(FCC),3 the frequency band of UWB (the cat-egory of communications and measurementsystems) should be contained between 3.1 and10.6 GHz. Figure 1 shows the spectrum allo-cation of the current UWB system for multi-band OFDM (MBOA) and direct sequence(DS) CDMA UWB. The MBOA has fourgroups (group A, B, C and D) and thirteenbands, each with a bandwidth of 500 MHz.

The DS-UWB system has a low bandfrom 3.1 to 5.15 GHz and a high bandfrom 6 to 10.1 GHz. Due to its extremelywide operating bandwidth, it could possi-bly interfere with other existing electronicsystems operating at the same time. In

H.R. CHUANG, C.C. LINAND Y.C. KANNational Cheng Kung UniversityTainan, Taiwan, ROC

The emerging ultra-wideband (UWB)radio is the technology for transmittingand receiving short, information-en-

coded, electromagnetic impulses.1,2 UWBtechnology is loosely defined as any wirelesstransmission scheme that occupies a band-width of more than 25 percent of a center fre-quency, or more than 1.5 GHz. According tothe Federal Communications Commission

A PRINTED UWBTRIANGULARMONOPOLE ANTENNA

A planar printed triangular monopole antenna (PTMA) is presented for ultra-wideband (UWB) communications. The HFSS 3-D EM solver is employed for design simulation.A printed PTMA has been fabricated on a FR-4 substrate. The measured VSWR is less than 3 from 4to 10 GHz. In the UWB communications frequency range, the measured phase distribution of theinput impedance is quite linear and the H-plane patterns are almost omni-directional. The Kirchhoff’ssurface integral representation (KSIR) was adopted in the developed FDTD code to compute the far-field distributions from the near-field ones in the time domain. This is to investigate the radiatedpower spectral density (PSD) shaping to comply with the Federal Communications Commission(FCC) emission limit mask. The effect of various source pulses (first-order Rayleigh pulses with σ =20, 30 and 50 ps) on the radiated PSD shaping is also studied.

DS-UWB High Band

UWB MBOAGroup D

UWB MBOAGroup C

UWB MBOAGroup B

GHz

U-NII

5.125 5.725

~5.825~5.325

Hiperlan 802.11a

UWB MBOAGroup A

DS-UWB Low Band

3.432 3.960 4.488 5.016 5.806 6.336 6.864 7.392 7.920 8.448 8.976 9.504 10.032

Fig. 1 Spectrum allocation for UWBcommunications.

Reprinted with permission of MICROWAVE JOURNAL® from the January 2006 issue.©2006 Horizon House Publications, Inc.

order to make it compatible with ex-isting narrow-band radio services, themaximum permissible effectiveisotropic radiated power (EIRP) den-sity is set as –41.3 dBm/MHz.3

Hence, the emission limits of the ra-diated power are a critical considera-tion in UWB radio systems, especiallyfor the antenna design.

In general, there are two ways tolimit the radiated PSD shaping to con-form to the standard mask set by theFCC:4 the first is to design the antenna

as a special filter to suppress the un-wanted radiation outside the UWBband or, second, to select a sourcepulse in the specific band to let the ra-diated PSD meet the FCC requiredemission limits. In this article, the sec-ond approach is used. Here, a printedmonopole-type antenna is adopted forthe design of a broadband antenna forUWB application.5,6 The design simu-lation, fabrication and measurements ofa printed planar triangular monopoleantenna (PTMA), fabricated on a FR-4PCB, are reported. The HFSS 3-DEM simulator is employed for designsimulation. The antenna input VSWR,the phase of the input impedance andthe radiation patterns are presented.Also, an FDTD code, developed withthe Kirchhoff’s surface integral repre-sentation (KSIR), is used to computethe time-domain far-field distribution.

This is to investigate the radiated PSDshaping to comply with the FCC emis-sion limit mask. First-order Rayleighpulses with σ = 20, 30 and 50 ps areused and the resulting PSD are com-pared.

ANTENNA DESIGNIn this article, a printed PTMA is

developed, based on a triangular mono-pole antenna.5,6 The structure of thisantenna consists of a tapered radiatingelement excited by a suitable feed-structure, such as a coplanar waveguide(CPW) or microstrip line. As shown inFigure 2, the antenna geometry, thewidth, length and flare angle of the an-tenna are denoted by Wmono, Lmonoand α, respectively. A 50 Ω microstripline is used to feed the PTMA at theapex angle of the triangular patch. Thedistance between the end of the mono-pole and the terminal of the microstripline is denoted by L0. The antenna isprinted on one side of a FR-4 substratewith a width Ws, a length Ls and athickness T. On the other side of thesubstrate, a ground plane of width Wsand length Lg is printed. The detailedparameters of the antenna are summa-rized in Table 1. The figure also showsthe photograph of a printed PTMA fab-ricated on a FR-4 substrate.

MEASUREMENT RESULTSThe HFSS-simulated current distri-

butions of the printed PTMA at 3, 5, 7and 9 GHz are shown in Figure 3. Thesimulation shows that the currents ofthe PTMA are almost distributed alongthe same directions (z-axis), which issimilar to the behavior of a monopoleantenna. Figure 4 shows the measuredantenna input VSWR and the phase ofthe input impedance from 3 to 10GHz. The measured input VSWR isless than 2.5 from 4 to 10 GHz and themeasured phase distribution of the in-put impedance is also quite linear ex-cept in the frequency range from 5 to 6GHz. The measured representative H-plane (xy-plane, θ = 90°) and E-plane(xz-plane, Φ = 0°) antenna patterns at4, 5, 6 and 7 GHz are shown in Figure5. It can be seen that the H-plane pat-terns are all quite omni-directional.

RADIATED POWER SPECTRUMDENSITY (PSD)

For the conventional narrow-bandantenna design, the frequency-domaininformation is more useful and signifi-

TECHNICAL FEATURE

TABLE IANTENNA DIMENSIONS

Wmono (mm) 17

Lmono (mm) 7.6

L0 (mm) 1

α 90°

Ls (mm) 60

Ws (mm 20

Lg (mm) 50

T (mm) 1

PCB substrate (εr, tanδ) (4.7, 0.018)

Gound Plane(in the bottom)

Wmono

Ws

Lmono

Lo

Ls

Ws

x y

(a)

(b)

Lg

z

Fig. 2 Geometry and a realized printedPTMA.

(a)

3 GHz

7 GHz 9 GHz

5 GHz

(b)

(c) (d)

Fig. 3 HFSS-simulated current distribution of the printed PTMA at (a) 3, (b) 5, (c) 7 and (d)9 GHz.

cant than the one in the time domain.For a UWB radio system excited witha short pulse, the study of temporalproperties will be helpful in designingand analyzing the UWB antenna. Thedesired time-domain information canbe readily obtained by using time-do-main numerical methods, such as thefinite-difference time-domain(FDTD) method. However, since theFDTD method is inherently a near-field technique, a time-domain near-to far-field transformation is employedto efficiently compute the far-field an-tenna parameters.7,8 Ultimately, thefrequency-domain response can beobtained with the fast Fourier trans-form (FFT). The effect of varioussource pulses on the radiated PSDshaping are then studied by using thefirst-order Rayleigh pulses, which aredifferentiated Gaussian pulses. Theparameter σ is used to describe thetime duration when the normalizedsingle level, v0(σ), of the source pulseequals to e-1. The first-order Rayleighpulses with σ = 20, 30 and 50 ps areused in the FDTD computation. It isnoted that the first-order Rayleighpulses with σ > 60 ps are not consid-ered here because their correspondingspectra of 10 dB bandwidths do notfully occupy the desired 7.5 GHzbandwidth for UWB communication.Figure 6 shows the time-domain and

TECHNICAL FEATUREV

SWR

FREQUENCY (GHz)

4.0

3.5

3.0

2.5

2.0

−1.5

−1.03 4 5 6 7 8 9 10

PHA

SE (°)

FREQUENCY (GHz)

180

90

0

−90

−1803 4 5 6 7 8 9 10

(a)

(b)

Fig. 4 Measured antenna input VSWR(a) and phase of the input impedance (b).

(a)

(b)

4 GHz

90°

45°

270°

315°225°

180°

135°

0°

Y

X

5 GHz

90°

45°

270°

315°225°

180°

135°

0°

Y

X

6 GHz

90°

45°

270°

315°225°

180°

135°

0°

Y

X

7 GHz

90°

45°

270°

315°225°

180°

135°

0°

Y

X

4 GHz

0°

45°

180°

135°225°

270°

315°

90°

Z

X

5 GHz

0°

45°

180°

135°225°

270°

315°

90°

Z

X

6 GHz

0°

45°

180°

135°225°

270°

315°

90°

Z

X

7 GHz

0°

45°

180°

135°225°

270°

315°

90°

Z

X

0

-10

-20

-30

-40

0

-10

-20

-30

-40

0

-10

-20

-30

-40

0

-10

-20

-30

-40

0

-10

-20

-30

-40

0

-10

-20

-30

-40

0

-10

-20

-30

-40

0

-10

-20

-30

-40

Fig. 5 Measured antenna patterns; (a) H-plane and (b) E-plane.

frequency-domain waveforms of thesefirst-order Rayleigh pulses. Unlike theGaussian pulse, these Rayleigh pulsesare monocycle pulses in the time do-main and do not generate any directcurrent (DC) component in the fre-quency domain. For UWB antennadesign, the transfer function of the an-tenna is important both to comply

with the FCC power emission limitsand to preserve the transmitted wave-form information. The transfer func-tion of an antenna is defined as the ra-tio of radiated electric fields in the fre-quency domain and the spectrum of asource signal (voltage) at the transmit-ting antenna.4 For the FDTD calcula-tion, the transfer functions of the an-tenna can be obtained by applying thedefinition. For measurement, thetransfer functions can be derived fromthe transmission scattering parame-ters, S21, the input impedance and theantenna gain.9 The measured transferfunctions of the printed PTMA at Φ =0°, 90°, 180° and 270° in the H-planeare plotted in Figure 7. Due to the in-strument’s limitations in the anechoicchamber, only the frequency bandfrom 3 to 8 GHz is presented. A goodagreement among transfer functions atΦ = 0°, 90°, 180° and 270° is observedbecause of the omni-directional radia-tion pattern of the printed PTMA inthe H-plane. The magnitudes of thetransfer functions are close to a flat re-sponse over the interested frequencyband. From the signal point of view,

this PTMA antenna is a bandpass filterwith nearly constant magnitude.Hence, the desired radiated PSD ofthe printed PTMA can be achievedreadily once the source pulses havebeen properly evaluated. Figure 8shows the computed radiated PSD ofthe printed PTMA excited by the first-order Rayleigh pulses with σ = 20, 30and 50 ps. The co-polarized compo-nent of the printed PTMA, Eθ, in thedirection of θ = 90° is computed at thedistance of r = 2 m. All the computedresults of PSD are normalized to –41.3dBm/MHz. In comparison with theFCC’s indoor and outdoor masks, it isfound that the radiated PSD of thefirst-order Rayleigh pulses with σ =20, 30 and 50 ps all comply with theFCC’s indoor and outdoor mask from2 to 10.6 GHz. Beyond 10.6 GHz,however, only the pulse with σ = 50 pscan comply with the FCC’s indoor andoutdoor masks.

CONCLUSIONThis article presents a PTMA for

UWB communication. The HFSS 3-D EM simulator is employed for de-sign simulation. The printed PTMA isfabricated on a FR-4 PCB substrate.The measured VSWR is less than 3from 4 to 10 GHz. The measuredphase distribution of the input im-pedance is quite linear (except in thefrequency range from 5 to 6 GHz).The H-plane patterns are almostomni-directional in the UWB fre-quency band. The antenna transferfunctions at Φ = 0°, 90°, 180° and270° in the H-plane are measuredand a nearly flat response can be ob-served. The KSIR is used in the de-veloped FDTD code to compute thetime-domain far-field distribution.This is to investigate the PSD shapingto comply with the FCC emissionlimit mask. The effect of differentsource pulses (first-order Rayleighpulses with σ = 25, 50 and 100 ps) onthe radiated PSD shaping is studied.Due to the flat response of the anten-na transfer function, the desired radi-ated PSD of the printed PTMA canbe readily achieved with a propersource pulse. It is found that only theradiated PSD of the first-orderRayleigh pulse with σ = 50 ps cancomply with the FCC’s indoor maskabove 2 GHz. As for the outdoormask, the same pulse can complywith the FCC emission limit.

TECHNICAL FEATUREN

OR

MA

LIZE

DSI

GN

AL

LEV

EL

TIME (ps)

1.0

0.5

0.0

−0.5

−1.0−200 −100 0 100 200

NO

RM

ALI

ZED

PO

WER

SPEC

TRA

L D

ENSI

TY

FREQUENCY (GHz)

1.0

0.8

0.6

0.4

0.2

00 5 10 15 20

(b)

(a)

20ps30ps50ps

25ps50ps100ps

Fig. 6 Waveforms of first-order Rayleighpulses; (a) time domain and (b) frequencydomain.

MA

GN

ITU

DE

(dB

)

FREQUENCY (GHz)

0

−20

−40

−603 4 5 6 7 8

φ = 0°φ = 90°φ = 180°φ = 270°

Fig. 7 Measured antenna transferfunction at f = 0°, 90°, 180° and 270° in the H-plane.

PO

WER

SP

ECTR

AL

DEN

SITY

(dB

m/M

Hz)

PO

WER

SP

ECTR

AL

DEN

SITY

(dB

m/M

Hz)

FREQUENCY (GHz)

−40

−60

−80

−1000 5 10 15 20

FREQUENCY (GHz)(b)

(a)

20ps30ps50ps

−40

−60

−80

−1000 5 10 15 20

OutdoorMask

IndoorMask

Fig. 8 FDTD simulated PSD shaping of the E-field of the printed PTMA with first-order Rayleigh source pulses (σ = 20, 30and 50 ps); (a) indoor and (b) outdoor.

References1. K. Siwiak and D. McKeown, Ultra-wide-

band Radio Technology, John Wiley &Sons Inc., UK, 2004.

2. S. Roy, J.R. Foerster, V.S. Somayazulu andD.G. Leeper, “Ultra-wideband Radio De-sign: The Promise of High Speed, Short-range Wireless Connectivity,” Proceedingsof the IEEE, Vol. 92, February 2004, pp. 295–311.

3. US 47 CFR Part 15 Ultra-wideband Oper-ation FCC Report and Order, 22 April2002.

4. Z.N. Chen, X.H. Wu, H.F. Li, N. Yang andM. Chia, “Considerations for Source Puls-es and Antennas in UWB Radio System,”IEEE Transactions on Antennas and Prop-agation, Vol. 52, July 2004, pp. 1739–1748.

5. J.M. Johnson and Y. Rahmat-Samii, “TheTab Monopole,” IEEE Transactions on An-tennas and Propagation, Vol. 45, January1997, pp. 187–188.

6. H.M. Chan, “Microstrip-fed Dual Fre-quency Printed Triangular Monopole,”Electronics Letters, Vol. 38, June 2002, pp. 619–620.

7. A. Taflove, Advances in ComputationalElectromagnetics, Artech House Inc., Nor-wood, MA, 1998.

8. O.M. Ramahi, “Near- and Far-field Calcu-lations in FDTD Simulations Using Kirch-hoff’s Surface Integral Representation,”IEEE Transactions on Antennas and Prop-agation, Vol. 45, May 1997, pp. 753–759.

9. T.G. Ma and S.K. Jeng, “Planar MiniatureTapered-slot-fed Annular Slot Antennasfor Ultra-wideband Radios,” IEEE Trans-actions on Antennas and Propagation, Vol.53, March 2005, pp. 1194–1202.

Huey-Ru Chuang received his BSEE andMSEE degrees from National TaiwanUniversity, Taipei, Taiwan, in 1977 and 1980,respectively, and his PhD degree in electricalengineering from Michigan State University,East Lansing, MI, in 1987. He is currently aprofessor at the Institute of Computer andCommunication, National Cheng KungUniversity, Tainan, Taiwan. His researchinterests include mobile antenna design,RF/microwave integrated circuits andRFIC/MMIC for wireless communications,computational electromagnetics and itsapplications. He is a winner of the Agilent 2003Worldwide University Equipment Grants.

Chi-Chang Lin received his BSEE and MSEEdegrees from Tatung University, Taipei,Taiwan, in 1999 and 2001, respectively. He iscurrently working toward his PhD degree inelectrical engineering from National ChengKung University, Tainan, Taiwan. His researchinterests include EM computation and wirelesscommunication antenna design.

Yao-Chiang Kan received his BS degree fromNational Cheng Kung University, Tainan,Taiwan, in 1988, and his MS and PhD degreesin electrical engineering from Michigan StateUniversity, East Lansing, MI, in 1994 and2000, respectively. He is currently an assistantprofessor in the department of information andtelecommunications at Ming Chung University,Taipei, Taiwan. His research interests includecomputational electromagnetics and wirelesssensor networks.

TECHNICAL FEATURE