| Based on the advantages of terahertz high resolution and high frame rate imaging,frequency-swept antennas have important application value in these fields,such as target detection,security inspection and nondestructive inspection.This paper focuses on the theory and simulation of linear polarization,circular polarization frequency sweeping antennas and frequency coding metasurfaces technology around the terahertz frequency sweeping technology,focusing on the electromagnetic characteristics and array characteristics of the cell structure.The specific work content of this article is as follows:Firstly,the linear polarization frequency sweep performance of a terahertz metasurface array is simulated and studied.Through research and optimization,the electromagnetic characteristics of the metasurface patch unit structure in the 0.5-1.5THz band were obtained,and 16×16 unit metasurface array structures were constructed.The theoretical prediction is that the beam scanning range of the array structure in the range of 1-1.35THz is 33.78-48.59°.The simulation results show that under the perpendicularly incidence of x-polarization or y-polarization,the reflection angle of the metasurface array structure with the isotropic structure at each frequency point is the same,and the beam scanning range is 34-48°.Because the reflection coefficients are all above 0.6,it has good reflection efficiency.The simulation results are basically consistent with the theoretical calculation results.Secondly,the ultra-wideband terahertz metasurface circularly polarized frequency sweeping antenna was simulated and studied.The fixed size of the rotary unit is determined by the two factors of reflection coefficient and broadband,the relationship between the phase and the rotation angle and the array phase compensation factor are obtained,and a 24×24 array period is constructed.The simulation results show that the right-handed circularly polarized wave with normal incidence has a beam scanning range of-38°-17°within the range of 1-2.1 THz,and the reflection coefficient is more than0.74;the left-handed circularly polarized wave with normal incidence also has a beam scanning range of 17°38°within the range of 1-2.1 THz,and the reflection coefficient is more than 0.68.In addition,the right-handed circularly polarized wave and left-handed circularly polarized wave that are incident perpendicularly reach the maximum reflectioncoefficient at 1.5 THz,and their values are both 0.93.The simulation results are basically consistent with the theoretical calculation results,indicating that the metasurface has high efficiency and wideband scanning characteristics for terahertz circularly polarized waves.Finally,based on the coding supersurface theory,the array structure of 2-bit periodic frequency coding and non-periodic frequency coding with a working frequency range of0.4-1.1 THz is designed.For 2bit periodic frequency coding metasurface and non-periodic frequency coding metasurface are designed.For 2bit periodic frequency coding metasurface,when the linearly polarized terahertz wave is perpendicularly incident,a slight diffuse scattering phenomenon occurs,and as the frequency increasing,the energy of the new side lobe on the right side of the z-axis becomes stronger and stronger.For non-periodic terahertz frequency coding,as the frequency increasing,the reflected energy of the terahertz wave is transferred to the side lobes.The theoretical calculation shows that when the working frequency increases from the initial frequency f0=0.4THz to the ending frequency f1=1.1THz,the reflection angle increases from 0°to 11°.The simulation calculation results are basically consistent with the theoretical results,and the effectiveness of the coding method is verified.The frequency coding antenna studied in this paper is small in size,simple in processing and low in cost.It can be used in terahertz scanning imaging and satellite communication as an effective alternative to terahertz high-cost electronically controlled scanning antenna. |
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