Коррекция S-параметров при измерении материальных параметров магнитодиэлектрических композитов в свободном пространстве с применением диафрагмы

The method is developed for error correction of measurement results of S -parameters. This correction is conducted during determining complex permittivity and permeability of material samples in the centimeter wavelength range. The measurements of properties of materials are carried out in free space using the specific diaphragm of certain diameter by means of specialized measurement bench developed by ITAE RAS. The correction procedure is necessary when the size of test sample is less than two wavelengths of electromagnetic radiation in free space. The correction algorithm of reflection coefficient (parameter ) and transmission coefficient (parameter ) based on the representation of measuring bench in the terms of equivalent long-distance line is shown. The mathematical justification of correction algorithm in non-strict statement is described. The submission is suggested that a space of measurement bench has a wave impedance that differed in a times from the wave impedance of free space. A sample under the test is a quadripole with transmission matrix for measurement bench ( d - sample’s thickness, e and m - effective complex permittivity and permeability of test sample accordingly). Iterative procedure with fast convergence is proposed for determining effective permittivity and permeability obtained from measurement results of S-parameters. Error correction was done for measurement of material properties using small-sized diaphragm 80 mm in diameter which dimension is less than falling wavelength of electromagnetic radiation in the long-wave region of spectrum. As results the comparative dependences of complex permittivity and permeability of material properties of test samples in the low-frequency range in initial state and after correction procedure are submitted. Test samples are presented as thin films of sheet materials based on organosilicone or fluororganosilicone binder filled with modified iron with both different concentration and various degree of treatment. The obtained results allow us to minimize measurement errors of material properties in a frequency vicinity from 3 to 6 GHz. Due to this reason the accuracy of analytical estimates in designing of radio absorbing materials is essentially increased.