National Physical Laboratory

Test site evaluation

Anechoic chamberNPL 9 m x 6 m x 6 m anechoic room fully lined with ferrite tiles and hybrid pyramidal absorber and evaluated to cover the frequency range 30 MHz to 18 GHz.Outdoor Ground PlaneNPL open area test site, including a 60 m x 30 m metal ground plane that is flat to within ±5 mm over 95% of its area.

NPL can evaluate test facilities that are used for EMC measurements.

These include:

  • Open area test sites (OATS) and semi-anechoic chambers by the Reference Site method, RSM, or by the NSA method (Normalised Site Attenuation)
  • Fully anechoic rooms (FARs) by the volumetric NSA method and the SVSWR method
  • GHz transverse electromagnetic (GTEM) cells by field mapping
  • Stirred Mode (or Reverberation) Chambers by measurement and analysis.
  • Field uniformity for immunity testing to EN61000-4-3

Sites used for radiated emissions testing for conformance to various national standards must be of a certain quality.

This usually implies compliance with the criterion in CISPR Publication 16-1-4, which currently states that the measured normalised site attenuation (NSA) be within ±4 dB of the theoretical value.

NPL prefers to use the more precise RSM, of which the NSA and Dual-Antenna-Factor methods are derivatives. In the RSM the insertion loss is measured between two antennas at defined positions on the site-being-evaluated and compared with the insertion loss measured with the same antennas and geometry on a reference test site, which is defined in CISPR 16-1-5.

NPL provides traceability for physical parameters, which includes antenna factor for EMC antennas and calibration of field probes. NPL has the ability to measure the coupling between antennas very precisely, with over two decades of experience in such measurements.

NPL is active in CISPR sub-committee A in the development of improved methods for the evaluation of test sites and has contributed to CISPR 16-1-4, CISPR 16-1-5, IEC 61000-4-20 on GTEM cells and IEC 61000-4-21 on Reverberation chambers.


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Last Updated: 25 Mar 2010
Created: 8 Jun 2007


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