EP1225654A1 - Multiband antenna for portable devices - Google Patents

Abstract

The invention relates to an antenna (1) of a radiocommunication device, comprising two radiant conductive planes (2, 5) electrically connected (4), a slot (3) in at least one of the planes, a supply link (6 ) arranged on one of the planes and a short-circuit link (7) connected to a ground (8), arranged on the same conductive plane as the supply link. The invention also relates to a radiocommunication device in which an antenna according to the invention is placed. The invention also relates to a method of manufacturing such an antenna, comprising in particular a step of cutting a slot in a metal sheet and a step of folding the metal sheet by superimposing two parts of this sheet. <IMAGE>

Description

The invention relates to antennas produced using the patch technique. Such an antenna is typically used in a spectral range including the radiofrequencies and microwaves.

Most antennas have a resonant frequency band. In transmission, when the antennas are excited in this frequency band by a power line, they maintain electromagnetic waves stationary. These standing waves are then coupled to waves electromagnetic radiation in space. In reception, the waves take the same shapes but travel in the opposite direction. Different antennas of this type are known in the state of the art.

It is known to use microstrips on a plane as an antenna for transmit signals. There are conductive pads on the upper side of a dielectric substrate and a conductive layer is placed on the underside of the substrate. The substrate typically has a rectangular planar shape and thickness constant.

A multi-band antenna is also described in document FR-A-2 772 518. This antenna comprises a flat patch placed on the surface top of a dielectric substrate. A layer of mass is placed on the lower surface of the dielectric substrate. This antenna is of the quarter wave type because a short circuit conductor, disposed on a wafer of the dielectric substrate, connects the pellet to the mass layer. This antenna has conductors connection allowing the transmission of signals between the antenna and a device signal processing.

A publication presented at the Davos AP 2000 conference by Ollikainen, Kivekäs, Toropainen and Vainikainen, reports on a multi-band antenna. This antenna comprises three pellets placed on the upper surface of a substrate in Styrofoam (registered trademark). A mass layer is placed on the surface bottom of the dielectric substrate. A first patch intended for the low band is attached to a second patch intended for the upper band. These two lozenges thus form a first bi-band element having a zigzag shape and comprising a diet. This dual-band element has a short circuit in the form of a junction with the ground layer. A third patch is positioned next to the second patch to obtain a double resonance in the upper band, with a widened bandwidth. The third patch has a short circuit in the form of junction with the mass.

The document Novel meandered planar inverted F-antenna for triple frequency operation published in Microwave and optical technology letters page 58, volume 27 N ° 1 of October 5, 2000, describes a multi-band antenna. This antenna presents three pastilles placed in the same plane as a mass, following a pattern "meandering". These three lozenges contain a single feed.

These antennas have drawbacks. On the one hand, they require large flat pads, incompatible with reduced dimensions cases of mobile communication devices. On the other hand, these antennas require the mounting of capacitive loads to widen the bandwidth which increases the cost and complexity of the antenna. In addition, these antennas require the most often to be fed by their center to present a good level of adaptation.

In addition, these antennas have a number of frequency bands of limited resonance and whose bandwidth is also limited, and only deal thus not all the frequency bands used for the transmission of information. It may therefore be necessary to equip devices with different antennas according to their country of use. They also do not allow easy adjustment of the resonant frequencies and the bandwidths of these frequencies.

There is therefore a need for an antenna which resolves these different problems.

The invention relates to an antenna comprising two conducting planes radiant electrically connected, a slit in at least one of the planes radiant conductors, a supply link arranged on and connected physically at one of the planes, a short circuit link, arranged and connected physically on the same conductive plane as the supply link.

According to a variant, the conductive planes are electrically connected by a of their edges.

According to another variant, the slot, the short-circuit connection and the connection supply are arranged in the same conductive plane.

According to yet another variant, the conductive planes are formed of a sheet folded metal.

According to yet another variant, the supply link is a tongue formed in the metal sheet.

According to another embodiment, the short-circuit link is a tongue formed in the metal sheet.

According to a variant, the slot extends over the two conducting planes.

According to another variant, the conducting planes have dimensions different.

According to yet another embodiment, the antenna comprises a substrate dielectric disposed between the two conducting planes.

Alternatively, the antenna includes a dielectric substrate disposed between one of the conducting planes and a mass.

According to another variant, at least one of the substrates is produced with a material with a relative permittivity of less than 2.

According to yet another variant, at least one of the substrates is produced with a material having a dissipation factor of less than 10 ^-3 .

The antenna can also have at least two resonance bands, one of the two resonance bands being formed by two resonance frequencies complementary.

Alternatively, the antenna has at least three resonance bands.

The invention also relates to a radiocommunication device. comprising an antenna according to the invention, and has a thickness less than 20mm, a length less than 120mm and a width less than 50mm.

The invention further relates to a method of manufacturing an antenna. comprising a step of cutting from a metal sheet a slot, a supply link, a short circuit link and a step of folding the sheet metallic by superimposing two parts of this sheet.

According to a variant, the method further comprises a step of carrying out a plane electrical connection between the two conducting planes, by making two folds substantially parallel in the sheet.

• figure 1, une vue en perspective d'une antenne selon un premier mode de réalisation de l'invention;
• figure 2, une vue de dessus de l'antenne de la figure 1 dont les plans conducteurs sont alignés;
• figure 3, représente une vue en perspective d'une antenne selon un deuxième mode de réalisation de l'invention;
• figure 4, représente un diagramme de spectre des fréquences de réflexion typique d'une antenne selon le deuxième mode de réalisation;
• figure 5, représente une vue de dessus d'une antenne de test dont les plans conducteurs sont alignés;
• figure 6, un diagramme de spectre des fréquences de réflexion en entrée de l'antenne de la figure 5;

Other characteristics and advantages of the invention will appear on reading the following description of embodiments of the invention, given by way of example and with reference to the appended drawings which show:

• Figure 1, a perspective view of an antenna according to a first embodiment of the invention;
• Figure 2, a top view of the antenna of Figure 1 whose conductive planes are aligned;
• Figure 3 shows a perspective view of an antenna according to a second embodiment of the invention;
• FIG. 4 represents a spectrum diagram of the reflection frequencies typical of an antenna according to the second embodiment;
• Figure 5 shows a top view of a test antenna whose conductive planes are aligned;
• FIG. 6, a spectrum diagram of the reflection frequencies at the input of the antenna of FIG. 5;

The invention proposes an antenna in which a first is superimposed conductive plane with a slot, a second conductive plane, the two planes being electrically connected.

The following antenna will be described in its operation as a transmitter, in which it transforms an electric current into an electromagnetic field. he It will be clear to those skilled in the art that the operation of the antenna in receiver is similar, an electromagnetic field being transformed into current electric by antenna.

Figure 1 shows a perspective view of an antenna according to a first embodiment of the invention. Figure 2 shows the same antenna when the conducting planes are aligned in the same plane. The antenna 1 presents a first radiating conductive plane 2, in which a slot 3 is produced from one of the edges of this plane. On the opposite edge, an electrical connection 4, produced here by a conductive strip of defined width, electrically connects the foreground radiating conductor 2 and a second plane radiating conductor 5. The second conductive plane is superimposed on the conductive foreground as it is represented in FIG. 1. The superposition of the conducting planes 2 and 5 makes it possible to reduce the surface area of the antenna compared to the antennas of the prior art.

The first conductive plane has a supply link 6 and a short-circuit link 7 connected to ground 8. More specifically, the link supply 6 and short-circuit link 7 are in physical contact with at minus one of the conductive plans.

The supply link 6 is usually connected on the other hand, to a signal generation and processing device, not shown, which sends a signal in the form of electric current.

A first resonance mode is obtained by means of the slot 3, insulating two edges of the foreground radiating conductor 2. An electric current bypasses this slit. The electrical path starts from the short-circuit connection to the radiation area 21 indicated in phantom in Figure 2. A field electromagnetic is generated by induction at the radiation area 21. The wavelength of this electromagnetic field is therefore determined by the length of this slot, that is to say its largest dimension. This resonance is quarter-wave type because the short-circuit connection requires a field node electric. Thus, the length of the electrical path is of the order of λ / 4, λ being the radiated wavelength.

A second mode of resonance is obtained by means of the second plane radiant conductor superimposed on the first. The second driver plane is excited on the one hand by electromagnetic coupling with the first conducting plane, and on the other hand by direct electrical coupling with this same plane via the electrical connection 4. Thus, a quarter wave type resonance is generated in the second driver plane. The electromagnetic field is mainly generated at the level of the radiation zone 22. This resonant frequency is determined by the dimensions of the first and second conductive plane. So the length to consider, to determine the resonant frequency of this mode, roughly corresponds to the distance between the short circuit connection and the area of radiation 22. The conductive plane being short-circuited by means of the link 4 and short-circuit link 7, the dimensions of the antenna can thus be reduced for a given resonant frequency. In addition, as the plan conductor 5 is superimposed on the conductor plane 2, the surface area of the antenna is reduced.

A third resonance mode is generated in the foreground conductor by means of the combination of the supply link and the link short circuit. Indeed, the supply link 6, by virtue of its arrangement, excites directly the first conducting plane 2 which, by radiating, in turn excites the slot 3 and the second conductive plane 5.

The mass provides a quarter wave type resonance by imposing a node electric field at the short circuit and a belly at the edge opposite, i.e. at the level of the radiation area 23. The largest dimension of the conducting plane, i.e. the distance between the short-circuit connection and the radiation area 23, is of the order of a quarter of the wavelength radiated.

The covering of the radiation area 23 of the first conducting plane by the second conducting plane strongly influences the values of the frequencies f2 and f3 by electromagnetic coupling of the two conducting planes. So the superposition of the radiating zones of the two conducting planes 2 and 5 causes appreciable modifications of the values of the frequencies f2 and f3 compared to the values obtained from the quarter wave model.

In the embodiment shown in Figures 1 and 2, a second conductive plane of dimension substantially different from the dimension of the leading driver. Using a second conductive plane of dimensions close to those of the first conducting plane, we obtain a second frequency of resonance distant from the third resonance frequency. With dimensions of appropriate slot, three separate resonant frequencies can be obtained. We thus increases the number of frequency bands in which the antenna can issue. In contrast, using a second conductive plane of dimensions reduced, we get a second resonant frequency close to the third resonant frequency.

In the embodiment shown in Figures 1 and 2, the planes conductors are connected by the electrical connection 4. This connection 4 is thus arranged on an edge of the conducting planes 2 and 5. It is here formed of a metal strip of a defined width. This type of connection, produced on the edges of the conducting planes, is easier to manufacture, in particular by the method described below. However, in the context of the invention, it is also possible to make the electrical connection between the conductive planes elsewhere than by their edge. We can also connect at suitable points in their central areas.

The width of the electrical connection 4 has an influence on the values of the resonance frequencies f2 and f3. Thus by reducing the width of the link 4, the resonance frequencies f2 and f3 decrease. The location of link 4 on the width of planes 2 and 5 also has an influence on the value of the frequency of resonance f2. The farther the link 4 is removed from the short-circuit link 7, the more frequency f2 decreases.

The power supply link is coupled to a transmitter or a signal processing by a connection line not shown. We can make this connection for example using a coaxial cable. In order to avoid parasitic reflections of the signals between the supply link and the transmitter by example it is better to have a uniform impedance along the line of connection. For this, it is useful that the connection link is formed of a tongue starting from a conducting plane and extending to form the line of connection.

Furthermore, to have an optimal gain, i.e. a ratio between the signal strength radiated by the antenna and signal strength transmitted by the transmitter, it is desirable that the input impedance presented by the antenna is equal to the output impedance of the transmitter or signal processing device. Preferably, this impedance is fixed at 50 ohms to obtain losses minimum.

To improve the gain and facilitate the manufacture of the antenna, it is also preferable to have the supply link and / or the short-circuit link on the edges of conductive planes. By placing the short-circuit connection on one of the edges of the antenna, a zero electric field is imposed at this point. We can thus impose quarter-wave operation on the antenna. By arranging the link feed on an edge of a conducting plane, the level is increased adaptation.

There is also preferably the supply link 6 and the link short-circuit 7 on the same conductive plane. We can thus better control the input impedance of the antenna. By modifying the relative position of the link power supply in relation to the short-circuit link, the resonant frequencies as well as adaptation levels. For this, we place the links 6 and 7 at appropriately chosen locations.

FIG. 3 shows a second embodiment of an antenna according to the invention. A substrate 9 is arranged between the second conductive plane 5 and the first conductive plane 2. This substrate provides mechanical strength to the conductive planes. This substrate can also be used to maintain the conductive layers at a fixed distance from each other. It is desirable to choose a substrate material whose relative permittivity is close to that of air, preferably less than 2. We will also preferably choose a material having a very low dissipation factor and more particularly a lower dissipation factor at 10 ^-3 . The gain of the antenna is thus improved. It is thus possible to produce the substrate 9 in foam such as a polymethacrylimide foam. Such foam provides good mechanical strength.

A substrate 10 can also be placed between one of the layers conductive and a flat mass 8. So as to allow the folding of a tab of mass return, a substrate 10 is used whose edge is at the same level or in setback from an edge of the leading plane 2, as is shown in Figure 3. The mounting of the antenna is thus simplified. To improve the gain, it is also desirable to make such a substrate with a material whose relative permittivity is close to that of air, preferably less than 2. We will also preferably choose a material with a very low factor of dissipation. One can for example use materials similar to those described for the substrate 9. A thickness of substrate is preferably chosen which allows tune frequencies and expand bandwidths. The thickness of the substrate 10 is limited by the dimensions of the radiocommunication device.

In the embodiment of Figure 3, the slot extends over substantially the entire length of the foreground conductor. The resonance frequencies f2 and f3 are close enough. Thus, resonance f2 is complementary to resonance f3 to form a frequency band of greater bandwidth. As the slot 3 extends substantially over the entire length of the conducting plane 2, the frequency resonance f1 will be approximately half the frequency f3.

In the embodiments shown, the slot 3 has a shape rectangular. It extends at an angle to the edges of the plane conductor comprising it - of substantially parallelepipedal shape -, so that its length is maximum, while maintaining a minimum dimension of the plan driver.

Figure 4 shows a spectrum of input reflection frequencies antenna, typical of an antenna according to the second embodiment. A weak reflection of the antenna at a given frequency corresponds to a resonance. We observe that the frequencies f2 and f3 are complementary to form a band of extended frequency B.

FIG. 5 represents a top view of a test antenna whose conductive planes are aligned. This antenna has the following dimensions: a = 40mm b = 25mm c = 0.75mm d = 7mm e = 10mm f = 5mm g = 3mm h = 8mm i = 22mm j = 22mm k = 3mm l = 3mm m = 4mm n = 5mm

The conductive planes are formed from a folded copper sheet of 100 μm thick. The electrical connection is formed by the folding side of the sheet. This antenna has a substrate separating the two conductive planes and a substrate separating the first conducting plane from a mass. The two substrates are made in polymethacrylimide foam.

The diagram in Figure 6 represents the frequency spectrum of reflection at the input of the antenna of the embodiment of FIG. 5. The first resonance frequency f1 can be used in the field of E-GSM (880-960 MHZ). The second resonance frequency f2 can be used in the field DCS (1710-1880 MHZ) or PCS (1850-1990 MHZ). It is greater than the first frequency f1 because the electrical path for this resonant frequency is less than the electrical path of the first resonant frequency. The third resonant frequency f3 is greater than the second frequency f2. This third frequency f3 can for example be used in the UMTS domain (1900-2170 MHZ).

As for the test antenna described, a metallic sheet can be used folded back to form the conducting planes. It is also possible to carry out the supply link in the form of a tab made in the metal sheet. It is also possible to make the short-circuit connection in the form of a tab made in the metal sheet.

The invention further relates to a radiocommunication device. comprising an antenna as described above. The antenna can be arranged inside a protective housing of the device.

The invention also relates to a method of manufacturing an antenna. Such a manufacturing method comprises a step of cutting a slot in a metallic sheet. It also includes a step of folding the metal sheet by superimposing two parts of this metallic sheet. According to a variant, the step of folding includes making a plane electrical connection between the two planes conductors, by making two folds 11 and 12 substantially parallel in the sheet.

According to a variant, this method comprises a step of cutting a short circuit tab. According to another variant, the method comprises a step for cutting a supply link. According to yet another variant, the method includes a step of cutting an electrical connection over part of the width metal sheet.

Of course, the present invention is not limited to the examples and modes described and represented, but it is likely to be numerous variants accessible to those skilled in the art.

Thus, even if previously described conductive planes, it is also possible to use curved conductive surfaces to match the shape of a mobile phone case for example. It is also possible to make a slit which extends over the two conducting planes, passing through the connection electric. We can also use conductive planes of different shapes presented rectangles, as well as wavy or curved conducting planes. It is still possible to fold the supply and short-circuit tabs if necessary applicable.

Claims (18)

Multi-band antenna (1) including two radiant conductive planes (2, 5) electrically connected to each other (4); a slot (3) in at least one of the radiating conductive planes; a supply link (6) disposed on and physically connected to one of the conductive planes; a short-circuit link (7), arranged and physically connected on the same conductive plane as the supply link. The antenna of claim 1, characterized in that the conductive planes are electrically connected (4) by one of their edges. The antenna of one of claims 1 or 2, characterized in that the slot, the short-circuit connection and the supply connection are arranged in the same conducting plane. The antenna of one of the preceding claims, characterized in that the conductive planes are formed of a folded metal sheet. The antenna of claim 4, characterized in that the feed link is a tongue formed in the metal sheet. The antenna of claim 4 or 5, characterized in that the short circuit connection is a tab formed in the metal sheet. The antenna of one of claims 1 to 7, characterized in that the slot extends over the two conducting planes. The antenna of one of the preceding claims, characterized in that the conductive planes have different dimensions. The antenna of one of the preceding claims, characterized in that it comprises a dielectric substrate (9) disposed between the two conducting planes. The antenna of one of the preceding claims, characterized in that it comprises a dielectric substrate (10) disposed between one of the conductive planes and a ground (8). The antenna of claim 9 or 10, characterized in that at least one of the substrates (9, 10) is made of a material having a relative permittivity of less than 2. The antenna of one of claims 9 to 11, characterized in that at least one of the substrates (9, 10) is made with a material having a dissipation factor of less than 10 ^-3 . The antenna of one of the preceding claims, characterized in that it has at least two resonance bands, one of the two resonance bands being formed by two complementary resonance frequencies. The antenna of one of the preceding claims, characterized in that it has at least three resonance bands. Radiocommunication device characterized in that it comprises a multi-band antenna according to one of the preceding claims. Radiocommunication device according to claim 15, characterized in that it has a thickness of less than 20mm, a length of less than 120mm and a width of less than 50mm. Method of manufacturing a multi-band antenna comprising a step of cutting a slot, a connection in a metal sheet supply, a short-circuit connection and a step of folding the sheet metallic by superimposing two parts of this sheet. The manufacturing method of claim 16, characterized in that it further comprises a step of producing a plane electrical connection between the two conductive planes, by making two folds (11, 12) substantially parallel in the sheet.

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