Whitepaper

Field Analyzers in EMC Radiated Immunity Testing

Published by Amplifier Research

This application note from AR RF/Microwave Instrumentation explains the limitations of conventional RF field probes in EMC radiated immunity testing and introduces Field Analyzers as a more capable alternative. Standard diode-based probes are designed to measure RMS continuous wave fields, but produce unreliable or erroneous results when measuring modulated fields because their analog response time and slow sample rates interact unpredictably with modulation envelopes. Thermocouple-based probes can average pulsed fields but require prior knowledge of the modulation to derive maximum RMS values and cannot display the modulation envelope visually, leaving no way to verify waveform integrity or detect distortion such as overshoot, droop, or ringing introduced by amplifiers driven into saturation. AR's FA7000 series Field Analyzers address these limitations by using an isotropic diode-based field sensor that samples the composite electric field at a significantly faster rate than conventional probes, transmitting data digitally over optical fiber to a processor unit. This architecture enables direct measurement of maximum, minimum, and average RMS values for both AM and pulsed fields, as well as pulse rise time, period, and duty cycle from a time-domain oscilloscope-style display accessible via an embedded webpage on any web-enabled device. The system supports frequency correction factor tables for up to 30 points, multiple trigger modes including free-run, level, and external, and full remote control via USB, GPIB, and Ethernet for integration into automated test software. The sensors are laser powered, eliminating battery management during continuous testing. Compatible modulations covered include those required by DO-160, IEC 61000-4-3, ISO 11452, and MIL-STD-461.