Patent Publication Number: US-6662028-B1

Title: Multiple frequency inverted-F antennas having multiple switchable feed points and wireless communicators incorporating the same

Description:
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, planar inverted-F antennas that can radiate within multiple frequencies for use within communications devices, such as radiotelephones. As used throughout, a “linear” 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. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of an exemplary radiotelephone within which an antenna according to the present invention may be incorporated. 
     FIG. 2 is a schematic illustration of a conventional arrangement of electronic components for enabling a radiotelephone to transmit and receive telecommunications signals. 
     FIG. 3 is a perspective view of a conventional planar inverted-F antenna. 
     FIG. 4A is a perspective view of a planar inverted-F antenna having multiple switchable feed points according to an embodiment of the present invention, and wherein a first feed is connected to ground, a second feed is connected to RF circuitry, and third and fourth feeds are open such that the antenna is operative within a first frequency band. 
     FIG. 4B is a perspective view of the antenna of FIG. 4A, wherein the first and second feeds are connected to ground, the third feed is connected to RF circuitry, and the fourth feed is open such that the antenna is operative within a second frequency band. 
     FIG. 4C is a perspective view of the antenna of FIG. 4A, wherein the first, second, and third feeds are connected to ground, and the fourth feed is connected to RF circuitry such that the antenna is operative within a third frequency band. 
     FIG. 5A is a side elevation view of a dielectric substrate having the antenna of FIGS. 4A-4C disposed thereon, and wherein the dielectric substrate is in adjacent, spaced-apart relation with a ground plane within a communications device, according to another embodiment of the present invention. 
     FIG. 5B is a side elevation view of a dielectric substrate having the antenna of FIGS. 4A-4C disposed therewithin, and wherein the dielectric substrate is in adjacent, spaced-apart relation with a ground plane within a communications device, according to another embodiment of the present invention. 
     FIG. 6A is a perspective view of a planar inverted-F antenna having multiple switchable feed points according to an embodiment of the present invention, and wherein a first feed is connected to ground, a second feed is connected to RF circuitry, and a third feed is open such that the antenna is operative within a first frequency band. 
     FIG. 6B is a graph of the VSWR performance of the antenna of FIG.  6 A. 
     FIG. 7A is a perspective view of a planar inverted-F antenna having multiple switchable feed points according to an embodiment of the present invention, and wherein first and second feeds are connected to ground, and a third feed is connected to RF circuitry such that the antenna is operative within a second frequency band. 
     FIG. 7B is a graph of the VSWR performance of the antenna of FIG.  7 A. 
     FIG. 8A is a perspective view of a planar inverted-F antenna having multiple switchable feed points according to another embodiment of the present invention, and wherein a first feed is connected to ground, a second feed is connected to RF circuitry, and third, fourth, fifth, sixth, and seventh feeds are open such that the antenna is operative within a first frequency band. 
     FIG. 8B is a perspective view of the antenna of FIG. 8A, wherein the first and second feeds are connected to ground, the third feed is connected to RF circuitry, and the fourth, fifth, sixth, and seventh feeds are open such that the antenna is operative within a second frequency band. 
     FIG. 8C is a perspective view of the antenna of FIG. 8A, wherein the first, second, and third feeds are connected to ground, the fourth feed is connected to RF circuitry, and the fifth, sixth, and seventh feeds are open such that the antenna is operative within a third frequency band. 
     FIG. 9 is a bottom plan view of a multi-frequency planar inverted-F antenna according to another embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. In the drawings, the thickness of layers and regions may be exaggerated for clarity. Like numbers refer to like elements throughout the description of the drawings. It will be understood that when an element such as a layer, region or substrate is referred to as being “on” another element, it can be directly on the other element or intervening elements may also be present. In contrast, when an element is referred to as being “directly on” another element, there are no intervening elements present. 
     Referring now to FIG. 1, a radiotelephone  10 , within which antennas according to various embodiments of the present invention may be incorporated, is illustrated. The housing  12  of the illustrated radiotelephone  10  includes a top portion  13  and a bottom portion  14  connected thereto to form a cavity therein. Top and bottom housing portions  13 ,  14  house a keypad  15  including a plurality of keys  16 , a display  17 , and electronic components (not shown) that enable the radiotelephone  10  to transmit and receive radiotelephone communications signals. 
     A conventional arrangement of electronic components that enable a radiotelephone to transmit and receive radiotelephone communication signals is shown schematically in FIG. 2, and is understood by those skilled in the art of radiotelephone communications. An antenna  22  for receiving and transmitting radiotelephone communication signals is electrically connected to a radio-frequency transceiver  24  that is further electrically connected to a controller  25 , such as a microprocessor. The controller  25  is electrically connected to a speaker  26  that transmits a remote signal from the controller  25  to a user of a radiotelephone. The controller  25  is also electrically connected to a microphone  27  that receives a voice signal from a user and transmits the voice signal through the controller  25  and transceiver  24  to a remote device. The controller  25  is electrically connected to a keypad  15  and display  17  that facilitate radiotelephone operation. 
     As is known to those skilled in the art of communications devices, an antenna is a device for transmitting and/or receiving electrical signals. A transmitting antenna typically includes a feed assembly that induces or illuminates an aperture or reflecting surface to radiate an electromagnetic field. A receiving antenna typically includes an aperture or surface focusing an incident radiation field to a collecting feed, producing an electronic signal proportional to the incident radiation. The amount of power radiated from or received by an antenna depends on its aperture area and is described in terms of gain. 
     Radiation patterns for antennas are often plotted using polar coordinates. Voltage Standing Wave Ratio (VSWR) relates to the impedance match of an antenna feed point with a feed line or transmission line of a communications device, such as a radiotelephone. To radiate radio frequency (RF) energy with minimum loss, or to pass along received RF energy to a radiotelephone receiver with minimum loss, the impedance of a radiotelephone antenna is conventionally matched to the impedance of a transmission line or feed point. 
     Conventional radiotelephones typically employ an antenna which is electrically connected to a transceiver operably associated with a signal processing circuit positioned on an internally disposed printed circuit board. In order to maximize power transfer between an antenna and a transceiver, the transceiver and the antenna are preferably interconnected such that their respective impedances are substantially “matched,” i.e., electrically tuned to filter out or compensate for undesired antenna impedance components to provide a 50 Ohm (Ω) (or desired) impedance value at the feed point. 
     Referring now to FIG. 3, a conventional planar inverted-F antenna is illustrated. The illustrated antenna  30  includes a linear conductive element  32  maintained in spaced-apart relationship with a ground plane  34 . Conventional inverted-F antennas, such as that illustrated in FIG. 3, derive their name from a resemblance to the letter “F.” The illustrated conductive element  32  is grounded to the ground plane  34  as indicated by  36 . An RF connection  37  extends from underlying RF circuitry through the ground plane  34  to the conductive element  32 . 
     Referring now to FIG. 4A, a multi-frequency inverted-F antenna  40  having a compact, linear configuration according to an embodiment of the present invention, is illustrated. The illustrated antenna  40  includes a linear conductive element  42  having opposite first and second sides  42   a ,  42   b , and extending along a longitudinal direction D. The multi-frequency inverted-F antenna  40  is illustrated in an installed position within a wireless communications device, such as a radiotelephone (FIG.  1 ). The linear conductive element  42  is maintained in adjacent, spaced-apart relationship with a ground plane  43 , such as a printed circuit board (PCB) within a radiotelephone (or other wireless communications device). 
     A first feed  44   a  is electrically connected to the linear conductive element  42  and extends outwardly from the linear conductive element first side  42   a  at a first location L 1 , as illustrated. A second feed  44   b  is electrically connected to the linear conductive element  42  and extends outwardly from the linear conductive element first side  42   a  at a second location L 2 , as illustrated. The second location L 2  is spaced-apart from the first location along the longitudinal direction D, as illustrated. A third feed  44   c  is electrically connected to the linear conductive element  42  and extends outwardly from the linear conductive element first side  42   a  at a third location L 3 , as illustrated. The third location L 3  is spaced-apart from the first and second locations L 1 , L 2  along the longitudinal direction D, as illustrated. A fourth feed  44   d  is electrically connected to the linear conductive element  42  and extends outwardly from the linear conductive element first side  42   a  at a fourth location L 4 , as illustrated. The fourth location L 4  is spaced-apart from the first, second, and third locations L 1 , L 2 , L 3  along the longitudinal direction D. 
     Still referring to FIG. 4A, a first switch  46   a , such as a micro-electromechanical systems (MEMS) switch, is electrically connected to the first feed  44   a  and is configured to selectively connect the first feed  44   a  to ground (e.g., to the ground plane  43 ). Alternatively, the first feed  44   a  may be directly connected to ground without a MEMS (or other) switch. It is understood that in each embodiment of the present invention, one or more feeds (typically the first feed and/or second feed) may be directly connected to ground without requiring a MEMS (or other) switch. 
     A MEMS switch is an integrated micro device that combines electrical and mechanical components fabricated using integrated circuit (IC) compatible batch-processing techniques and can range in size from micrometers to millimeters. MEMS devices in general, and MEMS switches in particular, are understood by those of skill in the art and need not be described further herein. Exemplary MEMS switches are described in U.S. Pat. No. 5,909,078. It also will be understood that conventional switches including relays and actuators may be used with antennas according to embodiments of the present invention. The present invention is not limited solely to the use of MEMS switches. 
     A second switch  46   b , such as a MEMS switch, is electrically connected to the second feed  44   b  and is configured to selectively connect the second feed  44   b  to ground, to a receiver/transmitter that receives and/or sends wireless communications signals (e.g., radiotelephone signals), or to maintain the second feed  44   b  in an open circuit (i.e., the second MEMS switch  46   b  can be open). A third switch  46   c , such as a MEMS switch, is electrically connected to the third feed  44   c  and is configured to selectively connect the third feed  44   c  to ground, to a receiver/transmitter that receives and/or sends wireless communications signals (e.g., radiotelephone signals), or to maintain the third feed  44   c  in an open circuit (i.e., the third MEMS switch  46   c  can be open). A fourth switch  46   d , such as a MEMS switch, is electrically connected to the fourth feed  44   d  and is configured to selectively connect the fourth feed to ground, to a receiver/transmitter that receives and/or sends wireless communications signals (e.g., radiotelephone signals), or to maintain the fourth feed in an open circuit (i.e., the fourth MEMS switch  46   c  can be open). 
     FIGS. 4A-4C illustrate how the various MEMS switches  46   a - 46   d  allow the multi-frequency inverted-F antenna  40  to radiate within multiple, different frequency bands, according to an embodiment of the present invention. As illustrated in FIG. 4A, the antenna  40  radiates in a first frequency band when the first MEMS switch  46   a  electrically connects the first feed  44   a  to ground (indicated by G) or when the first feed  44   a  is directly connected to ground (indicated by G), when the second MEMS switch  46   b  electrically connects the second feed  44   b  to a receiver/transmitter (indicated by RF), and when the third and fourth MEMS switches  46   c ,  46   d  are open (indicated by O). 
     As illustrated in FIG. 4B, the antenna  40  radiates in a second frequency band that is different from the first frequency band when the first MEMS switch  46   a  electrically connects the first feed  44   a  to ground (indicated by G) or when the first feed  44   a  is directly connected to ground (indicated by G), when the second MEMS switch  46   b  electrically connects the second feed  44   b  to ground (indicated by G), when the third MEMS switch  46   c  electrically connects the third feed  44   c  to a receiver/transmitter (indicated by RF), and when the fourth MEMS switch  46   d  is open (indicated by O). The second frequency band may be greater than the first frequency band. For example, the first frequency band may be between about 900 MHz and 960 MHz and the second frequency band may be between about 1200 MHz and 1400 MHz. However, it is understood that the second frequency band may also be a lower frequency band than the first frequency band. 
     As illustrated in FIG. 4C, the antenna  40  radiates in a third frequency band that is different from the first and second frequency bands when the first, second, and third MEMS switches  46   a ,  46   b ,  46   c  electrically connect the respective first, second, and third feeds  44   a ,  44   b ,  44   c  to ground (indicated by G) or when the first feed  44   a  is directly connected to ground (indicated by G), and when the fourth MEMS switch  46   d  electrically connects the fourth feed  44   d  to a receiver/transmitter (indicated by RF). The third frequency band may be greater than the first and second frequency bands. For example, the third frequency band may be between about 2200 MHz and 2400 MHz and the first and second frequency bands may be between about 900 MHz-960 MHz and 1200 MHz-1400 MHz, respectively. However, it is also understood that the third frequency band may be a lower frequency band than the first and second frequency bands. 
     According to another embodiment of the present invention, illustrated in FIG. 5A, the planar, conductive element  42  of the antenna of FIGS. 4A-4C may be formed on a dielectric substrate  50 , for example by etching a metal layer formed on the dielectric substrate. An exemplary material for use as a dielectric substrate  50  is FR4 or polyimide, which is well known to those having skill in the art of communications devices. However, various other dielectric materials also may be utilized. Preferably, the dielectric substrate  50  has a dielectric constant between about 2 and about 4. However, it is to be understood that dielectric substrates having different dielectric constants may be utilized without departing from the spirit and intent of the present invention. 
     The antenna  40  of FIG. 5A is illustrated in an installed position within a wireless communications device, such as a radiotelephone. The dielectric substrate  50  having a conductive element  42  disposed thereon is maintained in adjacent, spaced-apart relationship with a ground plane  43 . In the illustrated configuration, the first, second, and third feeds  44   a ,  44   b ,  44   c  are electrically connected to ground (e.g., the ground plane  43 ) via respective first, second, and third MEMS switches (not shown). The fourth feed  44   d  is electrically connected to a receiver/transmitter  24  via a fourth MEMS switch (not shown). Each of the first, second, third and fourth feeds  44   a ,  44   b ,  44   c ,  44   d  extend through respective apertures  47  in the dielectric substrate  50 . The distance H between the dielectric substrate  50  and the ground plane  43  is preferably maintained at between about 2 mm and about 10 mm. 
     According to another embodiment of the present invention, a linear conductive element  42  may be disposed within a dielectric substrate  50  as illustrated in FIG.  5 B. In the illustrated configuration, the dielectric substrate  50  is in adjacent, spaced-apart relationship with a ground plane  43  within a wireless communications device, such as a radiotelephone. The first, second, and third feeds  44   a ,  44   b ,  44   c  are electrically connected to ground (e.g., the ground plane  43 ) via respective first, second, and third MEMS switches (not shown). The fourth feed  44   d  is electrically connected to a receiver/transmitter  24  via a fourth MEMS switch (not shown). Each of the first, second, third and fourth feeds  44   a ,  44   b ,  44   c ,  44   d  extend through respective apertures  47  in the dielectric substrate  50 . 
     A preferred conductive material out of which the linear conductive element  42  of FIGS. 4A-4C and FIGS. 5A-5B may be formed is copper, typically 0.5 ounce (14 grams) copper. For example, the conductive element  42  may be formed from copper foil. Alternatively, the conductive element  42  may be a copper trace disposed on a substrate, as illustrated in FIG.  5 A. However, a linear conductive element  42  according to the present invention may be formed from various conductive materials and is not limited to copper. 
     Referring now to FIGS. 6A-6B, an antenna  40  according to the above-described embodiment of the present invention has a plurality of MEMS switches configured such that the antenna  40  resonates around 1900 MHz (FIG.  6 B). The illustrated antenna  40  includes first, second, and third feeds  44   a ,  44   b , and  44   c . Each feed includes a respective MEMS switch  46   a ,  46   b ,  46   c , as described above. The first MEMS switch  46   a  electrically connects the first feed  44   a  to ground. Alternatively, the first feed  44   a  may be directly connected to ground. The second MEMS switch  46   b  electrically connects the second feed to a receiver/transmitter. The third MEMS switch  46   c  is open. In the illustrated embodiment, the linear conductive element  42  is spaced-apart from the ground plane  43  by a distance of eight millimeters (8 mm). The first and second feeds  44   a ,  44   b  are separated by 4 mm, and the second and third feeds are separated by 6 mm. 
     Referring now to FIGS. 7A-7B, an antenna  40  according to the above-described embodiment of the present invention has a plurality of MEMS switches configured such that the antenna  40  resonates around 2500 MHz (FIG.  7 B). The illustrated antenna  40  includes first, second, and third feeds  44   a ,  44   b , and  44   c . Each feed includes a respective MEMS switch  46   a ,  46   b ,  46   c , as described above. The first and second MEMS switches  46   a ,  46   b  electrically connect the respective first and second feeds  44   a ,  44   b  to ground. Alternatively, the first feed  44   a  may be directly connected to ground. The third MEMS switch  46   c  electrically connects the second feed to a receiver/transmitter. In the illustrated embodiment, the linear conductive element  42  is spaced-apart from the ground plane  43  by a distance of eight millimeters (8 mm). The first and second feeds  44   a ,  44   b  are separated by 4 mm, and the second and third feeds are separated by 6 mm. 
     Referring now to FIGS. 8A-8C, a multi-frequency planar inverted-F antenna  140  according to another embodiment of the present invention is illustrated. The antenna  140  includes a generally rectangular, linear conductive element  142  having opposite first and second sides  142   a ,  142   b  and extending along a longitudinal direction D. The multi-frequency inverted-F antenna  140  is illustrated in an installed position within a wireless communications device, such as a radiotelephone (FIG.  1 ). The linear conductive element  142  is maintained in adjacent, spaced-apart relationship with a ground plane  43 , such as a printed circuit board (PCB) within a radiotelephone (or other wireless communications device). 
     First and second feeds  144   a ,  144   b  are electrically connected to the conductive element  142  and extend outwardly from the conductive element first side  142   a  in adjacent spaced-apart relationship at a first location L 1 , as illustrated. Third and fourth feeds  144   c ,  144   d  are electrically connected to the conductive element  142  and extend outwardly from the conductive element first side  142   a  in adjacent spaced-apart relationship at a second location L 2 , as illustrated. The second location L 2  is spaced-apart from the first location L 1  along the longitudinal direction D, as illustrated. Fifth and sixth feeds  144   e ,  144   f  are electrically connected to the conductive element  142  and extend outwardly from the conductive element first side  142   a  in adjacent spaced-apart relationship at a third location L 3 , as illustrated. The third location L 3  is spaced-apart from the first and second locations L 1 , L 2  along the longitudinal direction D, as illustrated. A seventh feed  144   g  is electrically connected to the conductive element  142  and extends outwardly from the conductive element first side  142   a  in adjacent spaced-apart relationship at a fourth location L 4 , as illustrated. The fourth location L 4  is spaced-apart from the first, second, and third locations L 1 , L 2 , L 3  along the longitudinal direction D, as illustrated. 
     Respective first and second MEMS switches  146   a ,  146   b  are electrically connected to the respective first and second feeds  144   a ,  144   b . The first MEMS switch  146   a  is configured to selectively connect the first feed  144   a  to ground. Alternatively, the first feed  144   a  may be directly connected to ground. The second MEMS switch  144   b  is configured to selectively connect the second feed  144   b  to ground. Alternatively, the second feed  144   b  may be directly connected to ground. 
     Respective third and fourth MEMS switches  146   c ,  146   d  are electrically connected to the respective third and fourth feeds  144   c ,  144   d . The third and fourth MEMS switches  144   c ,  144   d  are configured to selectively connect the respective third and fourth feeds  144   c ,  144   d  to ground, to a receiver/transmitter that receives and/or sends wireless communications signals (e.g., radiotelephone signals), or to maintain the respective third and fourth feeds  144   c ,  144   d  in an open circuit (i.e., the third and fourth MEMS switches  146   c ,  146   d  can be open). 
     Respective fifth and sixth MEMS switches  146   e ,  146   f  are electrically connected to the respective fifth and sixth feeds  144   e ,  144   f . The fifth and sixth MEMS switches  144   e ,  144   f  are configured to selectively connect the respective fifth and sixth feeds  144   e ,  144   f  to ground, to a receiver/transmitter that receives and/or sends wireless communications signals (e.g., radiotelephone signals), or to maintain the respective fifth and sixth feeds in an open circuit (i.e., the fifth and sixth MEMS switches  146   e ,  146   f  can be open). 
     A seventh MEMS switch  146   g  is electrically connected to the respective seventh feed  144   g . The seventh MEMS switch  144   g  is configured to selectively connect the seventh feed  144   g  to a receiver/transmitter that receives and/or sends wireless communications signals (e.g., radiotelephone signals), or to maintain the seventh feed in an open circuit (i.e., the seventh MEMS switch  146   e ,  146   f  can be open). 
     FIGS. 8A-8C illustrate how the various MEMS switches  146   a - 146   g  allow the multi-frequency inverted-F antenna  140  to radiate within multiple, different frequency bands. As illustrated in FIG. 8A, the antenna  140  radiates in a first frequency band radiates in a first frequency band when the first and second MEMS switches  146   a ,  146   b  electrically connect the first and second feeds  144   a ,  144   b  to ground (indicated by G) or when the first and/or second feeds  144   a ,  144   b  are directly connected to ground, when the fourth MEMS switch  146   d  electrically connects the fourth feed  144   d  to the receiver/transmitter (indicated by RF), and when the third, fifth, sixth, and seventh MEMS switches  146   c ,  146   e ,  146   f ,  146   g  are open (indicated by O). 
     As illustrated in FIG. 8B, the antenna  140  radiates in a second frequency band when the first, second, third, and fourth MEMS switches  146   a ,  146   b ,  146   c ,  146   d  electrically connect the respective first, second, third, and fourth feeds  144   a ,  144   b ,  144   c ,  144   d  to ground (indicated by G), when the fifth MEMS switch  146   e  electrically connects the fifth feed  144   e  to the receiver/transmitter (indicated by RF), and when the remaining MEMS switches (i.e., the sixth and seventh MEMS switches  146   f ,  146   g  ) are open (indicated by O). The second frequency band may be greater than the first frequency band. For example, the first frequency band may be between about 900 MHz and 960 MHz and the second frequency band may be between about 1200 MHz and 1400 MHz. However, it is understood that the second frequency band may also be a lower frequency band than the first frequency band. 
     As illustrated in FIG. 8C, the antenna  140  radiates in a third frequency band that is different from the first and second frequency bands when the first, second, third, fourth, fifth, and sixth MEMS switches electrically connect the respective first, second, third, fourth, fifth, and sixth feeds to ground (indicated by G), and when the seventh MEMS switch  146   g  electrically connects the seventh feed  144   g  to the receiver/transmitter (indicated by RF). The third frequency band may be greater than the first and second frequency bands. For example, the third frequency band may be between about 2200 MHz and 2400 MHz and the first and second frequency bands may be between about 900 MHz-960 MHz and 1200 MHz-1400 MHz, respectively. However, it is also understood that the third frequency band may be a lower frequency band than the first and second frequency bands. 
     The antenna  140  may be operative within additional frequency bands by connecting the various feeds in different configurations via the various MEMS switches ( 146   a - 146   g ). 
     As described above with respect to FIGS. 5A-5B, the illustrated antenna  140  of FIGS. 8A-8C may have the conductive element  142  formed on a dielectric substrate  50  (See FIG.  5 A). Alternatively, the illustrated antenna  140  of FIGS. 8A-8C may have the conductive element  142  disposed within a dielectric substrate  50  (See FIG.  5 B). 
     Referring now to FIG. 9, a multi-frequency planar inverted-F antenna  240  according to another embodiment of the present invention is illustrated. The antenna  240  includes a generally rectangular, linear conductive element  242  having opposite first and second sides  242   a ,  242   b  and extending along a longitudinal direction D. A plurality of pairs of feeds  243   a - 243   d  are electrically connected to the conductive element  242  and extend outwardly from the conductive element first side  242   a  in adjacent, spaced-apart relationship along the longitudinal direction D. A respective one of the feeds in each pair is configured to be electrically connected to ground. The other one of the feeds in each pair is configured to be electrically connected to a receiver/transmitter. When a particular pair of feeds are “active”, the remaining pairs of feeds are open circuited. 
     For example, first and second feeds  244   a ,  244   b  make up the first pair of feeds  243 a and are electrically connected to the conductive element  242 . The first and second feeds  244   a ,  244   b  extend outwardly from the conductive element first side  242   a  in adjacent spaced-apart relationship at a first location L 1 . Third and fourth feeds  244   c ,  244   d  make up a second pair of feeds  243 b and are electrically connected to the conductive element  242 . The third and fourth feeds  244   c ,  244   d  extend outwardly from the conductive element first side  242   a  in adjacent spaced-apart relationship at a second location L 2 . As illustrated, the second location L 2  is spaced-apart from the first location L 1  along the longitudinal direction D. 
     Fifth and sixth feeds  244   e ,  244   f  make up a third pair of feeds  243   c  and are electrically connected to the conductive element  242  and extend outwardly from the conductive element first side  242  in adjacent spaced-apart relationship at a third location L 3 , as illustrated. The third location L 3  is spaced-apart from the second location L 2  along the longitudinal direction D, as illustrated. 
     Seventh and eighth feeds  244   g ,  244   h  make up a fourth pair of feeds  243 d and are electrically connected to the conductive element  242 . The seventh and eighth feeds  244   g ,  244   h  extend outwardly from the conductive element first side  242   a  in adjacent spaced-apart relationship at a fourth location L 4 , as illustrated. The fourth location L 4  is spaced-apart from the first, second, and third locations L 2 , L 3 , L 4  along the longitudinal direction D, as illustrated. 
     Respective first and second MEMS switches (not shown) are electrically connected to the respective first and second feeds  244   a ,  244   b . The first MEMS switch is configured to selectively connect the first feed  244   a  to ground or to open. The second MEMS switch is configured to selectively connect the second feed  244   b  to a receiver/transmitter that receives and/or sends wireless communications signals (e.g., radiotelephone signals), or to maintain the second feed  244   b  in an open circuit. 
     Respective third and fourth MEMS switches (not shown) are electrically connected to the respective third and fourth feeds  244   c ,  244   d . The third MEMS switch is configured to selectively connect the third feed  244   c  to ground or to maintain the third feed  244   c  in an open circuit. The fourth MEMS switch is configured to selectively connect the fourth feed  244   d  to a receiver/transmitter that receives and/or sends wireless communications signals (e.g., radiotelephone signals), or to maintain the fourth feed  244   d  in an open circuit. 
     Respective fifth and sixth MEMS switches (not shown) are electrically connected to the respective fifth and sixth feeds  244   e ,  244   f . The fifth MEMS switch is configured to selectively connect the fifth feed  244   e  to ground or to maintain the fifth feed  244   e  in an open circuit. The sixth MEMS switch is configured to selectively connect the sixth feed  244   f  to a receiver/transmitter that receives and/or sends wireless communications signals (e.g., radiotelephone signals), or to maintain the sixth feed  244   f  in an open circuit. 
     Respective seventh and eighth MEMS switches (not shown) are electrically connected to the respective seventh and eighth feeds  244   g ,  244   h . The seventh MEMS switch is configured to selectively connect the seventh feed  244   g  to ground or to maintain the seventh feed  244   g  in an open circuit. The eighth MEMS switch is configured to selectively connect the eighth feed  244   h  to a receiver/transmitter that receives and/or sends wireless communications signals (e.g., radiotelephone signals), or to maintain the eighth feed  244   h  in an open circuit. 
     The antenna  240  radiates in a first frequency band when the first MEMS switch electrically connects the first feed  244   a  to ground, when the second MEMS switch electrically connects the second feed  244   b  to a receiver/transmitter, and when the remaining MEMS switches (i.e., the third, fourth, fifth, sixth, seventh, and eighth MEMS switches) are open. 
     The antenna  240  radiates in a second frequency band different from the first frequency band when the third MEMS switch electrically connects the third feed  244   c  to ground, when the fourth MEMS switch electrically connects the fourth feed  244   d  to a receiver/transmitter, and when the remaining MEMS switches (i.e., the first, second, fifth, sixth, seventh, and eighth MEMS switches) are open. 
     The antenna  240  radiates in a third frequency band different from the first and second frequency bands when the fifth MEMS switch electrically connects the fifth feed  244   e  to ground, when the sixth MEMS switch electrically connects the sixth feed  244   f  to a receiver/transmitter, and when the remaining MEMS switches (i.e., the first, second, third, fourth, seventh, and eighth MEMS switches) are open. 
     The antenna  240  radiates in a fourth frequency band different from the first, second, and third frequency bands when the seventh MEMS switch electrically connects the seventh feed  244   g  to ground, when the eighth MEMS switch electrically connects the eighth feed  244   h  to a receiver/transmitter, and when the remaining MEMS switches (i.e., the first, second, third, fourth, fifth, and sixth MEMS switches) are open. 
     As described above with respect to FIGS. 5A-5B, the illustrated antenna  240  of FIG. 9 may have the conductive element  242  formed on a dielectric substrate  50  (See FIG.  5 A). Alternatively, the illustrated antenna  240  of FIGS. 8A-8C may have the conductive element  242  disposed within a dielectric substrate  50  (See FIG.  5 B). 
     It is to be understood that the present invention is not limited to the illustrated configurations of the conductive elements  42 ,  142 ,  242  of FIGS. 4A-4C,  8 A- 8 C, and  9 , respectively. Various configurations may be utilized, without limitation. For example, conductive elements  42 ,  142 ,  242  may have non-rectangular and/or non-planar configurations. 
     Antennas according to the present invention may also be used with wireless communications devices which only transmit or receive radio frequency signals. Such devices which only receive signals may include conventional AM/FM radios or any receiver utilizing an antenna. Devices which only transmit signals may include remote data input devices. 
     The foregoing is illustrative of the present invention and is not to be construed as limiting thereof. Although a few exemplary embodiments of this invention have been described, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention as defined in the claims. Therefore, it is to be understood that the foregoing is illustrative of the present invention and is not to be construed as limited to the specific embodiments disclosed, and that modifications to the disclosed embodiments, as well as other embodiments, are intended to be included within the scope of the appended claims. The invention is defined by the following claims, with equivalents of the claims to be included therein.