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

This letter presents a novel wideband active load—pull (LP) system that leverages vector network analyzer frequency extenders (VNA-EXTs) for precise millimeter-wave (mmW) device characterization under modulated signal excitation. Unlike conventional VNA-EXT-based LP systems, typically limited to continuous-wave (CW) testing, the proposed system integrates advanced signal generation and analysis capabilities to enable comprehensive LP measurements with wideband modulated signals. At its core, an iterative linearization algorithm with a novel adaptive cost function is proposed to simultaneously linearize the frequency multipliers (FXs) within the VNA-EXTs and synthesize accurate load impedances at the device-under-test (DUT) output reference plane. Proof-of-concept experiments were conducted at 57.6 GHz using Oleson Microwave Labs (OMLs) VNA-EXTs with a V-band power amplifier (PA) as the DUT. Active LP measurements used a 256-QAM orthogonal frequency division multiplexing (OFDM) signal with a 400-MHz modulation bandwidth. The system demonstrated accurate load synthesis across a 1.2-GHz bandwidth, achieving voltage standing wave ratio (VSWR) circles up to 5:1 and a load synthesis error below −39.1 dB. Furthermore, the proposed algorithm enabled precise reflection coefficient generation over frequency, including arbitrary responses such as the letter “A.” The system was also used to evaluate the DUT’s resilience to VSWR variations with and without linearization. Adjacent channel power ratio (ACPR) and error vector magnitude surfaces were measured across the Smith chart, providing insights into the impact of load variations on DUT’s linearity.