Research On Measuring Complex Permittivity Technology By Reflection Method

In the microwave frequency,the dielectric material has been widely used as a circuit substrate,a radome,etc.It requires accurate knowledge of the dielectric constant of the material.In this paper,the complex permittivity of the material is measured by the noncontact and contact reflection method.Three types of antennas are used to measure the dielectric material without destruction.The data calculates the permittivity and loss parameters of the sample under measuring.In the contact measurement system,an open waveguide with a flange was used as a measurement antenna,and the influence of the flange size on the waveguide port admittance was simulated to determine the flange size.Since the waveguide itself is non-ideal and has a certain length,there is a loss and phase error.This paper uses a metal plate to calibrate the two coefficients.This paper uses two different Gaussian integration and optimization algorithm to calculate the relative permittivity and loss parameters,and the actual measurement results show that the results obtained using this method meet the material nominal value.When the horn antenna is not in contact with the material to be measured,two cases of material termination and non-contacting of the metal plate are tested in this paper,and the equation between the corresponding complex reflection coefficient and the electrical parameters of the material is deduced from the transmission line theory.There are some requirements for such reflection measurement methods,such as far field conditions,sample size,and test environment,which are discussed in this article.Traditional calibration methods often use to move the metal plate to divide the wavelength(?/n)distance.Travel length may need to be in the micron range.This article adopts a more flexible method of moving the millimeter distance;through the measurement data found that this method can achieve the same accuracy of the traditional measurement.Since the horn antenna is measured by placing the material to be measured in the far field to approximate the equivalent transmission line,there is an error in doing so.In order to carry out more convenient testing and improve test accuracy,this paper proposes a method of obtaining the dielectric constant of the material by using the outgoing plane beam lens and the horn antenna to measure the reflected wave.This method can apply the transmission line model and does not require the far field test.Through some theoretical assumptions,a new calibration method is proposed.This method does not require moving the metal plate and the operation is more convenient.By measuring the complex permittivity of various materials and comparing them with the nominal values,the results are close to each other and the hypothesis is verified.