Study On Planar Circularly Polarized Complementary Dipole Antenna

Circularly polarized(CP)antennas have got widely applications in many fields,such as radio frequency identification systems,satellite communication systems and mobile communication systems,because of its superior advantages of high receiving efficiency and multi-path interference suppression ability to linearly polarized antenna.In general,most planar small-element CP antennas have broadside radiation patterns or end-fire beam in perpendicular with the plane of the antenna.If an end-fire CP beam in parallel with the plane of the antenna is desired,additional orthogonal elements will be introduced and they may lead to non-planar configurations.Therefore,it is challenging to design a planar CP wideband antenna with an end-fire beam in parallel with its plane while maintaining a simple,planar structure and a relatively small size as well.To solve these problems,a series of design approach of an annular planar CP antenna are developed and proposed in this thesis.The proposed approaches can be employed to realize wideband planar endifre CP antennas having dual-resonant characteristics in both impedance and axial ratio frequency responses,while maintaining the antenna's inherent endfire CP properties.The main contents of this thesis are organized as follows:1.In this thesis,the principle and performance of the narrow-band planar circular-polarization antenna are analyzed at first.The simulation and experimental results show that the antenna can achieve the circular polarization performance,but the impedance bandwidth is only 1.90%,can't meet the actual needs.2.The concept of multimode radiation is introduced into this thesis.A pair of rectangular stubs is unilaterally loaded along the electric dipole of narrow-band planar end-fire CP antenna so that the second odd-order dipole mode is excited and moved downwards the fundamental one.The impedance bandwidth and the axial ratio bandwidth of the antenna are greatly increased.Both the impedance and the axis ratio frequency response curves of the antenna exhibit dual-resonant characteristics.However,the simulation and the measured results show that the endfire gain of the antenna are degraded seriously due to a deviated main beam.3.Then,the structure of the antenna is further improved with the original rectangle structure replaced by a concentric circular arc structure.The initial unilateral loading tuning stubs are also changed to bilateral ones.In order to carry out experimental research on the antenna,HFSS software is used to optimize the performance of the antenna.Prototypes are fabricated and measured.The experimental results show that the antenna has an impedance bandwidth(| S11 | <-10dB)from 2.29 GHz to 2.94 GHz with 24.8% available bandwidth which is about 5 times to 5.3% of the reference one under single-mode,about 10 times to 1.9% of rectangular single-mode planar circularly polarized antenna.The axial ratio frequency response in the endfire direction exhibits a dual-resonant characteristic,too,which resulted in an bandwidth of 3dB axial ratio of 18.8%.The developed antennas promising for replacing the bulky external antennas in wireless router.