Study Of The Self-Adaptive Focusing Antenna Array Based On Time Reversal Technique

Time Reversal is a unique self-focusing technique for spatial and temporal focusing. The time reversed acoustic waves or electromagnetic wave could adaptively match to transmission channels, and efficiently depress or even make use of multipath interference to improve reliability of information transmission and detecting precision. In recent years, this technique has been successfully applied to target detection, underwater communication, non-destructive testing, earthquake prediction, and so on. It also becomes a hot research in the field of electromagnetic wave. This paper is mainly focused on the self-adaptive focusing antenna array based on time reversal technique, investigates focusing properties of time reversed electromagnetic waves and the interation mechanism between transmission environment and waves. Several new methods for target detection, beam forming and radiation analysis of pulsed antenna array are proposed by combining antenna array theory and time reversal technique, aiming to provide some new ideas on the development of antenna array based on time reversal technique.First in this paper, the focusing principles and characteristics of time reversed electromagnetic waves are introduced. On this basis, the model and algorithm of time reversal electromagnetic waves are set up and incorporated with Taguchi optimization algorithm to discuss the influence factors of focusing quality. Starting from the time reversal symmetry of wave equation and reciprocity of electromagnetic wave propagation, the focusing principles of time reversed electromagnetic waves using time reversal cavity and time reversal mirror are studied by using green function method and multipath channel model. Then a new algorithm is proposed by introducing the time reversal operator to the finite difference time domain. This algorithm is used in combination with Taguchi optimization algorithm to simulate and analyze the factors influencing the focusing quality of time reversed electromagnetic waves, which including position of time reversal mirror, length of recoding time, waveform of recording signal and array configuration. These works lay a good foundation for the realization of self-adaptive focusing antenna array based on time reversal technique.Secondly, this dissertation has studied the pulsed antenna array’s analysis and design method, and presents a transceiver model according to the time reversal characteristics of pulsed antenna’sending and receiving waveforms, which can be used to analyze mutual coupling of arrays. Pulsed antenna array can reduce the request on antenna elements, improve effectively the radiation properties of system in alliance with speed switches, and has the power of beamforming and beam scanning. So it is an effective way to implement self-adaptive focusing antenna system. Since the theory of pulsed antenna is still in development stage, there are many difficulties and problems in the analysis and design process. This dissertation attempts to address these concerns:a fast radiation-pattern computing method for pulsed antenna array based on point-source analytical method and simulation is proposed, which extremely improves the running speed and reduces the memory; maximum spatial power combinating condition for multi-channel signals is derived directly in time domain, and used to design an array fed parabolic cylinder antenna to achieve UWB high power microwave narrow beam; the dissertation also investigates the sending and receiving waveforms of pulsed antenna under the same excitation, and figures out the time reversal characteristics between them; a transceiver model of pulsed antenna array according to the above conclusion is proposed, and applied to separate radiation waveform in mutual coupling analysis and antenna array design. The simulation example of one-dimensional TEM array validates the correctness and effectiveness of the presented models.And then, time reversal technique and parabolic equation method are combined in realizing the localization of transmitter in troposphere environment. Direction-of-arrival estimation is a prerequisite for beamforming, but the multipath effect in troposphere environment distorts receiving signal, which affects the conventional algorithm’s estimation precision, even results in an unsuccessful localization. A time reversal parabolic equation method for source localization in troposphere waveguide is proposed, in which time reversal electromagnetic waves are loaded on the initial field. The simulation results show that the proposed strategy has the same positioning accuracy with inverse diffraction parabolic equation. In order to accommodate more flexible modeling, an improved method in which time reversal electromagnetic waves are loaded on the transmitting radiation pattern is presented. The antenna number has been reduced by 10 times under the same accuracy limit after using this method.At last, the time reversal technique is introduced into the beamforming algorithm, by which focused beamforming in near-field and beamforming in far-field are investigated, respectively. Adopting time reversed waves in near-field can compensate the amplitude and phase of the spherical waves, and achieve the focused beam, at the same time, focused beamforming algorithm with exclusion of autospectra is employed to obtain the beam with narrower main-lobe and lower sidelobe level. In far-field, with the time reversal technique, the signals are adaptively matched and focused, that is, the time reversal message of the received signals is directly set as the initial parameter of amplitude and phase, and under combining iterative Fourier transform algorithm, the magnitude of the array excitation is optimized and multi-beam antenna array with lower sidelobe level is achieved.