Manipulations Of Electromagnetic Waves And Their Applications Based On Metasurfaces

Microwave and millimeter-wave circuits and systems and wireless communications are rapidly developing topics.Because of unique structural advantages and performance advantages,metasurface has become one of the research hotspots,and plays an increasingly important role.With the intensive study of metasurface,many excellent scientific research results have been reported.On this basis,two types of metasurfaces are emphatically studied in this thesis,including spoof surface plasmon polaritons(SPPs)and digital coding metasurfaces.The main contributions are summarized as follows:1.Through etching a group of circular split-ring resonators(SRRs)with the same size or multiple groups of circular SRRs with different sizes on the spoof SPP transmission line,a single-frequency rejection filter,a double-frequency rejection filter,and a broad band-stop filter with bandwidth of 1.5GHz are designed and fabricated.The simulation and measurement results verify good filtering performance of the proposed structures.2.Through etching a group of rectangular SRRs with same size or two groups of rectangular SRRs with different sizes on the SPP transmission line,a single-frequency rejection filter and a double-frequency rejection filter are designed and fabricated.3.Based on the tapered microstrip structure to connned microstrip lines,spoof SPP waveguide and traditional substrate integrated waveguide(SIW),a novel hybrid circuit is proposed.The spoof SPP waveguide of the hybrid circuit is made of two anti-symmetric corrugated metallic strips.The main physical significance of the hybrid circuit is the efficient conversion between spoof SPP modes,quasi-transverse-electromagnetic(TEM)mode and ransverse electric(TE)mode in both wideband and narrowband,which has been verified by measurements Based on the properties of spoof SPPs and SIW,efficient filters with the performance of adjustable bandwidth can be achieved4.Combining binary particle swarm optimization(BPSO)and electromagnetic field simulation software,a design method is proposed to automatically acquire structures of digital coding unit cells which meet the design requirements.Based on this design method,1-bit digital coding unit cells with broadband,2-bit digital coding unit cells with broadband,and 4-bit digital coding unit cells in specific frequency are realized5.Based on 1-bit coding unit cells,a digital coding metasurface are designed and fabricated with 0101.../1010...periodic coding sequence,and its performance has been verified via the experiment.Utilizing 4-bit coding unit cells,two complicated functional metasurfaces are proposed for shaping beam,including a quasi-circular digital coding metasurface to radiate circularly shaped beams,and a quasi-elliptic digital coding metasurface to radiate elliptically shaped beams6.A deep-learning method based on Resnet-101 neural network is proposed to predict the vast and complex systems for obtaining the reflection phases of discretely random lattice unit cells quickly and accurately.Based on BPSO and deep-learning neural network,a machine-learning method is proposed with a link between the deep learning and BPSO.Through the machine-learning method,it is convenient to search the coding unit cells whose reflection phases meet the design requirements of various parameters.Considering the design parameters of reflection phase difference of anisotropic coding unit cells in the orthogonal directions and the reflection phase difference between adjacent coding unit cells,eight kinds of 1-bit coding elements with 3-bit phase differences in the orthogonal directions of 0°/180°,-45°/135°,-90°/90° and-135°/45° are presented7.Using 1-bit kinds of 1-bit coding elements with phase differences of 0°/180°obtained by the machine-learning method,a digital coding metasurface is fabricated for radiating a left-handed circular polarization(LHCP)beam and a right-handed circular polarization(RHCP)beam.Using 1-bit kinds of 1-bit coding elements with phase differences of-45°/135°,a coding metasurface is fabricated for radiating a LHCP beam and a linear polarization(LP)beam.Based on all 3-bit kinds of 1-bit coding elements for increasing the complicated functions of metasurfaces,a digital coding metasurface is fabricated for radiating a LHCP beam,a LP beam and a RHCP beam.Simulated and experimental results of all three kinds of digital coding metasurfaces conform to design requirements,and also verify the correctness of the design method.