Note: Descriptions are shown in the official language in which they were submitted.
1
Specification ~ ~ l~ ~ ~~ '~~
2
"Dual Band Frequency Reuse Antenna"
4
BACKGROUND OF THE: INVENTION
6 Field of the Invention
This invention relates to antennas having frequency reuse
8 capabilities, and more particularly to antennas having a four
9 port network or quadruplexer located in the antenna waveguide,
a feed horn attached to the waveguide, and a polarizes disposed
11 at the aperture of the antenna for converting linearly polarized
12 signals to circularly polarized signals.
13
14 Descrinti~r ~f the Prior art
It has become well known in the field of satellite
16 communications to utilize a single antenna to transmit and
17 receive signals in two frequency bands with two orthogonal,
18 linearly polarized signal components within each band.
19 Waveguides that incorporate such features are known as four-port
networks and/or quadruplexers. U.S. Patent 4,630,059 issued to
21 Morz on December 16, 1986 teaches a four-port network suitable
22 for satellite communication. Two orthogonal ports of the Morz
23 waveguide are utilized to introduce orthogonal linearly
24 polarized signals in the four GHz band which are converted to
circularly polarized signals in the throat of the waveguide for
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2
1 transmission through the grooved conical horn. Two other
2 orthogonally disposed ports are arranged to receive linearly
3 polarized signals in the six GHz band.
4 Another prior art four port waveguide network antenna has
been designed by COMSAT Laboratories. This device includes two
6 coaxial waveguides, the outer waveguide being used for the
7 transmission and reception of the four GHz band and the inner
8 coaxial waveguide being utilized for the six GHz band. A
9 tunable configuration of screws and baffles within the
waveguides are utilized to convert the linearly polarized
11 signals into circularly polarized signals. The device utilizes
12 a grooved conical horn to transmit and receive signals.
13 Additional prior art antennas that are of interest include
14 those described in U.S. Patent-4,797,681 to Kaplan et al. on
January 10, 1989; U.S. Patent 4,707,702 issued to Withers on
16 November 17, 1987; U.S. Patent 4,573,054 issued to Bouko et al.
17 on February 25, 1986: U.S. Patent 4,358,770 issued to Satoh et
18 al. on November 9, 1982: U.S. Patent 4,219,820 issued to Crail
19 on August 26, 1980 and U.S. Patent 3,898,667 issued to Raab on
August 5, 1975.
21 The efficiency of a satellite antenna which transmits and
22 receives different information .utilizing orthogonal
23 polarizations of the same frequency band depends to a
24 significant measure upon the elimination of cross-polarization
between the orthogonal polarized signals. It is known that a
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3
1 circularly polarized signal can be reduced to a linearly
2 polarized signal utilizing a meanderline polarizes. Such
3 meanderline polarizers produce minimal cross-polarization and
4 therefore promote efficiency. U.S. Patent 3,754,271 issued to
Epis on August 21, 1973 describes a meanderline polarizes having
6 a plurality of stacked substantially identical arrays of
7 laterally spaced square-wave shaped meanderlines. The device
8 is positioned at the aperture of a pyramidal horn for conversion
9 of circularly polarized waves into linearly polarized waves.
11 SUMMARY OF THE INVENTION
12 The present invention is a dual frequency band antenna (10)
13 having frequency reuse capability. The antenna waveguide (12)
14 includes a four port waveguide network which transmits arid
receives orthogonal, linearly polarized signals of each of two
16 frequencies. A pyramidal horn (14) is engaged to the mouth of
17 the waveguide, and a meanderline polarizes (16) is engaged to
18 the aperture (17) of the horn (14)~ to convert the signals from
19 linear polarizations to circular polarizations. The meanderline
polarizes (16) includes five separated layers of meanderlines,
21 wherein the first and fifth layers (50 and 58 respectively)
22 include identical meanderlines, the second and fourth (52 and
23 56 respectively) layers include identical meanderlines that
24 differ from those of the first and fifth layers, and the third
layer (54) includes meanderlines that differ from the others in
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1 the first, second, fourth and fifth layers. I t i s a n
2 advantage of the present invention that it provides a dual band
3 frequency reuse antenna having minimal cross-polarization.
4 It is another advantage of the present invention that it
provides a dual band frequency reuse antenna which includes a
6 linear-to-circular polarization device that is disposed in the
7 aperture of the feed horn to reduce cross-polarization effects
8 that axe created within the waveguide and the horn of the
9 antenna.
to It is a further advantage of the present invention that it
11 provides a dual band frequency reuse antenna which utilizes an
12 improved meanderline polarizes to provide reduced cross-
13 polarization.
14 It is yet another advantage of the. present invention that
it provides a dual band frequency reuse antenna including a four
16 port waveguide network incorporated into a square waveguide, a
17 pyramidal horn and a meanderline polarizes to achieve increased
18 signal gain and reduced cross-polarization.
19 It is yet a further advantage of the present invention that
it utilizes a polarizes fabrication technique that provides
21 dimensional stability over a broad thermal range, whereby the
22 antenna is usable in an earth orbital environment.
23 The foregoing and other features and advantages of the
24 present invention will be apparent from the following detailed
description of the preferred embodiment which makes reference
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1 to the several figures of the drawing.
2
3 IN THE DRAWING
4 Fig. 1 is a perspective view of the present invention;
5 Fig. 2 is a side elevational view of the antenna of the
6 present invention and a reflector;
7 Fig. 3 is a perspective view of the waveguide of the
8 present invention;
9 Fig. 4 is a side elevational view of the waveguide of the
present invention;
11 Fig. 5 is an end elevational view of the waveguide of the
12 present invention;
13 Fig. 6 is a perspective view of the meanderline polarizes
14 of the present invention having~cutaway.portions; and
Fig. 7 is a top plan view of portions of the meanderline
16 traces of the meanderline polarizes.
17
18 DETAILED DESCRIPTION OF THE PREFERRED EMBODIMEZZTT
i9 As depicted in Fig. 1, the antenna 10 includes three main
components, a waveguide 12, a horn 14 and a meanderline
21 ~ polarizes 16 that is attached to the aperture 17 of the horn 14.
22 As depicted in Fig. 2, the antenna 10 is preferably designed to
23 be used with a parabolic reflector 18, such that the antenna 10
24 is fixedly mounted to a structure (not shown) and the antenna
beam is scanned by movement of the reflector l8 relative to the
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6
1 fixedly mounted antenna 10.
2 As depicted in Figs. 3, 4 and 5, the waveguide 12 includes
3 a four port waveguide network. Two of the ports 20 and 22 are
4 designed for the transmission of orthogonal, linearly polarized
signals of a first frequency, which in the preferred embodiment
6 is a 4.035 to 4.200 GHz transmission band frequency. The other
7 two ports 24 and 26 are designed for the reception of
8 orthogonal, linearly polarized signals of a different frequency,
9 which in the preferred embodiment is a 6.260 to 6.425 GHz
l0 receiving band frequency. The four independent, linearly
11 polarized signals (1 from each port) are coupled into the common
12 square waveguide 12, which in turn excites the pyramidal feed
13 horn 14 . At the aperture 17 of the horn 14 , the meanderline
14 polarizes 16 then converts the~linearly polarized signals to
circular polarizations, such that two oppositely, circularly
16 polarized fields are radiated from the antenna 10 at the
17 transmission band frequency. The meanderline polarizes also
18 converts two oppositely, circularly polarized signals to two
19 orthogonal, linearly polarized signals at the receiving band
frequency.
21 Each port 20, 22, 24 and 26 of the
four port
waveguide
22 network includes an attachment flange 32, 34 and 36
30,
23 respectively, disposed about outer end to which signal
its
24 transmitting or receiving devices(nat shown)are coupled.
In
the preferred embodiment depictedin Figs. 3, 4 and 5,
the
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1 orthogonal ports 24 and 26 feed directly into the side and
2 throat respectively of the waveguide 12, whereas orthogonal
3 ports 20 and 22 are provided with additional waveguide
4 structures 40 and 42 respectively which lead to the body of the
waveguide 12.
6 As is known to those skilled in the art, the dimensions of
7 the various waveguide openings and structures are of
8 significance in obtaining acceptable antenna performance. For
9 ease of comprehension and enablement purposes, various
significant dimensions, in inches, are provided in Figs. 3, 4,
11 and 5. The waveguide structures 40 and 42 comprise a series of
12 rectangular corrugations formed perpendicularly to the central
13 axis of the waveguide structures 40 and 42. In the preferred
14 embodiment, support straps 46 are engaged across the outer
surface of the corrugations to provide structural rigidity to
16 the waveguide structures 40 and 42. The corrugated waveguide
17 structures 40 and 42 are dimensionally configured to act as a
18 short circuit to the six GHz signals while allowing the four GHz
19 signals to pass therethrough. Thus, the linearly polarized six
GHz receiving signal does not propagate into waveguide
21 structures 40 and 42, but rather continues through the body of
22 the waveguide 12 to the ports 24 and 26. Additionally, a
23 central section 48 of the waveguide 12 located behind ports 20
24 and 22 is dimensionally sized to prevent the propagation of the
four GHz transmission signals backwards through the waveguide
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8
1 12 to the six GHz ports 24 and 26.
2 In the preferred embodiment, the feed horn 14 is a
3 pyramidal horn having a flare angle of approximately 10 degrees
4 and a square aperture having a side measurement of approximately
6 inches; its aperture 17 is located approximately 3.5 inches
6 towards the reflector 18 from the focal point 50 of the
7 reflector 18.
8 As is seen in Fig. 1, in the preferred embodiment, the
9 meanderline polarizes is oriented relative to the square
aperture 17 of the feed horn 14, such that the meanderlines run
11 diagonally across the aperture 17 of the feed horn 14. The
12 improved meanderline polarizes 16 serves to transform the
13 linearly polarized signals into circularly polarized signals at
14 the aperture 17 of the antenna horn 14.~ Thus, the signals that
propagate within the horn 14 and waveguide 12 are entirely
16 orthogonal, linearly polarized signals, and no circularly
17 polarized signals propagate within the horn 14 or waveguide 12.
18 This configuration results in the transmission and reception
19 within the waveguide of orthogonal, linearly polarized signals
with significantly reduced cross-polarization, whereby improved
21 signal gain and reduced noise is achieved.
22 In the preferred embodiment, as depicted in Fig. 6, the
23 meanderline polarizes 16 is a sandwich structure including five
24 thin layers 50, 52, 54, 56 and 58, each having a plurality of
meanderline traces 60, 62, 64, 66 and 68, respectively, formed
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1 thereon. Four foam-like spacers 70, 72, 74 and 76 serve to
2 separate the five meanderline layers. The use of meanderline
3 polarizers that are generally configured as described
4 hereinabove is well known in the art, as particularly taught in
U.S. Patent 3,754,271 issued to J. Epis on August 21, 19?3. A
6 significant difference between the polarizes 16 of the present
7 invention and the prior art polarizers resides in the
8 utilization of meanderline traces of differing dimensions in the
9 various layers 50, 52, 54, 56 and 58. Specifically, the
meanderline traces in layers 50 and 58 are identical, the
11 meanderline traces in layers 52 and 56 are identical, although
12 differing in dimensions from the meanderline traces in layers
13 50 and 58. The meanderline traces in layer 54 are different in
14 dimension from those of any other layer.
Proper selection of the meanderline trace dimensions
16 provides the required dual band conversion to pure circular
17 polarization. In the preferred embodiment, the polarizes is a
18 9.0~~ square by 2.0~~ thick sandwich construction. The sandwich
19 consists of the four spacers 60, 62, 64 and 66 composed of
Stanthyne 817 Foam, and the five layers 50, 52, 54, 56 and 58
21 are composed of etched 1/2 oz. copper clad 3 mill Kapton bonded
22 together with Hysol 9309 adhesive. Bonding is done so as not
23 to cover the traces. The polarizes is bonded to a fiberglass
24 frame 19 which is bolted to the aperture 17 of the horn 14. The
traces are preferably formed on the Kapton layers utilizing
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1 printed circuit board techniques to provide close tolerances and
2 reliability to the device.
3 As is depicted in Fig. 7, the dimensions of the meanderline
4 traces in each layer can be expressed by four parameters that
5 are designated as: A, the periodicity of a meanderline trace;
6 H, the height of the, meanderline trace; W, the width of the
7 meanderline trace; and B, the distance between adjacent
8 meanderline traces. The following table provides the dimensions
9 for each of the layers of the meanderline polarizer 16.
l0
11 __
'
_
12 Layers 50 & 58 Layers Layer 54
52 & 56
13
14 A 0.046 0.174 0.134
H 0.180 0.336 0
409
16 W 0.011 0.043 .
0
034
17 B 0.782 0.782 .
0
782
18 ' .
i9 It
is
advantageous
that
the
present
invention
provides
a
reuse
frequency
capability.
That_is,
that
the
same
frequency
21 can
be
used
for
transmitting
two
signals,
one
of
which
is
22 circularly
polarized
in
a
first
sense
and
the
other
of
whi
h i
c
s
23 circularly
polarized
in
an
opposite
sense.
Additionally,
the
24 utilization
of
four
ports
in
the
waveguide
network
permits
the
simultaneous
utilization
of
two
reuse
frequency
signals,
26 approximately
4
GHz
and
approximately
6
GHz
The
use
f
.
o
a
27 meanderline
polarizer
at
the
aperture
17
of
the
feed
harn
14
28 provides
improved
performance
as
compared
to
prior
art
devices
29 which
attempt
to
convert
signals
from
circular
polarization
to
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1 linear polarization within the waveguide. The improved
2 meanderline polarizer reduces cross-polarization and thus
3 contributes to the improved performance of the invention.
4 While the invention has been particularly shown and
described with reference to certain preferred embodiments, it
6 will be understood by those skilled in the art that various
7 alterations and modifications in form and detail may be made
8 therein. Accordingly, it is intended that the following claims
9 cover all such alterations and modifications as may fall within
the true spirit and scope of the invention.
11 What I claim is:
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