Study On FDTD Method And Its Application For The Design Of New Artificial Plane Electromagnetic Structure

Artificial electromagnetic material is not existed in nature,which is man-made and has special physical properties.The two-dimensional form of artificial electromagnetic material is artificial plane electromagnetic structure,which is also called Meta-surface.In this thesis,modeling method,which uses finite-difference time domain algorithm(FDTD),for artificial plane electromagnetic structure is studied.Simulations are done both for artificial plane electromagnetic periodical and non-periodical structres using FDTD algorithm.Then,the filtering effects of frequency selective surface(FSS)for electromagnetic waves carrying orbital angular momentum(OAM)are observed and studied.At the same time,the validation of this FDTD algorithm is verified.Electromagnetic(EM)waves with orbital angular momentum(OAM)has a new degree of freedom,which is very promising for channel multiplexing and improving channel capacities in communication systems.Studies of OAM-based communication systems have become a hotspot and it is vital to find functional antennas for the generation of vortex waves.Although many ways to generate vortex radio waves have been proposed,modes of these generated OAM waves cannot be tuned in radio frequency.In this thesis,A reconfigurable reflectarray is proposed for the first time to generate vortex radio waves in radio frequency domain and OAM generating reflectarray is simulated by in-house-developed finite difference time domain algorithm,which is validated by comparing the simulated vortex radio waves with its counterpart obtained by commercial software.Simulations show that the 0,±1,±2 mode of vortex radio waves can be generated at 3.5 GHz by properly assigning the value of capacitance of variable capacitance diode,which is placed between two mental patches on each unit.Next,the structure of reflective cells is redesigned and a reflectarray antenna capable of operating independently in dual-polarization for different OAM modes is proposed.Compared to previous types of reflective cells,the proposed one can achieve smooth reflection phase tuning in dual-polarization with little mutual coupling effect.In this thesis,full-wave simulation software is used to do analyses for this proposed reflectarray antenna.To better understand the principles of proposed unit structure and achieve fast design purpose,we use a simple equivalent circuit model.At the end,dates from full-wave software are used to do post-processing,which include efficiency analysis and purity checking of different generated OAM modes.