FR2690789A1 - Antenna array for radar - has multiple element conducting lines mounted in triangular horn section with vertical stacking and fed centrally - Google Patents

Abstract

Each triangular section is fed from a waveguide line feed (32) with a central conducting strip. Each section has a central conducting circuit mounted between a metallic base and top held in place by low dielectric supports (54). A number of lines (46) of set lengths form the central circuit and terminate in a radiating pillar (50), at the horn shaped end of the antenna radiating section. Each line is coupled to the feed line by a stub line in proximity with the feed, and ring coupler (58) with load (62). Matching stubs are placed near the radiation pillar to give a good output match. Arrays can be added vertically and horizontally to achieve the desired array performance. ADVANTAGE - Gives good radiation pattern. Lightweight.

Description

RADAR ANTENNA IN A LINEAR NETWORK OR NON-DISPERSITIVE PLAN
POWERED BY A CENTRAL BLADE GUIDE BETWEEN TWO GROUND PLANS
The present invention relates to radar antennas arranged in the form of linear arrays of microwave emission sources or flat arrays composed of superimposed linear arrays.

 These antennas will be described as transmitting antennas, it being understood that they could also be reception antennas.

 Linear or planar array antennas are used in particular to define, by precise control of the intensities and relative emission phases of each of the sources, desired radiation patterns having a very pointed main lobe and of well known direction, and lobes lateral and very low diffuse.

They are used in particular to obtain a so-called non-dispersive emission ", that is to say having a main lobe of direction independent of the frequency in a wide frequency band.

 The invention will be described with respect to non-dispersive antennas produced in superimposed linear arrays comprising at each level two arrays supplied in parallel, each of the arrays comprising a series supply of several aligned emission sources, with identical propagation paths for reach each individual source.

 However, the invention is not limited to this particular type of antenna.

 Many kinds of radar antennas have been designed to date, including linear antennas with serial feed with constant propagation paths on all channels, and slab antennas produced by stacking superimposed linear arrays. The types of antenna used depend on the application envisaged. But the essential problem remains a problem of producing low-weight and low-cost antennas which nevertheless have very good performance from the point of view of the quality of the radiation pattern obtained, the ease of obtaining a shape. desired diagram, minimization of ohmic losses, and the ability to emit significant power. Without going into the details of the existing embodiments, it can be mentioned that certain array antennas use waveguides with couplings by T connections to each of the individual sources. This is heavy and expensive equipment. Others use printed conductors to connect a main supply line to individual sources (dipoles, propellers, etc.) which are connected to the end of secondary lines via coaxial sockets. However, these antennas are only suitable for low powers and small dimensions; they have very high ohmic losses and a limited coupling dynamic between the supply line and the different sources, so that the desired radiation diagram shapes cannot be produced.

To obtain very good radiation characteristics (very low lateral and diffuse lobes), minimum ohmic losses, a capacity to emit a high power and above all a low weight and a low manufacturing price, the present invention provides an antenna comprising at least one linear network of emission sources with a serial power line having the following characteristics
a supply line propagates energy simultaneously to all the sources of the network, these being coupled to the line at positions which succeed each other between an upstream end and a downstream end of a portion of this line,
- the linear network comprises two parallel conductive plates forming two extended ground planes, on one side of the antenna emission, by two divergent walls forming a linear emission horn extending on this side, the supply line and the sources being arranged inside the non-partitioned cavity formed by these two plates.

the supply line is a thin conductive strip centered in a median plane between the two conductive plates,
each source is constituted by a linear flat conductive tape centered between the two conductive plates and by asymmetrical obstacles placed between the tape and the conductive plates, transverse to the plane of the latter, in the end region of the ribbon near the linear emission horn, the ribbon extending in a direction away from the portion of the supply line to which it is directly coupled, and the ends of the ribbons near the emission horn being aligned parallel to the opening of this cone.

 It is therefore a network in which the supply takes place in series for a certain number of sources, by virtue of a supply line constituted by a guide with a central blade between two ground planes; from this line, several other lines (the ribbons) are made successively, which lie side by side in the single cavity formed between the two ground planes; finally, it is the ends themselves of the ribbon which radiate in this cavity, near an opening in horn which is common to all the sources and which is constituted by a flaring of the edges of the ground planes.

 The asymmetrical obstacles inducing the radiation can be constituted for example by a conductive bar placed at the end of a ribbon and connecting the ribbon to one of the ground planes (preferably alternately one then the other of the planes of mass for consecutive ribbons).

 The ribbons are preferably coupled to the central supply blade each by a directional coupler constituted by a flat conductive ring with four terminations, one of which is extended by the ribbon itself, another is embedded in an absorbent filler, and the the last two are placed directly near the central plate to perform capacitive coupling.

Other characteristics and advantages of the invention will appear on reading the detailed description which follows and which is given with reference to the appended drawings in which
- Figure 1 is a general perspective view of an antenna according to the invention with superimposed linear arrays
- Figure 2 is a partial perspective section of the superimposed networks on the side of their supply lines
- Figure 3 is a cross section of two superimposed networks
- Figure 4 is a top view of the interior of the cavity between ground planes of a network, with the central supply blade and the ribbons forming individual sources of radiation.

 In FIG. 1, the general appearance of the antenna according to the invention is seen, composed of several superimposed linear networks of which only a few are shown.

 The networks are understood to be on either side of a riser 10 for supplying energy, from which supply lines 12 go to a first group of superimposed networks 14 and supply lines 16 to a second group of superimposed networks 18; the individual radiating sources 20 of the first group and 22 of the second group are represented very schematically by ends of conductive lines; these ends all end in the same plane to constitute a transmission plan network. Phase shifters can be placed between column 10 and each line 12. Other types of distribution to the different networks can be provided.

 Each network comprises two parallel ground planes (only an upper ground plane 24 being visible in FIG. 1) which constitute a cavity in which there is both a flat conductor of energy supply to the network and a distribution system of energy from this conductor to the various individual sources 20 or 22.

 The ground planes have an isosceles triangular shape extended from the top by linear portions corresponding to the supply lines 12 and 16. This isosceles triangular shape corresponds to a concern for establishing identical propagation paths between the upstream side of a supply line (to column 10) and each of the individual sources, in order to obtain a non-dispersive linear frequency network.

 Indeed, the flat conductor used to bring energy to a network is understood from column 10 towards the triangular part of the network, and, in this part, it runs along one of the equal sides of the triangle (dimension 26). From the portion of supply conductor located along this side 26 leave lines parallel to the other of the equal sides of the isosceles triangle (side 28) to end at the third side (30) of the triangle, along which all lie the radiating ends of the network. This arrangement makes the paths of energy propagation between the upstream side of a supply line (12 for example) and each of the radiating sources (20) of the network supplied by this line legal.

 FIG. 1 thus makes it possible to understand that there is a linear linear variation in the distance between an individual source 20 (or 22) and the general supply conductor which runs along the side 26 of the cavity and which successively supplies the series various sources.

 Figure 2 shows in section and in perspective a part of the interior of the superimposed network cavities on the supply side (side 26): a thin conductive central strip 32, centered in a plane of symmetry parallel to the parallel ground planes 24 and 34, runs along the edge 26 and constitutes the energy supply conductor. This blade extends inside the cavity formed by the supply line 12 joining the central energy supply column.

 This central strip 32 is coupled, at successive positions along the strip between an upstream end (on the side of the line 12) and a downstream end, conductive tapes not shown, extending in the direction of the arrows 36, that is to say parallel to the side 28 of the cavity.

 The parallel ground planes 24 of the various superimposed networks can be supported for example by spacers 38 fixed to a common support wall 40.

 Figures 3 and 4 show the detail of the interior of the cavities of the networks, and in particular the constitution of the individual radiating sources and their coupling system with the central blade 32 of energy supply.

 In FIG. 3, we can still see the parallel ground planes 24 of two superimposed networks. The conductive strip 32 is. view in cross section along the edge 26. It is kept centered parallel to the ground planes for example by blocks 42 of low loss dielectric material (polyethylene) which at the same time serve as spacers to maintain the spacing of the ground planes 24 .

 The parallel ground planes end in divergent walls 44 running along the side 30 where the ends of the radiating sources are located. These walls 44 form a linear emission horn open all along the side 30 and serving as an adaptation between the exterior and the cavity formed by the ground planes. The edges of a divergent wall 44 of a network are preferably contiguous with the edges of a wall of a linear network immediately adjacent above or below the first.

 FIGS. 3 and 4 combined show that the individual sources of radiation are formed by the extremists 46 of planar conductive ribbons 48 centered like the blade 32 in a plane of symmetry parallel to the ground planes 24. These ends are connected, to generate radiation in transverse electromagnetic mode, to one of the ground planes. This connection is made by a conductive bar 50. The ends 46 and the bar 50 constituting the radiating termination are located inside the parallel ground planes, near the horn opening. As the horn opening is understood obliquely (see FIG. 1) relative to the blade 32, it can be seen that the ribbons 48 have ends aligned obliquely relative to this blade.

 In FIG. 4, an oblique angle of 45 degrees has been chosen and the ribbons are heard perpendicular to the direction of the blade 32.

 To make an adaptation preventing unwanted energy reflections along the ribbon as a result of the inductive impedance of the conductive bar 50, it is possible to provide adaptation rods 52 which are heard transversely to the ribbon 48 at a short distance from the end 46. These rods are fixed on the ribbon but do not extend to the ground planes. It is not actually necessary to dissociate the functions of radiation excitation and adaptation of the bar 50 and of the rods 52, the bar and the rods each having both a function of excitation and mutual adaptation.

 The ribbon 48 can be supported from place to place by blocks 54 of low-loss dielectric material serving at the same time as spacers for maintaining the parallelism of the ground planes.

 Between the ribbons and upstream from their end 46, provision is preferably made of conductive pillars 56, being understood from one ground plane to the other, over a width sufficient to constitute an effective short-circuit of the radiation capable of propagate in transverse electromagnetic mode (TEM) of the even type inside the cavity, but sufficiently weak so that there remains between the pillar and the ribbons on each side of the pillar a space allowing the propagation essentially without disturbance of the electric field in electromagnetic transverse mode of the odd type along the ribbons. The order of magnitude of the space left between two pillars 56 for the passage of a ribbon 48 is one third of the wavelength of the propagated field while the ribbons can be arranged at a pitch corresponding to the half-length wave.

 According to an important characteristic of the invention, the coupling of the ribbons with the central strip 32 which supplies the energy is a coupling of the capacitive type, carried out by a directional coupler constituted by a plane conducting ring (square ring 58) with four terminations; one of the terminations is constituted by the ribbon 48 itself; another by a short portion of ribbon 60 parallel to the ribbon 48, being understood like this in a direction extending away from the blade 32 and spaced from the ribbon 48 by a distance equal to a quarter of the wavelength, and terminated by an absorption load 62; the other two terminations 64 and 66, spaced apart from each other by a quarter of the wavelength, are directed towards the blade 32, in directions opposite to the ribbon 48 and to the portion of ribbon 60 which they extend . These last two terminations are placed near the blade, at a distance which is small and which in principle varies from one ring to the other to adjust the coupling coefficient defining the ratio between the energy incident on the blade 32 and the energy sent on a ribbon 48.

 The two branches of the coupler (branch 48, 66 and branch 60, 64) adapt to each other due to their spacing (quarter of the wavelength) and the presence of the load 62.

 the assembly of a ribbon 48 and of the ring 58 which corresponds to it consists of a single flat conductive plate, placed in the plane of symmetry between the two ground planes this plate is preferably made of copper cut by photoengraving according to a shape such as that which is visible in FIG. 4. The rings are all identical but the lengths of ribbon 48 vary from one ribbon to another in order to respect the condition of legality of the propagation paths towards the different radiating ends of the ribbons .

 It will be noted that the conductive strip 32 can be terminated at its downstream end by an absorbent charge, not shown, avoiding energy reflections.

 The cavity located between the ground planes is largely dimensioned, that is to say that its height (between the ground planes) is of the order of one fifth of the wavelength, so that the network has low losses and a propagation index very close to unity.

 A particularly easy and highly efficient production antenna has thus been described, making it possible in particular to produce non-dispersive antennas. The desired radiation pattern is obtained by choosing the distances (d) between the blade 32 and the different coupling rings 58.

Claims (8)

 1. Antenna comprising at least one linear network of emission sources (20), of the type in which a feed line propagates energy simultaneously to all the sources of the linear network which are coupled to the line at positions succeeding between an upstream end of the line and a downstream end, characterized by the fact  - that the linear array comprises two parallel conductive plates (24) forming two extended ground planes, on one side of the antenna emission, by two divergent walls (44) forming a linear emission horn extending over this side, the supply line and the sources being arranged inside the non-partitioned cavity formed by these two plates  - that the supply line is a thin conductive strip (32) centered in a median plane between the two ground planes  - that each source is constituted by a linear flat conductive tape (48) centered between the two conductive plates, and by asymmetrical obstacles (50, 52) placed between the tape (48) and the parallel conductive plates (24) transversely to the plane of these, in the end region (46) of the ribbon close to the emission horn, the ribbon extending in a direction extending from the portion of the supply line to which it is directly coupled, and the ends of the ribbons near the horn being aligned parallel to the opening of the latter.  2. Antenna according to claim 1 characterized in that each strip is terminated, on the side of the supply line, by a directional coupler (58) constituted by a plane conductive ring with four terminations, one of which is extended by the linear tape (48) itself, another (60) is embedded in an absorbent filler (62), and the last two (64, 66) are placed opposite the supply line (32).  3. Antenna according to claim 2 characterized in that the last two terminations (64, 66) of each coupler are placed in the immediate vicinity of the line, in the plane of the latter, at various distances (d) for the various couplers, depending on the desired coupling between the line and the source corresponding to a given coupler.  4. Antenna according to any one of claims 1 to 3, characterized in that two linear flat ribbons corresponding to two consecutive sources along the supply line are separated by at least one conductive pillar (56) joining the walls flat conductors (24) and extending over a certain width transversely to the direction of the ribbons, this width being sufficient to constitute a short circuit with respect to the electric field propagating in transverse electromagnetic mode of the even type and sufficiently small to leave between the pillar (56) and the ribbons (48) on each side a space allowing the propagation essentially without disturbance of the electric field in electromagnetic transverse mode of the odd type.  5. Antenna according to claim 4, characterized in that the asymmetrical obstacles (50, 52) are located beyond the pillars (56) in the direction of propagation of the supply line towards the end of the ribbons on the side of the emission horn.  6. Antenna according to any one of claims 1 to 5, characterized in that the length of the ribbons varies from one source to another depending on the position of the ribbon relative to the supply line, so that the propagation paths between the upstream end of the line and each of the ends of the tape are identical.  7. Antenna according to claim 6, characterized in that it comprises at least two networks placed in the same plane and supplied in parallel, the supply line of the first network having a portion from which the ribbons of the first leave perpendicularly network and the supply line of the second network having a portion, perpendicular to the corresponding portion of the first network, from which the conductors of the second network leave perpendicularly, the openings of the emission horns of the two networks extending longitudinally in the same direction.  8. Antenna according to any one of claims 1 to 7, characterized in that the asymmetrical obstacles are constituted, for each ribbon essentially by a conductive connection (50) between the end of the ribbon and one of the parallel conductive plates forming planes mass, as well as by adaptation elements (52).