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

Abstract

Abstract. Radio-frequency (RF) scattering parameters (S-parameters) play an important role to characterise RF signal transmission and reflection of active and passive devices such as transmission lines, components, and small-signal amplifiers. Vector network analysers (VNAs) are employed as instrumentation for such measurements. During the last years, the upper frequency limit of this instrumentation has been extended up to several hundreds of GHz for waveguide measurements. Calibration and verification procedures are obligatory prior to the VNA measurement to achieve accurate results and/or to obtain traceability to the International System of Units (SI). Usually, verification is performed by measuring well-matched devices with known S-parameters such as attenuators or short precision waveguide sections (shims). In waveguides, especially above 110 GHz, such devices may not exist and/or are not traceably calibrated. In some cases, e.g. filter networks, the devices under test (DUT) are partly highly reflective. This paper describes the dependency of the S-parameters a) on the calibration procedure, b) on the applied torque to the flange screws during the mating process of the single waveguide elements. It describes further c) how highly-reflective devices (HRD) can be used to verify a calibrated VNA, and d) how a measured attenuation at several hundreds of GHz can be substituted by a well-known coaxial attenuation at 279 MHz, the intermediate frequency (IF) of the VNA, to verify the linearity. This work is a contribution towards traceability and to obtain knowledge about the measurement uncertainty of VNA instrumentation in the millimetre-wave range.

Establishing Traceability to the International System of Units for Scattering Parameter Measurements From 750 GHz to 1.1 THz

“…Therefore, it is characterized using a uniform PDF. The equivalent standard uncertainty, u(dA), is therefore established in the usual way [24]: (6) The equation used to calculate the error due to mismatch, M TM , is also given in [36]: (7) where S 11 , S 22 , S 21 and S 12 are the measured S-parameters of the DUT, M is the VNA residual test port match, and L is the VNA residual load match.…”

Investigation of Verification Artifacts in WR-03 Waveguides

“…The cross-guide device is a precision waveguide section which is connected in such a way that its aperture is rotated by 90 degrees with respect to rectangular waveguide aperture. These devices act as below-cutoff sections and provide significant transmission loss as verification standards [3][4][5][6][7][8][9]. Cross-guide devices can be used as calculable verification standards for different frequency bands depending on the dimensions of the waveguide aperture [8].…”

“…Such a custom-made circular iris section also provides comparable transmission losses when inserted between the rectangular waveguide test ports. Therefore, it can also be used as verification standard at millimeter and sub-millimeter frequencies [4,9].…”

Investigations of connection repeatability for waveguides with different size apertures

“…In response, the national metrology institutes (NMIs) are being challenged to develop new S-parameter national standards and measurement systems [4][5][6][7][8]. At sub-millimeter wave frequencies, connection repeatability of waveguide flanges is the dominant issue impacting accurate measurement.…”