Research On The Application Of Metamaterials In The Design Of Microwave Filters And Filtering Antennas

Metamaterial(MTM)is an artificial electromagnetic material with special properties such as negative refractive index and inverse Doppler effect.Its physical properties are not available in other materials in nature.It is precisely because of its unique electromagnetic characteristics that it has attracted the attention of many researchers since it was proposed,and it has a very wide range of applications in the design of microwave devices.Filters and filtering antennas designed with metamaterials can well meet the requirements of communication systems for device miniaturization,integration and adjustment,and have broad development prospects.This article first introduces the research status of metamaterials and the development of 5G communication technology,and summarizes the applications of the metamaterial unit structure Complementary Split Ring Resonator(CSRR)and other metamaterial structures in device design.Secondly,it summarizes the related theories of CSRR,the theory of composite left and right-handed transmission lines,and the theory of slot-coupled antennas.Finally,based on metamaterials,two microwave filters covering the 5G communication frequency band and a filtering antenna with a new structure were designed.Several specific research contents are as follows:The first filter has metal through holes at the four corners of the substrate,and uses the CSRR structure to improve its in-band and out-of-band characteristics.Since the resonant frequency of CSRR is related to its size,changing the size of the ring at different locations will produce four different transmission characteristics.The optimized two passbands are 3.22-3.78 GHz and 4.50-5.00 GHz respectively,the insertion loss in the passband is less than 0.78 d B,and the frequency band selectivity is better.The second filter is designed using the theory of composite left and right-handed transmission lines.A double L-shaped microstrip line is set on the upper surface of the dielectric substrate,the grounding plate etches CSRR,and the TEM mode perpendicular to the grounding plate can meet the excitation conditions of CSRR.The metal strip is used to realize the on-off of the fixed-value capacitor and the microstrip line,so as to achieve the purpose of adjusting the frequency band of the filter.The designed filter has a wide passband of 3.23-5.44 GHz when the metal strip is disconnected,and a stopband of 3.30-4.71 GHz after the metal strip is connected,indicating that the passband and stopband can be switched by controlling the metal band.The bottom of the third filtering antenna is fed by a microstrip coupling slot,and the upper metasurface is composed of uniform fractal metal sheet units.After measurement,the 10-d B impedance bandwidth of the filtering antenna is23.6%(3.22-4.08GHz),the average antenna gain in the passband is 8.1d Bi.No additional filter circuit is involved in the filtering antenna,and the insertion loss is ideally eliminated.Therefore,by using a well-designed metasurface,the antenna can achieve low profile,high gain,and broadband filtering performance.