Research On Application Of Time Reversal Technique In Electromagnetic Communication System

Time reversal electromagnetic wave has characteristic of adaptive spatial-temporal synchronous focusing and can achieve far-field super-resolution focusing combining with near-field sub-wavelength scatterers.With these features,the time reversal technique will help to achieve high-speed,safe and miniaturized electromagnetic communication systems.In this paper,the application basis and new application schemes of time reversal technology in the field of electromagnetic communication are deeply studied.Firstly,the background and development trends of time reversal electromagnetic application systems,especially the electromagnetic communication systems,are introduced in the dissertation.Schemes of current time reversal pulse communication system and the method of designing compacted receiving arrays based on super-resolution feature are reviewed.The direction of further research on the time reversal electromagnetic communication system is pointed out.Also,the dispersion code multiple access communication system and its relation with time reversal technology are introduced.The potential for convergence of these two communication technologies is proposed.Secondly,the specific performance of traditional time reversal pulse communication system is analyzed.Based on this,some modified time reversal schemes are proposed and compared with the traditional scheme.Traditional time reversal communication scheme has the best power focusing characteristic.It can achieve the highest peak power with a certain total transmission power and environment.The proposed modified time reversal schemes can effectively reduce the time-domain power spreading of the signal,then reduce the inter symbol interference.Also the modified schemes can improve the fidelity of pulse signal.Different time reversal schemes needs to choose in the practical applications based on the communication environment and application needs.In this paper,a new time reversal high-speed communication scheme based on the overlapping pulse position modulation and a new time reversal secure communication system based on the artificial noise loading technique are proposed.The actual communication experiment results show these two new time reversal pulse communication systems work well and in line with the expected results.The new proposed schemes expand and promote the application of the time reversal technology in the field of electromagnetic pulse communication.Then,the diffusion phenomenon of the time reversal field in the application system is analyzed based on the time reversal cavity theory.And a new multi-target imaging technique based on the elimination of the time reversal field diffusion using CLEAN algorithm is proposed.The effects of time reversal mirrors have also been analyzed in the practical discrete time reversal mirror model and corresponding equilibrium algorithm to counteract these effects is proposed.Using the near-field arranged periodic sub-wavelength metal grating as example,the conversion between evanescent wave and propagation wave in time reversal system is studied.In the time reversal system,the reconstructed evanescent wave component is not only based on the initial wave but also the specified scatters structure.A new method to re-construct the initial evanescent wave based on both changing the position of the scatters and multiple measurements is proposed and verified.Based on these research of physical mechanism of time reversal super resolution,a new time reversal super-resolution communication system using pulse shaping network to achieve single antenna multiplexing is proposed.The test results of the actual communication system show that it can realize multiple independent communication on the basis of not increasing the number of receiving antennas and not reducing the single communication rate.At last,the way of using time reversal to improve the performance of dispersion code multiple access communication system is proposed.Time reversal device can be used to solve the precise matching problem and attenuation control issues in the dispersion code devices design process.The design methods of the dispersion code device,which is core device both in dispersion code multiple access communication system and in time reversal system,are deeply studied.The method to design dispersion code device with arbitrary group delay response using cascaded strip line C-section structure is proposed and simulated.Also the method to design dispersion code device using nonuniform micro-strip line C-section structure is proposed.In the method,defected ground plane structures are used to offset the forward coupling in the micro-strip line C-section structure.Measurement results verify that the new proposed micro-strip dispersion code device works well.The research on design of dispersion code devices is helpful for the realization of practical time-reversal devices and the technical development of time reversal multi-user communication system using the dispersive devices.