Title: Multiband radially distributed phased array antenna with a stepped ground plane and associated methods
Abstract: A multiband phased array antenna includes a substrate, and dipole element arrays extending outwardly from an imaginary center point on the substrate. Each dipole element array includes dipole antenna elements arranged in end-to-end relation and having a dipole size different than a dipole size of dipole antenna elements of at least one other dipole element array. A ground plane is adjacent the dipole element arrays, and a spacing between the dipole element arrays and the ground plane is different between the dipole element arrays having different size dipole antenna elements. The ground plane has a plateau shape for providing the different spacing between the dipole element arrays.
Patent Number: 6,956,532 Issued on 10/18/2005 to Durham, et al.
| Inventors:
|
Durham; Timothy E. (Palm Bay, FL);
Vanstrum; Mark (Indialantic, FL);
Jones; Anthony M. (Palm Bay, FL);
Gothard; Griffin K. (Satellite Beach, FL)
|
| Assignee:
|
Harris Corporation (Melbourne, FL)
|
| Appl. No.:
|
702853 |
| Filed:
|
November 6, 2003 |
| Current U.S. Class: |
343/725; 343/729 |
| Intern'l Class: |
H01Q 021/00; H01Q 001/00 |
| Field of Search: |
343/725,729,770,776,798,799
|
References Cited [Referenced By]
U.S. Patent Documents
| 4081803 | Mar., 1978 | Dempsey.
| |
| 5321414 | Jun., 1994 | Alden et al.
| |
| 6417813 | Jul., 2002 | Durham.
| |
| 6512487 | Jan., 2003 | Taylor et al.
| |
| 6552687 | Apr., 2003 | Rawnick et al.
| |
| 6657577 | Dec., 2003 | Gregersen et al.
| |
| 6744411 | Jun., 2004 | Osterhues et al.
| |
| 6822616 | Nov., 2004 | Durham et al.
| |
| 2004/0100406 | May., 2004 | Okado.
| |
| 2004/0100408 | May., 2004 | Okado.
| |
| 2004/0104860 | Jun., 2004 | Durham et al.
| |
| 2004/0155820 | Aug., 2004 | Sreenivas et al.
| |
Primary Examiner: Wong; Don
Assistant Examiner: Vy; Hung Tran
Attorney, Agent or Firm: Allen, Dyer, Doppelt, Milbrath & Gilchrist, P.A.
Claims
1. A multiband phased array antenna comprising:
a substrate; and
a plurality of dipole element arrays extending outwardly from an imaginary center
point on said substrate;
each dipole element array comprising a plurality of dipole antenna elements arranged
in end-to-end relation and having a dipole size different than a dipole size of
dipole antenna elements of at least one other dipole element array.
2. A multiband phased array antenna according to claim 1, wherein said plurality
of dipole element arrays are radially distributed from the imaginary center point,
with the radial distribution being symmetrical.
3. A multiband phased array antenna according to claim 1, further comprising
a ground plane adjacent said plurality of dipole element arrays, and a spacing
between said plurality of dipole element arrays and said ground plane is different
between the dipole element arrays having different size dipole antenna elements.
4. A multiband phased array antenna according to claim 3, wherein said ground
plane has a plateau shape for providing the different spacing between said plurality
of dipole element arrays.
5. A multiband phased array antenna according to claim 1, wherein each dipole
antenna element comprises a printed conductive layer.
6. A multiband phased array antenna according to claim 1, wherein said plurality
of dipole antenna elements are sized and relatively positioned within each respective
dipole element array so that the multiband phased array antenna has a total bandwidth
equal to or greater than 20-to-1.
7. A multiband phased array antenna according to claim 1, wherein said plurality
of dipole antenna elements in each dipole element array are arranged in rows and
columns, with outer columns of dipole antenna elements being resistively loaded.
8. A multiband phased array antenna according to claim 7, further comprising
feed lines connected to at least one inner column of dipole antenna elements.
9. A multiband phased array antenna according to claim 1, wherein each dipole
antenna element comprises a medial feed portion and a pair of legs extending outwardly
therefrom, adjacent legs of adjacent dipole antenna elements including respective
spaced apart end portions having predetermined shapes and relative positioning
to provide increased capacitive coupling between the adjacent dipole antenna elements.
10. A multiband phased array antenna according to claim 9, wherein each leg comprises:
an elongated body portion; and
an enlarged width end portion connected to an end of the elongated body portion.
11. A multiband phased array antenna according to claim 9, wherein each leg comprises:
an elongated body portion;
an enlarged width end portion connected to an end of the elongated body portion;
and
a plurality of fingers extending outwardly from said enlarged width end portion.
12. A multiband phased array antenna according to claim 9, wherein each dipole
element array has a desired frequency range, and wherein the spacing between the
end portions of adjacent legs is less than about one-half a wavelength of a highest
desired frequency.
13. A multiband phased array antenna according to claim 9, further comprising
a respective impedance element electrically connected between the spaced apart
end portions of adjacent legs of adjacent dipole antenna elements for further increasing
the capacitive coupling therebetween.
14. A multiband phased array antenna according to claim 9, further comprising
a respective printed impedance element adjacent the spaced apart end portions of
adjacent legs of adjacent dipole antenna elements for further increasing the increased
capacitive coupling therebetween.
15. A multiband phased array antenna comprising:
a substrate;
a plurality of dipole element arrays radially distributed from an imaginary center
point on said substrate;
each dipole element array comprising a plurality of dipole antenna elements arranged
in end-to-end relation and having a dipole size different than a dipole size of
dipole antenna elements of at least one other dipole element array; and
a ground plane adjacent said plurality of dipole element arrays, and a spacing
between said plurality of dipole element arrays and said ground plane being different
between the dipole element arrays having different size dipole antenna elements.
16. A multiband phased array antenna according to claim 15, wherein the radial
distribution of said plurality of dipole element arrays is symmetrical.
17. A multiband phased array antenna according to claim 15, wherein said ground
plane has a plateau shape for providing the different spacing between said plurality
of dipole element arrays.
18. A multiband phased array antenna according to claim 15, wherein each dipole
antenna element comprises a printed conductive layer.
19. A multiband phased array antenna according to claim 15, wherein said plurality
of dipole antenna elements in each dipole element array are arranged in rows and
columns, with outer columns of dipole antenna elements being resistively loaded.
20. A multiband phased array antenna according to claim 19, further comprising
feed lines connected to at least one inner column of dipole antenna elements.
21. A multiband phased array antenna according to claim 15, wherein each dipole
antenna element comprises a medial feed portion and a pair of legs extending outwardly
therefrom, adjacent legs of adjacent dipole antenna elements including respective
spaced apart end portions having predetermined shapes and relative positioning
to provide increased capacitive coupling between the adjacent dipole antenna elements.
22. A multiband phased array antenna according to claim 21, wherein each leg comprises:
an elongated body portion; and
an enlarged width end portion connected to an end of the elongated body portion.
23. A multiband phased array antenna according to claim 21, wherein each leg comprises:
an elongated body portion;
an enlarged width end portion connected to an end of the elongated body portion;
and
a plurality of fingers extending outwardly from said enlarged width end portion.
24. A multiband phased array antenna according to claim 21, wherein each dipole
element array has a desired frequency range, and wherein the spacing between the
end portions of adjacent legs is less than about one-half a wavelength of a highest
desired frequency.
25. A multiband phased array antenna according to claim 21, further comprising
a respective impedance element electrically connected between the spaced apart
end portions of adjacent legs of adjacent dipole antenna elements for further increasing
the capacitive coupling therebetween.
26. A multiband phased array antenna according to claim 21, further comprising
a respective printed impedance element adjacent the spaced apart end portions of
adjacent legs of adjacent dipole antenna elements for further increasing the coupling therebetween.
27. A method for making a multiband phased array antenna comprising:
providing a substrate; and
forming a plurality of dipole element arrays extending outwardly from an imaginary
center point on the substrate, each dipole element array comprising a plurality
of dipole antenna elements arranged in end-to-end relation and having a dipole
size different than a dipole size of dipole antenna elements of at least one other
dipole element array.
28. A method according to claim 27, wherein the plurality of dipole element arrays
are radially distributed from the imaginary center point on the substrate, with
the radial distribution being symmetrical.
29. A method according to claim 27, further comprising forming a ground plane
adjacent the plurality of dipole element arrays, and a spacing between the plurality
of dipole element arrays and the ground plane is different between the dipole element
arrays having different size dipole antenna elements.
30. A method according to claim 29, wherein the ground plane has a plateau shape
for providing the different spacing between the plurality of dipole element arrays.
31. A method according to claim 27, wherein each dipole antenna element comprises
a printed conductive layer.
32. A method according to claim 27, wherein the plurality of dipole antenna elements
in each dipole element array are arranged in rows and columns; and further comprising
connecting resistive loads to the outer columns of dipole antenna elements.
33. A method according to claim 32, further comprising connecting feed lines
to at least one inner column of dipole antenna elements.
34. A method according to claim 27, wherein forming each dipole antenna element
comprises forming a medial feed portion and a pair of legs extending outwardly
therefrom, with adjacent legs of adjacent dipole antenna elements including respective
spaced apart end portions having predetermined shapes and relative positioning
to provide increased capacitive coupling between the adjacent dipole antenna elements.
35. A method according to claim 34, wherein forming each leg comprises forming
an elongated body portion, and forming an enlarged width end portion connected
to an end of the elongated body portion.
36. A method according to claim 34, wherein forming each leg comprises forming
an elongated body portion, forming an enlarged width end portion connected to an
end of the elongated body portion, and forming a plurality of fingers extending
outwardly from the enlarged width end portion.
37. A method according to claim 34, wherein each dipole element array has a desired
frequency range, and wherein the spacing between the end portions of adjacent legs
is less than about one-half a wavelength of a highest desired frequency.
38. A method according to claim 34, further comprising electrically connecting
a respective impedance element between the spaced apart end portions of adjacent
legs of adjacent dipole antenna elements for further increasing the capacitive
coupling therebetween.
39. A method according to claim 34, further comprising forming a respective printed
impedance element adjacent the spaced apart end portions of adjacent legs of adjacent
dipole antenna elements for further increasing the coupling therebetween.
Description
FIELD OF THE INVENTION
The present invention relates to the field of communications, and more particularly,
to a multiband phased array antenna.
BACKGROUND OF THE INVENTION
Existing microwave antennas include a wide variety of configurations for
various applications, such as satellite reception, remote broadcasting, or military
communication. The desirable characteristics of low cost, light weight, low profile
and mass producibility are provided in general by printed circuit antennas.
The simplest forms of printed circuit antennas are microstrip antennas wherein
flat conductive elements, such as monopole or dipole antenna elements, are spaced
from a single essentially continuous ground plane by a dielectric sheet of uniform
thickness. An example of a microstrip antenna is disclosed in U.S. Pat. No. 6,417,813
to Durham, which is assigned to the current assignee of the present invention and
is incorporated herein by reference in its entirety.
The antennas are designed in an array and may be used for communication systems
requiring such characteristics as low cost, light weight and a low profile. The
bandwidth of such antennas is about 10-to-1. However, a 10-to-1 bandwidth can be
limiting for certain applications. For example, electronic warfare support measures
(ESM) and electronic intelligence (ELINT) radar systems require antennas having
a bandwidth typically greater than 20-to-1, which offers a higher probability of
intercepting signals.
One approach for increasing the bandwidth of an array of dipole antenna elements
is disclosed in U.S. Pat. No. 6,552,687 to Rawnick et al., which is also assigned
to the current assignee of the present invention and is incorporated herein by
reference in its entirety. The multiband phased array antenna in the '687 patent
includes a first array of dipole antenna elements operating over a first frequency
band, and a second array of dipole antenna elements operating over a second frequency
band so that the phased array antenna is a multiband antenna.
The size of the dipole antenna elements in the first array is different from
the size of the dipole antenna elements in the second array. Consequently, the
ground plane spacing is different between the first and second arrays. One disadvantage
of this configuration is that since the higher frequency dipole antenna elements
are surrounded by the lower frequency dipole antenna elements, there is a gap or
hole in the aperture distribution of the lower frequency dipole antenna elements.
Consequently, the layout of the different size antenna elements in the '687 patent
presents difficulties in controlling the antenna pattern since this gap or hole
may have undesired effects, such as raising the sidelobe levels of the antenna.
In addition, the fact that the physical aperture size does not change over a large
bandwidth (approximately 10:1) means that the electrical size of the aperture will
vary considerably over the band, making this approach unsuitable as a feed for
a reflector.
A different type antenna that offers a wide bandwidth (greater than 20-to-1)
is
a spiral antenna. To cover multiple frequency bands, multiple spirals may be used,
i.e., a spiral for each frequency band. However, the multiple spirals are non-concentric
about the focal point of the antenna when operating as a feed for a reflector,
which results in a loss of efficiency due to scan loss compared to that of a completely
concentric aperture. In addition, another disadvantage is that the efficiency of
spiral antennas is typically much less than 50% since their performance depends
on an absorber-filled back cavity.
SUMMARY OF THE INVENTION
In view of the foregoing background, it is therefore an object of the present
invention to provide a multiband antenna that has high efficiency while achieving
a constant beamwidth and pattern control.
This and other objects, features, and advantages in accordance with the present
invention are provided by a multiband phased array antenna comprising a substrate,
and a plurality of dipole element arrays extending outwardly from an imaginary
center point on the substrate. Each dipole element array may comprise a plurality
of dipole antenna elements arranged in an end-to-end relation and having a dipole
size different than a dipole size of dipole antenna elements of at least one other
dipole element array.
The plurality of dipole element arrays may be radially distributed from the imaginary
center point, with the radial distribution being symmetrical. The radial distribution
of the dipole element arrays advantageously provides a constant beamwidth when
operating the multiband phased array antenna as a reflector feed since all of the
arrays use the same focal point. In addition, the pattern of the multiband phased
array antenna can be more easily controlled because the radial distribution of
the dipole element arrays provides a choice of the radial feed point location,
thereby allowing the electrical size of the aperture to be kept relatively constant.
The multiband phased array antenna further comprises a ground plane adjacent
the plurality of dipole element arrays, and a spacing between the plurality of
dipole element arrays and the ground plane may be different between the dipole
element arrays having different size dipole antenna elements. The ground plane
may have a plateau shape for providing the different spacing between the plurality
of dipole element arrays.
Each dipole antenna element may comprise a printed conductive layer. The plurality
of dipole antenna elements are preferably sized and relatively positioned within
each respective dipole element array so that the multiband phased array antenna
has a total bandwidth equal to or greater than 20-to-1.
The plurality of dipole antenna elements in each dipole element array are preferably
arranged in rows and columns, with outer columns of dipole antenna elements being
resistively loaded. The passive elements in the outer columns allow the active
elements in the center column to receive sufficient current, which is normally
conducted through the dipole antenna elements on the substrate. Feed lines are
connected to at least one inner column of dipole antenna elements.
Each dipole antenna element comprises a medial feed portion and a pair of legs
extending outwardly therefrom. Adjacent legs of adjacent dipole antenna elements
may include respective spaced apart end portions having predetermined shapes and
relative positioning to provide increased capacitive coupling between the adjacent
dipole antenna elements. Each leg may comprise an elongated body portion, and an
enlarged width end portion is connected to an end of the elongated body portion.
The spaced apart end portions in adjacent legs may comprise interdigitated portions.
The multiband phased array antenna may further comprise a respective impedance
element electrically connected between the spaced apart end portions of adjacent
legs of adjacent dipole antenna elements for further increasing the capacitive
coupling therebetween. Alternately, a respective printed impedance element may
be adjacent the spaced apart end portions of adjacent legs of adjacent dipole antenna
elements for further increasing the capacitive coupling therebetween.
Another aspect of the present invention is directed to a method for making
a multiband phased array antenna by providing a substrate or multiple substrates,
and forming a plurality of dipole element arrays extending outwardly from an imaginary
center point on the substrate. Each dipole element array may comprise a plurality
of dipole antenna elements arranged in end-to-end relation and having a dipole
size different than a dipole size of dipole antenna elements of at least one other
dipole element array.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic diagram illustrating a multiband phased array antenna
mounted on an aircraft in accordance with the present invention.
FIG. 2 is a top plan view of the multiband phased array antenna in accordance
with the present invention.
FIGS. 3 and 4 are cross-sectional views of the multiband phased array antenna
as shown in FIG. 2 respectively taken along radial axes R
1 and R
2.
FIG. 5 is an enlarged schematic view of a center column of one of the dipole
element arrays as shown in FIG. 2.
FIG. 6 is a plot of computed VSWR versus frequency for the low-frequency band
arrays in the multiband phased array antenna as shown in FIG. 2.
FIGS. 7A and 7B are enlarged schematic views of the spaced apart end portions
of adjacent legs of adjacent dipole antenna elements as may be used in the multiband
phased array antenna of FIG. 2.
FIG. 7C is an enlarged schematic view of an impedance element connected across
the spaced apart end portions of adjacent legs of adjacent dipole antenna elements
as may be used in the multiband phased array antenna of FIG. 2.
FIG. 7D is an enlarged schematic view of an impedance element selectively connected
across the spaced apart end portions of adjacent legs of adjacent dipole antenna
elements as may be used in the multiband phased array antenna of FIG. 2.
FIG. 7E is an enlarged schematic view of another embodiment of an impedance
element connected across the spaced apart end portions of adjacent legs of adjacent
dipole antenna elements as may be used in the multiband phased array antenna of
FIG. 2.
FIGS. 8A and 8B are respectively enlarged schematic views of a discrete resistive
element and a printed resistive element connected across the medial feed portion
of a dipole antenna element as may be used in the multiband phased array antenna
of FIG. 2.
FIG. 9 is top plan view of another aspect of the multiband phased array antenna
in accordance with the present invention.
FIG. 10 is a cross-sectional view of the multiband phased array antenna as shown
in FIG. 9 taken along radial axis R
1.
FIGS. 11A and 11B are respectively a top plan view and a corresponding side
view of another embodiment of the multiband phased array antenna as shown in FIG. 9.
FIG. 12 is a plot of the computed VSWR versus frequency for one of the dipole
element arrays having an edge element on a second surface of the substrate as shown
in FIG. 11B.
FIG. 13 is top plan view of another aspect of the multiband phased array antenna
in accordance with the present invention.
FIG. 14 is a cross-sectional view of the multiband phased array antenna as shown
in FIG. 13 taken along radial axis R
1.
FIG. 15 is top plan view of another aspect of the multiband phased array antenna
in accordance with the present invention.
FIG. 16 is a cross-sectional view of the multiband phased array antenna as shown
in FIG. 15 taken along radial axis R
1.
FIG. 17 is a plot of measured and computed VSWR versus frequency over a frequency
range of 2 to 18 GHz for the multiband phased array antenna as shown in FIG. 16.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention will now be described more fully hereinafter with reference
to the accompanying drawings, in which preferred embodiments of the invention are
shown. This invention may, however, be embodied in many different forms and should
not be construed as limited to the embodiments set forth herein. Rather, these
embodiments are provided so that this disclosure will be thorough and complete,
and will fully convey the scope of the invention to those skilled in the art. Like
numbers refer to like elements throughout, and prime, double prime and triple prime
notations are used to indicate similar elements in alternative embodiments.
Referring initially to FIG. 1, a multiband phased array antenna
50
in accordance with the present invention will now be described. One or more multiband
phased array antennas
50 may be mounted on an aircraft
52, for example.
The illustrated multiband phased array antenna
50 is connected to a beam
forming network (BFN)
54 which is connected to a plurality of transceivers
561-
56n.
Since the multiband phased array antenna
50 covers multiple frequency
bands, each transceiver
561-
56n functions over
one or more frequency bands. The BFN
54 controls the phase of the multiband
phased array antenna
50 to create the desired sum and difference patterns,
which forms the desired antenna beams, as readily understood by those skilled in
the art. An example BFN
54 is a Butler matrix.
One aspect of the multiband phased array antenna
50 comprises a substrate
60, and a plurality of dipole element arrays
62,
64 extending
outwardly from an imaginary center point
66 on the substrate, as illustrated
in FIG.
2. The plurality of dipole element arrays
62,
64 may
be radially distributed from the imaginary center point
66, with the radial
distribution being symmetrical. The radial distribution of the dipole element arrays
62,
64 advantageously provides no scan loss and therefore high efficiency
when operating the multiband phased array antenna
50 as a reflector feed
since all of the arrays use the same focal point, i.e., the imaginary center point
66. In addition, the pattern of the multiband phased array antenna
50
can be more easily controlled because the radial distribution of the dipole element
arrays
62,
64 allows for a choice of one or more feed points. Different
feed points correspond to different electrical sizes for the array. By choosing
different feed points for different bands of operation, the electrical size may
be maintained relatively constant over an extremely broad bandwidth. In addition,
yet another benefit of the radial distribution is that it provides the polarization
diversity required to obtain sum and difference patterns that are relatively azimuthally
constant in amplitude if the proper beam forming network is utilized.
Each dipole element array
62,
64 comprises a plurality of dipole
antenna elements
70a,
70b arranged in an end-to-end
relation and having a dipole size different than a dipole size of dipole antenna
elements of at least one other dipole element array. Each dipole element array
62,
64 is arranged in rows and columns, such as the 3×5 arrays
illustrated in FIG.
2. The 3×5 arrays are for illustrative purposes,
and the actual size of the arrays
62,
64 may vary depending on the
intended application.
As will be discussed in greater detail below, the center column of dipole antenna
elements
70a,
70b are active, whereas the outer columns
of dipole antenna elements are passive. The passive elements in the outer columns
allow the active elements in the center column to receive sufficient current, which
is normally conducted through the dipole antenna elements
70a,
70b
on the substrate
60.
The multiband phased array antenna
50 illustrated in FIG. 2 includes two
sets of dipole element arrays
62,
64. These dipole element arrays
62,
64 are separated into high-frequency band arrays and low-frequency
band arrays. Dipole element arrays
64 are the low-frequency band arrays,
which may cover a frequency range of 4 to 18 GHz, for example. Dipole element arrays
62 are the high-frequency band arrays, which may cover a frequency range
of 19 to 28 GHz, for example. In this example, the multiband phased array antenna
50 covers a total bandwidth of 7-to-1.
To increase the total bandwidth, additional dipole element arrays may simply
be
added to the substrate
60 to cover a different frequency range. For example,
if the additional dipole element arrays (not shown) cover 1 to 4 GHz, then the
total bandwidth is significantly increased to 28-to-1.
The size of the dipole antenna elements
70b in the low-frequency
band arrays
64 is different than the size of the dipole antenna elements
70a in the high-frequency band arrays
62. In particular, the
size of the dipole antenna elements
70a in the high-frequency band
arrays
62 is less than the size of the dipole antenna elements
70b
in the low-frequency band arrays
64.
The multiband phased array antenna
50 further includes a ground plane
80. FIGS. 3 and 4 are cross-sectional views of the multiband phased array
antenna
50 as shown in FIG. 2 respectively taken along radial axes R
1
and R
2. The spacing X of the ground plane
80 for the dipole antenna
elements
70 in the low-frequency band arrays
64 is greater than the
spacing Y of the ground plane for the dipole antenna elements in the high-frequency
band arrays
62. The ground plane
80 is preferably spaced from the
different size dipole element arrays
62,
64 less than about one-half
a wavelength of a highest desired frequency within each respective array, as readily
appreciated by those skilled in the art.
The different spacing between the ground plane
80 and the respective dipole
antenna elements
70a,
70b may be provided by a plateau
shaped ground plane. In other words, the ground plane
80 has a stepped shape
or thickness between the low-frequency band arrays
64 and the high-frequency
band arrays
62. A dielectric material
81 may be between the ground
plane
80 and the respective dipole antenna elements
70.
Referring now to FIG. 5, a plurality of feed lines
90 may be connected
to the active dipole antenna elements
70a,
70b in each
array
62,
64. As noted above, the center column of each array
62,
64 includes active dipole antenna elements
70a,
70b,
whereas the outer columns include passive dipole antenna elements. This advantageously
reduces the complexity of connecting the feed lines
90 to the dipole antenna
elements in the multiband phased array antenna
50. The active dipole antenna
elements
70b as shown in FIG. 5 represent the center column of a
low-frequency band array
64. The feed
72 for each active dipole antenna
element
70b therein may be referred to as a port. Consequently, the
five active dipole antenna elements
70b have five ports
72
that may be connected to five separate feed lines
90.
FIG. 6 is a plot of VSWR versus frequency for the low-frequency band arrays
64 with respect to each of the five ports
72. Port
1 is represented
by line
100, port
2 is represented by line
102, port
3
is represented by line
104, port
4 is represented by line
106
and port
5 is represented by line
108. Lines
106 and
108
overlap one another so that it appears that only one line represents both ports
4 and
5. Between 4 and 18 GHz, the VSWR for all five ports
72
is substantially the same when operating the multiband phased array
50 as
a feed for a reflector. This results in a substantially constant beamwidth over
the entire operating bandwidth of the array.
Between 2 and 4 GHz, however, the VSWR significantly increases for the outer
ports (ports
4 and
5), whereas for the inner ports (ports
1,
2 and
3), the VSWR slightly increases. Each port
72 is a different
radial distance from the phase center of the multiband phased array antenna—which
is the imaginary center point
66 on the substrate
60.
Since the wavelength changes as the frequency changes, it is preferred that
the multiband phased array antenna
50 remains electrically the same for
the different size dipole antenna elements
70a,
70b.
The radial distance of each port
72 from the phase center
66 determines
the beamwidth. Consequently, a corresponding transceiver
561-
56n
may be connected to any one of the five ports
72 and receive substantially
the same antenna performance. This is because the electrical size of the various
feeds
90 remains substantially the same as the frequency varies across the
multiband phased array antenna by choosing the correct port
50.
Nonetheless, the transceivers
561-
56n
may be selectively connected to a particular port
72 within the radial distribution
of dipole antenna elements
70a,
70b to achieve constant
beamwidth and pattern control. Similarly, the dipole antenna elements
70
for the different frequency bands may be weighted (e.g., amplitude weighted) to
also achieve constant beamwidth and pattern control, as readily appreciated by
those skilled in the art.
A single transceiver may be connected to one or more of the five ports
72
on the low-frequency band arrays
64, or multiple transceivers may connected.
For example, a first transceiver
561 operating over the frequency
range of 4-to-8 GHz may be connected to port
1, a second transceiver
562
operating over the frequency range of 8-to-12 GHz may be connected to port
2, and a third transceiver
563 operating over the frequency
range of 12-to-18 GHz may be connected to port
3. Different transceivers
564-
56n may likewise be connected to the different
ports on the high-frequency band arrays
62.
Since the high and low frequency band arrays
62,
64 operate over
different frequency bands, the respective transceivers
561-
56n
can operate simultaneously. Even though the illustrated low and high frequency
bands are continuous (4-to-18 GHz and 18-to-28 GHz), the multiband phased array
antenna
50 may be designed to operate over non-continuous frequency bands,
as readily appreciated by those skilled in the art. For example, the low-frequency
band arrays
64 may still cover 4 to 18 GHz, but the high-frequency band
arrays
62 may cover a different frequency band, such as 30 to 33 GHz instead
of 18 to 28 GHz, for example.
Referring to FIGS. 7A-7E, and also to FIG. 5, the dipole antenna elements
70a,
70b as used in the multiband phased array antenna
50 will now be described in greater detail. The dipole antenna elements
70a,
70b are on a substrate
60, which is a printed
conductive layer. Each dipole antenna element
70a,
70b
comprises a medial feed portion (or port)
72 and a pair of legs
74
extending outwardly therefrom. Respective feed lines
90 would be connected
to each feed portion
72 from the opposite side of the substrate
60.
Adjacent legs
74 of adjacent dipole antenna elements
76 have
respective spaced apart end portions
78 to provide increased capacitive
coupling between the adjacent dipole antenna elements, as shown in FIG.
7A.
Increasing the capacitive coupling counters the inherent inductance of the dipole
antenna elements when they are closely spaced, and this is done in such a manner
that as the frequency varies a wide bandwidth may be maintained.
The adjacent dipole antenna elements
76 have predetermined shapes and
relative positioning to provide the increased capacitive coupling. For example,
the capacitance between adjacent dipole antenna elements
76 is between about
0.016 and 0.636 picofarads (pF), and preferably between 0.159 and 0.239 pF. Of
course, these values will vary as required depending on the actual application
to achieve the same desired bandwidth, as readily understood by one skilled in
the art.
As shown in FIG. 7A, the spaced apart end portions
78 in adjacent legs
74 may have overlapping or interdigitated portions
80, and each leg
74 comprises an elongated body portion
82, an enlarged width end
portion
84 connected to an end of the elongated body portion, and a plurality
of fingers, e.g., four, extending outwardly from the enlarged width end portion.
Each dipole antenna element array
62,
64 has a desired frequency
range (4 to 18 GHz or 18 to 28 GHz, for example) and the spacing between the end
portions
78 of adjacent legs
74 is less than about one-half a wavelength
of a highest desired frequency.
Alternatively, as shown in FIG. 7B, adjacent legs
74′
of adjacent dipole antenna elements
76 may have respective spaced apart
end portions
78′ to provide increased capacitive coupling between
the adjacent dipole antenna elements. In this embodiment, the spaced apart end
portions
78′ in adjacent legs
74′ comprise enlarged
width end portions
84′ connected to an end of the elongated body
portion
82′ to provide the increased capacitive coupling between
adjacent dipole antenna elements
76.
To further increase the capacitive coupling between adjacent dipole antenna elements
76, a respective discrete or bulk impedance element
110" is electrically
connected across the spaced apart end portions
78" of adjacent legs
74"
of adjacent dipole antenna elements, as illustrated in FIG.
7C.
In the illustrated embodiment, the spaced apart end portions
78" have
the
same width as the elongated body portions
82". The discrete impedance elements
110" are preferably soldered in place after the dipole antenna elements
70a,
70b have been formed so that they overlay the
respective adjacent legs
74" of adjacent dipole antenna elements
76.
This advantageously allows the same capacitance to be provided in a smaller area,
which helps to lower the operating frequency of the respective dipole antenna element
arrays
62,
64.
The illustrated discrete impedance element
70" includes a capacitor
112"
and an inductor
114" connected together in series. However, other configurations
of the capacitor
112" and inductor
114" are possible, as would be
readily appreciated by those skilled in the art. For example, the capacitor
112"
and inductor
114" may be connected together in parallel, or the discrete
impedance element
110" may include the capacitor without the inductor or
the inductor without the capacitor. Depending on the intended application, the
discrete impedance element
110" may even include a resistor.
The discrete impedance element
110" may also be connected between the
adjacent legs
74 with the overlapping or interdigitated portions
80
illustrated in FIG.
7A. In this configuration, the discrete impedance element
110" advantageously provides a lower cross polarization in the antenna patterns
by eliminating asymmetric currents which flow in the interdigitated capacitor portions
80. Likewise, the discrete impedance element
110" may also be connected
between the adjacent legs
74′ with the enlarged width end portions
84′ illustrated in FIG.
7B.
Another advantage of the respective discrete impedance elements
110"
is that they may have different impedance values so that the bandwidth of the respective
dipole antenna element arrays
62,
64 can be tuned for different applications,
as would be readily appreciated by those skilled in the art. In addition, the impedance
is not dependent on the impedance properties of the adjacent dielectric layer
81.
Since the discrete impedance elements
110" are not effected by the dielectric
layer
81, this approach advantageously allows the impedance between the
dielectric layer
81 and the impedance of the discrete impedance element
110" to be decoupled from one another.
Yet another aspect of the present invention is directed to selectively coupling
a discrete impedance element
110a"-
110n" between a
respective pair of adjacent legs
74" of adjacent dipole antenna elements,
as illustrated in FIG.
7D. Each dipole antenna element
70a,
70b has associated therewith a plurality of selectable impedance
elements
110a"-
110n" and a corresponding switch
75".
The illustrated switch
75" is a single pole multiple throw (SPMT) switch.
Alternately, more than one impedance element
110a"-
110n"
may be connected at one time to achieve the desired impedance coupling values.
In this case, a multiple pole multiple throw (MPMT) switch would be required.
A switch controller
77" is connected to all of the switches
75"
in
the multiband phased array antenna
50. The switch controller
77"
may operate so that the respective impedance elements
110a"-
110n"
associated with all of the dipole antenna elements
70a,
70b
are synchronously switched. Alternately, the respective impedance elements
110a"-
110n" for each dipole antenna element
70a,
70b may be asynchronously switched with respect to the other dipole
antenna elements.
The switches
75" and corresponding impedance elements
110a"-
110n"
advantageously allow the multiband phased array antenna
50 to be retuned.
For example, the frequency band of the phased array antenna may be adjusted, i.e.,
lower or higher. This adjustment may be as much as 10 to 20 percent of the frequency
band depending on the range of the impedance values associated with the impedance
elements
110a"-
110n". In addition, better performance
may be achieved at specific frequencies, particularly where the antenna can be
better matched, i.e., to operate with a lower VSWR. The active switching may also
be combined with the variable height ground plane
80, as readily appreciated
by those skilled in the art.
Yet another approach to further increase the capacitive coupling between adjacent
dipole antenna elements
76 includes placing a respective printed impedance
element
110"′ adjacent the spaced apart end portions
78"′
of adjacent legs
74"′ of adjacent dipole antenna elements
76,
as illustrated in FIG.
7E.
The respective printed impedance elements
110"′ are separated from
the adjacent legs
74"′ by a dielectric layer, and are preferably
formed before the dipole antenna layer is formed so that they underlie the adjacent
legs
74"′ of the adjacent dipole antenna elements
76. Alternatively,
the respective printed impedance elements
110"′ may be formed after
the dipole antenna layer has been formed. For a more detailed explanation of the
printed impedance elements, reference is directed to U.S. patent application Ser.
No. 10/308,424 which is assigned to the current assignee of the present invention,
and which is incorporated herein by reference.
Referring now to FIGS. 8A and 8B, a resistive load may be connected across
the medial feed portions
72′ of the dipole antenna elements
70a′,
70b′ in the outer columns of the respective dipole antenna
element arrays
62,
64. As discussed above, the passive elements
70a′,
70b′ in the outer columns allow the active elements in the
center column to receive sufficient current, which is normally conducted through
the dipole antenna elements on the substrate
60.
The resistive load may include a discrete resistor
120, as illustrated
in FIG. 8A, or a printed resistive element
122, as illustrated in FIG.
8B.
Each discrete resistor
120 is soldered in place after the dipole antenna
elements
70a,
70b have been formed. Alternatively,
each discrete resistor
120 may be formed by depositing a resistive paste
on the medial feed portions
72, as would be readily appreciated by those
skilled in the art.
The respective printed resistive elements
122 may be printed before, during
or after formation of the dipole antenna elements
70a,
70b,
as would also be readily appreciated by those skilled in the art. The resistance
of the load is typically selected to match the impedance of a feed line connected
to an active dipole antenna element, which is in a range of about 50 to 100 ohms.
Other aspects of the present invention will now be discussed. One such aspect
is still directed to a multiband phased array antenna
150, as illustrated
in FIG.
9. The multiband phased array antenna
150 is also a radially
distributed phased array antenna covering multiple frequency bands.
However, the multiband phased array antenna
150 comprises a substrate
160, and a plurality of dipole element arrays
161,
162,
163,
164 and
165 extending outwardly from an imaginary center point
166
on the substrate
160. The imaginary center point
166 is not necessarily
the center of the substrate
160, but may be slightly off center.
Each dipole element array
161-
165 comprises a plurality of dipole
antenna elements (generally referred to by reference numeral
170) arranged
in end-to-end relation and having a dipole size different than a dipole size of
dipole antenna elements of at least one other dipole element array. In other words,
each dipole element array
161-
165 is sized to cover a respective
frequency band so that collectively, the multiband phased array antenna
150
covers a wide bandwidth.
As the dipole element arrays
161-
165 decrease from a larger size
to a smaller size, the frequency inversely changes, as readily understood by those
skilled in the art. For example, the five dipole element arrays may cover the following
five frequency bands: 0.1 to 1 GHz for dipole element array
161, 1 to 2
GHz for dipole element array
162, 2 to 4 GHz for dipole element array
163,
4 to 8 GHz for dipole element array
164, and 8 to 16 GHz for dipole element
array
165.
Only five dipole element arrays
161-
165 within a single "pie"
section are illustrated in FIG.
9. Depending on the intended application,
the five dipole element arrays
161-
165 are repeated in other pie
sections around the substrate
160. The distribution of the dipole element
arrays
161-
165 may be symmetrical, although this is not required.
The embodiment of five dipole element arrays
161-
165 is for illustrative
purposes only, and the actual number of dipole element arrays may vary, as readily
appreciated by those skilled in the art.
Each dipole element array
161-
165 includes an active dipole antenna
element (which is the center element), and may include passive dipole antenna elements
adjacent to the active element. The passive dipole antenna elements include a resistive
load (not shown) connected across the medial feed portions. The resistive load
may be a discrete resistor
120, as illustrated in FIG. 8A, or a printed
resistive element
122, as illustrated in FIG.
8B. The passive elements
allow the active element in the center to receive sufficient current, which is
normally conducted through the dipole antenna elements
170 on the substrate
160.
The actual size of each dipole element array
161-
165 may vary,
as readily appreciated by those skilled in the art. As illustrated in FIG. 9, each
dipole element array
161-
165 is a 1 by 3 array. Depending on the
intended application, the size of the arrays
161-
165 may be adjusted
accordingly. For example, a 2 by 3 or a 3 by 5 array would be readily applicable.
As noted above, a ground plane for a multiband phased array antenna is preferably
spaced from the different size dipole element arrays
161-
165 less
than about one-half a wavelength of a highest desired frequency within each respective
array. Referring now to FIG. 10, a cross-sectional view of the multiband phased
array antenna
150 as shown in FIG. 9 is taken along radial axis R
1.
The ground plane
180 has a different spacing from the plurality of dipole
element arrays
161-
165 in an outward direction from the imaginary
center point
166.
In other words, the illustrated ground plane
180 is sloping so that the
spacing between the ground plane and the dipole element arrays
161-
165
increases. Alternately, the dipole element arrays
161-
165 may be
positioned so that the spacing between the ground plane
180 and the dipole
element arrays
161-
165 decreases. When the slope of the ground plane
180 increases, the lower frequency arrays are positioned on the substrate
160 further away from the imaginary center point
166, whereas the
higher frequency arrays are positioned closer to the imaginary center point. Furthermore,
the position of each dipole element array
161-
165 on the substrate
160 may also be radially adjusted for the different frequency bands to achieve
a constant beamwidth across the total bandwidth.
The slope of the ground plane
180 does not necessarily have to be constant.
For example, the slope of the ground plane
180 may be logarithmic or exponential.
In this case, position of the dipole element arrays
161-
165 would
be adjusted accordingly to provide the preferred spacing between the ground plane
180 and the respective dipole antenna elements
170 based upon their
size. A dielectric material
181 is between the ground plane
180 and
the respective dipole antenna elements
170.
Depending on the desired overall size of the multiband phased array antenna
150, crowding of the dipole antenna elements
170 within each pie
section on the substrate
160 could be a problem. One approach to alleviating
this problem is to turn the outermost passive dipole antenna elements near the
edge of the substrate 90 degrees, as illustrated in FIGS. 11A (top view) and
11B
(side view).
In this embodiment of the multiband phased array antenna
150′,
the
substrate has a first surface
160a′, and a second surface
160b′ adjacent thereto and defining an edge
169′
therebetween. In the illustrated embodiment, the second surface
160b′
is orthogonal to the first surface
160a′. The substrate
160a′,
160b′ may be a monolithic flexible substrate, and the second
surface is formed by simply bending the substrate so that one of the legs of the
edge elements
170b′ extends onto the second surface.
Dipole element arrays
163′,
164′ and
165′
extend outwardly from the imaginary center point
166′ only the first
surface
160a′ of the substrate
160a′,
and dipole element arrays
161′ and
162′ extend outwardly
from the imaginary center point
166′ on both the first and second
surfaces
160a′,
160b′ of the substrate.
The dipole antenna elements on the first surface of the substrate
160a′
are indicated by reference
170a′, whereas the dipole antenna
elements on the second surface of the substrate
160b′ (partially
or fully thereon) are indicated by reference
170b′.
The dipole antenna elements
170b′ on the second surface
160b′ of the substrate may also be referred to as "edge elements."
A plot of the computed VSWR versus frequency for the low frequency dipole element
array
161′ having a dipole antenna element
170b′
on the second surface
160b′ of the substrate is represented
by line
186 in FIG.
12.
Another aspect of the present invention is directed to a multiband phased
array antenna
250, as illustrated in FIG.
13. The multiband phased
array antenna
250 is also a radially distributed phased array antenna covering
multiple frequency bands. In particular, the multiband phased array antenna
250
comprises a substrate
260, and a plurality of dipole element arrays
262
extending outwardly from an imaginary center point
266 on the substrate.
The distribution of the dipole element arrays
262 may be symmetrical, although
this is not required.
Each dipole element array
262 comprises a plurality of dipole antenna
elements
270a-
270e arranged in end-to-end relation
and having different dipole sizes for dipole antenna elements in a direction extending
outwardly from the imaginary center point
266. In other words, the multiband
phased array antenna
250 is "graded" in the sense that the size of the dipole
antenna elements
270a-
270e changes from the imaginary
center point
266 toward the outer edge of the substrate
260.
Each illustrated dipole element array
262 comprises five active dipole
antenna elements
270a-
270e. The actual number of elements
could vary depending on the intended application. The multiband phased array antenna
250 may cover the following frequency bands: dipole antenna element
270a
covers 0.1 to 1 GHz, dipole antenna element
270b covers 1 to
2 GHz, dipole antenna element
270c covers 2 to 4 GHz, dipole antenna
element
270d covers 4 to 8 GHz and dipole antenna element
270e
covers 8 to 16 GHz. Of course, the active dipole antenna elements
270a-
270e
vary in size to cover different frequency bands, as readily appreciated by
those skilled in the art.
As noted above, a ground plane for a multiband phased array antenna is preferably
spaced from the different size dipole element arrays
262 less than about
one-half a wavelength of a highest desired frequency within each respective array.
Referring now to FIG. 14, a cross-sectional view of the multiband phased array
antenna
250 as shown in FIG. 13 is taken along radial axis R
1.
The ground plane
280 has a different spacing from the different dipole antenna
elements
270a-
270e in the plurality of dipole element
arrays
262.
The illustrated ground plane
280 is sloping so that the spacing between
the ground plane and the dipole antenna elements
270a-
270e
increases as you move from the imaginary center point
266 toward the
outer edge of the substrate
260. Consequently, the lower frequency dipole
antenna elements
270d and
270e are positioned on the
substrate
260 further away from the imaginary center point
266, whereas
the higher frequency dipole antenna elements
270a,
270b
and
270c are positioned closer to the imaginary center point.
The transceivers
561-
56n may be selectively
connected to a particular port within the radial distribution of dipole antenna
elements
270a-
270e to achieve constant beamwidth and
pattern control. Although not illustrated in FIG. 13, passive elements may be connected
to the innermost and outermost dipole antenna elements
270a,
270e
to increase bandwidth. In addition, each dipole element array
262 is
not limited to a 1×5 matrix of dipole antenna elements, and other size arrays
are acceptable, as readily appreciated by those skilled in the art.
As noted above, the slope of the ground plane
280 does not necessarily
have to be constant. For example, the slope of the ground plane
280 may
be logarithmic or exponential. In this case, position of the dipole element arrays
262 would be adjusted accordingly to provide the preferred spacing between
the ground plane
280 and the respective dipole antenna elements
270a-
270c
based upon their size. A dielectric material
281 is between the ground
plane
280 and the respective dipole antenna elements
270a-
270e.
Yet another aspe
