Note: Descriptions are shown in the official language in which they were submitted.
ANTENNA ARRAY FOR RADIO DIRECTION FINDING AND RADIO LOCATING UNIT UTILIZING
SAME
FIELD
This invention relates to an antenna array for radio direction finding and an
improved locating system
using such an antenna array.
BACKGROUND
Radio signal tracking is used to determine the location of tagged assets and
to locate missing people who
have wandered. Current systems are often large and unwieldy, or difficult to
use, requiring training, or
lacking sensitivity and tracking range. It is difficult to design a system
that has excellent tracking range, is
simple to use, and is compact and portable.
Directional radio signal detectors rely on phase measurement, signal strength
measurement, or Doppler
frequency shifts in received signals. The signal strength approach relies on
the characteristic of an
antenna or antennas where the signal strength varies depending on the incident
angle on the antenna or
antennas. Some examples of directional antennas include loops, Yagi, and quad
antennas.
Loop antennas are often used because they are easy to build and can have deep
signal strength nulls
resulting in good directional accuracy. A loop antenna has a symmetric
response so the direction of the
signal has an ambiguity of 180 degrees.
Yagis are multi-element antennas with reflector and director elements arranged
along a boom. Yagi
antennas have good directionality but are relatively large because of the
multiple elements required to
form the beam pattern. The distance between the elements is typically 1/4 of a
wavelength and the
element lengths are approximately 1/2 of a wavelength. The antenna must be
swept slowly over the
whole horizon, effectively pointing the directional "beam" of reception at all
the points of the compass.
Quad antenna systems often use sophisticated electronic switching circuits to
create a pseudo-Doppler
frequency shift in the received radio signal. While these systems are simple
to use and provide a bearing
to the radio source, the antenna array does not typically have any gain. This
results in poor sensitivity and
tracking range.
United States Patent 4,121,216 discloses the use of an energy receiving
antenna having two orthogonally
mounted vertically oriented, loop antennas, a monopole antenna and a
horizontally oriented loop
antenna. Signals from the two orthogonally mounted loop antennas contain
bearing information for
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processing in a phase comparison system. The monopole antenna signal provides
for elimination of any
ambiguity in the bearing information signal as received from the two
orthogonally mounted loop
antennas. Sensing the polarization of the energy waves at the receiving
antennas is provided by
comparison of the horizontal loop antenna signal with the resultant signal
obtained by the quadrature
summation of the signal from the two vertical loop antennas. A bearing
indication from the two
orthogonally mounted loop antennas is generated by phase shifting one of the
antenna signals. This phase
shifted signal is combined with the second loop antenna signal in both a
summing network and a
difference network. A phase detector coupled to the summing network and the
difference network
provides a signal representing a multiple of the bearing angle between the
emitting source and the
receiving antenna. The ambiguity in this multiple of the bearing angle is
removed by coupling a phase
detector to the summing network and the monopole antenna. The output of this
second phase detector
is combined with the output of the first phase detector in an ambiguity
resolver to produce a true bearing
angle. This is a bulky three-dimensional antenna system. Further, it has no
inherent gain. It is also
impossible to determine the direction of a signal based on the two loops
alone. A third antenna is needed
to determine the whether the signal is coming from the front or back of a
particular loop.
United States Patent 6,088,002 discloses an antenna system including a support
structure and an antenna
assembly having an open grid reflector structure in a closed ring and dipole
elements. The antenna
assembly includes a number of antenna panels, each including a number of the
dipole elements, the
closed ring is self-supporting and connected to the support structure by
radial beams and struts, and the
antenna panels are interconnected by a variable angle connection.
United States Patent Publication 20140049428 discloses an apparatus for
direction finding a received
radio signal. The receiving apparatus selectively receives on a predetermined
frequency to match the
transmitter frequency. The receiving apparatus is comprised of one non
directional antenna and two or
more loop antennas. The loop antennas modify the field of the incident radio
signal by absorbing the
incident radio frequency energy to create a non-ambiguous gain pattern on the
sense antenna that can
be used to determine the direction of the incident RF signal.
United States Patent Publication 20140002306 discloses an apparatus for
direction-finding a received
radio signal. The receiving apparatus selectively receives on a predetermined
frequency to match the
transmitter frequency. The receiving apparatus comprises of two or three
antennas, including one or two
loop antennas that work in conjunction with a third reference antenna (whose
phase does not vary when
its orientation changes relative to the transmitter) such as a dipole,
monopole or helical antenna. By
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comparing the phase between the antennas the direction of the incoming radio
frequency signal can be
determined. In some embodiments, the windings of the two loop antennas are
wound in reverse with
respect to each other in order to substantially double the sensitivity of the
signal-detection capabilities.
It is a phase comparison system, hence it does not have the range afforded by
the signal strength system.
What is needed is an antenna array for radio direction finding that has good
sensitivity and high gain. The
system should be compact, light-weight, and sealed to the environment, to
permit portable hand held
operation. The antenna would preferably have excellent impedance matching to
the radio equipment. It
would be easy to operate and provide full coverage over all directions of the
compass. It would be of
further advantage if it had a small bandwidth for selective reception and
minimal interference.
SUMMARY
In accordance with various aspects of the subject invention in at least one
embodiment the invention
presents an improved antenna array for radio direction finding and an improved
locating system utilizing
such an antenna array in which a compact, lightweight, and portable unit
enables determining the location
of radio tags connected to assets or people.
The subject invention results from the realization that, in part, an improved
antenna array for radio
direction finding can be achieved through radio frequency coupling of adjacent
antennas in a radial
arrangement of antennas. The performance of each of the antennas in the
antenna array was improved
through this coupling mechanism. In particular, the standing wave ratio (SWR),
the return loss (RL), and
the impedance match of each antenna was improved by this coupling mechanism.
In addition, the
radiation pattern of each of the antennas in the array was improved through
the coupling mechanism.
The preferred embodiments of the antenna array may include three identical
antennas. Each of the
antennas is rectangular in shape, comprising a bent dipole element on the
outer part of the rectangle and
a bent reflector element on the inner part of the rectangle. A calibrated gap
is situated between the bent
dipole element and the bent reflector element. This Moxon style antenna has
excellent gain in the forward
direction and minimal signal from the back side. The radiation pattern for
this antenna is perfectly suited
for this radial arrangement of antennas, with the beam pattern sufficiently
wide to provide balanced
coverage over all points of the compass.
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The antenna array is arranged in one plane. This co-planar array permits
setting the radio frequency
coupling between adjacent reflector elements in each of the antennas. The
geometry of the co-planar
antenna array permits simple mechanical support and sealing cover for portable
hand-held operation.
The angles and distances of the elements of the receiver array are fixed and
non-adjustable in a given
embodiment.
In one embodiment, a fixed, radial array of antennas for use with a
transceiver radio and electronics
module for radio direction tracking is provided, the array comprising a
plurality of co-planar, rectangular
antennas and a radio frequency coupling calibrated space between each adjacent
pair of antennas, the
radial array defining a periphery and a central zone, each antenna forming a
rectangle comprising: a bent
dipole element at the periphery of the array, the bent dipole element
including a pair of legs and a dipole
length terminating in a pair of ends, each leg extending orthogonally from the
dipole length at the ends
and each terminating in a leg end; a reflector, which includes a pair of legs
and a reflector length
terminating in a pair of ends, each leg extending orthogonally from the
reflector length to define a corner
and terminating in a leg end; and a gap between the ends of the legs of the
bent dipole element and the
ends of the legs of the reflector.
The fixed, radial array may further comprise a substrate, the substrate
located in the radio frequency
coupling calibrated space.
In the fixed, radial array the corners of the reflectors of each adjacent pair
of antenna may define the
radio frequency coupling calibrated space.
The fixed, radial array may further comprise a plurality of bent coupling
wires, each coupling wire including
a length and a pair of bent ends, the coupling wires extending between each
adjacent pair of antennas,
each bent end and each leg of the reflector defining the radio frequency
coupling calibrated space.
The fixed, radial array may further comprise a support, which has a planar
surface, the array mounted on
the planar surface.
The fixed, radial array may comprise three antennas.
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The fixed, radial array may include the transceiver radio and electronics
module which is in electronic
communication with each antenna.
In the fixed, radial array the transceiver radio and electronics module may be
located in the central zone
of the array and is co-planar with the array.
In another embodiment, an antenna system for radio direction finding is
provided, the system including a
housing, a transceiver radio and electronics module retained in the housing
and a fixed, radial array of
antennas retained in the housing, the array comprising a plurality of co-
planar, rectangular antennas and
a radio frequency coupling calibrated space between each adjacent pair of
antennas, the radial array
defining a periphery and a central zone, each antenna in electronic
communication with the transceiver
radio and electronics module and each antenna forming a rectangle comprising:
a bent dipole element at
the periphery of the array, the bent dipole element including a pair of legs
and a dipole length terminating
in a pair of ends, each leg extending orthogonally from the dipole length at
the ends and each terminating
in a leg end; a reflector, which includes a pair of legs and a reflector
length terminating in a pair of ends,
each leg extending orthogonally from the reflector length to define a corner
and terminating in a leg end;
and a gap between the ends of the legs of the bent dipole element and the ends
of the legs of the
reflector.
The antenna system may further comprise a substrate, the substrate located in
the radio frequency
coupling calibrated space.
In the antenna system the corners of the reflectors of each adjacent pair of
antenna may define the radio
frequency coupling calibrated space.
The antenna system may further comprise a plurality of bent coupling wires,
each coupling wire including
a pair of bent ends and a length therebetween, the coupling wires extending
between each adjacent pair
of antennas, each bent end and each leg of the reflector defining the radio
frequency coupling calibrated
space.
The antenna system may comprise three antennas.
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In the antenna system the transceiver radio and electronics module may be
located in the central zone of
the array and is co-planar with the array.
The antenna system may further comprise a direction indicator which is
retained by the housing.
The antenna system may further comprise an electronic display which is in
electronic communication with
the transceiver radio and electronics module and is either retained by the
housing or is remote to the
housing.
In another embodiment, a radio tracking system is provided, the tracking
system comprising a radio
transmitter and an antenna system in radio communication with the radio
transmitter, the antenna
system including a housing, a transceiver radio and electronics module
retained in the housing and a fixed,
radial array of antennas retained in the housing, the array comprising a
plurality of co-planar, rectangular
antennas and a radio frequency coupling calibrated space between each adjacent
pair of antennas, the
radial array defining a periphery and a central zone, each antenna in
electronic communication with the
transceiver radio and electronics module and each antenna forming a rectangle
comprising: a bent dipole
element at the periphery of the array, the bent dipole element including a
pair of legs and a dipole length
terminating in a pair of ends, each leg extending orthogonally from the dipole
length at the ends and each
terminating in a leg end; a reflector, which includes a pair of legs and a
reflector length terminating in a
pair of ends, each leg extending orthogonally from the reflector length to
define a corner and terminating
in a leg end; and a gap between the ends of the legs of the bent dipole
element and the ends of the legs
of the reflector.
In the radio tracking system the corners of the reflectors of each adjacent
pair of antenna may define the
radio frequency coupling calibrated space.
The radio tracking system may further comprise a plurality of bent coupling
wires, each coupling wire
including a pair of bent ends and a length therebetween, the coupling wires
extending between each
adjacent pair of antennas, each bent end and each leg of the reflector
defining the radio frequency
coupling calibrated space.
The radio tracking system may comprise three antennas.
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FIGURES
Figure 1 is a schematic of a locator system for radio direction finding.
Figure 2 is an isometric view of the multi-antenna system with radio coupling
between reflector elements
achieved by close physical proximity of the corners of adjacent reflector
elements.
Figure 3 is an isometric view of the multi-antenna system with radio coupling
between reflector elements
achieved with coupling elements added between reflector elements.
Figure 4 is an isometric view of the multi-antenna system with radio coupling
between reflector elements
achieved with the radio properties of the mechanical support structure.
Figure 5 is an isometric view of an alternate embodiment of Figure 2, with a
four antenna system.
Figure 6A is an alternative embodiment with a five antenna system; and Figure
6B is an alternative
embodiment with coupling wires and material in the calibrated space.
Figure 7 is a polar log antenna pattern for the transceiver array of Figure 2.
Figure 8 is vector network analysis showing Smith diagram of an uncoupled
transceiver array.
Figure 9 is vector network analysis showing Smith diagram for the transceiver
array of Figure 2.
Figure 10 is a vector network analysis showing Standing Wave Ratio (SWR) and
Return Loss (RL) of an
uncoupled transceiver array.
Figure 11 is a vector network analysis showing Standing Wave Ratio (SWR) and
Return Loss (RI) for the
transceiver array of Figure 2.
DESCRIPTION
Definitions:
Plurality ¨ in the context of the present technology, plurality refers to
three or more.
Co-planar ¨ in the context of the present technology, co-planar refers to
approximately the same plane,
and preferably the same plane.
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Rectangular ¨ in the context of the present technology, rectangular refers to
the overall shape of the
antenna and does not refer to a closed structure, but rather one that has a
gap between the ends of the
reflector legs and the ends of the dipole element legs.
Detailed Description:
Except as otherwise expressly provided, the following rules of interpretation
apply to this specification
(written description and claims): (a) all words used herein shall be construed
to be of such gender or
number (singular or plural) as the circumstances require; (b) the singular
terms "a", "an", and "the", as
used in the specification and the appended claims include plural references
unless the context clearly
dictates otherwise; (c) the antecedent term "about" applied to a recited range
or value denotes an
approximation within the deviation in the range or value known or expected in
the art from the
measurements method; (d) the words "herein", "hereby", "hereof", "hereto",
"hereinbefore", and
"hereinafter", and words of similar import, refer to this specification in its
entirety and not to any
particular paragraph, claim or other subdivision, unless otherwise specified;
(e) descriptive headings are
for convenience only and shall not control or affect the meaning or
construction of any part of the
specification; and (f) "or" and "any" are not exclusive and "include" and
"including" are not limiting.
Further, the terms "comprising," "having," "including," and "containing" are
to be construed as open
ended terms (i.e., meaning "including, but not limited to,") unless otherwise
noted.
Recitation of ranges of values herein are merely intended to serve as a
shorthand method of referring
individually to each separate value falling within the range, unless otherwise
indicated herein, and each
separate value is incorporated into the specification as if it were
individually recited herein. Where a
specific range of values is provided, it is understood that each intervening
value, to the tenth of the unit
of the lower limit unless the context clearly dictates otherwise, between the
upper and lower limit of that
range and any other stated or intervening value in that stated range, is
included therein. All smaller sub
ranges are also included. The upper and lower limits of these smaller ranges
are also included therein,
subject to any specifically excluded limit in the stated range.
Unless defined otherwise, all technical and scientific terms used herein have
the same meaning as
commonly understood by one of ordinary skill in the relevant art. Although any
methods and materials
similar or equivalent to those described herein can also be used, the
acceptable methods and materials
are now described.
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Radio apparatus design requires careful consideration to the performance of
the antenna. A properly
matched antenna is required to efficiently convert electrical signals to
electromagnetic waves, and vice
versa. The designer must balance trade-offs of efficiency, bandwidth,
radiation pattern, gain, frequency,
and antenna matching, with available size and housing constraints. It is
almost impossible to achieve the
desired antenna without compromising some element of performance.
Through numerous experiments with several types of antenna patterns, it was
discovered that an
improved antenna array for direction finding could be realized. It was found
that the standard bent dipole
and reflector arrangement of a Moxon style antenna could be combined into a
multi-antenna array that
achieved superior performance, when compared to the properties of a single
antenna.
Many antennas require a sizeable ground plane to achieve acceptable
performance. This is particularly
true of small patch antennas, trace antennas printed on circuit boards, and
short whip antennas. The
bent dipole antennas with matching reflector elements used in this multi-
antenna array do not require a
ground plane to function, as the ground return path is part of the dipole
element. This provides excellent
performance without the need of large and heavy grounding components.
The mechanism for the improved antenna performance when using these combined
antennas in the array
was not initially clear. Tests eventually showed that radio frequency coupling
between adjacent reflector
elements in the antenna array was responsible for the improvements.
Furthermore, it was found that
there are several means of achieving this coupling. Some of the methods of
coupling that were tested
included: direct coupling through close proximity of the reflector elements,
coupling through the radio
frequency properties of the supporting mechanical structure, and coupling
through the addition of a
parasitic coupling elements.
A locator system for radio direction finding, generally referred to as 10 is
shown in Figure 1. It includes
an electronic display 12, which may be remote, a hand-held antenna system 16,
and a radio transceiver
18. The radio transceiver 18 is attached to an asset, a person, or wildlife
and is remote to the hand-held
antenna system 16. The hand-held antenna system 16 has a housing 22, which has
an outer edge 26 and
a central zone 28, and a handle 29. The central zone 28 of the antenna system
16 may include electronics
for radio transceivers, control, communications, and compass direction 14.
As shown in Figure 2, the antenna system 16 includes three bent dipole
elements - a first dipole element
30, a second dipole element 32, and a third dipole element 34. The dipole
elements 30, 32, 34 are identical
and are co-planar to one another. Each element 30, 32, 34 includes an element
length 40, a first element
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leg 42 and a second element leg 44. The element legs 42, 44 are orthogonal and
co-planar to the element
length 40, parallel with one another and extend inward to the middle of the
system. There are three
reflectors, a first reflector 50, a second reflector 52 and a third reflector
54. The reflectors 50, 52, 54 are
identical, co-planar with one another and co-planar with the bent dipoles 30,
32, 34. Each reflector 50,
52, 54 has a reflector length 60, a first reflector leg 62 and a second
reflector leg 64. The reflector legs 62,
64 are orthogonal and co-planar to the reflector lengths 60, parallel with one
another and extend outward
towards the outer edge 28 of the hand-held antenna system 16. The reflector
legs 62, 64 oppose the
dipole element legs 42, 44 of the corresponding element - the first reflector
50 is aligned with the first
dipole element 30, the second reflector 52 is aligned with the second dipole
element 32 and the third
reflector 54 is aligned with the third dipole element 34. A space 70 is
defined between the ends 66 of the
reflector legs 62, 64 and the ends 46 of the dipole element legs 42, 44. Each
dipole element 30, 32, 34
and its corresponding reflector 50, 52, 54 are an antenna 71.
Radio frequency coupling between adjacent reflectors is provided by a
calibrated space 72 between
adjacent reflector corners 68. Specifically, the calibrated space 72 provides
radio frequency coupling
between the first reflector 50 and the second reflector 52, between the second
reflector 52 and the third
reflector 54 and between the third reflector 54 and the first reflector 50.
A transceiver radio and electronics module 24 is located in the central zone
28 of the system 16. A wire
80 extends between each dipole element 30, 32, 34 and the module 24 for bi-
directional communication
of the radio signal. The module 24 is co-planar or approximately co-planar to
the dipole elements 30, 32,
34, and the reflectors 50, 52, 54. The radial array 73 of antennas defines a
periphery 27.
The specific dimensions for one fixed, radial array 73 are as follows: the
length of the dipole element of
each antenna is about 245 mm to about 253 mm, more preferably about 249 mm;
the width is about 91
to about 95 mm, more preferably about 93 mm, the gap is about 12 to about 16
mm, preferably about 14
mm, the wire rod for the antenna is about 2 to about 4 mm, preferably about 3
mm in diameter; the
distance between the centre of the array and the periphery is about 160 to
about 172 mm, preferably
about 166 mm; the radius of the corners is about 7 to about 9 mm, preferably
about 8 mm and the
diameter of the transceiver radio and electronics module is about 100 to about
116 mm, preferably about
108 mm.
As shown in Figure 3, an alternate embodiment of the multi-antenna, co-planar
system includes bent
coupling wires 90. The co-planar arrangement of bent dipole elements, 30, 32,
34 and reflectors, 50, 52,
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54 are similar to those in Figure 2. The coupling between adjacent reflectors
50, 52, 54 is achieved with
the coupling wires 90, as opposed to the close physical proximity of the
corners 68 of the reflectors 50,
52, 54, and the calibrated space 72. The coupling wires 90 have bent ends 92.
The calibrated space 74 is
defined between the bent ends 92 and the reflector legs 62, 64. The calibrated
space 74 provides radio
frequency coupling between the first reflector 50 and the second reflector 52,
between the second
reflector 52 and the third reflector 54 and between the third reflector 54 and
the first reflector 50.
As shown in Figure 4, an alternate embodiment of the multi-antenna, co-planar
system includes a
supporting material 100, which has a planar surface 94 over much of the
surface and which fills the
calibrated space 76. The preferred support is polyvinyl chloride expanded
foam. The co-planar
arrangement of bent dipole elements, 30, 32, 34 and reflectors, 50, 52, 54 are
similar to those in Figure 2.
The coupling between adjacent reflectors is achieved through the radio
frequency properties of the
mechanical support 100. The nature and quantity of the supporting material 75
in the calibrated space
76 between the corners 68 of the reflectors 50 52, 54, is carefully chosen to
provide the correct coupling
between the reflectors 50, 52, 54. The calibrated space 76 provides radio
frequency coupling between
the first reflector 50 and the second reflector 52, between the second
reflector 52 and the third reflector
54 and between the third reflector 54 and the first reflector 50. This may
include bent coupling wires 90.
In an alternative embodiment, the material in the calibrated space 76 is
different to the material of the
supporting material 100.
Figure 5 shows an alternate embodiment of the multi-antenna, co-planar array
73 with four antennas 71.
Each of the antennas 71 include the bent dipole elements 30, 32, 34, 36,
reflectors 50, 52, 54, 56, and
connecting wires 80. This figure shows the antenna calibrated space 72 between
reflector elements 50,
52, 54, 56. The calibrated space 72 provides radio frequency coupling between
the first reflector 50 and
the second reflector 52, between the second reflector 52 and the third
reflector 54, between the third
reflector 54 and the fourth reflector 56 and between the fourth reflector 56
and the first reflector 50.
Other alternative embodiments include a multi-antenna, co-planar array 73 with
more than four antennas
71, for example, but not limited to, five antennas 71 or six antennas 71. A
five antenna array is shown in
Figure 6A. In Figure 6B, it is shown that these may include includes bent
coupling wires 90 and may also
include the supporting material 75 in the calibrated space 74. In all
embodiments, the antenna 71 are
arranged in a fixed, radial array 73.
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Figure 7 shows a polar log radiation pattern for the multi-antenna, co-planar
array. Measurements of
radiation pattern for each of the antennas in the multi-antenna array showed
improvements to the
pattern over a single antenna. The front to back ratio showed a measured
improvement with the coupled
reflector elements altering the radiation pattern. The front lobe was slightly
broader, which helped to
improve the omni-directional coverage of the antenna array. In addition, the
forward gain of the antennas
was slightly larger than for the stand alone antennas.
Figure 8 shows a vector network analysis showing Smith diagram for an
uncoupled multi-antenna, co-
planar array.
Figure 9 shows a vector network analysis showing Smith diagram for the radio
frequency coupled multi-
antenna, co-planar array. Measurements using a vector network analyzer showed
the impedance match
of each antenna in the multi-antenna array, over a range of frequencies. These
were plotted on a Smith
Chart to assist in visualizing the real and imaginary components of impedance.
The Smith Chart showed
the ideal 50 ohm impedance match at the desired frequency. The impedance
change with frequency also
indicated the good match over the desired bandwidth of the antenna. These
results show that the system
is superior to that of the prior art and to the uncoupled array of Figure 8.
Figure 10 shows a vector network analysis showing Standing Wave Ratio (SWR)
and Return Loss (RI) for
an uncoupled multi-antenna, co-planar array.
Figure 11 shows a vector network analysis showing Standing Wave Ratio (SWR)
and Return Loss (RI) for
the radio frequency coupled multi-antenna, co-planar array. Measurements using
a vector network
analyzer showed the standing wave ratio of each of the antennas in the array
was improved to the ideal
1.0 : 1. The standing wave ratio, SWR, indicates the amount of electrical
energy from a radio that is
converted into electromagnetic radiation. Typically a fraction of the energy
is bounced back from an
antenna and appears as a mismatched antenna load. Commercial antennas
typically have an SWR of 2 : 1
to 1.5 : 1. These results show that the system is superior to that of the
prior art and to the uncoupled
array of Figure 10.
Another aspect of antenna design for radio apparatus is how the antenna
behaves with external loading
on the antenna. When antennas are deployed in real world applications the
housing and support
structures for the antenna will alter the antenna frequency response, the
standing wave ratio, and the
antenna match to the transceiver circuit. Often antennas designed to be
embedded in housings are
purposely designed to be out-of-band, or tuned to a different frequency than
desired. This allows the
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antenna to be loaded by the housing and pulled into the correct frequency. The
nature of the coupling
between the reflector elements in the multi-antenna array ensures that the
effects of the housing and
support structure is incorporated into the design and nature of the system.
While example embodiments have been described in connection with what is
presently considered to be
an example of a possible most practical and/or suitable embodiment, it is to
be understood that the
descriptions are not to be limited to the disclosed embodiments, but on the
contrary, is intended to cover
various modifications and equivalent arrangements included within the spirit
and scope of the example
embodiment. Those skilled in the art will recognize or be able to ascertain
using no more than routine
experimentation, many equivalents to the specific example embodiments
specifically described herein.
Such equivalents are intended to be encompassed in the scope of the claims, if
appended hereto or
subsequently filed.
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