Research On Determining Permittivity And Permeability From Scattering Coefficients

The measurement of electromagnetic parameters have extensive application in the fields of microwave circuit,bioelectromagnetism,radar absorbing material and stealth technology,so it has great practical significance to study on this problem.At present,the common methods of the measurement of electromagnetic parameters are standing wave method,probe method,free-space method,cavity resonator method,transmission/reflection method etc.The transmission/reflection method(also known as NRW method),which has the advantages of simple operation,wide band tidth and high precision,is widely used.However,some problems in NRW method can not be ignored,such as half-wave divergence,phase jump and multi-value problem.This paper is researched on those problems.Firstly,through studying the NRW theory and the algorithm of D.R.Smith et al,the paper analyzes the reason of the half-wave divergence and multi-value problem during the traditional scattering coefficeient inversion electromagnetic parameters.At the same time,according to the NRW method,D.R.Smith's algorithm,this thesis proposed a simple and effective method to solve the multi-value problem with using certain restrictive conditons(imaginary part of refractive index is not less than zero,real part of impedance is not greater than zero and the relationship of tangent angle of refraction index limited by that of impedance)and the continuity of electromagnetic parameter between adjacent frequency points.Secondly,this thesis proposed an adaptive calculation method to solve the uncertainty of 1l and 2l,which is caused by the placement of the sample,1l and 2l are the distance between left side of sample and the left port of fixture and the distance between right side of sample and the right port of fixture.This method can improve the accuracy of the scattering coefficients and reduce systematic error,which lays the foundation for the solve of electromagnetic parameters.Finally,the scattering coefficients of a plurality of carbonyl iron specimens during fixtures were measured by network vector analyzer Aigilent PNA N5244A(0.1-18GHz).The proposed algorithms was implemented by software programming and be used to obtain the electromagnetic parameters.The reliability and effiectiveness of the improved NRW method and adaptive algorithm,on solving the multi-value problems and reducing the systematic error,is verified by comparing the results obtained by proposed method with the results of exist literature and related instruments.