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Mobile Phone Patent Abstract
The balanced, retractable dipole antenna comprises a first radiator
element that is selectively extendable from, and retractable into,
a mobile phone casing, a second radiator element, and a counterpoise
that is electrically isolated from a printed wire board (PWB) of
a mobile phone. The balanced, retractable dipole antenna further
comprises a signal balancing means coupled between a signal source
and at least the second radiator element and counterpoise to generate
first and second signals, respectively. The first and second signals
are substantially equal in magnitude but out of phase by 180 degrees.
When the first radiator is extended, the first signal is transferred
to the first and second radiator elements, and the second signal
is transferred to the counterpoise. When the first radiator element
is retracted, the first signal is transferred to the second radiator,
while the second signal is transferred to the counterpoise and the
first radiator element. The first and second signals produce balanced
currents, thereby producing a symmetric radiation pattern.
Mobile Phone Patent Claims
What is claimed is:
1. A balanced, retractable dipole antenna for use in a mobile phone
having a casing, and a signal source, transmit and receive circuits,
and a printed wire board (PWB) having a ground plane formed thereon
for the signal source and for the transmit and receive circuits
contained in the casing, comprising:
a first radiator element formed of a conducting material and being
selectively extendable from and retractable into the casing;
a second radiator element formed of a conducting material;
a counterpoise formed of a conducting material and electrically
isolated from the PWB ground plane;
a signal balancing means coupled between the signal source and
at least said second radiator element and counterpoise to generate
first and second signals, respectively, wherein said first and second
signals are substantially equal in magnitude but out of phase by
180 degrees;
means for transferring said first signal to said second radiator
element;
means for transferring said second signal to said counterpoise;
means for transferring said first signal to said first radiator
element when said first radiator element is extended; and
means for transferring said second signal to said first radiator
element when said first radiator element is retracted.
2. The balanced, retractable dipole antenna of claim 1, wherein
said second radiator element is a helical conductor.
3. The balanced, retractable dipole antenna of claim 1, wherein
said first radiator element is a whip conductor.
4. The balanced, retractable dipole antenna of claim 1, wherein
said second radiator element is a substrate radiator.
5. The balanced, retractable dipole antenna of claim 1, wherein
said means for transferring said first signal to said first radiator
element comprises means for electromagnetically coupling said first
radiator element to said second radiator element.
6. The balanced, retractable dipole antenna of claim 1, wherein
said means for transferring said first signal to said first radiator
element comprises means for electrically connecting said first radiator
element to said signal balancing means.
7. The balanced, retractable dipole antenna of claim 6, wherein
said means for electrically connecting said first radiator element
to said signal balancing means comprises a conducting clip attached
to said first radiator element.
8. The balanced, retractable dipole antenna as recited in claim
1, wherein said counterpoise is printed on the PWB.
9. The balanced, retractable dipole antenna as recited in claim
1, wherein said counterpoise is a conducting wire.
10. The balanced, retractable dipole antenna as recited in claim
1, wherein said counterpoise is a metallic strip.
11. The balanced, retractable dipole antenna as recited in claim
1, wherein said first and second signals are in cellular frequency
band.
12. The balanced, retractable dipole antenna as recited in claim
1, wherein said first and second signals are in PCS frequency band.
13. The balanced, retractable dipole antenna as recited in claim
1, wherein the total length of the antenna is .lambda., where .lambda.
is the wavelength corresponding to an operating frequency.
14. The balanced, retractable dipole antenna as recited in claim
1, wherein the total length of the antenna is .lambda./2, where
.lambda. is the wavelength corresponding to an operating frequency.
15. The balanced, retractable dipole antenna as recited in claim
1, wherein the total length of the antenna when said first radiator
element is extended is substantially equal to the total length of
the antenna when said first radiator element is retracted.
16. A balanced, retractable dipole antenna for use in a mobile
phone having a casing, and a signal source, transmit and receive
circuits, and a printed wire board (PWB) having a ground plane formed
thereon for the signal source and for the transmit and receive circuits
contained in the casing, comprising:
a composite radiator element that is selectively extendable from
and retractable into the casing having a first radiator element
formed of a conducting material, a connecting element coupled to
said first radiator element, and a second radiator element formed
of a conducting material coupled to said connecting element, wherein
said connecting element electrically connects said first and second
radiator elements when said composite radiator is extended and electrically
disconnects said first and second radiator elements when said composite
radiator is retracted;
a counterpoise formed of a conducting material and electrically
isolated from the PWB ground plane;
a signal balancing means coupled between the signal source and
at least said second radiator element and counterpoise to generate
first and second signals, respectively, that are substantially equal
in magnitude but out of phase by 180 degrees;
means for transferring said first signal to said first radiator
element and said second radiator element when said composite radiator
element is extended; and
means for transferring said first signal to said second radiator
element and said second signal to said first radiator element when
said composite radiator element is retracted.
17. The balanced, retractable dipole antenna of claim 16, wherein
said second radiator element is a helical conductor.
18. The balanced, retractable dipole antenna of claim 16, wherein
said first radiator element is a whip conductor.
19. The balanced, retractable dipole antenna as recited in claim
16, wherein said counterpoise is printed on the PWB.
20. The balanced, retractable dipole antenna as recited in claim
16, wherein said counterpoise is a conducting wire.
21. The balanced, retractable dipole antenna as recited in claim
16, wherein said counterpoise is a metallic strip.
22. The balanced, retractable dipole antenna as recited in claim
16, wherein said first and second signals are in cellular frequency
band.
23. The balanced, retractable dipole antenna as recited in claim
16, wherein said first and second signals are in PCS frequency band.
24. The balanced, retractable dipole antenna as recited in claim
16, wherein the total length of the antenna is .lambda., where .lambda.
is the wavelength corresponding to an operating frequency.
25. The balanced, retractable dipole antenna as recited in claim
16, wherein the total length of the antenna is .lambda.,/2, where
.lambda., is the wavelength corresponding to an operating frequency.
26. The balanced, retractable dipole antenna as recited in claim
16, wherein the total length of the antenna when said composite
radiator element is extended is substantially equal to the total
length of the antenna when said composite radiator element is retracted.
Mobile Phone Patent Description
BACKGROUND OF THE INVENTION
I. Field of the Invention
The present invention relates generally to antennas. More specifically,
the present invention relates to a balanced, retractable dipole
antenna for mobile phones.
II. Description of the Related Art
Recent advancements in electronics have significantly improved
the performance of mobile phones. For example, advancements in integrated
circuit technology have led to high performance radio frequency
(RF) circuits. The RF circuits are used to construct transmitters,
receivers and other signal processing components typically found
in mobile phones. Also, advancements in integrated circuit technology
have led to a reduction in the size of RF circuits, thereby leading
to a reduction in the overall size of a mobile phone.
Similarly, advancements in battery technology have resulted in
smaller, lighter and longer lasting batteries used in mobile phones.
These advancements have resulted in smaller and lighter mobile phones
that operate for a longer period of time on a single charge.
Generally, a user of a mobile phone must be able to communicate
with another user or a ground station that can be located in any
direction from the user. For this reason, the antenna in the user's
mobile phone must be able to receive and transmit signals from and
in all directions. Consequently, it is desirable that the antenna
exhibit a symmetric radiation pattern having a uniform gain in the
azimuth. In addition, it is desirable for mobile phones to have
antennas that are retractable.
Unfortunately, antennas found in today's typical mobile phones
do not exhibit a symmetric radiation pattern. Mobile phones generally
utilize monopole antennas (for example, a whip antenna) that, due
to the presence of unbalanced currents, exhibit asymmetric radiation
patterns. This is primarily due to the fact that the shape and dimension
of a monopole are not equivalent to to the shape and dimension of
a ground plane of a printed wire board (PWB) used as a counterpoise,
resulting in an unequal current distribution in the monopole and
in the ground plane.
As a result, it has been recognized that there is a need for an
antenna for a mobile phone that exhibits a symmetric radiation pattern.
SUMMARY OF THE INVENTION
The present invention is directed to a balanced, retractable dipole
antenna for mobile phones, such as cellular and PCS phones. The
balanced, retractable dipole antenna comprises a first radiator
element that is selectively extendable from, and retractable into,
a mobile phone casing, a second radiator element, and a counterpoise
that is electrically isolated from a printed wire board (PWB) of
a mobile phone. The balanced, retractable dipole antenna further
comprises a signal balancing means coupled between a signal source
and at least the second radiator element and counterpoise to generate
first and second signals, respectively. The first and second signals
are substantially equal in magnitude but out of phase by 180 degrees.
When the first radiator is extended, the first signal is transferred
to the first and second radiator elements, and the second signal
is transferred to the counterpoise. When the first radiator element
is retracted, the first signal is transferred to the second radiator,
while the second signal is transferred to the counterpoise and the
first radiator element. The first and second signals produce balanced
currents, thereby producing a symmetric radiation pattern.
Further features and advantages of the invention, as well as the
structure and operation of various embodiments of the invention,
are described in detail below with reference to the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
In the drawings, like reference numbers generally indicate identical,
functionally similar, and/or structurally similar elements. The
drawing in which an element first appears is indicated by the leftmost
digit(s) in the reference number.
The present invention will be described with reference to the accompanying
drawings, wherein:
FIG. 1 illustrates a monopole antenna used in a typical mobile
phone;
FIG. 2 shows current vectors in a monopole antenna;
FIG. 3 illustrates a dipole antenna;
FIG. 4 shows current distributions in dipole antennas of different
lengths;
FIG. 5A illustrates the radiation patterns of a half wavelength
dipole antenna;
FIG. 5B illustrates the radiation pattern of a full wavelength
dipole antenna;
FIGS. 6A and 6B illustrate a balanced, retractable dipole antenna
according to one embodiment of the present invention;
FIGS. 7A and 7B illustrate a balanced, retractable dipole antenna
according to a further embodiment of the present invention;
FIGS. 8A and 8B illustrate a balanced, retractable dipole antenna
according to yet a further embodiment of the present invention;
and
FIGS. 9, 10 and 11 illustrate baluns in accordance with three embodiments
of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
I. Overview of the Present Invention
As noted before, antennas found in today's typical mobile phones
do not exhibit a symmetric radiation pattern. Mobile phones generally
utilize monopole antennas that, due to the presence of unbalanced
currents, exhibit asymmetric radiation patterns. This is illustrated
further in FIGS. 1 and 2.
FIG. 1 illustrates a monopole antenna 100 used in a typical mobile
phone 101. The phone 101 contains transmit/receive circuits and
other ancillary electronic and mechanical components needed to send
and receive calls and to perform all other normal phone operations.
These components are well known and are not shown or described further
as they form no part of the present invention. Monopole antenna
100 comprises a radiator (a monopole) 104, a printed wire board
(PWB) 108, a reactive matching network 112 and a signal source 116.
Reactive matching network 112 comprises first and second outputs
120 and 124. First output 120 is connected to monopole 104 and second
output 124 is connected to ground plane 128 of PWB 108. Ground plane
128 acts as a counterpoise in order to provide a return path for
currents in monopole radiator 104.
Reactive matching network 112 forms an unbalanced feed to monopole
104. The unbalanced feed causes unbalanced currents to flow along
ground plane 128. This is primarily due to the fact that the shape
and dimension of monopole 104 are not equivalent to the shape and
dimension of ground plane 128, resulting in unequal current distribution
in monopole 104 and in ground plane 128. As a result, monopole 104
and ground plane 128 form an asymmetric dipole, thereby causing
an asymmetric radiation pattern (that is, a distorted radiation
pattern).
FIG. 2 shows the current vectors I.sub.1 and I.sub.2 in monopole
104 and ground plane 128, respectively. The horizontal component
I.sub.2x of the current I.sub.2 in ground plane 128 is balanced
by the horizontal component I.sub.1x of the current I.sub.1 in monopole
104. However, the vertical component I.sub.2y of the current I.sub.2
in ground plane 128 remains unbalanced, because of a lack of an
opposing vertical component in monopole 104. The shape and dimension
of monopole 104 prevent the formation of a vertical component of
the current vector I.sub.1. As a result, unbalanced currents flow
along ground plane 128, causing a distorted radiation pattern.
Furthermore, monopole antenna 100 provides less flexibility as
its radiation pattern is driven by the size and/or shape of PWB
108. Since the size and/or shape of PWB 108 are driven in large
part by the size and/or shape of the mobile phone's case that houses
PWB 108, designers are often handicapped in their selection of a
radiation pattern by the pre-existing size and/or shape of a mobile
phone's case.
The present invention provides a solution to the aforementioned
problems. The present invention is a balanced, retractable dipole
antenna for a mobile phone, for example, a PCS phone or a cellular
phone. The present invention advantageously incorporates a balanced
dipole antenna in a mobile phone that significantly improves the
radiation pattern of a mobile phone. In addition, the present invention
provides an antenna that is retractable. Furthermore, the present
invention allows designers to select desired radiation patterns
for mobile phones without being constrained by the shape of PWBs.
The balanced, retractable dipole antenna allows superior performance
over conventional antennas found in mobile phones today by enabling
a user of a mobile phone to communicate uniformly in all directions,
that is, 360 degrees.
As noted above, the present invention incorporates the advantages
of a dipole antenna in a mobile phone. Simply stated, a dipole antenna
is a diverging two-wire transmission line. FIG. 3 illustrates a
dipole antenna 300. Dipole antenna 300 comprises first and second
radiators 304 and 308, respectively, connected to a signal source
312 by a two-wire transmission line 316.
Dipole antenna 300 can be of any length L, such as L=.lambda.,
.lambda./2, .lambda./4, where .lambda. corresponds to the wavelength
of the operating frequency .function. of dipole antenna 300. The
current distributions in first and second radiators 304 and 308
are sinusoidal provided that the diameter of each radiator is less
than .lambda./100. Examples of the approximate current distributions
in a number of dipole antennas of different lengths are illustrated
in FIG. 4.
Dipole antenna 300 exhibits a symmetric radiation pattern. A symmetric
radiation pattern provides uniform gain in 360 degrees, thereby
allowing equally effective communication in all directions. FIGS.
5A and 5B illustrate the radiation pattern of dipole antenna 300
having selected lengths. The current distribution in dipole antenna
300 is assumed to be sinusoidal.
FIG. 5A illustrates the radiation pattern of a dipole antenna having
a length L=.lambda./2. The radiation pattern for L=.lambda./2 is
given by the following equation. ##EQU1##
FIG. 5B illustrates the radiation pattern of a dipole antenna having
a length L=.lambda.. The radiation pattern for L=.lambda. is given
by the following equation. ##EQU2##
II. The Invention
FIGS. 6A, 6B, 7A, 7B, 8A, and 8B illustrate three embodiments of
the present invention. Each of these embodiments is a balanced,
retractable dipole antenna. FIGS. 6A and 6B illustrate a first antenna
600 according to one embodiment of the present invention. First
antenna 600 comprises a first radiator 604, a second radiator 606,
a counterpoise 608, a PWB 612, and a balun 616. First antenna 600
can exist in both an extended state and a retracted state. In the
extended state, first radiator 604 extends out of a casing 602.
In the retracted state, first radiator 604 is retracted into casing
602. In a preferred embodiment, extension and retraction of first
radiator 604 is accomplished by a user sliding it along guides provided
by casing 602. However, extension and retraction of first radiator
604 may be accomplished through other techniques known to persons
skilled in the relevant arts. FIG. 6A illustrates antenna 600 in
its extended state. FIG. 6B illustrates antenna 600 in its retracted
state.
A signal source 620 is connected to balun 616. Signal source 620
has first and second terminals 624 and 628, respectively. First
terminal 624 is connected to balun 616, whereas second terminal
628 is grounded. In one embodiment, signal source 620 is mounted
on PWB 612. In operation, signal source 620 provides a single ended
RF signal to balun 616 by first terminal 624.
In addition to signal source 620, PWB 612 supports on board circuitry,
such as, a receiver, a transmitter, and other signal processing
circuitry needed for a mobile phone's operation. PWB 612 has a ground
plane that provides a ground for all on board circuitry.
In general, the purpose of a balun is to connect a balanced antenna
to an unbalanced source (or an unbalanced transmission line). In
this embodiment, balun 616 links first radiator 604, second radiator
606, and counterpoise 608 to an unbalanced source, that is, signal
source 620. Since the output of signal source 620 is single ended,
it is unbalanced. If the single ended output from signal source
620 is directly coupled to first radiator 604, second radiator 606,
and counterpoise 608, it would result in unbalanced currents in
first antenna 600. Thus, balun 616 is used to convert an unbalanced
source to a balanced source.
Balun 616 has first and second output terminals 632 and 636, respectively.
First and second output terminals 632 and 636 are connected to second
radiator 606 and counterpoise 608, respectively. Balun 616 converts
the single ended signal to first and second signals that are carried
on first output terminal 632 and second output terminal 636, respectively.
First and second signals have equal magnitudes, but are out of phase
by 180 degrees. The operation of balun 616 is described in detail
later.
In order for first antenna 600 to operate satisfactorily, counterpoise
608 must be electrically isolated from the ground plane of PWB 612.
Isolation of counterpoise 608 ensures that current will not flow
from counterpoise 608 to the ground plane of PWB 612. If counterpoise
608 is not electrically isolated from this ground plane, unbalanced
currents will flow along the ground plane of PWB 612, thereby resulting
in a distorted radiation pattern. Isolation for counterpoise 608
can be provided by maintaining a gap between PWB 612 and counterpoise
608. For example, counterpoise 608 can be placed parallel to PWB
612 as shown in FIGS. 6A and 6B. Alternatively, counterpoise 608
can be constructed on PWB 612 by various known techniques described
later. In that case, counterpoise 608 is generally separated from
the ground plane of PWB by a dielectric material.
According to the present invention, radiators linked to first output
terminal 632 are excited by a first signal. In addition, counterpoise
608, and any radiators connected to it, are excited by a second
signal carried on second output terminal 636 that has equal magnitude,
but which is out of phase with the first signal by 180 degrees.
These connections result in balanced currents circulating in the
radiators carrying the first signal and the counterpoise (and any
connected radiators) carrying the second signal. As a result, first
antenna 600 produces a symmetric radiation pattern.
Counterpoise 608 will generally be enclosed inside the mobile phone's
casing 602. In other words, counterpoise 608 will not be visible
from the outside. In one embodiment, first radiator 604 and counterpoise
608 have substantially similar dimensions and/or shapes. However,
first radiator 604 and counterpoise 608 may have dissimilar shapes
and/or dimensions. Counterpoise 608 may be printed on PWB 612. Alternatively,
counterpoise 608 may be a metallic strip or a conducting wire embedded
in a mobile phone's case. Counterpoise 608 may be constructed using
other techniques known in the art.
In the embodiment shown in FIGS. 6A and 6B, first radiator 604
is a straight conductor. Such straight conductors are generally
known as whips. A non-conducting tip 610 that is made of a non-conducting
material is affixed to the top end of first radiator 604. In a preferred
embodiment, non-conducting tip 610 is made out of plastic and is
non-radiating. However, in alternate embodiments, non-conducting
tip 610 may be made out of any non-conducting material known to
persons skilled in the relevant arts. In a preferred embodiment,
non-conducting tip 610 includes a nub at its end. This nub enables
a user to extend first radiator 604 when it is retracted.
Second radiator 606 is a helical conductor. Second radiator 606
is physically connected to first output terminal 632 and protrudes
out of casing 602. Helical radiators are well known to persons skilled
in the relevant arts.
FIG. 6A illustrates first antenna 600 in its extended state. In
this state, first radiator 604 extends outward from casing 602,
through the center of the helix of second radiator 606, and beyond.
In this position, first radiator 604 radiates the signal carried
on first output terminal 632. In a preferred embodiment, the signal
carried on first output terminal 632 is transferred to first radiator
604 via second radiator 606. This transfer does not require first
radiator 604 to be connected to either first output terminal 632
or second radiator 606. Instead, first radiator 604 is electromagnetically
excited by second radiator 606. However, in alternate embodiments,
first radiator 604 can be physically connected to second radiator
606 and/or first output terminal 632 when first antenna 600 is in
its extended state. When extended, first radiator 604 dominates
over second radiator 606 in radiating RF energy.
FIG. 6B illustrates first antenna 600 in its retracted state. Here,
first radiator 604 is retracted into casing 602. First radiator
604 no longer radiates the signal carried on first output terminal
632. Rather, first radiator 604 is physically connected to counterpoise
608. Thus, first radiator 604 acts as a counterpoise when first
antenna 600 is in its retracted state. When retracted, first radiator
604 does not pass through any part of the helix of second radiator
606. Therefore, second radiator 606 does not electromagnetically
excite first radiator 604. When first antenna 600 is in its retracted
state, non-conducting tip 610 is located in the center of the helix
of second radiator 606 with its nub protruding out of the top portion
of second radiator 606. This protrusion enables a user to pull on
first radiator 604 and place first antenna 600 into its extended
state.
FIGS. 7A and 7B illustrate a second antenna 700 according to a
further embodiment of the present invention. This embodiment contains
the same components connected in the same manner as in first antenna
600, except that second radiator 606 is replaced with a substrate
radiator 706. Also, a conductive clip 708 is attached to first radiator
604. Substrate radiator 706 is a conductor etched on a printed circuit
board. Substrate radiator 706 is connected to first output terminal
632. In a preferred embodiment, substrate radiator 706 is etched
on PWB 612. However, in alternate embodiments, substrate radiator
706 can be etched on a separate circuit board. Like first antenna
600, second antenna 700 can exist in both an extended state and
a retracted state.
FIG. 7A illustrates second antenna 700 in its extended state. Here,
first radiator 604 extends outward from casing 602 and is electrically
connected to first output terminal 632. In a preferred embodiment,
this connection is provided by clip 708. Clip 708 is attached to
first radiator 604 and establishes physical contact with first output
terminal 632 when first radiator 604 is extended. In alternate embodiments
of second antenna 700, first radiator 604 is not physically connected
to either first output terminal 632 or substrate radiator 706 when
extended. Rather, in these embodiments, first radiator 604 is electromagnetically
excited by substrate radiator 706 when extended.
FIG. 7B illustrates second antenna 700 in its retracted state.
Here, first radiator 604 is retracted into casing 602. When retracted,
clip 708 no longer contacts first output terminal 632. Thus, first
radiator 604 no longer radiates the signal carried on first output
terminal 632. Rather, in its retracted state, first radiator 604
is physically connected to counterpoise 608. Thus, first radiator
604 acts as a counterpoise when second antenna 700 is in its retracted
state. In addition, when second antenna 700 is in its retracted
state, first radiator 604 is not electromagnetically excited by
substrate radiator 706.
FIGS. 8A and 8B illustrate a third antenna 800 according to another
embodiment of the present invention. This embodiment contains the
same components as in first antenna 600, except that first radiator
604 and second radiator 606 are absent from this embodiment. Instead,
third antenna 800 includes a composite radiator 812. Composite radiator
812 comprises a first radiating element 804, a connecting element
806, and a second radiating element 810. Second radiating element
810 is above connecting element 806, and connecting element 806
is above first radiating element 804. In a preferred embodiment,
first radiating element 804 is a whip conductor, while second radiating
element 810 is a helical conductor. However, in alternate embodiments,
other conductor shapes may be employed. Connecting element 806 links
first radiating element 804 with second radiating element 810. Connecting
element 806 contains a switch that electrically connects and disconnects
first radiating element 804 and second radiating element 810 based
on the position of composite radiator 812. Like first antenna 600
and second antenna 700, third antenna 800 can exist in both extended
and retracted states.
Thus, composite radiator 812 can extend out of casing 602 and into
casing 602. In a preferred embodiment, connecting element 806 contains
a mechanical switch that closes when composite radiator 812 is extended
and opens when composite radiator 812 is retracted. Such mechanical
switches are known to persons skilled in the relevant arts. In alternate
embodiments, connecting element 806 employs an electronic switch.
FIG. 8A illustrates third antenna 800 in its extended state. Here,
composite radiator 812 extends out of casing 602. When extended,
connecting element 806 electrically connects first radiating element
804 and second radiating element 810. Since these elements are connected,
composite radiator 812 is a single radiating conductor connected
to first output terminal 632 when extended. Counterpoise 608 is
connected to second output terminal 636.
FIG. 8B illustrates third antenna 800 in its retracted state. Here,
composite radiator 812 is retracted into casing 602, leaving only
second radiating element 810 protruding out of casing 602. In this
state, connecting element 806 electrically isolates first radiating
element 804 and second radiating element 810. Therefore, in this
position, only second radiating element 810 is connected to first
output terminal 632. First radiating element 804 is connected to
counterpoise 608. Thus, when composite radiator 812 is in its retracted
state, first radiating element 804 acts as a counterpoise to second
radiating element 810.
According to the present invention, each balanced, retractable
dipole antenna has a total length. This total length is the sum
of two components. The first component is the combined length of
radiators transmitting the signal carried on first output terminal
632. The second component is the length of counterpoise 608, along
with the length of any radiators, that are transmitting the signal
carried on second output terminal 636. In a preferred embodiment,
this total length is the same in both the extended and retracted
states. For example, when first antenna 600 is in its extended state,
the total length of first antenna 600 is the combined length of
first radiator 604 and counterpoise 608. However, when first antenna
600 is in its retracted state, where first radiator 604 is acting
as a counterpoise, the total length of antenna 600 is the combined
length of second radiator 606 and first radiator 604. Both of these
total lengths are substantially equal. Likewise, this principle
applies for second antenna 700, third antenna 800, and other embodiments
of balanced, retractable dipole antennas according to the present
invention.
In a preferred embodiment, total length is .lambda./2, where .lambda.
is a wavelength corresponding to an operating frequency. However,
other total lengths can be used, such as, .lambda., .lambda./4,
etc. In one embodiment, total length is sized to operate over a
cellular frequency band (approximately 900 MHz). In another embodiment,
total length is sized to operate over a PCS frequency band (approximately
1.9 GHz).
Although, the balanced, retractable dipole antennas described according
to the present invention have been described for use in mobile phones,
the underlying concept behind the present invention can be adapted
to other communications devices. Furthermore, antennas described
herein are capable of both signal transmission and signal reception.
FIG. 9 illustrates a balun 900 in accordance with one embodiment.
Balun 900 receives a single ended, unbalanced signal from a signal
source and outputs a balanced signal to a dipole antenna. Balun
900 comprises two inductors 904, 908 and two capacitors 912, 916.
Inductor 904 and capacitor 912 are connected at one end to a signal
source 920. Inductor 908 is connected at one end to capacitor 912
while the other end of inductor 908 is grounded. Capacitor 916 is
connected at one end to inductor 904 while the other end of capacitor
916 is grounded. Output signals 924 and 928 are balanced and are
phase shifted from each other by 180 degrees.
FIG. 10 illustrates a balun 1000 in accordance with another embodiment.
Balun 1000 comprises a power splitter 1004 that receives a single
ended output from a signal source 1024 and outputs a balanced signal
at output terminals 1008 and 1012. An inductor or choke 1016 is
connected in series to an output terminal 1012. Output terminal
1008 is connected to a radiator 1030, while output 1012 is connected
to a counterpoise 1020 through inductor 1016.
The function of the power splitter 1004 is to split a signal from
signal source 1024 into two signals each having an equal magnitude.
The first signal is provided to radiator 1030. The second signal
is phase shifted 180.degree. by inductor 1016 and the phase shifted
signal is then provided to counterpoise 1020. Baluns 900 and 1000
are described as illustrative examples only.
FIG. 11 illustrates a folded balun 1100 that allows direct connection
of a coaxial line 1102 to a dipole antenna 1108. A coax outer conductor
1112 is connected to a pole 1116 fed from a center conductor 1120.
Coax 1112 runs alongside a feeder coax 1104 for a quarter wavelength.
Another pole 1128 connects directly to the shield of feeder coax
1104. While a few selected baluns have been described, it will become
apparent to persons skilled in the art that other types of baluns
can be easily used in the present invention.
While various embodiments of the present invention have been described
above, it should be understood that they have been presented by
way of example only, and not limitation. Thus, the breadth and scope
of the present invention should not be limited by any of the above-described
exemplary embodiments, but should be defined only in accordance
with the following claims and their equivalents.
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