| The rapid development of wireless communication technology has deeply affected people's lives.Because of this,the development of various communication devices puts higher requirements on the performance of the antenna.In order to enable the device to work simultaneously in multiple bands without mutual interference,multiband/wideband antennas have gradually entered people's attention,because its superior characteristics make it gradually become the focus of research.This thesis mainly focuses on the multi-band and wideband antennas loaded with left-handed materials(LHM):First,the research background and significance of multi-band and wideband antennas are reviewed,as well as the development status of multi-band and wideband antennas at home and abroad in recent years.At the same time,methods for multi-band and wideband antennas are introduced.Then,basic knowledge such as circuit parameters,far-field radiation parameters,and feeding methods used in the antenna design and testing process are concluded and summarized.Second,the definition,development status,principle and characteristics of left-handed materials are briefly introduced.Two new types of LHM unit structures are designed based on the principles of LHM: a)Design and simulation of a windmill-type LHM with a central symmetrical structure,the calculation results show that the double negative band of this LHM structure is 3.4GHz-3.6GHz;b)Design and simulation of double-layer tri-band LHM,by printing two basic reciprocally symmetric cell structures on both sides of the dielectric substrate,the original single-band LHM structure becomes a tri-band LHM structure..Three double-negative bands can be obtained by calculation: 2.7 GHz—4 GHz,6.5 GHz—6.7 GHz,and 10.1 GHz—10.7 GHz.Third,atri-band antenna is designed by loading the windmill-type LHM on a rectangular patch monopole antenna.The method used to load the structure is to etch the complementary structure of the windmill LHM on the radiating element,because there are kinds of ways to load the LHM,We have selected the optimal loading method through comparison and analysis,besides this,we analyze the structure that affects the performance of each frequency band through surface current,we obtain the best size of antenna through analyzing the position of the loaded LHM.Through the processing and testing of the designed antenna,the tri-band of this antenna are 2.31GHz—2.57GHz?3.41GHz—3.57 GHz and 4.90GHz—5.95 GHz,which indicate that the antenna can be effectively used in WLAN and Wi MAX systems.Forth,an ultra-wideband(UWB)antenna loaded with double-layer tri-band LHM cladding is designed.Firstly,an ultra-wideband antenna is designed by using the quasi fractal method.The impedance bandwidth of the antenna is 2.4GHz—10.8GHz,and the parameters of the antenna are analyzed to determine the optimal size.Then the antenna gain is increased by loading the LHM cladding structure above the radiation patch of the antenna.Due to the double negative bands of the LHM are three,the optimum loading height is selected after comprehensively comparing the impedance bandwidth and gain performance of the antenna when loading different height claddings.The designed antenna is processed and tested,and the working frequency band of the antenna is 2.4GHz—10.8GHz,which satisfies the bandwidth requirement of the UWB antenna,and through adding the cladding,the peak gain of the antenna is maximally increased by 1.7 d Bi. |
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