EP0302596A1 - Electromagnetically-transparent laminate - Google Patents

Electromagnetically-transparent laminate Download PDF

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Publication number
EP0302596A1
EP0302596A1 EP88306093A EP88306093A EP0302596A1 EP 0302596 A1 EP0302596 A1 EP 0302596A1 EP 88306093 A EP88306093 A EP 88306093A EP 88306093 A EP88306093 A EP 88306093A EP 0302596 A1 EP0302596 A1 EP 0302596A1
Authority
EP
European Patent Office
Prior art keywords
ptfe
layer
laminate
structure according
membrane
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
EP88306093A
Other languages
German (de)
French (fr)
Other versions
EP0302596B1 (en
Inventor
Robert L. Sassa
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
WL Gore and Associates Inc
Original Assignee
WL Gore and Associates Inc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by WL Gore and Associates Inc filed Critical WL Gore and Associates Inc
Publication of EP0302596A1 publication Critical patent/EP0302596A1/en
Application granted granted Critical
Publication of EP0302596B1 publication Critical patent/EP0302596B1/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q1/00—Details of, or arrangements associated with, antennas
    • H01Q1/02—Arrangements for de-icing; Arrangements for drying-out ; Arrangements for cooling; Arrangements for preventing corrosion
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q1/00—Details of, or arrangements associated with, antennas
    • H01Q1/42—Housings not intimately mechanically associated with radiating elements, e.g. radome
    • H01Q1/422—Housings not intimately mechanically associated with radiating elements, e.g. radome comprising two or more layers of dielectric material

Definitions

  • the present invention relates to a structure for covering and protecting a radio antenna such as a radar antenna, against weather and moisture, while remaining electromagnetically transparent.
  • radome a covering structure of some kind to protect them from the weather, i.e. sunlight, wind, and moisture and which will preferably be gas-tight; this covering structure is referred to as a radome.
  • a radome is an inflatable radome.
  • a gas-tight balloon shrouds the antenna.
  • a blower inflates the balloon and spaces the structure away from the antenna so that the antenna may move or rotate freely.
  • a popular form of such covering is the geodesic dome or metal space frame radome, which is formed from many metal (or other structural material) geometric shaped segments, such as triangles and others, which are covered with an appropriate radio frequency transmitting membrane, then affixed to each other to form a part-spherical dome surrounding the radar antenna, which rotates or moves inside the radome.
  • Positive gas pressure is not required inside the metal space frame radome, but may be useful at times, for example, to dislodge snow from the outside of the dome, or to aid in controlling the environment within the dome.
  • Another type of installation has solid segmented covering doors over the radio antenna which open to allow the antenna to function through the opening.
  • a semicircular track up which is drawn each edge of a large, nearly electromagnetically transparent sheet of protective membrane to cover the antenna while in use.
  • Other forms of antennas can also be suitably covered by such membranes held above or affixed around them in various ways to keep out moisture and the effects of weather.
  • an electromagnetically-transparent structure which is weather, moisture, and gas-resistant, for enclosing and protecting a radio antenna
  • a layer of laminate comprising adhered layers of polytetrafluoroethylene (PTFE) membrane, thermoplastic polymer, a second layer of PTFE membrane, and a backing fabric, comprising woven fibres of PTFE.
  • the preferred membranes and fibres are of porous PTFE and preferably of porous expanded PTFE (EPTFE) prepared as described in U.S. Patents 3,953,566; 4,096,227; 4,187,390; 4,110,392; 4,025,679; 3,962,153, and 4,482,516.
  • Figure 1 illustrates a laminate 1 according to the invention in cross-section showing various layers.
  • the outer layer 2 is of polytetrafluoroethylene (PTFE), preferably porous PTFE, and most preferably EPTFE.
  • PTFE polytetrafluoroethylene
  • EPTFE is the porous expanded PTFE membrane material made by stretching PTFE in the manner described in the U.S. patents listed above. EPTFE has superior dielectric constant and loss tangent characteristics thus aiding electromagnetic transmission.
  • the outer layer 2 is bonded by means of a thermoplastic polymer layer 3 to a second layer 2 of EPTFE which has previously been adhered or bonded to a textile backing layer 4 comprising woven fibres of PTFE.
  • the preferred form of PTFE is EPTFE.
  • Layer 3 of thermoplastic polymer is preferably a fluorinated ethylene-propylene co-polymer (FEP), but other fluorinated thermoplastic polymers might be used where their PTFE-adhesive properties, radar wavelength transparency, and gas-resistant properties are suitable for use in the particular laminate being prepared.
  • FEP fluorinated ethylene-propylene co-polymer
  • Other non-fluorinated thermoplastic polymers may be used for layer 3 where they meet the criteria of sufficient adhesiveness, electromagnetic transmission characteristics, and gas-proofness or gas-resistance to be adequately functional and useful.
  • Useful thermoplastic polymers may include perfluoroalkoxy­tetrafluoroethylene polymers, ethylene-tetrafluoro­fluoroethylene copolymers, copolymers of vinylidene fluoride and hexafluoropropylene, polychlorotri­fluoroethylene, copolymer of hexafluoropropylene and tetrafluoroethylene, polyethylene and polypropylene.
  • Layer 4 is a woven textile backing fabric for the laminate where the fibres are PTFE, preferably porous PTFE, and most preferably EPTFE. Layer 4 provides strength properties to the laminate, and additional layers of this material may be added where an increase in laminate strength is needed and desired.
  • the woven PTFE or EPTFE fabric is coated with commercially available PTFE dispersion or thermoplastic polymer dispersion to about three to ten percent by weight dispersed PTFE add-on and laminated to an EPTFE film under hot pinch-roll conditions under pressure. Another EPTFE membrane is adhered to FEP film under heat and pressure. The FEP side of this second laminate is then laminated to the EPTFE side of the first laminate by hot pressure rolling to form a four-layer laminate, such as that depicted in cross-section in Figure 1. Additional pairs of layers 2 and 3 may be laminated to the EPTFE face of the laminate in like manner, if desired, to change the electromagnetic transmission characteristics or gas resistance.
  • the laminate provides significant gas-resistance or gas-proof properties associated with the thermopolastic layer or layers so as to be useful for positive pressure type structures in which gas pressure within the dome or shelter holds the covering away from the rotating or moving parts of the antenna housed therein.
  • Figure 2 shows a large metal space frame radome for sheltering and enclosing a radio antenna 5.
  • the segments 6 of the dome have been made by covering geometric shaped frames, usually of metal or other stiff construction materials such as metal or plastic tubing or shaped bar stock, with laminate of this invention. Segements 6 are then assembled into a radome as shown. Other methods for making such a frame, not involving geometric segments, can be made to serve as well and other methods for covering the domes with the laminate 1 of the invention may be used.
  • Figure 3 depicts a different type of housing or shelter for a radio antenna 9, in which the entire housing revolves, a roof shutter 7 and doors 8 roll out of the way of antenna 9, and a large sheltering sheet 11 of composite membrane of the invention is drawn up track 10 to which it is attached at each end to protect the antenna while it is in use.
  • Sheet 11 of Figure 3 and the covering 6 of each segment of the geodesic dome of Figure 2 each embody one form of the present invention.
  • the laminates are inert to and unaffected by the elements, including sunlight, ozone, temperature extremes, wind, rain, and snow, and are inert, hydrophobic and gas-resistant. They are very thin and strong, have excellent colour reflectance and electromagnetic transmission, low dielectric constant, and low loss tanget.
  • the laminates when used in radomes reduce maintenance costs, provide lower cost structural enclosures, allow more accurate measurements, and provide for increased viewing time, do not need to be painted or otherwise maintained as do other materials, and have low adhesion and excellent release for snow and ice which might form on the surface of the radome.

Abstract

An electromagnetically-transparent structure, which is weather-, moisture-, and gas-resistant, for enclosing and protecting a radio antenna including a layer of laminate, comprising adhered layers of polytetrafluoro­ethylene (PTFE) membrane (2), thermoplastic polymer (3), a second layer of PTFE membrane (2), and a backing fabric (4) comprising woven fibres of PTFE.

Description

  • The present invention relates to a structure for covering and protecting a radio antenna such as a radar antenna, against weather and moisture, while remaining electromagnetically transparent.
  • Large radio antennas, such as radar installations and radio telescopes, often need a covering structure of some kind to protect them from the weather, i.e. sunlight, wind, and moisture and which will preferably be gas-tight; this covering structure is referred to as a radome. One type of radome is an inflatable radome. In this case, a gas-tight balloon shrouds the antenna. A blower inflates the balloon and spaces the structure away from the antenna so that the antenna may move or rotate freely. A popular form of such covering is the geodesic dome or metal space frame radome, which is formed from many metal (or other structural material) geometric shaped segments, such as triangles and others, which are covered with an appropriate radio frequency transmitting membrane, then affixed to each other to form a part-spherical dome surrounding the radar antenna, which rotates or moves inside the radome. Positive gas pressure is not required inside the metal space frame radome, but may be useful at times, for example, to dislodge snow from the outside of the dome, or to aid in controlling the environment within the dome. Another type of installation has solid segmented covering doors over the radio antenna which open to allow the antenna to function through the opening.
  • On each side of the opening is affixed a semicircular track, up which is drawn each edge of a large, nearly electromagnetically transparent sheet of protective membrane to cover the antenna while in use. Other forms of antennas can also be suitably covered by such membranes held above or affixed around them in various ways to keep out moisture and the effects of weather.
  • While useful in varying degrees, the various forms and compositions of membrane hitherto known in the art, such as polytetrafluoroethylene fibre-glass laminates, have not solved all of the problems associated with use of this type of covering for protecting radio antennas.
  • According to the present invention there is provided an electromagnetically-transparent structure, which is weather, moisture, and gas-resistant, for enclosing and protecting a radio antenna including a layer of laminate, comprising adhered layers of polytetrafluoroethylene (PTFE) membrane, thermoplastic polymer, a second layer of PTFE membrane, and a backing fabric, comprising woven fibres of PTFE. The preferred membranes and fibres are of porous PTFE and preferably of porous expanded PTFE (EPTFE) prepared as described in U.S. Patents 3,953,566; 4,096,227; 4,187,390; 4,110,392; 4,025,679; 3,962,153, and 4,482,516.
  • The invention will now be particularly described, by way of example, with reference to the accompanying drawings in which:-
    • Figure 1 is a cross-section of a preferred laminate according to the invention;
    • Figure 2 is a broken-away view of a space frame radome covering and protecting a rotating radio antenna, and
    • Figure 3 shows a radio telescope housing, where shutter and doors are drawn aside and a covering sheet of composite membrane is being drawn over the antenna.
  • Figure 1 illustrates a laminate 1 according to the invention in cross-section showing various layers. The outer layer 2 is of polytetrafluoroethylene (PTFE), preferably porous PTFE, and most preferably EPTFE.
  • EPTFE is the porous expanded PTFE membrane material made by stretching PTFE in the manner described in the U.S. patents listed above. EPTFE has superior dielectric constant and loss tangent characteristics thus aiding electromagnetic transmission. The outer layer 2 is bonded by means of a thermoplastic polymer layer 3 to a second layer 2 of EPTFE which has previously been adhered or bonded to a textile backing layer 4 comprising woven fibres of PTFE. Here again, the preferred form of PTFE is EPTFE.
  • Layer 3 of thermoplastic polymer is preferably a fluorinated ethylene-propylene co-polymer (FEP), but other fluorinated thermoplastic polymers might be used where their PTFE-adhesive properties, radar wavelength transparency, and gas-resistant properties are suitable for use in the particular laminate being prepared. Other non-fluorinated thermoplastic polymers may be used for layer 3 where they meet the criteria of sufficient adhesiveness, electromagnetic transmission characteristics, and gas-proofness or gas-resistance to be adequately functional and useful. Useful thermoplastic polymers may include perfluoroalkoxy­tetrafluoroethylene polymers, ethylene-tetrafluoro­fluoroethylene copolymers, copolymers of vinylidene fluoride and hexafluoropropylene, polychlorotri­fluoroethylene, copolymer of hexafluoropropylene and tetrafluoroethylene, polyethylene and polypropylene. Layer 4 is a woven textile backing fabric for the laminate where the fibres are PTFE, preferably porous PTFE, and most preferably EPTFE. Layer 4 provides strength properties to the laminate, and additional layers of this material may be added where an increase in laminate strength is needed and desired.
  • The woven PTFE or EPTFE fabric is coated with commercially available PTFE dispersion or thermoplastic polymer dispersion to about three to ten percent by weight dispersed PTFE add-on and laminated to an EPTFE film under hot pinch-roll conditions under pressure. Another EPTFE membrane is adhered to FEP film under heat and pressure. The FEP side of this second laminate is then laminated to the EPTFE side of the first laminate by hot pressure rolling to form a four-layer laminate, such as that depicted in cross-section in Figure 1. Additional pairs of layers 2 and 3 may be laminated to the EPTFE face of the laminate in like manner, if desired, to change the electromagnetic transmission characteristics or gas resistance.
  • Some variation among the fluorinated thermoplastics available for layer 3 may be utilized as well to adjust the electromagnetic transmission characteristics and frequency demand. The laminate provides significant gas-resistance or gas-proof properties associated with the thermopolastic layer or layers so as to be useful for positive pressure type structures in which gas pressure within the dome or shelter holds the covering away from the rotating or moving parts of the antenna housed therein.
  • Figure 2 shows a large metal space frame radome for sheltering and enclosing a radio antenna 5. The segments 6 of the dome have been made by covering geometric shaped frames, usually of metal or other stiff construction materials such as metal or plastic tubing or shaped bar stock, with laminate of this invention. Segements 6 are then assembled into a radome as shown. Other methods for making such a frame, not involving geometric segments, can be made to serve as well and other methods for covering the domes with the laminate 1 of the invention may be used.
  • Figure 3 depicts a different type of housing or shelter for a radio antenna 9, in which the entire housing revolves, a roof shutter 7 and doors 8 roll out of the way of antenna 9, and a large sheltering sheet 11 of composite membrane of the invention is drawn up track 10 to which it is attached at each end to protect the antenna while it is in use. Sheet 11 of Figure 3 and the covering 6 of each segment of the geodesic dome of Figure 2 each embody one form of the present invention.
  • The laminates are inert to and unaffected by the elements, including sunlight, ozone, temperature extremes, wind, rain, and snow, and are inert, hydrophobic and gas-resistant. They are very thin and strong, have excellent colour reflectance and electromagnetic transmission, low dielectric constant, and low loss tanget. The laminates when used in radomes reduce maintenance costs, provide lower cost structural enclosures, allow more accurate measurements, and provide for increased viewing time, do not need to be painted or otherwise maintained as do other materials, and have low adhesion and excellent release for snow and ice which might form on the surface of the radome.

Claims (6)

1. An electromagnetically-transparent structure, which is weather, moisture, and gas-resistant, for enclosing and protecting a radio antenna including a layer of laminate, characterised in that it comprises adhered layers of polytetrafluoroethylene (PTFE) membrane, thermoplastic polymer, a second layer of PTFE membrane, and a backing fabric comprising woven fibres of PTFE.
2. A structure according to claim 1, characterised in that the first and second layers of PTFE are porous.
3. A structure according to claim 2, characterised in that the first and second layers of PTFE are porous expanded PTFE (EPTFE).
4. A structure according to claim 3, characterised in that the backing fabric is EPTFE.
5. A structure according to claim 4, characterised in that the thermoplastic polymer is a fluorinated ethylene- propylene co-polymer (FEP).
6. A structure according to claim 5, characterised in that the thermoplastic polymer is perfluoroalkoxytetrafluoroethylene (FPA), an ethylene­tetrafluoroethylene copolymer, a copolymer of vinylidene fluoride and chlorotrifluoroethylene, a copolymer of vinylidene fluoride and hexafluoro­propylene, polychlorotrifluoroethylene, a copolymer of hexafluoropropylene and tetrafluoroethylene, poly­ethylene, or polypropylene.
EP88306093A 1987-08-06 1988-07-04 Electromagnetically-transparent laminate Expired - Lifetime EP0302596B1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US8374687A 1987-08-06 1987-08-06
US83746 1987-08-06

Publications (2)

Publication Number Publication Date
EP0302596A1 true EP0302596A1 (en) 1989-02-08
EP0302596B1 EP0302596B1 (en) 1993-03-03

Family

ID=22180425

Family Applications (1)

Application Number Title Priority Date Filing Date
EP88306093A Expired - Lifetime EP0302596B1 (en) 1987-08-06 1988-07-04 Electromagnetically-transparent laminate

Country Status (16)

Country Link
EP (1) EP0302596B1 (en)
JP (2) JP2642958B2 (en)
KR (1) KR890004466A (en)
CN (1) CN1015414B (en)
AT (1) ATE86411T1 (en)
AU (1) AU603900B2 (en)
CA (1) CA1310573C (en)
DE (1) DE3878777T2 (en)
DK (1) DK438988A (en)
ES (1) ES2038293T3 (en)
FI (1) FI90928C (en)
GB (1) GB2207814A (en)
IE (1) IE62504B1 (en)
IS (1) IS1500B (en)
NO (1) NO173962C (en)
PT (1) PT88153A (en)

Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1993016875A1 (en) * 1992-02-19 1993-09-02 W.L. Gore & Associates, Inc. Chemically resistant diaphragm
WO1994001899A1 (en) * 1992-07-02 1994-01-20 W. L. Gore & Associates, Inc. Sealing frame and protective membrane for a radar dish or horn
EP0786823A1 (en) * 1996-01-22 1997-07-30 W.L. GORE & ASSOCIATES, INC. Non-woven electro-magnetically transparent material
US5904978A (en) * 1995-12-15 1999-05-18 W. L. Gore & Associates, Inc. Electrically conductive polytetrafluoroethylene article
US5945217A (en) * 1997-10-14 1999-08-31 Gore Enterprise Holdings, Inc. Thermally conductive polytrafluoroethylene article
US5947918A (en) * 1996-11-18 1999-09-07 Gore Enterprise Holdings, Inc. Impact energy absorbing composite materials
NL1026919C2 (en) * 2004-08-27 2006-02-28 Nedap Agri B V Ultra-wide-band system for determining animals.
CN109462003A (en) * 2018-10-11 2019-03-12 江苏三和欣创通信科技有限公司 A kind of measurement antenna system based on full frequency band
US10450697B2 (en) 2014-09-16 2019-10-22 Dsm Ip Assets B.V. Space frame radome comprising a polymeric sheet

Families Citing this family (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2250804B (en) * 1990-11-07 1994-06-01 Colebrand Ltd Protective device for a sensing head
FR2753007B1 (en) * 1996-09-04 1998-11-27 Bourquin Patrick SATELLITE RECEPTION ANTENNA
AU4173297A (en) * 1996-09-13 1998-05-11 W.L. Gore & Associates, Inc. Satellite dish cover
US6770577B2 (en) * 2001-10-29 2004-08-03 Gore Enterprise Holdings, Inc. Architectural fabric
EP2244878B1 (en) 2008-02-05 2018-11-07 Saint-Gobain Performance Plastics Corporation Multi-layer article
CN101364669B (en) * 2008-09-25 2012-08-29 东华大学 Polyethylene reinforced radar cowl of ultra-high molecular weight, preparation and application thereof
JP5498501B2 (en) * 2008-11-12 2014-05-21 サン−ゴバン パフォーマンス プラスティックス コーポレイション Barrier structure and manufacturing method thereof
US8859102B2 (en) 2008-11-12 2014-10-14 Saint-Gobain Performance Plastics Corporation Barrier structure and method for making
TWI397620B (en) * 2010-06-30 2013-06-01 Method for Making Tensile Teflon (ePTFE) Line
CN110808465B (en) * 2019-09-27 2021-02-02 浙江瑞堂塑料科技股份有限公司 High-wave-transmittance radome and preparation process thereof

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3953566A (en) * 1970-05-21 1976-04-27 W. L. Gore & Associates, Inc. Process for producing porous products
US4025679A (en) * 1976-08-06 1977-05-24 W. L. Gore & Associates, Inc. Fibrillated polytetrafluoroethylene woven filter fabric
EP0155599A2 (en) * 1984-03-22 1985-09-25 Dornier Gmbh Radome material
EP0158116A1 (en) * 1984-03-22 1985-10-16 DORNIER SYSTEM GmbH Method for manufacturing radomes
DE3421196A1 (en) * 1984-06-07 1985-12-19 Dornier System Gmbh, 7990 Friedrichshafen Radome material
US4615933A (en) * 1984-04-06 1986-10-07 Rogers Corporation Radome structure and method of manufacture thereof

Family Cites Families (4)

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Publication number Priority date Publication date Assignee Title
JPS56110304A (en) * 1980-02-05 1981-09-01 Mitsubishi Electric Corp Film material for radome
JPS5925808U (en) * 1982-08-04 1984-02-17 三菱樹脂株式会社 Cover for parabolic antenna
JPS6082813U (en) * 1983-11-14 1985-06-08 日東電工株式会社 Antenna reflector cover structure
JPS6286714U (en) * 1985-11-20 1987-06-03

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3953566A (en) * 1970-05-21 1976-04-27 W. L. Gore & Associates, Inc. Process for producing porous products
US4025679A (en) * 1976-08-06 1977-05-24 W. L. Gore & Associates, Inc. Fibrillated polytetrafluoroethylene woven filter fabric
EP0155599A2 (en) * 1984-03-22 1985-09-25 Dornier Gmbh Radome material
EP0158116A1 (en) * 1984-03-22 1985-10-16 DORNIER SYSTEM GmbH Method for manufacturing radomes
US4615933A (en) * 1984-04-06 1986-10-07 Rogers Corporation Radome structure and method of manufacture thereof
DE3421196A1 (en) * 1984-06-07 1985-12-19 Dornier System Gmbh, 7990 Friedrichshafen Radome material

Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1993016875A1 (en) * 1992-02-19 1993-09-02 W.L. Gore & Associates, Inc. Chemically resistant diaphragm
WO1994001899A1 (en) * 1992-07-02 1994-01-20 W. L. Gore & Associates, Inc. Sealing frame and protective membrane for a radar dish or horn
US5904978A (en) * 1995-12-15 1999-05-18 W. L. Gore & Associates, Inc. Electrically conductive polytetrafluoroethylene article
EP0786823A1 (en) * 1996-01-22 1997-07-30 W.L. GORE & ASSOCIATES, INC. Non-woven electro-magnetically transparent material
US5947918A (en) * 1996-11-18 1999-09-07 Gore Enterprise Holdings, Inc. Impact energy absorbing composite materials
US5945217A (en) * 1997-10-14 1999-08-31 Gore Enterprise Holdings, Inc. Thermally conductive polytrafluoroethylene article
NL1026919C2 (en) * 2004-08-27 2006-02-28 Nedap Agri B V Ultra-wide-band system for determining animals.
WO2006022548A1 (en) * 2004-08-27 2006-03-02 Nedap Agri B.V. Ultra wide band system for animal location
US10450697B2 (en) 2014-09-16 2019-10-22 Dsm Ip Assets B.V. Space frame radome comprising a polymeric sheet
CN109462003A (en) * 2018-10-11 2019-03-12 江苏三和欣创通信科技有限公司 A kind of measurement antenna system based on full frequency band

Also Published As

Publication number Publication date
AU603900B2 (en) 1990-11-29
ES2038293T3 (en) 1993-07-16
FI883578A (en) 1989-02-07
DE3878777T2 (en) 1993-06-09
PT88153A (en) 1989-06-30
CN1015414B (en) 1992-02-05
JP2662381B2 (en) 1997-10-08
DK438988D0 (en) 1988-08-05
DE3878777D1 (en) 1993-04-08
CA1310573C (en) 1992-11-24
ATE86411T1 (en) 1993-03-15
FI90928C (en) 1994-04-11
IS1500B (en) 1992-07-30
NO883421D0 (en) 1988-08-02
NO173962B (en) 1993-11-15
AU1750888A (en) 1989-02-09
GB2207814A (en) 1989-02-08
NO173962C (en) 1994-02-23
FI90928B (en) 1993-12-31
GB8815837D0 (en) 1988-08-10
IE62504B1 (en) 1995-02-08
IS3379A7 (en) 1989-02-07
CN1031050A (en) 1989-02-15
NO883421L (en) 1989-02-07
DK438988A (en) 1989-02-07
KR890004466A (en) 1989-04-22
IE882367L (en) 1989-02-06
JPH01114101A (en) 1989-05-02
JP2642958B2 (en) 1997-08-20
EP0302596B1 (en) 1993-03-03
JPH08181522A (en) 1996-07-12
FI883578A0 (en) 1988-07-29

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