| As the demand for location information and remote communication in various industries increases in recent years,the number of applications of BeiDou Navigation Satellite System(BDS),integrating location and communication functions,will grow.Therefore,designing a miniaturized multiband and high-performanced navigation antenna,which can be applied in positioning terminal of various industries,is imminent.This article takes our BDS terminal antennas as the engineering application background,designs different kinds of dual-frequency circularly polarized microstrip using the electromagnetic simulation software,and makes them into physical antenna.The issues of this paper mainly include:1.A BDS dual-frequency circularly polarized antenna with parallel structure is designed,for improving the first generation BDS antenna whose size affects its integration in BDS Navigation Terminal.This antenna is composed of L band and S band ceramic antenna arranging on a 20mm*46mm FR4 substrate,and the circularly polarized radiation is realized by combining the independent feeding mode and the triangular tangent angle.The simulation results show that the standing wave and isolation of the antenna ports can meet the index requirements,but antenna pattern is slightly worse because of the asymmetry of structure.In order to solve the problem,a BDS dual-frequency circularly polarized antenna with laminated structure is designed.Its size is 45mm*45mm.This antenna realizes the L/S dual-frequency circularly polarized radiation in combination of the upper and lower stacked patch and independent feeding mode.The simulation results show that the standing-wave ratio is less than 1.5 and the port isolation reaches 47dB in the L/S frequency.The gaining of L/S frequency is-2.2dB and-0.9dB at the elevation of 20 degrees.The antenna has a good performance and fulfills the requirements of BDS.2.A miniaturized and low profile BDS dual-frequency circularly polarized antenna is designed,for improving the high profile of the laminated structure antenna.This antenna realized the dual-frequency functions by innovative inner-outer nesting structure,and the inner and outer antenna serves for S-frequency and L-frequency separately.It realizes the left and right hand circularly polarized radiation by combining the independent feed and the tangential angle perturbation,and loads short circuit wall at the center of the structure to enhance the isolation between the feed ports.The simulation results show that the impedance bandwidth(VSWR<2)of the L-band antenna and the S-band antenna are 24MHz and 66MHz,and the isolation degree between the receiving and dispatching terminals reaches 40.19dB.The gaining of L/S frequency is 3.8dB and 2.7dB at the elevation of 50 degrees,0 dB and-1.8dB at the elevation of 20 degree.The antenna has a good performance and fulfills the requirements of BDS.3.A double point feed BDS dual-frequency circularly polarized antenna is designed,for improving the single point feed circularly polarized antenna whose performance is greatly affected by its structure.It insures the axial ratio performance by double point feed so as to raise the 3dB axial ratio bandwidth of antenna.L-frequency antenna realizes circularly polarization characteristics by using Wilkinson power supply network combining with λ/4 delay line controlling 90° phase.The S-frequency antenna removes the feed point position to the patch center by introducing the u-shaped slot in the center of radiation patch so as to improve the isolation between ports.The simulation results show that the standing-wave ratio is less than 1.5 during both L and S frequency.The 3dB axial ratio bandwidth of the dual-band antenna is 90MHz(1.57GHz～1.66GHz)and 11MHz(2.489～2.500 GHz).The isolation between feed ports is 27.6 dB,and the antenna out of roundness within ± 1dB.The antenna has a superior performance,and its indexes totally meet the design requirements. |
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