EP0714151B1 - Broadband monopole antenna in uniplanar printed circuit technology and transmit- and/or receive device with such an antenna - Google Patents

Description

The field of the invention is that of radio transmissions. More specifically, the invention relates to transmit and / or receive antennas, in particular for smaller equipment, such as portable devices.

The invention thus applies, in particular, to radiocommunication systems with mobiles. Indeed, the extension of radiocommunication networks with land mobile requires the development of portable autonomous stations having the dual functionality for transmitting and receiving microwave signals. These stations must therefore include an integrated antenna.

The frequencies currently used for these applications (of the order of 2 GHz), as well as various constraints linked to the ergonomics and aesthetics of combined (integration of the antenna in the design of the device, ease of storage and use, fragility of large antennas, ...) lead to use antennas of very reduced dimensions. We thus know several types of antennas, including the dimensions are less than the wavelength of the microwave signal.

These antennas are generally in the form of a radiating element installed outside a metal case, for example of rectangular shape, constituting the shielding of one or more electronic cards ensuring in particular modulation and demodulation functions of microwave signals, in transmission and in reception respectively.

A first known type of antenna is the half-wave doublet, that is to say a doublet of length λ / 2, with λ the operating wavelength.

The half-wave doublet, which generally consists of line elements two-wire (i.e. conductive cylindrical rods) supplied by a line power supply, has relatively broadband performance, which makes it usable in many applications.

However, several drawbacks are linked to its use. Indeed, the lines supply lines (for example coaxial lines) are generally asymmetrical, so that the radiating elements are symmetrical. Therefore, so that the radiation half-wave doublet is acceptable, a balun should be used. A balun traditionally presents itself as a transformer involving localized or distributed impedances, and allowing, when placed between an element radiating symmetrical and an asymmetrical power line, making the currents symmetrical on the radiating structure. Such a balun has the disadvantage major to require always a delicate development.

We also know half-wave doublets which are self-symmetrized, so be able to be used without a balun. However, due to the use of rods conductive cylindrical, such an autosymmetry characteristic cannot be obtained that at the cost of increased complexity of the antenna structure.

Finally, in general, the half-wave doublets with cylindrical rods have difficult mechanical handling and too much space important (although reduced), the minimum length of the antenna being imposed by the length of the main strands, about λ / 2.

As noted earlier, the reduction in footprint has become a essential objective for antenna designers.

A second type of antenna, even more compact than the half-wave doublet, therefore has been designed. This is the inverted F antenna, which consists of a conductive element horizontal rectangular and a vertical rectangular conductive element. The element vertical ensures a short circuit function on the horizontal element, by connecting one of its ends to a ground plane. The length of the horizontal element is generally L = λ / 4. In other words, the horizontal element is placed in a plane parallel to the plane of mass and at a height h thereof.

Thus, for frequencies of the order of 2 GHz, these dimensions are of the order a few centimeters. The antenna obtained is therefore very compact (its minimum length is λ / 4 instead of λ / 2 for the half-wave doublet).

However, this antenna has very dispersive characteristics in frequency, and therefore, consequently, a very low bandwidth, and for example of in the range of 2 to 3%. This is due to the fact that this antenna structure behaves much like a λ / 4 resonator.

The bandwidth of an antenna is here defined as the frequency band on which the Stationary Wave Ratio (R.O.S) is less than 2. This last parameter represents the ability of the antenna to transmit the active power supplied to it, this which is most critical for small antennas.

This quantity is directly related to the input impedance of the antenna, which must be adapted to the impedance of the transmission line carrying the microwave signal to send and / or receive. For optimal functioning of the antenna, it is necessary that this impedance remains substantially constant (i.e. the R.O.S remains lower at 2, an R.O.S. equal to 1 corresponding to a perfect adaptation) over a large band of frequency. A bandwidth of 2 to 3% as obtained using an F-antenna is generally insufficient.

Furthermore, document US 4,825,220 describes a radiating element comprising a dipole integrated into a "balun" structure. The ground plane of the line of unbalanced micro ribbon transmission is divided by a central slot so as to form a balanced transmission line acting with the slot located between part of the arms of the dipole formed. The ground plane is used as such on a part of the microstrip supply line.

The invention particularly aims to overcome the drawbacks of the various known types of antenna, including those of half-wave dipoles and F-shaped antennas reversed.

More specifically, an objective of the invention is to provide an antenna small footprint with a large pass. Thus, the invention has in particular aims to provide such an antenna, whose bandwidth is at least of the order from 20 to 30% and having a reduced bulk especially in relation to an antenna in inverted F.

The invention also aims to provide a self-symmetrized antenna, and does not therefore requiring no balun.

The invention also aims to provide such an antenna, which can operate over a wide range of input impedances, and in particular for input impedances between 10 and 200 Ohms.

These objectives, as well as others that will appear later, are achieved according to the invention using a signal transmitting and / or receiving antenna The microwave described by claim 1.

The antenna of the invention is therefore produced in printed technology, which allows considerable space savings and much easier mechanical maintenance.

Furthermore, the main surface of the conductive deposit, constituting a plane of ground for the supply line, ensures that the supply is autosymmetrized. In in other words, the antenna according to the invention does not require the joint use of a balun.

The supply line feeds the radiating strand through the slit coupling.

The antenna according to the invention is based in particular on a new adaptation and inventive of the inverted F antenna. Indeed, the two-dimensional configuration of the inverted F antenna was projected in a single plane containing the entire antenna. In in other words, the radiating strand and the ground plane are no longer in two planes separate parallels, but in the same plane. Compared to the inverted F antenna, the antenna of the invention is therefore much more compact since it overcomes the height h between the radiating strand (or horizontal conducting element) and the ground plane.

In addition, the antenna of the invention has a much wider bandwidth than that of an inverted F antenna. This is explained in particular by the fact that for the inverted F antenna, the radiating strand is located just above the ground plane and forms with this a cavity which is very selective in frequency (generally 2 to 3% of bandwidth). On the other hand, in the case of the invention, the ground plane and the strand radiating are located in the same plane, so the cavity effect is much less marked. This achieves bandwidths close to 25%, and simultaneously cover the transmit band and the receive band.

Advantageously, said supply line and said coupling slot are cross at a point called cross point, said supply line having a end portion, or series stub, extending beyond said crossing point of a first adaptable length, and said coupling slot having a portion end, or parallel stub, extending beyond said crossing point by one second adaptable length.

Thus, it is possible to implement the known principle of double adaptation stubs (series and parallel). A suitable choice of these series and parallel stubs, and possibly other parameters (width of the radiating strand, width of the slit coupling, thickness of the conductive deposition link part connecting the radiating strand to the main surface, position of the supply line in relation to the connecting part conductive deposition) allows the antenna to be adapted over a wide bandwidth.

Preferably, at least one of the elements belonging to the group comprising said radiating strand, said main surface, and said coupling slot, is shaped substantially rectangular.

Advantageously, said conductive deposit comprises at least two strands radiant, the longitudinal space between each of said radiating strands and said main surface forming a separate coupling slot.

• une diversité de polarisation, en associant la ligne d'alimentation à un diviseur;
• une polarisation circulaire, en associant la ligne d'alimentation à des diviseurs et des déphaseurs.

Thus, we can obtain:

• a diversity of polarization, by associating the supply line with a divider;
• circular polarization, by associating the supply line with dividers and phase shifters.

Advantageously, the antenna comprises at least two feed lines, each of said radiating strands cooperating with one of said supply lines.

In this way, a duplex multiband antenna can be obtained.

Preferably, said radiating strand has at least one bend, so that said radiating strand extends at least partially along at least two sides of said main surface.

In this way, the overall size of the antenna is limited since the minimum antenna dimension is no longer linked to the total length of the radiating strand but only along the sides of the main surface of the conductive deposit.

Preferably, said radiating strand has a variable width. So, the bandwidth of the antenna is increased.

Advantageously, said radiating strand exhibits at least one offset on the at least one of the longitudinal edges and / or at least one light on its surface. The light on the surface of the radiating strand is for example a slot.

In an advantageous embodiment of the invention, the antenna comprises also a ground plane placed at a predetermined distance from said line Power.

If the ground plane is without radiating element, it makes it possible to remove the stray radiation from the power line and get radiation in a half space only

According to an advantageous variant, said ground plane is a conductive deposit of same shape as that located on the second face of said substrate plate, comprising a main surface and at least one radiating strand.

In this case, the ground plane makes it possible to obtain a symmetrical radiation of each side of the antenna.

Preferably, said supply line has an impedance substantially between 10 Ohms and 200 Ohms.

Advantageously, the length of said radiating strand is substantially understood between λ / 8 and λ / 4, λ being the wavelength of said microwave signals.

The invention also relates to a device for transmitting and / or receiving microwave signals, comprising at least one antenna as described above.

• les figures 1A et 1B présentent chacune une vue, respectivement de dessus et de côté, d'un premier mode de réalisation d'une antenne selon l'invention ;
• la figure 2 est une vue détaillée partielle de l'antenne présentée sur la figure 1A ;
• la figure 3 présente une courbe de variation, en fonction de la fréquence, du rapport d'onde stationnaire pour un exemple d'antenne selon l'invention ;
• la figure 4 est un diagramme de Smith présentant la courbe d'impédance correspondant à un exemple d'antenne selon l'invention ;
• les figures 5, 6 et 7 présentent chacune une vue de dessus d'un mode de réalisation distinct (second, troisième et quatrième respectivement) d'une antenne selon l'invention.

Other characteristics and advantages of the invention will appear on reading the following description of several preferred embodiments of the invention, given by way of non-limiting example, and the accompanying drawings, in which:

• FIGS. 1A and 1B each show a view, respectively from above and from the side, of a first embodiment of an antenna according to the invention;
• Figure 2 is a partial detailed view of the antenna shown in Figure 1A;
• FIG. 3 shows a variation curve, as a function of frequency, of the standing wave ratio for an example antenna according to the invention;
• FIG. 4 is a Smith diagram showing the impedance curve corresponding to an example of antenna according to the invention;
• Figures 5, 6 and 7 each show a top view of a separate embodiment (second, third and fourth respectively) of an antenna according to the invention.

The invention therefore relates to a reduced-size antenna with wide bandwidth. This antenna is in particular intended to equip portable devices, and for example transmitters / receivers of radiocommunication networks with land mobiles.

FIGS. 1A and 1B, which are respectively a top view and a view of side, illustrate a first embodiment of the invention.

In this embodiment, the antenna comprises a substrate plate 1 (not shown in FIG. 1), a supply line 2 and a conductive deposit 3.

The substrate plate 1 is for example a low loss Duroid substrate of the teflon glass type having a relative permittivity ε _r = 2.2 and a reduced thickness of 0.76 mm.

The supply line 2 is located on a first face (the lower face by example) of the substrate plate 1. This is for example a microstrip line.

The conductive deposit 3, for example of copper, is located on a second face (the upper side for example) of the substrate plate 1 and can decompose (fictitiously, since it is in practice made in one piece) in three parts: a main surface 4, an intermediate part 5 and a radiating strand 6.

The main surface 4 (rectangular in this example) of the conductive deposit 3 constitutes a ground plan for the supply line 2 located on the other side of the substrate plate 1. The antenna therefore generates symmetrical currents on the strand radiating 6. In other words, the antenna of the invention is autosymmetrized.

In this example, the radiating strand 6 is rectangular and has a first end connected to the main surface 4 of the conductive deposit 3 by the intermediate part 5, and a second free end extending partially along one side of the surface main 4 of the driver depot 3.

The length of the radiating strand 6 is close to λ / 4, with λ the wavelength the antenna.

Thus, the antenna of the invention, which is planar and whose maximum length is λ / 4, has a smaller footprint than that of a dipole of length λ / 2 or else than that of an inverted F antenna of length λ / 4 but whose radiating strand is spaced a height h from the ground plane.

The antenna of the invention not only has a very small footprint but also a large bandwidth. Indeed, the main surface 4 of the depot conductor 3 behaves like a ground plane, especially with respect to the line supply 2 and the coupling slot 7, and very little vis-à-vis the radiating strand 6, this which greatly reduces the selectivity of the antenna. In addition, the cavity effect (and therefore the antenna selectivity) is much less marked than for an inverted F antenna since the ground plane (that is to say the main surface 4 of the conductive deposit 3) and the radiating strand 6 are located in the same plane.

In general, the antenna according to the invention has a bandwidth of 20 to 30% and can be easily incorporated inside an ultra-light portable handset.

The longitudinal space between the radiating strand 6 and the main surface 4 of the conductive deposit 3 forms a coupling slot 7 through which the supply line 2 supplies the radiating strand 6.

In the example shown in FIG. 1A, the coupling slot 7 is also rectangular.

Figure 2 is a partial detailed view of the antenna shown in Figure 1A.

• la longueur l₁ d'un stub série, le stub série étant la portion d'extrémité de la ligne d'alimentation 2 qui dépasse du point de croisement 9 entre la ligne d'alimentation 2 et la fente de couplage 7 ;
• la longueur l₂ d'un stub parallèle, le stub parallèle étant la portion d'extrémité de la fente de couplage 7 qui dépasse du point de croisement 9 ;
• la largeur e₁ du brin rayonnant 6 ;
• la profondeur p de la fente de couplage 7 ;
• la largeur g de la fente de couplage 7 ;
• l'épaisseur e₂ de la partie intermédiaire 5 reliant le brin rayonnant 6 la surface principale 4 ;
• la distance e_p entre la ligne d'alimentation 2 et la partie intermédiaire 5.

In order to fine-tune the antenna and to adjust its bandwidth in particular, several parameters can be modified, and in particular:

• the length l ₁ of a series stub, the series stub being the end portion of the supply line 2 which protrudes from the crossing point 9 between the supply line 2 and the coupling slot 7;
• the length l ₂ of a parallel stub, the parallel stub being the end portion of the coupling slot 7 which protrudes from the crossing point 9;
• the width e ₁ of the radiating strand 6;
• the depth p of the coupling slot 7;
• the width g of the coupling slot 7;
• the thickness e ₂ of the intermediate part 5 connecting the radiating strand 6 to the main surface 4;
• the distance e _p between the supply line 2 and the intermediate part 5.

Thus, although produced in printed technology, the antenna of the invention includes a serial stub and a parallel stub. These series and parallel stubs allow adaptation of the antenna according to the known principle of double stub adaptation, on a wide frequency band.

FIG. 3 presents a variation curve, as a function of the frequency, of the standing wave ratio (or ROS) for an example of antenna according to the first mode of embodiment of FIGS. 1A and 2.

• l₁ = 13 mm ;
• l₂ = 22,6 mm ;
• e₁ = 5 mm ;
• e₂ = 6 mm ;
• g = 5 mm ;
• e_p = 1,65 mm ;
• p = 24,25 mm.

In this example, the antenna parameters have the following values:

• l ₁ = 13 mm;
• l ₂ = 22.6 mm;
• e ₁ = 5 mm;
• e ₂ = 6 mm;
• g = 5 mm;
• e _p = 1.65 mm;
• p = 24.25 mm.

This curve is used to calculate the bandwidth [f1, f2], defined here as the frequency band for which the ROS remains below 2. This bandwidth can also expressed as a percentage, obtained by dividing the width (f2, f1) of the bandwidth by the central frequency f3 of this band.

In the above example, the bandwidth is substantially between f1 = 1.823 GHz and f2 = 2.333 GHz.

With a center frequency f3 = 2.078 GHz, this bandwidth is approximately equal to 25%. The antenna according to the invention therefore has a bandwidth wide enough to simultaneously cover the transmission band and the transmission band reception.

Figure 4 presents a variation curve, in a Smith chart, of the input impedance for the previous antenna example. Remember that if there is a loop around the center of the abacus (which is the point of perfect adaptation with respect to 50 Ω power line), this guarantees low frequency dispersion and reflects the effectiveness of adaptation.

It should be noted however that the antenna is not, in this example, perfectly optimized. Indeed, better centering of the loop relative to the center of the abacus Smith would increase the performance of the antenna.

In this example, the impedance of the power line carrying the HF signal to was set at 50 Ω, but this value does not constitute a characteristic decisive, because the input impedance of the antenna according to the invention can take any value between 10 and 200 Ω.

FIG. 5 presents a top view of a second embodiment of the antenna according to the invention. This second embodiment differs from the first in that that the radiating strand 6 has an elbow 51 and extends along two sides of the main surface 4 of the conductive deposit 3. Thus, the overall size of the antenna is further reduced. If the length of radiating strand 6 is equal to λ / 4, we can, by creating a elbow 51 at mid-length, reach dimensions close to λ / 8. It is clear that the elbow 51 is not necessarily in the center of the radiating strand 6, or else that the radiating strand 6 may include more than one bend, so as to extend along more than two sides of the main surface 4.

FIG. 6 presents a top view of a third embodiment of the antenna according to the invention. This third embodiment differs from the first in that the radiating strand 6 has a variable width over its length. This width variable, when chosen appropriately, increases bandwidth of the antenna. In the example shown in Figure 6, the radiating strand 6 has a recess 61, 62 on each of its longitudinal edges. It should be noted that in other embodiments, the radiating strand 6 may have a slit in the middle, or have several recesses on each of its longitudinal edges, or present one or more recesses on only one of its longitudinal edges.

Figure 7 shows a top view of a fourth embodiment of the antenna according to the invention. In this fourth embodiment, the antenna comprises several radiating strands 6 _A , 6 _B , 6 _C , 6 _D (four in this example). Each radiating strand 6 _A , 6 _B , 6 _C , 6 _D is connected to the main surface 4 by an intermediate part 5 _A , 5 _B , 5 _C , 5 _D , and each longitudinal space comprised between a radiating strand 6 _A , 6 _B , 6 _C , 6 _D and the main surface 4 forms a separate coupling slot 6 _A , 6 _B , 6 _C , 6 _D.

Depending on the applications, the radiating strands 6 _A , 6 _B , 6 _C , 6 _D may or may not be identical.

Likewise, a single supply line can supply all the radiating strands 6 _A , 6 _B , 6 _C , 6 _D , or else several supply lines can be used. Thus, by increasing the number of feed lines and by associating each of the radiating strands with a separate feed line, it is possible to obtain a duplex multiband antenna.

In the example presented in FIG. 7, the antenna comprises means 71 for shaping the HF signals received from a main supply line (not shown) and to be transmitted on the various secondary supply lines 2 _A , 2 _B , 2 _C , 2 _D associated with the different radiating strands 6 _A , 6 _B , 6 _C , 6 _D.

• soit de la diversité de polarisation linéaire, si les moyens 71 comprennent un diviseur ;
• soit de la polarisation circulaire, si les moyens 71 comprennent des diviseurs et des déphaseurs.

These means 71 make it possible to obtain:

• either of the linear polarization diversity, if the means 71 comprise a divider;
• or circular polarization, if the means 71 comprise dividers and phase shifters.

The elements (dividers, phase shifters) constituting the means 71 for shaping signals can be produced by different lengths of supply lines, by hybrid rings, or by any other solution known to those skilled in the art profession and performing the desired function.

It is clear that many other embodiments of the invention can be considered. The antenna may for example include another ground plane, placed at a predetermined distance from the supply line and separated from it by air or by a dielectric. In the latter case, the antenna comprises the successive layers following: a ground plane, a dielectric, a supply line, a plate substrate and a conductive deposit. The role of the additional ground plane is for example remove stray radiation from the power line and obtain a radiation in half a space only.

It can also be provided that the additional ground plane is produced under form of a conductive deposit also comprising a main surface and a strand radiating associated with a slit. In this case, we obtain a symmetrical radiation of each side of the antenna.

The characteristics of the various embodiments presented above can also be combined in multiple ways to provide even more embodiments of the antenna of the invention. So, for example, a strand radiating can have a variable width and extend on two sides of the surface main of the driver's depot.

The invention also relates to any device for transmitting and / or receiving microwave signals equipped with an antenna according to the invention. Possibly, such device can comprise several antennas, and in particular a transmitting antenna and a receiving antenna.

Claims (13)

1. Transmitting and/or receiving antenna for microwave signals, comprising:

   a substrate plate (1);

   at least one feeder (2; 2_A to 2_D) located on a first face of said substrate plate;

   a conductive deposition (3) deposited on a second face, opposite to said first face of said substrate plate (1) so as to define:

   a principal surface (4) forming the ground plane for said feeder (2; 2_A to 2_D);

   at least one radiating strand (6; 6_A to 6_D) comprising a first end connected to said principal surface (4) and a second free end extending at least partially along at least one side of said principal surface (4);

   characterised in that a longitudinal space between each of said radiating strands (6; 6_A to 6_D) and said principal surface (4) forms a coupling slot (7; 7_A to 7_D) with one feeder.
2. Antenna according to Claim 1, characterised in that said feeder (2; 2_A to 2_D) and said coupling slot (7; 7_A to 7_D) intersect at a point termed the crosspoint,
   in that said feeder(2; 2_A to 2_D) has an end portion, or series stub, extending beyond said crosspoint, of a first adaptable length,
   and in that said coupling slot (7; 7_A to 7_D) has an end portion, or parallel stub, extending beyond said crosspoint, of a second adaptable length.
3. Antenna according to any of Claims 1 and 2,
   characterised in that at least one of the elements belonging to a group comprising said radiating strand (6; 6_A to 6_D), said principal surface (4), and said coupling slot (7; 7_A to 7_D), is of a substantially rectangular shape.
4. Antenna according to any of Claims 1 to 3, characterised in that said conductive deposition (3) comprises at least two radiating strands (6_A to 6_D), the longitudinal space between each of said radiating strands and said principal surface forming a distinct coupling slot (7_A to 7_D).
5. Antenna according to Claim 4, characterised in that it comprises at least two feeders (2_A to 2_D), each of said radiating strands (6_A to 6_D) co-operating with one of said feeders.
6. Antenna according to any of Claims 1 to 5, characterised in that said radiating strand (6; 6_A to 6_D) has at least one elbow (51), so that said radiating strand extends at least partially along at least two sides of said principal surface (41).
7. Antenna according to any of Claims 1 to 6, characterised in that said radiating strand (6; 6_A to 6_D) has a variable length.
8. Antenna according to Claim 7, characterised in that said radiating strand (6; 6_A to 6_D) has at least one offset (61, 62) on at least one of the longitudinal edges and/or at least one opening, for example a slot, on its surface.
9. Antenna according to any of Claims 1 to 8, characterised in that it also comprises a supplementary ground plane superimposed at a predetermined distance from said feeder, said supplementary ground plane not forming any radiating element and allowing a radiation from the antenna to be obtained in a unique semi-space.
10. Antenna according to any of Claims 1 to 8, characterised in that it also comprises a supplementary ground plane superimposed at a predetermined distance from said feeder, said supplementary ground plane being a conductive deposition of the same shape as that situated on the second face of said substrate plate, comprising a principal surface and at least one radiating strand, said supplementary ground plane allowing a radiation from the antenna to be obtained that is symmetrical on each side of the antenna.
11. Antenna according to any of Claims 1 to 10,
    characterised in that said feeder (2; 2_A to 2_D) has an input impedance that is substantially between 10 Ohms and 200 Ohms.
12. Antenna according to any of Claims 1 to 11,
    characterised in that the length of said radiating strand (6; 6_A to 6_D) is substantially between _/8 and _/4, _ being the wavelength of said microwave signals.
13. Transmitting and/or receiving device for microwave signals, characterised in that it comprises at least one antenna according to any of Claims 1 to 12.

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