FR2864353A1 - Transmission/reception antenna for mobile telephone, has plane radiation surface divided into two radiation zones separated by junctions that comprise of switches to resonate entire or part of surface - Google Patents

Abstract

The antenna has a ground plane (1) and a plane radiation surface (2) that extends to the right of and in parallel to the ground plane. The radiation surface is divided into two radiation zones (51, 52) separated by junctions. The junctions between the radiation zones comprise of switches (60) to resonate entire or part of the radiation surface by electrically connecting entire or part of the zones. An independent claim is also included for a telephone comprising an antenna.

Description

ANTENNA WITH SURFACE (S) RADIANT (S) PLANE (S) MULTIBAND AND TELEPHONE

  PORTABLE COMPRISING SUCH ANTENNA.

GENERAL TECHNICAL FIELD.

  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 telephones planar antennas called PIFA (Planar Inverted-F Antenna or inverted F type plane antenna) which comprise, as illustrated in FIG. 1, a ground plane 1 and a plane 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 LAG between the point A and the point G, the length LAG being referenced 3 in Figure 1. It also adds to LAG twice the length h to obtain a length to find the resonant frequency of the antenna.

  The resonant frequency can be approximated by: f 2. (LAC + 2h) c where c 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 make it possible, as illustrated in the graph of FIG. 2, for the antenna to have two frequency bands, one around 900 MHz, the other around 1.8 GHz.

  However, the use of a "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 English terminology. Saxon generally used by those skilled in the art, led to use for the transmission and reception frequencies fTx, fRx the edges of the resonant bands of the antenna, where the adaptations are unsatisfactory.

  Figures 3A to 3C show that there are known antennas for radiating on several frequencies.

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

  For all the antennas having flat radiating surfaces according to FIGS. 3A to 3C, the low resonance frequency is defined by the length denoted LB and the high resonance frequency by the length denoted LH.

  We define LB by the longest path on surface 2 to go from A to G, to which the distance h is added twice. We define LH by an equivalent dimension of the slot to which the distance h is added twice. The calculation of LH is known to those skilled in the art.

  FIG. 4 shows that transmit / receive multiband antennas are also known comprising at least one plane radiation surface 2 comprising two slots 30 separating radiation sections 21, 22 and 23.

  The radiation sections 21, 22 and 23 are connected by means Z1 and Z2 defining adaptive passive circuits known to those skilled in the art which, on transmission as on reception, are resonant on simultaneously with the least two frequency bands.

  In particular, the means Z1 and Z2 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 an on state and a blocked state.

  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 inductance for the low frequencies and a capacity for the high frequencies.

  The antennas of FIGS. 3A to 4 provide acceptable radiation performance, particularly in far-field measurements, while locally producing a lower near-field than the whip antennas or helical antennas known elsewhere.

  For example, it is possible to obtain, simultaneously with an antenna comprising a plate 2 according to FIG. 4, performances grouped together in table 1, for example for a domain corresponding to the GSM and for a domain corresponding to the DCS 1800 or Digital Communication System (DCS) system. 1800 MHz.

GSM DCS

  Bandwidth at -5 dB 80 MHZ 190 MHz Efficiency -3 dBlso -3 dBliso

Table 1.

  Thus, the antennas of the state of the art of FIGS. 3A to 4 are designed such 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.

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 15 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 proposes a transmitting / receiving antenna comprising a ground plane and at least one plane radiation surface which extends to the right of said ground plane and parallel thereto, the radiation surface being divided into at least two zones of radiation, characterized in that the junctions between the radiation zones comprise means forming switches able to resonate all or part of the radiation surface by electrically connecting all or part of the radiation zones.

  The invention is advantageously completed by the following features, taken alone or in any of their technically possible combination: at least one radiation zone comprises at least one radiation slot; the slot is able to allow radiation of the radiation surface in a first frequency band when all the radiation zones are connected to each other; said first band is the frequency band at around 900 MHz, preferably that of the global mobile communications system (GSM), in particular from 824 MHz to 960 MHz; the opening of at least one slot, the opening being situated at the periphery of the radiation surface, comprises means forming switches capable of allowing current to flow on the periphery of the radiation surface in a state closed or to allow 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 at around 1800 MHz, preferably that of the DCS 1800 or Digital Communication System (DCS) 1800 MHz system, in particular from 1710 MHz to 1990 MHz; the switch means are active switches with low loss and high insulation power; the switches comprise a PIN diode; the switches comprise an active element of the field effect transistor type; in an exemplary embodiment with PIN diodes or an active element of field-effect transistor type, a radiation zone comprises a point of attack, and another zone has a point of grounding, the two zones being separated by a junction comprising decoupling means able to force the passage of direct current from the point of attack to the point of grounding through the periphery of the radiation surface.

  the means forming switches are electromechanical microsystems.

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

PRESENTATION OF THE FIGURES.

  Other characteristics, 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: FIG. 1, already discussed, represents schematically a PIFA type antenna according to a known state of the art; FIG. 2, also already discussed, is an adaptation / frequency graph illustrating the distribution of the transmission / reception frequencies with respect to the frequency bands of a dual band PIFA type antenna according to a known state of the art; FIGS. 3A to 3C are diagrammatic representations in plan view of antenna radiating surfaces according to a known state of the art; - Figure 4 is a schematic representation in plan view of a radiating surface of another antenna according to a known state of the art; - Figure 5 is a schematic representation in plan view of a radiating surface of another antenna according to the invention; FIGS. 6A and 6B schematically represent the equivalences of the surface of FIG. 5 according to two states; - Figure 7 shows schematically a possible device for controlling the active diode; FIG. 8 diagrammatically represents another possible embodiment of a radiation surface according to the invention; and FIG. 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 in FIG. 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 electronics 15 for supplying / receiving RF signals (connection point A). .

  As shown in FIG. 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.

  FIG. 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.

  FIG. 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 FIG. 5 is equivalent to a radiating surface 2 as shown in FIG. 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 FIG. 5 is equivalent to a radiating surface 2 as shown in FIG. 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, preferably that of the DCS 1800 or Digital Communication System (DOS) 1800 MHz system, in particular from 1710 MHz to 1990 MHz.

  With a radiation area 2 equivalent to that of FIG. 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 d on the one hand, and on the other hand with a radiation area 2 equivalent to that of FIG. 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 being still substantially equal to 18 mm), the performances given in Table 2 are obtained. It is specified that the distance h to the ground plane is equal to about 9 mm.

GSM DCS

  Bandwidth at -5 dB 150 MHZ 300 MHz Efficiency -2 dBliso -2 dBliso

Table 2.

  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 the points A and G. To obtain the means 60 and 61, it is not enough to make passive circuits making it possible to model a closed circuit or an open circuit as a function of 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 of type P, the other type N. The PIN diode preferably has 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 15 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 Ron 0.5 Ohm and a voltage at its terminals of 0.8 Volt.

  In the off state, such an active diode will have a through current of 0 mA for a capacitance Ce 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.

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

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

  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.

  Figure 8 schematically shows another possible embodiment of a radiation surface according to the invention.

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

  The areas 51 and 53 are separated from each other by the junction 41 which has a slot having at its ends the means E1 and E2.

  The means E1 are located on the periphery 7 of the surface, whereas the means E2 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 in FIG. 9, is connected to the point d 'attack.

  The presence of the junction 41 and means E1 and E2 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 E1 and E2 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 E1 and E2 are indeed transparent for the 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 has a slot having at its ends, on the periphery 7 of the surface 2, the means S1 and S2.

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

  Two BAR BAR diodes 88 and two S2 diodes are preferably placed 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 in FIG. 9.

  In this figure 9, the elements having functions similar to those shown in FIG. 7, bear identical reference numerals.

  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.

  The foregoing developments advantageously apply to switching means having diodes.

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

Claims (1)

CLAIMS.   An emission / reception antenna comprising a plane (1) of mass and at least one plane radiation surface (2) which extends in line with and parallel to said ground plane, the surface (2) of radiation being divided into at least two (51, 52) radiation zones, characterized in that the junctions (4, 42) between the radiation zones comprise means (60) forming switches capable of resonating all or part of the radiation surface by electrically connecting all or part of the radiation areas (51, 52).   2. Antenna according to claim 1, characterized in that at least one radiation zone (51, 52) comprises at least one slot (5) of radiation.   3. Antenna according to claim 2, characterized in that the slot (5) is adapted to allow radiation of the radiation surface (2) in a first frequency band when all the radiation areas (51, 52) are connected. between them.   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 of mobile communications (GSM), including 824 MHz to 960 MHz.   Antenna according to one of Claims 2 to 4, characterized in that the opening (6) of at least one slot (5), the opening being situated at the periphery (7) of the surface ( 2), comprises means (61) forming switches adapted to allow current flow on the periphery (7) of the radiation surface in a closed state or to allow current flow on the inner periphery (8) of the slot (5) in an open state.   6. Antenna according to one of claims 1 to 5, characterized in that the radiating 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 .   Antenna according to claim 6, characterized in that said second band is the frequency band at around 1800 MHz, preferably that of the DCS 1800 or Digital Communication System (DOS) 1800 MHz system, in particular from 1710 MHz to 1990 MHz .   8. Antenna according to one of claims 1 to 7, characterized in that the means (60, 61) forming switches are active switches low loss and high insulating power.   9. Antenna according to claim 8, characterized in that the switches (60, 61) comprise a PIN diode.   10. Antenna according to claim 8, characterized in that the switches (60, 61) comprise a field-effect transistor type active element.   11. Antenna according to one of claims 9 or 10, characterized in that a radiation zone (53) comprises a point of attack (A), and another zone (51) comprises a point (G) of the mass, the two zones being separated by a junction comprising decoupling means capable of forcing the passage of the direct current from the point of attack (A) towards the point of grounding (G), passing through the periphery (7). ) of the radiation surface.   12. Antenna according to one of claims 1 to 7, characterized in that the means (60, 61) forming switches are electromechanical microsystems (MEMS).   13. Telephone, characterized in that it comprises an antenna according to one of the preceding claims.