Research On Antennas In Mobile Communication System

With the fast development of mobile communication system, the system is more and more complex, which demands the character of antenna better. So the research on antennas in mobile communication system is an important issue with great theory and engineering meaning. Being associated with three research projects, this dissertation makes deeply insight into the antennas in mobile communication system, including board antenna and smart antenna and so on. The author's major contributions are as follows:1. Based on the moment matrix and voltage feed, a new definition of eigen-driven model in moment method is proposed, or one element of the array fed with others short. The current excitation coefficient of array obtained by other methods based on array factor are changed into voltage excitation coefficient with eigen-driven model, which can be used directly into array with mutual coupling and form the same pattern with ideal array. The method can be used for optimization of complex array and the process of pattern synthesis of practical array is shortened because of the reduced electromagnetic analysis. Some examples are illustrated to prove the conclusion.2. The pattern synthesis of horizontal plane and vertical plane of sector antennas is studied. The antenna approximated with wire grid is analyzed with Method of Moment and synthesized using Genetic Algorithm to realize expected pattern. Through the proper choice of target function, the gain, beamwidth and backlobe are comprehensively considered during optimizing. The method can used to analyze other array of the same kind with different radiating element. The result is very useful for engineering and theory analysis. According to the design, antenna samples are made and the measured results are consistent with the computed. The samples are put into practical use in base station.3. Genetic algorithm is used to design the sectored array antenna in smart antenna system. The sectored array antenna is applied to the base station of TD-SCDMA. The research includes array element, failed element, feed network, pattern realization and the affect of random on pattern. Genetic algorithm is used to optimize the weights to realize the sectored coverage mode (namely Broadcast Beam) and working mode (Work Beam) of the smart antenna system. The antenna prototype is already used in the TD-SCDMA system experimentation.4. The mutual coupling in antenna array of smart antenna system was discussed. Aberrance of the horizontal pattern of pole was concerned, which was caused by the mutual coupling in antenna array. During the analysis of pole pattern, mutual coupling caused by un-excited elements and loading caused by cable connected to them were considered. According to the theorem of multi-port system, the configuration was considered as a multi-port system. And the matching impedance of un-excited port would be calculated by tumbling method. With configuration symmetry considered, the loading impedance of un-excited port equaled the input one of excited port in order to reduce the aberrance and un-roundness of the horizontal pattern of pole and hence match the requirement of the smart antenna system. Some design examples are illustrated.5. The affect of the angle between two arms of dipole on pattern is studied. Antenna with wide beamwidth in E plane is obtained by adjusting the angle, based on which two kinds of horizontal polarization antenna with wide beamwidth are designed. Also the shaped beam antenna in E plane is realized by change of angle or position of feed point. Designed examples are illustrated to prove the theory correct.