Fractal unit cells of increased phasing range and low slopes for single-layer microstrip reflectarrays

This study reports investigations into phase characteristics of a unit cell of a single-layer microstrip reflectarray exploiting fractal geometries. The aim is to have the phase range larger than 360° accompanied by a smaller slope of the reflected wave phase as a function of the elements° size. These are required to achieve a wide operational bandwidth and a smaller sensitivity to manufacturing errors. To achieve this goal, multi-resonance fractal elements are investigated. It is shown that sliced patches of square and circular shapes as well as multiple rings printed on a thick substrate can offer slower phase slopes while maintaining phase ranges exceeding 360°. The achieved ranges and slopes of these elements are comparable with those of double-stacked patches printed on the equivalent low permittivity dielectric substrate. Choosing suitable dimensions and scaling factors of these elements, the phase characteristic can be made approximately a linear function of their size.