Antenna assembly

Information

  • Patent Grant
  • 6348900
  • Patent Number
    6,348,900
  • Date Filed
    Tuesday, January 25, 2000
    24 years ago
  • Date Issued
    Tuesday, February 19, 2002
    22 years ago
Abstract
An antenna apparatus for a communication device operating in the frequency range of between 800 and 3000 MHz, comprises at least one radiator (1), which is galvanically connected to one end of a spiral conductor (2). This is, in turn, connected to a transceiver (4). An earthed conductor (6) extends along the extent of the spiral (2) to form a capacitance therewith distributed along the spiral.
Description




TECHNICAL FIELD




The present invention relates to an antenna apparatus for a communication device operating in the frequency range of between 800 and 3000 MHz, comprising at least one radiator which is Galvanically connected to one end a of a spiral conductor which in turn is connected to a transceiver.




BACKGROUND ART




The connection impedance to a transceiver of the type employed in so-called mobile telephones is often of the order of magnitude of 50 ohm. Depending, upon the design and type of radiator, its impedance may vary greatly, for example, within the range of between 100 and 1000 ohm. Thus, adaptation of the impedance is necessary.




In prior art designs and constructions, it is normal to build up an adaptation network of discrete components which are often placed on a circuit card in the communication device. Even if impedance adaptation in such designs and constructions may be satisfactory, these designs and constructions are generally expensive and suffer from high losses. Further, it is not possible, in this type of adaptation network, simply to include the antenna construction proper, as would be desirable since this would realise a simple and compact integral construction.




In mobile telephones in the stand-by mode, i.e., when the mobile telephone device is ready for receiving an incoming, signal, a small and compact antenna is further required, which, moreover must be mechanically durable and well protected. The degree of efficiency of such an antenna need not be sufficient to give complete range and transmission quality in the activated state, i.e., during talks. In order to realise a higher degree of efficiency in the antenna, use is often made of a retractable antenna which is employed in the activated state. Such a construction also presupposes the incorporation of an adaptation network between the antenna/antennas and the transceiver. There is a serious need in the art that all of these components can be downscaled to miniature and given good mechanical protection.




Problem Structure




The present invention has for its object to realise an apparatus which obviates the problems inherent in prior art constructions. Thus, the present invention has for its object to realize an antenna apparatus which may have one or two radiators and which has an integrated adaptation network, in which the adaptation network has a high degree of efficiency, is mechanically stable and extremely space-saving. The present invention further has for its object to realize an apparatus which is simple and economical in manufacture.




Solution




The invention relates to an antenna apparatus for a communication device operating in the frequency range of between 800 and 3000 MHz. The antenna apparatus is of the type having at least one radiator which is galvanically connected to one end of a spiral conductor, which, in turn is connected to a transreceiver at a connection point. The apparatus is characterized in that an earthed conductor extends along the extent of the spiral so that substantially all ofthe capacitance formed by the position of the earthed conductor is distributed along the spiral conductor.




In one aspect of the invention, the connection point is located on an opposite end of the spiral spaced away from the radiator. In another aspect, the connection point is disposed between the ends of the spiral.




In yet another aspect of the invention, the spiral and the transreceiver are galvanically interconnected with one other. Also, the axial direction of the spiral can be substantially parallel to the longitudinal direction of the radiator.




Preferably, the spiral is substantially of helical configuration and the earthed conductor is disposed concentrically in the spiral. An air space can lie between the earthed conductor and the inside of the spiral. In another embodiment, a sleeve of dielectric material is disposed about the earthed conductor with the spiral being wound on the sleeve.




In a first embodiment, the spiral is substantially helical in configuration, while the earthed conductor is disposed concentrically in the spiral.




In a second embodiment, the spiral is substantially planar, which also applies to the earthed conductor which has an outer contour approximately adhering to the outer contour of the spiral.




Further advantages will be attained according to the present invention if the subject matter of the present invention is also given one or more of the characterizing features as set forth in appended subclaims


4


to


15


.











BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS




The present invention will now be described in greater detail hereinbelow, with particular reference to the accompanying drawings. In the accompanying drawings:





FIG. 1

is an electric equivalent diagram of the present invention;





FIG. 2

shows a modified embodiment of the present invention according to

FIG. 1

;





FIG. 3A

shows one practical version of the present invention according to

FIG. 1

;





FIG. 3B

shows the practical version of

FIG. 3A

installer in a socket.





FIG. 4A

shows one practical version of the present invention according to

FIG. 2

;





FIG. 4B

shows the practical version of

FIG. 4A

installed in a socket.





FIG. 5

shows an alternative embodiment of the present invention;





FIG. 6

is a partial magnification of

FIG. 5

;





FIG. 7

is a schematic cross section through a modified embodiment comprising two radiators, of which one is a rod radiator which is in the protracted state;





FIG. 8

shows the antenna apparatus of

FIG. 7

with the rod radiator in the retracted state;





FIG. 9

is a magnified cross section through the lower portion of the antenna apparatus according to

FIGS. 7 and 8

; and





FIG. 10

is a top plan view of the antenna apparatus according to FIG.


9


.











DESCRIPTION OF PREFERRED EMBODIMENTS




In

FIG. 1

, reference numeral


1


relates to a radiator which is galvanically connected to one end of a helical conductor or coil


2


, i.e., an inductance. The coil


2


has an input point


3


via which it is connected to a transceiver


4


. In connection with the coil


2


, there is provided a conductor


6


connected to earth at


5


, the conductor extending along the coil


2


and having the same spatial extent as the coil. There will thereby be formed between the coil


2


and the earthed conductor


6


a capacitance distributed along the coil. The coil


2


and the earthed conductor


6


form an adaptation network which transforms the higher impedance of the radiator to a value of the order of magnitude of 50 ohm, which corresponds with the 50 ohm of the transceiver.




The apparatus according to

FIG. 1

may operate both as a quarter wave antenna and as a half wave antenna. If the antenna is set for the 800 MHz band and quarter wave operation it will, as half wave antenna, be set for approximately 1600 MHz, i.e. approximately twice the lower frequency.





FIG. 2

shows a variation of the present invention in which the relationship between the resonance frequencies in half wave operation and quarter wave operation deviates from 2. This has been realized by a displacement of the input point


3


along the coil


2


so that the coil extends on both sides of the input point. Because of the extra impedancc which is realized by the free portion


7


of the coil, the radiator


1


is seen electrically to be longer than it actually is. This implies that it will be resonant at a lower frequency than would have been the case in a pure quarter wave radiator.




In half wave operation, because of the extra capacitance the coil will be seen as shorter than would have been the case for a pure half wave adaptation. This gives a shorter antenna, for which reason the resonance frequency will be higher than would have been the case in a pure half wave antenna. By suitable dimensioning it is thus possible to cause the antenna to operate as a quarter wave antenna in the 800 MHz band while operating as a half wave antenna in the 1900 MHz band. The relationship between the two frequencies is here greater than 2.





FIG. 3

shows an example of a physical array construction of an apparatus according to FIG.


1


. The antenna according to

FIG. 3

has a sleeve


8


which is earthed in the apparatus and is provided with an internal insulator


9


. A contact pin


17


extends concentrically through the insulator and merges, on the upper side of the sleeve


8


, into a spiral conductor, preferably of helical configuration, or a coil


10


. The radiator proper is connected at the upper end of the coil


10


and, in this embodiment, the radiator is designed as a rod antenna


11


. Suitably, the coil


10


is designed as a cylindrical helix with constant pitch along its length, and the rod extends along the axial direction of the coil.




In

FIG. 3

, the earthed conductor carrying reference numeral


6


in

FIG. 1

has its counterpart in a straight conductor


12


which is disposed interiorly in the coil


10


. The conductor


12


extends concentrically along the entire Length of the coil


10


and thereby forms a capacitance with the coil


10


which is distributed continually over the coil


10


. Suitably, the conductor


12


is enveloped by a tube or a sleeve of a dielectric material so that the capacitance may thereby be increased. The tube consists, for example, of polytetrafluoroethene (which is sold under the trademark Teflon®) and may serve as winding support when the coil


10


is wound thereon. In its lower end, the conductor


12


is galvanically connected to the earthed sleeve


8


. It will also be apparent that the conductor


12


and the rod antenna


11


are suitably coaxial or approximately coaxial with one another.




In the right-hand portion of

FIG. 3

, it is shown how the earthed sleeve


8


is inserted in a socket


14


provided in the casing


13


of the device, the socket having a mechanical connection arrangement with resilient tongues for snap-in action into a circumferential groove


15


in the sleeve


8


. It will further be apparent that the entire antenna apparatus may be cast in an insulating protective housing which is indicated by the ghosted line


16


.




In one practical version, the antenna according to

FIGS. 1 and 3

has, in half wave design, a rod length of approximately 110 mm in the 900 MHz band, and approximately 50 mm in the 1800 MHz band. The wire diameter in the rod


11


and in the coil


10


is approximately 0.8 mm and the coil has an inner diameter of approximately 1.5 mm. On setting to 1800 MHz, the coil has approximately 7 turns while the number of turns is approximately 12 in 900 MHz.





FIG. 4

shows one example of the physical construction of an apparatus according to FIG.


2


. In terms of design and construction, the difference vis-a-vis the apparatus according to

FIG. 3

is only that the contact pin


17


has been upwardly extended and has a portion


18


which extends up on the outside along a portion of the coil


10


. As a result, the input point


3


will be located between the ends of the coil, for which reason the coil will have a lower portion


7


which terminates as an appendix. Also in this embodiment, the concentrically disposed and earthed conductor


12


extends throughout the entire length of the coil and therefore forms a capacitance distributed continuously along the coil, both with the upper portion of the coil and with its lower portion


7


. Also in this version, the conductor


12


is suitably enveloped by a tube or sleeve of dielectric material, on which sleeve the helically designed conductor


7


and


10


is wound.




It will be apparent from the right-hand portion of

FIG. 4

that also this embodiment may have an outer, insulating protective housing which is illustrated by the ghosted line


16


.




In one practical version of the antenna according to

FIGS. 2 and 4

, the rod antenna length in half wave operation and at 1800 MHz, as well as at quarter wave operation and 900 MHz is approximately 50 mm. The coil


10


has a total of approximately 10 turns, of which the lower portion


7


terminating as an appendix accommodates approximately two turns. The wire diameter in the rod


11


and the coil


10


is 0.8 mm and the coil has an inner diameter of 1.5 mm.




DESCRIPTION OF ALTERNATIVE EMBODIMENTS





FIGS. 5 and 6

show a modified embodiment of the apparatus according to the invention. In electric terms, this modified embodiment may be executed according to both FIG.


1


and FIG.


2


.




It will be apparent from

FIG. 5

that the antenna in this embodiment has an earthed sleeve


8


with an interior insulator


9


and a contact pin


17


. At the upper end of the sleeve


8


, there is a radially projecting flange


19


(

FIG. 6

) on which rests a washer or disk


20


of insulating material. On its underside, the disk


20


has a metal coating


21


which substantially continuously covers the entire underside of the disk. The metal coating


21


is galvanically connected to the sleeve


8


and its flange


19


, for example by soldering


22


.




On the upper side of the disk


20


, there is disposed a helical conductor


23


which is planar and is secured on the disk. The spiral


23


has an inner or central connecting portion


24


which, via soldering


25


, is connected to the upper end of the contact pin


17


. The various turns


23




a


,


23




b


,


23




c


, etc., of the helical spiral extend around the connecting portion


24


. At one outer portion of the spiral


23


, this is provided with an outer connecting portion


26


in which a conductor


27


is soldered. The conductor


27


extends to a position a slight distance above the upper end of the contact pin


17


where it is galvanically connected to a coupling


28


which also galvanically connects to a rod antenna


11


.




If the outer connecting portion


26


is located at the outer end of the spiral


23


, there will be realized an apparatus of the type illustrated in FIG.


1


. If, on the other hand, the connecting portion


26


is located between the ends of the spiral, i.e. partly in from the outer end of the spiral, there will be realized an apparatus of the type illustrated in FIG.


2


.




As has been mentioned above, the spiral


23


is substantially planar and its different turns may be substantially circular or round, but may also be designed as a polygon, for example with four or more sides.




In one practical version, the disk


20


is ideally a double-sided circuit card and the spiral


23


is produced by etching of the upper face of the circuit card, while the under face of the circuit card is left untouched.




It will be apparent from

FIG. 6

that the lower metal layer


21


on the disk


20


has an aperture


29


through which the contact pin


17


extends without forming any galvanic contact with the metal layer


21


. As a result of this feature, there will be achieved a capacitance distributed over the spiral


23


which is realized by the metal layer


21


and which may suitably have an extent which corresponds to the outer contour of the spiral


23


.




In order not to cause unnecessary losses, the spiral


23


is, as far as possible, enveloped by a gaseous dielectric, preferably air. This, as is apparent from

FIG. 5

, is realized in that at least a part of the coupling


28


and an upper portion of the sleeve


8


(preferably its flange


19


) are enclosed in a retainer body


30


which has a cavity


31


surrounding the disk


20


and the conductor


27


. An insulating protective casing


32


is then disposed on the outside of the retainer body


30


.




In one practical embodiment of the antenna according to

FIGS. 5 and 6

, the rod


11


in half wave operation has a length of 110 mm at 900 Mhz, and approximately 50 mm at 1800 MHz. The conductor


27


has a length of approximately 6 mm and a diameter of 0.8 mm. The circuit card


23


has a laminate thickness of 0.8 mm and a diameter of 8 mm. At 1800 MHz and half wave operation, the plarar etched coil


23




a


-


23




c


has approximately 1.3 turns, in which each turn has a thickness (radial width) of approximately 0.5 mm. At 900 Mhz and half wave operation, the number of turns is approximately 2.8. The protective outer casing surrounding the rod


11


has an outer diameter of approximately 11 mm, and the antenna a total length of approximately 65 mm, designed for 1800 MHz and half wave operation.




In all of the above-described embodiments, the radiator


1


has been illustrated as a rod, but, of course, this may be of other design, for example as a helix.




As an alternative to employing a double-sided circuit card in production of the disk


20


, a single-sided such card may be employed. In order, in this alternative, to realise a counterpart to the metal layer


21


, the flange


19


is extended in the radial direction so as to cover substantially the whole of the underside of the disk


20


and thereby replace the metal layer


21


.




As an alternative to the galvanic coupling (via the conductor


27


) between the lower end of the rod


11


and the spiral conductor


23


, both capacitative and inductive coupling may be employed.




A capacitative coupling will be realized if the lower end of the rod


11


is galvanically connected to a metal plate which is approximately parallel with the plane of the spiral conductor


23


and which is designed in slight spaced apart relationship therefrom. The gap between the plate and spiral conductor


23


may be filled with air but may also contain a dielectric material such as the insulating layer in a single-sided circuit card in which the plate has been worked into its upper, conductive metal layer.




The inductive coupling, may be realized if the plate is replaced by a spiral.





FIGS. 7-10

illustrate an antenna apparatus which has two different radiators, of which one is used in the stand-by mode, while the other is employed during talk.




In

FIG. 7

, reference numeral


1


relates to a first radiator and reference numeral


33


to a second radiator. The radiators


1


and


33


are arranged, via a coupling device, such that when the first radiator


1


is active, the second radiator


33


is passive, and vice versa. This is achieved via a mechanical coupling device whereby the radiators are alternatingly connectable to a transceiver (not shown on the Drawing) which, via a suitable conductor, is connected to the terminal


34


of the antenna apparatus. Possibly, both of the radiators may be galvanically connected in parallel when the second radiator


33


is in the active state.




The second radiator is designed as a rod


11


which is shiftable in its longitudinal direction from the protracted position of use (the active position) according to

FIG. 7

to the retracted and passive position according to FIG.


8


. In such instance the rod


11


extends through the first radiator


1


which is designed as a helix


35


. The helix is, according to the invention, cast or otherwise disposed internally in a protective body


16


produced from insulating material and provided with a channel through which the rod


11


is protractible and retractable.




In order to permit switching between the two radiators


1


and


33


, the rod


11


has, in its upper end, an electrically insulating portion


37


which, in the retracted position of the rod in

FIG. 8

, is located interiorly in the helix


35


and extends at least along the major portion of its length. Given that the helix will hereby have an inner body of dielectric material, its radiation properties will not be appreciably affected, for which reason the helix


35


will, in this case, be active and operate without any actuation from the rod


11


. At the lower end, the rod


11


has an electrically conductive portion


38


made of metal and, in the protracted position of the rod according to

FIG. 7

, is located interiorly in the helix


35


and extends, in the longitudinal direction, throughout substantially the entire length of the helix. By placing a metallic, electrically conductive body interiorly in the helix, this will be “short-circuited” and thereby cease lo function as radiation element. The helix


35


may, in this case, possibly be considered as a portion which is integrated in electric terms with the rod


11


, or as a radiator connected in parallel with the rod.




The conductive portion


38


is, in the position of the rod


11


according to

FIG. 7

, coupled via the mechanical coupling device to the transceiver


4


, for which reason the rod in this position will alone function as a radiator. However, the helix


35


may, in this position, be considered in electric terms as a part of the rod. Ideally, the rod has been set to half wave operation while the helix is designed for quarter wave operation. However, the rod may also be set for quarter wave operation.





FIG. 9

shows more clearly the details and parts in the construction according to FIG.


7


. It will be apparent from this Figure that the lower, conductive portion


38


of the rod


11


extends through the helix


35


substantially throughout the entire length thereof, and down into a sleeve


39


produced of metal and provided with contact fingers


40


. Hereby, the rod


11


will be galvanically connected to the sleeve


39


. The sleeve


39


has, in an upper region, a radially projecting flange


41


on whose upper side rests the helix


35


. The sleeve


39


further extends one or slightly more than one turn interiorly up in the helix via a bushing


42


which thereby offers the possibility of positional fixing of the helix


35


so that this and the rod


11


may be kept approximately coaxial in relation to one another. The lower end of the helix is anchored in the bushing


42


and/or the flange


41


and is, galvanically connected to one or both of them.




In the retracted position according to

FIG. 8

, the upper, insulated portion


37


of the rod


11


will be located interiorly in the helix


35


and also extend down into the electrically conductive sleeve


39


, whereby no electric contact (galvanic contact) is formed between the sleeve


39


and the rod


11


. This is, hence, electrically disconnected and inactive in this position, while, on the other hand, the helix


35


is galvanically connected to the sleeve.




Both of the radiators


1


and


33


have a connection impedance of the order of magnitude of 130 Ω, while the transceiver has an impedance of approximately 50 Ω. Between the terminal


34


and the common coupling point of both radiators


1


and


33


in the region of the bushing


42


and the flange


41


, there is disposed an adaptation network


43


.




The terminal


34


has an inner, central conductor or contact pin


17


which is surrounded by a concentrically disposed, insulating sleeve


9


. The sleeve


9


is, in its turn, surrounded by an electrically conductive sleeve


8


, which is connected to earth. The contact pin


17


has, in its upper end, a joint or bracket


44


in which the lower end of the spiral conductor


10


is secured and galvanically connected to the contact pin. The upper end of the spiral conductor


10


is, via an electrically conductive joint or coupling


45


, galvanically connected to the lower end of the helix


35


or to the sleeve


39


in the region of the flange


41


and/or the bushing


42


.




On galvanic contact with the earthed sleeve


8


, a conductor


12


extends up through the spiral conductor


10


. The conductor


12


has, in its lower end, an annular formation which is accommodated and galvanically connected in a groove in the sleeve


8


. The conductor


12


extends along the path of extent of the spiral conductor


10


whereby there is formed between them a capacitance which is distributed along the spiral conductor. Suitably, the conductor


12


may be straight and approximately parallel with the longitudinal direction of the rod


11


and may also be surrounded by a sleeve of electrically insulating material, such as polytetrafluorocthene (sold under the trademark Teflon®). The spiral conductor may suitably be designed as an approximately cylindrical helix, which is wound onto the above-mentioned sleeve. The earthed conductor


12


and the spiral conductor


10


together form an adaptation network for impedance adaptation of both of the radiators


1


and


33


.




In the top of the helix


35


, there is disposed a top loop


46


, which preferably has approximately twice the diameter of the helix


35


and which may amount to approximately 1 turn. The top loop has a plane of extent which is approximately at right angles to the axis of the helix


35


and the longitudinal direction of the rod


11


and is of one piece manufacture with the helix


35


and connected to upper end thereof via a connecting portion


47


which is approximately U-shaped in side elevation. The bottom shank of this connecting portion constitutes an approximately tangentially directed continuation of the upper end of the helix


35


, while the upper shank connects from beneath to the top loop


46


.




In one practical version of the apparatus according to the present invention intended for the 900 Mhz band and with the helix


35


working as a quarter wave antenna and the rod


11


working as a half wave antenna, the following detailed design and construction may apply:




The rod


11


has a total length of approximately 103 mm, while its lower, electrically conductive portion has a length of approximately 78 mm, and a suitable diameter is 1.5 mm.




The helix antenna


35


comprises


8


turns distributed over a length (height) of 8.75 mm and with an inner diameter of 2.5 mm. The length (height) of the top loop


46


, including connection portion


47


, is 3.75 mm. The top loop comprises approximately 1 turn and has an inner diameter of 6 mm.




The spiral conductor


10


has 3.75 turns distributed over a length (height) of 4.7 mm and an inner diameter of 2 mm. The distance between the center axes of the spiral conductor


10


and the helix antenna


35


is 7 mm. The wire diameter in both the helix


35


and the spiral conductor is 0.75 mm.




It has been presupposed in the foregoing that a galvanic coupling were to take place between the lower end of the rod


11


and the sleeve


39


. It is however also possible to provide a capacitative coupling between the lower end of the rod and the sleeve


39


, possibly also in relation to the helix


35


.




The rod


11


has been assumed to be designed as a half wave antenna, but may also be dimensioned for quarter wave operation.




The spiral conductor


10


is shown and described as a cylindrical helix, but it may also be a planar spiral which is disposed on one side of disk of insulating material, in which event this disk is provided on the opposing side with a plate which electrically corresponds to the conductor


12


. The plane of extent of the plate and the outer contour of the spiral are approximately equal.




As an alternative to the contact fingers


40


of the sleeve


39


, use may be made of contact fingers on the under end portion of the rod. These contact fingers or springs borne by the rod


11


are insertable from beneath into the sleeve


39


which, in this embodiment, is rigid. Regardless of whether the contact fingers are disposed in the sleeve or on the rod, they serve the double purpose of, on the one hand, galvanically interconnecting the sleeve


39


and the rod


11


and, on the other hand, of mechanically retaining the rod


11


in the protracted position.




Further modifications of the present invention are possible without departing from the spirit and scope of the appended claims.



Claims
  • 1. An antenna apparatus for a communication device operating in the frequency range of between 800 and 3000 MHz, comprising at least one radiator which is galvanically connected to one end of a spiral conductor which in turn is connected to a transceiver at a connection point, characterized in that an earthed conductor extends along the extent of the spiral so that substantially all of the capacitance formed by the position of the earthed conductor is disturbuted along the spiral conductor.
  • 2. The apparatus as claimed in claim 1 wherein the connection point of the spiral with the transceiver is located on an opposite end of the spiral spaced away from the radiator.
  • 3. The apparatus as claimed in claim 1 wherein the connection point of the spiral with the transceiver is disposed between the one end and an opposite end of the spiral.
  • 4. The apparatus as claimed in claim 1 wherein the spiral and the transceiver are galvanically interconnected with one another.
  • 5. The apparatus as claimed in claim 1 wherein one axial direction of the spiral is substantially parallel to the longitudinal direction of the radiator.
  • 6. The apparatus as claimed in claim 1 wherein the spiral is substantially of helical configuration and the earthed conductor is disposed concentrically in the spiral.
  • 7. The apparatus as claimed in claim 6 and further comprising an air space between the earthed conductor and the inside of the spiral.
  • 8. The apparatus of claim 6 wherein a sleeve of dielectric material is disposed about the earthed conductor with the spiral being wound on the sleeve.
  • 9. An antenna apparatus for a communicating device operating in the frequency range of between 800 and 3000 MHz, the apparatus comprising:at least one radiator; one spiral conductor, said spiral conductor being solely connected to said radiator and a transceiver, the connection of the radiator being accomplished at one end of the spiral conductor and the connection to said transceiver at a feed point; and one conductor solely connected to earth, said conductor extending in proximity with and along the extent of said spiral conductor so that substantially all of the capacitance formed by the position of the earthed conductor is distributed along the extent of the spiral conductor.
Priority Claims (2)
Number Date Country Kind
9501872 May 1995 SE
9501873 May 1995 SE
Parent Case Info

This application is a continuation of U.S. patent application Ser. No. 08/974,306, filed Nov. 17, 1997, now U.S. Pat. No. 6,064,346 which is a continuation of International Patent Application No. PCT/SE96/00608 filed on May 9, 1996, pending, which claims priority from Sweden Application Nos. 9501872-7 and 9501873-5, both filed on May 19, 1995.

US Referenced Citations (9)
Number Name Date Kind
2636122 Hayes Apr 1953 A
2894260 Ellis Jul 1959 A
3825864 Ramstrom Jul 1974 A
4080604 Wosniewski Mar 1978 A
4462033 Grashow et al. Jul 1984 A
4725845 Phillips Feb 1988 A
4980695 Blaese Dec 1990 A
5563615 Tay et al. Oct 1996 A
6064346 Blom May 2000 A
Continuations (2)
Number Date Country
Parent 08/974306 Nov 1997 US
Child 09/491188 US
Parent PCT/SE96/00608 May 1996 US
Child 08/974306 US