Research On Broadband Circularly Polarized Relfectarrays

Microstrip reflectarray antenna combines the advantages of parabolic reflectors andmicrostrip arrays, with small size，light weight, and simple feed form, has a obvious advantage inconformal, mobile, hidden application and so on. It has become one of hot research direction inthe antenna field. In many applications, the circular polarization (CP) has been chosen becauseof its robustness against environmental interference and polarization matching is good. Therefore,a variety of different CP reflectarrays (CPRA) has a broad application prospects in satellitecommunications, space exploration, radar technology, radio astronomy and televisionbroadcasting and other fields.This article focus on the problems of narrowband cross-polarization suppression. First,according to the difference of the feed polarization and phase compensation, we give threemethods to realize CPRA, which is linearly polarized to circularly polarized transformation(LP-CP) reflectarray, variable-size circularly polarized reflectarray and CPRA using angularrotation technique. Then, we study the bandwidth limiting factor and use different broadbandtechnologies and to achieve CPRA. The measured results show that the obtained antenna1-dBgain bandwidth and3-dB axial-ratio bandwidth of the linearly polarized to right-hand circularlypolarized transformation (LP-RHCP) reflectarray can reach as large as24%and35%,respectively, the best aperture efficiency is48.7%. We focus on the CPRA using angular rotationtechnique: the measured results show that the obtained antenna1-dB gain bandwidth and3-dBaxial-ratio bandwidth of the reflectarray with double-ring-shaped element can reach as large as31%and43%, respectively, the best aperture efficiency is58.5%, and the reflectarray withI-ring-shaped element can reach32%1-dB gain bandwidth and41%3-dB axial-ratio bandwidth,the best aperture efficiency is up to59.4%The main work and innovations of this paper are as follows:(1) In order to solve the problem of large simulation and difficult to get accurate size ofelement because of correlation phase compensation and realization of CP, we let the realizationof CP into phase compensation, greatly simplifies the designing of the polarized transformationreflectarray, and derive the ideal element shall meet the conditions of symmetry and independent;we study the independence of the four most common reflectarray elements:square patch, squarering, cross ring and cross oscillator, we find that the cross oscillator element is the most idealLP-RHCP reflectarray element, and we use the double-stack structure to achieve a broadbandcircularly polarized.(2) From the definition axis of CP antenna, we get the element amplitude determinationcondition and element judgment conditions, give a clear determination condition between two relationship and usage scenarios, from the test performance reflectarray antenna prove that theelement determines the accuracy and practicality.(3) Based on the idea of single-layer multiple-resonance structure for linearly polarizedreflectarray, two broadband circularly polarized reflectarray elements are presented. One isdouble-ring shaped element, and the other is I-ring shaped element. Then, by using angularrotation technique, reflectarrays with these two elements are designed and measured. We discussthe improvement of the gain characteristics of the low frequency, It is shown that changing thefeed location leads to a considerable shift in operating frequency window of the reflectarray andimprovement of the gain characteristics.