High-gainwaveguide-fed circularly polarized Spidron fractal aperture antenna

A high-gain rectangular waveguide-fed aperture antenna that uses a Spidron fractal structure to produce circular polarization is proposed. The antenna consists of a Spidron fractal aperture etched onto the ground plane of a dielectric substrate that is directly excited by a WR (Waveguide Rectangular)-90 waveguide-to-coax adapter. A superstrate was implemented at an appropriate distance above the antenna to enhance the broadside gain significantly. An antenna prototype was fabricated and tested to validate the design. The measured impedance bandwidth for |S ₁₁ | ≤ - 10 dB is 9.89-11.58 GHz (15.74%). The corresponding measured 3 dB axial ratio (AR) bandwidth is 10.68-11.00 GHz (2.95%), and within the measured 3 dB AR bandwidth, a maximum realized gain of 9.59 dBic is achieved. The radiation patterns of the proposed antenna are presented and discussed.