Studying Electromagnetic Wave-guiding and Resonating Devices

Various electromagnetic wave-guiding and resonating structures are studied. The structures in question are rather complicated and thus, significant part of the used analysis methods are numerical. Numerical field computation is based on finite-difference method (FD) or on finite-difference time-domain method (FDTD). When possible, analytical methods have been used, often in conjunction with numerical computation. Most of the structures, if not all, find real-life applications. Thus, the focus has been much on such issues as fluency of structure design and quickness of analysis. Firstly, combline-filter structures are investigated. These components are widely used in mobile communication devices, in radio-frequency and microwave regime, for example. A semianalytic analysis method, which is based on multiconductor-transmission-line theory and 2-D numerical field computation via FD method, is found very efficient. Computationally costly 3-D numerical field computation is avoided. This speeds up the design process of combline filters. Secondly, so-called hard-surface-waveguide components are analytically studied. When approximating the longitudinally corrugated waveguide wall with an ideal hard surface, one can concentrate on the effects caused by the media inside the tube. First waveguide component is filled with uniaxial anisotropic medium. For this structure, which can be used as a polarisation transformer, analytical solutions are found for transmitted and reflected field, and especially for the helicity of the transmitted field. Second waveguide component is filled with gyrotropic medium, which is electrically controllable ferrite in this case. This component can be used as a mode transformer, for example, from TM to TE mode. Analytical solutions are found for reflected and transmitted fields. Finally, wave-guiding structures based on photonic-bandgap (PBG) material are studied. This kind of periodically inhomogeneous material is also known as photonic crystal (PhC), having the ability to inhibit the propagation of electromagnetic wave inside the crystal. Carefully designed PBG components may find several applications, for example, in the integrated optics. In this thesis, the focus has been on PBG material based on triangular lattice of air holes etched through dielectric background. Further, waveguide bends have been of special interest, partly because they give a chance of realising tight light-channel bends for integrated optics. Various issues related to FDTD analysis and design of PBG structures are discussed. The importance of PBG-component optimisation is demonstrated. Promising results are obtained for extremely tight bends, although radiation losses in real 3-D structures are recognized as a problem. Some basic components, 60 and 120 degree waveguide bends, and a taper, have been designed.