SNR Analysis and Optimization in Near-Field Scanning and EMI Applications


In a near-field scanning system, each element of the measurement chain contributes to the thermal noise power density: probe, cables, amplifiers, and the measuring instrument. The signal-to-noise ratio (SNR) is strongly affected by the source output impedance, source temperature, the lossy transmission lines between probe and amplifiers, amplifier noise, amplifier temperature, and amplifier gain. By minimizing the loss between the probe and by using ultralow-noise amplifiers (noise figure (NF) < 0.5 dB), SNR improves by >10 dB, compared to a setup using a 1-m cable and a 3-dB NF amplifier. A resonant probe that is cooled with liquid nitrogen improves measurement SNR by an additional 10-12 dB, as compared to a broadband probe of similar loop size. To combine the advantages of a resonant probe, without sacrificing the ability to measure broadband, a proof of concept is demonstrated that uses a tunable resonant probe which is synchronized to the frequency sweep of the spectrum analyzer.


Electrical and Computer Engineering

Research Center/Lab(s)

Electromagnetic Compatibility (EMC) Laboratory

Keywords and Phrases

Cables; Electromagnetic Pulse; Global Positioning System (GPS); Global System for Mobile Communications; Liquid Nitrogen; Nitrogen; Noise Figure; Probes; Signal Interference; Spectrum Analyzers; Thermal Noise; Uncertainty Analysis; Wi-Fi; Field Sensors; Lossy Transmission Line; Measurement Uncertainty; Measuring Instruments; Near Fields; Near-field Scanning; Resonant Probes; Source Temperature; Signal to Noise Ratio (SNR); Electromagnetic Interference (EMI); Field Sensors and Probes; GSM; Near-Field Modeling and Measurements; Probe Cooling

International Standard Serial Number (ISSN)

0018-9375; 1558-187X

Document Type

Article - Journal

Document Version


File Type





© 2018 Institute of Electrical and Electronics Engineers (IEEE), All rights reserved.

Publication Date

01 Aug 2018