Improved accuracy of measurements of complex permittivity and permeability using transmission lines

Strong damping of Higher-Order-Modes (HOMs) excited by the beam in accelerating cavities is a necessary condition for achievement of high currents and low emittances in storage rings, electron-positron colliders, and high average power Energy Recovery Linacs (ERLs). Characterization of the electromagnetic properties of lossy ceramics and ferrites used in HOM loads is therefore an essential part of constructing these accelerators. Here we show how to improve these measurements beyond the state of the art. In the past, significant discrepancies have been typical between measured properties for different batches of the same material. Here we show that these can be explained not only by technological deviations in the material production but also by errors in the dimensions of the measured samples. We identify the main source of errors and show how to improve the accuracy of measuring the electromagnetic parameters of absorbing materials.