Calibration of commercial power density meters at RF and microwave frequencies

A calibration of 73 different probes from three different manufacturers has been carried out at the frequencies 27 and 2450 MHz, respectively. The power density levels used were in the range 10–100 W/m
²
. The investigation was carried out at the Swedish National Primary Calibration Center, whose standards are traceable to the National Bureau of Standards, USA. The total uncertainty in the measurements is estimated to ±0.7 dB both for 27 and 2450 MHz. A considerable spread in values was found with regard to the absolute value of the indicated field strength, as well as to the isotropicity of the probe. At 27 MHz only 55 percent of instruments had a mean indicated value within ± 1 dB of the nominal value, and 48 percent of probes showed an isotropicity better than ± 1 dB. The corresponding results from the calibration at 2450 MHz are somewhat better, with 65 percent of the instruments having a mean value within ±1 dB of the nominal value and an isotropicity better than ± 1 dB fcr 79 percent of the probes. In many cases the values found were well beyond the accuracy limits specified by the manufacturer. Of the total number of instruments tested in this study 5 percent did not work at all, although their owners thought they did.