| With the advantages of the short-range and high-speed wireless communications, ultra-wideband (UWB) technology is one of the most interested research fields in modern wireless communication systems. As a key component of the UWB system, the antenna has critical influences on the performance of the system. This dissertation mainly makes insight to the design of multiple band-notched UWB printed slot antennas and miniaturized UWB antennas. The author's major contributions are as follows:1. The design and realization of two printed slot antennas with multiple band-notched characteristics are present. By loading two or three different resonating structures at the proper region on the reference antenna, the UWB antennas with dual and multiple band-notched characteristics are realized. The conceptual equivalent circuit models, which are based on the surface current distributions on the resonating configurations, are also shown to further analyze the band-notched characteristics and the operation principles of the resonating configurations. In addition, the aforementioned antennas are fabricated and measured, and the measured results show that both of them have good band-notched UWB characteristics.2. Two novel compact internal ultra-wideband antennas are proposed for wireless USB dongle applications. The first antenna mainly comprises a folded metal plate with two sides beveled and a short-circuited pin connected to the system ground plane. Moreover, by etching a pair of slots in the bevel sides of the folded metal plate, a more miniaturized internal antenna for WUSB applications is obtained. The size of the second antenna is reduced by 25% compared to that of the first one. By using the commercial software Ansoft HFSS, these two antennas are simulated, and their optimal dimensions are obtained. Prototypes of the antennas are fabricated and measured. The measured results indicate that both of the miniaturized antennas present good ultra-wideband performance.3. As the main part of a research project, a compact ultra-wideband monocone antenna is presented. The proposed antenna is a simple modification of the classical monocone antenna by adding a cylinder at the end of the cone and loading a matching network between the cone and the circular ground plane. HFSS software is also utilized to analyze and optimize the dimensions of the antenna. The monocone antenna is of a vertical height 0.023λF, whereλF is the wavelength corresponding to the lowest operating frequency of the antenna. A prototype of the antenna is manufactured and tested. The measured results indicate that the compact ultra-wideband monocone antenna has a 100:1 impedance bandwidth with VSWR below 2.5:1, and the H-plane radiation patterns of the antenna are nearly omni-directional. |
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