FR2643511A1 - ANTENNA SYSTEM FOR RECEIVING DIRECT DIFFUSION SATELLITE - Google Patents

Abstract

The antenna system consists of a parabolic reflector (1) associated with source means (2, 3), the reflector being positioned and held by means of a support foot formed from a hollow tubular body (7) fixed at its upper part to the rear central zone of the reflector and hinged at its lower part on a base about a horizontal axis (XX) in order to define the elevation of the antenna. The base comprises a part (24) which is movable in rotation in order to define the azimuth of the antenna. The tubular body (7) of the support foot has a sufficient cross-section to contain all the circuits associated with the antenna. Application, in particular to satellite reception, of which the radiated powers are greater than 50 dBW.

Description

Antenna system for direct broadcast satellite reception

  The invention relates to the field of reception of direct broadcast TV satellites, and more particularly to

  a receiving antenna system.

  In the field of reception of direct broadcast satellites, in particular for DB S satellites (Direct Broadcasting Satellite) such as TDF 1, TV SAT, OLYMPUS, BSD etc ... different kinds of known antennas could be used A first known antenna type uses a paraboloid of

  revolution, with a source placed at the focus of this paraboloid.

  The antenna access is made either directly to the focus of the dish at the source access, or at the rear of the antenna a guide butt connecting the source and the back of the antenna. The antenna is placed on a support dimensioned according to the size of the dish, this support allowing azimuth and elevation pointing in the direction of the dish.

satellite to receive.

  The disadvantage of this type of antenna is that the projected shadow of the source, its support, and its holding arms obscures part of the reflector, which leads to a decrease in performance. In addition, the use of a waveguide to access the back of the antenna protects the low-noise converter (LNB) but causes a transmission loss which results in a decrease in gain and increase in the noise temperature of the antenna. In addition, this type of antenna is of high cost, in particular because of the number of mechanical parts to be used to make the antenna structure and to allow its orientation. The latest developments of this type of antenna have made it possible, thanks to the AsGa PET transistors, to obtain low-noise converters of small size which could be placed directly behind the source, at the focus of the paraboloid so as to reduce the transmission losses. . But, in doing so we further increases the mask on the reflector, especially for small diameter antennas. In addition, the electronics are then subjected more directly to the climatic conditions, variations of

  temperature in particular, and induced vibrations.

  Another type of known antenna uses an off-center parabolic reflector. This type of antenna is commonly called an "off-set" antenna. It is an antenna whose reflector is constituted by a portion of paraboloid of revolution, the source, separated from the axis of this paraboloid, not projecting shade on the opening. For this the reflector is obtained by cutting a paraboloid by a cylinder of diameter D, centered on an axis parallel to the focal axis of the paraboloid. The source is then placed at paraboloid focus F and targets the middle of the paraboloid portion. The antenna access is usually done at the source access, the low-noise converter being then placed

  directly behind the source, in front of the reflector.

  The main advantage of this "off-set" structure is the increase of the antenna efficiency by reducing the mask effect of the source; moreover, the antenna is not very sensitive to climatic conditions and because of its structure

  the antenna pointed towards the satellite is practically vertical.

  However, this second type of antenna also has significant disadvantages the realization of this type of reflector, which is not revolutionary, is difficult and poorly suited to manufacture by spinning or stamping. Moreover, the radiation patterns of the antenna are not revolution and the ellipticity rate of an antenna of this type used in circular polarization is higher than with an antenna using a paraboloid-shaped reflector of revolution. . Furthermore the low noise converter is placed in front of the reflector, and therefore subject to climatic conditions (temperature in particular). Finally, since the reference plane in elevation is not easily defined, it is not easy to

  point the antenna towards the satellite to be received.

  The invention relates to a compact antenna system for receiving the signals emitted by a satellite, integrating the low noise converter amplifier to amplify the signals received by the antenna and to convert them into the required band, this antenna being intended to integrate all or part of the electronic functions necessary for the reception compatibility of TV images, while being of a very low cost and a great simplicity of pointing. These characteristics are obtained thanks to a very small number of elements, to realize - the adjustment in site, - the adjustment in azimuth, - the protection and the integration of the electronics,

- and fixing.

  According to the invention, an antenna system for direct broadcast satellite reception, is characterized in that it comprises a parabolic reflector whose rear central portion is fixed to a hollow tubular body of a support leg via a fixing piece, the reflector, the fastener and the tubular body of the support leg being traversed by a tube of the same axis as the reflector, containing the source and forming a protection and centering means of the source in the reflector, the tubular body of the support leg being articulated at its base on a horizontal axis carried by a base and associated with locking means fixing the elevation of the antenna, the base being rotatable about a vertical axis to fix the azimuth of the antenna, all the circuits of the antenna system and its power supply means being

  fixed inside the tubular body of the support leg.

  The invention will be better understood and others

  characteristics will appear using the description that

  follows with reference to the accompanying figures.

  FIG. 1 is a sectional diagram of a first embodiment of

  realization of the antenna system according to the invention.

  FIG. 2 is a second embodiment of the system

antenna according to the invention.

  In the following description, the embodiments

  described in detail are specially adapted for receiving satellites transmitting in the band 11.7 to 12.5 GHz, in right or left circular polarization. But the antenna can be modified to be adapted to another frequency band

  or other types of polarization.

  The antenna system according to the invention consists mainly of an antenna with its diameter reflector adapted to the power received from the satellite and its source, a support leg ensuring the geometry of the antenna and simultaneously allowing its adjustment for pointing the satellite, and electronic circuits basically the low-noise converter amplifier, possibly supplemented by other circuits. By way of example, FIG. 1 represents the embodiment of the antenna system according to the invention for receiving the TDF 1 satellite which radiates a power of 63 dBW: the reflector 1 of the antenna is a parabolic reflector of diameter 0.33 meters. The system is adaptable to larger diameters for powers emitted by other lower satellites, up to 0.7 meters without modification, for example

  for ASTRA which radiates a power of 52 dBW.

  The reflector i is a paraboloid of revolution whose ratio between the focal length and the diameter is 0.3 which considering the diameter of 0.33 m leads to a distance

  focal length of 97 mm. The opening angle of the dish is 161.

  This reflector is made of aluminum 15 tenths of a millimeter thick, and is obtained by spinning for small quantities or by stamping for larger quantities. The tolerance on the reflector profile leads to an average square deviation of 0.5 mm compared to the theoretical profile, which causes a loss of gain of the order of 0.28 dB at a center frequency F = 12.1 GHZ . This reflector 1 is fixed directly by its central part on the support leg

as will be explained below.

  The source allows reception of the circularly polarized signals of the frequency band 11.7 to 12.5 GHz. This source consists of a semi-rigid PTFE dielectric cable, copper tube, 2, surmounted by the illuminant 3 which uses the radiation properties of the surface waves: this illuminant 3 is in the form of a helix or any other source that allows the electronics to be moved away from the back of the antenna reflector. In the optimized embodiment shown, the illuminant is a helix whose turns have been obtained by winding on a cylinder of diameter 6 mm with a pitch of 12 mm, the angle of inclination of the turns being 30. The attenuation provided by the semi-rigid coaxial cable used in the 12 GHz band is of the order of 1.5 dB per meter, which is reflected for the antenna described by a reduction in gain of the order of 0 , 2 dB. Due to the structure of the source with respect to the reflector, the losses created by the masking of the reflector by the source are limited to 0.01 dB. This source (coaxial cable surrounded by the helical illuminant) is fixed in a polypropylene tube 4 of the same axis as the reflector through which it passes through its center; this tube closed at its end illuminant side by a cap 5 form radome and seals the runoff. The radome losses measured are at the operating frequencies of 0.2 dB. At the rear of the reflector, the tube 4 is held in position in a centering piece 6 fixed on the one hand to the rear of the reflector, on the other hand to a hollow tube 7 forming the body of the support leg. So is

  ensured the rigidity of the feed line.

  Thus the source is centered in the tube 4 and held in position by the part 6 centered at the rear of the reflector, itself held by screws on the body 7 of the support foot. This is how centering and positioning is achieved

  longitudinal direction of the source relative to the reflector.

  The dimensioning of the body 7 of the support foot is such that the replacement of the reflector is possible by simply removing the fixing screws of the latter on the part 6 and as

  indicated above, the diameter of the reflectors can be changed.

  The support stand has three functions: - to ensure the geometry of the antenna as indicated above; I G - contain and protect the electronics needed to process signals received from the satellite - allow fast pointing of the antenna, even

non specialist.

  The source assembly, power supply and conversion head 10 is fixed in the body of the support leg 7 via

of a piece 8.

  The conversion head secured to the body of the support leg, is protected from runoff through a cover 9 which protects it from the weather, this cover closing the upper part of the tube 7 forming the body of the support foot. At the opposite end, the tube 7 forming the support leg 2 is not closed, which allows a circulation of air preventing condensation due to this

opening at the bottom.

  The access reception at the output of the support leg is performed via a cable 20 secured to the conversion head 10 and passing through an opening made in part

lower body 7 of the support foot.

  The reflector, source, conversion head is compact and contains all the necessary elements to capture

the satellite signals.

  To allow rapid pointing of the antenna, even by a non-specialist, the assembly described above is held on a base by means of two screws 15 forming a hinge on a vertical tube 11 which allows the tilting

  of the antenna around a horizontal axis XX.

  The base consists of two mechanical parts: a fixed part 21, in the form of a cross for example, which is fixed horizontally (or vertically) by means of screws placed in the holes 22 of its arms. On this fixed part is placed a bubble 23 to perfectly define a horizontal or vertical plane and thus to obtain a plane of

  reference for the definition of the elevation of the antenna.

  - A movable portion 24 surmounted by the tube 11, centered in rotation on the fixed part and secured to the latter by means of two screws 25. These screws slide in the countersink of the movable part. The locking of these two screws ensures the immobilization of the azimuth axis of the antenna after the rotation of the movable part in rotation 24 relative to the fixed part 21 has defined the azimuth axis. To preposition the antenna towards the satellite, a magnetic needle is placed on this moving part as well

  than possibly an orientation dial.

  The tube 11 of this movable part supports the body 7 of the oscillating foot on the axis defined by the two screws 15 shown on the partial section AA of FIG. 1. The elevation adjustment of the antenna is effected by moving a 26, in a maximum sector defined by a movable stop 17, the blocking and the immobilization after adjustment is effected by blocking the

screw 15 and the movable stop.

  All parts of this support stand are made of aluminum, and all forms adopted are simple shapes that can for very large series be obtained by molding, or stamping thus minimizing production costs. In order to simplify the pointing of the antenna, the positioning indexes placed for the adjustment of the elevation and azimuth axes comprise graduations and possibly

  the indication of the satellites pointed.

  For some applications, the moving part 24 and the fixed part 21 of the support assembly can be replaced by the single cylindrical tube 11, which can be directly fitted into a standard tube usually serving as a support for the radio reception antennas. FIG. 2 represents an embodiment of an antenna according to the invention thus simplified intended to be nested directly in a standard tube; the same references designate the same elements as on the

figure 1.

  The essential difference is that the foot of the support tube 11 is directly nested in a standard tube support outside the antenna system, 50. Of course in this case the horizontal part of the support foot is removed, and the reference axis is given directly by the standard tube positioned for this purpose vertically. In this figure is also illustrated in strong lines the parabolic reflector i of 0.33 meter in diameter, and in broken lines a reflector 1 'of a different diameter, for example 0.7 meter. Similarly, to illustrate the adjustment of the orientation of the antenna, the support tube 7 has been shown in three different positions, one in continuous lines and the other two in broken lines to show the possible angular displacement of the antenna.

system.

  The invention is not limited to the embodiments described and shown. In particular, the source has been represented in the figures as a simple helicoid having a free end. This type of source is perfectly suited to the circularly polarized emissions of a satellite such as TDF 1. Of course this provision is not limiting and the source will be adapted to the polarization mode of satellite emissions. Thus, if for the emissions of the TDF satellite 1 the polarization is circular, the polarization for the emissions

  received from the ASTRA satellite is planned horizontally or vertically.

  Likewise some satellites will emit in two circular polarizations, right and left. The corresponding sources will be adapted to receive these different types of polarizations. The tube 4 forming a radome may be made of a material other than polypropylene, provided that this material does not create

no losses.

  The structure thus obtained for the antenna system is particularly compact and very easy to install: all seals are made in the factory and no precaution

  particular is required during installation.

Claims (7)

  An antenna system for reception of a direct broadcast satellite, characterized in that it comprises a parabolic reflector (1) whose rear central portion is fixed to a hollow tubular body (7) of a support leg by means of a intermediate of a fastener (6), the reflector (1), the fastener (6) and the tubular body of the support leg being traversed by a tube (4) of the same axis as the reflector containing the source ( 2, 3) and forming protection and centering means of the source in the reflector, the tubular body (7) G of the support leg being articulated at its base on a horizontal axis (XX) carried by a base and associated with means locking device (26) fixing the elevation of the antenna, the base being rotatable about a vertical axis for fixing the azimuth of the antenna, all the antenna system circuits, and its means for power supply being fixed inside the body tubular support foot.   2. Antenna system according to claim 1, characterized in that the base of the support leg is a tube (11) intended to be simply fitted into a standard vertical axis tube (50) usually used for radio reception antennas. . 3. Antenna system according to claim 1, characterized in that the base of the support leg is formed of two parts: - a first part (21) intended to be fixed on a support, horizontal or vertical, - a second part ( 24) movable in rotation with respect to   the first around a vertical axis, fixing the azimuth of the antenna.   4. Antenna system according to claim 3, characterized in that the fixed part (21) of the base of the support leg is provided with a bubble mark defining a reference plane relative to   to which the elevation adjustment is obtained precisely.   5. Antenna system according to claim 4, characterized in that graduated indexes are provided on the part (24) movable in rotation of the base and on the tubular body of the support foot (7) to locate the axes azimuth and elevation of the antenna during installation.   6. Antenna system according to claim 1, characterized in that the tubular body of the support leg is sealingly closed at its upper part and open at its lower part. Antenna system according to claim 1, characterized in that, for receiving a satellite transmitting circularly polarized waves, the source is formed of a helicoidal illuminant (3) associated with a coaxial cable. (2), all centered in the cylindrical tube (4) made of a material which does not produce losses.