The present invention relates generally to antennas, and more particularly to antennas used with wireless communications devices.
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.
In view of the above discussion, the present invention can provide compact, planar inverted-F antennas that can radiate within multiple frequencies for use within communications devices, such as radiotelephones. As used throughout, a xe2x80x9clinearxe2x80x9d conductive element is a conductive element that is straight (e.g., not bent or curved).
According to one embodiment of the present invention, a multi-frequency inverted-F antenna, includes a linear conductive element having opposite first and second sides and that extends along a longitudinal direction. First, second and third signal feeds are electrically connected to the linear conductive element and extend outwardly from the linear conductive element first side at respective first, second and third spaced-apart locations. A first switch, such as a micro-electromechanical systems (MEMS) switch, is electrically connected to the first feed and is configured to selectively connect the first signal feed to ground. Alternatively, the first feed may be directly connected to ground. A second switch, such as a MEMS switch, is electrically connected to the second feed and is configured to selectively connect the second feed to either ground or a receiver and/or a transmitter that receives and/or transmits wireless communications signals. In addition, the second switch can be opened to electrically isolate the second signal feed. A third switch, such as a MEMS switch, is electrically connected to the third signal feed and is configured to selectively connect the third feed to either ground or a receiver/transmitter. In addition, the third switch can be opened to electrically isolate the third signal feed.
Antennas according to this embodiment of the present invention can radiate in a first frequency band when the first switch electrically connects the first feed to ground, when the second switch electrically connects the second feed to a receiver/transmitter, and when the third switch is open. Antennas according to this embodiment of the present invention may also radiate in a second frequency band different than the first frequency band when the first and second switches electrically connect the respective first and second feeds to ground, and when the third switch electrically connects the third feed to the receiver/transmitter.
According to another embodiment of the present invention, an additional signal feed may be utilized. For example, a fourth signal feed may be electrically connected to the above-described linear conductive element and extend outwardly from the linear conductive element first side at a fourth location. A fourth switch, such as a MEMS switch, may be electrically connected to the fourth feed and may be configured to selectively connect the fourth feed to either ground or a receiver/transmitter. In addition, the fourth switch can be opened to electrically isolate the fourth signal feed. Accordingly, antennas according to this embodiment of the present invention may radiate within a third frequency band that is different than the first and second frequency bands when the first, second, and third switches electrically connect the respective first, second, and third feeds to ground, and the fourth switch electrically connects the fourth feed to a receiver/transmitter.
Inverted-F antennas may be provided with various configurations of signal feeds according to additional embodiments of the present invention. As such, 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. In addition, antennas according to the present invention, wherein one RF feed is activated at a time, overcome the need to isolate multiple, simultaneously operating antennas.