VNA-Based in-Band Spectral Purity Assessment for MM-Wave Frequency Extenders

This work presents a method for measuring the inband spectral content of mm-wave extenders using a vector network analyzer. In active device characterization, controlling the output power of the extenders through their low-frequency input signal power requires high spectral purity to avoid affecting the measurement results. To assess the frequency harmonic content, the proposed approach combines vector power calibration with a harmonic scanning technique, where only the local oscillator of the extender under test is varied across a predefined frequency grid. Since the measurement relies solely on the vector network analyzer, this method enables high-speed evaluation of in-band harmonic contributions with a high dynamic range. The paper first compares the proposed approach with broadband PM5 measurements, demonstrating a very good agreement with a maximum deviation of 0.8 dB. Subsequently, a complete characterization of the Virginia Diodes WR6.5 extender $(110-170 \text{GHz})$ is presented. The results indicate an in-band harmonic contribution of less than 1.4 dB up to an output power of −60 dB.