EP0880196B1 - Compact monopulse source for an antenna with optical focusing - Google Patents

Description

The present invention relates to a primary source to at least two-way, so-called monopulse, compact for an optical antenna focusing, for example Cassegrain type or lens, connected to a circuit microwave transmission and reception made for example in microstrip technology. It applies in particular to radars millimeters equipping motor vehicles. More generally, she applies to millimeter radars requiring a high level integration and a low cost of implementation.

A so-called monopulse source has for example two paths and simultaneously generates two radiation patterns, a diagram sum and a difference diagram. This source must present compatible radio characteristics of adaptation performance and radiation of a complete focusing antenna. These features particularly the adaptation frequency band, the formation of the diagram of the difference path in the plane of the electric field E and the openings and the relative level of channel radiation patterns sum and difference.

• facilité de connexion et d'implantation au plus près du circuit d'émission et de réception hyperfréquence, ce dernier étant réalisé en technologie en micro-ruban, dite microstrip, de manière à minimiser les longueurs de lignes dont les pertes importantes dans la bande millimétrique, de l'ordre par exemple de 80 dB, peuvent limiter rapidement les performances du système ;
• blindage du circuit d'émission et de réception hyperfréquence vis-à-vis des contraintes électromagnétiques externes en dehors de la bande de fonctionnement du système ;
• faible encombrement en profondeur de la source primaire, par exemple inférieur à 5 mm ;
• étanchéité et éventuellement herméticité du circuit d'émission et de réception vis-à-vis des contraintes d'environnement extérieures, l'ensemble constitué du circuit d'émission et de réception et de la source primaire pouvant constituer un macro-composant ;
• réalisation par des moyens de fabrication classiques et présentation d'un fonctionnement tolérant vis-à-vis des dispersions dimensionnelles obtenues avec ces moyens de fabrication dans le cadre d'une production de masse à très faible coût.

In some applications, such as an application to motor vehicles for example, the source must also meet particular technical, technological and economic criteria of a general nature and also particular. These criteria are for example the following:

• ease of connection and implementation closer to the microwave transmission and reception circuit, the latter being made in microstrip technology, so as to minimize the lengths of lines whose significant losses in the millimeter band , of the order of eg 80 dB, can quickly limit the performance of the system;
• shielding the microwave transmission and reception circuit against external electromagnetic stresses outside the operating band of the system;
• low bulk in the depth of the primary source, for example less than 5 mm;
• sealing and possibly hermeticity of the transmission and reception circuit vis-à-vis external environmental constraints, the assembly consisting of the transmission and reception circuit and the primary source may constitute a macro-component;
• realization by conventional manufacturing means and presentation of a tolerant operation vis-à-vis the dimensional dispersions obtained with these manufacturing means in the context of mass production at very low cost.

A solution for realizing a primary source satisfying some previous criteria, is to use an excited pyramidal horn by a magic tee folded in the plane of the electric field E. Next access used, this magic tee allows to generate in the cornet the transverse mode electric TE01, even mode, or TM11 magnetic transverse mode, mode odd, respectively forming the sum and difference diagrams. However, this solution has a deep space requirement important and requires, for its realization, the manufacture and assembly of several pieces of high precision leading to the use of methods expensive machining processes such as wire electro-erosion or electroforming.

Another solution is to make a printed source on the same substrate as the microwave transmission circuit. To train radiation patterns with the desired directivity, this source must consist of a network of radiating elements of "Patch" fed for example by a hybrid ring. This solution has the advantage of not requiring any mechanical parts and have a minimum footprint in depth but does not meet the requirements of requirements for electromagnetic shielding and protection against environmental constraints for the components of the transmission and microwave reception. Moreover, the radiating elements of "Patch" have a frequency selective operation and are therefore very sensitive to the characteristics of the substrate such as in particular its dielectric constant or its thickness, as well as etching tolerances.

The object of the invention is to overcome the aforementioned drawbacks and allow in particular to achieve a source meeting the criteria outlined previously. For this purpose, the subject of the invention is a monopulse source antenna for focusing optics, as defined by claim 1.

The main advantages of the invention are that it also applies well to an antenna with folded optics that a direct optics antenna, that it allows an access of the source by a microstrip line, that it allows to modify the directivity of the radiation patterns in the plane magnetic H and in the electrical plane E, it allows low leakage radio, that it allows to dispose the active components of the circuit transmission and reception near the source, that it is simple to implement and is economical.

• la figure 1a, un exemple d'antenne à optique repliée alimentée par une source primaire monopulse ;
• la figure 1b, un exemple d'antenne à optique directe alimentée par une source primaire monopulse ;
• la figure 2, un exemple de réalisation selon l'art antérieur d'une source primaire ;
• la figures 3, un autre exemple selon l'art antérieur d'une source primaire ;
• la figure 4, un mode de réalisation possible d'un exemple de source selon l'invention, par une vue de face suivant F', en regard de la semelle métallique;
• la figure 5, une vue en coupe suivant F de la figure 4 ;
• la figure 6, un détail de la figure 4 au niveau des éléments rayonnant ;
• les figures 7a et 7b, un mode de réalisation possible de source selon l'invention où l'usinage de la semelle métallique modifie le diagramme de rayonnement, la figure 7b étant une vue en coupe de la figure 7a selon AA..

Other characteristics and advantages of the invention will become apparent with the aid of the following description made with reference to appended drawings which represent:

• FIG. 1a, an example of a folded optical antenna powered by a monopulse primary source;
• Figure 1b, an example of direct optics antenna powered by a monopulse primary source;
• Figure 2, an exemplary embodiment according to the prior art of a primary source;
• FIG. 3, another example according to the prior art of a primary source;
• FIG. 4, a possible embodiment of an example of a source according to the invention, with a front view along F 'opposite the metal soleplate;
• Figure 5, a sectional view along F of Figure 4;
• Figure 6, a detail of Figure 4 at the radiating elements;
• FIGS. 7a and 7b, a possible source embodiment according to the invention in which the machining of the metal sole modifies the radiation pattern, FIG. 7b being a sectional view of FIG. 7a according to AA.

FIG. 1a shows an example of an antenna with folded optics powered by a primary source 1 called monopulse, that is to say a source two-way, a sum channel Σ and a difference channel Δ. The antenna comprises in particular a main reflector 2, for example of the type parabolic, and a subreflector 3. The primary source 1 is arranged behind the main reflector 2 and radiates through a hole 4 made in this last. The subreflector 3 is arranged opposite the source primary 1. The rays 5 emitted from the primary source 1 are reflected on the subreflector 3 and then on the main reflector 2. After reflection on the latter, the radii 5 'are emitted in parallel at the antenna output.

The invention applies for a folded optical antenna, but it can also be applied for example for a direct optical antenna as shown in Figure 1b. For example, the latter includes dielectric lens 11 which focuses to infinity the rays 5 emitted by the source 4.

FIG. 2 shows an exemplary embodiment according to the art prior. Primary source 1 uses a rectangular waveguide 26 prolonged by a pyramidal cone 27. The sum and difference paths of a tee magic 28 are fed through guide-microstrip transitions 21, 22. Transmitting and receiving circuits 23, in technology microstrip, are in turn implanted on a dielectric substrate 24, itself for example disposed on a metal sole 25. The waveguide is excited by the magic tee 28 folded in the plane of the electric field E. Depending on the access used, this magic tee can generate in the cornet the TE10 transverse electric mode, even mode, or transverse mode Magnetic TM11, odd mode, respectively forming the diagrams of radiation sum and difference. The access of the way difference of the tee magic can be obtained, via an elbow made in the plane of the field electric E, in the same plane as the access of the way sum. This source can then be connected to the transmission and reception circuit 23 by via two microstrip-guide transitions 21, 22. This solution unfortunately has a large footprint in depth, the order for example of 35 mm in millimetric band, and requires, as previously mentioned, the manufacture and assembly of several pieces of high precision, such as for example a magic tee 28 and transitions microstrip-guide 21, 22, which leads to the use of machining methods expensive. These methods are, for example, wire EDM or electro-forming.

Figure 3 shows another known example of embodiment. The source is printed on the same substrate as the transmission and reception. It comprises in particular a hybrid ring 31 balanced type 4λ / 4 and a network of two pairs of elements or "patches" 32, 33. To form the radiation diagrams presenting the desired directivity, the ring 31 feeds the radiating elements by two outputs 34, 35 one of which is elongated by a quarter wavelength λ / 4 relative to each other so as to feed in phase or opposition of phase the two pairs of radiating elements 32, 33 according to the input 36, 37 of the ring that is excited. The radiation pattern of the sum track is thus formed when the two pairs are excited in phase and the radiation pattern of the difference way is thus formed when the two pairs are excited in phase opposition. As indicated previously, this embodiment has the advantage of not require no mechanical parts and present a clutter minimal in depth but it does not meet the shielding requirements electromagnetic and protective vis-à-vis the environmental constraints for the components of the microwave transmission and reception circuit. Moreover, the radiating "patches" 32, 33 exhibit an operation selective in frequency and are therefore very sensitive to the characteristics of the substrate such as in particular its dielectric constant or its thickness as well as engraving tolerances.

FIGS. 4, 5 and 6 show an exemplary embodiment possible of a primary source according to the invention. This source has two radiating waveguides 41, 42 machined in the metal sole 25 supporting the microwave transmission and reception circuit of the antenna, this circuit being for example in microstrip technology and / or MMIC according to the Anglo-Saxon expression "Monolithic Microwave Integrated Circuit". The transmission and reception circuit is for example arranged on a substrate dielectric 24, itself mounted on the metal soleplate 25. The lines microstrip are for example screen printed or etched on the substrate. The long side of the waveguides 41, 42 is for example sized for allow the propagation of the transverse electric mode TE01 and to obtain in the magnetic plane H, the desired directivity of the radiated diagram in sum way. The distance between the two waveguides 41, 42 is example determined to obtain in the plane of the electric field E, the desired directivity of the diagram radiated in sum channel. Advantageously, it is possible to modify the directivity of the diagrams of radiation in the plane of the magnetic field H by playing on the size of the long side of the waveguides 41, 42 and it is possible to modify this directivity in the plane of the electric field E by playing on the distance separating these two guides.

The ground plane metal of the microstrip circuit is removed at right of the two waveguides 41, 42 so as to let the radiation. Etching 60, 61 of the ground plane on the substrate dielectric then bypasses the end of the guides. Each waveguide is for example excited by a transition 44, 45 with the transmission circuit and reception, for example in microstrip technology, the transition being constituted for example by an engraved pattern 44, 45 on the same substrate as the one supporting the microstrip circuit, and by a short circuit microwave 43 closing the waveguide. The significant mismatch of the radiating mouth 46 of each guide 41, 42 is compensated by a section change placed at a given distance from this mouthpiece, each waveguide extending into a waveguide reduced 47, 48 from this section change. Section reduction is for example performed on the long side of the guide, in a factor of two for example. Each transition 44, 45 with the microstrip circuit is positioned in the section change plan. A transition 44, 45 is adapted by the microwave short-circuit 43 closing the waveguide reduced 47, 48 and placed at a distance substantially equal to a quarter of the wavelength λ / 4 of the signal transmitted by the microstrip circuit. Each transition 44, 45 is for example powered by a microstrip line 49, 50 passing under a tunnel 51, 52 made in the wall of the reduced waveguide. Each transition 44, 45 is then for example connected to a hybrid ring 53 of the type 4λ / 4 of which one of the outputs 55 is extended by a quarter of wavelength λ / 4 with respect to the other 54. These links 49, 54, 50, 55 allow to feed in phase or in phase opposition the two radiating elements according to the inlet 56, 57 of the ring 53 which is excited and thus make it possible to form the diagrams of the sum and difference channels, the difference diagram being for example obtained in the plane of the field E. The two inputs 56, 57 of the hybrid ring are connected to the remainder of the transmission and reception circuit 23. Each radiating element aforementioned is in fact constituted by a mouth 46 of waveguide and a transition 44, 45 with the microstrip circuit. Active components of the circuit transmission and reception may be placed near the source, this which allows in particular to limit the microwave losses. Advantageously, the protection of the transmission and reception circuit microwave against parasitic electromagnetic radiation outside the operating band of the radar, is ensured by the presence of waveguides that act as a high-pass filter.

The section of the waveguides 41, 42, 47, 48 is for example oblong instead of being rectangular, this notably avoids the use of expensive machining methods such as wire electro-erosion. The oblong sections can, they simply be realized by a means economical machining such as milling. In addition, the architecture of a source according to the invention allows it to present a wide band passing through, in particular through the use of a non-excitation element selective, making the manufacturing tolerances of the parts less sensitive mechanical and microstrip circuits, and thus further contributes to reducing manufacturing costs.

Short-circuit 43 for adapting transitions 44, 45 and the guides reduced section 47, 48 can be machined in the same room. it in particular to reduce the number of workpieces. This piece can be assembled and positioned relative to the metal sole 25, and therefore in particular with respect to the microstrip circuit and the waveguides 41, 42 by any method, such as, for example, screwing, brazing or collage. In order to limit microwave leakage, this room 43, 47, 48 may be electrically connected by at least one point, but preferably by several, to the metal sole 25 supporting the circuit in technology microstrip. For this purpose, metallized holes can be made in the dielectric substrate giving for example on the periphery of the guides 41, 42 machined in the metal sole 25.

The metal soleplate 25 in which the radiating guides 41, 42 are made may for example be an integral part of the housing containing the transmit and receive circuit, which makes the realization even more compact and also reduces the number of workpieces.

Figures 7a and 7b show a possible embodiment of a primary source according to the invention for obtaining a diagram of particular radiation of the sum and / or the difference of the source, for example to get a better adaptation to the characteristics of focusing optics. For this purpose, false slots 71, 72 are added to the vicinity of the waveguides 41, 42 machined in the metal soleplate 25. These false slots 71, 72 are holes that do not completely cross the sole 25. These false slots, which have for example the same section transversal waveguides, are actually traps that are excited by coupling thanks to the proximity of the waveguides. The energy captured by coupling with these waveguides 41, 42 is radiated. In this way there is the equivalent of four radiating sources, of which we can for example control the phase by adjusting the position of the traps and their depth. This allows in particular to obtain a radiation pattern more directive, which avoids energy losses, especially in the case from application to focusing optics. Indeed, a more directive diagram prevents some of the radiation from being intercepted by the lens, this which therefore decreases the aforementioned losses which are generally called losses by spill-over. The false slots 71, 72 have the effect of remove the coincidence of the phase centers from the field plans electrical and magnetic. According to the invention, to make it coincide again these centers of phase, the thickness of the sole is decreased at the level of waveguides and fake slits. For that, a surface 73 is example made by countersinking, inside the sole 25. This surface 73, as well as the false slots 71, 72 are for example obtained during of the same machining operation as the waveguides 41, 42 of the soleplate 25. Preferably, to better ensure the coincidence of the centers phase, the decrease in the thickness of the sole 25 begins substantially at right 74 waveguides 41, 42 and false slots 71, 72.

FIGS. 4, 5, 6 and 7 describe an exemplary embodiment of a monopulse two-way primary source. The invention can nevertheless be applied for three-way sources, for example with a sum channel and a path difference in the plane of the electric field E and a path difference in the plane of the magnetic field H. This source is then by example obtained by combining four radiating elements powered by four hybrid rings, each radiating element being for example consisting of a waveguide mouth 46 and a transition with the microstrip circuit as previously described.

The invention can also be applied for the realization a primary source illuminating a multi-beam antenna. This source is for example formed by several radiating elements, such as those mentioned above, placed in the focal plane of a type reflector system Cassegrain or in the focal plane of a dielectric lens, each element beam generating a beam whose inclination depends on the position of the elementary source with respect to the focus.

Advantageously, the invention allows a very good protection circuits against environmental constraints, such as for example moisture or corrosion, partially or completely filling guides radiating by a dielectric material. Such protection is particularly advantageous for radars equipping automobiles and which are likely to suffer the aforementioned constraints.

Finally, a source produced according to the invention occupies a small space e depth, this may for example be of the order of 5 mm in millimetric band, this congestion ranging from the outer end of the short-circuit microwave 43 to the output 46 of a waveguide 41, 42.

Claims (15)

1. Monopulse source for an antenna with optical focusing, the source comprising at least two waveguides (41, 42) machined in the metal flange (25) supporting the microwave transmission reception circuit (23, 49, 50, 53, 54, 55, 56, 57) of the antenna (2, 3, 11), each waveguide (41, 42) extending as a waveguide of reduced section (47, 48), each waveguide (41, 42) being exited by a microwave short-circuit (43) closing the waveguide of reduced section (47, 48) and by a transition (44, 45) with the transmission and reception circuit, each transition (44, 45) being positioned in the section-changing plane of the guide.
2. Source according to Claim 1, characterized in that the transmission and reception circuit is placed on a dielectric substrate (24) itself mounted on the metal flange (25).
3. Source according to Claim 2, characterized in that the transmission and reception circuit comprising microstrip technology lines, the latter are screenprinted on the dielectric substrate (24).
4. Source according to Claims 2 or 3, characterized in that the transitions (44, 45) are constituted by patterns etched on the same substrate (24) as that supporting the transmission and reception circuit.
5. Source according to any one of the preceding claims, characterized in that each transition (44, 45) is fed by a microstrip line (49, 50) passing under a tunnel (51, 52) made in the wall of the waveguide.
6. Source according to Claim 5, characterized in that the lines (49, 50) are linked to a hybrid ring (53) making it possible to feed the transitions in phase or in phase opposition, so as to form the sum or difference diagrams depending on the input (56, 57) of the ring that is excited.
7. Source according to any one of the preceding claims, characterized in that the section of the waveguides (41, 42, 47, 48) is oblong.
8. Source according to any one of the preceding claims, characterized in that the short -circuit (43) for matching the transitions (44, 45) and the guides of reduced section (47, 48) are machined in one and the same component.
9. Source according to Claims 2 and 8, characterized in that metallized holes (58) are made in the dielectric substrate (24) so as to electrically link the component to the metal flange (25).
10. Source according to any one of the preceding claims, characterized in that the metal flange (25) forms an integral part of the pack containing the transmission and reception circuit.
11. Source according to any one of the preceding claims, characterized in that the waveguides (41, 42, 47, 48) are filled with dielectric material.
12. Source according to any one of the preceding claims, characterized in that false slots (71, 72), radiating by coupling with the waveguides (41, 42) are added in the vicinity of the latter.
13. Source according to Claim 12, characterized in that the false slots (71, 72) have substantially the same cross section as the waveguides (41, 42).
14. Source according to any one of Claims 12 or 13, characterized in that the thickness of the flange (25) is reduced at the level of the waveguides (41, 42) and of the false slots (71, 72).
15. Source according to Claim 14, characterized in that the reduction in the thickness of the flange (25) begins substantially in the neighbourhood (74) of the waveguides (41, 42) and of the false slots (71, 72).

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