Study Of Electromagnetic Wave Radiation Based On Metasurface

Metamaterial has been developed for more than twenty years since last century.Metasurface is regarded as a two-dimensional case of metamaterial,it has received widespread attention with advantages of low profile,less loss,low cost,flexible to design and easy to fabricate.In this thesis,a method of generating Bessel beams by using holographic metasurface is proposed,the mechanism of two-dimensional leaky wave radiations is also analyzed and several types of beam shaping are designed.The concept of surface impedance is applied to the spoof SPP supported by subwavelength corrugated metal structure,and several typical characteristics of radiation are studied and experimentally verified.The main contents and contributions are summarized as follows:· Generation of spatial Bessel beams using holographic metasurface.Backward periodic leaky waves sup-ported by holographic metasurface was designed in the microwave frequency regime,so that it forms a conical beam in the far field and a corresponding Bessel beam in the near field.The characteristics of the Bessel beam are verified both from simulation and experiment,and the sweeping frequency characteris-tics of the Bessel beam are observed.The dynamic focal-depth control of Bessel beam is expected to be used in the near field detection,wireless energy transmission,and medical imaging.· Mechanism analysis and beam shaping design of two-dimensional leaky-waves based on holographic metasurface.How surface wave in a pointed azimuth angle generate leaky-wave radiations in other az-imuth angled directions is analyzed directly from the leakage wave mechanism,so as to have an equivalent comparison with the previous holographic analysis method.It is found that the leakage wave mechanism analysis method explains more clearly about how azimuth angle and polar angle changes by sweeping frequency.The types of beam shaping design are studied based on holographic metasurface,including multiple-beams,elliptical cone beams,pseudo-elliptical cone beams,combined beams,and inclined cone beams.· Leaky-wave radiations by modulating surface impedance on one-dimensional subwavelength corrugated metal structures.The concept of surface impedance is applied to the one-dimensional subwavelength metal grooving structure supporting spoof SPP,since spoof SPP is a kind of transverse magnetic sur-face wave.The corresponding surface impedance of unit cell is calculated.By modulating the surface impedance periodically,and utilizing a central waveguide coupling with a slit to fed the structure,a di-rectional broadside radiation is achieved.· Leaky-wave radiations by modulating surface impedance on two-dimensional subwavelength corrugated metal disc structure.The surface impedance of the one-dimensional structure is applied to the two-dimensional disc structure,since the dispersion curves of the sub-wavelength metal grooved structure insensitive to its thickness.The far-field conical Beams and near-field Bessel beams are both designed and verified based on backward leaky-waves.According to the influence of the polarization of surface waves,a new scheme of discrete spiral antenna based on subwavelength corrugated metal structure is proposed.