Electrical characterization of waveguide shim and uncertainty analysis

In this paper we propose a method to characterize waveguide shims, which are being used in almost all calibration kits for waveguide connectors and also used as impedance standard in Thru-Reflect-Line (TRL) calibration, for their length and aperture width and height. Also given are preliminary uncertainty analyses for the electrical characterization of the length, actually the phase shift through the shim, for two calibration methods for the Vector Network Analyzer (VNA).

I. Introduction

In RF and microwave region impedance standards have been referenced to and implemented using coaxial beadless airlines and waveguide shims, which are made of a straight uniform waveguide section. To establish the impedance standards their mechanical dimensions and the electric conductivity are measured and used for the calculation of the characteristic impedance of them [1]. For coaxial air lines the outer diameter of the inner conductor and the inner diameter of the outer conductor are measured along the length for several azimuth planes and their averaged values are used for the calculation of the characteristic impedance or a cascade model of small sections are used to calculate the scattering parameters of them. The length of them is also measured and used when the data is necessary in the calibration and calculation, e.g., LRL calibration and calculation of scattering parameters. In coaxial calibration kit data, the characteristic impedance and the delay calculated from the dimensional measurements are specified and used [2].