Circularly polarized hybrid fractal antenna for Ku band application

Abstract

This article presents a hybrid fractal microstrip antenna design, referred to as the Vicsekcross & Koch Curve Fractal Antenna (VKFA). The term “hybrid” reflects the integration of two distinct fractal geometries—Vicsekcross and Koch curves—within the same antenna structure. This combination leverages the unique properties of both geometries: the space-filling characteristic of the Vicsekcross fractal, which enhances the effective electrical length for improved miniaturization, and the self-similarity of the Koch fractal, which optimizes bandwidth and gain. The advantages of the proposed hybrid fractal microstrip antenna are enhanced bandwidth, compact size, and enhanced key parameters like gain and efficiency. Finally, it reduces the fabrication cost. The antenna integrates a 2nd order Vicsekcross fractal geometry along with a 2nd order Koch Curve fractal, optimizing its structure for multiband operation and miniaturization. The proposed VKFA covers an operational frequency range from 16.92 GHz to 18.74 GHz, demonstrating a peak gain of 5.14 dBic at 17.19 GHz, with good gain throughout the band. The current vector distribution plot reveals that the antenna features two L-shaped slots positioned 180° apart at the center of the radiating patch to achieve circularly polarized (CP) radiation. By etching these L-shaped slots into the patch, two orthogonal field components are generated, enabling CP characteristics. This occurs due to the establishment of currents on the radiating patch, which results in the formation of two orthogonal modes with a 90° phase shift, essential for CP radiation. The antenna exhibits right-hand circular polarization (RHCP) with a 3 dB axial ratio bandwidth (ARBW) spanning from 17.12 GHz to 18.04 GHz, making it highly suitable for circular polarization applications. The structure is fabricated on an inexpensive FR4 Epoxy substrate with a dielectric constant (${\epsilon }_r)$ 4.4. The patch antenna achieves compactness, with overall dimensions of 2.18λ₀ × 2.18λ₀ × 0.09λ₀ at a resonance frequency $\left(f_r\right)$ of 17.9 GHz. The Comparative analysis of the measured and simulated results reveals a high level of agreement after the evolution of the antenna’s effectiveness. Due to its compact size, high gain, and broad ARBW, the VKFA can be a suitable candidate for applications in the Ku-band, especially for satellite communications and radar systems.