Design And Implementation Of Broadband Microstrip Reflectarrays

The reflectarray antenna is a new kind of high gain antennas.Compared with traditional phased array antenna,the reflectarray antenna has some advantages such as low profile,low cost and rich functions,which is widely applid in many fields such as high-performance radar,long-distance communication,aerospace measurement and control,as well as deep space exploration.However,the microstrip reflectarray antenna has the inherent narrow band disadvantage,which restricts its development and application areas.This thesis focuses on designing new wideband microstrip reflectarray elements and the corresponding microstrip reflectarray antennas.First,basic working principle of the microstrip reflectarray antenna is introduced,the commonly used methods for expanding bandwidth of the microstrip reflectarray antennas and the methods for analyzing the reflectarry elements are described,and the design flow of broadband microstrip reflectarray antennas is summarized.Then,based on the above analysis,a broadband linearly polarized reflectarray using multi-resonant element is designed.This element has a phase range covering more than 360°,and obtain nearly parallel and highly linear phase shift curves in a relatively wide frequency band.Based on the proposed reflectarray element,by compensating the phase shift of each element in the planar microstrip reflectarray,a broadband reflectarray antenna with 77 elements is designed.The planar microstrip reflectarray is offset-fed by a pyramid horn antenna.According to the design results,the broadband linearly polarized reflectarray antenna prototype is fabricated and measured.The measured results indicate that the reflectarray antenna achieves up to 38.7 % 1-d B gain bandwidth,and its highest radiation efficiency is 49.5 %,which is achieved at the center frequency.Finally,based on the LP-CP method,a broadband LP-to-CP conversion reflectarray element with a single-layer substrate is designed.Based on the proposed reflectarray element,a 109-element broadband CP reflectarray antenna is designed.The reflectarray antenna is center-fed by an antipodal Vivaldi antenna.According to the design results,the broadband CP reflectarray antenna prototype is fabricated and measured.The measured results indicate that the reflectarray antenna achieves 33.2 % 1-d B gain bandwidth and 37 % 3-d B axial ratio bandwidth,and its highest radiation efficiency is up to 66.5 %.