Paneled center-fed reflectarray for bandwidth enhancement

Abstract

Regardless of the bandwidth of reflectarray (RA) elements, the RA bandwidth is narrower for many possible reasons. For a RA with small f/D, the ray path length varies as we move away from the center, which is compensated by the elements that are designed at the center frequency. However, as the frequency changes, the path length phase errors grows, as we move away from the center, at a more rapid rate than the element frequency phase variation. Therefore, the phase errors introduced as the frequency changes are so significant deteriorating the aperture phase distribution that causes very low aperture efficiency and in return limiting the gain bandwidth. In order to reduce the path length as we move away from the center, the RA is divided into annular planar panels centered with a small square sub-RA. The annular panels are displaced towards the feed position reducing the path length within each panel. A circularly polarized refectarray designed at 30 GHz with wideband cross Bowtie elements is used as an example. The RA size is 25.25λ × 25.25λ, which is corresponding to 101 × 101 elements. The performance of the antenna is compared with the original RA of the same diameter. The proposed method exhibits the maximum simulated aperture efficiency of 48 %, a 1-dB gain bandwidth of 16.9 %, and the 0.5-dB axial ratio bandwidth of 25.6 %.