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Proc. of Int. Conf. on Control, Communication and Power Engineering 2010

CPW-Fed UWB Slot Antenna with Reconfigurable Rejection Bands J. William and R. Nakkeeran Pondicherry Engineering College, Department of ECE, Pondicherry, India Email: wilsus@rediffmail.com, rnakeeran@pec.edu GHz. In this paper a new method is proposed to obtain the reconfiguration in the frequency notch bands for WiMax, WLAN 802.11a and HYPERLAN/2 systems by making ‘on’ and ‘off’ the diodes placed over the ground slot. This intern changes the tuning length of the slot, which is responsible for the desired frequency notch band. The simulation software used for this analysis is IE3D [16].

Abstract— A coplanar waveguide (CPW) fed Ultra Wideband (UWB) slot antenna with reconfigurable rejection bands is presented in this paper. The antenna has a rectangular slot with triangular structure that acts as a tuning stub with CPW feed. The notch band is achieved by inserting a rectangular slot in the ground plane with a length of λ/2. The rejection of the bands 3.1 GHz – 3.9 GHz, 4 GHz–5.3 GHz and 4.1 GHz–5.9 GHz are achieved by switching the diodes placed over the ground slot. The characteristics of the designed structure are investigated by using MoM based solver, IE3D. Detailed simulation results of the proposed antenna are presented in this paper. The simple configuration and low profile of the proposed antenna leads to easy fabrication that may be built in any wireless UWB device applications where reconfigurable rejection bands are required. Index Terms— coplanar waveguide, reconfiguration, slot antenna, UWB

notch

band,

I. INTRODUCTION The release of UWB by FCC in the year 2002, it gains a lot attention by the researchers due to its inherent properties of low power consumption, high data rate and simple configuration [1]. Designing an antenna to operate in the UWB band is quiet challenging one because it has to satisfy the requirements such as ultra wide impedance bandwidth, omni directional radiation pattern, constant gain, high radiation efficiency, constant group delay, low profile easy manufacturing etc [2]. Interestingly the planar slot antennas with CPW fed posses the above said features [3]. One of the major problems associated with UWB system is the interference from the other communication systems such as WiMax (3.3 – 3.7 GHz), IEEE 802.11a (5.15 - 5.35 GHz and 5.725 – 5.825 GHz) and HYPERLAN/2 (5.15 - 5.35 GHz and 5.47 – 5.825 GHz). To mitigate this effect many antenna designs have been proposed in the literature [4-8]. The rejection of interference is done either by inserting half wavelength slits, stripes in the tuning stub [9], or inserting stub in the aperture connected to the ground planes [10], or inserting square ring resonator in the tuning stub [11], or inserting ‘L’ branches in the ground plane [12], or with complementary split ring resonator [13], or inserting strip in the slot [14]. All the above methods are used for rejecting a fixed band of frequencies. To effectively utilize the UWB spectrum and to improve the performance of the UWB system, it is desirable to design the UWB antenna with reconfigurable notch band. It will help to minimize the interference between the systems. In [15] RF MEMS switches are used for the reconfigurabilty of rejection band between the frequencies 5 GHz to 6

Figure 1. Geometry of the proposed reconfigurable slot antenna.

II. ANTENNA GEOMETRY The structure of the antenna is shown in Fig 1. The antenna consists of rectangular slot with width ‘W1’ and length ‘L1’. The tuning stub comprises a triangular patch with height ‘H’. The distance between the tuning stub and feed line is ‘d’, ‘W’ and ‘L’ are the overall width and length of the antenna respectively. In this study, dielectric substrate FR4 with thickness of 1.6 mm with relative permittivity of 4.4 is chosen. The CPW feed is designed for 50 Ω characteristic impedance with fixed 2.4 mm feed line width and 0.5 mm ground gap. The effective length of the rectangular slot introduced in the ground plane is approximately 0.5 λeff at the desired notch center frequency. The effective wavelength of the slot is,

λ

154 © 2009 ACEEE

=

c

, ε

ε +1

≈ r

(1) 2 ε n eff where ‘fn’ is the centre frequency of the notch band. The placement of the diodes is desired by the effective wavelength for the different notch frequencies. eff

f

eff


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