A three-antenna MIMO system capable of generating a wide operating bandwidth of 2400-5850 MHz for access-point applications is introduced. The proposed design is based on a bent metal-plate monopole antenna with a compact size of 20 × 20 × 14 mm3. The three antennas are equally spaced along the perimeter of a circular ground and all generate a wide bandwidth of larger than 4 GHz. With the antenna short-circuiting facing the center of the ground, not only the overall antenna size is reduced but also good isolation of less than -20 dB can easily be obtained. Calculated envelope correlation is also less than 0.002 across the operating band.

1. 2008 IEEE AP-S
International Symposium
Internal Wideband Monopole
Antenna for MIMO Access-
Point Applications
*Saou-Wen Su, Ph.D.
Network Access Strategic Business Unit
Lite-On Technology Corp., Taipei, Taiwan
*E-mail: stephen.su@liteon.com
July 9, 2007

2. Outlines
(I) Introduction
Conventional wideband antennas
Conventional MIMO antennas
MIMO technology and antenna design
consideration
(II) Design Considerations & Results
Constructed prototype
Antenna performance
(III) Application Examples
Antenna on desktop chassis
Remote AP antenna
(IV) Conclusion
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3. Conventional Wideband Antennas 1
Wideband planar monopole antenna
antenna perpendicular to a large ground plane
impedance matching controlled by
shaping antenna geometry and/or
adjusting antenna structure around feeding
MOTL, vol 42, pp 463-466, IEEE AP, vol 53, pp 1626-1629,
Sep 2004 Apr 2005
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4. Conventional Wideband Antennas 2
Wideband planar monopole antenna in
various shapes and sizes
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5. Conventional MIMO Antennas 1
Height incl. antenna and
enclosure at least > 80 mm
Antenna type: dipole,
monopole, collinear antenna
D-link wireless N series
Invax MIMO antenna
5 M.gear MIMO antenna

6. Conventional MIMO Antennas 2
for 802.11b/g
3Com wireless 11n adapter
for 802.11b/g/a
Despite internal antennas,
only single or dual-band Airgain MaxBeam smart antenna
operation can be obtained
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7. MIMO Technology
use multiple antennas to increase data throughput
signals transmitted in the same radio channel at the same time
multiple wireless data capacity w/o extra frequency spectrum
multidimensional signals: each of multiple signals is
transmitted from a different radio and antenna
http://www.eetasia.com/ART_8800432129_499488_TA_3d8cb44b.HTM
Closely spaced antennas give rise to mutual
coupling
Effects of mutual coupling
change in driving point impedance of each
antenna less efficient power transfer
change in radiation pattern constructive
and destructive interference
Z12: induced voltage on ant.1 by driving current on ant. 2
7 antenna platform design rules for MIMO wireless architectures, Intel

8. MIMO Antenna Design Consideration
Isolation (e.g. S21, S12)
larger antenna separation results in less mutual coupling (better isolation)
for two antennas at the same frequency, the separation is empirically chosen
about 0.5 wavelength of the antenna operating frequency for isolation < -15dB
arrangement of antennas and positions of antenna short-circuiting can largely
affect isolation integration of cellular and WLAN antennas
MOTL, vol. 47,Nov. 2005
with design techniques, we can locate antennas in the vicinity while maintaining
small isolation level
Envelope correlation
numerically/experimentally obtained from far-field radiation pattern of the antenna
ρe < 0.3 (Intel and Dell spec.)
can be derived directly from S parameters
EL, vol. 39, May 2003
Radiation pattern (polarization)
Other issues
coaxial-cable loss (attenuation) (dB/m): @2.4 GHz ~ 2.7 dB; @5.2 GHz ~ 4.1 dB
cable routing (1.13mm, manufacturing) and length (power)
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9. Design Consideration 1-
Three-antenna MIMO system
equally spaced along the perimeter
of a circular ground
MIMO system comprises:
three bent, metal-plate
monopole antennas and
a circular ground;
Flat plate onto a base of size
20 x 20 x 14 mm3
9 US/TW/CN patent pending

10. Design Consideration 2-
Proposed low-profile, wideband antenna
Antenna mainly comprises:
a shorted monopole antenna
and
a supporting metal plate;
Antenna height about 11%
wavelength of lower-edge
operating frequency at 2.4 GHz
prior art
IEE Microwave AP, vol 153,
pp 456-460, Oct 2006
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11. Design Consideration 3-
S parameters and envelope correlation
10-dB RL BW easily covers
entire band of 2400~5850 MHz;
S21 remains < -20 dB
S11: reflection coefficient
S21: isolation
Band 1: 2400-2690 MHz
Band 2: 3400-3800 MHz
Band 3: 5150-5850 MHz
11 MOTL, vol 48, pp 832-834, May 2006

12. Design Consideration 4-
Envelope correlation
1987
from far-field antenna radiation pattern
2003
from S parameters
2005
commonly cited!
12 correct form for 3 antenna!!

13. Design Consideration 5-
Measured 3-D radiation patterns
Measured radiation patterns
at 2.5, 3.6, and 5.5 GHz
Peak gain levels about 2.4, 2.5, and
3.6 dBi over Bands 1, 2, and 3;
Measured radiation efficiency > 73%
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14. Applications Examples 1.2-
Antenna on desktop chassis
antenna carrier
three MIMO
three MIMO
antennas
antennas
strain relief
on chassis
antenna location
US/TW/CN patent pending
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15. Applications Examples 2.2-
Remote AP antenna
antenna fed by long coaxial cable
for flexibility in arrangement
low profile
low profile
20 mm only
20 mm only
circular ground
constructed prototype antenna
15 US/TW/CN patent pending
old hat!

16. Applications Examples 3.2-
Indoor AP antenna
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17. Conclusion
Proposed antenna has a low profile
(14 mm) and is easy to construct by
stamping a metal plate
Wide BW covers entire 2.4/5-GHz
WLAN and 2.5/3.5/5-GHz WiMAX
bands with low isolation (< -20 dB)
More designs of MIMO antennas
embedded in wireless AP, desktop,
and notebooks are in progress
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18. THANK YOU FOR YOUR ATTENTION!
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