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Title: Wideband shorted bowtie patch antenna
Other Titles: Kuan pin jie di die xing tie pian tian xian
Authors: Mak, Ka Ming (麥嘉銘)
Department: Department of Electronic Engineering
Degree: Master of Philosophy
Issue Date: 2008
Publisher: City University of Hong Kong
Subjects: Microstrip antennas.
Broadband communication systems.
Notes: vi, 99 leaves : ill. 30 cm.
Thesis (M.Phil.)--City University of Hong Kong, 2008.
Includes bibliographical references (leaves 95-98)
CityU Call Number: TK7871.67.M5 M35 2008
Type: thesis
Abstract: This thesis presents a study on a novel wideband planar antenna, designated as the shorted bowtie patch antenna. The structure and feeding mechanism of this antenna is different from the conventional bowtie planar antennas in that the two ends of the patches are shorted to a grounded reflector and the gap of the two patches is fed by an air microstrip line. It possesses attractive features such as wide bandwidth and directional radiation patterns. With the addition of an electric dipole, backlobe suppression, gain enhancement and symmetrical radiation patterns in both principal planes are able to be accomplished. Based on the geometry for linear polarization, dual and circularly polarized antennas have been developed. Parametric studies of the antennas are performed by the IE3D simulator, and most of the results are verified by the experiments. Firstly, a linearly polarized shorted bowtie patch antenna fed by an air microstrip transmission line is presented. The antenna is formed by two shorted triangular patches facing each other and the feeding mechanism (air microstrip line) utilized for antenna excitation is similar to the conventional technique for exciting an electric dipole. It is found that a wide impedance bandwidth of over 60% and broadside radiation pattern can be achieved. In addition to the bowtie-shape, other configurations- rectangular and semicircular- have also been studied for comparison. Secondly, an electric dipole is added on top of the shorted bowtie patch antenna in order to suppress the back radiation. Through this approach, an equivalent magnetic dipole due to the shorted bowtie patch and an electric dipole are excited together. Almost equal radiation patterns in both E- and H-planes are obtained, while the broadband characteristic of the antenna can be preserved, which is still over 60%. Not only the measured cross polarization and back-lobe level of the antenna can be reduced by about 10dB, the measured gain can also be enhanced and becomes stable over the frequency range from 2.16GHz to 4.13GHz. Except utilizing the electric dipole, a method of using a reflector to suppress the backlobe radiation of the antenna is also examined. Thirdly, a dual polarized design is studied. Two shorted bowtie patch antennas with two electric dipoles are integrated together to form a dual polarized antenna. This antenna is useful for the existing DCS, PCS, and 3G mobile communication systems operating between 1.71 and 2.17GHz. The simulated and measured results show that the antenna has stable and symmetrical radiation patterns at slanted ±45° as well as low back radiation of about -19dB. Good isolation of -28dB between the two input ports is achieved. The gain of the dual polarized antenna is also stable over the operating frequency range and the average value is about 6.6dBi. Finally, a Wilkinson power divider is integrated to the structure of the proposed dual polarized antenna for generating circular polarization radiation. The antenna attains wide 3-dB axial ratio bandwidth of 29% (from 1.62 to 2.17GHz). Very stable and symmetrical radiation patterns with low cross polarization level have been obtained over the operating band. The 3-dB beamwidth is about 85° and the gain of the antenna is about 6.3dBi with small variation. The shorted bowtie patch antenna is novel in design. By applying the complementary antenna approach to the antenna, good electrical characteristics can be obtained. This antenna is suitable for linear, dual and circular polarization operation.
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