Design And Research Of Terminal Antennas Based On The Characteristic Mode

The environment of terminal antenna is complex,and with the rapid update of communication technology and the rapid development and popularization of Internet of things technology,personalized requirements,metallized appearance and new functional requirements make its environment worse,and the design difficulty is increasing day by day.The traditional antenna design methods,such as manual forced debugging and full wave scanning simulation,are not only time-consuming and labor-consuming,but also difficult to achieve the initial goal.Therefore,in the face of increasingly difficult design requirements,designers need to consider the needs and environment and other factors at the beginning of design,and give a proper antenna scheme.The characteristic mode(TCM)has clear physical significance,which can explain the radiation mechanism of the antenna reasonably,and can show the radiation and scattering characteristics of arbitrary shaped antenna at different frequencies in detail.Its guiding role in antenna design is brilliant at this stage.As an inherent property of the object,the characteristic mode reflects the potential radiation ability of the radiator at a fixed frequency point.The characteristic current and characteristic field of different modes are orthogonal.The real current and radiation field can be obtained by weighting the characteristic current and characteristic field,and the distribution of characteristic current also provides guidance for the excitation position and mode.Therefore,the characteristic mode theory has great advantages and significance in guiding the design of terminal antenna.In this paper,based on the characteristic mode theory,a series of related researches on the antenna of multimode antenna,handset antenna,RFID far-field tag antenna and RFID near-field tag antenna are carried out,which makes the research innovation and practical application more closely combined.In the aspect of analysis and design of multi-mode antenna based on the characteristic mode theory,firstly,the design criteria of multi-mode antenna is proposed by combining the characteristic mode theory,and then a broadband sleeve monopole antenna with omnidirectional radiation is designed.By successively exciting the first characteristic mode of the thin-floor joint and the sleeve-floor joint,the horizontal omnidirectional radiation characteristics in the frequency range of 400-698 MHz are realized.Then focusing on the bad influence of the complete metal frame on the mobile phone antenna,aiming at the problem that it is difficult to design the built-in mobile phone antenna without destroying the metal frame,a design method of seven bandnarrow frame mobile phone antenna with complete metal ring is proposed based on the analysis of characteristic mode theory.Through the adjustment of the metal ring and the floor connection point,the characteristic modes with potential radiation ability of the new connection structure in the required frequency band are evenly distributed,and the corresponding modes are successively excited to make the required frequency band completely covered.This method provides a new idea for the design of this kind of multi band mobile antenna.Finally,a dual-band integrated metal ring watch antenna is designed.A new radiation structure is formed by connecting the metal ring and the floor,and the two different characteristic modes are excited respectively,so the GPS and WiFi/Bluetooth frequency bands are covered.In the aspect of analysis and design of linear polarization synthesis handset antenna based on the characteristic mode theory,this paper first discusses the factors which can influence the polarization direction of linear polarization antenna,and applies the idea to a small-scale RFID handset antenna.Aiming at the difficulty that circular polarization antenna cannot be designed in a long and narrow space,a small-scale handset antenna with directional tilt polarization is proposed.By studying and adjusting the connection type of different radiation structures,the two characteristic modes which have orthogonal polarization characteristics in the same frequency band can be combined organically.Finally,a small-size handset antenna with 45 degree oblique polarization in the required radiation direction is synthesized.In the aspect of analysis and design of RFID far-field tag antenna based on the characteristic mode theory,this paper takes the influence of the surrounding environment of the antenna into full consideration by using the theory of plane layered characteristic mode theory.In this paper,three kinds tag antennas are taken as examples,different antenna solutions are proposed for different environments and required antenna performance,which fully demonstrates the guidance role of plane layered characteristic mode theory on tag antenna design with complex environments.In this paper,firstly,the radiation mechanism of dipole tag antenna is studied by using the characteristic mode theory,and a highly adaptive jewelry tag antenna is designed after considering the environment.Then a design method of tag antenna against central metal column is proposed.Aiming at the problem that the original design is easy to be exposed and destroyed,this method analyzes the characteristic mode of circular patch by using the characteristic mode theory.By selecting the appropriate mode,the radiation characteristics with 45 degree omnidirectional circular polarization aresynthesized,so that the tag can be hidden at the bottom of the metal column and its radiation characteristics are not sensitive for the centered metal column.Finally,based on the design principle of metasurface antenna,a design method of flexible anti-metal tag antenna with low profile and dual polarization is proposed based on the characteristic mode theory.The high isolation performance of dual port is realized by exciting the diagonal structure with symmetrical center.In the aspect of the analysis and design of RFID near-field tag antenna based on the characteristic mode theory,this paper focuses on the near-field magnetic field distribution characteristics of the existing UHF band RFID near-field transmitting antenna,aiming at the problem that the size of the existing closed electric small ring antenna cannot be increased,based on the characteristic mode theory,a new type of logarithmic spiral antenna structure is analyzed and proposed.In this method,the characteristic mode theory is combined with particle swarm optimization algorithm,and the uniformity of the characteristic current under the selected mode is taken as the fitness function.Finally,the antenna structure parameters with the most uniform normal distribution of the magnetic field above are obtained.The new type of near-field label has simple structure and stronger adaptability.After being processed,it is compared with many kinds of labels,which fully proves the correctness of the theory.