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WIDE FLARE ANGLE K U BAND AXIALLY CORRUGATED HORN FOR OFFSET
VSAT ANTENNAS
hlarcos G. Castello Braiico Eniilio Abud Filho
c' P q D / Tele 1) r 6,s Rodovia C'aiiipinas-Mogi Mirim, Km.
118,.5
13088-OB0 - C'ampiiias - S.Paulo - Brazil
Luiz Costa d a Silva
C'ETUC' - PUC'/RJ Rua Marquks de S5o Vicente, 225
22453-900 - Rio de Janeiro - R . J . - Brazil
Abstract
A wide semi-flare angle linearly tapered corrugated horn, with
eight axial slots, has been developed for use in single offset
antelinas for VSAT earth statioiis with low cro~,s-polarizatioii
peak levels from 10.7 GHz to 14.8 GHz. Tlie iiiode-iiiatcliiiig
techniques [1],[2] have been siic- cessfully applied to the horn
return loss and radiation pattern prediction and 1 he critical
effects of the ridges and output flange thicknesses have been
verified.
1 Introduction
Single Offset Very Small Aperture Terminal (VSAT) antelilia
configurations require wide flarcb aiigle lioriis with very low
cross-polarizatioii level, coiiipatible with dual baiirl operation
(traiisiiiil and receive) for satellite coiiiiiiunicatioii purpose.
( 'ross-polarization peak levels lower thaii -20 dB. relative to
the iiiaiii beam co-polar gain, are very difficult t o achieve
specially for wide baiidwitlths and low VSVJR designs. For these
cases, single or dual depth corrugated horiis with shaped profiles
have been coiiinionly used. increasing aiiteiiiia feed weight and
ilianufact uriiig
This paper presents ii wide I
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The iiiipleiiieiited iiiodel, tha t approximated each inclined
ridge edge by three smooth waveg- uide sections instead of one. for
the mode-matching techiiiclues application, is ilustrated in figure
'2. Its efficiency is demolistrated in the CO ancl Cros5-pOhr
pattern aiialysis shown iii figure 3 for 10.7 G H z , where the
three waveguide section iiiodel (11) is compared with the one
section iiiorlel ( a ) aiicl with the experimental iesults.
Diffeieiices greater than 5 dB lietween the cross- polar peak level
predictioiis for the two iiiodels Inay be juqtified by corrugation
slot lengths inaccuracies due to the horn wide semi-flare angle and
ridge thickness (apros. 1.5 mni) .
3 Experimental results
Two different horn prototypes have been manufactured foi
esperiiiiental evaluation (see figure 1). The first one, s h o ~ i
i in fiquie l a . contained a thick (alnimt 11 nim) output aperture
flange foi a flat poliester radome fixing. The second one.
ilustrated in figure l h , had the flange thickness reduced to
almo4t one ridge dimeniioii. This second option , a5 shown in
figure 4, allowed a significant reduction of the cross-polar
effects due to the aperture flange edge currents. In this case,
iadome shoulcl have a cup shape and he fixed 111 the flange
external face.
Prot otypes ineasuieiiients were peiforined in an anechoic
chamber and u4ng an HP-X.5lOB iietworl, analyser setup. Figure :3
coiitaiiis the theorectical and experinieiital results of the horn
returii loss in tlie full 10.7 G H z t o 14.8 GHz hand. The CO and
cross-polar patterns of the second horn prototype. relative to the
45" plane. are presented 111 figures G ( a ) aiicl G ( b ) ,
iespectively for frequeiicie5 of 12.7.5 GHz and 14.8 GHz,
ieinforcing the quite good theorectical predictions and very low
cross-polarization peak levels (better than -26 d B ) .
4 Conclusions
A Iiu h i i d axially corrugated wide flaie angle horn lias been
developed to be used in siiigle offset antennas for VSAT
applications. The design resulted in a low cost compact horn with
return loss aiitl cross-polarization levels adequate to the
intended applicatioiis. The mode- matching techniques were
adequately apphed t o the thick ridges aiialysis ant1 sucessfully
reproduced the esperiniental results of tlie horn return loss
(better than 23dB) and cross-polar peak levels (l~elow -2GrlB ) in
a 32% bandwiclth (froni 10.7 GHz to 14.8 G H z ) .
eferences
[l] - James, G.L., aiicl Thomas, B.hI.,1982. "TE11 to HE11
cyliiidrical wa.veguide mode coii- verters usiiig riiig-loa.ded
slot,s", IEEE Tra,ns.. MTT-30: pa.ges 278-28.5.
['2] - da. Silva,,L.C. - "Coupling structures hetween srnoot.11
a,iid corrugated wa.veguicle feeds" - In t,erii a1 Report : C ET U
C' - U - X- 0 1 - Nj. C' ET l i / PIT C' ( C.! a.t liolic TT iiiv .
of R . J )- Feb 1980:.
[ 3 ] - Iiubn. E. a,iid Hoiiilmch, V . - "C:oiiiput.er-a.ided
a.iia.lysis of corruga.t,ed horns with axial or ring-loa.ded
radia.1 s1ot.s" - ICL4P/19P3.
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a) 8
Figure I: %Vide flare angle, Iiu output flange
band corrugated horn prototypes: PVith ( a ) and without ( b )
thick
Figure 2: Asially corrugated horii ridge iiiodels f0r hI
.iClatch. analysis: a ) Mean value iiiterllal radius ridge : b )
Thee circular waveguide sections
dw
Figure 3: Horn ridge models results ~ 1
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I
..-............
0.00 10.00 20.00 40.00 so.00
Figure 4: Thick flange effect in the horn q ie r ture at 10.7 G
H Z
10.70 11.21 11.72 12.24 13.26 13.77 14.29 I BO
Figure 5 : Three c.wg. sections model Return Loss results
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Figure G: Three c.wg. sections model pattern results at: a )
12.7.5 GHz aid b ) 14.8 GHz,
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