Research On Key Techniques Of Complex Permittivity And Permeability Measurement In Microwave And THz Bands

Complex permittivity and permeability of materials in microwave and THz bands are known as the key design parameters for various systems in wireless communications,radars,microwave remote sensing,radioastron,etc.Therefore,measurement of complex permittivity and permeability in microwave and THz bands has been a bottleneck problem in development of these fields.Up to now,various measurement methods based on different fixtures have been proposed.Among the methods,two-port transmission line method(T-PTLM)is widely used thanks to the excellent performance in simplicity,broadband and moderate accuracy.The core of the T-PTLM is how to extract complex permittivity and permeability from the transmission/reflection(T/R),reflection-only(R-O)or transmission-only(T-O)measurement S-parameters effectively and accurately.In this thesis,the extraction methods and techniques in the literature are roundly summarized and analyzed.Then,specific methods are proposed to overcome the drawbacks of the common extraction methods and techniques in the literature.According to the measured S-parameters and the layers of the measured materials,the work of this thesis is divided into three parts.The main contributions of this thesis are as follows:1.For extracting the complex permittivity of single-layer plates from the T/R measurements,resonance,multi-solution and position-dependence of the extractions are the three drawbacks.Firstly,a novel analytical extraction method based on the electromagnetic field theory is proposed to improve the theory of suppressing the resonance.Secondly,an innovative combinatorial extraction technique with low complexity is forward to overcome the three drawbacks simultaneously.The proposed above are validated with the experiments and simulations.2.For extracting the complex permittivity and permeability of thin films on substrates and powders/particles sandwiched between plates from the T/R measurements,there are still drawbacks.The analytical extraction method based on the electromagnetic field theory is expanded to overcome the drawbacks.The expanded method has advantages of low complexity and compatibility to TE₁₀ and TEM transmission lines.What's more,multi-solution for films on substrates and resonance for powders/particles between plates are solved.The proposed above are validated with the experiments and simulations.3.When the T/R measurement is unavailable,the R-O and T-O measurements are adopted for the extraction.In general,the R-O and T-O measurements are only applicable to single-layer plates.For extracting the complex permittivity and permeability of single-layer plates from the R-O measurements,there are two still drawbacks.Some solutions are araised to overcome the two draebacks.Firstly,the reflection coefficient equations are analyzed in detail to solve the multi-solution of the extractions.Secondly,the artificial neural network(ANN)is used to eliminate the influences of the sample position on the extractions.Another hand,the initial-value estimation brings difficults to extracting the complex permittivity of single-layer plates from the T-O measurements in THz band.A model based on the transmission coefficient is proposed to estimate the correct initial values to solve the problem.The proposed above are validated with the experiments and simulations.