Design of the satellite Ku-band CP array antennas and its initial study of Optimization

• Main Authors: Fai-Lung Tuen, 段龍輝
• Other Authors: Ching-Lieh Li
• Format: Others
• Language: zh-TW
• Published: 2009
• Online Access: http://ndltd.ncl.edu.tw/handle/15308765791915026077

碩士 === 淡江大學 === 電機工程學系碩士班 === 97 === The purpose of this thesis is to design a Ku-band circular polarization array for satellite application. Ku-band microwave frequency ranges from 12GHz to 18GHz in general. The objective of this thesis is to explore the circular polarization array antenna for fixed satellite services and satellite broadcasting services covering 11.45 ~ 12.75GHz frequency range. At first, one need to design a single antenna element with circular polarization that meet Ku-band satellite bandwidth requirements. The single antenna element need to achieve broadband characteristics of circular polarization, but also have high isolation. This thesis presents an array of circular polarization satellite antenna, of which the structure is based on a simple slot-coupled patch antenna. The patch antenna has three matellic layers, of which the upper layer is where a square patch radiator resides. Meanwhile, the middle layer is the metallic ground plane, where the coupling slots are etched, and the lower layer is intended for the 50Ω feed line and/or feeding network. When the feed line for slot 1 and slot 2, respectively, exhibits 90-degree phase difference the circular polarization of radiation can be generated. In addition, in order to reduce the backscattered radiation another metal surface is added to form a four-layer metallic structure. We found that putting the excitation slot at the corner of the patch can improve the isolation as compared with putting the excitation slot at the edge of the patch. Thus the structure with excitation slot being at the corner of the patch is adopted for the successive investigation. In addition, for the feeding network the Wilkinson power splitter is used to feed input signal power regarding the frequency bandwidth. Taking into account of the coupling effect between the feed lines of near paths, careful adjustment for the path length is necessary. We have examined the simulated characteristics of the 2X1 and 2X2 arrays, and the prototype of the 2X2 array is fabricated and measured. The simulation and measurement results are found in very good agreement. Then, in this thesis the genetic algorithm is applied to further optimize the design for the circular polarization array antenna. The objective is to scan the main beam by suitable adjustments of the phase of the excitation current. During the course of scanning the characteristics of circular polarization must be maintained, meanwhile, the sidelobe level (SLL) is kept low, for which the coupling effect between the antenna elements must be took into account. To accomplish this, we have to calculate in advance the radiated E fields of the entire antenna array (at least including the neighboring components) with only a single antenna element being excited. The full-wave simulation software is employed to simulate the the 2X2 array antenna as mentioned. The far zone E fields rE of all the angles (up to one degree resolution) are obtained and saved for successive optimization using GA algorithm. In GA, the far zone E fields must be updated for different phase adjustments of the excitation current. Finally, for the optimal excitation phase searching for the 2X2 phase array, one must first select the appropriate optimization conditions and weights: as a circular polarization array antenna is considered, the conditions of high-gain, low sidelobe level (SLL) and low axial ratio are included into the searching fitness criteria. Then through the genetic algorithm the optimal solution to achieve the required scanning angle can be obtained, and the list of the excitation phases of the current is calculated and saved for practical usage. The results of GA optimization are compared with the simulation results by software, and the results show very good accuracy and consistency with error less than 1%