| The shortage of spectrum resources and the increasingly complex electromagnetic environment urgently require the rapid upgrading of wireless systems such as communication and radar.The development of antenna technology is a key factor affecting this process.In order to enable the system to better cope with changes in the electromagnetic environment,designers not only hope to obtain wider bandwidth and higher radiation gain from traditional antennas,but also hope to design new antennas with adjustable radiation performance to adapt to dynamically changing application environments.The artificial electromagnetic structure(AEMS)technology provides a new method for electromagnetic wave regulation,and its appearance brings new design inspiration and methods to electromagnetic devices,especially antennas.Focusing on the application of AEMS in low-profile and programmable antennas,this thesis first studies the design theory and implementation methods of AEMS elements,and then focuses on performance characteristics of application in enhancing the radiation performance of traditional antennas and the design of programmable beam scanning antennas.Main research works:1.The design theory and method of AEMS are studied,several element structures with surface impedance and dispersion characteristics modulation capability are proposed,and an ultra-broadband element that can modulate dual-polarized electromagnetic waves is designed.Firstly,three basic AEMS elements are proposed.On the basis of studying the surface wave dispersion characteristics of three different forms of structural elements,the impedance characteristics of the elements are analyzed,and the equivalent modeling and analysis method of AEMS is proposed.Aiming at the problems of narrow bandwidth,complex structure and high profile when the existing AEMS is applied in traditional antennas,an ultra-wideband electromagnetic structure element and design method with a working bandwidth of 2GHz-20GHz(relative bandwidth164%)are proposed.The electromagnetic parameters such as the equivalent permittivity and refractive index of the element are extracted,and the feasibility of the element in the application of the low-profile antenna is verified by combining the surface current distribution,which provides support for the application of the AEMS element in the traditional antenna.2.Analyzed the modulation mechanism of AEMS in antennas,proposed a modeling and analysis method for electromagnetic lenses,and designed two ultra-wideband,high-gain lenses Vivaldi antenna.Aiming at the problems of limited low-frequency operating bandwidth,directivity and gain deterioration in the application of traditional Vivaldi antennas,the influence of a new type of electromagnetic lenses composed of AEMS on the performance of Vivaldi antennas is analyzed.A metasurface lens with high dielectric constant and high refractive index is designed,which can modulate the electromagnetic wave at the antenna aperture.The lens is integrated at the aperture of the antenna,and by analyzing the amplitude and phase distribution of the electric field,the work mechanism and modulation method of the lens on the electromagnetic wave at the aperture of the antenna are clarified,and the optimal lens structure is obtained.According to different application scenarios,two Vivaldi antennas loaded with metasurface lenses and their design methods are proposed.The simulation and measurement results show that the low-frequency operating bandwidth of the designed miniaturized Vivaldi antenna loaded with lenses is extended by 2 GHz,and the maximum radiation gain of the two antennas is increased respectively.3.7d B and3.2d B,the directivity has also been significantly improved.3.A novel of radiation-type AEMS element and design scheme are proposed,and a programmable beam scanning antenna with dual modulation capability of radiation phase and reflection phase is designed.Aiming at the problems of high profile,large volume and non-uniform feeding of the existing programmable AEMS antenna,a method of integrating the feeding structure and the phase modulation structure is adopted,and a low-profile radiation-type AEMS antenna element operating in the X-band is proposed.Two PIN diodes are loaded on the antenna element,changing the on-off state of the diodes can adjust the current flow direction and the electric field distribution area on the antenna,so that the far-field radiation phase difference of the antenna has two adjustable states of 0° and 180°,with 1-bit digital adjustable features.Programmable beam scanning array antennas with 1×32 elements and 8×16 elements are designed respectively,and each element in the array antenna is coded by combining with the theory of digital holographic,and the flexible beamforming of the radiated electromagnetic wave without phase shifter components is realized.The one-dimensional array antenna realizes beam scanning of-60°～60°,and the two-dimensional array antenna realizes beam scanning of-60°～60° on the azimuth plane and-40°～40° on the elevation plane.Compared with the existing mainstream works,the profile height of the proposed radiating array antenna under the same index is compressed by nearly 300 times.Combined with the design principle of the reflective programmable antenna,the reflected wave modulation effect of the designed reconfigurable element is analyzed.The simulation results show that the element also has a 1-bit modulation function for the reflected wave phase.On the basis of electromagnetic calculation,control circuits,switch arrays and programmable electromagnetic structure arrays were fabricated,and programmable radiation-type array antennas and reflective array antennas are assembled.The measured data in the anechoic chamber are in good agreement with the simulation results,which verifies the flexible modulation capability of the programmable array on the radiation beam and the reflected beam under the same aperture. |
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