Electric and magnetic fields in the vicinity of strong sources of radiation (e.g. radar and broadcasting) can exceed the limits mentioned in the national standards for the exposition of persons. Field probes are needed to warn personnel if they are going too close to the RF-sources. For acceptance reasons the field probes should be universal in such a way that no user adjustment of frequency is required. The limits for power density, electric and magnetic field strength depend on the frequency. In contrast, field probes covering a large frequency range, e.g. 1 MHz to 18 GHz or even larger, normally have a flat frequency response. Therefore, the person using the field probe has to know the frequency of the electromagnetic field and to evaluate fieldstrength with respect to the frequency dependent limit value defined by law. Human mistakes while making that evaluation can lead to expositions above the limit value. On the other hand, the evaluation of the power density in the presence of multiple strong sources of radiation at different frequencies with different limit values also leads to measurement problems. A new approach has been undertaken to overcome these difficulties in the development of a rectifying field probe. It consists in shaping the antenna factor of the probe inversely proportional to the limit value. The isotropic response of field probes can be achieved, if three dipole antennas are arranged perpendicular to each other. The presence of dielectric supporting material leads to degradation of the isotropic response of such a field probe. The effect will be investigated. For typical substrates the isotropic response is degraded by up to 3.8 dB. An compensation for this effect will be proposed that leads to a residual unisotropic response of less than 0.2 dB.

Electric and magnetic fields in the vicinity of strong sources of radiation (e.g. radar and broadcasting) can exceed the limits mentioned in the national standards for the exposition of persons. Field probes are needed to warn personnel if they are going too close to the RF-sources. For acceptance reasons the field probes should be universal in such a way that no user adjustment of frequency is required. The limits for power density, electric and magnetic field strength depend on the frequency. In contrast, field probes covering a large frequency range, e.g. 1 MHz to 18 GHz or even larger, normally have a flat frequency response. Therefore, the person using the field probe has to know the frequency of the electromagnetic field and to evaluate fieldstrength with respect to the frequency dependent limit value defined by law. Human mistakes while making that evaluation can lead to expositions above the limit value. On the other hand, the evaluation of the power density in the presence of multiple strong sources of radiation at different frequencies with different limit values also leads to measurement problems. A new approach has been undertaken to overcome these difficulties in the development of a rectifying field probe. It consists in shaping the antenna factor of the probe inversely proportional to the limit value. The isotropic response of field probes can be achieved, if three dipole antennas are arranged perpendicular to each other. The presence of dielectric supporting material leads to degradation of the isotropic response of such a field probe. The effect will be investigated. For typical substrates the isotropic response is degraded by up to 3.8 dB. An compensation for this effect will be proposed that leads to a residual unisotropic response of less than 0.2 dB.