Whitepaper

Non-contact Probing of RF Circuits with the Beehive 100 Series Probes

Published by Beehive Electronics

This application note from Beehive Electronics explains the advantages of passive non-contact probing for testing RF circuits on highly integrated printed circuit boards, where traditional coaxial test connections no longer exist. The document contrasts non-contact probes with conventional contact probes, noting that contact probes suffer from capacitive loading, ground inductance from lead connections, and the physical difficulty of simultaneously maintaining a signal and ground connection without accidentally shorting a circuit. Non-contact probes eliminate all three problems because they couple to the electromagnetic field around a conductor without touching it. The document distinguishes E-field probes, which measure voltage-proportional electric fields and offer fine spatial resolution down to individual IC pins, from H-field probes, which measure current-proportional magnetic fields and are available in different loop sizes to trade off sensitivity against frequency range and spatial resolution. Measured coupling factors between each probe model and 50-ohm microstrip lines on three standard FR4 substrate thicknesses are provided across frequency, enabling absolute power estimates from relative probe readings. A fault-finding demonstration on a test board containing amplifiers, attenuators, and a splitter shows that a faulty amplifier with a disconnected power supply could be identified by walking the probe along the signal chain in under a minute. The document also demonstrates that probe sensitivity is sufficient for high-dynamic-range measurements such as phase noise, showing a 39 dB margin above the spectrum analyzer noise floor in a worked example at 3 GHz.