High Attenuation Measurement of Step Attenuators

By Sulan Zhang

This paper introduces a solution for high attenuation measurement of step attenuators. Fundamentally, this high attenuation measurement method is based on the cascaded 2-port network and S-parameter theory. This method is to compute the S-parameters of high attenuation (> 80 dB) using the measured S-parameters of lower attenuation (< = 80 dB) settings, the calculations of which depend on attenuator card sequence and physical structure of the step attenuator. Such a method can measure attenuation as low as 120 dB. This is not a straight dB addition; rather, this solution can offer considerable accuracy only using a VNA (Vector Network Analyzer) and T-matrix (as known as transmission parameter or cascade parameter) method which can make the calculations easier. Measurement uncertainties are derived from uncertainties of cascaded S-parameters, for example, measurement uncertainty for 80 dB @ 18 GHz is less than 0.8 dB and 110 dB @ 18 GHz is less than 1.0 dB. Read the Full Article in PDF