Research And Design Of Wideband Circularly Polarized Nonuniform Metasurface Antenna Based On Characteristic Mode

With the rapid development of wireless communication systems,circularly polarized antennas have been widely used because they can receive arbitrarily polarized electromagnetic waves.The traditional microstrip patch antenna is widely used in the design of circular polarized antenna due to its advantages of low profile,easy machining and low cost,but it also has the inherent shortcoming of narrow impedance band.In recent years,metasurface has attracted much attention due to its extraordinary ability to regulate electromagnetic wave.By designing the metasurface structure and combining it with the traditional antenna,the performance of low profile,high gain and broadband circular polarization can be achieved.Therefore,the design and analysis of metasurface structure are very important.The characteristic mode theory provides a good method for the design of the metasurface.In the absence of excitation,the characteristic mode and radiation characteristics of the metasurface are studied,and then the mode required by the excitation of the feed structure is designed,and the antenna with corresponding radiation characteristics can be obtained.The characteristic mode analysis method is not only fast and efficient,but also can provide the physical meaning of the antenna clearly.Therefore,this paper adopts the characteristic mode theory to study the wideband circularly polarized metasurface antenna.The main research contents are as follows:1.A wideband circularly polarized slot antenna based on non-uniform metasurface is proposed.The antenna consists of a microstrip coupled slit structure and a 4×4 non-uniform metasurface.The microstrip and gap are coupled to generate linearly polarized waves,and the non-uniform metasurface is used to convert linearly polarized waves to circularly polarized waves.The proposed non-uniform metasurface has two innovations: first,the metasurface element is loaded with branches to increase the current flow length and equivalent series capacitance,so that the metasurface resonates at a lower frequency;Second,by loading different lengths of branches on the middle metasurface and the surrounding metasurface,two modes with similar resonant frequencies and similar current distribution on the surface are fused,so that the bandwidth of the original mode is extended and the two modes are pulled apart to obtain a wider axial ratio bandwidth.The mechanism of circular polarization radiation and the principle of axial ratio bandwidth broadening of non-uniform metasurface antennas are revealed through characteristic mode analysis.The simulation results show that the impedance bandwidth and axial ratio bandwidth of the non-uniform metasurface antenna proposed in this paper are not only better than the other two kinds of uniform metasurface antenna,but also better than that of the metasurface antenna in the literature.2.A wideband circularly polarized patch antenna based on non-uniform metasurface is proposed.The antenna is novel in two aspects: first,L-shaped branches are loaded on the truncated square drive patch.Compared with the metasurface antenna without L-shaped branches,the antenna impedance bandwidth and axial ratio bandwidth are greatly improved.Second,the eight metasurface elements around the uniform metasurface are reduced to the center.After optimizing the feed structure parameters,the new mode is excited,and the impedance bandwidth and axial ratio bandwidth of the antenna are further improved.The mechanism of circular polarization radiation and the reason of broadband formation are revealed by characteristic mode analysis.The simulation results show that the impedance bandwidth and axial ratio bandwidth of the proposed metasurface antenna are better than those of other literatures.