| With the rapid development of wireless electronic systems, antenna arrays are playing a more and more important role in the performance enhancement of the entire wireless system. The antenna arrays which are widely applicated in various electromagnetic environments are usually required to have the features of low sidelobe levels, multi-beam, beam scanning, beamforming, etc. These requirements usually pose the difficulty of antenna design, the complexity of feeding network, and the high precision requirements of the feeding network devices. The four dimensional(4D) antenna array which is formed by introducing time as a new design freedom can be used to reduce the difficulty of antenna design and decrease the denpence of the accuracy of feeding amplitudes and phases. In addition, the unique radiation characteristics of the 4D antenna arrays which are diffierent from the conventional antenna arrays are being exploited and getting more and more attention.Based on the frequency-domain characteristics of the 4D antenna arrays, the in-depth research of efficient design and system level application of 4D antenna arrays are carried out in this thesis. Focused on these two aspects, the contents of the thesis are as follows:In the aspect of efficient design of 4D antenna array, focusing on the optimization efficiency of the ON-OFF time sequences, the bitwise evolutionary genetic algorithm(BEGA) is proposed in this thesis. Considering the characteristics of periodic time modulation, the mathematical expression of ON-OFF time sequence and its physical meaning are combined organically in the proposed algorithm. Every gene in chromosomes is regards as an independent evolution unit in BEGA. The concept of gene retain probability is also introduced into the algorithm. Through the method of retaining the high quality genes and reversing the poor quality genes, the genes are evolved by the application of the whole individuals. By the combination of optimization algorithm and physical meaning, BEGA improves the directivity of the iterations significantly. Moreover, BEGA has better optimization performance than existing algorithm in the situation of large array synthesis with large number of parameters. A mass of simulation verified that BEGA not only can achieve better radiation performance, but also can improve design efficiency when applied in the design of 4D antenna arrays.In the aspect of the system level application of 4D antenna array, taking full advantages of the sideband signals of 4D antenna arrays, signals at central frequency and multiple sidebands are applied I simultaneously in the area of spatial spectrum estimation. Firstly, considering that the array type of 4D antenna array is time-varying, the classic multiple signal classification(MUSIC) algorithm was modified, where the signal space is made up of several sideband signals rather than the received signals of each element antenna. Secondly, a method of combining the MUSIC algorithm and differential evaluation(DE) or BEGA is proposed to avoid fake peaks, thus improving the probability of resolution and decreasing the root mean square error of DOA estimation at the same time. With the combined optimization, the performance of spatial spectrum estimation is further improved with various time modulated schemes which have significant advantages over conventional antenna arrays. Finlly, an experiment platform of spatial spectrum estimation based on 4D antenna array is built, which accomplishes the process of signal transmitting, receiving and discrete signal processing. The experimental results verified the feasibility of the application of 4D antenna array in the area of spatial spectrum estimation. |
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