Free Space Measurement Of Complex Permittivity And Complex Permeability At Microwave Frequencies

Absorbing material is not only used in microwave anechoic chamber、electromagnetic screen、ships and other domestic facility, but also used in military field,such as radar stealth technology、electronic countermeasure technology and so on.Structured stealth materials as one of the main stealth materials have good mechanicalproperties and it can absorb the electromagnetic wave. Stealth technology is towards toimproving stealth performance, extending frequency range and reducing costs. In orderto realize wideband radar stealth technology, it is very important to research on theelectromagnetic properties of sample. Besides, a set of universal electromagneticparameters test system needs to construct on account of measurement techniques ofexotic material, such as plasma and microwave dielectric ceramics and so on. Thefree-space measurement method is established to meet the requirement of practical andbroad-band. It is nondestructive and contactless. According to the orientations of thesample in the measurement system, the microwave signal incident to the sample may benormal or oblique to the sample.This paper analyzes the usual measurement methods of complex permittivity andcomplex permeability of dielectric materials, and then analyzes the theory about thefree-space techniques in detail. Many problems encountered during the dielectricmaterial testing have been solved. By using the imaginary part of the effectivecompensation principle to solve the phase shift ambiguity problem. There is a minimumin the amplitude of S11whenever the thickness is a multiple of a half-wavelength. Inorder to solve the half-wavelength divergence, the thickness of the sample is controlledless the half-wavelength. By building the system block diagram, an UWB double-ridged TEM horn antenna is designed based on the electromagnetic simulationsoftware CST. In order to improve the test precision and realize automatic measurement,The TRL calibration technology based on10-errors-module is studied by MATLABlanguage. Finally, material samples are tested. The system is capable of operating in the4~14GHz frequency range. Due to the restrictions of performance of antenna, the measure result is not accurate between2~4GHz and14~18GHz frequency range. Thistest method has the feature of fast, simple structure, convenient and accurate positioning,high test accuracy and so on.The result indicates that after calibrating the test system by TRL calibrationtechnique, systematic error of the test system is eliminated. Spot-focusing lens antennawith broadband, high performance can effectively broaden working frequency band.Free space measurement system built in this paper not only can meet the normaltemperature test requirements, also be applied to the temperature test and also suitablefor flexible medium test.So it has good universality.