Research Of The Wave Routing And Radiation Based On The Periodically Loade Waveguide

The transmission line theory is widely employed in the design the microwave devices,in which the whole structure can be divided into several subwavelength lumped elements that can be analyzed with low frequency circuit theory.Recently,some new electromagnetic（EM）mate-rials,e.g.,photonic crystals and metamaterials,developed in analogy to natural crystals,provide a different avenue to manipulate EM phenomena by regulating the EM resonances and the spa-tial distributions of the meta-atom.Unlike natural materials,artificial materials or metamaterials are composed of meta-atoms with subwavelength dimensions.As a typical application,periodi-cal loading of metamaterials in microwave devices gives a fresh perspective on efficient control of the EM waves and the device design.This thesis focuses on the periodical loading technol-ogy in microwave engineering and discusses its applications in the wave guiding and radiation applications.The main contents of this thesis are summarized as follows:1)We propose the concept of high-order mode waveguide,and investigate the method of generating a desired high-order waveguide mode with high purity.By analyzing the dispersion curves of the periodically loaded waveguide,one can optimize the dimensions of the periodical loading and generate the desired high-order mode in the bandgap of other low-order modes.Moreover,a glide-symmetric loading method is proposed to control the bandwidth of the single high-order mode.To stimulate the high-order mode in an overmoded waveguide,we separate the original TE_n0mode into several TE₁₀modes,and then use this TE₁₀mode as the feeding port to stimulate the desired high-order mode.2)We propose a millimeter wave（mm W）antenna array fed by the high-order mode waveg-uide.Compared with the 1-to-n-way power divider employed in traditional antenna arrays,an input signal can be automatically divided into n-way-independent output signals by the high-order mode waveguide,with equiamplitudes and opposite phases,and therefore,the total num-ber of physical channels is dramatically decreased,which facilitates in reducing the complexity and transmission losses of the mm W devices.In additional,a relatively thick substrate,deliv-ered by the antiphase feature between adjacent antenna elements,offers another approach for relaxing the design and test constraints for the mm W devices.3)We propose the concept of the high scanning rate and scanning linearity for the leaky-wave antennas（LWAs）.By analyzing the frequency-dependent beam scanning propriety of the traditional LWAs,the definitions of the scanning rate under different conditions are given.Then,the key factor of improving the scanning rate is also given using an ideal linear dispersion model.Additionally,we further discover the possibility of the scanning linearity using the ideal dispersion model with relative high linearity.A glide symmetric loading method is proposed in a rectangular waveguide to develop a prototype of LWA with high scanning rate and scanning linearity.4)We propose the concept of dispersion compensation in a periodically loaded waveguide for fixing the radiation beam of LWAs over a wide operating band.The condition of how to fix the beam is given in this chapter.We separate the desired compensation values of the propagation constant into two parts:the linear and the nonlinear parts.Then,we design a triangular lens consisted by periodical loading in the parallel-plate waveguide and a gradient metasurface to offer the values of these compensation values.By cascading the traditional LWA,the lens and the gradient metasurface,a fixed-beam LWA is realized.Moreover,the direction of the fixed beam can be customized from backward to forward if we just re-optimize the parameters of the lens and the metasurface.5)We propose the technique of wideband endfire LWA using general transverse electrical（TE）mode in the waveguide.Several double-sided slots acting as radiation elements are notched on the waveguide to produce an endfire pattern.To overcome the restriction associated with the endfire radiation condition of a linear array,a metallic core periodically loaded with pins is used to control the dispersion of the proposed double-sided-slot waveguide.By optimizing the height distribution of the loading pins along the longitudinal direction using a cosine function,stable endfire radiation can be achieved over a broad operating band.