IJRIT International Journal of Research in Information Technology, Volume 2, Issue 3, March 2014, Pg: 194201

International Journal of Research in Information Technology (IJRIT) www.ijrit.com

ISSN 2001-5569

Design of Fractal Patch Antenna for Multiband Applications Jeena Sara Thomas1, Jincy Rachel Thomas2, T. Mary Neebha3 and M. Nesasudha4 1

2

3

4

PG Scholar, Department of Electronics and Communication Engineering, Karunya University Coimbatore, Tamil Nadu, India [email protected]

PG Scholar, Department of Electronics and Communication Engineering, Karunya University Coimbatore, Tamil Nadu, India [email protected]

Assistant Professor, Department of Electronics and Communication Engineering, Karunya University Coimbatore, Tamil Nadu, India [email protected]

Associate Professor, Department of Electronics and Communication Engineering, Karunya University Coimbatore, Tamil Nadu, India [email protected]

Abstract The design and analysis of E-shaped fractal patch antenna is proposed for multiband applications. The micro strip antenna has some disadvantages such as low gain, low efficiency, high loss and narrow bandwidth. Some efforts to overcome these disadvantages have been investigated by using fractals. The performance of the fractal patch antenna is compared and the best antenna is selected based on the number of iterations performed and antenna parameters like VSWR and return loss (S11).

Keywords: Fractal Patch antennas, FEKO, VSWR , Return loss.

1. Introduction A micro strip or patch antenna is a low profile antenna that has a number of advantages over other antennas. They are lighter in weight, low volume, low cost, low profile, smaller in dimension and ease of fabrication and conformity. Moreover, the patch antennas can provide dual and circular polarizations and dual-frequency operation. A micro strip patch antenna (MPA) consists of a conducting patch of any planar or non-planar geometry on one side of a dielectric substrate with a ground plane on other side. These antennas are well known for their performance and their robust design, fabrication and their extent usage. Micro strip antennas have several advantages over conventional microwave antenna and therefore are widely used in many practical applications. MPAs in its simplest configuration are shown in Fig1. It consists of a radiating patch on one side of dielectric substrate which has a ground plane on other side. These antennas are characterized by a larger number of physical parameters than are conventional microwave antennas. They can be designed to have many geometrical shapes and dimensions. Micro strip antennas are spreading widely in all the fields and areas and now they are booming in the commercial aspects due to their low cost of the substrate material and the fabrication. Their applications are Jeena Sara Thomas,

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IJRIT International Journal of Research in Information Technology, Volume 2, Issue 3, March 2014, Pg: 194201

in various fields such as in medical applications, satellite and mobile communication application, Global Positioning System applications, Radio Frequency Identification (RFID), Radar Application and even in the military systems. [1], [2] and [3] describes various properties, applications and characteristics of the basic microstrip patch antenna. [4] displays a circularly polarized patch antenna. A normal fractal antenna and an E- shaped fractal antenna are shown in [5], [6] and [7]. A high gain microstrip patch antenna is designed in [8]. An I-shaped fractal and an E-shaped fractal are displayed in [9] and [10]. [11] and [12] display a U-slotted microstrip patch antenna. [13] shows a wideband microstrip patch antenna. Bandwidth enhancement of patch antennas is discussed in [14]. [15] shows the design of an L-shaped fractal antenna.

Fig 1 Micro strip Antenna Configuration

1.1 Fractal Patch Antennas The word “Fractal” is outcome of Latin word “fractus” which means linguistically “broken” or “fractured”. Benoit Mandelbrot, a French mathematician, introduced the term about 20 years ago in his book “The fractal geometry of Nature”. The term fractal was coined by Mandelbrot in 1975, but many types of fractal shapes have been proposed long before. There has been an ever growing demand, in both the military as well as the commercial sectors, for antenna design that possesses the following highly desirable attributes: i) Compact size ii) Low profile iii) Conformal iv) Multiband or broadband There are a variety of approaches that have been developed over the years, which can be utilized to achieve one or more of these design objectives. The use of fractal geometry is a solution to the design of multiband antennas. The term fractal, which means broken or irregular fragments, was originally used to describe a family of complex shapes that possess an inherent self similarity in their geometrical structure. What this means, is that as the structure is zoomed in upon, the structure repeats itself. The self-similarity of certain fractal structures results in a multiband behavior. Also, in the case of fractal patch antennas, by increasing the number of iterations, the number of operating bands are also increased. It is evident that the reduction in patch area decreases with higher iterations. This is shown in Eg.(1). Patch area = (Length)2 - area of slits or/and grooves

(1)

1.2 Software Requirement The software used for the simulation of the fractal patch antenna is FEKO. FEKO is a computational electromagnetics software product developed by EM Software & Systems - S.A. (Pty) Ltd. The name is derived from the German acronym "FEldberechnung für Körper mit beliebiger Oberfläche", which can be translated as "Field Calculations for Bodies with Arbitrary Surface". The software is based on the Method of Moments (MoM) integral formulation of Maxwell's equations. It enables users to solve a wide range of electromagnetic problems. The multiple solution techniques available within FEKO make it applicable to a wide range of problems. Typical applications include: •

Antennas: analysis of horns, microstrip patches, wire antennas, reflector antennas, conformal antennas, broadband antennas, arrays.

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• • •

Antenna placement: analysis of antenna radiation patterns, radiation hazard zones, etc. with an antenna placed on a large structure, e.g. ship, aircraft, armoured car. RF components: analysis of waveguide structures, e.g. filter, slotted antennas, directional couplers. 3D EM circuits: analysis of microstrip filters, couplers, inductors, etc.

2. Methodology and Design The new E-shape fractal geometry is designed in an iterative fashion, leading to self-similar structures. This iterative generating procedure can be best conveyed pictorially, as shown in Fig2. The original E-shape fractal starts out with two cut solid rectangles in one of the main rectangle lengths, as illustrated as a first iteration. This is the simplest E-shape fractal geometry. Higher iterations of the E-shape fractal are formed by subtracting smaller and smaller rectangles to the structure. This fractal function in a particular iteration is clarified by Eq.(2), nk = LBk / ( LSk – LBk )

, k = 1,2,……..,N

(2)

where, k is the number of iteration, LBk is the width of subtracted rectangle, and LSk is the width of main rectangle. Also in each iteration, 3k new branches are generated.With the increase in iterations, the surface of the radiating patch reduces.

Fig 2 Iterations of E-Shaped Fractal

The antenna is constructed of a single patch on top and is supported by FR4 substrate with relative dielectric constant of 4.4, thickness of h = 1mm, and tanδ = 0.02. In order to investigate the effect of the different iterations of E-shape fractal on the antenna performance, three iterations of E-shape fractal as shown in Fig 2.1 are chosen as follows: first iteration with n1 = LB1 / LS1 consist of three branches (1EFPA); second iteration with n1 = LB1 / LS1 and n2 = 2n1 consist of nine branches (2EFPA); third iteration with n1 = LB1 / LS1, n2 = 2n1 and n3 = n1 and consists of 27 branches (3EFPA). The values from Fig 2.1 is given as, LS1 = 130mm, LB1 = 50mm, LS2 = LB1 =50mm and LB2 = LB1 / 2 = 25mm.

3. Results and Discussions First, an E-Shaped Fractal Patch Antenna (FPA) is designed with three iterations. The antenna has specifications – Length of patch = 130mm Width of patch = 150mm Height of substrate = 1mm Length of substrate = 230mm Width of substrate = 250mm εr = 4.4 Frequency = 940MHz Jeena Sara Thomas,

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The Cadfeko model for E-Shaped FPA after the first iteration is given in Fig3. Return Loss represents how much power is reflected from the antenna. Lower the value of return loss, better the impedance match. VSWR is Voltage Standing Wave Ratio. Smaller the value of VSWR, more power will be delivered to the antenna.

Fig 3 E-Shaped FPA -- first iteration, Cadfeko model Graphs for Return loss and VSWR were plotted for the antenna after the first iteration in Fig 4(a) and (b) respectively. VSWR was found to be greater than 1.5 and return loss of -9.8dB with 2 frequency bands.

(a)

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(b) Fig 4 E-Shaped FPA – first iteration (a) Return Loss (b) VSWR The Cadfeko model for E-Shaped FPA after the second iteration is given in Fig 5.

Fig 5 E-Shaped FPA -- second iteration, Cadfeko model

Graphs for Return loss and VSWR were plotted for the antenna after the second iteration in Fig 6 (a) and (b) respectively. VSWR was found to be between 1 and 2 and return loss of -14.9dB with 4 frequency bands.

(a) Jeena Sara Thomas,

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(b) Fig 6 E-Shaped FPA – second iteration (a) Return Loss (b) VSWR The Cadfeko model for E-Shaped FPA after the third iteration is given in Fig7.

Fig 7 E-Shaped FPA -- third iteration, Cadfeko model Graphs for Return loss and VSWR were plotted for the antenna after the third iteration in Fig 8 (a) and (b) respectively. VSWR was found to be between 1 and 2 and return loss of -16dB with 5 frequency bands.

(a)

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(b) Fig 8 E-Shaped FPA – third iteration (a) Return Loss (b) VSWR The comparison table can be shown in Table 1 which compares E-shaped Fractal Patch Antenna based on number of iterations, antenna parameters like return loss and VSWR and the total number of frequency bands. Table 1 ITERATION

RETURN LOSS (dB)

1 2 3

-9.8 -14.9 -16

NUMBER OF FREQUENCY BANDS 2 4 5

VSWR

> 1.5 b/w 1 and 2 b/w 1 and 2

4. Conclusions Therefore, in the case of E-Shaped Fractal Patch Antenna, the best performance in the case of return loss and multiband applications or maximum number of frequency bands was found to be the antenna with the third iteration. The maximum return loss was -16dB and the number of frequency bands increased from 2 to 4 and finally to 5 in the final iteration.

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