Design Of Small Broadband Antenna Based On Different Application Environment

With the rapid development of electronic technology,higher requirements including miniaturization and multi-functional are put forward to the wireless system designs.The antenna,as the most front-end devices in wireless systems,its designation is closely related with the overall performance of the system,and in engineering practice,the antenna design must be optimized according to the requirements of different system applications.In this paper,to meet the requirements of human breast microwave detection system and electromagnetic interference test system,two broadband directional high gain antennas are designed respectively,which includes a dipole antenna using multi-layer patch and a 2×2 element electro-magnetic dipole antenna array.First,a low profile directional high gain antenna which composed of multi-layer patch to be used in the sensor of microwave breast cancer detection system is designed.The antenna is composed of three-layer dielectric substrates.The first layer is a circular metal patch which is connected with the driven patch in the second layer through a metal post.The driven patch is a circular monopole with a fractal structure,by which the bandwidth of the monopole is expanded.The third layer is a circular parasitic patch,it not only helps to improve the antenna forward gain,but also broaden its bandwidth by adding extra resonance points.The overall size of the antenna is 19×13.5mm2,and the measured results of the antenna shows that the antenna covers a band width from 3GHz to 4.7GHz with S11<-10 dB,with the maximum gain of 8dBi.The antenna is then applied to the microwave breast cancer detection system for the simulation and experiment to verify the validity of the antenna.And then,a 2 × 2 element circular polarization broadband electro-magnetic dipole antenna array is designed for electromagnetic interference test system.The antenna element uses the electromagnetic dipole structure,in which the components are realized by a high precision CNC machine tool.Multi-level Wilkinson power divider is used in the feed network at the back of the antenna to guarantee the antenna's broadband characteristics.The antenna is mounted on a circular platform,and two metal boards are provided between the elements on the platform to reduce the mutual coupling between the elements.The metal boards,together with the metal walls around the array effectively improve the antenna gain in the low frequency band.The simulation result of the antenna shows that the maximum gain is 14 dBic and the axial ratio bandwidth(AR<3dB)is 1.0-2.2GHz.The measured result of the antenna shows that the impedance bandwidth(S11<-10dB)is 1.0-2.0GHz.This antenna basically meets the requirements of a certain electromagnetic interference test system.At last,conclusion is given and ends with the prospect of the future research works.