| As one of the most important components in wireless systems,antenna has always been the research hotspot in various civilian andmilitary applications, such as satellite communications, broadcast,navigation radar, remote sensing, and etc. Among them, circularlypolarized antenna has a wide range of application due to its ability ofanti-fading in transmission, which is conductive to improve the channelstability and channel utilization in complex environments. As thetransmission rate is required to be higher and higher, the performance ofthe circularly polarized antenna is also required to reach a higher level,such as wide band, high gain and low axial ratio(AR), meanwhile, thepattern stability, the profile of the antenna must also be taken intoaccounted at the same time, which brings big challenge in circularpolarized antenna designs. On the other hand, conventional antenna designis mostly depend on the designer’s relevant background knowledge andexperience, however, as the antenna structure becomes more complicatedthan ever before, such “cut and try” method is cumbersome andinefficiency. Hence, it would be meaningful to investigate the method ofusing advanced computer calculation to find the optimized antennastructure dimension.This paper focuses on modeling and optimization of wide band lowprofile circularly polarized antenna designs. The article begins with anoverview of the background and significance of this study. The currentdevelopment of the circularly polarized antenna, low profile antenna andantenna optimization are summed up. The basic theories of thecircularized-polarized antennas are briefly described, also, the basic theory of PSO algorithm and PSO algorithm optimization of antenna design areintroduced.Then, based on the theoretical analysis, two optimized models ofantenna design are given, which are validated through special designedmicrostrip patch antennas. The configuration of the first model is achievedby modifying the objective function of the PSO algorithm procedure,which is then imported to CST Microwave studio (CST), using macrolanguage. And the automatic design of the antenna can be performed easily.The structure of the antennas contains a radiated patch and a parasiticpatch, both of which are modeled in the PSO algorithm procedure usingdiscrete grid, and at last it is realized by the Boolean operation in computercalculation. To further reduce the limitation of this algorithms procedureand expand its application, a modified optimization model has also beendesigned to get better versatility and compatibility. Except that theparasitic layers adopts discrete grid, the model of radiating patch ismodified to increase the optimized freedom. Moreover, the entire antennastructure is optimized in CST using its embed PSO algorithm to improveefficiency.And then, based on the analytical model, two wide-band circularlypolarized antennas using two feeding methods are designed, one is usingcut away style coaxial balun and the other is using microstrip to parallelstrip balun. The antenna adopts conventional cavity-back equiangularspiral structure, and to improve the circular polarization performance, twoparasitic layers, making up of a few small patches with varying sizes, areinserted into between the spiral and the cavity. What’s more, the parasiticlayers are made rotationally symmetrical to enhance the circularlypolarized field of the antenna. The dimension of the spiral, the patchparameters of the parasitic layers, and the feeding positions are alloptimized using the established optimization method. The simulatedperformance of the final optimized antenna exhibits wide band circularpolarization. Last, the two optimized spiral antennas with parasitic layers insertedare fabricated and tested. The measured results agreed well with thesimulated ones, which validates the effectiveness of the modeling andoptimizing of the method. The designed antenna has a low profile, which issuitable for various wireless communication applications. |
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