Note: Descriptions are shown in the official language in which they were submitted.
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TRANSMISSION LINE FOR MOBILE ELECTRONIC DEVICE
FIELD
[0001] The specification relates generally to mobile electronic devices,
and
specifically to a transmission line for a mobile electronic device.
BACKGROUND
[0002] Mobile electronic devices, such as smartphones, are generally
becoming more compact. In addition, there is an increased demand from
consumers for smartphones and other devices without external antennas.
Providing internal antennas, or at least antennas that do not extend from the
main body of the devices, is challenging as the antennas tend to be located
closely to other components that may interfere with antenna performance.
[0003] In addition, the housings of smartphones can include metal
components which also interfere with antenna performance. Further, the
introduction of network technologies such as LTE, which employ lower
frequencies, can heighten the difficulties in obtaining acceptable performance
from smaller antennas.
GENERAL
[0004] According to an aspect of the specification, a mobile electronic
device
is provided, comprising: an electrical ground member supporting at least one
antenna; a housing containing the electrical ground member and having a
conductive ring defining the perimeter of the housing; and a conductive tuning
member disposed between the conductive ring and the electrical ground
member, for transforming an impedance between the electrical ground member
and the conductive ring; wherein the conductive tuning member is connected to
the conductive ring by a first short, and to the electrical ground member by a
second short.
[0005] According to another aspect of the specification, a method is
provided,
comprising: fastening a conductive tuning member between a conductive ring
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defining a perimeter of a housing of a mobile electronic device, and an
electrical
ground member contained within the housing; selecting a first short location
for
connecting the conductive tuning member to the conductive ring; and selecting
a
second short location for connecting the conductive tuning member to the
electrical ground member.
BRIEF DESCRIPTIONS OF THE DRAWINGS
[0006] Embodiments are described with reference to the following
figures, in
which:
[0007] Figure 1 depicts a mobile electronic device, according to a non-
limiting
embodiment;
[0008] Figure 2 depicts certain internal components of the mobile
electronic
device of Figure 1, according to a non-limiting embodiment;
[0009] Figure 3 depicts a cross sectional view of the mobile electronic
device
of Figure 1, according to a non-limiting embodiment;
[0010] Figure 4 depicts a partial view of the cross section of Figure 3,
according to a non-limiting embodiment;
[0011] Figure 5 depicts the open space performance of an antenna of the
device of Figure 1, according to a non-limiting embodiment;
[0012] Figure 6 depicts the performance of the antenna of the device of
Figure 1 when installed in the device of Figure 1, according to a non-limiting
embodiment;
[0013] Figure 7 depicts the performance of the antenna of the device of
Figure 1 when a conductive tuning member is provided, according to a non-
limiting embodiment;
[0014] Figure 8 depicts the conductive tuning member of Figure 4,
according
to a non-limiting embodiment; and
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[0015] Figures 9A, 9B, 10A, 10B, 11A, 11B and 12 depict the performance
of
the antenna of the device of Figure 1 for various configurations of the
conductive
tuning member of Figure 4, according to a non-limiting embodiment.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0016] Figure 1 depicts a mobile electronic device 100, which in the
present
embodiment is based on the computing environment and functionality of a hand-
held wireless communication device. It will be understood, however, that
mobile
electronic device 100 is not limited to a hand-held wireless communication
device. Other mobile electronic devices are also contemplated, such as
cellular
phones, smart phones, Personal Digital Assistants ("PDAs"), media or MP3
players, tablet computers, laptop computers, and the like.
[0017] Mobile electronic device 100 includes a housing 104 which
supports
the various other components of mobile electronic device 100. Housing 104
includes a conductive (that is, electrically conductive) ring 108 (also
referred to
herein simply as "ring 108") defining the perimeter of housing 104. In the
embodiment shown in Figure 1, ring 108 extends continuously around the
perimeter of housing 104. Ring 108 can be constructed of any electrically
conductive material, including any one or combination of aluminum and other
metals. The remaining portion of housing 104 can be constructed of any
suitable
material, or combination of materials, including without limitation plastics
(e.g.
Polycarbonate/Acrylonitrile Butadiene Styrene ("PC/ABS")) and metals (e.g.
aluminum or other metals).
[0018] Mobile electronic device 100 also includes one or more output
devices,
including without limitation a display 112 and a speaker 116. Other output
devices are also contemplated but not shown, such as a Light Emitting Diode
(LED) indicator, a vibrating motor, and the like.
[0019] Mobile electronic device 100 additionally includes one or more
input
devices, including without limitation a microphone 120, a keypad 124. Keypad
124 can be a full QWERTY keyboard or a reduced QWERTY keyboard. Mobile
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electronic device can also include a pointing device such as a touchpad 128.
It is
contemplated that other combinations of input and output devices than those
shown in Figure 1 can be provided. For example, touchpad 128 can be replaced
with a trackball. As a further example, one or both of keypad 124 and touchpad
128 can be omitted, and a touch screen input device can be integrated with
display 112. In still another example, the touch screen input device can be
provided in addition to keypad 124 and touchpad 128. In a further example, one
or more function keys can be provided in addition to keypad 124. Further
combinations and variations will occur to those skilled in the art.
[0020] Referring now to Figure 2, certain internal components of mobile
electronic device 100 are shown. Mobile electronic device 100 includes a
processor 132 interconnected with a computer readable storage medium (that is,
a non-transitory medium) in the form of a memory 136. Memory 136 can be any
suitable combination of volatile (e.g. Random Access Memory ("RAM")) and non-
volatile (e.g. read only memory ("ROM"), Electrically Erasable Programmable
Read Only Memory ("EEPROM"), flash memory, magnetic computer storage
device, or optical disc) memory.
[0021] Mobile electronic device 100 also includes a communications
interface
140 interconnected with processor 132. Communications interface 140 allows
mobile electronic device 100 to communicate with other computing devices via a
link 142 and a network 144. Network 144 can include any suitable combination
of
wired and/or wireless networks, including but not limited to a Wide Area
Network
("WAN") such as the Internet, a Local Area Network ("LAN"), cell phone
networks, WiFi networks, WiMax networks and the like. Link 142 can therefore
be a wireless link based on Global System for Mobile communications ("GSM"),
General Packet Radio Service ("GPRS"), Enhanced Data rates for GSM
Evolution ("EDGE"), and the third-generation mobile communication system (3G),
Institute of Electrical and Electronic Engineers ("IEEE") 802.11 (WiFi), Long
Term
Evolution (LIE), or other wireless protocols. In other embodiments, link 142
can
be a wired link.
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[0022] Communications interface 140 is selected for compatibility with
link
142 and network 144. Communications interface 140 thus includes one or more
transmitter/receiver assemblies, or antennas, and associated circuitry. For
example, as shown in Figure 2, communications interface 140 includes an
antenna 150, and can also include processing circuitry for controlling antenna
150. Further discussion of antenna 150 will be provided below.
[0023] The above-mentioned input and output devices of mobile electronic
device 104 can also be seen in Figure 2. In particular, microphone 120, keypad
124 and touchpad 128 are shown interconnected with processor 132. The input
devices are configured to receive input and provide data representative of
such
input to processor 132. Thus, keypad 124 can receive input in the form of the
depression of one or more keys, and can then provide data representative of
such input to processor 132. The data provided to processor 132 can be, for
example, an American Standard Code for Information Interchange (ASCII) value
for each of the depressed keys. Touch pad 128 can receive input in the form of
depression of touch pad 128 or swipe gestures along the surface of touch pad
128, and can then provide data representative of such input to processor 132
in
the form of, for example, coordinates representing the location of a virtual
cursor.
[0024] Display 112 is also shown interconnected with processor 132.
Display
112 includes display circuitry 152 controllable by processor 132 for
generating
interfaces including representations of data and/or applications maintained in
memory 136. Display 112 includes a flat panel display comprising any one of,
or
any suitable combination of, a Liquid Crystal Display (LCD), a plasma display,
an
Organic Light Emitting Diode (OLED) display, and the like. Circuitry 152 can
thus
include any suitable combination of display buffers, transistors, LCD cells,
plasma cells, phosphors, LEDs and the like. When the input devices of mobile
electronic device 104 include a touch screen input device as discussed above,
the touch screen can be integrated with display 112.
[0025] The various components of mobile electronic device 100 are
interconnected, for example via a communication bus. Mobile electronic device
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100 can be powered by a battery (not shown), though it will be understood that
in
some non-limiting embodiments, mobile electronic device 100 can be supplied,
in
addition to or instead of the battery, with electricity by a wired connection
to a
wall outlet or other power source.
[0026] Turning now to Figure 3, a cross-section of mobile electronic device
100 is shown, taken as indicated by the line "X3-X3" in Figure 1. As seen in
Figure 3, mobile electronic device 100 includes an electrical ground member
300
which supports or is otherwise coupled to antenna 150. Antenna 150 can take a
wide variety of configurations, depending on intended application of antenna
150
(that is, the intended nature of link 142 and network 144 with which mobile
electronic device 100 will interact).
[0027] In the present example, electrical ground member 300 is a printed
circuit board (PCB), and will therefore be referred to herein as PCB 300. PCB
300 supports various internal components of mobile electronic device,
including
processor 132. PCB 300 can also be electrically connected to other components
of mobile electronic device 100, such as display 112, as well as the other
input
and output devices of mobile electronic device.
[0028] Also seen in Figure 3 is conductive ring 108, which surrounds PCB
300
and antenna 150. As will now be apparent, display 112 is also conductive and
ring 108 in combination with display 112 can therefore form a conductive open
box around antenna 150. Further, display 112 can be electrically connected to
ring 108 in some examples. In other words, ring 108 and display 112 can
present
obstacles to radiation generated by antenna 150.
[0029] Mobile electronic device 100 also includes a conductive tuning
member 304 disposed between ring 108 and PCB 300. In general, conductive
tuning member 304 is for transforming an impedance between electrical ground
member (e.g. PCB) 300 and conductive ring 108. Tuning member 304 is
connected at a first end (i.e. shorted) to ring 108 by a first short 308, and
to PCB
300 (specifically, to a ground plane of PCB 300) by a second short 312. Second
short 312, as seen in Figure 3, need not be located at the second end
(opposite
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the first end) of tuning member 304. Instead, second short 312 can be located
at
a point along tuning member 304 between the first and second ends of tuning
member 304, such that the second end of tuning member 304 is an open end. In
other examples, however, second short 312 can be located at second end 804 of
tuning member 304.
[0030] Turning to Figure 4, tuning member 304 is shown in greater detail
in a
partial view of the cross-section of Figure 3. As discussed above, Figure 4
shows
a portion of ring 108, as well as tuning member 304 and PCB 300 and shorts 308
and 312 between ring 108 and PCB 300.
[0031] In the present example, tuning member 304 is a transmission line
formed from a conductive material, such as copper; tuning member 304 will
therefore also be referred to as transmission line 304 herein. In particular,
transmission line 304 can be a conductive sheet, arranged substantially in
parallel to ring 108, on the interior of ring 108 in a space defined between
ring
108 and PCB 300. It is contemplated that transmission line 304 need not be
exactly parallel to ring 108. In other words, Figure 4 shows an edge of
transmission line 304, and the faces of transmission line 104 lie orthogonally
to
the page on which Figure 4 appears. It is contemplated that the size of the
space
between ring 108 and PCB 300 has been exaggerated for illustrative purposes in
Figure 4; the space can be smaller (or greater) than shown.
[0032] Transmission line 304 is connected to ring 108 by way of a
fastener
400, such as a strip of insulating (that is, non electrically conductive)
tape. Other
suitable fasteners can also be employed, as will now be apparent to those
skilled
in the art. In general, any suitable fastener may be employed to position
transmission line 304 such that transmission line 304 is electrically
connected to
ring 108 and PCB 300 by shorts 308 and 312 (and, as will be discussed in
greater detail below, any additional connections between transmission line 304
and PCB 300) but is otherwise electrically isolated from ring 108 and PCB 300.
It
is contemplated that in some examples, further shorts in addition to shorts
308
and 312 may be provided.
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[0033] When mobile electronic device 100 (and, more specifically,
antenna
150) is in operation, transmission line 304 alters the impedance between PCB
300 and ring 108, in comparison to the impedance between PCB 300 and ring
108 in the absence of transmission line 304. Thus, the flow of current in PCB
300
and transmission line 304 is altered. As will be appreciated by those skilled
in the
art, bodies of material, such as the ground plane of PCB 300 and ring 108, can
act as radiators themselves, particularly at low frequencies, and can
therefore
interfere with the radiation from antenna 150. The flow of electrical current
through ring 108 and PCB 300 determines the nature and extent of any
interference. It has been determined that in the absence of transmission line
304,
electrical current flows through ring 108 in a direction opposite from the
current
flow in the nearby edges of PCB 300, which can negatively affect the
performance of antenna 150. Therefore, the alteration of current flow caused
by
transmission line 304 can lead to reduced interference by ring 108 and
improved
antenna performance.
[0034] To illustrate the effects of transmission line 304 discussed
above,
reference is made to Figures 5-7, which each plot the S11 (return loss)
performance of antenna 150 versus the frequency at which antenna 150 is
configured to radiate. In particular, Figure 5 shows the free-space
performance of
an example antenna 150. In other words, Figure 5 shows the performance of
antenna 150 when antenna 150 is not installed within mobile electronic device
100. Antenna 150 can be, for example, an antenna as set out in PCT Application
No. PCT/CA2011/050508, filed August 19, 2011.
[0035] Turning to Figure 6, the performance of antenna 150 is shown when
antenna 150 is installed within housing 104 of mobile electronic device 100 as
discussed above, but in the absence of transmission line 304. As seen in
Figure
6, antenna 150 becomes narrow-banded (about -2 dB each side), in comparison
with the free space performance shown in Figure 5. However, an additional
resonance also appears in Figure 6, at about 700MHz.
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[0036]
Turning now to Figure 7, the performance of antenna 150 is shown
when antenna 150 is installed within housing 104 of mobile electronic device
100, and when transmission line 304 is connected as shown in Figures 3 and 4.
As seen in Figure 7, the bandwidth of antenna 150 is broadened, and a 698MHz
to 746MHz band (suitable for use in LTE networks, for example) can also be
obtained. In addition, antenna 150 can cover the GSM 850/900MHz bands.
[0037]
Therefore, it will now be apparent to those skilled in the art that
transmission line 304, when connected to ring 108 and PCB 300, can improve
the performance of antenna 150 by altering the impedance between ring 108 and
PCB 300 and thereby disrupting the current flow between PCB 300 and ring 108.
[0038] The effect of transmission line 304 on the performance of antenna 150
is determined at least in part by the configuration of transmission line and
shorts
308, 312. Referring now to Figure 8, the configuration of transmission line
304
will be discussed in greater detail.
[0039]
Figure 8 depicts transmission line 304 and shorts 308 and 312 in
isolation, for illustrative purposes. As discussed above, short 308 provides
the
electrical connection between transmission line 304 and ring 108 (not shown in
Figure 8), while short 312 provides the electrical connection between
transmission line 304 and PCB 300 (not shown in Figure 8). Transmission line
304 has first and second ends, labelled as ends 800 and 804 respectively in
Figure 8.
[0040]
The parameters determining the effect of transmission line 304 include
the distance between first short 308 and second short 312, denoted "L1" in
Figure 8. The parameters determining the effect of transmission line 304 also
include the total length of transmission line 304, meaning the distance
between
first end 800 and second end 804, denoted "L2" in Figure 8.
[0041] In the present example, first short 308 is adjacent first end
800 of
transmission line 304. In other words, first short 308 is located close to,
but not
necessarily exactly at, first end 800 (although first short 308 can be exactly
at
first end 800 in some examples).
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[0042] The parameters discussed above can be selected to influence the
performance of antenna 150 as desired (for example, based on the nature of
network 144 with which mobile electronic device 100 will be interacting, and
on
the nature of link 142 over which such interactions will be carried). An
example
mobile electronic
device 100 will now be discussed, in conjunction with various
values for the above parameters and their effects on antenna performance. It
is
contemplated that transmission line 304 or other conductive tuning members can
be used with a wide range of other configurations for mobile electronic device
100; the discussion below is non-limiting and provided for illustrative
purposes.
[0043] The example
mobile electronic device 100 to be discussed below is as
shown in Figures 1 and 3. The example mobile electronic device 100 has
external dimensions of 108mm (height) x 60mm (width) x 8mm (depth). The
height of antenna 150 is about 3.2mm and the ground clearance of antenna 150
is about 10mm; the thickness of PCB 300 is about 0.8mm.
[0044] Referring
now to Figures 9A-11B, the performance of antenna 150 is
shown for various values of the parameter L1 (that is, the distance between
the
first short and the second short. In particular, Figure 9A shows antenna
performance with L1=5mm; Figure 9B shows antenna performance with
L1=15mm; Figure 10A shows antenna performance with L1=25mm; Figure 10B
shows antenna performance with L1=40mm; Figure 11A shows antenna
performance with L1=55mm; and Figure 11B shows antenna performance with
L1=70mm.
[0045] As seen in the above-mentioned drawings, increasing L1 from 5mm to
15mm and then 25mm results in the resonances at about 700MHz and about
830MHz, which are partially overlapping (forming a "joint resonance") in
Figure
9A, separating such that, in Figure 10A those two resonances appear instead at
about 680MHz and about 950MHz.
[0046] At L1=40mm
(shown in Figure 10B), an additional minor resonance
appears, at about 780MHz. The impedance-matching of this additional
resonance increases as L1 is increased to 55mm and then to 70mm, and also
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shifts lower in frequency. Thus, as shown in Figure 11B, the additional
resonance
has shifted to about 740MHz, in addition to becoming better impedance-matched
(that is, forming a larger negative spike in S11 performance).
[0047] It is contemplated that the value for L1 can therefore be chosen
from
among those discussed above, or a variety of other values, depending on the
final performance required of antenna 150. For example, an L1 value of 5mm
may provide improved performance in the LTE 698-798MHz band. As another
example, an L1 value of 40mm may provide improved performance in the
CDMA850/GSM900MHz band. In addition, as L1 is increased beyond 40mm, it
may be possible to obtain acceptable antenna performance in all three of the
above-mentioned bands.
[0048] Turning now to Figure 12, the performance of antenna 150 is shown
for various values of the parameter L2 (that is, the total length of
transmission
line 304). In the experimental set-up used to obtain the measurements shown in
Figure 12, first short 308 is adjacent first end 800 and second short 312 is
adjacent second end 804. Thus, in this particular example, L1 and L2 are equal
to each other.
[0049] As seen in Figure 12, an L2 value of 10mm is illustrated by curve
1200;
an L2 value of 20mm is illustrated by curve 1204; an L2 value of 30mm is
illustrated by curve 1208; an L2 value of 40mm is illustrated by curve 1212;
and
an L2 value of 50mm is illustrated by curve 1216. At L2=10mm, resonances at
about 870MHz and 680Mhz are present. As L2 increases towards 50mm, an
additional resonance appears, and shifts in frequency, beginning at about
830MHz for curve 1208 (L2=30mm) and decreasing to about 760MHz for curve
1216 (L2=50mm).
[0050] From the above, a method of tuning mobile electronic device 100
will
now be apparent to those skilled in the art. The method can include fastening
conductive tuning member 304 (such as a transmission line) between conductive
ring 108 and electrical ground member 300 (such as a PCB). Following the
attachment of conductive tuning member 304, the method can include selecting
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first and second short locations for connecting conductive tuning member 304
to
conductive ring 108 and electrical ground member 300, respectively. The method
can further include measuring the performance of antenna 150, and adjusting
the
selected parameters based on the results of the measuring.
[0051] Variations to the above are contemplated. For example, although
conductive tuning member 304 is shown inside ring 108, it is possible to mount
conductive tuning member externally to ring 108 in some examples.
[0052] In other variations, conductive tuning member 304 need not be a
conductive sheet as described. Indeed, a variety of tuning member structures
are
contemplated, including a coax line, buried microstrip lines, and the like.
Additional tuning member geometries will now occur to those skilled in the
art.
[0053] In an additional variation, in some examples conductive tuning
member
304 can be connected to electrical ground member 300 at a plurality of
locations,
instead of the single second short 312 discussed above. The plurality of
locations
can be connected to electrical ground member 300 via ON/OFF pins, which can
be set to either closed (e.g. shorted) or open positions to select the
parameter
Ll. The setting of such pins or other suitable switching components, in some
examples, can be conducted automatically by processor 132 based on the
currently active operation frequency of antenna 150.
[0054] In another variation, rather than providing ON/OFF pins on
electrical
ground member 300, electrical grounding member 300 can carry discrete
components or other circuitry, such as LC circuits (that is, "resonant
circuits") at
each of the locations at which conductive tuning member 304 is connected to
electrical ground member 300. As will now be apparent to those skilled in the
art,
LC circuits can be selected for frequency response, such that at some
frequencies, the LC circuit behaves as an open circuit while at other
frequencies
the LC circuit behaves as a short. Thus, which of the plurality of short
locations
are "active" (that is, which locations are actually shorting conductive tuning
member 304 to electrical ground member 300) at any given time depends on the
operating frequency of antenna 150.
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[0055] Persons skilled in the art will appreciate that there are yet more
alternative implementations and modifications possible for implementing the
embodiments, and that the above implementations and examples are only
illustrations of one or more embodiments. The scope, therefore, is only to be
limited by the claims appended hereto.
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