Investigations On Ultra-Broadband Antennas For Through-Wall Radar And Ground-Penetrating Radar

Since the concept of Ultra Wideband Radar system was introduced in the nineteen-fifties and sixties, it has attracted a lot of attention of researchers due to its advantages of high range resolution, robust anti-jamming and low probability of interception, and it has extended applications such as passive target indentification, precise position, target imaging and so on. The envelopemt of UWB radar systems demands high gain and miniaturization for the UWB antennas. In this thesis, two kinds of promising UWB antennas, i. e. Vivaldi antenna and Archimedean spiral antenna has been comprehensively analysed and modified under the guidance of the aforementioned tendency.Firstly, the significance and background of the Vivaldi antenna are introduced as well as the development situation. Based on the basic structure and radiation mechanisms of the antipodal Vivaldi antenna, a flow path of designing a Vivaldi antenna is studied and an original antipodal Vivaldi antenna is designed. Then working principle and influence of the choke current structure are researched and the orginal Vivaldi antenna with the choke current structure is designed, farbracatied, and tested. The measurement results demonstrate the validity of this method of miniaturization.Secondly, the radiation mechanisms of the double exponential Vivaldi antenna are researched and an original double exponential Vivaldi antenna is designed. By analyzing the the reseason of deterioration of its patterns at high frequency and summarizing the current existing solutions, a method of graded dielectric substrate loaded is proposed. According to the working principle, a Vivaldi antenna loaded with graded dielectric substrate, operating at broader bandwidth and achieving a higer gain, is designed and fabricated.Thirdly, this dissertation introduces the utra-wideband feature of Archimedean spiral antenna in terms of the frequency indepent antenna and analyzes the operating mechanism of this antenna. The design process of Archimedean spiral antenna is given and a prototype of this antenna is designed to verify the utra-wideband performance.Finally, summarizing the improved methods of Archimedean spiral antenna and comparing the advantages and disadvantages, the Archimedean spiral antenna coverd with multi-layer dielectrics is designed according to the principle that the uneven phase and amplitude at the apeture of an antenna covered with dielectric are improved. The simulation shows that the gain of this Archimedean spiral antenna is increased.