Abstract:
An antenna system includes a dielectrically-loaded loop element electromagnetically coupled to a planar element. The antenna system exhibits uniform, broadband radiation and reception patterns.

Description:
This application is a continuation of patent application Ser. No. 12/764,788, filed Apr. 21, 2010, which is a division of patent application Ser. No. 11/486,223, filed Jul. 12, 2006, now U.S. Pat. No. 7,773,041, which are hereby incorporated by reference herein in their entireties. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to antenna systems and, in particular, to antenna systems for wireless communication devices. 
     BACKGROUND OF THE INVENTION 
     Advances in semiconductor technology have allowed wireless communication devices, such as cell phones, personal digital assistants (PDA&#39;s) and pagers, to become smaller and smaller. However, the antenna systems for these devices have not evolved at the same pace because antenna efficiency generally decreases with reductions in antenna size. To maintain reasonable gain and non-directional receive/transmit patterns, most conventional antenna designs have relied on external monopole antennas, either fixed or telescoping. Other designs have realized internal antennas of different varieties (e.g., monopole, dipole, helical and patch antennas). However, these antennas are susceptible to performance degradation due to the proximity of other components. For example, coupling to the electric fields of internal components (e.g. oscillators, amplifiers, mixers) can degrade the signal-to-noise ratio of the receiving section of the wireless device, and internal ground planes and metallic enclosures can distort antennas patterns or completely block transmission and reception in some directions. Therefore, in order to obtain reasonable antenna performance, these internal antennas are normally kept away from other components in the wireless device by placing them in separate areas, adding size and volume to the wireless devices. 
     SUMMARY OF THE DESCRIPTION 
     Various embodiments of an antenna system are described. In one exemplary embodiment, an antenna system includes a dielectrically-loaded loop element and a substantially planar element. The substantially planar element is disposed substantially parallel to a major axis of the dielectrically-loaded loop element, substantially perpendicular to a minor axis of the dielectrically-loaded loop element and within an induction field region of the dielectrically-loaded loop element. Features and benefits of the various embodiments of the invention will be apparent from the description. 
     At least certain embodiments of the present invention include a portable device having an antenna structure therein, the antenna structure including a generally U-shaped loop element coupled with a support element having a substantially planar portion, wherein the substantially planar portion has an electrical length along a first dimension proximate to one wavelength of a frequency of interest, and an electrical length along a second dimension proximate to one-half wavelength of the frequency of interest, where the support element is located within an induction field of the loop element. 
     At least certain embodiments of the present invention include an embodiment of the antenna system as part of a digital media player, such as a portable music and/or video media player, which includes a media processing system to present the media, a storage device to store the media and a radio frequency (RF) transceiver to couple the antenna system to the media processing system. The RF transceiver uses the antenna system to transmit or receive the media, which may be one or more of music, still pictures or motion pictures, for example. The portable media player may include a media selection device, such as a click wheel device, a touchpad, pushbuttons or other similar selection devices as are known in the art. The media selection device may be used to select the media stored on the storage device. The portable media player may, at least in certain embodiments, include a display device, such as an LCD display, coupled to the media processing system to display titles or other indicators of media selected with the input device and presented, through a speaker and/or earphones or on the display device or on both the display and a speaker and/or earphones. In certain embodiments, the display device may also be the media selection device such as, for example, an LCD touch screen device. 
     At least certain embodiments of the present inventions include an embodiment of the antenna system as part of a wireless device such as a cellular telephone, smart phone or personal digital assistant, for example, which includes a digital radio frequency (RF) transceiver. The digital RF transceiver uses the antenna system to send and receive digital voice and/or data signals. The wireless device may include a digital processing system coupled to the transceiver to control the transceiver and manage the digital signals. The digital processing system may be coupled to a storage device to store data, to a display device such as an LCD display to display data and/or receive user input (e.g., via touch screen sensors), to an input device such as a keypad, and to audio transducers (e.g., microphone and/or speaker) with associated analog/digital converters and device drivers. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the present invention are illustrated by way of example and not limitation in the figures of the accompanying drawings in which like references indicate similar elements. 
         FIG. 1A  illustrates an antenna system in one embodiment; 
         FIG. 1B  illustrates a loop element of an antenna assembly in one embodiment; 
         FIG. 1C  illustrates a cross-section of a planar antenna element in one embodiment; 
         FIG. 1D  illustrates another cross-section of a planar antenna element in one embodiment; 
         FIG. 2  illustrates a plane view of the antenna system embodiment of  FIG. 1A ; 
         FIG. 3  is an exploded view illustrating a dielectrically-loaded loop element in one embodiment; 
         FIG. 4  is a partially assembled antenna system illustrating a dielectrically-load loop element in one embodiment; 
         FIG. 5  is a cross-sectional view illustrating an antenna system in a wireless communications device in one embodiment; 
         FIG. 6A  is a plane view of the embodiment of  FIG. 5 ; 
         FIGS. 6B through 6E  illustrate alternative embodiments of the invention; 
         FIG. 7  is a graph illustrating an exemplary return loss of an antenna system in one embodiment; 
         FIG. 8A  is a gain plot illustrating a horizontally polarized azimuth radiation pattern of an antenna system in one embodiment; 
         FIG. 8B  is a gain plot illustrating a vertically polarized azimuth radiation pattern of an antenna system in one embodiment; 
         FIG. 9  illustrates an orientation of a wireless communications device for the azimuth (X-Y plane) radiation patterns of  FIGS. 8A and 8B ; 
         FIG. 10A  is a gain plot illustrating a vertically polarized elevation radiation pattern of an antenna system in one embodiment; 
         FIG. 10B  is a gain plot illustrating a horizontally polarized elevation radiation pattern of an antenna system in one embodiment; 
         FIG. 11  illustrates an orientation of a wireless communications device for the elevation (X-Z plane) radiation patterns of  FIGS. 10A and 10B ; 
         FIG. 12  is a cross-sectional view illustrating another embodiment of an antenna system in a wireless communications device; 
         FIG. 13  is a plane view of the embodiment of  FIG. 12 ; 
         FIG. 14  is a block diagram illustrating a system in which embodiments of the invention may be implemented; and 
         FIG. 15  is a flowchart illustrating a method of manufacture in one embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Various embodiments and aspects of the invention will be described with reference to details discussed below, and the accompanying drawings will illustrate the various embodiments. The following description and drawings are illustrative of the invention and are not to be construed as limiting the invention. Numerous specific details such as dimensions and frequencies are described to provide a thorough understanding of various embodiments of the present invention. However, in certain instances, well-known or conventional details are not described in order to not unnecessarily obscure the embodiments of the present invention. 
     At least certain embodiments of the present invention include a portable device having an antenna structure therein, the antenna structure including a generally U-shaped loop element coupled with a support element having a substantially planar portion, wherein the substantially planar portion has an electrical length along a first dimension proximate to one wavelength of a frequency of interest, and an electrical length along a second dimension proximate to one-half wavelength of the frequency of interest, where the support element is located within an induction field of the loop element. 
     At least certain embodiments of the antenna system described herein may be part of a digital media player, such as a portable music and/or video media player, which includes a media processing system to present the media, a storage device to store the media and a radio frequency (RF) transceiver coupled with the antenna system and the media processing system. In certain embodiments, media stored on a remote storage device may be transmitted to the media player. The media player may receive the transmitted media via the antenna system and RF transceiver, and may store and/or stream the media. In other embodiments, the media player may transmit the media to a remote storage device and/or another media player. The media may be, for example, one or more of music or other audio, still pictures, or motion pictures. The portable media player may include a media selection device, such as a click wheel device on an iPod® or iPod Nano® media player from Apple Computer, Inc. of Cupertino, Calif., a touch screen device, pushbutton device, movable pointing device or other selection device. The media selection device may be used to select the media stored on the storage device and/or the remote storage device. The portable media player may, in at least certain embodiments, include a display device which is coupled to the media processing system to display titles or other indicators of media being selected through the input device and being presented, either through a speaker or earphone(s), or on the display device, or on both the display device and a speaker or earphone(s). In certain embodiments, the display device may also be the media selection device (e.g., a touch screen display device). Examples of a portable media player are described in published U.S. Patent Applications 2003/0095096 and 2004/0224638, both of which are incorporated herein by reference. 
       FIG. 1A  illustrates an antenna system  100  according to one embodiment of the invention. In  FIG. 1A , a generally U-shaped dielectrically-loaded loop element  104  includes a loop element  101  loaded with a dielectric material  103 . Dielectrically-loaded loop element  104  is located in proximity to an element with a substantially planar portion  102  (referred to as “planar element” hereinafter for convenience), having a substantially rectangular footprint. As illustrated in  FIG. 1B , the loop element  101  has terminals  101   a  and  101   b  (driven end of the loop), an aperture  101   c , a major axis  101   d  and a minor axis  101   e . Loop element  101  may be, for example, a metallic ribbon or tape, as illustrated in  FIG. 1A . Alternatively, loop element  101  may be a wire element, a printed circuit element or any combination thereof. Dielectric material  103  may be any low loss dielectric material such as epoxy-fiberglass printed-circuit board material, poly-tetraflouroethylene (PTFE) fiberglass or the like. Dielectrically-loaded loop element  104  may have a total electrical length between approximately one-half wavelength and one wavelength at a center frequency of the antenna system. 
     Planar element  102  may have a width W and a length L. As illustrated in  FIGS. 1C and 1D , the “planar element”  102  may have a shape more complex than a simple plane. For example, planar element  102  may have a flanged edge or a curved portion and/or section in addition to a planar portion, and may still be considered substantially planar. For example, planar element  102  may be part of a case assembly (e.g., a backplate) of a wireless communications device (e.g., a cellular phone, smart phone, PDA and the like) or a media player. Planar element  102  may be, for example, a metal-plated insulator or dielectric material such as molded plastic or the like. Alternatively, planar element  102  may be a fabricated, cast or formed piece of metal. In one embodiment, as illustrated in  FIG. 1A , a face  102   b  of planar element  102  may be disposed substantially parallel to the major axis  101   d  of the aperture  101   c , and substantially perpendicular the minor axis  101   e  of loop element  101 . In one embodiment, the major axis  101   d  of loop element  101  may be disposed substantially parallel to an edge  102   a  of the planar element  102 . In other embodiments, the dielectrically-loaded loop element  104  may be located at any location and at any orientation with respect to the planar element  102 , provided that minor axis  101   e  is substantially perpendicular to planar element  102  and major axis  101   d  is substantially parallel to planar element  102 . The distance between dielectrically-loaded loop element  104  and planar element  102  may be adjusted to tune the input impedance of dielectrically-loaded loop element  104 . In one embodiment, dielectrically-loaded loop element  104  may be separated from planar element  102  by less than or equal to one-fortieth of a free-space wavelength at an operating frequency of the antenna system  100 . 
       FIG. 2  illustrates a plane view of antenna system  100  in one embodiment. In  FIG. 2 , dielectrically-loaded loop element  104  is formed by wrapping loop element  101  around the dielectric material  103  such that the terminals  101   a  and  101   b  of loop element  101  are co-planar on one surface of dielectric material  103 . The terminals  101   a  and  101   b  may be driven by an RF (radio frequency) voltage source, illustrated schematically as RF voltage source  105 . In one embodiment illustrated, dielectric material  103  may be a printed circuit board (PCB) assembly and RF voltage source  105  may be a PCB-mounted RF voltage source. 
     In one embodiment, as illustrated in  FIG. 3 , a dielectrically-loaded loop element, such as dielectrically-loaded loop element  101 , may be integrated into the assembly of an electronic device such as a communications device or media player, for example, such that planar element  102  serves as a physical support element for dielectrically-loaded loop element  101 .  FIG. 3  is an exploded view  300  of an exemplary assembly of a printed circuit board (PCB) and an LCD display. In  FIG. 3 , a first section of a dielectrically-loaded loop element may be embodied as a printed trace  301   a  on a PCB  302 . A second section of a dielectrically-loaded loop element may be embodied as a printed trace on a flexible circuit  301   b . PCB  302  may then be loaded with PCB mounted components such as LCD display  303 , and the second section of the dielectrically-loaded loop element  301   b  may be formed around the PCB/LCD assembly and may be soldered or otherwise bonded with section  301   a  to form the loop element, wherein the loop element is integrated with the PCB assembly. The trace on the flex circuit may have a gap in an appropriate location (not shown) to provide terminal connections for the driven end of the loop as described above. The PCB assembly may then be mounted within the planar element  102  as illustrated in  FIG. 5  and described below. 
       FIG. 15  is a flowchart illustrating a method  1500  for manufacturing the antenna system described herein in one embodiment. In operation  1501 , a first portion of a loop element is printed on a printed circuit board (PCB). In operation  1502 , a second portion of the loop element is printed as a trace on a flexible circuit. In operation  1503 , the PCB is loaded with PCB components to fabricate a PCB assembly. In operation  1504 , the second portion of the loop element is attached to the first portion of the loop element. In operation  1505 , the second portion of the loop is formed to the PCB assembly, wherein the loop element is formed and integrated with the PCB assembly. In operation  1506 , the PCB assembly is mounted within a support element having a substantially planar portion. 
       FIG. 4  illustrates an alternative embodiment  400  of a dielectrically-loaded loop element. In  FIG. 4 , a single long piece of flex circuit  401  may be wrapped around and conformed to PCB  302  and/or LCD  303 , with loop terminals  402  exposed as the driven end of the loop. A dielectrically-loaded loop element may be formed in a variety of different ways including (but not limited to) forming a loop by printing traces on both sides of a PCB and connecting the traces with wrap-around connections or plated feedthroughs. 
       FIG. 5  illustrates a cross-sectional view  500  of one exemplary embodiment of an antenna system in a wireless communications device, where the antenna system is configured to transmit and receive RF signals in a bandwidth around 2.4 GHz. In  FIG. 5 , a dielectrically-loaded loop element  501  is wrapped around a PCB  503  and an LCD display  504 , as described above. Backplate  502  functions as a planar element as described above. A plastic cover  505  completes the assembly. For clarity of illustration, other components which may be present in a wireless communications device (e.g., a radio frequency transceiver, a digital processing system, a storage device and a battery) are not shown. 
       FIG. 6A  illustrates another view of device  500 , rotated 90 degrees and with plastic cover  505  removed. In the embodiment illustrated in  FIGS. 5 and 6 , dielectrically-loaded loop element  501  includes an aperture of approximately 36 millimeters (mm) by 3.2 mm and backplate  502  has a footprint of approximately 90 mm by 40 mm. PCB  503  has a footprint of approximately 87 mm by 38 mm and a thickness of 0.6 mm. PCB  503  may be fabricated from G10/FR-4 fiberglass epoxy laminate material conforming to Mil-I-24768/2 and/or Mil-24768/27, for example. Plastic cover  505  may be any plastic housing material as is normally used in portable electronic devices (e.g., ABS, polycarbonate, polystyrene or the like). 
     Each of PCB  503 , LCD  504  and plastic cover  505  may be characterized by a dielectric constant that, as is known in the art, reduces the propagation velocity of electromagnetic energy and increases the electrical length (in contrast to the physical length) of those materials and surrounding structures which are electromagnetically coupled with the dielectric materials. For the configuration illustrated in  FIGS. 5 and 6A , it has been determined experimentally that the electrical length of the long dimension of backplate  502  (i.e., approximately 90 mm) is approximately one-wavelength at approximately 2.4 GHz and the electrical length of the short dimension of backplate  502  (i.e., approximately 40 mm) is approximately one-half wavelength at approximately 2.4 GHz. It will be appreciated that device  500  is an exemplary embodiment, and that the dimensions of device  500  may be scaled to achieve comparable electrical lengths at other frequencies of interest. 
     Exemplary embodiment  500  is illustrated in  FIG. 6A  with a substantially rectangular footprint. Other embodiments of the invention, as illustrated in  FIGS. 6B through 6E , for example, may have other footprints, such as a substantially square footprint ( FIG. 6B ), a substantially circular footprint ( FIG. 6C ), a substantially elliptical footprint ( FIG. 6D ), a substantially semi-circular footprint ( FIG. 6E ) or combinations thereof having principle dimensions (e.g., perimeters, diameters, diagonals, etc.) compatible with half-wave and full-wave resonant modes at a frequency of interest. For example, in  FIGS. 6B through 6E , principle dimensions d1, d2, d3 or d4 may be approximately a half wavelength at a frequency of interest in various alternative embodiments. In yet other embodiments, principle dimensions d1, d2, d3 or d4 may be approximately one wavelength at a frequency of interest. 
       FIG. 7  is a plot  1000  of return loss versus frequency at the driven end  507  of dielectrically-loaded loop element  501  in device  500 . As is known in the art, return loss is a direct measure of the impedance match at the input of a circuit, and is an indirect measure of the efficiency of an antenna system. As shown by plot  1000 , the return loss is greater than or equal to approximately 8 decibels (dB) from 2.25 GHz to 2.95 GHz, which represents approximately 85% efficiency (ignoring resistive losses) over a 13.5% bandwidth. 
       FIG. 8A  is a horizontally polarized azimuth (X-Y plane) antenna pattern  800 A of device  500  for the orientation illustrated in  FIG. 9 . Antenna pattern  800 A includes superimposed patterns at 2.400 GHz, 2.440 GHz and 2.485 GHz, having average gains of −2.5 dBi (dB relative to an isotropic radiator), −2.6 dBi and −3.0 dBi, respectively. 
       FIG. 8B  is a vertically polarized (cross-polarized) azimuth (X-Y plane) antenna pattern  800 A of device  500  for the orientation illustrated in  FIG. 9 . Antenna pattern  800 B includes superimposed patterns at 2.400 GHz, 2.440 GHz and 2.485 GHz. 
       FIG. 10A  is a vertically polarized (co-polarized) elevation (X-Z plane) antenna pattern  1000 A of device  500  for the orientation illustrated in  FIG. 11 . Antenna pattern  1000 A includes superimposed patterns at 2.4 GHz, 2.44 GHz and 2.485 GHz, having peak gains of approximately 0 dBi at zero degrees and 180 degrees and 3 dB (half-power) beamwidths of approximately 60 degrees. 
       FIG. 10B  is a horizontally polarized elevation (X-Z plane) antenna pattern  1000 B of device  500  for the orientation illustrated in  FIG. 11 . Antenna pattern  1000 A includes superimposed patterns at 2.4 GHz, 2.44 GHz and 2.485 GHz. 
       FIGS. 12 and 13  illustrate one embodiment of an antenna system in a wireless communication device  1200 . Device  1200  may include a dielectrically-loaded loop element  501 , a PCB  503 , a backplate  502  and a plastic cover  505  as previously described. As noted above, the device  1300  may be dimensionally scaled to achieve antenna resonance at other frequencies of interest. 
       FIG. 14  is a block diagram illustrating a wireless device  1400 , as described above, in which embodiments of the antenna system described herein may be implemented. Wireless device  1500  may be, for example, a portable media player, a cellular telephone, a smart phone, a personal digital assistant (PDA) or other portable wireless device. Wireless device  1400  may include an antenna system  1401 , which may be antenna system  500  or  1200 , for example. Wireless device  1400  may also include a digital radio frequency (RF) transceiver  1402 , coupled to the antenna system  1401 , to transmit and/or receive digital voice, data and/or media signals through antenna system  1401 . Wireless device  1400  may also include a digital processing system  1403  to control the digital RF transceiver and to manage the digital voice, data and/or media signals. Digital processing system  1403  may be a general purpose processing device, such as a microprocessor or controller for example. Digital processing system  1403  may also be a special purpose processing device, such as an ASIC (application specific integrated circuit), FPGA (field-programmable gate array) or DSP (digital signal processor). Digital processing system  1403  may also include other devices, as are known in the art, to interface with other components of wireless device  1400 . For example, digital processing system  1403  may include analog-to-digital and digital-to-analog converters to interface with other components of wireless device  1400  as described below. Digital processing system  1403  may include a media processing system  1409 , which may also include a general purpose or special purpose processing device to manage media. 
     Wireless device  1400  may also include a storage device  1404 , coupled to the digital processing system, to store data and/or operating programs for the wireless device  1400 . Storage device  1404  may be, for example, any type of solid-state or magnetic memory device. Wireless device  1400  may also include one or more input devices  1405 , coupled to the digital processing system  1403 , to accept user inputs (e.g., telephone numbers, names, addresses, media selections, etc.) Input device  1405  may be, for example, one or more of a keypad, a touchpad, a touch screen, a pointing device in combination with a display device or similar input device. Wireless device  1400  may also include a display device  1406 , coupled to the digital processing system  1403 , to display information such as messages, contact information, pictures, movies and/or titles or other indicators of media being selected via the input device  1405 . Display device  1406  may be, for example, an LCD display device such as LCD display  504 . In one embodiment, display device  1406  and input device  1405  may be the same device (e.g., a touch screen LCD). Wireless device  1400  may also include a battery  1407  to supply operating power to components of the system including digital RF transceiver  1402 , digital processing system  1403 , storage device  1404 , input device  1405 , audio transducer  1408  and display device  1406 . Battery  1407  may be, for example, a rechargeable or non-rechargeable lithium or nickel metal hydride battery. Wireless device  1400  may also include audio transducers  1408 , which may be one or more speakers and/or microphones for example. 
     In one embodiment, digital RF transceiver  1402 , digital processing system  1403  and/or storage device  1404  may include one or more integrated circuits disposed on a PCB such as PCB  501  described above and included within a volume defined by or adjacent to the substantially planar element  502 . 
     As is known in the art, antenna systems are governed by the laws of reciprocity. Therefore, it will be appreciated that any discussion above with respect to transmission properties of embodiments of the described antenna systems applies equally to reception properties. Conversely, any discussion above with respect to reception properties of embodiments of the described antenna systems applies equally to transmission properties. 
     In the foregoing specification, the invention has been described with reference to specific exemplary embodiments thereof. It will be evident that various modifications may be made thereto without departing from the broader spirit and scope of the invention as set forth in the following claims. The specification and drawings are, accordingly, to be regarded in an illustrative sense rather than a restrictive sense.