Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01Q—ANTENNAS, i.e. RADIO AERIALS
  • H01Q3/00—Arrangements for changing or varying the orientation or the shape of the directional pattern of the waves radiated from an antenna or antenna system
  • H01Q3/26—Arrangements for changing or varying the orientation or the shape of the directional pattern of the waves radiated from an antenna or antenna system varying the relative phase or relative amplitude of energisation between two or more active radiating elements; varying the distribution of energy across a radiating aperture
  • H01Q3/30—Arrangements for changing or varying the orientation or the shape of the directional pattern of the waves radiated from an antenna or antenna system varying the relative phase or relative amplitude of energisation between two or more active radiating elements; varying the distribution of energy across a radiating aperture varying the relative phase between the radiating elements of an array
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01Q—ANTENNAS, i.e. RADIO AERIALS
  • H01Q11/00—Electrically-long antennas having dimensions more than twice the shortest operating wavelength and consisting of conductive active radiating elements
  • H01Q11/02—Non-resonant antennas, e.g. travelling-wave antenna
  • H01Q11/08—Helical antennas
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01Q—ANTENNAS, i.e. RADIO AERIALS
  • H01Q21/00—Antenna arrays or systems
  • H01Q21/06—Arrays of individually energised antenna units similarly polarised and spaced apart
  • H01Q21/061—Two dimensional planar arrays
  • H01Q21/067—Two dimensional planar arrays using endfire radiating aerial units transverse to the plane of the array

Definitions

• the present invention relates to antennas for traveling satellites.
• the antennas used by the scrolling satellites are either omnidirectional type antennas (SPOT, ERS, etc.) or pointable directional type antennas (LANDSAT, etc.).
• the beam is Gaussian and the scanning is carried out using a pointing mechanism, the antenna behaving as a centered parabolic reflector of conventional design.
• An object of the invention is to provide an antenna for a scrolling satellite which does not require any pointing mechanism, which has a gain greater than the omnidirectional antennas and which is compact and of low cost.
• the invention provides an antenna for the retransmission on the ground of images collected by instruments for taking a view of a scrolling satellite, characterized in that it comprises a plurality of elementary radiation antennas of the type having a plurality of strands distributed regularly in a helix around the same generator of revolution as well as means of equi-amplitude supply of the different strands, in that these different elementary antennas are aligned and in that the plane in which these different elementary antennas are distributed is intended, when the satellite is in orbit, to be perpendicular to the direction of the speed vector of the satellite and in that it comprises means of phase shifting of the supply of these different elementary antennas which are capable of producing electronic offset of the elongated beam generated by said elementary antennas.
• the beam The emission emission is a beam of elliptical type ("fan beans" according to English terminology) which extends in a direction parallel to that of the speed vector of the satellite.
• the depointing of this beam on a given longitude makes it possible to reach, during all the time of passage of a satellite, a station being at this longitude, and this without needing to modify this depointing as the satellite advanced. It is understood that such an antenna structure does not require complicated electronics and allows high transmission rates.
• the number of elementary radiating elements is equal to or greater than five; the elementary radiating elements are offset with respect to one another with a pitch chosen so as to avoid the lobes of networks;
• the pitch between two elementary antennas is around 19 mm;
• phase shift means are coded on 3 to 8-bits; the phase shifting means are of the ferrite type.
• FIG. 1 is a schematic representation illustrating an antenna according to an embodiment of the invention
• FIG. 2 is a graph on which the diagram of an elementary radiating element of the antenna of FIG. 1 has been plotted
• FIGS. 3 to 6 illustrate different diagrams of covers obtained with the antenna of FIG. 1.
• the antenna illustrated in FIG. 1 comprises a plurality of elementary radiating elements referenced by 1. These elementary radiating elements 1 each comprise a plurality of helical strands distributed regularly around the same generator of revolution.
• the generator is for example conical or cylindrical. These strands are equally supplied.
• these strands are four in number and define four identical helices, offset by ⁇ / 2 relative to each other. These four strands are advantageously supplied with phase quadrature.
• the angular radiation diagram of such an elementary radiating element is of the type illustrated in FIG. 2.
• This diagram corresponds to the diagram obtained for an axial height of radiating element of 0.050 m, a basic radius of 0.018 m, as well as an emission frequency of 8000 MHz. It relates to a measuring sphere 10 m in diameter.
• the elementary radiating elements with several helical strands have, as will be seen below, the advantage of having more gains at 50 ° than at 0 ° and therefore making it possible to compensate for the loss of deflection.
• the elementary radiating elements 1 are distributed in line in a plane perpendicular to the direction of the speed vector.
• the pitch between said radiating elements 1 is for example 19 mm for a transmission frequency of 8000 MHz, which makes it possible to have no network lobes.
• the network pitch d is such that d ⁇ / (l + sin ⁇ ) where ⁇ is the wavelength of the radiation, and ⁇ the maximum depointing desired.
• the radiating elements 1 are supplied via phase shifters 2 of the ferrite type and couplers 3, by a power distributor 6 (in this case 1: 5), which is for example of the waveguide type.
• phase shifters 2 are controlled by a unit 4, which is the on-board computer of the satellite, to which they are connected by control electronics 5.
• phase-shifters of the ferrite type has the advantage of making it possible to always keep the same offset.
• the consumption of the control electronics is then limited.
• the phase shifts imposed on the different radiating elements 1 make it possible to achieve the desired depointing, and this up to +. 62 °.
• the choice for radiating elements 1 of a propeller structure makes it possible to have a gain at 50 ° greater by 2 dB than the gain presented at 0 ° (excluding compensation for space attenuation difference difference -62 ° lift satellite with respect to the zenith) and therefore to naturally compensate for the loss of deflection.
• the optimal number of elementary radiant elements will vary from five to twelve depending on the needs of the mission.
• the phase shifters 2 have, for example, quantization steps of 22.5 ° and are coded on 4 bits.
• FIG. 3 illustrates the coverage obtained with the antenna which has just been described, in the case of a zero phase shift between the different radiating elements 1. There is then no depointing and the maximum directivity of the antenna is 11.55 dB.
• the diagram is then deviated by + 18 °.
• the directivity is 11.52 dB.
• the depointing is then 32 °, the directivity of 11.49 dB.
• the distortion obtained is 48 °, the maximum directivity of 11.45 dB.
• the directivity obtained at 65 ° is greater than 9 dB, i.e. a gain greater than 7.5 dB if we consider losses of 0.5 dB on the distributors, 0.5 dB for the phase shifters, 0, 25 dB at the connector level and 0.25 dB at the power supply level.
• the antenna with deflection which has just been described allows high transmission rates on the ground and allows retransmissions of High resolution images.
• the beam switching is preferably carried out before passage, so as to avoid the problems of phase jump on the generated coverage.
• the antenna diagram does not compensate for the attenuation of space, it is possible to envisage changes in transmission speed in order to best use the gains of the antenna in the areas close to the transition to the zenith.
• the depointing antenna which has just been described has the advantage of being of low cost and above all of compactness.
• the size of the radiating part is 90mm in length, 5mm in width and 50mm in height.
• the antenna comprises several online antennas of the type which has just been described and switching means making it possible to switch from one online antenna to another according to the movements of the satellite, and in particular of its roll movements.
• the antenna includes motorization means which make it possible to modify the orientation of the line (s) of elementary radiating elements in order to compensate for the potential movements of the satellite, in particular its roll movements.

Landscapes

• Variable-Direction Aerials And Aerial Arrays (AREA)
• Radio Relay Systems (AREA)
• Details Of Aerials (AREA)

Applications Claiming Priority (3)

Publications (2)

Family

ID=9504893

Family Applications (1)

Country Status (8)

Families Citing this family (10)

Family Cites Families (6)

• 1997
  • 1997-03-17 FR FR9703250A patent/FR2760900B1/fr not_active Expired - Fee Related
• 1998
  • 1998-03-17 EP EP98917183A patent/EP1010214B1/de not_active Expired - Lifetime
  • 1998-03-17 AT AT98917183T patent/ATE247871T1/de not_active IP Right Cessation
  • 1998-03-17 US US09/381,537 patent/US6252562B1/en not_active Expired - Lifetime
  • 1998-03-17 CA CA002284872A patent/CA2284872A1/fr not_active Abandoned
  • 1998-03-17 WO PCT/FR1998/000535 patent/WO1998042042A1/fr not_active Ceased
  • 1998-03-17 JP JP54020198A patent/JP2001516536A/ja active Pending
  • 1998-03-17 DE DE69817373T patent/DE69817373T2/de not_active Expired - Lifetime

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events