Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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METHOD AND SYSTEM FOR PRODUCING DUAL POLARIZATION
STATES WITH CONTROLLED RF BEAMWIDTHS
TECHNICAL FIELD
S The present invention is generally directed to an antenna for communicating
electromagnetic signals, and relates more particularly to a planar array
antenna having
patch radiators exhibiting dual polarization states and producing
substantially
rotationally symmetric radiation patterns with controlled beamwidths.
BACKGROUND OF THE INVENTION
Diversity techniques at the receiving end of a wireless communication link can
improve signal reception without additional interference. One such diversity
technique is generating dual simultaneous polarization states. The term "dual
simultaneous polarization states" typically means that an antenna has at least
two
different radiators, where each radiator simultaneously generates or receives
RF
energy according to a separate and unique polarization relative to an opposing
active
radiator. Therefore, unlike circular polarization which employs phasing
between
respective radiators, dual simultaneous polarization states requires
respective radiators
to be fed in phase. Those skilled in the art recognize that an antenna's
polarization is
defined to be that of its electric field, in the direction where°field
strength is
maximum.
Dual polarization states can increase performance of a base station antenna
that is designed to communicate with portable communications units having
mobile
antennas. The effectiveness of dual polarization for a base station antenna
relies on
the premise that transmit polarization of a typically linearly polarized
mobile or
portable communications unit will not always be aligned with a vertical linear
polarization for the antenna at a base station site nor will it necessarily be
in a linearly
polarized state. Further, depolarization, which is the conversion of power
from a
reference polarization into the cross polarization, can occur along the multi-
path
propagation between the mobile user and a base station.
In order to compensate for the effects of depolarization, dual polarization
can
be employed at a base station antenna in order to communicate with mobile or
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portable communication units. However, dual polarization or polarization
diversity
typically requires a significant amount of hardware that can be rather complex
to
manufacture. Further, conventional dual polarized antennas typically cannot
provide
symmetrical radiation patterns where respective electric field (E) and
magnetic field
(H) plane beamwidths are substantially equal. Additionally, conventional
antenna
systems usually cannot provide for a wide range of magnetic field (H) plane
beamwidths from a compact antenna system. In other words, the conventional art
typically requires costly and bulky hardware in order to provide for a wide
range of
operational beamwidths, where beamwidth is measured from the half power points
(
3dB to -3dB) of a respective RF beam.
Another draw back of the conventional art relates to the manufacturing of an
antenna system and the potential for passive intermodulation (PIM) that can
result
because of the material used in conventional manufacturing techniques. More
specifically, with conventional antenna systems, dissimilar materials, ferrous
materials, metal-to-metal contacts, and deformed or soldered junctions are
used in
order to assemble a respective antenna system. Such manufacturing techniques
can
make an antenna system more susceptible to PIM and therefore, performance of a
conventional antenna system can be substantially reduced.
A fi.~rther problem in the conventional art is the ability to effectively
control
the beamwidth of the resulting radiation patterns of a dual polarized antenna
system.
The conventional art typically does not provide for any simple techniques for
controlling beamwidth of a dual polarized antenna system.
Unrelated to the problems discussed above, antenna designers are often forced
to design antennas in a backward fashion. For example, because of the
increasing
public concern over aesthetics and the "environment", antenna designers are
typically
required to build an antenna in accordance with a radome that has been
approved by
the general public, land owners, government organizations, or neighborhood
associations that will reside in close proximity to the antenna. Radomes are
typically
enclosures that protect antennas from environmental conditions such as rain,
sleet,
snow, dirt, wind, etc. Requiring antenna designers to build an antenna to fit
within a
radome as opposed to designing or sizing a radome after an antenna is
constructed
creates many problems for antenna designers. Stated differently, the antenna
designer
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must build an antenna with enhanced functionality within spatial limits that
define an
antenna volume within a radome. Such a requirement is counterproductive to
antenna
design since antenna designers recognize that the size of antennas are
typically a
function of their operating frequency. Therefore, antenna designers need to
develop
high performance antennas that must fit within volumes that cut against the
ability to
size antenna structures relative to their operating frequency.
Accordingly, there is a need in the art for a substantially compact antenna
system that can fit within a predefined volume and that can exhibit dual
polarization
states while also providing for adjustable beamwidths. There is a further need
in the
art for a compact dual polarization antenna system that can provide radiation
fields
having substantially rotationally symmetric radiation patterns. There is also
a need in
the art for a compact antenna system that can generate RF radiation patterns
where the
beamwidth of respective RF fields for respective radiating elements are
substantially
equal and are relatively large despite the compact, physical size of the
antenna
1 S system. There is a further need in the art for a compact antenna system
exhibiting
dual polarization states that can also provide for adjustable beamwidths in a
fairly
simple manner. Further, there is another need in the art for a compact antenna
system
that can be manufactured with ease and that can utilize manufacturing
techniques
which substantially reduce passive intermodulation. There is an additional
need in the
art for a substantially . compact antenna system that can handle the power
characteristics of conventional antenna systems without degrading the
performance of
the antenna system.
SUMMARY OF THE INVENTION
The present invention solves the aforementioned problems with an antenna
system that can generate RF radiation fields having dual simultaneous
polarization
states and having substantially rotationally symmetric radiation patterns. The
term
"rotationally symmetric" typically means that radiation patterns of respective
radiators
having different polarizations are substantially symmetrical and substantially
equal.
In other words, the present invention can generate RF radiation patterns where
the
beamwidths of respective RF fields for respective radiating elements are
substantially
equal and are relatively large despite the compact, physical size of the
antenna
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system. For example, the present invention can produce radiation patterns
where each
RF polarization produced by an individual radiating element is substantially
equal to a
corresponding orthogonal RF polarization produced by another individual
radiating
element. For example, the beamwidths produced by each radiating element can be
S adjusted from widths of approximately sixty-five (65) to ninety (90)
degrees, where
beamwidth is measured from the half power points (-3dB to -3db) of a
respective RF
beam. Other beamwidths are not beyond the scope of the present invention.
This enhanced functionality can be achieved with a compact antenna system,
where the antenna system (without a radome) can typically have a height of
approximately less than one seventh (1/7) of a wavelength and a width that is
less
than or equal to six-tenths (0.6) of a wavelength. With a radome, the antenna
system
can have a height of approximately one-fifth (1/5) of a wavelength. The
antenna
system can comprise one or more patch radiators and a non-resonant patch
separated
from each other by an air dielectric and by relatively small spacer elements.
The
patch radiators and non-resonant patch can have predefined shapes for
increasing
polarization discrimination.
In one exemplary embodiment, the patch radiators and non-resonant patch can
have a substantially circular shape. The circular shape can enable the patch
radiators
and non-resonant patch to maintain orthogonality of two polarizations over a
given
angular region to ensure that any two RF signals are highly de-correlated. The
circular shape of the patch radiators can also keep E (electric field) and H
(magnetic
field) plane beamwidths of individual radiating elements substantially equal
and
symmetrical.
The beamwidth of RF energy generated by one or more lower resonant patch
radiators can be controlled by an upper non-resonant patch. The upper non-
resonant
patch is typically spaced at a non-resonant distance relative to the lower
patch
radiators to prevent resonance while controlling the beamwidth of the
resultant RF
radiation patterns.
The lower patch radiators can be mounted to a printed circuit board that can
comprise an RF feed network and a ground plane which defines a plurality of
symmetrically, shaped slots. In one exemplary embodiment, the slots can
comprise a
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double-H shape that has an electrical path length that is less than or equal
to a half
wavelength.
The slots within the ground plane of the printed circuit board can be excited
by
stubs that are part of the feed network of the printed circuit board. The
slots, in turn,
5 can establish a transverse magnetic mode of RF radiation in a cavity which
is
disposed adjacent to the ground plane of the printed circuit board and a
ground plane
of the antenna system.
The slots can be aligned along a diagonal of a cavity while the cavity can be
concentrically aligned with geometric centers of the patch radiators. The feed
network of the printed circuit board can be aligned with portions of the
cavity such
that the portions of the cavity function as a heat sink for absorbing or
receiving
thermal energy produced by the feed network. Because of this efficient heat
transfer
function, the printed circuit board can comprise a relatively thin dielectric
material
that is typically inexpensive.
The cavity disposed between the printed circuit board and the ground plane of
the antenna system can function electrically as a closed boundary when
mechanically,
the cavity has open corners. The open corner design facilitates ease in
manufacturing
the cavity. The open corners of the cavity can also have dimensions that
permit
resonance while substantially reducing Passive Intermodulation (PIM).
PIM can be further reduced by planar fasteners used to attach respective
flanges and a planar center of a respective cavity to the ground plane of the
printed
circuit board and the ground plane of the antenna system. The planar fasteners
can
comprise a dielectric adhesive. In addition to the dielectric adhesive, the
present
invention can also employ other types of fasteners that reduce the use of
dissimilar
materials, ferrous materials, metal to metal contacts, deformed or soldered
junctions
and other similar materials in order to reduce PIM.
For example, the patch radiators and non-resonant patch can be spaced apart
by plastic fasteners that permanently "snap" into place. Such fasteners not
only
reduce PIM, but such fasteners substantially reduce labor and material costs
associated with the manufacturing of the antenna system.
While providing a product that can be manufactured efficiently, the present
invention also provides an efficient RF antenna system. The RF energy produced
by
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the cavity, slots, and stubs can then be coupled to one or more lower patch
radiators.
The one or more lower patch radiators can then resonate and propagate RF
energy
with a wide range of H-plane beamwidths that can extend between approximately
sixty-five (65) and ninety (90) degrees.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is an illustration showing an elevational view of the construction of
an exemplary embodiment of the present invention.
Figure 2 is an illustration showing a side view of the exemplary embodiment
shown in Figure 1.
Figure 3 is an illustration showing an isometric view of the exemplary
embodiment shown in Figures 1 and 2.
Figure 4 is an illustration showing an isometric view of some core components
of an exemplary embodiment of the present invention.
Figure 5 is a cross-sectional view of the exemplary embodiment illustrated in
Figure 4 taken along the cut line 5-5.
Figure 6 is a block diagram illustrating some of the core components of the
exemplary embodiment illustrated in Figure 5.
Figure 7A is an illustration showing an elevational view of the exemplary
embodiment illustrated in Figure 4 while also showing hidden views of the
slots
which feed the cavity and one or more radiating elements.
Figure 7B is an illustration showing an exemplary slot according to the
present
invention.
Figure 8 is an illustration showing an exploded view of an exemplary
embodiment of the present invention.
Figure 9 is an illustration showing a bottom or rear view of a ground plane of
the printed circuit board comprising the feed network as illustrated in Figure
8.
Figure 10A is an illustration showing an isometric view of an exemplary
resonant cavity for the present invention.
Figure lOB is an illustration showing an enlarged area focused on an
exemplary corner structure of the resonant cavity shown in Figure 10A.
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Figure 11 is an illustration showing a typical mounting arrangement for an
antenna provided by an exemplary embodiment of the present invention.
Figure 12A is a graph illustrating the beamwidths of (E) and (H) plane
radiation patterns according to one exemplary embodiment of the present
invention.
Figure 12B is a radiation pattern in terms of voltage illustrating the
beamwidths of (E) and (H) planes according to the exemplary embodiment
illustrated
in Figure 12A.
Figure 13A is a graph illustrating beamwidths of another (E) and (H) plane
radiation pattern according to an alternative exemplary embodiment of the
present
invention.
Figure 13B is a radiation pattern in terms of voltage illustrating the
beamwidths of (E) and (H) planes according to the alternative exemplary
embodiment
illustrated in Figure 13A.
Figure 14 is an exemplary logical flow diagram describing a method for
producing dual simultaneous polarization states and a rotationally symmetric
radiation
pattern where the electric field and magnetic field beamwidths of individual
radiating
elements are substantially equal and symmetrical.
Figure 15 is a logical flow diagram illustrating an exemplary slot excitation
routine of Figure 14.
Figure 16 is another logical flow diagram illustrating an exemplary beamwidth
adjustment routine of Figure 14.
DETAILED DESCRIPTION OF THE PRESENT INVENTION
The antenna of the present invention can solve the aforementioned problems
and is useful for wireless communications applications, such as personal
communication services (PCS) and cellular mobile radio telephone (CMR)
service.
The antenna of the present invention can use polarization diversity to
mitigate the
deleterious effects of fading and cancellation resulting from a complex
propagation
environment. The antenna system can include a patch radiator, a printed
circuit board
disposed adjacent to the patch radiator, and plurality of slots disposed
within a ground
plane of the printed circuit board. The antenna further includes a cavity
disposed
adjacent to the ground plane of the printed circuit board and a second ground
plane
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disposed adjacent to the cavity. The antenna system radiates RF energy having
dual
simultaneous polarization states and having substantially rotationally
symmetric
radiation patterns.
Turning now to the drawings, in which like reference numerals refer to like
elements, Figure 1 is an illustration showing an elevational view of one
exemplary
embodiment of the present invention. Referring now to Figure l, an antenna
system
100 is shown for communicating electromagnetic signals with the high frequency
spectrums associated with conventional wireless communication systems. An
antenna
system 100 can be implemented as a planar array of radiating elements 110,
known as
wave generators or radiators, wherein the array is positioned along a vertical
plane of
the antenna as viewed normal to the antenna site.
The antenna system 100, which can transmit and receive electromagnetic
signals, includes radiating elements 110, a ground plane 120, and a feed
network 130.
The antenna system 100 further includes beam shaping elements 140, a printed
circuit
board 150 and ports 160A and 160B.
Referring now to Figure 2 which illustrates the side view of the antenna
system 100 of Figure 1, the spatial relationship between beam forming elements
140
and the radiating elements 110 are more clearly shown. On a side of the
printed
circuit board 150 opposite to the radiating elements 110 and beam forming
elements
140 are a plurality of cavities 200 which will be discussed in further detail
below.
The ports 160A and 160B can comprise coaxial cable type connectors.
Figure 3 further illustrates an isometric view of the antenna system 100 which
can comprise one or more radiating elements 110 and beam forming elements 140.
The antenna system 100 as illustrated in Figure 3 is very compact yet high
performance product that can be placed or positioned in a very narrow or small
volume such as a radome. For example, in one exemplary embodiment, the length
L
can be approximately 48 inches while the width W can be approximately 8
inches.
The height H of the antenna system 100 (including a radome) can be 2.75
inches. In
this exemplary embodiment the operating frequency range is approximately from
806
MHz to 896 MHz. In terms of wavelength, this means that the width W can be
less
than or equal to a six-tenths (0.6) of a wavelength. Similarly, the height H
can be less
than or equal to one-seventh (1/7) of a wavelength without a radome. With a
radome,
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the antenna system can have a height of approximately one-fifth (1/5) of a
wavelength. The length L can be varied depending upon the number of radiating
elements 110 desired to be in the antenna system 100.
Refernng now to Figure 4, this figure illustrates some of the core components
of antenna system 100 in more enlarged detail. Figure 4 illustrates how ground
plane
120 further includes groves 400 that can support a radome (as will be
discussed in
further detail below). As mentioned above, the present invention can include
one or
more radiating elements 110 while, typically (in an exemplary embodiment),
only one
beam forming element 140 is employed.
Referring now to Figure 5, this figure illustrates a cross-section of the
antenna
system 100 illustrated in Figure 4. This particular cross-section is taken
along the cut
line S-5 as illustrated in Figure 4. Figure 5 provides further details of the
mechanical
elements which form the inventive antenna system 100. The sizes of materials
illustrated in Figure 5 are not shown to scale. In other words, some of the
materials
have been exaggerated in size so that these materials can be seen easily. A
more
accurate depiction of the relative sizes of materials will be illustrated
below with
respect to Figure 11.
The beam forming element 140 is spaced from the radiating element 110 by a
spacing S1. Spacing S1 is typically a nonresonant dimension. That is, the
parameter
S 1 relative sizes is typically neither a resonant dimension nor a dimension
that
promotes resonance of the beam forming element 140. The beamwidth of the
present
invention can be controlled by adjusting the spacing parameter S l and by
adjusting
the diameter Dlao of the beam forming element 140. The diameter Dlao is also
typically a non-resonant dimension.
By increasing the spacing parameter S 1 (the space between the beam forming
element 140 and the radiating element 110) the beamwidth of the
electromagnetic
radiation emitted by the antenna system 100 can be increased. Conversely,
beamwidth can be decreased by lowering the S1 parameter (decreasing the
spacing
between the upper and lower patches) and by increasing the diameter D,4o of
the beam
forming element 140.
The radiating antenna element 110 can be spaced from the printed circuit
board 150 by a spacing parameter S2 which is typically a resonant value. In
other
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words, the parameter S2 is one that typically promotes resonance of the
radiating
patch element 110. In terms of wavelength, the parameter S2 is typically
between
0.03 to 0.04 wavelengths (or 0.42 to 0.55 inches at the exemplary operating
frequency
range). The diameter Dl~o of the radiating element is typically between 0.40
to 0.47
5 wavelengths. However, the present invention is not limited to these values.
Other
resonant dimensions are not beyond the scope of the present invention.
The beam forming element 140 is typically held in place relative to the
radiating element 110 by spacer elements/fasteners 500 which can comprise
dielectric
stand-offs. The radiating element 110 is similarly spaced from the printed
circuit
10 board 150 by a plurality of spacers/fasteners 500. The spacers/fasteners
500 are
typically designed to permanently "snap" into place in order to eliminate or
reduce the
use of soldering points of the present invention. This, in turn, also
substantially
reduces work in the manufacturing process of the Antenna System 100. Further,
by
using such spacers/fasteners passive intermodulation (PIM) can also be
substantially
reduced or eliminated. However, the present invention is not limited to "snap"
type
fasteners. Other fasteners or dielectric supports that can reduce PIM are not
beyond
the scope of the present invention. For example, slim or narrow blocks of
dielectric
foams could be used to support the radiating elements 110 and beam forming
elements 140. Also, the fasteners 500 do not need to permanently fix these
elements.
That is, releasable fasteners 500 could be employed and not depart from the
scope and
spirit of the present invention.
As illustrated in Figures 4 and 5, the beam forming element 140 and the
radiating element 110 typically comprise patch elements. The beam forming
element
140 and radiating element 110 are typically made from conductive materials
such as
aluminum. Specifically, both elements can be made from aluminum 5052.
Similarly,
the cavity 200 can also be constructed from aluminum. However, other
conductive
materials are not beyond the scope of the present invention for the resonating
structures. Further, the radiating element 110 and beam forming element 140
can also
be constructed with combinations of materials such as dielectric materials
coated with
a metal. Those skilled in the art will appreciate the various ways in which
radiating
elements can be constructed without departing from the scope and spirit of the
present
invention.
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In one preferred exemplary embodiment, both the beam forming element 140
and Radiating Element 110 are substantially circular in shape. The circular
shape of
the patches 140, 110 in combination with the apertures or slots 700 (as will
be
discussed below) and resonating cavity 200 increase polarization
discrimination by
S the antenna system 100. The circular shape of the Patches 140, 110 can also
contribute to maintaining the orthogonality of two polarizations over a given
angular
region to ensure that any two RF signals are highly de-correlated.
The circular shape of the beam forming element 140 and radiating element
110 can also maximize the performance of the polarization by keeping the
electric (E)
and magnetic (H) plane beamwidth substantially equal. The circular shape of
the
beam forming element 140 and radiating element 110 also permits the antenna
system
100 to keep radiation patterns symmetrical. However, the present invention is
not
limited to circularly shaped elements. Other shapes include, but are not
limited to,
square, rectangular, and other similar shapes that maximize the performance of
dual
polarization by keeping electric (E) and magnetic (H) plane beamwidth
substantially
equal.
Figure 5 illustrates further details of the antenna system 100 that are not
shown in the previous figures. For example, portions of the feed network 130
are
substantially aligned over portions of the cavity 200. By aligning portions of
the feed
network 130 over portions of the cavity 200, such as flanges 520 (as will be
discussed
in further detail below) the present invention can dissipate heat energy
formed within
the feed network 130 more efficiently and rapidly. The flanges 520 can serve
as a
heat sink to portions of the feed network 130.
By using portions of the resonating 200 cavity as a heat sink, a relatively
thin
printed circuit board 150 can be used. The cavity 200 can be fastened to the
printed
circuit board 150 (and more specifically, the ground plane 530 of the printed
circuit
board 150) by using a planar fastener 540 such as a dielectric adhesive. This
planar
fastener 540 can then reduce the thermal resistance between the feed network
130 and
the flange 520.
The cavity 200 can also be attached to the ground plane 120 with a similar
planar fastener 540 such as a dielectric adhesive discussed above. Using such
fasteners not only reduces the thermal resistance between the feed network 130
and
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the cavity, it also substantially reduces passive intermodulation (PIM). With
portions
of the cavity 200 functioning as a heat sink for the feed network 130 disposed
upon a
printed circuit board 150, a relatively thin substrate of material can be used
as the
printed circuit board 150. The cavity 200 is attached to the ground plane 530
of the
printed circuit board 150 with a planar fastener 540. Similarly, the cavity
200 is
attached to the radome supporting ground plane 120 by a planar fastener 540.
The cavity 200 typically propagates a transverse magnetic (TMoI) mode of RF
energy for the two polarizations supported by the antenna system 100. Since
cavity
200 resonates, the height or spacing S3 of the cavity has a resonant dimension
of
0.027 wavelengths (or a dimension of 0.375 inches at the exemplary operating
frequency). The width W 1 of the resonant cavity 200 can have a resonant
dimension
of 0.433 wavelengths. However, the present invention is not limited to these
values.
Other resonant dimensions are not beyond the scope of the present invention.
While
propagating a transverse magnetic mode of RF energy, cavity 200 can also
substantially increase the front to back ratio of the antenna system 100. The
cavity
200 is excited by two or more slots 700 as will be discussed in further detail
below.
Figure 6 is a functional block diagram illustrating the various components
which make up the compact antenna system 100. This figure highlights one
exemplary and preferred arrangement of the components of the antenna system
100.
Of the components illustrated in Figure 6, there are a select few which may be
considered the core components of the Antenna System 100 that provide the
enhanced
functionality in such a compact antenna volume. The core components may be
considered as the beam forming element 140, the radiating element 110, the
printed
circuit board 150, the ground plane 530 with slots 700, and the cavity 200.
Refernng now to Figure 7A, further details of the slots 700A-C disposed
within the ground plane 530 are shown. The slots 700A-C are excited by a
corresponding number of stubs 710A-C that are positioned within the feed
network
130 disposed on one side of the Printed Circuit Board 150. The slots 700 are
typically
symmetrically-shaped in order to reduce cross-polarization between respective
slot.
The slots 700A, 710C are oriented perpendicular to the central slot 700B. Such
an
orientation of the slots 700 sets up or establishes dual polarization states.
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Further, it is desirable to orient the slots 700 along geometric diagonals
720A
and 720B in order to maintain slant forty-five polarizations over an intended
region of
operation while improving port-to-port isolation. Placing the slots 700 along
the
geometric diagonals 720A and 720B can also reduce cross-polarization between
the
S two dual polarization states established by the antenna system 100. The
slots 700 are
also designed to be narrow and symmetrical in order to increase port-to-port
isolation.
The spacing and orientation of the slots' 700 relative to the radiating
element 110 can
optimize the desired transverse magnetic TMoI mode of operation within the
resonating cavity 200 for the two polarizations. In this embodiment, two
orthogonal
TMo~ modes are generated in the cavity 200.
Optimization can be accomplished by placing these slots 700 along the
geometric diagonals 720A, 720B and using the center of the cavity 200 as the
origin
for the radiating patches 110. That is, the geometric centers of the radiating
element
110, beam forming element 140, and cavity 200 can be substantially aligned.
However, the present invention is not limited to this number and combination
of slots.
For example, instead of three separate slots the present invention could
employ a
cross-shaped slot (not shown) to feed the antenna patches. But with this cross-
shaped
design, two soldering connections would be required for a respective crossed-
slot.
And soldering connections could degrade antenna performance somewhat because
of
the resulting PIM.
Refernng now to Figure 7B, the slots 700 can also have a predefined shape.
For example, in one exemplary embodiment, each Slot 700 have the substantially
double-h shape. However, the present invention is not limited to this shape.
Other
shapes include, but are not limited to, shapes that have an electrical length
that is less
than or equal to one-half the wavelength. The electrical length of a slot is
typically
found by measuring the one-half of the perimeter of the opening, starting at
one far
end of the slot to another far end. An electrical length of less than or equal
to one-half
of a wavelength facilitates efficient coupling of RF energy to the cavity 200
and patch
radiating element 110. The orientation and placement of the slot 700 should be
designed for equal beamwidths of the polarizations so that the polarization
factor can
be maintained at a value of 45.
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Referring now to Figure 8, this figure illustrates an exploded view of the
components of the antenna system 100. A protective radome 800 comprising a PVC
material can be used to cover the antenna system 100. A radome 800 preferably
comprises a PVC material manufactured in the desired form by an extrusion
process.
The radome 800 is attached to the grooves 400 formed in the ground plane 120.
A
pair of end caps 810A and 810B are positioned along a minor dimension at an
end of
the ground plane 120 and cover the remaining openings formed at the end of the
combination of the ground plane 120 and the radome 800. Encapsulation of the
antenna system 100 within the sealed enclosure formed by the ground plane 120,
a
radome 800, and the end caps 810A-B protects the antenna system 100 from
environmental elements, such as direct sunlight, water, dust, dirt and
moisture.
The printed circuit board 150 is a relatively thin sheet of dielectric
material
and can be one of many low-loss dielectric materials used for the purpose of
radio
circuitry. In one preferred and exemplary embodiment, the material used can
have a
relative dielectric constant values of dk = 3.38 (and sr = 2.7 - when
substrate is used as
microstrip). In the preferred exemplary environment, teflon-based substrate
materials
are typically not used in order reduce cost. However, TEFLON-based and other
dielectric materials are not beyond the scope of the present invention.
Disposed
adjacent to the printed circuit board 150 is the ground plane 530 which is
illustrated
with further detail in Figure 9.
Refernng now to Figure 9, the ground plane 530 contains the slots 700 used to
excite the cavity 200. These slots 700 can be preferably etched out of the
ground
plane 530 by photolithography techniques.
Referring now to Figure 10A, this figure further illustrates the details of
the
resonant cavity 200. The cavity 200 is preferably made from aluminum and has a
design which promotes accurate repeatability while substantially reducing
passive
intermodulation (PIM). However, other conductive materials are not beyond the
scope of the present invention. The cavity 200 comprises walls 1000A-D that
are
spaced apart from each other by a predetermined distance d (See Figure 10B).
This
predetermined distance d between the walls 1000 at the corners allows for
reasonable
tolerances in manufacturing, but is typically small enough such that the
cavity 200
electrically operates as a closed boundary for RF energy propagating within
the cavity
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200. In other words, the cavity 200 can function electrically as a closed
boundary
when mechanically the cavity has open corners. The open corners of the cavity
typically have dimensions that permit resonance while substantially reducing
passive
intermodulation (PIM). The open corners of the cavity also function as
drainage holes
S for any condensation that may form within a respective cavity 200.
Referring now to Figure 10B, a distance d exists between cavity walls 1000C
and 1000D. As mentioned above, distance d is sized such that the cavity can
resonate
while at the same time it can substantially reduce passive intermodulation
since there
is no metal-to-metal contact between the respective walls 1000C and 1000D. PIM
is
10 further reduced by the present invention because dissimilar materials,
ferrous
materials, metal-to-metal contacts, and deformed or soldered junctions are
preferably
not used in order to substantially reduce or eliminate this physical
phenomenon.
For example, in addition to the open corners of the cavity 200, the present
invention employs (as discussed above) planar fasteners 540 to attach the
Flanges 520
15 of the cavity 200 to the ground plane 530 of the printed circuit board 120.
Meanwhile, the base of the cavity 200 can be attached to the radome-supporting
ground plane 120 by another dielectric planar fastener. Similarly, the
radiating
element 110 is supported by non-soldered spacers/fasteners 500, and also
supports
additional spacers/fasteners 500 to support the beam forming element 140.
Referring now to Figure 11, this figure further illustrates a more accurate
depiction of the relative sizes (thickness) of materials which make up the
antenna
system 100. Further mechanical details of the spacers/fasteners 500 are shown.
As
mentioned previously, these spacers/fasteners are preferably constructed from
dielectric materials to reduce (PIM) while also permitting ease of
manufacturing of
the antenna system 100. That is, the spacers/fasteners 500 can be permanently
"snapped" into place without the use of any deformed or soldered junctions.
Referring now to Figure 12A, this figure illustrates a linear plot of antenna
gain versus the angular position of a radiation pattern for a ninety (90)
degree
beamwidth embodiment of antenna system 100. That is, this graph illustrates
the gain
for an antenna system 100 designed to have 90 degrees of coverage between
respective three (3) dB or half power points in a radiation pattern. This
graph
demonstrates that the (E) and (H) beamwidth of an independent polarization are
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substantially equal. Substantially equal (E) and (H) plane beamwidths will
maintain
the orthogonality of the two polarization states over a given angular region
to insure
that two received signals are highly decorrelated. Two polarization states are
not
shown in Figure 12A, only one polarization state with substantially equal E
and H
planes is illustrated. For this particular exemplary embodiment, the angular
region
has been designed for 90 degrees.
To obtain a 90 degree beamwidth the diameter and spacing S 1 of the gain
forming element 140 can be adjusted. As noted above, to increase the (E) and
(H)
plane beamwidth, the spacing between the beam forming element 140 and the
radiating element 110 is increased, while the diameter of the Beam Forming
Element
140 can be reduced. Conversely, to decrease the (E) and (H) plane beamwidth,
the
separation S 1 between the beam forming element 140 and the radiating element
110
can be decreased while the diameter Dlao of the beam forming element can be
increased. With the present invention, it is possible to maintain about five
degrees of
difference between 3 dB beamwidths of respective (E) and (H) plane radiation
patterns of a particular polarization.
Refernng to Figure 12B, this figure is a radiation pattern in polar
coordinates
and in terms of voltage illustrating the ninety (90) degree beamwidth
embodiment
discussed in Figure 12A. The pattern illustrates the (E) plane radiation
pattern with a
solid line and the (H) plane pattern with a dashed or dotted line.
Refernng now to Figure 13A, this figure illustrates a plot of antenna gain
versus the angular position of a radiation pattern for a sixty-five (65)
degree
beamwidth embodiment of antenna system 100. That is, this graph illustrates
the gain
for an antenna system 100 designed to have 65 degrees of coverage between
respective three (3) dB or half power points in a radiation pattern. This
graph also
demonstrates that the (E) and (H) beamwidth of an independent polarization are
substantially equal. Substantially equal (E) and (H) plane beamwidths will
maintain
the orthogonality of the two polarization states over a given angular region
to insure
that two received signals are highly decorrelated. Two polarization states are
not
shown in Figure 13A, only one polarization state with substantially equal E
and H
planes is illustrated.
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Referring to Figure 13B, this figure is a radiation pattern in polar
coordinates
and in terms of voltage illustrating the sixty-five (65) degree beamwidth
embodiment
discussed in Figure 13A. The pattern illustrates the (E) plane radiation
pattern with a
solid line and the (H) plane pattern with a dashed or dotted line.
Figure 14 illustrates a logical flow diagram 1400 for a method of generating
RF radiation fields having dual, simultaneous polarization states and having
substantially rotationally symmetric radiation patterns. The logical flow
diagram
1400 highlights some key fimctions of the antenna system 100.
Step 1410 is the first step of the inventive process 1400 in which the slot
700
disposed within the ground plane 530 are oriented orthogonal to one another.
By
orienting the slots orthogonal to one another in step 1410, isolation between
separate
RF polarizations can be maintained while cross-polarization can be reduced.
Next, in step 1420, the antenna system 100 is assembled without
metal-to-metal contacts and soldering. More specifically, in this step, the
antenna
system 100 can be manufactured in a way to substantially reduce passive
intermodulation (PIM). Dissimilar materials, ferrous materials, metal-to-metal
contacts, and deformed or soldered junctions are typically not employed or are
limited
in the antenna system 100 in order to substantially reduce or eliminate PIM.
One way
in which PIM is substantially reduced or eliminated is the use of dielectric
planer
fasteners 540 in order to connect portions of the cavity 200 to the slotted
ground plane
530 and the ground plane 120. Another way in which PIM is reduced or
substantially
eliminated is by employing open corners in the cavity 200 where respective
walls,
such as walls 1000C and 1000D of Figure l OB, are spaced apart by the
predetermined
distance d.
Next, in step 1430 RF energy is propagated along the feed network 130 of the
printed circuit board 150. In step 1440, heat is dissipated from the feed
network 130
into flanges 520 of the cavity 200.
In routine 1450, the slots disposed in ground plane 530 set up or establish a
transverse magnetic (TM) mode of RF energy in the cavity 200. Further details
of
routine 1450 will be discussed in further detail below with respect to figure
15.
In step 1460, the radiating elements such as the lower patch radiators 110 are
excited with RF energy emitted from the slot 700 or the stubs 710 or both.
Next, in
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step 1470, RF radiation is produced with nearly equal dual polarizations by
the
substantially compact antenna system 100. In routine 1480, the nearly equal
dual
polarizations are maintained and beamwidths can be adjusted with the beam
shaping
element 140. Further details of routine 1480 will be discussed below with
respect to
Figure 16.
Figure 15 illustrates an exemplary slot excitation routine 1450 of Figure 14.
Routine 1450 begins with step 1500. In step 1500, the slots 700 are aligned
along
geometric diagonals 720 of the cavity 200, as illustrated in Figure 7. This
alignment
of the slots 700 produces a desired transverse magnetic mode of RF energy in
the
cavity 200 while substantially reducing cross-polarization and increasing
isolation
between respective ports 160A and 160B.
Next, in step 1510, the slots 700 are shaped to be symmetrical and sized such
that each slot 700 has an effective electrical length of less than or equal to
a half
wavelength for efficient RF coupling to or from the feed network 130 and the
cavity
200 or radiating patch 110. The routine then returns to step 1460 of figure
14.
Figure 16 illustrates an exemplary beam width adjustment routine 1480 of
Figure 14. Routine 1480 begins with step 1600, in which it is determined
whether the
beamwidth of the antenna system 100 needs adjustment. If the inquiry to
decision
step 1600 is positive, then the "yes" branch is followed to step 1610. In step
1610, the
beamwidth of the antenna system 100 can be adjusted by changing the spacing
between the beam forming element 140 and the radiating element 110. Typically,
the
spacing is of a non-resonant dimension since in one exemplary feature of the
present
invention, the beam forming element 140 does not resonate RF energy. If the
inquiry
to decision step 1600 is negative, then the "no" branch is followed to step
1640.
In step 1620, it is determined whether further beamwidth adjustment is
needed. If the inquiry to decision step 1620 is positive, then the "yes"
branch is
followed to step 1630, in which the beamwidth of the antenna system 100 can be
adjusted by changing the diameter of the beam forming element 140. It is noted
that
the present invention is not limited to the sequence or chronology of steps
illustrated
in these logic flow diagrams. Therefore, one of ordinary skill in the art
recognizes
that the beamwidth of antenna system 100 can be first adjusted by changing the
diameter of the beam forming element 140 instead of first changing the spacing
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between the beam forming element 140 and radiating element 110. Further, those
skilled in the art will also recognize that adjustments to beamwidth can also
be made
by changing both the spacing between the beam forming element 140 and the
radiating element 110, as well as changing the size of the beam forming
element 140.
S In step 1640, the routine returns to Figure 14.
The present invention provides an aperture or slot coupled patch elements that
generate dual slant 45 degree polarization in addition to substantially
rotationally
symmetric radiation patterns. The present invention generates RF radiation
patterns
where the beamwidths of respective RF fields for respective radiating elements
are
substantially equal and are relatively large despite the compact, physical
size of the
antenna system. For example, the present invention produces radiation patterns
where
each RF polarization produced by an individual radiating element is
substantially
equal to a corresponding orthogonal RF polarization produced by another
individual
radiating element.
The present invention provides a compact antenna system that has a height
(without radome) of less than one-seventh (1/7) of a wavelength and a width
that is
less than or equal to one-half of a wavelength. With a radome, the height can
be one-
fifth (1/5) of a wavelength. While being compact, the present invention is
power
efficient. The present invention incorporates an efficient heat transfer
design such
that a feed network transfers its heat to a resonating cavity used to set up
desired
transverse magnetic modes of RF energy. The efficient heat transfer permits
the
present invention to utilize relatively thin dielectric materials for the
printed circuit
board supporting the feed network.
The present invention employs circular metallic radiating elements for the
purpose of obtaining circular and symmetric (E) and (H) plane 3 dB beamwidths
having simultaneous slant 45 dual polarization states. The spacing S2 of the
radiating
element 110 relative to the printed circuit board 150 and the diameter of the
radiating
element 110 is used to improve the impedance beamwidths of the antenna system
100.
The beam forming element 140 is used to vary the 3 dB beamwidths to obtain
desired
values by adjusting its diameter and varying its spacing S1 between the
radiating
element 110 and the beam forming element 140. The present invention further
incorporates a low PIM design approach by utilizing capacitive coupling of all
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potential metal-to-metal junctions through employing non-conductive planar
fasteners
and open corners for the resonant cavity 200. The low PIM design approach also
yields efficient and low cost manufacturing methods. For example, the planar
fasteners 540 eliminate any need for soldering the resonant cavity 200 to the
ground
5 plane 530. The use of dielectric spacers 500 further eliminates any need for
costly
dielectric spacer sheets while also reducing assembly time.
The present invention also employs two orthogonal forty-five degree slanted
slots that are non-collocated along perpendicular lines of symmetry at forty-
five
degrees from an array axis. Such slots eliminate a need for a feed line to
cross over to
10 provide improved cross-polarization and port-to-port isolation.
Alternative embodiments will become apparent to those skilled in the art to
which the present invention pertains without departing from its spirit and
scope. Thus,
although this invention has been described in exemplary form with a certain
degree of
particularity, it should be understood that the present disclosure has been
made only
1 S by way of example and that numerous changes in the details of construction
and the
combination and arrangement of parts may be resorted to without departing from
the
spirit and scope of the invention. Accordingly, the scope of the present
invention is
defined by the appended claims rather than the foregoing description.
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