In this thesis, two types of handset antenna design respectively for dual-band GSM850/1900 operation and seven¡Vband LTE/WWAN operation are presented. The proposed antennas can achieve decreased antenna size and enhanced operating bandwidth by shaping the system ground plane of the handset. The seven-band LTE/WWAN antenna is printed on the system circuit board with good radiation characteristics and occupies a small size of 24.5 x 10 mm2. At first, we propose a half-loop antenna structure which integrates its facing edge of the system ground plane as the resonant path of the antenna. In this case, the required length of the half-loop antenna structure is only about a half compared with the traditional loop antenna. Next, to enhance the operating bandwidth of the antenna, a parasitic shorted monopole strip is added and a shaped system circuit board is used. The shaped system circuit board can integrate the battery with the circuit board to help reduce the thickness of handset. Also, much enhanced operating bandwidth for the lower band can be obtained, owing to the enhanced surface current excitation in the system ground plane resulting from properly shaping the system circuit board. Effects of the user¡¦s head and hand on the proposed antenna are studied, and the simulated SAR and HAC results are also analyzed for bio-compatibility issue.

In recent years, microstrip antennas are suitable for applications in wireless communication systems because they have the characteristics of compact size, light weight, low cost and easy to manufacture. So, they play an important role in the navigation equipment of the rocket, space shutter, personal communication, etc. However, in the design and synthesis of antennas, there are a large number of design variables that affect the antenna performance. In early stages, some researchers did not use any optimization tool in parameter tuning of antennas design. The one utilized most is the ¡§trial and error¡¨ method, which is very time-consuming in order to find a suitable solution to verify the possibilities of the antenna structure. Genetic algorithms have been shown to be effective in the design of broadband microstrip antenna. However, their effectiveness with various degrees depends on the skills of the different genetic algorithms. In this dissertation, we propose a Genetic Algorithm (GA)-based refined method to enhance the effectiveness and to solve the gap-coupled microstrip antenna design problem (largest impedance bandwidth). The refined method with optimization process improves the computing performance comparing with the conventional genetic algorithm. By the refined GA method, bandwidth can be widened up to 3.84 times that of a single excited patch. Furthermore, we present a new design for Ultra Wideband (UWB) antenna. In the new research topic, it is expected that the genetic algorithm can find out a range of feasible (range-based) solutions instead of a few of solutions. As a result, the manufacturing process will have more convenience and practicability. Finally, we propose a new method to overcome the problem of signal interference with the UWB system operations. A band notched characteristic is achieved for the antenna to restrain the interference bandwidth. The disclosed antenna and the circuitry for the antenna system are easily integrated. With the simple structure, the fabrication cost for the antenna is also reduced.

Novel broadband designs of microstrip antennas have been proposed in this dissertation, including bandwidth enhancement using integrated reactive loading, broadband circularly polarized designs, broadband dual-frequency design, bandwidth enhancement using a slotted ground plane and practical applications. First, bandwidth enhancement of microstrip antennas using integrated reactive loading is proposed and experimentally studied. Results show that the proposed antennas can have an operating bandwidth more than 2.0 times that of a conventional one at a given operating frequency. Second, by selecting a thick air substrate, a wideband circularly polarized microstrip antenna with improved CP quality has been implemented. In addition to the improved CP quality obtained, a 2-dB axial-ratio bandwidth as large as about 38% is also achieved. Third, by bending a planar rectangular patch into an inverted L-shaped patch, a dual-frequency planar antenna has been obtained. Experimental results show that the proposed antenna has a tunable frequency ratio of about 1.66-2.29. Fourth, by embedding meandering slots or slits in the antenna¡¦s ground plane, it is observed that the impedance bandwidth of the microstrip antenna is twice larger than the conventional one. The experimental results show that the resonant frequency is significantly lower, which can lead to a large antenna size reduction for a fixed frequency operation. In addition, enhanced antenna gain is also obtained. Finally, a shorted patch antenna suitable for applications in DCS (1710-1880 MHz) base station is presented.

Antennas are designed to radiate or receive electromagnetic waves in the part of transmitting or receiving system. They are transducers which transform electric energy into waves so as to radiate radio waves, that¡¦s the primary purpose of antennae. Utilizing the characteristics of helical antennae operating in the axial mode including high directivity, broad bandwidth and circular polarization in satellite communication (ex. GPS) is detailed described in this thesis. The microwave dielectric ceramic material becomes very popular in satellite and wireless communication in recent years because of its high-K, high-Q,and stable-temperature-coefficient characteristics.Our study also utilizes its feature of high dielectric coefficient to shrink the size of the antenna significantly. In this study, we fabricate and analyze the antenna combining the advantages of the helical antenna and the microwave dielectric ceramic material.

Thesis (Ph. D.)--University of Texas at Austin, 1999. / Vita. Includes bibliographical references (leaves 108-116). Available also in a digital version from Dissertation Abstracts.

Thesis (Ph. D.)--University of Texas at Austin, 2000. / Vita. Includes bibliographical references (leaves 103-111). Available also in a digital version from Dissertation Abstracts.

Thesis (Ph. D.)--University of Queensland, 2001. / Includes bibliographical references.

Thesis (Ph. D.)--University of Texas at Austin, 2000. / Vita. Includes bibliographical references (leaves 130-139). Available also in a digital version from Dissertation Abstracts.

Thesis (Ph. D.)--Lehigh University, 2001. / Includes vita. Includes bibliographical references (leaves 106-114).

Thesis (Ph. D.)--University of Texas at Austin, 2000. / Vita. Includes bibliographical references (leaves 91-96). Available also in a digital version from Dissertation Abstracts.