Fast electromagnetic field strength probes

Diode detectors and thermocouple detectors are conventionally used to measure electromagnetic field strength. Both detectors have some disadvantages for applications where a fast response and a high dynamic range is required. The diode detector is limited in dynamic range. The dynamic range is important when considering modern pulsed wireless systems with a high peak-average ratio. The thermocouple is too slow to measure fast changing fields, such as the ones created by pulse-modulated wireless systems, modern radars, and in reverberation chambers under fast mode-stirring operation. Mobile devices can dynamically measure and control their output power using a logarithmic amplifier. Circuits 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 in-house, fast, broadband and high dynamic range field strength probe. The concept is described and simulation results are shown. Prototype probes have been built.