EP1346442B1 - Printed patch antenna - Google Patents

Description

The present invention relates to an antenna "pastille" type printed in plated technology, linear or circular polarization, to operate at frequencies on the order of a few Gigahertz. In particular, this antenna is intended to be reproduced to be integrated into a network of reception and / or transmission of telecommunications, embedded in a machine, such as a low-orbiting satellite, or installed in a base station in conjunction with a satellite of telecommunications, or installed in a basis for radiocommunications with terminals mobile.

More particularly, the invention is directed to a printed antenna of the half-wave type "patch" comprising a dielectric substrate and two conductive layers respectively on the substrate faces. One of the layers constitutes a ground plan. The other layer is a plate rectangular or square conductor, called "pastille" (patch in English). Such an antenna elementary print is easily integrated and has a low manufacturing cost thanks to a simple machining process.

However, the electrical characteristics of the antenna depend greatly on the material dielectric of the substrate on which the two layers conductive are engraved.

When the dielectric substrate is thin and has a high dielectric permittivity, the antenna is not very efficient and its bandwidth is low.

To obtain a more efficient antenna, the dielectric substrate must be thick and be made of a material of low permittivity dielectric. However the size of the antenna as well obtained is significantly larger, which makes difficult to integrate it into a network. In addition, the opening of the radiation diagram of the antenna is reduced.

The object of the present invention is to provide a printed antenna of the "pastille" half-wave type at high efficiency, having a size smaller than that according to the prior art mentioned above, and presenting a radiation diagram more open.

To this end, a printed antenna of the half-wave type comprising a dielectric substrate and two conductive layers respectively on the faces of the substrate and symmetrically with respect to a plane symmetry of the antenna perpendicular to the faces of the substrate, is characterized in that one of the faces of the substrate has a projection extending longitudinally to the plane of symmetry and one of conductive layers extends over and along the jump.

For a linearly polarized antenna, the conductive layer of the antenna which extends over and the along the projection can have a contour for example rectangular and constitute a radiating element, and the other conductive layer can constitute a plane of mass. According to another embodiment, the layer conductive which extends over and along the projection can be a ground plane, and the other layer conductive can be flat, for example rectangular, and constitute a radiating element.

The projection which can have a section transverse to the plane of symmetry which is rectangular or sinusoidal, or trapezoidal or triangular, has a height substantially equal to the half difference in lengths of large and small sides of the rectangular layer extending over and the along the projection. However, the height of the projection is generally chosen according to the level of targeted compactness of the antenna; the higher the the larger the projection, the smaller the antenna size scaled down.

The other side of the substrate may include another projection extending longitudinally to the plane of symmetry and covered by the other conductive layer.

For a cross-polarized antenna, in particular with circular or elliptical polarization, one of the faces of the antenna substrate has two perpendicular projections forming a cross protruding, extending longitudinally in two planes of respective symmetry of the perpendicular antenna. The conductive layer of the antenna which extends over and along the projections can occupy a surface rectangular or square on the dielectric substrate whose sides have respectively the lengths of projections.

The cross-polarized antenna includes preferably a hybrid coupler which is produced on a dielectric support and housed in the substrate dielectric and which has at least one access connected to the end of the internal conductor of a probe coaxial, and at least one other access connected by a metallic crossing at the conductive layer spanning and along one of the projections.

As a variant, the two projections on one of the substrate faces are replaced by a jump to axial symmetry about an axis perpendicular to substrate faces.

The invention also relates to a method of manufacture of the printed antenna "patch", which includes machining one side of a substrate block dielectric to form cavities separated by at minus a strip having the section of a projection extending longitudinally to the plane of symmetry, a metallization at least of the face of the block dielectric machined to form one of the layers conductive, and a cutout of the printed antenna substantially in the center of the metallized machined block along the outline of the antenna.

• les figures 1 et 2 sont respectivement une vue en coupe prise suivant la ligne I-I dans la figure 2 et une vue de dessus d'une antenne imprimée de type "pastille" à polarisation linéaire selon une première réalisation préférée de l'invention ;
• les figures 3 et 4 sont respectivement une vue en coupe prise suivant la ligne III-III dans la figure 4 et une vue de dessus d'une antenne imprimée de type "pastille" à polarisation linéaire selon une deuxième réalisation préférée de l'invention ;
• la figure 5 montre deux diagrammes de rayonnement de champ électrique relatifs respectivement à une antenne "pastille" selon la technique antérieure et une antenne "pastille" selon la première réalisation ;
• les figures 6 et 7 sont respectivement des vues de dessus et en perspective d'un bloc de mousse diélectrique brut lors d'une première étape de fabrication d'une antenne selon l'invention ;
• les figures 8 et 9 sont respectivement des vues de dessus et en perspective du bloc de mousse diélectrique usiné lors d'une deuxième étape du procédé de fabrication ;
• les figures 10 et 11 sont respectivement des vues de dessus et en perspective du bloc de mousse usiné et métallisé lors d'une troisième étape du procédé de fabrication ;
• les figures 12 et 13 sont respectivement des vues de dessus et en perspective du bloc de mousse usiné et métallisé après une autre étape d'usinage selon le procédé de fabrication;
• les figures 14 et 15 sont des vues en coupe analogues à la figure 1, montrant des ressauts à profils sinusoïdal et en marche d'escalier, respectivement ;
• la figure 16 est une vue en coupe analogue aux figures 1 et 3, d'une antenne à deux ressauts superposés respectivement sur les deux faces du substrat ;
• la figure 17 est une vue en perspective d'une antenne imprimée du type "pastille" à polarisation circulaire avec coupleur hybride, selon une troisième réalisation de l'invention, un quart de secteur d'antenne ayant été arraché ;
• les figures 18 et 19 sont des vues de dessus et en coupe prises le long de la ligne XIX-XIX de l'antenne montrée à la figure 17 ;
• la figure 20 montre des variations d'adaptation et de transmission en fonction de la fréquence pour l'antenne selon la troisième réalisation ; et
• la figure 21 est une vue en perspective d'une antenne imprimée à polarisations croisées.

Other characteristics and advantages of the present invention will appear more clearly on reading the following description of several preferred embodiments of the invention with reference to the accompanying drawings in which:

• Figures 1 and 2 are respectively a sectional view taken along line II in Figure 2 and a top view of a printed antenna type "patch" with linear polarization according to a first preferred embodiment of the invention;
• Figures 3 and 4 are respectively a sectional view taken along line III-III in Figure 4 and a top view of a printed antenna type "patch" linear polarization according to a second preferred embodiment of the invention;
• FIG. 5 shows two electric field radiation diagrams relating respectively to a “patch” antenna according to the prior art and a “patch” antenna according to the first embodiment;
• Figures 6 and 7 are respectively top and perspective views of a block of raw dielectric foam during a first step of manufacturing an antenna according to the invention;
• FIGS. 8 and 9 are respectively top and perspective views of the block of dielectric foam machined during a second step of the manufacturing process;
• Figures 10 and 11 are respectively top and perspective views of the block of foam machined and metallized during a third step of the manufacturing process;
• Figures 12 and 13 are respectively top and perspective views of the block of machined and metallized foam after another machining step according to the manufacturing process;
• Figures 14 and 15 are sectional views similar to Figure 1, showing projections with sinusoidal profiles and staircase, respectively;
• Figure 16 is a sectional view similar to Figures 1 and 3, of an antenna with two projections superposed respectively on the two faces of the substrate;
• FIG. 17 is a perspective view of a printed antenna of the circular polarization "patch" type with hybrid coupler, according to a third embodiment of the invention, a quarter of the antenna sector having been cut away;
• Figures 18 and 19 are top and sectional views taken along line XIX-XIX of the antenna shown in Figure 17;
• FIG. 20 shows variations in adaptation and transmission as a function of the frequency for the antenna according to the third embodiment; and
• FIG. 21 is a perspective view of a printed antenna with crossed polarizations.

Referring to Figures 1 and 2, an antenna polarized half-wave "pastille" type print linear 1a according to the first embodiment of the invention comprises a dielectric substrate 2a, a first electrically conductive layer 3a extending over a first face of the substrate and constituting a ground plane, and a second layer electrically conductive rectangular 4a extending to the center of the second face of the substrate and having a central parallelepiped projection 5a. The second conductive layer 4a has a contour rectangular and covers the top and sides of the projection 5a. The antenna thus has a symmetrical structure with respect to a plane of symmetry YY perpendicular to the faces of the substrate 2a and longitudinal to the projection 5a. Layer 4a has a U-shaped section with a potent end, as shown in Figure 1, with wings extending over the second face of the substrate 2a and having a width L1 much larger than the width L2 of the projection 5a. In general, the height h of the projection 5a is equal to or greater than the thickness e of the substrate 2a.

Compared to a flat radiating element (patch) according to the prior art having a width W and a length L very often equal to W, as shown in dotted lines in FIG. 2, the length La of the antenna la according to the invention is reduced to: La = 2L1 + L2 = L - 2h. Thanks to the projection 5a over the entire width W of the antenna, the length of the radiating element constituted by the second conductive layer 4a is reduced significantly. This reduction in length brings the radiating slots 6a closer to symmetrical ends of the “patch” antenna 1a, which opens the radiation pattern in the electric field plane perpendicular to the projection 5a.

Significant thickening in the center of the substrate 2a formed by the projection 5a covered with the layer conductor 4a electrically lengthens the dimension resonant of the half-wave antenna and thus increases the characteristic impedance at the center of the antenna which is equivalent to a pseudo short circuit. The jump significantly reduces the size of the antenna for an operating frequency given. The higher the jump impedance at the center of the antenna is high, the more the width L2 of the projection must be decreased for a given frequency below the resonance condition.

In Figure 2 is also shown a microstrip line 7a having a width W7 significantly smaller than the width W of the element radiating 4a and extending perpendicular to this one, to the middle of the long side of a wing of width L1 of layer 4a. This microstrip line corresponds to a quarter wave transformer, and plays the role of impedance adapter with respect to the characteristic impedance, typically 50 Ω, of the antenna feed line. To feed the antenna, another solution is to use a coaxial probe, whose internal conductor is connected to an antenna point, such as a wing of layer 4a, having an input impedance equal to the characteristic impedance.

In Figures 3 and 4 concerning a second production of half-wave type printed antenna 1b "tablet" according to the invention, similar elements to those in antenna 1a according to the first achievement are designated by the same mark numeric followed by the letter b instead of the letter a.

The printed antenna of the half-wave "patch" type 1b is a dual variant of the first embodiment while still having symmetry with respect to a plane of symmetry YY perpendicular to the faces of the substrate 2b and by providing the symmetrical projection 5a, not on the second face of the dielectric substrate 2a supporting the rectangular radiating element 4a, but on the first face of the substrate 2b supporting the first conductive layer 3b constituting the ground plane of the antenna 1b. The radiating element 1b is a completely flat rectangular conductive plate 4b, extending along the axis of the projection 5b above it. The length Lb of the conductive layer 4b is still conserved according to the preceding relation: Lb = L - 2h, where h denotes the height of the jump 5b of width L2.

As an example, table I below indicates the resonance frequency corresponding to a wavelength λ, the bandwidth centered on the resonance frequency in percentage relative to it, and the directivity for an antenna TA according to the prior art comprising a flat square plate of width W = L = 50 mm = λ / (2 ε _r ) and a substrate having a thickness e = 2 mm and made of foam with relative permittivity ε _r = 1.07, substantially equivalent to an air space, and for antennas conformed with linear polarization 1a1 to 1a4 according to the first embodiment (Figures 1 and 2), with a length La = L - 2h <λ / (2 ε _r ). YOUR 1a1 1 to 2 1a3 1a4 h (mm) 0 2 4 6 8 Resonance frequency (GHz) 2.63 2.43 2.28 2.21 2 Bandwidth 1.7% 1.9% 2% 2.2% 2.4% Directivity (dB) 9.4 8.47 7.68 7.14 6.64

According to table 1 above, the higher the height h of the projection 5a is large, or more precisely the more m / e ratio is great, and to a lesser extent, the larger the width L2 of the projection 5a, the greater the antenna bandwidth increases and the more antenna directivity decreases.

As shown in Figure 5, the diagram of radiation in the electric field plane perpendicular to the projection 5a has an opening proportional to the height h of the projection, a lot wider, for example for antenna 1a4, than the opening of the antenna radiation diagram RT according to the prior art. Half-power opening radiated (3 dB) reaches approximately 120 ° for antenna 1a4.

These properties offer more freedom over relative positions of the antennas according to the invention put into a network because of the relative reduction dimensions of the antenna. In addition, the beam of a network with antennas according to the invention can to be more largely depointed since the diagram of radiation from the antenna is more open.

So by appropriately adapting the height h of the jump 5a, the diagram openings radiation at 3 dB can vary from 60 ° to at minus about 120 °. The radiation efficiency remains greater than 90% for all antennas according to the invention.

Similar results have been observed for antennas 1b1 to 1b4 according to the second embodiment of the invention, with a ground plane 3b shaped with a projection 5b, as shown in table 2 below for antennas always with the dimensions Lb = L = 50 mm and e = 2 mm. TA test 1b1 1b2 1b3 1b4 h (mm) 0 2 4 6 8 Resonance frequency (GHz) 2, 63 2.3 2, 09 1.95 1.82 Bandwidth 1.7% 1.9% 2.1% 2.3% 2.5% Directivity (dB) 9.4 7.9 7 6.4 6.1

A preferred method of manufacturing an antenna printed with linear polarization 1a according to the invention mainly comprises four stages E1, E2, E3 and E4 respectively illustrated in FIGS. 6-7, 8-9, 10-11 and 12-13.

In the initial step E1, the production starts with a block of thin foam BL of thickness h + e, of width greater than W and of length greater than La. The dielectric material of the block BL in which the dielectric substrate will be machined 2a has a relative permittivity typically of the order of 1.07 in correspondence with a length L = 50 mm <λ _r / 2 with λ _r = λ / ε _r , where λ is the wavelength corresponding to a frequency of the order of 2 GHz.

In step E2, two rectangular cavities C with a bottom of thickness e, are machined symmetrically relative to the transverse axis in one face of the block BL so that the cavities are separated by a strip transverse BA having the section (h.L2) of the projection 5a. The cavities C have a width greater than L1 and a length greater than W.

Then in step E3, the upper face of the block BL with the cavities is metallized by depositing a layer of metallic paint to form the conductive layer 4a. In particular, the painting metal covers the BA strip and the bottom of the cavities C. Metallic paint also covers the underside of the block so as to constitute the ground plane 3a. Alternatively, instead of the metallization of the underside, the ground plane 3a is constituted by a metal support on which the machined foam block is fixed.

Finally in step E4, the antenna 1a is cut in D by a second machining in the block metallized along the rectangular outline (W.La) of the conductive layer 4a and the rectangular outline lengthened from the microstrip supply line 7a.

By steps analogous to the previous steps E1 to E4, an antenna 1b with a ground plane 3b conformed with a projection 5b can also be machined from a block of BL dielectric foam.

The section of the projection 5a, 5b transverse to the plane of symmetry YY is not limited to the profile rectangular or square shown in Figures 1 and 3. The reduction of the length from L to La, Lb of the antenna generating a central zone of very high impedance may result from another symmetrical profile of the cross section of the projection, for example substantially sinusoidal 51, as shown in the figure 14, or substantially isosceles trapezoidal or isosceles triangular, or even substantially in stair steps 52 as shown in FIG. 15, with bearings parallel or inclined with respect to to the faces of the substrate.

According to another variant, the antenna comprises at both parallel projections superimposed on the substrate faces. For example, as shown in the Figure 16, the faces of the substrate 2ab of the antenna 1ab respectively comprise a first projection 52ab to rectangular cross section for the first conductive layer of ground plane 3ab and a second 51ab jump with cross section sinusoidal for the second conductive layer of radiating element 4ab. The 52ab and 51ab projections extend one above the other longitudinally to the plane of symmetry YY and are covered respectively by layers 3ab and 4ab.

Compared to a quarter wave antenna mass return which is not symmetrical with respect to in two planes, the half-wave antenna 1a, 1b according to the invention retains, despite the jump 5a, 5b a double symmetry along the plane of symmetry YY longitudinal to the projection and a plane of symmetry XX perpendicular to the projection and longitudinal to the line supply 7a, as shown in Figures 2 and 4.

This double symmetry provides the advantages of the jump to a two antenna crossed polarizations, and more particularly to a circularly polarized antenna described below.

Referring now to Figures 17, 18 and 19, a printed antenna with circular polarization 1c according to the invention has a doubly structure symmetrical with respect to two planes of symmetry XX and YY perpendicular to each other and to the faces of the antenna.

The antenna 1c comprises on a first face of a thin dielectric substrate 2c of thickness e a metal layer 3c, which can be a metal base, to constitute the ground plane of the antenna 1c, and in the center of a second face of the substrate 2c, a conductive layer 4c covering two projections 5c of identical size perpendicular to each other to form a central cross with four equal branches. Like the projections 5a and 5b, the projections 5c have a height h generally greater than the thickness e of the substrate 2c and a length Lc such that: Lc = L2 + 2.L1 = L - 2h, where L2 denotes the width of each projection, L1 the width of the four square surfaces of the metal layer 4c situated at the base of the cross formed by the projections 5c and arranged on the second face of the substrate 2c, and L the corresponding length of a flat square patch of an antenna according to the prior art.

The antenna 1c thus presents two planes longitudinal XX and YY perpendiculars 5c cross-over and one layer respectively conductive 4c forming a radiating element having a reduced square area (Lc.Lc) on the substrate 2c.

In practice, the dielectric substrate 2c is composed of a substrate 2c of dielectric foam of low permittivity ε _r = 1.07, the upper face of which is machined in a manner analogous to the substrate 2a, 2b to obtain the crossed projections 5c, and a small square dielectric support 21c embedded in a central cavity of the first face of the substrate 2c and covered by the metal layer 3c. The relative permittivity of the support 21c is higher, like the dielectric AR1000 from the company ARLON with a permittivity ε _r = 10.2.

As shown in detail in Figures 17-19, the antenna 1c is supplied by a coaxial probe 7c whose external conductive base is fixed to the ground plane 3c and whose internal conductor only passes through the dielectric support 21c. The end of the internal conductor of the probe coaxial 7c is welded to the end of a branch 81c forming an access to a vertex of a coupler 8c hybrid at 3dB-90 °. The coupler 8c is configured substantially along the outline of a square and photo-etched on the upper face of the support 21c. A another vertex, located in front in Figures 17 and 18, can be connected to the internal conductor of a second coaxial probe (not shown) for a cross polarization operation. Both other vertices 82c of the coupler 8c are extended by metallic bushings 83c which are provided at through the ends of the two projections 5c and of which the ends are in metallic contact by welds 84c with the conductive layer 4c extending on the tops of the projections 5c.

The relative permittivity of the dielectric support 21c is significantly higher than that of the substrate 2c so that for the operating frequencies of the gigahertz antenna, the dimensions of the 8c coupler are small and therefore compatible with the compactness of the antenna.

The antenna 2c is manufactured, substantially according to steps analogous to steps E1 to E4, with regard to relates to the block of dielectric foam 21c, in machining four cavities to form two cross bands forming after cutting the two perpendicular projections 5c, and by digging a underlying cavity to receive the support dielectric 21c supporting the hybrid coupler 8c.

For example, the dielectric substrate 21c has a overall thickness e of 10 mm with a cavity 635 µm thick to receive the support dielectric 21c having a thickness of 635 μm. The conductive layer 4c covering the crossed projections 5c has a width Lc = 25 mm, for 5c projections having a height h = 8 mm compared to a useful thickness e = 2 mm of the substrate 2c.

For the antenna 1c as dimensioned above, Figure 20 shows adaptation A and the TC transmission for circular polarization preferred turning in the opposite direction of clockwise compared to a TD transmission rotating in the direct direction of clockwise, depending on the frequency. The antenna resonates around a frequency of 2 GHz with an adaptation to 10 dB of around 20% for the bandwidth, which corresponds to a width of 410 MHz band. The effective bandwidth in transmission is lower, around 13%.

Alternatively, the lengths of the projections 5c are different for polarization operation elliptical with a probe, or crossed polarizations with two probes.

The invention is not limited to projections crossed parallelepiped 5c for operation with crossed polarizations, in particular with polarization circular. For example, the two projections can be replaced by a symmetrical central projection axial around a central axis of symmetry ZZ perpendicular to the faces of the substrate 2d coated with conductive layers 3d and 4d. According to the example illustrated in figure 21, the projection 5d is a macaroon. More generally, the projection has a shape discoid, frustoconical or conical or domed or bell, with a circular or elliptical base on the substrate. At least two coupler ends supply 84d are provided on the 5d projection, on two axes perpendicular to each other and to the axis of symmetry ZZ, at equal or different distances from the ZZ axis.

Claims (11)

1. A half-wave printed antenna (1a; 1b) comprising a dielectric substrate (2a; 2b) and two conductive layers (3a, 4a; 3b, 4b) extending on respective faces of the substrate and symmetrical with respect to a plane of symmetry (XY) of the antenna perpendicular to the faces of the substrate, characterized in that one of the faces of the substrat (2a; 2b) has a raised portion (5a; 5b) extending lengthwise of the plane of symmetry and one of the conductive layers (4a; 3b) extends over and along the raised portion.
2. The antenna according to claim 1, wherein the conductive layer (4a) which extends over and along the raised portion (5a) constitutes a radiating element, and the other conductive layer (3a) constitutes a ground plane.
3. The antenna according to claim 1, wherein the conductive layer (3b) which extends over and along the raised portion (5b) constitutes a ground plane, and the other conductive layer (4b) constitutes a radiating element.
4. The antenna according to any one of claims 1 to 3, wherein the raised portion (5a; 5b) has a height (h) substantially equal to half the distance between the lengths of the longer and shorter sides of the rectangular layer (4a; 4b) extending over and along the raised portion.
5. The antenna according to any one of claims 1 to 4, wherein the raised portion (51, 52) has a rectangular, or sinusoidal, or trapezoidal or triangular cross section in the plane of symmetry (YY).
6. The antenna according to any one of claims 1 to 5, characterized in that the other face of the substrate (2ab) includes another raised portion (52ab; 51ab) extending lengthwise of the plane of symmetry (YY) and covered by the other conductive layer (3ab; 4ab).
7. The antenna (1c) according to any one of claims 1 to 6, wherein one face of the substrate (2c) includes two mutually perpendicular raised portions (5c) extending lengthwise of two respective planes of symmetry (XX, YY) of the antenna.
8. The antenna according to claim 7, wherein the conductive layer (4c) extending over and along the raised portions occupies a rectangular surface on the dielectric substrate (2c) whose sides are the same lengths as the raised portions (5c) respectively.
9. The antenna according to claim 7 or 8, including a hybrid coupler (8c) that is formed on a dielectric support (21c) and lodged in the dielectric substrate (2c) and has at least a port (81c) connected to an end of an inner conductor of a coaxial probe (7c), and at least another port (81c) connected by a metal via (83c) to the conductive layer (4c) extending over and along the raised portions (5c).
10. The antenna according to one of claims 7 to 9, wherein said two raised portions on one face of the substrate (2d) are replaced by a raised portion (5d) with axial symmetry about an axis (ZZ) perpendicular to the faces of the substrate.
11. A method of fabricating a half-wave printed antenna (1a; 1b; 1c) including a dielectric substrate (2a; 2b) and two conductive layers (3a, 4a; 3b, 4b) extending on respective faces of the substrate and symmetrical with respect to a plane of symmetry (XY) of the antenna perpendicular to the faces of the substrate, characterized in that it comprises a machining one face (E2) of a block of dielectric substrate (BL) to form cavities (C) separated by at least one strip (BA) having the same section as a raised portion (5a; 5b; 5c) extending lengthwise of the plane of symmetry, metallizing (E3) at least the face of the block with the machined dielectric raised portion to form one of the conductive layers (4a; 3b; 4c), and cutting out (E4) the printed antenna substantially at the center of the metallized and machined block following the contour of the antenna.

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