U.S. patent application number 13/620188 was filed with the patent office on 2013-01-10 for bezel gap antennas.
Invention is credited to Ruben Caballero, Robert J. Hill, Nanbo Jin, Qingxiang Li, Mattia Pascolini, Robert W. Schlub, Juan Zavala.
Application Number | 20130009828 13/620188 |
Document ID | / |
Family ID | 43828008 |
Filed Date | 2013-01-10 |
United States Patent
Application |
20130009828 |
Kind Code |
A1 |
Pascolini; Mattia ; et
al. |
January 10, 2013 |
Bezel Gap Antennas
Abstract
Electronic devices are provided that contain wireless
communications circuitry. The wireless communications circuitry may
include radio-frequency transceiver circuitry and antenna
structures. A parallel-fed loop antenna may be formed from portions
of an electronic device bezel and a ground plane. The antenna may
operate in multiple communications bands. An impedance matching
circuit for the antenna may be formed from a parallel-connected
inductive element and a series-connected capacitive element. The
bezel may surround a peripheral portion of a display that is
mounted to the front of an electronic device. The bezel may contain
a gap. Antenna feed terminals for the antenna may be located on
opposing sides of the gap. The inductive element may bridge the gap
and the antenna feed terminals. The capacitive element may be
connected in series between one of the antenna feed terminals and a
conductor in a transmission line located between the transceiver
circuitry and the antenna.
Inventors: |
Pascolini; Mattia;
(Campbell, CA) ; Hill; Robert J.; (Salinas,
CA) ; Zavala; Juan; (Watsonville, CA) ; Jin;
Nanbo; (Sunnyvale, CA) ; Li; Qingxiang;
(Mountain View, CA) ; Schlub; Robert W.;
(Campbell, CA) ; Caballero; Ruben; (San Jose,
CA) |
Family ID: |
43828008 |
Appl. No.: |
13/620188 |
Filed: |
September 14, 2012 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
12630756 |
Dec 3, 2009 |
8270914 |
|
|
13620188 |
|
|
|
|
Current U.S.
Class: |
343/702 |
Current CPC
Class: |
H01Q 7/00 20130101; H01Q
13/10 20130101; H01Q 9/42 20130101; H01Q 1/243 20130101 |
Class at
Publication: |
343/702 |
International
Class: |
H01Q 1/24 20060101
H01Q001/24 |
Claims
1. An electronic device, comprising: a housing having a periphery;
a conductive structure that runs along the periphery and that has
at least one gap on the periphery; and an antenna formed at least
partly from the conductive structure.
2. The electronic device defined in claim 1 further comprising a
display, wherein the conductive structure comprises a bezel for the
display.
3. The electronic device defined in claim 2 further comprising
first and second antenna feed terminals for the antenna, wherein
the antenna comprises a parallel-fed loop antenna.
4. The electronic device defined in claim 3 further comprising: a
substantially rectangular ground plane, wherein a portion of the
loop antenna is formed from the substantially rectangular ground
plane.
5. The electronic device defined in claim 4 wherein the second
antenna feed terminal is connected to the substantially rectangular
ground plane.
6. The electronic device defined in claim 4 wherein the second
antenna feed terminal is connected to the substantially rectangular
ground plane and wherein the first antenna feed terminal is
electrically connected to the bezel.
7. The electronic device defined in claim 1 wherein the conductive
structure forms a conductive loop path, the electronic device
further comprising an inductor interposed in the conductive loop
path.
8. The electronic device defined in claim 1 further comprising
first and second antenna feed terminals for the antenna, wherein
the first and second antenna feed terminals are located on opposing
sides of the gap.
9. The electronic device defined in claim 1 further comprising a
transmission line having first and second conductors respectively
connected to first and second antenna feed terminals for the
antenna and a capacitor between the first conductor of the
transmission line and the first antenna feed terminal.
9. The electronic device defined in claim 1 further comprising
first and second antenna feed terminals for the antenna and an
inductor coupled between the first and second antenna feed
terminals.
10. An electronic device, comprising: a housing having a periphery;
a ground plane in the housing; a conductive structure that runs
along the periphery and that has at least one gap on the periphery;
an open antenna slot formed partly by the conductive structure and
partly by the ground plane, wherein the open antenna slot has an
opening formed by the gap.
11. The electronic device defined in claim 10 further comprising: a
closed antenna slot formed partly by the conductive structure and
partly by the ground plane.
12. The electronic device defined in claim 11 further comprising:
an L-shaped conductive region that forms edges of both the open and
closed antenna slots and that is disposed between the open and
closed antenna slots.
13. The electronic device defined in claim 12 further comprising:
radio-frequency transceiver circuitry; first and second antenna
feed terminals; and a transmission line having positive and ground
conductors, wherein the transmission line is coupled between the
radio-frequency transceiver circuitry and the first and second
antenna feed terminals.
14. The electronic device defined in claim 13 wherein the first
antenna feed terminal is located on the ground plane and wherein
the second antenna feed terminal is located on the L-shaped
conductive region.
15. The electronic device defined in claim 14 further comprising a
display, wherein the conductive structure comprises a bezel for the
display.
16. Wireless circuitry, comprising: a ground plane; a conductive
electronic device bezel having a gap; a solid dielectric that fills
the gap; and first and second antenna feed terminals, wherein the
ground plane, bezel, and first and second antenna feed terminals
form a parallel-fed loop antenna.
17. The wireless circuitry defined in claim 16 wherein the
parallel-fed loop antenna comprises an open slot, wherein the open
slot has an opening formed by the gap in the conductive electronic
device bezel.
18. The wireless circuitry defined in claim 17 wherein the first
and second antenna feed terminals are located on opposing sides of
the gap.
19. The wireless circuitry defined in claim 18 wherein the
parallel-fed loop antenna further comprises a closed slot, wherein
the open and closed slots are each partly defined by the conductive
electronic device bezel and by the ground plane, the wireless
circuitry further comprising L-shaped conductive structures
separating the open and closed slots.
20. The wireless circuitry defined in claim 19 wherein the open
slot has approximately rectangular shaped interior region and
wherein the open slot has an approximately L-shaped interior
region.
Description
[0001] This application is a continuation of patent application
Ser. No. 12/630,756, filed Dec. 3, 2009, which is hereby
incorporated by referenced herein in its entirety. This application
claims the benefit of and claims priority to patent application
Ser. No. 12/630,756, filed Dec. 3, 2009.
BACKGROUND
[0002] This relates generally to wireless communications circuitry,
and more particularly, to electronic devices that have wireless
communications circuitry.
[0003] Electronic devices such as handheld electronic devices are
becoming increasingly popular. Examples of handheld devices include
handheld computers, cellular telephones, media players, and hybrid
devices that include the functionality of multiple devices of this
type.
[0004] Devices such as these are often provided with wireless
communications capabilities. For example, electronic devices may
use long-range wireless communications circuitry such as cellular
telephone circuitry to communicate using cellular telephone bands
at 850 MHz, 900 MHz, 1800 MHz, and 1900 MHz (e.g., the main Global
System for Mobile Communications or GSM cellular telephone bands).
Long-range wireless communications circuitry may also handle the
2100 MHz band. Electronic devices may use short-range wireless
communications links to handle communications with nearby
equipment. For example, electronic devices may communicate using
the WiFi.RTM. (IEEE 802.11) bands at 2.4 GHz and 5 GHz and the
Bluetooth.degree. band at 2.4 GHz.
[0005] To satisfy consumer demand for small form factor wireless
devices, manufacturers are continually striving to implement
wireless communications circuitry such as antenna components using
compact structures. At the same time, it may be desirable to
include conductive structures in an electronic device such as metal
device housing components. Because conductive components can affect
radio-frequency performance, care must be taken when incorporating
antennas into an electronic device that includes conductive
structures.
[0006] It would therefore be desirable to be able to provide
improved wireless communications circuitry for wireless electronic
devices.
SUMMARY
[0007] Electronic devices may be provided that include antenna
structures. An antenna may be configured to operate in first and
second communications bands. An electronic device may contain
radio-frequency transceiver circuitry that is coupled to the
antenna using a transmission line. The transmission line may have a
positive conductor and a ground conductor. The antenna may have a
positive antenna feed terminal and a ground antenna feed terminal
to which the positive and ground conductors of the transmission
line are respectively coupled.
[0008] The electronic device may have a rectangular periphery. A
rectangular display may be mounted on a front face of the
electronic device. The electronic device may have a rear face that
is formed form a plastic housing member. Conductive sidewall
structures may run around the periphery of the electronic device
housing and display. The conductive sidewall structures may serve
as a bezel for the display.
[0009] The bezel may include at least one gap. The gap may be
filled with a solid dielectric such as plastic. The antenna may be
formed from the portion of the bezel that includes the gap and a
portion of a ground plane. To avoid excessive sensitivity to touch
events, the antenna may be fed using a feed arrangement that
reduces electric field concentration in the vicinity of the gap. An
impedance matching network may be formed that provides satisfactory
operation in both the first and second bands.
[0010] The impedance matching network may include an inductive
element that is formed in parallel with the antenna feed terminals
and a capacitive element that is formed in series with one of the
antenna feed terminals.
[0011] The inductive element may be formed from a transmission line
inductive structure that bridges the antenna feed terminals. The
capacitive element may be formed from a capacitor that is
interposed in the positive feed path for the antenna. The capacitor
may, for example, be connected between the positive ground
conductor of the transmission line and the positive antenna feed
terminal.
[0012] Further features of the invention, its nature and various
advantages will be more apparent from the accompanying drawings and
the following detailed description of the preferred
embodiments.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a perspective view of an illustrative electronic
device with wireless communications circuitry in accordance with an
embodiment of the present invention.
[0014] FIG. 2 is a schematic diagram of an illustrative electronic
device with wireless communications circuitry in accordance with an
embodiment of the present invention.
[0015] FIG. 3 is a cross-sectional end view of an illustrative
electronic device with wireless communications circuitry in
accordance with an embodiment of the present invention.
[0016] FIG. 4 is a diagram of an illustrative antenna in accordance
with an embodiment of the present invention.
[0017] FIG. 5 is a schematic diagram of an illustrative series-fed
loop antenna that may be used in an electronic device in accordance
with an embodiment of the present invention.
[0018] FIG. 6 is a graph showing how an electronic device antenna
may be configured to exhibit coverage in multiple communications
bands in accordance with an embodiment of the present
invention.
[0019] FIG. 7 is a schematic diagram of an illustrative
parallel-fed loop antenna that may be used in an electronic device
in accordance with an embodiment of the present invention.
[0020] FIG. 8 is a diagram of an illustrative parallel-feed loop
antenna with an inductance interposed in the loop in accordance
with an embodiment of the present invention.
[0021] FIG. 9 is a diagram of an illustrative parallel-fed loop
antenna having an inductive transmission line structure in
accordance with an embodiment of the present invention.
[0022] FIG. 10 is a diagram of an illustrative parallel-fed loop
antenna with an inductive transmission line structure and a
series-connected capacitive element in accordance with an
embodiment of the present invention.
[0023] FIG. 11 is a Smith chart illustrating the performance of
various electronic device loop antennas in accordance with
embodiments of the present invention.
DETAILED DESCRIPTION
[0024] Electronic devices may be provided with wireless
communications circuitry. The wireless communications circuitry may
be used to support wireless communications in multiple wireless
communications bands. The wireless communications circuitry may
include one or more antennas.
[0025] The antennas can include loop antennas. Conductive
structures for a loop antenna may, if desired, be formed from
conductive electronic device structures. The conductive electronic
device structures may include conductive housing structures. The
housing structures may include a conductive bezel. Gap structures
may be formed in the conductive bezel. The antenna may be
parallel-fed using a configuration that helps to minimize
sensitivity of the antenna to contact with a user's hand or other
external object.
[0026] Any suitable electronic devices may be provided with
wireless circuitry that includes loop antenna structures. As an
example, loop antenna structures may be used in electronic devices
such as desktop computers, game consoles, routers, laptop
computers, etc. With one suitable configuration, loop antenna
structures are provided in relatively compact electronic devices in
which interior space is relatively valuable such as portable
electronic devices.
[0027] An illustrative portable electronic device in accordance
with an embodiment of the present invention is shown in FIG. 1.
Portable electronic devices such as illustrative portable
electronic device 10 may be laptop computers or small portable
computers such as ultraportable computers, netbook computers, and
tablet computers. Portable electronic devices may also be somewhat
smaller devices. Examples of smaller portable electronic devices
include wrist-watch devices, pendant devices, headphone and
earpiece devices, and other wearable and miniature devices. With
one suitable arrangement, the portable electronic devices are
handheld electronic devices such as cellular telephones.
[0028] Space is at a premium in portable electronic devices.
Conductive structures are also typically present, which can make
efficient antenna operation challenging. For example, conductive
housing structures may be present around some or all of the
periphery of a portable electronic device housing.
[0029] In portable electronic device housing arrangements such as
these, it may be particularly advantageous to use loop-type antenna
designs that cover communications bands of interest. The use of
portable devices such as handheld devices is therefore sometimes
described herein as an example, although any suitable electronic
device may be provided with loop antenna structures, if
desired.
[0030] Handheld devices may be, for example, cellular telephones,
media players with wireless communications capabilities, handheld
computers (also sometimes called personal digital assistants),
remote controllers, global positioning system (GPS) devices, and
handheld gaming devices. Handheld devices and other portable
devices may, if desired, include the functionality of multiple
conventional devices. Examples of multi-functional devices include
cellular telephones that include media player functionality, gaming
devices that include wireless communications capabilities, cellular
telephones that include game and email functions, and handheld
devices that receive email, support mobile telephone calls, and
support web browsing. These are merely illustrative examples.
[0031] Device 10 of FIG. 1 may be any suitable portable or handheld
electronic device. Device 10 includes housing 12 and includes at
least one antenna for handling wireless communications. Housing 12,
which is sometimes referred to as a case, may be formed of any
suitable materials including, plastic, glass, ceramics, composites,
metal, or other suitable materials, or a combination of these
materials. In some situations, parts of housing 12 may be formed
from dielectric or other low-conductivity material, so that the
operation of conductive antenna elements that are located within
housing 12 is not disrupted. In other situations, housing 12 may be
formed from metal elements.
[0032] Device 10 may, if desired, have a display such as display
14. Display 14 may, for example, be a touch screen that
incorporates capacitive touch electrodes. Display 14 may include
image pixels formed form light-emitting diodes (LEDs), organic LEDs
(OLEDs), plasma cells, electronic ink elements, liquid crystal
display (LCD) components, or other suitable image pixel structures.
A cover glass member may cover the surface of display 14. Buttons
such as button 19 may pass through openings in the cover glass.
[0033] Housing 12 may include sidewall structures such as sidewall
structures 16. Structures 16 may be implemented using conductive
materials. For example, structures 16 may be implemented using a
conductive ring member that substantially surrounds the rectangular
periphery of display 14. Structures 16 may be formed from a metal
such as stainless steel, aluminum, or other suitable materials.
One, two, or more than two separate structures may be used in
forming structures 16. Structures 16 may serve as a bezel that
holds display 14 to the front (top) face of device 10. Structures
16 are therefore sometimes referred to herein as bezel structures
16 or bezel 16. Bezel 16 runs around the rectangular periphery of
device 10 and display 14.
[0034] Bezel 16 may have a thickness (dimension TT) of about 0.1 mm
to 3 mm (as an example). The sidewall portions of bezel 16 may be
substantially vertical (parallel to vertical axis V). Parallel to
axis V, bezel 16 may have a dimension TZ of about 1 mm to 2 cm (as
an example). The aspect ratio R of bezel 16 (i.e., the of TZ to TT)
is typically more than 1 (i.e., R may be greater than or equal to
1, greater than or equal to 2, greater than or equal to 4, greater
than or equal to 10, etc.).
[0035] It is not necessary for bezel 16 to have a uniform
cross-section. For example, the top portion of bezel 16 may, if
desired, have an inwardly protruding lip that helps hold display 14
in place. If desired, the bottom portion of bezel 16 may also have
an enlarged lip (e.g., in the plane of the rear surface of device
10). In the example of FIG. 1, bezel 16 has substantially straight
vertical sidewalls. This is merely illustrative. The sidewalls of
bezel 16 may be curved or may have any other suitable shape.
[0036] Display 14 includes conductive structures such as an array
of capacitive electrodes, conductive lines for addressing pixel
elements, driver circuits, etc. These conductive structures tend to
block radio-frequency signals.
[0037] It may therefore be desirable to form some or all of the
rear planar surface of device from a dielectric material such as
plastic.
[0038] Portions of bezel 16 may be provided with gap structures.
For example, bezel 16 may be provided with one or more gaps such as
gap 18, as shown in FIG. 1. Gap 18 lies along the periphery of the
housing of device 10 and display 12 and is therefore sometimes
referred to as a peripheral gap. Gap 18 divides bezel 16 (i.e.,
there is generally no conductive portion of bezel 16 in gap
18).
[0039] As shown in FIG. 1, gap 18 may be filled with dielectric.
For example, gap 18 may be filled with air. To help provide device
10 with a smooth uninterrupted appearance and to ensure that bezel
16 is aesthetically appealing, gap 18 may be filled with a solid
(non-air) dielectric such as plastic. Bezel 16 and gaps such as gap
(and its associated plastic filler structure) may form part of one
or more antennas in device 10. For example, portions of bezel 16
and gaps such as gap 18 may, in conjunction with internal
conductive structures, form one or more loop antennas. The internal
conductive structures may include printed circuit board structures,
frame members or other support structures, or other suitable
conductive structures.
[0040] In a typical scenario, device 10 may have upper and lower
antennas (as an example). An upper antenna may, for example, be
formed at the upper end of device 10 in region 22. A lower antenna
may, for example, be formed at the lower end of device 10 in region
20. The lower antenna may, for example, be formed partly from the
portions of bezel 16 in the vicinity of gap 18.
[0041] Antennas in device 10 may be used to support any
communications bands of interest. For example, device 10 may
include antenna structures for supporting local area network
communications, voice and data cellular telephone communications,
global positioning system (GPS) communications, Bluetooth.degree.
communications, etc. As an example, the lower antenna in region 20
of device 10 may be used in handling voice and data communications
in one or more cellular telephone bands.
[0042] A schematic diagram of an illustrative electronic device is
shown in FIG. 2. Device 10 of FIG. 2 may be a portable computer
such as a portable tablet computer, a mobile telephone, a mobile
telephone with media player capabilities, a handheld computer, a
remote control, a game player, a global positioning system (GPS)
device, a combination of such devices, or any other suitable
portable electronic device.
[0043] As shown in FIG. 2, handheld device 10 may include storage
and processing circuitry 28. Storage and processing circuitry 28
may include storage such as hard disk drive storage, nonvolatile
memory (e.g., flash memory or other
electrically-programmable-read-only memory configured to form a
solid state drive), volatile memory (e.g., static or dynamic
random-access-memory), etc. Processing circuitry in storage and
processing circuitry 28 may be used to control the operation of
device 10. This processing circuitry may be based on one or more
microprocessors, microcontrollers, digital signal processors,
applications specific integrated circuits, etc.
[0044] Storage and processing circuitry 28 may be used to run
software on device 10, such as internet browsing applications,
voice-over-internet-protocol (VOIP) telephone call applications,
email applications, media playback applications, operating system
functions, etc. To support interactions with external equipment,
storage and processing circuitry 28 may be used in implementing
communications protocols. Communications protocols that may be
implemented using storage and processing circuitry 28 include
internet protocols, wireless local area network protocols (e.g.,
IEEE 802.11 protocols--sometimes referred to as WiFi.RTM.),
protocols for other short-range wireless communications links such
as the Bluetooth.RTM. protocol, cellular telephone protocols,
etc.
[0045] Input-output circuitry 30 may be used to allow data to be
supplied to device 10 and to allow data to be provided from device
10 to external devices. Input-output devices 32 such as touch
screens and other user input interface are examples of input-output
circuitry 32. Input-output devices 32 may also include user
input-output devices such as buttons, joysticks, click wheels,
scrolling wheels, touch pads, key pads, keyboards, microphones,
cameras, etc. A user can control the operation of device 10 by
supplying commands through such user input devices. Display and
audio devices such as display 14 (FIG. 1) and other components that
present visual information and status data may be included in
devices 32. Display and audio components in input-output devices 32
may also include audio equipment such as speakers and other devices
for creating sound. If desired, input-output devices 32 may contain
audio-video interface equipment such as jacks and other connectors
for external headphones and monitors.
[0046] Wireless communications circuitry 34 may include
radio-frequency (RF) transceiver circuitry formed from one or more
integrated circuits, power amplifier circuitry, low-noise input
amplifiers, passive RF components, one or more antennas, and other
circuitry for handling RF wireless signals. Wireless signals can
also be sent using light (e.g., using infrared communications).
Wireless communications circuitry 34 may include radio-frequency
transceiver circuits for handling multiple radio-frequency
communications bands. For example, circuitry 34 may include
transceiver circuitry 36 and 38. Transceiver circuitry 36 may
handle 2.4 GHz and 5 GHz bands for WiFi.RTM. (IEEE 802.11)
communications and may handle the 2.4 GHz Bluetooth.RTM.
communications band. Circuitry 34 may use cellular telephone
transceiver circuitry 38 for handling wireless communications in
cellular telephone bands such as the GSM bands at 850 MHz, 900 MHz,
1800 MHz, and 1900 MHz, and the 2100 MHz data band (as examples).
Wireless communications circuitry 34 can include circuitry for
other short-range and long-range wireless links if desired. For
example, wireless communications circuitry 34 may include global
positioning system (GPS) receiver equipment, wireless circuitry for
receiving radio and television signals, paging circuits, etc. In
WiFi.RTM. and Bluetooth.RTM. links and other short-range wireless
links, wireless signals are typically used to convey data over tens
or hundreds of feet. In cellular telephone links and other
long-range links, wireless signals are typically used to convey
data over thousands of feet or miles.
[0047] Wireless communications circuitry 34 may include antennas
40. Antennas 40 may be formed using any suitable antenna types. For
example, antennas 40 may include antennas with resonating elements
that are formed from loop antenna structure, patch antenna
structures, inverted-F antenna structures, slot antenna structures,
planar inverted-F antenna structures, helical antenna structures,
hybrids of these designs, etc. Different types of antennas may be
used for different bands and combinations of bands. For example,
one type of antenna may be used in forming a local wireless link
antenna and another type of antenna may be used in forming a remote
wireless link.
[0048] With one suitable arrangement, which is sometimes described
herein as an example, the lower antenna in device (i.e., an antenna
40 located in region 20 of device 10 of FIG. 1) may be formed using
a loop-type antenna design. When a user holds device 10, the user's
fingers may contact the exterior of device 10. For example, the
user may touch device 10 in region 20. To ensure that antenna
performance is not overly sensitive to the presence or absence of a
user's touch or contact by other external objects, the loop-type
antenna may be fed using an arrangement that does not overly
concentrate electric fields in the vicinity of gap 18.
[0049] A cross-sectional side view of device 10 of FIG. 1 taken
along line 24-24 in FIG. 1 and viewed in direction 26 is shown in
FIG. 3. As shown in FIG. 3, display 14 may be mounted to the front
surface of device 10 using bezel 16. Housing 12 may include
sidewalls formed from bezel 16 and one or more rear walls formed
from structures such as planar rear housing structure 42. Structure
42 may be formed from a dielectric such as plastic or other
suitable materials. Snaps, clips, screws, adhesive, and other
structures may be used in attaching bezel 16 to display 14 and rear
housing wall structure 42.
[0050] Device 10 may contain printed circuit boards such as printed
circuit board 46. Printed circuit board 46 and the other printed
circuit boards in device 10 may be formed from rigid printed
circuit board material (e.g., fiberglass-filled epoxy) or flexible
sheets of material such as polymers. Flexible printed circuit
boards ("flex circuits") may, for example, be formed from flexible
sheets of polyimide.
[0051] Printed circuit board 46 may contain interconnects such as
interconnects 48. Interconnects 48 may be formed from conductive
traces (e.g., traces of gold-plated copper or other metals).
Connectors such as connector 50 may be connected to interconnects
48 using solder or conductive adhesive (as examples). Integrated
circuits, discrete components such as resistors, capacitors, and
inductors, and other electronic components may be mounted to
printed circuit board 46.
[0052] Antenna 40 may have antenna feed terminals. For example,
antenna 40 may have a positive antenna feed terminal such as
positive antenna feed terminal 58 and a ground antenna feed
terminal such as ground antenna feed terminal 54. In the
illustrative arrangement of FIG. 3, a transmission line path such
as coaxial cable 52 may be coupled between the antenna feed formed
from terminals 58 and 54 and transceiver circuitry in components 44
via connector 50 and interconnects 48. Components 44 may include
one or more integrated circuits that implement the transceiver
circuits 36 and 38 of FIG. 2. Connector 50 may be, for example, a
coaxial cable connector that is connected to printed circuit board
46. Cable 52 may be a coaxial cable or other transmission line.
Terminal 58 may be coupled to coaxial cable center connector 56.
Terminal 54 may be connected to a ground conductor in cable 52
(e.g., a conductive outer braid conductor). Other arrangements may
be used for coupling transceivers in device 10 to antenna 40 if
desired. The arrangement of FIG. 3 is merely illustrative.
[0053] As the cross-sectional view of FIG. 3 makes clear, the
sidewalls of housing 12 that are formed by bezel 16 may be
relatively tall. At the same time, the amount of area that is
available to form an antenna in region 20 at the lower end of
device 10 may be limited, particularly in a compact device. The
compact size that is desired form forming the antenna may make it
difficult to form a slot-type antenna shape of sufficient size to
resonant in desired communications bands. The shape of bezel 16 may
tend to reduce the efficiency of conventional planar inverted-F
antennas. Challenges such as these may, if desired, be addressed
using a loop-type design for antenna 40.
[0054] Consider, as an example, the antenna arrangement of FIG. 4.
As shown in FIG. 4, antenna 40 may be formed in region 20 of device
10. Region 20 may be located at the lower end of device 10, as
described in connection with FIG. 1. Conductive region 68, which
may sometimes be referred to as a ground plane or ground plane
element, may be formed from one or more conductive structures
(e.g., planar conductive traces on printed circuit board 46,
internal structural members in device 10, electrical components 44
on board 46, radio-frequency shielding cans mounted on board 46,
etc.). Conductive region 68 in region 66 is sometimes referred to
as forming a "ground region" for antenna 40. Conductive structures
70 of FIG. 4 may be formed by bezel 16. Regions 70 are sometimes
referred to as ground plane extensions. Gap 18 may be formed in
this conductive bezel portion (as shown in FIG. 1).
[0055] Ground plane extensions 70 (i.e., portions of bezel 16) and
the portions of region 68 that lie along edge 76 of ground region
68 form a conductive loop around opening 72. Opening 72 may be
formed from air, plastics and other solid dielectrics. If desired,
the outline of opening 72 may be curved, may have more than four
straight segments, and/or may be defined by the outlines of
conductive components. The rectangular shape of dielectric region
72 in FIG. 4 is merely illustrative.
[0056] The conductive structures of FIG. 4 may, if desired, be fed
by coupling radio-frequency transceiver 60 across ground antenna
feed terminal 62 and positive antenna feed terminal 64. As shown in
FIG. 4, in this type of arrangement, the feed for antenna 40 is not
located in the vicinity of gap 18 (i.e., feed terminals 62 and 64
are located to the left of laterally centered dividing line 74 of
opening 72, whereas gap 18 is located to the right of dividing line
74 along the right-hand side of device 10). While this type of
arrangement may be satisfactory in some situations, antenna feed
arrangements that locate the antenna feed terminals at the
locations of terminals 62 and 64 of FIG. 4 tend to accentuate the
electric field strength of the radio-frequency antenna signals in
the vicinity of gap 18. If a user happens to place an external
object such as finger 80 into the vicinity of gap 18 by moving
finger 80 in direction 78 (e.g., when grasping device 10 in the
user's hand), the presence of the user's finger may disrupt the
operation of antenna 40.
[0057] To ensure that antenna 40 is not overly sensitive to touch
(i.e., to desensitize antenna 40 to touch events involving the hand
of the user of device 10 and other external objects), antenna 40
may be fed using antenna feed terminals located in the vicinity of
gap 18 (e.g., where shown by positive antenna feed terminal 58 and
ground antenna feed terminal 54 in the FIG. 4 example). When the
antenna feed is located to the right of line 74 and, more
particularly, when the antenna feed is located close to gap 18, the
electric fields that are produced at gap 18 tend to be reduced.
This helps minimize the sensitivity of antenna 40 to the presence
of the user's hand, ensuring satisfactory operation regardless of
whether or not an external object is in contact with device 10 in
the vicinity of gap 18.
[0058] In the arrangement of FIG. 4, antenna 40 is being series
fed. A schematic diagram of a series-fed loop antenna of the type
shown in FIG. 4 is shown in FIG. 5. As shown in FIG. 5, series-fed
loop antenna 82 may have a loop-shaped conductive path such as loop
84. A transmission line composed of positive transmission line
conductor 86 and ground transmission line conductor 88 may be
coupled to antenna feed terminals 58 and 54, respectively.
[0059] It may be challenging to effectively use a series-fed feed
arrangement of the type shown in FIG. 5 to feed a multi-band loop
antenna. For example, it may be desired to operate a loop antenna
in a lower frequency band that covers the GSM sub-bands at 850 MHz
and 900 MHz and a higher frequency band that covers the GSM
sub-bands at 1800 MH and 1900 MHz and the data sub-band at 2100
MHz. This type of arrangement may be considered to be a dual band
arrangement (e.g., 850/900 for the first band and 1800/1900/2100
for the second band) or may be considered to have five bands (850,
900, 1800, 1900, and 2100). In multi-band arrangements such as
these, series-fed antennas such as loop antenna 82 of FIG. 5 may
exhibit substantially better impedance matching in the
high-frequency communications band than in the low-frequency
communications band.
[0060] A standing-wave-ratio (SWR) versus frequency plot that
illustrates this effect is shown in FIG. 6. As shown in FIG. 6, SWR
plot 90 may exhibit a satisfactory resonant peak (peak 94) at
high-band frequency f2 (e.g., to cover the sub-bands at 1800 MHz,
1900 MHz, and 2100 MHz). SWR plot 90 may, however, exhibit a
relatively poor performance in the low-frequency band centered at
frequency f1 when antenna 40 is series fed. For example, SWR plot
90 for a series-fed loop antenna 82 of FIG. 5 may be characterized
by weak resonant peak 96. As this example demonstrates, series-fed
loop antennas may provide satisfactory impedance matching to
transmission line 52 (FIG. 3) in a higher frequency band at f2, but
may not provide satisfactory impedance matching to transmission
line 52 (FIG. 3) in lower frequency band f1.
[0061] A more satisfactory level of performance (illustrated by
low-band resonant peak 92) may be obtained using a parallel-fed
arrangement with appropriate impedance matching features.
[0062] An illustrative parallel-fed loop antenna is shown
schematically in FIG. 7. As shown in FIG. 7, parallel-fed loop
antenna 90 may have a loop of conductor such as loop 92. Loop 92 in
the FIG. 7 example is shown as being circular. This is merely
illustrative. Loop 92 may have other shapes if desired (e.g.,
rectangular shapes, shapes with both curved and straight sides,
shapes with irregular borders, etc.). Transmission line TL may
include positive signal conductor 94 and ground signal conductor
96. Paths 94 and 96 may be contained in coaxial cables, micro-strip
transmission lines on flex circuits and rigid printed circuit
boards, etc. Transmission line TL may be coupled to the feed of
antenna 90 using positive antenna feed terminal 58 and ground
antenna feed terminal 54. Electrical element 98 may bridge
terminals 58 and 54, thereby "closing" the loop formed by path 92.
When the loop is closed in this way, element 98 is interposed in
the conductive path that forms loop 92. The impedance of
parallel-fed loop antennas such as loop antenna 90 of FIG. 7 may be
adjusted by proper selection of the element 98 and, if desired,
other circuits (e.g., capacitors or other elements interposed in
one of the feed lines such as line 94 or line 96).
[0063] Element 98 may be formed from one or more electrical
components. Components that may be used as all or part of element
98 include resistors, inductors, and capacitors. Desired
resistances, inductances, and capacitances for element 98 may be
formed using integrated circuits, using discrete components and/or
using dielectric and conductive structures that are not part of a
discrete component or an integrated circuit. For example, a
resistance can be formed using thin lines of a resistive metal
alloy, capacitance can be formed by spacing two conductive pads
close to each other that are separated by a dielectric, and an
inductance can be formed by creating a conductive path on a printed
circuit board. These types of structures may be referred to as
resistors, capacitors, and/or inductors or may be referred to as
capacitive antenna feed structures, resistive antenna feed
structures and/or inductive antenna feed structures.
[0064] An illustrative configuration for antenna 40 in which
component 98 of the schematic diagram of FIG. 7 has been
implemented using an inductor is shown in FIG. 8. As shown in FIG.
8, loop 92 (FIG. 7) may be implemented using conductive regions 70
and the conductive portions of region 68 that run along edge 76 of
opening 72. Antenna 40 of FIG. 8 may be fed using positive antenna
feed terminal 58 and ground antenna feed terminal 54. Terminals 54
and 58 may be located in the vicinity of gap 18 to reduce electric
field concentrations in gap 18 and thereby reduce the sensitivity
of antenna 40 to touch events.
[0065] The presence of inductor 98 may at least partly help match
the impedance of transmission line 52 to antenna 40. If desired,
inductor 98 may be formed using a discrete component such as a
surface mount technology (SMT) inductor. The inductance of inductor
98 may also be implemented using an arrangement of the type shown
in FIG. 9. With the configuration of FIG. 9, the loop conductor of
parallel-fed loop antenna 40 may have an inductive segment SG that
runs parallel to ground plane edge GE. Segment SG may be, for
example, a conductive trace on a printed circuit board or other
conductive member. A dielectric opening DL (e.g., an air-filled or
plastic-filled opening) may separate edge portion GE of ground 68
from segment SG of conductive loop portion 70. Segment SG may have
a length L. Segment SG and associated ground GE form a transmission
line with an associated inductance (i.e., segment SG and ground GE
form inductor 98). The inductance of inductor 98 is connected in
parallel with feed terminals 54 and 58 and therefore forms a
parallel inductive tuning element of the type shown in FIG. 8.
Because inductive element 98 of FIG. 9 is formed using a
transmission line structure, inductive element 98 of FIG. 9 may
introduce fewer losses into antenna 40 than arrangements in which a
discrete inductor is used to bridge the feed terminals. For
example, transmission-line inductive element 98 may preserve
high-band performance (illustrated as satisfactory resonant peak 94
of FIG. 6), whereas a discrete inductor might reduce high-band
performance.
[0066] Capacitive tuning may also be used to improve impedance
matching for antenna 40. For example, capacitor 100 of FIG. 10 may
be connected in series with center conductor 56 of coaxial cable 52
or other suitable arrangements can be used to introduce a series
capacitance into the antenna feed. As shown in FIG. 10, capacitor
100 may be interposed in coaxial cable center conductor 56 or other
conductive structures that are interposed between the end of
transmission line 52 and positive antenna feed terminal 58.
Capacitor 100 may be formed by one or more discrete components
(e.g., SMT components), by one or more capacitive structures (e.g.,
overlapping printed circuit board traces that are separated by a
dielectric, etc.), lateral gaps between conductive traces on
printed circuit boards or other substrates, etc.
[0067] The conductive loop for loop antenna 40 of FIG. 10 is formed
by conductive structures 70 and the conductive portions of ground
conductive structures 66 along edge 76. Loop currents can also pass
through other portions of ground plane 68, as illustrated by
current paths 102. Positive antenna feed terminal 58 is connected
to one end of the loop path and ground antenna feed terminal 54 is
connected to the other end of the loop path. Inductor 98 bridges
terminals 54 and 58 of antenna 40 of FIG. 10, so antenna 40 forms a
parallel-fed loop antenna with a bridging inductance (and a series
capacitance from capacitor 100).
[0068] During operation of antenna 40, a variety of current paths
102 of different lengths may be formed through ground plane 68.
This may help to broaden the frequency response of antenna 40 in
bands of interest. The presence of tuning elements such as parallel
inductance 98 and series capacitance 100 may help to form an
efficient impedance matching circuit for antenna 40 that allows
antenna 40 to operate efficiently at both high and low bands (e.g.,
so that antenna 40 exhibits high-band resonance peak 94 of FIG. 6
and low-band resonance peak 92 of FIG. 6).
[0069] A simplified Smith chart showing the possible impact of
tuning elements such as inductor 98 and capacitor 100 of FIG. 10 on
parallel-fed loop antenna 40 is shown in FIG. 11. Point Y in the
center of chart 104 represents the impedance of transmission line
52 (e.g., a 50 ohm coaxial cable impedance to which antenna 40 is
to be matched). Configurations in which the impedance of antenna 40
is close to point Y in both the low and high bands will exhibit
satisfactory operation.
[0070] With parallel-fed antenna 40 of FIG. 10, high-band matching
is relatively insensitive to the presence or absence of inductive
element 98 and capacitor 100. However, these components may
significantly affect low band impedance. Consider, as an example,
an antenna configuration without either inductor 98 or capacitor
100 (i.e., a parallel-fed loop antenna of the type shown in FIG.
4). In this type of configuration, the low band (e.g., the band at
frequency f1 of FIG. 6) may be characterized by an impedance
represented by point X1 on chart 104. When an inductor such as
parallel inductance 98 of FIG. 9 is added to the antenna, the
impedance of the antenna in the low band may be characterized by
point X2 of chart 104. When a capacitor such as capacitor 100 is
added to the antenna, the antenna may be configured as shown in
FIG. 10. In this type of configuration, the impedance of the
antenna 40 may be characterized by point X3 of chart 104.
[0071] At point X3, antenna 40 is well matched to the impedance of
cable 50 in both the high band (frequencies centered about
frequency f2 in FIG. 6) and the low band (frequencies centered
about frequency f1 in FIG. 6). This may allow antenna 40 to support
desired communications bands of interest. For example, this
matching arrangement may allow antennas such as antenna 40 of FIG.
10 to operate in bands such as the communications bands at 850 MHz
and 900 MHz (collectively forming the low band region at frequency
f1) and the communications bands at 1800 MHz, 1900 MHz, and 2100
MHz (collectively forming the high band region at frequency
f2).
[0072] Moreover, the placement of point X3 helps ensure that
detuning due to touch events is minimized. When a user touches
housing 12 of device 10 in the vicinity of antenna 40 or when other
external objects are brought into close proximity with antenna 40,
these external objects affect the impedance of the antenna. In
particular, these external objects may tend to introduce a
capacitive impedance contribution to the antenna impedance. The
impact of this type of contribution to the antenna impedance tends
to move the impedance of the antenna from point X3 to point X4, as
illustrated by line 106 of chart 104 in FIG. 11. Because of the
original location of point X3, point X4 is not too far from optimum
point Y. As a result, antenna 40 may exhibit satisfactory operation
under a variety of conditions (e.g., when device 10 is being
touched, when device 10 is not being touched, etc.).
[0073] Although the diagram of FIG. 11 represents impedances as
points for various antenna configurations, the antenna impedances
are typically represented by a collection of points (e.g., a curved
line segment on chart 104) due to the frequency dependence of
antenna impedance. The overall behavior of chart 104 is, however,
representative of the behavior of the antenna at the frequencies of
interest. The use of curved line segments to represent
frequency-dependent antenna impedances has been omitted from FIG.
11 to avoid over-complicating the drawing.
[0074] The foregoing is merely illustrative of the principles of
this invention and various modifications can be made by those
skilled in the art without departing from the scope and spirit of
the invention.
* * * * *