Improved array antenna of the type comprising a plurality of series-fed planar radiating elements

Abstract

Improved array antenna of the type comprising a plurality of series-fed planar radiating elements This array antenna (1), which comprises a plurality of series-fed radiating elements (2i) arranged along a vertical axis (V), operates in horizontal polarization, by connecting two successive radiating elements (2i, 2i+1) along the vertical axis by a pair of differential lines (3i, 4i), each line having a length (d) equal to the wavelength guided in said line, one end of a line being connected to a horizontal edge of a radiating element and the other end of said line being connected to the horizontal edge opposite the other radiating element, a single radiating element being provided with at least one horizontal excitation point (PH), positioned outside the vertical axis (V), preferably close to a vertical edge of the single radiating element. Figure for abstract: Figure 2

Description

Title of the invention: Improved array antenna of the type comprising a plurality of planar radiating elements fed in series

[0001] The present invention relates to network antennas of the type comprising a plurality of planar radiating elements (or “patch” antennas) fed in series -SFPA (“Series-Fed Patch Antenna”).

[0002] [Fig.l] represents an antenna according to the state of the art.

[0003] The antenna 101 results from the vertical series connection of a plurality of planar radiating elements 102, of length L and width Wi, making it possible to generate a vertically polarized wave, that is to say parallel to the axis V along which the different planar radiating elements of the antenna are arranged.

[0004] This antenna geometry is based directly on the TM 10 resonance mode of each planar radiating element.

[0005] In this resonance mode, as illustrated on the central element 1023, the electric field between the ground plane and the metal plane constituting respectively the lower face and the upper face of the planar radiating element is antisymmetrical with respect to the horizontal axis H, which is the axis orthogonal to the vertical axis V. On the horizontal, upper and lower edges, this electric field is homogeneous, that is to say it is either positive or negative, and substantially constant. Conversely, on the left and right edges, the electric potential varies and changes sign at the horizontal axis H.

[0006] Such a potential structure makes it possible to generate a wave whose electric field E is oriented along the vertical axis V, that is to say a vertically polarized wave.

[0007] Under these conditions, to propagate the TM10 resonance mode from one element to its neighbor, a micro-strip feed line 105; is used, which electrically connects the center of the horizontal edge, for example upper, of a radiating element 102; and the center of the lower horizontal edge of the neighboring radiating element 102i+i. In addition, this single line has a length equal to 'kgll (with Xg the wavelength guided in the line) in order to invert the electric field between the two ends of the line, that is to say the field on the upper horizontal edge, with respect to the field on the lower horizontal edge, and thus make the two radiating elements thus connected resonate in phase.

[0008] In the network antenna 101, the power supply is provided by a single excitation point Pv located on the axis V, but away from the axis H.

[0009] For the entire antenna to resonate at the desired frequency, all radiating elements must also resonate at the same frequency. Consequently, the length Li of each element is substantially identical from one element to another, and is close to 'kgll (the electric field of the lower and upper edges of the same element being in phase opposition). Strictly speaking, as each element does not have the same neighborhood, different couplings are established, which shifts the resonance frequency. This shift can be overcome by adjusting the length Li of each element.

[0010] In polarimetric radar applications, such as synthetic-aperture radar (SAR), antennas with orthogonal polarizations are required.

[0011] In the case of linear V / H polarization, to guarantee the symmetry of the radiation patterns, as well as good integrability, it is necessary that the antennas operating in horizontal polarization and those operating in vertical polarization have the same physical footprint.

[0012] However, at present, there is no SFPA type antenna operating according to a polarization oriented in the axis orthogonal to the axis of the array of planar radiating elements, that is to say in horizontal polarization when the radiating elements are aligned vertically.

[0013] The aim of the present invention is therefore to propose a horizontally polarized SFPA antenna.

[0014] For this purpose, the invention relates to an array antenna of the type comprising a plurality of planar radiating elements supplied in series, the planar radiating elements being arranged along a so-called vertical axis, a so-called horizontal axis, orthogonal to the vertical axis, intersects the latter at a central point, characterized in that, for operation in horizontal polarization, two successive planar radiating elements along the vertical axis are electrically connected to each other by a pair of differential lines, each line of the pair of differential lines having a length equal to an integer multiple of the wavelength guided in said line, one end of a line of the pair of differential lines being connected to a horizontal edge of a planar radiating element and the other end of said line being connected to the horizontal edge opposite the other planar radiating element,the guided wavelength corresponding to the resonant frequency of the array antenna, a single planar radiating element of the plurality of planar radiating elements being provided with at least one horizontal excitation point, for operation in horizontal polarization, the horizontal excitation point being off the vertical axis, preferably close to a vertical edge of said single planar radiating element.

[0015] According to other advantageous aspects of the invention, the antenna comprises one or more of the following characteristics, taken in isolation or in all technically possible combinations:

[0016] - the different planar radiating elements are rectangular in shape and have a dimension along the horizontal axis that is substantially equal and, preferably, a dimension along the vertical axis that decreases as a function of a distance from the planar radiating element to the central point.

[0017] - the network antenna is symmetrical with respect to the vertical axis and symmetrical by relative to the horizontal axis.

[0018] - the single planar radiating element of the plurality of planar radiating elements is equipped with two horizontal excitation points, for differential excitation of the network antenna.

[0019] - for operation in vertical polarization, simultaneously or alternately for operation in horizontal polarization, two successive planar radiating elements along the vertical axis are further electrically connected to each other by a single line, the single line having a length equal to half a wavelength guided in said single line, one end of the single line being connected to a horizontal edge of a planar radiating element and the other end of the single line being connected to the horizontal edge opposite the other planar radiating element, and a single planar radiating element of the plurality of planar radiating elements is provided with at least one vertical excitation point, for operation in vertical polarization, the vertical excitation point being off the horizontal axis, preferably close to a horizontal edge of the planar radiating element.

[0020] - the single planar radiating element of the plurality of planar radiating elements is equipped with two vertical excitation points, for differential excitation of the network antenna.

[0021] - a line is a microstrip line or a coplanar line or a stripline line.

[0022] - each planar radiating element is a patch antenna.

[0023] - the network antenna comprises M groups of planar radiating elements, each group comprising a plurality of N planar radiating elements arranged along the vertical axis, the different elements of a group being arranged along the vertical axis and the different groups being arranged along the horizontal axis, two successive radiating elements along the vertical axis of a group being coupled by a pair of differential lines of a guided wavelength, and a single radiating element of a group being coupled to a single radiating element of another group by a single line of half a wavelength guided along the horizontal direction.

[0024] - the antenna comprises M groups of planar radiating elements, each group comprising a plurality of N planar radiating elements arranged along the vertical axis, the different elements of a group being arranged along the vertical axis and the different groups being arranged along the horizontal axis, two radiating elements successive along the vertical axis of a single group being coupled by a pair of differential lines of a guided wavelength, and each radiating element of a group being coupled to a neighboring radiating element of another group by a single line of half a wavelength guided along the horizontal direction.

[0025] The invention will appear more clearly on reading the description which follows, given solely by way of non-limiting example, and made with reference to the drawings in which:

[0026] [Fig-1] [Fig.l] is an embodiment of an array antenna according to the state of the technique resulting from the vertical series connection of a plurality of planar radiating elements operating in vertical polarization;

[0027] [Fig.2] [Fig.2] is an embodiment of an array antenna according to the invention resulting from the vertical series connection of a plurality of planar radiating elements operating in horizontal polarization;

[0028] [Fig.3] [Fig.3] is a graph of gain versus frequency for the antenna of [Fig.2];

[0029] [Fig.4] [Fig.4] represents the radiation diagrams, in azimuth section and in sectional elevation, of the antennas of figures 1 and 2 respectively;

[0030] [Fig.5] [Fig.5] is a first variant embodiment of the antenna of [Fig.2];

[0031] [Fig.6] [Fig.6] is a second variant embodiment of the antenna of [Fig.2]; And,

[0032] [Fig.7] [Fig.7] is a second embodiment of the antenna according to the invention to obtain dual horizontal and vertical polarization.

[0033] [Fig.2] represents an embodiment of an antenna according to the invention.

[0034] The antenna 1 results from the series connection along a vertical axis V of a plurality of N planar radiating elements 2; (or elementary patch antennas) for operation in horizontal polarization. N is an integer greater than or equal to two. An element is indexed by an integer i between 1 and N.

[0035] The antenna 1 comprises for example five elements: a second lower element 2b, a first lower element 22, a central element 23, a first upper element 24 and a second upper element 25.

[0036] The different planar radiating elements 2; are arranged along the vertical axis V. The axis orthogonal to the vertical axis V is the horizontal axis H. It crosses the vertical axis V at the origin point O.

[0037] The antenna 1 is symmetrical with respect to the vertical axis V.

[0038] Antenna 1 is symmetrical with respect to the horizontal axis H.

[0039] The center O is therefore a center of symmetry of the antenna 1.

[0040] In the embodiment of [Fig.2] where the network antenna comprises an odd number of elements, the center of the central element 23 coincides with the origin point O.

[0041] Each element 2; has a width Wi along the H axis and a length L; along the V axis.

[0042] In the embodiment of [Fig.2], the elements have a substantially identical width. The length L; decreases as one moves away from the center O of the antenna 1.

[0043] Two planar radiating elements 2; and 2i+i successive along the axis V are electrically connected to each other by a pair of differential feed lines, for example microstrip lines, 3; and 4;.

[0044] More precisely, the upper horizontal edge of the element 2; and the lower horizontal edge of the neighboring element 2i+i, located immediately above the element 2;, are connected, on the one hand, by a line 3; to the left of the vertical axis V and, on the other hand, by a line 4;, to the right of the vertical axis V.

[0045] In this way, a differential coupling is established between two successive planar radiating elements of the array antenna.

[0046] The network antenna is excited by a suitable electrical signal, which is applied to the metal plane of one of the elements, preferably the central element 23, at an excitation point PH.

[0047] The point PH is located on the horizontal axis H, but outside the vertical axis V, preferably close to an edge, for example the left vertical edge, of the central element 23 in order to guarantee good linear polarization.

[0048] Applying the electrical excitation signal to point PH makes it possible to make element 23 resonate according to mode TM01.

[0049] The electric field in the planar radiating element 23 is represented schematically in [Fig.2] by “+” and “-”. This electric field is for example negative on the left and positive on the right of the V axis over a half period of the excitation signal and vice versa over the following half period. The electric field is distributed symmetrically with respect to the H axis, but antisymmetrically with respect to the V axis.

[0050] Thus, the excitation of the radiating element according to the TM01 mode makes it possible to generate a horizontally polarized wave, that is to say one whose electric field E is oriented along the horizontal axis H.

[0051] To electrically associate two neighboring planar radiating elements, 2; and 2i+i, and make them resonate in phase, the two lines 3; and 4; have a length equal to the guided wavelength Xg (or to an integer multiple of the guided wavelength Xg) so as to introduce a phase shift of 360° between the electric field at one end of the lines and the electric field at the other end of the lines, 3; and 4;.

[0052] The wavelength kg is determined at the resonance frequency Fo of the array antenna 1.

[0053] In this way, the same distribution of the electric field is obtained in each of the elements 2;.

[0054] In other words, the radiating elements are excited in phase according to the TM01 mode.

[0055] The adaptation of the performance of the antenna 1 is carried out in the same way as for the antenna 101 according to the state of the art.

[0056] Adjusting the widths W; allows the resonance frequency to be fixed and adjusting the length L; allows the antenna aperture to be made more or less wide by fixing the gain of each radiating element and thus creating a weighting to minimize the secondary lobes.

[0057] The antenna 1 has a parameter S having the form shown in [Fig.3]. The antenna 1 can be more or less narrow band around the resonance frequency Fo, depending on the thickness and permittivity of the substrate, the values ​​of the lengths Li chosen as well as the location of the feed point PH.

[0058] [Fig.4] allows the radiation patterns of antennas 1 and 101 to be compared at the same resonance frequency Fo equal to 24 GHz.

[0059] The radiation patterns, Cv for antenna 101 and CH for antenna 1, are very close, both in elevation (plane containing the V axis and the normal to the plane of the radiating elements) (Figure 4A) and in azimuth (plane containing the H axis and the normal to the plane of the radiating elements) (Figure 4B). This result is the one sought and is perfectly consistent since the topologies are ultimately very close.

[0060] A very important piece of data when doing polarimetry is the cross-polarization, that is to say the energy radiated in the polarization orthogonal to the desired one. The lower this value, the more efficient the antenna is for a polarimetry application. The topology of antenna 1 makes it possible to achieve cross-polarization values ​​of the order of -25 dB, without special adjustments.

[0061] Alternatively, instead of being rectilinear, the interconnection lines between planar radiating elements may form one or more meanders. By folding the lines in this way, the spacing between the elements may be reduced, while maintaining the constraint on the length of the lines. In particular, this makes it possible to give the array antenna according to the invention a physical footprint identical to that of the antenna of [Fig.l].

[0062] Alternatively, the microstrip lines can be replaced by coplanar lines or by striplines.

[0063] In the embodiment shown in [Fig.2], the power supply is provided by a single excitation point PH.

[0064] More generally, it is possible to achieve this power supply by considering all known types of power supply for patch antennas. In particular, the power supply can be achieved by two vias, arranged along the axis H, symmetrically with respect to the center O of the element to be excited, and powered in phase opposition (differential assembly). The power supply can also be achieved by coupling through one or more slots provided in a ground plane of the radiating element, directly above the excitation point on the metal plane forming the upper surface of the radiating element.

[0065] The advantage of using two excitation points for operation in horizontal polarization and / or two excitation points for operation in vertical polarization can make it possible quite easily to gain 3 dB of radiated power in transmission, while improving the quality of the insulation with the crossed polarization and the symmetry of the diagram.

[0066] In the embodiment of [Fig.2], the antenna forms an IxN matrix.

[0067] As illustrated in Figures 5 and 6, it is possible to produce antennas network forming a matrix of M lines and N columns operating in horizontal polarization, by combining coupling by a single line in the horizontal direction and by a pair of differential lines in the vertical direction.

[0068] For example, in the first variant of [Fig.5], the array antenna 201 forms a 3x3 matrix resulting from the association along the H axis of three column array antennas identical to each other and to the antenna of [Fig.2]. This association is made by connecting the central element of each column array antenna by a simple link of a guided half-wavelength.

[0069] For example, in the second variant of [Fig.6], the antenna 301 forms a 3x3 matrix resulting from the association along the V axis of three line array antennas identical to each other and to the antenna of [Fig.l] (by means of a 90° rotation). This association is made by connecting the central element of each line array antenna by a pair of differential lines of a guided wavelength.

[0070] In these two variants, the positioning of the excitation point PH makes it possible to propagate the TM01 mode from the central element to the peripheral elements of the network antenna.

[0071] [Fig.7] represents a second embodiment of the antenna according to the invention which can operate in horizontal polarization and / or in vertical polarization.

[0072] The antenna 401 combines the SFPA topology in horizontal polarization and the SFPA topology in vertical polarization, thus enabling dual polarization operation.

[0073] For this, each radiating element 402; is of substantially square shape so that it can be excited according to the TM 10 mode and the TM01 mode.

[0074] The central element 4023 is provided with two power supply points, respectively a PH point for exciting the horizontal polarization and a Pv point for exciting the vertical polarization. The desired polarization can then be chosen by suitably powering each of the ports.

[0075] In accordance with what has been explained previously, two neighboring radiating elements are connected by three lines: - A simple line 415; of length Xg / 2 for polarization along the V axis; - Two differential lines, 413; and 414; of length Xg for polarization along the H axis.

[0076] The lines which are to connect two radiating elements being of different lengths, one or the other of the tracks is no longer rectilinear, but curvilinear (curved, angled, meandering, etc.)

[0077] To minimize the problems of coupling the signal from the horizontal polarization by common mode to the vertical polarization, one can play on the spacing and the impedance of the differential lines.

[0078] Furthermore, by exciting both ports simultaneously with a chosen phase shift, one can have polarization agility to generate circular or tilted polarizations relative to the H and V axes.

[0079] It is also possible to have the vertical configuration V and the horizontal configuration H which operate in two different frequency bands. This is achieved by varying the vertical and horizontal dimensions of the unitary antenna elements.

[0080] The fields of application of the invention are radars, jammers, radios and data links, as well as multifunction systems using electronically scanned array antennas.

[0081] In particular, the present invention finds an application for radars with a large number of unit antennas, where it may be advantageous to couple the radiating elements directly to each other by feed lines, and to have to excite the network antenna by only one element. This makes it possible to reduce the number of transmission and reception modules for generating the electrical signal in transmission, or acquiring the electrical signal in reception.

[0082] The present invention is also compatible with conventional bandwidth expansion techniques, such as stacked patch antennas, as presented in reference A. A. Serra, P. Nepa, G. Manara, G. Tribellini and S. Cioci, "A Wide-Band Dual-Polarized Stacked Patch Antenna," in IEEE Antennas and Wireless Propagation Letters, vol. 6, pp. 141-143, 2007, doi: 10.1109 / LAWP.2007.89 3101.

Claims

Claims

1. Array antenna (1) of the type comprising a plurality of planar radiating elements (2;) supplied in series, the planar radiating elements being arranged along a so-called vertical axis (V), a so-called horizontal axis (H), orthogonal to the vertical axis, crosses the latter at a central point (0), characterized in that, for operation in horizontal polarization, two successive planar radiating elements (2;, 2i+i) along the vertical axis (V) are electrically connected to each other by a pair of differential lines (3i, 4;), each line of the pair of differential lines having a length (d) equal to an integer multiple of the guided wavelength in said line, one end of a line of the pair of differential lines being connected to a horizontal edge of a planar radiating element and the other end of said line being connected to the horizontal edge opposite the other planar radiating element, the guided wavelength corresponding to the resonance frequency (Fo) of the array antenna, a single planar radiating element of the plurality of planar radiating elements (2;) being provided with at least one horizontal excitation point (PH), for operation in horizontal polarization, the horizontal excitation point being outside the vertical axis (V), preferably close to a vertical edge of said single planar radiating element.;

2. An array antenna according to claim 1, wherein the different planar radiating elements (2;) are rectangular in shape and have a dimension (Wi) along the horizontal axis (H) that is substantially equal and, preferably, a dimension (L;) along the vertical axis (V) that decreases as a function of a distance from the planar radiating element (2;) to the central point.

3. An array antenna according to any preceding claim, wherein the array antenna (1) is symmetrical about the vertical axis (V) and symmetrical about the horizontal axis (H).

4. An array antenna according to any preceding claim, wherein the single planar radiating element of the plurality of planar radiating elements (2;) is provided with two horizontal excitation points, for differential excitation of the array antenna.

5. Array antenna (401) according to any one of the preceding claims, in which, for operation in vertical polarization, simultaneously or alternatively to operation in horizontal polarization, two successive planar radiating elements (402; , 402i+i) along the vertical axis (V) are further electrically connected to each other by a single line (405;), the single line having a length equal to half a guided wavelength in said single line, one end of the single line being connected to a horizontal edge of a planar radiating element and the other end of the single line being connected to the horizontal edge opposite the other planar radiating element, and a single planar radiating element of the plurality of planar radiating elements is provided with at least one vertical excitation point (Pv), for operation in vertical polarization, the vertical excitation point being outside the horizontal axis (H), preferably close to a horizontal edge of the planar radiating element.;

6. An array antenna according to claim 5, wherein the single planar radiating element of the plurality of planar radiating elements (2;) is provided with two vertical excitation points, for differential excitation of the array antenna.

7. An array antenna according to any preceding claim, wherein a line is a microstrip line or a coplanar line or a stripline.

8. An array antenna according to any preceding claim, wherein each planar radiating element is a patch antenna.

9. An array antenna according to any preceding claim, wherein the array antenna comprises M groups of planar radiating elements, each group comprising a plurality of N planar radiating elements arranged along the vertical axis (V), the different elements of a group being arranged along the vertical axis (V) and the different groups being arranged along the horizontal axis (H), two successive radiating elements along the vertical axis of a group being coupled by a pair of differential lines of a guided wavelength, and a single radiating element of a group being coupled to a single radiating element from another group by a single line of half a wavelength guided in the horizontal direction.

10. An array antenna according to any one of claims 1 to 9, wherein the antenna comprises M groups of planar radiating elements, each group comprising a plurality of N planar radiating elements arranged along the vertical axis, the different elements of a group being arranged along the vertical axis (V) and the different groups being arranged along the horizontal axis, two successive radiating elements along the vertical axis of a single group being coupled by a pair of differential lines of a guided wavelength, and each radiating element of a group being coupled to a neighboring radiating element of another group by a single line of half a wavelength guided along the horizontal direction.

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