VNA-Based Testbed for Accurate Linearizability Testing of RF Beamforming Arrays Under Modulated Signals

This paper presents a vector network analyzer (VNA) based testbed for accurate phased arrays linearity and linearizability testing under wideband modulated signals. The proposed testbed relies on a standard horn based channel calibration to de-embed over-the-air receiver hardware frequency response and utilizes two of the VNA’s receivers to simultaneously capture accurate representation of the array input and radiated signals. The testbed corrects the linear and nonlinear distortions exhibited by the transmitter underlying components (e.g., arbitrary waveform generator, up-converter, driver amplifiers, and couplers) as well as for the channel and receiver hardware frequency responses so that the linearizability testing is solely indicative of the performance of the array under test. Experiments conducted using an 8x8 RF beamforming array operated at 28 GHz confirmed the capacity of the proposed testbed to support digital predistortion based linearization testing under 5G NR 400 MHz OFDM test signal. More importantly, the pre- correction of the linear and nonlinear distortions exhibited by the testbed yielded an improvement of the adjacent channel power ratios of the array radiated signal by up to 2-3 dB compared to the uncorrected case while using 48% less number of coefficients.