Broadband phase resolving spectrum analyzer measurement for EMI scanning applications

EMI scanning application requires phase and magnitude information for the creation of equivalent radiation models and for far-field prediction. Magnitude information can be obtained using rather an inexpensive spectrum analyzer (SA). Phase-resolving instruments such as vector network analyzers (VNA) or oscilloscopes are very expensive for frequencies above 5 GHz. For this reason, this paper proposes a method that utilizes a SA for phase-resolved magnitude measurements. The basic principle is to measure the sum or difference of two signals for different phase shifts and deduct the phase from the combined output of those measurements. The phase is retrieved using an optimization procedure. It is shown that the proposed approach can recover phase deviation within 20° when using six steps of variable attenuator control voltage for the test cases between 5 and 12 GHz.