Precisely Synchronized NVNA Setup for Digital Modulation Signal Measurements at Millimeter-Wave Test Bands
In this paper, we present a novel Nonlinear Vector Network Analyzer (NVNA) setup for generating and measuring digital modulation signal at millimeter-wave test bands. The first difference between this setup and commercial NVNAs is the use of a user-defined multisine signal as the phase reference, in order to enable more precise synchronization and denser spectral grid. To achieve this, a single 12.5-GHz microwave source is used for generating both the 64-QAM test signal and the phase reference, which not only triggers the arbitrary waveform generator for user-defined intermediate frequency (IF) waveform generation at 3 GHz, but also provides the 25-GHz local oscillator drive after frequency doubling. The second novelty of this work is the use of pulsed-RF signals for NVNA phase calibration. By replacing the 64-QAM IF waveform with a pulsed-RF, tone-by-tone phase calibration on a dense spectral grid of 500 kHz can be easily achieved without any modification of the precisely-synchronized NVNA setup. According to the experimental verification at 28 GHz, the errors of NVNA phase calibration are less than ±2 deg. within the 125-MHz measurement bandwidth, and the measured EVM of 100-MSymbol/s 64-QAM test signal is 2.2% after waveform reconstruction and demodulation.