EP0048190A1 - Non-dispersive antenna array and its application to electronic scanning - Google Patents

Abstract

Non-dispersive network antenna, of the prism antenna type in which the primary dispersive input network (I) and the secondary output network (IV) make an angle α between them, produced by stacking one-dimensional non-dispersive network antennas, for each which propagation between said networks is guided. Application to electronic scanning prism antennas.

Description

The present invention relates to a network antenna and more particularly to an antenna of this type which is non-dispersive and has a small footprint. By non-dispersive array antenna is meant an antenna for which the direction of maximum radiation is practically independent of the frequency. The present invention also relates to the application of such an antenna to the production of an electronic scanning antenna.

Network antennas are known which respond to the characteristic of non-dispersivity and we can cite a so-called candlestick network antenna for which the feed path divides and each new feed path thus obtained is connected to radiating elements capable of constitute basic sources according to the terminology used in network antennas. Such an antenna structure which includes a certain number of magic Tees or dividers, is complex to say the least, cumbersome, and risks being heavy and of a high cost price.

Another non-dispersive antenna structure is also known which comprises a supply guide to which are coupled, by means of directional couplers, guides supplying elementary sources, the assembly being such that the electrical lengths of each circuit of supply from an elementary source are equal.

This antenna structure, although less bulky than the first cited, has the defect of being complicated from the point of view of its mechanical production which, from a large number of elementary sources, of the order of a hundred , again results in some annoying bulk.

Other embodiments of non-dispersive antennas can also be cited, in particular active lenses and reflective arrays which are supplied with free space by means of a simple primary source. However, these antennas have the drawback a longitudinal size equal to the focal length of the system which is large; on the other hand, there is a risk of overflow of the primary radiation on the periphery of the network which can produce annoying diffuse radiation.

Another embodiment of a non-dispersive array antenna has been proposed by the Applicant in its French patent application No. EN 77.07331 which consists of a first dispersive array supplying a second array whose general direction makes a certain angle with the first, the supply of the second network by the first by propagation in free space.

dans laquelle Ko est le nombre d'onde 2π/λo en espace libre et Kgo le nombre d'onde dans le guide à fentes constituant le réseau primaire à la fréquence fo.It has been demonstrated for such an antenna, called a prism array antenna, that for a frequency fo of the traveling wave supplying the primary array, the values of the angle 0: between the two arrays as a function of the direction of radiation eo of the array primary were given by the formula:

in which Ko is the wave number 2π / λo in free space and Kgo the wave number in the slot guide constituting the primary network at the frequency fo.

FIG. 1 represents this prism array antenna of the prior art in which 1 is the linear dispersive primary array, a simple slotted guide supplied by its end 2 with its other end closed on an absorbent load 3. An absorbent panel 8 can be provided on the third side of the triangle, absorbing the reflected radiation linked to the active coefficient of the networks. The secondary network 4, also linear, makes an angle α with the primary network. In FIG. 1, this secondary network is a double-sided network, the faces of which consist of radiating elements of the horn 5 and 6 type. Between the two faces of the secondary network are phase-shifters 7, which for the example described, have a fixed value each, the set of phase shifts following a linear law from the first phase shifter to the last. This law is such that . the wave radiated by the secondary network has a direction of radiation perpendicular to said network. It follows that the phase shift to which the wave supplying the secondary network is subjected has the effect of compensating for the phase law produced by the oblique incidence on the secondary network of the primary radiated wave, thus determining a law on the secondary network. stationary phase.

In the patent application cited above, the lessons learned from the one-dimensional realization of the array antenna have been extended to a two-dimensional array antenna with which it is desired to carry out an electronic scan.

Figure 2 shows an embodiment of this antenna also falling within the prior art.

The network 1 is formed by a number of slot guides 91 to 9n similar to the guide 1 in FIG. 1, each comprising the same number of slots 10. All these guides are fed in parallel by one of their ends, by a channel. 11. Phase shifters 12 of the electronic type for example are provided to allow electronic scanning with this antenna to be carried out in a vertical plane perpendicular to the plane of the figure.

The secondary network IV is constituted by a panel 13 comprising a certain number of radiating elements which are, in the described case, rotary propellers 14 powered by dipoles 15. The use of rotary propellers makes it unnecessary to interpose phase shifters between the two sides of the network IV. The third face of the trihedron is an absorbent panel 16.

An antenna with electronic scanning such as that which has been described has the advantages of being aperiodic in the first order and of exhibiting neither mask effect nor overflow. However, the optimization of the non-dispersivity of the pointing as a function of the frequency is not carried out for all the sites scanned. Indeed, during a depointing in the site plane, the propagation of the wave between the primary network 1 and the secondary network IV is no longer strictly done in the field plane, but in an inclined plane of the value of l 'angle of site considered. Therefore, during the electronic scanning, differences in electrical length are created for the waves propagating between the two networks, differences which are no longer compensated for by the secondary network.

An object of the invention is to remedy this drawback.

According to the invention, a non-dispersive array antenna comprising a directional primary array constituted by a superposition of one-dimensional primary arrays, each supplied through a phase shifter, a secondary array in the form of a panel comprising elementary sources on the internal faces and external of the panel, with passive phase shifters introduced between the two faces, the secondary network making an angle α with the primary network, and an absorbing panel closing the defined angle between the two networks, is characterized in that the wave propagation between the primary and secondary networks are carried out in space guided by parallel planes arranged in such a way that they materialize the antenna as a stack of a plurality of elementary non-dispersive one-dimensional antennas, for each of which the propagation between the primary network and the secondary network is guided.

• - la figure 3, une antenne réseau monodimensionnelle suivant l'invention ;
• - la figure 4, une antenne réseau bidimensionnelle suivant l'invention ;
• - la figure 5, un exemple de réseau primaire photogravé en technologie ligne à fente ;
• - la figure 6, un exemple du réseau primaire photogravé en technologie ligne microstrip.

Other characteristics and advantages of the invention will appear in the description which follows, given with the aid of the figures which also represent Figures 1 and 2 relating to the prior art:

• - Figure 3, a one-dimensional array antenna according to the invention;
• - Figure 4, a two-dimensional array antenna according to the invention;
• - Figure 5, an example of primary network photo-etched in slot line technology;
• - Figure 6, an example of the primary network photo-etched in microstrip line technology.

We have seen in the foregoing that a so-called prism antenna can be produced in a one-dimensional form and in a two-dimensional form, the latter making it possible to carry out an electronic scanning of the space.

The main characteristic of these antennas is that the direc tion of the maximum radiation is practically independent of the frequency, this characteristic being linked to the fact that the primary and secondary networks which constitute this antenna form between them an angle lX which can be chosen and determined optimally so that the phase of the wave supplying the secondary network is stationary, the propagation between the primary network and the secondary network taking place in free space.

dans laquelle pour la fréquence fo, Ko(Z) est la constante de propagation dans l'espace entre les réseaux, que cette propagation soit libre ou guidée, c'est-à-dire qu'en espace libre, Ko(Z) prend une valeur Ko et qu'en espace guidé, Ko(Z) prend la valeur Kgo, sauf dans le cas où le vecteur polarisation est vertical et alors Ko(Z) est égal à Ko, et Ko(R1) est la constante de propagation dans le guide que constitue le réseau primaire. Cette formule est identique à celle donnée pour la réalisation suivant l'art antérieur pour laquelle la propagation se fait en espace libre.In operation, such an antenna mainly when it is one-dimensional, does not pose any problem, except in the event of overflow where part of the wave directly emitted by the primary network can recombine with the wave leaving the secondary network and alter direction. Such a drawback is remedied by eliminating the overflow, by closing the free space existing between the primary and secondary networks. Under these conditions the emitted wave propagates in guided space and the overflow cannot take place. The performance of the antenna, the structure of which is thus modified relative to the array antenna of the prior art, is not modified. In fact, a calculation, in All points similar to that which was made in the patent application already cited shows that, as well with a propagation in free space as with a propagation in guided space between the primary and secondary networks, one can obtain values of the angle α between the two linear networks for which the secondary network is supplied with a wave whose phase is stationary. This value of the angle α as a function of the direction of radiation Go of the primary network at the frequency fo is given by the formula

in which for the frequency fo, Ko (Z) is the propagation constant in the space between the networks, whether this propagation is free or guided, that is to say that in free space, Ko (Z) takes a value Ko and that in guided space, Ko (Z) takes the value Kgo, except in the case where the polarization vector is vertical and then Ko (Z) is equal to Ko, and Ko (R1) is the propagation constant in the guide that constitutes the primary network. This formula is identical to that given for the embodiment according to the prior art for which the propagation takes place in free space.

FIG. 3 represents a one-dimensional array antenna according to the invention. This figure is not very different from that of Figure 1 so that the elements common to the two figures have the same references. We thus find the primary network 1 supplied by its end 2, the other end being closed by an absorbent load 3, the secondary network 4 with for radiating sources in the case of the figure, propellers 6 supplied on the internal face of the network 4 by the dipoles 5. It will be noted that the use of propellers makes it possible to suppress the stage of phase shifters between the internal face and the external face of the secondary network 4. In 17 the plate closing the upper opening of the propagation space between networks 1 and 4. An identical plate is located on the side of the lower opening which is not visible in FIG. 3.

In 8 there is shown an absorbent charge closing the angle α between the linear networks 1 and 4.

It can be seen that, according to the invention therefore, a compact module has been produced, usable as such as a one-dimensional non-dispersive array antenna.

According to the invention, such a module is used to constitute an element of a two-dimensional array antenna, such an antenna being constituted by a stack of a plurality of these elements. Produced in this way, such an antenna no longer exhibits the drawback indicated in the case of electronic scanning.

In fact, in the definition of the prior art, we have seen that a non-dispersive electronic antenna with electronic scanning cannot be optimized for any value of the elevation angle and that for the scanned sites, the compensation of the electrical lengths in the free propagation space between the networks is no longer correctly performed by the output network and that an error in the direction ensues pointing in deposit.

By constituting, according to the invention, the two-dimensional antenna by a stack of modules, as they have been defined previously and described in support of FIG. 3, modules in which the propagation is guided, it can be seen that at level of each module, that is to say at the level of the elementary horizontal array antennas in the example described that they constitute, the phase shift introduced by the phase shifter, disposed at the input of the feed guides of an antenna elementary, is fully retransmitted to the secondary network so that for the entire antenna the phase law applied to these phase shifters is fully transmitted in the site map at the output of the secondary network.

FIG. 4 represents a two-dimensional array antenna according to the invention, a representation which does not differ much from the representation of FIG. 2 where the propagation between the primary or input and the secondary or output linear networks takes place in free space. Under these conditions, the parts common to the two figures bear the same references.

We thus find panel I, a network consisting of a certain number of slot guides 91 to 9n each with the same number of slots 10. The input of each of these guides comprises a phase shifter, the assembly of which is identified by 12 and the power is supplied by a guide 11. The electronic phase shifters 12 allow electronic scanning to be carried out in a vertical plane perpendicular to the plane of the figure.

The secondary IV array is constituted by a panel 13 comprising a certain number of radiating elements, rotary propellers for example 14 supplied by dipoles 15. An absorbent panel 16 is provided to complete the trihedron that constitutes this two-dimensional array antenna. This antenna structure is completed by parallel planes 18 which materialize, inside the two-dimensional array antenna, the elementary array antennas or modules conforming to FIG. 3, in which the propagation is guided.

It will be noted that in the antenna structure according to the invention, in which the propagation between the primary and secondary networks is guided that the polarization of the transmitted waves is of horizontal or vertical type; on the other hand, the polarization of the wave leaving the secondary network can be arbitrary, depending only on the radiating elements.

It will also be noted that in the exemplary embodiments, the primary network has been considered as a slotted guide supplied by a traveling wave. The slots are arranged on the short or the long side of the guide. However, the primary network can equally well be a network composed of radiating elements coupled in some way with a supply line. This line can be a guide but also a line produced by any photogravure process, that is to say deposited on a dielectric substrate, as in the slit line, two-wire line, microstrip, triplate technologies. The radiating elements, if they have a plane geometry, can also be etched on this same dielectric. These elements can be quarter wave strands, dipoles, half or whole wave, yagis, zigzag, periodic log, lines with flared radiating slits.

Figures 5 and 6 show examples of a photoetched primary network. FIG. 5 represents an embodiment in slot line technology with couplers 19 and flared lines 20 and FIG. 6 an embodiment in microstrip technology with couplers 19 and dipoles 21.

The elements internal and external to the output network can be made up of any type of radiating elements photograved or not.

If the polarization emitted on the two faces of the secondary network remains the same, all of the radiating elements of this secondary network with passive phase shifters interposed between them can be achieved by metallization of a single dielectric plate. The photo-etched elements are the same as those designated for the primary network.

We have thus described a non-dispersive array antenna of small size and reduced weight with electronic scanning, which can be produced by stacking a plurality of modules each constituting themselves a non-dispersive one-dimensional antenna.

Claims (8)

1. Non-dispersive network antenna comprising a directional primary network (I) constituted by a superposition of one-dimensional primary networks (91 to 9n), each supplied through a phase shifter (12) to allow electronic scanning, a secondary network ( IV) in the form of a panel (13) comprising elementary sources (15-14) on its internal and external faces with passive phase shifters (7) introduced between the two faces, the secondary network making an angle c (with the primary network, and an absorbent panel (16) closing the angle defined between the two networks, characterized in that the propagation of the waves between the primary (I) and secondary (IV) networks takes place in a space guided by planes parallels (18) arranged in such a way that they materialize the antenna as a stack of a plurality of one-dimensional non-dispersive antennas (FIG. 3) for each of which the propagation between the primary network (1) and the secondary network ( 4) is guided. 2. A non-dispersive network antenna according to claim 1, characterized in that each one-dimensional elementary antehne (FIG. 3) constitutes a reproducible optimizable compact module. 3. network antenna according to one of claims 1 or 2, characterized in that the primary network (1) of a module is a slot guide (9) supplied by a traveling wave, and that the secondary network (4) is a double-sided network with radiating elements (5-6) on the internal and external faces and phase-shifting elements (7) located between them. 4. Network antenna according to claim 3, characterized in that the secondary network (4) comprises dipoles (15) on the internal face of the network and rotary propellers (14) incorporating phase shifters on the external face. 5. Network antenna according to one of claims 1 or 2, characterized in that the primary network (1) of a module is a line produced on a dielectric substrate by photoengraving, the radiating elements of the network being, if they have a plane geometry, etched on this substrate. 6. Network antenna according to one of claims 1 or 2, characterized in that the secondary network of a module is produced by photoengraving on a dielectric substrate. 7. Network antenna according to one of claims 1 or 2, for which the polarization of the waves entering and leaving the secondary network remains the same, characterized in that all of the radiating elements of the secondary network and passive phase shifters located between them is made by metallization of a single dielectric plate. 8. Network antenna according to one of claims 1 or 2, characterized in that in the propagation space between the primary (1, 1) and secondary (2, IV) networks the polarization of the transmitted waves is either vertical or horizontal .

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