| In today’s advanced mobile communications,users have an increasing demand for highspeed data transmission,as well as higher and higher requirements for wireless communication equipment.In order to meet the growing demand for communication,reconfigurable antenna is born.It can realize the superposition of multiple antennas without increasing the number of antennas,and has many advantages.And it can change its working bandwidth,working frequency,radiation pattern or polarization mode according to the needs of the communication system.Among them,the pattern reconfigurable antenna has a variety of different radiation patterns and working states,which can make the antenna have the advantages of good channel capacity and high security,so its application prospect is very broad.In this thesis,two novel pattern reconfigurable antennas are designed by using the theory of characteristic mode(TCM).The specific work is as follows:(1)Design of pattern reconfigurable antenna.Based on the TCM,this thesis presents a pattern-reconfigurable antenna with two operating states at the 3.5 GHz.The antenna consists of twelve rectangular metal patches as radiators and a feeding structure with diodes.By adjusting the state of the diodes in the working frequency band,two different modes can be excited to realize two different radiation patterns,and then two possible working states of the reconfigurable antenna can be realized.The simulation results show that the cross polarization of the pattern reconfigurable antenna is lower than-30 d B,and the maximum radiation gain of the pattern is above 11.8 d Bi in both states.(2)Design of dual-port pattern reconfigurable MIMO antenna.Based on the TCM,this thesis presents a novel pattern reconfigurable dual-port MIMO antenna with four operating states at the 2.45 GHz.The proposed antenna consists of the rectangular platform(RP),excitation units,and reconfigurable feeding networks.Four elaborate characteristic modes(CMs)of the RP can be stimulated effectively by six groups of balanced inductive exciters(BIEs)with a reasonable excitation purity to achieve high isolation degree within the designed frequency band.A reconfigurable feeding network controlled by four switches related to two ports has been designed to feed the BIEs.By controlling the ON/OFF states of the four switches,the feeding network can generate four different excitation combinations,resulting in four possible operating states for this reconfigurable dual-port MIMO antenna.Furthermore,the isolation performance of the proposed MIMO antenna is better than 36 d B due to the orthogonality of radiation patterns between the CMs in each of the four states. |
