Repeatable Phase Spectrum Measurements of 75–110-GHz Modulated Signals Using a VNA-Based LO Phase Cancellation Technique

Abstract

In this paper, we present a vector network analyzer (VNA) based measurement scheme and setup to obtain repeatable phase spectrum measurements of 75-110 GHz modulated radio-frequency (RF) signals. In order to remove the random phase contribution of sweeping local oscillator (LO) in harmonic down-conversion, the LO signal is coupled out into an auxiliary measurement channel where its random phase at the fundamental can be derived after additional modulation and down-conversion treatments. Afterwards, user-defined math equation is used inside the VNA for LO phase cancellation, based on the traces of RF- and auxiliary-channel raw measurements. The key point of proposed LO phase cancellation technique is measuring the 75-110 GHz test signal and the auxiliary-channel signal at the same GHz intermediate frequency, so that the receivers of VNA can measure both of them simultaneously when working on the peculiar continuous-wave or zero-span mode. According to the method validation at 78, 93, and 108 GHz, a phase fluctuation of ±2 deg. for single-run measurements is found reachable in practice.