Design Of Wireless Communication Antennas And Optimization Synthesis Of Time Modulated Arrays

With the progress of science and technology, modern wireless communication systems have worked deeply in our life. As an indispensable part of the communication system, the design requirements of antenna are becoming more and more stringent, such as antenna miniaturization, antenna bandwidth broadening and antenna polarization problem. Recently, the complementary antenna and magneto-electric dipole antenna have been widely studied and applied for their simple structure, wide bandwidth and ease to achieve circular polarization. At the same time, antenna arrays, especially the phased antenna array, have become popular in order to realize lower sidelobe, or higher antenna gain. However the requirements of amplitude and phase control systems of phased array are extremely high, the phased arrays have low tolerance of the deviation and high machining precision, which will limit their application. By introducing the time dimension, the time modulated array (TMA), which modulates the emission signal and receiving signal, can reduce the design requirements of amplitude and phase control systems. This dissertation is mainly concerned with the design of complementary antennas, the circularly polarized magneto-electric antennas and the optimization of TMA. The major works and contributions of this dissertation are outlined as follows:1. The wideband and dual band antennas with complementary structure are studied. First of all, to solve the bandwidth problem and the volume problem of Yagi antenna, a novel director array is presented which is composed of loop antennas and thin dipole. Compared with the traditional electric dipole director, this novel director array has smaller size and wider bandwidth. The directivity of slot-loop antenna can be effectively improved in a wide frequency band by arranging the director array in front of it. Then a printed antenna based on the self-complementary structure is proposed. Through the slot etched on the antenna, which will change the surface current, dual band circular polarization is realized. Experimental results show that the performance of proposed antennas is well, and they can meet the needs of modern communication systems, such as LTE, DCS and WLAN.2. The wideband magneto-electric dipole antenna is discussed. The circular polarization is widely used in modern communication systems because it has the characteristics of small attenuation, strong anti-interference ability and strong propagation ability. Two wideband circularly polarized antennas based on the magneto-electric dipole antenna are presented in this dissertation. Firstly, a wideband phase shifter is presented based on defected ground structure. Then a novel wideband circularly polarized antenna is designed by combining the phase shifter and the two orthogonal magneto-electric dipole antennas. A single feed wideband circularly polarized antenna using the coupling feeding and parasitic patch technology is proposed in order to reduce the design complexity and save the antenna installation space. Compared with the traditional circularly polarized patch antenna, this two presented antennas show wider axial ratio bandwidth and higher antenna gain.3. The optimization of time modulated array based on the modified differential evolution algorithm is investigated. Firstly, a modified differential evolution (MDE) algorithm, which employs the simplified quadratic interpolation algorithm and adaptively adjusts the parameter CR and mutation strategy, is presented. Benchmark functions have been provided to verify the performance of the MDE. Then the time modulated linear array and concentric ring array (CCRA) are optimized by the MDE. Numerical results reveal that the peak sidelobe level and the peak sideband level of optimized TMA are much lower, and the MDE can optimize the TMA faster and better.4. The multi-objective optimization design of the TMA is studied. In view of the limitation of single objective optimization algorithm, multi-objective optimization algorithm is adopted to optimize dual-objective or tri-objective linear TMA and dual-objective CCRA. Also the optimized results are compared with the single-objective one. Finally, the high-quality optimal solutions which meet engineering design requirements are obtained by analyzing the numerical results in detail. It will be seen that the multi-objective optimization algorithm can be an effective method to optimize the TMA.