EP0880196A1 - Compact monopulse source for an antenna with optical focusing - Google Patents

Abstract

The invention relates to a monopulse source for antenna focusing.

The source comprises at least two waveguides (41, 42) machined in the metal soleplate (25) supporting the emission circuit and microwave reception (23, 49, 50, 53, 54, 55, 56, 57) from the antenna (2, 3, 11).

Application: in particular primary sources for radars operating in millimeter wave.

Description

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

A so-called monopulse source for example has two channels and generates two radiation patterns simultaneously, one diagram sum and a difference diagram. This source must present compatible radio characteristics of adaptation performance and radiation from a complete focusing antenna. These characteristics especially the adaptation frequency band, the formation of diagram of the path difference in the plane of the electric field E and the openings and the relative level of the radiation patterns of the channels 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 certain applications, such as an application to motor vehicles for example, the source must also respond in particular to technical, technological and economic criteria of a general and also specific nature. These criteria are for example the following:

• ease of connection and installation as close as possible to the microwave transmission and reception circuit, the latter being produced using micro-ribbon technology, known as microstrip, so as to minimize line lengths, including significant losses in the millimeter band , for example of the order of 80 dB, can quickly limit the performance of the system;
• shielding of the microwave transmission and reception circuit against external electromagnetic constraints outside the operating band of the system;
• small overall depth of the primary source, for example less than 5 mm;
• sealing and possibly hermeticity of the transmission and reception circuit with respect to external environmental constraints, the assembly consisting of the transmission and reception circuit and of the primary source being able to constitute a macro-component;
• realization by conventional manufacturing means and presentation of an operation tolerant with respect to the dimensional dispersions obtained with these manufacturing means in the context of mass production at very low cost.

A solution to achieve a primary source satisfying some previous criteria, is to use an excited pyramid horn by a magic tee folded in the plane of the electric field E. According to the access used, this magic tee allows to generate in the horn the transverse mode electric TE01, even mode, or transverse magnetic mode TM11, mode odd, respectively forming the sum and difference diagrams. However this solution presents a congestion in depth important and requires, for its realization, the manufacture and assembly of several pieces of high precision leading to the use of methods expensive machining such as wire EDM or electro-forming.

Another solution is to produce 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 the type 〈〈 patch 〉〉 powered for example by a hybrid ring. This solution has the advantage of not requiring any mechanical parts and have a minimum size at depth but does not meet the electromagnetic shielding and protection requirements environmental constraints for the components of the transmission circuit and microwave reception. Furthermore, the radiating elements of the type 〈〈 patch 〉〉 have a selective frequency 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 to allow in particular to produce a source meeting the criteria set out previously. To this end, the invention relates to a monopulse source for antenna with focusing optics, characterized in that it comprises minus two waveguides machined in the metal sole supporting the antenna microwave transmission and reception circuit

The main advantages of the invention are that it also applies both to a folded optics antenna and to a direct optics antenna, that it allows access from the source by a microstrip line, that it allows to modify the directivity of the radiation diagrams in the plane magnetic H and in the electric plane E, that it allows weak leaks radioelectric, that it allows to have the active components of the circuit transmission and reception near the source, that it is simple to implement and that it 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 description which follows given with reference to the appended drawings which represent:

• FIG. 1a, an example of an antenna with folded optics supplied by a primary monopulse source;
• Figure 1b, an example of direct optical antenna powered by a primary monopulse source;
• Figure 2, an embodiment according to the prior art of a primary source;
• Figures 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, by a front view along F ', opposite the metal sole;
• 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 embodiment of a source according to the invention where the machining of the metal sole changes the radiation diagram, FIG. 7b being a sectional view of FIG. 7a along AA.

Figure 1a shows an example of an antenna with folded optics powered by a primary source 1 called monopulse, that is to say a source with two channels, 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 sub-reflector 3. The primary source 1 is arranged behind the main reflector 2 and radiates through a hole 4 made in this last. The sub-reflector 3 is arranged opposite the source primary 1. The rays 5 emitted from the primary source 1 are reflected on the sub-reflector 3 then on the main reflector 2. After reflection on the latter, the rays 5 'are emitted in parallel at the antenna outlet.

The invention applies to an antenna with folded optics, but it can also be applied for example for a direct optical antenna as shown in Figure 1b. This last comprises for example a dielectric lens 11 which focuses the rays 5 emitted by the source 4 at infinity.

Figure 2 shows an exemplary embodiment according to art prior. Primary source 1 uses a rectangular waveguide 26 extended by a pyramid cone 27. The sum and difference paths of a tee magic 28 are fed via microstrip guide transitions 21, 22. The transmission and reception circuits 23, in technology microstrip, are implanted on a dielectric substrate 24, itself for example arranged on a metal sole 25. The waveguide is excited by the magic tee 28 folded in the plane of the electric field E. According to the access used, this magic tee allows to generate in the cornet the transverse electric mode TE10, even mode, or transverse mode magnetic TM11, odd mode, respectively forming the diagrams of sum and difference radiation. Access to the difference path from 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 to the sum track. 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 significant bulk in depth, the order for example of 35 mm in millimeter strip, and requires, as indicated above, the manufacture and assembly of several pieces of high precision, such as 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.

FIG. 3 shows another known example of embodiment. The source is printed on the same substrate as the transmission circuit and reception. It includes in particular a balanced hybrid ring 31 of the type 4λ / 4 and a network of two pairs of elements or 〈〈 patches 〉〉 radiant 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 extended by a quarter wavelength λ / 4 relative to each other so as to feed in phase or in opposition to phase the two pairs of radiating elements 32, 33 following the entry 36, 37 of the ring which is excited. The radiation pattern of the sum channel is thus formed when the two pairs are excited in phase and the radiation pattern of the difference pathway is thus formed when the two pairs are excited in phase opposition. As indicated previously, this exemplary embodiment has the advantage of not require no mechanical parts and present a space requirement minimal in depth but does not meet shielding requirements electromagnetic and protection against environmental constraints for the components of the microwave transmission and reception circuit. Furthermore, the radiating 〈〈 patches 32 32, 33 have an operation frequency selective 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.

Figures 4, 5 and 6 show an exemplary embodiment possible from 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 and / or MMIC technology 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 sole 25. The lines microstrip are for example screen printed or engraved on the substrate. The long side of the waveguides 41, 42 is for example dimensioned 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 on track. The distance between the two waveguides 41, 42 is by example determined to obtain in the plane of the electric field E, the desired directivity of the radiated diagram 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 dimension 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 metal of the ground plane of the microstrip circuit is removed at the right of the two waveguides 41, 42 so as to allow the radiation. The etching 60, 61 of the ground plane on the substrate dielectric then bypasses the ends 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 advantageously compensated by a change of section placed at a given distance of this mouth, each waveguide extending into a waveguide reduces 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 plane. A transition 44, 45 is adapted by 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 supplied 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 balanced type 4λ / 4 with one of the outputs 55 extended by a quarter of wavelength λ / 4 relative to the other 54. These links 49, 54, 50, 55 allow the two to be supplied in phase or in phase opposition radiating elements following the entry 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 electric E. The two inputs 56, 57 of the hybrid ring are connected to the rest of the transmission and reception circuit 23. Each radiating element aforementioned consists in fact of a mouth 46 of waveguide and a transition 44, 45 with the microstrip circuit. Active components of the circuit transmission and reception can be placed near the source, this which allows in particular to limit microwave losses. Advantageously, the protection of the transmission and reception circuit microwave against parasitic electromagnetic radiation outside and located outside the radar operating band, is ensured by the presence of waveguides which play the role of 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 EDM. The oblong sections can be simply made by a means economical machining such as milling. Furthermore, the architecture of a source according to the invention allows it to present a wide band busy, thanks in particular to the use of an excitation element not selective, which makes parts manufacturing tolerances less sensitive mechanical and microstrip circuits, and therefore further contributes to reducing manufacturing costs.

The short circuit 43 for adapting the transitions 44, 45 and the guides of reduced section 47, 48 can be machined in the same part. That allows in particular to reduce the number of parts to be machined. 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 leaks, this part 43, 47, 48 can 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 for example on the periphery of the guides 41, 42 machined in the metal sole 25.

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

Figures 7a and 7b show a possible embodiment a primary source according to the invention making it possible to obtain a diagram particular radiation of the sum and / or difference channels of the source, for example to obtain a better adaptation to the characteristics of focusing optics. For this purpose, false slots 71, 72 are added to the in the vicinity of the waveguides 41, 42 machined in the metal sole 25. These false slots 71, 72 are holes which do not completely cross the sole 25. These false slots, which for example have the same section transverse as the 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 one can for example control the phase by adjusting the position of the traps and their depth. This allows in particular to obtain a more directive, which avoids energy losses, especially in the case of application to a focusing optic. Indeed, a more directive diagram prevents part of the radiation from being intercepted by the lens, which therefore reduces the aforementioned losses which are generally called losses by 〈〈 spill-over 〉〉. The false slots 71, 72 have in particular the effect of remove the coincidence of the phase centers of the field plans electric and magnetic. According to the invention, to make coincide again these phase centers, the thickness of the sole is reduced at the level of the waveguides and false slots. For this, a surface 73 is by example made, by counterbore, 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 sole metallic 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 of the waveguides 41, 42 and of the false slots 71, 72.

Figures 4, 5, 6 and 7 describe an exemplary embodiment of a two-channel monopulse 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 associating four radiating elements supplied by four hybrid rings, each radiating element being for example consisting of a waveguide mouth 46 and a transition with the microstrip circuit as described above.

The invention can also be applied for the production from 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 radiating generating a beam whose inclination depends on the position of the elementary source compared to the hearth.

Advantageously, the invention allows very good protection circuits against environmental constraints, such as for example moisture or corrosion, partially or completely filling the guides radiating with dielectric material. Such protection is particularly advantageous for radars fitted to automobiles and which are liable to undergo the above-mentioned constraints.

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

Claims (15)

Monopulse source for antenna with focusing optics, characterized in that it comprises at least two waveguides (41, 42) machined in the metal soleplate (25) supporting the transmission and microwave reception (23, 49, 50, 53, 54, 55, 56, 57) of the antenna (2, 3, 11), each waveguide (41, 42) being excited by a short circuit microwave (43) closing it and by a transition (44, 45) with the transmission and reception circuit, each waveguide (41, 42) is extending into a reduced section waveguide (47, 48), each transition (44, 45) being positioned in the section change plane of the guide. Source according to claim 1, characterized in that the transmission and reception circuit is arranged on a dielectric substrate (24) itself mounted on the metal sole (25). Source according to claim 2, characterized in that the transmission and reception circuit comprising lines in technology microstrip, these are screen printed on the dielectric substrate (24). Source according to any one of the claims previous, characterized in that a transition (44, 45) is constituted by a pattern engraved on the same substrate (24) as that supporting the circuit transmission and reception. Source according to any one of the claims previous, 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. Source according to claim 5, characterized in that the lines (49, 50) are connected to a hybrid ring (53) for supplying transitions in phase or in phase opposition, to form the sum or difference diagrams according to the entry (56, 57) of the ring which is excited. Source according to any one of the claims previous, characterized in that the waveguide section (41, 42, 47, 48) is oblong. Source according to any one of the claims previous, characterized in that the short circuit (43) for adapting the transitions (44, 45) and the reduced section guides (47, 48) are machined in the same room. Source according to claims 2 and 8, characterized in that metallized holes (58) are made in the dielectric substrate (24) to electrically connect the part to the metal soleplate (25). Source according to any one of the claims previous, characterized in that the metal sole (25) is part integral of the case containing the transmission and reception circuit. Source according to any one of the claims previous, characterized in that the waveguides (41, 42, 47, 48) are filled with dielectric material. Source according to any one of the claims previous, characterized in that false slots (71, 72), radiating by coupling with the waveguides (41, 42) are added in the vicinity of these latter. Source according to claim 12, characterized in that the false slots (71, 72) have substantially the same cross section as the waveguides (41, 42). Source according to any one of claims 12 or 13, characterized in that the thickness of the sole (25) is reduced to the level waveguides (41, 42) and false slots (71, 72). Source according to claim 14, characterized in that the reduction of the thickness of the sole (25) begins substantially at the right (74) waveguides (41, 42) and false slots (71, 72).

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