Читать книгу Handbook of Microwave Component Measurements - Joel P. Dunsmore - Страница 107

With mixers used as VNA receivers, the critical performance attributes are noise floor and input compression point. A fundamental LO provides best performance; using a third‐order harmonic of the LO to obtain higher RF frequency response theoretically degrades the conversion loss by 9 dB, and fifth harmonic degrades it by 14 dB, based the idea that the LO drives the mixer into square‐wave conversion. This degradation in conversion loss is represented as an increase in noise floor for most VNAs, due to the internal factory‐based response correction.