Electromagnetic Characteristics Analysis Of Metamaterial And Its Application In Antenna Optimization Design

Metamaterials,as artificial composite materials,have attracted extensive attention in recent years because of their unique electromagnetic properties,which are not common in nature.Its special electromagnetic properties mainly depend on the change and design of its own microstructure,so the use of appropriate design means to establish metamaterials with specific functions has broad application prospects for electromagnetic,optics and other fields,especially to improve the performance of antennas.Based on the theory of equivalent medium,this paper simulates metamaterial elements by FDTD and S-parameter inversion method,analyzes the possibility of application of different electromagnetic characteristics of metamaterial in antenna optimization design,and proposes an electrical tape gap structure（EBG）metamaterial for synchronous switching noise suppression.The multi-frequency antenna,wearable dual-band dual circularly-polarized（DBDCP）antenna and DBDCP MIMO antenna are optimized by using metamaterials,and the miniaturization,gain enhancement,and isolation enhancement of these microwave devices are achieved respectively.The specific research contents and results are as follows.1.The equivalent medium theory of periodic structured metamaterials is studied.Based on the theory of equivalent medium,the classical open resonant ring（SRR）metamaterial structure is analyzed and verified by FDTD algorithm and S-parameter inversion method.The backward propagation characteristics of negative refractive index metamaterials,the metamaterial zero reflection phase characteristics of artificial magnetic conductor（AMC）and the impedance matching theory of metamaterial absorber are reviewed,and the working principles of the negative refractive index metamaterial in antenna miniaturization,gain enhancement and isolation improvement are explained,which provides theoretical support for the application in antenna optimization design in the following paper.2.A checkerboard-shaped electromagnetic bandgap（C-EBG）structure is proposed for the suppression of synchronous switching noise（SSN）in high-speed digital systems.A meander line metamaterial absorber（ML-MA）has been designed to form the EBG unit,and its equivalent circuit has been analyzed.The absorption bandwidth of the ML-MA absorber ranges from 7.0 GHz to 14.7 GHz,with an absorption rate exceeding 80%.By arranging ML-MA EBG units periodically along with three-ring nested L-bridge EBG units,a final C-EBG metasurface is formed,enabling broadband suppression of SSN from 0.9 GHz to over 40 GHz.Through the composite effect between ML-MA and L-bridge EBG units,C-EBG exhibits high impedance surface characteristics across the entire operating band,resulting in a suppression depth exceeding 30 d B.3.A microstrip antenna operating at four frequencies is proposed based on double negative metamaterial（DNG-MTM）to achieve miniaturization.Initially,a single-sided metamaterial unit（DNG-MTM）with three double negative frequency bands is formed by combining the structure of a single negativeε-metamaterial（ENG-MTM）and a single negativeμ-metamaterial（MGG-MTM）.The DNG-MTM unit is optimized to design a microstrip antenna with four resonant bands in the form of a radiation patch.The final electrical size of the antenna measures0.23λ₀×0.37λ₀,enabling realization of the following resonant bands through machining and testing:2.84-3.55 GHz（22.2%）,6.6-7.18 GHz（8.4%）,7.44-9.08 GHz（19.9%）,and 11.-14.74GHz（28.2%）.The peak gains are 5.3 d Bi,6.3 d Bi,5.8 d Bi,and 3.4 d Bi respectively,while the antenna radiation efficiencies reached 96%,82%,91%,and 86%correspondingly.These frequency bands effectively cover applications in the C-band,X-band,Ku-band for satellite systems as well as the emerging demands of the 5G spectrum at around 3.5 GHz.Notably,compared to conventional design approaches,the proposed metamaterial-based antenna achieves a remarkable size reduction of approximately 55%.This outcome convincingly demonstrates the efficacy of metamaterials in optimizing miniaturized multi-frequency antennas.4.A wearable dual-band dual-circularly polarized（DBDCP）antenna,based on the artificial magnetic conductor（AMC）,is proposed and designed to enhance antenna gain.The implementation of this antenna took the form of a quadruple inverted-F antenna（QIFA）with a relatively wide axial ratio bandwidth（ARBW）spanning from 3.5 GHz to 4.0 GHz（13.3%,LHCP）and from 4 to 5.9 GHz（8.8%,RHCP）.DBDCP is achieved by combining two 1-4power dividers operating at 3.5 GHz（LHCP）and 5.8 GHz（RHCP）,respectively.A hat-shaped AMC reflector is designed,utilizing an array of AMC units with varying sizes to achieve a broad reflection bandwidth of 0,thereby enhancing the gain of lower frequency band.The measured operating bandwidths of the antenna are 3.4-4.4 GHz（25.6%）and 5.1-6.5 GHz（24.1%）,making it suitable for utilization in industrial Io T systems such as 5G,Industrial Science and Medical（ISM）,WLAN（5.8 GHz）,and Wi MAX（3.5 GHz）.By incorporating AMC,the peak gain of the antenna increases from 7.9 d Bic to 11.9 d Bic in the first operating band and from 8.9 d Bic to 10.5 d Bic in the second operating band when compared to an antenna without AMC,thus validating metamaterials’role in optimizing DBDCP antenna gain.5.A dual-band dual-circularly polarized MIMO antenna with metamaterial to improve isolation is proposed.DBDCP MIMO antenna is a research direction to improve the communication performance in multi-path environment.Although right-handed and left-handed circular polarization are orthogonal,placing right-handed and left-handed circularly polarized antennas next to each other usually results in more complex coupling to each other.After the initial arrangement of MIMO antenna element is selected by considering the radiation characteristics such as isolation degree and axial ratio,a metamaterial absorbing element based on fractal technology is proposed,which can realize the double absorbing frequency band of3.5 GHz and 5.8 GHz.By loading the absorbing unit near the port of the DBDCP MIMO antenna unit,the axial ratio bandwidth is increased from 3.6-3.7 GHz（2.7%,RHCP）and 5.4-5.8 GHz（7.1%,LHCP）to 3.3-3.9 GHz（16.7%,RHCP）and 5.3-6.6 GHz（21.8%,LHCP）,the isolation is increased by more than 10 d B,and can reach an isolation level of greater than 30d B in the entire working band.The metamaterial absorber maintains the DBDCP performance of the antenna on the premise of improving the antenna isolation,thus realizing the optimization of DBDCP MIMO antenna.