Square Ring Element Reflectarrays With Improved Radiation Characteristics by Reducing Reflection Phase Sensitivity

A reflectarray with square ring (SR) elements that are designed to reduce the reflection phase sensitivity on a thin substrate is proposed. Generally, the SR element is designed with a fixed ring width, or a fixed ratio between the ring width and the outer length of the ring. However, it is difficult to obtain both a reflection phase range close to 360° and sufficiently low phase sensitivity simultaneously with the conventional methods. Thus, a modified design method to reduce the phase sensitivity without sacrificing the phase range by introducing two procedures (changing the outer and inner lengths of the ring in opposite directions, and changing the inner length while fixing the outer length) is proposed to design a reflectarray on a 0.039λ0 thick substrate at 15 GHz. The radiation characteristics of the reflectarray designed with the proposed method are compared to those of the conventionally designed SR element reflectarray, and gain enhancement of 2.2 dB is achieved at 15 GHz.