PATENT DOCUMENT

Publication Number: US-9178268-B2
Application Number: US-201213540999-A
Country: US
Kind Code: B2

Title: Antennas integrated with speakers and methods for suppressing cavity modes

Abstract:
An electronic device may be provided with a speaker box antenna for transmitting and receiving radio-frequency signals. A speaker box antenna may be formed from a hollow dielectric speaker box containing a speaker driver. An opening in the speaker box adjacent to the speaker driver may be aligned with a speaker port opening in a conductive electronic device housing structure. The speaker box may be surrounded by conductive structures that form a cavity for the antenna. The conductive structures may include parts of the conductive electronic device housing structure. The speaker box may have opposing upper and lower surfaces. Metal plates may form parts of the upper and lower surfaces and may be shorted together using a conductive layer such as a strip of metal tape. Frequencies of operation may be selected for the antenna that suppress undesired cavity modes and enhance antenna performance.

Claims:
What is claimed is: 
     
       1. A cavity antenna that is configured to operate in an electronic device within a frequency band extending from a lower band edge to an upper band edge, comprising:
 a speaker box; 
 a conductive antenna cavity formed from conductive structures surrounding the speaker box; and 
 an antenna resonating element on the speaker box, wherein the conductive structures are configured to cut off an electromagnetic mode of order N at a cutoff frequency that lies below the lower band edge and to cut off an electromagnetic mode of order N+1 at a cutoff frequency that lies above the upper band edge. 
 
     
     
       2. The cavity antenna defined in  claim 1  wherein the speaker box has opposing upper and lower surfaces containing respective first and second metal plates. 
     
     
       3. The cavity antenna defined in  claim 2  further comprising a conductive layer that electrically connects the first metal plate to the second metal plate. 
     
     
       4. The cavity antenna defined in  claim 3  wherein the conductive layer comprises a strip of metal tape. 
     
     
       5. The cavity antenna defined in  claim 4  wherein at least one of the conductive structures comprises metal electronic device housing structures. 
     
     
       6. The cavity antenna defined in  claim 5  wherein at least one of the conductive structures comprises button structures. 
     
     
       7. The cavity antenna defined in  claim 6  wherein the metal electronic device housing structures have an opening configured to form a speaker port for the speaker box and wherein the strip of metal tape has an opening that matches the opening in the metal electronic device housing structures. 
     
     
       8. An electronic device, comprising:
 a conductive electronic device housing including an opening; and 
 a cavity antenna having:
 a speaker box configured to emit sound through the opening; 
 a conductive antenna cavity formed from conductive structures surrounding the speaker box including at least part of the conductive electronic device housing; and 
 an antenna resonating element on the speaker box, wherein the conductive structures are configured to cut off an electromagnetic mode of order N at a cutoff frequency that lies below the lower band edge and to cut off an electromagnetic mode of order N+1 at a cutoff frequency that lies above the upper band edge. 
 
 
     
     
       9. The electronic device defined in  claim 8  wherein the speaker box is hollow and has speaker box walls surrounding a hollow interior, the electronic device further comprising a speaker driver in the hollow interior. 
     
     
       10. The electronic device defined in  claim 9  further comprising at least one metal member that forms part of the speaker box walls. 
     
     
       11. The electronic device defined in  claim 10  further comprising a layer of metal tape that is electrically connected to the metal member. 
     
     
       12. The electronic device defined in  claim 11  wherein the at least one metal member and the metal tape cover portions of the speaker box adjacent to the speaker driver and wherein the metal tape has an opening through which sound from the speaker driver passes. 
     
     
       13. The electronic device defined in  claim 11  further comprising at least one additional metal member that forms part of the speaker box walls, wherein the speaker box has opposing upper and lower surfaces, and wherein the metal member forms part of the upper surface and the additional metal member forms part of the lower surface. 
     
     
       14. The electronic device defined in  claim 13  wherein the speaker box has an elongated shape with first and second opposing ends and wherein the speaker driver, the metal member, and the additional metal member are located nearer to the first end than to the second end. 
     
     
       15. The electronic device defined in  claim 14  further comprising a display and a display cover layer that covers the display. 
     
     
       16. The electronic device defined in  claim 15  wherein a portion of the display cover layer overlaps the speaker box. 
     
     
       17. The electronic device defined in  claim 16  wherein the speaker box is located in a corner portion of the conductive electronic device housing and wherein the conductive electronic device housing is configured to overlap at least three wall surfaces on the speaker box. 
     
     
       18. The electronic device defined in  claim 8  wherein the antenna resonating element comprises a flexible printed circuit antenna resonating element. 
     
     
       19. The electronic device defined in  claim 8  wherein the speaker box has an elongated length and has at least one wall running along the elongated length and wherein the conductive structures include a metal tape that covers only part of the elongated length so that some of the wall is uncovered by metal tape. 
     
     
       20. A method of operating a speaker box cavity antenna having a cavity formed from conductive structures surrounding a speaker box, comprising:
 transmitting and receiving radio-frequency electromagnetic signals with the speaker box cavity antenna within a frequency band having a lower band edge and an upper band edge selected to cut off an electromagnetic mode of order N at a cutoff frequency that lies below the lower band edge and to cut off an electromagnetic mode of order N+1 at a cutoff frequency that lies above the upper band edge; 
 wherein transmitting and receiving the radio-frequency electromagnetic signals with the speaker box cavity antenna comprises using a flexible printed circuit antenna resonating element on the speaker box to transmit and receive signals.

Description:
BACKGROUND 
     This relates generally to electronic devices, and more particularly, to antennas for electronic devices. 
     Electronic devices such as portable computers and cellular telephones are often provided with wireless communications capabilities. For example, electronic devices may use long-range wireless communications circuitry such as cellular telephone circuitry to communicate using cellular telephone bands. Electronic devices may use short-range wireless communications circuitry such as wireless local area network communications circuitry to handle communications with nearby equipment. Electronic devices may also be provided with satellite navigation system receivers and other wireless circuitry. 
     To satisfy consumer demand for small form factor wireless devices, manufacturers are continually striving to implement wireless communications circuitry such as antenna components using compact structures. At the same time, it may be desirable to include conductive structures in an electronic device such as metal device housing components and electronic components. Because conductive components can affect radio-frequency performance, care must be taken when incorporating antennas into an electronic device that includes conductive structures. For example, care must be taken to ensure that the antennas and wireless circuitry in a device are able to exhibit satisfactory performance over a range of operating frequencies. 
     It would therefore be desirable to be able to provide wireless electronic devices with improved antenna structures. 
     SUMMARY 
     Electronic devices may be provided that contain wireless communications circuitry. The wireless communications circuitry may include radio-frequency transceiver circuitry and antennas. 
     An electronic device may be provided with a speaker box antenna for transmitting and receiving radio-frequency signals. The speaker box antenna may have a conductive cavity supported by a speaker box. The speaker box may be formed from a hollow dielectric structure having an air-filled interior. A speaker driver may be mounted in the air-filled interior of the speaker box. 
     An opening in the speaker box may be aligned with a speaker port opening in a conductive electronic device housing structure. The speaker box may be surrounded by conductive structures that form the cavity for the antenna. The conductive structures may include parts of the conductive electronic device housing structure. The conductive structures may also include electrical components such as button components. 
     The speaker box may have opposing upper and lower surfaces. Metal plates may form parts of the upper and lower surfaces and may be shorted together using a conductive layer such as a strip of metal tape. The metal plates and metal tape may form part of the conductive structures that form the cavity for the antenna. The conductive cavity of the antenna may be configured to suppress undesired cavity modes and enhance antenna performance. 
     Further features of the invention, its nature and various advantages will be more apparent from the accompanying drawings and the following detailed description of the preferred embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an illustrative electronic device with wireless communications circuitry in accordance with an embodiment of the present invention. 
         FIG. 2  is a schematic diagram of an illustrative electronic device with wireless communications circuitry in accordance with an embodiment of the present invention. 
         FIG. 3  is a schematic diagram of an illustrative antenna in accordance with an embodiment of the present invention. 
         FIG. 4  is a cross-sectional side view of a cavity antenna in accordance with an embodiment of the present invention. 
         FIG. 5  is a top view of a speaker box in accordance with an embodiment of the present invention. 
         FIG. 6  is a cross-sectional side view of the speaker box of  FIG. 5  in accordance with an embodiment of the present invention. 
         FIG. 7  is a top view of an illustrative speaker box mounted in a corner portion of an electronic device housing in accordance with an embodiment of the present invention. 
         FIG. 8  is a cross-sectional side view of a speaker box adjacent to a housing wall in an electronic device in accordance with an embodiment of the present invention. 
         FIG. 9  is a perspective view of a portion of a speaker box in the vicinity of an audio port in accordance with an embodiment of the present invention. 
         FIG. 10  is a simplified perspective view of an illustrative speaker box that may be used in forming a cavity antenna in accordance with an embodiment of the present invention. 
         FIG. 11  is a graph showing how an antenna cavity may be configured so that a frequency band of operation lies between cutoff frequencies for successive cavity modes in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Electronic devices such as electronic device  10  of  FIG. 1  may be provided with wireless communications circuitry. The wireless communications circuitry may be used to support wireless communications in one or more wireless communications bands. The wireless communications circuitry may include one or more antennas. 
     The antennas may include one or more cavity antennas. Cavity-backed antennas may include an antenna resonating element and an associated conductive cavity. The cavity may be formed from conductive structures mounted to a support structure such as a speaker box. Conductive antenna structures may also be formed using conductive electronic device structures such as portions of conductive housing structures. Examples of conductive housing structures that may be used in forming an antenna (e.g., a cavity for an antenna or an antenna resonating element) include conductive internal support structures such as sheet metal structures and other planar conductive members, conductive housing walls, a peripheral conductive housing member such as a display bezel, peripheral conductive housing structures such as conductive housing sidewalls, a conductive planar rear housing wall and other conductive housing walls, or other conductive structures. Conductive structures for antennas may also be formed from parts of electronic components, such as switches (e.g., button components for a menu button or other button), integrated circuits, display module structures, flexible printed circuits associated with carrying signals for components such as display components, etc. Shielding tape, shielding cans, conductive foam, and other conductive materials within an electronic device may also be used in forming antenna structures. 
     Antenna structures such as antenna resonating element structures may be formed from patterned metal foil or other metal structures. If desired, antenna structures may be formed from conductive traces such as metal traces on a substrate. The substrate may be a plastic support structure or other dielectric structure, a rigid printed circuit board substrate such as a fiberglass-filled epoxy substrate (e.g., FR4), a flexible printed circuit (“flex circuit”) formed from a sheet of polyimide or other flexible polymer, or other substrate material. If desired, antenna structures may be formed using combinations of these approaches. For example, an antenna may be formed partly from metal structures (e.g., ground conductor structures) supported by and/or adjacent to a plastic support structure such as a hollow speaker box and may be formed partly from metal traces on a printed circuit (e.g., patterned traces on a rigid printed circuit board or a flexible printed circuit for forming antenna resonating element structures). 
     As shown in  FIG. 1 , electronic device  10  may have a housing such as housing  12 . Housing  12  may be formed from conductive structures (e.g., metal) or may be formed from dielectric structures (e.g., glass, plastic, ceramic, etc.). Antenna windows formed from plastic or other dielectric material may, if desired, be formed in conductive housing structures. An antenna for device  10  may be mounted adjacent to a dielectric housing wall or may be mounted under an antenna window structure so that the antenna window structure overlaps the antenna. During operation, radio-frequency antenna signals may pass through dielectric antenna windows and other dielectric structures in device  10 . If desired, device  10  may have a display with a cover layer. Antennas for device  10  may be mounted so that antenna signals pass through the display cover layer in addition to or instead of passing through a dielectric antenna window. 
     Electronic device  10  may be a portable electronic device or other suitable electronic device. For example, electronic device  10  may be a laptop computer, a tablet computer, a somewhat smaller device such as a wrist-watch device, pendant device, headphone device, earpiece device, or other wearable or miniature device, a cellular telephone, or a media player. Device  10  may also be a television, a set-top box, a desktop computer, a computer monitor into which a computer has been integrated, or other suitable electronic equipment. 
     Device  10  may have a display such as display  14  that is mounted in housing  12 . Display  14  may, for example, be a touch screen that incorporates capacitive touch electrodes or may be insensitive to touch. A touch sensor for display  14  may be formed from capacitive touch sensor electrodes, a resistive touch array, touch sensor structures based on acoustic touch, optical touch, or force-based touch technologies, or other suitable touch sensors. 
     Display  14  may include image pixels formed from light-emitting diodes (LEDs), organic LEDs (OLEDs), plasma cells, electrowetting pixels, electrophoretic pixels, liquid crystal display (LCD) components, or other suitable image pixel structures. A cover layer may cover the surface of display  14  or a display layer such as a color filter layer or other portion of a display may be used as the uppermost (or nearly uppermost) layer in display  14 . 
     The display cover layer or other outer display layer may be formed from a transparent glass sheet, a clear plastic layer, or other transparent member. As shown in  FIG. 1 , openings may be formed in the outermost display layer to accommodate components such as button  16 . 
     Display  14  may have an active portion and, if desired, may have an inactive portion. The active portion of display  14  may contain active image pixels for displaying images to a user of device  10 . The inactive portion of display  14  may be free of active pixels. The active portion of display  14  may lie within a region such as central rectangular region  22  (bounded by rectangular outline  18 ). Inactive portion  20  of display  14  may surround the edges of active region  22  in a rectangular ring shape. 
     In inactive region  20 , the underside of the display cover layer for display  14  or other portions of the display layers in display  14  may be coated with an opaque masking layer. The opaque masking layer may be formed from an opaque material such as an opaque polymer (e.g., black ink, white ink, a coating of a different color, etc.). The opaque masking layer may be used to block interior device components from view by a user of device  10 . The opaque masking layer may, if desired, be sufficiently thin and/or formed from a sufficiently non-conductive material to be radio transparent. This type of configuration may be used in configurations in which antenna structures are formed under inactive region  20 . As shown in  FIG. 1 , for example, antenna structures such as one or more antennas  40  may be mounted in housing  12  so that inactive region  20  overlaps the antenna structures. 
     One or more antennas  40  may be mounted adjacent to audio port  17 . For example, a conductive cavity for a cavity antenna may be formed from conductive structures that are attached to or mounted adjacent to a speaker box or that otherwise surround the speaker box. The speaker box may therefore form as a cavity support structure for the cavity antenna. The speaker box may also contain a speaker driver for producing sound that passes through an opening in housing  12  (i.e., speaker port  17 ). 
     Housing  12 , which may sometimes be referred to as a case, may be formed of plastic, glass, ceramics, fiber composites, metal (e.g., stainless steel, aluminum, etc.), other suitable materials, or a combination of these materials. In some situations, housing  12  or parts of housing  12  may be formed from dielectric or other low-conductivity material. In other situations, housing  12  or at least some of the structures that make up housing  12  may be formed from metal elements. 
     In configurations for device  10  in which housing  12  is formed from conductive materials such as metal, antennas  40  may be mounted under the display cover layer for display  14  as shown in  FIG. 1  (e.g., under inactive region  20 ) and/or antennas  40  may be mounted adjacent to one or more dielectric antenna windows in housing  12 . During operation, radio-frequency antenna signals can pass through the portion of inactive region  20  of the display cover layer that overlaps antennas  40  (and, if a dielectric window structure is used, antenna signals may pass through the window structure). In general, antennas  40  may be located in any suitable location in device housing  12  (e.g., along the edges of display  14 , in corners of device  10 , under an antenna window or other dielectric structure on a rear surface of housing  12 , etc.). 
     Device  10  may have a single antenna or multiple antennas. In configurations in which multiple antennas are present, the antennas may be used to implement an antenna array in which signals for multiple identical data streams (e.g., Code Division Multiple Access data streams) are combined to improve signal quality or may be used to implement a multiple-input-multiple-output (MIMO) antenna scheme that enhances performance by handling multiple independent data streams (e.g., independent Long Term Evolution data streams). Multiple antennas may also be used to implement an antenna diversity scheme in which device  10  activates and inactivates each antenna based on its real time performance (e.g., based on received signal quality measurements). In a device with wireless local area network wireless circuitry, the device may use an array of antennas  40  to transmit and receive wireless local area network signals (e.g., IEEE 802.11n traffic). Multiple antennas may be used together in both transmit and receive modes of operation or may only be used together during only signal reception operations or only signal transmission operations. 
     Antennas in device  10  may be used to support any communications bands of interest. For example, device  10  may include antenna structures for supporting wireless local area network communications such as IEEE 802.11 communications (e.g., communications in bands such as the IEEE 802.11 bands at 2.4 GHz and 5 GHz) or Bluetooth® communications, voice and data cellular telephone communications, global positioning system (GPS) communications or other satellite navigation system communications, etc. 
     A schematic diagram of an illustrative configuration that may be used for electronic device  10  is shown in  FIG. 2 . As shown in  FIG. 2 , electronic device  10  may include control circuitry such as storage and processing circuitry  28 . Storage and processing circuitry  28  may include storage such as hard disk drive storage, nonvolatile memory (e.g., flash memory or other electrically-programmable-read-only memory configured to form a solid state drive), volatile memory (e.g., static or dynamic random-access-memory), etc. Processing circuitry in storage and processing circuitry  28  may be used to control the operation of device  10 . The processing circuitry may be based on one or more microprocessors, microcontrollers, digital signal processors, baseband processors, power management units, audio codec chips, application specific integrated circuits, etc. 
     Storage and processing circuitry  28  may be used to run software on device  10 , such as internet browsing applications, voice-over-internet-protocol (VOIP) telephone call applications, email applications, media playback applications, operating system functions, etc. To support interactions with external equipment, storage and processing circuitry  28  may be used in implementing communications protocols. Communications protocols that may be implemented using storage and processing circuitry  28  include internet protocols, wireless local area network protocols such as IEEE 802.11 protocols—sometimes referred to as WiFi® and protocols for other short-range wireless communications links such as the Bluetooth® protocol, cellular telephone protocols, etc. 
     Input-output circuitry  30  may be used to allow data to be supplied to device  10  and to allow data to be provided from device  10  to external devices. Input-output circuitry  30  may include input-output devices  32 . Input-output devices  32  may include touch screens, buttons, joysticks, click wheels, scrolling wheels, touch pads, key pads, keyboards, microphones, speakers, tone generators, vibrators, cameras, sensors, light-emitting diodes and other status indicators, data ports, etc. A user can control the operation of device  10  by supplying commands through input-output devices  32  and may receive status information and other output from device  10  using the output resources of input-output devices  32 . 
     Wireless communications circuitry  34  may include radio-frequency (RF) transceiver circuitry formed from one or more integrated circuits, power amplifier circuitry, low-noise input amplifiers, passive RF components, one or more antennas, and other circuitry for handling RF wireless signals. Wireless signals can also be sent using light (e.g., using infrared communications). 
     Wireless communications circuitry  34  may include satellite navigation system receiver circuitry  35  such as Global Positioning System (GPS) receiver circuitry (e.g., for receiving satellite positioning signals at 1575 MHz) or may include satellite navigation system receiver circuitry associated with other satellite navigation systems. Wireless local area network transceiver circuitry  36  may handle 2.4 GHz and 5 GHz bands for WiFi® (IEEE 802.11) communications and may handle the 2.4 GHz Bluetooth® communications band. Circuitry  34  may use cellular telephone transceiver circuitry  38  for handling wireless communications in cellular telephone bands such as bands in frequency ranges of about 700 MHz to about 2200 MHz or bands at higher or lower frequencies. Wireless communications circuitry  34  can include circuitry for other short-range and long-range wireless links if desired. For example, wireless communications circuitry  34  may include wireless circuitry for receiving radio and television signals, paging circuits, near field communications circuitry, etc. In WiFi® and Bluetooth® links and other short-range wireless links, wireless signals are typically used to convey data over tens or hundreds of feet. In cellular telephone links and other long-range links, wireless signals are typically used to convey data over thousands of feet or miles. 
     Wireless communications circuitry  34  may include one or more antennas  40 . Antennas  40  may, if desired, include on or more cavity antennas. 
     A schematic diagram of an illustrative configuration for an antenna in device  10  is shown in  FIG. 3 . In the example of  FIG. 3 , antenna  40  is an inverted-F antenna. This is merely illustrative. Antenna  40  may, in general, be based on any suitable type of antenna (e.g., a loop antenna, a patch antenna, a monopole antenna, a dipole antenna, a directly fed antenna, an indirectly fed antenna, a slot antenna, a planar inverted-F antenna, other antenna types, or hybrids formed from two or more of these antennas). 
     As shown in  FIG. 3 , inverted-F antenna  40  may include an antenna resonating element such as antenna resonating element  42  and an antenna ground such as antenna ground  44 . Antenna resonating element  46  may have a main antenna resonating element arm such as arm  46 . Arm  46  may have one or more branches. Short circuit branch  48  may be used to couple resonating element arm  46  to ground  44 . Antenna feed  50  may be coupled between antenna resonating element arm  46  and ground  44  in parallel with short circuit branch  48 . 
     In a cavity antenna, a conductive cavity structure may be configured to form antenna ground  44 . A cross-sectional side view of an illustrative cavity antenna is shown in  FIG. 4 . As shown in  FIG. 4 , antenna  40  may include an antenna resonating element such as antenna resonating element  42  and may include a conductive cavity such as conductive ground cavity  44 . Display layer  52  may overlap antenna resonating element  42  and cavity  44 . During operation, radio-frequency signals associated with antenna  40  (e.g., signals transmitted and/or received using resonating element  42 ) may pass through layer  52  of display  14 . Layer  52  may be a display cover layer, a color filter layer, or other display layers associated with display  14  (as examples). 
     If desired, the conductive structures that form antenna cavity  44  may be mounted on a support structure such as a speaker box.  FIG. 5  is a top view of an illustrative speaker box of the type that may be used to provide sound to audio port  17 . A speaker driver may be mounted within speaker box  54  for producing sound  64 . Speaker box  54  may be aligned with port  17  so that sound  64  passes through port  17  during operation. Speaker box  54  may be formed from plastic, metal, fiber-based composites, other materials, or combinations of these materials. As an example, speaker box  54  may be formed from a hollow molded plastic structure having opposing upper and lower walls. Speaker box  54  may have a roughly rectangular shape. As shown in  FIG. 5 , for example, speaker box  54  may have walls such as left wall  54 L, right wall  54 R, front wall  54 F, and rear wall  54 X that surround the periphery of speaker box  54 . With this type of configuration, speaker box  54  may exhibit a roughly rectangular footprint (i.e., speaker box  54  may occupy an approximately rectangular area when viewed from above as in  FIG. 5 ). Curved edge portion  54 CE may be used to accommodate speaker box  54  within a curved corner portion of housing  12 . Recessed portion  55  may be used to accommodate a flexible printed circuit cable for display  14  or other components in device  10 . If desired, speaker box  54  may have a footprint of other shapes. The example of  FIG. 5  is merely illustrative. 
     Metal structures such as metal plate  62  may be attached to speaker box  54  or embedded within the walls of speaker box  54 , if desired. As shown in  FIG. 5 , for example, metal plate  62  may be formed on the upper wall of speaker box  54  (e.g., plate  62  may form part of the upper surface of speaker box  54 ). 
     A cross-sectional side view of speaker box  54  taken along line  58  of  FIG. 5  and viewed in direction  60  is shown in  FIG. 6 . As shown in  FIG. 6 , metal plate  52  may form part of upper speaker box wall  54 T. Speaker box  54  may also have an opposing planar wall structure such as lower wall  54 B. The walls of speaker box  54  form a hollow rectangular-box-shaped air-filled interior region (interior  70 ). Speaker driver  68  may be mounted in air-filled interior region  70 . During operation of device  10 , speaker driver  68  may produce sound  64  ( FIG. 5 ). An opening in rear wall  54 X ( FIG. 5 ) may allow sound to escape through speaker port  17  ( FIG. 1 ). A planar metal structure such as metal plate  66  may be formed in lower wall  54 B. Plate  66  may, for example, be formed below speaker driver  68  and may form part of the lower surface of speaker box  54 . Metal plate  62  may overlap speaker driver  68  and metal plate  66 . Metal plate  66  may overlap speaker box  54  and plate  62 . Metals such as aluminum, stainless steel, and other metals may be used in forming structures such as metal plate  62  and metal plate  66 . In some configurations, metal wall structures may be stronger than plastic wall structures of the same thickness, so the use of metal plates in forming parts of the walls in speaker box  54  may help allow the dimensions of speaker box  54  to be minimized. 
       FIG. 7  is a top view of a corner portion of device  10  showing how speaker box  54  may be surrounded by conductive structures such as housing  12  and flexible printed circuit  72 . Flexible printed circuit  72  may contain metal traces that form signal paths for conveying signals associated with operating a touch sensor array for display  14  between the touch sensor array and circuitry on a printed circuit board. Metal tape, display structures, and other conductive structures may run along wall  54 F of speaker box  54 . Wall  54 X may be covered by portions of housing  12 . Portions of housing  12  may also cover part of upper speaker box wall  54 T and lower speaker box wall  54 L ( FIG. 6 ). An edge portion of printed circuit  72  may cover part of upper speaker box wall  54 T. Conductive structures  78  such as conductive switch structures and other conductive structures associated with button  16  of  FIG. 1  or other button components may cover speaker box wall  54 L. Opposing end wall  54 R may be covered by portions of housing  12 . By covering the walls of speaker box  54  in this way, the conductive structures surrounding speaker box  54  allow speaker box  54  to form a conductive cavity for antenna  40  (e.g., an elongated rectangular box-shaped cavity having opposing ends, opposing front and rear surfaces, and opposing upper and lower surfaces). 
     Antenna resonating element  42  may be formed from conductive metal traces on a rigid printed circuit or conductive metal traces on a flexible printed circuit (as examples). Antenna resonating element  42  may be mounted in an opening in the upper surface of the antenna cavity formed by speaker box  54 , as illustrated by antenna cavity  44  in antenna  40  of  FIG. 4 . In a fully assembled version of device  10 , dielectric display layers such as display layer  52  of  FIG. 4  (e.g., a portion of a color filter layer, thin-film transistor layer, and/or a display cover layer) may cover speaker box  54 , including antenna resonating element  42  and the other structures shown in the corner of device  10  of  FIG. 7 . 
       FIG. 8  is a cross-sectional end view of speaker box  54  taken along line  74  of  FIG. 7  (at the left end of speaker box  54 ) and viewed in direction  76 . As shown in  FIG. 8 , a layer of conductive tape such as tape  80  may be wrapped around the side of speaker box  54  at one of the opposing ends of the elongated speaker box such as the left end of speaker box  54  adjacent to wall  54 L. Conductive tape  80  may be formed from a layer of metal such as copper, from a conductive fabric, or other conductive materials. Conductive adhesive, welds, fasteners, or other conductive attachment mechanisms  88  may be used to short conductive tape  80  to upper speaker box plate  62  and lower speaker box plate  66 . 
     A portion of tape  80  may cover rear speaker box wall  54 X. Speaker box wall  54 X may have an opening such as opening  84 . Tape  80  may have a mating opening such as opening  82  that is aligned with opening  84 . Gasket  86  may surround opening  82  and may be interposed between housing wall  12  and tape  80 . By aligning openings  84 ,  82 , and  17  in housing wall  12  with the mating opening formed in the center of gasket  86 , sound  64  may be allowed to pass from speaker driver  68  through these openings to the exterior of device  10 . 
     The shape of openings  84 ,  82 , and  17  may be rectangular (so that gasket  86  has a rectangular ring shape), may be circular (so that gasket  86  has a circular ring shape), or may have other suitable matched shapes. 
       FIG. 9  is a perspective view of a portion of speaker box  54  showing how conductive tape  80  may wrap around sidewall portion  54 X and may short plates  62  and  66  to each other, thereby grounding plate  62  and plate  66 . Tape  80  may wrap around speaker box  54  along the entire length of speaker box wall  54 X or may, as shown in  FIG. 9 , only wrap around speaker box  54  in the portion of speaker box  54  near the left end of speaker box  54  that includes plates  62  and  66  (e.g., the left half of speaker box  54 ). Grounding plate  62  to plate  66  in this way influences the loading on antenna  40  and can be used to adjust the supported cavity modes in cavity  44  for a frequency band of interest and thereby enhance antenna performance. 
     Cavity  44  for cavity antenna  40  may be formed by the conductive structure that surround speaker box  54 . As shown in  FIG. 10 , speaker box  54  may roughly have the shape of a six-sided rectangular box. Housing structures  12  may serve as conductive ground structures  96 ,  94 , and  98  on walls  54 R,  54 X, and  54 B, respectively. Conductive ground structures  102  for covering wall  54 L may be formed from electrical components in device  10  such as button structures associated with button  16  (e.g., a dome switch, a button flexible printed circuit with button switch traces, metal support structures, etc.). Conductive ground structures  90  may be formed by an overlapping display flexible printed circuit cable such as cable  72  of  FIG. 7  or other conductive material. Conductive ground structures  92  may be formed from an overlapping portion of housing  12 . Conductive ground structures  100  may be formed by metal plate  62 . Tape  80  and lower plate  66  may also form conductive ground structures surrounding box  54 . 
     Speaker box  54  may have an elongated length along which elongated front wall  54 F runs. Front wall  54 F of speaker box  54  may be covered by conductive display components and, if desired, layer of conductive tape. The conductive tape may, as an example, cover a portion of wall  54 F, as shown in  FIG. 10 , while leaving an end portion (e.g., a fraction of the length of wall  54 F adjacent to right end  54 R of box  54 ) uncovered by tape. The use of a partly covered configuration for wall  54 F may help adjust the supported cavity modes in cavity  44  for a frequency band of interest and thereby enhance antenna performance. 
     Antenna resonating element  42  of antenna  40  may be mounted on the upper surface of speaker box  54 , so that the ground structures that surround speaker box  54  serve as antenna cavity  44  for cavity antenna  40 . 
     The conductive materials that surround speaker box  54  to form cavity  44  such as tape  104 , tape  80 , plates  62  and  66 , and the other portions of cavity  44  may be configured to suppress undesired cavity modes, thereby enhancing antenna performance.  FIG. 11  is a graph showing how the real part β of the propagation constant for electromagnetic waves traveling within cavity  44  may vary as a function of operating frequency f. In the illustrative scenario of  FIG. 11 , it is desired to operate device  10  and antenna  40  in a frequency band FB extending from a lower band edge at low frequency f L  to an upper band edge at high frequency f H . With one suitable arrangement, low frequency f L  may be 5.15 GHz and high frequency f H  may be 5.85 GHz (e.g., the frequency band of interest may be associated with 802.11 5 GHz communications). Frequency band FB may, in general, correspond to a cellular telephone band, a wireless local area network band, or other communications band of interest. 
     In the propagation constant graph for cavity  44  of  FIG. 11 , curve  106  represents the propagation constant associated with a mode of order N and curve  108  represents the propagation constant associated with a successive mode of order N+1. Curve  106  may be characterized by a cutoff frequency fc 1 . Curve  108  may be characterized by a cutoff frequency fc 2 . In accordance with curves  106  and  108 , cavity  44  will not support the N-order mode below frequency fc 1  (i.e., the mode of order N will be cut off below fc 1 ) and will not support the N+1 order mode below frequency fc 2  (i.e., the mode of order N+1 will be cut off below fc 2 ). The value of N may be one or may be another suitable integer (i.e., lower order modes may be supported by cavity  44  in addition to the mode of order N). 
     With the illustrative configuration shown in  FIG. 11 , band FB lies in the frequency range extending between frequency fc 1  to fc 2  (i.e., frequency fc 1  is spaced below frequency f L  and frequency fc 2  is spaced above frequency f H ). The magnitudes of fc 2 −f H  and f L −fc 1  may, for example, be equal or may be close to equal to each other (e.g., within 80% or within 20% of each other to center band FB within the spacing created between cutoff frequencies fc 1  and fc 2  for the two successive cavity modes N and N+1). This configuration enhances antenna performance by reducing frequency variations in cavity mode coupling. 
     In general, there are many potential locations for cutoff frequencies fc 1  and fc 2  relative to band FB. For example, it might be possible to configure cavity  44  so that fc 1  falls within band FB or lies at the same frequency as lower band edge f L . However, in situations such as these and in other situations that differ from the preferred arrangement of  FIG. 11 , the efficiency with which electromagnetic waves are coupled into cavity  44  (and not radiated by antenna  40 ) will vary considerably as a function of frequency f within band FB. The arrangement of  FIG. 11  avoids these fluctuations. 
     The radio-frequency energy that is coupled into antenna  40  is ideally all radiated. In practice, however, some cavity modes will typically be supported (i.e., it may not be practical to ensure that the cutoff frequency for the lowest order mode is above f H ), leading to some unavoidable cavity mode signal losses. By configuring cavity  44  as shown in  FIG. 11 , however, any cavity losses that occur due to the coupling of radio-frequency electromagnetic signals into a supported cavity mode (e.g., mode N, represented by the overlap of curve  106  and active communications band FB) will be relatively constant as a function of operating frequency f. The presence of cavity  44  (and mode N) will therefore not impart undesirable cavity coupling resonances as a function of frequency f in band FB when cavity  44  is configured to exhibit cavity mode characteristics of the type shown in  FIG. 11 . 
     The foregoing is merely illustrative of the principles of this invention and various modifications can be made by those skilled in the art without departing from the scope and spirit of the invention.

Metadata:
Filing Date: 20120703
Publication Date: 20151103
Grant Date: 20151103
Priority Date: 20120703
Inventors: ZHU JIANG
LI QINGXIANG
GOMEZ ANGULO RODNEY A.
SAMARDZIJA MIROSLAV
COUTTS GORDON
SCHLUB ROBERT W.
Assignee: APPLE INC
CPC Classifications: [{"code": "H01Q9/42", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q1/2266", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01Q1/243", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q9/42", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q1/243", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q1/2266", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 48699328