What Is NSA? Validating an Anechoic Chamber to CISPR 16
What the NSA (normalized site attenuation) measurement is and how it is done to show a semi-anechoic chamber is fit for emission testing.
3 min readOctober 20, 2026
Semi-Anechoic Chamber (SAC)
In a semi-anechoic chamber the walls and ceiling are covered with absorbing material, while the floor is metal and reflects the signal. This setup is the indoor equivalent of an open area test site that mimics the product's real environment.
Most of the emission and immunity tests for certifications such as CE are performed in semi-anechoic chambers. They are named SAC-3, SAC-5 and SAC-10 after the test distance.
Fully Anechoic Chamber (FAR)
In a fully anechoic chamber every surface, including the floor, is covered with absorbers. There are no reflections from any surface; the antenna is measured as if it were in truly empty space.
It is preferred for measuring antenna gain, pattern performance and the over-the-air performance of wireless devices.
Which One Should I Choose?
If you are preparing your product for certification testing, you usually need a semi-anechoic chamber. If you measure antenna or wireless performance, a fully anechoic chamber is the right choice.
Some chambers can serve both purposes by adding removable absorbers to the floor. Reviewing your test plan together is the soundest way to decide.
Budget and Building Impact
The choice between the two chamber types sets not only the test type but also building needs. A semi-anechoic chamber has no floor absorbers, so internal volume is used more efficiently for the same test distance; in a fully anechoic chamber, floor absorbers add height.
Absorber type affects cost too. Ferrite and pyramid absorbers perform differently at different frequencies. You can review typical sizes on our semi-anechoic chamber and fully anechoic chamber pages.
Frequently Asked Questions
Can antenna measurements be done in a semi-anechoic chamber?
Some can, with temporary absorbers on the floor, but precise pattern measurements need a fully anechoic chamber.
Can a fully anechoic chamber be used for EMC certification?
Some standards allow it for certain tests, but most emission standards require a semi-anechoic chamber.
Which one costs more?
For the same volume, a fully anechoic chamber usually costs more because of floor absorbers.
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