Evaluating EVM Performance in Millimeter-Wave OTA Test Using Digitally Modulated Stimuli With Pre-Distortion and a NVNA Test Bench

In this article, we present a frequency-domain measurement setup for millimeter-wave over-the-air (OTA) test, which uses digitally modulated stimuli to evaluate the error vector magnitude (EVM) performance of antennas. The proposed nonlinear vector network analyzer (NVNA) like test bench sweepingly measures the magnitude and phase spectra of 64-QAM transmit/receive (TX/RX) signals, and derives the EVMs from reconstructed waveforms based on calibrated measurements in the frequency domain. Pre-distortion is also performed to compensate the distortion arising from 64-QAM generation and up-conversion, so that low-EVM test stimuli can be used to inspect the antenna performance under on- and off-axis scenarios. The validity of proposed NVNA setup is experimentally verified at 28 and 39 GHz, where typical EVMs of 100-MSymbol/s 64-QAM test signals are less than 0.3% for pre-distorted TX measurements, and from 1.03% to 5.68% for RX results under different positioning situations.