Communications: radio wave antennas – Antennas – With radio cabinet
Reexamination Certificate
2000-05-22
2001-03-20
Phan, Thu (Department: 2821)
Communications: radio wave antennas
Antennas
With radio cabinet
C343S7000MS, C455S090300
Reexamination Certificate
active
06204819
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 been 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 centimeters in length. As a result, there is increasing interest in small antennas that can be utilized as internally-mounted antennas for radiotelephones.
In addition, it is becoming desirable for radiotelephones to be able to operate within multiple frequency bands in order to utilize more than one communications system. For example, GSM (Global System for Mobile) is a digital mobile telephone system that operates from 880 MHz to 960 MHz. DCS (Digital Communications System) is a digital mobile telephone system that operates from 1710 MHz to 1880 MHz. The frequency bands allocated for cellular AMPS (Advanced Mobile Phone Service) and D-AMPS (Digital Advanced Mobile Phone Service) in North America are 824-894 MHz and 1850-1990 MHz, respectively. Since there are two different frequency bands for these systems, radiotelephone service subscribers who travel over service areas employing different frequency bands may need two separate antennas unless a dual-frequency antenna is used.
In addition, radiotelephones may also incorporate Global Positioning System (GPS) technology and Bluetooth wireless technology. GPS is a constellation of spaced-apart satellites that orbit the Earth and make it possible for people with ground receivers to pinpoint their geographic location. Bluetooth technology provides a universal radio interface in the 2.45 GHz frequency band that enables portable electronic devices to connect and communicate wirelessly via short-range ad hoc networks. Accordingly, radiotelephones incorporating these technologies may require additional antennas tuned for the particular frequencies of GPS and Bluetooth.
Inverted-F antennas are designed to fit within the confines of radiotelephones, particularly radiotelephones undergoing miniaturization. As is well known to those having skill in the art, inverted-F antennas typically include a linear (i.e., straight) conductive element that is maintained in spaced apart relationship with a ground plane. Examples of inverted-F antennas are described in U.S. Pat. Nos. 5,684,492 and 5,434,579 which are incorporated herein by reference in their entirety.
Conventional inverted-F antennas, by design, resonate within a narrow frequency band, as compared with other types of antennas, such as helices, monopoles and dipoles. In addition, conventional inverted-F antennas are typically large. Lumped elements can be used to match a smaller non-resonant antenna to an RF circuit. Unfortunately, such an antenna may be narrow band and the lumped elements may introduce additional losses in the overall transmitted/received signal, may take up circuit board space, and may add to manufacturing costs.
Unfortunately, it may be unrealistic to incorporate multiple antennas within a radiotelephone for aesthetic reasons as well as for space-constraint reasons. In addition, some way of isolating multiple antennas operating simultaneously in close proximity within a radiotelephone may also be necessary. As such, a need exists for small, internal radiotelephone antennas that can operate within multiple frequency bands.
SUMMARY OF THE INVENTION
In view of the above discussion, the present invention can provide compact antennas that can radiate within multiple frequency bands for use within wireless communications devices, such as radiotelephones. An antenna according to an embodiment of the present invention includes first and second conductive branches. A first conductive branch has opposite ends, and first and second feeds extending therefrom adjacent one of the ends. The first and second feeds terminate at respective first and second micro-electromechanical systems (MEMS) switches. The first MEMS switch is configured to selectively connect the first feed to either ground or to a receiver and/or a transmitter that receives and/or transmits wireless communications signals. The second MEMS switch is configured to selectively connect the second feed to either the same receiver/transmitter (or a different receiver/transmitter) or to maintain the second feed in an open circuit (i.e., electrically isolating the second feed).
A second conductive branch is in adjacent, spaced-apart relationship with the first conductive branch and has opposite ends. One end of the second conductive branch terminates at a third MEMS switch configured to selectively connect the second conductive branch to either a receiver/transmitter or to maintain the second conductive branch in an open circuit. The opposite end of the second conductive branch is connected to the first conductive branch via a fourth MEMS switch. The fourth MEMS switch is configured to be selectively closed to electrically connect the first and second conductive branches such that the antenna radiates as a loop antenna in a first frequency band. The fourth switch is also configured to open to electrically isolate the first and second conductive branches such that the antenna radiates as an inverted-F antenna in a second frequency band different from the first frequency band.
When the fourth MEMS switch is closed to electrically connect the first and second conductive branches, the first MEMS switch is connected to the receiver/transmitter, the second MEMS switch is open to isolate the second feed from the first conductive branch, and the third MEMS switch is connected to a receiver/transmitter. When the fourth MEMS switch is open to electrically isolate the first and second conductive branches, the first MEMS switch is connected to ground, the second MEMS switch is connected to the receiver/transmitter, and the third MEMS switch is open.
When the first and second conductive branches of an antenna according to the present invention are electrically connected such that the antenna radiates as a loop antenna in a first frequency band, the first MEMS switch may be connected to a first receiver that receives wireless communications signals in the first frequency band, such as a GPS receiver. When the first and second conductive branches are electrically isolated such that the antenna radiates as an inverted-F antenna in a second frequency band, the second switch may be connected to a second, different receiver that receives wireless communications signals in the second frequency band, such as a Bluetooth receiver.
According to additional embodiments of the present invention, portions (or all) of the first and second conductive branches may be disposed on or within one or more dielectric substrates. In addition, antennas according to the present invention may include second conductive branches with meandering configurations.
Antennas according to the present invention may be particularly well suited for use within a variety of communications systems utilizing different frequency bands. Furthermore, because of their compact size, antennas according to the present invention may be easily incorporated within small communications devices. Furthermore, antennas according to the present invention are ideal for use with receive-only applications such as GPS.
REFERENCES:
patent: 6025805 (2000-02-01), Smith et al.
patent: 2316540 (1998-02-01), None
patent: 10-224142 (1998-08-01),
Hayes Gerard James
Sadler Robert A.
Clinger James
Myers Bigel & Sibley & Sajovec
Phan Thu
Telefonaktiebolaget L.M. Ericsson
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