Multiple frequency band branch antennas for wireless...

Details Multiple frequency band branch antennas for wireless... Multiple frequency band branch antennas for wireless...

1999-07-22

2001-03-06

Wong, Don (Department: 2821)

Communications: radio wave antennas

Antennas

With radio cabinet

C343S895000, C343S722000, C343S725000

Reexamination Certificate

active

06198442

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 Communications 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 a branch antenna having a dielectric substrate with high and low frequency band radiating elements that are controllably coupled with each other disposed on a surface thereof. The high and low frequency band radiating elements have meandering patterns and are electrically connected to a feed point that electrically connects the antenna to RF circuitry within a communications device. Lumped electrical elements are electrically connected in series between the high and low frequency band radiating elements and the feed point to reduce coupling effects between the high and low frequency band radiating elements. Preferably, a capacitor is electrically connected in series with the high frequency band radiating element to increase resonant bandwidth thereof. Preferably, an inductor is electrically connected in series with the low frequency band radiating element to increase resonant bandwidth thereof.
According to another embodiment of the present invention, a dielectric substrate having a folded configuration includes a pair of high and low frequency band radiating elements disposed on various sides thereof. A low frequency band radiating element is disposed on a first side of the dielectric substrate and is electrically connected to a feed point that is also located on the first side. A high frequency band radiating element is disposed on a first side of the dielectric substrate and is electrically connected to the feed point. A portion of the high frequency band radiating element is disposed on a second side of the folded substrate opposite from the first side.
A first lumped electrical element is disposed on the dielectric substrate first side and is electrically connected in series with the high frequency band radiating element at the feed point. A second lumped electrical element is disposed on the dielectric substrate first side and is electrically connected in series with the low frequency band radiating element at the feed point.
Antennas according to the present invention are particularly well suited for operation within various communications systems utilizing multiple, widely separated frequency bands. Furthermore, because of their small size, antennas according to the present invention can be utilized within very small communications devices.


REFERENCES:
patent: 5635945 (1997-06-01), McConnell et al.
patent: 5706019 (1998-01-01), Darden, IV et al.
patent: 5936587 (1999-10-01), Gudilev et al.
patent: 5969684 (1999-10-01), Oh et al.

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