Flat dual frequency band antennas for wireless communicators

Details Flat dual frequency band antennas for wireless communicators Flat dual frequency band antennas for wireless communicators

1999-07-22

2001-03-20

Wong, Don (Department: 2821)

Communications: radio wave antennas

Antennas

Spiral or helical type

C343S7000MS, C343S872000

Reexamination Certificate

active

06204826

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates generally to antennas, and more particularly to antennas used with wireless communications devices.
BACKGROUND OF THE INVENTION
Radiotelephones generally refer to communications terminals which provide a wireless communications link to one or more other communications terminals. Radiotelephones may be used in a variety of different applications, including cellular telephone, land-mobile (e.g., police and fire departments), and satellite communications systems.
Radiotelephones typically include an antenna for transmitting and/or receiving wireless communications signals. Historically, monopole and dipole antennas have perhaps been most widely employed in various radiotelephone applications, due to their simplicity, wideband response, broad radiation pattern, and low cost.
However, radiotelephones and other wireless communications devices are undergoing miniaturization. Indeed, many contemporary radiotelephones are less than 11-12 centimeters in length. As a result, antennas utilized by radiotelephones have also undergone miniaturization. In addition, it is becoming desirable for radiotelephones to be able to operate within widely separated frequency bands in order to utilize more than one communications system. For example, GSM (Global System for Mobile communication) is a digital mobile telephone system that typically operates at a low frequency band, such as between 880 MHz and 960 MHz. DCS (Digital Communication System) is a digital mobile telephone system that typically operates at high frequency bands between 1710 MHz and 1880 MHz.
Small radiotelephone antennas typically operate within narrow frequency bands. As a result, it can be difficult for conventional radiotelephone antennas to operate over widely separated frequency bands. Furthermore, as radiotelephone antennas become smaller, the frequency bands within which they can operate typically become narrower.
Helix antennas are increasingly being utilized in handheld radiotelephones that operate within multiple frequency bands. Helix antennas typically include a conducting member wound in a helical pattern. As the radiating element of a helix antenna is wound about an axis, the axial length of the helix antenna can be considerably less than the length of a comparable monopole antenna. Thus, helix antennas may often be employed where the length of a monopole antenna is prohibitive.
FIG. 1
illustrates a conventional helix antenna
5
configured for dual frequency band operation. As shown in
FIG. 1
, the antenna
5
generally includes an antenna feed structure
6
, a radiating element
7
, and a parasitic element
8
. The radiating element
7
and parasitic element
8
are housed within a plastic tube or radome
9
with an end cap
10
. Unfortunately, helix antennas can be somewhat complex to manufacture, particularly with regard to positioning of the radiating and parasitic elements
7
,
8
.
Branch antennas are also being utilized in handheld radiotelephones that operate within multiple frequency bands. Branch antennas typically include a pair of conductive traces disposed on a substrate that serve as radiating elements and that diverge from a single feed point.
FIG. 2
illustrates a conventional branch antenna
15
configured for dual frequency band operation. As shown in
FIG. 2
, the antenna
15
generally includes a flat substrate
16
having a pair of meandering radiating elements
17
a
,
17
b
disposed thereon. The meandering radiating elements
17
a
,
17
b
diverge from a feed point
18
that electrically connects the antenna
15
to RF circuitry within a radiotelephone.
Each of the meandering radiating elements
17
a
,
17
b
is configured to resonate within a respective frequency band.
Unfortunately, branch antennas may transmit and receive electrical signals within a band of frequencies that are too narrow for radiotelephone operation. Furthermore, in order to decrease the size of a branch antenna, it is typically necessary to compress the meandering pattern of each radiating element. Unfortunately, as the meandering pattern of a radiating element becomes more compressed, the frequency band within which the radiating element can operate typically becomes more narrow.
Thus, in light of the above-mentioned demand for multiple frequency band radiotelephones and the problems with conventional antennas for such radiotelephones, a need exists for small radiotelephone antennas that are capable of operating in multiple widely separated frequency bands.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide small antennas for wireless communicators, such as radiotelephones, that are capable of operating in multiple widely separated frequency bands.
It is also an object of the present invention to facilitate radiotelephone miniaturization.
These and other objects of the present invention can be provided by an antenna having a continuous radiating element disposed on a dielectric substrate surface wherein meandering segments of the continuous radiating element are configured to couple with each other thereby causing the antenna to resonate within different first and second frequency bands. The continuous radiating element is a conductive trace (e.g., copper trace) that includes a first end electrically connected to a feed point and an opposite free end.
A first meandering segment of the conductive trace extends from the first end to an intermediate segment between the first end and the free end. The intermediate segment is spaced apart from the conductive trace first end preferably by a distance of less than or equal to about 2 millimeters (mm). However, the distance between the intermediate segment and the conductive trace first end may vary depending on the geometry of the antenna and the resonant frequencies at which the antenna is desired to resonate. A second meandering segment of the conductive trace extends from the intermediate segment to the free end. The conductive trace first and second meandering segments are configured to electrically couple with each other such that the antenna resonates at two separate and distinct (i.e., low and high) frequency bands.
The conductive trace has a substantially constant width except for a portion of the first or second meandering segments which has an increased width. The portion with the increased width is a tuning parameter which can affect the frequency band and center frequency of both the low and high frequency bands.
According to another embodiment of the present invention, a conductive element may be disposed on the second surface of the dielectric substrate in overlying juxtaposition with one or both of the conductive trace first and second meandering segments. The conductive element is configured to parasitically couple with at least one of the conductive trace first and second meandering segments to thereby affect the frequency band and center frequency within which the antenna resonates.
Antennas according to the present invention are particularly well suited for operation within various communications systems utilizing multiple frequency bands. Furthermore, because of their small size, antennas according to the present invention can be utilized within very small communications devices. In addition, because a single substrate is utilized, antennas according to the present invention can be easier to manufacture than conventional dual-band antennas.


REFERENCES:
patent: 5986609 (1999-11-01), Spall
patent: 5986616 (1999-11-01), Edvardsson
patent: 6016126 (2000-01-01), Holshouser
patent: 6040803 (2000-03-01), Spall
patent: 6069592 (2000-05-01), Wass
patent: 0 520 197 A2 (1992-05-01), None
patent: 0 923 158 A2 (1999-06-01), None
International Search Report dated Oct. 13, 2000, International Application No. PCT/US00/16516.

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