Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
z~ ss
ANTENNA SYSTEM FOR RECEP~ION~PROM
DIR~CT BROADCASTING~SATELLITES
B~CKGROUND OF THE INVENTION
l. Field of the Inventlon :
The invention pertains ~o the:field of~ reception
from direct~ broadcasting TV satelllte :~and,~ more
particularlyj to a recept~lon antenna;~system.~ :
2. De~cr~ption of the Pr~or Art:~
In the field o~ receptlon~from~dlrect'broadcastlng
satellltes~(D.B.S.~ such as TDF l, TV 9AT, OLYMPUS,~B9D
etc., different sorts of known antennas may~be used.
A firæt type~of known antenna~uses;a paraboloid of
~revolution, wlth a source placed in the~focal~point: of
thls~parabolold. The antenna BCCeBB is~obtalned either
directly at the focal point of the parabola, at the
~ sourcs access, or ln the~ rear o~ the antenna, a
; crosshead f~rmed ~y a guide: making ~he connectlon
between the 30urce and the~ rear of the antenna. The
~ntenna i8 placed on a support: dimensioned as a
function of the Bize of the parabola. ThlB Bupport
enables aimlng, in azimuth and elevation, toward~ the : :
satellite to be received. ~ ~ :
The drawback of this:~ype o~ antenna i~ that: the
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shadow projected from the source, from its support and :
from its holding arms masks a part of: he reflector: :
this causes a reduction in ef~iciency. ~oreover, the
use of a waveguide to have access to the rear of the
::
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2G~ S,~
antenna makes it possible to protect the low-noi~e
converter ~LNC) but cause~ a loss o transmission ~hat
implie~ a reduction in gain and an increase ln the
~oise temperature of the antenna. Furthermore, thls i~
2 high-co3t type o~ antenna,~no~ably because o~ the
number of mechanical~part~ that have to be u~ed to make
the antenna st~ucture and enable its orientatio~. The
latest deve1opments in this type of antenna have made
it possible, by means of GaAB FET transistors, to
obtain small-sized low-noise conver~ers which it has
been possible to place dlrectly behind the ~ource, at
the focal polnt of the paraboLoid, 80 as to reduce the
transmis~ion losses. But, in doing this, the mask on
the re~lector i5 further increa~ad, notably for
small-diametér antenna~.~ Furthermore, tho electronic
circuitry is then more directly ~ubjected to climat1c
conditions, especially variations in temperature, and
to the vibration~ induce~.
Another type o~ known antenna U8e9 an off-centered
parabollc re~lector and i~ commonly called an off-set
antenna. The reflector of th1s antenna i3 formed by a
portion of parabolold o~ revolution. The source,
which 1s away from the axis of thi~ para~oloid,
project6 no ~hadow on the aperture. To this end, the
reflector i5 obtained by cutting out a paraboloid in
cylinder wi~h a diameter D, cen~ered on an axis
parallel to the ~ocal axis of the paraboloid~ The
2~
source 18 then placed at the~focu~ F o~ the paraboloid
and is aimed at the middla of the paraboloid portion.
The antenna access i8 generally obtained at the source
S acce3~, and the low-noise converter, in thi3 case, is
placed directly behind the source, before the
reflector.
The chief advantage of thi~ "of-set" structure is
the increa~e in the ef~iciency o~ the antenna~throug~ a
reduction in the mask effect o~ the source. Moreover,
the antenna has little sen~itivity to cllmatic
condltions and, by i~8 structure, the antenna aimed
towards the satellite is practically vertical. However,
this second type of antenna also~has ma~or ~drawbacks:
the making of this type of reflecto~, which is not~of a
shaps generated by revolutlon, is difficult and little
suitQd to fabrication by metal-spinning o~ drawing.
Noreover, the radiation pattern~ of the antenna are not
generated by revolutlon and tha rate of ellip~lcity of
an antenna such as thi~, used in circular polarizatlonJ
is higher ~han with an antenna using a reflector in the
shape of a poraboloid o~ revolution. Besldee, the
low-noise converter iB placed before the reflector, and
i8 therefore sub~ected to climatic conditions
~tempera~ure in particular). Flnally, since the
reference plane in elevat~on is not easily defined, it
is not easy to im the antenna in the direction of the
satellite to be received.
2G1~55
SU~MARY OF THE INVENTION
An obiect:o~ the lnventlon 18 a compact antenna
8y8tem, de~lgned to pick up the signal~ emitted by a
S ~atellite, integrating a low-noiso~ converter-amplifier
: to ampli~y the ~ignals recoived by~the~antonna and to
convert them into the requisite band,~thl~ antenna
being desig~ed ~to lntegrate ~all or ~a part of the
electronic functlons needed for the~compatibility of
roception of the TV images,~whlla~ at tho~ 8amO tlme
being of very modQrate cost~and having great aiming
simpllcity. Those charactoristics aro~obtained by means
of a very re~tricted number of element~ to achieve~
- the~etting in elevation,~
- the azimuthal setting,~
- the protection and integration o~
the: electronic circDitr
:
: - and the~fi~ing.
According to the invention, there i8 proposed an
antenna Dystem for diroct broadca~ting satellite
reception, comprising a parabolic re~lector, tho ~rear
central part of which ~s fixed to a hollow tu~ular body
of a supporting ~oot by moans of a fi~ing~part, the
reflector, the fixing part and the tubular body of ~ the
supporting foot having a tubo going through them, with
the SamQ axls as the re~lector, containing the source
and forming a ~protection and~means for centering the
source in tho ~reflector, tho ~tubular body F the
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supporting foot being hinged to lt ba~e on a
horizontal a~i~ borne by a pede~tal and associated with
locking means that fix the elevation of the antenna,
the pede~to1 be~ng movable in rotation around a
vertical axis to ~i~ the azimuth of the antenna, all
the circults o~ the antenna sy~tem and i~8 e1sctrlcal
~upply means being fixed to the interior of the tubular
body o~ thQ supp~rtlng foot.
RIEF D~SCRIPTION OF T~ DRAWINGS
~he invention will be understood~more clearly, and
other characteristics will appear from the following
de~cription, made with re$erence to ~he appended
fi~ures, wherein: ~
- Figure 1 i8 a sectional drawing showing a first
embodiment of the antenDa system according to the
invention;
- Figure 2 shows a ~econd embodiment of ~he system
accordlng to the invention.
:20 DESCRII'TIOII OF I III~F~EIIII~ ODI2OENTS
In the ollowing description, the embodlments
described in detail are suited~ to the reception o~
satellites transmitting in the ll.7 to 12.5 GHz band,
ln right or left circular polarization. However, the
antenna may be modified to be adapted to another
frequency band or to other type~ of polarization.
The antenaa system according to the inven~ion i~
formed chiefly by an antsnna with it~ reflector having
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a di~meter adapted to the power received from the
satellite and its ~ource, a supporting foot that
provldes for the geometry of the antenna and
simultaneously enables lts setting for the alming of
the satellite and electronlc rircuits, e~3entially the
low-noise converter-ampli~ier, po~ibly complemented by
- :
other circuits. By way of an example, figure
represents the embodiment of the antenna sy~tem,
according to the~ lnvention, for the reception of the
satellite TDF 1 which radiatos power o~ 63 dBW: the
reflector 1 of the antenna is a parabollc reflector
with a diameter of 0.33 meters. The sy~tem can be
adapted to greater diametors for values of ~power
transmltted by other smaller ~atollltes, up to 0.7
meters without modification, for example for th~ :A~TRA
satellite whlch radiatos powor of 52 dBW.
The re$1ec~or 1 i8 a paraboloid o~ revolution. The
ratio between the focal distance and the diameter of
thi~ parabolo~d i8 0.3~, and this fact, glven the
diameter of 0.33 m., leads to a focal distance of 97
m~. The angle of aperture of the para~oloid is 161
degrees. Thi~ reflector i8 made of aluminium with a
thickness of 15/lOth of a mlllimeter, and i~ obtained
by "fluo-turning" for small quantitie~ or by draw~ng
for larger guantities. The tolerance a~ regard~ the
contour o~ tha reflector leads to a mean square
deviation of 0.5 mm. from the theoretlcal con~our. Thl3
Z~ S5
results in a 1095 of gain of the order of 0.28 ds at a
central frequency F = 12.1 GHz . This ref lector 1 is
dlrectly flxed by it~cantral part to the supporting
foot, as shall be explained hereina~ter.
The source enables ~he reception of the circularly
polarized slgnal of the frequency band 11.7 to 12.5
GHz. Thi~ source is formed by a semi-rigid coaxlal
cable 2 with PTF~ dielectric, under copper tubIng,
surmounted~by illumlnant 3 wAlch uses the properties of
radiatiun of the surface wave~: this illumlnant 3 takes
the form of a helix or o~ any other source enabling the
elec~ronic clrcultry to be shi~ted to the rear of the
reflector of the antenna. In the optimi2ed embodiment
shown, tha lllumlnant is~a hellx, the turn~of which
have been obtained by winding on a 6 mm diameter
cylinder wlth a:~ pitch o~ 12 mm, the angle o~
inclination of the ~urns being 30 degrees. The
attenuation provided by the semi-rigid coaxial cable
used in the 1~ GHz band ~5 of the order of 1.5 dB per
meter. For the antenna described, thi~ mean~ ~a
reduction in gain of the order of 0.~ dB. Owing to the
structure of the source with respect to the reflector,
the 108~e8 created by the masking of the reflector by
Z5 the source are restricted to 0.01 ds. This source
(coaxial cable surrounded by the helical illuminant) is
fixed in a polypropylene tube 4 having th same axis as
the reflectDr and going through ~he center of this
2C~10~S5
reflector. Thi~ tube, whlch i~ clo~ed at itD ~nd on the
illuminan~ slde by a cap 5, fo~ms a radome and provides
imperviousne~s to dripping. The measured losncs of the
S radome are at tha operatlng f~equencie~ of 0.2 dB. In
the rear of the re~lector, the tube 4 i~ held i~
po~ition by a qentering plcce 6 flxed,:firstly, to the
rear o~ the reflector and,~nccondly, to a holl~w tube 7
forming the :body of the supporting foot. Thus, the
rigldity of the ~upply llne ls cnsurcd.
Thu3, the source i9 centered in:the tube 4 and
kept in posltion by the part 6 ccntered on the rear of
the reflector, which i8 itæel held by means of ~ screws
to the body 7 of the ~upporting foot. Thus, the
centering and the longitudlnal~:positioning of the
source with respect to thc reflcctor are achleved.
The di~ensionIng o~ the body 7 of the supporting
tube is such ~hat the reflec~or can be replaced by
simply laying down screws to ~lx this re1ector to the
part 6 and/ a~ lndica~ed above, the diame~er o~ the
reflectors;may be modi~ied.
The ~upportlng foot has thrce functions:
- to provide for the geometry of thc antenna as
indicated above;
- to contain and pro$ect the electronic circuitry
needed to process the 8ignal3 received from ~he
satelllte;
- to ~nable ~ast aiming of the antenna, evan by a
- non-speciallst.
The assembly ~oxmed by the ~ource, supply and
convers~on head 10 i~ fixed in the body of the
~upporting Xoot 7 by means o~ a part 8.
The converslon head, which i8 ~ixedly joined to
body of the supporting foot, is shlelded from drlpping
by meanB of a cover 9 which shields it from adverse
wsather condition~. This cover closes the upper part of
the tube 7 closing the body o~ the support~ng foot. ~t
the opposite end, ~he tu~e 7 foxming the supporting
foot 2 i~ not clo~ed: thls enables a flow of air
preventing condensation because of this aperture at the
bottom.
~he reception access at output of the supporting
foot i9 got by mean~ o~ a cable 20 fixedly ioined to
the conversion head 10 and golng through an aperture
made at the bottom part of the body 7 o~ the ~upporting
~oot.
The as~embly formed by the reflector, source and
conversion head i8 compact and cont~ins all the
elements needed to picX up the signals $rom the
sat~llite.
To enable fast aiming of the antenna, even by a
non-specialist, the above-described assembly is held on
a pedestal by means of two screwæ 15 that form a hinge
' .
on a vertical tube 11 enabling the antenna to swivel
around a horlzontal axls XX.
The pedestal i8 formed by two mechanical part~:
S - a f~ixed part 21,:cross-~haped for example, which
i8 fixed horlzontally (or~ vertically) ~by means of
: ~crews placed in the holes ~22 of its arms. On this
fixed part, there is placed a level indicator 23
enabling ~ perfeat deflnitlon of a horizontal or
vertical plane and, hence,~ the obtalning of a reference
plane for the def1nition of the antenna elevatlon.
- a movable part 24, surmoun~ed by the tube 11,
centered in rotatlon on th ; fixed~part ~nd fixedly
~oined to thls fixed part by mean~ of~two sarews 2~5.
These ~crews sllde in ~he facing~of the movable part.
The locking ~of the6e ~wo screws ensures that the
azimuthal a~l~ of .the antenna i~: made immobile after
the rotation of the movable part 24 around the fixed
part 21 has enabled the a~imuthal axis~to be defined.
To prQ-posltlon the antenna toward~ the ~atelllte, a
magnetized nGedle i8 placed on th~ movlng part as well
as, possibly, an orientatlon dial.
The tube 11 of :thls movable part suppport~ the
body 7 of the oscilla~ing ~foot on the axis~deflned by
the two screw~ 15 shown on the partial ~ectlon AA of
figure 1. The elevatio~al setting of the antenna is
done by mov~ng a screw 26 in a maximum ~ector defined
by a movable stop 17. The locking and fixing in
~1025S
11
po~ition a~ter setting is done by the locking of the
screws 15 and of the movable stop.
All the parts of thi~ ~upportlng~foot are made o~
5 aluminium, and all the shapes adopted are simple shapes
that can be obtained by moldlng or swaging, thus
reducing productlon costs to the~minimum.:In order to
simpllfy the aimlng of :the antenna, the positioning
polnters placed for the setting of the elevation and
az~muthal axes lnclude graduations and, possibly, the
indi~ation o~ the s~tellites aimed at.
For certain appllca~ion~, the assembly formed by
the movable part 24 and the fixed part 21 of the
support can be replaced solely:by the~cyllndrical tube
ll, which can be directly fitted into a standard tub:e,
commonly u~ed a~ a support ~or radio reception
ante~nas. Figure 2 shows a thus simplified embodlment
of an antenna accord~ng to the invention, designed to
be fitted directly into a standard tube. The same
re~erences are repeated for the same element~ as in
figure 1.
The essenti:al di~ference here is that the foot of
the supporting tube ll i8 airectly fitted into a
standard supporting ~ube external to the antenna ~ystem
50. Naturally, in this case, the horizontal part of the
supporting ~oot iY elimina~ed, and the reference axis
i8 ~iven d~rectly by the s~andard tube which, to this
effect, is positioned ver~lcally. This figure also use8
12 20~0X5S
heavy lines ~to illu~trate the parabolic reflector l,
with a 0.33 meter diameter, and dots and dashes to show
a reflector l' with a dlf~erent di~meter, for e~ample
0.7 meters. In the same way, to~illuAtrate the setting
of the tube orlentatlon, the supportlng tube 7 has been
shown in three di~ferent posltions,~; oDe~ wlth solid
lines and tha other two dots~and dashes, to~show the
po~slble angular deflectlon of the~system.
The ~nventlon is Dot~restrlcted to the embodiments
de~cribed and shown. In particular, the ~ource has bee~
shown in the f igures a~ a simple helicoid havlng an
unoccupied end. Thi~ type of source is perfectly well
~uited to cicularly polarized trànsm~ssions from a
:~ :
satellite such as the TDF 1. Naturally, thls devlce is
not restrictive, and the source will be adapted to the~
mode of polarization of ~he satellite transmissions.
Thus while thé polarlza~ion for transMission rom the
satellite TDF l i8 circular, the polarization for the
transmi~sion received from the ~STRA satellite i9
designed to be horizontal and ver~ical. Similarly, some
satellites wlll transm1t in two polarlzatlon modes,
left-hand and right-hand. The ~corresponding source~
will be adapted to these different types of
polarization.
The radome-forming tube g can be made of a
material other than polypropylene, provided that this
material creates no losses.
~o~oz~
13
The structura thus obtalned ~or ~he antenna sy~tem
15 particularly compact and very~easy to set up. A11
the prooflng i5 done in the~ factory and no special
S precautions are necessary durlng in~tallation.
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