Basic antenna of the polarisation-agile type and cavity antenna type; network antenna comprising a plurality of such basic antennas

Abstract

This elementary antenna (101) has a cavity (102) delimited by front and rear faces (110, 130) and side walls (122), the front face being provided with first and second slots (112, 113) arranged in a cross, so that, when the cavity (102) operates in a TE210 mode, a wave polarized perpendicular to the first slot (112) is emitted and when the cavity operates in a TE120 mode, a wave polarized perpendicular to the second slot (113) is emitted. This elementary antenna is characterized in that the rear face (130) is brought to a reference electrical potential, and in that the elementary antenna includes an excitation device, such as a metallized via, capable of exciting the front face through the cavity, the excitation device exciting the front face at a plurality of excitation points (111), distributed over the front face and exhibiting a common predefined impedance.

Description

[0001] The invention relates to elementary antennas that are agile in polarization.

[0002] Such elementary antennas find applications in radar imaging, jammers and data links.

[0003] More specifically, in the field of radar imaging, antennas are sought with increased transmission efficiency, improved linearity as a function of transmission power, improved signal-to-noise ratio, and increased reception power handling.

[0004] The Applicant has thus developed elementary antennas of the planar antenna type, or “patch” antenna in English, excited by slots, such as for example those described in patent FR 3062523.

[0005] In order for the different transmission / reception paths to be perfectly balanced, it is necessary that the excitation points of the radiating element of the elementary antenna have a common impedance, preferably equal to 50 ohms.

[0006] However, on an elementary antenna of the patch antenna type, the excitation points on the surface of the radiating element presenting such an impedance are limited in number.

[0007] The aim of the present invention is therefore to solve this problem by proposing an elementary antenna agile in polarization offering a greater number of possible excitation points.

[0008] For this purpose, the invention relates to an elementary antenna of the polarization-agile type and of the cavity antenna type, comprising a cavity delimited axially by a front face and a rear face and laterally by side walls, the front face, which constitutes the radiating plane of the elementary antenna, being provided with a first rectilinear slot and a second rectilinear slot, the first and second slots being arranged so as to form together a cross, which is centered on a geometric center of the front face and which defines four quadrants on the front face, so that, when the cavity is placed in a TE210 mode, a wave polarized perpendicular to the first rectilinear slot is emitted and when the cavity is placed in a TE120 mode, a wave polarized perpendicular to the second rectilinear slot is emitted.This elementary antenna is such that the rear face is brought to a reference electrical potential, and the elementary antenna comprises an excitation device, positioned at the rear of the cavity and capable of exciting the front face through the cavity, the excitation device exciting the front face at a plurality of excitation points which have a common predefined impedance, each dial of the front face carrying at least one excitation point.

[0009] According to particular embodiments, the elementary antenna comprises one or more of the following characteristics, taken in isolation or in any technically possible combination.

[0010] The front face and the back face are square and the first and second slots are arranged parallel to the edges of the front face.

[0011] The common preset impedance of the excitation points is equal to 50 Ohms.

[0012] The back face acts as a mirror electrical plane between a power layer of the excitation device, with the power layer located on one side of the back face while the front face is located on the other side of the back face.

[0013] Two excitation points arranged symmetrically with respect to the first straight slit or with respect to the second straight slit are excited by signals in phase opposition.

[0014] The excitation device comprises a plurality of metallized vias electrically connecting a power supply layer, located at the rear of the rear face, and the front face, the power supply layer comprising a plurality of power supply lines, each power supply line being associated with a metallized via, each metallized via opening, on the front face, at an excitation point.

[0015] Each metallized via is isolated from the rear face to the crossing of the latter.

[0016] The excitation device comprises a plurality of slots provided in the rear face and a feed layer located at the rear of the rear face and comprising a plurality of feed lines, each feed line being associated with a slot, and overlapping the associated slot such that the crossing point of the feed line and the associated slot is located directly above an excitation point of the front face.

[0017] The slits form circular openings.

[0018] The slots form rectilinear openings, the plurality of slots forming a cross, a square parallel to the edges of the elementary antenna, or a square parallel to the diagonals of the elementary antenna.

[0019] The invention also relates to a network antenna composed of a plurality of elementary antennas such as that presented previously.

[0020] The invention and its advantages will be better understood upon reading the detailed description which follows, of a particular embodiment, given solely as a non-limiting example, this description being made with reference to the appended drawings in which: [ Fig.1 ] there Figure 1 is a representation of the amplitude of the electric field in a cavity excited in a TE210 mode; [ Fig. 2 ] there Figure 2 schematically represents an elementary antenna according to the invention, the front face of which is provided with two cross-shaped slots to provide polarization agility in transmission and reception; [ Fig. 3 ] there Figure 3 is an exploded perspective representation of a first embodiment of an elementary antenna according to the invention, in which the front face of the cavity is excited by metallized vias; [ Fig. 4 ] there Figure 4 is a cross-sectional representation in the vicinity of a via of the elementary antenna of the Figure 3 ; [ Fig. 5 ] there Figure 5 is an exploded perspective representation of a second embodiment of an elementary antenna according to the invention, in which the front face is excited by slots; [ Fig. 6 ] there Figure 6 is a cross-sectional representation in the vicinity of a slot of the antenna of the Figure 5 ; And, [ Fig. 7 ] [ Fig. 8 ] [ Fig. 9 ] [ Fig. 10 ] [ Fig. 11 ] THE Figures 7 à 11 represent, in view from below, the rear face of different variants of the antenna of the Figure 5 .

[0021] There Figure 1 schematically represents an elementary antenna of the cavity antenna type in top view.

[0022] Cavity antennas are known, for example from the article G. Srivastava and A. Mohan, "A Differential Dual-Polarized SIW Cavity-Backed Slot Antenna," in IEEE Transactions on Antennas and Propagation, vol. 67, no. 5, pp. 3450-3454, May 2019.

[0023] The front face of the cavity, which constitutes the radiating element of the elementary antenna 10, lies in a plane defined by first and second directions, D1 and D2. The first and second directions intersect at a point C, the geometric center of the front face. The front face being preferably square in shape, the first direction corresponds to one diagonal of the front face and the second direction corresponds to the other diagonal of the front face.

[0024] The front face is provided with a pair of slots, 12 and 13, rectangular and forming a cross pattern. This cross is centered on point C. The slots are arranged so as to be parallel to the edges of the front face. The cross defines four quadrants on the front face of the elementary antenna.

[0025] Is represented on the Figure 1 the amplitude of the electric field inside the cavity when it is excited in the TE210 excitation mode. In this mode, the amplitude of the electric field has two lobes, 14 and 15, symmetrical with respect to the first slit 12. The electric field in these two lobes is in phase opposition: at a given instant, if the electric field in the upper lobe 15 is directed towards the front of the plane of the Figure 1 , then the electric field in the lower lobe 14 is directed towards the rear of the plane of the Figure 1 .

[0026] In the TE210 excitation mode and in transmission, the elementary antenna 10 emits a wave polarized perpendicular to the direction of the first slot 12, conventionally called “vertical” polarization.

[0027] Conversely, in reception, a vertically polarized incident wave is likely to place the cavity in the TE210 excitation mode.

[0028] Of particular interest, all of the points on the front face located along curves 24 and 25 have an impedance of 50 Ohms for an electronic transmission / reception module electrically connected to one of these points.

[0029] There is therefore a multiplicity of points on the surface of the front face having an impedance of 50 Ohms and which can be chosen to excite the front face of the elementary antenna 10 to emit a vertically polarized wave.

[0030] By symmetry with respect to the first direction D1, when the cavity is excited in the T120 mode, the amplitude of the electric field has two lobes, 16 and 17 ( Figure 2 ), symmetrical with respect to the second slit 13. The electric field in these two lobes is in phase opposition.

[0031] In the TE120 excitation mode and in transmission, the elementary antenna 10 emits a wave polarized perpendicular to the direction of the second slot 13, conventionally called “horizontal” polarization.

[0032] Conversely, in reception, a horizontally polarized incident wave is likely to place the cavity in the TE120 excitation mode.

[0033] All the points on the front face located along curves 26 and 27 have an impedance of 50 Ohms for an electronic transmission / reception module electrically connected to one of these points.

[0034] There is therefore a multiplicity of points on the surface of the front face having an impedance of 50 Ohms and which can be chosen to excite the front face of the elementary antenna 10 to emit a horizontally polarized wave.

[0035] Thus, for the elementary antenna 10 to be agile, that is to say to be able to transmit according to a first polarization or according to a second polarization, it is appropriate to excite the front face at excitation points which are selected along the curves 24 and 25 AND along the curves 26 and 27. It is this property which is implemented in the present invention.

[0036] By choosing the relative phase of the signals applied to the excitation points of two different dials, the polarization in transmission or reception can then be chosen either according to the first polarization (so-called vertical polarization - upper part of the Figure 2 ), or according to the second polarization (so-called horizontal polarization - lower part of the Figure 2 ), or according to a right circular polarization, or a left circular polarization, or, by exciting only the points of opposite dials by the symmetry of center C, +45° (that is to say according to the first line D1) or - 45° (that is to say according to the second line D2).

[0037] Referring now to the Figure 3 , a first embodiment of an elementary antenna 101 according to the invention will be presented.

[0038] The elementary antenna 101 is of the cavity-backed antenna type. The elementary antenna 101 therefore comprises a cavity 102.

[0039] In this embodiment, a front face of the cavity, which also constitutes the radiating element of the elementary antenna, is excited by a device which, in this first embodiment, takes the form of a series of metallized vias crossing the cavity to connect a feed layer to a plurality of excitation points of the front face.

[0040] The elementary antenna 101 comprises, successively along an axis A, a front face 110, a first substrate 120, a rear face 130, a second substrate 140 and a feed layer 150.

[0041] The cavity 102 is delimited along the axis A by the front and rear faces, 110 and 130, and laterally by side walls 122. Preferably, when the front face is square, the cavity has the shape of a rectangular parallelogram with a square section (perpendicular to the axis A).

[0042] The front face 110 is made of a layer of an electrically conductive material, preferably a metal.

[0043] The front face 110 being square, the first diagonal corresponds to a first direction D1 and the second diagonal corresponds to a second direction D2. The first and second diagonals intersect at point C, which constitutes a geometric center of the front face.

[0044] The front face 110 is provided with a first rectangular slot 112 and a second rectangular slot 113. The first and second slots together form a cross, which is arranged at point C so that the arms of this cross are parallel to the edges of the front face. The cross delimits four dials on the front face 110.

[0045] The front face 110 is provided with a plurality of perforations 115. Each perforation 115 is centered at an excitation point 111. Each perforation 115 constitutes the end of a metallized via. The inner face of each perforation 115 is metallized. To simplify the Figure 3 , the front face 110 of the antenna 101 has only two excitation points per dial, but a greater number of excitation points could be provided. An excitation point 111 associated with a perforation 115 is positioned on the front face 110 so that the front face 110 constitutes an electrical load of 50 Ohms for a transmission / reception module electrically connected to the front face by means of the via opening at the level of the excitation point considered.

[0046] The first substrate 120 is made of an insulating material.

[0047] The side walls 122 of the cavity 102 are delimited in the substrate 120. Advantageously, a technique used to produce substrate integrated waveguides - SIW ("Substrate integrated waveguide") is implemented to produce the side walls of the cavity 102. A side wall is then produced by a row of metallized vias establishing a short circuit between the rear face 130 and the front face 110 of the cavity 102.

[0048] Furthermore, the substrate 120 has through holes 125 corresponding to the metallized vias opening onto the front face 110. An internal face of each through hole is metallized.

[0049] The rear face 130 is made of a layer of a material that conducts electrical current, preferably a metal.

[0050] Layer 130 is electrically connected to a reference potential. It acts as an electrical mirror plane between the power supply layer and the front face.

[0051] The rear face 130 comprises a plurality of perforations 135, which correspond to the metallized vias connecting the power supply layer 150 and the front face 110.

[0052] To avoid any short circuit between a metallized via and the material constituting the rear face 130 at the crossing thereof, an insulating ring 136 is provided around each of the perforations 135. The internal face of the perforations is metallized.

[0053] The second substrate 140 is made of an insulating material.

[0054] The second substrate 140 comprises a plurality of through holes 145 respectively constituting portions of the metallized vias between the power supply layer 150 and the front face 110. The inner face of each through hole is covered with a metal film.

[0055] Finally, the power supply layer 150 comprises perforations 155 which constitute the ends of the metallized vias between the power supply layer 150 and the front face 110. The inner face of each perforation is covered with a metal film.

[0056] Each perforation 155 is associated with a power supply line 157 which is electrically connected to a transmission / reception module making it possible, in transmission, to inject an electrical signal to excite the front face in order to emit an electromagnetic wave in the half-space in front of the front face and, in reception, to acquire an electrical signal resulting from the excitation of the front face by an electromagnetic wave incident on the front face.

[0057] There Figure 4 represents an axial section of the elementary antenna 101 of the Figure 3 in the vicinity of a metallized via 105 electrically connecting the power supply layer 150 and the front face 110 through the cavity. The layer 150 has been etched to delimit the power supply line 157 allowing the end of the metallized via 105 to be powered.

[0058] At the crossing of the rear face 130, an insulating ring 136 is interposed between the rear face metal 130 and the metallization of the via 105 so as to electrically isolate the via 105 from the rear face 130 brought to the reference potential.

[0059] A via constituting the side wall 122 of the cavity 102 is shown which creates a short circuit between the rear face 130 and the front face 110 so as to delimit the cavity 102.

[0060] Each via is therefore positioned so that it opens, on the front face, at an excitation point characterized by an impedance of 50 Ohms.

[0061] Given the property of a cavity antenna to present a large number of excitation points characterized by an impedance of 50 Ohms, we can therefore multiply the vias.

[0062] The emitted wave has a power which is the sum of the powers of the excitation signals applied to each of the vias. Thus, by multiplying the vias and feeding each channel with a signal close to the saturation of the corresponding transmission / reception channel, a high-power wave can be emitted.

[0063] Symmetrically, in reception, the power of the incident wave is distributed between the different vias. Therefore, by multiplying the vias, each transmission / reception path operates far from saturation.

[0064] There Figure 5 represents a second embodiment of an elementary antenna of the cavity antenna type according to the invention. In this second embodiment, the excitation device of the front face of the cavity comprises slots.

[0065] A component of the second embodiment that is identical or similar to a component of the first embodiment is identified by a reference numeral that is equal to the reference numeral identifying that identical or similar component of the first embodiment, increased by one hundred.

[0066] The elementary antenna 201 comprises a cavity 202.

[0067] The elementary antenna 201 comprises a front face 210, a first substrate 220, a rear face 230, a second substrate 240 and a feed layer 250.

[0068] The front face 210, square and metallic, has a pair of slots, 212 and 213, together forming a cross, centered at point C, and whose arms are parallel to the edges of the front face.

[0069] In the present embodiment, the front face 210 does not have any perforation. Only the excitation points 211 have been shown on the Figure 5 .

[0070] The first substrate 220 delimits the side walls 222 of the cavity 202, preferably by means of a row of metallized vias shorting between the front face and the rear face of the cavity 202.

[0071] The square, metallic rear face 230 is brought to a reference potential. It acts as a mirror electrical plane between the power supply circuit and the front face.

[0072] The rear face 230 has openings 234 constituting slots. These openings have characteristic dimensions greater than those of the perforations and vias of the first embodiment.

[0073] On the Figure 5 , each slot is a circular opening which is positioned directly above an associated excitation point 211 on the front face.

[0074] The second substrate 240 is full.

[0075] Finally, the power supply layer 250 has been etched so as to have a plurality of power supply tracks 237. Each power supply track 237 is associated with a slot 234.

[0076] There Figure 6 represents an axial section of the elementary antenna 201 in the vicinity of a slot 234.

[0077] The track 237 associated with the slot 234 is rectilinear and has an inner end 238 and an outer end 239. The track 234 is arranged astride the slot 234.

[0078] The crossing point of track 237 and slot 234 is directly above the associated excitation point 211.

[0079] By properly positioning the power supply traces 237 and the slots 234, a plurality of points on the front face having a characteristic impedance can be excited.

[0080] On the figures 7 à 11 , different variants of the second embodiment are shown.

[0081] To the figure 7 , the slots are circular openings. Two slots are provided per dial. Each slot is associated with a feed track. A feed track is straight and overlaps the associated slot in the first direction D1 or the second direction D2.

[0082] In the variant shown in the Figure 8 , the number of slots is reduced to one slot per quadrant. To maintain symmetry, the slots are centered on the first direction D1 or the second direction D2. Two feed tracks are associated with each slot. The feed tracks are straight and extend parallel to the edges of the elementary antenna.

[0083] In the variant shown in the Figure 9 , the slots are rectangular openings. In this variant, the rear face is provided with four slots. They extend parallel to the first direction D1 or to the second direction D2, but away from the geometric center C to form substantially a square. Each slot is associated with a single feed track. The feed track overlaps the associated slot in the median plane of said slot.

[0084] On the variant shown in the Figure 10 , the rear face is provided with a pair of rectilinear slots crossing at right angles directly above point C. They therefore form a cross whose arms are parallel to the edges of the elementary antenna. Each slot is excited by a pair of feed lines. A feed line overlaps one of the arms of the associated slot. The feed lines of the same slot are arranged symmetrically by central symmetry.

[0085] On the variant shown in the figure 11 , the rear face of the cavity is provided with four rectilinear slots, independent of each other. The slots are arranged parallel and close to the edges of the elementary antenna. Each slot is associated with a pair of feed lines, which are arranged symmetrically with respect to a median plane of the associated slot.

[0086] In these different figures, the ends of the power supply tracks of the power supply layer, on which electrical transmission signals are applied and / or on which reception signals are collected, are referenced 1+, 1-, 2+, 2-, and possibly 3+, 3-, 4+, 4-.

[0087] The following table gives the phase shifts between the electrical signals on each end of the feed tracks for operation of the elementary antenna according to a defined polarization. [Table 1] 1+ 2+ 3+ 4+ 1- 2- 3- 4- Polarisation 0° 0° 0° 0° 180° 180° 180° 180° Verticale 0° 0° 180° 180° 0° 0° 180° 180° Horizontale 0° 0° 90° 90° 270° 270° 180° 180° RHCP 0° 0° 270° 270° 90° 90° 180° 180° LHCP OFF OFF 0° 0° 180° 180° OFF OFF 45° 0° 0° OFF OFF OFF OFF 180° 180° -< 45°

[0088] By "vertical" polarization is meant a linear polarization along the bisector between the first and second directions and by "horizontal" polarization is meant a linear polarization along an orthogonal direction. "RHCP" polarization is a right circular polarization while "LHCP" polarization is a left circular polarization. A 45° polarization is along the first direction, while -45° polarization is along the second direction.

[0089] The phase shifts between the electrical signals on the feed layer tracks detailed in this table for the antennas of the Figures 7 à 11 also applies to the antenna according to the first embodiment ( Figures 3 And 4 ) as well as to the antenna according to the second embodiment ( Figures 5 And 6 ).

[0090] If the case of excitation points having a common impedance of 50 Ohms has been presented above in detail, as a variant the excitation points of the antenna have a common impedance having another value, such as 30 Ohms or 75 Ohms, knowing that we have the property that the different access points are arranged along a specific curve of the impedance value retained.

[0091] Thus, the elementary antenna is agile in polarization, both in transmission and in reception, by adjusting the phase shift of the electrical signals at the level of each feed line of the excitation device.

[0092] It should be noted that not only according to theory but also according to various simulations, the teaching of the present description, presented for the case of a cavity with a square cross-section, applies to other geometries, in particular a cavity with a circular cross-section. Whatever the geometry of the cavity section, the name of the modes is preserved: we still speak of TE210 and TE120 mode for a circular cross-section for example.

Claims

1. An elementary antenna (101, 201) of the polarization agile type and of the cavity antenna type, including a cavity (102, 202) delimited axially by a front face (110, 210) and a rear face (130, 230) and laterally by side walls (122, 222), the front face, which constitutes the radiating plane of the elementary antenna, being provided with a first straight slot (112, 212) and a second straight slot (113, 213), the first and second straight slots being arranged so as to form together a cross which is centered on a geometric center of the front face and which defines four quadrants on the front face, the elementary antenna being configured such that when the cavity (102, 202) is placed in a TE210 mode, a wave polarized perpendicularly to the first straight slot (112, 212) is emitted and when the cavity is placed in a TE120 mode, a wave polarized perpendicularly to the second straight slot (113, 213) is emitted, the rear face (130, 230) is brought to a reference electrical potential, the elementary antenna being characterized in that the elementary antenna includes an excitation device (105, 234), positioned at the rear of the cavity (102, 202) and capable of exciting the front face through the cavity, the excitation device exciting the front face at a plurality of excitation points (111, 211) which present a common predefined impedance, each quadrant of the front face carrying at least one excitation point.

2. The elementary antenna according to claim 1, wherein the front face and the rear face are square and the first and second slots are arranged parallel to the edges of the front face.

3. The elementary antenna according to claim 1 or claim 2, wherein the common predefined impedance of the excitation points (111, 211) is 50 Ohms.

4. The elementary antenna according to any one of the preceding claims, wherein the rear face (130, 230) acts as an electrical mirror plane between a power supply layer (150, 250) of the excitation device, the power supply layer being located on one side of the rear face while the front face is located on the other side of the rear face.

5. The elementary antenna according to any one of the preceding claims, wherein two excitation points (111, 211) symmetrically arranged relative to the first straight slot (112, 212) or relative to the second straight slot (113, 213) are excited by signals in phase opposition.

6. The elementary antenna according to any one of the preceding claims, wherein the excitation device includes a plurality of metallized vias (105) electrically connecting a power supply layer (150), located at the rear of the rear face (130), and the front face (110), the power supply layer (150) including a plurality of power supply lines (157), each power supply line being related to a metallized via, each metallized via opening, onto the front face (110), at an excitation point (111).

7. The elementary antenna according to claim 6, wherein each metallized via (105) is insulated from the rear face (130) as it passes through the latter.

8. The elementary antenna according to any one of the claims 1 to 6, wherein the excitation device includes a plurality of slots (234) provided in the rear face (230) and a power supply layer (250) located at the rear of the rear face and including a plurality of power supply lines (237), each power supply line being related to a slot, and straddling the related slot such that the point of intersection of the power supply line and the related slot is located in line with an excitation point (211) of the front face (210).

9. The elementary antenna according to claim 8, wherein the slots (234) form circular openings.

10. The elementary antenna according to claim 8, wherein the slots form straight openings, the plurality of slots forming a cross, a square parallel to the edges of the elementary antenna, or a square parallel to the diagonals of the elementary antenna.

11. An array antenna including a plurality of elementary antennas, characterized in that each elementary antenna is in accordance with any of the preceding claims.

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