Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01Q—ANTENNAS, i.e. RADIO AERIALS
  • H01Q21/00—Antenna arrays or systems
  • H01Q21/30—Combinations of separate antenna units operating in different wavebands and connected to a common feeder system
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01Q—ANTENNAS, i.e. RADIO AERIALS
  • H01Q13/00—Waveguide horns or mouths; Slot antennas; Leaky-waveguide antennas; Equivalent structures causing radiation along the transmission path of a guided wave
  • H01Q13/02—Waveguide horns
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01Q—ANTENNAS, i.e. RADIO AERIALS
  • H01Q13/00—Waveguide horns or mouths; Slot antennas; Leaky-waveguide antennas; Equivalent structures causing radiation along the transmission path of a guided wave
  • H01Q13/20—Non-resonant leaky-waveguide or transmission-line antennas; Equivalent structures causing radiation along the transmission path of a guided wave
  • H01Q13/24—Non-resonant leaky-waveguide or transmission-line antennas; Equivalent structures causing radiation along the transmission path of a guided wave constituted by a dielectric or ferromagnetic rod or pipe
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01Q—ANTENNAS, i.e. RADIO AERIALS
  • H01Q21/00—Antenna arrays or systems
  • H01Q21/06—Arrays of individually energised antenna units similarly polarised and spaced apart
  • H01Q21/061—Two dimensional planar arrays
  • H01Q21/065—Patch antenna array
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01Q—ANTENNAS, i.e. RADIO AERIALS
  • H01Q21/00—Antenna arrays or systems
  • H01Q21/28—Combinations of substantially independent non-interacting antenna units or systems
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01Q—ANTENNAS, i.e. RADIO AERIALS
  • H01Q5/00—Arrangements for simultaneous operation of antennas on two or more different wavebands, e.g. dual-band or multi-band arrangements
  • H01Q5/40—Imbricated or interleaved structures; Combined or electromagnetically coupled arrangements, e.g. comprising two or more non-connected fed radiating elements
  • H01Q5/45—Imbricated or interleaved structures; Combined or electromagnetically coupled arrangements, e.g. comprising two or more non-connected fed radiating elements using two or more feeds in association with a common reflecting, diffracting or refracting device
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01Q—ANTENNAS, i.e. RADIO AERIALS
  • H01Q9/00—Electrically-short antennas having dimensions not more than twice the operating wavelength and consisting of conductive active radiating elements
  • H01Q9/04—Resonant antennas
  • H01Q9/0407—Substantially flat resonant element parallel to ground plane, e.g. patch antenna
  • H01Q9/0414—Substantially flat resonant element parallel to ground plane, e.g. patch antenna in a stacked or folded configuration

Definitions

• the invention relates to a device for receiving / transmitting electromagnetic waves.
• Wireless interactive telecommunication services are growing rapidly. These services concern telephony, fax, television, especially digital, the so-called "multimedia" domain and the Internet.
• the equipment for these mass-market services must be available at a reasonable cost. This is the case, in particular, for the receiver / transmitter of the user who must communicate with a server, most often by means of a telecommunications satellite.
• These communications are generally carried out in the microwave domain.
• the C band is used: from 3.7 Ghz to 4.2 Ghz (3.4 Ghz to 4.2 Ghz in extended C band) for reception and from 6.4 Ghz to 6.7 Ghz for transmission.
• the subject of the invention is a device for receiving / transmitting electromagnetic waves, comprising a body, characterized in that it comprises in combination:
• reception plate incorporated in the body, comprising a first network of n radiating elements of microstrip structure for the reception of electromagnetic waves in a first frequency band, - means for transmitting electromagnetic waves with longitudinal radiation defining an axis of radiation for the emission of electromagnetic waves in a second frequency band, said means comprising excitation means for exciting means of longitudinal radiation, said emission means being of substantially constant section in the body, perpendicularly cutting the reception plate into a circular opening around which said radiating elements are arranged symmetrically, said reception and emission means being arranged so that their centers respective phase are substantially arranged in a so-called focusing area.
• Such a hybrid type device (that is to say with waveguide technology and microstrip technology) can be produced at moderate cost. Its size and weight are reduced. Excellent insulation is obtained between the transmit and receive signals.
• the use of means with longitudinal radiation makes it possible to benefit from a wide frequency band for transmission. It should be noted above all that the use of such means with longitudinal radiation of constant section makes it possible to limit the surface occupied by these means on the plane of the reception plate with respect to a horn, which allows reception and transmission in near frequency bands. and which also makes it possible to bring the radiating elements closer together and therefore to reduce the number n of the latter.
• the device according to the invention allows a ratio between the central frequencies of the respective transmission and reception bands less than or equal to three, this being demonstrated at the end of the present application.
• said focusing area is reduced to a point forming the phase center of said device.
• said radiation means comprise a dielectric rod with longitudinal radiation of axis coinciding with the axis of emission radiation.
• said excitation means comprise a waveguide.
• said radiation means comprise a helical device comprising a set of turns.
• said excitation means comprise a coaxial line.
• n is equal to 4.
• said dielectric rod is shaped into a cylinder of conical ends.
• said excitation means are coupled to a microstrip emission plate arranged in a cross section of the excitation means in the body for the emission of electromagnetic waves.
• the device according to the invention comprises a pair of probes placed on the emission plate and at right angles to each other and capable of emitting orthogonally polarized waves.
• the microstrip transmission plate includes a frequency conversion circuit.
• the microstrip reception plate includes a frequency conversion circuit.
• the device according to the invention comprises an intermediate plate comprising at least part of the frequency conversion circuit associated with the reception plate and / or with the transmission plate.
• an auxiliary plate is associated in parallel with the reception plate and comprises a second network comprising a plurality of radiating elements opposite respectively the plurality of radiating elements of the first network and of resonance frequency close to that (F 0 ) of the first network so that the pair of networks of radiating elements facing one another is the equivalent of a single network of widened bandwidth.
• the waveguide (1 9, 24) is closed by a cavity (24 2 ) quarter wave ( ⁇ GT / 4) of length equal to a quarter of the wavelength ( ⁇ GT ) of the guided wave emitted.
• the subject of the invention is also a system for receiving / transmitting electromagnetic waves comprising means for focusing waves, characterized in that it is equipped with a device according to the invention.
• said focusing means comprise a reflector, preferably parabolic, and in that the device is arranged so that said focusing area coincides substantially with the focus of said reflector, said device thus operating as the primary source of the system.
• said focusing means may also comprise an electromagnetic lens and in that said device is arranged so that said focusing zone coincides substantially with the focal point of said electromagnetic lens, said device thus functioning as the primary source of the system.
• FIG. 1 represents the basic concept of the user channel towards a satellite or return channel implemented by an embodiment of a satellite reception / transmission system according to the invention
• FIG. 2 represents a view in vertical section according to section A-A of FIG. 3. a of an embodiment of a device according to the invention
• FIG. 3. a shows a top view along section BB of Figure 2 of an embodiment of the receiving plate according to the invention while Figure 3.b shows a bottom view according to section CC of FIG. 2 of an embodiment of the auxiliary plate according to the invention, FIG. 3.c representing an enlarged view of an area D of FIG. 2,
• FIG. 4 shows a perspective view of a variant of the invention.
• FIG. 5 represents a variant of the embodiment of FIG. 2.
• FIG. 1 represents the basic concept of the return channel implemented by a satellite reception / transmission system according to the invention.
• the information distributed by the reception / transmission system according to the invention can in particular come from satellites, recording studios, cable networks, or can be exchanged within the framework of an MMDS ("Multipoint Multichannel") system. Distribution System "in English), LMDS (" Local Multipoint Distribution System “in English) or MVDS (" Multipoint Video Distribution System “in English) well known to those skilled in the art.
• the framework envisaged is that of a bidirectional satellite - user - satellite link.
• a satellite 1 sends information and programs 2 made available to users. This information and programs 2 are received at the level of each user by means of the reception / transmission system comprising an antenna 3 of small diameter placed on the roof of a dwelling 4 for example.
• the antenna 3 comprises a reflector 5 intended to focus the energy received at its focus in the vicinity of which is housed a primary source 6 capturing and radiating the energy thus exchanged, comprising a frequency conversion device not shown for reasons of clarity.
• This converter converts the signals received by satellite into intermediate frequencies and transmits them, by connection means, for example a coaxial cable 8, to an indoor unit 9 arranged inside the house 4 comprising a decoder / encoder 1 0 connected to means for using the information transmitted, for example a television receiver 1 1.
• this antenna 3 can be placed, thanks to its small size, in the vicinity of the one-story balcony.
• a receiving / transmitting antenna can be placed at the top of the building and can be equipped with a first converter at higher frequencies (in the neighboring frequency bands 40 GHz) to distribute by a link. wireless signals to different floors.
• the antenna 3 then has the role of collecting the signals thus distributed and a second frequency converter has the function of converting them into intermediate frequencies.
• Said antenna 3 is, in the invention, also used for the return channel 1 2 or uplink 1 2.
• the user by means of a remote control for example, can respond to an interactive service.
• the information is coded and then transmitted, by means of the cable 8, to the high frequency converter which converts said information into a higher transmission frequency band.
• the uplink "user" 1 2 transmits return data to the satellite 1 which therefore, among other things, has the role of collecting and centralizing the data transmitted by the users for retransmitting for further processing.
• the embodiment thus described therefore shows a reception / transmission system in which the primary source 6 points in the same direction for transmission and reception.
• the reception / transmission system according to the invention must include a primary source 6, the reception antenna and the transmission antenna of which are such that their respective radiation patterns are maximum in a one and the same direction.
• the information 2 can for example come from satellite 1 and the return data can be transmitted to the earth station MMDS 1 3.
• This return channel is shown in dotted lines in FIG.
• the system according to the invention must include a reception antenna and a transmission antenna pointing in two different directions, this requiring at least one of the two antennas to be defocused.
• the C band can be used, given the significant attenuation of signals introduced by rain in the Ku band in the equatorial regions.
• the uplink 1 2 operates in the frequency band [6.4 Ghz - 6.7 Ghz] while the downlink 2, to designate the reception channel by the antenna 3 of the information transmitted by the satellite 1, operates in the band frequencies [3.7 Ghz - 4.2Ghz].
• the extended C band the downlink 2 of which operates in the frequency band [3.4 Ghz; 4.2 Ghz].
• the data transmitted on the uplink 1 2 can be the data relating to pay television, or more generally interactive television which gives the user access to films, interactive games, teleshopping, downloading software but also to services such as database consultation, reservations, etc.
• FIG. 2 shows a vertical sectional view along section AA of Figure 3. a of an embodiment of a device 1 5 according to the invention in which there is provided a receiving plate 1 6, a plate of transmission 27 and an auxiliary plate 1 7.
• FIG. 3. a represents a top view according to section BB of FIG. 2 of an embodiment of the reception plate 1 6 according to the invention while FIG. 3. b represents a bottom view along section C- C of FIG. 2 of an embodiment of the auxiliary plate 1 7, FIG. 3.c representing an enlarged view of an area D of FIG. 2 giving a detailed overview of the various constituent elements at the level of the reception plate 1 6 and of the auxiliary plate 17.
• FIG. 4 represents a perspective view of a variant of the embodiment of the invention described in FIGS. 2, 3. a to 3.c.
• the device 1 5 comprises a support or body 1 8 of parailITApi regardsdique shape and conductive material, and a rod 1 9.
• the rod 1 9 comprises a cone 20 emerging from the upper face 21 of said body 1 8, the circular base of which is centered at the intersection of the diagonals of said upper rectangular face 21 and the apex of which points towards the space towards which the waves radiate or from which they are picked up .
• This cone 20 extends at its base into a cylinder 22 and ends in a cone 23 whose apex points in the direction opposite to that of the cone 20.
• the rod 1 9 formed of the cone 20, of the cylinder 22 and of the cone 23 comprises compressed polystyrene for example, constituting a dielectric antenna of longitudinal radiation, namely of relatively fine radiation diagram, called "rod" in English.
• the configuration of this rod 1 9 explains its name of cylindrical-conical antenna.
• the rod 1 9 operates as a waveguide and the mode it transmits is such that the maximum radiation can appear in the axis of the direction of the rod 1 9.
• the rod 1 9 is dig.
• the technique of such dielectric antennas is for example explained. in the book “Engineering techniques - Electronic Treaty” E3 283 - p.1 1, version 3- 1 991.
• the rod 1 9 is surrounded downstream of the base of the cone 20 in the direction of reception of the waves, by a cylindrical base 24 of axis D coinciding with the axis of the rod 1 9.
• This base 24 has, in the example, an external diameter of 3.66 cm and an internal diameter of 3.25 cm.
• the base 24 extends inside the body 18 perpendicular to the cross sections of the latter and ends in a part emerging from the underside 25 of the body 18.
• This base 24 of conductive material forms a waveguide whose walls are in contact with the body 1 8.
• the end part of the base 24 emerging from the upper face 21 is open while that emerging from the lower face 25 of the base 24 is closed by a metal plate 26.
• the base 24 forms with its bottom 26 a resonant cavity.
• the base 24 is divided perpendicularly into two parts 24-, and 24 2 between which is placed, in a cross section of the base 24, the emission plate 27 of circuit in microstrips for emitting electromagnetic waves.
• the base 24 and the rod 1 we will call, in the following, guide the combination formed by the base 24 and the rod 1 9.
• the plate 27, forming a substrate is made of a material with a given dielectric permittivity, for example Teflon glass. It has an upper surface 27, directed towards the rod 1 9 and a lower surface 27 2 disposed on the other face of the substrate.
• the lower surface 27 2 is metallized, forming a ground plane, and is in contact with the conductive walls of the base 24.
• the plate 27 is supplied by two coplanar probes 280, and 280 2 which are etched on the upper surface 27, and which penetrate inside the base 24 through openings without touching the wall of the base 24. To allow the emission of orthogonally polarized waves, the two probes 280, and 280 2 are arranged at right angles to each other. the other.
• This transmission circuit arranged in the present embodiment on the wafer 27, comprises a power amplifier and a frequency converter connected to the indoor unit 9 by the coaxial cable 8.
• the device further comprises a radiator 36 disposed at the rear of the emission plate 27 of microstrip emission circuit intended to dissipate the heat given off by a power amplifier not shown and arranged in the transmission circuit on the plate 27.
• a radiator 36 disposed at the rear of the emission plate 27 of microstrip emission circuit intended to dissipate the heat given off by a power amplifier not shown and arranged in the transmission circuit on the plate 27.
• elements fulfilling identical functions in the subject of the invention can be represented only in one of FIGS. 2 , 3. a to 3.c or 4.
• the part 24 2 closing the base 24 is a quarter wave guide section of length ⁇ GT / 4 (Guided wavelength) forming a resonant cavity and functioning as an open circuit in the plane of the wafer 27 for the transmitted waves, ⁇ TG representing the wavelength of the guided wave emitted.
• the upper face 21 has a substrate 28 successively followed in the direction of reception of the waves, of a network of radiating elements 29,, 29 2 , 29 3 , 29 4 of reception of electromagnetic waves, of a space filled with foam over a height, for example, from 4 mm to 7 mm, a network of radiating elements 30,, 30 2 , 30 3 , 30 4 for receiving electromagnetic waves associated with an excitation circuit 31 in microstrip engraved on a substrate 320.
• the radiating elements of the substrate 28 consist of four flat pads 29,, 29 2 , 29 3 , 29 4 , of square shape, etched on the underside 28, of the turned substrate 28 towards the inside of the body 1 8, and arranged in a regular manner around the center of the substrate 28.
• the radiating elements of the plate 1 6 consist of four flat pads 30,, 30 2 , 30 3 , 30 4 , of square shape. , etched on the upper face of the substrate 320 of the plate ette 1 6, each of the pads 30, 30 4 being disposed respectively opposite the corresponding pad 29, 29 4 .
• the lower surface 320 of the substrate 320 facing the cavity 24 2 is metallized, forming a ground plane, and is in contact with the conductive walls of the base 24 while the upper surface facing the cone 20 has the pellets 30,, 30 2 , 30 3 , 30 4 and the excitation circuit 31.
• Figure 3 a details the different elements of the receiving plate 1 6. It has a circular opening whose center merges with that of the plate 1 6 through which passes the base 24 and around which are arranged the four pads 30,, 30 2 , 30 3 , 30 4 .
• the plate 1 6 also has the excitation circuit 31 comprising lines 32 capable of carrying vertically polarized waves and lines 33 capable of conducting horizontally polarized waves.
• quadrants 34,, 34 2 , 34 3 , 34 4 delimited by the horizontal median lines 35, and vertical 35 2 of the plate 1 6 passing respectively through the midpoints of the vertical and horizontal sides of the plate 1 6.
• These quadrants 34,, 34 2 , 34 3 , 34 4 respectively comprise the pads 30,, 30 2 , 30 3 , 30 4 , each pad being arranged symmetrically with the pad contained in the bordering quadrant with respect to the horizontal median lines 35, and vertical 35 2 .
• Each pad 30,, 30 2 respectively has a connection point A 2 between the upper side of said pad 30,, 30 2 and respectively a vertical excitation line L,, L 2 able to guide vertically polarized waves. These two lines L,, L 2 respectively undergo a right angle bend and meet at a point of intersection C, located on the vertical median line 35 2 .
• each pad 30 3 and 30 4 respectively has a connection point A 3 , A 4 between the lower side of said pad 30 3 , 30 4 with respectively a vertical excitation line L3, L4 capable of guiding polarized waves vertically.
• These two lines L 3 , L 4 respectively undergo a right angle bend and meet at a connection point C 2 located on the vertical median line 35 2 .
• the pads 30,, 30 3 respectively have a connection point B,, B 3 respectively between the right lateral side of the pads 30,, 30 3 and respectively a horizontal excitation line L 5 , L 6 able to guide horizontally polarized waves.
• the pads 30 2 , 30 4 respectively have a point of intersection B 2 , B 4 between the left lateral side of said pads 30 2 , 30 4 and a horizontal excitation line L 7 , L 8 capable of guiding horizontally polarized waves.
• Lines L 5 and L 7 meet at a point C5 included in quadrant 34, and distant from the middle line 35 2 of ⁇ L while lines L 6 and L 8 meet at a point C 6 included in quadrant 34 3 and distant from the center line 35 2 also from ⁇ L, so that said points C and C 6 are symmetrical with respect to the center line 35,. From these points C 5 and C 6 start two lines which meet at a point C 7 located on the middle line 35, from which a main excitation line capable of guiding horizontally polarized waves which ends at a connection point C 8 .
• the upper face 21 is square with a side length of 10 cm and the body has a height of approximately 8 cm.
• the base 24 has an internal diameter of 3.25 cm and an external diameter of 3.66 cm.
• a Teflon-based substrate loaded with ceramic can be used.
• Figure 3.b details the different components of the auxiliary plate 1 7. This presents the four pads 29,, 29 2 , 29 3 , 29 4 and a circular opening centered in the center of the plate 1 7 through which the base 24 passes.
• FIG. 3.c represents an enlarged view of zone D of FIG. 2, giving a detailed overview of the various constituent elements at the level of the two plates 1 6 and 1 7.
• the height of foam ⁇ can be, in the present mode of realization, of the order of 0.06 to 0.08 times the wavelength ⁇ GR of the received wave, that is to say of the order of 4 mm to 7 mm.
• the device comprises an intermediate plate 37 on which is arranged the reception circuit (not shown) comprising at least a low noise amplifier and a frequency converter.
• Coaxial cables (for reasons of clarity, a single coaxial cable 38 has been drawn) connect the connection points C 4 and C 8 to the reception circuit of the wafer 37 for the processing of the signals received.
• the output of the reception circuit is connected, through an opening 39 made in the body 18, to the coaxial cable 8.
• the same oscillator can be used for the conversion at high frequencies of the signals intended to be transmitted and for the conversion at low frequencies of the signals intended to be received. More generally, several same elements can be used for the conversion of the received and transmitted signals.
• the plate 37 can serve as a support for these various elements.
• at least one coaxial cable is arranged between the plate 37 and the transmission plate 27.
• Figure 5 shows an interesting variant of the embodiment of Figure 2.
• the rod 1 9 is advantageously replaced by a coaxial line 42, one end of which is connected to the transmission circuits and the other of which is connected to a helix 40 composed of a set of turns 41, this helix antenna operating in axial mode.
• the right circular section of the propeller is then reduced to the wavelength divided by three.
• the diameter of the base 24 undergoes a discontinuity at the level of the connection between the coaxial line and the propeller.
• the device according to the invention operates in the following manner:
• the electromagnetic waves arriving on the reflector 5 are reflected and focused at the focal point of the latter located substantially at the geometric center of the network of the plate 1 7.
• the network of the plate 1 6 operates on a frequency central resonance F 0 while the array of plate 1 7 operates on a resonance frequency F 0 'slightly offset from said frequency F 0 , so that the combination of the two plates 1 6 and 1 7 behaves like a single broadband network.
• the pellets 30,, 30 2 , 30 3 , 30 4 are all supplied in phase and with the same amplitude by two power dividers in microstrip, the feeding of the pellets having to be done in phase so that the fields electric add up in the direction of propagation of the guided waves.
• B,, B 2 are excited by opposite lateral sides of the pellets.
• the pad 30, is excited by its right lateral side, which creates, at an instant t, a field E oriented from right to left, while, simultaneously, the pad 30 2 is excited by its left lateral side, which creates, at the same time t, a field E oriented from left to right, which ultimately creates fields out of phase with ⁇ .
• Said waves, received and carried by lines 32 and 33, are delivered, via cable 38, to the reception circuit of wafer 37 for example which transmits after conversion of signals received into intermediate frequencies, these latter to the indoor unit 9 via the cable 8.
• the signals from said unit 9 pass through the frequency conversion circuit, arranged on the wafer 27 for example, and supply the probes 280,, 280 2 with waves to be transmitted to the rod 1 9 which transmits the maximum power in the direction of the axis D of the rod 1 9.
• the device according to the invention makes it possible to obtain a single device capable of operating simultaneously and fully decoupled according to a reception channel and a transmission channel.
• the guide (1 9, 24) and the array of radiating elements (30 ,, 30 2 , 30 3 , 30 4 ) are arranged so that their respective phase centers are substantially merged into a single point forming the phase center of said device, allowing said device to function as a primary source pointing in a given direction in reception and in emission, this primary source being disposed at the focus of focusing means of a reception / emission system according to the invention such as a parabola or an electromagnetic lens.
• At least one of the phase centers can be defocused to transmit in a direction other than the reception direction.
• the devices according to the invention can also be used in constellations of satellites in circular orbit, in particular in low orbit ("Low Earth Orbit” or LEO in English) or in medium orbit (“Mid Earth Orbit” or MEO in language English).
• the device according to the invention allows a ratio between the central frequencies of the respective transmission and reception bands less than or equal to three, with a small number of pads such as 4, to minimize the complexity of the device.
• the invention is not limited to the embodiments described. This is how the guide can be chosen rectangular if one polarization is to be preferred over the other.
• the pellets 29,, 29 2 , 29 3 , 29, 30,, 30 2 , 30 3 , 30 4 can be circular or rectangular.
• the difference in length ⁇ L may be zero.
• reception and transmission circuits of the device according to the invention can also be arranged on a single plate having the dual function of supporting the reception circuit and supporting the transmission circuit.
• said circuits are arranged so as to avoid any electromagnetic coupling between the reception circuit and the transmission circuit.
• any crossings between the excitation lines of the receiving circuit and those of the transmitting circuit would be carried out, for example, by bridges.

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• Physics & Mathematics (AREA)
• Electromagnetism (AREA)
• Variable-Direction Aerials And Aerial Arrays (AREA)
• Waveguide Aerials (AREA)

Applications Claiming Priority (3)

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• 1997
  • 1997-12-31 FR FR9716767A patent/FR2773271B1/fr not_active Expired - Fee Related
• 1998
  • 1998-12-30 ID IDW20001285A patent/ID27106A/id unknown
  • 1998-12-30 EP EP98964558A patent/EP1044482A1/fr not_active Ceased
  • 1998-12-30 KR KR1020007007171A patent/KR100592422B1/ko not_active Expired - Fee Related
  • 1998-12-30 JP JP2000527992A patent/JP2002501315A/ja active Pending
  • 1998-12-30 WO PCT/FR1998/002922 patent/WO1999035711A1/fr not_active Ceased
  • 1998-12-30 US US09/582,395 patent/US6362788B1/en not_active Expired - Lifetime
  • 1998-12-30 CN CN98812824A patent/CN1114244C/zh not_active Expired - Lifetime

Non-Patent Citations (1)

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