VNA-Based Modulated Measurements for Polynomial Modeling and Linearization of RF Multipliers

Radio-frequency (RF) multipliers (FreqX) are nonlinear devices causing wide spectral regrowth of the modulated input excitation at a given output harmonic. As such, they could be exploited for wideband signal generation at high frequencies. However, the strong nonlinear distortion involved and the bandwidth (BW) expansion feature does not allow for a straightforward prediction of the output signal. In this paper, we leverage a measurement setup based on a Vector Network Analyzer (VNA) with spectral and signal analysis functionalities and tailor it for characterizing the input and output complex signal envelopes of FreqXs. The measured data are used to implement and validate a cross-harmonic memory polynomial (MP) behavioral model for a doubler and a tripler at a 6-G Hz output carrier frequency, allowing for the prediction of their nonlinear dynamic behavior under a 4-QAM modulated input excitation. MP model inversion is then shown to allow for the linearization through digital predistortion (DPD) of both the considered FreqXs.