Research On Beam Synthesis And Control Based On Holographic Electromagnetic Metasurface

The principle of holographic antennas is derived from holographic imaging technology in the optical field.The holographic antenna system only includes a high impedance surface and a feed source without complicated feeding network,so the structure is very simple;To design a holographic antenna is relatively easy,and a holographic pattern that can realize arbitrary beam pointing can be easily designed.However,at present,most holographic antennas use simple square metal patch as its unit structure,which is non-reconfigurable.Due to the fixed structure,one holographic antenna has only one single function.To realize reconfigurable holographic antenna,it is the key to find a reconfigurable unit structure.This thesis aims to achieve reconfigurable holographic antenna.Based on a systematic acknowledge of the working principle of holographic antenna,a scheme for achieving reconfigurable holographic antenna based on PIN diodes is proposed: a PIN diode is integrated on each unit,which has the lowest radiation energy when the PIN diode is turned on,and when the PIN diode is blocked,its radiation energy is the largest.Under the action of an external DC bias voltage,each unit can realize one of these two states(similar to "0" and "1" in binary).Therefore,the array of these units can approximately record information of arbitrary interference field.Then two specific reconfigurable structures are proposed in this paper: a rectangular slot structure(structure 1)with one PIN diode integrated in each cell and a quad-symmetric cELC structure(structure 2)with two PIN diodes integrated in each cell.First,the above two unit structures are simulated based on the equivalent circuit model of PIN diode to verify the reconfigurability.Then,the antenna structures based on the two reconfigurable units were simulated and analyzed separately.Both structures finally realized Two-dimensional beam scanning: 360 ° full coverage in azimuth and 65 ° in elevation;The antenna of structure 2 also realizes polarization reconfiguration(including linear polarization and circular polarization)and multiple beam.Then we tried using a quarter-cylindrical wave as the reference wave,and implemented the feeding coaxial at the corner of the holographic surface,and as a result,the aperture efficiency of antenna with structure 2 is twice that of antenna with structure 1.And we find that aperture efficiency can be further improved by optimizing the propagation constant.Finally,a DC bias network was designed for both antenna structures—including metal vias,bias lines,and fan-shaped branches,and simulations verified that the impact of the DC bias network on antenna performance was acceptable,which proves the rationality of the bias network.