Study On Modeling And Implementation Of Time Reversal Super-resolution Focusing

One of the advantages of time reversal is adaptive spatial and temporal focusing.A signal emitted by a source in the space,then it is received,reversed and re-emitted by time reversal mirrors,and finally it is focused on the original source point.The super-resolution characteristic of the time reversal technique refers to the sub-wavelength resolution that is obtained by breaking the diffraction limit on the basis of adaptive spatial and temporal focusing.This feature makes time reversal technique a research hotspot,and it is widely used in acoustics,ultrasound and electromagnetic fields.The research of this thesis is mainly about the super-resolution focusing characteristic of time reversal.The basic principles of time reversal focusing characteristics are summarized,some factors that may influence super-resolution focusing of time reversal are validated,and two sub-wavelength arrays for time reversal communication are designed.First,this thesis gives the time reversal solution of the wave equation,which proves the existence of the time reversal signal.Based on Maxwell's equations,this thesis expounds the basic theory of the focusing characteristic of electromagnetic wave time reversal cavity.This thesis introduces the concept of time reversal mirror and its application,and confirms that the time reversal mirror also has a focusing characteristic.Based on the analysis of channel correlation theory,the super-resolution theory of sub-wavelength arrays is provided.Next,this thesis analyzes the factors influencing the super-resolution focusing characteristic of time reversal.The factors include the placement of time reversal mirrors,the sub-wavelength array with or without loaded wires,and the uniform distribution of loaded wires or not.Simulation experiments show that,without loaded wires,the time reversal mirror which is composed of multi-antennas and placed in the near field is easy to achieve super-resolution focus effect.If the sub-wavelength array is surrounded by a non-periodic distribution wire array,the time inversion channel will have rich multipath components,which can help to show the time reversal super-resolution focusing.Finally,this thesis presents two sub-wavelength arrays.One is an array etched cross structures.The array consists of four same ultra-wideband antennas,and the distance between each other is smaller than half of the wavelength.The evanescent wave is reconstructed and the sub-wavelength information is propagated to the far field,by etching cross structures on the radiating surface and the ground of the unit antenna.Thereby the super-resolution focusing characteristic is realized.The other one is a stacked MIMO array,which contains three planar four-cell MIMO antennas.Each planar MIMO unit antenna is a miniaturized broadband antenna.The time reversal technique is introduced into the sub-wavelength array antenna.Simulation analysis shows that the characteristic of super-resolution focusing can be realized around each unit antenna.