A Compact Monopole CPW-Fed Band Notch Square- ring Antenna for UWB Applications

This paper presents the design of compact CPW-fed band notched UWB square ring antenna. The main objective of this proposed research work is to reduce the size of antenna and avoid interference between UWB and WLAN application at 5.5GHz. The antenna consists of a square-ring metal patch and 50Ω coplanar waveguide fed. The structure of the antenna is miniaturized by optimizing its square ring profile and the required total size to obtain only 35×31 mm dimension. The antenna is then modified to possess band rejection at the wireless local area network (4.8–6.2 GHz) band by adding two slits within the CPW element. The geometry parameters of antenna are investigated and optimized with HFSS. The result show that the proposed antenna achieves an impedance bandwidth of 3.1-10.6GHz with VSWR<2, except in the band of 4.8 – 6.2 GHz. An omnidirectional radiation pattern and stable gain are observed except notched band. KeywordsCoplanar waveguide (CPW), Microstrip antennas, wireless communication, UWB, band notched, HFSS. 1. NTRODUCTION In February 2002, the federal communication (FCC) allocated the 3.1 -10.6 GHz spectrum for unlicensed use of UWB [3]. a considerable amount of researches have been devoted to the development of Ultra Wideband (UWB) antenna [1-2], for its enabling high data transmission rates, low power consumption and simple hardware configuration in communication applications. Since that UWB technology has been rapidly advancing as a promising high data rate wireless communication technology for various applications. Beside the consideration of ultra wideband performance, the design of antennas for the UWB communication also need a bandrejected filter to avoid an interference with existing wireless networks with standards such as IEEE 802.11a in U.S.A (5.15GHz-5.35GHz, 5.725GHz-5.825GHz) and HIPERLAN/2 in Europe (5.15GHz-5.35GHz, 5.47GHz-5.725GHz) [4] so that UWB transmitters can not cause any electromagnetic interference on nearby communication system such as Wireless LAN (WLAN) applications. However, the use of a filter will increase the system complexity. To tackle this problem, many novel antennas [5~14] with band-notched characteristic have been presented. In these designs, the filter can be eliminated and the radio frequency systems will be simplified. Among the newly proposed UWB antenna designs, the printed monopole antenna [6~14] has been received much attention for their wideband matching characteristic, omnidirectional radiation patterns, high radiation efficiency and compact size. These antennas make use of different structures to meet the requirements of return loss and radiation patterns. These structures include two monopoles with a small strip bar [7], half-bowtie shape[8], coplanar waveguide (CPW) resonant cell (CCRC) [9], a new microstrip-fed folded strip monopole antenna with band-notched characteristics [10], a planar half ellipseshaped radiation patch with an ellipse-shaped slot and three steps, and the parasitic strip [11], the main patch by inserting a modified inverted U-slot [12], two L-shaped slots in the radiation element [13]. Some of the important properties of UWB antenna are compact size, omnidirectional radiation pattern, wide impedance bandwidth, low power consumption, ease of manufacture and unipolar configuration. Now a day’s printed monopole antenna with large bandwidth are highly in demand as they have most of the above properties. A conventional Coplanar waveguide (CPW) on a dielectric substrate consists of centre strip conductor with semi-infinite ground planes on either side is used to feed the printed antenna which offers various advantages over Microstrip feed line such as lesser dispersion characteristics at higher frequencies, broader impedance bandwidth, coplanar configuration and it does not require backing ground. The allocated bandwidth of UWB spectrum already occupy the some narrow band services such as wireless local-area network (WLAN) IEEE802.11a and HIPERLAN/2 WLAN operating in the 5–6 GHz band. Some time there is also use of filters to remove this existing band from UWB spectrum, but it makes system complex. This problem is solved by notching the existing frequency band from UWB frequency spectrum so that interference does occur. Thus the UWB antenna with a notched WLAN band from 4.8-6.2 GHz is designed to ———————————————— Mr.Deepak Kumar is currently pursuing masters degree program in electronics and communication engineering at TIT, Bhopal, RGPV, Bhopal , India, PH-919457287363. E-mail: [email protected]. Mr. Tejbir Singh is currently working as Asst. professor at Department of electronics and communication engineering, SITE, SVSU, Meerut, India., PH-917520270827. E-mail: [email protected]. Prof. Vikash Gupta is professor in Department of electronics and communication engineering at TIT, Bhopal , RGPV,, Bhopal India . PH-919424467817.E-mail: [email protected]. Prof. Hema Singh is professor in Department of electronics and communication engineering at TIT, Bhopal , RGPV,, Bhopal India . E-mail: [email protected]. International Journal of Scientific & Engineering Research Volume 3, Issue 7, June-2012 2 ISSN 2229-5518 IJSER © 2012 http://www.ijser.org minimize the interference between UWB system and narrowband system (WLAN). This paper presents a simple and compact CPW-fed UWB printed antenna with single notch of WLAN band. The ground plane at each side is modified for better matching impedance and CPW fed. The single band notched characteristics is achieved by simply etching slot from the ground plane. It can be observed that without slot designed antenna shows the UWB characteristics from 3.1 to 10.6 GHz with VSWR< 2 and after etching slot from the ground plan it has band notched characteristics from 4.8 to 6.2 GHz with VSWR>2. The designed antenna is simulated with HFSS 13 and various antenna parameters have been observed as a result. 2.ANTENNA DESIGN The geometry of the proposed antenna is shown in Fig. 1 with various dimensions. The antenna is mounted on FR-4 printed circuit board substrate (WsubxLsub=35×31) with a dielectric constant of εr=4.4 and thickness of h=1.6mm. The CPW feed line has a single strip with a dimension of Wf x Lf and gap of distance Wc is made for a 50 Ω characteristic impedance. The radiating part of antenna is square ring patch at the middle of substrate with outer length and inner length of L and Ln respectively. (a) (b) Fig. 1: Geometry of the proposed CPW-fed UWB antennas (a) without notch, (b) with single notch