504 IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS, VOL. 12, 2013

UWB CPW-Fed Fractal Patch Antenna WithBand-Notched Function Employing

Folded T-Shaped ElementM. Naser-Moghadasi, R. A. Sadeghzadeh, T. Sedghi, T. Aribi, and B. S. Virdee, Member, IEEE

AbstractA compact coplanar waveguide (CPW) monopole an-tenna is presented, comprising a fractal radiating patch in whicha folded T-shaped element (FTSE) is embedded. The impedancematch of the antenna is determined by the number of fractal unitcells, and the FTSE provides the necessary band-notch function-ality. The filtering property can be tuned finely by controlling oflength of FTSE. Inclusion of a pair of rectangular notches in theground plane is shown to extend the antennas impedance band-width for ultrawideband (UWB) performance. The antennas pa-rameters were investigated to fully understand their affect on theantenna. Salient parameters obtained from this analysis enabledthe optimization of the antennas overall characteristics. Experi-mental and simulation results demonstrate that the antenna ex-hibits the desired VSWR level and radiation patterns across theentire UWB frequency range. The measured results showed theantenna operates over a frequency band between 2.9411.17 GHzwith fractional bandwidth of 117% for , except at thenotch band between 3.34.2 GHz. The antenna has dimensions of14 18 1 mm .

Index TermsBand-notch, coplanar waveguide (CPW)-fed,fractal, monopole antennas, ultrawideband (UWB) applications.

I. INTRODUCTION

U LTRA-WIDEBAND (UWB) communication systemspossess extensive bandwidth enabling high-speed datarate transmission to be achieved [1]. According to the FederalCommunications Commission (FCC), the operational band-width of UWB antennas is defined between 3.110.6 GHz [2].This technology has offers unique advantages not achievableby conventional narrowband technology, which includes lowpower requirements, high-speed transmission, immunity tomultipath propagation, and simple hardware configuration.UWB is targeted as a cable replacement technology. Applica-tions include wireless home networking, high-density use inbusiness cores, wireless speakers, wireless USB, high speed

Manuscript received February 10, 2013; revised March 17, 2013; acceptedMarch 19, 2013. Date of publication April 12, 2013; date of current versionApril 18, 2013.M. Naser-Moghadasi, T. Sedgh, and T. Aribi are with the Faculty of Engi-

neering, Science and Research Branch, Islamic Azad University, Tehran, Iran(e-mail: mn.moghaddasi@srbiau.ac.ir).R. A. Sadeghzadeh is with the Department of Electrical and Computer Engi-

neering, Khajeh Nasir Toosi University of Technology, Tehran, Iran.B. S. Virdee is with the Faculty of Life Sciences and Computing, Center

for Communications Technology, London Metropolitan University, London N78DB, U.K.Color versions of one or more of the figures in this letter are available online

at http://ieeexplore.ieee.org.Digital Object Identifier 10.1109/LAWP.2013.2256455

WPAN, wireless sensors networks, wireless telemetry, andtelemedicine. The UWB antenna is a crucial component of suchsystems. The best choice for implementation of ultrawidebandantennas is on planar technology as it allows easy integrationwith microwave integrated circuits (MICs) and is lightweightand relatively low-cost [3]. UWB technology requires electri-cally small antennas for wireless and personal communicationsystems. This is essential and presents a design challenge.Miniaturized and low-profile antennas have undesirable in-trinsic attributes such as narrow bandwidth and inefficientradiation characteristics resulting from reducing the antennasdimensions smaller than a quarter-wavelength at operatingfrequency. It has been demonstrated that fractal geometries,which are based on space filling and self-similarity attributes,can be useful to improve the performance of antenna [4]. Also,fractal-based antennas can effectively couple energy to freespace [5][7]. In addition, different feeding methodologiescan be applied on fractal antennas without degrading theirperformancefor example, microstrip lines [8] and coplanarwaveguide (CPW) [9]. CPW transmission-line feed method ispopular because of lower loss, low radiation leakage, and moreconvenience with shunt and series connection on the same sideof substrate avoiding via holes [10].Interference is a significant problem for UWB systems.

Therefore, in these systems, rejection of interfering signalsfrom WiMAX (IEEE 802.16) [11] and 4-GHz C-bands [12]satellite communications systems (for downlinks) is an es-sential requirement. One approach to suppress interferingsignal is to utilize a spatial filter such as a frequency selectivesurface (FSS) [13], however these require precious space andprecludes miniaturization. To mitigate this problem, UWBantennas need to incorporate within them band-reject function,which for printed monopole antennas can be achieved by:1) embedding specific shaped slots (U-shaped, arc-shaped)on the radiator [14]; 2) utilizing parasitic elements beside theantenna radiator to reject the specified band [15]; and 3) placinga slit in the ground plane or feedline [16].In this letter, a novel CPW-fed UWB antenna with band-

notched characteristic is proposed. The antenna consists of afractal patch resembling a tree structure with a folded T-shapedelement (FTSE) etched on it. To extend the antennas impedancebandwidth, the ground plane is curved in the vicinity of thepatch, and rectangular notches are cut out from its sides. Thesenotches affect the antennas upper- and lower-band edge fre-quencies, thus enabling control of the antennas impedance band-width. It is also shown that by increasing the number of fractal

1536-1225/$31.00 2013 IEEE

NASER-MOGHADASI et al.: UWB CPW-FED FRACTAL PATCH ANTENNA WITH BAND-NOTCHED FUNCTION EMPLOYING FTSE 505

Fig. 1. Configuration of proposed monopole fractal antenna.

Fig. 2. Steps required in the implementation of the fractal antenna.

unit cells, the antennas impedance bandwidth is enhanced. Re-jection band functionality is achieved by the folded T-shapedelement that is attached to the fractal patch. Controlling thelength of the folded T-shaped element is important for tuningthe frequency of the notch band. By optimizing the length ofthe folded T-shaped structures arms, WiMAX (IEEE802.16,3.33.7 GHz) and C-band satellite communication at down-link (3.74.2 GHz) are filtered from UWB band. The proposedmethod is validated through simulation and practical measure-ment. Detail of the antenna design and comparison between theexperimental and simulation results are presented.

II. ANTENNA DESIGN

The configuration and parameters of the CPW-fed fractal an-tenna are shown in Fig. 1. The antenna is printed on commer-cial dielectric substrate FR4 with a thickness of 1 mm,of 0.024, and relative permittivity of 4.4. The substrate dimen-sions are , and the feedline has a widthmm, which corresponds to a characteristic impedance of 50 ,and mm. The feedline is tapered to optimize theimpedance matching to the antennas fractal tree patch [7].The fabricated CPW-fed antenna consists of a fractal

patch with an array of fractal unit cells oriented to resemblethe branches of a tree and includes a symmetrically placedfolded T-shape element. The antennas rectangular groundplane is etched on the same side as the patch. The process ofground-plane modification consists of curving the rectangularground plane at the top and cutting out rectangular-shapedslots from its sides, as illustrated in Fig. 2. This modificationto the ground plane enhances the matching characteristicsbetween the patch and the feedline, which results in the antennaexhibiting UWB performance.To achieve band-notch property by the antenna in the

WiMAX band, the FTSE structure is added to the antennasfractal patch. The FTSE structures dimensions dictate theband notch and the filtering performance of the antenna. Fig. 2depicts the steps used to develop the antenna, namely thefollowing.

Fig. 3. Simulated VSWR characteristic for Ant. 0 and Ant. 1 as a function of.

Step 1) Create a tapered CPW feedline forming the trunk forthe fractal patch, and add four fractal unit cells toform the branches in the patch (Ant. 0).

Step 2) Add another four unit cells to the patch (Ant. 1).Step 3) Apply ground-plane modification in order to extend

the antennas impedance bandwidth for UWB per-formance (Ant. 2).

Step 4) Embed a folded T-shaped structure (Ant. 3).The antenna dimensions were optimized through para-metric study using Ansofts High Frequency StructureSimulator (HFSS). Optimal parameters of the proposedantenna are as follows: mm, mm,

mm, mm, mm, mm,mm, mm, mm, mm,mm, mm, mm, mm,

mm, mm. The length ofis set to , ( corresponding to notch frequency of3.7 GHz.) By parametric study, optimized value is set to

.

III. RESULTS AND DISCUSSION

In this section, the parameters of the CPW-fed fractal an-tenna are discussed, and the numerical and experimental resultspresented. The antennas dimensions were determined throughthe optimization process. The effect of individual parameterswas ascertained by changing the parameter in question whilekeeping all other parameters fixed. It was observed that theground-plane length ( ) has a major effect on the antennasimpedance matching property. Fig. 3 depicts the variation ofVSWR with parameter for Ant. 0 and Ant. 1. The upper andlower values of relative to its optimized value ( mm)decreases the operational bandwidth of Ant. 1. The upper- andlower-frequency edge of the antennas UWB response is con-trolled by curving the top of the ground plane and embeddingrectangular notches in its sides, transforming Ant. 1 to Ant. 2.The VSWR of Ant. 2 is marginally affected by varying the di-mensions of the rectangular slot configuration in the groundplane as shown in Fig. 4. This figure clearly shows how the rect-angular notches in the ground plane can extend the antennasimpedance bandwidth, i.e., the lower-band edge extends back-wards from 3.78 to 3.1 GHz, and the upper-band edge extendsfrom 9.89 to 11.1 GHz, thus satisfying the requirement of UWBband. It is observed in Fig. 4 that by increasing both parameters

506 IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS, VOL. 12, 2013

Fig. 4. Simulated VSWR as a function of ground-plane slot dimensions forAnt. 2.

Fig. 5. Simulated VSWR curves with different values of for Ant. 3.

Fig. 6. Simulated VSWR curves for Ant. 3 as a function FTSE arm lengths forfixed arm width ( ) of 5.5 mm.

from their optimized value ( mm and mm), thematching characteristics deteriorates along with some reductionin the bandwidth performance. The optimum values for andwere obtained through parametric study.The proposed fractal patch is composed of repeating unit-cell

patterns in which the folded T-shape element structure is em-bedded to provide the antenna with filtering function. It is ob-vious that by increasing the iteration of the fractal patch, the an-tennas impedance matching is improved. The process of addingthe band-notch function to the antenna consists of three steps.Step 1) A single vertical stripline is added to fractal patch of

antenna, as depicted in Fig. 5.Step 2) A pair of horizontal arms is added to vertical

stripline.Step 3) A pair of vertical arms is added to Step 2, as shown

in Fig. 6.

Fig. 7. Surface current distribution at notch frequency of 3.6 GHz for Ant. 3.

Fig. 8. Measured and simulated VSWR response for Ant. 2 and Ant. 3. Insetis the photograph of the two antennas.

As shown in Fig. 5, the vertical stripline element leads toreduction in the antennas bandwidth because of mismatching.However, by attaching two horizontal arms to the verticalstripline, the impedance bandwidth improves, and the notchproperty is realized. The effect of FTSE width ( ) onAnt. 3 is shown in Fig. 5. The size of the width determines thedegree of notching function as well as its frequency location.Fig. 6 shows how the antennas performance is affected bythe length ( ) of the vertical stripline sections added to theFTSE structure. The optimum value of is 1.5 mm for ourgoal. Fig. 7 shows the simulated current distribution over Ant. 3at the notch frequency of 3.6 GHz. It is clear that the FTSEssurface current flows in reverse direction of the fractal patchand feedline Thus, the total effective radiation is very low, andtherefore notched band is obtained.Fig. 8 shows the simulated and measured responses of Ant. 2

and Ant. 3. The results show that Ant. 2 covers the UWB rangefor . The measured impedance bandwidth for Ant. 2is 3.111.1 GHz, and for Ant. 3 is 2.9411.17 GHz with the ex-ception of the stopband. Fig. 9 shows the extracted peak gain forthe fabricated antennas over 211 GHz. Themeasured peak gainof Ant. 3 decreases drastically over the rejected band between

NASER-MOGHADASI et al.: UWB CPW-FED FRACTAL PATCH ANTENNA WITH BAND-NOTCHED FUNCTION EMPLOYING FTSE 507

Fig. 9. Simulated and measured peak gain of Ant. 2 and Ant. 3.

Fig. 10. Measured radiation patterns at 3.6, 6, and 10 GHz.

3.34.2 GHz, however it gradually increases with rise in fre-quency. The measured H-plane and E-plane radiation patternsof the final antenna at 3.6, 6, and 10 GHz are shown in Fig. 10.The H-plane radiation pattern results show that the proposed an-tenna is characterized by omnidirectional pattern for all in-bandfrequencies with cross polarization down by more than 27 dB.Although the E-plane radiation is bidirectional, it becomes in-creasingly omnidirectional with increase in frequency. In theE-plane, the cross polarization is down by around 27 dB.

IV. CONCLUSIONThis letter described a novel and compact CPW-fed fractal

antenna incorporating a folded T-shape element structure toprovide a band-rejection function to suppress interferencewith existing WiMAX (IEEE 802.16) and C-band systems.The ground plane is curved and includes dielectric notches atits side to enhance the antennas impedance bandwidth. Thedimensions of the notches effectively control the upper- andlower-band edges of the antenna. The antenna exhibits omni-directional radiation pattern in the H-plane over the full UWBfrequency range. The antenna dimensions are 14 18 1mm .These attributes makes the antenna suitable for UWB wirelesssystems that require low-profile antennas.

REFERENCES[1] M. Koohestani and M. Golpour, U-shaped microstrip patch antenna

with novel parasitic tuning stubs for ultra wide band applications,Mi-crow. Antennas Propag., vol. 4, pp. 938946, 2010.

[2] Federal Communications Commission, Washington, DC, USA,First report and order in the matter of revision of Part 15 of theCommissions rules regarding ultra-wideband transmission systemsET-Docket98-153, 2002.

[3] K. Zh, Y. Li, and Y. Long, Band-notched UWB printed monopole an-tenna with a novel segmented circular patch, IEEE Antennas WirelessPropag. Lett., vol. 9, pp. 12091212, 2010.

[4] M. Naser-Moghadasi, R. A. Sadeghzadeh, T. Aribi, T. Sedghi, and B.S. Virdee, UWB monopole microstrip antenna using fractal tree unit-cells, Microw. Opt. Technol. Lett., vol. 50, no. 10, pp. 936939, Oct.2012.

[5] M. N. Jahromi, A. Falahati, and R. M. Edwards, Bandwidth andimpedance-matching enhancement of fractal monopole antennasusing compact grounded coplanar waveguide, IEEE Trans. AntennasPropag., vol. 59, no. 7, pp. 24802487, Jul. 2011.

[6] B. Ozbakis and A. Kustepeli, The resonant behavior of the Fibonaccifractal tree antennas, Microw. Opt. Technol. Lett., vol. 50, no. 4, pp.10461050, Oct. 2008.

[7] H. Oraizi and S. Hedayati, Miniaturized UWB monopole microstripantenna design by the combination of Giusepe Peano and Sierpinskicarpet fractals, IEEE Antennas Wireless Propag. Lett., vol. 10, pp.172175, 2011.

[8] M. Naser-Moghadasi, H. Rousta, R. A. Sadeghzadeh, and B. S. Virdee,Compact UWB planar monopole antenna, IEEE Antennas WirelessPropag. Lett., vol. 8, pp. 13821385, 2009.

[9] M. Naser-Moghadasi, R. A. Sadeghzadeh, M. Katouli, and B. S.Virdee, CPW-fed compact slot antenna for WLAN operation in alaptop computer, Microw. Opt. Technol. Lett., vol. 52, pp. 870873,2010.

[10] C. Deng, Y. J. Xie, and P. Li, CPW-fed planar printed monopole an-tenna with impedance bandwidth enhanced, IEEE Antennas WirelessPropag. Lett., vol. 8, pp. 13941397, 2009.

[11] C. C. Lin, P. Jin, and R. W. Ziolkowski, Single, dual and tri-band-notched ultra wide band (UWB) antennas using capacitively loadedloop (CLL) resonators, IEEE Trans. Antennas Propag., vol. 60, no. 1,pp. 102109, Jan. 2012.

[12] N. Ojaroudi and M. Ojaroudi, Dualband-notch square monopole an-tenna with a modified ground plane for UWB applications, Microw.Opt. Technol. Lett., vol. 54, no. 12, pp. 27432747, Dec. 2012.

[13] K. S. Ryu and A. A. Kishk, UWB antenna with single or dual band-notches for lower WLAN band and upper WLAN band, IEEE Trans.Antennas Propag., vol. 57, no. 12, pp. 39423950, Dec. 2009.

[14] M. Mehranpour, J. Nourinia, C. Ghobadi, and M. Ojaroudi, Dualband-notched square monopole antenna for ultra wide band applica-tions, IEEE Antennas Wireless Propag. Lett., vol. 11, pp. 172175,2012.

[15] H. Mardani, C. Ghobadi, and J. Nourinia, A simple compactmonopole antenna with variable single and double filtering functionfor UWB applications, IEEE Antennas Wireless Propag. Lett., vol. 9,pp. 10761079, 2010.

[16] D. O. Kim and C. Y. Kim, CPW-fed ultrawide band antenna withtriple-band notch function, Electron. Lett., vol. 46, no. 18, pp.12461248, Sep. 2010.