Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01Q—ANTENNAS, i.e. RADIO AERIALS
  • H01Q19/00—Combinations of primary active antenna elements and units with secondary devices, e.g. with quasi-optical devices, for giving the antenna a desired directional characteristic
  • H01Q19/10—Combinations of primary active antenna elements and units with secondary devices, e.g. with quasi-optical devices, for giving the antenna a desired directional characteristic using reflecting surfaces
  • H01Q19/12—Combinations of primary active antenna elements and units with secondary devices, e.g. with quasi-optical devices, for giving the antenna a desired directional characteristic using reflecting surfaces wherein the surfaces are concave
  • H01Q19/13—Combinations of primary active antenna elements and units with secondary devices, e.g. with quasi-optical devices, for giving the antenna a desired directional characteristic using reflecting surfaces wherein the surfaces are concave the primary radiating source being a single radiating element, e.g. a dipole, a slot, a waveguide termination
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01Q—ANTENNAS, i.e. RADIO AERIALS
  • H01Q15/00—Devices for reflection, refraction, diffraction or polarisation of waves radiated from an antenna, e.g. quasi-optical devices
  • H01Q15/0006—Devices acting selectively as reflecting surface, as diffracting or as refracting device, e.g. frequency filtering or angular spatial filtering devices
  • H01Q15/0013—Devices acting selectively as reflecting surface, as diffracting or as refracting device, e.g. frequency filtering or angular spatial filtering devices said selective devices working as frequency-selective reflecting surfaces, e.g. FSS, dichroic plates, surfaces being partly transmissive and reflective
  • H01Q15/0026—Devices acting selectively as reflecting surface, as diffracting or as refracting device, e.g. frequency filtering or angular spatial filtering devices said selective devices working as frequency-selective reflecting surfaces, e.g. FSS, dichroic plates, surfaces being partly transmissive and reflective said selective devices having a stacked geometry or having multiple layers
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01Q—ANTENNAS, i.e. RADIO AERIALS
  • H01Q15/00—Devices for reflection, refraction, diffraction or polarisation of waves radiated from an antenna, e.g. quasi-optical devices
  • H01Q15/14—Reflecting surfaces; Equivalent structures
  • H01Q15/148—Reflecting surfaces; Equivalent structures with means for varying the reflecting properties
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01Q—ANTENNAS, i.e. RADIO AERIALS
  • H01Q15/00—Devices for reflection, refraction, diffraction or polarisation of waves radiated from an antenna, e.g. quasi-optical devices
  • H01Q15/14—Reflecting surfaces; Equivalent structures
  • H01Q15/16—Reflecting surfaces; Equivalent structures curved in two dimensions, e.g. paraboloidal
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01Q—ANTENNAS, i.e. RADIO AERIALS
  • H01Q19/00—Combinations of primary active antenna elements and units with secondary devices, e.g. with quasi-optical devices, for giving the antenna a desired directional characteristic
  • H01Q19/10—Combinations of primary active antenna elements and units with secondary devices, e.g. with quasi-optical devices, for giving the antenna a desired directional characteristic using reflecting surfaces
  • H01Q19/12—Combinations of primary active antenna elements and units with secondary devices, e.g. with quasi-optical devices, for giving the antenna a desired directional characteristic using reflecting surfaces wherein the surfaces are concave
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01Q—ANTENNAS, i.e. RADIO AERIALS
  • H01Q19/00—Combinations of primary active antenna elements and units with secondary devices, e.g. with quasi-optical devices, for giving the antenna a desired directional characteristic
  • H01Q19/10—Combinations of primary active antenna elements and units with secondary devices, e.g. with quasi-optical devices, for giving the antenna a desired directional characteristic using reflecting surfaces
  • H01Q19/12—Combinations of primary active antenna elements and units with secondary devices, e.g. with quasi-optical devices, for giving the antenna a desired directional characteristic using reflecting surfaces wherein the surfaces are concave
  • H01Q19/13—Combinations of primary active antenna elements and units with secondary devices, e.g. with quasi-optical devices, for giving the antenna a desired directional characteristic using reflecting surfaces wherein the surfaces are concave the primary radiating source being a single radiating element, e.g. a dipole, a slot, a waveguide termination
  • H01Q19/132—Horn reflector antennas; Off-set feeding

Definitions

• the present invention relates to the field of satellite dishes.
• the parabolic reflectors commonly used today are formed of structures either entirely metallic, or provided with a metallization which serves as a reflecting surface.
• the object of the present invention is to propose a new parabolic antenna which makes it possible to eliminate the drawbacks of the prior art.
• This object is achieved according to the present invention, thanks to a reflector consisting of n contiguous strips of dielectric material, defined by n + 1 surfaces of distinct parabolic equations shaped to define a common electromagnetic focus.
• each blade is a piece of homogeneous dielectric (plastic, ceramic, air, etc.) with a dielectric constant ⁇ greater than or equal to 1 and having low losses.
• These blades can either be stacked by simple juxtaposition and held by an external crimping, or glued against each other.
• all the blades are delimited by the same outline.
• the useful frequency bandwidth depends on the choice of materials and the number of blades, - it can offer very low losses, even at very high frequencies, and
• FIG. 1 shows a schematic sectional view of a laminated dielectric reflector according to the present invention
• FIG. 2 schematically illustrates a parabolic contour surface, in an orthonormal reference frame for the definition of a paraboloid equation
• FIG. 3 schematically illustrates the directivity of a cylindrical reflector according to the present invention
• FIG. 4 schematically illustrates the directivity of a rectangular contour reflector according to the present invention
• FIG. 9 represents a particular embodiment of stacking of blades in accordance with the present invention
• FIG. 10 represents the modulus of the reflection coefficient, as a function of frequency, for this stacking
• FIGS. 11 and 12 schematically illustrate respectively a reflector with a centered focus and a reflector with an off-center focus
• FIG. 13 represents the theoretical directivity of a dielectric reflector according to the present invention
• FIG. 14 represents the directivity measured on a dielectric reflector according to the present invention.
• FIG. 15 shows schematically a dual-band antenna.
• a reflector according to the present invention, consisting of n contiguous strips referenced 1, 2, 3 ... n-1, n, made of dielectric material, each defined by two parabolic surfaces.
• the stack of n blades defines n + 1 surfaces of parabolic equations Si, S 2 ... S ( ... S n , S hinder+ ⁇ .
• Each plate has a respective dielectric constant ⁇ i, ⁇ 2 , ⁇ 3 ... ⁇ n .
• each strip 1 to n is a homogeneous piece of dielectric, for example plastic, ceramic, air, etc. having a dielectric constant ⁇ greater than or equal to 1 and having low losses.
• Figure 1 is symbolized under the reference Se an external crimp capable of maintaining by simple juxtaposition the stack of blades thus formed. Alternatively, one can consider gluing said blades against each other.
• contour C can be the subject of numerous variants.
• the strips of dielectric material making up the reflector according to the present invention may have a rectangular or circular outline.
• the dimensions of the blades, the materials which constitute them and the relative positioning of each of these blades are preferably chosen on the basis of the following elements, so as to present, in a given frequency band, the properties of an excellent reflector .
• the surfaces of the blades 1 to n coincide with paraboloids and their relative positions are identified by the position of the focus of each of the paraboloids.
• the juxtaposition of the dielectric plates which make up the reflector is then defined by the set of focal point-focal distance couples (I ,, f,) Each of these two parameters depends on the operating frequency of the reflector and on the permittivity ⁇ , of each dielectric strip
• the reflector can be defined on the basis of the following parameters
• the directivity of the uniformly illuminated reflector is directly connected to the projected surface S of the reflector (or section of the envelope cylinder) and defined by the following relation
• the dimensions of the reflector will be fixed according to the desired directivity by applying the previous formulas.
• the standard radiation pattern can be checked based on the following items.
• the normalized radiation diagram corresponds to the spatial Fourier transform of the geometry of the opening.
• the quality of the reflector is essentially defined by the number of blades composing it.
• the number of plates depends on the contrast of the permittivities &, between the directly neighboring plates.
• the operating frequency associated with the knowledge of the permittivities ⁇ i makes it possible to determine the distance ⁇ j which separates the two faces Si and S i + ⁇ of each plate. This distance is taken on the axis h, Pi which passes through the focal point I-, and the vertex Pi of the parabolic surface considered.
• the determination of the focus position and the focal distance for each surface can be determined based on the following
• R ma represents the greatest distance between the axis I ,, P, and the contour of the blades
• the f are the only parameters missing at this stage of the design since the positions of the foci I, are a function of the e, and of the f. A very good compromise to avoid too many calculations is to take the same section for all the blades
• Each blade is characterized by its thickness e, given on the axis of revolution of the system, by the focal distance f, defining the surface concave parabolic S, - of the blade and by the convex parabolic surface S, - + 1 of focal length +1.
• This operation is done gradually, interface by interface, starting with the blade closest to the focus.
• the choice of the first focal length f1 associated with the surface S1 imposes the focal length of the dielectric reflector. That is to say that the focus of the complete reflector coincides with the focus of the first interface S1.
• the method consists in calculating the wave impedance brought back to the level of the first interface Si.
• the calculation must be carried out in the space of complex numbers.
• To start the resolution we bring the effect of the last blade n to the level of the interface n.
• the result provides the impedance seen by the electromagnetic wave at the interface n.
• the reasoning is repeated to determine the impedance seen at the interface n-1 and this until the impedance is known on the first interface Si.
• the next step follows the same reasoning. This involves removing the interface between z 2 and z e3 and replacing the plate 2 with a medium of impedance z e2 (see Figure 7).
• the reflection coefficient is known in module and in phase and the frequency band usable for the reflector can then be assessed.
• FIG. 9 There is shown schematically in FIG. 9 an example of association of blades having different dielectric constants.
• FIG. 9 corresponds to a structure comprising:
• the modulus of the reflection coefficient obtained by calculation on the basis of this structure is illustrated in FIG. 10.
• a parabolic reflector used in reception concentrates at the focal point the incident energy which comes from its pointing direction (direction of the axis ( ⁇ u Pj)).
• the center focus reflectors There are, however, two families: the center focus reflectors and the center focus reflectors.
• the focal point is in the path of the incident wave, as illustrated in FIG. 11. This means that the electromagnetic energy reception system shadows the incident beam.
• An additional simplification may consist in using air as a dielectric, which ultimately amounts to using only one solid material constituting the second alternating dielectric.
• the permittivity contrast between ⁇ i and ⁇ 2 becomes less important and the number of layers required increases.
• the reflector obtained operates around 40 GHz.
• the directivity curves illustrated in FIG. 13 are indicated as a function of the frequency.
• the inventors also produced another parabolic reflector using blades made of a single material alternated with air interfaces.
• the inventors have in particular produced reflectors comprising 7 identical blades of ⁇ r alternated with air blades.
• the theoretical directivity curve of this reflector as a function of the frequency and the real directivity curve measured always as a function of the frequency are illustrated in FIG. 14.
• the useful frequency bandwidth around f 0 can be adjusted by an appropriate choice of the materials used
• a defect can be formed by the addition in a stack of blades respecting a given periodicity, of a separate blade (or of several blades) specific (s) not respecting the same periodicity, or of the absence one (or more) blade (s) in the periodicity.
• Such a break in one or more places, in the periodicity of the stack makes it possible to create frequency bands, in the reflection band of the reflector, for which the energy passes through the structure and no longer reaches the focus.
• the device can respond in two completely different ways for two neighboring frequencies: to be transparent for the first and to concentrate the energy at the focus for the second.
• the dielectric blades can be obtained by molding of plastic material, which means a low manufacturing cost.
• Such a system is intended to operate in the vicinity of a frequency of 75 GHz.
• the feasibility of a dielectric reflector made with materials having permittivities close to common plastics has been considered.
• the diameter of the reflector is of the order of 80mm.
• a focal length f1 0.04m has been chosen arbitrarily.
• the present invention is not limited to this focal distance or to the pairs of permittivities ( ⁇ i, ⁇ 2 ) indicated.
• TV reception is at 12 GHz.
• the first group of dielectric plates reflects and concentrates the electromagnetic energy contained in the first useful frequency band and the second group of plates concentrates the energy contained in the second frequency band.
• the diameter of the reflector is around 180cm.
• the choice of ⁇ i, ⁇ 2 and focal lengths can be adapted to the desired working frequency bands and to the materials available. Such a reflector can meet the following characteristics:
• one of the materials used can have electrical characteristics (permittivity, permeability) which vary and depend on an external source.
• the reflective operating frequency band of the reflector will then be dependent on the level of the source applied.
• the operating band in reflection and the bands in transmission are then controllable.
• E-2, E-3, E-4 denote respectively 10 "2 m, 10 " 3 m and 10 "4 m.
• the respective geometric focal points distinct from the various parabolic surfaces involved are not confused with the electromagnetic focal point, that is to say the focal point at which a beam arriving on the reflector with an incidence parallel to the axis of the reflector.
• the electromagnetic focus of the reflector is coincident with the geometric focus of the first concave parabolic surface.
• the offset between the electromagnetic focus and the geometric foci of the following parabolic surfaces results from the fact that the waves reflected on these following interfaces do not reach the respective geometric focus of each of these interfaces, but the common electromagnetic focus because these waves undergo the cumulative effect of the previous blades crossed back and forth.

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• Physics & Mathematics (AREA)
• Electromagnetism (AREA)
• Aerials With Secondary Devices (AREA)
• Laminated Bodies (AREA)

Applications Claiming Priority (3)

Publications (2)

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• 1998
  • 1998-11-17 FR FR9814394A patent/FR2786031A1/fr not_active Withdrawn
• 1999
  • 1999-11-17 US US09/856,406 patent/US6456254B1/en not_active Expired - Fee Related
  • 1999-11-17 EP EP99956064A patent/EP1131858B1/de not_active Expired - Lifetime
  • 1999-11-17 ES ES99956064T patent/ES2198157T3/es not_active Expired - Lifetime
  • 1999-11-17 WO PCT/FR1999/002816 patent/WO2000030215A1/fr active IP Right Grant
  • 1999-11-17 DE DE69907948T patent/DE69907948T2/de not_active Expired - Fee Related
  • 1999-11-17 AU AU12758/00A patent/AU1275800A/en not_active Abandoned
  • 1999-11-17 JP JP2000583122A patent/JP2002530911A/ja active Pending

Non-Patent Citations (1)

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