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TECHNICAL FEATUREMICROW

AVE JOURNAL

ED

ITORIAL BO

ARD

REVIEWED

ly. In order to effectively receive the commu-nications signal, a polarization-diversity anten-na for wireless communications may becomean important requirement. A polarization-di-versity antenna may have a pair of linearly-po-larized antennas, and the radio signal receivedon both antenna is sampled and compared at

HUEY-RU CHUANG, LIANG-CHEN KUO,CHI-CHANG LIN ANDWEN-TZU CHENNational Cheng Kung University,

Tainan, Taiwan

In wireless communication systems, such aswireless local area networks (WLAN), re-search and development efforts are aiming

at smaller size and better performance. In ad-dition to the use of signal processing tech-niques to improve communication channel ca-pacity, the radiation characteristics of theportable antenna system is also very importantfor communication performance.

In urban or indoor environments, the radiowave will propagate through complicated re-flection or scattering processes. The polariza-tion of the radio wave may change significant-

A 2.4 GHZ

POLARIZATION-DIVERSITY

PLANAR PRINTED DIPOLE

ANTENNA FOR WLAN AND

WIRELESS COMMUNICATIONAPPLICATIONSThis article presents the design simulation, fabrication and measured

performance of a 2.4 GHz polarization-diversity printed dipole antenna for

wireless communication applications. Two orthogonal printed dipole antennas,

each with a microstrip via-hole balun for vertical and horizontal polarization, are

combined and fabricated on a PCB substrate. PIN diodes are used as switches toselect the desired antenna polarization. The 3D finite-element-method (FEM)

electromagnetic EM simulator, HFSS, is used in the design simulation of this

planar antenna structure. Numerical and measured results of the antenna

radiation characteristics, including input SWR, radiation pattern coverage and

polarization-diversity, are presented and compared.

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certain time intervals. Then the an-tenna with the best signal quality isselected.

A typical dipole antenna radiates avertically polarized EM wave and hasan omnidirectional antenna pattern. Inorder to have a preferred planar an-tenna structure for this 2.4 GHz polar-ization-diversity antenna, a printed di-pole antenna with a microstrip via-hole balun is designed. As shown in

Figure 1, two orthogonal printed di-pole antennas, for vertical and hori-zontal polarization, respectively, arecombined and fabricated on a PCBsubstrate. PIN diodes are used toswitch and select the desired antenna

polarization.In the antenna design, the high

frequency structure simulator(HFSS), based on a 3D FEM, wasemployed for design simulation of thecomplete printed dipole structure. Aprinted dipole antenna and a polar-ization-diversity planar dipole anten-na board (with a polarization-selec-tion PIN diode circuit) have beenfabricated on FR-4 PCB substrates. Acomplete 3D structure FEM simula-tion and the measured performance

TECHNICAL FEATURE

dimensions of the printed dipole stripand the microstrip balun structureare determined by numerical simula-

tion, using HFSS.The simulation results for a 2.4

GHz printed dipole antenna placedhorizontally with a microstrip via-holebalun and fabricated on an FR-4 sub-strate are shown inFigure 3. The in-put SWR is less than 1.5 from 2.2 to2.6 GHz. The simulated E- and H-plane antenna patterns are very closeto those of an ideal dipole antenna,where the H-plane pattern is omnidi-rectional.Figure 4 is a photograph ofa realized antenna. The measured in-put SWR and antenna patterns (mea-

sured with the dipole placed vertically)agree well with the simulation results,as shown inFigure 5.

PLANARPOLARIZATION-DIVERSITYPRINTED DIPOLE ANTENNA

Figure 6 shows photographs of arealized 2.4 GHz planar polarization-diversity antenna consisting of twoorthogonal printed dipole antennaswi th a pola ri za tion-swi tched PINdiode circuit. Each printed dipole has

of the realized printed dipole-anten-na are compared. The measured radi-ation characteristics of the polariza-

tion-diversity planar dipole antenna,including input SWR, radiation pat-tern coverage and polarization diver-sity, are presented.

PRINTED DIPOLE ANTENNAWITH MICROSTRIP BALUN

As shown in Figure 2, a printeddipole antenna has a printed mi-crostrip balun which acts as an unbal-anced-to-balanced transformer fromthe feed coaxial line to the two print-ed dipole strips. The length of the di-pole strip and the balun microstrip

are both about 1/4 wavelength. Theground plane of the microstrip lineand the dipole antenna strips are inthe same plane. A via-hole permitsthe feed point 2 of a printed dipolestrip to have the same phase as thefeed point 1 of the other printed di-pole strip. Due to the 180 phase dif-ference between the top strip and theground plane of the microstrip line,the feed point 2 of the printed dipolestrip will have 180 phase differencewith the other feed point 1. Accurate

VERTICALPOLARIZATION

PRINTED DIPOLE ANTENNA

PRINTEDDIPOLEANT

ENNA

MICROSTRIPBALUN

MICROSTRIP

BALUN

HORIZONTALPOLARIZATION

POLARIZATION-DIVERSITYPIN DIODE

SELECTIONCIRCUIT

Fig. 1 A 2.4 GHz polarization-diversity antenna.

PRINTEDDIPOLE STRIP

PRINTEDDIPOLE STRIP

GROUND METAL PLANE

VIA-HOLE

PRINTED BALUN

COAXIALSMA

MICROSTRIP

MICROSTRIP LINE STRIP (TOP)DIPOLE STRIP & MICROSTRIP

GROUND METAL (BOTTOM)

2

1

Fig. 2 Printed dipole antennawith a microstrip balun.

2.2.52.

FREQUENCY GHza

2.2.

3.

2.

2.

1.

1.

SWR

2

3

21 50

18b

2

3 60

3

33

H-PLANEE-PL N

18c

Fig. 3 Simulated performance of a 2.4 GHz printed dipole antenna placed horizontally; (a) input SWR, (b) E-plane patternand (c) H-plane pattern.

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TECHNICAL FEATURE

a microstrip via-hole balun. The ter-minals of the two baluns are connect-ed to a PIN diode selection circuit.Voltages from the transceiver circuit(5.0V) are fed through a cable to theinput of the PIN diode circuit sec-tion, to short or open-circuit the PINdiodes. Hence, either the vertical or

horizontal printed dipole can be se-lected and connected to the trans-ceiver.

Since the two dipoles are veryclose to each other and near the PINdiode circuit section, EM couplingwill degrade the performance of eachdipole. Figure 7 shows the inputSWR simulation results with the ver-tical dipole antenna selected (+5V toPIN diode switching circuit). The in-put SWR is less than 2 from 2.25 to2.60 GHz. The simulated E- and H-plane antenna patterns are all very

close to those of an ideal dipole an-tenna, of which the H-plane patternis still omnidirectional, as shown in

Figure 8. Note that the dominantpolarization is the vertical (E) field,which agrees with the selection of thevertical dipole. The antenna patternhas some attenuation in the directionof the PIN diode circuit board. It canalso be seen that a certain level of theinput RF signal is induced to the hor-izontal antenna path by EM coupling,which generates some level of cross-

polarization field.Figure 9 shows thesimulation results with the horizontaldipole antenna selected (5V to PINdiode switching circuit). Results simi-lar to the ones obtained for the verti-cal dipole antenna can be observed,except that the dominant polarizationis the horizontal (E) field, whichagrees with the selection of the hori-zontal dipole.

The measured antenna input SWR

with vertical or horizontal dipole se-lection confirms the input SWR ofeach dipole antenna (through thePIN diode selection circuit) is lessthan 1.5 from 2.2 to 2.6 GHz, whichagrees with the HFSS simulation re-sults. The measured antenna patternswith the selection of the vertical orhorizontal dipole shows that for theselection of the vertical dipole, theH-plane pattern is still quite omnidi-rectional (as an ideal vertical dipole)with some attenuation in the direc-

Fig. 4 A 2.4 GHz printed dipole antennawith a microstrip via-hole balun; (a) top viewand (b) bottom view.

(a)

(b)

Fig. 6 A 2.4 GHz planar polarization-diversity antenna with a polarization-switched PIN diode circuit; (a) top viewand (b) bottom view.

(a)

(b)

9.0

7.0

5.0

3.0

1.0 2.602.522.442.36

FREQUENCY (GHz)(a)

(b)

2.282.20

SWR

10

20

30

40302010

330 30

60300

270 90

120240

210 150

0

E E

180

10

20

30

40302010

120 60

30150

180 0

330210

240 300

90

270

(dB) (dB)

Fig. 5 Measured input SWR (a) and radiation patterns (b).

3.

2.

2.

1.

1.2.2.2.

FREQUENCY GHz

2.2.

W

Fig. 7 Input SWR simulation of a 2.5GHz polarization-diversity dipole antenna

with the vertical dipole selected.

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tion of the PIN diode circuit board.Figures 10 and 11show the mesured SWR and antenna patterns, respective-ly. A certain level of the induced cross-polarization pat-tern is observed as predicted by the HFSS simulation dueto the proximity of the horizontal dipole strip and the PINdiode circuit board. As for the selection of the horizontaldipole, the E-plane pattern is also close to that of an ideal

horizontal dipole. Also, the induced cross-polarizationpattern is observed, which is the same situation as the se-lection of the vertical dipole. The measured data shows agood agreement with the HFSS simulation results andhow the antenna polarization-diversity is working.

CONCLUSION3D FEM design simulation, realization and measure-

ments of a 2.4 GHz printed dipole antenna (with a mi-crostrip via-hole balun) and a planar polarization-diversityprinted dipole antenna are presented. The planar polariza-tion-diversity antenna consists of two orthogonal printed di-pole antennas for vertical and horizontal polarization and isfabricated on a FR-4 PCB board. A PIN diode switching cir-

cuit is used to select the desired antenna polarization. Satis-factory agreement between simulation and measurements isobserved. The measured input SWR of the realized printeddipole antenna is less than 1.5 from 2.2 to 2.6 GHz. Themeasured input SWR of the vertical and horizontal dipole(through the PIN diode switching circuit) of the realized pla-nar polarization-diversity antenna is less than 1.5 from 2.3 to2.6 GHz. The measured E- and H-plane patterns of the po-larization-diversity antenna show that the selected vertical orhorizontal dipole have a performance close to a single dipoleantenna in a vertical or horizontal position. The designedplanar polarization-diversity antenna can be used for wirelesscommunication and WLAN applications.

TECHNICAL FEATURE

a at = 2

2

3 6

33 3

a =

18a b

21 15

12

240

2

3 60

33 3

18c 1 15

12

1

24

2

3 6

33 30

a =

1821 15

12

240

2

3 6

33 3

18d 21 15

12

24

Fig. 8 Simulation of a 2.5 GHz polarization-diversity dipoleantenna with the vertical dipole selected; (a) E-field E-plane pattern,(b) E-field H-plane pattern, (c) E-field (cross-polarization) E-planepattern and (d) E-field (cross-polarization) H-plane pattern.

3.0

2.5

2.0

1.5

1.02.62.52.

FREQUENCY GHz(a)

(b) (c)

(d) e

2.2.2

0

180

352515

330

330

270

240

210 150

12

6

30

E at=/20

180

3525155 5

330

33

2

24

210 150

120

90

60

30

0

180

352515

330

330

270

240

210 150

12

6

300

180

3525155 5

330

33

2

24

210 150

120

90

60

30

SWR

E at= 0

E at=/2 E at= 0

Fig. 9 Simulation of a 2.4 GHz polarization-diversity printeddipole antenna (with the horizontal dipole selected); (a) input SWR,(b) E-field E-plane pattern, (c) E-field H-plane pattern, (d) E-field(cross-polarization) E-plane pattern and (e) E-field (cross-polarization) H-plane pattern.

9.0

7.0

5.0

3.0

1.02.602.562.442.36

FREQUENCY (GHz)(a)

(b)

2.282.20

SWR

9.0

7.0

5.0

3.0

1.02.602.562.442.36

FREQUENCY (GHz)

2.282.20

SWR

Fig. 10 Measured input SWR of a 2.4 GHz polarization-diversityprinted dipole antenna; (a) vertical dipole selectionand (b) horizontal dipole section.

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Huey-Ru Chuangreceived his BSEE andMSEE degrees from

National TaiwanUniversity, Taipei,Taiwan, in 1977 and1980, respectively, andhis PhD degree inelectrical engineering

from Michigan StateUniversity, East

Lansing, MI, in 1987.From 1987 to 1988, he was a post-doctoralresearch associate at the Engineering ResearchCenter of Michigan State University. From1988 to 1990, he was with the PortableCommunication Division of Motorola Inc., Ft.

Lauderdale, FL. He joined the department ofelectrical engineering of National Cheng KungUniversity, Tainan, Taiwan, in 1991, where he

is currently a professor. His research interestsinclude portable antenna design,RF/microwave circuits and RFIC/MMIC for

wireless communications, electromagneticcomputation of human interaction with mobileantennas, EMI/EMC, microwavecommunication and detection systems.

Liang-Chen Kuoreceived his BSEEdegree from Nan-TaiInstitute of Technology,Tainan, Taiwan, andhis MSEE degree fromTatung Institute ofTechnology, Taipei,Taiwan, in 1987 and

1996, respectively. Heis currently workingtoward his PhD degree

in electrical engineering from National ChengKung University, Tainan, Taiwan. His research

interests include computationalelectromagnetics and antenna design.

Chi-Chang Linreceived his BSEE andMSEE degrees fromTatung Institute ofTechnology, Taipei,Taiwan, in 1999 and

2001, respectively. Heis currently workingtoward his PhD degree

in electricalengineering fromNational Cheng Kung

University, Tainan, Taiwan. His researchinterests include EM simulation andmicrowave antenna design.

Wen-Tzu Chenreceived his PhDdegree from NationalCheng KungUniversity, Tainan,Taiwan, in 1998. He iscurrently an assistant

professor at theInstitute of Computerand Communication,Shu-Te University, Yen

Chau, Taiwan. Hisresearch interests include numericalcomputation of EM interaction between theantenna and the human body, and microwaveantenna design.

TECHNICAL FEATURE

ACKNOWLEDGMENTThe authors would like to thank

Ansoft Inc. for its support of theHFSS software.

References1. K. Fujimoto and J. R. James, Mobile An-

tenna Systems Handbook, Artech HouseInc., Norwood, MA 1994.

2. B. Edward and D. Rees, A BroadbandPrinted Dipole with Integrated Balun, Mi-crowave Journal, May 1987, pp. 339344.

3. K. Hettak, G.Y. Delisle and M.G. Stubbs, ANovel Variant of Dual Polarized CPW FedPatch Antenna for Broadband WirelessCommunications, IEEE Antennas andPropagation Society International Sympo-

sium Digest, Vol.1, 2000, pp. 286289.

4. L. Zhu and K. Wu, Model-based Charac-terization of CPS-fed Printed Dipole forInnovative Design of Uniplanar IntegratedAntenna, IEEE Microwave and GuidedWave Letters, Vol. 9, No. 9, September1999, pp. 342344.

5. N. Michishitai and H. Arai, A Polariza-tion-diversity Antenna by Printed Dipoleand Patch With a Hole, IEEE Antennasand Propagation Society InternationalSymposium Digest, 2001, pp. 368371.

18

330 3

1

1

60

CO-POLA IZATION C OSS-POLA IZATIO

3

2

a b

1224

21 1518

330 3

603

2

1224

21 15

Fig. 11 Measured co-and cross-polarized patterns of a 2.4 GHz polarization-diversityprinted dipole antenna; (a) vertical dipole selected and (b) horizontal dipole selected.