| The active antenna is studied in the paper, and an wide-band active receivingantenna used in satellite navigation is designed. The band of the antenna covers theGPS, the GLONASS, the GALILEO and the BeiDou(COMPASS)Navigation SatelliteSystem. It could be used in the front-end of the multi-mode navigation receivers.A low-noise amplifier, which owns a very low noise figure (NF) and a widefrequency band, is designed by using the ATF54143chip. By introducing the negativefeedback, the LNA owns a low gain flatness, which is less than1decibel. Meanwhile,the matching of the input and output of this LNA and its stability perform very well.In order to achieve the characteristic of circular polarization, two differentwide-band navigation antennas are designed, and each of them has a differentstructure of four-point-feed with each phase of0°,90°,180°and270°. the bandwidthis increased by using the structure of the ridge-type ground plane and the inversecapacitive probe feed structure. After simulation, most of the indicators meet therequirements, except the unsatisfactory pattern of the antenna with the structure ofridge-type ground plane.Combination of the antenna, a wideband feed network is designed to achieve thefunction of the phase shift of0°,90°,180°and270°. The feed network is formedwith the Wilkinson power divider and a modified Schiffman wideband phase shifter.By the simulation, the feeding network achieved the function of phase shifting andequal-power distributing.The software Ansoft Designer is used to combine the low-noise amplifier, thewideband antenna and the feeding network together to simulate the S-parameters. It isfound that the combining results perform great as well, and the designing is proved tobe valid. |
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