Types of RE Testing
RE testing splits into distinct measurement types by frequency range and field type, and is performed in one of three standardized test environments. Choosing the right combination of test type and environment is essential to getting repeatable, standards-compliant results. This module shows exactly how each test type is physically performed and what each environment looks like inside.
Four core test types cover the full frequency and field-type range a product might need to be evaluated against:
| Test Type | Frequency Range | Application / Notes |
|---|---|---|
| Standard Radiated Emission Test | 30 MHz – 1 GHz | Measures electric field strength. Consumer electronics, industrial equipment, medical equipment, automotive ECUs. |
| High Frequency Radiated Emission | 1 GHz – 18 GHz | Measures emissions above 1 GHz. High-speed digital electronics, FPGA systems, DDR4/DDR5, PCIe, USB 3.x, WiFi products. |
| Magnetic Field Emissions | 9 kHz – 30 MHz | Used for SMPS, transformers, inductive chargers. Measured using loop antennas. |
| Electric Field Emissions | 30 MHz – 40 GHz | Measured using biconical, log periodic, and horn antennas. |
The EUT sits on a turntable, and a biconical or log-periodic antenna on a motorized mast measures the E-field it radiates from 30 MHz to 1 GHz. The antenna height sweeps (typically 1–4 m) and the turntable rotates 360° while the receiver records the maximum reading at each frequency — because the true worst-case emission angle and height are not known in advance.
Above 1 GHz, wavelengths shrink to a few centimeters, so a horn antenna — a directional, higher-gain antenna shaped like its name — replaces the biconical/log-periodic antennas used below 1 GHz. The setup is otherwise similar (turntable rotation, height scan) but the measurement distance is often reduced and a spectrum analyzer or EMI receiver with a wider frequency range is required. This test type exists specifically because modern high-speed digital buses (DDR4/DDR5, PCIe, USB 3.x) and WiFi/5G radios push harmonic energy well above 1 GHz.
Below 30 MHz, a source's near-field is dominated by magnetic (H-field) coupling rather than a fully formed propagating wave (recall Module 01's near-field/far-field discussion). A shielded loop antenna is held close to the EUT — often scanned directly across the surface of an SMPS, transformer, or inductive charging coil — because the loop's own magnetic sensitivity peaks exactly where a true far-field antenna would be least effective at this frequency range.
Electric field testing is the broadest category, spanning 30 MHz all the way to 40 GHz, and is really three antenna technologies covering different sub-ranges of that span: a biconical antenna for the lower VHF range (roughly 30–300 MHz), a log-periodic antenna for the upper VHF/UHF range (roughly 200 MHz–1 GHz, deliberately overlapping the biconical's top end), and a horn antenna above 1 GHz. Test engineers physically swap antennas partway through a frequency sweep to stay matched to the antenna each is most efficient in.
RE measurements must be made in a controlled environment that suppresses reflections and external ambient signals. Three environments are in common use:
| Environment | Advantages | Disadvantages | Typical Use |
|---|---|---|---|
| Open Area Test Site (OATS) | Accurate, standardized | Weather dependent, large land requirement | Reference-grade compliance measurements |
| Semi-Anechoic Chamber (SAC) | Indoor, repeatable, fast, shielded | Higher facility cost than OATS | Most common commercial EMC lab |
| Fully Anechoic Chamber (FAC) | Highest measurement accuracy | Most expensive, largest chamber footprint | Military, automotive, antenna measurements |
Open Area Test Site (OATS)
An OATS is an outdoor, flat metallic ground plane, free of nearby reflective structures, with the EUT and antenna mast positioned at a fixed measurement distance. It is the historical reference environment against which chamber-based correlations are validated.
Semi-Anechoic Chamber (SAC)
A SAC is a shielded room lined with pyramidal RF-absorbing foam on the walls and ceiling to suppress reflections, but with a solid metallic floor left exposed — deliberately reproducing the reflective ground plane of an OATS indoors, where weather and ambient RF are no longer a factor.
Fully Anechoic Chamber (FAC)
A FAC absorbs reflections on every surface, including the floor (typically via a suspended mesh floor with absorber beneath it), eliminating the ground-plane reflection entirely. This models true free-space radiation and is preferred for antenna measurements and product categories tested without a ground-plane reflection assumption.
Module 4 Quiz
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