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7/18/2019 A Planar Reconfigurable Yagi-Uda Antenna With End-fire Beam Scan
Abstract — A novel planar reconfigurable antenna on a thindielectric substrate based on the Yagi-Uda design rationale isproposed. This design not only can provide the end-fire beamscan with high directivities (at least 7.6 dBi) over a 60° coveragebut also can operate at a fixed frequency without frequency shiftwhen beam scans. The efficiencies of the antenna in all scanningscenarios are better than 78.5% or −1 dBi in terms of the 3D
average gain. Index Terms — Reconfigurable antennas, planar antennas,
Yagi-Uda antenna, end-fire, beam scan.
I. I NTRODUCTION
Due to the increasing demand for portable devices with
GPS functions, the embedded GPS antennas have gained
more and more attractiveness. For better communication
with GPS satellites, the radiation patterns of the embedded
GPS antennas should direct to the sky [1]-[2]. Because of the
complex environment and weak GPS signal, reconfigurable
patterns with high directivities from the embedded GPS
antennas can enhance the GPS communication qualities.
Antennas with reconfigurable patterns in the broadside have
been well studied [3]-[4]; however, the planar antennas with
end-fire reconfigurable patterns will be more suitable to the
portable devices because of low profile and better
conformability [5]. A new planar reconfigurable Yagi-Uda
antenna with end-fire beam scan is hence designed especially
for the GPS functions in mobile devices, such as smartphones,
GPS navigators, Notebooks, or Ultra-Mobile PCs (UMPCs).
In addition, a WLAN access point or a smart antenna system
(SAS) with better scanning resolution can also be attained by
adequately placing the antennas in a special arrangement,
such as a triangle, a square, a pentagon, and so on.
II. PRINCIPLES
To achieve a highly directive pattern scanning in the end-
fire direction instead of the broadside one, a Yagi-Uda design
is used. In Fig. 1, this planar antenna consists of a driven
dipole, a reflector, a director, two floating arms, and six
switches. Besides, a phase shifter is designed to maintain the
target frequency workable without the significant return loss
degradation due to the frequency shift when the beam scans.
scans.return loss degradation because of the frequency shift
wh
(a) Top metal layer
(b) Bottom metal layer
(c) Tilted view (assuming the dielectric substrate is transparent)
antenna with high directivities when beam scans can achieve
more scan angles or finer angular resolutions by employing
more side directors. Besides, the size of the antenna can be
further reduced by clever transformation of the arms of the
driven dipole, such as the meander type. Furthermore, to
broaden the scanning coverage, the shape of the ends of the
driven arms can be tilted or curved. Last, by employing more
such proposed antennas in an appropriate arrangement, asimple smart antenna system (SAS) can be attained.
ACKNOWLEDGEMENT
The work was support by the National Science Council,
Taiwan, under Contract NSC 97-2221-E-002-061-MY3.
R EFERENCES
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[3] S. Zhang, G. H. Huff, J. Feng, and J. T. Bernhard, “A PatternReconfigurable Microstrip Parasitic Array,” IEEE Trans. Antennas & Propag., vol. 52, no. 10, pp. 2773-2776, Oct. 2004.
[4] M. J. Slater, H. K. Pan, and J. T. Bernhard, “PreliminaryResults in the Development of a Compound ReconfigurableAntenna,” in Proc. IEEE Antennas & Propag. Society Int.Symp., Jul. 2008, pp. 1-4.
[5] G. Yao, Z. Xue, and W. Li, and Z. Liu, “Multi-Feed Comparedwith Single-Feed End-Fire Antenna,” in Proc. IEEE Antennas, Propag. & EM Theory Int. Symp., Nov. 2008, pp. 240-243,.
[6] N. Honma, T. Seki, K. Nishikawa, K. Tsunekawa, and K.Sawaya, “Compact Six-Sector Antenna Employing ThreeIntersecting Dual-Beam Microstrip Yagi-Uda Arrays withCommon Director,” IEEE Trans. Antennas & Propag., vol. 54,no. 11, pp. 3055-3062, Nov. 2006.
Fig. 4. Directivity patterns at 1575MHz when SW1 is on and SW2 is off.
Fig. 5. Directivity patterns at 1575MHz when SW1 is on and SW2 is on.