Research On Circularly Polarized Antenna Array With Wide-angle Scanning

Compared with linearly polarized radiation waves,circularly polarized radiation waves have many advantages such as anti-multipath interference,anti-Faraday rotation effect,and suppression of polarization mismatch.Circularly polarized phased arrays use electronic scanning to flexibly change the beam pointing,and are compatible with a very wide range of application scenarios.The scanning angle is an important parameter of phased arrays.However,to realize a good scanning performance with good circular polarization is a difficult task.Generally,the impedance bandwidth and beam width should be taken into account when designing a circular polarization phased array antenna,which can realize beam scanning performance.Furthermore,how to widen its scanning angle is also a research hotspot in recent years.Starting from designing a circularly polarized antenna unit,this thesis has studied a series of researches on widening both the half-power beamwidth and 3d B axial ratio beamwidth,and then designs a large-angle scanning circularly polarized phased array.The content of this thesis is as follows:(1)A dual circularly polarized antenna unit using a crossed Y-shaped feed network is designed,which exploits two linearly polarized radiation patterns with high polarization purity to synthesize a circularly polarized radiation pattern with a wide beamwidth of 3d B axial ratio.The antenna unit achieves a 3d B axial ratio beamwidth of 202° in the operating frequency band,and uses the feed network to realize the switching between the left and right hand circular polarization radiation modes.Using this unit to form a phased array realizes a two-dimensional scanning of ±65°with a lower axis ratio when scanning at a large angle.(2)A circularly polarized antenna unit with wide beam performance is designed by combining the circularly polarized microstrip patch antenna with the quadrifilar helical antenna.Two different feeding methods are used to feed the antenna unit,and a four-fed wide-beam antenna unit with a wide impedance bandwidth and a dual-feed wide-beam antenna unit with simple structure are respectively obtained.The half-power beamwidth and 3d B axial ratio beamwidth of the four-feed antenna unit can reach 180°while the halfpower beamwidth and the 3d B axial ratio beamwidth of the double-feed antenna unit can reach 110°and 160°respectively.A phased array consists of several proposed double-fed antenna elements has been designed,simulated and measured.The results of simulation and measurement has shown that the phased array can realize a circularly polarized beam scanning range of ±60°.