The Researches On Broadband Antennas With Miniaturization

Recently, the requirement of large capacity, high reliability and high quality in wireless communication systems is increasing generally and a variety of service is emerging. New technologies and new standards in wireless applications are coming out one after the other, and promoting the development of wireless technologies. The rapid development of communication system raises higher demand for communication equipments. Small volume and wide band of the communication equipment put forward the development of miniature and wideband antennas, which are known as key components of the communication systems. So the development of miniature and wideband antennas with good performance is an urgent and important issue in theory and applications. In the dissertation, the design principle, limitation and the status quo at home and abroad about miniature and wideband antennas are described. The thesis mainly consists of following parts:First, two new ultra-wide band (UWB) antennas are designed, including miniature fractal UWB antennas and band-notched UWB antennas. After the basic theory, the formation method and the characteristics of the fractal geometry are introduced, the self-similar characteristics and space filling property of the fractal geometry are used to design a miniature UWB antenna. Test results verify that the UWB antenna covers the frequency scale from 3.1GHz to 10.6GHz. In addition, a new UWB antenna structure with band-notch is also given, which is constructured by embedding an inverse trapeziform gap into the structure to realize 5GHz to 6GHz band-notched function. To improve the omnidirectional characteristic of the radiation pattern, the planar structure is extended to solid structure. The band-notched UWB antenna with omnidirectional radiation pattern is designed.Secondly, intelligent algorithm is used to design of UWB antennas. To save the time, the mixed model of genetic algorithm (GA) and finite-difference time-domain (FDTD) is used to optimize structure parameters of UWB antennas in the dissertation. The fitness function is evaluated by FDTD. A new UWB antenna from 3GHz to 11GHz is designed by this method. To design a UWB antenna in limited size, the 2-dimension genetic algorithm (2-D GA) is used to design automatically UWB antennas and band-notched UWB antennas. To avoid the slow convergence rate in GA, the 2-D GA and the binary particle swarm optimization (BPSO) is mixed. A UWB antenna with 24mm×24mm sizes and less than 1.5 VSWR from 3.1GHz to 10.6GHz is designed by the method.Finally, a metal reflector is adopted for adding the gain of antenna arrays, including the miniature reconfigurable array for wireless local area networks (WLAN) systems and wideband array for satellite communication systems. In the design of miniature reconfigurable array, not only the omni-directional/directional radiation switch is realized, but also pattern diversity in the multi-in multi-out (MIMO) systems is realized. In the design of the array for satellite communications, the array structure not only increases the bandwidth, but also improves the gain of the array. The characteristics of the arrays constituted by the fractal structure and the traditional disc structure are compared. The results prove the superiority of the fractal structure.