EP0013240B1 - Common antenna for primary and secondary radar - Google Patents

Abstract

A bifunctional antenna of a primary/secondary radar system comprises a reflector having a concave front surface formed with a row of slots along a horizontal generatrix, the slots lying in front of respective cavities excitable to radiate interrogation signals in a directive sum pattern and supplemental radiation in a differential control pattern designed to blank minor lobes of the interrogation pattern. Some of the cavities and slots are symmetrically duplicated on a dielectric cap covering the convex rear surface of the reflector. The reflector and its cap form a closed shell of dielectric material, specifically a glass mat impregnated with epoxy resin, overlain at the front by a fiber-glass fabric incorporating orthogonally intersecting insulated copper wires. The fabric also lines the inner walls of each cavity which is filled with dielectric material; its radiating slot is spanned only by horizontal wires paralleling the plane of polarization of target-seeking radiation from a source illuminating the reflector.

Description

The present invention relates to a common antenna for primary radar and secondary radar.

Frequently, in a radar station, it is necessary to associate several antennas in the same operating site. But this association poses the problem of the coexistence of these materials in a volume which is, in the case of weapons systems for example, extremely limited. The association of a primary radar antenna and a secondary radar antenna can be carried out in two different ways. On the one hand, the antenna of the secondary radar is distinct from the antenna of the primary radar; the antennas installed in this way are essentially of the "beam" type. On the other hand, the secondary radar antenna is integrated with the primary radar antenna, thus realizing a true dual-function primary radar and secondary radar antenna.

A dual-function antenna for primary and secondary radars is generally constituted by a single mirror supplied in such a way that it is able to radiate energy in space in order to detect a target or an aircraft, this is what called the primary radar function, and also to send an interrogation signal to this aircraft, which has on board a transponder automatically sending its response, this is called the secondary radar function.

In the embodiment of a dual-function antenna described in US Pat. No. 3,550,135, this antenna is constituted by a single reflector, parabolic, illuminated by a primary source emitting a wave according to a first radiation diagram and also constituted by a linear network of radiating elements placed along a director of the reflector, and emitting a wave according to a second radiation diagram. This second antenna formed by the network can radiate according to a "sum" diagram or a "difference" diagram which can be used as primary and secondary radars.

These radiating elements can be unipoles, dipoles or slots produced in triplate technology.

The radiated beam carrying the interrogation is directive, interrogating in the direction where the aircraft has been detected; however, it was found that the responder of the aircraft questioned could be triggered by the side lobes of the interrogation diagram, the level of which is likely to be relatively high compared to that of the main lobe. To remedy this drawback, so-called control means comprising radiating elements acting on the reception of the interrogation by the interrogated answering machine and on the reception of the latter's response by the receiver concerned are added to the single antenna considered. which radiate according to an almost omnidirectional diagram whose level is such that it covers the secondary lobes of the diagram radiated by the main antenna.

This arrangement makes it possible by comparison, made in the associated circuits, of the amplitude of the pulses received from the responder and those of control, to determine the pulse received in response to the interrogation by the main lobe.

The control means intended to produce this control diagram and which act on the emission of an interrogation signal and on the reception of a response signal from a target interrogated must be such as the gain of the associated control is greater than that of the interrogation and reception channels in the angular zones comprising secondary lobes of the directive interrogation diagram but much weaker in the direction of their main lobe.

In current embodiments, such as that described in French patent FR 2284997, the control means consist of radiating elements, wave radiators, whose radiation diagram is of the omnidirectional type, placed either on the near mirror. from the phase center or from the upper part of the reflector; they can also consist of the source of emission of the interrogation signal supplied for a determined time to reveal a radiation diagram of the difference type whereas the diagram according to which the interrogation takes place is a diagram of the sum type.

However, despite the precautions that have been taken, it appears that the radiation pattern of the control means does not fully play its role, either because it is not completely omnidirectional, or because certain high-level side lobes of the directive main diagram are not covered and also because in some cases, the main lobe itself, whose level is a little low, may be suffocated by the omni-directional diagram. In addition, the control diagrams can be disturbed by certain exterior arrangements, such as the radomes under which the antennas are placed.

Finally, all of these additional elements, such as wave radiators, cause phenomena of mask of the primary source due to the shadow created by these radiators on the surface of the mirror.

The object of the invention is to provide a common antenna for primary radar and secondary radar comprising a single reflector illuminated by a primary source acting as a source of transmission-reception of the function of the primary radar and also comprising, along '' a director D of the reflector, a network of radiating slots producing the food source both the interrogation channel of the secondary radar, channel whose radiation diagram is of the "sum" or "even" type, each of these slots being associated with a resonant cavity, totally integrated in the reflector and comprising excitation means, characterized in that the reflector and the cavities associated with the slots are made from a dielectric material covered by a glass fiber fabric carrying covered metallic wires, these metallic wires being crossed over the entire surface of the reflector and inside cavities, except in front of the slots where they are arranged in the direction of polarization of the source of the primary radar.

To have an optimal directional diagram in the horizontal plane, the slots are arranged on a horizontal director. The section of the reflector of the primary radar antenna can be circular, elliptical or rectangular.

• - la figure 1, une coupe d'un réflecteur d'antenne commune par radars primaire et secondaire, selon l'invention;
• - la figure 2, un diagramme schématique montrant la liaison entre un déphaseur 0­-π et le diviseur de puissance, selon l'invention;
• - la figure 3, la forme du diagramme de rayonnement de la voie interrogation-réception dans le plan gisement, de l'antenne bi-fonction selon l'invention;
• la figure 4, le recouvrement du diagramme de rayonnement de la voie interrogation-réception par le diagramme de rayonnement de la voie de contrôle.

Other objects and advantages of the invention will be better understood with the aid of the detailed description below and of Figures 1 2, 3 and 4 which represent:

• - Figure 1, a section of a common antenna reflector by primary and secondary radars, according to the invention;
• - Figure 2, a schematic diagram showing the connection between a 0-π phase shifter and the power divider, according to the invention;
• - Figure 3, the shape of the radiation diagram of the interrogation-reception path in the reservoir plane, of the dual-function antenna according to the invention;
• FIG. 4, the overlap of the radiation pattern of the interrogation-reception channel with the radiation pattern of the control channel.

In space surveillance, mainly at aerodrome approaches, the advantage of combining a so-called primary and a so-called secondary radar is no longer to be demonstrated. The primary radar detects aircraft in particular by their direction relative to the radar and their distance, and the secondary radar interrogates them, answering machines provided for this purpose on board the aircraft, sending information to the interrogator on the ground. altitude, their identity, their speed, etc ... The interrogation by the secondary radar of the aircraft being done in the direction of the aircraft detected by the primary radar, it is advantageous, either to couple the antennas of the two radars, or to use only one and the same antenna capable of fulfilling the two functions which have been defined. However, as expressed in the introduction, the primary radar-secondary radar system has drawbacks which affect its proper functioning and its performance. In particular, the radiation diagram of the secondary radar has, in addition to a main lobe which transmits the interrogation and receives the response from the aircraft questioned, secondary lobes the level of which may be sufficient for a responder to be triggered which may either belong to the aircraft really questioned, that is, to be the responder of another aircraft.

In this case, errors may follow, the consequences of which may be dangerous.

We then sought to remedy these drawbacks, by trying to remove the secondary or lateral lobes from the interrogation diagram; the method which has been adopted consists in covering these lateral lobes by an omnidirectional diagram, created from so-called control elements which in fact are a separate antenna called control antenna, or also by a diagram of the so-called difference type , it can be created from the interrogation channel supplied adequately.

-These measures are however not sufficient and for example in the case of an overlap of the side lobes of the interrogation diagram by an omnidirectional diagram, this overlap is imperfect, often due to external causes, radome, etc.

We then seek to form on the one hand an interrogation-reception radiation diagram of the "sum" or "even" type and on the other hand a radiation diagram of the control channel of the "difference" or "odd" type. The main advantage of this type of odd illumination lies in the fact that the axis of the crevice of the difference diagram is preserved in elevation, thus giving better centering of the arc of inter-, rogation and, in principle, increased stability of the latter along the site coverage. Beyond the central area of the radiation pattern, the problem of overlapping the side lobes of the radiation pattern of the primary radar is resolved by judiciously composing the laws of amplitude and phase of the radiating elements.

To do this, according to the invention, a linear array is formed in the antenna reflector of the primary radar, along one of its guidelines passing through the phase center of the antenna to have a larger span. radiant slots. The choice of the director of the reflector depends on the plane of deposit determined for the propagation. The fact of having the network on one of the central guidelines of the reflector makes it possible to have a large number of slots therefore a good resolution.

Each slot is associated with a cavity excited by an element for example of the plunger or cross-bar type, in which are created the resonance phenomena of certain, modes as well as well-known radiation phenomena. Such an association is described in the Swiss patent CH.A.328 923. An adequate excitation of all the radiating slots of the network for the interrogation reception channel according to an even phase law and a law attenuated in amplitude, such that the Gaussian law, makes it possible to obtain a radiation diagram of the "sum" type and an excitation of a certain number of slits, distributed symmetrically around the phase center, according to an odd phase law, makes it possible to obtain a "difference" type radiation pattern for the control channel.

The integration of the secondary antenna in the reflector of the primary antenna has the advantage of avoiding an increase in the volume of the primary antenna, therefore of weight and wind resistance. The drive mechanism of the device remains relatively simple and of small volume, which is particularly convenient in weapon systems.

FIG. 1 schematically represents a sectional view of a common antenna reflector 1 for primary and secondary radar, comprising a linear network 2 of radiating slots 2 _j , i varying from 1 to n with n representing the total number of slots of the network. The slots are arranged along a direction D preferably over the entire opening of the reflector 1. The pitch h of the grating is of the order of 0.6 to 0.8 A in a preferred embodiment. The reflector 1 is made of dielectric 3 - of glass mat impregnated with epoxy-covered by a fabric 4 of glass fibers carrying metallic wires 40 and 41 crossed. These wires are generally made of thin copper.

• ― Pour une fréquence d'émission de 10⁴ MHz par exemple, le diamètre des fils métalliques 40 et 41 est de 12/100 mm et la distance entre chaque fil est de l'ordre de 1,5 mm.

Behind each slot 2, of the network 2 is produced a radiating cavity 5, paralelepipedic, from the same dielectric 3 as the reflector 1 covered in the same way by a fabric 4 of glass fibers carrying metallic wires. The polarizations of the sources of the primary and secondary antennas being perpendicular, the metal wires 40 and 41 are crossed over the entire surface of the reflector 1, and also inside the cavities 5 ,, while in front of the slots there is only the wires 40 arranged parallel to the director, in the direction of the polarization chosen for the source of the primary antenna, horizontal in the example described.

• - For an emission frequency of 10 ⁴ MHz for example, the diameter of the metal wires 40 and 41 is 12/100 mm and the distance between each wire is of the order of 1.5 mm.

The covering of the metallic threads with glass fibers allows the fabric to have a uniform elasticity.

To reduce the volume of the cavities 5, and constitute a monolithic assembly of simple construction, the cavities are filled with dielectric 3. The exciting elements 6 of these cavities 5 ₁ ―of the plunger or cross-bar type ― are inserted into .Ie dielectric 3 filling the cavities and comprising a coaxial base 7 allowing the adaptation between the cavities 5, and the coaxial lines 8 which connect them to a power divider system 9 placed on the back of the reflector 1. This power divider 9, which may be constituted by distributors, is connected by a microwave link line to a conventional interrogator-receiver assembly, not shown in FIG. 1. The rear of the reflector is protected by a waterproof cover 10, made of dielectric 3.

If it turns out that the diagram of the control channel given by the slots _2j of the network, radiating towards the front, does not ensure correct recovery of the rear part of the directive diagram of the interrogation channel, this control channel is equipped with one or more additional elements radiating towards the rear. This could possibly be one or more slots 11 formed in the dielectric of the cover 10 behind which cavities 12 are formed, constituted in the same way as the cavities 5 _j radiating towards the front of the reflector 1. These slots 11 are reduced in number and placed in the cover 10, in the plane of symmetry of the reflector 1 containing the slots radiating towards the front.

As we have seen previously, it is via the power divider 9 that the cavities 12 associated with the slots 2, and 11 are excited to give respectively a directional radiation diagram of the "sum" type for the interrogation channel. -reception and a "difference" type diagram for the control channel. The slots of the control channel, whether they radiate towards the front or towards the rear of the reflector 1, are divided into two equal groups, excited in phase opposition, thanks to phase shifters of π located in the power divider 9 .

As shown in Figure 2 representing a 0 ― π hybrid phase shifter 15, the two outputs 13 and 14 of the phase shifter 15, in phase opposition, are connected to channels 16 and 17 of the power distributor 9, these last two channels supplying the two groups of slots 2, of the control channel.

The terminals 130 and 140 of the phase shifter 15 are inputs.

FIG. 3 gives the shape of the radiation diagram of the "sum" or "even" type of the interrogation channel of the secondary radar function, in the plane bearing identified by the abscissa axes θ ― bearing angle ― and ordinate G-gain in dB. It has a width L at -3 dB of the main lobe 18 linked to the desired gain in the direction of the maximum radiation, also linked to low lateral lobe levels 19 which are not very high and finally to a diffuse radiation level, represented by the lobes 20 , as low as possible.

These characteristics must be maintained not only in the plane containing the direction of the maximum radiation, but also preserved throughout the opening in site of the operating volume. In such conditions, it will be easier to ensure that this diagram is overlapped by that of the control channel.

Figure 4 shows the overlap of a directive diagram I of the interrogation-reception channel tion by a C diagram of the difference type control channel. The axis of the crevice 21 of the difference diagram C is the same as that of the main lobe 18 of the sum diagram I. The side lobes 19 of the radiation diagram of the primary radar are covered by the radiation diagram of the control channel C.

We have thus described a common antenna for primary radar and secondary radar whose secondary radar function is integrated in the reflector of the antenna of the primary radar, this reflector being produced, as well as the slots and cavities which are associated with them and which constitute the secondary radar function, in a dielectric material.

Claims (13)

1. Common primary and secondary radar antenna comprising a single reflector (1) irradiated by a primary source operating as the transmitter-receiver source of the primary radar function, and further comprising an array of radiating slots (2i) along one directrix D of the reflector and forming the source feeding the interrogation path of the secondary radar, said path having a radiation diagram of the "sum" or "pair" type, each of these slots (2i) being associated with a resonance cavity (5i) completely integrated into the reflector (1) and comprising excitation means, characterized in that the reflector (1) and the cavities (5i) associated with the slots (2i) are made from a dielectric material (3) covered by a glass fiber tissue (4) carrying overspun metallic wires (40-41), these metallic wires being crossed over the whole surface of the reflector and inside the cavities, excepted in front of the slots where they are arranged along the polarisation direction of the primary radar source.

2. Common antenna in accordance with claim 1 or 2, characterized by the fact that the directive interrogation-reception path of the secondary radar function comprises a path termed as control path and comprising a certain number of slots (2i) associated with resonance cavities (5i) of the linear array, and lying in the neighborhood of and symmetrically on both sides of the phase center of the antenna, the radiation diagram of the control path of the secondary radar being of "difference" or "odd" type.

3. Common antenna in accordance with claim 1, characterized by the fact that the dielectric (3) is an epoxy impregnated glass mat.

4. Common antenna in accordance with claim 1 or 2, characterized by the fact that the cavities (5i) associated with the slots (2i) are filled by the same dielectric (3) as that used for making the reflector (1 ).

5. Common antenna in accordance with claim 1 or 2, characterized by the fact that the cavities (5i) associated with the slots (2i) are excited by elements (6) of plunger or cross-bar type inserted into the dielectric filling the cavities.

6. Common antenna in accordance with claim 5, characterized by the fact that the excitation elements (6) of the cavities (5) have a coaxial base (7).

7. Common antenna in accordance with claim 6, characterized by the fact that the excitation means (6) of the cavities (5i) are connected through coaxial lines (8) to a power divider (9) applied against the back of the reflector (1).

8. Common antenna in accordance with any of claims 1 to 7, characterized by the fact that the back side of the reflector is protected by a sealing hood (10) formed of the same dielectric (3) as the reflector (1 ).

9. Common antenna in accordance with any of claims 1 to 8, characterized by the fact that the control path of the secondary radar is adapted to comprise one or several elements (11) radiating towards the backside of the reflector (1) and placed in the symmetry plane of the reflector (1) containing the slots (2i) radiating towards the front side.

10. Common antenna in accordance with claim 9, characterized by the fact that the supplementary radiating elements of the control path are one or a plurality of slots (11) inserted into the back hood (10) and associated with resonance cavities (12), and formed and fed in the same manner as the slots (2i) associated with the cavities (5i) inserted into the reflector (1

11. Common antenna in accordance with claim 2, characterized by the fact that the two groups of slots (2i) symmetrically distributed about the phase center of the antenna and forming the interrogation-reception path of the secondary radar are excited in accordance with an amplitude attenuated law and a pair phase law.

12. Common antenna in accordance with claim 11, characterized by the fact that the amplitude attenuated law is a gaussian law.

13. Common antenna in accordance with claim 2, characterized by the fact that the two groups of slots (2i) symmetrically distributed about the phase center of the antenna and forming the control path of the secondary radar are excited with opposed phase.

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