Radiated Emissions

Radiated emissions are unwanted electromagnetic disturbances that are emitted into free space from electronic devices. These emissions can cause interference with nearby equipment and must be controlled to ensure electromagnetic compatibility (EMC) in residential, commercial, and industrial environments.

Radiated emissions testing is required for devices with high-speed digital circuits, switching power supplies, or any equipment that generates electromagnetic fields during normal operation. Compliance with radiated emission standards is essential for product approval in regulated markets worldwide.

Why Radiated Emissions Matter

Electronic devices with fast switching signals, high clock frequencies, or inadequate shielding can radiate electromagnetic energy that interferes with other equipment. Without proper design measures, these emissions may:

• Disrupt radio communications or wireless devices

• Cause malfunctions in sensitive electronic equipment

• Violate regulatory emission limits

Regulatory Impact:

• Products exceeding radiated emission limits cannot be sold in regulated markets

• Redesigning products after production is costly and time-consuming

• Pre-compliance testing helps identify issues early in the development cycle

Measurement Setup

Test Environment

Radiated emission measurements are performed in controlled electromagnetic environments:

• Semi-Anechoic Chamber (SAC): Shielded room with RF-absorbing materials on walls and ceiling, conductive floor for ground plane

• Fully Anechoic Room (FAR): Complete RF absorption on all surfaces, used for antenna pattern and wireless device testing

• Open Area Test Site (OATS): Outdoor or large indoor space with minimal reflections, calibrated for compliance testing

Required Equipment

• Measurement antennas (biconical, log-periodic, or horn antennas depending on frequency)

• EMI receiver or spectrum analyzer

• Turntable for rotating the device under test (DUT)

• Antenna mast with adjustable height (typically 1 to 4 meters)

• Shielded environment to eliminate external interference

Test Procedure

1. The DUT is placed on a turntable at a specified distance (typically 3 m, 10 m, or 30 m depending on equipment size and test site)

2. The device operates in normal or worst-case modes

3. Emissions are measured across the specified frequency range (typically 9 kHz to 6 GHz or higher)

4. The antenna height and DUT orientation are varied to find maximum emission levels

5. Results are compared against applicable limits

Frequency Range and Limits

Radiated emissions are typically assessed from 9 kHz to 6 GHz or higher, with measurement results expressed in dBµV/m (electric field strength).

Limits vary depending on:

• Product category (e.g., residential, industrial)

• Measurement distance (3m, 10m or 30m)

• Operating environment classification

Applicable Standards

Radiated emission limits are defined in regional and international standards:

Europe:

• EN 55032 (CISPR 32) – Multimedia equipment

• EN 61000-6-3 – Generic standard for residential, commercial, and light industrial environments

• EN 61000-6-4 – Generic standard for industrial environments

United States:

• FCC Part 15 Subpart B – Unintentional radiators (§15.109, §15.209)

International:

• CISPR 11 – Industrial, scientific, and medical equipment

• CISPR 22 – Information technology equipment (superseded by CISPR 32)

Common Causes of Non-Compliance

Typical sources of excessive radiated emissions include:

• High-speed digital signals without proper filtering or termination

• Inadequate enclosure shielding (gaps, seams, ventilation openings)

• Unshielded or poorly routed internal cables

• PCB layout issues (long signal traces, inadequate ground planes)

• Missing or ineffective cable shielding and connector grounding

Design Recommendations:

• Use proper PCB layout techniques (ground planes, controlled impedance)

• Shield enclosures with conductive gaskets at seams and openings

• Apply ferrite beads or common-mode chokes to cables

• Implement proper cable routing and shielding practices

• Filter high-speed signals at enclosure penetrations

Addressing these issues during the design phase significantly reduces the risk of compliance failures during formal testing.

Need radiated emission testing? Our ISO 17025 accredited laboratory performs EMC compliance testing to CISPR, EN, and FCC standards in fully equipped anechoic chambers: → EMC Testing