Multi-Band Antenna Design And Related Device

The performance of communication equipment plays a key role in the development of communication system.As a key component of communication system,antenna's research gradually tends to MIMO structure,multi-band,6G communication and terahertz direction.Multi-band technology can meet people's demand for frequency band resources,MIMO system can improve communication quality and transmission rate more effectively.Meanwhile,terahertz band will become a research hotspot of 6G communication in the future due to its advantages of rich widewidth and high-speed transmission rate.Graphene antennas can work in the terahertz band,because of graphene's excellent electrical conductivity and physical properties.Meanwhile,graphene and other low-latitude materials are also used to design various functional devices.In this thesis,a dual-band wideband MIMO antenna,a terahertz multi-band graphene antenna and a terahertz Bragg reflector are designed and studied for multi-band antennas and related devices.The main work of this thesis is as follows:Firstly,a dual-band wideband MIMO array antenna is designed by placing two identical antenna elements in parallel.The antenna structure consists of a radiation patch,a ground plate and an epoxy resin(FR4)substrate.The low-frequency resonance depends on the rectangular patch,and the high-frequency resonance is induced by the coupling between the U-shaped slot and the radiation ring.A T-shaped isolated grounding patch is added between the two antenna units,which increases the current path and changes the current distribution of the entire antenna,finally making the MIMO antenna meet the isolation requirements.The electromagnetic simulation software HFSS 15.0 is used to simulate and optimize the antenna parameters.The results show that the designed MIMO antenna has dual-band characteristics of 3.24-4.8 GHz and5.9-6.9 GHz,which achieves broadband characteristics of 38.8% and 15.6% relative bandwidth in the two working bands,respectively.The isolation degree of antenna with T-shaped element is improved to below-20 d B.Antenna has good radiation characteristics,the envelope correlation coefficient is less than 0.5,which can be used in wireless communication system.Secondly,according to the structure of dual-band wideband MIMO antenna,a graphene antenna which can work in the terahertz band is designed with a size of 40 ?m×58.9 ?m.The antenna can work in three frequency bands: 1.99-2.13 THz,2.47-2.63 THz and 3.85-4.07 THz.The echo loss of corresponding resonant points is-19 d B,-20 d B and-34 d B respectively,and the gain can reach more than 5 d Bi.The antenna was further placed orthogonal to obtain a two-port terahertz graphene MIMO antenna with a size of 55 ?m×45.8 ?m.The antenna works in three frequency bands of 2.0-2.2 THz,2.5-2.6 THz and 3.4-3.6 THz,which gain reaches up to 6 d Bi at the resonant point.Compared with the metal PEC antenna in the same frequency band,the isolation degree of the designed antenna is improved by 10 d B.At the same time,the dual polarization characteristic of the antenna is realized,which is helpful to further enhance the isolation degree of the antenna.Finally,the four antenna elements are orthogonal to form a four-port MIMO antenna array,and the return loss at the resonant point is-36 d B,-26 d B and-43 d B,respectively.The maximum gain is more than 7 d Bi,which is better than that of two-port antenna.The multi-band terahertz graphene antenna designed in this chapter has the characteristics of small size,good return loss and high isolation.Finally,a terahertz Bragg reflector consisting of a double-layer Dirac semi-metallic alternating spacing dielectric grid is designed using the properties of low-latitude materials such as graphene.The transmission of the proposed reflector can be tuned via not only varying the permittivity of the dielectric grating but also changing the period number of the unit cells.By adjusting the separation distance of the parallel BDS sheets,we can derive another degree of freedom to tune the Bragg band gap.In addition,the transmission spectra can also be freely tuned by means of alka-line metal doping.At last,the defect resonant mode is realized in the Bragg reflector.Our proposed Bragg reflector will have potential prospects in designing integrated photonic circuits at terahertz frequencies.