Assessment of VNA Frequency Extender Linearity by Attenuation Build-Up Method

This paper presents an attenuation build-up method for assessing the linearity of vector network analyzer (VNA) frequency extenders. In place of a primary attenuation standard, a pre-characterized 3 dB step of a rotary vane attenuator (RVA) is used as a working reference. The 0 dB and 3 dB steps of this RVA are measured at incremental attenuation steps from 0 to 120 dB, with the increments provided by a build-up attenuator. The limits of the measurement system were investigated to determine the highest measurable attenuation level. In order to achieve suitable measurement accuracy at high attenuation levels, measurements were taken in phases, with the base attenuation level of the setup increased for each phase. The final linearity results combined from four phases of measurements are compared with those of the base VNA at microwave frequencies. These were assessed using traditional traceable methods. The results indicate that the frequency extenders have only a small contribution to the overall non-linearity of the measurement system at attenuation levels as high as 85 dB.