Analysis and Elimination of Unwanted Resonances for Wideband Reflectarray Antenna Design at Sub-Millimeter Waves

Abstract

In this study, unwanted additional resonances are analyzed and a method is developed to eliminate them for wideband offset dual reflectarray antenna at sub-millimeter waves. In the terahertz range, the additional resonances can usually be generated within the target bandwidth, depending on the angle of incidence, which cannot be predicted by the normal incidence characteristics of a reflectarray. To evaluate the effects of the additional resonances, the phase error and element patterns of the reflectarray are checked by using the equivalence principle and full-wave simulation. It is found that the additional resonances result in the performance deterioration of the reflectarray antenna due to undesirable phase variation and element pattern changes. Therefore, a sub-wavelength unit-cell is employed to eliminate the additional resonances so that the phase error and element pattern distortion of the reflectarray elements can be avoided in the target bandwidth even for a large angle of incidence. A reflectarray with the sub-wavelength unit-cell is then designed, fabricated, and measured to show the improved gain and bandwidth performances of the reflectarray demonstrating the validity of the proposed analysis.