Information
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Patent Grant
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6198943
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Patent Number
6,198,943
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Date Filed
Monday, May 17, 199925 years ago
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Date Issued
Tuesday, March 6, 200123 years ago
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Inventors
-
Original Assignees
-
Examiners
Agents
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CPC
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US Classifications
Field of Search
US
- 455 90
- 455 129
- 455 575
- 455 552
- 455 553
- 343 742
- 343 702
- 343 866
- 343 867
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International Classifications
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Abstract
An internal, loop dipole antenna for a mobile terminal is capable of operating in two distinct RF bands. The antenna includes a resonating element and a parasitic tuning element. The resonating element has a looped, dipole configuration including a primary tuning loop, a secondary tuning loop, and a ground loop. The parasitic tuning element is disposed in a plane spaced from the plane of the resonating element. The parasitic element includes a first portion that generally follows the ground loop on the resonating element, and a second portion that bisects the primary tuning loop on the resonating element. First and second tuning arms extend along opposing ends of the parasitic tuning element. The length of the tuning arms is adjusted to tune the resonance of the antenna in the primary and secondary operating bands.
Description
FIELD OF THE INVENTION
The present invention relates to mobile terminals for use in analog and digital-based cellular communication systems, and, in particular, to an improved antenna configuration for dual-band operation.
BACKGROUND OF THE INVENTION
Mobile terminals, and especially mobile telephones and headsets, are becoming increasingly smaller. These terminals require a radiating element or antenna for radio communications. Conventionally, antennas for such terminals are attached to and extend outwardly from the terminal's housing. These antennas are typically retractably mounted to the housing so that the antenna is not extending from the housing when the terminal is not in use. With the ever decreasing size of these terminals, the currently used external antennas become more obtrusive and unsightly, and most users find pulling the antenna out of the terminal housing for each operation undesirable. Furthermore, these external antennas are often subject to damage during manufacture, shipment and use. The external antennas also conflict with various mounting devices, recharging cradles, download mounts, and other cooperating accessories.
Application Ser. No. 09/189,890 describes an internal loop dipole antenna for a cellular telephone. The antenna includes extra traces and tuning elements on the same physical plane as the antenna element to enable dual-band operation. As phone designs become increasingly smaller and the antenna is brought closer to the ground plane (PCB) of the phone, the antenna begins to lose its effectiveness. It has been discovered that the effective bandwidth of the antenna is narrowed as the antenna is brought closer to the ground plane of the antenna. Also, tuning of the resonance frequencies becomes problematic due to the strays and parasitics caused by the antenna's close proximity to the ground plane. The extra traces and tuning elements did not provide sufficient bandwidth in both bands of operation. Also, lumped elements such as capacitors and inductors did not adequately eliminate the strays and parasitics.
Accordingly, there remains a need for a dual band antenna that will operate effectively in two distinct operating bands even when the antenna is brought in close proximity to the ground plane of the phone.
SUMMARY OF THE INVENTION
The present invention provides an internal antenna for mobile terminals that provides performance comparable with externally mounted antennas, even when placed in close proximity to the ground plane. The antenna includes a resonating element and a parasitic tuning element. The resonating element has a looped, dipole configuration including first and second tuning loops and a ground loop. The tuning loops and ground loop are electrically connected by tuning elements which, preferably, are in the same plane as the tuning loops and ground loop. The loops of the resonating elements may be placed around other components of the phone without significantly impinging on precious physical space. For example, the loops may be disposed around the keypad or display in the housing, in a flip portion pivotally connected to a main section of the housing, or in a distinct printed circuit board enclosed in the housing.
The parasitic element is disposed in a plane spaced from the plane of the resonating element. The parasitic element includes a first portion that generally follows the contour of the ground loop on the resonating element, and a second portion that bisects one of the tuning loops on the resonating element. First and second tuning arms extend along opposing ends of the parasitic tuning. The parasitic element is shifted in the x-y plane to tune the resonant frequency of the antenna to a first operating band. The length of the tuning arms is adjusted in order to tune the antenna to a second operating band.
An advantage of the present invention is that it allows the design engineer to match the antenna to a VSWR of approximately 2:1 in two distinct operating bands (typically the 900 MHz and 1800 MHz bands) even at the band edges. This allows the antenna to obtain broad bandwidth in both bands of operation and prevents loss of gain due to mismatch of the VSWR. No prior art antennas have been able to obtain these advantages in an antenna spaced in close proximity to the ground plane.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1
is a functional block diagram of a cellular telephone constructed in accordance with the present invention.
FIG. 2
is a section view of the cellular telephone showing the printed circuit board and antenna insert.
FIGS. 3A and 3B
are top plan views of the antenna insert showing the parasitic tuning element superimposed over the resonating element.
FIGS. 4A and 4B
is a top plan view and bottom plan view respectively of an alternate embodiment of the antenna insert showing the parasitic tuning element and resonating element on opposing sides of the insert.
FIGS. 5A and 5B
are top plan views showing two separate antenna inserts for the resonating element and tuning element respectively.
DETAILED DESCRIPTION OF THE INVENTION
Referring now to the drawings, and particularly to
FIGS. 1 and 2
, a mobile communication device, such as a cellular telephone, is shown and indicated generally by the numeral
10
. Mobile telephone
10
is a fully functional radio transceiver capable of transmitting and receiving digital and/or analog signals over an RF channel according to known standards, such as Telecommunications Industry Association (TIA), IS-54, and IS-136. The present invention, however, is not limited to cellular telephones, but may also be implemented in other types of communication devices including, without limitation, pagers and personal digital assistants.
The mobile telephone
10
includes an operator interface
12
and a transceiver unit
24
contained in a housing
100
. Users can dial and receive status information from the mobile telephone
10
via the operator interface
12
. The operator interface
12
consists of a keypad
16
, display
18
, microphone
20
, and speaker
22
. The keypad
16
allows the user to dial numbers, enter data, respond to prompts, and otherwise control the operation of the mobile telephone
10
. The display
18
allows the operator to see dialed digits, call status information, messages, and other stored information. An interface control
14
interfaces the keypad
16
and display
18
with the telephone's control logic
26
. The microphone
20
and speaker
22
provide an audio interface that allows users to talk and listen on their mobile telephone
10
. Microphone
20
converts the user's speech and other sounds into audio signals for subsequent transmission by the mobile telephone
10
. Speaker
22
converts audio signals received by the mobile telephone
10
into audible sounds that can be heard by the user. In general, the microphone
20
and speaker
22
are contained in the housing of the mobile telephone
10
. However, the microphone
20
and speaker
22
can also be located in a headset that can be worn by the user.
The transceiver unit
24
comprises a transmitter
30
, receiver
40
, and antenna assembly
50
. The transceiver circuitry is typically contained on a printed circuit board
106
disposed in the phone's housing
100
. The transmitter
30
includes a digital signal processor
32
, modulator
34
, and RF amplifier
36
. The digital signal processor
32
converts analog signals from the microphone
20
into digital signals, compresses the digital signal, and inserts error-detection, error-correction, and signaling information. Modulator
34
converts the signal to a form that is suitable for transmission on an RF carrier. The RF amplifier
36
amplifies the signal to a suitable power level for transmission. In general, the transmit power of the telephone
10
can be adjusted up and down in two decibel increments in response to commands it receives from its serving base station. This allows the mobile telephone to only transmit at the necessary power level to be received and reduces interference to nearby units.
The receiver includes a receiver/amplifier
42
, demodulator
44
, and digital signal processor
46
. The receiver/amplifier
42
contains a band pass filter, low level RF amplifier, and mixer. Received signals are filtered to eliminate side bands. The remaining signals are sent to a low-level RF amplifier and routed to an RF mixer assembly. The mixer converts the frequency to a lower frequency that is either amplified or directly provided to the demodulator
44
. The demodulator
44
extracts the transmitted bit sequence from the received signal. The digital signal processor
46
decodes the signal, corrects channel-induced distortion, and performs errordetection and correction. The digital signal processor
46
also separates control and signaling data from speech data. The control and signaling data are passed to the control logic
26
. Speech data is processed by a speech decoder and converted into an analog signal which is applied to speaker
22
to generate audible signals that can be heard by the user.
The control logic
26
controls the operation of the telephone
10
according to instructions stored in a program memory
28
. Control logic
26
may be implemented by one or more microprocessors. The functions performed by the control logic
26
include power control, channel selection, timing, as well as a host of other functions. The control logic
26
inserts signaling messages into the transmitted signals and extracts signaling messages from the received signals. Control logic
26
responds to any base station commands contained in the signaling messages and implements those commands. When the user enters commands via the keypad
16
, the commands are transferred to the control logic
26
for action.
The antenna assembly
50
is operatively connected to the transmitter
30
and receiver
40
for radiating and receiving electromagnetic waves. Electrical signals from the transmitter
30
are applied to the antenna assembly
50
which converts the signal into electromagnetic waves that radiate out from the antenna
50
. Conversely, when the antenna
50
is subjected to electromagnetic waves radiating through space, the electromagnetic waves are converted by the antenna
50
into an electrical signal that is applied to the receiver
40
.
In a hand-held mobile telephone, the antenna assembly
50
is typically an integral part of the mobile telephone
10
. Commonly, the antenna for a mobile telephone
10
comprises an external quarter-wavelength rod antenna. One purpose of the present invention is to eliminate this type of external rod antenna. Instead, the antenna
50
of the present invention is a loop dipole antenna that can be mounted internally in the housing
100
of the telephone
10
or integrated into the housing
100
itself.
The antenna
50
of the present invention is shown in
FIGS. 3A and 3B
. The antenna includes two elements, referred to herein as the resonating element
52
and the parasitic tuning element
70
. The resonating element
52
includes a ground loop
54
and a primary tuning loop
56
for a first RF band. The resonating element
52
also includes tuning elements
58
that join the ground loop
54
and primary tuning loop
56
to form a secondary tuning loop for a second RF band. A signal is fed to the antenna
50
by a transmission line. The ground of the transmission line is connected to the ground loop
54
. The main conductor of the transmission line is connected to the primary loop
56
. The primary tuning loop
56
and ground loop
54
are sized to provide a half-wave dipole antenna in a primary band of operation. In the disclosed embodiment, the primary operating band is the 1800 MHz band. The secondary tuning loop is sized so that the antenna
50
can also receive signals in a secondary RF band. In the disclosed embodiment, the secondary band is the 900 MHz band.
The parasitic tuning element
70
is spaced above the resonating element
52
. The parasitic tuning element
70
includes a pair of tuning arms
72
,
74
which are joined by a central connector
76
. The central connector includes a first portion
77
that generally follows the outline of the ground loop
54
on the resonating element
52
, and a second part
78
that bisects the primary tuning loop
56
.
In one embodiment of the invention, the resonating element
52
and tuning element
70
are disposed on a first surface of a flat insert
80
made of a dielectric material as seen in
FIGS. 3A and 3B
. The insert
80
is disposed within the housing
100
so that the antenna
50
is less than 10 mm from the printed circuit board
106
, and preferably less than 6 mm from the printed circuit board
106
. The resonating element
52
may be photo-etched on the surface of the insert
80
, then covered by a TEFLONĀ® tape or other dielectric laminate material. The parasitic tuning element
70
is placed over the resonating element
52
with the laminate separating the two elements. The insert
80
with the antenna assembly
50
thereon can be mounted within the housing
100
of the mobile telephone with the insert
80
separating the resonating element
52
of the antenna from the printed circuit board inside the phone. The thickness of the insert or dielectric constant of the material can be varied as needed to increase or decrease the effective distance of the antenna from the ground plane (i.e., printed circuit board).
Those skilled in the art will recognize that other methods exist for constructing the antenna
50
. For example, the resonating element
52
and tuning element
70
could both be photo-etched on opposing sides of the antenna insert
80
, as shown in
FIGS. 4A and 4B
. The thickness or dielectric constant of the insert
80
could then be varied as needed for proper tuning. Another alternative would be to use separate inserts
80
,
82
for the resonating element
52
and tuning element
70
, respectively, as shown in
FIGS. 5A and 5B
. The tuning element
70
could also be photo-etched on the inside of the front cover
102
and covered with a TEFLONĀ® tape or other dielectric laminate material. These examples are intended to illustrate some of the various methods that may be used to construct the antenna
50
, and those skilled in the art will recognize that other equivalent methods may exist.
It has been found that the antenna
50
can be tuned for dual band operations. Ideally, the antenna should be tuned to obtain a voltage standing wave ratio (VSWR) of approximately 2:1 in both bands of operation. To find the proper location of the tuning element
70
with respect to the resonating element
52
, the tuning element
70
is placed in an initial position and the VSWR is determined. The parasitic tuning element
70
is then shifted in the x-y plane (i.e., the plane in which the tuning element
70
lies) to center the primary band so that it is as close to the 2:1 ratio as possible. Once the tuning element
70
is properly positioned, the lengths of the tuning arms
72
,
74
are adjusted to tune the antenna in both the primary and secondary band. It has been observed that adjusting the length of the tuning arm
72
affects the resonance primarily in the secondary band and secondarily in the primary band. Adjusting the length of tuning arm
74
has the opposite effect. The lengths of both tuning arms
72
,
74
are adjusted as needed to obtain the best possible match, in both bands of operation, recognizing that it may not be possible to obtain an ideal match in either band.
The loop dipole antenna of the present invention enables the antenna to be tuned to two distinct operating bands, even when the antenna is placed in close proximity to the ground plane of the phone
10
. Using the present invention, it is possible to obtain a VSWR of approximately 2:1 in both bands of operation. This prevents the loss of gain due to mismatch caused by poor bandwidth. Another advantage of the present invention is that it is less vulnerable to damage as compared to external antennas.
The present invention may, of course, be carried out in other specific ways than those herein set forth without departing from the spirit and essential characteristics of the invention. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive, and all changes coming within the meaning and equivalency range of the appended claims are intended to be embraced therein.
Claims
- 1. A loop dipole antenna for a mobile radio communication device capable of dual band operation, comprising:a. a ground plane; b. a resonating element disposed in a first plane spaced from said ground plane, said resonating element including a first tuning loop for tuning said antenna to transmit and receive signals in a first operating band and a ground loop, said first tuning loop and said ground loop being arranged in a looped dipole configuration; and c. a parasitic tuning element disposed in spaced relationship to said resonating element, said parasitic tuning element including first and second tuning arms interconnected by a central connecting member, wherein said central connecting member includes a first portion that generally follows the ground loop on the resonating element and a second portion that bisects said first tuning loop.
- 2. The loop dipole antenna according to claim 1 wherein the first tuning loop and said ground loop lie in a common plane.
- 3. The loop dipole antenna according to claim 1 further including a second tuning loop for tuning said antenna to transmit and receive signals in a second operating band.
- 4. The loop dipole antenna according to claim 3 wherein said second tuning loop lies in the same plane as said first tuning loop.
- 5. The loop dipole antenna according to claim 3 wherein said resonating element is spaced approximately 6mm or less from said ground plane.
- 6. The loop dipole antenna according to claim 1 wherein said antenna further includes a planar base member made of a dielectric material having the resonating element on one surface thereof.
- 7. The loop dipole antenna according to claim 6 wherein said parasitic tuning element is applied to a surface of said base member.
- 8. The loop dipole antenna according to claim 7 wherein said resonating element and said parasitic tuning element are both on the same surface of the base member separated by a dielectric layer.
- 9. The loop dipole antenna according to claim 7 said resonating element and said parasitic tuning element are on opposing surfaces of said base member.
- 10. The loop dipole antenna according to claim 6 wherein said parasitic element is applied to a surface of a housing of the communication device.
- 11. A loop dipole antenna for a mobile radio communication device capable of dual band operation, comprising:a. a first tuning loop for transmitting and receiving signals in a primary band of operation; b. a ground loop lying in the same plane as said first tuning loop, wherein said first tuning loop and said ground loop are arranged in a dipole configuration; c. a parasitic tuning element disposed in a parallel plane to said first tuning loop and said ground loop, said parasitic tuning element including a first portion that generally follows said ground loop and a second portion that bisects said first tuning loop.
- 12. The loop dipole antenna according to claim 11 further including a second tuning loop for tuning said antenna to transmit and receive signals in a second operating band.
- 13. The loop dipole antenna according to claim 12 wherein said second tuning loop lies in the same plane as said first tuning loop.
- 14. The loop dipole antenna according to claim 13 further comprising a ground plane, wherein said first and second tuning loops are spaced approximately 6 mm or less from said ground plane.
- 15. The loop dipole antenna according to claim 11 wherein said parasitic tuning element further includes first and second tuning arms disposed at opposing ends of said parasitic tuning element.
- 16. A radio communication device comprising:a. a housing; b. a printed circuit board disposed in said housing containing radio communication electronics; c. a loop dipole antenna electrically disposed in said housing in spaced relationship with said printed circuit board and coupled to said radio communication electronics, said antenna being arranged so that said printed circuit board functions as a ground plane for said antenna, said antenna including: i. a resonating element including a first tuning loop for tuning said antenna to transmit and receive signals in a first operating band and a ground loop, said first tuning loop and said ground loop being arranged in a looped dipole configuration; and ii. a parasitic tuning element disposed in a parallel plane to said first tuning loop and said ground loop, said parasitic tuning element including a first portion that generally follows said ground loop and a second portion that bisects said first tuning loop.
- 17. The radio communication device according to claim 16 wherein said antenna further includes a planar base member made of a dielectric material having the resonating element on one surface thereof.
- 18. The radio communication device according to claim 17 wherein said parasitic tuning element is applied to a surface of said base member.
- 19. The radio communicating device according to claim 18 wherein said resonating element and said parasitic tuning element are both on the same surface of the base member with a dielectric separating material disposed between them.
- 20. The radio communicating device according to claim 18 said resonating element and said parasitic tuning element are on opposing surfaces of said base member.
- 21. The radio communication device according to claim 17 wherein said parasitic tuning element is applied to a surface of said housing.
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|
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|
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|