Document Sample
					                           TECHNICAL FEATURE
         AVE JOU





        OR             A
             IAL B O

                           A 2.4 GHZ
                           PLANAR PRINTED DIPOLE
                           ANTENNA FOR WLAN AND
                           WIRELESS COMMUNICATION
                           This 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 to
                           select 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.

                               n wireless communication systems, such as     ly. In order to effectively receive the commu-
                               wireless local area networks (WLAN), re-      nications signal, a polarization-diversity anten-
                               search and development efforts are aiming     na for wireless communications may become
                           at smaller size and better performance. In ad-    an important requirement. A polarization-di-
                           dition to the use of signal processing tech-      versity antenna may have a pair of linearly-po-
                           niques to improve communication channel ca-       larized antennas, and the radio signal received
                           pacity, the radiation characteristics of the      on both antenna is sampled and compared at
                           portable antenna system is also very important
                           for communication performance.
                              In urban or indoor environments, the radio     HUEY-RU CHUANG, LIANG-CHEN KUO,
                           wave will propagate through complicated re-       CHI-CHANG LIN AND WEN-TZU CHEN
                           flection or scattering processes. The polariza-   National Cheng Kung University,
                           tion of the radio wave may change significant-      Tainan, Taiwan
                                                    TECHNICAL FEATURE
                                                                                                                                    DIPOLE STRIP
        VERTICAL                                    PRINTED DIPOLE ANTENNA                                                           GROUND METAL PLANE
                                                                                                 HORIZONTAL                             VIA-HOLE


                           PRINTED DIPOLE ANTENNA

                                                                                                                                   1                                  COAXIAL
                                                                                                                                       PRINTED BALUN
                                                         BALUN           POLARIZATION-                                                   PRINTED
                                                                           DIVERSITY                                                   DIPOLE STRIP
                                                                           PIN DIODE
                                                                           SELECTION                                                       MICROSTRIP LINE STRIP (TOP)
                                                                            CIRCUIT                                                        DIPOLE STRIP & MICROSTRIP
                                                                                                                                            GROUND METAL (BOTTOM)

                                                                                                                            ▲ Fig. 2 Printed dipole antenna
▲ Fig. 1   A 2.4 GHz polarization-diversity antenna.                                                                        with a microstrip balun.

                  3.0                                                                               E-PLANE                                     H-PLANE
                                                                                                       0                                           0
                                                                                                0             30                          330             30
                                                                                          0                          6
                                                                                                                     60            300                          60

                                                                                       270                             90
                                                                                                                       9          270                         9
                  1.5                                                                                 − −     −     −5 5                           − −25 15 − 5
                                                                                                                                                       5 5

                                                                                          0                         120
                                                                                                                    1                0
                                                                                                                                   240                          120
                    2.2   2.3    2.4    2.5                            2.6
                           FREQUENCY (GHz)                                                      0
                                                                                              210             150
                                                                                                              1                             0
                                                                                                                                          210             1
            (a)                                                                  (b)                  180                   (c)                    180

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

certain time intervals. Then the an-                                   of the realized printed dipole-anten-                dimensions of the printed dipole strip
tenna with the best signal quality is                                  na are compared. The measured radi-                  and the microstrip balun structure
selected.                                                              ation characteristics of the polariza-               are determined by numerical simula-
   A typical dipole antenna radiates a                                 tion-diversity planar dipole antenna,                tion, using HFSS.
vertically polarized EM wave and has                                   including input SWR, radiation pat-                      The simulation results for a 2.4
an omnidirectional antenna pattern. In                                 tern coverage and polarization diver-                GHz printed dipole antenna placed
order to have a preferred planar an-                                   sity, are presented.                                 horizontally with a microstrip via-hole
tenna structure for this 2.4 GHz polar-                                                                                     balun and fabricated on an FR-4 sub-
ization-diversity antenna, a printed di-                               PRINTED DIPOLE ANTENNA                               strate are shown in Figure 3. The in-
pole antenna with a microstrip via-                                    WITH MICROSTRIP BALUN                                put SWR is less than 1.5 from 2.2 to
hole balun is designed. As shown in                                        As shown in Figure 2, a printed                  2.6 GHz. The simulated E- and H-
Figure 1, two orthogonal printed di-                                   dipole antenna has a printed mi-                     plane antenna patterns are very close
pole antennas, for vertical and hori-                                  crostrip balun which acts as an unbal-               to those of an ideal dipole antenna,
zontal polarization, respectively, are                                 anced-to-balanced transformer from                   where the H-plane pattern is omnidi-
combined and fabricated on a PCB                                       the feed coaxial line to the two print-              rectional. Figure 4 is a photograph of
substrate. PIN diodes are used to                                      ed dipole strips. The length of the di-              a realized antenna. The measured in-
switch and select the desired antenna                                  pole strip and the balun microstrip                  put SWR and antenna patterns (mea-
polarization.                                                          are both about 1/4 wavelength. The                   sured with the dipole placed vertically)
   In the antenna design, the high                                     ground plane of the microstrip line                  agree well with the simulation results,
frequency structure simulator                                          and the dipole antenna strips are in                 as shown in Figure 5.
(HFSS), based on a 3D FEM, was                                         the same plane. A via-hole permits
employed for design simulation of the                                  the feed point 2 of a printed dipole                 PLANAR
complete printed dipole structure. A                                   strip to have the same phase as the                  POLARIZATION-DIVERSITY
printed dipole antenna and a polar-                                    feed point 1 of the other printed di-                PRINTED DIPOLE ANTENNA
ization-diversity planar dipole anten-                                 pole strip. Due to the 180° phase dif-                  Figure 6 shows photographs of a
na board (with a polarization-selec-                                   ference between the top strip and the                realized 2.4 GHz planar polarization-
tion PIN diode circuit) have been                                      ground plane of the microstrip line,                 diversity antenna consisting of two
fabricated on FR-4 PCB substrates. A                                   the feed point 2 of the printed dipole               orthogonal printed dipole antennas
complete 3D structure FEM simula-                                      strip will have 180° phase difference                with a polarization-switched PIN
tion and the measured performance                                      with the other feed point 1. Accurate                diode circuit. Each printed dipole has
                               TECHNICAL FEATURE




                                                                      2.20       2.28           2.36     2.44          2.52           2.60
                                                                                               FREQUENCY (GHz)
 (a)                                                                                                                  Eφ
                                                                                 0                                    90
                                                                           330           30                     120            60
                                                                                  −10                                  −10
                                                                     300          −20           60     150             −20            30
                                                                                        (dB)                                 (dB)
                                                                                  −30                                  −30

                                                                 270              −40−30−20−10 90     180              −40−30−20−10 0

                                                                     240                        120    210                            330

                                                                           210            150                  240              300
                                                                                 180                                  270

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

▲ Fig. 4   A 2.4 GHz printed dipole antenna
with a microstrip via-hole balun; (a) top view                                                                3.0
and (b) bottom view.
a microstrip via-hole balun. The ter-

minals of the two baluns are connect-                                                                         2.0
ed to a PIN diode selection circuit.
Voltages from the transceiver circuit                                                                         1.5
(±5.0V) are fed through a cable to the
input of the PIN diode circuit sec-                                                                             2.2    2.3     2.4     2.5    2.6
tion, to short or open-circuit the PIN                                                                                   FREQUENCY (GHz)
diodes. Hence, either the vertical or
horizontal printed dipole can be se-                                                                  ▲ Fig. 7   Input SWR simulation of a 2.5
                                                                                                      GHz polarization-diversity dipole antenna
lected and connected to the trans-                                                                    with the vertical dipole selected.
   Since the two dipoles are very                                                                     polarization field. Figure 9 shows the
close to each other and near the PIN                                                                  simulation results with the horizontal
diode circuit section, EM coupling                                                                    dipole antenna selected (–5V to PIN
will degrade the performance of each                                                                  diode switching circuit). Results simi-
dipole. Figure 7 shows the input                                                                      lar to the ones obtained for the verti-
SWR simulation results with the ver-                                                                  cal dipole antenna can be observed,
tical dipole antenna selected (+5V to                                                                 except that the dominant polarization
PIN diode switching circuit). The in-                                                                 is the horizontal (E φ ) field, which
put SWR is less than 2 from 2.25 to                                                                   agrees with the selection of the hori-
2.60 GHz. The simulated E- and H-                                                                     zontal dipole.
plane antenna patterns are all very                                                                      The measured antenna input SWR
close to those of an ideal dipole an-                                                                 with vertical or horizontal dipole se-
tenna, of which the H-plane pattern                                                                   lection confirms the input SWR of
is still omnidirectional, as shown in                                                                 each dipole antenna (through the
Figure 8. Note that the dominant                                                                      PIN diode selection circuit) is less
polarization is the vertical (Eθ) field,                                                              than 1.5 from 2.2 to 2.6 GHz, which
which agrees with the selection of the                                                                agrees with the HFSS simulation re-
vertical dipole. The antenna pattern                                                                  sults. The measured antenna patterns
has some attenuation in the direction                                                                 with the selection of the vertical or
of the PIN diode circuit board. It can           (b)
                                                                                                      horizontal dipole shows that for the
also be seen that a certain level of the                                                              selection of the vertical dipole, the
input RF signal is induced to the hor-           ▲ Fig. 6   A 2.4 GHz planar polarization-
                                                                                                      H-plane pattern is still quite omnidi-
                                                 diversity antenna with a polarization-
izontal antenna path by EM coupling,             switched PIN diode circuit; (a) top view             rectional (as an ideal vertical dipole)
which generates some level of cross-             and (b) bottom view.                                 with some attenuation in the direc-
                                        TECHNICAL FEATURE
               Eθ at   =0                                   Eθ at θ = /2
         330                     30                   330                  30                                        3.0

   300                                 60       300                               60                                 2.5

  270                            −       90   270                                   90
                        5−            −5 5
                                       5                         −35 25−
                                                                  35 2           −5 5
   240                                 120      240                               120
         210                     150                  210                  150                                         2.2          2.3     2.4     2.5             2.6
                   180                                          180
 (a)                                          (b)                                                          (a)                        FREQUENCY (GHz)

               Eφ at φ = 0                                  Eφ at θ = /2                                Eφ at θ = π/2                                     Eφ at φ = 0
                                                                                                              0                                                0
         330                     30                   330                  30                     330                        30                     330                   30

   300                                 60       300                               60        330                                     60       330                                60

 270                                 90       270                                   90    270                                 90          270                               90
                        5−   −15 −5 5                             −   25− −5 5
                                                                      25                                         −35−25−15 −5 5                                −35−25−15 −5 5

   240                                 120      240                               120       240                                     120      240                                120

         210                 150                      210                  150                    210                      150                      210                   150
 (c)              180                         (d)               180                                            180                                            180
                                                                                          (b)                                                      (c)
                                                                                                        Eθ at θ = π/2                                     Eθ at φ = 0
▲ Fig. 8    Simulation of a 2.5 GHz polarization-diversity dipole                                             0                                                0
antenna with the vertical dipole selected; (a) Eθ-field E-plane pattern,                          330                        30                     330                   30
(b) Eθ-field H-plane pattern, (c) Eφ-field (cross-polarization) E-plane
pattern and (d) Eφ-field (cross-polarization) H-plane pattern.                              330                                     60       330                                60

tion of the PIN diode circuit board. Figures 10 and 11                                     270                                90           270                               90
show the mesured SWR and antenna patterns, respective-                                                           −35−25−15 −5 5                                 −35−25−15 −5 5

ly. A certain level of the induced cross-polarization pat-                                  240                                     120      240                                120
tern is observed as predicted by the HFSS simulation due
to the proximity of the horizontal dipole strip and the PIN                                       210
                                                                                                                           150                      210
diode circuit board. As for the selection of the horizontal                               (d)                                              (e)
dipole, the E-plane pattern is also close to that of an ideal
horizontal dipole. Also, the induced cross-polarization
pattern is observed, which is the same situation as the se-                              ▲ Fig. 9    Simulation of a 2.4 GHz polarization-diversity printed
lection of the vertical dipole. The measured data shows a                                dipole antenna (with the horizontal dipole selected); (a) input SWR,
good agreement with the HFSS simulation results and                                      (b) Eφ-field E-plane pattern, (c) Eφ-field H-plane pattern, (d) Eθ-field
how the antenna polarization-diversity is working.                                       (cross-polarization) E-plane pattern and (e) Eθ-field (cross-
                                                                                         polarization) H-plane pattern.
    3D FEM design simulation, realization and measure-
ments of a 2.4 GHz printed dipole antenna (with a mi-                                                          9.0
crostrip via-hole balun) and a planar polarization-diversity                                                   7.0

printed dipole antenna are presented. The planar polariza-                                                     5.0
tion-diversity antenna consists of two orthogonal printed di-                                                  3.0
pole antennas for vertical and horizontal polarization and is                                                  1.0
                                                                                                                2.20         2.28     2.36  2.44    2.56        2.60
fabricated on a FR-4 PCB board. A PIN diode switching cir-                                                                          FREQUENCY (GHz)
cuit is used to select the desired antenna polarization. Satis-                                          (a)
factory agreement between simulation and measurements is
observed. The measured input SWR of the realized printed                                                       9.0
dipole antenna is less than 1.5 from 2.2 to 2.6 GHz. The                                                       7.0

measured input SWR of the vertical and horizontal dipole                                                       5.0
(through the PIN diode switching circuit) of the realized pla-                                                 3.0
nar polarization-diversity antenna is less than 1.5 from 2.3 to                                                1.0
                                                                                                                2.20         2.28     2.36  2.44    2.56        2.60
2.6 GHz. The measured E- and H-plane patterns of the po-                                                                            FREQUENCY (GHz)
larization-diversity antenna show that the selected vertical or                                          (b)
horizontal dipole have a performance close to a single dipole
antenna in a vertical or horizontal position. The designed                               ▲ Fig. 10   Measured input SWR of a 2.4 GHz polarization-diversity
planar polarization-diversity antenna can be used for wireless                           printed dipole antenna; (a) vertical dipole selection
communication and WLAN applications.                                                     and (b) horizontal dipole section.
                                  TECHNICAL FEATURE
                                                                                                                               Liang-Chen Kuo
                            CO-POLARIZATION        CROSS-POLARIZATION                                                          received his BSEE
                                                                                                                               degree from Nan-Tai
                       0                                                  0                                                    Institute of Technology,
             330                  30                           330                   30                                        Tainan, Taiwan, and
                         10                                                −10                                                 his MSEE degree from
                                                                                                                               Tatung Institute of
       300              −20
                         2                60             300               −20
                                                                            20               60                                Technology, Taipei,
                                                                           −30                                                 Taiwan, in 1987 and
                          0                                                 30
                                                                                                                               1996, respectively. He
                        −     −   −     −10 90
                                         10                                −     −   −     −10                                 is currently working
  270                                              270                                           90
                                                                                                                               toward his PhD degree
                                                                                                      in electrical engineering from National Cheng
                                                                                                      Kung University, Tainan, Taiwan. His research
       240                                120            240                                 120      interests include computational
                                                                                                      electromagnetics and antenna design.
             210                  150                          210                   150                                      Chi-Chang Lin
                      180                                                180                                                  received his BSEE and
 (a)                                               (b)                                                                        MSEE degrees from
                                                                                                                              Tatung Institute of
▲ Fig. 11   Measured co-and cross-polarized patterns of a 2.4 GHz polarization-diversity                                      Technology, Taipei,
printed dipole antenna; (a) vertical dipole selected and (b) horizontal dipole selected.                                      Taiwan, in 1999 and
                                                                                                                              2001, respectively. He
ACKNOWLEDGMENT                                                              Huey-Ru Chuang                                    is currently working
                                                                            received his BSEE and                             toward his PhD degree
  The authors would like to thank                                           MSEE degrees from
Ansoft Inc. for its support of the                                                                                            in electrical
                                                                            National Taiwan                                   engineering from
HFSS software. ■                                                            University, Taipei,                               National Cheng Kung
                                                                            Taiwan, in 1977 and       University, Tainan, Taiwan. His research
References                                                                  1980, respectively, and   interests include EM simulation and
 1. K. Fujimoto and J. R. James, Mobile An-                                 his PhD degree in         microwave antenna design.
    tenna Systems Handbook, Artech House                                    electrical engineering
                                                                            from Michigan State                                Wen-Tzu Chen
    Inc., Norwood, MA 1994.
                                                                            University, East                                   received his PhD
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                                                                            Lansing, MI, in 1987.                              degree from National
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                                                  From 1987 to 1988, he was a post-doctoral                                    Cheng Kung
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