Low-profile circular-polarized fractal antenna design with reduced orbital angular momentum beam divergence

The authors introduce a novel low-profile circular-polarized three-layer fractal antenna design to reduce beam divergence in orbital angular momentum (OAM) applications at microwave frequencies. The top layer of the proposed design has a printed Koch fractal antenna that is coupled to a rotated rectangular patch antenna in the mid-layer fed through a microstrip line. The bottom layer consists of a metallic ground plane to improve beam collimation. The antenna was developed from a new fractal geometry generated in Scilab (TM). Characteristic mode theory was used in the antenna design to obtain two orthogonal current modes in quadrature that generate circular polarization with OAM fields of order l = -1 at 5.88 GHz. The proposed fractal antenna system has good potential to improve the performance of microwave OAM systems.