Research On Dual-polarized Antenna With High Polarization Purity Based On Differential Feed

In recent years, the advantages of broadband dual-polarized antenna with compactstructure have become more and more obvious in mobile communication systems, and ithas aroused wide attention from many scholars. For instance, dual-polarized antennas arewidely used in cellular-phone base stations to realize frequency reuse or polarizationdiversity. By using these schemes not only can increase the communication capacity, butalso can improve the rate of data transmission in the communication system. In addition,dual-polarized antennas with high isolation and low cross polarization are able to reducethe multipath effect and improve the polarization mismatch between the transmitter andreceiver. Therefore, the research on dual-polarized antenna with high performance is veryurgent and it is also of important theoretical significance and practical value.On the application background of base station antenna and according to the industrystandards of mobile communication for dual-polarized base station antenna, thebroadband dual-polarized antenna with high polarization purity has been researched byutilizing differencial feeding technology in this thesis. The main work and obtainedachievements are as follows:1. A broadband dual-polarized antenna with integrated Marchand balun has beendesigned. The antenna is composed of a cross dipole, a folded ground, two feedingnetworks, and a reflector. The impedance bandwidth has been enhanced by utilizing themutual coupling between the two dipoles. A kind of meandering folded Marchand balunis skillfully integrated on the support column of the antenna to excite the dipoledifferentially. By using this feeding method, the proposed antenna gains high portisolation and low cross polarization over the entire operating frequency band(1.71GHz-2.17GHz) of standing wave ratio (SWR) less than1.5. The radiation patterns ofthe proposed antenna are stable with frequency and it can be easily formed an array.2. In order to obtain wider bandwidth, the antenna designed above has beenimproved on radiation structure, feeding networks and reflector, respectively. After aseries of simulation and optimization, the operating bandwidth of the improved antennaachieves1.7GHz-2.7GHz which can cover2G,3G and4G communication frequencyband simultaneously. The improved antenna has also been fabricated and tested accordingto the optimized model, and the measuring methods of the directional dual-polarized base station antenna are introduced too. Through the comparison and analysis, it can be foundthat the measured results match well with the simulated one and meet the designrequirements, so the feasibility of the theoretical simulation has been verified.3. Based on the improved broadband dual-polarized antenna element, thecharacteristic parameters of a uniform linear array which composed of six identical unitsare simulated and analyzed, especially the radiation parameters of the antenna array aresimulated and optimized. In the whole operating frequency band (1.7GHz-2.7GHz), theproposed antenna array achieves good radiation characteristics in both horizontal planeand vertical plane which satisfy the industry standards of mobile communication.