RF Test Equipment Series: RF Anechoic Chambers

RF Test Equipment Series: RF Anechoic Chambers

RF Test Equipment Series: RF Anechoic Chambers

RF anechoic chambers are used throughout the industry for prototyping testing and conformance testing. The purpose of an anechoic chamber is to provide both electromagnetic isolation from external sources as well as from internal RF radiation generators. Other types of testing that require complete RF isolation also depend on anechoic chambers, including radar cross section (RCS) testing.

An anechoic chamber is typically built into a Faraday cage screened room, which shields the interior chamber from external electromagnetic interference (EMI). The interior of an anechoic chamber is typically covered in radiation absorbent materials (RAMs) that are constructed and placed in such a way to absorb incident RF radiation down to a required frequency. RAM material is needed covering the interior walls of anechoic chamber, as without the RAM covering, RF radiation would merely be reflected throughout the chamber.

As the size of the RAM physical features and absorption capabilities are proportional to the lowest wavelength requiring absorption, there are generally physical constraints that limit low frequency performance of an anechoic chamber. For instance, a pyramidal RAM material must be of a height approximately one-quarter of the wavelength of the lowest frequency. As increasing the height of a pyramidal RAM directly increases cost and limits interior working space, there is usually a trade-off of economics and low frequency performance.

Many types of antenna testing, including both near-field (NF) and far-field (FF) testing. Also, antenna radiation pattern testing is done within an anechoic chamber. Electromagnetic conformance (EMC) testing can also be performed in an anechoic chamber. Anechoic chambers are generally sized to accommodate a range or type of RF equipment. For instance, there are compact and modular anechoic chambers with automated fixtures designed for testing 5G handsets and base station equipment, and there are very large anechoic chambers designed to fit an entire war fighter for radar performance and radar cross-section testing.

There are several types of RF test equipment used alongside anechoic chambers, including network analyzers, spectrum analyzers, signal generators, EM probes, calibrated antennas, and etc. Special types of shielding cabling and RAMs are used to prevent any test equipment from introducing reflections. Hence, much of the RF test equipment is generally external to the anechoic chamber with precision shielded cabling running from the test equipment to the DUT within the anechoic chamber.

Useful Anechoic Chamber Links

Courtesy of Pasternack 

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