Semi-Anechoic vs Fully Anechoic Chamber: Which Test Goes Where?
We compare the semi-anechoic chamber, with its reflective floor, and the fully anechoic chamber, with absorbers on every surface, and where each is used.
3 min readOctober 21, 2026
Reflection as a Tool, Not a Problem
In an anechoic chamber the aim is to eliminate reflections. A reverberation chamber does the opposite: metal walls without absorbers reflect the signal over and over, creating a strong, complex field inside.
Large rotating metal paddles in the middle, called stirrers, constantly change this field. Averaged over a period, the device under test has been exposed to the field equally from every direction and in every polarization.
Advantages
Far less amplifier power is needed than in an anechoic chamber to reach the same field strength. Because the walls don't absorb energy, the chamber behaves like a resonator and high fields can be produced with little power.
This makes it economical to reach the very high field strengths required in military and aerospace testing. And since the device receives the field from all directions, the test doesn't need repeating at different angles.
Which Tests Use It?
IEC 61000-4-21 defines emission and immunity tests performed in a reverberation chamber. MIL-STD-461 and RTCA DO-160 also accept this method as an alternative for some tests. It is also used to measure the total radiated power of wireless devices.
But it isn't suitable for every test. Measurements needing directional information, such as antenna patterns, can only be done in a fully anechoic chamber. Most civilian certification tests still require a semi-anechoic chamber.
Limitations
A reverberation chamber can't create a uniform field below its lowest usable frequency. This frequency depends on chamber size; reaching low frequencies requires a large chamber.
When deciding, the standards in your test plan, the frequency range and the target field strength should be assessed together. In some labs the same shielded shell can serve both purposes by fitting and removing absorbers.
Frequently Asked Questions
Is a reverberation chamber cheaper than an anechoic one?
It's usually more economical since there are no absorber costs, but the stirrer mechanism and measurement software require extra investment.
Can the same chamber serve both purposes?
It's possible with removable absorbers, but performance in each mode must be validated separately.
How is the lowest usable frequency calculated?
It's estimated from the resonant modes that depend on chamber dimensions; the exact value is verified by measurement.
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