Unfortunately, in the world of EMC, where field strength measurements are our daily business, this antenna is not known for its accuracy. Indeed, its resonance frequency band is fuzzy and therefore wide inducing a very low accurate gain.?
See an excellent commercial realization of this antenna with the corresponding plots here :
http://schwarzbeck.de/Datenblatt/ksga2450.pdf
Therefore it is much more usual to use half-wave resonant dipoles as already indicated by Dr Kirkby. Of course any other calibrated antenna can also be used.
But field strength measurements have the distinction of having one of the highest inaccuracies recognized by the world of laboratory metrology since when we claim to have a measurement uncertainty of less than 3 dB, we are usually questioned by the auditors of accreditation bodies as to whether we are really being honest. In general, 4 dB of measurement uncertainty is accepted by all international standards.
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