Research On The Design And Application Of Characteristic Mode Theory In Broadband And Frequency Reconfigurable Antennas

As a radio frequency front-end component,the antenna plays a key role in realizing signal transmission and reception and ensuring communication quality.With the continuous iterative upgrade of communication technology,the contradiction between user needs and the shortage of communication resources continues to expand,wide bandwidth and reconfigurable antennas have become an inevitable trend of development.The characteristic mode theory has a clear theoretical explanation,which can guide the design of the antenna from the theoretical level and improve the design efficiency of the antenna.Therefore,the application research of characteristic mode theory in broadband antennas and frequency reconfigurable antennas has very important practical significance.This thesis firstly derives the characteristic mode theory,and then designs several 5G antennas operating at 3.5GHz based on the characteristic mode theory.The main research contents are as follows:1.Two broadband antenna design based on characteristic modeFirst of all,this thesis proposes a low-profile planar inverted-F antenna based on a U-shaped slot.According to the characteristic mode theory,the current distribution and radiation characteristics of different modes are analyzed.And the shorting pin is used to move the TM_0,1/2 mode to high frequency and close to the mode generated by the U-shaped slot to form a broadband.The measured slot antenna achieves a low profile of 0.033?0 while maintaining stable radiation performance.Secondly,a planar inverted F wideband antenna fed by the L probe is designed.The principle of antenna bandwidth broadening is explained by the characteristic mode theory.The actual measurement results of the antenna show that the broadband antenna achieves a relative bandwidth of 56.7%(3.35GHz-6GHz).2.Two frequency reconfigurable antenna design based on characteristic modeFirstly,this thesis designs a reconfigurable antenna with tunable bandwidth based on characteristic mode theory.Analyze its design principle through characteristic mode theory,and using a pair of short-circuit pins and?-type slot to adjust the TM_0,1/2 and TM_0,3/2 modes,the two modes are close to each other to form a dual-mode broadband antenna.On this basis,the shape of the?-type slot is changed,and a PIN diode is introduced to form an antenna with tunable bandwidth.Among them,when the PIN diode is turned off,the antenna works in TM_0,1/2 mode,and when the PIN diode is turned on,the antenna works in both TM_0,1/2 and TM_0,3/2 modes.As a result,the wide and narrow adjustment of the antenna bandwidth is formed,and the tunable antenna bandwidth is switched between 3.27GHz-3.56GHz(8.5%)and 3.26GHz-3.75GHz(14%).Finally,a frequency reconfigurable circularly polarized antenna based on metasurface is designed according to the characteristic mode theory.According to the mode current distribution of different characteristic modes of the antenna,the formation mechanism of circular polarization is analyzed.The equivalent electromagnetic parameter model of the metasurface is analyzed,and the impedance bandwidth and axial ratio of the antenna can be reconstructed by rotating the metasurface.