EP0512487A1 - Antenna with shaped lobe and high gain - Google Patents

Abstract

The invention comprises a shaped array on a surface of revolution of arbitrary profile, which comprises several generatrices (12) of radiating elements (13), lying in a plane passing through the axis of revolution ( DELTA ); all the radiating elements of a given generatrix are linked to a single control point. Application in particular to the field of space transmissions. <IMAGE>

Description

The invention relates to a high-gain shaped lobe antenna.

Antennas of this type are very useful in the space field. Thus the traveling and low-orbiting satellites have a very open cone of visibility of the earth: at an altitude of 800 km, the half-angle at the top of the cone is 63 °. The distance of such a satellite to a station inside this cone varies from 800 km (at Nadir) to 2300 km on the edge of the cone. In the case of a telemetry or remote control mission between this satellite and this station, an attempt is made to provide an isoflux link, whatever the relative position of this station in the cone. The antennas used for such missions must therefore present a diagram such that the size of PIRE has a maximum at the edge of the cone and is decreasing until Nadir; The dynamics then being of the order of 12 dB. Such templates can include, in addition, either a provision for low levels (at Nadir, the dynamic falling to around 10 dB) or on the contrary a compensation for atmospheric attenuation (proportional to the distance), the dynamic becoming greater than 13 dB. These jigs are revolution in azimuth and have the shape of a bowl. They therefore require the use of formed lobe antennas.

• les réflecteurs conformés :
  Ce sont des réflecteurs de révolution dont le profil est optimisé pour suivre le gabarit formé en élévation. Le problème de ces réflecteurs est qu'ils ont un diagramme de révolution, parce qu'ils doivent assurer la liaison dans tout le cône. Il est donc difficile d'obtenir un gain élevé, tout en ayant des dimensions raisonnables de réflecteur. Un réflecteur de ce type est analysé dans un article intitulé "Method of moment analysis of a cavity-fed shaped beam reflector antenna" de Bridges; Shafaï, et Kishk (Antenn'90 conference proceedings; August 15, 17-1990; Winniped; Canada).
• les antennes réseau :
  A partir de la constatation précédente, on a eu l'idée d'utiliser des antennes réseau à balayage électronique qui présentent un lobe d'antenne directif, de gain élevé, que l'on déplace par commande électronique. De telles antennes sont décrites dans l'ouvrage intitulé "Antenna Engineering handbook" (de R.C.Johnson et H. Jasik; McGraw-Hill; chapitre 20 "Phased Arrays" de R.Tang et R.W. Burns; pages 20-1 à 20-5). La liaison n'est alors plus assurée sur tout le cône simultanément mais uniquement dans la direction de la station visée. On distingue ici deux familles de réseaux : les réseaux plans et les réseaux conformés.

• . Les réseaux plans :
  Si l'on s'affranchit des lobes de réseaux par des techniques classiques de dimensionnement de réseaux jouant sur le pas, c'est-à-dire sur la distance entre deux sources adjacentes, on peut obtenir, pour des dimensions semblables une directivité bien supérieure à celle obtenue avec un réflecteur formé. La phase d'alimentation de chaque source étant commandée par un déphaseur, on déplace le diagramme en modifiant ces phases. Cette solution présente deux inconvénients majeurs :
  • il faut dépointer le lobe en élévation de ± 60° environ, voire plus, à plus basse altitude. Ceci nécessite de rapprocher beaucoup les sources.
  • Il est très difficile d'obtenir un maximum de rayonnement vers 60° et un creux dans l'axe; ce qui nécessite d'avoir des sources dont la directivité est élevée à 60°, même si leur diagramme présente l'allure du gabarit, c'est-à-dire avec un maximum de rayonnement à 60° (hélices par exemple). Par conséquent, si l'on veut obtenir un gain élevé (>20 dBi par exemple), il faut des dimensions relativement importantes et donc un grand nombre de sources et de déphaseurs (entre 50 et 100 selon la directivité élémentaire à 60°). Ce type d'antenne nécessite donc un grand nombre de points de commandes.
• . Les réseaux conformés :
  Pour obtenir un maximum de rayonnement sur un cône à 60°, on peut disposer les sources sur une surface conformée (hémisphère par exemple). En commandant chaque source par un déphaseur on balaye le lobe en élévation et en azimut. Mais avec de tels réseaux :
  • on ne peut plus utiliser toutes les sources à la fois.
  • on peut utiliser des éléments rayonnants dont le maximum de directivité est à 0° mais il faut, de plus, pouvoir dépointer à 60°.

Among the few techniques known for obtaining such templates, there are two main families.

• conformed reflectors:
  These are revolution reflectors whose profile is optimized to follow the template formed in elevation. The problem with these reflectors is that they have a revolution diagram, because they have to bond across the cone. It is therefore difficult to obtain a high gain, while having reasonable reflector dimensions. A reflector of this type is analyzed in an article entitled "Method of moment analysis of a cavity-fed shaped beam reflector antenna" by Bridges; Shafaï, and Kishk (Antenn'90 conference proceedings; August 15, 17-1990; Winniped; Canada).
• network antennas:
  From the previous observation, we had the idea of using electronic scanning array antennas which have a directional antenna lobe, of high gain, which is moved by electronic control. Such antennas are described in the work "Antenna Engineering handbook" (by RCJohnson and H. Jasik; McGraw-Hill; chapter 20 "Phased Arrays" by R.Tang and RW Burns; pages 20-1 to 20-5) . The connection is then no longer provided over the entire cone simultaneously but only in the direction of the target station. Two families of networks are distinguished here: flat networks and conformed networks.

• . Plan networks:
  If one overcomes the lobes of networks by conventional techniques of dimensioning of networks playing on the step, that is to say on the distance between two adjacent sources, one can obtain, for similar dimensions a directivity well greater than that obtained with a formed reflector. The supply phase of each source being controlled by a phase shifter, the diagram is moved by modifying these phases. This solution has two major drawbacks:
  • it is necessary to spot the lobe in elevation of ± 60 ° approximately, or even more, at lower altitude. This requires bringing the sources very close.
  • It is very difficult to obtain maximum radiation around 60 ° and a trough in the axis; which requires having sources whose directivity is high at 60 °, even if their diagram presents the shape of the template, that is to say with a maximum radiation at 60 ° (propellers for example). Consequently, if one wants to obtain a high gain (> 20 dBi for example), relatively large dimensions are required and therefore a large number of sources and phase shifters (between 50 and 100 depending on the elementary directivity at 60 °). This type of antenna therefore requires a large number of control points.
• . The conformed networks:
  To obtain maximum radiation on a 60 ° cone, the sources can be placed on a shaped surface (hemisphere for example). By controlling each source by a phase shifter, the lobe is scanned in elevation and in azimuth. But with such networks:
  • we can no longer use all sources at once.
  • it is possible to use radiating elements the maximum directivity of which is at 0 ° but it is also necessary to be able to spot at 60 °.

The object of the invention is to produce an antenna which makes it possible to overcome these drawbacks: that is to say to reduce the number of control points of said antenna, while effectively ensuring the mission considered.

To this end, it provides a high-gain shaped lobe antenna, characterized in that it comprises a shaped array on a shaped surface of any profile having an axis of symmetry, which comprises several generators of radiating elements located in a plane passing through the axis of symmetry of the antenna; all the radiating elements of the same generator being connected to a single phase and amplitude control point; the sweep in elevation and in azimuth of the lobe formed being obtained solely from the control of the phase of the generators by these control points.

Advantageously, all the radiating elements of the same generator are connected to a passive distributor and to a controllable phase shifter. The laws of amplitude and phase of the radiating elements of each generator are thus determined by the radioelectric characteristics of the passive distributor of each generator. The elevation diagram of said antenna is adjusted by controlling said phase shifters, the azimuth scanning being ensured by switching the generators.

In fact that the shaped network according to the invention is on a shaped surface of any profile having an axis of symmetry, advantageously, the profile can be optimized to determine the shape of the radiation pattern of a generator. To do this, the normal to the generator in a plane passing through the axis of symmetry will have a variable orientation depending on the position on the generator. As a result, the radiating elements on the generator will have different orientations. In other words, the inclination of a radiating element relative to the axis of symmetry is optimized to obtain the desired shape of the radiation diagram of a generator.

Such an antenna has the great advantage of allowing two-plane scanning using a single unidirectional control which is distributed in the azimuth plane. It also makes it possible to reduce the number of controls required (one per generator) compared to a conventional antenna which requires control by radiating element.

In addition, by playing on the passive distributor and the variable inclination of the radiating elements relative to the axis of symmetry, the shape of the radiation lobe can be optimized.

A third degree of freedom is thus released in the process of a column of radiating elements located on the same generator. This allows efficient use of the radiating elements in the directions where they must work, and this is all the more interesting as the scanning range is large, with a large deflection, for example greater than +/- 60 °. . This capacity of the invention makes it possible to ensure large deflections and is a decisive advantage compared to planar solutions which suffer from a loss of efficiency in the directions at high site.

• la figure 1 illustre un exemple d'une antenne selon l'invention ;
• les figures 2 et 3 illustrent plusieurs caractéristiques de l'exemple d'antenne de la figure 1 ;
• les figures 4 à 7 illustrent d'autres exemples de réalisation de l'antenne selon l'invention.

The characteristics and advantages of the invention will become apparent from the description which follows, by way of nonlimiting example, with reference to the appended figures in which:

• FIG. 1 illustrates an example of an antenna according to the invention;
• Figures 2 and 3 illustrate several features of the example antenna of Figure 1;
• Figures 4 to 7 illustrate other embodiments of the antenna according to the invention.

The antenna of the invention comprises a shaped array 10 arranged on a shaped surface 11 having an axis of symmetry and having any profile (conical, spherical, elliptical, parabolic, hyperbolic, etc.). This network consists of generators 12 composed of several sources or radiating elements 13. Each generator 12 is at the intersection of the shaped surface 11 and a plane passing through the axis of symmetry Δ (for example the axis of Nadir ). In FIG. 1, the surface 11 is a conical surface and the generators 12 each have three radiating elements 13.

In the antenna according to the example of FIG. 1, only one phase shifter 14 per generator 12 is considered; a passive distributor 15, dividing the signal in amplitude and in phase between each of the sources, being arranged between the output of this phase shifter 14 and the input of each source 13. This distributor 15 is the same for each generator, so that the geometry of the antenna of the example of FIG. 1 is completely of revolution. This distributor 15 is calculated to obtain a certain diagram of the radiations emitted by the sources 13 of each generator 12 and produce a certain resulting diagram from all the sources 13 of the antenna.

• le premier effet est une rotation φ du plan de polarisation autour de l'axe de révolution Δ. Cette rotation est constante ; Elle est liée à la géométrie du réseau, comme représenté sur la figure 2 ;
• le deuxième effet est un retard de propagation proportionnel à la distance relative d'une source par rapport à un plan de référence P orthogonal à la direction de visée. Pour un plan de référence P donné, les distances à ce plan des sources d'une même génératrice peuvent varier.

In order to obtain sufficient directivity, one or more adjacent generators are made to radiate simultaneously. The rotation of the generators has two effects on the phase of the radiation:

• the first effect is a rotation φ of the plane of polarization around the axis of revolution Δ. This rotation is constant; It is related to the geometry of the network, as shown in Figure 2;
• the second effect is a propagation delay proportional to the relative distance of a source with respect to a reference plane P orthogonal to the direction of sight. For a given reference plane P, the distances to this plane from the sources of the same generator can vary.

The role of phase shifters is to compensate for these effects. But as there is only one phase shifter per generator and since the compensation for this propagation delay must be the same for all the sources, we are led to calculate the average of the delays. These propagation delays depend on the direction of sight in elevation; that is to say of the inclination of the reference plane P. In FIG. 3, we note that in a direction corresponding to the axis Δ, for example at Nadir, all the generators are in phase (ϑ = 0 °): The phase shifters must only compensate for the rotation of the polarization plane in azimuth. On the other hand there are big variations when the line of sight is at 60 ° (ϑ = 60 °). It is therefore impossible to add several adjacent generators in phase simultaneously over the entire elevation area; which results in a deterioration of the diagram outside the intended direction.

Thus, even if the diagram of a generator 12 respects all the template, when the propagation delays are compensated, in a direction of 60 °, for example, this remains true for ϑ = 60 ° but not at all elsewhere, especially for ϑ = 0 ° where the diagram obtained is located clearly below the template.

It is possible to oversize the generator to compensate for this degradation: that is to say to increase the energy supplied to the sources of this generator to obtain a diagram located clearly above the planned template.

But it is also possible to play on the phase shifters to distort the diagram and adapt it to the elevation of the target station. When the latter is at ϑ = 60 °, the propagation delays in this direction are compensated for. When the elevation decreases, we distort the diagram by playing on the phase shifters: Indeed, for example, when the station is located around ϑ = 30 °, at 30 ° the diagram rises above the gauge while it drops below at 60 ° and so on until 0 ° where the diagram no longer corresponds at all to the 60 ° template.

The azimuth scanning is ensured by a simple switching of the generators since the geometry is of revolution.

In such an embodiment, the number of phase shifters is restricted as far as there are sources on a generator, compared to a conventional shaped structure. With a much lower number of control points, the phase shifters of the generators 12 being activated simultaneously, it is possible to carry out scanning in azimuth and in elevation of the antenna. One thus obtains a shaped solution where one wishes to obtain a diagram formed in elevation respecting a gauge, which one simply switches in azimuth, with generators of weak directivity, and of small dimensions.

Thus in an example of application, to carry out a telemetry mission according to the template of PIRE (Equivalent Isotropic Radiated Power) of Figure 4 (with a curve of maxima 16 and a curve of minima 17) which is a TMCU template (Telemetry payload for an optical or radar observation satellite) high speed X band (8 to 12 GHz). The objective is to comply with the EIRP gauge with the minimum radiated power. For example with 10 W radiated there will be a maximum gain of 21 dBi. The directivity will be 22 dBi taking into account a loss of 1 dB. An antenna 20 of pseudo-conical shape is dimensioned, as shown in FIG. 5. This antenna comprises 36 generators 21 from 4 sources 22. Each of these sources 22 is produced in printed technology; a copper block being etched on a shaped dielectric substrate which produces the pseudo-conical surface whose profile is not linear but has an α-break of approximately 10 ° on the first source from the top. Between the 4 sources 22 of the same generator 21, and on the same substrate as these, the distributor is etched in the form of copper tracks; itself being connected to a phase shifter. Of the 36 generators, only 9 are active simultaneously. All radiation is therefore controlled by 9 phase shifters at the same time.

FIG. 6 shows the minimum template 25 and the diagram obtained 26 by compensating for the propagation delays in a direction of 62 °. In FIG. 7, which shows the same minimum gauge 27 and the diagram obtained 28, the value of the 9 phase shifters has only been modified to compensate for the delays in an elevation direction of 5 ° (these FIGS. 6 and 7 corresponding to directivities Di in dBi).

It is understood that the present invention has only been described and shown as a preferred example and that its constituent elements can be replaced by equivalent elements without, however, departing from the scope of the invention.

In particular, the shaped surface can be of any profile, as long as it has any axis of symmetry. In the examples described, the surface has an axis of symmetry of revolution, but the surface may as well have a symmetry of order 2 (reflection in a plane), such as an ellipse, a parabola or a hyperbola, for example, or it can have a higher order symmetry giving more complex surfaces, without departing from the scope of the invention.

Claims (5)

Lobe antenna formed and with a large gain, characterized in that it comprises a shaped network on a shaped surface of any profile, this surface having at least one axis of symmetry; this shaped surface comprising several generatrices (12) defined by the intersection of a plane and the shaped surface, this plane being normal to said surface at its intersection with said surface, and containing said axis of symmetry; each generator comprising several radiating elements (13); all the radiating elements (13) of the same generator (12) being connected to a single phase control and switching point of said generator; the elevation scanning, as well as the azimuth scanning in a plane perpendicular to said axis of symmetry being obtained solely from the control of the phase of said generators by means of said only control points of each generator. Antenna according to claim 1, characterized in that it further comprises a passive distributor for each generator, said radiating elements of the same generator being connected to said single control point by said passive distributor, the laws of phase amplitudes between said elements of said generator being fixed by the radio characteristics of said passive distributor. Antenna according to claim 1 or 2, in which the normal to the generator in said plane containing said generator is of fixed or variable orientation for all the elements of the same generator, depending on the shape of the shaped surface of any profile, and wherein the orientation of said normal determines the shape of the radiation pattern of said generator, and characterized in that the orientation of said normal is optimized for the shape of the radiation pattern that is desired. Antenna according to any one of claims 1 to 3, characterized in that said shaped surface of any profile is a surface of revolution about an axis (Δ), this axis being parallel to said mean direction of said formed lobe. Antenna according to any one of claims 1 to 3, characterized in that said shaped surface of any profile is only part of a surface of revolution about an axis (Δ), this axis being parallel to said mean direction of said lobe formed.

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