Design Of A Wideband System For Measuring Dielectric Properties Based On AD8302

Relative permittivity and loss tangent are the two important parameters of microwave dielectric materials.In recent years,with the development of electromagnetic material,which higher demands are proposed for the precise measurement of the dielectric properties.In this paper we first introduces the existing mature measurement methods for measuring the dielectric properties.Then a new method which used in the paper is discussed in detail.Based on the method we design a wideband measurement system that including a UWB directional antenna unit,a wideband RF circuit as well as a data processing unit.This thesis is devoted to introduce the three units,and includes the following contents:1.Introducing the derivation process of the using method,and decompose the wideband measurement system into three parts:the antenna part,the RF circuit part and the data programming part.2.The design of antenna:Through the research of UWB antennas,and use the wideband technology,this paper designs and produces a planar monopole antenna with an ultra-wide bandwidth from 1.1 to 6 GHz.The dimensions of the antenna are 90mm×90mm×1mm.The measured and simulated results show that the antenna has a-10dB return loss bandwidth from 1.1 GHz to 6 GHz.The antenna is well directional in the operational band.By simulation and measurement results,the antenna has directional patterns in the XOZ plane and YOZ plane and a highest gain over the frequency band of 8dBi.3.The design of RF circuit:Based on the the gain and phase detector chip AD8302,we design two different RF circuit which can be used to measure the antenna impedance in the frequency band 1.1-2.7G,2.8-5.5GHz respectively.4.The design of base band signal processing:Collecting the DC voltage come from the AD8302 by STM32,and finally realize the measure of dielectric properties.