Whitepaper

Spectrum Analyzer Based Phase Measurement for Near-Field EMI Scanning

Published by IEEE Paper

This paper introduces and optimizes a spectrum analyzer (SA)-based phase measurement method for near-field EMI scanning — a cost-effective alternative to vector network analyzers (VNAs) and oscilloscopes. Phase and magnitude data are both essential for creating equivalent radiation models and performing near-field to far-field transformations (NFFFT). Because SAs natively measure only magnitude, the authors developed a hardware and algorithmic system to extract phase using vector summation of a main probe signal and a reference probe signal through different phase-shift cables and variable attenuation levels. A Nelder-Mead simplex optimization (fminsearch) algorithm is used to resolve the phase difference from the magnitude-only measurements. The method is validated against VNA and oscilloscope measurements and CST full-wave simulation over a 5 GHz resonant trace structure.