Optimization And Design Of Antennas In Wireless Communication Systems

With the rapid development of microelectronics technology and manufacturing process, the wireless communication equipment has led the way toward miniaturization, broadband and multifunction. Being the indispensable component of wireless communication systems, the capability of the antennas directly influences the communication quality. So, research on antennas in wireless communication system is an important issue with practical significance. The antennas in mobile communication system have three key types: terminal antennas, outdoor base station antennas and indoor coverage antennas. On the other hand, with the increasing rise of the short-range wireless communication technology, the UWB systems have gotten more and more attention. The operating bandwidth of UWB system is 3.1-10.6GHz. Meanwhile, some other communication systems such as WLAN and WiMAX also exist in this frequency range. Therefore, to avoid EM interferences between these systems and UWB communication system, a band elimination characteristic is necessary in UWB antennas. Being associated with these demand mentioned above, this dissertation makes deeply insight into the design of mobile phone antennas, indoor coverage wideband antennas, optimization of base station antenna's pattern with high performance and UWB antenna with band-notched characteristics. The author's major contributions can be summarized as follows:1. Three miniaturization and multiband planar antennas for mobile phone are investigated and designed. A planar antenna which consists of a monopole and a loop antenna covering GSM/DCS/PCS/Bluetooth/WiFi band is studied. Another two multiband co-planar inverted-F antenna are also studied for mobile phone application. In addition, by locating these two antennas at the bottom of the mobile phone, the SAR values of them decrease greatly.2. A low profile conical antenna with ultra-wideband characteristic for indoor wireless communication is investigated and designed. The antenna structure consists of a mono-conical conducting body, a parasitic ring shorted to a finite-sized ground plane in order to achieve low-profile characteristic and a sleeve attached to the ground for improving the performance at the higher frequency of bandwidth. The antenna exhibits a broad impedance bandwidth from 747MHz to 5900MHz with VSWR below 2.5.3. The combination of genetic algorithm and the HFSS software is studied, where the HFSS software as a subprogram that can do a full-wave analysis and return desired results to the main program. As examples, one antenna which consists of a taper-shaped monopole and a sleeve and occupies 90×120mm2 covering CDMA/GSM/DCS/PCS/ UMTS band and another multi-stubs monopole antenna which has a size of 110×110mm2 covering CDMA/GSM/DCS/PCS/UMTS/Bluetooth/WLAN band are designned using this method. Both of them have a planar structure which can be hidden almost anywhere while still providing full sized RF performance.4. Aiming at the drawbacks of standard genetic algorithm (SGA), such as prematurity and poor ability in local optimum, a hybrid genetic algorithm formed by integrating a step accelerating method and adaptive thought into the real-coded genetic algorithm is proposed. The simulation results on 3 benchmark functions show that the hybrid genetic algorithm is more effective than SGA.5. A more accurate synthesis of antenna array with shaped beam pattern is studied. With the aid of the HFSS software, the proposed synthesis has taken the actual element patterns into account, which removes the error caused by the neglect of the mutual coupling in traditional synthesis and improves the accuracy of the optimization. The optimization method combined with the hybrid genetic algorithm mentioned above is utilized to optimize the radiation pattern of the base station array. The good agreement between the optimized and measured results shows that the proposed synthesis is effective.6. To avoid the potential EM interference between UWB wireless communication system and other systems, such as WiMAX and WLAN, three UWB antennas with band-notched characteristics are presented. By adjusting the axial ratio and using the corner-cut technique, the antennas achieve the ultra-wideband characteristic. By using the parasitic strip and tuning stub, band elimination characteristic is created.