A Study Of K-band Microstrip Antenna Arrays

In automatic highway toll systems, there is a phenomenon that two cars in theadjacent ways or two adjacent cars in the same way interference each other, which leadsto misdetect and misjudgment for not enough detection precision to the cars. Using abeam scanning antenna array with high gain and narrow beam, the problem of misdetectand misjudgment can be solved. Due to its advantages of low cost, simple design andeasy manufacture, microstrip antennas are widely used in the microwave and millimeterwave communication systems. In this thesis, a K-band microstrip phased array antenna,with high accuracy and low cost, is presented and studied for the vehicle detectionapplication, which has a potential engineering application. The major works aresummarized as follows:(1)Feed networks for K-band microstrip antenna arrays are studied. The traditionalparallel and series feed networks are designed, simulated and analyzed. It is found thatparallel feed networks at K-band have complex structures and higher insertion loss forthe long length of microstrip lines; Series feed networks have narrow bandwidth andlead to the main beam deviate from the expected direction owing to the feeding powerattenuates along the transmission line. A series/parallel hybrid feed network is proposedand designed, an out-of-phase power divider is used to feed two series-feed linear arrays,which is composed of a parallel mode. The problem of unbalanced feed amplitude inantenna arrays is solved and the insertion loss of the feed networks is improved.(2) A K-band microstrip phased array antenna is designed. F irstly, the elementpatch operated at24GHz is designed and the performance of the patch in arrays isinvestigated. Secondly, a1×16linear array is constructed by using the patch antennaand the series/parallel hybrid feed network, then an8×16planar array is constructed byeight1×16linear arrays. The8×16planar array has eight independent feed ports.H-plane beam scanning is realized by controlling the phase of the eight independentfeed ports for the antenna array. The simulated results show that the scanning range inH-plane reaches±20°for the main beam. The antenna gain is greater than27.5dBi andthe beamwidths in E-plane and H-plane are4.4°-4.5°and8.3°-8.8°, respectively, whichindicates that the results meet the design requirements. In addition, the realizationscheme of the antenna is also discussed.