IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 53, NO. 8, AUGUST 2005 2631

Single Feed Compact Quad-Band PIFA Antenna forWireless Communication Applications

Dalia Mohammed Nashaat, Hala A. Elsadek, Member, IEEE, and Hani Ghali, Member, IEEE

Abstract—In this paper, a novel compact single feed quad-bandplanar inverted F-antenna (PIFA) is presented. Two techniques toreduce the physical size are illustrated. First, we insert U-shapedslits within the antenna-radiating surface. This forces the current toflow around the obstacles hence, reducing the resonant frequency.This technique reduces the size by about 30% from the originalPIFA. Second, a capacitive plate is loaded between the radiatingsurface and the ground plane. The size is reduced more to reach55% of the original. The relation between the capacitance loadvalue and the antenna size reduction ratio is studied. Using dif-ferent U-shaped slits at different appropriate positions, multiple(dual, tri, and quad) band capabilities are realized. The four centerfrequencies are chosen to lie within the GSM band, DCS band, Blue-tooth (IEEE802.11a) ISM band, and WLAN (IEEE802.11b) band,respectively. Foam dielectric substrate is used for rigid structureand easy shielding purposes. The reduced size and thin substratethickness ( 0 15 0) allow the design to be compatible withwireless and portable communication systems. Experimentalmeasurements verify the design and simulation criteria.

Index Terms—Capacitance load, multiband antenna, planar in-verted F-antenna (PIFA), size reduction, U-shaped slits.

I. INTRODUCTION

DUE TO THE rapid progress in the wireless communi-cation technology and the ever increasing demand for

multisystems applications, there is a growing trend toward thedesign of a multisystem handset. Recently, there has been anenhanced thrust in internal antennas because of their inherentadvantages. Planar inverted F-antenna (PIFA) has proved to bethe most widely used internal antenna in commercial applica-tions of wireless communication. In most of the research onmultiband PIFA technology, the major success achieved hasbeen in the design of a single feed PIFA with dual resonantfrequencies. Depending upon the wide bandwidth around theresonant frequencies, the dual resonant PIFA can potentiallycover more than two bands [1]. However, system applicationssuch as Bluetooth (IEEE 802.11) or wide-band local-areanetwork (WLAN) have frequency bands that are significantlyfar from the cellular bands (GSM/DCS). So, enhancing thebandwidth of a dual-band PIFA to additionally cover the Blue-tooth/WLAN applications can prove to be a very difficult task.

In this paper, a practical method to design a single feed multi-band PIFA that covers both the cellular and noncellular bandsis developed. From the commercial point of view, there arenow different frequency bands for portable cellular/noncellular

Manuscript received July 20, 2003; revised October 4, 2004.D. M. Nashaat and H. A. Elsadek are with the Microstrip Department, Elec-

tronics Research Institute, Giza, Egypt (e-mail: hala@eri.sci.eg).H. Ghali is with the Electronics and Communication Department, Ain Shames

University, Cairo, Egypt (e-mail: hani_ghali@yahoo.com).Digital Object Identifier 10.1109/TAP.2005.851872

devices such as the conventional 0.9 GHz GSM band for mobilephones and 1.8 GHz DCS band for wireless cellular applications.Furthermore, the Bluetooth wireless technology at 2.4 GHz isalready applied nowadays in many portable devices and soonwill be the standard in most wireless communication systems,such as mobile phones, laptops, personal digital assistants, carstereos, audio speakers, toys, etc. [2]. Moreover, the band ofWLAN at 5.2 GHz is being applied in some applications.

The multiband functionality is not the only required demand insuch antenna systems for wireless communication applicationsbut also other characteristics should be satisfied such as smallsize, light weight, omnidirectional radiation pattern, reasonablegain, and acceptable bandwidth. Unfortunately, none of the ex-ternal antennas satisfies these requirements. It was found thatsome of external antennas lose more than 80% of their efficiencybeside the human body [3]. The most promising technique to re-duce the interaction between the portable device and the humanbody is to use internal integrated antenna that can be shieldedeasily. Probably the most suitable candidate is the PIFA.

Quad-band PIFA with single coaxial probe feeding is inves-tigated. Foam substrate is used for light weight, rigid structure,and easy shielding purposes. Three U-shaped slots are addedwith certain dimensions and at appropriate positions for op-eration at the aforementioned four frequency bands. The sizereduction is 30% from conventional PIFA. Additional reduc-tion by 15% is achieved by adding a capacitance load in thevertical direction. The impedance bandwidth is fairly accept-able. The antenna gain is satisfactory and the radiation patternis quasi-isotropic at the respective four bands of interest. Theproposed concept of adding U-shaped slots is a distinct advan-tage of the design since the bands of operation are independentof each other except the small controllable mutual coupling be-tween the slots. Sections II–IV will introduce the detailed designand the experimental measurements of the antenna.

II. ANTENNA GEOMETRY

The structure for the proposed quad-band (PIFA) is shown inFig. 1(a) while the photo of the fabricated antennas is shownin Fig. 1(b). The resonance frequencies of the antenna can beapproximately determined by (1) [3]–[6]

(1)

whereresonance wave length at band ;

and length and width of the radiating surface at op-erating band ;dielectric constant of the substrate.

0018-926X/$20.00 © 2005 IEEE

2632 IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 53, NO. 8, AUGUST 2005

Fig. 1. (a) Geometrical dimensions of the fabricated quad-band PIFA with a capacitive load. The inner slot dimensions are (L ;W ), the middle slot dimensionsare (L ;W ), and the outer slot dimensions are (L ;W ). (b) Photo of fabricated multiple (dual, tri, and quad) band PIFA on a foam substrate.

The length and width are replaced by and ofthe PIFA rectangular radiating surface to determine the first res-onance frequency (0.9 GHz). While are replacedby the dimensions of the largest U-slot , to generatethe second resonance frequency (1.8 GHz). They are alsoreplaced by the length and width of the middle U-slotto get the third resonance frequency (2.45 GHz). Finally,

are replaced by of the smallest U-slot to havethe fourth resonance frequency at (5.2 GHz). This multi-band antenna has approximately the same size as a single-bandPIFA operating at the lowest frequency band. The radiating el-ement is grounded with a shorting wall. It is found that thewidest bandwidth is achieved when the width of this wall isequal to the width of the PIFA radiating plate. The antenna isfed using coaxial cable at the appropriate matching point for thefour bands of operation. The antenna impedance can be matchedto 50 by controlling the distance between the feed point andthe shorting wall. The PIFA antenna is fabricated on a foam sub-strate with dielectric constant in order to have rigidstructure that can be easily shielded. Adding U-slot on the PIFAradiating surface reduces its size by about 30% from the con-ventional PIFA shape. For further reduction in size, a capacitorplate load is added between the radiating surface and the groundplane. This increases the reduction in size to be about 45%.

Ansoft HFSS software package was used to model andsimulate the multiband PIFA. The antenna was fabricated byphotolithographic technique and was measured by HP8719ESvector network analyzer. The experimental results show goodagreement with the simulated ones.

Fig. 2. Comparison between the measured and simulated reflection coefficientof the conventional PIFA at single band.

Fig. 3. Comparison between the measured and simulated reflectioncoefficients of dual-band PIFA with one U-shaped slot at operating frequencies0.95 and 2 GHz, respectively.

NASHAAT et al.: SINGLE FEED COMPACT QUAD-BAND PIFA ANTENNA 2633

Fig. 4. Comparison between measured and simulated reflection coefficients of tri-band PIFA with two U-shaped slots at operating frequencies (a) 0.95, 1.8, and2.45 GHz and (b) 1.8, 2.45, and 5.2 GHz, respectively.

III. ANTENNA ANALYSIS AND DESIGN

To understand the operation of the proposed design, we beginwith a conventional PIFA (the U-shaped slots and the parasiticcapacitive plate are removed). The foam substrate is with height

mm ( at the 5.2 GHz operating wave-length). The antenna dimensions are mm.The coaxial feed is connected directly to the top plate at a dis-tance equals 22 mm from the shorting edge. The antenna groundplane is with length mm (0.3 ) and width

mm (0.18 ) [7], [8]. The resonance frequency obtainedby using HFSS simulation is 1 GHz at reflection coefficient

dB. The bandwidth is 10%, as shown in Fig. 2,i.e., the impedance bandwidth of the antenna is for reflectioncoefficient less than or equal to 10 dB. The first U-slot isadded with dimensions mm on the centerof radiating surface at distance of 18.5 mm from the shortingedge. The length and width of this slot forms the size of theobstacle that the input current is forced to propagate around tocreate the second resonance. The antenna resonance frequen-cies as obtained from the simulator are 0.95 and 2 GHz withreflection coefficients 27 and 13 dB, respectively. The band-widths are 6% and 5% for the lower and upper bands, respec-tively. Fig. 3 illustrates the results of this dual-band PIFA. By thesame concept, the second U-shaped slot is added to generate theantenna third resonance at GHz. The dimensions of themiddle U-slot are mm. The simulated fre-quencies of this tri-band antenna are 0.95, 1.8, and 2.45 GHz,respectively, as shown in Fig. 4(a). The impedance bandwidthsare 6%, 5%, and 5%; respectively. It is worth mention that fre-quency scaling is done for the tri-band structure to make the op-erating frequencies at 1.8, 2.4, and 5.2 GHz, respectively. Com-parison between the simulated and measured results is shownin Fig. 4(b). Finally, the third U-shaped slot is added with di-mensions mm. The simulated resonancefrequencies are 0.95, 1.8, 2.45, and 5.2 GHz with measured re-flection coefficients 21, 20, 18, and 28 dB, respectively.The four bandwidths are around 5%.

Fig. 5 presents the simulation and experimental results ofthe targeted quad-band PIFA. From the figure, one can noticethat there is small discrepancy between the simulated and mea-sured results of second, third, and fourth resonance frequencies.This may be attributed to the fabrication circumstances and the

Fig. 5. Comparison between measured and simulated reflection coefficients ofquad-band PIFA with three U-shaped slots at operating frequencies of 0.95, 1.8,2.45, and 5.2 GHz, respectively.

TABLE IEFFECT OF THE GEOMETRICAL PARAMETERS OF THE PROPOSED ANTENNA ON

ITS RESONANCE FREQUENCIES AND THEIR CORRESPONDING BANDWIDTHS

bonding material distribution between the copper and the foamlayers (i.e., we use two foam layers to reach the required sub-strate thickness).

The antenna gain is about 9 dBi, which is accepted for mostmobile and wireless applications. Matching of the upper threeresonant frequencies can be controlled by slot widths , ,and . The best result of impedance matching is obtained whenthe gap widths are equal. The impedance bandwidth can be af-fected by changing for all slots. From simulation results, wefound that when , acceptable bandwidthat all bands is reached [2], [4], [9]. Table I illustrates the effectof the geometrical parameters on the four resonant frequencybands and their corresponding bandwidths. From this table, wenotice that the resonating bands are independent of each other.

2634 IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 53, NO. 8, AUGUST 2005

TABLE IIEFFECT OF THE CAPACITANCE LOAD VALUE ON THE SIZE REDUCTION RATIO AND THE IMPEDANCE BANDWIDTH OF THE QUAD-BAND PIFA

Fig. 6. The relation between capacitor load in PF and antenna percentagereduction ratio compared to conventional PIFA.

This is a clear distinct advantage of the design proposed in thispaper since it has more than three degrees of freedom. It is foundthat the extension to more than four bands of frequencies has nolimit and can be easily adjusted by adding U-slots with appro-priate dimensions according to (1) if there is available space onthe radiating surface.

IV. CAPACITIVE LOAD DESIGN

The first approach for size reduction deals with the antennalateral dimensions by inserting U-slots to act as current obsta-cles to increase its path length. The second approach is achievedby adding a capacitive load in the vertical direction betweenthe radiating surface and the ground plane. The reduction of theresonance frequency depends on the capacitor plate dimensions[6], [10]. This size reduction is at the expense of the operatingbandwidth. The effect of decreasing the bandwidth can be com-pensated by optimizing the width of the PIFA shorting plate aswell as the width of the gaps of the U-shaped slots [11].

Table II illustrates the effect of the capacitive load value onthe antenna size reduction ratio as well as its effect on the band-width for all the four bands of operation. From the table, it isclear that the capacitor load effect on the bandwidth can be ne-glected. Fig. 6 illustrates the relation between the antenna reduc-tion ratio and the value of the equivalent load capacitance

Fig. 7. Comparison between the measured and simulated reflectioncoefficients of quad-band PIFA with capacitive load at two different capacitancevalues C = 1:5 PF and C = 0:34 PF.

, where is the area of the capacitor plateand is its separation from the ground plane. From the figure,there is a linear relation between the size of the capacitor loadand the antenna reduction ratio until certain load value at whichthe reduction ratio saturates. From the PIFA structure, it is notedthat the capacitor plate length is limited by the position of thefeed point. Fig. 7 illustrates a comparison between the sim-ulated and measured reflection coefficients of the quad-bandPIFA at two different capacitance load values. The antenna pro-vides good far-field radiation pattern in the four bands of oper-ation as shown in Fig. 8.

V. CONCLUSION

Quad-band PIFA has been developed and implemented suc-cessfully. A rigid structure was fabricated on a foam substrate.U-shaped slots were added in the lateral direction of the ra-diating surface for both size reduction and multiband opera-tion. Capacitive load was added in antenna veretical directionfor more compact size achievement. The relation between thecapacitance value and the antenna size reduction was studied.Acceptable bandwidth was achieved for all bands of operationby controlling the gap width of the U-shaped slots. The an-

NASHAAT et al.: SINGLE FEED COMPACT QUAD-BAND PIFA ANTENNA 2635

Fig. 8. Simulated radiation pattern of quad-band PIFA with 10 PF shortingcapacitor plate at four different resonating frequencies at (a) parallel E-plane atphi = 0 and (b) perpendicular H-plane at phi = 90.

tenna gain and radiation patterns were found to be reasonable atthe four bands of operation. Exprimental measurments showedgood agreement with simulated results that verfiied the designs.The new design with the technique of single feed multibandPIFA proposed in this paper will find useful applications in wire-less and mobile communication

ACKNOWLEDGMENT

The authors would like to thank Prof. E. A. Abdallah for herhelpful review and comments on the initial manuscript. The au-thors would also like to thank the anonymous reviewers for theirconstructive comments.

REFERENCES

[1] G. R. Kadambi, K. D. Simmons, J. L. Sullivan, and T. Hebron, “Singlefeed multiband PIFA for cellular and non cellular applications,” Centu-rion Wireless Technologies, Inc., 2002.

[2] Bluetooth. [Online]. Available: www.anycom.com; Bluetooth@anycom.com

[3] M. Sanad and N. Hassan, “A compact dual band microstrip antenna forportable GPS/cellular phones,” presented at the Proc. IEEE AntennasPropagation Int. Symp., Salt Lake City, UT, Jul. 1999.

[4] P. Salonen, M. Keskilammi, and M. Kivikoski, “Single-feed dual planarinverted-F antennas with U-slot,” IEEE Trans. Antennas Propag., vol.48, no. 8, pp. 1262–1264, Aug. 2000.

[5] D. Nashhat, H. Elsadek, and H. Ghali, “Dual-Band reduced size PIFAantenna with U-slot for bluetooth and WLAN applications,” presented atthe Proc. IEEE Antennas Propagation Int. Symp., Columbus, OH, Jun.22–27, 2003.

[6] K. Ogawa and T. Uwano, “A diversity antenna for very small 800-MHzband portable phone,” IEEE Trans. Antennas Propag., vol. 42, no. 9, pp.1342–1345, Sep. 1994.

[7] A. T. Arkko and E. A. Lehtola, “Simulated impedance bandwidth, gains,radiationpatterns and SAR values of a helical and a PIFA antenna ontop of different groundplanes,” in Proc. Inst. Elect. Eng. 11th Int. Conf.Antennas Propagation, Apr. 2001, pp. 651–654.

[8] A. T. Arkko, “Effect of ground plane size on the free-space performanceof a mobile handset,” Nokia Mobile Phones Rep., Finland, 2002.

[9] Y. X. Guo, C. L. Mak, K. M. luk, and K. F. Lee, “Analysis and design ofL-probe proximity fed patch antennas,” IEEE Trans. Antennas Propag.,vol. 49, no. 2, pp. 145–149, Feb. 2001.

[10] C. R. Rowell and R. D. Murch, “A capacitively loaded PIFA for compactmobile telephone handsets,” IEEE Trans. Antennas Propag., vol. 45, no.5, pp. 837–841, May 1997.

[11] K. l. Virga and Y. Rahmat-Sami, “Low profile enhanced-bandwidthPIFA antennas for wireless communication packaging,” IEEE Trans.Microwave Theory Tech., vol. 45, no. 10, pp. 1879–1888, Oct. 1997.

Dalia Mohammed Nashaat was born in Giza,Egypt, in 1976. She received the B.S. and M.S.degrees in electrical and communication engineeringfrom Ain Shams University, Cairo, Egypt, in 1998and 2004, respectively, where she is currentlyworking toward the Ph.D. degree.

Her master’s thesis was about the design ofmicrostrip PIFA antennas for mobile handsets. From2000 to 2004, she was a Research Assistant andsince 2004, she has been an Assistant Researcherwith the Microstrip Department, Electronic Research

Institute, Cairo. She has received one patent and published seven papers inpeer-refereed journals and international conferences in the area of microstripantenna design. Her current research interests are in microstrip antennas theoryand design and electromagnetic wave propagation.

Hala A. Elsadek (S’01–M’02) was born in Cairo,Egypt, in August 1969. She received the B.S. degreein electronics and communication engineering fromAin Shams University, Cairo, in 1991. She receivedthe M.S. degree from Gunma University, Japan, in1996 and the Ph.D. degree from Cairo University,Cairo, in 2002, both in electronics and communica-tion engineering.

From 2000 to 2002, she was with the Universityof California, Irvine, as a Graduate Researcher in theHigh Frequency Electronics Laboratory. From 1997

to 2000, she was a Research Assistant with the Microstrip Department, Elec-tronics Research Institute, Cairo. She is currently an Assistant Professor withthe same institute. She has received two patents and published more than 25 pa-pers in peer-refereed journals and international conferences in the areas of mi-crostrip antenna design, antenna systems and arrays, full wave electromagneticmethods of analysis (MOM, FDTD), microwave holography, and 3-D interac-tive wireless devices.

Dr. Hala has been a Reviewer for the IEEE Antennas and Propagation Societysince 2003.

Hani Ghali (S’85–M’95) was born in Cairo, Egypt,in 1961. He received the B.Sc. and M.Sc. degreesin electronics and communication engineering fromAin Shams University, Cairo, in 1983 and 1988, re-spectively, and the Ph.D. degree in electronics fromthe National Institute of Applied Sciences, Rennes,France, in 1992.

In 1989, he joined the National Institute of Ap-plied Sciences, Rennes, France. Since 1992, he hasbeen with the Electronics and Communication En-gineering Department, Faculty of Engineering, Ain

Shams University, initially as an Assistant Professor and currently as a Pro-fessor. His field of interest includes RF microelectromechanical systems, micro-machined antennas, applications of fractal and space-filling curves in antennasand circuits, ultrawide-band antennas, and genetic optimization.

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