Optimizing Mixer Group Delay Measurements

Explore methods to optimize group delay measurements in mixers and frequency-converting devices, particularly when local oscillator (LO) access is unavailable. This application note focuses on using R&S®ZNA vector network analyzers, leveraging their two-tone stimulus capabilities to achieve precise and repeatable results. The document highlights challenges posed by modern, integrated designs and offers practical tips to overcome them.

Key techniques include automating measurement setups for consistency, selecting optimal signal combining methods, and fine-tuning power levels, attenuation, and tone spacing to minimize noise and error. It also discusses the importance of narrow intermediate frequency (IF) bandwidth and averaging during calibration for noise reduction and enhanced accuracy.

Further, it introduces features like LO tracking for troubleshooting frequency drift and utilizing dual internal receiver LOs for faster, more accurate measurements. Small attenuators are recommended to mitigate mismatches between the device under test (DUT) and analyzer, while vector error correction ensures precise S-parameter measurements.

Results from applying these techniques are demonstrated with two DUTs: a satellite block converter and a calibration mixer. Optimizations yielded significant reductions in peak-to-peak variation in group delay, with improvements ranging from 5x to 39x. These approaches are applicable to various frequency-conversion devices and provide a robust framework for enhancing measurement quality in demanding applications.