The Researches On Miniaturization Technology And Broadband Characteristics For Antennas

The dissertation is mainly on the topics of miniaturization technology and broadband characteristics for antennas with a lot of theoretical and experimental studies. Several design schemes related to the topics are introduced and much attentions are paid to the engineering application.In Chapter 1, the current developments about the antenna's miniaturization and frequency bandwidth extension technology are reviewed. It is known that the design of small antennas with broadband is a topic of current interest. it can be seen that although much progresses has been made in that category, the antenna's dimension and bandwidth are still the principal obstacle to the communication system miniaturization. The reduction of the electrical size of an antenna is at the expense of other parameters such as bandwidth and efficiency. Antenna's miniaturization techniques require a compromise between all the parameters involved. Consequently, there are a lot of problems to be solved. This research in this dissertation has important significance both in theory or application and represents the frontier topics in the IT world .In Chapter 2, the fundamental theory for the finite element method(FEM) are firstly introduced. With this technique, the performances of impedance and radiation pattern for biconical antennas with finite length and arbitrary cone angle, including symmetrical and asymmetrical are summarized and investigated. More importantly, a biconical antenna with elliptic cross section and a V cone antennas for finite length are studied. By the comparative analysis, the antenna properties, varied with different geometric parameters, is obtained. According to these analysis and the requirement of omnidirectional radiation, a new type of antenna combined a wide angle solid cone with several wires are fabricated, which has broadband properties.In Chapter 3, some monopole antennas are studied, which is focused on the realization of light weighted and miniaturization of the antennas. At first, the theory of method of moments(MOM) and its application in antenna design are summarized. With MOM, a wire conical monopole antenna is analyzed in detail and the emphasis is the relationship among the impedance properties and a number of geometrical parameters. On the basis of these analysis, a practical wire conical antenna is constructed, which has ultra wideband capability and the -15 dB operation frequency bandwidth is between 0.85GHz~2.44GHz. The other research in this Chapter is about the electrically small planar monopole antenna. The dependances of input impedance on conic angles, width and gap length of the antenna are investigated. The conclusions herein are very helpful to the design of this sort of electrically small antennas.In Chapter 4, the meander line and fractal technique are introduced to the design of antenna. Firstly, the description about fractal fundament, fabricating method and...