EP1548877B1 - Multi-band antenna with planar radiating surfaces and portable phone comprising such an antenna - Google Patents

Description

The present invention relates to an antenna of the type with radiating surface (s) plane (s).

The invention proposes in particular an antenna of this type capable of being used in transmission / reception over at least two frequency bands, and having improved performances compared to antennas of the state of the art.

It also offers a mobile phone structure comprising such an antenna.

STATE OF THE ART

It has already been proposed to use for mobile phones planar antennas called PIFA ("Planar Inverted-F Antenna" or flat antenna type F inverted) which comprise, as illustrated by the figure 1 , a ground plane 1 and a flat conductive surface 2 which is superimposed on this ground plane 1, and extends to the right and parallel thereto.

Such an arrangement has a resonance wavelength which is a function of the dimensions of the plane conductive surface 2 and the height which separates it from its ground plane 1.

Thus, the planar conductive surface 2 comprises a current driving point A and a grounding plane G. The resonance frequency is notably related to the greatest peripheral length L _AG between the point A and the point G, the length L _AG being referenced by 3 on the figure 1 . The length h is also added to L _AG twice to obtain a length making it possible to find the resonant frequency of the antenna.

où c est la vitesse de la lumière.The resonant frequency can be approximated by: $$f=\frac{\mathrm{<figure-callout\; id="2"\; label="vs"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">vs</figure-callout>}}{2\cdot \left({\mathrm{The}}_{\mathit{AG}}+2h\right)}$$

where is the speed of light.

These antennas have a particular advantage in terms of congestion and integration ability in mobile phones.

However, a limitation of these antennas is that their bandwidth is all the more restricted as the height h which separates their radiating surface 2 from their ground plane 1 is small, or in a general way that the volume the antenna is weak.

This prevents in fact having an optimal gain on all the channels used on the same bandwidth.

In particular, we already know mobile phones that use antennas of the aforementioned type which comprise two radiating surfaces which are of different dimensions and which are arranged in the same plane, above the same ground plane.

These two radiating surfaces allow, as illustrated by the graph of the figure 2 , to have for the antenna two frequency bands, one around 900 MHz, the other around 1, 8 GHz.

However, the use of "duplex" separation on transmission / reception, as is usually the case in systems conforming to the global system of mobile communications or "global system for mobile communications (GSM)" according to the terminology Anglo-Saxon generally used by those skilled in the art, led to use for the transmitting and receiving frequencies f _TX , _RX the edges of the resonant bands of the antenna, where the adaptations are unsatisfactory.

The FIGS. 3A to 3C show that we know antennas for radiating on several frequencies.

These figures schematically show top views of the flat surfaces 2 of such antennas.

For all antennas with flat radiating surfaces conforming to FIGS. 3A to 3C , the low resonant frequency is defined by the length denoted by L _B and the high resonance frequency by the length denoted L _H.

We define L _B by the longest path on surface 2 to go from A to G, to which the distance h is added twice.

We define L _H by an equivalent dimension of the slot to which we add twice the distance h. The calculation of L _H is known to those skilled in the art.

The figure 4 shows that we also know transmitting / receiving multiband antennas having at least one plane 2 radiation surface having two slots 30 separating radiation sections 21, 22 and 23.

The radiation sections 21, 22 and 23 are connected by means Z ₁ and Z ₂ defining adaptive passive circuits known to those skilled in the art which, on transmission as on reception, are resonant on simultaneously at least two frequency bands.

In particular, the means Z ₁ and Z ₂ define passive matching circuits and are generally connected in parallel with capacitive or inductive means themselves connected in series with means able to be switched selectively between a passing state and a starch. blocked.

The capacitive or inductive means offset the resonance bands of the antenna, depending on whether the means capable of being switched are in the on state or in the off state. In general, the means Z ₁ and Z ₂ comprise a plug circuit known to those skilled in the art which will be equivalent to an inductor for the low frequencies and a capacity for the high frequencies.

The antennas Figures 3A to 4 provide acceptable radiation performance, especially in far-field measurement, while locally producing a lower near field than whip antennas or helical antennas otherwise known.

For example, it is possible to obtain simultaneously with an antenna comprising a plate 2 according to the figure 4 performance grouped in Table 1, for example for a domain corresponding to the GSM and for a domain corresponding to the DCS 1800 system or "Digital Communication System (DCS) 1800 MHz". Table 1. GSM DCS Bandwidth at -5 dB 80 MHZ 190 MHz yield -3 dB / iso -3 dB / iso

Thus, the antennas of the state of the art of Figures 3A to 4 are designed in such a way that multiband performance is average in the different bands.

Indeed, to realize a single-band antenna leads to very good results. However, these results deteriorate, especially as regards the antenna efficiency or the bandwidth, from the moment when we want to create several resonance bands.

The document WO 01/20718 discloses an antenna according to the preamble of claim 1.

It does not disclose an antenna with a single command, especially for switches.

US Patent 4780724 discloses a switch control technique, however the switches are connected to the ground plane.

PRESENTATION OF THE INVENTION

The invention proposes to overcome these disadvantages.

An object of the invention is to overcome at least one of the disadvantages of antennas of the prior art.

In particular, one of the aims of the invention is to propose an antenna for which multiband performance is very close to several single-band antennas.

Another object of the invention is to provide an antenna having a plurality of resonance bands and having a very large bandwidth with respect to the multiband antennas of the state of the art.

Another object of the invention is to provide an antenna having a plurality of resonance bands and having a very high yield compared to the multiband antennas of the state of the art.

One of the other aims of the invention is to propose an antenna comprising several resonance bands, at least one of which is in the GSM domain and at least one in the DCS 1800 domain, the antenna compensating for at least one of the disadvantages of the antennas. the prior art.

For this purpose, the invention provides an antenna according to claim 1.

In all embodiments of the invention, the control current of the switches arrives at the antenna by the point of attack.

Preferred embodiments are provided in the subclaims.

• au moins une zone de rayonnement comporte au moins une fente de rayonnement ;
• la fente est apte à permettre le rayonnement de la surface de rayonnement dans une première bande de fréquences lorsque toutes les zones de rayonnement sont reliées entre elles ;
• ladite première bande est la bande de fréquences aux alentours de 900 MHz, de préférence celle du système mondial de communications mobiles (GSM), notamment de 824 MHz à 960 MHz ;
• l'ouverture d'au moins une fente, l'ouverture étant située au niveau de la périphérie de la surface de rayonnement, comporte des moyens formant commutateurs aptes à permettre la circulation de courant sur la périphérie de la surface de rayonnement dans un état fermé ou à permettre la circulation de courant sur la périphérie interne de la fente dans un état ouvert ;
• la surface de rayonnement est apte à rayonner dans une deuxième bande de fréquences lorsque certains des commutateurs situés aux jonctions des zones de rayonnement sont dans un état ouvert ;
• ladite deuxième bande est la bande de fréquences aux alentours de 1800 MHz, de préférence celle du système DCS 1800 ou « Digital Communication System (DCS) 1800 MHz », notamment de 1710 MHz à 1990 MHz;
• les moyens formant commutateurs sont des commutateurs actifs à faible perte et à grand pouvoir isolant ;
• les commutateurs comportent une diode PIN ;
• les commutateurs comportent un élément actif de type transistor à effet de champ;
• dans un exemple de réalisation avec des diodes PIN ou un élément actif de type transistor à effet de champ, une zone de rayonnement comporte un point d'attaque, et une autre zone comporte un point de mise à la masse, les deux zones étant séparées par une jonction comportant des moyens de découplage aptes à forcer le passage du courant continu du point d'attaque vers le point de mise à la masse en passant par la périphérie de la surface de rayonnement.
• les moyens formant commutateurs sont des microsystèmes électromécaniques.

The invention is advantageously completed by the following features, taken alone or in any of their technically possible combination:

• at least one radiation zone has at least one radiation slot;
• the slot is adapted to allow radiation of the radiation surface in a first frequency band when all the radiation zones are connected together;
• said first band is the frequency band around 900 MHz, preferably that of the global system of mobile communications (GSM), in particular from 824 MHz to 960 MHz;
• the opening of at least one slot, the opening being located at the periphery of the radiation surface, comprises switch means capable of allowing current flow on the periphery of the radiation surface in a closed state or allowing current flow on the inner periphery of the slot in an open state;
• the radiation surface is capable of radiating in a second frequency band when some of the switches located at the junctions of the radiation zones are in an open state;
• said second band is the frequency band around 1800 MHz, preferably that of the DCS 1800 system or "Digital Communication System (DCS) 1800 MHz", in particular from 1710 MHz to 1990 MHz;
• the switch means are active switches with low loss and high insulative power;
• the switches have a PIN diode;
• the switches comprise an active element of the field effect transistor type;
• in an exemplary embodiment with PIN diodes or a field effect transistor active element, a radiation zone has a point of attack, and another zone has a grounding point, the two zones being separated by a junction comprising decoupling means capable of forcing the passage of direct current from the point of attack to the point of grounding through the periphery of the radiating surface.
• the switch means are electromechanical microsystems.

The invention also relates to a telephone comprising an antenna according to the invention.

This has the advantage of having a single point of order. Such a control is simpler and more economical than the controls of the prior art.

PRESENTATION OF FIGURES

• la figure 1, déjà discutée, représente schématiquement une antenne de type PIFA conforme à un état de la technique connu ;
• la figure 2, également déjà discutée, est un graphe adaptation/fréquence illustrant la répartition des fréquences d'émission/réception par rapport aux bandes de fréquences d'une antenne de type PIFA double bande conforme à un état de la technique connu ;
• les figures 3A à 3C sont des représentations schématiques en vue de dessus de surfaces rayonnantes d'antennes conformes à un état de la technique connu ;
• la figure 4 est une représentation schématique en vue de dessus d'une surface rayonnante d'une autre antenne conforme à un état de la technique connu ;
• la figure 5 est une représentation schématique en vue de dessus d'une surface rayonnante d'une autre antenne conforme à l'invention ;
• les figures 6A et 6B représente schématiquement les équivalences de la surface de la figure 5 selon deux états ;
• la figure 7 montre schématiquement un dispositif possible de contrôle de la diode active ;
• la figure 8 représente schématiquement un autre mode de réalisation possible d'une surface de rayonnement ; et
• la figure 9 montre schématiquement un autre dispositif possible de contrôle de la diode active.

Other features, objects and advantages of the invention will emerge from the description which follows, which is purely illustrative and nonlimiting, and which should be read with reference to the appended drawings in which:

• the figure 1 , already discussed, schematically shows a PIFA type antenna according to a known state of the art;
• the figure 2 , also already discussed, is an adaptation / frequency graph illustrating the distribution of the transmit / receive frequencies with respect to the frequency bands of a dual band PIFA type antenna according to a known state of the art;
• the FIGS. 3A to 3C are schematic representations in top view of radiating surfaces of antennas according to a state of the prior art;
• the figure 4 is a schematic representation in plan view of a radiating surface of another antenna according to a known state of the art;
• the figure 5 is a schematic representation in plan view of a radiating surface of another antenna according to the invention;
• the Figures 6A and 6B schematically represents the equivalences of the surface of the figure 5 in two states;
• the figure 7 schematically shows a possible device for controlling the active diode;
• the figure 8 schematically represents another possible embodiment of a radiation surface; and
• the figure 9 schematically shows another possible device for controlling the active diode.

In all of the figures, the elements having similar functions have identical reference numerals.

DETAILED DESCRIPTION

The transmitting / receiving antenna shown on the figure 5 comprises a ground plane 1 and a plane radiating surface 2 which extends superimposed on said ground plane 1, being parallel thereto.

An antenna according to the invention may also comprise more than one plane radiating surface.

At one of its ends, the radiating surface 2 is connected on one side to the ground plane 1 (connection point G) and on the other side to an RF signal supply / reception electronics (connection point A).

As shown in figure 5 , the radiation surface 2 is divided into at least two radiation zones 51 and 52 separated by a junction 4 formed over most of its length with a slot.

The radiation surface 2 may of course have more than two radiation zones 51 and 52 and more than one junction 4.

The ends of the junction 4 located on the periphery 7 of the radiation surface 2 comprise means 60 forming mechanical links and forming electrical switches between the radiation zones 51 and 52.

The electrical switches 60 are able to resonate all or part of the radiation surface 2 by electrically connecting all or part of the radiation zones.

The figure 5 shows that at least the radiation zone 51 comprises at least one radiation slot 5. The opening 6 of the slot 5 is located at the periphery 7 of the radiation surface 2.

The figure 5 thus shows that the opening 6 of the slot 5 comprises means 61 able to form a mechanical connection between the two sides of the slot 5 at the periphery 7 of the radiation surface 2.

The means 61 also form electrical switches between these two sides.

Thus, the means 61 are able to allow the flow of current on the periphery 7 of the radiation surface 2 in a closed electrical state, or to allow the flow of current on the inner periphery 8 of the slot 5 in an open electrical state. .

Thus, when the switches 60 are in a closed electrical state and when the switch 61 is in an open electrical state, the surface of the figure 5 is equivalent to a radiating surface 2 as represented on the Figure 6A . All radiation zones are electrically connected to each other.

In this configuration, the radiation surface 2 is able to radiate in accordance with the global system of mobile communications (GSM) and there is a flow of current as indicated by reference 3, namely a circulation on the inner periphery 8 of the slot 5.

Thus, the slot 5 is able to allow radiation of the radiation surface 2 at around 900 MHz, preferably in accordance with the global system of mobile communications (GSM), in particular from 824 MHz to 960 MHz.

When the switches 60 are in an open electrical state and when the switch 61 is in a closed electrical state, the surface of the figure 5 is equivalent to a radiating surface 2 as represented on the Figure 6B . Zone 52 is not electrically connected to zone 51, although it is still mechanically connected to it.

In this configuration, the radiation surface 2 is capable of radiating in the frequency band at around 1800 MHz, from preferably that of the DCS 1800 or "Digital Communication System (DCS) 1800 MHz", in particular from 1710 MHz to 1990 MHz.

With a radiation area 2 equivalent to that of the Figure 6A and having dimensions such that the dimension 80 of the long side of the surface 2 is substantially equal to 39 mm, and the dimension 81 of the short side is substantially equal to 18 mm on the one hand, and on the other hand with a surface 2 radiation equivalent to that of the Figure 6B and having dimensions such that the dimension 82 of the long side is substantially equal to 21 mm (the dimension 81 of the short side still being substantially equal to 18 mm), the performances given in Table 2 are obtained. to the ground plane is equal to about 9 mm. Table 2. GSM DCS Bandwidth at -5 dB 150 MHZ 300 MHz yield -2 dB / iso -2 dB / iso

We therefore see that the bandwidth is very greatly increased compared to the antennas of the state of the art.

The multiband performance of the antennas according to the invention are very close to those of n single-band antennas.

Indeed, it is considered that -5 dB of reflection rate at the edge of the band is a suitable value. This corresponds to an antenna with a loss of 1.5 dB at the edge of the band relative to the center of the band.

It will be understood that the foregoing developments advantageously apply to two resonance zones, one in the GSM domain and another in the DCS domain.

It is also understood that other bands may be provided, by placing other resonance zones on the radiating surface and by electrically or electrically connecting them depending on the resonance frequency that is desired. The resonance zones connected by a switch to the open state intervene in the operation of the antenna, because of their proximity, but only in the second order. The resonance frequency is mainly defined by the part connected to points A and G.

To obtain the means 60 and 61, it is not enough to make passive circuits for modeling a closed circuit or an open circuit according to the frequency, as is the case in antennas of the state of the art. Performance in terms of efficiency and in terms of bandwidth are indeed very bad, this being due to the excessive selectivity of the passive elements.

Therefore, the switch means is provided by active low loss and high insulative switches.

Several embodiments are possible.

For example, it is possible to use, for the means 60 and 61, switches comprising a PIN diode, that is to say a semiconductor comprising an intrinsic region (formed of an intrinsic semiconductor) between two regions, one of which type P, the other type N.

The PIN diode preferably comprises in the on state a very low resistance, for example of the order 1 Ohm.

The PIN diode preferably comprises in the off state a very low capacitance, for example of the order 0.1 pF.

It is also possible for the means 60 and 61 to use means comprising an active element of the field effect transistor type or an active diode, for example at least one BAR type diode 88.

In the on state, such an active diode will have, for example, a through current of 25 mA for a resistance R _on 0.5 Ohm and a voltage across its 0.8 volt.

In the off state, such an active diode will have a through current of 0 mA for a capacitance C _off of 0.22 pF for a voltage at its terminals greater than 10 volts. Two BAR diodes 88 are then available to provide sufficient isolation.

To avoid the formation of harmonics and keep their intensity lower than -36 dBm, the voltage across the active diode is preferably greater than 20 volts.

The figure 7 schematically shows a possible device for controlling the active diode.

A control terminal 79 is provided for controlling, through a resistor 80, means 78 forming a transistor.

The means 78 are also connected firstly to a control voltage of 3 or 5 volts on a terminal 83 and secondly to a voltage of -20 volts, for example on a terminal 81, for example through the resistors 77. and 76. This -20 Volt voltage prevents the formation of harmonics and allows the blocking of the diode.

A branch having a shock inductor 74 is connected by the terminal 82 located between the resistors 77 and 76.

Said branch connects the means 78 to an RF radio frequency power source, connected to the control device at point 73. The inductor 74 has a very high impedance for radio frequencies.

The radio frequency current source is connected to the antenna from the terminal 73 via the two diodes 71 and 72, passing in this direction.

A decoupling capacitor 75, having a very low impedance for the radio frequencies, is arranged between the ground and the terminal 82.

The figure 8 schematically represents another possible embodiment of a radiation surface.

According to this embodiment, the surface comprises three radiation zones 51, 52 and 53.

The zones 51 and 53 are separated from each other by the junction 41 which comprises a slot having at its ends the means E ₁ and E ₂ .

The means E ₁ are located on the periphery 7 of the surface, while the means E ₂ are located in the middle of the radiation surface 2.

The grounding point G is located on the zone 51, while the point of attack A is located on the zone 53. A control circuit 90, described in more detail on the figure 9 , is connected to the point of attack.

The presence of the junction 41 and the means E ₁ and E ₂ makes it possible to force the passage of the direct current from the point A towards the point G through the periphery 7 of the radiating surface.

Preferably, the means E ₁ and E ₂ comprise decoupling capabilities GSM and DCS. Capacities are typically of the order of 22 pF in size 0402.

This control device therefore defines two different paths for the direct current and for the radiofrequency current. The means E ₁ and E ₂ are indeed transparent for radio frequency currents.

The zones 51 and 53 on the one hand are separated from the zone 52 on the other hand by the junction 42 which comprises a slot having at its ends, on the periphery 7 of the surface 2, the means S ₁ and S ₂ .

The junctions 41 and 42 are located substantially perpendicular to each other.

Two BAR type diodes 88 are preferentially placed at S ₁ and two diodes at S ₂ , in order to obtain the appropriate isolation value.

The passing directions of the diodes are placed so that a current can flow from A to G on the periphery 7 of the surface 2.

A slot 5 made in the zone 52 makes it possible to give the surface 2 the GSM resonance.

The control system 90 is shown schematically at the figure 9 .

On this figure 9 , the elements having functions similar to those represented on the figure 7 , bear identical numerical references.

A control terminal 83 connected to a current source of 25 mA, for example, is provided for controlling electrical switch means 78.

The means 78 are also connected to a voltage of -20 volts for example on a terminal 81, for example through the resistor 76. This voltage of -20 volts prevents the formation of harmonics.

A branch having a shock inductance 74 is connected by the terminal 82 situated between the means 78 and the resistor 76.

Said branch connects the means 78 to an RF radio frequency power source, connected to the control device at point 73. The inductor 74 has a very high impedance for radio frequencies.

The radio frequency current source is connected to the antenna from the terminal 73 via at least one diode 71, passing in this direction.

A decoupling capacitor 75, having a very low impedance for the radio frequencies, is arranged between the ground and the terminal 82.

In the example illustrated in the present application, the GSM mode is engaged when the means 78 are in a closed state, and the DCS mode is engaged when the means 78 are in an open state.

It is understood that in all embodiments of the developments that precede the switch control current arrives at the antenna by the point of attack. The single DC component circulates properly in the switches, on the one hand by the geometry of the radiating surface and / or by the decoupling between the radiation zones, and on the other hand the controls. This has the advantage of having a single point of order.

The foregoing developments advantageously apply to switching means having diodes.

The means forming switches may also comprise microelectromechanical systems of a MEMS technology or "microelectronic mechanical system" according to the English terminology generally used by those skilled in the art.

Claims (12)

1. Transmission/reception antenna comprising a ground plane (1) and at least one planar radiation surface (2) which extends in front of said ground plane (1) and parallel to it, wherein the radiation surface (2) is divided into at least two radiation zones (51, 52; 51, 52, 53) separated by at least one junction (4; 41, 42), wherein the at least one junction (4; 41, 42) between the radiation zones (51, 52; 51, 52, 53) comprises means (60, 61; E1, E2, S1, S2) forming switches for bringing in resonance all or part of the radiation surface (2) by connecting electrically all or part of the radiation zones (51, 52), wherein the planar radiation surface (2) comprises a grounding point (G) and an attack point (A), characterized
   in that the control current of the switches arrives at the antenna through the attack point (A); and
   by at least one slit (5) having an opening (6), the opening (6) being located at the periphery (7) of the radiation surface (2); and
   by means (61) forming switches capable of permitting the flow of current at a periphery (7) of the radiation surface (2) in a closed state or permitting the flow of current at an internal periphery (8) of the slit (5) in an open state.
2. Antenna according to claim 1, characterized in that at least one radiation zone (51, 52) comprises the at least one slit (5) and in that the slit (5) comprises a radiation slit (5).
3. Antenna according to claim 2, characterized in that the slit (5) is capable of permitting the radiation of the radiation surface (2) in a first frequency band when all the radiation zones (51, 52) are connected to each other.
4. Antenna according to claim 3, characterized in that said first band is the frequency band around 900 MHz, preferably that of the global system for mobile communications (GSM), in particular from 824 MHz to 960 Mhz.
5. Antenna according to one of claims 1 to 4, characterized in that the radiation surface is capable of radiating in a second frequency band when some of the switches (60) located at the junctions of the radiation zones are in an open state.
6. Antenna according to claim 5, characterized in that said second band is the frequency band around 1800 MHz, preferably that of the Digital Communication System (DCS) 1800, in particular from 1710 MHz to 1990Mhz.
7. Antenna according to one of claims 1 to 6, characterized in that the means (60, 61) forming switches are active switches having low losses and a high insulating capability.
8. Antenna according to claim 6, characterized in that the switches (60, 61) comprise a PIN diode.
9. Antenna according to claim 6, characterized in that the switches (60, 61) comprise an active element of the field effect transistor type.
10. Antenna according to one of claims 8 or 9, characterized in that a radiation zone (53) comprises the attack point (A) and another zone (51) comprises the grounding point (G), wherein the two zones are separated by a junction comprising decoupling means capable of forcing the flow of the direct current from the attack point (A) towards the grounding point (G) through the periphery (7) of the radiation surface.
11. Antenna according to one of claims 1 to 6, characterized in that the means (60, 61) forming switches are micro-electromechanical systems (MEMS).
12. Telephone, characterized in that it comprises an antenna according to one of the previous claims.

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