# High-Gain Multi-Band Koch Fractal FSS Antenna for Sub-6 GHz Applications
###### Abstract  
This study introduces a novel antenna based on the binary operation of a modified circular patch in conjunction with the Koch fractal. The antenna is intended for applications in the sub-6 GHz band, partial C-band, and X-band. The low-cost antenna is fabricated on a 1.6-mm-thick FR-4 substrate. A frequency-selective surface (FSS) is used to overcome the decreased values of the gain and bandwidth due to the fractal operations. The introduced split ring resonator (SRR) and the antenna substrate dimension reduction reduce the bandwidth and antenna gain. The air gap between the FSS and the antenna not only enhances the antenna gain but also controls the frequency tuning at the design frequency. The antenna size is miniaturized to 36.67%. A monopole antenna ground loaded with an SRR results in improved closest tuning (3.44 GHz) near the design frequency. The antenna achieves a peak gain of 9.37 dB in this band. The FSS-based antenna results in a 4.65 dBi improvement in the gain value with the FSS. The measured and simulated plots exhibit an excellent match with each other in all three frequency bands at 2.96-4.72 GHz. These bands cover Wi-MAX (3.5 GHz), sub-6 GHz nr77 (3300-3800 MHz), nr8 (3300-4200 MHz), and approximately n79 (4400-4990 MHz), in addition to C-band applications. Footnote †: journal: _Sci_  
in the papers by [PERSON] et al. and [PERSON] et al. [21; 28]. References [21; 28] address the growing need for numerous frequency band applications, showcasing the promise of fractal architectures. Furthermore, the research conducted by [PERSON] and [PERSON] offers a thorough examination of hybrid fractal antennas, including valuable perspectives on the antennas' performance parameters and applications, as well as various fractal antenna configurations [29]. The literature survey shows a growing interest in miniaturized fractal antennas for wireless applications. Researchers are exploring different fractal geometries, feeding techniques, and structures to improve the antenna performance while reducing the size. Fractal antennas have unique properties like self-similarity and space filling, making them promising for future wireless communication systems. Fractal antennas offer a versatile platform for the design of miniaturized antennas with enhanced performance across various frequency bands. [PERSON] et al. propose a multi-band high-gain slotted fractal antenna with circular and rectangular fractal structures for X-band and Ku-band applications, highlighting the potential of integrating different fractal shapes for successful multi-band applications [30]. [PERSON] introduces a CPW-fed hexagonal ring fractal antenna with a labyrinth resonator, demonstrating its use for omnidirectional wireless applications [31]. [PERSON] et al. explore the use of Koch, Sierpinski, and Minkowski shapes for ultra-wide-band metamaterial microstrip array antennas due to their self-similarity features [32]. [PERSON] et al. developed an arrow cross-shaped slotted fractal antenna with an enhanced bandwidth for Wi-Fi, WiMAX, and WLAN applications, catering to the growing demand for high-speed wireless communication systems [33]. Meanwhile, [PERSON] and [PERSON] optimized a Vicsek snowflake-box fractal microstrip patch antenna using a defective ground structure, demonstrating the effectiveness of fractal unit cells for miniaturization and improved bandwidths [34]. [PERSON] and [PERSON] suggest a Sierpinski carpet fractal monopole antenna for ultra-wide-band applications. The proposed fractal antenna is intended to achieve multiple bandwidth applications [35]. The literature shows various applications and advantages of using different fractal geometries in antenna design, including multi-band operation, enhanced bandwidths, and miniaturization. However, challenges remain, especially for 5G sub-6 GHz applications. [PERSON] et al. presented an outer appended tri-arm rectangular arm circular antenna with an SRR triplet, improving the gain (7.16 dBi) and bandwidth without an FSS [36]. [PERSON] et al.