Characterization of Digitally Modulated Signals at Millimeter-wave Frequency Bands up to 100 GHz

In this paper, a vector network analyzer (VNA) based precisely synchronized setup is presented for digitally modulated-signal measurements up to 100 GHz. To achieve frequency extension towards 100 GHz, two external passive harmonic mixers are utilized to down-convert the millimeter-wave components of 64-QAM test signal and multisine phase reference to the microwave band, which are later measured by the VNA receivers with a limited frequency band less than 67 GHz. Power and phase calibrations are performed to correct the systematic errors of frequency-domain measurements, so that time-domain waveform can be reconstructed for digital demodulation. By applying pre-distortion according to calibrated measurements, the error vector magnitude (EVM) of user-defined 64-QAM signals can be lowered. According to the experimental results at 94.5 and 100.5 GHz under a 64-QAM symbol rate of 100 MSymbol/s, the nominal EVM values of pre-distorted signals is from 0.91% to 2.45% in this work.