Design Of Broadband Antenna Based On The Theory Of Characteristic Mode

In recent years,the application of characteristic mode theory(CMT)in antenna design has been becoming more and more common.Compared with the analytic method,it has the same accuracy without its limitation and has a clear physical explanation.The theory of characteristic mode is only related to the geometrical structure and material properties of the antenna,and has nothing to do with its feeding.It can provide valuable insights in the design of the antenna,which also makes the characteristic mode theory provide important guiding for the design of the antenna.Based on the characteristic mode theory,this thesis discusses the application of characteristic mode in the design process of broadband antenna.Several different antennas are analyzed with the characteristic mode theory,and the new design idea is presented based on the characteristic mode theory.The main contents of the thesis are as follows:The problem of mode tracking for antenna with complicated structure is studied.Firstly,the eigenvalues and eigenvectors are obtained from the impedance matrix of the antenna.Then,the correlation between the eigenvectors is calculated by MATLAB programming.Finally,the tracking algorithm is used to track the modes of the broadband antenna.Based on the characteristic mode theory,the planar monopole antenna and planar folded monopole antenna are analyzed.The design guidance of monopole antenna is presented by combining the eigenvalues,characteristic current(also called model current)distribution and the magnitude of mode current.With this guidance,the bandwidth of the monopole antenna is widened and the resonant frequency band of the planar folded monopole antenna is transferred.By analyzing the design process of monopole antenna with the characteristic mode theory,methods of reducing the VSWR of antenna are obtained.A multi-band border mobile phone antenna is designed based on the characteristic mode theory.By using the characteristic mode theory,the modes with resonance characteristics are selected.By observing the distribution feature of the mode current,the different positions in the antenna structure are selected to stimulate the different modes.Finally,the influence of the different high order modes on antenna performance is analyzed.Ultimately,by stimulating multiple modes at the same time,the phone antenna covers the GSM?DCS?CDMA?WLAN?LTE band.