What is Artificial Network in EMC?

Abstract:Understanding what is artificial network in EMC testing is fundamental to conducting reproducible conducted electromagnetic interference (EMI) measurements. An artificial network, also known as a line impedance stabilization network (LISN), provides a standardized impedance interface between the power mains and the equipment under test (EUT).

This paper presents a technical analysis of artificial networks, covering operational principles, regulatory standards (CISPR 16-1-2, CISPR 15, EN55022), and engineering design considerations. The discussion includes impedance stabilization, isolation requirements, and coupling mechanisms. Furthermore, the LISUN LISN series is examined as a practical implementation, with models ranging from 5 A to 200 A, covering both single-phase and three-phase applications across the 9 kHz to 30 MHz frequency range. The paper concludes with selection guidelines for EMC test laboratories.

1. Introduction

Conducted emissions testing is a critical part of electromagnetic compatibility (EMC) compliance for electronic products. However, the impedance of real-world power lines varies with location and time, making direct measurements unrepeatable. The artificial network—often referred to as a line impedance stabilization network (LISN)—solves this problem by presenting a defined, stable impedance to the EUT across the frequency range of interest (typically 9 kHz to 30 MHz). It also isolates the measurement from mains-borne noise and couples the interference signals to the EMI receiver. This paper explores the technical foundations of artificial networks, the relevant international standards, and the engineering considerations that ensure accurate and repeatable conducted emission measurements.

LISN-C Artificial Network | Line Impedance Stabilization Network

2. Regulatory Standards Framework

2.1 CISPR 16-1-2: The Core Specification

CISPR 16-1-2 is the basic standard that defines the performance requirements for artificial networks. It specifies the nominal impedance (50 Ω), impedance tolerance, isolation (insertion loss), and coupling characteristics. All compliant LISNs must meet these requirements over the designated frequency range. The standard also covers asymmetric artificial networks (AANs) and coupling/decoupling networks for emissions (CDNE) for higher frequencies.

2.2 Product-Specific Emission Standards

Product families reference CISPR 16-1-2 for the measurement apparatus while setting their own emission limits. For example:

• CISPR 15 / EN55015 applies to lighting equipment.
• CISPR 32 / EN55022 applies to information technology equipment.
• GB 17743-2007 is the Chinese equivalent for lighting equipment.
• FCC Part 15 in the United States also requires LISNs meeting CISPR 16-1-2.

Artificial networks used for compliance testing must be validated against these standards; the LISUN LISN series explicitly states compliance with CISPR 16-1-2, FCC, EN55015, and EN55022.

3. Core Technical Principles

3.1 Impedance Stabilization and Network Topology

The artificial network presents a 50 Ω impedance to the EUT across the measurement band. This is achieved by a V-network topology consisting of a series inductor (typically 50 μH or 250 μH) and shunt capacitors, terminated by a 50 Ω resistor at the measurement port. The inductor blocks RF noise from the mains while passing power frequency current; the capacitors provide a low-impedance path to ground for RF signals. The LISUN LISN series implements a 50 Ω/50 μH network (with an additional 5 Ω in single-phase models) to meet CISPR 16-1-2 requirements.

3.2 Isolation and Filtering Performance

Isolation (or insertion loss) quantifies how well the network attenuates noise coming from the mains side. CISPR 16-1-2 mandates minimum isolation values (e.g., >60 dB above 150 kHz). High isolation ensures that ambient mains noise does not affect the measurement of EUT emissions. The filter network within the LISN, combining the series inductor and shunt capacitors, provides this isolation. Professional LISNs use carefully designed inductors (often air-core) to maintain linearity and avoid saturation at high currents.

3.3 Coupling and Measurement Port

The interference voltage generated by the EUT is coupled to the 50 Ω measurement port via a capacitive divider. The port must maintain precise 50 Ω impedance to match the EMI receiver input and prevent reflections. Coupling capacitors must have low equivalent series resistance (ESR) and inductance (ESL) to ensure flat frequency response. The LISUN LISN series is designed with high-quality components to preserve signal integrity across the 9 kHz–30 MHz band.

4. Equipment Engineering Design Requirements

Designing a precision artificial network requires careful attention to component selection, mechanical layout, and grounding.

Inductors: Air-core inductors are preferred to avoid saturation and non-linearities, especially at high currents. Multi-layer air-core designs must minimize inter-winding capacitance to keep self-resonance above 30 MHz.

Capacitors: Metallized polypropylene film capacitors are commonly used for mains blocking due to low ESR and high insulation resistance. Coupling capacitors require stable dielectric materials (e.g., ceramic) with low voltage coefficient.

Grounding: Low-inductance bonding to the ground plane is essential. Chassis should have multiple ground studs, and braided straps are used instead of wire for connections.

Thermal management: High-current models (e.g., 100 A, 200 A) require adequate heat dissipation to prevent drift in component values.

5. Practical Implementation: LISUN LISN Series

The LISUN LISN series offers a range of artificial networks covering diverse testing needs, from low-power single-phase equipment to high-power three-phase industrial machinery. Table 1 summarizes the key specifications of the series, as provided in the product documentation.

Table 1. LISUN LISN Series Specifications

All models comply with CISPR 16-1-2, CISPR 15, EN55015, EN55022, and FCC requirements. The LISN-C (16 A single-phase) is a common choice for general consumer electronics, while the LISN-T series addresses three-phase equipment such as industrial drives and large lighting systems. The frequency range for three-phase models starts at 150 kHz, consistent with typical conducted emission limits for such equipment. Each unit is supplied with a calibration certificate verifying its impedance and isolation characteristics.

6. Discussion: Selection Guidelines for Test Laboratories

When selecting an artificial network, engineers should consider:

• Current and voltage ratings: Must exceed the EUT’s maximum ratings, including inrush current.
• Frequency range: Ensure it covers all required measurement bands (e.g., 9 kHz–30 MHz for most commercial standards; 150 kHz–30 MHz for three-phase equipment).
• Phase configuration: Single-phase vs. three-phase depending on the EUT.
• Impedance network: Verify that the network meets the 50 Ω/50 μH (or other required) specification.
• Calibration and traceability: Choose models with accredited calibration certificates to maintain measurement integrity.
• Grounding and integration: Consider physical layout and connection to the ground plane to minimize parasitic effects.

The LISUN series provides a comprehensive portfolio, allowing laboratories to select the appropriate model based on these criteria. For example, a lab testing primarily single-phase IT equipment would find the LISN-C suitable, while a lab testing three-phase industrial products would opt for the LISN100A-T or LISN200A-T.

7. Conclusion

For those seeking clarity on what is artificial network in EMC, it serves as an essential tool for reproducible conducted emissions testing, providing a standardized impedance interface, isolation from mains noise, and proper coupling to the measurement receiver. Compliance with CISPR 16-1-2 and product-specific standards such as CISPR 15 and EN55022 is mandatory for valid test results. Engineering considerations—including inductor linearity, capacitor quality, grounding, and thermal management—directly impact measurement accuracy. The LISUN LISN series exemplifies a well-engineered product line that meets these requirements across a wide range of currents and phase configurations, supporting EMC laboratories in achieving reliable compliance data.