Repeatable Phase Measurement of Millimeter-wave Modulated Signals using a VNA-based LO Phase Cancellation Technique

In this paper, we present a vector network analyzer (VNA) based measurement scheme and setup to obtain repeatable phase spectrum measurements of millimeter-wave modulated 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 a second measurement channel where its random phase at the fundamental can be derived after additional modulation and down-conversion treatments. The key point of proposed LO phase cancellation technique is measuring the millimeter-wave test signal and the LO-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.