A Study Of The Electromagnetic Applications Based On Hyperuniform Disordered Distribution And Piecewise Homogenous Dielectric Superstrate

In recent decades,modern communications have imposed challenging constraints and requirements on antennas,for example:high gain and wideband.At the same time,the antenna also needs to have low cost and low radar cross section(RCS).The designs with periodic structure cannot meet all these requirements.In this dissertation,well performed phased array,reconfigurable reflectarray and Luneburg lens designed with hyperuniform disorder are investigated.Meanwhile,diffused metasurface with hyperuniform disorder is designed to reduce the RCS.Besides,using the superstrate to achieve gain enhancement for large antenna arrays has not been investigated yet.A dielectric slab superstrate based on piecewise homogenous structure designed for the dual-polarized antenna and the corresponding large arrays with high gain enhancement,low cost and easy fabrication is also investigated.The main contents in this dissertation can be summarized as follows:1.Ultra-wideband phased array with hyperuniform disorder:Because of the unavoidable limitations regarding the grating lobes,the conventional periodic antenna arrays are usually designed with limited inter-element spacing.A novel and simple design technique based on the concept of hyperuniformity to generate an aperiodic antenna array topology,which is able to suppress grating lobes and achieve low sidelobe level(SLL)values during scanning over a wide bandwidth.We reveal the connection between the structure factor and the array factor formulas,which explains hyperuniform disordered antenna arrays have predictable radiation properties,a feature that belongs to periodic antenna arrays.Furthermore,because the antenna array is also disordered,it can achieve grating lobe suppression over a wide bandwidth during beam steering.The optimization is applied to the subarray unit cell that can then be replicated along its axes,leading to a total structure that will maintain the prescribed radiation characteristics,thus saving huge amounts of computational time that would otherwise be required in order to optimize the whole structure.2.Reconfigurable reflectarray antenna with hyperuniform disorder:To solve the problem of the unavoidable limitations to the grating lobes that the conventional periodic antenna arrays are usually designed with small interelement spacing,one kind of RRA based on hyperuniform disorder is proposed.The RRA avoids the design of complicated feeding network for the disordered phased array antenna and realize a similar radiation property with reduced number of elements compared with the corresponding traditional(periodic distributed)RRA designed with smaller interelement spacing.Meanwhile,it prevents the appearance of grating lobes.To present the superiority of hyperuniform disorder,an RRA with perfect compensation phase has been designed.A 64-element1-bit RRA controlled by PIN diode and a programmable FPGA-based controller is used to achieve a beam-scanning angles within±50°range have been obtained with a peak gain of 17.4 dBi at 12.5 GHz.The proposed RRA reduces the number of active components and reduces the overall cost which is of great importance when a large number of active elements are required.3.Luneburg lens based on hyperuniform disorder with low radar cross section:To solve the problem of the wave scattering from periodic structures,known as Bragg diffraction,occurs in a periodic structure at specific wavelengths and incident angles producing intense peaks of reflected radiation,a Luneburg lens based on hyperuniform disorder and MaxwellGarnett approach is designed.From the simulated results that a purpose-designed hyperuniform disordered structure such as the Luneburg lens will demonstrate reduced back scattering.For comparison,a counterpart Luneburg lens based on the periodic structure is designed.The two lenses function similarly in the operating frequency band,but their characteristics of out-ofband scattering are rather different.Specifically,two holey Luneburg lenses based on respective hyperuniform disordered and periodic structures(e.g.,triangular lattice structure)are fabricated.Experimental results agree very well with simulated results,showing that the Luneburg lens made of triangular lattice structure possesses distinctive reflection at specific angles.In contrast,the hyperuniform disordered structure based lens presents diffused reflection.4.Diffusive metasurface based on hyperuniform disorder for radar cross section reduction:One of the important functions that a metasurface can realize is the radar cross section(RCS)reduction by diffusing incoming electromagnetic waves into different directions.A general and highly predictable design method of diffusive metasurfaces with a reduced RCS is proposed based on hyperuniform disorder and coding metasurface.The 1-bit metasurface with hyperuniform disorder is designed and show how the disordered distribution offers an additional degree of freedom for the generation of higher diffusion.Both simulated and experimental results demonstrate that the metasurface with the hyperuniform disorder performs better than the periodic metasurface by enlarging the operating bandwidth with a significant reduction in the radar cross section of the surface.When the frequency operating frequency increases,only one reflected beam is observed for the metasurfaces based on hyperuniform disordered distribution,which is in contrast to the periodic metasurface where several multiple reflected beams are observed.5.Dual-polarized antenna array gain enhancement using piecewise homogenous dielectric superstrate:To solve the problem of gain enhancement for dual-polarized antenna array,dielectric superstrate of leaky wave effects and the edge diffractions is proposed for gain enhancement of dual-polarized patch antenna and the corresponding arrays.The dielectric superstrate for a single antenna is investigated firstly to lay a solid foundation for the design of dielectric superstrate for large arrays.The measured results show that the superstrate has little effect on the impedance bandwidth but can increase the gain by 10.7 and 11.2 dB for the two ports,respectively.Different from the existing research work,the superstrate used to enhance the gain for large arrays is discussed.A piecewise homogeneous dielectric superstrate with slots is proposed and fabricated for 2 × 2 array with a measured peak gain of 18.3 and 18.4 dBi for two polarizations.The piecewise homogeneous superstrate and source antenna array hold the advantages of high gain,large aperture efficiency and easy processability.The piecewise homogeneous dielectric superstrates for 4×4 and 8×8 array are also designed and the simulated results show that the superstrate can be effective for larger arrays.