Research Of High Gain Ultra-widebamd Antenna Based On TEM Mode

Ultra-wideband is an international hotspot technology developing very rapidly at present. As one of the important components of the ultra-wideband system, ultra-wideband antenna has been a challenging research topic. Meanwhile, higher requirements for not only the ultra-wide band characteristics but also the high gain characteristics of the antenna are put forward when it comes to modern communications, radar and wireless monitoring and management applications.In this dissertation, the international research situation is summarized firstly. Afterward, the fundamental conceptions and theory is introduced briefly, and the performance parameters of the ultra-wideband antenna are defined. On this basis, the high gain ultra-wideband antenna based on TEM mode is researched detailedly.As the key component of the ultra-wideband antenna, the ultra-wideband characteristic and high gain characteristic of the feed will decide characteristics of the antenna. Therefore, the ultra-wideband feed based on TEM mode is studied in detail. The TEM horn has great ultra-wideband characteristic, however, when it is used as the feed of a paraboloid antenna, the metal plate will shadow the electromagnetic radiation hence decreasing the gain. Researches show that the surface current distribution of the TEM horn is mainly at the side edge, thus holding the concentrated region of the surface current will form the TEM mode four wirelike feed arms model. Compared with feeding by TEM horn, the paraboloid antenna with TEM mode four wirelike feed arms can maintain the good impedance characteristic, while the antenna gain is quite higher owing to the reduction of the blockage Then, three forms of feed arms are researched respectively, and the effect of different structure on antenna impedance performance has been given, which can be the theoretical basis for the design and optimization of feed arms.The ultra-wideband paraboloid antenna based on TEM mode is studied systematically, and design methods of four types of feed arms are proposed. The ultra-wideband paraboloid antenna with triangular feed arms can be designed by analytic means, and it has obtained good impedance and radiation characteristics. The operating frequency range of the antnna is 1.5 to 9.5GHz; and the gain is 10.2~23.9dB within the band, and the aperture efficiency is 0.53~0.69. In order to reduce the current at the end of triangular feed arms, fusiform feed arms are designed, and meanwhile, the angle between feed arms is optimized. The operating frequency range of the antenna can be extended to 1.1 to 18.4GHz, and the gain is 11.3~28.4dB within the band. The average gain is 3dB higher than that with triangular feed arms, and the aperture efficiency is 0.7~0.76. To further optimize the antenna performance, exponential tapered feed arms are proposed. This structure can broaden the operating frequency range of the antenna to 1.05 to 20GHz, and the maximum gain is 28.9dB within the band, and the aperture efficiency is 0.71~0.77. Furthermore, in order to improve the low-frequency characteristic, composite tapered feed arms are presented, which is formed by adding a linear term to the expression of exponential curve. The lowest operating frequency of the antenna is expanded to 0.7GHz, which is 33% lower than that of the exponential tapered feed arms, thus the lowest operating frequency is decreased effectively. In addition, further reduction of the lowest operating frequency can be realized by loading resistances at the end of feed arms. And the low limit frequency of the antenna has been decreased to 0.3GHz, and the effect of the low-frequency expansion is obviously.Besides the paraboloid antenna, the lens antenna can also be employed to be the high gain ultra-wideband directional antenna.The dielectric lens attached at the aperture of the TEM horn can compensate and eliminate the chromatic dispersion brought by the phase contrast, and can enhance the far field radiation effectively hence increasing the antenna gain. The hyperbolic lens, meniscus lens, single layer spherical lens, and double layers spherical lens are designed respectively. Compared with the TEM horn antenna, both of the hyperbolic lens antenna and the meniscus lens antenna can increase the antenna gain over 10dB, while the ultra-wideband impedance characteristic and directionality are kept very well. The spherical lens antenna can further extend the antenna bandwidth to 0.76 to 20GHz, and moreover, the double layers spherical lens will improve the gain of high band obviously, and the maximal increased gain can be 5.5dB. The design idea of stratified dielectric has good value to the practical application.The main purpose of this dissertation is to research and design the high gain ultra-wideb antenna based on TEM mode. Several antenna models are proposed , and experiments are preformed. The design ideas and methods presented in this dissertation have good value to practical application, and will provide consultation for the design of high gain ultra-wideband directional antenna in the future.