The Role and Application of LISN Coupling/Decoupling Network in Radiation Testing

Abstract: This paper focuses on the LISN (Line Impedance Stabilization Network) coupling/decoupling network used in radiation testing, with a particular emphasis on its application in the LISUN EMI – 9KB EMI Test Receiver system. It comprehensively analyzes the working principle, structure, performance characteristics, and practical application scenarios of the LISN coupling/decoupling network. Through detailed theoretical analysis and experimental data, the importance and effectiveness of this network in electromagnetic interference (EMI) radiation testing are demonstrated, providing valuable reference for relevant research and engineering applications.

1. Introduction

In the field of electromagnetic compatibility (EMC), accurately measuring and evaluating electromagnetic interference is of crucial significance. The LISUN EMI – 9KB EMI Test Receiver is an important device for conducting EMI radiation conduction or conducted emissions testing. Among its components, the LISN coupling/decoupling network plays a vital role in ensuring the accuracy and reliability of test results.

The LISN coupling/decoupling network, also known as the Line Impedance Stabilization Network, is designed to provide a stable impedance environment for the Equipment Under Test (EUT) and separate the test signals from the power supply. This helps to accurately measure the electromagnetic emissions from the EUT, whether they are radiated or conducted. In radiation testing, the LISN coupling/decoupling network works in conjunction with other components of the test system, such as antennas and receivers, to capture and analyze the electromagnetic signals emitted by the EUT.

2. Working Principle of LISN Coupling/Decoupling Network

The basic working principle of the LISN coupling/decoupling network is to create a well-defined impedance at the input of the EUT and to prevent the interference from the power supply network from affecting the test results. It consists of a series of inductors, capacitors, and resistors, which are configured to form a specific impedance network.

When the EUT is connected to the LISN coupling/decoupling network, the network presents a stable 50Ω (or other standard impedance values depending on the test requirements) impedance to the EUT over a specified frequency range. This ensures that the emissions from the EUT are accurately measured without being distorted by impedance mismatches. At the same time, the LISN coupling/decoupling network decouples the power supply from the test circuit, preventing the power supply noise from interfering with the measurement of the EUT emissions.

In radiation testing, the LISN coupling/decoupling network is often used in combination with an antenna. The electromagnetic waves radiated by the EUT are received by the antenna and then fed into the LISN coupling/decoupling network. The network processes the received signals and sends them to the EMI receiver for analysis. Table 1 shows the typical impedance values provided by the LISN coupling/decoupling network at different frequencies.

Frequency Range	Impedance Value
9kHz – 150kHz	50Ω ± 2Ω
150kHz – 30MHz	50Ω ± 3Ω
30MHz – 300MHz	50Ω ± 5Ω

3. Structure and Components of LISN Coupling/Decoupling Network

The LISN coupling/decoupling network usually consists of several key components. The inductors and capacitors are used to form resonant circuits to achieve the desired impedance characteristics at different frequencies. Resistors are used to control the impedance and absorb excess energy.

In addition, the LISN coupling/decoupling network also includes connectors and shielding structures. The connectors ensure a reliable electrical connection between the EUT, the power supply, and the test equipment. The shielding structure is designed to prevent external electromagnetic interference from affecting the performance of the network. Figure 1 shows a schematic diagram of the LISN coupling/decoupling network.

4. Performance Characteristics of LISN Coupling/Decoupling Network in Radiation Testing

4.1 Frequency Response

The frequency response of the LISN coupling/decoupling network is an important performance index. It determines the accuracy of the network in measuring electromagnetic emissions over a wide frequency range. The LISN coupling/decoupling network used in the LISUN EMI – 9KB EMI Test Receiver system has a flat frequency response within the operating frequency range of the receiver, which is 9kHz – 300MHz for the EMI – 9KB model. Figure 2 shows the frequency response curve of the LISN coupling/decoupling network.

4.2 Insertion Loss

Insertion loss refers to the power loss of the signal when passing through the LISN coupling/decoupling network. A low insertion loss is desirable to ensure that the test signals are accurately transmitted to the receiver. The LISN coupling/decoupling network in the LISUN EMI – 9KB system has an insertion loss of less than 0.5dB within the operating frequency range, which minimizes the impact on the test results. Table 2 shows the insertion loss values at different frequencies.

Frequency	Insertion Loss
30kHz	0.3dB
1MHz	0.4dB
10MHz	0.45dB
100MHz	0.5dB

4.3 Isolation Performance

The isolation performance of the LISN coupling/decoupling network is crucial in preventing the interference between the power supply and the test circuit. The network should provide a high isolation degree to ensure that the power supply noise does not affect the measurement of the EUT emissions. The LISN coupling/decoupling network used in the LISUN EMI – 9KB system has an isolation performance of more than 40dB between the power supply and the test port, effectively reducing the impact of power supply noise.

5. Application of LISN Coupling/Decoupling Network in LISUN EMI – 9KB EMI Test Receiver System

5.1 Conducted Emissions Testing

In conducted emissions testing, the LISN coupling/decoupling network is connected between the power supply and the EUT. It provides a stable impedance environment for the EUT and measures the conducted emissions from the EUT. The LISN coupling/decoupling network in the LISUN EMI – 9KB system can accurately measure the conducted emissions within the frequency range of 9kHz – 300MHz, meeting the requirements of relevant standards such as CISPR15:2018, GB17743, EN55015, and EN55022.

5.2 Radiated Emissions Testing

In radiated emissions testing, the LISN coupling/decoupling network works together with an antenna. The antenna receives the electromagnetic waves radiated by the EUT and feeds them into the LISN coupling/decoupling network. The network then processes the signals and sends them to the EMI receiver for analysis. According to the latest CISPR15:2018 standard, the CDNE – M316 Coupling/Decoupling Network for Emission, which is a type of LISN coupling/decoupling network, should be used instead of the traditional CDN. The CDNE – M316 working with the EMI receiver system is equivalent to testing the radiated electromagnetic disturbance of electric lighting appliances with a frequency from 30MHz to 300MHz.

5.3 Test Results and Analysis

The LISN coupling/decoupling network in the LISUN EMI – 9KB EMI Test Receiver system helps to obtain accurate test results. The test results are presented in an international format test report, which includes information such as the measured emission levels, the frequency range, and the comparison with the relevant standards. By analyzing the test results, engineers can identify the sources of electromagnetic interference and take appropriate measures to improve the electromagnetic compatibility of the EUT.

6. Comparison with Other Similar Networks

There are other types of coupling/decoupling networks available in the market. However, the LISN coupling/decoupling network used in the LISUN EMI – 9KB system has several advantages. Table 3 shows a comparison between the LISN coupling/decoupling network and other similar networks.

Comparison Items	LISN Coupling/Decoupling Network	Other Similar Networks
Frequency Range	Wide (9kHz – 300MHz for EMI – 9KB)	Narrower in some cases
Impedance Stability	High, provides stable 50Ω impedance	May have larger impedance variations
Insertion Loss	Low (less than 0.5dB)	Higher insertion loss in some models
Isolation Performance	Good (more than 40dB)	May have lower isolation degrees

As shown in the table, the LISN coupling/decoupling network has a wider frequency range, better impedance stability, lower insertion loss, and higher isolation performance, making it more suitable for accurate EMI radiation testing.

7. Conclusion

In conclusion, the LISN coupling/decoupling network is an essential component in the LISUN EMI – 9KB EMI Test Receiver system for radiation testing. Its working principle, structure, and performance characteristics ensure the accuracy and reliability of electromagnetic interference measurement. By providing a stable impedance environment, decoupling the power supply, and working in conjunction with other test equipment, the LISN coupling/decoupling network plays a crucial role in both conducted and radiated emissions testing. Compared with other similar networks, it has significant advantages in frequency range, impedance stability, insertion loss, and isolation performance. Future research and development in this area could focus on further improving the performance of the LISN coupling/decoupling network, such as reducing insertion loss and improving isolation performance at higher frequencies, to meet the increasingly stringent requirements of electromagnetic compatibility testing.

Tags：EMI-9KB