Fast, Broadband, and High-Dynamic Range 3-D Field Strength Probe

Electromagnetic fields are conventionally measured using diode detectors or thermocouple detectors. The diode is limited in dynamic range. The dynamic range is important when considering modern pulsed wireless systems with a high peak-average ratio or crest factor. The thermocouple is too slow to measure fast changing fields, such as the ones created by the pulse-modulated wireless system, and in reverberation chambers. In modern mobile phones, a radio signal strength indicator circuit, with a logarithmic amplifier, is used to measure, and via a feedback circuit, control the output power. Devices with a frequency range up to 10 GHz, a dynamic range of more than 80 dB and response time less than 50 ns are available. Three orthogonal monopole antennas connected to three logarithmic amplifiers result in a fast, broadband, and high-dynamic range field strength probe. The concept is described and simulation results are shown. Prototype probes have been built, and the design data and results of experiments are given. Possible applications and additional features of the probes are described.