United States Patent (19)
`Kaplan
`
`Patent Number:
`11
`45) Date of Patent:
`
`4564,935
`Jan. 14, 1986
`
`54)
`
`TROPOSPHERC SCATTER
`COMMUNICATION SYSTEM HAVING
`ANGLE OVERSITY
`
`(75)
`
`73
`
`Inventor:
`
`Philip D. Kaplan, Nashua, N.H.
`
`Assignee: The United States of America as
`represented by the Secretary of the
`Air Force, Washington, D.C.
`
`21).
`
`Appl. No.: 569,644
`
`22)
`
`Filed:
`
`Jan. 10, 1984
`
`51
`(52)
`58)
`
`Int, Cl." ............................................... H04B 7/08
`U.S. C. ...................................... 370/38; 343/373;
`343/381; 455/276
`Field of Search ............... 343/373, 380,381, 382,
`343/383,384, 853; 455/137,273,276, 277,278;
`370/38; 37.5/100
`
`56)
`
`References Cited
`U.S. PATENT DOCUMENTS
`3,618,092 11/1971 Waineo ............................... 34.3/853
`3,618,093 11/1971 Dickey ......
`... 343/17.1 R
`3,702,479 11/1972 Uhrig .................................. 343/705
`3,824,500 7/1974 Rothenberg ......
`... 343/373
`4,075,566 2/1978 D'Arcangelis ...
`... 455/276
`4,196,436 4/1980 Westerman ......................... 343/381
`Primary Examiner-Joseph A. Orsino, Jr.
`Attorney, Agent, or Firm-Donald J. Singer; Richard J.
`Donahue
`ABSTRACT
`57
`A tropospheric scatter communication system provides
`diverse angle transmission paths which may be utilized
`alone or in conjunction with frequency and/or other
`known diversity system arrangements for improved
`performance. The diverse angle transmission paths are
`routed through sum and difference "monopulse' beams
`displaced in azimuth.
`
`4 Claims, 4 Drawing Figures
`
`
`
`?t and a
`HYBRD
`
`coMs Ner
`
`ERICSSON v. UNILOC
`Ex. 1012 / Page 1 of 6
`
`

`

`U.S. Patent Jan. 14, 1986
`
`Sheet 1 of 2
`
`4,564,935
`
`2
`
`
`
`V
`
`
`
`f,
`m
`- DUPLEXER
`16
`TRANSMITTER
`A
`
`PRE
`SELECTOR
`f:
`If,
`
`DUPLExer-fi is
`TRANSMITTER
`B
`
`PRE
`SELECTOR
`&
`f
`
`2 AND A
`HYBRD
`
`2(F3)
`
`A (fa)
`
`
`
`RECEIVER
`
`RECEIVER
`
`6 D
`
`6 A
`
`
`
`
`
`RECEIVER
`
`6C
`
`RECEIVER
`
`COMBINER
`
`24
`
`F G. 1
`
`
`
`ERICSSON v. UNILOC
`Ex. 1012 / Page 2 of 6
`
`

`

`U.S. Patent Jan. 14, 1986
`
`Sheet 2 of 2
`
`4,564,935
`
`SCATTERING VOLUME, 3 O
`
`TRANSMITTER
`(SITE 1)
`
`- -
`
`-
`
`- -
`
`- FG. 2 A
`
`RECEIVER -/
`(SITE 2)
`
`TRANSMITTER BEAMS
`(f fa)
`
`RECEIVER BEAMS (f)
`A
`
`
`
`
`
`TRANSMITTER
`(SITE 1)
`
`RECEIVER
`(STE2)
`
`FG. 2 B
`
`s EY
`94.
`
`
`
`( A RECEIVE (f, F)
`TRANSMIT (f, F)
`
`
`
`U
`
`O
`
`al
`S
`C.
`
`H - /.
`
`O
`ANGE
`
`--
`
`F. G. 3
`
`ERICSSON v. UNILOC
`Ex. 1012 / Page 3 of 6
`
`

`

`1.
`
`TROPOSPHERIC SCATTER COMMUNICATION
`SYSTEM HAVING ANGLE DIVERSITY
`
`4,564,935
`2
`It is another object of the present invention to pro
`vide a tropospheric scatter communication system hav
`ing angle diversity.
`It is a further object of the present invention to pro
`vide a tropospheric scatter communication system hav
`ing both diverse angle and diverse frequency signal
`paths.
`The angle diversity system disclosed herein provides
`an independent (dual diversity) transmission path hav
`ing desirable cost saving features and which when com
`bined with frequency diversity (quad diversity) or addi
`tionally with polarization or time diversity (eight fold
`diversity) provides increasingly higher system reliabil
`ity.
`15
`In the angle diversity mode described herein, alter
`a nate angle transmission paths are routed through sum
`and difference "monopulse' beams formed by a dual
`feed antenna whose feed elements are displaced in azi
`muth. The received sum and difference signals are com
`pared at the receiver site and the signal having the
`greatest amplitude is selected for further processing and
`Se.
`BRIEF DESCRIPTION OF THE DRAWINGS
`The foregoing and other objects of the invention will
`be more clearly understood from the following descrip
`tion and accompanying drawings, in which:
`FIG. 1 is a functional block diagram representation of
`the present invention;
`FIGS. 2A and 2B are illustrations of the vertical and
`azimuthal antenna pattern linking relationships respec
`tively of a pair of communication sites utilizing the
`present invention; and
`FIG. 3 is a graph depicting the transmitter and re
`ceiver azimuthal plane antenna gain patterns of a single
`site.
`
`25
`
`DESCRIPTION OF THE PREFERRED
`EMBODIMENT
`FIG. 1 is a functional block diagram of the quadruple
`(angle/frequency) diversity implementation of the pres
`ent invention. A dual feed antenna 2 having feed ele
`ments 4 and 6 with displaced phase centers in the azi
`muthal plane, simultaneously serves a pair of transmit
`ters, denoted transmitter A and transmitter B, and four
`monopulse receivers 6A-6D. Transmitters A and B and
`receivers 6A-6D are isolated through duplexers 8 and
`10. Feed elements 4 and 6 are connected to duplexers 8
`and 10 via feed lines 12 and 14 respectively. Transmit
`ters A and B operate at "diverse' frequencies f and f2
`and their output signals are applied via their respective
`output leads 16 and 18 to duplexers 8 and 10 respec
`tively and thence to their respective feed elements 4 and
`6. Thus one half of the available aperture of antenna 2 in
`the azimuthal plane transmits at frequency f1 and the
`other half transmits at frequency f2.
`On receive, signals at two frequencies, fs and f4, ar
`rive at both of the antenna feed elements 4 and 6, pass
`through duplexers 8 and 10 and preselectors 12 and 14,
`to form separated signals of frequencies f and f4 at the
`outputs of each of the preselectors 12 and 14. These
`signals are then combined in sum and difference hybrid
`circuits 20 and 22 and yield the quadruple diversity
`channels X(f), A(f3), X(f), A(f) for application to the
`four receivers 6A-6D. The four channel receiver out
`puts are then "combined' in a post detection combiner
`unit 24 using conventional circuitry and methods.
`
`55
`
`65
`
`5
`
`10
`
`STATEMENT OF GOVERNMENT INTEREST
`The invention described herein may be manufactured
`and used by or for the Government for governmental
`purposes without the payment of any royalty thereon.
`BACKGROUND OF THE INVENTION
`The present invention relates to a tropospheric scat
`ter communication system, and more particularly, to a
`tropospheric scatter communication system having an
`angle diversity response capability.
`Tropospheric communication has emerged from its
`uncertain beginnings in the early nineteen fifties to be
`come a robust communication system that fills a gap
`between line-of-sight microwave links and long range
`20
`HF or LF links. Tropospheric forward scatter occurs in
`the region between the stratosphere and the earth's
`surface in the presence of "blobs' of atmosphere having
`refractive index variations. Such variations are the re
`sult of differences in temperature, pressure and gaseous
`constituents, the main variable being water vapor.
`When irradiated by microwave or UHF signals the
`blobs re-radiate the signals in all directions, some of
`which scatter in the forward direction to produce elec
`tromagnetic fields at the receiving location.
`30
`The collection and analysis of empirical data from
`experimental and operational tropospheric scatter sites
`characterize its statistical performance in terms of short
`term and long term amplitude-time distributions. Short
`term distributions, measured over intervals of tens of
`35
`seconds, describe a Rayleigh distribution, from which
`hourly median values are obtained. Long term distribu
`tions represent the variation of the hourly median val
`ues over longer periods of time, a month a season or
`year, and vary considerably with the season of the year
`40
`and with geographical location.
`Methods of coping with short term (Rayleigh) fading
`have been devised through the use of "diversity' trans
`mission paths; paths that are independent and therefore
`afford greater reliability than a single transmitter/-
`45
`receiver at each end. Effectively proven methods em
`ploy space diversity, (two or more antennas spaced
`approximately 200 wavelengths apart), frequency di
`versity, (two or more carriers separated in the MHz),
`50
`polarization diversity, and time diversity (repetition of
`the same information when slow data rates are in
`volved).
`The use of any one method may be utilized indepen
`dently in dual diversity, or may be combined judi
`ciously in quadruple diversity. In many operational
`systems, space and frequency diversity are combined to
`provide reliable communication links. However, since
`two widely separated antennas are required for space
`diversity, this necessitates a large communications site.
`60
`Furthermore, substantial costs are involved in the con
`struction of the remote second antenna, its mounting
`base, and the transmission of signals thereto.
`SUMMARY OF THE INVENTION
`It is therefore an object of the present invention to
`provide a tropospheric scatter communication system
`of improved performance and reduced cost.
`
`ERICSSON v. UNILOC
`Ex. 1012 / Page 4 of 6
`
`

`

`5
`
`4,564,935
`3
`4.
`The preferred combining process entails individual
`signal from each feed horn would be combined as be
`amplitude detectors associated with each of the quadru
`fore to produce the sum and difference signals thereof.
`ple diversity channels. The channel exhibiting maxi
`What is claimed is:
`mum amplitude at any given time is selected for further
`1. A tropospheric scatter communication system hav
`information processing, while the other three channels
`ing diverse angle and diverse frequency signal transmis
`go unused. This preferred post detection combining
`sion modes of operation comprising:
`process offers greater reliability than predetection com
`a dual feed antenna system having first and second feed
`biners, with nearly identical signal to noise ratios.
`elements whose phase centers are displaced in the
`azimuthal plane;
`FIGS. 2A and 2B, illustrate the transmitter and re
`ceiver antenna pattern relationships in the vertical and
`10
`a first and a second preselector unit;
`azimuthal planes respectively. In the vertical plane the
`a first duplexerfor coupling signals of frequency f. from
`scattering volume 30 is seen at the intersection of the
`a first transmitter to said first feed element and for
`transmitter and receiver beams. The relationships be
`coupling signals received by said first feed element to
`tween the sum (X) and difference (A) beam patterns in
`said first preselector unit;
`15
`the azimuthal plane are shown in FIG. 2B. For the X.
`a second duplexer for coupling signals of frequency f2
`pattern the scattering volume resides directly above the
`from a second transmitter to said second feed element
`great circle path joining the transmitter and receiver.
`and for coupling signals received by said second feed
`For the A pattern, the scattering volume resides on
`element to said second preselector unit;
`either side of the X scattering volume.
`said first and said second preselector units each separat
`20
`FIG. 3 illustrates the azimuthal plane antenna gain
`ing signals of frequencies f and f4 received thereby;
`patterns at a single communications site. It will be noted
`first and second hybrid units each having first and sec
`that the A Receive antenna pattern is symmetrically
`ond inputs, a signal sum output and a signal difference
`disposed on either side of the X Receive pattern. Fur
`output;
`ther, it is included within the angle occupied by the
`means for coupling signals of frequency f. from said first
`25
`Transmit pattern and that each has approximately one
`preselector, unit to the first input of said first hybrid
`half the power of the X Receiver pattern.
`unit;
`The utilization of angle diversity as an alternate trans
`means for coupling signals of frequency f. from said
`mission path through the generation of "monopulse'
`second preselector unit to the first input of said sec
`antenna beams provides a performance advantage over
`ond hybrid unit;
`30
`space diversity, as seen in the following example:
`means for coupling signals of frequency f. from said first
`DEW Line tropospheric scatter sites utilize pairs of
`preselector unit to the second input of said second
`60 foot reflector dishes separated by approximately 250
`hybrid unit;
`feet to achieve space diversity in combination with
`means for coupling signals of frequency f. from said
`frequency diversity. By design, the signals that arrive at
`second preselector unit to the second input of said
`35
`the antennas are uncorrelated and accordingly the
`first hybrid unit;
`transmitter gain, receiving aperture, and beamwidth
`first and second receiver means having their inputs
`(nominally 1.5) are governed by the individual antenna
`coupled to the signal sum and signal difference out
`size (normally 60 feet).
`puts respectively of said first hybrid unit;
`As an alternative, the angle diversity implementation
`third and fourth receiver means having their inputs
`described herein would mount two 60 foot dishes side
`coupled to the signal sum and signal difference out
`by-side. In such proximity, the signals at the two feeds
`puts respectively of said second hybrid unit; and
`are essentially correlated. Thus the receiving aperture is
`a signal combiner having its inputs coupled to the out
`essentially doubled; the X azimuthal beam approaches
`puts of said first, second, third and fourth receiver
`0.75, and the beams approach 1.5. The emitted radia
`means and providing a single output signal related to
`45
`tion power, however, would be akin to the space diver
`the signal of maximum amplitude applied to its inputs.
`sity case, as the two half apertures are emitting separate
`2. A tropospheric scatter communication system hav
`frequencies. Signal to noise improvement may therefore
`ing diverse angle and diverse frequency signal paths
`approach 3 dB.
`comprising:
`Furthermore, single installation of the massive an
`an antenna system having first and second feed elements
`50
`tenna mounts would appear to be less costly and the
`whose phase centers are displaced in the azimuthal
`plane;
`construction more conveniently maintained than the
`alternative. In particular, as the troposites serving the
`a first and a second preselector unit coupled to said first
`DEW Line operate as relay links, the case for single
`and second feed elements respectively;
`antenna installation is doubly advantageous.
`said first and said second preselector units each separat
`55
`Although the invention has been described with ref.
`ing signals of frequencies f and f4 received thereby;
`erence to the preferred embodiment thereof, it will be
`first and second hybrid units each having first and sec
`understood to those skilled in the art that the invention
`ond inputs, a signal sum output and a signal difference
`is capable of a variety of alternative embodiments
`output;
`within the spirit and scope of the appended claims. If,
`means for coupling signals of frequency f. from said first
`for example, it is desired to provide a system having
`preselector unit to the first input of said first hybrid
`only angle diversity (dual diversity), the system would
`unit;
`utilize only one of the pair of feed elements 4 or 6 for
`means for coupling signals of frequency f. from said
`transmitting the single frequency. This is the case since
`second preselector unit to the first input of said sec
`the use of both of the feed elements during transmission
`ond hybrid unit;
`65
`would produce a narrow transmitter beam, incapable of
`means for coupling signals of frequency f. from said first
`linking with the A Receive beams at the receiver site.
`preselector unit to the second input of said second
`For signal reception however, the single frequency
`hybrid unit;
`
`ERICSSON v. UNILOC
`Ex. 1012 / Page 5 of 6
`
`

`

`4,564,935
`6
`5
`said first and said second preselector means each sepa
`means for coupling signals of frequency f. from said
`rating signals of frequencies f and f4 received
`second preselector unit to the second input of said
`thereby;
`first hybrid unit;
`first means coupled to said first and said second prese
`lector means for providing sum and difference signals
`first and second receiver means having their inputs
`of signals of frequency fs;
`coupled to the signal sum and signal difference out
`second means coupled to said first and said second pre
`puts respectively of said first hybrid unit;
`selector means for providing sum and difference sig
`third and fourth receiver means having their inputs
`nals of signals of frequency f;
`coupled to the signal sum and signal difference out
`and combiner means coupled to said first means and said
`second means for selecting the signal of greatestam
`puts respectively of said second hybrid unit; and
`plitude of said sum and difference signals.
`a signal combiner having its inputs coupled to the out
`4. A tropospheric scatter communication system hav
`puts of said first, second, third and fourth receiver
`ing diverse angle signal transmission paths comprising:
`means and providing a single output signal related to
`a reflector type antenna having a pair of feed elements
`of substantially identical geometry and signal re
`the signal of maximum amplitude applied to its inputs.
`sponse characteristics and whose phase centers are
`3. A tropospheric scatter communication system hav
`displaced in the azimuthal plane;
`ing diverse angle and diverse frequency signal paths
`a hybrid unit having a pair of inputs coupled to respec
`comprising:
`tive ones of said pair of feed elements, a signal sum
`20
`output and a signal difference output;
`an antenna system having first and second feed elements
`and means coupled to the signal sum output and the
`whose phase centers are displaced in the azimuthal
`signal difference output of said hybrid unit for select
`plane;
`ing the signal of greatest amplitude at said signal sun
`first and second preselector means coupled to said first
`output and said signal difference output.
`and second feed elements respectively;
`
`5
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`O
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`15
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`k
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`25
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`30
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`35
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`45
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`50
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`55
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`65
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`ERICSSON v. UNILOC
`Ex. 1012 / Page 6 of 6
`
`