평면 주기 구조 및 모바일 루프 안테나 해석 연구

Abstract

This dissertation proposes a simple circuit model for a planar periodic slot, explores the design theories for an artificial magnetic conductor and a frequency selective surface, and presents reconfigurable loop antennas developed for mobile phones.The electromagnetic scattering of the thick slot structure composed of periodic conductor and dielectric layers, which represents a part of an oxide-layered steel coil, is analyzed. The proposed model, based on Floquet theory and circuit theory, provides a physical insight into the Fabry-Perot resonance and extraordinary transmission when the wave impinges on the slot structure obliquely. The higher evanescent Floquet modes near the slot contribute to fringing capacitance, and the extraordinary transmission occurs before the onset of the first grating lobe. The model produces accurate results of the transmission coefficient when the slot width is much smaller than the period. Transmission bandwidth and material loading effects are also studied.The periodic mushroom structure for use as an AMC is analyzed using a mode-matching method. The fields in each region are represented by either Floquet modes or waveguide modes. The unknown mode coefficients and dispersion diagram are calculated by applying the tangential boundary conditions and by using the matrix equations. The bandwidth of a Jerusalem AMC is studied, where the bandwidth increases with the thickness and permeability, but not with FSS loadings and permittivity. The Jerusalem AMC is positioned below a mobile antenna to reduce the hand effect. The radiation efficiency is improved with good impedance matching if the AMC surface is used. The AMC is applied in a rectangular waveguide to realize a quasi-TEM mode for a limited frequency range. The dispersion equation is derived using a TE mode and the averaged boundary condition.A band-pass FSS with a periodic patch and grid is proposed. Low-loss substrate and glass fiber reinforced polymer substrates are used for the inner and outer layers, respectively, taking into account both the electrical and the mechanical characteristics. The geometric parameters are selected by taking into account the higher-mode interaction between the layers. A multi band-pass FSS is proposed by supplementing a ring with the patch and grid. The operating bands of the FSS can be independently controlled by proper selection of the parameters. A double split ring resonator FSS is proposed for CDMA/RFID isolation. The proposed FSS has better isolation characteristics than a dipole FSS. When the FSS is placed on a patch antenna, the CDMA gain is maintained but the RFID gain is reduced.Finally, a dual-band frequency reconfigurable loop antenna is proposed to overcome input mismatch of an open loop antenna at high frequency. The high frequency can be easily tuned without changing the low frequency by using a chip inductor in the matching circuit. The input impedance can be adjusted by changing the stub length and the inductor position. The proposed antenna is compact, which operates at two different frequencies. A single-band frequency reconfigurable mushroom antenna is proposed, the operating frequency of which can be adjusted by controlling the inductance without a matching circuit.