Abstract—This paper presents a planar microstrip-fed tab monopole antenna for ultra wideband wireless communications applications. The impedance bandwidth of the antenna is improved by adding slit in one side of the mono pole, introducing at apered transition between the mono poleand the feedline,and adding two-step stair casenotchin the ground plane. Numerical analysis for the antenna dimensional parameters using Ansoft HFSS is performed and presented. The proposedantennahasasmallsizeof16×19mm,andprovidesan ultra wide bandwidth from 2.8 to 28 GHz with low VSWR level and good radiation characteristics to satisfy the requirements of the current and future wireless communications systems.
1. INTRODUCTION
From mobile telephones to wireless Internet access to networked appliance sand peripherals,there is anincreasing reliance on wireless communications to provide functionality for products and services.Therefore,the technologies for wireless communications always need further improvement to satisfy higher resolution and data requirements. That is why ultra wideband (UWB) communications systems covering 3.1 GHz to 10.6 GHz released by the Federal Communications Commission (FCC) in 2002 [1] are currently under development.However,thereisalwaysanincreasingdemandfor smallersize,andgreatercapacitiesandtransmissionspeeds,which will certainly require more operating bandwidth in the near future.
Inthelastfewyears,researchershaveinvestigatedseveralkindsof microstrip slot and printed antennas for UWB applications [2–15]. One
of the best antennas in the last decade is the tap monopole antenna. The planar tap monopole antennas have been adopted and studied extensively for UWB communications systems because of their many appealing features. These features include wide impedance bandwidth, simplestructure,smallsize,lowprofile,andomni-directionalradiation patterns.Numberofwidebandtapmonopoleconfigurations,suchas rectangular,elliptical,pentagonal,andhexagonalhasbeenproposed for UWB applications [5:15]. Wide impedance bandwidth of (1:1.7), (1:2.25),(1:2.87),(1:3.4),(1:3.5),(1:3.7),(1:3.75)and(1:10.7)for VSWR<2,andanantennasizeof20,24,20,23,16,26,30,andmore than52mmarereportedin[7–14],respectively.
Recently,wepresentedamodifiedprintedtapmonopoleantenna forUWBapplicationswithaslit,notchedgroundplane,andtapered transition between the tap monopole and the feed line with a very wideimpedancebandwidthof(1:7.9)[15].Inthispaper,wepresent numerical analysis of the antenna in [15] to show the effect of each dimensional parameter. The numerical analysis results in a much betterbandwidthof(1:10),withalowVSWRleveloflessthan1.75, andasmallsizeof16mm,whichissmallerthantheantennaspresented in [2–14]. The results in this paper are obtained from Ansoft HFSS simulations,whicharebasedontheFiniteElementMethod(FEM). Verification of the final results is performed using a FDTD based code designed by the author.
2. ANTENNA GEOMETRY AND PARAMETERS
The geometry and parameters of the proposed broadband tap monopole antenna are depicted in Fig. 1. The antenna is printed on an FR4Epoxysubstratewitharelativedielectricconstant(εr)of4.4,a tangentialloss(tanσ)of0.02,athickness(h)of1.6mm,awidth(Ws) of 16 mm and a length (Ls ) of 19 mm. The basic antenna structure consistsofarectangularpatchwithanarrowslit,ataperedtransition, afeedline,andatruncatedgroundplanewithatwo-stepstaircase notch.
The rectangular patch has a width P1 and a height P2. A narrow slit of width S1 and depth S2 is cut on the patch’s right side and placed at a distance S3 away from the lower right corner of the patch. The slit is placed to create additional path for the surface current, which producesan additional resonance, andasaresult, increases the band width when the dimension sareproperly chosen,whichis proven in [15] by comparing VSWRs for antennas with and without slit. Additionally, because this slotis very narrow itdoes not disturb the existing resonances of the tap monopole.
A. A. Eldek
Department of Computer Engineering
Jackson State University JSUBox17098,Jackson,MS39217-0198,USA
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