Millimeter-Wave Wideband Active Load-Pull System Using Vector Network Analyzer Frequency Extenders

This paper introduces a novel wideband active load-pull system leveraging vector network analyzer (VNA) frequency extenders (FXs) for precise device characterization at millimeter-wave frequencies. At the core of the system is an innovative iterative linearization algorithm with an adaptive cost function that simultaneously linearizes the frequency multipliers (FMs) within the VNA-FXs and synthesizes desired load impedances at the DUT output port. Proof-of-concept experiments were conducted at V-band (57.6 GHz) using OML VNA-FXs with a V-band PA as the DUT. Active Load-pull measurements were performed using a 256-QAM-OFDM signal featuring a modulation bandwidth of 400 MHz. Furthermore, the system demonstrated load synthesis capabilities across a bandwidth of up to 1.2 GHz. The proposed algorithm enabled the precise generation of reflection coefficients across the Smith chart, including VSWR circles up to 5:1, and the accurate synthesis of arbitrary gamma responses, such as the letter "A", achieving a load synthesis error below -39.1dB.