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
  • H01Q19/18—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 having two or more spaced reflecting surfaces
  • H01Q19/19—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 having two or more spaced reflecting surfaces comprising one main concave reflecting surface associated with an auxiliary reflecting surface
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01Q—ANTENNAS, i.e. RADIO AERIALS
  • H01Q1/00—Details of, or arrangements associated with, antennas
  • H01Q1/52—Means for reducing coupling between antennas; Means for reducing coupling between an antenna and another structure
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01Q—ANTENNAS, i.e. RADIO AERIALS
  • H01Q13/00—Waveguide horns or mouths; Slot antennas; Leaky-waveguide antennas; Equivalent structures causing radiation along the transmission path of a guided wave
  • H01Q13/02—Waveguide horns
• • 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
  • H01Q19/02—Details
  • H01Q19/021—Means for reducing undesirable effects
• • 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
  • H01Q19/18—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 having two or more spaced reflecting surfaces

Definitions

• the present invention relates to the technical field of electronics and more specifically to information and communication technologies using double reflector antennas.
• Antenna systems are currently under constant evolution to enable them to be upgraded for satellite communications and to meet current and future requirements for electrically small reflector antenna systems.
• the dual reflector configuration is the most compact geometry for high gain antenna systems.
• reflectors can be cylindrical, spherical, as well as offset, symmetrical, or shaped for a custom radiation pattern.
• sub-reflector and main configurations there is a blockage produced by the sub-reflector, the struts, the power support mechanism, the alignment, etc.
• Geometries such as the offset dual reflector avoid blocking by the sub-reflector, although this increases cross polarization.
• the sub-reflector is several times smaller than the main reflector, with symmetric AD (offset axis) systems measuring around 2l - 4l.
• AD systems can be compatible with dual band feeders.
• the dielectric to support the sub-reflector can also be used to match impedances.
• Using a single choke on the horn has been shown to improve adaptation and lighting quite efficiently. In this sense, the so-called "coffee can" design implements a single choke as the main improvement. This artifact is reproduced coaxially multiple times in the Chaparral-type antenna aperture to enhance the purity of linear polarization. Therefore, the implementation of shocks reduces the cross polarization, as well as the level of the lateral lobe.
• the state of the art contemplates in one of the solutions systems powered by a sub-reflector formed by chokes called 'Hat'.
• this type of power supply is initially proposed to reduce cross-polarization, it has been applied to increase the efficiency of the antenna, improving the lighting on the edge of the main reflector, achieving reduction of the lateral lobe and phase error compensation.
• the dielectric lens has been implemented for various reasons, for adjusting the impedance, to adapt the aperture field to the sub-reflector surface, and to support the sub-reflector.
• the state of the art also includes solutions that propose a reflective antenna, to improve return losses with respect to previously developed systems, based on a circular waveguide antenna supply with a flat sub-reflector that has a radial dielectric lens that together they reflect the waveguide energy on a rotationally symmetric main reflector.
• the dimensions of the antenna feed are also chosen so that their radiation pattern has zero amplitude along the antenna feed axis. The latter further improves return losses by minimizing the amount of energy from the main reflector that is directed back to the feed opening.
• the same solution features a feed radiation pattern with asymmetric amplitude narrowing to improve the lateral lobe ratio in a preferred plane.
• the state of the art also includes a dual reflector, low secondary lobe antenna solution. , with a relationship between the focal length of the reflector and the diameter of the reflector set to less than 0.25.
• the system uses a waveguide coupled at its end to a convex reflector, which provides illumination to the main reflector.
• a dielectric block coupled to one end is used which, in addition to adapting the opening of the waveguide, supports the convex sub-reflector.
• the diameter of the sub-reflector is dimensioned to be 2.5 wavelengths or more than a desired operating frequency. The latter makes it a multi-band system and improves its efficiency.
• Another possibility found in the state of the art proposes a reduction in the density of the surface current near the edges of the antenna of the parabolic reflector to decrease the level of the secondary lobe of the reflector. To do this, the current density is reduced by placing conical resistive edge loads on the reflector to gradually decrease the conductivity from the center of the reflector to the edge.
• a solution that improves the previous techniques contemplates an antenna with sub-reflector with reduction of side lobes.
• Said solution comprises a conical and corrugated convex anisotropic sub-reflector connected to a waveguide, and this is in the focus of a deep main reflector with the focal point very close to the aperture.
• the sub-reflector has variable depth corrugations. Variable depths of corrugations result in reactance variable, or an adjustment (taper) of the sub-reflector reactance.
• This convex sub-reflector has a conical shape designed in such a way that it guides or directs the energy from the antenna supply to the main reflector, guaranteeing that the side lobes are greatly reduced.
• the sub-reflector has a shape that can be shaped to direct or guide the energy in the desired direction in an optimized way.
• the deep geometry of the main reflector allows the small sub-reflector to be placed within the edge of the main reflector, so that the assembly can be covered with a flat radome.
• a first aspect of the invention refers to a feeder system for double reflector antennas, comprising: a feed horn coupled to a waveguide; and a sub-reflector plate that has a front face to reflect radiation emitted by the power horn, and a rear face, where the system is characterized in that it comprises at least a first high-impedance surface arranged on the rear face of the plate. sub-reflector.
• the high impedance surfaces implemented in the system of the present invention reduce surface currents and the generated electric field, which are responsible for undesirable increases in the secondary lobes and the anti-polar component.
• the first high impedance surface comprises at least one axial corrugation.
• the first high impedance surface comprises at least one choke of certain dimensions tuned to a critical frequency.
• the high impedance corrugated surfaces are implemented on the rear face of the sub-reflector, unlike other state-of-the-art designs that use corrugations to obtain a certain illumination.
• the corrugations axial also known as chokes, tuned to the critical frequencies at which you want to eliminate the contribution of the fields that may be generated on the surface of the sub-reflector. In this way, their contribution to the secondary lobes and to the counter-polar component is reduced.
• the first high-impedance surface can be defined by its dimensions according to certain parameters: a first depth parameter, a second slot width parameter and a third wall width parameter.
• the values assigned to said parameters are equal to or greater than 1/4, 1/8 and 1/80, respectively.
• the first high impedance surface comprises at least five chokes, where each of the chokes has different or equal dimensions to the others.
• the present invention contemplates a second high impedance surface arranged on the waveguide.
• the second high impedance surface has at least one set of lateral chokes arranged externally on the waveguide, transversely.
• the support means can be selected from a radome, a lens or dielectric element and rods.
• the waveguide is contemplated to be arranged internally along a supply mast, attachable at one end to a main reflector plate of the double reflector system and attachable at the end opposite the supply horn.
• a main reflector plate is contemplated, coupled to a first end of the supply mast, where the supply mast comprises two high impedance surfaces with five chokes each; and where the sub-reflector plate is supported by a radome, so that the front face of the sub-reflector plate is arranged in a position facing the feed horn that reflects radiation towards the main reflector plate, and where the front face
• the sub-reflector plate has an elliptical geometry.
• the feeder system of the present invention is not only applicable for new designs of double reflector systems, but can advantageously be implemented in already designed systems, which are desired to be improved by reducing their level of anti-polar component and their level of secondary lobes.
• the advantages for double reflector antenna systems are multiple.
• the reduction of the level of secondary lobes and the anti-polar component which in systems with a low focal distance ratio with respect to the diameter of the main reflector (f / D) and of electrically small main reflectors of few lambdas ( ⁇ 50l), is a design challenge.
• FIG 1 shows the general embodiment of the SLL bass feeder system and anti-polar component for double reflector antennas.
• Figure 2 shows an embodiment option where the surface that receives the fields from the feeder and reflects them towards the main reflector is of a hyperbolic type.
• Figure 3 shows another embodiment option, where the surface that receives the fields from the feeder and reflects them towards the main reflector is of the elliptical type, making in this case that the system is offset axis with an elliptical sub-reflector.
• Figures 4A, 4B and 4C show the rear face of the sub-reflectors, the which influences the behavior of surface currents in the case of electrical surfaces and for the case when implementing high-impedance surfaces with chokes.
• the gray scale represents the intensity of the surface currents, with the lightest shade corresponding to the highest current intensity.
• Figures 5A and 5B show the mast of the feeder system and the influence on the behavior of surface currents for the cases when one or two sets of high impedance surfaces are implemented with chokes.
• Figures 6A, 6B, 6C and 6D show different propagation surfaces, which imply different behaviors of the electromagnetic plane waves TEM, TE and TM.
• the present invention discloses a feeder solution for dual reflector antennas with reduced secondary lobe level and cross-polarization component.
• the description of components of the feeder system and techniques used are based on the embodiments represented in the figures, previously commented, with illustrative intentions.
• the present invention can be implemented in any primary and secondary double reflector system, although its greatest contribution to optimization occurs in centered double reflector systems.
• the feeder system of the present invention achieves its advantageous effects by reducing the currents produced by the fundamental mode and the higher ones generated by the opening or horn implemented. These currents are reduced at the horn mast and at the rear face of the sub-reflector. Said currents can be produced by the field delivered to the waveguide that feeds the horn, and therefore existing at the aperture, as well as by the fields diffracted from the other components or structure of the antenna system. In this way the objective of reducing the level of unwanted secondary lobes and anti-polar component in the system is achieved.
• the specific configuration of the system of the present invention, which produces the effect of reducing unwanted currents, is based on the implementation of chokes with variable dimensions adjusted to each problem, on the metal surfaces considered critical.
• one of the embodiments of the invention focuses on arranging corrugations in metallic planes with canonical wave solution and where the Kildal correction can be applied.
• This analysis can also be used in the reduction of surface waves of electric fields since they are supported on magnetic surfaces.
• FIGS 1, 2 and 3 show a general diagram with the parts and components of the feeder system of the present invention, according to different embodiments that disclose different options of support elements and geometries of the surface of the sub-reflector that receives the fields from the feeder.
• the bands of operation of the system can be any, both for narrow-band systems, for broadband, and for multi-band systems, and regardless of the type of polarization used.
• the proposed feeder has the following elements: feeder mast 4, where the mast in turn comprises the waveguide, which supplies a horn or opening 2, and high impedance surfaces 31 and 32.
• the number of surfaces can vary, as can be seen in the different masts represented in Figures 5A and 5B, where these surfaces are implemented as sets of N (first set 51) and L (second set 52) chokes, which are defined based on the needs of the system to reduce the currents coming from the opening, by the displaced currents and by the contribution by dispersion of the different components of the system; support elements of the sub-reflector, which depend on the type of sub reflector implemented.
• these support elements may be a radome 23 that integrates with the exterior of the horn and holds the sub-reflector, a lens or dielectric element 22 that adapts to the aperture or horn, and this support the sub-reflector , or struts 24 (rods) that can be attached to the mast or from the main reflector 5 and that hold the sub-reflector. All these options ensure the correct position of the sub-reflector according to the electromagnetic design of the system; and sub-reflector 10 with a high impedance surface on the back surface 11, and with any geometry or type of design for face 12 that receives the fields from the feeder and reflects them to the main reflector.
• the double reflector systems comprised by the present invention can be classic or optimized.
• classics are for example, the Cassegrain, Gregorian and ADE (Axial Displaced Elliptical) double systems, while among the non-classics, we can list the modified ADE systems in which the sub reflector is not elliptical, but is replaced another type of self-supporting sub-reflector such as those discussed in the state of the art, such as the “Hat-fed” type powered system, among others.
• Figures 6A-6D present the different types of surfaces contemplated, which influences the behavior of electromagnetic waves as will be seen below. Note that typically, “overshoot" problems, or exceeding the requirement masks, are more critical in the frequency bands defined for transmission, so the reduction of unwanted currents can be concentrated for those frequencies. However, a narrow band approximation cannot be used, therefore the periodic use of resonant corrugations with constant depth of quarter lambda is rejected.
• TE field waves define the electric field vector in the direction parallel to the XY plane, where this plane belongs to the surface under study with its orthogonal magnetic field vector, and both orthogonal to the propagation direction.
• plane waves TM define the vector of the magnetic field parallel to the XY plane that belongs to the surface under study, with its orthogonal electric field vector and both orthogonal to the propagation direction. In both cases, electric and magnetic vectors comply with the right-hand rule that describes the direction of propagation.
• the surface 61 of FIG. 6A is a constant electrical surface in which the electric field of the surface is zero for its components in the XY plane.
• surface 64 of Figure 6D which belongs to a stage with several sources located at different distances from its center and surrounding it in almost all impact directions, the sources provide fields under evaluation, so they have to deal with the characteristics of the dispersive surface. Therefore, surface 64 has different depths, grooves, and wall widths to cover the entire frequency band. This means that a flat corrugated surface with chokes of depth exactly equal to a quarter of a lambda mitigates the oblique plane wave whose vectors are perpendicular to the corrugations, which can be independent of the direction of the field. In this sense, these surfaces are known as polarization independent surfaces.
• the preferred embodiment of the SLL bass feeder system and anti-polar component for double reflector antennas consists of: a feeder mast 4 with two high impedance surfaces 31 and 31 of five chokes each, where the mast contains the waveguide feeding a horn 2 arranged at its end to feed a sub-reflector; a horn or opening 2 of one or two front chokes; a radome 23 as a support element for the sub reflector; and a sub-reflector 10 with a high-impedance surface on the back surface 11 consisting of five chokes of varying dimensions, and with any geometry for face 12 that receives the fields from the feeder and reflects them towards the elliptical-type main reflector, or shaped elliptical.

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• 2019
  • 2019-01-17 ES ES201930025A patent/ES2707900B2/es active Active
  • 2019-12-19 WO PCT/ES2019/070867 patent/WO2020148467A1/es unknown
  • 2019-12-19 EP EP19909691.8A patent/EP3913745A4/de not_active Withdrawn

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