Calibrated Digital Predistortion Using a Vector Network Analyzer as the Receiver

This paper reports the first demonstration of the behavior modeling and predistortion linearization of a power amplifier (PA) for periodic modulated signals using a vector network analyzer (VNA) operated in the receiver mode. In this demonstration a PA operated at 2.3 GHz is characterized using a 5 MHz LTE signal with a peak-to-average power ratio (PAPR) of 10.2 dB. The phases of the Fourier spectrum of the periodic signal measured by the VNA receiver are calibrated using a 20 MHz OFDM signal. The calibrated phases and amplitudes of the 5 MHz LTE signal in the frequency domain are then used to reconstruct the signal in the time domain. After synchronization, the NMSE, dynamic AM-AM and AM-PM, ACPR, EVM, and BER of the PA before and after predistortion can then be calculated from the measured data. The predistortion linearization of the PA validates the accuracy of the VNA phase calibration and synchronization methodology used for the modulated waveforms. This work demonstrates that the same VNA and calibrated testbed can be used to characterize both the (1) continuous-wave (CW) and (2) modulated nonlinear response of a device without breaking electrical contacts with it.