EP1564842B1 - Ultrawideband antenna - Google Patents

Description

The present invention relates to the field of antennas.

More precisely, the present invention relates to the field of antennas intended for broadcasting high-speed services, in particular in the UWB (Ultra Wide Band or Ultra Wide Band) domain, but also for wireless networks, such as WLAN (Wireless Lan). and WIFI (registered trademark) (Wireless Fidelity), as well as in the field of multiband cellular telecommunications.

The rise of telecommunication systems to meet the needs of mobile communications and broadband service delivery, inexorably tends to a saturation of available spectral resources or frequencies.

A new system, called UWB, which allows the reuse of frequency bands already allocated for other applications is being developed for civil telecommunication applications. To avoid interference with other systems, the UWB transmits at a very low level (of the order of noise) a coherent signal but spread over a very wide band of frequencies (hence the name "Ultra Wide Band"). Coherence is ensured by Gaussian pulse coding and it is essential that each element of the transmission chain, including the antenna, has the most neutral transfer function possible over the entire width of the band (typically 3 at 10 GHz) so that the receiving system is able to recover the useful signal in the middle of the noise.

In the literature, for example document [1], documents highlighting the need to evaluate system performance and to control the performance and design of this type of antenna in order to ensure competitiveness on this new transmission channel.

The antenna behaves like a band pass filter which conditions the performance of the complete system.

The existence on the market of compact antennas usable in UWB and planar technology (to be integrated on the printed circuit boards of PCB terminals) is still marginal.

If we ignore structures on ceramics or dielectrics with very high permittivity, which are difficult to master technically, the state of the art remains based on 3D monolithic structures on a ground plane (see, for example, documents [2]). and [3]). The structures described in these documents seem effective in terms of bandwidth (theoretical 2-12 GHz) and compactness of the monopoly. However, the need for a large-size ground plane orthogonal to the monopoly excludes an important level of integration, particularly on a terminal PCB.

In addition, publications show antennas in microstrip printed technology with an integrated ground plane, but with limited bandwidth or multiband performance, for example document [4].

We have schematised on the figure 1 appended, such a printed antenna structure comprising in a first plane a ground plane PM and in a second plane a microstrip excitation line LE associated with a monopole MO.

Attempts to use this printed technology for making coplanar antennas can lead as illustrated on the figure 2 to a coplanar guide-type structure in which an excitation microstrip line LE is flanked by two ground plane elements PM and separated therefrom by two narrow slot lines LF (typically 0.1mm wide for an impedance of 50 Ohms) which open on the straight edge BR of the ground plane PM. However, the inventors have found that this extrapolation, for a coplanar antenna, of the known microstrip printing technology, leads to failure since such an antenna leads to the impossibility of a broadband operation because of a non-natural regime. propagative and therefore of a high rate of standing waves. The document DE 197 29 664 A describes antennas where the edge of the ground plane is convex towards the monopoly. In this context, the inventors have not identified, to date, known solutions that reconcile compact uniplanar structure and Ultra Wide Band performance (Fmax / Fmin> 5).

The main object of the present invention is to remedy this situation by proposing a new antenna that makes it possible to meet these specifications, that is to say an antenna capable of transforming the incident energy into radiated energy over a very wide range. frequency band (Fmax / Fmin> 5).

Another auxiliary object of the present invention is to provide an antenna whose geometry remains small vis-à-vis the wavelength.

Yet another auxiliary object of the present invention is to provide an antenna that can easily be integrated on a PCMCIA or PCB type circuit board (ie Printed Circuit Board), for example in the form of a structure. coplanar etched on one side of an electronic substrate, facilitating the subsequent integration of active elements.

These objects are achieved within the framework of the present invention by means of an antenna as defined by claim 1. The inventors have indeed determined that it is essential in the context of the present invention that the edge of the ground plane directed towards the monopoly is not straight to reach a wide bandwidth.

• la figure 1 précédemment décrite représente schématiquement une antenne connue du document [4] de l'état de la technique,
• la figure 2 représente schématiquement une possibilité d'extrapolation de la technologie imprimée connue pour la réalisation d'une antenne coplanaire, conduisant à un régime stationnaire,
• la figure 3 représente schématiquement une première variante d'antenne pouvant être appliquée à la présente invention,
• les figures 4 à 12 représentent 9 autres variantes d'antenne pouvant être appliquées à la présente invention ou conformes à la présente invention,
• la figure 13 représente le rapport d'ondes stationnaire en fonction de la fréquence de l'antenne illustrée sur la figure 3,
• la figure 14 représente différents diagrammes de rayonnement de cette même antenne,
• la figure 15 représente une vue d'une autre variante d'antenne pouvant être appliquée à la présente invention, plus précisément, la figure 15a représente une vue en plan d'un monopole, de sa ligne d'alimentation associée et d'un plan de masse coplanaire et représente par une ligne interrompue le contour d'un plan de masse auxiliaire disposé sur la seconde face du substrat diélectrique et par des points une série de pions assurant une liaison électrique entre les plans de masse prévus sur les deux faces du substrat, tandis que la figure 15b représente avec la même convention, cette second face du substrat et la figure 15c représente une vue en coupe de ce dernier substrat passant par un plan contenant de tels pions, ,
• la figure 16 représente une variante comprenant deux antennes coplanaires orthogonales pour un fonctionnement bipolarisation (même fréquence, deux pôlarisations), et
• la figure 17 représente une autre variante comprenant quatre antennes coplanaires orthogonales permettant d'assurer de la diversité d'espace et de polarisation.

Other features, objects and advantages of the present invention will appear on reading the detailed description which will follow, and with reference to the accompanying drawings, given as non-limiting examples and in which:

• the figure 1 previously described schematically represents a known antenna of the document [4] of the state of the art,
• the figure 2 schematically represents a possibility of extrapolation of the known printed technology for producing a coplanar antenna, leading to a stationary regime,
• the figure 3 schematically represents a first antenna variant that can be applied to the present invention,
• the Figures 4 to 12 represent 9 other antenna variants that can be applied to the present invention or in accordance with the present invention,
• the figure 13 represents the standing wave ratio as a function of the frequency of the antenna illustrated on the figure 3 ,
• the figure 14 represents different radiation patterns of this same antenna,
• the figure 15 represents a view of another antenna variant that can be applied to the present invention, more specifically, the figure 15a is a plan view of a monopole, its associated feed line and a coplanar ground plane, and represents a broken line the outline of an auxiliary ground plane disposed on the second face of the dielectric substrate and by points a series of pins providing an electrical connection between the ground planes provided on both sides of the substrate, while the figure 15b represents with the same convention, this second face of the substrate and the figure 15c represents a sectional view of the latter substrate passing through a plane containing such pins,,
• the figure 16 represents a variant comprising two orthogonal coplanar antennas for a bipolarization operation (same frequency, two polars), and
• the figure 17 represents another variant comprising four orthogonal coplanar antennas for ensuring diversity of space and polarization.

We can see on the figure 3 , an antenna comprising a support 10 of dielectric material which carries a monopole 100 and a ground plane 200.

The support 10 may be made of any suitable material and may have any suitable geometry and dimensions.

It is preferably of rectangular or square contour.

The monopoly 100 and the ground plane 200 are coplanar. They are made in printed technology and by engraving on the same face of the support 10.

By way of nonlimiting example, the support 10 has dimensions of the order of 57.5 mm × 47 mm and a thickness of about 1.5 mm.

According to the embodiment shown on the figure 3 , the monopole 100 and the ground plane 200 have a symmetry with respect to a plane OO. This plane OO passes through the central axis of an excitation line 110.

The excitation line 110 is formed of a rectilinear ribbon 112 of constant width delimited by two lateral edges 114, 115 parallel to each other and parallel to the plane O-O. The excitation line 110 thus extends, from the middle of one of the edges of the wafer, perpendicularly to this edge, toward the center of the support 10.

The monopole 100 is connected to the inner end of the excitation line 110. It has a general shape flared away from the ground plane 200. The contour of the monopole 100 directed towards the ground plane 200 may have a continuous curvature. However, preferably this contour is delimited by a series of successive rectilinear sections whose inclination with respect to the plane OO increases away from the ground plane 200. By way of non-limiting example, the monopoly 100 can thus be delimited by three sections successive 120, 122 and 124 having respective inclinations of the order of 10 °, 30 ° and 45 ° and respective lengths of the order of 17 mm, 7 mm and 20 mm. The monopoly 100 is also limited, opposite the excitation line 110, by a straight edge 130, transverse to the plane OO, for example a length of the order of 37 mm. Monopoly 100 thus formed has the general shape of a planar cone with multiple slopes.

As indicated above, the ground plane 200 comprises two blocks 210, 220 located respectively on either side of the feed line 110, being separated therefrom.

Furthermore, the ground plane 200 has a border 230 directed towards the monopole 100 which is not completely rectilinear. The curvature of this border 230 may be continuous. However according to the embodiment illustrated on the figure 3 , this border 230 is delimited by a series of successive rectilinear sections. More precisely according to the embodiment shown on the figure 3 each block 210, 220 is delimited, starting from the edge of the support 10 on which the feed line 110 opens, by a rectilinear internal section 240, parallel to the plane OO, of the same length as the feed line 110, and by a rectilinear outer portion 242, also parallel to the plane OO, of a length greater than the section 240, typically of the order of twice the latter, for example of the order of 23.5mm.

The two sections 240, 242 are connected by a plurality of sections 244, 246, 247, 248, which in combination define a convex shape, for each block, in the direction of the monopole 100. More precisely according to the particular and nonlimiting embodiment illustrated on the figure 3 the section 244 extends the section 242 and converges towards the plane OO in the direction of the monopole 100. The three sections 246, 247 and 248 follow each other from the internal section 240. They diverge, with progressively increasing angles, with respect to the plane. OO, close to the monopoly 100. The sections 244 and 248 meet at a point 249 which is the point of the ground plane 200 farthest from the edge of the support 10 on which the feed line 110 opens.

The overall width of the ground plane 200, considered perpendicular to the plane OO, is substantially identical to the largest width of the monopole 100, at the edge 130.

Thus the tip 249 of the ground plane 200 is located substantially opposite the outer quarter of the width of the expansion of the monopoly 100.

Between the monopole 100 and the ground plane 200 extends the dielectric support 10.

The geometry of the ground plane 200 and that of the monopole 100 are preferably adapted such that the monopole defines an impedance at least substantially constant along its profile.

The monopole 100, the feed line 110 and the ground plane 200 are advantageously made in printed circuit technology.

More precisely still, the geometry of the ground plane 200 and that of the monopole 100 are adapted to reduce as much as possible the sizes and to optimize the shapes of the ground plane 200 as well as that of the coplanar monopole 100, so as to guarantee excitation by a line 110 coplanar characteristic impedance typical of telecommunications applications (ie in the range 50 Q - 70 Ω) over the largest possible bandwidth.

We have shown on the figure 4 an alternative embodiment in which the monopoly 100, of polygonal shape, is asymmetrical with respect to the plane OO, while the ground plane 200 remains symmetrical with respect to this plane OO. The monopoly 100 is delimited, starting from the feed line 110, by two rectilinear sections 140, 142 diverging with respect to the plane OO away from the ground plane 200, at different angles, two parallel sections 144, 146 between they and parallel to the plane OO which respectively extend the two sections 140, 142, and the aforementioned end edge 130. Each block 210, 220 of the ground plane 200 is itself delimited by an internal generator 240, an external generator 242 , parallel to each other and parallel to the plane OO (the internal generator 240 having a length substantially identical to the feed line 110), an end section 250 rectilinear and perpendicular to the plane OO, connected to the internal generator 240 and two straight sections successive 252 and 254, which connect the end portion 250 and the external generator 242, which sections 252 and 254 diverge relative to the monopole 100 away from the plane OO

The outer sections 242 are shorter than the inner sections 240. The sections 250, 252 and 254 define in combination a convex shape in the direction of the monopole 100.

According to figure 4 , the overall width of the ground plane 200, considered perpendicular to the plane OO is greater than the width of the monopoly 100.

The figure 5 represents an antenna variant that differs from that shown on the figure 4 by the fact that according to the figure 5 each inclined section 140, 142 of the monopole 100 is itself divided into two sections 1400, 1402 and 1420, 1422.

We have shown on the figure 6 another antenna variant that differs from that illustrated on the figure 5 by the fact that according to the figure 6 the directed edge of the ground plane directed towards the monopole defines a concave, and not convex, edge in the direction of the monopole 100. This concave edge is defined by a section 250 perpendicular to the plane OO, connected to the internal section 240 and extended by two auxiliary sections 256, 258 to the outer section 242. The first section 256 diverges with respect to the plane OO in the direction of the monopole 100. The second section 258 is perpendicular to the plane OO and joins the outer section 242.

We have shown on Figures 7 and 8 two variants of figures 3 and 6 , which differ from the latter in that the ground plane 200 has grooves or "corrugations" 260. More precisely according to the particular embodiment and not limiting illustrated on the Figures 7 and 8 each block 210, 220 of the ground plane 200 is provided with three rectilinear grooves 262, 263 and 264, parallel to each other and perpendicular to the plane O0, which open on the outer section 242. According to Figures 7 and 8 the grooves 260 are equidistant two by two. Their length decreases in approximation of the monopoly 100.

Such grooves 260 make it possible to lower the minimum operating frequency of the structure, which increases the compactness for a given frequency band. They also stop the electric currents that would tend to "leak" behind the ground plane 200 causing parasitic radiation or parasitic coupling with the power supply.

We have shown on the figure 9 an alternative embodiment, according to the present invention, which differs from the figure 5 in that monopoly 100 comprises grooves 160. More precisely according to the particular and nonlimiting embodiment illustrated in FIG. figure 9 , the monopole 100 is provided with three straight grooves 162, 163 and 164, parallel to each other and perpendicular to the plane OO, which open on the outer sections 144, 146. According to the figure 9 the grooves 160 are equidistant two by two. Their length increases in approximation of the ground plane 200.

Such grooves 160 also make it possible to lower the minimum operating frequency of the structure.

We have shown on the figure 10 another variant of embodiment that differs from the figure 4 in that a short-circuit 170 connects the monopole 100 and the ground plane 200. Specifically the short-circuit 170 is here formed of a rectilinear ribbon parallel to the plane OO, which connects the section 142 and the section 250 .

We illustrated on the figure 11 another variant embodiment, according to the present invention, which differs from the figure 6 by the presence of slot lines 174, 178 in the monopole 100 and slot lines 274, 278 in the ground plane 200.

According to figure 11 the slotted lines 174, 178 open onto the sections 144. The slot line 174 comprises a rectilinear section 175 perpendicular to the plane OO, which opens on a section 144, a rectilinear section 176 parallel to the plane OO and a rectilinear section 177 perpendicular to the plane OO, of length less than section 175. The three sections 175, 176 and 177 generally define a U-shaped configuration.

The slotted line 178 comprises a rectilinear section 179 perpendicular to the plane OO, which opens on the second section 144, and a rectilinear section 180 parallel to the plane OO, directed towards the section 130. The two sections 179 and 180 generally define an L-shaped configuration.

According to figure 11 the slot lines 274, 278 provided in the ground plane 200 have a geometry similar to that of the slot lines 174, 178 provided in the monopoly 100.

Thus, the slit line 274 comprises a rectilinear section 275 perpendicular to the plane OO, which opens onto a section 242, a rectilinear section 276 parallel to the plane OO and a rectilinear section 277 perpendicular to the plane OO, of length less than section 275. The three sections 275, 276 and 277 generally define a U-shaped configuration.

The slit line 278 comprises a rectilinear section 279 perpendicular to the plane OO, which opens on the second section 242, and a rectilinear section 280 parallel to the plane OO, directed towards the monopole 100. The two sections 279 and 280 generally define a configuration in FIG. L.

It will be noted that according to figure 11 the second sections 176, 276 are directed towards the opposite of the section 130 away from the section 175, 275 which opens respectively to the outside of the monopole 100 at the section 144 and at the outside of the ground plane 200 at the level of section 242.

Slotted lines 174, 178, 274 and 278 enable auxiliary modes of operation to be introduced into the structure.

We also illustrated on the figure 12 annexed, another variant embodiment, in accordance with the present invention, which differs from figure 3 in that slots, rings or holes are inserted in the monopole 100 or in the ground plane 200. Such slots, rings or holes make it possible to advantageously introduce secondary modes of resonance into the structure.

Such slots, rings or holes can be the subject of many variants and many combinations between them. For this reason, their geometry will not be described in detail later.

• une fente rectiligne 182 perpendiculaire au plan O-O, symétrique par rapport à celui-ci et qui couvre sensiblement 60% de la largeur du monopole 100,
• dans le monopole 100 une seconde fente en U 184, disposée entre la fente 182 et le tronçon extrême 130, la fente 184 comprenant un tronçon principal 185 perpendiculaire au plan O-O, symétrique par rapport à celui-ci et qui couvre sensiblement 50% de la largeur du monopole 100 pourvue à chacune de ces extrémités de tronçons auxiliaires 186,187, parallèles au plan O-O, dirigées vers le plan de masse 200 et dont la longueur est de l'ordre du tiers de la longueur du tronçon principal 185,
• dans le pavé 210 du plan de masse 200, un trou 282 de contour circulaire ayant un diamètre de l'ordre du tiers de la hauteur du pavé 210 considéré parallèlement au plan O-O, sensiblement centré sur ce pavé,
• dans le pavé 220 du plan de masse 200, un anneau 284 ayant une largeur de l'ordre de 1mm et un diamètre de l'ordre de la moitié de la hauteur du pavé 220 considéré parallèlement au plan O-O.

It will be noted, however, that the non-limiting variant embodiment illustrated on the figure 12 includes:

• a rectilinear slot 182 perpendicular to the plane OO, symmetrical with respect thereto and covering substantially 60% of the width of the monopole 100,
• in the monopole 100 a second U-shaped slot 184, disposed between the slot 182 and the end portion 130, the slot 184 comprising a main section 185 perpendicular to the plane OO, symmetrical with respect thereto and which covers substantially 50% of the width of the monopole 100 provided at each end of auxiliary sections 186, 187, parallel to the plane OO, directed towards the ground plane 200 and whose length is of the order of one third of the length of the main section 185,
• in the block 210 of the ground plane 200, a hole 282 of circular contour having a diameter of about one-third of the height of the block 210 considered parallel to the plane OO, substantially centered on this block,
• in the block 220 of the ground plane 200, a ring 284 having a width of the order of 1 mm and a diameter of the order of half the height of the block 220 considered parallel to the plane OO.

We have shown on the figure 13 , the antenna adaptation curve represented on the figure 3 , more precisely the standing wave ratio (ROS) as a function of frequency. We note in the examination of this figure 13 that the standing wave ratio remains below 2 between 1.8GHz and 6.1GHz and remains below 2.6 between 1.5GHz and 11GHz.

Such an antenna, of compact dimensions since they are of the order of 47mm × 37 mm × 1.5 mm, makes it possible to ensure ultra-wide band operation of 1.5 to more than 11 GHz, ie a ratio between the maximum frequency and the minimum frequency greater than 7.

The associated radiation patterns are represented on the figure 14 . They are characterized by a minimum of radiation on the OZ axis of the monopole coinciding with the plane OO, (characteristic sign a monopolar radius) as well as omnidirectional diagrams (at least up to 6GHz) on the cones having monopoly axis and directions which are generally between 60 ° and 120 ° around this axis with a maximum directivity which varies from 2 to 5dB.

This antenna is therefore an excellent candidate to be integrated into the transmission chain of future UWB systems.

Of course, the present invention is not limited to the particular embodiments which have just been described but extends to any variant within its spirit.

We have schematised on the figure 15 annexed, another variant embodiment that can be applied to the present invention according to which the monopole 100 and its associated supply line 110 as well as the ground plane 200 are provided on a first face 12 of the dielectric support 10 while the second face 14 of this dielectric substrate 10 carries an auxiliary ground plane 300 of electrically conductive material. The auxiliary ground plane 300 is connected to each of the two blocks 210, 220 forming the coplanar ground plane 200 of the monopole 100 via a plurality of electrically conductive pins 310 passing through the substrate 10.

In this context, the power supply of the antenna is made between the lower auxiliary ground plane 300 and the power supply line 110.

Finally, there is Figures 16 and 17 attached, other embodiments that can be applied to the present invention associating on the same printed circuit board, several coplanar antennas orthogonal to each other.

More specifically, there is shown on the figure 16 attached, a first embodiment comprising two coplanar antennas of the type described above, orthogonal to each other, while it has been shown on FIG. figure 17 annexed, another variant comprising four coplanar antennas of the type previously described orthogonal two by two, distributed in the form of a pair at two diagonally opposite corners of the substrate. Preferably, the diet of antennas according to the variants represented on the Figures 16 and 17 is provided between a ground plane provided on the lower surface 14 of the substrate 10 and the feed line 110.

REFERENCES

• Document [1]: SIBILLE A. et al. «Design and Characterization of ULB Antennas for High Speed Multimedia Communication» SEE - ULB Days, 58, June 19-20, 2003 .
• Document [2]: AMMANN MJ, Zhi Ning CHEN "Wideband Shorted Planar Monopoly with Bevel" IEEE Trans. on Antennas and Propagation, vol 51, No. 4, April 2003, pp 901 - 903 .
• Document [3]: AMMAN MJ Zhi Ning CHEN, "Wideband Monopoly Antennas for Multiband Wireless Systems" IEEE Antennas and Propagation Magazine, Vol 45, No. 2, April 2003, pp 146-150 .
• Document [4]: SONG CTP, HALLS PS, GHAFOURI-SHIRAZ H. "Perturbed Sierpinsky Multiband Fractal Antenna with Improved Feeding Technique" IEEE Trans. on Antennas and Propagation, Vol 51, No. 5, May 2003, pp1011-1017 .

Claims (16)

1. Antenna, notably for the broadcasting of high-bitrate services comprising:

   - a support (10) made of dielectric material, which bears the following elements produced in printed technology:

   - a monopole (100) linked to a power supply line of the coplanar guide type (110), and

   - a coplanar ground plane (200) consisting of two blocks (210, 220) situated respectively on either side of the power supply line (110), being separated therefrom,

   in which the monopole (100) is flared away from the ground plane (200) and the latter has a border (244-249; 250-254; 250-258) directed towards the monopole (100) which is not totally rectilinear, characterized in that said border of the ground plane is concave or convex towards the monopole, and characterized in that at least the monopole (100) comprises lines with slots (174, 178; 274, 278) and/or holes and/or rings introducing secondary resonance modes.
2. Antenna according to Claim 1, characterized in that the ground plane (200) comprises lines with slots (274, 278) and/or holes (282) and/or rings (284) introducing secondary resonance modes.
3. Antenna according to Claim 1 or 2, characterized in that said border of the ground plane (200) forms a point towards the monopole (100).
4. Antenna according to any one of Claims 1 to 3, characterized in that said border of the ground plane (200) has a continuous curvature.
5. Antenna according to any one of Claims 1 to 4, characterized in that said border of the ground plane (200) is delimited by a succession of rectilinear sections.
6. Antenna according to one of Claims 1 to 5, characterized in that the ground plane (200) has a polygonal overall form.
7. Antenna according to one of Claims 1 to 6, characterized in that the monopole (100) exhibits a symmetry relative to a plane passing through the power supply line (110).
8. Antenna according to one of Claims 1 to 6, characterized in that the monopole (100) is asymmetrical.
9. Antenna according to one of Claims 1 to 8, characterized in that the power supply line (110) is formed by a rectilinear strip.
10. Antenna according to one of Claims 1 to 9, characterized in that the support made of dielectric material (10) has an auxiliary ground plane (300) on its face opposite the monopole (100), which auxiliary ground plane (300) is linked to the ground plane (200) coplanar with the monopole by conductive pins (310) passing through the support.
11. Antenna according to one of Claims 1 to 10, characterized in that the border of the monopole (100) directed towards the ground plane (200) exhibits a continuous curvature.
12. Antenna according to one of Claims 1 to 10, characterized in that the border of the monopole (100) directed towards the ground plane (200) is defined by a series of successive rectilinear sections.
13. Antenna according to one of Claims 1 to 12, characterized in that the monopole (100) and/or the ground plane (200) comprise grooves (262, 263, 264; 162, 163, 164) which emerge on the flanks thereof.
14. Antenna according to one of Claims 1 to 13, characterized in that a short-circuit (170) links the monopole (100) and the ground plane (200).
15. Antenna according to one of Claims 1 to 14, characterized in that it comprises two coplanar orthogonal monopoles.
16. Antenna according to one of Claims 1 to 15, characterized in that it comprises four coplanar monopoles, in the form of two pairs of orthogonal monopoles positioned on opposite corners of the support (10).

Images