Patent Publication Number: US-6909402-B2

Title: Looped multi-branch planar antennas having multiple resonant frequency bands and wireless terminals incorporating the same

Description:
FIELD OF THE INVENTION 
   The present invention relates to the field of communications, and, more particularly, to antennas and wireless terminals incorporating the same. 
   BACKGROUND OF THE INVENTION 
   The size of wireless terminals has been decreasing with many contemporary wireless terminals being less than 11 centimeters in length. Correspondingly, there is increasing interest in small antennas that can be utilized as internally mounted antennas for wireless terminals. Inverted-F antennas, for example, may be well suited for use within the confines of wireless terminals, particularly wireless terminals undergoing miniaturization. Typically, conventional inverted-F antennas include a conductive element that is maintained in a spaced apart relationship with a ground plane. Exemplary inverted-F antennas are described in U.S. Pat. Nos. 6,538,604 and 6,380,905, which are incorporated herein by reference in their entirety. 
   Furthermore, it may be desirable for a wireless terminal to operate within multiple frequency bands in order to utilize more than one communications system. For example, Global System for Mobile communication (GSM) is a digital mobile telephone system that typically operates at a low frequency band, such as between 880 MHz and 960 MHz. Digital Communications System (DCS) is a digital mobile telephone system that typically operates at high frequency bands, such as between 1710 MHz and 1880 MHz. In addition, global positioning systems (GPS) or Bluetooth systems use frequencies of 1.575 or 2.4-2.48 GHz. The frequency bands allocated for mobile terminals in North America include 824-894 MHz for Advanced Mobile Phone Service (AMPS) and 1850-1990 MHz for Personal Communication Services (PCS). Other frequency bands are used in other jurisdictions. Accordingly, internal antennas are being provided for operation within multiple frequency bands. 
   Conventionally, PIFA configurations have branched structures such as described in U.S. Pat. No. 5,926,139, and position the PIFA a relatively large distance, typically from about 7-10 mm, from the ground plane to radiate effectively. Kin-Lu Wong, in  Planar Antennas for Wireless Communications , Ch. 1, p. 4, (Wiley, January 2003), illustrates some potential radiating top patches for dual-frequency PIFAS. The contents of each of these references are hereby incorporated by reference in their entirety herein. Despite the foregoing, there remains a need for alternative multi-band planar antennas. 
   SUMMARY OF THE INVENTION 
   Embodiments of the present invention provide antennas for communications devices and wireless terminals. The antennas include a looped conductive planar element that may be particularly suitable for a planar inverted-F antenna (PIFA) element. 
   In certain embodiments, planar inverted-F antennas are configured to operate at a plurality of resonant frequency bandwidths of operation (typically between about 2-4) and include: (a) a signal feed; (b) a ground feed; and (c) a looped conductive element in communication with the signal and ground feed. 
   In certain embodiments, the antennas can be positioned about 3 mm from the ground plane that may be provided by a printed circuit board (overlying or underlying the looped antenna element). The ground plane may also be looped in a size and configuration that substantially corresponds to the looped conductive element. 
   In some embodiments, the looped conductive element is configured with a center aperture that extends substantially the entire distance between the internal edge portions of the looped conductive element. The conductive element can have a substantially rectangular shaped perimeter, with each side being contiguous with the two adjacent sides, the perimeter with a width of about 37 mm and a height of about 46.5 mm. 
   In particular embodiments, the antenna is configured to operate at a first (low band) of between about 824-894 MHz and at least one second (high band) of between about 1850-1990 MHz. 
   Certain embodiments are directed to a planar inverted-F antenna having a plurality of resonant frequency bandwidths of operation. The PIFA includes: a signal feed; a ground feed; and a conductive element in communication with the signal and ground feed. The conductive element includes a looped track element that, in operation, provides a high band resonator and a low band resonator. 
   Other embodiments are directed toward wireless terminals. The wireless terminals include: (a) a housing configured to enclose a transceiver that transmits and receives wireless communications signals; (b) a ground plane disposed within the housing; (c) a planar inverted-F antenna disposed within the housing and electrically connected with the transceiver; (d) a signal feed electrically connected to a looped track element; and (e) a ground feed electrically connected to the looped track element proximate the signal feed. The antenna includes: a planar dielectric substrate and a planar conductive element disposed on the planar dielectric substrate. The conductive element includes a looped track conductive element having a length and width and a center portion encased by the looped track, the looped track being configured to define about a ¼ wave resonator at a low frequency band and about a ½ wave resonator at a high frequency band. 
   In certain embodiments, the looped track element comprises an endless perimeter with four sides, wherein the ground and signal feeds are positioned adjacent each other proximate a common side at an upper or lower edge portion of the common side of the looped track element. 
   Still other embodiments are directed to methods for exciting a planar inverted F antenna having low and high band operational modes. The method includes: (a) providing a conductive element with a looped track element, the looped track element configured to form about a ¼ wave resonator at a low frequency band and about a ½ wave resonator at a high frequency band; (b) generating a current null along at least one portion of the looped track at a selected low band operation; and (c) generating a current null at two spaced apart portions (typically substantially opposing sides) of the looped track at a selected high band operation. 
   These and other embodiments will be described further below. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1A  is an enlarged schematic top view of a looped planar inverted-F antenna configuration according to embodiments of the present invention; 
       FIG. 1B  is a schematic diagram of the antenna shown in  FIG. 1A  with an exemplary simulated high band radiation pattern with in-phase current as indicated by the current vectors. 
       FIG. 1C  is a schematic diagram of the antenna shown in  FIG. 1A  with an exemplary simulated low band ¼ wave resonance pattern with current direction indicated by the current vectors. 
       FIG. 1D  is a top view of a looped antenna illustrating a high band current vector plot according to embodiments of the present invention. 
       FIG. 1E  is a top view of a looped antenna similar to that shown in  FIG. 1D  but with supplemental tuning features according to embodiments of the present invention. 
       FIG. 2A  is a top view of another looped planar inverted-F antenna according to embodiments of the present invention. 
       FIG. 2B  is a VSWR graph at 3 mm and 6 mm height (from a ground plane) of the antenna shown in FIG.  2 A. The 6 mm (higher) element is shown with a heavier line weight. 
       FIG. 2C  is a polar coordinate graph of a front elevation radiation pattern at 1850 MHz of the antenna shown in  FIG. 2A  measured at about a 6 mm antenna height. 
       FIG. 2D  is a polar coordinate graph of a front elevation radiation pattern at 1990 MHz of the antenna shown in  FIG. 2A  measured at about a 6 mm antenna height. 
       FIG. 3A  is a top view of a planar inverted-F antenna according to additional embodiments of the present invention. 
       FIG. 3B  is a VSWR graph of the antenna shown in  FIG. 3A  positioned at about 3 mm from the ground plane. 
       FIG. 3C  is a polar coordinate graph of a front elevation radiation pattern at 1580 MHz (GPS) of the antenna shown in  FIG. 3A  measured at about a 3 mm antenna height. 
       FIGS. 3D-3F  are polar coordinate graphs of a front elevation, side elevation, and azimuth directions, respectively, of the radiation pattern at 2.1 GHz of the antenna shown in  FIG. 3A  measured at about a 3 mm antenna height. 
       FIG. 4A  is a top view of a planar inverted-F antenna according to yet other embodiments of the present invention. 
       FIG. 4B  is a VSWR graph of the antenna shown in  FIG. 4A  positioned at about a 3 mm height from the ground plane. 
       FIG. 4C  is a polar coordinate graph of a front elevation radiation pattern at 1850 MHz of the antenna shown in  FIG. 4A  measured at about a 3 mm antenna height. 
       FIG. 4D  is a polar coordinate graph of a front elevation radiation pattern at 1990 MHz of the antenna shown in  FIG. 4A  measured at about a 3 mm antenna height. 
       FIG. 5A  is a top view of a planar inverted-F antenna according to still further embodiments of the present invention. 
       FIG. 5B  is a VSWR graph of four different resonant bands provided by the antenna shown in FIG.  5 A. 
       FIG. 6A  is a looped antenna configuration with a gray scale pattern of current density at 0.95 GHz with a scale ranging from 0 db to −40 db of electric current (with 0 db=29.796 A/m). 
       FIG. 6B  is the looped antenna configuration shown in  FIG. 6A  with a gray scale pattern of current density at 2.4 GHz with a scale ranging from 0 db to −40 db of electric current (with 0 db=29.796 A/m). 
       FIG. 7  is a VSWR plot of a basic looped design antenna according to embodiments of the present invention. 
       FIGS. 8A and 8B  are top views of a looped antenna configuration with current vectors illustrating that high band currents can oscillate between opposing corners according to embodiments of the present invention. 
       FIG. 9A  is top view of a looped antenna with a modified ground plane design that substantially corresponds to the looped antenna configuration according to embodiments of the present invention. 
       FIG. 9B  is a VSWR plot of the antenna shown in FIG.  9 A. 
       FIG. 10A  is a top view of the antenna shown in  FIG. 4A  with a simulated excitation of the antenna at 1850 MHz operation according to embodiments of the present invention. 
       FIG. 10B  is the simulated radiation pattern of the average current simulation shown in FIG.  10 A. 
       FIG. 10C  is a top view of the antenna shown in  FIG. 4A  with a simulated excitation of the antenna at 1990 MHz operation according to embodiments of the present invention. 
       FIG. 10D  is the simulated radiation pattern of the average current simulation shown in FIG.  10 C. 
       FIG. 11A  is a top view of the antenna shown in  FIG. 2A  with a simulated excitation of the antenna at 1850 MHz operation according to embodiments of the present invention. 
       FIG. 11B  is the simulated radiation pattern of the average current simulation shown in FIG.  11 A. 
       FIG. 11C  is a top view of the antenna shown in  FIG. 2A  with a simulated excitation of the antenna at 1990 MHz operation according to embodiments of the present invention. 
       FIG. 11D  is the simulated radiation pattern of the average current simulation shown in FIG.  11 C. 
       FIG. 12  is a partial side view of a wireless communication device according to embodiments of the present invention. 
       FIGS. 13A-13C  are schematic front views of wireless communication devices having a looped antenna configuration positioned about the perimeter of a display according to embodiments of the present invention. 
       FIGS. 14A-14C  are schematic front views of wireless communication devices having a looped antenna configuration positioned about the perimeter of a keypad or keyboard according to embodiments of the present invention. 
   

   DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION 
   The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which 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. Like numbers refer to like elements throughout. It will be appreciated that although discussed with respect to a certain antenna embodiment, features or operation of one antenna embodiment can apply to others. 
   In the drawings, the thickness of lines, layers, features, components and/or regions may be exaggerated for clarity. It will be understood that when a feature, such as a layer, region or substrate, is referred to as being “on” another feature or 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 feature or element, there are no intervening elements present. It will also be understood that, when a feature or element is referred to as being “connected” or “coupled” to another feature or element, it can be directly connected to the other element or intervening elements may be present. In contrast, when a feature or element is referred to as being “directly connected” or “directly coupled” to another element, there are no intervening elements present. The terms “looped” or “loop” track means a track or trace having a closed or substantially closed turn or an endless configuration. 
   Embodiments of the present invention will now be described in detail below with reference to the figures. The inverted-F conductive element can be configured to operate at a plurality, typically at least first and second, of resonant frequency bands and, in certain particular embodiments, can also be configured to operate at a third or more resonant frequency bands. Antennas according to embodiments of the present invention may be useful in, for example, multiple mode wireless terminals that support two or more different resonant frequency bands, such as world phones and/or dual mode phones. In certain embodiments, the antennas of the present invention can operate in a low frequency band and a high frequency band. The terms “low frequency band” or “low band” are used interchangeably and, in certain embodiments, include frequencies below about 1 GHz, and typically comprises at least one of 824-894 MHz or 880-960 MHz. The terms “high frequency band” and “high band” are used interchangeably and, in certain embodiments, include frequencies above 1 GHz, and typically frequencies between about 1.5-2.5 GHz. Frequencies in high band can include selected ones or ranges within about 1700-1990 MHz, 1990-2100 MHz, and/or 2.4-2.485 GHz. 
   In certain particular embodiments, the high frequency band may include frequencies that are less than twice that of the frequencies of the low frequency band. For example for a low band mode operating with frequencies between about 824-894 MHz, the high band mode can operate at frequencies below about 1.648-1.788 GHz. 
   In certain embodiments, the antenna may be configured to provide resonance for a global positioning system (GPS) as the terminal into which this antenna is to be built, can include a GPS receiver. GPS operates at approximately 1,575 MHz. GPS is well known to those skilled in the art. GPS is a space-based triangulation system using satellites and computers to measure positions anywhere on the earth. Compared to other land-based systems, GPS is less limited in its coverage, typically provides continuous twenty-four hour coverage regardless of weather conditions, and is highly accurate. In the current implementation, a constellation of twenty-four satellites that orbit the earth continually emit the GPS radio frequency. The additional resonance of the antenna as described above permits the antenna to be used to receive these GPS signals. 
   As used herein, the term “wireless terminal” may include, but is not limited to, a cellular wireless terminal with or without a multi-line display; a Personal Communications System (PCS) terminal that may combine a cellular wireless terminal with data processing, facsimile and data communications capabilities; a PDA that can include a wireless terminal, pager, internet/intranet access, web browser, organizer, calendar and/or a GPS receiver; and a conventional laptop and/or palmtop receiver or other appliance that includes a wireless terminal transceiver. Wireless terminals may also be referred to as “pervasive computing” devices and may be mobile terminals. 
   It will be understood by those having skill in the art of communications devices that an antenna is a device that may be used for transmitting and/or receiving electrical signals. During transmission, an antenna may accept energy from a transmission line and radiate this energy into space. During reception, an antenna may gather energy from an incident wave and provide this energy to a transmission line. The amount of power radiated from or received by an antenna is typically described in terms of gain. 
   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 wireless terminal. To radiate radio frequency energy with minimum loss, or to pass along received RF energy to a wireless terminal receiver with minimum loss, the impedance of a wireless terminal antenna is conventionally matched to the impedance of a transmission line or feed point. Conventional wireless terminals typically employ an antenna that is electrically connected to a transceiver operatively associated with a signal processing circuit positioned on an internally disposed printed circuit board. In order to increase the power transfer between an antenna and a transceiver, the transceiver and the antenna may be interconnected such that their respective impedances are substantially “matched,” i.e., electrically tuned to compensate for undesired antenna impedance components, to provide a 50-Ohm (Ω) (or desired) impedance value at the feed point. 
   Referring to  FIG. 1A , the antenna  20  includes a conductive element  21  with at least one conductive looped track element  22  having four sides  22   1 ,  22   2 ,  22   3  and  22   4 . As shown, edge portions of adjacent sides are contiguous. The looped track element  22  also has an associated center aperture  22   a . The antenna  20  includes a signal feed  28  and ground feed  25 . In certain embodiments, the ground  25  may be positioned on a common side portion of the element  21  below the signal feed  28  a distance of about 3-6 mm. 
   As shown, the center aperture  22   a  can be sized with a length and width, L 2 , W 2 , respectively, that separate the inner perimeter of the track a sufficient distance to inhibit parasitic coupling of opposing sides of the track. Examples of separation distances configured to limit coupling at conventional frequencies is at least about 3-4 mm. In certain particular embodiments, L 2  may be about 39 mm and W 2  may be about 29 mm with the element track  22  having a width (W 1 -W 2  or L 1 -L 2 ) between about 3-6 mm. 
   In certain embodiments, larger separation distances are used to that the high-band can be approximately twice the frequency of the low band. As the aperture  22   a  size or length L 2  and/or width W 2  decreases, the high-band frequency increases. With separations between the opposite sides of the tracks of less than 10 mm, it is possible to tune the antenna for a resonance of about 800-900 MHz in addition to frequencies of 2.2 GHZ or higher high band operation. However, for applications using about an 800-900 MHz resonance in addition to a 1.7-1.9 MHz resonance, larger separations of the primary parallel radiating branches (shown as left  22   3  and right  22   1  sides) may be desirable. 
   The aperture  22   a  can be an air space or filled with a non-conductive material (or a combination thereof). In operation, gain or tuning should not be degraded if a user positions fingers or hand over the non-conductive center region. In particular embodiments, the looped track element  22  is sized to provide an aperture  22   a  that can receive a display (such as a LCD) or other component therein. The length of the track L 1  may be on the order of about 47 mm and the width W 1  may be on the order of about 37 mm. 
   The looped antenna  20  configuration may be particularly suitable for clam-shell or flip type housing (wireless communication) designs. Claim-shell designs can have low profiles, larger image areas to accommodate a larger display on the flip and the user may place a digit in the center of the flip during operation. The looped antenna  20  can be used with these designs because it also has a relatively low (flat) profile, certain embodiments can be configured without center components (inhibiting user detuning during operation), and it uses a relatively large x, y area (length and width) relative to other PIFA or portable communication device antenna designs. 
   Generally described, in operation at low band (which can be described as band “A”), the conductive element  21  can act like a substantially solid conductive sheet with about a ¼ wave resonance. The resonant frequency in low band can be established by the selection of a suitable length (L 1 ) and width (W 1 ) of the looped track element  22  and/or adjusting the distance from the feed  28  to the upper edge portion  22   e   1  of the looped track element  22 . Increasing the area (L 1  and/or W 1 ) of the looped track element  22  can lower the resonant frequency while decreasing the area (L 1  and/or W 1 ) can raise the resonant frequency. The low band may also or alternatively be tuned by adjusting the distance from the feed and ground connections to the null corner  22   n  (FIG.  1 C). 
   At high band, the looped track element  22  can provide a primary high-band resonator (which can be described as “B 1 ”). In operation at high band, as shown in  FIGS. 1B ,  1 D and  1 E two distinct standing waves form on opposing sides or edges of the looped track  22 , each at about a ½ wavelength resonance. Two non-adjacent sides (shown as the left and right sides  22   3 ,  22   1 ) of the looped track  22  can be at increased or maximum current while the opposing two sides of the looped track  22  are at a reduced or lower current (the low current sides are shown as top and bottom sides  22   4 ,  22   2 ). In this way, this configuration substantially functions as two parallel radiators with the horizontal components canceling and the radiation being generated substantially vertically and which may provide a cross-polarization that is about 10 db below the primary polarization. The main radiation peak is away from the looped track  22  and the back radiation can be relatively low.  FIG. 1E  also illustrates extra tuning branches  23  positioned on the left side  22   3  of the antenna  20  which may be particularly suitable for tuning 900/1800 bands used in Europe or other jurisdictions. 
   In certain embodiments, such as shown in  FIGS. 1D and 1E , the ground plane  125  can have substantially the same shape as the element  22 . This is not required but may allow the element  22  to be positioned closer to the ground plane  125 . The configuration of the ground plane  125  away from the element  22  is shown as extending laterally a further distance, however this dimension and/or shape may be adjusted so that it aligns substantially with the element  22  (such as for the right side of the figure). 
   The high band resonance can be tuned or adjusted by altering the size of the inner perimeter (or spacing) of the looped track element  22  path (i.e., L 2  and/or W 2 ) and by adding tuning components such as the tuning branch  23  (shown as an optional feature by the broken line designation in FIG.  1 A). In certain embodiments, the width (W 2 ) of the looped track and/or the width of the sides of the track  22  (particularly the left and right sides or the primary resonator sides) can be selected to tune the resonance at high band to a desired operational band. The external tuning branch  23  may be particularly suitable for tuning for when the second resonance band is less than about twice the frequency of the primary resonance band. 
   In certain embodiments, as will be discussed further below, the antenna  20  is configured to have between about 2-4 resonant bands with the low band including frequencies in the range of between about 824-894 MHz. The looped configuration (alone or with secondary branches as will be discussed below) can allow for multiple high-band resonances as well as a multi-band PIFA with good gain for high band at a distance of about 3 mm from the ground plane (typically defined by an underlying printed circuit board). 
     FIG. 1B  illustrates a simulated high band radiation pattern with current vectors illustrated. As shown, the current is substantially in-phase in high band operation and there are two null corners  22   n  located at substantially diametrically opposing edge portions of the looped track  22  (where the horizontal sides merge into the vertical sides away from the ground and signal feeds  25 ,  28 ). 
     FIG. 1C  illustrates a simulated low band radiation (such as at about 850 MHz) with a radiation pattern with current vectors illustrated. In this embodiment, a null corner  22   n  is disposed on a different edge portion of the looped track  22  than in the high band operation. As shown, the null corner  22   n  is located on the edge portion furthermost away from the signal and ground feed  28 ,  25 , respectively. 
     FIG. 2A  illustrates that the antenna  20  may include a conductive element  21  that comprises the looped track  22  that provides a primary high band resonator “B 1 ” as well as a secondary branch  30  that provides a secondary resonator “B 2 ” (about a ¼ wave resonator) at high band. The secondary branch  30  may be configured with an aperture  30   a  that separates two substantially parallel strips as shown. The secondary branch  30  may be configured to angularly extend away from the side of the looped track  22  so as to inhibit destructive interference with the first high-band resonance B 1 . 
   In addition, the secondary branch  30  may be positioned internal of the looped track  22  proximate the signal and ground  28 ,  25 , as shown, or may alternatively be positioned to extend external of the looped track and outwardly away therefrom (not shown). The antenna conductive element  22  may comprise a corner member  32  between two adjacent sides  22  that can be used to tune the antenna  20 . The gain of this antenna configuration can be a mixture of horizontal and vertically polarized components, which may be due in part to the angle at which the secondary branch  30  is oriented. The secondary branch  30  may be capacitively coupled to a portion of the looped track  22  such as a far corner portion thereof to have this resonance (B 2 ) be adjacent the other high-band resonance (B 1 ). 
   The secondary branch  30  is shown as the inner branch in this embodiment and, in operation, provides one resonance (in this embodiment the higher of the two high-band frequencies). The inner secondary branch  30  has polarization diversity and can provide a more omni-directional pattern. The outer loop  22  forms the lower high-band resonance and is vertically polarized with relatively low (typically about −10 db) cross polarization. Accordingly, the VSWR of the high band can be better than about 4:1 at about a 3 mm height which can be improved to about 2.5:1 at about a 6 mm height, across the high band (for example, across 1850-1990 MHz). Alternatively, the secondary high band resonance B 2  can be separated for other frequency bands such as UMTS or Bluetooth (2.1 or 2.4 GHz). When used for higher frequencies, the bandwidth may be wider. 
   The length (L 1 ) of the looped track  22  can be about 46.5 mm; the width can be about 37 mm. The height or separation distance from the ground plane may be about 5 mm or less, and typically about 3 mm, although performance may be improved by increasing this distance (particularly low band performance). The ground pin may be positioned about 5 mm vertically below the feed. In the configuration shown in  FIG. 2A , the antenna operates at low and high bands of about 824-894 MHz and 1850-1900 MHz, respectively.  FIG. 2B  is a representative VSWR graph illustrating low band resonance “A,” primary high band resonance B 1  (from the looped track  22 ) and secondary high band resonance B 2  (from branch  30 ) corresponding to the antenna  20  shown in  FIG. 2A  (at 3 mm and 6 mm heights). At the 3 mm height, VSWR at band edges is about 8:1 for low and 3-4:1 for high band. At 6 mm height, VSWR is closer to 4:1 for low band a 2.5:1 for high band. In the figures where lower and higher element positions are drawn on the same plot, the outermost lines correspond to the higher placed elements  22 . 
     FIGS. 2C and 2D  illustrate an exemplary antenna radiation pattern at about a 6 mm antenna height at 1850 MHz ( FIG. 2C ) and 1900 MHz ( FIG. 2D ) associated with the antenna configuration shown in FIG.  2 A. 
     FIG. 3A  is another embodiment of an antenna  20  with a looped track  22 . In this embodiment, the antenna  20  is configured to generate three resonance bands, a low band “A” at between about 824-894 MHz, and two high bands B 1 , B 2 . The high bands can be tuned so that one is at 1575 MHz and one at 2.1-2.4 GHz (the higher band being B 1  and primarily attributed to the looped track  22 ). The antenna  20  includes a secondary band branch  135  (which creates band B 2  at the GPS resonance (1575 MHz) and can widen the high-band resonance). The high band range can be broadened by thickening (increasing the area or the width of the conductive trace) maximal current regions of the radiating element  22 . The secondary branch  135  can be formed by slotting or splitting the left side (leg  22   3 ) of the looped element  22  and can provide additional bandwidth, as well as an additional resonant frequency. The additional resonant frequency can be tuned by adjusting the length of the slot used to create the secondary branch  135 . As shown, the first side  22   1  has an extra-strip or width of track  130  that, in operation, can form part of the high band and low band resonators. In certain embodiments, the extra thickness may provide increased bandwidth in high band operation. 
   The antenna conductive element  22  can include a slit  135  along the vertical side  22   3  positioned across from the signal  28 . The upper side  22   4  may be narrower across than the other sides. The high-band can be tuned to higher frequencies as desired.  FIG. 3B  illustrates a VSWR graph of the embodiment shown in  FIG. 3A  at about a 3 mm height. In this embodiment, the high band B 1  is relatively wide and can cover about 15% bandwidth (2150-2485 MHz) at VSWR of about 3:1. The length L 1  and width W 1  of the track  22  may be about 46.5 mm and 39 mm, respectively. 
     FIG. 3C  illustrates an exemplary radiation pattern that may be provided by the antenna  20  shown in  FIG. 3A  at about 1580 MHz (generally corresponding to GPS). Peak values for front, side and azimuth directions are along −1.23, −2.3, and −0.85 dbi, respectively.  FIGS. 3D-3F  illustrate exemplary radiation patterns that may be provided by the antenna  20  shown in  FIG. 3A  at about 2.1 GHz (2.4 GHz patterns were similar). The pattern shown is directional with high vertical gain, particularly at Azimuth. The peak gain values are between about 3 and 4 dbi. 
     FIG. 4A  illustrates yet another embodiment of the antenna  20  having a conductive element  21  with a looped track  22 . The length L 1  and width W 1  of the looped track element  22  may be about 45 mm and 38 mm, respectively. The ground  25  for the main looped element  22  may be located at about 3 mm below the signal feed  28 . The conductive element  21  can include a secondary branch  235  that is a side parasitic element  235 . The parasitic element  235  can be positioned proximate but spaced apart from (devoid of direct contact with) the looped track  22 . 
   The parasitic element branch  235  can be disposed on the left and outside the left most side  22   3  of the track  22  and can be grounded  25  at its top outer edge portion as shown. Because this edge portion can be in a high current zone, the branch  235  can be excited and a resonance generated. Unlike the primary high band resonance, this resonance can radiate predominantly about the edge of the printed circuit board, which may provide an increased omni-directional pattern and multiple polarizations. The parasitic element  235  may be a vertical strip with a length that is greater than a major portion of the length of one of the longer sides  22   3  of the track  22 . The length of the parasitic element can be sized to substantially correspond (approximately) to the electrical wavelength of the resonance (i.e., ¼ wavelength of the resonance frequency). The left side  22   3  may have a cut out receiving region  22   r  that is sized to receive the parasitic element  235  therein with the left side  223  being narrower alongside the portion adjacent the parasitic element  235 . The antenna conductive element  21  may include tuning corner members  132  and  232 . 
   The parasitic element  235  can be the dominant radiator at the high end of the high band (typically about 1930-1990 MHz). The antenna  20  radiates at low band at between about 824-894 MHz. The high band B may operate between about 1.85-1.99 MHz.  FIG. 4B  illustrates an exemplary VSWR graph for the embodiment shown in  FIG. 4A  at a 3 mm height from the ground plane. 
     FIG. 4C  illustrates an exemplary radiation pattern for the antenna  20  shown in  FIG. 4A  at 1850 MHz measured at about a 3 mm height.  FIG. 4D  illustrates an exemplary radiation pattern for the antenna shown in  FIG. 4A  at 1990 MHz measured at about a 3 mm height. 
   The embodiments shown in FIG.  2 A and  FIG. 4A  may provide omni-directional gain at the higher end of the band. Thus, in receive mode, the communications device may be inhibited from dropping a call or signal based on the user&#39;s position (i e., which direction the user is facing). 
     FIG. 5A  illustrates yet another antenna  20  having a looped track  22 . This embodiment is a quad-band antenna. It operates at low band “A” and high bands B, C and D (FIG.  5 B). As before, a secondary branch  135  can be positioned along the outer side of one of the legs of the looped track  22  (typically the side opposite the side holding the signal and ground) and run a major portion of the length L 1  (typically at least about 75% of the length, and more typically substantially the entire length L 1 ). This secondary branch  135  can generate resonance B (typically about 1575 MHz for GPS). The looped track  22  can provide radiation at 1850-1990 (typically primarily from the left and right sides). As shown, the conductive element  21  also includes a third resonance branch  335  and a fourth resonance branch  435 . The third resonance branch  335  can contribute to resonance C (typically about 1850-1890 MHz) and/or generate resonance D. The fourth branch  435  can generate or contribute to resonance D (typically about 2400-2485 for Bluetooth). As before the ground  25  can be placed below the signal feed  28  between about 3-6 mm, and typically between about 4-6 mm. 
   The fourth branch  435  can be the top branch and can be configured to primarily control tuning for high band C (such as 1850-1990 MHz) and/or the third (center) branch  335  can be configured to tune for band D (Bluetooth). The configuration of the secondary branch  135  (shown as the left branch) can be used to tune GPS (1575 MHz). As before, the length and width of the looped track (L 1 , W 1 ,  FIG. 1 ) and/or the width of the element sides can be used to tune or define the low band resonance. 
     FIG. 6A  illustrates simulated electric current for the antenna  20  (with looped track  22 ) and underlying looped ground  125  with sides configured to substantially correspond to the sides of the element track  22  shown at 0.95 GHz with the adjacent gray scale chart illustrating current density A/m from 0 (29.7696 A/m) to −40 db.  FIG. 6B  illustrates the same antenna  20  with the electric current simulated at 1800 MHz. In certain embodiments, the looped ground plane  125  may have sides that are wider or longer but a center aperture that substantially corresponds to the center aperture  22   a  of the looped track  22  (not shown). 
     FIG. 7  illustrates an exemplary VSWR of an antenna  20  having a basic looped track  22  according to embodiments of the present invention with the antenna having about a 3 mm antenna height from ground. As shown, there is a ¼ wave resonance at low band (913 MHz) and a plurality of high band resonances including ½ wave resonance at 1.8 GHz. Other high band resonances include 2.9 GHz, 3.45 GHz, 4.75 GHz and 5.95 GHz. Additional higher order modes may be present but were not measured with the equipment used. 
     FIGS. 8A and 8B  illustrate that high-band currents can oscillate between opposing sides (shown for example, as corners C 1 , C 2 ) of the looped track  22 . The current on the left and right (and top and bottom) is substantially parallel and traveling in the same direction (i.e., they are not canceling each other). 
     FIG. 9A  again illustrates the antenna  20  with looped track  22  positioned about 3 mm (Z distance) from a ground plane  125  that also has a looped track  125   t  configuration (shown positioned under the antenna track  22 ). Removing the ground below the antenna aperture  22   a  and replacing it with a similarly shaped ground element  125 , acceptable bandwidth and gain can be achieved at about a 3 mm height. The front to back ratio may still be about 4 db at high band, though low-band may become omni-directional. In this embodiment, the gain may be substantially vertical at both high and low bands.  FIG. 9B  illustrates an exemplary VSWR of the antenna  20  and ground plane  125  shown in FIG.  9 A. 
     FIGS. 10A and 10C  illustrate simulated average currents for the antenna  20  shown in  FIG. 4A  at 1850 MHz ( FIG. 10A ) and 1990 MHz ( FIG. 10C ) over a printed circuit board  161 .  FIG. 10B  illustrates a simulated radiation pattern for the 1850 MHz current shown in FIG.  10 A.  FIG. 10D  illustrates a simulated radiation pattern for the 1990 MHz current shown in FIG.  10 C. The pattern at 1990 MHz is more omni-directional than that at 1850 MHz. 
     FIGS. 11A and 11C  illustrate simulated average currents for the antenna  20  shown in  FIG. 2A  at 1850 MHz ( FIG. 11A ) and 1990 MHz (FIG.  11 C).  FIG. 11B  illustrates a simulated radiation pattern for the 1850 MHz current shown in FIG.  11 A.  FIG. 11D  illustrates a simulated radiation pattern for the 1990 MHz current shown in FIG.  11 C. The top center of the printed circuit board  161  at 1990 MHz illustrates increased activity under the center branch. Thus, in this embodiment, the center branch  30  is the primary radiator. 
   The simulations were carried out using the commercial available software package IE3D available from Zeland Software, Inc., located in Fremont, Calif. 
   It is noted that although the looped track element  22  is shown in the figures as being substantially rectangular, other looped track configurations may be used. For example, ovals, parallelograms, or even appropriately configured curvilinear tracks with sufficient separation between opposing sides. In certain embodiments, the minimum distance around the inner loop should be sufficient to define two ½ wavelength paths for the high band operation. In certain embodiments, the outer distance around the loop (or distance from the feed/ground to the opposite side) should be sufficient to define two ¼ wavelength paths for the primary resonance. 
   Further, as is known to those of skill in the art, matching components may be added to improve the impedance match to a 50 Ohm source and/or to increase bandwidth and low-band gain. For example, adding about 1-3 nH of inductance in series with the feed may improve low-band without significantly influencing high-band. The ground plane may be modified by adding slots, apertures, and the like to make the antenna appear further from the ground plane to improve performance. A high-dielectric material may be added between the conductive element  21  and the ground plane  125  to allow for additional shrinking of the geometry of the antenna  20 . Reducing the aperture  22   a  size may reduce gain. Resonating slots can be added to the ground plane  125  to significantly increase bandwidth at low-band and/or high band. Gain may be “shifted” from high band to low band as desired by bringing the ground pin closer to the signal feed. 
   An inverted-F antenna according to some embodiments of the invention can be assembled into a device with a wireless terminal such as a radiotelephone terminal with an internal ground plane and transceiver components operable to transmit and receive radiotelephone communication signals. The ground plane may be about 40 mm wide and about 125 mm in length. 
   The antenna  20  can be disposed substantially parallel to the ground plane  125  and is connected to the ground plane and the transceiver components via respective ground and signal feeds. The antenna  20  may be formed or shaped with a certain size and a position with respect to the ground plane so as to conform to the shape of the radiotelephone terminal housing or a subassembly therein. For example, the antenna may be placed on a substrate that defines a portion of an enclosed acoustic chamber. Thus, the antenna may not be strictly “planar” although in the vernacular of the art, it might still be referred to as a planar inverted-F antenna. 
   In addition, it will be understood that although the term “ground plane” is used throughout the application, the term “ground plane”, as used herein, is not limited to the form of a plane. For example, the “ground plane” may be a strip or any shape or reasonable size and may include non-planar structures such as shield cans or other metallic objects. 
   The antenna conductive element may be provided with or without an underlying substrate dielectric backing, such as, for example, FR4 or polyimide. In addition, the antenna may include air gaps in the spaces between the branches or segments. Alternatively, the spaces may be at least partially filled with a dielectric substrate material or the conductive pattern formed over a backing sheet. Furthermore, an inverted-F conductive element, according to embodiments of the present invention, may have been disposed on and/or within a dielectric substrate. 
   The antenna conductive element  21  may be formed of copper and/or other suitable conductive material. For example, the conductive element branches may be formed from copper sheet. Alternatively, the conductive element branches may be formed from copper layered on a dielectric substrate. However, conductive element branches for inverted-F conductive elements according to the present invention may be formed from various conductive materials and are not limited to copper as is well known to those of skill in the art. The antenna can be fashioned in any suitable manner, including, but not limited to, metal stamping, forming the conductive material in a desired pattern on a flex film or other substrate whether by depositing, inking, painting, etching or otherwise providing conductive material traces onto the substrate material. 
   It will be understood that, although antennas according to embodiments of the present invention are described herein with respect to wireless terminals, embodiments of the present invention are not limited to such a configuration. For example, antennas according to embodiments of the present invention may be used within wireless terminals that may only transmit or only receive wireless communications signals. For example, conventional AM/FM radios or any receiver utilizing an antenna may only receive communications signals. Alternatively, remote data input devices may only transmit communications signals. 
   Referring now to  FIG. 12 , a wireless terminal  200  is illustrated. As shown, the antenna  20  includes a conductive element  21  that is maintained in spaced apart relationship with a ground plane  125  that is typically held on a printed circuit board  161 . The antenna element  21  is in communication with a signal feed  28  and a ground feed  25 . The signal and ground feeds  28 ,  25  can be positioned adjacent each other and disposed on a common edge portion of the element  21 . In certain embodiments, the signal and ground feeds  28 ,  25  are positioned proximate a common outer edge portion. The term “common outer edge portion” means the signal and ground feeds are positioned adjacent each other near or on an outside or end portion of the looped track  22  of the conductive element  21  (with no conductive element spacing them apart). This configuration is in contrast to where the ground is positioned on a first portion of the element and the signal across from the ground with an expanse of conductive element that separates the signal and feed (such as for center fed configurations). 
   Referring again to  FIG. 12 , a conventional arrangement of electronic components that allow a wireless terminal  200  to transmit and receive wireless terminal communication signals will be described in further detail. As illustrated, an antenna  20  for receiving and/or transmitting wireless terminal communication signals is electrically connected to transceiver circuitry components  161   s . The components  161   s  can include a radio-frequency (RF) transceiver that is electrically connected to a controller such as a microprocessor. The controller can be electrically connected to a speaker that is configured to transmit a signal from the controller to a user of a wireless terminal. The controller can also electrically connected to a microphone that receives a voice signal from a user and transmits the voice signal through the controller and transceiver to a remote device. The controller can be electrically connected to a keypad and display that facilitate wireless terminal operation. The design of the transceiver, controller, and microphone are well known to those of skill in the art and need not be described further herein. 
   The wireless communication device  200  shown in  FIG. 12  may be a radiotelephone type radio terminal of the cellular or PCS type, which makes use of an antenna  20  according to embodiments of the present invention. As shown, the device  200  includes a signal feed  28  that extends from a signal receiver and/or transmitter (e.g., an RF transceiver) comprising electronic transceiver components  161   s . The ground plane  125  serves as the ground plane for the planar inverted-F antenna  20 . The antenna  20  may include a dielectric substrate backing shown schematically by dotted line  208 . The antenna  20  can include wrapped portions  212 , which serve to connect the conductive element  21  to the signal and ground feeds  28 ,  25 . The ground feed  25  is connected to the ground plane  125 . The antenna  20  can be installed substantially parallel to the ground plane  125 , subject to form shapes, distortions and curvatures as might be present for the particular application, as previously discussed. The signal feed  28  can pass through an aperture  214  in the ground plane  125  and is connected to the transceiver components  161   s . The transceiver components  161   s , the ground plane  125 , and the inverted-F antenna  20  can be enclosed in a housing  165  for the wireless (i.e., radiotelephone) terminal. The housing  165  can include a back portion  165   b  and front portion  165   f . The wireless device  200  may include other components such as a keypad and display as noted above. The ground plane  125  may be configured to underlie or overlie the antenna  20 . 
   It is noted that the branch pattern configurations of the antennas  20  shown herein may be re-oriented, such as rotated such as 10-90, typically 90, 180 or 270 degrees. In addition or alternatively, the configurations may be re-oriented in a mirrored pattern (such as left to right). The antennas  20  may be configured to occupy an area that is less than about 1200 mm 2 . Typically, the antenna has a perimeter that is less than about 40 mm height×40 mm width×11 mm depth. In certain embodiments, the antenna  20  can be configured to be equal to or less than about 31 mm height and/or width with a depth that is less than about 11 mm (typically 4-7 mm). 
     FIGS. 13A-13C  are schematic front views of wireless communication devices  200  having an antenna  20  with a looped conductive element positioned about the perimeter of a display  500  according to embodiments of the present invention. The display  500  can be any suitable graphic or image display such as an LCD. The looped conductive element  22  may be sized and configured to be offset a distance from the display perimeter or to be closely spaced relative thereto. The device  200  may include a keypad (alphanumeric key entry) on the same surface as shown in  FIG. 13A , on a different member (in a flip or clam-shell configuration as shown in FIG.  13 B), or on a rear surface (FIG.  13 C). The flip configuration may be particularly suitable to form a wireless communication device such as a cellular telephone, which employs two attached housing members that flip or pivot from a closed stored position to an open position. 
     FIGS. 14A-14C  are schematic front views of wireless communication devices  200  having an antenna  20  with a looped conductive element  22  positioned about the perimeter of a keypad or keyboard  505  according to embodiments of the present invention. The keypad  505  may be disposed in different configurations on the device similar to the configurations discussed for the displays  500  above. The device  200  may include looped elements in more than one location, such as combinations of the positions shown in  FIGS. 13A-13C  and  14 A- 14 C. The looped element  22  may also be positioned on the rear surface below the display or keypad (not shown). 
   In the drawings and specification, there have been disclosed embodiments of the invention and, although specific terms are employed, they are used in a generic and descriptive sense only and not for purposes of limitation, the scope of the invention being set forth in the following claims. Thus, 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. In the claims, means-plus-function clauses, where used, are intended to cover the structures described herein as performing the recited function and not only structural equivalents but also equivalent structures. 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.