| Summary: | 博士 === 逢甲大學 === 電機與通訊工程博士學位學程 === 101 === ABSTRACT
In this thesis, these type of CPW-fed circular slot antennas embedded with different ring-type strip structures for dual-frequency linear polarizations operations, dual-frequency circular polarizations operations and tri-band circular/elliptical polarizations operations are present. Then, each type of antenna structures is investigated. The purpose is to design a circular polarization antenna which has the characteristic of good quality, good S11 parameters, better AR value and wide 3-dB AR bandwidth. In this study, the circularly polarized radiation is formed by asymmetric perturbation due to the loading of ring-type strip structure into a CPW-fed slot antenna. Finally, the aim of this thesis presents a novel tri-band circular/elliptical polarized single-feed circular slot antenna for wireless local area network and worldwide interoperability for microwave access systems.
The first proposed antenna is a dual-band CPW-fed slot antenna, which is implemented on a 0.8 mm FR-4 thick substrate with r = 4.4. The embedded ring-type strip offers extended path for the electric current flow to achieve 45.1% size reduction of the fundamental resonant mode. The ratio of the center frequencies of the first two resonant bands can be tuned within a range wider than 1.81 by increasing the radius and line width of ring-type strip.
The second proposed antenna is a novel dual-band circular polarized CPW-fed slot antenna with two opened-ground rings facing in opposite directions and embedded in the circular slot. By adjusting the relevant parameters, we can obtain the dual-band at 1.57 GHz and 2.46 GHz, respectively. A small frequency ratio of 1.56 is presented. The measured 10 dB return loss impedance bandwidth were 380 MHz (24.68%) for 1.57 GHz band and 210 MHz (8.33%) for 2.46 GHz band. The measured 3 dB axial ratio bandwidth for 1.57 GHz and 2.46 GHz bands were 13.38% and 8.13%, the polarization of radiation patterns are RHCP and LHCP for each band and the antenna gain are 3.72 and 3.21 dBic, respectively.
The third proposed antenna is constructed with two asymmetrical C-shaped strips facing in opposite directions and embedded in the circular slot and the enhanced feed strip of coplanar waveguide. By adjusting the relevant parameters, we can obtain the tri-band responses at 2.4, 3.5 and 5.25 GHz, respectively. The circular/elliptical polarizations (CP/EP) of each band are presented. The measured 10 dB return loss impedance bandwidth were 270 MHz (11.1%) for 2.4 GHz band, 380 MHz (11.0%) for 3.5 GHz band, and 290 MHz (5.6%) for 5.25 GHz band. The 3 dB axial ratio bandwidth for each band were 10.4, 5.7 and 2.9%, the polarization of radiation patterns are right-hand CP, right-hand EP, and left-hand CP, and the antenna gain are 3.2, 4.3, and 5.2 dBic, respectively.
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