| A conventional electromagnetic metasurface is an artificial structure formed by periodic or nonperiodic arrangement of subwavelength-sized elements on a two-dimensional plane or surface,which has been attracting attention for its design flexibility,small thickness,low loss,and high integration capability.Unlike conventional electromagnetic metasurfaces,which are characterized by continuous parameters,programmable electromagnetic metasurfaces are characterized by quantizing the phase or amplitude of reflection/transmission,and their far-field scattering beams and near-field distributions are also determined by the arrangement of different digital states of encoded elements on the metasurface,which changes the way researchers understand,analyze,and design electromagnetic metasurfaces.In this dissertation,the amplitude and phase of reflective programmable electromagnetic metasurfaces are investigated,the research background and significance of electromagnetic metasurface are mainly introduced,and the current status of domestic and international research on conventional electromagnetic metaurface and programmable electromagnetic metasurface are collected and summarized.The work is focused on the following points:(1)The basic theory and basic working principle of programmable electromagnetic metasurfaces antenna are explained in detail,including the array structure and beam scanning principle,the calculation of radiation performance and the calculation method of far-field directional map based on FFT.(2)The design process of two types of programmable metasurfaces based on the phase modulated elements is mainly introduced.The design of the broadband active 1-bit reflective phase tunable element and the Ka-band 2-bit phase tunable element can be realized by controlling the state of PIN diodes loaded on the surface of the coding element,whose diode control circuit is simple and each element is independently controllable.The simulation results show that the reflection phase curve of the broadband active 1-bit reflective phase tunable element can achieve 1-bit phase characteristics in the frequency range of 5.56 GHz,and the bandwidth is significantly better than the existing research on broadband active reflective elements;the conventional digital programmable metasurfaces in domestic are usually designed at low frequencies such as C-band and X-band,however there are not many metasurfaces are designed at high frequencies.The reflection amplitude of the Ka-band 2-bit phase tunable element is less than-3 d B near the center frequency of27.46 GHz.The 2-bit programmable metasarface composed of the element can achieve dynamic beam deflection of up to ±50° and multi-beam function.(3)The programmable metasurface is extended to combine amplitude and phase modulation,and two types of amplitude-phase independently tunable programmable metasurface elements are proposed to achieve higher degrees of freedom in the modulation of electromagnetic waves,filling the research gap of active element control of amplitude and phase.The simulation results show that the1-bit amplitude-phase independent tunable element can be found near the center frequency of 29.56 GHz,and the 2-bit amplitude-phase independent tunable element can be found in the range of 8.4 ～ 9.07 GHz.After the waveguide test of the element,the 2-bit amplitude-phase independent tunable results can still be obtained.Finally,the work in the above four chapters is mainly summarized and discussed as well as the shortcomings of the paper and the outlook of the subsequent research. |
