Research On Key Techniques For Broadband Frequency Selection Electromagnetic Structures

Frequency-selective electromagnetic structures are one kind of electromagnetic structure specifically designed with metal or non-metal materials,and that can effectively control and adjust characteristic parameters of incident electromagnetic waves such as amplitude,phase,polarization,frequency,etc.,and it can determine the reflection,transmission,absorption,transformation,etc.,of the impinging electromagnetic wave within a specific working bandwidth.Dimensions of frequency-selective electromagnetic structure unit cells are usually smaller than the working wavelength,and they can be arranged in periodic or non-periodic array structures.Common frequency-selective structures include antenna elements and arrays,frequency-selective surfaces,electromagnetic metamaterials/metasurfaces,which have been widely used in many technical fields such as modern wireless communications,satellite communications,radar,navigation,etc.Among them,resonant frequency-selective structures based on metal or dielectric materials have flexible construction methods,and they have been extensively researched and developed for the implementation of antennas,frequency-selective surfaces,electromagnetic metamaterials/metasurfaces,etc.However,due to the inherent resonant characteristics of this kind of frequency-selective structures,their operative bandwidth is limited,and for this reason traditional frequency-selective electromagnetic structures cannot overcome the theoretical limit represented by the trade-off between the working bandwidth and the unit structure size(Rozanov limit).This dissertation focuses on the key scientific problems of the above mentioned narrow bandwidth metal frequency-selective structures,and takes traditional metal antennas and electromagnetic metamaterials/metasurfaces as the main research objective;it carries out systematic in-depth research,and proposes specific ways to widen their working bandwidth.Finally,a new ultra-wideband frequency-selective electromagnetic structure that breaks the technological barrier of Rozanov limit is realized.Main research work and innovative contributions of this dissertation are as follows:1.assuming half-wavelength microstrip patch antenna frequency-selective structures as the research objective,by revealing narrowband characteristics of traditional microstrip patch antennas,the design of a broadband high-gain antenna based on a substrate integrated coaxial line(SICL)is proposed.Simulation,verification,and optimization processes have been carried out to design and develop broadband high gain linearly and circularly polarized antenna elements and array structures for ultra-high frequency(UHF)radio frequency identification(RFID)applications.Experimental test results show that the achieved bandwidth can cover the whole UHF RFID spectrum 860-960 MHz.At the same time,3 dB axial ratio bandwidth of antenna arrays with SICL and microstrip feed networks are 18.2% and 28.8%,respectively.Finally,developed antenna arrays possess stable high gain performance,with gain values higher than 12 dBi;2.assuming electromagnetic metasurface structures having sub-wavelength characteristics as the research objective,by studying the highly resonant and narrowband working mechanism and essential characteristics of traditional reflective electromagnetic metasurface structures,the design of broadband metasurfaces loaded with air medium is proposed.Taking this as the basic unit structure,broadband high-efficiency electromagnetic radiation and high-efficiency wireless energy collection capabilities have been studied systematically.Experimental results show that the radiation efficiency of the broadband metasurface frequency-selective unit structure loaded with air medium reaches 92%,while energy conversion efficiency is 84.4%,and for this reason such structure can be widely applied for the design of broadband and high efficiency electromagnetic beam forming and energy collection.3.assuming electromagnetic absorption frequency-selective structures having sub-wavelength characteristics as the research objective,through an in-depth study of the theoretical limit(Rozanov limit)between the absorption bandwidth and the size and thickness of traditional electromagnetic absorption frequency-selective structures and other peculiar characteristics,the design of an active ultra-thin and ultra-wideband electromagnetic wave frequency-selective structure system loaded with both a non-Foster active impedance and magnetic materials is proposed.Through an in-depth theoretical research,electromagnetic simulation and verification,and structure optimization,an ultra-wideband electromagnetic absorption frequency-selective structure which covers the bandwidth 0.5-18 GHz and effectively breaks the Rozanov limit has been developed,and its absorption rate within the whole working bandwidth is larger than 80%,making it suitable in military and civilian fields for applications such as electromagnetic compatibility,radar absorption,stealth technology,etc.This thesis overcomes working bandwidth limitations of frequency-selective electromagnetic structures such as traditional antennas,electromagnetic metasurfaces,and absorber structures,developing broadband high-gain linear/circular polarization antennas and arrays,broadband high-efficiency electromagnetic metasurface unit cells and arrays loaded with air media,and ultra-thin ultra-wideband microwave absorbers loaded with both non-Foster devices and magnetic materials,and performing in-depth systematic theoretical research,electromagnetic simulation,design and optimization,manufacturing,measurements and testing for each broadband frequency-selective electromagnetic structure described.Obtained research results can be widely applied in modern engineering technological fields such as Internet of Things communications,electromagnetic radiation control,electromagnetic compatibility,radar absorption and stealth technology.