Note: Descriptions are shown in the official language in which they were submitted.
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DUAL-BAND F-SLOT PATCH ANTENNA
[0001] The invention described herein relates generally to a multi-band
antenna for a
handheld wireless communications device. In particular, the invention relates
to a dual-
band patch antenna.
[0002] Patch antennas are common in wireless handheld communication devices
due
to their low profile structure. Further, patch antennas can be implemented
with a virtually
unlimited number of shapes, thereby allowing such antennas to conform to most
surface
profiles. Since modern handheld communication devices are required to operate
in
multiple frequency bands, multi-band patch antennas have been developed for
use in such
devices.
[0003] For instance, Wen (US 7,023,387) describes a dual-band antenna that
comprises a first C-shaped patch antenna structure, and a second C-shaped
patch antenna
structure coupled to the first patch antenna structure, each patch antenna
structure having a
respective slot structure. The first patch antenna structure includes a signal
feed point, and
the second patch antenna structure includes a ground point that is proximate
the signal
feed point.
[0004] On the other hand, planar inverted-F antennas (PIFA) are becoming more
common in wireless handheld communication devices due to their reduced size in
comparison to conventional microstrip antenna designs. Therefore, PIFA
antennas have
been developed which include multiple resonant sections, each having a
respective
resonant frequency. However, since conventional PIFA antennas have a very
limited
bandwidth, broadband technologies, such as parasitic elements and/or multi-
layer
structures, have been used to modify the conventional PIFA antenna for multi-
band and
broadband applications.
[0005] These approaches increase the size of the antenna, making the resulting
designs
unattractive for modern handheld communication devices.
[0006] Also, the additional resonant branches introduced by these approaches
make
the operational frequencies of the antennas difficult to tune. Further, the
additional
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branches can introduce significant electromagnetic compatibility (EMC) and
electromagnetic interference (EMI) problems.
GENERAL
[0007] According to one embodiment of the invention described herein, a dual-
band
patch antenna may comprise a pair of interconnected F-slot structures, and a
loop strip
structure that is disposed around the F-slot structures.
[0008] In accordance with a first aspect of the invention, there may be
provided a
dual-band patch antenna that comprises a planar conductive layer comprising a
conductive
region and a central non-conductive region. The conductive region and the non-
conductive
region together may defme a pair of interconnected F-slot structures, and a
loop strip
structure that is coupled to and disposed around the F-slot structures.
[0009] In accordance with a second aspect of the invention, there may be
provided a
wireless communication device that comprises a radio transceiver section, and
a dual-band
antenna coupled to the radio transceiver section. The dual-band antenna may
comprise a
dual-band patch antenna that comprises a planar conductive layer. The
conductive layer
may comprise a conductive region and a central non-conductive region. The
conductive
region and the non-conductive region together may define a pair of
interconnected F-slot
structures, and a loop strip structure that is coupled to and disposed around
the F-slot
structures.
[0010] In accordance with a third aspect of the invention, there may be
provided a
dual-band patch antenna that comprises a first F-slot patch antenna, and a
second F-slot
patch antenna that is coupled to the first F-slot patch antenna. The dual-band
antenna also
may comprise a loop strip structure that is coupled to and disposed around the
first and
second F-slot patch antennas.
[0011] As will become apparent, the dual-band antenna may be suitable for WLAN
2.45 GHz and 5 GHz applications. Further, the structure of the dual-band
antenna may
have reduced design and fabrication difficulty in comparison to conventional
dual-band
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antennas, and allows the frequencies of the upper and lower bands to be
adjusted
independently of one another, with improved impedance matching.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] The invention will now be described, by way of example only, with
reference
to the accompanying drawings, in which:
Fig. I is a front plan view of a handheld communications device according to
the
invention;
Fig. 2 is a schematic diagram depicting certain functional details of the
handheld
communications device;
Fig. 3 is a top plan view of a dual-band F-slot patch antenna of the handheld
communications device, suitable for use with a wireless cellular network;
Fig. 4 to 7 are computer simulations of the return loss for the dual-band F-
slot
patch antenna; and
Fig. 8 depicts the computer simulated and actual return loss for a preferred
implementation of the dual-band F-slot patch antenna.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0013] Turning to Fig. 1, there is shown a sample handheld communications
device
200 in accordance with the invention. Preferably, the handheld communications
device
200 is a two-way wireless communications device having at least voice and data
communication capabilities, and is configured to operate within a wireless
cellular
network. Depending on the exact functionality provided, the wireless handheld
communications device 200 may be referred to as a data messaging device, a two-
way
pager, a wireless e-mail device, a cellular telephone with data messaging
capabilities, a
wireless Internet appliance, or a data communication device, as examples.
[0014] As shown, the handheld communications device 200 includes a display
222, a
function key 246, and data processing means (not shown) disposed within a
common
housing 201. The display 222 comprises a backlit LCD display. The data
processing
means is in communication with the display 222 and the function key 246. In
one
implementation, the backlit display 222 comprises a transmissive LCD display,
and the
function key 246 operates as a power on/off switch. Alternately, in another
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implementation, the backlit display 222 comprises a reflective or trans-
reflective LCD
display, and the function key 246 operates as a backlight switch.
[0015] In addition to the display 222 and the function key 246, the handheld
communications device 200 includes user data input means for inputting data to
the data
processing means. As shown, preferably the user data input means includes a
keyboard
232, a thumbwheel 248 and an escape key 260. The keyboard 232 includes
alphabetic and
numerical keys, and preferably also includes a "Send" key and an "End" key to
respectively initiate and terminate voice communication. However, the data
input means
is not limited to these forms of data input. For instance, the data input
means may include
a trackball or other pointing device instead of (or in addition to) the
thumbwheel 248.
[0016] Fig. 2 depicts functional details of the handheld communications device
200.
As shown, the handheld communications device 200 incorporates a motherboard
that
includes a communication subsystem 211, and a microprocessor 238. The
communication
subsystem 211 performs communication functions, such as data and voice
communications, and includes a primary transmitter/receiver 212, a secondary
transmitter/receiver 214, a primary internal antenna 216 for the primary
transmitter/receiver 212, a secondary internal antenna 300 for the secondary
transmitter/receiver 214, and local oscillators (LOs) 213 and one or more
digital signal
processors (DSP) 220 coupled to the transmitter/receivers 212, 214.
[0017] Typically, the communication subsystem 211 sends and receives wireless
communication signals over a wireless cellular network via the primary
transmitter/receiver 212 and the primary internal antenna 216. Further,
typically the
communication subsystem 211 sends and receives wireless communication signals
over a
local area wireless network via the secondary transmitter/receiver 214 and the
secondary
internal antenna 300.
[0018] Preferably, the primary intemal antenna 216 is configured for use
within a
Global System for Mobile Communications (GSM) cellular network or a Code
Division
Multiple Access (CDMA) cellular network. Further, preferably the secondary
internal
antenna 300 is configured for use within a WLAN WiFi (IEEE 802.11 x) or
Bluetooth
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network. More preferably, the secondary internal antenna 300 is a dual-band
patch
antenna that is configured for use within 802.11 b/g, 802.11 a/j and Bluetooth
WLAN
networks. Although the handheld communications device 200 is depicted in Fig.
2 with
two antennas, it should be understood that the handheld communications device
200 may
5 instead comprise only a single antenna, with the dual-band antenna 300 being
connected to
both the primary transmitter/receiver 212 and the secondary
transmitter/receiver 214.
Further, although Fig. 2 depicts the dual-band antenna 300 incorporated into
the handheld
communications device 200, the dual-band antenna 300 is not limited to mobile
applications, but may instead by used with a stationary communications device.
The
preferred structure of the dual-band antenna 300 will be discussed in detail
below, with
reference to Figs. 3 to 8.
[0019] Signals received by the primary internal antenna 216 from the wireless
cellular
network are input to the receiver section of the primary transmitter/receiver
212, which
performs common receiver functions such as frequency down conversion, and
analog to
digital (A/D) conversion, in preparation for more complex communication
functions
performed by the DSP 220. Signals to be transmitted over the wireless cellular
network
are processed by the DSP 220 and input to transmitter section of the primary
transmitter/receiver 212 for digital to analog conversion, frequency up
conversion, and
transmission over the wireless cellular network via the primary internal
antenna 216.
[0020] Similarly, signals received by the secondary internal antenna 300 from
the
local area wireless network are input to the receiver section of the secondary
transmitter/receiver 214, which performs common receiver functions such as
frequency
down conversion, and analog to digital (A/D) conversion, in preparation for
more complex
communication functions performed by the DSP 220. Signals to be transmitted
over the
local area wireless network are processed by the DSP 220 and input to
transmitter section
of the secondary transmitter/receiver 214 for digital to analog conversion,
frequency up
conversion, and transmission over the local area wireless network via the
secondary
internal antenna 300. If the communication subsystem 211 includes more than
one DSP
220, the signals transmitted and received by the secondary
transmitter/receiver 214 would
preferably be processed by a different DSP than the primary
transmitter/receiver 212.
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[0021] The communications device 200 also includes a SIM interface 244 if the
handheld communications device 200 is configured for use within a GSM network,
and/or
a RUIM interface 244 if the handheld communications device 200 is configured
for use
within a CDMA network. The SIM/RUIM interface 244 is similar to a card-slot
into
which a SIM/RUIM card can be inserted and ejected like a diskette or PCMCIA
card. The
SIM/RUIM card holds many key configurations 251, and other information 253
including
subscriber identification information, such as the International Mobile
Subscriber Identity
(IMSI) that is associated with the handheld communications device 200, and
subscriber-
related information.
[0022] The microprocessor 238, in conjunction with the flash memory 224 and
the
RAM 226, comprises the aforementioned data processing means and controls the
overall
operation of the device. The data processing means interacts with device
subsystems such
as the display 222, flash memory 224, RAM 226, auxiliary input/output (I/O)
subsystems
228, data port 230, keyboard 232, speaker 234, microphone 236, short-range
communications subsystem 240, and device subsystems 242. The data port 230 may
comprise a RS-232 port, a Universal Serial Bus (USB) port or other wired data
communication port.
[0023] As shown, the flash memory 224 includes both computer program storage
258
and program data storage 250, 252, 254 and 256. Computer processing
instructions are
preferably also stored in the flash memory 224 or other similar non-volatile
storage. Other
computer processing instructions may also be loaded into a volatile memory
such as RAM
226. The computer processing instructions, when accessed from the memory 224,
226
and executed by the microprocessor 238 define an operating system, computer
programs,
operating system specific applications. The computer processing instructions
may be
installed onto the handheld communications device 200 upon manufacture, or may
be
loaded through the cellular wireless network, the auxiliary I/O subsystem 228,
the data
port 230, the short-range communications subsystem 240, or the device
subsystem 242.
[0024] The operating system allows the handheld communications device 200 to
operate the display 222, the auxiliary input/output (I/O) subsystems 228, data
port 230,
keyboard 232, speaker 234, microphone 236, short-range communications
subsystem 240,
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and device subsystems 242. Typically, the computer programs include
communication
software that configures the handheld communications device 200 to receive one
or more
communication services. For instance, preferably the communication software
includes
internet browser software, e-mail software and telephone software that
respectively allow
the handheld communications device 200 to communicate with various computer
servers
over the internet, send and receive e-mail, and initiate and receive telephone
calls.
[0025] Fig. 3 depicts the preferred structure for the dual-band antenna 300.
The dual-
band antenna 300 comprises a planar conductive layer 302. Preferably, the
planar
conductive layer 302 is disposed on a substrate layer (not shown). As shown,
the
conductive layer 302 has a substantially rectangular shape having two opposed
pairs of
substantially parallel edges. Preferably, the dual-band antenna 300 is
implemented as a
printed circuit board. with the planar conductive layer 302 comprising copper
or other
suitable conductive metal.
[0026] The conductive layer 302 comprises a conductive region 308 and a
central non-
conductive region 310. In contrast to the conductive region 308, the non-
conductive
region 310 is devoid of conductive metal. Typically, the non-conductive region
310 is
implemented via suitable printed circuit board etching techniques.
[0027] As will become apparent, the non-conductive region 310 and the
surrounding
conductive region 308 define first and second interconnected high frequency
planar F-slot
structures 312, 314, and a lower frequency planar loop strip structure 316
that is coupled
to and disposed around the F-slot structures 312, 314. Together, the F-slot
structures 312,
314 and the loop strip structure 316 comprise a dual-band F-slot patch
antenna. The
phrase "F-slot structure" is used herein to indicate that the structures 312,
314 each have
slots that are arranged into a planar "F" structure.
[0028] The non-conductive region 310 comprises a first non-conductive section
318, a
second non-conductive section 320, and a non-conductive connecting branch 322
that
interconnects the first and second non-conductive sections 318, 320. The first
non-
conductive section 318 and the second non-conductive section 320 are
substantially
parallel to each other.
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[0029] Preferably, the first and second non-conductive sections 318, 320 are
parallel
to one pair of opposing edges of the conductive layer 302. Further, preferably
the
connecting branch 322 is parallel to the other pair of opposing edges of the
conductive
layer 302.
[0030] As shown, the first F-slot structure 312 comprises the first non-
conductive
section 318 and a portion of the connecting branch 322. Similarly, the second
F-slot
structure 314 comprises the second non-conductive section 320 and the
remaining portion
of the connecting branch 322.
[0031] The first F-slot structure 312 also comprises a first non-conductive
branch 324
that is implemented within the non-conductive region 310. The first non-
conductive
branch 324 is continuous with the first non-conductive section 318 at one end
of the first
non-conductive branch 324, and extends substantially perpendicularly from the
first non-
conductive section 318 towards the opposite end of the first non-conductive
branch 324.
[0032] In addition, the first F-slot structure 312 comprises a first
conductive branch
326 that is implemented within the conductive region 308. The first conductive
branch
326 is disposed between the first non-conductive branch 324 and the non-
conductive
connecting branch 322. Preferably, the first conductive branch 326 is
substantially
parallel to the non-conductive connecting branch 322.
[0033] Further, the first F-slot structure 312 also comprises a first
conductive section
328 that is implemented within the conductive region 308. The first conductive
section
328 is disposed between the second non-conductive section 320 and the opposite
end of
the first non-conductive branch 324.
[0034] Similarly, the second F-slot structure 314 also comprises a second non-
conductive branch 330 that is implemented within the non-conductive region
310. The
second non-conductive branch 330 is continuous with the second non-conductive
section
320 at one end of the second non-conductive branch 330, and extends
substantially
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perpendicularly from the second non-conductive section 320 towards the
opposite end of
the second non-conductive branch 330.
[0035] In addition, the second F-slot structure 314 comprises a second
conductive
branch 332 that is implemented within the conductive region 308. The second
conductive
branch 332 is disposed between the second non-conductive branch 330 and the
non-
conductive connecting branch 322. Preferably, the second conductive branch 332
is
substantially parallel to the non-conductive connecting branch 322.
[0036] Further, the second F-slot structure 314 also comprises a second
conductive
section 334 that is implemented within the conductive region 308. The second
conductive
section 334 is disposed between the first non-conductive section 318 and the
opposite end
of the second non-conductive branch 330.
[0037] The low frequency loop strip structure 316 comprises a radiating
element, a
signal feed portion, and a shorting portion that are implemented within the
conductive
region 308. The radiating element is coupled to and disposed around the first
and second
F-slot structures, 312, 314, and extends continuously around the circumference
of the
conductive layer 302 from the signal feed portion to the shorting portion. The
loop strip
structure 316 also comprises a non-conductive slot 336 that is disposed
between the signal
feed portion and the shorting portion, and extends inwardly from one edge of
the
conductive layer 302. As shown, a feed pin 304 is connected to the signal feed
portion,
and a ground pin 306 is connected to the shorting portion.
[0038] Fig. 4 to 8 are computer simulations of the return loss for the dual-
band F-slot
patch antenna 300. In these simulations:
W is the width of the conductive layer 302
L is the length of the conductive layer 302
Lr is the length of the first non-conductive branch 324
Lõ is the length of the non-conductive connecting branch 322
L. is the length of the non-conductive slot 336, as measured from the edge of
the
conductive layer 302
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[0039] Fig. 4 depicts the variation in return loss of the dual-band antenna
300 with
width W. In this simulation, L = 14mm; Lf = 2mm; L, = 10.5 mm; Lg = 9mm. This
simulation reveals that the width of the loop strip structure 316 has a
preferential impact
on the centre frequency and impedance of the lower frequency band, in
comparison to the
5 higher frequency band. This result is advantageous since it reveals that the
frequency and
impedance of the lower frequency band can be adjusted by varying the length of
the loop
strip structure 316, without significantly impacting the characteristics of
the upper
frequency band.
10 [0040] Fig. 5 depicts the variation in return loss with L. In this
simulation, W
21mm; L = 14mm; Lf = 2mm; Lg = 9mm. This simulation reveals that the centre
frequency and impedance of the upper frequency band are sensitive to
variations in the
length of the non-conductive connecting branch 322 and the second non-
conductive
branch 330. This result is advantageous since it reveals that the frequency
and impedance
of the upper frequency band can be adjusted by varying the width of the second
F-slot
structure 314, without impacting the characteristics of the lower frequency
band.
[0041] Fig. 6 depicts the variation in return loss with Lf. In this
simulation, W
21mm; L = 14mm; Lõ = 10.5 mm; Lg = 9mm. This simulation reveals that the
centre
frequency and impedance of the upper frequency band are sensitive to
variations in the
length of the first non-conductive branch 324. Further, the centre frequency
of the lower
frequency band is insensitive, and the impedance of the lower frequency band
is
moderately sensitive, to variations in the length of the first non-conductive
branch 324.
This result is advantageous since it reveals that the centre frequency of the
upper
frequency band can be adjusted independently of the centre frequency of the
lower
frequency band, by varying the width of the first F-slot structure 312.
Further, the
impedance of the lower frequency band can be adjusted independently of its
centre
frequency.
[0042] Fig. 7 depicts the variation in return loss with Lg. In this
simulation, W
21 mm; L = 14mm; Lf = 2mm; Lõ = 10.5 mm. This simulation reveals that the
impedance
of the upper frequency band is sensitive to variations in the length of the
non-conductive
slot 336. Further, the centre frequency and impedance of the lower frequency
band is
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insensitive to variations in the length of the non-conductive slot 336. This
result is
advantageous since it reveals that the impedance of the upper frequency band
can be
adjusted by varying the slot length of the loop strip structure 316, without
impacting the
characteristics of the lower frequency band.
[0043] Fig. 8 depicts the computer simulated and actual performance of a dual-
band F-
slot patch antenna 300 having the following dimensions: W = 21mm; L = 14mm; Lf
=
2mm; Lõ = 10.5 mm; Lg = 9mm. This graph reveals that the dual-band antenna 300
has a
low frequency range that extends from 2.3 GHz to 2.59 GHz, and a centre
frequency of
2.45 GHz. The graph also reveals that the dual-band antenna 300 has a wide
higher
frequency range that extends from 4.75 GHz to 5.85 GHz, and a centre frequency
around 5
GHz.
[0044] As will be appreciated from the foregoing discussion, the low frequency
band
of the dual-band antenna 300 is suitable for WLAN 802.11b/g or Bluetooth
applications,
and the higher frequency band of the dual-band antenna 300 is suitable for
WLAN 802.11
a/j applications. However, in contrast to conventional dual-band antenna
designs, the
frequency of the upper and lower bands of the dual-band antenna 300 can be
adjusted
independently of one another, with improved impedance matching. These results
are
obtained in a structure having reduced design and fabrication difficulty.
[0045] The scope of the monopoly desired for the invention is defined by the
claims
appended hereto, with the foregoing description being merely illustrative of
the preferred
embodiment of the invention. Persons of ordinary skill may envisage
modifications to the
described embodiment which, although not explicitly suggested herein, do not
depart from
the scope of the invention, as defined by the appended claims.
