Research On Wideband Two-Dimensional Large-Angle Scanning Array Antenna

Antenna plays a crucial role in modern communication systems with the increasing demands for large user volume,high speed and low latency data transmission.Many types of antennas have been developed for the variety of application demands.Among them,circularly-polarized antennas are more desirable than linearly-polarized cases because they can mitigate the multi-path effect of signal transmission and the Faraday rotation effect when electromagnetic waves transverse through ionosphere.Besides,circularlypolarized antenna can make antenna orientation more flexible.Phased array antenna has gathered much attention because its unique characteristics which not exist in single antenna such as beam fast-steering,large range beam coverage and high gain.In the applications of fast-moving target tracking and satellite communication systems,the demands for array antenna working bandwidth and wide beam coverage are growing and so,it's quite necessary to do research on wideband two-dimensional large-angle scanning array antenna.Traditional methods to obtain wide-angle scanning array antenna are using wide beamwidth element,wide-angle impedance match technology,etc.In practical applications,these methods commonly have technical defects such as narrow bandwidth,scanning dimension and polarization limitations.Conformal array antenna is insusceptible to these limitations but its bulky volume often results in restricted application scenarios.Based on the problems mentioned above,this thesis carries out some research and discussion about the mechanism of grating lobes generation and suppression,a further research about antenna gain enhancement and sidelobe suppression method is developed.First,this thesis introduced the background of phased array antenna and the research status of current technologies about array antenna wideangle scanning and antenna gain enhancement.Second,the theory about phased array antenna's beam steering and grating lobes suppression are discussed,and then a new idea inspired by pattern compensation is proposed to realize wide-angle scanning.Third,based on such idea and combined with requirements of wideband operation and two-dimensional beam scanning,a circularly-polarized element with stable radiation pattern is designed and a novel ripple-shaped array layout is proposed.Simulation verifications of such array layout with 64 and 256 elements are performed and the 64-elements array antenna is fabricated and measured.Measured results show that,in 8?9GHz and beam scanning range of 0°? ±65°,this antenna exhibits minimum gain fluctuation of 1.61 dB,active voltage standing wave ratio basically less than 2.5 and main beam axial ratio less than 2.5dB.This array antenna has a low overall profile and that's a very attractive characteristic.Finally,research about antenna gain enhancement and sidelobe suppression are carried out and a bowl-shaped reflector based on high-impedance surface is proposed.Performance comparison is carried out about a 2×2 array antenna with three kinds of reflectors with the same aperture size: bowlshaped reflector with high-impedance surface,smooth bowl-shaped reflector and planar round reflector.Simulation results show that the reflector with high-impedance surface enhances antenna gain about 1.1?4.2dB than the planar case in frequency band from 7.5GHz to 9.5GHz.And in the midfrequency 8.5GHz,the array antenna's sidelobe level is reduced about 5.1dB.