Research On Design Of Antenna And Antenna Array Optimization Based On Characteristic Mode Theory

Characteristic mode theory(CMT)has received a great deal of attention in the field of antenna engineering since it was proposed,for it provides the clear physical conception and it can characterize the modal resonant behavior of arbitrarily shaped objects such as antennas and scatterers.Besides,it can bring the physical insight to explain the radiating phenomena taking place in the antenna and help designers to understand and guide the antenna design in the engineering.Charcteritic modes represent an inherent property of an object and are independent of any external source.The characteristic currents exhibit the orthogonality property in the source area and characteristic fields are also orthogonal with each other in the far-field range.Due to the above characterisics,characteristic mode theory has been widely used to analyze and design various antennas.In this paper,anti-metal RFID tag antenna,MIMO antenna,metasurface antenna and reactively controlled antenna array(RCAA)are studied concretely based on CMT,respectively.For the analysis and design of the anti-metal RFID tag antenna based on CMT,an approach to design the anti-metal RFID tag integrated with the metal objects is first proposed using CMT.By characteristic mode analysis(CMA)of the metal objects,the desired modes to be excited and excited location are determined and the annular coupling structure is adopted.A detailed small rectangle loop with ceramic material,which atcs as ICE and is placed on a specific position of a metal object,has been designed to excite some desired characteristic modes of the objects and realize the conjugate impedance matching with the chip.For the up-tilted pattern beam of license plate RFID tag antenna is required,a direct CMT-based radiation pattern synthesis procedure is adopted to achieve the desired pattern.By choosing reasonable characteristic modes to be excited and proper loacation,designing the right feed structure,desired modes has been excited according to the requirments and undesired modes has been suppressed.Finally,the license plate itself as a tag antenna with desired up-tilted pattern beam has been successfully designed.For the analysis and design of MIMO antenna based on CMT,the isolation and envelope correlation coefficient(ECC)of MIMO antenna have been discussed from the perspective of CMT and connection and relationship between them have been built.Next,a compact ?-shaped 2-ports 5GHz MIMO antenn with multiple characteristic modes has been analyzed using the obtained connection and relationship,which can provide an impressive explanation about the character of high isolation and low ECC.By the characteristic mode analysis of the stacked dielectric cuboid,the feed structure has been designed reasonable using two different excitation methods of characteristic modes.Finally,a 2-port wideband dielectric MIMO antenna with high isolation has been successfully designed.For the analysis and design of metasurface antenna based on CMT,the characteristic mode analysis of a coaxial probe feed dual-layer metasurface antenna has been performed,which gives a clear explanation of the radiation mechanism of the proposed antenna.Since the dual-layer design increases the profile and fabrication complexity,single-layer metasurface antenna using coaxial probe feed is proposed using CMT.According to the mode information from CMA,proper feed location has been determined and slot-loaded method has been adopted to improve impedance matching.Finally,a single-layer wideband low-profile U-slot loaded linearly polarized metasurface antenna and a single-layer wideband low-profile L-slot loaded polarised polarized metasurface antenna have been proposed.To verify the design,the prototype is also fabricated and measured.The optical design of reactively controlled antenna array(RCAA)base on CMT is studied.The disadvantage of single genetic algorithm(GA)and particle swarm optimization(PSO)when applied to antenna array pattern synthesis is the premature convergence.Taking advantages of both methods,a hybrid GA-PSO optimization algorithm has been proposed.Some numerical experiments including several typical test functions and optimization examples of antenna array pattern synthesis have show that the proposed hybrid optimization algorithm has faster convergence speed and higher convergence accuracy than single GA and PSO.Next,the proposed GA-PSO algorithm together with N-port CMT are used to control the radiation pattern beam of RCAA.The modal weighted significance(MWC)is used as optimized variables.Finally,using the obtaind loaded reactance,full-wave simulation by HFSS is perfomed to verify the design method.