CA1211836A - Small angular beamwidth antenna system - Google Patents
Small angular beamwidth antenna systemInfo
- Publication number
- CA1211836A CA1211836A CA000455214A CA455214A CA1211836A CA 1211836 A CA1211836 A CA 1211836A CA 000455214 A CA000455214 A CA 000455214A CA 455214 A CA455214 A CA 455214A CA 1211836 A CA1211836 A CA 1211836A
- Authority
- CA
- Canada
- Prior art keywords
- antenna
- elements
- patterns
- pattern
- receiving
- 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.)
- Expired
Links
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01Q—ANTENNAS, i.e. RADIO AERIALS
- H01Q21/00—Antenna arrays or systems
- H01Q21/29—Combinations of different interacting antenna units for giving a desired directional characteristic
- H01Q21/293—Combinations of different interacting antenna units for giving a desired directional characteristic one unit or more being an array of identical aerial elements
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01Q—ANTENNAS, i.e. RADIO AERIALS
- H01Q25/00—Antennas or antenna systems providing at least two radiating patterns
- H01Q25/002—Antennas or antenna systems providing at least two radiating patterns providing at least two patterns of different beamwidth; Variable beamwidth antennas
Abstract
Abstract of the Disclosure A relatively narrow beamwidth (10° or less) receiving antenna pattern is formed at the receiver end of a radio fre-quency transmission link where a plurality of radiating sources are operating in a dense communications environment. The antenna pattern comprises the difference between two antenna receiving patterns where the beamwidth of one pattern is wider by a pre-determined angular amount than the other pattern. In the pre-ferred embodiment, a phased linear array of antenna elements is operated as two sets of elements wherein one set of elements comprising a number of elements less than the total number of elements provides a beamwidth that is broadened by a predeter-mined angular sector greater than the beamwidth formed by the entire array. The antenna elements are progressively phase shifted to provide overlapping beam patterns and the pattern of one set of elements is scanned so that one side of both patterns are substantially coincident. The received signals from the elements developing the two antenna patterns are respectively combined and linearly subtracted to provide cancellation of all the received radiation except over the small angular sector defined by the difference between the two patterns.
Description
lZ11836 This invention relates generally to communications systems and more particularly to radio frequency communications trunk transmission systems in which antenna pattern cancellation arrangements are utilized to automatically eliminate or reduce external interference at the receiving end of the transmission communications link.
One of the major concerns of designers of antenna system trunk transmission communications links is the elimination or reduction of external interference sources such as jamming ~0 and self-interference in a dense communications environment. For this purpose it is desirable to employ an extremely small beam-width. However, the beamwidth of the antenna is constrained by the allowable physical size of its aperture and most arrangements which attempt to resolve the problems of external interference do so in a relatively complex manner, often utilizing very large directional antennas or antennas having hundreds or more elements to reduce the received beamwidth.
Mobility requirements and cost restrictions generally prevent utilizing an antenna size that provides a beamwidth of ~0 less than one degree in present state of the art transmission systems.
The aim of the present invention is to provide an improved narrow beamwidth antenna for eliminating undesired inter-ference signals at the receiving end of a transmission link.
According to the present invention there is provided a narrow beamwidth receiving antenna system for eliminating undesired interference signals at the receiver end of mobile tactical communications trunk transmission links operating in a dense communications and jamming enfironment, comprising:
- 1- .,.~
lZ~1836 first receiving antenna means having a relatively narrow beamwidth antenna pattern defining a predetermined angular sector;
second receiving antenna means having a relatively narrow beamwidth antenna pattern defining an angular sector greater than that of said first antenna means;
means for orienting said antenna patterns such that said patterns overlap and one side thereof is substantially mutually coincident, providing thereby a single small incremental pattern sector where said antenna patterns do not overlap; and means for subtracting signals received by said first and second antenna means, whereby signal cancellation occurs of substantially all signals arriving from any direction except over said incremental pattern sector.
This interference cancelling system affords an operation which simulates that of a very narrow beam directional antenna in eliminating or reducing external interference sources.
The first and second receiving antenna means may comprise a first and second linear array of antenna elements having beamwidth between 1 and 10.
In the preferred embodiment, a phased linear array of antenna elements are operated as two sets of receiving antenna elements which are progressively phase shifted to provide one pattern having a beamwidth which is broadened by a predetermined incremental angular section relative to the other pattern and scanned so that the two beam patterns substantially line up on one side. The RF signals received by the two sets of elements are respectively combined with the output of the combinear for lZ~ 336 the broadened beam being linearly subtracted from the combiner for the other beam to provide a cancellation of interference from all directions except over a small incremental angular sector where the patterns are not overlapping.
In the accompany drawings, which illustrate an exemplary embodiment of the present invention:
Figure 1 is a functional block diagram illustrative of the preferred embodiment of a receiving antenna system in accordance with the principles of the subject invention;
Figure 2 is a diagram illustrative of the receiving antenna beam patterns formed by the antenna elements shown in Figure l;
Figure 3 is a diagram illustrative of the operation of the subject inventiQn for receiving a desired signal while ' eliminating undesired external interference si~nals; and Figure 4 is a diagram further helpful in understand-ing the principles of the invention.
Referring now to the drawings and more particularly to Figure 1, shown therein is an interference cancelling receiving antenna arrangement particularly adapted for use in tactical mobile trunk transmission systems such as a line of sight transmission link operating in a dense communications environment where severe jamming is encountered and where such systems typically operate in the UHF and SHF frequency bands or in a 12~ 3~
surveillance system which requires extremely small angular resolution such as a beamwidth of less than one degree.
The embodiment of the invention as shown in Figure 1 takes the form of a linear phased array of receiving elements comprised of nine antenna elements 10, 12, 14 ... 26. As is known, the size of the aperture or received pattern beamwidth is a function of the number of elements in the arra~, with the beamwidth of the pattern being reduced as the number of elements increases. In the subject invention, the linear array is operated to provide two receiver antenna beam patterns by utilizing all of the elements 10 through 26 for generating a first beam pattern 28 having an angular beamwidth ~1~ as shown in Figure 2, while a selected number, for example, five of the inner elements 14, 16, 18, 20 and 22 are operated to generate a second pattern 30 having an angular beamwidth of ~2 and which is broader than the beamwidth ~1 by a predetermined angle ~. The beamwidth of the larger angular segment ~2 is designed to be in the range o~ 0 to 10 Further as shown in Figure 1, the antenna elements 10 through 26 are coupled as a fir~t set of elementR to a first signal combiner 32 by phase shifting means 34, 36, 3~ ... 50 while the inner elements 14 through 22 which form the larger beam pattern are coupled as a second set of elements to a second signal combiner 52 through respective phase shifting means 54, 5G, ... 62 coupled to outputs of the phase shifters 38 through 46. The phase shifters 34 through 50 provide phase shifts in multiples of 0 on either side of the center element 18. Thus the phase shifters lZ11836 40, 38, 36 and 34 provide respective phase shifts of -0, -2~, -30 and -40, whereas phase shifters 44, 46, 48 and 50 provide phase shifts of ~, 20, 30 and 40. The phase shifters 54 through 62 provide additional phase shifts in multiples of ~0 on either side of the center element 18. As shown, the phase shifters 56 and 54 provide phase shifts of - ~ 0 and -2 ~0, respectively whereas t~e phase shifters on the right side of the center element, namely, the phase shifters 60 and 62 provide phase shifts of ~0 and 2 ~0, respectively.
The progressive additional phase shifts provided in the inner elements by phase shifters 54 through 62 result in a beamwidth of the pattern 30 for the second or inner set of antenna elements 14 through 22 which is broadened by a ~ and scanned by ~ 0/2 relative to the beam pattern 28 formed by all of the ele~
ments 10 through 26 of the antenna array, which results in the two received patterns 28 and 30 being aligned as shown in Figure 3. The phase shifters 34, 36 ... 50, act to electronically scan the composite beamwidth pattern.
Again, referring to Figure 1, the output of the combiner 52 for the broadened beam ~2 Of pattern 30 is linearly subtracted from the output of the combiner 32 for the narrower beam ~1 of pattern 28 by means of a subtractor 64 which provides a cancellation in the main beam, for example, signals Il and I2 shown in Figure 3 from all directions except over the small angular sector ~0 where the desired signal S is incident thereto.
Since some adjustment of the amplitude of the original beam pattern is necessary to account for amplitude differences between ~Z~1836 the output of the combiners 32 and 52 which results from slight differences in antenna gain, the embodiment of Figure 1 addition-ally discloses a variable attenuator 66 in the signal path between the combiner 32 and the linear subtractor 64. Further as shown, the output of the subtractor 64 is fed to radio receiver apparatus 68 which is operable to demodulate the RF
signals resulting from the differencing of the RF signals received by the first and second sets of antenna elements.
Figure 4 is intended to show~ that whereas an ideal difference pattern designated by reference numeral 70 would tend to have well defined steep sides at the edges of the angular sector ~0, hawever, in reality an actual or real diference pattern would resemble the characteristic designated by reference numeral 72.
Further by rotating the entire antenna array or elec-tronically scanning it, it is possible to direct the beam sector ~0 to any specific signal source while virtually eliminating all undesired signals withou~ requiring any complex adaptive process-ing or requiring a very large complex very narrow beam antenna.
Thus a relatively very narrow pencil beamwidth antenna system results which eliminates multiple interference in the main beam, except over the angular sector ~ and which is realized with practical hardware.
Whereas the pxeferred embodiment of Figure 1 is des-cribed with respect to a linear array, it should be understood that, when desirable, a planar array may be utilized to provide a two dimensional receive antenna pattern having a very high degree of angle of resolution in both azimuth and elevation. Addition-ally, it i5 also within the scope of the present invention to employ a lens or parabolic dish antenna, when desired, with a separate displaced feed to form the additional scanned beam having a different illumination pattern displaced wlth the other antenna feed to broaden its beamwidth pattern.
Having thus shown and described what is considered at present to be the preferred embodiment of the present invention, it will be readily apparent that modifications may be resorted to by those skilled in the art without departing from the spirit and scope of the invention. Accordingly, all alterations, changes and modifications coming within the scope of the invention as set forth in the appended claims axe hexein meant to be included.
One of the major concerns of designers of antenna system trunk transmission communications links is the elimination or reduction of external interference sources such as jamming ~0 and self-interference in a dense communications environment. For this purpose it is desirable to employ an extremely small beam-width. However, the beamwidth of the antenna is constrained by the allowable physical size of its aperture and most arrangements which attempt to resolve the problems of external interference do so in a relatively complex manner, often utilizing very large directional antennas or antennas having hundreds or more elements to reduce the received beamwidth.
Mobility requirements and cost restrictions generally prevent utilizing an antenna size that provides a beamwidth of ~0 less than one degree in present state of the art transmission systems.
The aim of the present invention is to provide an improved narrow beamwidth antenna for eliminating undesired inter-ference signals at the receiving end of a transmission link.
According to the present invention there is provided a narrow beamwidth receiving antenna system for eliminating undesired interference signals at the receiver end of mobile tactical communications trunk transmission links operating in a dense communications and jamming enfironment, comprising:
- 1- .,.~
lZ~1836 first receiving antenna means having a relatively narrow beamwidth antenna pattern defining a predetermined angular sector;
second receiving antenna means having a relatively narrow beamwidth antenna pattern defining an angular sector greater than that of said first antenna means;
means for orienting said antenna patterns such that said patterns overlap and one side thereof is substantially mutually coincident, providing thereby a single small incremental pattern sector where said antenna patterns do not overlap; and means for subtracting signals received by said first and second antenna means, whereby signal cancellation occurs of substantially all signals arriving from any direction except over said incremental pattern sector.
This interference cancelling system affords an operation which simulates that of a very narrow beam directional antenna in eliminating or reducing external interference sources.
The first and second receiving antenna means may comprise a first and second linear array of antenna elements having beamwidth between 1 and 10.
In the preferred embodiment, a phased linear array of antenna elements are operated as two sets of receiving antenna elements which are progressively phase shifted to provide one pattern having a beamwidth which is broadened by a predetermined incremental angular section relative to the other pattern and scanned so that the two beam patterns substantially line up on one side. The RF signals received by the two sets of elements are respectively combined with the output of the combinear for lZ~ 336 the broadened beam being linearly subtracted from the combiner for the other beam to provide a cancellation of interference from all directions except over a small incremental angular sector where the patterns are not overlapping.
In the accompany drawings, which illustrate an exemplary embodiment of the present invention:
Figure 1 is a functional block diagram illustrative of the preferred embodiment of a receiving antenna system in accordance with the principles of the subject invention;
Figure 2 is a diagram illustrative of the receiving antenna beam patterns formed by the antenna elements shown in Figure l;
Figure 3 is a diagram illustrative of the operation of the subject inventiQn for receiving a desired signal while ' eliminating undesired external interference si~nals; and Figure 4 is a diagram further helpful in understand-ing the principles of the invention.
Referring now to the drawings and more particularly to Figure 1, shown therein is an interference cancelling receiving antenna arrangement particularly adapted for use in tactical mobile trunk transmission systems such as a line of sight transmission link operating in a dense communications environment where severe jamming is encountered and where such systems typically operate in the UHF and SHF frequency bands or in a 12~ 3~
surveillance system which requires extremely small angular resolution such as a beamwidth of less than one degree.
The embodiment of the invention as shown in Figure 1 takes the form of a linear phased array of receiving elements comprised of nine antenna elements 10, 12, 14 ... 26. As is known, the size of the aperture or received pattern beamwidth is a function of the number of elements in the arra~, with the beamwidth of the pattern being reduced as the number of elements increases. In the subject invention, the linear array is operated to provide two receiver antenna beam patterns by utilizing all of the elements 10 through 26 for generating a first beam pattern 28 having an angular beamwidth ~1~ as shown in Figure 2, while a selected number, for example, five of the inner elements 14, 16, 18, 20 and 22 are operated to generate a second pattern 30 having an angular beamwidth of ~2 and which is broader than the beamwidth ~1 by a predetermined angle ~. The beamwidth of the larger angular segment ~2 is designed to be in the range o~ 0 to 10 Further as shown in Figure 1, the antenna elements 10 through 26 are coupled as a fir~t set of elementR to a first signal combiner 32 by phase shifting means 34, 36, 3~ ... 50 while the inner elements 14 through 22 which form the larger beam pattern are coupled as a second set of elements to a second signal combiner 52 through respective phase shifting means 54, 5G, ... 62 coupled to outputs of the phase shifters 38 through 46. The phase shifters 34 through 50 provide phase shifts in multiples of 0 on either side of the center element 18. Thus the phase shifters lZ11836 40, 38, 36 and 34 provide respective phase shifts of -0, -2~, -30 and -40, whereas phase shifters 44, 46, 48 and 50 provide phase shifts of ~, 20, 30 and 40. The phase shifters 54 through 62 provide additional phase shifts in multiples of ~0 on either side of the center element 18. As shown, the phase shifters 56 and 54 provide phase shifts of - ~ 0 and -2 ~0, respectively whereas t~e phase shifters on the right side of the center element, namely, the phase shifters 60 and 62 provide phase shifts of ~0 and 2 ~0, respectively.
The progressive additional phase shifts provided in the inner elements by phase shifters 54 through 62 result in a beamwidth of the pattern 30 for the second or inner set of antenna elements 14 through 22 which is broadened by a ~ and scanned by ~ 0/2 relative to the beam pattern 28 formed by all of the ele~
ments 10 through 26 of the antenna array, which results in the two received patterns 28 and 30 being aligned as shown in Figure 3. The phase shifters 34, 36 ... 50, act to electronically scan the composite beamwidth pattern.
Again, referring to Figure 1, the output of the combiner 52 for the broadened beam ~2 Of pattern 30 is linearly subtracted from the output of the combiner 32 for the narrower beam ~1 of pattern 28 by means of a subtractor 64 which provides a cancellation in the main beam, for example, signals Il and I2 shown in Figure 3 from all directions except over the small angular sector ~0 where the desired signal S is incident thereto.
Since some adjustment of the amplitude of the original beam pattern is necessary to account for amplitude differences between ~Z~1836 the output of the combiners 32 and 52 which results from slight differences in antenna gain, the embodiment of Figure 1 addition-ally discloses a variable attenuator 66 in the signal path between the combiner 32 and the linear subtractor 64. Further as shown, the output of the subtractor 64 is fed to radio receiver apparatus 68 which is operable to demodulate the RF
signals resulting from the differencing of the RF signals received by the first and second sets of antenna elements.
Figure 4 is intended to show~ that whereas an ideal difference pattern designated by reference numeral 70 would tend to have well defined steep sides at the edges of the angular sector ~0, hawever, in reality an actual or real diference pattern would resemble the characteristic designated by reference numeral 72.
Further by rotating the entire antenna array or elec-tronically scanning it, it is possible to direct the beam sector ~0 to any specific signal source while virtually eliminating all undesired signals withou~ requiring any complex adaptive process-ing or requiring a very large complex very narrow beam antenna.
Thus a relatively very narrow pencil beamwidth antenna system results which eliminates multiple interference in the main beam, except over the angular sector ~ and which is realized with practical hardware.
Whereas the pxeferred embodiment of Figure 1 is des-cribed with respect to a linear array, it should be understood that, when desirable, a planar array may be utilized to provide a two dimensional receive antenna pattern having a very high degree of angle of resolution in both azimuth and elevation. Addition-ally, it i5 also within the scope of the present invention to employ a lens or parabolic dish antenna, when desired, with a separate displaced feed to form the additional scanned beam having a different illumination pattern displaced wlth the other antenna feed to broaden its beamwidth pattern.
Having thus shown and described what is considered at present to be the preferred embodiment of the present invention, it will be readily apparent that modifications may be resorted to by those skilled in the art without departing from the spirit and scope of the invention. Accordingly, all alterations, changes and modifications coming within the scope of the invention as set forth in the appended claims axe hexein meant to be included.
Claims (15)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A narrow beamwidth receiving antenna system for eliminating undesired interference signals at the receiver end of mobile tactical communications trunk transmission links operating in a dense communications and jamming environment, comprising:
first receiving antenna means having a relatively narrow beamwidth antenna pattern defining a predetermined angular sector;
second receiving antenna means having a relatively narrow beamwidth antenna pattern defining an angular sector greater than that of said first antenna means;
means for orienting said antenna patterns such that said patterns overlap and one side thereof is substantially mutually coincident, providing thereby a single small incremental pattern sector where said antenna patterns do not overlap; and means for subtracting signals received by said first and second antenna means, whereby signal cancellation occurs of substantially all signals arriving from any direction except over said incremental pattern sector.
first receiving antenna means having a relatively narrow beamwidth antenna pattern defining a predetermined angular sector;
second receiving antenna means having a relatively narrow beamwidth antenna pattern defining an angular sector greater than that of said first antenna means;
means for orienting said antenna patterns such that said patterns overlap and one side thereof is substantially mutually coincident, providing thereby a single small incremental pattern sector where said antenna patterns do not overlap; and means for subtracting signals received by said first and second antenna means, whereby signal cancellation occurs of substantially all signals arriving from any direction except over said incremental pattern sector.
2. The antenna system of claim 1 wherein said first and second receiving antenna means are comprised of a first and second linear array of antenna elements having beamwidth of substantially between 1° and 10°.
3. The antenna system of claim 1 wherein said first and second receiving antenna means comprises antenna elements of a common array.
4. The antenna system of claim 1 wherein said first and second receiving antenna means comprise selected antenna elements of a common linear array.
5. The antenna system of claim 4 wherein said linear array comprises a phased array.
6. The antenna system of claim 4 wherein said linear array comprises a plurality of receiving antenna elements and wherein said first receiving antenna means includes substantially all of said receiving elements and wherein said second receiving antenna means comprises a predetermined number of antenna elements less than said first antenna means.
7. The antenna system of claim 4 wherein said linear array comprises a plurality of receiving antenna elements providing a beamwidth of 10° or less and wherein said first receiving antenna means comprises a greater number of said plurality of antenna elements than said second receiving antenna means.
8. The antenna system of claim 7 wherein said second receiving antenna means comprises a predetermined number of elements of the inner elements of said array.
9. The antenna system of claim 8 wherein said predetermined number of antenna elements of said second antenna means comprise centrally located elements of said array.
10. The antenna system of claim 9 and additionally including first signal combiner means for combining the signals received by said first antenna means and second signal combiner means for combining the signals received by said second antenna means and wherein said first and second signal combiner means are coupled to said means for subtracting signals.
11. The antenna system of claim 10 wherein said means for orienting said beam patterns comprises means for scanning the beam pattern of said second antenna means relative to the beam pattern of said first antenna means.
12. The antenna system as defined by claim 10 and wherein said means for orienting said beam patterns comprise respective first phase shifter means coupled between the antenna elements of said first antenna means and said first signal combiner means, and respective second phase shifter means coupled between respective said first phase shifter means coupled to said antenna elements of said first antenna means common to said second antenna means and said second signal combiner means.
13. The antenna system as defined by claim 12 wherein said first phase shifter means provide angular phase shifts of signals coupled to said first combiner means in multiples of said angular sector of said first receiving antenna means and wherein said second phase shifter means provide angular phase shifts of signals coupled to said second combiner means in multiples of said incremental angular sector between said beam patterns.
14. The antenna system as defined by claim 13 wherein said angular phase shifts of said first and second phase shifter means progressively increase and decrease on either side of the center element of said array.
15. The antenna system of claim 10 wherein said first phase shifter means provide angular phase shifts of signals coupled to said first combiner means in multiples of the required phase shift which will electronically scan the composite beam pattern so as to point the non-overlapping region of the two antenna patterns in the direction of the desired signal and wherein said second phase shifter means provide angular phase of signals coupled to said second combiner means in multiples of the required incremental phase shift so as to scan the beam pattern of said second antenna means by a predeterminded space angle to line up the two antenna patterns on one common side.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US06/526,735 US4638318A (en) | 1983-08-26 | 1983-08-26 | Small angular beamwidth antenna system |
| US526,735 | 1995-09-11 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1211836A true CA1211836A (en) | 1986-09-23 |
Family
ID=24098578
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000455214A Expired CA1211836A (en) | 1983-08-26 | 1984-05-25 | Small angular beamwidth antenna system |
Country Status (2)
| Country | Link |
|---|---|
| US (1) | US4638318A (en) |
| CA (1) | CA1211836A (en) |
Families Citing this family (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6653969B1 (en) * | 1993-02-19 | 2003-11-25 | Raytheon Company | Dispersive jammer cancellation |
| JP2556279B2 (en) * | 1993-12-14 | 1996-11-20 | 日本電気株式会社 | Radio link control method for mobile communication system |
| US6512934B2 (en) * | 1997-06-02 | 2003-01-28 | Ntt Mobile Communications Network, Inc. | Adaptive array antenna |
| WO2001089030A1 (en) * | 2000-05-18 | 2001-11-22 | Nokia Corporation | Hybrid antenna array |
| KR100433796B1 (en) * | 2001-12-28 | 2004-05-31 | 한국전자통신연구원 | Electronic active phase control array antenna and directional difference compensation method of the same antenna, and satellite tracking system and method thereof |
| IT1395141B1 (en) * | 2009-08-06 | 2012-09-05 | Siae Microelettronica Spa | METHOD AND EQUIPMENT FOR THE RECONSTRUCTION OF MULTIPLE SIGNALS AT HIGH FREQUENCY TRANSMITTED ON A SINGLE CHANNEL OF RADIO BRIDGES. |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3435453A (en) * | 1967-11-06 | 1969-03-25 | Us Navy | Sidelobe cancelling system for array type target detectors |
| CA1129086A (en) * | 1978-12-18 | 1982-08-03 | Frank S. Gutleber | Interference canceling device for use in antenna system |
| US4516126A (en) * | 1982-09-30 | 1985-05-07 | Hazeltine Corporation | Adaptive array having an auxiliary channel notched pattern in the steered beam direction |
-
1983
- 1983-08-26 US US06/526,735 patent/US4638318A/en not_active Expired - Fee Related
-
1984
- 1984-05-25 CA CA000455214A patent/CA1211836A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| US4638318A (en) | 1987-01-20 |
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Legal Events
| Date | Code | Title | Description |
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| MKEX | Expiry |