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Design and Implementation of Dual Mode Feed Horn for
Broadband W ireless Local Loop Antenna
*Woon Geun Yang, Sung Sik Kong, Won Kew Lee, Byung Ku Nah, De
Sun Kim
Department of Electronics Engineering, University of Incheon,
Incheon,
402-749, Korea, [email protected]
Hankook Antenna
Co .
Ltd., Bucheon, 420-130, Korea
1 Introduction
The electrical design of primary feed antennas involves a number
of dependent
factors. A primary feed can be any type of elementary antenna:
dipole, slot, hom, and
so
on.
And the principal characteristics to consider are matching of
the feed to the feed
guide, radiation pattern, polarization etc.
Although a conical hom antenna as primaly feed for reflector
antenna has
characteristics of axis symmetry beam, its beamwidth of E-plane
and H-plane is. not
equal and sidelobe level is very high. These problems could be
solved with multimode
or dual mode
hom
antenna. A corrugated hom antenna among
th
various multimode
hom antennas has profitable characteristics such as axis
symmetry beamwidth and
excellent cross polarization property, but it has disadvantages
of heavy weight, big
size and difficulties in fabrication process[13
In this paper, we designed dual mode horn antenna as a primary
feed for broadband
wireless local loop(24.25-26.7GHz) antenna. The dual mode hom
was first descibed
by P. D. Potter[2]. This hom has a very simple design. It may be
used as feed element
in reflector antennas where low cross polarization property is
required. As the
radiation pattern of this simple hom is almost rotationally
symmetrical, it may also
replace the single conical hom to obtain a higher aperture
efficiency of the reflector[3-
51
If we consider the cross-polar component and sidelobe, a dual
mode hom would be
a good choice. A most important application
of a
dual mode hom is as a feed of
cassegrain reflector or parabolic reflector, built, and tested
with relatively good
success in their performance.
2 Dual Mode Horn Antenna
A dual mode horn antenna exhibits suppressed sidelobe, equal
beamwidth, and
reduced cross-polarization. Fig. 1 shows how the superposition
the over the circular
guide aperture of modes
T E I I
and
T M l l
allows us to obtain an approximately
circularly symmetric illumination with almost zero cross
polarization. These two
modes are excited in the hom aperture with the appropriate
relative amplitude and
phase to effect sidelobe suppression, beamwidth equalization and
the cross
polarization suppression[2,5-71.
This work was supported in part by the Korea Science and
Engineering Foundation K0SEF) through the
Multimedia Research Center at University
of
Incheon.
@7803-7330-8/02$17.0002002C02
IEEE
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To achieve a desired radiation characteristic, it is necessary
to choose the type of horn;
the dimensions and geometry of the radiating aperture; the
geometry of the flared
section coupling the waveguide feeder to the radiating section;
and to design the throat
of the horn to provide appropriate matching and to avoid the
generation of unwanted
higher-order modes[6,7].
DUAL-MODE
Fig. 1. Radiation characteristics of dual mode hom. (a)
Radiation pattems, and (b)
Aperture electric field distribution for the
TE,
and TM, mode.
3 Simulation, Implementation and Measurement
The primary importance was given to the VSWR and radiation
properties within the
operating frequency band for our design. Test and adjustment was
made for primary
feed hom, which was assembled with cassegrain type
reflector[8].
A
Simulation for dual mode horn antenna
By using FEM(Finite Element Method) simulation software, Ansoft
HFSS, we get the
suitable values of hom antenna for Fig. 2(a) to meet the
required specification. Fig. 2
shows drawing and modeling of antenna, and simulation results.
The sizes of the
antenna are R1=4.45mm, R2=8.15mm, LI=30.50mm,L2=26.63mm,and a
=6.92 for
Fig. 2(a). The hom antenna was designed as tapered type hom,
which was connected
with input waveguide of rectangular type as a flange. Simulation
results show gain,
cross polarization, and sidelobe level. Fig.
2
shows that sidelobe level is less than
approximately -25dB and cross polarization is less than
-30dB.
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Fig.
2.
Simulation results for dual mode horn antenna. (a)
A
drawing, (b) Modeling,
(c) Gain pattern, and (d) Normalized gain pattern and cross
polarization.
Implementation and Measurement for dual mode horn antenna
Implemented samples are tested by using an HP 8510C network
analyzer and Near-
field system. The experimental results of antenna for broadband
wireless loci11 oop
are as follows.
Fig.
3
shows measured electrical characteristics such as
St
mpedance loci, VSWR.
They show relatively good performances. The measured VSWR is
less than 1.5 for all
frequency bands of broadband wireless local loop
...-
....
( 4 (b) (c)
Fig.
3.
Measured characteristics for a primary feed horn. (a) SI ,(b)
Impedance loci,
and (c) VSWR.
Fig.
4
hows measured near field data with characteristics of nearly
symmetric beam
pattern.
(a) (b) (c)
Fig.
4
Measured near field character istics for implemented horn.
a)
3-D
Radiation pattern, (b) X-axis, and (c) Y-axis.
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(a) (b)
Fig. 5. Developed antenna sample. (a) Developed primary feed
horn, and (b) The
assembled antenna with reflector.
Fig. 5 shows a developed primary feed horn, and photograph of
assembled antenna
with reflector.
We
have tried many hom samples and the shown feed is one of
them.
Dimensional constraints with cassegrain type reflector and
amplifier made some
limitation to improvement of performance.
4 Conclusion
In this paper, the dual mode feed horn for broadband wireless
local
loop
antenna was
designed by using simulation program and implemented. The
implemented antenna
was adjusted to get the proper electrical characteristics and
radiation pattern
properties. And the finally developed antenna is a cassegrain
type, which consists of
primary feed horn, main reflector and sub-reflector and is aimed
at high gain.
The designed hom shows cross polarization and sidelobe
characteristics which are
less
than -30dB and -25dB respectively. The developed dual mode hom
shows that
VSWR is
less
than 1.5 which is suitable characteristics for commercial
application.
The VSWR of assembled antenna was less than
2.0
for all frequency bands of
broadband wireless local loop, and its measured gain was above
than 35dBi, which is
sufficient for practical application.
References
[l] Constantine
A.
Balanis,
Horn Antennas
Chapter
n
Antenna Handbook:
Volume 2, Van Nostrand Reinhold, 1997.
[2] P. D. Potter, A New Hom Antenna with Suppressed Side Lobes
and Equal
Beamwidths,
Microwave Journal
pp.71-78, June 1963.
[3]
S.
Drabowitch, A. Papiernik, H. Griffiths,
J.
Encinas and Bradford L. Smith,
Primary eeds Chapter in Modern Antennas Chapman Hall, 1998.
[ ]A. W. Love, A. W. Rudge and A. D. Olver, Primary fe ed
antennas Chapter 4 in
The Handbook OfAntenna Design: volume
I Peter Pergrinus, 1982.
[5] Erik Liker, Cross Polarization from Dual Mode
Hom
Antennas,
IEEE
Transactions on Antennas and Propagation vol. AP-34, no. 1,
pp.106-110, Jan.
1986.
[6] A. W. Love, Electromagnetic Horn Antennas The Institute of
Electrical and
Electronics Engineers, 1976.
[7] A. W. Love,
Some
highlights in reflector antenna development,Radio Sci. vol.
[SI W.
G.
Yang, S. S. Kong, B. K. Nah, N. J. Bae, D. S. Kim, Development
of B-
11, pp.671-684, Aug. 1976.
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2000, pp.338-341, Aug. 2000.
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