A study of the low-frequency coaxial reflectometer measurement procedure for evaluation of RF absorbers' reflectivity

This paper presents a study on the low-frequency coaxial reflectometer measurement procedure. A time domain gating algorithm is developed by ETS-Lindgren and the results are validated after comparing to the Keysight 8753-time domain algorithm. The in-house time gating algorithm is then applied to the simulated reflectivity results of absorbers in reflectometer to the simulation results of the same absorbers with plane wave excitation using finite element method numerical computation. Based on the simulation results, the operable upper frequency limit and the minimum length of the straight coaxial section for the reflectometer are suggested. The errors introduced during measurement due to higher order modes are studied and the permissible limit for the errors is analyzed. The different higher order modes and their effects on field distribution are studied. The impact of the non-uniform field distribution on the absorber reflectivity measurement is also discussed.