Open Access
Yoo, Kyungho
Graduate Program:
Electrical Engineering
Doctor of Philosophy
Document Type:
Date of Defense:
August 30, 2010
Committee Members:
  • Raj Mittra, Dissertation Advisor
  • Raj Mittra, Committee Chair
  • James Kenneth Breakall, Committee Member
  • Anthony J Ferraro, Committee Member
  • Michael T Lanagan, Committee Member
  • Electromagnetic Band Gap
  • metamaterials
  • superstrates
  • dipole moment
  • characteristic basis function
  • equivalent medium
Electromagnetic Band Gap (EBG) structures, engineered to achieve desired transmission and reflection characteristics in specific frequency bands, have recently attracted considerable attention due to growing interest in improving antenna performance. Almost simultaneously, metamaterials (MTMs) became popular because they have unusual features, not readily available in nature, promised to make possible new applications for microwave circuits and antenna composites. EBGs and MTMs are typically created by using periodic inclusions of metallic or dielectric material embedded in a homogeneous background medium. Due to their unique bandgap features, EBG structures can be regarded as a special type of MTM. In fact, these two terms, EBG and MTM, are sometimes used interchangeably. Typical examples of their applications for enhancing antenna performance include high-directivity antennas, low-profile antennas, high impedance surfaces, and dichroic surfaces. In this dissertation, we focus primarily on three aspects. First, we develop a novel and systematic approach to enhancing the directivity of an antenna covered by an EBG and MTM and show that high directivity is achieved at the resonant frequency of the structure. We also illustrate the application of the above procedure by designing directivity-enhanced planar antennas, for instance, dipole and microstrip patch antenna arrays used as exciters for a Fabry–Perot cavity with a dielectric slab as the superstrate. Second, we describe two novel techniques involving a combination of the Dipole Moment (DM) method and the Characteristic Basis Function Method (CBFM) to model periodic structures of EBGs and MTMs. We show that combining the above two methods leads to a relatively small matrix, often only 2×2 or 3×3 in size, without running into ill-conditioning problems for many typical elements. Third, we develop guidelines for using the Equivalent Medium Approach (EMA) to the study of metamaterial structures. We examine the concept of effective material parameters by completing the retrieval process of these parameters according to the inversion approach and identify some fundamental problem areas encountered when applying the algorithm to a slab of artificial dielectrics. We then use a Gaussian beam to excite this structure in order to examine the direction of the beam’s wave propagation in such a medium.