Research On Reconfigurable Antenna And Its Application In Time Reversal System

The modern wireless information system is facing two challenges.Firstly,the system needs to achieve multi-polarization,multiband,low power consumption,miniaturization and easy integration.Secondly,the working environment of wireless system becomes increasingly complex and the communication nodes are distributed widely and randomly.Since a reconfigurable antenna could realize the function of multiple antennas with a single antenna aperture by switching the working states,and the time reversal(TR)technique could overcome the multipath effect and achieve synchronous space-time focusing,the reconfigurable antenna technology and time reversal technique provide new methods to deal with these challenges.This dissertation focuses on the research of reconfigurable antenna and its application in time reversal system,and the main contents are summarized as follows:The first part mainly researches on the reconfigurable cylindrical dielectric resonator antennas and achieves reconfigurable patterns and polarizations respectively.First of all,the basic theory of cylindrical dielectric resonator antenna is introduced.A dual-port multiband cylindrical dielectric resonator antenna is taken as an example to illustrate the theory.Then,a pattern-reconfigurable cylindrical dielectric resonator antenna is proposed,employing an annular slot as the coupling aperture.The high-order radiating mode is excited and used for quasi-endfire radiation.Eight switches,installed over the annular slot,are used to rotate the radiation patterns in horizontal plane.Finally,by using the symmetry of the cylindrical dielectric resonator and annular slot,we present a polarization-reconfigurable cylindrical dielectric resonator antenna.An annular slot is used as the feeding aperture,which can not only excite two orthogonal modes of the cylindrical dielectric resonator,but also produce a 90°phase difference.The left-or right-hand circular polarization could be switched by two PIN switches.Both reconfigurable dielectric resonator antennas have the advantages of simple feeding,little effect of switches and DC bias circuit and so on.The second part concentrates on the research of polarization-reconfigurable microstrip patch antennas.Firstly,an important numerical calculation method,the finite difference time domain(FDTD)method,is introduced for the full-wave analysis of microstrip patch antenna.An FDTD code is programed to simulate the radiation process of conventional patch antenna.Then,a polarization-reconfigurable circular patch antenna is designed.By controlling the states of four PIN diodes on the patch,this single port antenna can produce the linear polarization,left-or right-hand circular polarization.For each polarization sense,the antenna exhibits wide impedance bandwidth,high gain and low cross-polarization.Finally,a dual port polarization-reconfigurable square patch antenna is proposed,which can achieve the linear polarization,left-or right-hand circular polarization at each port.When it is operating in the linear polarization modes,the antenna can also be regarded as a frequency-reconfigurable dual-polarized antenna.Both polarization-reconfigurable antennas consist of two dielectric substrate layers.The air substrate and aperture-coupled feeding structure are employed to suppress the surface wave and to simplify the DC bias circuit of PIN switches.In the third part,the principal contents are the application of reconfigurable antennas in time reversal systems.Firstly,the derivation process of time reversal is described in detail,based on the analogue and digital combined technology.The results from FDTD simulation confirm the synchronous space-time focusing of time reversal,which is then used for the field reconstruction of multiple targets or the moving target.Secondly,aiming at the energy issue of wireless sensor network nodes,a microwave power transmission(MPT)system based on time reversal technique is studied.When the multiple transmitters of traditional MPT transmit simultaneously,the electromagnetic waves from different transmitters will be superposed with opposite phase at some special positions,resulting in low transmission efficiency.The TR-based MPT system will be able to overcome this problem effectively.The pattern-reconfigurable dielectric resonator antenna mentioned above is applied in the transmitter to improve the transmission efficiency.As the rectifier circuit is a key component of MPT receiver,a dual frequency rectifier circuit is also designed.In the end,the dual-port polarization-reconfigurable patch antenna mentioned above is used to explore the super-resolution focusing characteristic of different polarized TR microwave,with the help of metal thin wire array.The results demonstrate that a better imaging of target antenna can be obtained by switching the polarization.