On the Design of Circular Fractal Antenna with U-Shape Slot in CPW-Feed

Raj Kumar

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DOI: 10.4236/wet.2010.12012                

Abstract

A new ultawideband circular fractal antenna with notched-band characteristics is presented. A notched-band characteristic is achieved by employing a U-shape slot in 50 Ω feed lines. The ultra-wideband impedance matching and compact size have been obtained by using CPW-feed technique and the fractal concept. The measured result of proposed fractal antenna exhibits the ultra wideband characteristics from 3.0 to 18.0 GHz at VSWR 2:1 except notched-band frequency. The proposed antenna has been analyzed theoretically and experimentally with respect to design parameters. The measured radiation pattern of fractal antenna is nearly omnidirectional in azimuth plane throughout the operating frequency. This antenna is useful for UBW communication system.

Keywords

Monopole Antenna, Wideband Antenna, Resonant Frequency, Fractal Antennas, Multib, Antenna

1. Introduction

Ultra-wideband (UWB: 3.1-10.6 GHz) communication system has become more and more popular because of its advantages such as small size, high transmission rate, and low power consumption comparing with current wireless communication system [1]. Because of these advantages of an UWB system, significant research in the UWB antennas has been aroused in academic and industrial fields recently. However, over this allocated band, there are some existing narrow band services, such as IEEE 802.16 WiMAX system operating at GHz, and C-band satellite communication systems, which may cause electromagnetic interference to the UWB system. Thus, the UWB antenna with notched-band performance is required. The several UWB antennas with the notched frequency function have been reported [2-4], such as, attaching U-shaped slot, inverted U-slot, arc-shaped slot, C shaped slot, or small strip bar to the antenna. The UWB fractal antennas with notch have been reported for UWB applications [5-8]. In [5], Crown - Sierpinski microstrip antenna is proposed to reduce the size of a Crown square fractal. The frequency notched ultra-wideband microstrip slot antenna with a fractal tuning stub is proposed to achieve frequency notched function [6-7]. Raj Kumar et al. [8-9] have proposed a new UWB fractal antenna by adopting the fractal concept on the CPW-fed circular UWB antenna. This work proposed the UWB fractal antenna band-notched characteristics with detail study.

In this paper, a new circular fractal antenna with band-notched is proposed for the UWB system applications. The notched band is easy to tune by changing the length and width of the slot. The antenna has advantages of compact size, low manufacturing cost, easy fabrication, low profile, and very small ground plane suitable for integration with compact UWB systems. The performance of the proposed antenna is characterized in term of impedance bandwidth, band-notched and radiation pattern.

2. Antenna Geometry and U-Shape Slot

The iteration wise fractal antenna was constructed from simple conventional monopole antenna as shown in Figure 1. The solid circular monopole antenna has been designed on FR4 substrate ε_r = 4.3, h = 1.53 mm, with radius 9.1 mm. This is called the initiator or zeroth iteration shown in Figure 1(a). The first iteration of fractal antenna has been constructed by inscribing the square patch of dimension 12.8 × 12.8 mm inside the circle and subtracted it from circle. This is called 1^st iterative inscribed square circular fractal antenna as shown in Figure 1(b). The 2^nd iteration has been achieved by making the circle of diameter 12.8 mm and an inscribed square of dimension 9.05 × 9.05 mm has been subtracted from this inner one circle as shown in Figure 1(c). The 3^rd iteration is constructed by making the metallic circle of 9.05 mm diameter inside the square touching the metallic part of its and subtracting an inscribed square of dimension 6.4 × 6.4 mm as shown in Figure 1(d). In the fourth iteration, a circle of diameter 6.4 mm is made and an inscribed square of dimension 4.525 mm × 4.525 mm is subtracted as shown in Figure 1(e). This process can be repeated up to infinite iteration. Practically infinite iterative structure is not possible because of fabrication constraints. The fourth iterative fractal antenna has been finalized to design on the same substrate dielectric constant and thickness as conventional microstrip monopole antenna as shown in Figure 1. This antenna has been fed with the coplanar feed. The CPW-Fed and radiating elements both are printed on the top side of a low-cost FR-4 substrate with dielectric constant ε_r = 4.3, h = 1.53 mm and loss tangent tan δ = 0.02.

Figure 1 shows the geometry of the proposed fractal antenna. It is composed of inscribed square circular fractal radiating elements, fed by a U-shape slotted CPW-feed with a very small ground plane. There is no ground plane at the bottom of the substrate. It is known that CPW-feed is advantageous for less dispersion at higher frequency, broader matching, easy fabrication and integration with MIC/MMIC. The CPW-fed antenna not

Conflicts of Interest

The authors declare no conflicts of interest.

References

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