EP0524622A1 - Antenna array for ultra-high frequencies - Google Patents

Abstract

The width (lo, ... l3, ...) of the sources (Co, ..., C3d, C3g...) of this array increases progressively from the centre of the array (2) towards its ends. Moreover, these sources are arranged, with respect to one another, in such a way that this array exhibits no gaps in illumination. <IMAGE>

Description

The present invention relates to an array antenna for microwave waves, this array being for example, but not limited to, a linear array intended to be placed along the focal line of a cylindro-parabolic reflector.

The array antennas are designed for obtaining adaptive diagrams from a host of elementary sources such as: horns, propellers, dipoles, "patches" (small conductive patterns or "blocks", for example of rectangular shape , and etched on a substrate), etc ...

By associating with each of these elementary sources a controllable phase shifter, or produces an antenna with electronic scanning whose beam can "spot" (ie: sweep) very quickly.

The simplest array antenna is the conventional linear array antenna which comprises, on the same line, a greater or lesser number of identical elementary sources and spaced at a regular pitch, the pitch being the distance from the center of a source to that of the adjacent source.

By making a network in a simular manner, but in two orthogonal dimensions instead of one, we obtain a "planar network", often of rectangular outline, possibly with truncated corners.

In a similar way, and on condition of adopting a hexagonal mesh, one can realize a network of revolution in a plane.

The disadvantage of all these regular pitch array antennas is that, for a large antenna, the number of elementary sources to be provided can become very high, so that this kind of antenna is often of a prohibitive cost price.

To reduce the number of elementary sources, some authors have thought of creating so-called "rarefied" or "incomplete" networks, by eliminating certain sources either randomly or according to a deterministic law established mathematically according to the antenna theory , the number of sources removed increasing towards the edges of the array antenna. In all these embodiments, the elementary sources constituting the network remain identical to each other.

This rarefaction makes it possible to reduce the number of elementary sources without deteriorating the shape of the main lobe or making appear in the radiation pattern of the antenna "network lobes", that is to say peaks in unwanted directions. Unfortunately, it leads to a significant drop in antenna gain, which drops by 10 log R, R designating the proportion of remaining sources: if we remove half of the elementary sources, we lose 3dB on the total gain of the antenna .

• . pour une antenne d'émission de télécommunications, il faudrait, pour garder le même bilan de liaison, doubler la puissance émise, ce qui est rarement possible;
• . pour une antenne radar, pour laquelle le gain intervient à la fois en émission et en réception, il faudrait alors quadrupler cette puissance émise.

In many applications, such loss of gain is prohibitive:

• . for a telecommunications transmission antenna, to keep the same link budget, it would be necessary to double the transmitted power, which is rarely possible;
• . for a radar antenna, for which the gain occurs both in transmission and in reception, this transmitted power would then have to quadruple.

The invention aims to remedy these drawbacks. To this end, it relates to a network antenna composed of a multitude of similar elementary sources, this network being characterized by the fact that these elementary sources are of a width which overall increases progressively from the center of the network towards its ends, and are arranged with respect to each other so that there is practically no creation of illumination holes in this network.

Preferably, this progressive widening of the dimensions of the sources follows a law of variation in geometric progression.

• . Figure 1 est une vue de face de la partie centrale d'un réseau linéaire conforme à l'invention et composé d'une kyrielle de cornets, ce réseau étant par exemple destiné à être placé selon la ligne focale d'un réflecteur cylindro-parabolique;
• . Figure 2 est un schéma synoptique du circuit d'émission-réception à balayage électronique de faisceau qui peut être associé au réseau selon la figure 1;
• . Figure 3 est une vue en plan simplifiée d'une réalisation semblable à celle selon Figure 1, mais réalisée à l'aide de pavés résonnants ou "patchs"; et
• . Figure 4 est une variante de la réalisation selon Figure 3.

In any case, the invention will be well understood, and its advantages and other characteristics will emerge during the following description of a few non-limiting exemplary embodiments, with reference to the attached schematic drawing in which:

• . Figure 1 is a front view of the central part of a linear network according to the invention and composed of a series of horns, this network being for example intended to be placed along the focal line of a cylindro-parabolic reflector;
• . Figure 2 is a block diagram of the transmit-receive electronic beam scanning circuit which can be associated with the network according to Figure 1;
• . Figure 3 is a simplified plan view of an embodiment similar to that according to Figure 1, but performed using resonant pads or "patches"; and
• . Figure 4 is a variant of the embodiment according to Figure 3.

• . une première série de cornets C1d,C2d,C3d,..., à droite (sur le dessin) de ce cornet central Co; et
• . une deuxième série de cornets C1g,C2g,C3g,..., à gauche de ce cornet central Co.

Referring to Figures 1 and 2, it is a linear network 1 composed of a string of adjacent radiating horns, including a central horn Co framed on either side by two series, identical and symmetrical with respect to the central axis 2 of the cornet Co and therefore of the network 1, of horns:

• . a first series of horns C1d, C2d, C3d, ..., on the right (in the drawing) of this central horn Co; and
• . a second series of horns C1g, C2g, C3g, ..., to the left of this central horn Co.

So that there are no illumination holes in the radiation pattern of this network 1, there is practically no effective separation space between two adjacent horns, these being therefore separated l 'from one another by a common wall, such as the wall referenced 3 in the drawing and making the junction between the horn Co and the horn C1d.

Furthermore, these horns are not identical, and their width 1, and thereafter the pitch p which separates the respective axes of two adjacent horns, gradually increases, on either side of the central horn Co and in the same way right as to the left of the latter, as one moves away from this central horn Co towards the ends, right and left respectively, of this network 1.

où k est un facteur d'accroissement constant, par exemple égal à 0,1 , lo la largeur du cornet central Co, et ln la largeur du cornet de rang n, Cnd ou Cng.The law of variation in width of the horns is preferably a law in geometric progression, for example of the form:

${\text{ln = lo (1+ k)}}^{\text{n-1}}$

where k is a constant growth factor, for example equal to 0.1, lo the width of the central horn Co, and ln the width of the horn of rank n, Cnd or Cng.

Of course, in particular in the case of the network antenna 1 shown where all the sources touch, the pn step is defined from the po step by the same relation.

The antenna array according to FIG. 1 can, for example, be provided to be placed along the focal line of a conventional cylindro-parabollic reflector (not shown), in order to sweep a fine lobe through such an antenna. in the plane determined by the network and the line of the vertices of the parabolic sections.

The block diagram associated with the electronic block associated with network 1 is shown in Figure 2.

This scheme is a priori fairly conventional in structure. It comprises a microwave transceiver (4) which is coupled, via a bi-directional link 5, to a distributor 6 having the role of effecting a uniform distribution of the energy emitted, or received, on its different output channels. , or input, referenced Vo, V1d, V1g, V2d, V2g, V3d, V3g, ..., and respectively feeding the horns Co, C1d, C1g, C2d, C2g, C3d, C3g, ...

• . un déphaseur respectif Do....,D3d,D3g,..., recevant sur sa borne de commande Bo,...,B3d,B3g,..., un signal de commande de déphasage provenant d'un pointeur lui-même piloté par un calculateur central (non représentés), ce dernier élaborant classiquement la loi de phase en fonction du pointage souhaité;
• . puis, entre ce déphaseur et le cornet associé, un amplificateur de puissance hyper-fréquences, respectivement HPAo,..., HPA3d,HPA3g,...

On each of said channels, there are successively:

• . a respective phase shifter Do ...., D3d, D3g, ..., receiving on its control terminal Bo, ..., B3d, B3g, ..., a phase shift control signal coming from a pointer itself- even controlled by a central computer (not shown), the latter conventionally developing the phase law as a function of the desired pointing;
• . then, between this phase shifter and the associated horn, a hyper-frequency power amplifier, respectively HPAo, ..., HPA3d, HPA3g, ...

In the regular networks of the prior art, it was necessary to provide, downstream of the horns or other elementary sources, microwave amplifiers whose gain was decreasing as one moved away from the central horn, because the desired radiation pattern for this kind of antenna requires that the power density emitted gradually decrease as one moves away from the center of the network.

With the network according to the invention, this condition of power variation is achieved by construction, since the pitch of the network gradually increases as one moves away from the central horn Co.

Consequently, it is no longer necessary to have power amplifiers HPAo, ..., HPA3d, HPA3g, ..., the gain of which varies from one to the other, and these amplifiers are, according to a advantageous characteristic of the invention, all identical and of the same power.

This power very advantageously corresponds to the maximum and optimal power for which these amplifiers are calculated. Total power is therefore maximized, and energy efficiency is optimized because each amplifier operates at the maximum efficiency for which it is built.

The central horn Co has the same width, for example about 2 cm, as that of a regular network of the prior art.

Advantageously, in order not to increase the number of types of cones too much, the progressive increase in their width will be carried out by groups of cones. For example, five successive cones, on the right as on the left, will have the same width each time, the following five being all identical and a little wider, etc ...

The Applicant was thus able to halve the number of horns necessary for a linear network of nearly 6 meters having to sweep a beam lengthened by about 6 degrees on either side of its normal. For a comparable quality of the radiation pattern, the drop in gain was only on the order of 0.35 to 0.4 dB.

An exemplary embodiment of an antenna network of the same type, but based on resonant blocks, or "patches", is shown very schematically in Figure 3, where the denominations CO, C1d, C1g, C2d, C2g ,. .., for the elementary sources have been respectively replaced by Po, P1d, P1g, P2g, P2g, ..., designating the replacement patches of the previous horns.

Each of these patches is connected to its corresponding amplifier and phase shifter block by a respective line Lo, L1d, L1g, L2d, L2g, ...

   Par ailleurs, de façon que, toujours conformément à l'invention, il n'y ait aucun trou d'illumination dans ce réseau, tous les patchs sont séparés l'un de l'autre d'une même distance d entre bords adjacents qui est égale à la demi-longueur d'ondes guidée, cette condition étant, comme il est bien connu dans cette technique, la condition nécessaire pour éviter de tels trous d'illumination.According to the invention, the dimensions, that is to say in fact the non-resonant widths lo, l1d, l1g, l2d, l2g, ..., of these patches, gradually increase from the center Po of the network towards its two ends , according for example to the geometric law previously defined, and therefore such that:

${\text{l}}_{\text{not}}{\text{/ l}}_{\text{n-1}}\text{= 1 + k}$

Furthermore, so that, still according to the invention, there is no illumination hole in this network, all the patches are separated from each other by the same distance d between adjacent edges which is equal to the guided half-wavelength, this condition being, as is well known in this technique, the condition necessary to avoid such illumination holes.

Finally, FIG. 4 shows a more economical variant of the network according to FIG. 3, where patches are all identical to the central patch Po, but grouped, by electrical connections, according to several successive patches for each group, the number of patches per group. G1d, G1g, ..., gradually increasing as one moves away from the central patch Po.

In this exemplary embodiment, where of course each patch is as previously separated from the neighboring patch by an edge-to-edge distance d equal to the guided half-wavelength, the first two groups of patches G1d and G1g, which are located on either side of the single central patch Po, each have three patches whose power supplies are joined at a common point, 7 and 8 respectively, which defines the respective widths l1d and l1g. The next two groups G2d and G2g (not shown) each have five patches, the next two groups seven patches, and so on.

It goes without saying that the invention is not limited to the preceding embodiments. It also applies to the realization of two-dimensional flat networks: in such a case, the dimension of the sources increases from the center of the network towards its edges, both along the abscissa axis and along the ordinate axis. In the case of a network with a planar structure of revolution, the progressive increase in the dimensions of the sources takes place, similarly, from the center towards the periphery of this structure.

In the case of an antenna comprising a shaped array on a surface of revolution of any profile (circular cylindrical, frustoconical, ...), for example according to patent application in France N ° 91.05510 filed on May 6, 1991 by the Applicant , comprising several generators of radiating elements, each of these generators comprises a series of radiating elements comprising, as for example in FIGS. 3 and 4, a central element framed on either side, by similar radiating elements, but of width increasing progressively and arranged so as not to create illumination holes on this generator.

Claims (16)

Network antenna for microwave waves, composed of a multitude of analogous elementary sources (Co, C1d, C1g, C2d, C2g, C3d, C3g ...), characterized in that these elementary sources are of a width (lo, ... l3, ln-1, ln ...) which generally increases progressively from the center (2) of the network towards its ends, and are arranged (3) with respect to each other so that it does not there is practically no creation of illumination holes in this network. Array antenna according to claim 1, characterized in that this progressive enlargement in dimensions of the sources follows a law of variation in geometric progression. Array antenna according to claim 2, characterized in that the width (l _n ) of the row source (n) is linked to the width (l _n-1 ) of the row source (n-1) by a relation of shape : ${\text{ln / l}}_{\text{n-1}}\text{= (1 + k)}$

, where k is a constant increase factor. Array antenna according to one of claims 1 to 3, characterized in that this progressive increase in width is carried out on successive groups of identical sources. Array antenna according to one of claims 1 to 4, this antenna comprising a controllable phase shifter (Do, ..., D3d, D3g, ...) behind each source (Co, ..., C3d, C3g ... ) to ensure the electronic scanning of the beam, as well as a microwave power amplifier (HPAo, ..., HPA3d, HPA3g, ...) also behind each of these sources, characterized in that these amplifiers are all identical and deliver all the same power corresponding to their common optimal operating power. Array antenna according to one of claims 1 to 5, characterized in that, said elementary sources being radiating horns (Co, ..., C3d, C3g ...), each horn is separated from the adjacent horn by a wall common (3). Array antenna according to one of claims 1 to 5, characterized in that, said elementary sources being radiating blocks or "patches" (Po, ..., P2d, P2g, ...) each patch is separated from the adjacent patch by a distance (d) substantially equal to the guided half-wavelength. Array antenna according to claim 7, characterized in that each of these patches (G1d, G1g) is itself composed of a group of identical patches, electrically connected (7,8), and separated one from the other by a distance (d) substantially equal to the guided half-length of waves. Flat network antenna according to one of claims 1 to 8, characterized in that the progressive increase in the size of the sources takes place, along the two coordinate axes, from the center of this network to its edges. Plane antenna of revolution according to one of claims 1 to 8, characterized in that the progressive increase in the dimension of the sources takes place from the center towards the periphery of this plane structure of revolution. Array antenna according to one of claims 1 to 8, shaped on any surface of revolution of any profile and comprising several generators of radiating elements, characterized in that each of these generators comprises a series of radiating elements comprising a central element framed on both sides by similar radiating elements, but gradually increasing in width and arranged so as not to create illumination holes on this generator. Network antenna active in reception according to one of claims 1 to 4, characterized in that it comprises a low noise amplifier for each elementary source (Co, ..., C3d, C3g, ...) as well as a controllable phase shifter (D0, ... D3d, D3g, ...) behind each low noise amplifier. Network antenna active in transmission according to one of claims 1 to 4, characterized in that it comprises a controllable phase shifter (D0, ... D3d, D3g, ...) behind each elementary source (Co, ..., C3d, C3g, ...) as well as a microwave power amplifier (HHPAo, ... HPA3d, HPA3g, ...) also behind each of these sources. Active network antenna according to claims 12 and 13, for radar applications, characterized in that it comprises a transmission channel and a reception channel, switched alternately, each comprising a specific microwave amplifier. Network antenna according to any one of claims 13 or 14, characterized in that all the amplifiers operating in transmission all deliver the same power corresponding to their common optimal operating power. Array antenna according to any one of claims 1 to 15, placed along the focal line of a cylindro-parabolic reflector thus ensuring a high gain antenna scanning electronically in the plane formed by the linear array and the line of the vertices of the parabolic sections .

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