| Antenna is one of the most critical components in wireless communication equipment,it is used for transmitting and receiving RF signals and plays an important role in the quality of signals.The designed antenna with excellent performance,reasonable size and acceptable cost are the pursue goal that people have been working hard all the time.As a widely used passive device,broadband circular polarization antenna has many applications in aerospace communication,satellite communication,military industry and other fields.The application of broadband circularly polarized antenna have extremely high performance requirements,including the bandwidth,gain,radiation patterns and so on.As a kind of frequency independent antenna(FIA),the bandwidth of the spiral antenna is closely related to the size,in order to keep wideband characteristic with limited size,two different type wideband antenna are proposed,both of them are broadband,miniaturization and have simple feed structure.The detailed contents and contributions of this paper are as followsFirstly,the research status of spiral antenna and helix antenna is introduced in detail,and the technology of UWB is also introduced,summarized and analyzed.A method to obtain UWB antenna is proposed in this paperSecondly,to realize UWB characteristics,two stacked spirals antenna is proposed in this paper.Two stacked spiral with opposite polarization are connected together by two copper posts to broaden the bandwidth.By extending the current path to achieve broadband characteristics.A RF resistor is loaded at the center of the lower spiral to absorb the reflecting current to achieve wideband characteristics.In this way,the size of planar space and profile of antenna are greatly reduced.In addition to the advantage in size,the tapered microstripline is utilized to feed the spiral antenna.Compared with the traditional feeding structure,the spiral antenna solves the problem of difficult impedance matching and simplifies the antenna feeding.Simulation results show that the stacked spiral antenna greatly extends the impedance bandwidth from 5:1 to 17:1 and the AR bandwidth from 1.5:1 to 4.9:1,the simulated and measured results have a good consistency.Finally,this paper also presents a broadband circularly polarized helix-spiral composite antenna.This paper analyzes the characteristics of helix antenna,including operating mode,radiation characteristics,axial ratio and gain.By reducing the number of helix turns,the conic mode can be suppressed obviously,and the radiation null in broadside is also disappeared.In addition,in order to broadband characteristic,spiral arms of this design is cut to reduce the radius of helix antenna,and thereby moving the operating frequency to higher band,and finally making the lowest operating frequency of spiral antenna and the highest operating frequency overlapped,it makes the composite antenna have wideband characteristics.The planar microstripline and RF resistor are also utilized to feed the proposed composite antenna,for further bandwidth enhancement.The simulation results show that the axial ratio bandwidth of 0.88 to 7.39 GHz(8.39:1)and impedance bandwidth of 0.93 to 9 GHz(9.7:1). |
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