The doctoral dissertations of the former Helsinki University of Technology (TKK) and Aalto University Schools of Technology (CHEM, ELEC, ENG, SCI) published in electronic format are available in the electronic publications archive of Aalto University - Aaltodoc.

Studying Electromagnetic Wave-Guiding and Resonating Devices

Tero Uusitupa

Dissertation for the degree of Doctor of Science in Technology to be presented with due permission of the Department of Electrical and Communications Engineering for public examination and debate in Auditorium S4 at Helsinki University of Technology (Espoo, Finland) on the 19th of March, 2004, at 12 o'clock noon.

Overview in PDF format (ISBN 951-22-6980-5)   [537 KB]
Dissertation is also available in print (ISBN 951-22-7001-3)


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.

This thesis consists of an overview and of the following 6 publications:

  1. Uusitupa T. and Loukkola J., 2000. Application of multiconductor transmission-line theory to combline filter design. Microwave and Optical Technology Letters 27, number 2, pages 113-118.
  2. Viitanen A. J. and Uusitupa T. M., 2001. Fields in anisotropic hard surface waveguide with application to polarisation transformer. IEE Proceedings – Microwaves, Antennas and Propagation 148, number 5, pages 313-317.
  3. Uusitupa T. M. and Viitanen A. J., 2001. Mode transformer for hard-surface waveguides. In: Proceedings of the 31st European Microwave Conference (EuMC 2001). London, England, 24-27 September 2001, volume 1, pages 141-144.
  4. Uusitupa T. M. and Viitanen A. J., 2003. Analysis of finite-length gyrotropic hard-surface waveguide. Radio Science 38, number 2, 1026, doi:10.1029/2002RS002706.
  5. Uusitupa T., Kärkkäinen K. and Nikoskinen K., 2003. Studying 120° PBG waveguide bend using FDTD. Microwave and Optical Technology Letters 39, number 4, pages 326-333.
  6. Yliniemi S., Aalto T., Heimala P., Pekko P., Jefimovs K., Simonen J. and Uusitupa T., 2002. Fabrication of photonic crystal waveguide elements on SOI. Proceedings of SPIE Photonics Fabrication Europe Conference. Brugge, Belgium, 28 October - 1 November, 2002, volume 4944.

Errata of publications 1, 2, 3, 4 and 5

Keywords: waveguide, combline filter, photonic bandgap, photonic crystal, hard surface, finite-difference method, FDTD

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© 2004 Helsinki University of Technology

Last update 2011-05-26