Research On Asymmetric Structure Left-handed Material Series And Applications In Antennas

Left-handed material(LHM)is a new type of artificial electromagnetic material,which is different from the traditional right-handed material.LHM has many strange electromagnetic characteristics.Therefore,domestic and foreign researchers concentrate on the research and application of left-handed materials.Most of LHM are based on the traditional periodic arrangement of open-loop resonant rings and periodic double-sided symmetrical LH structures.These LHMs have obvious disadvantages:poor adjustability,high loss,large dimension and narrower bandwidth,thus greatly limiting the application of LHMs in microwave devices.The thesis mainly focuses on the design and application of the asymmetrical LH material structure series,and focuses on the study of the influence of different topological structures on the electromagnetic performance.At the same time,the antenna is loaded with LHMs to study the performance of antenna with different loading methods.The main research work of this article is summarized as follows:1.A series of LHMs based on G-shaped structure are proposed,and multi-bands designs are studied.Firstly,an asymmetrical G-shaped LHM cell structure is proposed,which composed of upper and lower circular arcs,middle long metal rods and transversely-coupled metal rods.The original resonance frequency of the structure is 5.16 GHz,and the LH working frequency is 5.0-5.25 GHz.Then G-shaped LH materials loaded with gaps,branches and loops are obtained respectively,and G-shaped LHM with a loaded ring can expand working bandwidth with a smaller size.The LHM of the binary G-shaped structure can be obtained through the study of the symmetry of the structure.After analyzing the current distribution and loading the connecting nodes,the double-pass LHM can be realized,ie,4.24-4.56 GHz and 6.28-6.34 GHz.Being Loaded with different sized cells,double magnetic resonances are introduced into the wide frequency band of equivalent negative dielectric constant can be controlled to multi-passband characteristics,the designed G-shaped LHM structure is consisted in triple-band LH properties.Finally,the influence of the structural defect asymmetry on the LHM is analyzed for the quaternary G-shaped structure.2.A leaf-shaped LHM series cell structure is proposed,and distributed load improvement is studied.Firstly,an asymmetric leaf-shaped LHM is designed.The left-hand characteristic frequency band of the structure is 5.77-6.17 GHz,and absolute bandwidth is 400 MHz.According to the conclusion in chapter 3,the LHM structure with multiple dimensions can be achieved by introducing different-sized LHM cell structures,and a four-element dual-frequency leaf-shaped LHM structure is proposed,the conclusion of the third chpter is further confirmed.A new topological structure is loaded inside the leaf-shaped LHM structure.Loading the "line-line" coupling structure,the effective current path of the structure is increased,the adjustability is improved,and the resonance frequency and the bandwidth are shifted to lower frequency bands.A"ring-ring"topology is loaded on the tail of the structure.Finally,the influence of the width between the two branch angles and the gap between the inner and outer ring gaps on the double negative characteristics is analyzed,so that the parameters of the structure can be flexibly adjusted to work in the intermediate frequency and of WiMAX the high frequency band of WLAN/WiMAX.3.For the application of LHMs on different antennas,a monopole antenna loaded with a G-shaped LHM was first designed to realize a dual-frequency antenna.Furthermore,the effect of loading left-handed materials with different number of passbands on the performance of UWB antenna is studied.The working bandwidth of the original antenna can be expanded from 2.93 to 9.42 GHz to 2.2?10.61 GHz.Notch antenna is proposed working on 5G dual-band and traditional WLAN bands.Then,the double-leaf-shaped LHM is loaded on the dual-frequency microstrip antenna in a peripheral and cover-layer way,and the peripheral loading antenna operates at 3.38 GHz(low frequency of 5G)and 5.41 GHz(high frequency band of WLAN/WiMAX),then rotational loading method is studied.Finally,the influence of the distance between the cover layer and the substrate on the performance of the antenna is analyzed,at the same time,an antenna with double cover layers are researched.