Verification of scattering parameter measurements in waveguides up to 325 GHz including highly-reflective devices

摘要

Radio-frequency (RF) scattering parameters (S-parameters) play an importantrole to characterise RF signal transmission and reflection of active andpassive devices such as transmission lines, components, and small-signalamplifiers. Vector network analysers (VNAs) are employed as instrumentationfor such measurements. During the last years, the upper frequency limit ofthis instrumentation has been extended up to several hundreds of GHz forwaveguide measurements. Calibration and verification procedures areobligatory prior to the VNA measurement to achieve accurate results and/orto obtain traceability to the International System of Units (SI). Usually,verification is performed by measuring well-matched devices with knownS-parameters such as attenuators or short precision waveguide sections(shims). In waveguides, especially above 110 GHz, such devices may not existand/or are not traceably calibrated. In some cases, e.g. filter networks,the devices under test (DUT) are partly highly reflective. This paperdescribes the dependency of the S-parameters a) on the calibrationprocedure, b) on the applied torque to the flange screws during the matingprocess of the single waveguide elements. It describes further c) howhighly-reflective devices (HRD) can be used to verify a calibrated VNA, andd) how a measured attenuation at several hundreds of GHz can be substitutedby a well-known coaxial attenuation at 279 MHz, the intermediate frequency(IF) of the VNA, to verify the linearity. This work is a contributiontowards traceability and to obtain knowledge about the measurementuncertainty of VNA instrumentation in the millimetre-wave range.