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What is an anechoic chamber?

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An anechoic chamber is a shielded enclosure lined with RF absorbing material so that waves striking the walls are absorbed rather than reflected, approximating free-space conditions in a central quiet zone where the antenna under test is placed. Pyramidal carbon-loaded foam absorbers are used for microwave frequencies and ferrite tiles or hybrid absorbers at low frequencies; quiet-zone reflectivity of −30 to −50 dB is typical of good chambers.[1][2]

How do absorbers work?

Pyramidal absorbers taper the impedance gradually from free space into a lossy carbon-loaded medium, minimizing reflection; their performance improves as pyramid height increases relative to wavelength, so low-frequency performance requires tall absorbers or ferrite tiles. Wedge absorbers guide waves in tapered chambers.[1]

What chamber shapes exist?

How is a chamber validated?

Free-space VSWR or field-probe methods move a probe antenna through the quiet zone and record ripple, from which reflectivity is estimated. EMC chambers (semi-anechoic with a ground plane) are validated by site attenuation methods instead.[1]

Frequently asked questions

Is an EMC chamber the same as an antenna chamber?

EMC chambers are often semi-anechoic with a reflective floor; antenna chambers are fully anechoic.

Why are chambers shielded?

To keep external signals out and test emissions in.

What limits low-frequency testing?

Absorber depth and chamber size relative to wavelength.

References

Online sources accessed October 21, 2026; printed works cited by edition. See all sources.

  1. “IEEE Recommended Practice for Antenna Measurements (IEEE Std 149-2021)”. IEEE Antennas and Propagation Society. 2022.
  2. “Antenna Engineering Handbook, 4th ed.”. J. L. Volakis (ed.), McGraw-Hill. 2007.
Categories: Measurement