed in claim 1, characterized in that: The specified frequency is determined by the current clamp cut-off frequency.

9. The modeling and simulation method for predicting PCB conducted interference and radiated interference as claimed in claim 1, characterized in that: The radiation interference field model includes an antenna model, a test table model and a cable model built based on the GB / T 18655-2018 standard.

10. The modeling and simulation method for predicting PCB conducted interference and radiated interference according to claim 9, characterized in that: The radiation interference simulation scheme adopted in the first frequency band includes the following steps: obtaining a common mode current as an excitation source by a measurement method; performing a frequency domain product operation on the excitation source and a transfer function of a conducted interference test system in the radiation interference model to obtain a receiving voltage distribution at an antenna port; performing a frequency domain operation on the receiving voltage and an antenna coefficient respectively to obtain a radiation interference frequency domain distribution reflecting the electric field strength and use it as a radiation interference simulation result of the first frequency band; The radiation interference simulation scheme adopted in the second frequency band includes the steps of: obtaining common mode current simulation results through the field-circuit joint model; The simulation result is substituted into the radiation interference model as an excitation source and a time domain simulation is performed to obtain the electric field intensity distribution at the receiving probe, which is used as the radiation interference simulation result of the second frequency band.

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