Fractal Reflectarray Antennas: State of Art and New Opportunities

Fractal geometries are appealing in all applications where miniaturization capabilities are required, ranging from antennas to frequency selective surfaces (FSS) design. Recently, some fractal patches configurations, giving low losses, reduced size, and quite good phase ranges, have been proposed for the design of reflectarray unit cells. This paper reviews existing fractal-based reflectarrays, highlighting their benefits and limitations. Furthermore, a comprehensive analysis of an innovative reflectarray unit cell, using a fractal-shaped fixed-size patch, is presented. The miniaturization capabilities of the Minkowski fractal shape are fully exploited to obtain a compact cell offering quite good phase agility, by leaving unchanged the patch size and acting only on the fractal scaling factor. Experimental validations are fully discussed on a realized 10 GHz 0.3λ×0.3λ cell. This is subsequently adopted to synthesize various reflectarray prototypes offering single or multiple-beam capabilities over a quite large angular region (up to 50 degrees). Finally, experimental validations on a realized 15×15 elements prototype are presented to demonstrate the wide angle beam-pointing capabilities as well as a quite large bandwidth of about 6%