Patent Publication Number: US-6903686-B2

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

Description:
RELATED APPLICATIONS 
   This application is a continuation-in-part of U.S. patent application Ser. No. 10/248,082, filed Dec. 17, 2002, entitled Multi-band, Inverted-F Antenna with Capacitively Created Resonance, and Radio Terminal Using Same, the contents of which are hereby incorporated by reference as if recited in full herein. 

   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. 5,684,492 and 5,434,579, 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. 
     FIG. 1  illustrates one example of a prior art PIFA (planar inverted “F” antenna) that uses a center signal fed planar antenna shape with capacitive coupling  10 . Generally stated, the high band element has an end portion that typically capacitively couples to a closely spaced apart end portion of the low band element, which, in operation, may cause a larger portion of the antenna element to radiate. U.S. Pat. No. 6,229,487 describes similar configurations for wireless devices, the contents of which are hereby incorporated by reference as if recited in full herein. Unfortunately, the increase in the coupling between the two elements by this configuration may result in degradation in bandwidth at the low-band element. In addition, the parasitic element may dictate tight manufacturing tolerances for proper operation that may increase production costs. 
   Kin-Lu Wong, in  Planar Antennas for Wireless Communications , Ch. 1, p. 4, (Wiley, Jan. 2003), illustrates some potential radiating top patches for dual-frequency PIFAS. As shown, the PIFA in FIG. 1.2( g ) has a plurality of bends, but the configuration is such that the capacitive coupling between the two branches (primary and secondary branches) is most likely very large. 
   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 conductive planar element may be particularly suitable for a planar inverted-F antenna (PIFA) element. 
   Planar inverted-F antennas are configured to operate at a plurality of resonant frequency bandwidths of operation and include: (a) a signal feed; (b) a ground feed; and (c) a conductive element in communication with the signal and ground feed. The conductive element includes a primary branch in communication with the signal and ground feeds. The primary (for example, low band) branch has opposing first and second end portions and a first current path length. The conductive element also includes a secondary branch in communication with the signal and ground feeds. The secondary (for example, high band) branch has opposing first and second end portions and a second current path length. The length of the second current path is shorter than that of the first current path. The conductive element also includes a bend segment having opposing end portions positioned intermediate the primary and secondary branches configured to join the primary and secondary branches. The antenna is configured to operate at first and second different resonant frequency bands, with the primary branch configured to radiate at the first band independent of proximity coupling to the secondary branch. 
   The bend segment and/or secondary branch is configured and positioned with respect to the signal and ground, so that in primary band operation, current flows primarily into the primary branch and bend segment and so that, in secondary band operation, current flows in at least a major portion of both the primary and secondary branches. 
   In certain embodiments, the ground and signal feeds can be positioned adjacent each other on a common portion (which may be proximate to and/or at a common outer edge portion) of the conductive element. The frequencies in the high band may be at least about twice that of the frequencies in the low band. In particular embodiments, the secondary branch is conductively coupled to the signal and ground feeds and the primary branch is also conductively coupled to the signal and ground feeds via the bend segment. The bend segment can provide a current path that is substantially orthogonal to the current path in the secondary branch. 
   The antenna conductive element is configured so that parasitic and/or capacitive coupling between the primary and secondary branches is not required to have the primary branch radiate at low band. 
   Other embodiments are directed to a planar inverted-F antenna having a planar conductive element and signal and ground feeds positioned on a common outer edge portion thereof. The conductive element includes: (a) first, second and third elongated branch segments, each having opposing first and second end portions, wherein the first, second and third elongated branch segments are spaced apart from each other with the second elongated segment being intermediate of the first and third elongated segments; (b) a first bend segment extending between the first and second elongated segments at a corresponding one of the first or second end portions thereof; and (c) a second bend segment extending between the second and third elongated segments at the other corresponding end portion. The antenna is configured to operate at least first and second different resonant frequency bands. The conductive element includes a primary current path that radiates during first band operation comprises two of the first, second and third elongated segments and at least one of the bend segments. The conductive element also includes a secondary current path that radiates primarily during high band operation that comprises the remaining one of the first, second or third elongated segment. The antenna is configured to operate at first and second different resonant frequency bands with the primary current path being configured to radiate at the first band independent of proximity coupling to the secondary current path. 
   In certain embodiments, the second resonant frequency band operates at frequencies that are greater than or equal to at least twice the value of the frequencies of the first resonant frequency band. 
   Other embodiments are directed to a wireless terminal, including: (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 the secondary branch or bend segment of the primary branch of the conductive element; and (e) a ground feed electrically connected to the conductive element proximate the signal feed. The antenna includes a planar dielectric substrate and a planar conductive element disposed on the planar dielectric substrate. The antenna conductive element includes: (a) a primary branch having a bend segment, the primary branch configured to define about a ¼ wave resonator at a low frequency band and about a ½ wave resonator at a high frequency band; and (b) a secondary branch sized and configured to provide about a ¼ wave resonator at the high frequency band. The conductive element is configured to allow the resonances of the secondary and primary branches to combine at the high frequency band. The signal and ground feeds may be positioned proximate to each other on a common portion of the conductive element. In particular embodiments, the signal and ground feeds may be positioned on an outer edge portion of the element. 
   Other embodiments of the present invention are directed toward methods for exciting a planar inverted F antenna having low and high band operational modes. The methods include: (a) providing a conductive element with primary and secondary resonant branches, the conductive element configured so that the secondary branch terminates into a bend region before extending into the primary branch, the primary branch being configured to form about a ¼ wave resonator at a low frequency band and a ½ wave resonator at a high frequency band, the secondary branch configured to act as about a ¼ wave resonant at the high frequency band and to substantially be devoid of irradiation at the low frequency band; (b) generating a high impedance node at the high frequency band to provide a current null proximate the bend region of the primary branch; and (c) causing the primary branch with the secondary branch resonance to provide about a ½ wave resonator at the high frequency band. 
   In further embodiments of the present invention, the first resonant frequency band may include at least one of 800 MHz, 900 MHz, 1800 MHz and/or 1900 MHz. The second resonant frequency band may include at least one different one of 800 MHz, 900 MHz, 1800 MHz and/or 1900 MHz. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a top view of a prior art planar inverted-F antenna configuration; 
       FIG. 2  is a top view of a planar inverted-F antenna according to embodiments of the present invention; 
       FIG. 3A  is a top view of a planar inverted-F antenna according to additional embodiments of the present invention; 
       FIG. 3B  is a side perspective view of the excitation of the antenna of  FIG. 3A  at low band operation according to embodiments of the present invention. 
       FIG. 3C  is a side perspective view of the excitation of the antenna of  FIG. 3A  at high band operation according to embodiments of the present invention; 
       FIG. 4  is a top view of a planar inverted-F antenna according to other embodiments of the present invention. 
       FIG. 5A  is a side perspective view of the excitation of the antenna of  FIG. 4  at low band operation according to embodiments of the present invention. 
       FIG. 5B  is a side perspective view of the excitation of the antenna of  FIG. 4  at high band operation according to embodiments of the present invention. 
       FIG. 6A  is a top view of a planar inverted-F antenna according to still further embodiments of the present invention. 
       FIGS. 6B and 6C  are opposing side perspective views of an exemplary configuration of the antenna shown in  FIG. 6A  according to embodiments of the present invention. 
       FIG. 6D  is a VSWR plot of the antenna shown in  FIG. 6A  according to embodiments of the present invention. 
       FIG. 6E  is a side perspective view of an additional exemplary configuration for the antenna shown in  FIG. 6A  according to embodiments of the present invention. 
       FIG. 7  is a partial side view of a wireless communication device according to embodiments of the present invention. 
       FIG. 8A  is a top view of a planar inverted-F antenna according to yet other embodiments of the present invention. 
       FIG. 8B  is a current vector plot of the antenna shown in  FIG. 8A  at 2.1 GHz. 
       FIG. 8C  is a current vector plot of the antenna shown in  FIG. 8B  at 1.0 GHz. 
       FIG. 9  is a VSWR plot of the antenna configuration shown in  FIG. 4  positioned about 6 mm over the ground plane. 
       FIG. 10A  is a current vector plot of the antenna shown in  FIG. 6A  at a low-band (894.5 MHz). 
       FIG. 10B  is a current vector plot of the antenna shown in  FIG. 6A  at a high band (1.9973 GHz). 
   

   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. As used herein, element number  20  generally refers to an antenna and this element number  20  is also used with uppercase alpha suffixes to denote certain embodiments thereof (i.e.,  20 A,  20 B,  20 C) for clarity of discussion. Feature  20   b  (lower case “b”) refers to the bend segment and not a general antenna element embodiment. 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. 
   Embodiments of the present invention will now be described in detail below with reference to  FIGS. 2 through 9 . The inverted-F conductive element can be configured to operate at first and second 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 embodiments, the high frequency band may include frequencies that are at least about 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 equal to or above 1.648-1.788 GHz. 
   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 global positioning system (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. 
   An inverted-F antenna  20  according to the invention can be assembled into a device with a wireless terminal  200  (as shown for example in  FIG. 7 ) such as a radiotelephone terminal with an internal ground plane  161   g  and transceiver components  161   s  operable to transmit and receive radiotelephone communication signals. The antenna  20  is disposed substantially parallel to the ground plane  161   g  and is connected to the ground plane  161   g  and the transceiver components  161   s  via respective ground and signal feeds,  61   g ,  61   s , respectively. 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 any number of branches disposed on and/or within a dielectric substrate. 
   The antenna conductive element 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. 2 , as illustrated, the antenna  20 A includes a conductive element  20   e  that is maintained in spaced apart relationship with a ground plane ( FIG. 7 ,  161   g ). The illustrated conductive element  20   e  has a primary branch  20   p  and a secondary branch  20   s  joined by a bend segment  20   b . The antenna element  20   e  is in communication with a signal feed  61   s  and a ground feed  61   g . The signal and ground feeds  61   s ,  61   g  are positioned adjacent each other and disposed on a common edge portion of the element  20   e . In certain embodiments, the signal and ground feeds  61   s ,  61   g  are positioned on or in proximity to a common portion of the conductive element  20   e . In particular embodiments, the signal and ground feeds  61   s ,  61   g  are positioned proximate a common outer edge portion. The term “common outer edge portion” means the signal and ground feeds  61   s ,  61   g  are positioned adjacent each other near or on an outside or end portion of the conductive element  20   e  (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). The primary branch  20   p  is positioned further away from the signal and ground feeds  61   s ,  61   g  than the secondary branch  20   s , as the two branches  20   p ,  20   s  are joined by the intermediately positioned bend segment  20   b.    
   As shown in  FIG. 2 , the secondary branch  20   s  is positioned with respect to the ground feed  61   g  and signal feed  61   s  so as to have a current path  21   c   1  that is shorter than the current path  21   c   2  of the primary branch  20   p . It is noted that the lengths of the current paths are shown for comparison in FIG.  2 : in operation, the actual length, configuration and particular current path vectors associated with the path that the current travels during radiation can vary from that shown. In addition, the current may travel along only a portion of the length of the respective branches  20   p ,  20   s . Typically, when both branches are fully radiating, current flows over at least a major portion of each branch. Similarly, if one branch is intended to be substantially non-radiating, current does not flow or flows in a reduced amount (such as over a minor portion of the length of the branch). For example, in low band operation, current may flow in the secondary branch  20   s , but if so, only about a minor portion of that branch and/or in a reduced amount relative to that in high band. 
   The bend segment  20   b  bridges or joins respective end portions of the two branches  20   p ,  20   s . In certain embodiments, the primary and secondary branches,  20   p ,  20   s , respectively, are each separately electrically fed by the signal and ground feeds  61   s ,  61   g  without requiring capacitive coupling therebetween. The non-joined end portions of the branches (shown in this embodiment as  50   e   2  and  30   e   1 ) can be spaced apart a sufficient distance from each other so as to be able to insulate them from parasitically coupling during operation. Stated differently, the element  20   e  can be configured so that the primary branch  20   p  is activated by the ground and signal feeds  61   g ,  61   s  during low band operation without coupling to the secondary branch  20   s . During high band operation, the primary and secondary branches  20   p ,  20   s  are both activated by the ground and signal feeds  61   g ,  61   s  with the two branches  20   p ,  20   s  configured to radiate independently at the desired frequency band(s) without requiring proximity (parasitic or capacitive) coupling therebetween. Although, in certain embodiments, supplemental parasitic coupling between segments of the primary and secondary branches  20   p ,  20   s  may be used as will be discussed further below. 
   The conductive element  20   e  bend segment  20   b  can be configured and positioned with respect to the signal and ground feeds  61   s ,  61   g  to define a current null space  21  provided by a relatively high impedance node in the conductive element  20   e  current path during high band operation. The high impedance node (and, thus current null) allows the resonances of the two branches to combine during high band operation. Impedance (Z) can be described as the voltage (V) divided by the current (I), (i.e., Z=V/I). At the feed point or location, current (I) is at a maximum and hence, impedance (Z) is low. At the low current (I) point, shown as  20   b , current (I) can approach zero and the impedance (Z) increases correspondingly. Thus, the high impedance node is the location in the current path where current approaches zero. 
   Typically, the high impedance node is located proximate the signal and ground feeds  61   g ,  61   s  about the bend segment  20   b  on branch  20   p . The bend segment  20   b  can be positioned at about 4-15 mm from the feed location to provide a suitable radiating pattern. The distance from the feed and ground  61   s ,  61   g  to the bend segment  20   b  can be measured from where the feed and ground segments  61   s ,  61   g  contact the main radiating element  20   p . If the feed and ground probes were connected, the bend segment  20   b  can be generally placed substantially perpendicular to the feed and ground  61   s ,  61   g  as shown in  FIGS. 2 and 4 . 
   In operation, in certain embodiments, the secondary branch  20   s  can form about a ¼ wave resonator at the high frequency band. The primary branch  20   p  can form about a ¼ wave resonator at the low frequency band. At high band operation, the configuration of the element  20   e  with the positioning of the signal feed  61   s  and ground feed  61   g  causes the primary and secondary branches  20   s  and  20   p  to resonate. A ½ wave resonance is formed between the bend  20   b  and  30   e   1  at high band. A ¼ wave resonance is formed on element  50 . Thus, the antenna  20  operates at both low and high frequency bands of operation such that at low band, current flow in the secondary path  21   c   1  is reduced relative to current flow therein during the high band of operation (where current flows in both the primary and secondary branches). 
   The ½ wave resonator can be tuned by adjusting the length and/or geometry of the high band (secondary) branch. During high band operation, the two resonances of the primary and secondary branches  20   p ,  20   s  can be combined to allow for a single, wider resonance band. In certain embodiments, because edge proximity capacitive coupling (such as those used in center fed C configurations) is not required, low-band performance may be improved relative to conventional designs. A substantial portion of the conductive element  20   e  can be configured to resonate at high-gain providing a relatively high band antenna. This additional gain may also allow a lower Z-height antenna to be used relative to past configurations. In addition, since conductive element embodiments of the present invention employ multiple high-band resonators, the VSWR at high band may be improved. 
   Still referring to  FIG. 2 , the conductive element  20   e  can be further described as a planar conductive element that includes first, second and third elongated branch segments,  30 ,  40 , and  50 , respectively. Each of the elongate branch segments  30 ,  40 ,  50  has opposing first and second end portions  30   e   1 ,  30   e   2 ,  40   e   1 ,  40   e   2 , and  50   e   1 ,  50   e   2 . As shown, the first, second and third elongate segments  30 ,  40 ,  50  are spaced apart from each other with the second elongated segment  40  being intermediate of the first  30  and third  50  elongated segments. The conductive element  20   e  further includes a first bend segment  55  extending between the first and second elongated segments  30 , 40  at a corresponding one of the first or second end portions thereof (shown at the second end portions  30   e   2 ,  40   e   2 ) and a second bend segment  60  extending between the second  40  and third  50  elongated segments at the other corresponding end portion (shown at the first end portions  40   e   1 ,  50   e   1 ). The signal feed  61   s  and ground  61   g  are electrically connected to the conductive element  20   e  at an outer edge portion thereof. The primary and secondary branches  20   p ,  20   s  can each be conductively coupled to the signal and ground  61   s ,  61   g  (the primary branch  20   p  via bend segment  20   b ). 
   The antenna  20  is configured to operate at least first and second different resonant frequency bands. The conductive element  20   e  and the first and/or second bend segments  55 ,  61  are configured to generate at least one current null space in the current path during one of the first or second bands of operation as described above. Typically, the current null space is generated in the high band operation at a position that allows the separate resonances of the two branches  20   p ,  20   s  to combine. 
   In this embodiment, the secondary branch  20   s  is defined by the third elongated segment  50  with the primary branch  20   p  including elongated segments  30 ,  40 , bend segment  55 , and may include a portion of bend segment  60 . In certain embodiments, some current may flow into segment  50  during low band operation, but this segment  50  is configured to primarily resonate (over a major portion of its length) during high band operation. 
     FIGS. 3A-3C  illustrate another embodiment of the present invention. As shown, the signal and ground feeds  61   s ,  61   g  are positioned about the bend segment  20   b  that is located intermediate the primary and secondary branches  20   p ,  20   s .  FIGS. 3B and 3C  illustrate a circuit board defining the ground plane  161   g . As for the embodiment discussed above, the conductive element  20   e  can be configured with three spaced apart elongated segments  30 ,  40 ,  50  joined by bend segments  55 ,  60  and the signal and ground  61   s ,  61   g  can be positioned about a common outer edge portion of the conductive element  20   e  proximate the second segment end portion  40   e   1 . The signal and ground  61   s ,  61   g  can also be positioned at other locations (for this and the other embodiments shown and/or described herein), such as inside of the outer edge portion. The secondary branch may include a tuning segment  30   t  as shown in  FIGS. 3B and 3C . The primary branch  20   p  includes a portion of the bend segment  60  as well as bend segment  55  and first and second elongate segments  30 ,  40 . The secondary branch  20   s  includes the third elongate segment  50 . 
   The darker shaded or cross-hatched portion of the conductive element  20   e  shown in  FIG. 3B  illustrates the current flow path and/or radiating portion of the element during low band operation, with the primary branch  20   p  radiating and secondary branch substantially free of radiation. The shaded portion of the conductive element  20   e  shown in  FIG. 3C  illustrates the current flow and/or radiating portion of the element  20   e  at high band operation with the primary and secondary branches  20   p ,  20   s  radiating. This embodiment may provide omni-directional gain at high band. 
     FIG. 4  illustrates an embodiment of the present invention similar to that shown in  FIG. 2  (a mirrored pattern configuration). Thus, the same functional output can be achieved. As shown the antenna  20 C includes a conductive element  20   e  with primary and secondary branches  20   p ,  20   s . In this embodiment, the first elongate segment  30  defines the secondary branch  20   s . The signal and ground feeds  61   s ,  61   g  are positioned about a common outer edge portion of the first segment  30 . The first bend segment  50  can join first edge portions  30   e   1 ,  40   e   1 , of the first and second elongate  30 ,  40  segments. The second bend segment  60  can join the second end portions  40   e   2 ,  50   e   2  of elongate segments  40 ,  50 . The first bend portion  55  may include a step that angularly extends down toward the second segment  40 . The first segment  30  may include a tuning component  30   t  as shown in FIG.  4 . The second segment  40  may be bent toward the third segment  50  (shown as the right branch) to tune the high band resonance lower to meet the desired operational frequency and desired dimensional configuration. The antenna element may be configured with about a 31 mm width×29 mm height×about a 6 mm depth. Additional depth may provide additional performance advantages. 
   Similarly, the third segment  50  may also include a tuning element  50   t  as shown in  FIGS. 4 and 5A ,  5 B.  FIGS. 5A and 5B  illustrate that the third segment tuning element  50   t  may turn back toward the second segment  40  and/or bend  55 . In certain embodiments, the third segment tuning component  50   t  may be sized and configured to capacitively couple with the second segment  40  or bend  55 . 
   The darker shaded or cross-hatched portion of the conductive element  20   e  shown in  FIG. 5A  illustrates the current flow path and/or radiating portion of the element during low band operation, with the primary branch  20   p  radiating and secondary branch  20   s  having reduced radiation (at least compared to high band as shown in FIG.  5 B). The shaded portion of the conductive element  20   e  shown in  FIG. 5B  illustrates the current flow and/or radiating portion of the element  20   e  at high band operation with the primary and secondary branches  20   p ,  20   s  radiating. 
     FIG. 6A  illustrates another embodiment of the present invention. As shown, the antenna  20 D includes conductive element  20   e . Similar to the embodiment shown in  FIG. 3A , the signal and ground feeds  61   s ,  61   g  are positioned intermediate the primary and secondary branches  20   p ,  20   s . However, this embodiment is configured to provide a third resonance. The third resonance may be used for any suitable application, such as, but not limited to GPS or Bluetooth systems. Thus, the antenna  20 D may provide two different high band modes along with a low band mode of operation. In this embodiment, the primary branch  20   p  includes the first segment  30 , a first bend segment  55   1 , the second segment  40  (which connects to the signal and ground  61   s ,  61   g ), a second bend segment  55   2 , and a fourth segment  150 . The second segment  40  and spaced apart bend segments  55   1 ,  55   2  can be described as an inverted “T” configuration. The secondary branch  20   s  includes segment  50  that connects to the signal and ground feeds  61   s ,  61   g , via bend segment  60 . The secondary branch  20   s  can include a supplemental proximity coupling (capacitively or parasitically coupled)  216  to the primary branch  20   p . As shown, the secondary branch  20   s  is proximity coupled connected at the end portion away from the signal feed  61   s  at bend segment  63 . 
     FIGS. 10A and 10B  illustrate exemplary current vector plots for the antenna  20 D shown in FIG.  6 A.  FIG. 10A  illustrates the current flow at one low band frequency (894.595 MHz) and  FIG. 10B  at one high band frequency (1.9973 GHz). As shown in  FIG. 10B , at high band, the branch  50  radiates because it is a resonant length. The branch  150  also has some current that is induced by capacitive coupling of the top portion of branch  50 . The first (left) branch  30  is also radiating. The radiation is caused by the impedance match presented by the right branch  150 . As shown in  FIG. 10A , at low band, the primary radiation and current path is through the center segment  40 . The current branches along each side of the center segment  40  and segments  30 ,  150  to both sides of the center segment  40  and each provide some radiation. The radiation of the segment  50  is attributed to the proximity coupling  216  to the “inverted T” configuration defined by the center segment  40  and bend regions  55   1 ,  55   2 . Absent the proximity coupling  216 , there would be very little low band current in the secondary branch  50 . 
     FIG. 6B  illustrates one example of a conductive element  20   e  configuration for the antenna embodiment  20 D shown in FIG.  6 A. The primary branch  20   p  connects the second segment  40  and includes segments  30 ,  40  and  150 . In this embodiment, the primary radiating branch  20   p  can create one base resonance at a fundamental frequency, roughly in the 800-900 MHz range, useful for certain cellular systems. In this particular embodiment, the antenna has a second base resonance frequency at approximately twice the fundamental frequency, approximately at 1,900 MHz. The bandwidth of the antenna in this area is great enough to accommodate both the 1,900 MHz band and the 1,800 MHz band. 
   In the embodiment of  FIG. 6A-6C , the antenna  20 D secondary branch  20   s  has a first end  50   e   1  which is connected to the signal feed  61   s  and ground feed  61   g  proximate to where the primary radiating branch  20   p  is connected. The secondary branch  20   s  includes a second end  50   e   2 , which capacitively couples  216  the secondary radiating branch  20   s  to the primary radiating branch  20   p . The capacitive coupling  216  can be adjusted to create an additional resonance, which is not necessarily harmonically related to the base resonances of the antenna. In this particular example, the additional resonance is for the global positioning system (GPS) as the terminal into which this antenna is to be built, will 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 orbiting 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. 
   In  FIGS. 6A-6C , the capacitive coupling  216  between the first branch and the second branch of the antenna is created by an overlapping area, shown in cross-hatch. An underlapping area can be used and would work in the same way. To a first approximation, a parallel plate capacitor is formed at the overlapping or underlapping area. The amount of capacitance, and hence the amount of coupling and the additional resonance frequency, can be controlled by controlling the distance between the branches in the crosshatched area, and the size of the area. This control, in effect, manipulates variables in the formula that are well-known for parallel plate capacitors: 
         C   =         ɛ   0     ⁢   A     d       ,       
 
where C is the capacitance in Farads, A is the area of the plates, corresponding to the overlap/underlap area, d is the distance between the plates, corresponding to the distance between the first and second radiating branches, and ε 0  is the permitivity constant.
 
     FIG. 6C  illustrates the PIFA shown in  FIG. 6B  from a different angle. This view also displays the overlap of the cross-hatched area at the second end  50   e   2  of the secondary radiating branch  20   s  of the antenna  20 D. Additionally, in this view, signal feed conductor  204  is more visible and ground feed conductor  61   g  is visible. Again, although in this example the second radiating branch is overlapping the first radiating branch, the same effect could be achieved by having the second radiating branch “underlap” the first radiating branch. The term “overlap” if used by itself in this disclosure is intended to encompass both possibilities. 
     FIG. 6D  is a graph illustrating the VSWR for the antenna illustrated in  FIG. 6A  as a function of frequency. However, it should be noted that the antenna  20 D of  FIG. 6A  has three resonance frequencies (F 1 , F 2 , F 3 ), each clearly visible as a local minimum in the VSWR curve. The particular antenna  20 D illustrated has two base resonance frequencies as previously mentioned, occurring at approximately 900 MHz and 1,900 MHz, respectively. The additional resonance (F 3 ) is for 1,575 MHz, and is visible as the local minimum. 
   It is noted that the capacitive coupling  216  between the primary radiating branch  20   p  and the secondary radiating branch  20   s  can be provided by a separate “parasitic” conductor (not shown) which may be installed with adhesive or otherwise structurally supported by the housing of the radiotelephone terminal. Again, this parasitic conductor could be either over or under the radiating branches as shown in this view. The parasitic does not have to be rectangular, but could vary in shape as well as size. Essentially all of the parasitic conductor area, with the exception of the portion that falls directly over the small space between the two radiating branches is capacitively coupled with one or the other of the two branches, as the case may be. Again, the area of capacitive coupling and the distance between the parasitic conductor and the branches can be adjusted to tune the additional resonance, based on the formula previously discussed, except that a designer is essentially dealing with two capacitors in series. Additional tuning extensions  30   t ,  150   t , and the like (not shown) can be added to the primary radiating branch to achieve appropriate resonances. 
     FIG. 6E  illustrates an example of an additional tuning extension  216   t  can also be added to the secondary branch  20   s  at the coupling  216 . In certain embodiments, the tuning for this member can be a U-shaped extension that creates an extended length coupling area for the secondary radiating branch  20   s  with an edge that runs generally parallel to and in substantially close proximity to the primary radiating branch  20   s  (about segments  40 ,  63  and  150 ). This pattern creates an area of capacitive coupling involving areas of the two radiating branches as marked in cross-hatch. It will be appreciated by those of skill in the art that this, in effect, creates a parallel plate capacitor “on its side” in which the thickness of the conductors of the antenna multiplied by the length of adjacency effectively defines the area of the capacitor, for application via the mathematical relationship previously described. It must be noted that this particular extension to the second radiating branch is shown by way of example only. It is possible to devise an antenna with radiating branches of other irregular shapes that can cause specific areas of the edges of the radiating branches to come in close proximity to each other for particular distances along the edges. 
   Referring now to  FIG. 7 , a conventional arrangement of electronic components that allow a wireless terminal to transmit and receive wireless terminal communication signals will be described in further detail. As illustrated, an antenna 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. 7  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  61   s  that extends from a signal receiver and/or transmitter (e.g., an RF transceiver) comprising electronic transceiver components  161   s . The ground plane  161   g  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  20   e  to the signal and ground feeds  61   s ,  61   g . The ground feed  61   g  is connected to the ground plane  161   g . The antenna  20  can be installed substantially parallel to the ground plane  161   g , subject to form shapes, distortions and curvatures as might be present for the particular application, as previously discussed. The signal feed  61   s  can pass through an aperture  214  in the ground plane  161   g  and is connected to the transceiver components  161   s . The transceiver components  161   s , the ground plane  161   g , 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  161   b  and front portion  161   f . The wireless device  200  may include other components such as a keypad and display as noted above. The ground plane  161   g  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 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). 
     FIG. 8A  is another example of an antenna  20  similar to that shown in  FIG. 2  having an antenna element  20   e  according to embodiments of the present invention.  FIG. 8B  is a current vector plot for the antenna shown in  FIG. 8A  with the electric current flow at 2.1 GHz.  FIG. 8C  is the current vector plot for the same antenna at 1.0 GHz.  FIG. 8B  can be described as representative of the current flow at high band and  FIG. 8C  as representative of current flow at low band. As shown, the secondary branch  20   s  is substantially free of current flow at low band (with the current null located proximate the bend segment  60  at the signal and ground feed region about the upper end of the segment  50 ) and radiating with the primary branch  20   p  at high band. 
     FIG. 9  is the VSWR plot of the embodiment shown in FIG.  4 . As shown, the plot represents the antenna  20  positioned about 5 mm over the ground plane. VSWR at high-band (1850-1990 MHz) is relatively wide and resonates well. VSWR at low band is slightly narrower than high band, but can be improved with additional height (such as 7-8 mm placement) of the antenna relative to the ground plane. 
   The operational frequency bands may be adjusted by changing the shape, length, width, spacing and/or state of one or more conductive elements of the antenna. For example, the resonant frequency bands may be changed by adjusting the spacing between the conductive element and the ground element. 
   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.