1 Bit Programmable Phase Modulated Matesurface For Microwave Imaging

As an important research direction of microwave science,microwave imaging is widely used in security inspection imaging systems and medical imaging.It has a wide range of uses.Because of its small size,light weight,and strong beam control capabilities,super surface has become a microwave and even optical field.Research hotspots.The traditional microwave imaging system has a large volume and a large weight,and it has great potential to replace the microwave imaging traditional dielectric lens with a super surface.The lens of the general imaging system adopts the structure of mechanical scanning because of the fixed focus,which not only increases the volume of the imaging system,but also has low real-time performance.Even the existing reconfigurable supersurfaces are mostly frequency reconfigurable.Diversity metasurfaces,because the different frequency response characteristics of the unit are used,the efficiency will be relatively low,and the degree of freedom of the radiation field is also limited and fixed at the corresponding frequency point.The emergence of programmable supersurfaces improves the freedom of control of supersurfaces,and almost all of the existing programmable supersurfaces cannot independently control each unit at the same time,and can only control one row or one column in time-sharing,which greatly reduces the performance of the supersurface,Even completely difficult to apply to imaging.The programmable metasurface in this study can achieve similar effects as the phased array,and there is no complicated phase shifter network,which is easy to maintain and the cost is greatly reduced.Once the traditional focusing hypersurface is completed,the characteristics of focus,focal length,working frequency band,etc.cannot be changed,and the programmable hypersurface increases the degree of freedom of the hypersurface to the maximum.In this paper,a programmable phase modulation supersurface with X-band microwave imaging is used.The annular slot reflection unit is used.The unit period is 10 mm.When the on-off state of the PIN diode on the unit is changed by programming,the reflection coefficient modulus is close to 1.And they are almost equal,the phase reversal of 0 and 180 is realized,and the influence of vias and traces on the unit is studied,so as to reduce the influence by using reasonable wiring.Using the equivalent circuit method to analyze the unit in theory,it is helpful to analyze the working principle of the unit.The calculation principle of the phase distribution of the array is the principle of the band plate.The phase distribution generated according to the program calculation can form the desired radiation field,and the combination of different phase distributions can achieve focusing at any position.The supersurface is composed of units,the supersurface has a side length of 340 mm,and the operating frequency is around 10 GHz.It can realize the independent control of the phase of each unit at the same time,and the performance is similar to that of the common geometrical phase modulation supersurface.The full wave simulation results show that The programming metasurface has a focusing efficiency close to 35%.At a focal length of 8 times the wavelength,the-3d B focal spot size is 0.93?,and the focal point offset angle is 45 degrees.-3d B focal spot size is 1.25?,and the focal spot size Under the premise of not exceeding 2?,when the focal dynamic focusing range increases the focal length in the longitudinal direction,the focal length can be adjusted to a maximum of 19?,and in the horizontal scanning,the maximum offset angle can reach 68 degrees,which has a particularly wide field of view.Using an ARM microcontroller as a microcontroller,the output pins are expanded through I2 C communication,and dynamic focusing can be achieved through the host computer and programming.Due to the super-surface programmable characteristics,if it is combined with various advanced algorithms for computational imaging,it can theoretically be Achieve various functions such as super resolution,beam scanning,holographic imaging,and beam shaping.