Note: Descriptions are shown in the official language in which they were submitted.
~ BACKGROUND OF THE INV~N~ION
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The invention relates generally to the field of multiple
input antenna systems and more particularly to the simultaneous
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use of an antenna array by a plurality of independent and
isolated radio devices.
There have been a number of different solutions to the
basic problem of simultaneously using a single antenna
structure in conjunction with a plurality of independent
transmitters while maintaining isolation therebetween.
One prior solution uses a single omnidirectional antenna
and couples each of the transmitters to this antenna through
an associated resonant cavity. Thus an omnidirectional
radiation pattern is obtained for each transmitter and the
output of each transmitter will not affect the output of any
other transmitter. The primary disadvantage of this system
is that it requires a separ~te tuned resonant cavity for
each transmitter. Since every transmitter must operate at a
substantially different frequency in order for the resonant
cavities to provide the required isolation, close channel
spacing in such a system is impractical. Also, because of
the requirement for a tuned xesonant c~yity, such a system
has an inherently narrow bandwidth, In addition, the
resonant cavity must be adjusted ~henever the operating
center frequency of a transmitter is ch~nged.
Another solution to the problem uses an array of hybrid
networks to produce a single output signal which is then
used to excite a single o~nidi~ectional antenna element.
Each of these hybrid networks combines two input signals to
produce a half power output signal at one port while dissi~
pating the rest of the power in a 50 ohm ~Idummy~ load. In
a typical eight transmitter network built according to this
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prior technique, a 9db loss in power is encountered. The
use of hybrid networks does, however, provide isolation
between the independent transmitters as well as permitting a
wide bandwidth of operation for the antenna system.
Still another solution to the problem is to couple in-
~- dividual omnidirectional antenna elements to each of the
transmitters. This solution is not practical because of the
large separation that would have to exist between each of
; the radiating elements in order to provide sufficient iso~
lation between each of the transmitters. Therefore the
resultant antenna system would require an extremely large
amount of space, especially if a large number of independent
transmitters were desired.
In still another solution to the problem, two trans-
mitters are combined by a single hybrid network and the two
output signals from this network are then used to excite the
two independant antenna elements in a turnstile antenna.
This technique provides isolation in addition to a wide
bandwidth of operation, but-cannot be readily extended to
more than two transmitters without using narrow band tuned
elements or sacrificing a substantial amount of transmitter
output power.
SUMMARY OF TH~ INVENTION
An object of the present inYention i~ to pxoYide an
improved multiple input antenna system for overcoming all of
the aforementioned deficiencies,
A more particular o~ject of the inYention is to provide
an improved multiple input antenna system for at least three
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independent radio devices in which a single antenna array is
simultaneously used by all of the radio devices while broad-
; band isolation between these devices is provided with no
substantial power loss.
In one embodiment of the present invention an improvedmultiple input antenna system is provided, comprising: a
plurality of at least three independent, isolated, electrical
devices each adaptable for processing radio frequency signals
at different radio frequencies, a plurality of isolated antenna
elements equal in number to at least the number of said
electrical devices, each of said elements disposed in a pre-
determined manner for generating an associated independent
radiation pattern; and a substantially lossless combining
network consisting of broadband components having bandwidths
including all of said radio frequencies, the network coupled
to each of the antenna elements and each of the electrical
devices for simultaneously coupling each of the devices to
each and every one of the antenna elements while maintaining
broadband isolation between all of the antenna elements and
all of the electrical devices; the combining network also
; creating a predetermined phase difference between each of
the radiation patterns produced by the antenna elements
such that these patterns combine to form a desired composite
radiation pattern.
The combining network comprises an array of hybrid net-
works in which the signals present at each output port of
each hybrid network are used to create the desired results
without any signal cancellations. Thus isolation between
individual electrical devices is maintained over a broad
bandwidth and no substantial loss in power is created by the
inventive antenna system.
When used as a multiple transmitter antenna system, the
present invention provides an easily expandable antenna
network for simultaneously radiating several independent
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; radio signals over a single broadband antenna system without incurring
a substantial loss in the radiated output signal. Basically, a plurality
of at least three transmitters, each supplying an input signal at a different
carrier frequency, is connected to a combining network comprising an
array of hybrid networksO The combining network maintains isolation
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between the transmitters and produces a number of isolated output signals ~ -
equal in number to at least the number of electrical transmitters. Each
one of the output signals is proportional to each and every one of the input
signals, and each output signal has a predetermined phase. An associated
10 antenna element receives each output signal and radiates it in a directive
substantially independent radiation pattern which is directed away from all
other antenna elementsO Because of the phase of each one of the output
- signals and the positioning of each one of the antenna elements, all of the
independent directive radiation patterns combine to form a desired
composite radiation pattern for each of the different frequency transmitters~ -
More particularly, there is provided an improved multiple trans-
mitter antenna system comprising:
a plurality of at least three electrical sources each generating an
independent input signal at a different predetermined radio frequency;
a combining network means consisting of broadband components having
bandwidths including all of the frequencies generated by said electrical
sources, said network means simultaneously coupled to said plurality of
sources for simultaneously receiving each of said input signals, maintaining
isolation between said input signals, and substantially losslessly producing
a number of isolated output signals equal in number to at least the number
of said input signals, each one of said output signals being related to each
and every one of said input signals; and
an antenna array coupled to said combining network, said array
comprising a plurality of antenna element means, each of said antenna
30 element means receiving and simultaneously radiating an associated one
of said output signals in a substantially independent directive associated
radiation pattern having a single main unidirectional lobe, each lobe being
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directed away frcm al 1 oth~æ antenna ele~nt means and in a s~bstantially
different direction than all other lobes and wherein sa~d indeper~lently
radiated lobes cambine to form a desired calposite radiation pattern for each
of sa~d plurality of electrical sources,
where~n said desired compo~ite radia~ion pattern i3 ~ub~tantially
identic 1 in s;hape and directivity for each of said plur~lity of different
frequency electrical source-.
There is further provided:-
An improved m~lt;ple l:nput ~T~tenna jystem, compriiing:
a plurality of at least three independent, isolated elect~ical devices
10 each adaptable for processing radio frequency signals at different radiofrequen cie s;
a plurality of isolated antenna elements equal in number to at least the
number of said electrical device-" each of said elements disposed in a
predeterm~ed manne.r and constructed for indepe~dently generating an
associated directional radiation pattern directed away from all other
antenna elements; and
a 3ubstantially lo~,sless combining network means consisting of
broadband components having barLdwidths including a1l of said radio
frequencies, said network means coupled to each of said a~tenna elements
ZO and each of 3aid electrical devices for simultaneously coupling each of
said dev~ces to each and every one of said antenna elements while ma~-
taLning broadband isolatioIl between all of said antenna elements and all of
said electrical devices;
said network means creating a predetermined phase difference between
each of said directive radiation patterns such that said patterns combine
to form a desiret composite radiation pattern for each of said plurality
of independent devices,
wherein said desired composite radiation pattern is subst~ntially
identical in shape and directivity for each of said different frequency
30 electrical device~.
There is also provided:- .
An improved multiple input antenna system, comprising:
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a plurality of at least three independent, isolated electrical devices ;
for processing radio frequency signals having different frequencies;
a plurality of at least four isolated antenna elements each of said
elements disposed in a predetermined manner and constructed for inde-
- pendently generating an associated directive radiation pattern directed
away from all other antenna elements; and
a combining network means coupled to each of said antenna elements :
and each of said electrical devices for simultaneously coupling each of
said devices to each and every one of said antenna elements while main-
taining isolation between all of said antenna elements and all of said
electrical devices;
said network means creating a predetermined phase difference between
each of said directive radiation patterns such that said patterns combine
to form a desired, composite, radiation pattern for each of said plurality
of independent devices;
said network means including a first circuit comprising first, second, ~ :
third, and fourth hybrid networks each having first, second, third and
fourth ports,
each of said ~ybrid networks capable of coupling a signal from either
of said first and second ports to said third and fourth ports, the signal
: coupled to said third port being substantially equal in magnitude to and ~ ;
: having a fixed phase difference from the signal coupled to said fourth port,
the third and fourth ports of said first hybrid network being coupled to
the first ports of said third and fourth hybrid networks, respectively, and
the third and fourth ports of said second hybrid being coupled to the
second ports of said third and fourth hybrid networks respectively,
wherein said desired composite radiation pattern is substantially
identical in shape and directivity for each of said plurality of different
frequency electrical devices.
There i9 further provided:-
An improved multiple input antenna system comprising:
a plurality of at least three independent, isolated electrical devices
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for processing radio frequency signals having different frequencies;
a plurality of at least four isolated antenna elements each of said
elements disposed in a predetermined manner and constructed for
independently generating an associated directive radiation pattern directed : :
away from all other antenna elements, wherein each of said antenna
elements comprises a corner reflector antenna; and
a combining network means coupled to each of said antenna elements and
each of said electrical devices for simultaneously coupling each of said
devices to each and every one of said an$enna elements while maintaining
10 isolation between all of said antenna elements and all of said electrical
device s;
said network means creating a predetermined phase difference between
each of said directive radiation patterns such that said patterns combine to
form a desired, composite, radiation pattern for each of said plurality of
independent devices;
said network means including a first circuit comprising first, second,
third, and fourth hybrid networks each having first, second, third and
fourth ports,
each of said hybrid networks capable of coupling a signal from either
ZO of said first and second ports to said third and fourth ports, the signal
coupled to said third port being substantially equal in magnitude to and
having a fixcd phase difference from the signal coupled to said fourth port,
the third and fourth ports of said first hybrid network being coupled to
the first ports of said third and fourth hybrid networks, respectively, and
the third and fourth ports of said second hybrid network being coupled :
to the second ports of said third and fourth hybrid networks respectively,
wherein said desired composite radiation pattern is substantially
identical in ~hape and directivity for each of said plurality of different
frequency electrical devicesO
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BRIEF DESCRIPTION OF THE DRAWINGS
For a more complete understanding of the invention reference
should be made to the drawings, in which:
Fig. 1 is a horizontal cross sectional diagram of a four ele-
ment vertical antenna array;
Fig. 2 is a graph illustrating the horizontal radiation pat-
tern created by each of the antenna elements in Fig. l;
Fig. 3 is a schematic diagram of a four input antenna system
which uses the antenna elements shown in Fig. l;
Fig. 4 is a diagram illustrating the electrical characteristics
of a hydrid network;
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Fig. 5 is a table illustrating various signal phase
xelationships in the antenna system shown in Fig. 3;
Fig. 6 is a graph illustrating a composite horizontal
radiation pattern produced by the antenna system in Fig. 3;
Fig. 7 is a horizontal cross sectional diagram of an
eight element vertical antenna array;
Fig. 8 is a graph illustrating the horizontal radiation
patterns of several of the antenna elements in Fig. 7;
Fig. 9 is a schematic diagram of an eight input antenna
system which uses the antenna elements shown in Fig. 7;
Fig. 10 is a table illustrating various signal phase
relationships in the antenna system shown in Fig. 9;
Fig. 11 is a graph of a composite horizontal radiation
pattern created by the system in Fig. 9; and
Fig. 12 is a graph illustrating another composite hori-
zontal radiation pattern.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
OF THE INVENTION
Fig. 1 illustrates an antenna array 20 for use at 900
MHz which comprises four corner reflector antenna elements
generally indicated at 21, 22, 23 and 24. The corner
reflectors are circularly disposed around a center axis 25,
and each has a 90D firing aperture which faces radially
outwardly. Corner reflector antennas are well known in the
state of the art and basically consist of two sides of a
bent reflector panel (such as 21a) and a center radiating
rod (such as 21b). In the present embodiment of the in-
vention, center axis 25 is a four inch diam~ter pipe. The
outer diamter of array 20 is 1.25 feet and therefore each
reflector antenna has a firing aperture of approximately one
foot. Typically the reflector panels are a grid of wires
rather than a solid sheet of metal.
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Fig. 2 illustrates the theoretical radiation patterns
produced by each of the antenna elements illustrated in Fig.
1. The corresponding radiation patterns have been designated
by prime notation. Each pattern consists, substantially, of
a single main unidirectional lobe radially directed outward
from a center point 25' which corresponds to center axis 25
in Fig. 1. Each pattern generated by an antenna element is
directed substantially away from all other antenna elements.
In this manner, the signal radiated by each antenna element
will not be received by other antenna elements and the array
20 can be compactly built since antennas can be placed close
together.
Fig. 2 has a nonlinear radial db scale. Each of the
individual radiation patterns is illustrated as having 3db
down points, such as points 26 and 27 for pattern 21', which
form substantially a 90 angle with the center point 25'.
Thus each radiation pattern is said to have a half power
beam width of 90. The 3db points of the adjacent radiation
patterns are substantially coincident. It should be em-
phasized that Fig. 2 merely depicts the individual radiation
patterns that are created by each of the four antenna
elements acting individually and not the composite radiation
pattern created by the simultaneous excitation of all four
of the antenna elements.
Fig. 3 shows a four input transmitter antenna system 30
which uses the antenna elements 21 through 24 depicted in
Fig. 1 and identically numbered. Independent and isolated
RF (radio frequency) generators 31, 32, 33, and 34, each
operative at a different carrier frequency, are shown
connected to the first and second input ports (41 and 42) of
hybrid network 40 and the first and second input ports (51
and 52) of hybrid network 50, respectively. The first,
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second, third and fourth ports of a typical hybrid network,
such as network 40, are designated as 41, 42, 43, and 44
respectively. Similar notation for the network ports will
be used for all subsequently referred to hybrid networks.
The antenna system 3~ also comprises a hybrid network 60
having its third and fourth ports (63 and 64~ coupled to ';
antenna elements 21 and 22 respectively, and a hybrid
network 70 having its third and fourth ports (73 and 75)
coupled to antenna elements 24 and 23, respectively, Input
10 ports 61 and 62 of hybrid network 60 are connected to ports
43 and 53, respectively, and input ports 71 and 72 of hybrid
network 70 are connected to ports 44 and 54, respectively.
The hybrid networks 40, 50, 60 and 70 form a combining
network 80, s~own dashed. Thus the antenna system 30
basically comprises a plurality of transmitters 31-34, a
plurality of antenna, e~ements 20-24, and a combininy network
80,
Fig~ 4 illustrates the electrical properties of a
typical hybrid network 90 having terminals 91, 92, 93 and
, ~ 20 94, An inpu~ signal X having a phase angle of 0 is shown
present at terminal 91 and results in output signals being
created at terminals 93 and 94, each having half the mag-
nitude of the input signal at terminal 91. The signal at
terminal 93 is 180 out, of phase wit~ the signal at terminal
91 and the signal at terminal 94 is 90 out of phase with
the signal at terminal 91, The signal present at terminal
91 creates no signal at terminal 92 and therefore this
ter~inal is re~erred to as the "isolated terminal". When
sepa~A~e ~ndependent si~nals at different frequencies are
applied t~ both terminals 91 and 92, broadband isolation is
maintained between these signals and ~n addition of com-
posite signals is obtained at terminals 93 and 94 which are
also isolated from each other. Hybrid networks, such as the
one shown in Fig. 4 are commonly available and are well
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~nown in the art as 90 hybrid couplers. There also exist
180 hybrid networks in which the p~ases of the signals at
terminals 93 and 94 differ by 180~ from each other. These
180 hybrid networks also maintain broadband isolation
between each of the input ports and each of the output
ports.
Fig. 5 is a table which illustrates the phase relation-
ships in Fig. 3 of each signal received by each antenna
element from each transmitter when all of the hybrid net-
works are 90 couplers. In this table a vector pointing in
a right hand direction is considered to have a phase of Oc,
a vector pointing in an upward direction has a phase of 90, i !
a Vector pointing in a left hand direction has a phase of
180, and a vector pointing in a downward direction has a
phase of 270, Hence each signal radiated by an antenna
element is 90 out of phase with the signals radiated by the
adjacent antenna elements. For example, the signals ra-
diated by antenna element 21 will be 90 out of phase with
the signals radiated by antenna elements 22 and 24. The
signal actually radiated by a typical antenna element, such
as element 21 for example, would be a composite signal
comprising one fourth t~e magnitude of the signal produced
by generator 31 at a phase angle of 0, one fourth o the
signal of generator 32 at an angle of 2~0, one fourth of
the signal of ~enerator 33 at an angle of 270, and one
fourth the signal of ~enerator 34 at an angle of 180.
Fig, 6 illustrates an actual composite radiation
pattern 95 created by the circuit 30, shown in Fig. 3, which
the antenna elements 21 through 24 are arranged as indicated
3~ in Fig. 1. Fig. 6 is plotted on a linear radial db scale.
The co~posite pattern 95 is roughly omnidirectional with the
largest null (95A) ~eing approximately 8db down from the
peak value (95B~ of the pattern, The composite patte~n is
generally omnidireCtional since each of the individua~ly
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created patterns is 90D out of phase from each of the
adjacent patterns and each pattern has its 3d~ points sub-
stantially coincident with the 3db points of the adjacent
patterns. Signals from each of the transmitters 31 through
34 will radiate in a pattern similar to that shown in Fig. 6
and all four of the transmitters can simultaneously radiate
signals from the same antenna elements 21 - 24 while iso-
lation is maintained between all the transmitters 31 - 34
and all the antenna elements 21 - 24. Therefore a single
antenna network has been provided for simultaneously ra-
diating a number of independently generated RF signals over
the same antenna array.
A significant aspect of the invention is the combining
o~ fou~ independent sources on a single compact antenna
structure without the creation of deep nulls on the com-
posite radiation patter~ and while maintaining broadband
isolation between all of the independent sources~ This is
acco~plished by the use of a substantially lossless broad-
band combining net~ork 80 in combination with a plurality of
antenna elements, each of which independently ge~erates a
directi~e radiatio~ p~ttern directed away from ~11 other
antenna ele~ents~ ~ desired composite radiation pattern is
then produced by the combination of these independent
directiye radiation patterns and by the network 80 proyiding
a desired 90 phase shift between each of these patterns.
The antenna system 3Q can be easily expanded to accomodate
a~y ~umber of additional different frequency generators~ as
will be explained subsequently. In addition~ any of the
tra~s~itters 31 throu~h 34 can be removed without impairing
the sy~tem operation~
~ hile tbe positioning of the a~tenna array 20 shown in
Fig~ 1 resulted in the radiation pattern shown in Fig, 6.
~ariations in this pattern ca~ be obtained by skewing the
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orientation of the antenna elements 21 through 24. This
skewing technique is well known in the prior art and has
been successfully used to create a better omnidirecti~nal
pattern when nulls have created problems on a composite
radiation pattern.
Fig. 7 shows another embodiment of the present in-
vention in which an antenna arr~y 100 for use at 9Q0 MHz is
illustrated as comprising eight corner reflector antenna
elements, generally indicated by 101 through 108, which are
circularly disposed about a center axis 109. The overall
diameter of array 100 is 4.5 feet and center axis 109
actually consists of a 4 inch pipe which is used to support
the reflector panels of each of the corner reflector an-
tennas, Each of the reflector antennas has a 45 firing
aperture,
In Fig, 8 (having the same scale as Fig. 2) a plurality
of tkeoretic~l horizontal radiation patterns corresponding
to several of the reflçctor antennas shown in Fig. 7 is
illustrated with corresponding patterns being designated by
prime notation~ Each of the radiation patterns is shown as
~aVing a 45 3db beam width, This is the reason for the
much larg~r oye~a~l diameter of array 100 as compared to
a~ay 20r since a lar~er firing a~erture dimension, gen- ~ -
erally indicated by reference number 110 in Fig. 7, is
required to produce a 45 D beam width radiation pattern.
Fig, 9 illustrates an eight transmitter antenna system
120, similar to the antenna system 30, which uses the
antenna array depicted in Fig, 7, Four hybrid networks 140,
150, 160 and 170 are interconnected and form a network 180
3D that is identical to the network 80 illustrat d in Fig. 3.
Four transmitters 121, 122, 123, and 124 are connected to
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network 180 and correspond to transmitter 31, 32, 33, and
34, respectively. Similarly, four hybrid networks 240,
250, 260, and 270 form a circuit 280 which is identical to
circuit 180, and four transmitters 125, 126, 127, and 128
are connected to network 280 and correspond to transmitters
121 - 124, respectively. Four additional hybrid networks
290, 300, 310, and 320 couple networks 180 and 280 to
antenna elements 101 through 108. Input ports 291 and 292
are coupled to ports 163 and 263, respectively, and output
ports 293 and 294 are coupled to antenna elements 101 and
108, respectively. Input ports 301 and 302 are coupled to
ports 164 and 264, respectively, and output ports 303 and
304 are coupled to antenna elements 102 and 105, respect-
ively. Input ports 311 and 312 are coupled to ports 173 and
272, respectively, and output ports 313 and 314 are coupled
to antenna elements 104 and 107, respectively. Input ports
321 and 322 are coupled to ports 174 and 274, respectively,
and output ports 323 and 324 are coupled to antenna elements
- 103 and 106, respectively.
Fig. 10 shows in tabular form the phase of each trans-
mitter signal coupled to each antenna element in the mul-
tiple antenna system 120. The same phase notation used in
Fig. 5 is also used in Fig. 10. By comparing Figs. 7 and 10
it can be seen that each of the corner reflector antennas in
Fig. 7 will radiate a signal which is 90 out of phase with
the signals radiated by each of the immediately adjacent
corner reflector antennas. This 90 out of phase relation-
ship between adjacent corner reflector antennas will result
in a desired vector addition of the radiated signals.
~0 Fig. 11 (having the same scale as Fig. 6) illustrates
the actual co~posite radiation pattern 325 which is created
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by antenna system 120. The pattern 325 has a generally
omnidirectional shape with a few relatively deep nulls
(325A) as compared to pattern 95 in Fig. 6. Antenna system
120 has therefore provided an improved multiple input trans- !
mitter antenna system for simultaneously radiating eight
independent signals in a substantially omnidirectional
pattern over a single antenna structure. The depth of these
deep nulls (325A) can be altered by skewing the antenna
elements 101 through 108. These deep nulls are primarily
caused by the larger physical size required by the antenna
array 100 as compared to the antenna array 20.
- In the preferred embodiment of the present invention
illustrated in Fig. 3, the phase shifts contributed by each
of the connections (such as the connection from terminal 43
to 61, terminal 63 to antenna 21, and transmitter 31 to
terminal 41) have been assumed to be zero. This preferred
embodiment will still function properly to produce a sub-
stantially omnidirectional pattern as long as the phase
shifts contributed by the connections between terminals 43-
61, 44-71, 53-62, and 54-72 are equal to each other, in
addition to the phase shifts contributed by each of the
antenna connections (e.g. terminal 63 to antenna 21~ also
being equal to each other. Similar statements apply to the
preferred embodiment illustrated in Fig. 9,
While the primary application of the present invention
is the creation of an omnidirectional antenna pattern, Fig.
12 illustrates a hypothetical non-symmetric radiation
pattern 326 which could be generated by appropriate place-
ment of radiating elements having appropriate 3db beam width
and phasing relationships. Thus the present inYentiOn is
not lLmited to the creati~n o~ a omnidirectional radiation
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pattern. Additionally, the present invention is not limited
to the use of the inventive antenna system in conjunction
with only transmitters, since receivers may be substituted
for any of the transmitters used in the foregoing illustra-
tions. Therefore the inventive antenna system, by recip-
rocity, can be used equally effectively with both receivers
and/or transmitters.
While I have shown and described specific embodiments
of this invention, further modifications and improvements
will occur to those skilled in the art. All such modifi-
cations which retain the basic underlying principles dis-
closed and claimed herein are within the scope of this
invention.
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