Improved elementary antenna of the slot fed radiating plane type and active antenna array

Abstract

This elementary antenna 1 comprises: two slots 32, 33 in a cross defining four half-slots; for each half-slot, excitation strips 41, 42, the first strip 41 being connected to a first via 61 and the second strip 42 being connected to a second via 62; an integrated circuit 70 carrying a plurality of ports; for each half-slot, strip feed tracks, the first track 51 running from a first port 71 to the first via 61 and the second track 52 running from a second port 72 to the second via 62, the first and second ports being two successive ports of the integrated circuit, differentially connected to a transmit / receive channel by first and second feed lines located inside the integrated circuit, the lines and tracks running so that there is no crossing in their respective routings.

Description

[0001] The present invention relates to an elementary antenna of the "slit-fed radiating plane" type for an active array antenna.

[0002] Such elementary antennas are known for example from documents US 2004 / 189527 A1, US 2019 / 372239 A1, US 2019 / 372240 A1, D4 US 5 241 321 A and CN 105 552 550 B.

[0003] An active array antenna, particularly an electronically scanned array (AESA - "Active Electronically Scanned Array"), is a mosaic of a plurality of identical elementary antennas.

[0004] For active network antennas, there is a need to be able to emit a signal with a high peak power.

[0005] If the electronic transmission chain upstream of the active antenna prepares this high-power signal, it requires amplifier summations with low efficiencies and additional losses at the end of the amplification stage—precisely when efficiency is most critical. Furthermore, this high-power signal must then be transmitted to the radiating element of each individual antenna, resulting in further losses and constraints for transmitting high-power signals.

[0006] Another alternative is to prepare this power signal in each elementary antenna by combining several reduced power signals applied to the input of the elementary antenna.

[0007] The power combination in the elementary antenna is achieved by two pairs of feed points (the number of feed points being four).

[0008] For example, as illustrated on the figure 1 The applicant company manufactures an active network antenna in which an elementary antenna 101 is of the slot-fed radiating plate type. The radiating element is here a metallic plate (or patch) or a combination of metallic plates, arranged on a front face of the elementary antenna, and which is excited by a pair of slots: the first and second slots, 132 and 133, orthogonal to each other so as to form a cross pattern.

[0009] Each slit is excited by a pair of striplines, 142 and 146 for the first slit, 132 and 144 and 148 for the second slit, 133, which overlap the slit at two excitation points arranged symmetrically on either side of the geometric center of the elementary antenna.

[0010] For powering the ribbons, an integrated circuit 170 is located on the rear face of the elementary antenna. The integrated circuit has as many power supply ports 172, 174, 176, and 178 as there are ribbons to be powered.

[0011] Electrical traces 152, 154, 156 and 158 connect each port of the integrated circuit 170 to the end of the associated ribbon (through vias 162, 164, 166 and 168).

[0012] In order to properly excite the main mode TE10 of a slot, it is necessary that the two excitation strips of this slot be supplied in opposite phase, i.e. in differential.

[0013] Thus, within integrated circuit 170, two opposing ports are connected to the output of the same transmit / receive channel by two power supply lines. Ports 172 and 176 are differentially powered from channel 182 by lines 192 and 196, and ports 174 and 178 are differentially powered from channel 183 by lines 194 and 198.

[0014] It is observed that it is then necessary to cross the power supply lines within the integrated circuit (crossing 184 on the figure 1 ) or the power supply tracks.

[0015] Routing inside or outside the integrated circuit is therefore not optimal and generates losses and imbalances between the ribbons and consequently in the operation of the elementary antenna.

[0016] Furthermore, reproducible routing from one elementary antenna to another is difficult to achieve, resulting in significant variation in the characteristics of the individual antennas that make up an antenna. Consequently, the antenna's properties are degraded.

[0017] The aim of the present invention is to provide a solution to this problem.

[0018] For this purpose the invention relates to an elementary antenna of the planar radiating type fed by slots, and an array antenna comprising a plurality of active antennas identical to the previous elementary antenna.

[0019] The invention and its advantages will be better understood upon reading the following detailed description of a particular embodiment, given solely by way of illustration and not limitation, this description being made with reference to the attached drawings in which: [ Fig 1 ] There figure 1is a schematic representation, viewed from below, of a basic antenna according to the prior art; [ Fig 2 ] There figure 2 is a cross-sectional representation of a preferred embodiment of an elementary antenna according to the invention; [ Fig 3 ] There figure 3 is a bottom-view representation of the elementary antenna of the figure 2 ; And, [ Fig 4 ] There figure 4 is an electrical representation of the power supply means of the elementary antenna of the figure 2 .

[0020] An active array antenna, particularly an electronically scanned array, is a mosaic made up of a plurality of identical elementary antennas.

[0021] The present invention relates to an active array antenna whose elementary antennas are of the slot-fed patch type. A patch is a metallic plate printed on a substrate. The radiating element of the elementary antenna consists of at least one patch.

[0022] There figure 2 is a cross-section of a preferred embodiment of an elementary antenna 1 according to the invention.

[0023] The elementary antenna 1 comprises four substrates, stacked one on top of the other along a Z-axis, referred to as "vertical": A first substrate 10, which is the so-called "antenna" substrate, has a first patch 11 etched on its upper surface. This upper surface constitutes the front face of the elementary antenna. A second substrate 20 has a second patch 21 etched on its upper surface. A third substrate 30 has an upper surface with a ground plane 31, which is equipped with slots. A fourth substrate 40 has an upper surface with a plurality of ribbons to excite the slots. A fifth substrate 50 has a lower surface with both the integrated circuit 70 and the ribbon power tracks. One track is connected to a port of the integrated circuit 70 on one side, and to a via on the other. The via passes through the fifth and fourth substrates to connect the track to the associated ribbon. Thus, there is one track per ribbon.The upper surface of the substrate 50, oriented towards the patch(s), has a lower ground plane 49 in which recesses (or holes) are engraved to achieve the connection via the previously mentioned.

[0024] The different substrates are joined together, for example by means of a suitable adhesive: an interface layer between the first and second substrates bears the reference 12 on the figure 2 ; an interface layer between the second and third substrates bears the reference 23 on the figure 2 ; an interface layer between the third and fourth substrates bears the reference 34 on the figure 2 ; and an interface layer between the fourth and fifth substrates bears the reference 45 on the figure 2 .

[0025] There figure 3 is a bottom view of elementary antenna 1 of the figure 2that is to say along a plane transverse to the Z axis. This transverse plane is defined by the X and Y axes. In this figure, patches 11 and 21, the ground plane 31 and the slits with which it is equipped, as well as the different excitation strips of the slits, are represented in dashed lines.

[0026] The elementary antenna 1 is preferably square in shape. It exhibits central symmetry with respect to its center O, but above all, rotational symmetry of 90° around the center O. Alternatively, the elementary antenna can take other shapes, notably rectangular or circular.

[0027] Two slots 32 and 33 are provided in the ground plane 31. These slots are oblong.

[0028] In the embodiment shown, they are rectangular, but alternatively they could have ends such that a slot has a "dog bone", "dumbbell", or other shape...

[0029] Each slit has a reduced width compared to its length, the latter being slightly less than that of the side of the elementary antenna.

[0030] The slits are arranged so that the major axis of the first slit 32 coincides with the Y axis and that of the second slit 33 coincides with the X axis.

[0031] The two slits therefore intersect at right angles at the geometric center O of the elementary antenna 1, so as to form a cross pattern.

[0032] This cross pattern can be seen as composed of four half-slits, respectively a first positive half-slit corresponding to the part of the first slit 32 above the X-axis, a first negative half-slit corresponding to the part of the first slit 32 below the X-axis, a second positive half-slit corresponding to the part of the second slit 33 to the right of the Y-axis, a second negative half-slit corresponding to the part of the second slit 33 to the left of the Y-axis on the figure 3 .

[0033] In what follows, unless otherwise stated, the elementary antenna is described in detail with respect to a particular half-slot, in this case the first upper half-slot.

[0034] The half-slit is excited by a pair of ribbons. This pair of ribbons comprises a first ribbon 41 and a second ribbon 42 which do not overlap.

[0035] In the present embodiment, a ribbon is made up of a plurality of straight portions. The first ribbon 41 thus comprises a proximal portion 411, an intermediate portion 412, and a distal portion 413. The second ribbon 42 thus comprises a proximal portion 421, an intermediate portion 422, and a distal portion 423.

[0036] The proximal portion of a ribbon is connected to a first via associated with the ribbon, respectively a first via 61 for the first ribbon 41 and a second via 62 for the second ribbon 42. The vias are here arranged on the periphery of the antenna near its edges.

[0037] The first ribbon 41 circulates for example from the via 61 (located to the left of the X axis) so that its proximal portion makes an angle of -45° with respect to the X axis of the half-slit, its intermediate portion overlaps the half-slit perpendicularly to the X axis of the half-slit and its distal portion makes an angle of +45° with respect to the X axis of the half-slit.

[0038] Similarly, the second ribbon 42 runs from via 62 (located to the right of the X axis) so that its proximal portion makes an angle of +45° with respect to the X axis of the half-slit, its intermediate portion overlaps the half-slit perpendicularly to the X axis of the half-slit, and its distal portion makes an angle of -45° with respect to the X axis of the half-slit.

[0039] Other paths are conceivable for the ribbons: straight portions making other angles with respect to the X axis (respectively the Y axis), curvilinear portions, etc.

[0040] The first ribbon 41 preferably crosses the half-slit orthogonally at a first excitation point. This first crossing is achieved by traversing the half-slit from left to right.

[0041] The second ribbon 42 crosses the half-slit orthogonally at a second excitation point, further from the center O than the first excitation point. A distance d separates the first and second excitation points along the X-axis. This distance is reduced to a minimum, while maintaining an electrical isolation gap between the ribbons.

[0042] The distance d is minimal so that the excitation of the half-slit by the pair of ribbons is essentially local, that is to say that we can consider that the application of a first electric excitation field at the level of the first excitation point and a second electric excitation field at the level of the second excitation point, is equivalent to the application of an electric excitation field (resulting from the sum of the first and second electric excitation fields) at the level of a midpoint between the first and second excitation points.

[0043] This second crossing is achieved by passing through the half-slit from right to left. The head-to-tail configuration of this particular embodiment requires, all other things being equal, that the electrical potential A- to which the second ribbon 42 is brought be phase-shifted by 180° with respect to the electrical potential A+ to which the first ribbon 41 is brought, so that the generated electric fields are in phase to properly excite the first slit.

[0044] The first and second ribbons circulate in parallel with each other. Preferably, a constant offset is maintained between the first and second ribbons 41 and 42 for reasons of coupling between the ribbons of the same pair of ribbons.

[0045] Each ribbon extends beyond the half-slot to optimize impedance matching (stubbing). The aim is to give both ribbons the same length so they present the same impedance. To achieve this, the proximal portion of the second ribbon, which is shorter in the diagrams, can be lengthened, for example, by a meander at the connection to the second via. Alternatively, a phase shift can be introduced between the signals delivered to each port of the integrated circuit. This phase shift can be achieved either by adding a length of line upstream of the port or directly by a phase shifter integrated into the integrated circuit.

[0046] A similar description could be made for the pair of excitation ribbons 43, 44 of the second positive half-slot (associated vias 63 and 64 and supply potentials D+ and D-), for the pair of excitation ribbons 45, 46 of the first negative half-slot (associated vias 65 and 66 and potentials B+ and B-), for the pair of excitation ribbons 47, 48 of the second negative half-slot (associated vias 67 and 68 and potentials C+ and C-).

[0047] The means of supplying power to the ribbons must apply voltages that are in phase so that the elementary antenna emits a polarized wave.

[0048] The table below shows the phase command for the elementary antenna to transmit according to different polarizations. [TABLE 1] A+ A- B+ B- C+ C D+ D- Polarization (with respect to the X-axis) 0° 180° 0° 180° 0° 180° 0° 180° 45° 0° 180° 0° 180° 180° 0° 180° 0° -45° 0° 180° 0° 180° 90° 270° 90° 270° Right circular 0° 180° 0° 180° 270° 90° 270° 90° Left circular 0° 180° 0° 180° OFF OFF OFF OFF Horizontal OFF OFF OFF OFF 0° 180° 0° 180° Vertical

[0049] It should be noted that a slit is excited symmetrically with respect to the center O by two pairs of ribbons so as to operate in the TE10 mode.

[0050] The means for supplying the pairs of ribbons include an integrated circuit 70 and supply traces running on the rear face of the elementary antenna.

[0051] Circuit 70 is, for example, a monolithic microwave integrated circuit - MMIC ("Monolithic Microwave Integrated Circuit").

[0052] For example, it is parallelepiped in shape. It also has a square outline in the transverse XY plane.

[0053] It is implanted at the center O of the rear face of the elementary antenna so that its sides are parallel to the sides of the elementary antenna.

[0054] Each of the four sides of the circuit has two ports (or connection pins), labeled 71 to 78 on the figure 3. Circuit 70 therefore has a total of eight output ports.

[0055] A power supply trace electrically connects a port of the circuit to a via associated with a ribbon.

[0056] Thus, to the pair of ribbons 41 and 42 exciting the first positive half-slot is associated a pair of power supply tracks 51 and 52. The first ribbon 41 is powered by a first track 51 dedicated through the via 61, while the second ribbon 42 is powered by a second track 42 dedicated through the via 62.

[0057] The first and second tracks 51 and 52 are connected to ports of the circuit 70 located on the same side of the integrated circuit 70, in this case ports 71 and 72 on the side of the circuit 70 oriented towards the vias 61 and 62.

[0058] Note that the vias are arranged here on the periphery of the elementary antenna near its edges. The first and second vias, 61 and 62, are successive vias along the periphery of the antenna.

[0059] The first track 51, for example, has the shape of an "L", with an axial section 511, which runs parallel to the X axis of the first positive half-slot from the port 71 connecting to the integrated circuit 70, followed by a lateral section 511 which runs transversely to the X axis to join the first via 61. Symmetrically, the second track 52 has an axial section 521, which runs parallel to the X axis, followed by a lateral section 522 which runs transversely to the X axis to join the second via 62.

[0060] The first and second vias, 61 and 62, pass through the fifth and fourth substrates, 50 and 40, to electrically connect an associated track and ribbon. Each via crosses the ground plane provided on the upper surface of the fifth substrate at a recess in this ground plane.

[0061] The impedances seen by each port 71 and 72 must be as close to each other as possible.

[0062] A similar description could be made for the supply of the pair of ribbons 43 and 44 from ports 73 and 74 by the supply tracks 53 and 54 respectively, for the supply of the pair of ribbons 45 and 46 from ports 75 and 76 by the supply tracks 55 and 56 respectively, and for the supply of the pair of ribbons 47 and 48 from ports 77 and 78 by the supply tracks 57 and 58 respectively.

[0063] There figure 4is an electrical representation illustrating the routing inside and outside the integrated circuit 70.

[0064] A pair of ports for powering a pair of ribbons, such as the power supply pair 71 and 72 for the ribbon pair in the first positive half-slot, is differentially powered at the output of a transmit / receive channel 81 (shown schematically on the figure 4 ), by a first line 91 connected to the first port 71 and a second line 92 connected to the second port 72.

[0065] Similarly, the power supply port pair 73 and 74 of the second positive half-slot ribbon pair is differentially powered at the output of a transmit / receive channel 83 by a first line 93 connected to the first port 73 and a second line 94 connected to the second port 74.

[0066] Similarly, the power supply port pair 75 and 76 of the ribbon pair in the first lower half-slot is differentially powered at the output of a transmit / receive channel 85 by a first line 95 connected to the first port 75 and a second line 96 connected to the second port 76.

[0067] Similarly, the power supply port pair 77 and 78 of the second negative half-slot ribbon pair is differentially powered at the output of a transmit / receive channel 87 by a first line 97 connected to the first port 77 and a second line 98 connected to the second port 78.

[0068] The person skilled in the art will see from this figure that the routing is now free of any crossings, whether between lines 91 to 97 inside the integrated circuit 70, or between tracks 51 to 58 outside the integrated circuit 70.

[0069] The routing process is thus greatly simplified. This simplifies the fabrication of the printed circuit board and the stacking of its constituent layers.

[0070] Furthermore, greater manufacturing precision is achieved for the elementary antennas, which positively impacts the overall operation of the active array antenna incorporating such radiating elements. The present invention has the advantage of presenting four pairs of excitation points for the slots, i.e., eight excitation points. This consequently doubles the emitted power compared to the configuration of the figure 1 .

[0071] This allows, in transmission, the combination of the powers of eight elementary signals in order to generate a higher power signal.

[0072] This allows the incident power to be distributed across a larger number of receive channels. The power level applied to the input of the low-noise amplifier (LNA) in the receive channel electronics chain is therefore reduced, preventing saturation and allowing the component to operate within an optimal linear range.

[0073] The present invention makes it possible to improve efficiency by minimizing losses.

[0074] Thanks to the summation in the elementary antenna, the printed circuit board no longer uses as many combiners. This contributes to reducing heat dissipation within the integrated circuit and to reducing the size of the printed circuit board.

[0075] It allows for programmable polarization.

[0076] The present invention has applications in the fields of radar, jammers, radio communications, remote power transfer, and data links.

Claims

1. An elementary antenna (1) for an active array antenna, the elementary antenna comprising a radiating plane fed by a plurality of slots, the radiating plane (11) being arranged on a front face of the elementary antenna, the elementary antenna including a ground plane having first and second slots (32, 33), the first and second slots being orthogonal to each other so as to form a cross-shaped pattern, the elementary antenna being characterized in that it comprises: - for each half-slot, a pair of striplines (41, 42) for exciting the half-slot, a first stripline (41) of the pair of striplines being connected at one end thereof to a first via (61) associated with the first stripline and overlapping the half-slot from a first side to a second side of the half-slot, a second stripline (42) of the pair of striplines being connected at one end thereof to a second via (62) associated with the second stripline and overlapping the half-slot from the second side to the first side of the half-slot, the first and second striplines of the pair of striplines running without crossing each other; - an integrated circuit (70) arranged on a rear face of the elementary antenna, a contour of the integrated circuit being provided with a plurality of ports; - for each half-slot, a pair of feed tracks of the pair of striplines enabling the half-slot to be excited, a first track (51) of the pair of feed tracks running from a first port (71) of the plurality of ports of the integrated circuit to the first via (61), a second track (52) of the pair of feed tracks running from a second port (72) of the plurality of ports of the integrated circuit to the second via (62), the first and second ports being two successive ports along the contour of the integrated circuit, which are differentially connected to a transmission / reception channel (81) of the elementary antenna by first and second feed lines (91, 92) situated within the integrated circuit, the feed lines and feed tracks running so that there is no crossing, in the routing, of the feed lines inside the integrated circuit, nor of the feed tracks outside the integrated circuit.

2. The elementary antenna (1) according to claim 1, wherein the integrated circuit (70) is a monolithic microwave integrated circuit.

3. The elementary antenna (1) according to any one of the preceding claims, wherein the first and second vias are arranged at a periphery of the elementary antenna, near an edge thereof and, for each half-slot, the first and second vias (61, 62) connected to the pair of striplines exciting the half-slot are two successive vias along the periphery of the elementary antenna.

4. The elementary antenna (1) according to any one of the preceding claims, wherein, for each half-slot, the first and second striplines of the pair of striplines exciting the half-slot have an identical length.

5. The elementary antenna (1) according to any one of the preceding claims, wherein, for each half-slot, the first and second striplines of the pair of striplines exciting the half-slot run in parallel with each other.

6. The elementary antenna (1) according to any one of the preceding claims, wherein, for each half-slot, the first and second striplines of the pair of striplines exciting the half-slot are spaced apart by a distance providing an electrical insulation of the first and second striplines, while exciting the half-slot at two excitation points, the two excitation points being positioned so as to consider the half-slot as being locally excited.

7. The elementary antenna (1) according to any one of the preceding claims, wherein the first stripline and / or the second stripline orthogonally intersects the half-slot.

8. The elementary antenna (1) according to any one of the preceding claims, wherein the first and second feed tracks of the pair of feed tracks associated with the half-slot have the same length.

9. The elementary antenna (1) according to any one of the preceding claims, wherein the elementary antenna is symmetrical by a 90° rotation about an axis (Z) normal to the radiating plane.

10. An active array antenna comprising a plurality of elementary antennas, wherein each elementary antenna is an elementary antenna according to any one of claims 1 to 9.

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