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Wideband Patch Antenna for 5-6 GHz WLANApplications

M. A& , T. Siltironnarit', V. K. Kunda', H A . Hwang', R. A. Sadle?, and G.

J. Hayes'I . Department of Elec trical Engineering, University of South Carolina,

Swevringen Building, Columbia. SC 29208. Tel: (803). 17 1 1488: Email:alimo@enm.sc.edu

2. Sany Ericsson Mobile Communications, P.O. Box 13969, 7001 DevelopmentDrive, Research Triangle Park, NC 27709.

Abstract

A wideband microstnp patch antenna has been analyzed, designed,

fabricated, and measured for wireless local area network (LAN) applications in

the 5-6 GHz frequency range. The antenna is internal to the housing of a personal

digital assistant (PDA), such as a PALM organizer and has the dimensions of 28

mm by 9 mm b y 3 mm on FR4 substrate. The antenna meets o r exceeds the

bandwidth requirements for the dual-band IEEE 802.1 l a wireless local areanetwork (WLAN) applications (5.15-5.35 GHr and 5.725-5.825 GHz) within 2: l

VSWR.

Introduction

The growth of wireless communications has created a tremendous demand

for miniature antennas. Since many devices support multiple operating hands

there is a growing need for minialure wide or multi-band antennas. The most

popular among miniature antenna choices is the microstrip patch antenna. Such an

antenna, however, is inherently narrow-band [I] . Therefore, researchers areexploring methods and techniques I o design widc or multi-hand patch antennas.

Most recent examples of research on wideband microstrip patch antennas can be

found in [21-[31.

The studies presented in [2]-[3] address the bandwidth issue using L-probe

proximity fed annular ring design and E-shaped design. We present a different

approach. We focus on a number of specific issues such as, (I ) wideband o r

multi-band operation specifically in th e IEEE 802.1 la wireless local zrca network

bands (5.15-5.35 GH z and 5.725-5.825 GHz), (2) thin (3 mm) design that can be

directly printed on the PCB (printed circuit board) and packaged (within Ih e

housing of a PDA). and (3) nearly uniform angular cnverage which IS generallyrequired for these kind of applications.

We consider a folded microstrip patch configmiltion described in [4].

Among other folded patch design concepts in the literature includes he one in [SI.

The antenna proposed in [41 is a narrowband antenna suitable for GP S or

Bluetooth application. We present a wideband design achieved through proximity

parasitic coupling that covers the 5.15 to 5.35 and 5.125 to 5.825 GH z bands

within 2:1 VSWR. The proposed design can also operate from 5. 1 to 5.9 GH z

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within 2 . 5 ~ 1VSWR making it suitable for widehand application. The dua-hand

or wideband design has been made possible by optimizing and utilizing t h e

coupling between the radiating parch and an extended PCB ground plane.

Antenna Geometry

The geometry of the antenna is shown in Figs. l a and I h. The top YEW is

shown in Fig. la . T he dimens ions of the PCB ar e I2 0 mm by 80 mm by 2 mm .

The folded microstrip patch antenna is printed on tw o layers bf dielectrics each

with ~ ~ 4 . 7 .he longer dimension of the patch is along the x-axis while the

shorter dimension is along the y-axis. More detail information about the antenna

feed can be obtained from Fig. 1h. The top PCB ground has been extcnded so that

it is in the middle o f b t h la ye rs o f the folded patch. This extended ground layer

when coupled with the driven patch provides the widehand characteristic. Thisconcept of multi-hand operatio n utilizing couplin g between radiating and parasitic

elements is known [6]-[8]. We present a detailed analysis using HFSS (high

frequency structure simulator) [9 ] which include impedance, bandwidth, radiation

pattern. and gam as function of antenna parameters, substrate parameters. and

PCB size.

Results

Computed VSWR versus frequency data as a function o f the overlapfunction, g r IS shown an Fig. 2d . Clearly for gr=3 mm. the coupling between the

driven patch and the parasitic ground is minimal since the overlap region is - 1

mm . As g r increases to 4, 5 . 1, nd 8 mm coupling increases and the antenna

starts to show broadband or dual-band response. When gr increases beyond 5 mm

the midhand VSWR starts to increase and for gr=7 and 8 mm the midhand

VSWR is considerably h igher making the antenna dual-band. To satisfy [he IEEE

802.1 la requirement the antenna can be operated either way as long as th e 5.15-

5.35 CHr and the 5.725-5.825 FHc bands fall within the specified VSWR

(preferably 2:l).Computed input impedance data as function of frequency are shown in

Fig. 2b. Note that as gr increases from 3 to 5 mm th e antenna impedance locus

shows B distinct loop indicating widehand im pedan ce characteristics. As g r startsto increase even further t h e loop slatis to get larger. Still there are tw o resonances.

but bandwidth is not as wide since the impedance locus is much larger.

A laboratory prototype o f the proposed antenna was built and tested far

VSWR. The antenna was mountcd on an FR3 printed circuit board and fed using

a coaxial cable. Unclad 1.S mm thick FR4 substrate pieccs were used to mount theradiating elements on hoth sides. Measured VSWR data compared with computed

data are shown in Fig. 3a . The agreement between the measured and th e

computed data is quite good. Computed and measured resonant frequencies are

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abnut the same. The measured bandwidths in both bands arc also in good

agreement with the computed bandwidths within 2:1 VSWR. It is clear that the

antenna satisfies the bandwidth requirements for the IEEE 802.1la LAN (5.15-

5.35 CH I and 5.725-5.82s GHz). The midband VSWR is only as high as 2.7:1.

Fig. 3b shows the current distribution for the antenna. We can clearly

observe that the intensity of cunent increases particularly in the overlap regionbetween the radiating element and the extended ground plane. This indicates the

presence of coupling between the radiating element and the extended ground

plane, which increases in intensity as the g r increases even further.

References

1. D.M. Pozar and D.H. Schaubert, Microstrip Antennas, Editors. IEEE

Press, 1995

2. Y. -X . Guo, K. -M. Luk, and K. -F. Lee, “L-Probe Proximity-Fed Annular

Rine Microstrio Antennas.” IEEE Trans. Aiireiinas Prooamt. . vol. 49 . no.I . ”I . pp . 19-21,Jan. 2001.

3. F. Yane, X. -X. Zhane, X . Ye, and Y. Rdhmat-Samii. ” Wide-Band E--Shaped Parch Antennas for Wireless Communications,” IEEE Trans.

Anter,!iuu Propugul., vol. 49, no. 7, pp. 1094-1100, July. 2001.

4 . A. Faraone and D. McCoy, ‘The Folded Patch Omnidirectional Antenna.”

IEEE Antennas and Propoagation Society International Symposium

Digest, 2001, vol. 2 . pp. 712-715.5 . C. G. Christodoulou. P. F. Wahid. M. R . Mahbub, and M. C. Bailey,

“Design of a minimum-loss series-fed foldable microstep,” IEEE Trans.

Antennas a n d P r o p q a 1 . . pp . 1264 -1267, August 2000,

6 . H. E. King and J. L. Wong, “An experimental S tudy of a balun-fed open-

sleeve dipole in front of a metallic reflector,” IEEE Trans. Antennas and

Propugol. ,pp. 201-204, March 1972.

7 . M . Ali. M. Okoniewski, M .A. Stuchly. and S.S. Stuchly, “Dual-Frequency

Strip-Sleeve Monopole for Laptop Computers,” I EEE Trans. Antennas

urrdPropagat. . Vol. 47. No. 2. Feb. 1999. pp. 317-323.8. M. Ali, G.J. Hayes, Huan Sheng-Hwung and R.A. Sadler, “Design of a

Multi--Band Intemill Antenna for Third Generation Mobile Phone

Handsets,” IEEE T m m Anterinas and Propagat. (to appear April 2003).

9. Ansoft HFSS, Ansoft Corporation: hrto:liwwwaosoft.co.iolhf~~.htm.

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. .4 5 - or --i

Figure 1:AnCma geometry.

(a) (b)

Figure 2 (a) computed VSWR versus frequency dam and (b) Smith chart plot aithg r(m)

ssparameter.

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