Classifications

• • 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
  • H01Q15/02—Refracting or diffracting devices, e.g. lens, prism
  • H01Q15/08—Refracting or diffracting devices, e.g. lens, prism formed of solid dielectric material
• • 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
  • H01Q19/06—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 refracting or diffracting devices, e.g. lens

Definitions

• the present invention relates to a production method of dielectric material suitable for dielectric antennas such as Luneburg-type lens antennas and to an according antenna.
• Dielectric antennas are well known, e . g from US 4 531 129. In this patent the use of Luneburg antennas and appropriate feeds are described for the use a satellite broadcasting receiver system to receive microwave signals. Such antennas can also be used as part of a transmitter system.
• Virtual dielectric antennas e.g. Luneburg-type antennas are known from the article "Virtual Source Luneburg Lenses”; G. D. PI. Peeler et al., IRE TRANSACTIONS - ANTENNAS AND PROPAGATION, July 1954.
• reflecting means realized as one or more reflectors, are arranged.
• Dielectric lenses can be produced by dielectric material e.g. with voids, which are created in solid plastic material by hemispherical indentations in plastic sheets which are vertically stacked and fixed together.
• dielectric material e.g. with voids, which are created in solid plastic material by hemispherical indentations in plastic sheets which are vertically stacked and fixed together.
• Such a method is known from the article "Artificial dielectrics utilizing cylindrical and spherical voids"; Proceedings of the IRE, Vol. 44, pp 171 174, 1956. It is an object of the present invention to provide a new method for the fabrication of dielectric antennas with reduced production costs.
• Dielectric antennas can be e.g. Luneburg-type lens antennas homogenous-type lens antennas, Eaton-Lippmann lens antennas, or thelike.
• the said antennas may be shaped e.g. spherical, hemispherical, quarter sphere, cylindrical or the like.
• the present invention is based on the following principle.
• a dielectric material composed of individual pieces will appear essentially homogeneous (continious) to signals whose frequency is such that their wavelength is greater than, the dimension of the pieces. This means, that at microwave frequencies of about 10 Ghz, normally used for direct broadcasting from a satellite (wavelength is in the range of about 2.5 cm), pieces of several mi Ii meters in dimension may be used to fabricate the dielectric material.
• the dielectric constant of the resulting material can be changed.
• the relative dielectric constant Er is related to the density of the material by
• Ero is the dielectric constant of the pieces.
• pieces of dielectric material are packed in a given shape, whereby a dielectric body with the desired resulting dielectric constant can be produced, which forms a dielectric antenna or is part of the antenna to be produced.
• spheres are the preferred shape and have an associated packing density of approximately 0,6.
• the resulting material would have a density of 0,63 g/cm 3 .
• Lighter densities could be achieved by using hollow spheres or indentations en their surface.
• the dielectric constant value could be accurately achieved in this way.
• the size of the dielectric pieces is very small with respect to the wavelength (that means less than about 1/10 of the wavelength), their symmetry becomes less important and the spheres could be replaced by other shapes, e.g. like tubes, of either solid or hollow form.
• the loss of an incoming wave increases with an increasing angle of incidence.
• the use of preferred kinds of virtual dielectric lens antennas with used reflecting means, e.g. a reflecting metal plate, which are extended outside the boundaries of the lens, has the advantage that the loss in gain with an angle of incidence not perpendicular to one of the reflecting means can be decreased.
• a feeder horn or an endfire or ⁇ backfire helical antenna or thelike can be used.
• an antenna outside the boundaries of the lens the system is more flexible for receiving waves from several directions, because the feeds have a greater physical separation and do not cause aperture blockage.
• the antenna system is more compact.
• Fig. 1 shows some dielectric pieces, which collectively
• Fig. 2 shows another kind of a dielectric piece
• Fig. 3 shows a radome cover containing dielectric pieces
• Fig. 4 shows a hemispherical Luneburg lens which is
• Fig. 5 shows a hemispherical Luneburg-type antenna
• Fig. 6 shows a quartersphere Luneburg-type antenna
• Fig. 7 shows a top view of di f ferent kind of dielectric lenses and in principle according runs of an incident wave.
• Fig. 1 shows some dielectric pieces 10, which collectively form a dielectric block, which itself has the shape of a dielectric antenna to be produced, from which such an antenna may be separated (cut), or which is a part of the said antenna.
• the pieces 10 may be fixed to eachother, e.g. by glueing, or may just lay near or on eachother.
• the pieces 10 are shaped as hollow spheres with a diameter d less than the wavelength of a radiation to be received or to be transmitted.
• the resulting dielectric constant Er depends on the dielectric constant of the dielectric material 11, which forms the pieces 10, and the relationship of densities d and do.
• do is given by the thickness t of the dielectric material 11 compared to the diameter h of the hollow interior 12.
• a variation of the resulting dielectric constant in dependence on the diameter of the Luneburg lens is required.
• This variation can be achieved e.g. by using different kinds of pieces 10, which collectively form the lens or by producing different kinds of blocks, e.g. shaped as a shell or the like, which collectively form the lens.
• Each of these blocks can be produced by pieces 10 identical inside of each block or with a variation in thickness t, diameter d or by using pieces 10 with a nonspherical shape.
• Fig. 2 shows another type of dielectric pieces 10'.
• the shape of piece 10' shows some indentations. By the number or the size of these indentations the resulting dielectric constant Er can be varied.
• a microwave lens antenna must be protected by a radome cover, which may also serve as a matching layer to reduce the amount of reflected signal at the lens surface.
• this radome cover is made of plastic and may be used as a vessel 13 to contain the unbound plastic pieces 10, 10' respectively.
• the vessel 13 shown in fig. 3 is used for the fabrication of a hemispherical Lens.
• spherical or hemispherical shaped vessels which can be used later as radome cover
• other kinds of vessels are possible.
• Other preferred types have the shape of a quarter sphere or a pyramid. Some of these pyramids may collectively form the dielectric antenna to be produced.
• a tool with a similiar function as a ice-cream shapemaker may be used.
• multiple shell Lenses could be made by employing several thin solid shells to seperate bands of different density pieces. The said shells can be removed after positioning the pieces.
• the medium density plastic material is necessary for Luneburg and homogeneous Lens applications where dielectric constants in the range 1 - 2,5 are typically required.
• dielectric constants in the range 1 - 2,5 are typically required.
• solid plastic material can be used.
• values in the range of approximately 1,8 to 2 can be achieved using low density polypropelene and finally values in the range of approximately 1 to 1,15 can be achieved using foamed plastic material.
• the intension of this invention is to provide a method for obtaining accurate Large volumes of dielectric material with a dielectric constant in the range of about 1,15 to 1,8, which does not require large cooling cycles.
• the pieces 10, 10' respectively could be made from a mixture of a first material with a high dielectric constant, such as ceramic material, ferroelectric ceramics, or thelike, and a second material with a low dielectric constant, such as foamed plastic material, e.g polyethelene.
• a first material with a high dielectric constant such as ceramic material, ferroelectric ceramics, or thelike
• a second material with a low dielectric constant such as foamed plastic material, e.g polyethelene.
• foamed plastic material e.g polyethelene
• sheets containing hollow spherical indentations may be used collectively to form material containing spherical voids simi lar to the material shown in fig. 1.
• These lines or sheets may be arranged in such a way that the shape of the antenna or the block to be produced is formed and that a variation of the dielectric constant is achieved as desired.
• a small round sheet with the effective dielectric constant Er1 of about 2,0 may be taken and laid on a core located in the center of the lens.
• a second one with a dielectric constant Er2 (smaller than Er1) is laid, where the size is a little bit larger than the one of the first sheet.
• This method is continued to a last sheet (n) with an effective dielectric constant Ern of about 1,0 and a quite big size.
• each line may be constant or may vary. With an appropriate variation each line may start in the center point of a (hemi-)spherical Luneburg lens and end at its surface. Such Lines can also be used for the fabrication of other parts, as pyramids, which collectively form the lens to be produced.
• n 1 ,7...1 ,35.
• the distance between the parts 10 can be smaller than the wavelength of a wave to be received.
• Fig. 4 shows the principle of a virtual dielectric Lens to be produced.
• a hemisperical Luneburg lens 110 with a radius R has a reflecting plate 111.
• a first part 112a of a beam 112 to be received is refracted by the Lens 110 and reflected by the plate 111 in such a way that it is focused in the focal point 113.
• the Location of this focal point is determined by the angle of incidence be relative to the perpendicular line 114 of the plate 111 and by the profile of the refraction index of the Lens 110.
• a non-shown antenna is Located, which can be realized e.g. as feeder horn or helical antenna.
• a second part 112b of the beam 112 to be received passes outside of the lens 110.
• the portion of the first part 112a of the beam decreases with increasing angle be and the portion of the second part 112b increases with increasing angle be. This shows that there is a loss of effective antenna area with angle be hence a Loss in antenna gain.
• Fig. 5 shows a first development of the antenna system of fig. 4. Means with the same function as those in fig. 4 are marked with the same reference numbers and they wi ll be explained only as far as it is necessary for the understanding.
• the main difference of this embodiment compared to the arrangement of fig. 4 is that the reflecting plate 111 is extended outside of the boundaries of the lens 110 by the lengh l. Thereby the second part 112b of the beam can also be reflected by the plate 111 and refracted by the lens 110 in such a way that it is essentially also focussed in the focal point 113.
• An embodiment has been realized as a hemi -spherical Luneburgtype Lens with a radius R of 15 cm and an extension length I of 15 cm. Measurements with a wave of 12 Ghz showed that the gain using this extension could be increased by about 2 dB at an angle of incidence be of about 62.5 degrees.
• Fig. 6 shows a three-dimensional sketch of another embodiment of an antenna to be produced.
• the main difference compared to the antenna system of fig. 5 is that a quartersphere Lens is used which can be shaped as a orange slice.
• the beam 112 to be received is transmitted from a satellite 115 and focussed by the quarter sphere lens 116 in the focal point 113 where a feeder horn 117 is provided.
• This lens 116 has twc reflector plates 111 and 111a respectively. These reflectors 111, 111a can have the same size as the according adjacent flat side of the quarter sphere lens 116, but they may also be extended in horizontal direction and/or in vertical direction. Thereby Losses can be reduced and the antenna gain can be maintained with scan angle, similiar to the construction of fig. 5.
• the reflectors are in the upper half than in the Lower half of the antenna. This is due to the elevation angle of satellites to be received being not equal to 0 degrees, but typically about 30 degrees.
• Fig. 7 shows a top view of a spherical lens 120, the hemispherical Lens 110 and the quartersphere Lens 116 and in principle according runs of the incident ray 112.
• the wave 112 is focussed at a focal point 113a which is on the opposite side compared to the direction of incidence of wave 112.
• the wave 112 is focussed at focal point 113b.
• a quarter of Lens 120 which means the quarter sphere lens 116 including the reflectors 111 and 111a the wave 112 is focussed at focal point 113c.
• the focal points 113 may be outside of the boundaries of the lenses 120, 110, 116 when using a homogeneous type lens with a relative dielectric constant Er where
• Er is about or less than 2 or when using a Luneburg-type lens but with a modified variation of the refraction index n with radius r as given by equation (2).
• Versions of the antennas to be produced may include at least one of the following variations: instead of a hemi-spherical or a quartersphere lens just a lens with a conical or pyrami de-like shape may be used. In this case it is preferred that the shape of the according reflecting means is varied in such a manner that it covers at least one of those sides of the lens which are not penetrated by the wave to be received. One or more of these reflecting means can be extended;
• a homogeneous-type lens may be used, which means that the refraction index may be essentially constant throughout the lens;
• the antenna system according to the invention may also be used as transmitter antenna; the antennas presented by this patent application may also be produced according to other fabrication methods, e.g. as presented by the European patent applications 90403051.7 and 91401444.4.
• the present invention a fabrication method for dielectric Lens antennas and according antenna systems are presented, where the said Lens is realized as a virtual source lens by using reflecting means. These reflecting means are preferably extended outside the boundaries of the Lens, whereby the gain of the antenna system can be increased.
• the maximum operating frequency for the antenna of a preferred embodiment is 12,75 Ghz and a void diameter of 8 mm and separation of 1 cm were chosen.
• the plastic material employed was polysterene with a dielectric constant of 2,44. This resulted in an effective dielectric constant of 1,52.
• the querter sphere lens is well suited to multi satellite reception because it provides the necessary scan range with minimum volume.

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• 1992
  • 1992-09-15 EP EP92921618A patent/EP0623247A1/de not_active Ceased
  • 1992-09-15 JP JP5508913A patent/JPH07505018A/ja active Pending
  • 1992-09-15 WO PCT/EP1992/002384 patent/WO1993010572A1/en not_active Application Discontinuation
  • 1992-09-15 AU AU27892/92A patent/AU2789292A/en not_active Abandoned

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