A Novel Modified Hexagonal Shaped Fractal Antenna with Multi Band Notch Characteristics for UWB Applications

Abstract

This document presents the design, simulation and measurement of a new fractal ultra-wideband CPW-fed antenna (UWB). The antenna uses a basic hexagonal shape, in which different modifications are made applying concepts of fractal geometry and Notch filters to obtain the optimal model. The simulation process is detailed until obtaining the ideal structure according to the UWB characteristics. The optimal structure generated presents the Koch fractal in the first iteration, additionally, smaller hexagonal slots are strategically placed to acquire the UWB characteristics. To reject the frequency band considered for IEEE 802.11a and WLAN-HIPERLAN/2 from 5.1 to 5.9GHz, the implementation of a Notch filter in U is made in the patch. The technique used for the design of the grooves of the ground plane allows to improve the reflection in the entire range of 3.1 to 10 GHz, specifically at low frequencies. To improve reflection at high frequencies, hexagonal filters are attached to the upper corners of the patch. The dimensions optimized for this fractal antenna are 25 $\times 25$ mm2 designed in a substrate FR4 with dielectric constant $\varepsilon r = 4.4$, a thickness of h = 1.5 and a tangent of losses of $\delta = 0.02$, obtaining a bandwidth of 2.38 a 9.82Ghz with a VSWR < 2 over the entire frequency range except for the rejected frequencies for WLAN. The compact antenna has a nearly omnidirectional radiation pattern with an adequate impedance and good return loss less than -10dB over the entire UWB range, these features offer several applications within telecommunications.