National Physical Laboratory

VHF antennas

NPL calibrates most types of antennas, for example those used for radio and TV reception, wireless communication and EMC testing. Antennas need to be calibrated in order to know the uncertainty in the measurement of electric or magnetic field strength and to confirm they are working to specification.

NPL is able to calibrate a large variety of antennas in the VHF/UHF band.

The principles of measurement are similar to those for our standard EMC antenna techniques, therefore our methods may be tailored to meet any non-standard antenna in the VHF or UHF bands.

NPL's capability includes vehicle mounted and body mounted antennas, both linear and circular polarised. In many techniques we use the good properties of our ground plane to achieve well characterised measurement configurations, e.g. using the fact that the handedness of circular polarisation is flipped upon reflection.

Also, see the NPL Good Practice Guide No. 73 on Antenna Calibration

Outdoor ground plane

The parameters NPL is able to offer include:

  • Antenna factor and/or gain
  • Reflection coefficient (mismatch)
  • Balun balance
  • Cross-polar rejection
  • Phase-centre position
  • Radiation pattern (angle resolution depending on weight and mobility of antenna)

Over the frequency range 20 MHz to 5 GHz NPL measures antenna factor of wire antennas to an uncertainty of ±0.5 dB; or, at lower cost, to uncertainties in the range ±1.0 dB to ±1.5 dB.

NPL holds the UK's national standard for field strength, which is based on a calculable dipole antenna, which in turn was proved on one of the largest and flattest outdoor ground planes in Europe, designed for the purpose of antenna calibration. The ground plane of dimensions 60 m x 30 m is built from seamlessly welded steel plates, and is flat to within ±6 mm over 95 % of its area. The site is available for hire. Calibrations are also performed in a 9 m long fully anechoic room.

NPL 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. The distance from the centre of the ground plane to the nearest trees, or wooden building, is 45 m.


Customer Service tel: +44 20 8943 6796

Last Updated: 22 Jul 2014
Created: 15 Apr 2009


Please note that the information will not be divulged to third parties, or used without your permission