Automotive component radiated emission testing measures the unwanted electromagnetic energy that electronic sub-assemblies (ESAs) such as ECUs, traction inverters, and infotainment modules emit into the surrounding space, ensuring they do not interfere with onboard radio receivers or safety-critical electronics. Conducted in accordance with CISPR 25, UN ECE Regulation No. 10, and their national adoptions such as GB 18655, this testing is a mandatory step in vehicle EMC homologation and OEM supplier approval. This article explains the principles, sample types, test items, measurement methods, and practical considerations involved in radiated emission (radiated disturbance) testing for automotive parts.
Technical Overview
Radiated emission testing, also known as radiated disturbance testing, evaluates the electromagnetic noise that an automotive component or module unintentionally propagates through free space. Fast-switching semiconductors, clock circuits, motor commutation, and wireless transmitters all generate high-frequency currents that couple onto harnesses, printed circuit boards, and enclosure seams, turning them into efficient antennas. If left uncontrolled, these disturbances can degrade or completely block the reception of AM/FM and DAB broadcast services, GNSS positioning, cellular connectivity, tire-pressure monitoring, and keyless-entry systems operating within the same vehicle.
The regulatory and engineering framework for this testing is built on several complementary documents. CISPR 25, published by the IEC special committee on radio interference, defines the measurement methods and graded limit classes (Class 1 through Class 5) for components and modules intended for installation on vehicles. UN ECE Regulation No. 10 makes these measurements part of the legal type-approval process for electrical and electronic sub-assemblies placed on the market in many regions. National adoptions such as GB 18655 in China apply essentially the same methodology, while vehicle manufacturers typically impose their own corporate EMC specifications derived from these standards with additional severity or frequency extensions.
In practice, radiated emission testing is performed inside absorber-lined shielded enclosures (ALSE) at accredited third-party laboratories or in-house EMC facilities. The test yields a frequency-domain spectrum of the electric field strength produced by the component and its representative harness, which is compared against the applicable limit lines. A successful test supports EMC type approval, supplier release, and trouble-free integration of the component into the vehicle electrical architecture.
Testing Samples
Virtually every electronic or electromechanical part installed on a modern vehicle may be subject to radiated emission testing. Typical sample categories and their EMC characteristics are summarized below.
Electronic Control Units and Body Electronics
Engine management controllers, transmission controllers, body control modules, gateways, and instrument clusters contain high-speed microprocessors and CAN, LIN, or Ethernet transceivers. Their dominant emission sources are crystal harmonics and fast digital edges coupling onto the wire harness.
Electric Drive and Power Electronics
Traction inverters, DC-DC converters, on-board chargers, and battery management systems use IGBT or silicon-carbide switching stages operating at tens of kilohertz with very fast rise times. These components generate strong broadband disturbances concentrated at the switching frequency and its harmonics, often extending into the hundreds of megahertz, and are among the most challenging samples to certify.
Infotainment and Connectivity Modules
Head units, displays, telematics control units, Wi-Fi, Bluetooth, and cellular modules, GNSS receivers, and DAB tuners combine intentional RF transmitters with noisy digital basebands. Testing must verify both the spurious out-of-band emissions of the radio function and the broadband noise of the digital circuitry.
ADAS Sensors and Safety Electronics
Cameras, millimeter-wave radar, LiDAR, ultrasonic park-assist sensors, and airbag or brake controllers must demonstrate particularly low emission levels because they are frequently mounted close to sensitive receivers and because self-interference could compromise safety functions.
Motors, Actuators, and Lighting
Fuel pumps, wiper motors, HVAC blowers, seat and mirror actuators, LED drivers, and headlamp modules generate brush or PWM-related noise. Aftermarket and retrofit electronic devices also fall within the scope of component-level emission requirements when installed on a vehicle.
For a meaningful evaluation, laboratories typically request two to four production-intent samples, the actual or representative wiring harness, the specified electrical loads, and documentation of the operating mode and firmware to be exercised during the test.
Testing Items
The core deliverable of radiated emission testing is a measured electric field spectrum compared with the limit lines of the applicable standard and limit class. The measurement program is typically structured as follows.
- Radiated emissions from 150 kHz to 30 MHz, measured with a vertical monopole (rod) antenna placed 1 m from the test setup, covering long-wave, medium-wave, and short-wave broadcast bands.
- Radiated emissions from 30 MHz to 300 MHz, measured with a biconical antenna in both horizontal and vertical polarization, covering VHF broadcast and land-mobile services.
- Radiated emissions from 300 MHz to 1000 MHz, measured with a log-periodic or bilog antenna in both polarizations, covering UHF broadcasting, cellular, and GNSS-related bands.
- Radiated emissions from 1 GHz to 2.5 GHz (extendable to approximately 6 GHz where OEM specifications or on-board transceiver bands require), measured with double-ridge horn antennas.
- Band-by-band evaluation against limit lines aligned with specific victim services, such as AM/FM/DAB audio bands, GNSS frequencies, and cellular uplink and downlink allocations.
- Peak, quasi-peak, and average detector measurements, with final compliance judged against the quasi-peak and average limits defined in CISPR 25.
- Complementary conducted measurements frequently executed in the same campaign, including conducted voltage disturbances on supply lines from 150 kHz to 108 MHz and transient conducted emissions per ISO 7637-2.
Testing Methods
ALSE Method (Absorber-Lined Shielded Enclosure)
The ALSE method is the reference technique for component radiated emissions. The equipment under test is placed on a low-permittivity support 50 mm above a grounded reference plane mounted on a 900 mm high bench, with its power and signal harness arranged parallel to the plane edge. Power is fed through artificial networks (50 µH / 50 Ω) bonded to the ground plane, which provide a defined RF impedance and isolate the laboratory mains. Antennas are positioned 1 m from the harness, and the chamber walls are lined with ferrite tiles and pyramidal absorbers to suppress reflections and approximate free-space conditions. Limit classes from Class 1 (most lenient, distant from receivers) to Class 5 (most stringent, close to sensitive receivers) are selected according to the intended installation location and OEM requirements.
TEM Cell Method
The transverse electromagnetic (TEM) cell method places the component inside a terminated transmission-line structure and measures the total power coupled to the cell output across the 150 kHz to 1 GHz range. The method offers compact, reproducible screening of small modules and is particularly useful for comparison measurements during development, although sample size is constrained to approximately one third of the cell height to preserve measurement validity.
Stripline Method
The stripline method routes the component harness between parallel conductor plates and captures the energy radiated by the wiring. It complements the TEM cell for samples whose dimensions are dominated by the cable bundle rather than the module itself, covering a comparable frequency range with good sensitivity to common-mode harness currents.
Measurement Procedure and Detector Requirements
A standard test sequence begins with an ambient noise verification with the EUT de-energized, followed by a fast peak-detector pre-scan across the full frequency range to identify candidate disturbance frequencies. At each identified frequency, final measurements are performed with quasi-peak and average detectors in accordance with CISPR 16-1-1. The component is exercised in its representative operating modes defined by the manufacturer, at nominal supply voltage, and results are recorded as field strength levels with margins against the applicable class limits. If limit violations are observed, laboratories can usually support near-field probing and troubleshooting to localize the emission mechanism.
Applications
Radiated emission test results for automotive components are used across the entire product lifecycle.
- Regulatory type approval of electrical and electronic sub-assemblies under UN ECE Regulation No. 10, enabling the E-mark certification required for market access in many regions.
- Compliance demonstration against national standards such as GB 18655 and GB 34660 for products sold in China.
- OEM supplier release and design sign-off, where manufacturer-specific EMC specifications demand CISPR 25 Class 3 to Class 5 performance or extended frequency coverage.
- Development and pre-compliance screening of new designs, allowing early detection of emission risks before formal certification.
- Verification of electric and hybrid vehicle powertrain components, where inverter and converter noise management is critical for receiver coexistence.
- Root-cause analysis and re-qualification after design changes such as new PCB layouts, firmware updates, alternative components, or modified shielding and filtering.
- Market surveillance support and after-sales investigation of field interference complaints involving aftermarket or retrofit electronic devices.
FAQ
What is the difference between radiated and conducted emission testing?
Radiated emission testing measures electromagnetic energy propagated through space from the component and its harness, whereas conducted emission testing measures disturbances injected directly onto power or signal lines through an artificial network. Both are typically required together for a complete CISPR 25 or UN R10 assessment.
Which frequency range is covered by component radiated emission testing?
The standard measurement range of CISPR 25 extends from 150 kHz to 2.5 GHz. Depending on the applicable regulation or OEM specification, coverage can be extended up to approximately 6 GHz to include on-board transceiver services and high-speed digital interfaces.
How is the correct limit class selected?
Limit classes depend on the proximity of the component to protected receivers in the vehicle. Class 5 applies to parts installed very close to antennas or satellite receivers, Class 4 and Class 3 to typical in-cabin and engine-bay installations, and Class 1 or 2 to locations far from any receiver. The OEM specification ultimately determines the required class.
Which components require UN ECE Regulation No. 10 approval?
Electronic sub-assemblies that are placed on the market as separate technical units, or whose EMC performance can be assessed independently of a specific vehicle, generally require ESA type approval under UN R10. This approval references CISPR 25 methods for the emission part of the assessment and ISO 11452 series methods for immunity.
How long does a radiated emission test take?
A complete component-level campaign, including setup, multiple operating modes, and both radiated and conducted measurements, typically takes one to three working days in the chamber, with reports issued within one to two weeks depending on laboratory scheduling and the complexity of the sample.
What should be done if the component exceeds the limit lines?
Common corrective measures include improving PCB grounding and partitioning, adding or repositioning decoupling capacitors and common-mode chokes, shielding the enclosure or harness, slowing digital edge rates, and adjusting switching frequencies or spread-spectrum modulation in power stages. An accredited third-party laboratory can support near-field scans to pinpoint the dominant radiation source before redesign.