| In recent years,metamaterial has attracted much attention for its powerful ability to manipulate electromagnetic waves(EM),and new EM devices and interesting phenomena were reported.However,the evolution of material devices is severely hindered by the difficulties of fabrication and the loss of material.Metasurfaces have vigorously developed over the last years as artificial planar structural material arranging periodic or aperiodic subwavelength scattering structures.The occurrence of metasurface devices has reduced the difficulty of manufacturing to achieve the high-precision processing requirement of microwave structures.Moreover,they have many advantages,such as low cost,lightweight,and high integration.The researchers have proposed a series of novel planar electromagnetic devices,whose working frequencies can cover optical and microwave wavelength range through elaborately designing the structure and arrangement of meta-atoms.With the sustainable development of system miniaturization and functional integration,the demand for multifunctional electromagnetic manipulation is increasing in related applications.The appearance of electromagnetic metasurface provides an ideal platform to design multifunctional devices that meet the various EM manipulation needs.Nevertheless,several design problems are still inevitable in the process of multifunctional electromagnetic metasurface when it continuously turns to practical application,such as the low-profile metasurface antenna.In this dissertation,a series of studies about multifunctional planar wavefront manipulation devices based on metasurface is conducted,focusing on lightweight,frequency reconfiguration,beam scanning,wideband achromatic,full-space,and multi-parameter modulation.The main research content of this dissertation is summarized as follows.1.A frequency reconfigurable thin-film metasurface(TFM)design method based on polarization multiplexing is proposed,which can realize the regulation of the radiation pattern,the operating bands are 11.5-13.5 GHz,and 13.25-15.25 GHz for the two polarized incidence cases,respectively.The vertical and horizontal polarization electromagnetic wave phase control is realized by two I-shaped resonant structures of different sizes.By controlling the length of the I-shape resonant structure,the phase modulation of the I-shaped resonant structure can be achieved exceeding 315°.The arrangement of metasurface meta-atoms has been carefully considered based on the phase configuration of the I-shaped resonant structure acquired by the quadratic phase function.Thus,the 2D beam scanning can be realized by moving the feed in the focal plane,and the scanning angle reaches ±60°.To verify the function of the designed metasurface device,a sample with a diameter of 810 mm was fabricated.The maximum gain of the sample is 30 d B,and the gain is 27 d B while the scanning angle reaches ±60°.The proposed reflective metasurface has the characteristics of low profile,lightweight,multiband,and large angle beam scanning,which is expected to be applied in communication and detection.2.A frequency reconfigurable radiation regulation thin film metasurface based on active devices has been carried out.This metasurface adapts the “?”-shape structure,whose phase gradient in the Y-axis direction can be controlled by changing the bias voltage of the varactor diode and PIN diode loaded on the reconfigurable metal atoms.Adjusting different voltage configurations can match different operating frequencies and obtain a relatively stable phase gradient,which ensures the stability of beam scanning and expands the working bandwidth of the metasurface.In the 9.1-10.1 GHz,the frequency regulation characteristics of the reconfigurable metasurface are verified successfully.Moreover,scattering regulation and polarization conversion can also be realized by appropriate voltage configuration.This study provides a new way to expand the bandwidth of the active reconfigurable metasurface,which has the characteristics of reconfigurable frequency and lightweight.3.A polarization-multiplexed transmission-reflection-integrated metasurface(TRIM)unit integrating a composite phase modulation structure and a resonant phase modulation structure is proposed,which can manipulate both transmitted and reflected electromagnetic waves.With the design of a Fabry-Pérot-like cavity and impedance match,the transition and reflection of the unit cell are 82.4% and 90.6%,respectively.In addition,wideband achromatic properties of transmissive mode and reflection mode are realized respectively based on frequency multiplexing and dispersion control techniques.A one-dimensional broadband achromatic transmission-reflection-integrated focused metasurface is designed at 12-18 GHz and 19-24 GHz.The simulation focusing efficiencies are 13.12-17.21%(transmissive mode)and 14.57-20.86%(reflection mode).To verify the feasibility of the proposed design scheme,a common aperture transmissive and the reflective integrated flat antenna is designed and manufactured.To broaden the working bandwidth,the transmission array and reflection array is designed in an adjacent working band.Because the electromagnetic response of the element itself is accompanied by a certain bandwidth,the operating frequency band of the resonant phase element array can be flexibly transferred to achieve a multi-band and multi-function integrated design.In general,our method overcomes the chromatic aberration problem existing in the transmissive and reflection integrated metasurface and opens up a new way for functional integrated devices.We believe that this typical design method has great application prospects in integrated optical imaging and wireless communication systems.4.A multi-parameter electromagnetic control full-space metasurface(FSM)structure based on a quadratic phase is proposed to achieve a variety of independent electromagnetic functions by changing the polarization,initial phase,and feed position.the mutually independent phase regulations of transmitted cross-polarized and reflected co-polarized electromagnetic waves are obtained through these metasurface units,which can cover 2?.At 30 GHz,the transmittance and reflectivity are higher than 84.8% and96.5%,respectively.Subsequently,a quadratic phase profile is used to construct a fullspace beam scanning metasurface.At 30 GHz,the quadratic phase transmissivereflective-integrated metasurface has an angular focusing range of over ±60° in both transmissive and reflection modes.A multifunctional flat antenna is fabricated and experimented with to validate the EM properties of the proposed metasurface.The beam scanning angle exceeds ±60° in both transmissive and reflection modes.At the same time,four typical polarization of electromagnetic waves is obtained utilizing the double beam coherence method.Arbitrarily polarized electromagnetic waves can be generated by adjusting the metasurface device.In addition,due to the symmetric structure of the metasurface,the proposed multi-functional flat antenna can also be used as a multi-beam antenna when multiple feed sources are used to illuminate the metasurface simultaneously.In summary,the designed multifunctional metasurface provides an avenue to full-space electromagnetic wave manipulation and has great prospects in the fields of integrated optics,radar detection,and wireless communication. |
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