Frequency reconfigurability analysis of electrically small antenna.

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Antennas that have the capability to tune their operation frequency-bands dynamically responding to external control attract considerable research efforts in the electromagnetics society recently. This reconfigurable antenna concept effectively solves the dilemma between the urgent trends of mobile terminal miniaturization and the physical bandwidth limits for electrically small antenna. In this thesis, author's works in the past few years for the design and analysis of several types of frequency reconfigurable electrically small antennas, by utilizing characteristic-tunable engineering metamaterials, or by loading tuning elements directly on the antenna radiation body, are summarized and presented.;For the first approach, various passive Electromagnetic Band-Gap Structure profiles, including single and double-layer square mushroom-like EBG, hexagonal mushroom-like EBG, Uni-planar Compact-PBG, and square patch array, have firstly been attempted as the substrates for microstrip antenna applications. Accurate Full-Wave Eigen-Mode modal analyses and computation-efficient lump-circuit Cascaded Multi-Port Network model have been developed to reveal the radiation mechanism and provide engineering guidelines for the EBG microstrip patch antenna design. Then, novel types of reconfigurable patch antenna based on the characteristic-tunable EBG substrate are invented. In brief, by means of changing EBG substrate tuning element status, the top microstrip structure propagation wavelength can be controlled, and the patch antenna radiating resonant frequency can be reconfigured externally.;In addition, according to the concepts of mounting tunable elements directly on the antenna radiation body, various types of varactor-loaded low-profile small antennas have been invented, which are fabricated either on rigid printed circuit board for low-profile applications, or on flexible polyimide tape clad with copper for three dimensional conformal applications. By applying varactors on the radiation arms, single or double frequency-band of these antennas can be tuned continuously over a wide dynamic range and with acceptable instant bandwidth.