Analysis of Modified Square Sierpinski Gasket fractal microstrip antenna for Wireless communications

Abstract

In this paper, the slot loaded microstrip antenna has been developed with Sierpinski gasket technique. The proposed Modified Square Sierpinski Gasket (MSSG) fractal antenna involves a square patch utilizing Sierpinski gasket (triangular) structure. Four triangular slots are loaded at each iteration. The structure is then simulated using commercially available Ansoft HFSS simulator. The multi-band operation has been achieved by the proposed antenna at 15.915 GHz, 20.045 GHz, 23.077 GHz, 27.77 GHz frequencies with −20 dB, −25 dB, −22 dB, −28 dB return loss respectively which works well for Ku (12–18 GHz) and K (18–27 GHz) band. The consistent result is obtained after simulation and the validity of fabricated design is checked by the measured result. The designed antenna is an attractive candidate for applications like wireless multi-band communication systems.

Introduction

Microstrip antenna (MSA) is one of the most popular antenna in the wireless communication market [1]. Recently MSAs has got the attention of scientists and researchers due to its attractive features for wireless applications [2]. Some important feature of MSA is low weight, low cost, low profile and conformal. It can easily be integrated with microwave integrated circuits [3]. In order to meet the demand of modern communication systems, the antenna is required to be multiband frequency along with high gain, high bandwidth, good radiation characteristics and compact in size [4]. Multiband antenna can be designed by using various methods such as thick dielectric substrate or slots [5] and notches [6] loaded on a patch or by fractals. When various notches or slots are loaded on the ground plane its known as Defected Ground Structure (DGS) and used for WLAN/WiMAX applications [7]. However, miniaturization of antenna design has always been an issue for wireless communication [8], [9]. Recently fractal techniques have been evolved which uses various fractal geometries to design the radiating element of MSA structure.

The antenna which uses self-similar geometries as radiating structures is known as a fractal antenna. The term ‘Fractal’ is coined by Mandelbrot in 1975[10]. Fractal is defined as a combination of complex self-similar structures that possess an inherent self-similarity in their geometrical shape [11]. The fractal geometries have been introduced to modify the MSA structure by reducing the overall geometrical size & increasing its effective length [12]. Generally, the fractal antenna is a series of combination of slots and notches in the same patch [13]. It is then repeating the predefined structure itself but with reduced dimension in each iteration. Space-filling & self-similarity are two main feature of the fractal antennas [14]. The electrical length of fractal geometries is more than its original shapes while the total surface area of the radiating patch is reduced [15]. The perimeter of the antenna is changed by loading notches and slots. Due to this change multiband and broadband behavior of the antenna is achieved and radiation pattern gets changed [16]. Fractal geometries are uneven shapes which can be separated into sub-parts & every sub-part is a small copy of the overall shape [17]. Various examples of fractal geometries [18] are - Sierpinski gasket (triangle) [19], Sierpinski carpet, Koch curve [20], Minkowski curve, Cohen-Minkowski curve, etc. Some advantages of fractal antennas are miniaturization & space filling, multiband performance, efficiency, and effectiveness, improve gain and improve directivity [21], etc.

The Sierpinski gasket also is known as Sierpinski triangle was named after Polish mathematician who explained its main feature in 1916 [22]. The Multi-resonant frequency behaviors of Sierpinski gasket structure having four iterations are used for Internet of things (IoT) applications [23]. Usually, Sierpinski gasket and Sierpinski carpet exhibit multiple bands operations [23]. The fractal antenna is generally used for wireless communication [24], [25] like satellite and radar applications [26]. The performance of fractal shape monopole antenna is studied and fabricated with metalized foam. Metalized foam is the materials that exhibit low dielectric constant [27]. Similarly, a Sierpinski fractal patch antenna utilizing multiband and miniaturization purpose has been designed and the performance is studied [28].

In this paper, the behavior of modified Sierpinski gasket fractal antenna is discussed and compared by means of experimental and computational results. Modified Square Sierpinski Gasket (MSSG) fractal antenna is analyzed for wireless communications. In MSSG antenna, the self-similarity 45° rotated square Sierpinski gasket geometry exhibits multi-band as well as a wideband application. In Section 2, the designing of the proposed antenna is discussed with theoretical circuit analysis. In Section 3, the concept of MSSG fractal antenna is described. Finally, the measured and simulated results are discussed in Section 4 which shows the multiband behavior of proposed antenna is achieved. The Gain of the proposed antenna is increased by comparing with reference antenna. The difference in Gain (dB) of 2.84 dB, 4.31 dB, 4.76 dB and 5.37 dB is achieved at the resonant frequencies. The parametric analysis of MSSG antenna has been done using HFSS software to optimize the performance at different frequencies.