One of the most consequential decisions in setting up an EMC test facility is choosing the right chamber type. Get it right and you have a facility that handles your test workload efficiently for decades. Get it wrong and you end up with a chamber that either can't support the standards you need or is significantly over-specified.
Semi-Anechoic Chamber (SAC)
A SAC has RF-absorbing material on the four walls and ceiling, with a conducting ground plane floor — replicating an open-area test site (OATS) inside a shielded enclosure. This is the workhorse of commercial product EMC compliance:
Radiated emission testing (CISPR 16-1-4) at standardised distances (3m, 5m, or 10m).
Radiated immunity testing (IEC 61000-4-3) from 80 MHz to 6 GHz, with field uniformity calibration performed in the SAC beforehand.
Military and defence EMC (MIL-STD-461, GJB151C) — the SAC floor naturally provides the ground plane bonding these standards require.
Automotive EMC (CISPR 25) — vehicle-level testing in a 10m SAC with turntable.
Finch SACs are available in 3m (quiet zone 1.5–8.0m, most widely deployed), 5m (quiet zone 2.0–4.0m, for larger EUT), and 10m (quiet zone 3.0–8.0m, the automotive reference configuration).
Full Anechoic Chamber (FAR)
A FAR has absorbing material on all six surfaces, including the floor — no ground plane. The EUT sits on a low-reflection support stand, producing a genuinely free-space environment, unlike the ground-plane-reflection environment most civil EMC standards assume.
What it's used for: antenna pattern measurement (true free-space radiation pattern without ground-plane confounding), 5G/mmWave OTA testing (TRP/TIS per 3GPP standards), satellite communication testing, radar cross-section measurement, defence system antenna qualification, and compact range testing using a shaped reflector for far-field-equivalent measurements at short distances.
Key distinction from SAC: a FAR cannot be used for conventional CISPR 16-1-4 emission testing, since those methods assume a ground-plane reflection. Many large facilities operate both, or use a convertible design.
Reverberation Chamber
The opposite of an anechoic chamber — highly reflective metal walls with a rotating mechanical stirrer continuously varying field distribution. Averaged over a full rotation, the result is a statistically isotropic, uniform field environment.
What it's used for: radiated immunity testing (IEC 61000-4-21) with all-aspect illumination reducing test time versus repositioning the EUT in a SAC; total radiated power (TRP) measurement; materials shielding effectiveness testing; and aerospace/defence testing where DO-160 Section 20 and MIL-STD-461 RS103 both permit reverberation chambers as SAC alternatives.
LUF — the key specification
Below the lower usable frequency (LUF), the chamber can't support enough electromagnetic modes for statistical uniformity. LUF is determined primarily by chamber size — larger chambers have lower LUF, with options from 80 MHz to 1 GHz available. DO-160 Section 20 (starting at 100 MHz) needs LUF ≤80 MHz; MIL-STD-461 RS103 (starting at 2 MHz) requires supplementary low-frequency methods.
Choosing Between Chamber Types
| Requirement | Recommended chamber |
|---|---|
| CISPR 16-1-4 radiated emissions | SAC (3m, 5m, or 10m) |
| IEC 61000-4-3 radiated immunity | SAC |
| CISPR 25 vehicle-level testing | 10m SAC |
| Antenna pattern / 5G OTA / compact range | FAR |
| IEC 61000-4-21 / DO-160 Section 20 | Reverberation chamber |
| TRP measurement | Reverberation chamber |
Many organisations need more than one chamber type. A defence contractor might operate a SAC for standard compliance, a reverberation chamber for avionics qualification, and access to a FAR for antenna work. A commercial lab typically starts with a 3m SAC and adds capacity as volume grows.
A Note on Microwave and Antenna Chambers
Beyond the three main types, a specialised family exists for RF system characterisation: near-field chambers, far-field chambers, compact range chambers, OTA testing chambers, and complex electromagnetic environment simulation chambers. These are typically custom-engineered to the application.
Talk to Us Before You Specify
The right chamber depends on your test programme, EUT sizes, frequency range, floor space, budget, and future capability plans. Finch EMC chambers are custom-built to specification, working through site survey and design review before fabrication begins.
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