Patent Publication Number: US-9425496-B2

Title: Distributed loop speaker enclosure antenna

Description:
BACKGROUND 
     This relates generally to electronic devices and, more particularly, to electronic devices with antennas. 
     Electronic devices are often provided with antennas. Challenges can arise in mounting antennas within an electronic device. For example, factors such as the relative position between an antenna and surrounding device structures and electrical components and factors such as the size and shape of antenna structures can have an impact on antenna tuning and bandwidth. If care is not taken, an antenna may become detuned or may exhibit an undesirably small efficiency bandwidth at desired operating frequencies. 
     It would therefore be desirable to be able to provide improved antennas for use in electronic devices. 
     SUMMARY 
     An electronic device may be provided with antenna structures. The antenna structures may be formed using a dielectric carrier structure such as a hollow plastic speaker enclosure, thereby allowing a volume in the interior of the device that is occupied by the speaker enclosure to be used as part of an antenna. A speaker driver may be mounted in the speaker enclosure. Openings in the speaker enclosure may be used to allow sound from the speaker driver to be emitted from the speaker enclosure. 
     The antenna structures may have first and second loop antenna resonating elements. The loop antenna resonating elements may be formed from metal traces on the speaker enclosure and, if desired, portions of a metal housing for the electronic device. 
     The first loop antenna resonating element may indirectly feed the second loop antenna resonating element. The second loop antenna resonating element may be formed from a strip of metal that loops around the speaker enclosure. A gap in the metal strip may form a capacitance in the second loop antenna resonating element. An inductance may also be formed in the second loop antenna resonating element. Openings in the second loop antenna resonating element may be aligned with the speaker enclosure openings. Segments of metal between the openings in the second loop antenna resonating element may collectively form the inductance for the second loop antenna resonating element. 
     The electronic device housing may have openings aligned with the speaker enclosure openings and the openings in the second loop antenna resonating element. 
     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 such as a laptop computer that may be provided with antenna structures in accordance with an embodiment of the present invention. 
         FIG. 2  is a perspective view of an illustrative electronic device such as a handheld electronic device that may be provided with antenna structures in accordance with an embodiment of the present invention. 
         FIG. 3  is a perspective view of an illustrative electronic device such as a tablet computer that may be provided with antenna structures in accordance with an embodiment of the present invention. 
         FIG. 4  is a perspective view of an illustrative electronic device such as a computer display with an integrated computer that may be provided with antenna structures in accordance with an embodiment of the present invention. 
         FIG. 5  is a schematic diagram of an illustrative electronic device with antenna structures in accordance with an embodiment of the present invention. 
         FIG. 6  is a schematic diagram of radio-frequency transceiver circuitry and antenna structures in accordance with an embodiment of the present invention. 
         FIG. 7  is a diagram of illustrative loop antenna structures in accordance with an embodiment of the present invention. 
         FIG. 8  is a graph of antenna performance as a function of operating frequency for an illustrative antenna of the type shown in  FIG. 7  in accordance with an embodiment of the present invention. 
         FIG. 9  is a perspective view of an illustrative speaker driver in accordance with an embodiment of the present invention. 
         FIG. 10  is a cross-sectional side view of an illustrative speaker driver showing how the speaker driver housing may be coated with an insulating coating in accordance with an embodiment of the present invention. 
         FIG. 11  is a top view of an illustrative speaker box of the type that may be used as an antenna carrier in accordance with an embodiment of the present invention. 
         FIG. 12  is a perspective view of an illustrative distributed loop antenna formed using conductive traces on dielectric antenna carrier such as a speaker box in accordance with an embodiment of the present invention. 
         FIG. 13  is a cross-sectional side view of an illustrative antenna mounted within an electronic device housing in accordance with an embodiment of the present invention. 
         FIG. 14  is a perspective view of a portion of an electronic device showing how the electronic device may have a housing with speaker holes in accordance with an embodiment of the present invention. 
         FIG. 15  is a perspective view of a portion of an electronic device showing how the electronic device may have a housing with speaker openings in the shape of slots in accordance with an embodiment of the present invention. 
         FIG. 16  is a cross-sectional side view of a portion of an electronic device showing how antenna structures in the electronic device may be mounted in accordance with an embodiment of the present invention. 
         FIG. 17  is a cross-sectional side view of a portion of an electronic device having antenna structures with a recessed portion to accommodate an electronic component such as a display module in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Electronic devices may include antennas. The antennas may be used to transmit and receive wireless signals. Illustrative electronic devices that may be provided with antennas are shown in  FIGS. 1, 2, 3, and 4 . 
       FIG. 1  shows how electronic device  10  may have the shape of a laptop computer having upper housing  12 A and lower housing  12 B with components such as keyboard  16  and touchpad  18 . Device  10  may have hinge structures  20  that allow upper housing  12 A to rotate in directions  22  about rotational axis  24  relative to lower housing  12 B. Display  14  may be mounted in upper housing  12 A. Upper housing  12 A, which may sometimes referred to as a display housing or lid, may be placed in a closed position by rotating upper housing  12 A towards lower housing  12 B about rotational axis  24 . Antenna structures may be mounted along the upper edge of upper housing  12 A under a display cover layer associated with display  14  or elsewhere in device  10 . 
       FIG. 2  shows how electronic device  10  may be a handheld device such as a cellular telephone, music player, gaming device, navigation unit, or other compact device. In this type of configuration for device  10 , housing  12  may have opposing front and rear surfaces. Display  14  may be mounted on a front face of housing  12 . Display  14  may, if desired, have a display cover layer or other exterior layer that includes openings for components such as button  26 . Openings may also be formed in a display cover layer or other display layer to accommodate a speaker port (see, e.g., speaker port  28  of  FIG. 2 ). Antenna structures may be mounted under an inactive peripheral portion of the display cover layer for display  14  or elsewhere in housing  12  of  FIG. 2 . 
       FIG. 3  shows how electronic device  10  may be a tablet computer. In electronic device  10  of  FIG. 3 , housing  12  may have opposing planar front and rear surfaces. Display  14  may be mounted on the front surface of housing  12 . As shown in  FIG. 3 , display  14  may have a display cover layer or other external layer with an opening to accommodate button  26  (as an example). Antenna structures may be mounted under one of the peripheral edges of the display cover layer or elsewhere within device  10 . 
       FIG. 4  shows how electronic device  10  may be a computer display or a computer that has been integrated into a computer display. With this type of arrangement, housing  12  for device  10  may be mounted on a support structure such as stand  27 . Display  14  may be mounted on a front face of housing  12 . Display  14  may, if desired, have a display cover layer. Antenna structures for device  10  of  FIG. 4  may be mounted under one or more of the peripheral edges of the display cover layer or elsewhere within device  10 . 
     The illustrative configurations for device  10  that are shown in  FIGS. 1, 2, 3, and 4  are merely illustrative. In general, electronic device  10  may be a laptop computer, a computer monitor containing an embedded computer, a tablet computer, a cellular telephone, a media player, or other handheld or portable electronic device, a smaller device such as a wrist-watch device, a pendant device, a headphone or earpiece device, or other wearable or miniature device, a television, a computer display that does not contain an embedded computer, a gaming device, a navigation device, an embedded system such as a system in which electronic equipment with a display is mounted in a kiosk or automobile, equipment that implements the functionality of two or more of these devices, or other electronic equipment. 
     Housing  12  of device  10 , which is sometimes referred to as a case, may be formed of materials such as plastic, glass, ceramics, carbon-fiber composites and other fiber-based composites, metal (e.g., machined aluminum, stainless steel, or other metals), other materials, or a combination of these materials. Device  10  may be formed using a unibody construction in which most or all of housing  12  is formed from a single structural element (e.g., a piece of machined metal or a piece of molded plastic) or may be formed from multiple housing structures (e.g., outer housing structures that have been mounted to internal frame elements or other internal housing structures). In configurations in which housing  12  is formed from metal or other conductive materials, dielectric structures such as plastic structures may be used to form antenna windows that overlap some or all of the antenna structures in device  10 . Antenna structures in device  10  may also be configured to transmit and receive radio-frequency antenna signals through display cover layers and other dielectric structures in device  10 . 
     Display  14  may be a touch sensitive display that includes a touch sensor or may be insensitive to touch. Touch sensors for display  14  may be formed from an array of 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 sensor components. 
     Displays for device  10  may, in general, 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 display 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 outermost (or nearly outermost) layer in display  14 . A display cover layer or other outer display layer may be formed from a transparent glass sheet, a clear plastic layer, or other transparent member. 
     Touch sensor components such as an array of capacitive touch sensor electrodes formed from transparent materials such as indium tin oxide may be formed on the underside of a display cover layer, may be formed on a separate display layer such as a glass or polymer touch sensor substrate, or may be integrated into other display layers (e.g., substrate layers such as a thin-film transistor layer). 
     A schematic diagram of an illustrative configuration that may be used for electronic device  10  is shown in  FIG. 5 . As shown in  FIG. 5 , electronic device  10  may include control circuitry  29 . Control circuitry  29  may include storage and processing circuitry for controlling the operation of device  10 . Control circuitry  29  may, for example, 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. Control circuitry  29  may include processing circuitry based on one or more microprocessors, microcontrollers, digital signal processors, baseband processors, power management units, audio codec chips, application specific integrated circuits, etc. 
     Control circuitry  29  may be used to run software on device  10 , such as operating system software and application software. Using this software, control circuitry  29  may present audio information to the user of device  10  using speakers and other audio circuitry, may use antenna structures and radio-frequency transceiver circuitry to transmit and receive wireless signals, and may otherwise control the operation of device  10 . 
     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 communications circuitry  32 . Communications circuitry  32  may include wired communications circuitry for supporting communications using data ports in device  10 . Communications circuitry  32  may also include wireless communications circuits (e.g., circuitry for transmitting and receiving wireless radio-frequency signals using antennas). 
     Input-output circuitry  30  may also include input-output devices  34 . A user can control the operation of device  10  by supplying commands through input-output devices  34  and may receive status information and other output from device  10  using the output resources of input-output devices  34 . 
     Input-output devices  34  may include sensors and status indicators  36  such as an ambient light sensor, a proximity sensor, a temperature sensor, a pressure sensor, a magnetic sensor, an accelerometer, and light-emitting diodes and other components for gathering information about the environment in which device  10  is operating and providing information to a user of device  10  about the status of device  10 . 
     Audio components  38  may include speakers and tone generators for presenting sound to a user of device  10  and microphones for gathering user audio input. 
     Display  14  may be used to present images for a user such as text, video, and still images. Sensors  36  may include a touch sensor array that is formed as one of the layers in display  14 . 
     User input may be gathered using buttons and other input-output components  40  such as touch pad sensors, buttons, joysticks, click wheels, scrolling wheels, touch sensors such as sensors  36  in display  14 , key pads, keyboards, vibrators, cameras, and other input-output components. 
     As shown in  FIG. 6 , communications circuitry  32  may include wireless communications circuitry such as radio-frequency transceiver circuitry  100  and antenna structures  102 . Communications circuitry  32  may include wireless circuitry formed from one or more integrated circuits, power amplifier circuitry, low-noise input amplifiers, passive radio-frequency components, one or more antennas such as antenna structures  102 , and other circuitry for handling radio-frequency wireless signals. 
     Communications circuitry  32  may include radio-frequency transceiver circuits for handling multiple radio-frequency communications bands. For example, transceiver circuitry  100  may include circuits for handling cellular telephone communications, wireless local area network signals, and satellite navigation system signals such as signals at 1575 MHz from satellites associated with the Global Positioning System. Transceiver circuitry  100  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  100  may include cellular telephone transceiver circuitry for handling wireless communications in cellular telephone bands such as the bands in the range of 700 MHz to 2.7 GHz (as examples). 
     Communications circuitry  32  can include wireless circuitry for other short-range and long-range wireless links if desired. For example, circuitry  32  may include wireless circuitry for receiving radio and television signals, paging circuits, 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. 
     Communications circuitry  32  may include antenna structures  102 . Antenna structures  102  may include one or more antennas. Antenna structures  102  may include inverted-F antennas, patch antennas, loop antennas, monopoles, dipoles, single-band antennas, dual-band antennas, antennas that cover more than two bands, or other suitable antennas. Configurations in which at least one antenna in device  10  is formed using loop antenna structures are sometimes described herein as an example. 
     To provide antenna structures  102  with the ability to cover communications frequencies of interest, antenna structures  102  may, if desired, be provided with tunable circuitry that is controlled by control circuitry  29 . For example, control circuitry  29  may supply control signals to tunable circuitry in antenna structures  102  during operation of device  10  whenever it is desired to tune antenna structures  102  to cover a desired communications band. 
     Transceiver circuitry  100  may be coupled to antenna structures  102  by signal paths such as signal path  104 . Signal path  104  may include one or more transmission lines. As an example, signal path  104  of  FIG. 6  may be a transmission line having a positive signal conductor such as line  106  and a ground signal conductor such as line  108 . Lines  106  and  108  may form parts of a coaxial cable or a microstrip transmission line having an impedance of 50 ohms (as an example). A matching network formed from components such as inductors, resistors, and capacitors may be used in matching the impedance of antenna structures  102  to the impedance of transmission line  104 . Matching network components may be provided as discrete components (e.g., surface mount technology components) or may be formed from housing structures, printed circuit board structures, traces on plastic supports, etc. 
     Transmission line  104  may be coupled to antenna feed structures associated with antenna structures  102 . As an example, antenna structures  102  may form an antenna having an antenna feed with a positive antenna feed terminal such as terminal  110  and a ground antenna feed terminal such as ground antenna feed terminal  112 . Positive transmission line conductor  106  may be coupled to positive antenna feed terminal  110  and ground transmission line conductor  108  may be coupled to ground antenna feed terminal  112 . Other types of antenna feed arrangements may be used if desired. The illustrative feed configuration of  FIG. 6  is merely illustrative. 
     Antenna structures  102  may be formed from metal traces or other patterned conductive material supported by a dielectric carrier. With one suitable arrangement, antenna structures  102  may be based on loop antenna structures. For example, antenna structures  102  may include a strip of conductive material that is wrapped into a loop. Because the strip of conductive material has an associated width across which material is distributed, loop antenna structures such as these may sometimes be referred to as distributed loop antenna structures. A distributed loop antenna may be fed using a direct feeding arrangement in which feed terminals such as terminals  110  and  112  are coupled directly to the strip of material that forms the loop, may be fed indirectly by using near-field electromagnetic coupling to couple a loop antenna feeding element or other element to the loop that is formed from the strip of material, or may be fed using other suitable feed arrangements. 
     A schematic diagram of a distributed loop antenna of the type that may be used in electronic devices  10  of  FIGS. 1, 2, 3, and 4  is shown in  FIG. 7 . As shown in  FIG. 7 , distributed loop antenna structures  102  (sometimes referred to as distributed loop antenna  102 ) may include a first loop antenna resonating element L 1  that is formed from a loop of conductor such as conductor  114  and a second loop antenna resonating element L 2  (a distributed loop element) that is formed from a loop of conductor such as conductor  116 . 
     As shown in  FIG. 7 , loop antenna resonating element L 2  may be indirectly fed using loop-shaped antenna resonating element L 1 , which serves as an indirect antenna feeding structure. As illustrated by electromagnetic fields  118  of  FIG. 7 , antenna element (feed structure) L 1  and loop-shaped antenna resonating element L 2  may be coupled using near-field electromagnetic coupling. 
     Antenna structures  102  of  FIG. 7  may be coupled to radio-frequency transceiver circuitry  100  ( FIG. 6 ) using transmission line  104 . For example, positive transmission line conductor  106  may be coupled to positive antenna feed terminal  110  and ground transmission line conductor  108  may be coupled to ground antenna feed terminal  112 . 
     In the illustrative configuration of  FIG. 7  in which the conductive lines of transmission line  104  are coupled to the feed terminals  110  and  112  of antenna element L 1 , antenna resonating element L 2  may be indirectly fed. If desired, antenna resonating element L 2  may be directly fed by coupling transmission line  104  across pairs of terminals in element L 2 . Indirect feeding arrangements for loop antenna structures  102  may sometimes be described herein as an example. This is, however, merely illustrative. In general, any suitable feeding arrangement may be used for feeding antenna  102  if desired. 
     Loop antenna structures  102  may be formed using conductive antenna resonating element structures such as metal traces on a dielectric carrier. The dielectric carrier may be formed from glass, ceramic, plastic, or other dielectric material. As an example, the dielectric carrier may be formed from a plastic support structure. The plastic support structure may, if desired, be formed from a speaker box enclosure that serves as a resonant cavity for a speaker driver. 
     The conductive structures that form loop antenna structures  102  may include wires, metal foil, conductive traces on printed circuit boards, portions of conductive housing structures such as conductive housing walls and conductive internal frame structures, and other conductive structures. 
     As shown in  FIG. 7 , antenna resonating element L 2  may have a longitudinal axis such as axis  120 . Axis  120  may sometimes be referred to as the longitudinal axis of loop distributed loop antenna structures  102 . Loop antenna structures  102  may have resonating element conductive structures that are spread out (“distributed”) along longitudinal axis  120  of loop L 2 . 
     Conductive structures  116  in resonating element loop L 2  of antenna structures  102  may include a strip or sheet of conductor that has a first dimension that is wrapped around longitudinal axis  120  and a second dimension (i.e., a width W) that extends along the length of longitudinal axis  120 . Conductive structures  116  may wrap around axis  120 . During operation, antenna currents can flow within the strip-shaped conductive material of loop L 2  around axis  120 . In effect, conductive material  116  will form a wide strip of conductor in the shape of a loop that is characterized by a perimeter P. The antenna currents flowing in loop L 2  tend to wrap around longitudinal axis  120 . When installed within device  10 , longitudinal axis  120  of antenna element L 2  may extend parallel to an adjacent edge of housing  12  in electronic device  10  (as an example). 
     It may be desirable to form distributed loop antenna structures  102  from conductive structures that exhibit a relatively small dimension P. In a loop without any break along periphery P, the antenna may resonate at signal frequencies where the signal has a wavelength approximately equal to P. In compact structures with unbroken loop shapes, the frequency of the communications band covered by antenna loop L 2  may therefore tend to be high. By incorporating a gap or other capacitance-generating structure into the loop, a capacitance C can be introduced into antenna loop L 2 . Conductive material  116  may also be configured to form one or more inductor-like paths to introduce inductance L into antenna loop L 2 . Material  116  may, for example, be configured to produce segments of conductive material  116  within loop L 2  that serve as inductance-producing wires. With the presence of capacitance C and inductance L within the perimeter of loop antenna element L 2 , the resonant frequency of antenna element L 2  may be reduced to a desired frequency of operation without enlarging the value of perimeter P. 
       FIG. 8  is a graph in which antenna performance (standing wave ratio) for antenna structures such as antenna structures  102  of  FIG. 7  has been plotted as a function of operating frequency. In the example of  FIG. 8 , antenna structures  102  have been configured to resonate in a lower frequency band LB and a higher frequency band HB. Communications bands LB and HB may be cellular telephone bands, satellite navigation system bands, local area network bands, and/or other suitable communications bands. As an example, low band LB may be associated with a 2.4 GHz wireless local area network band and high band HB may be associated with a 5 GHz wireless local area network band (as an example). 
     Dashed curve  122  of  FIG. 8  corresponds to the contribution of loop antenna resonating element L 1  to the performance of antenna structures  102 . Dashed-and-dotted curve  124  corresponds to the contribution of loop antenna resonating element L 2  to the performance of antenna structures  102 . 
     During operation, both elements L 1  and L 2  contribute to the overall performance of antenna structures  102  represented by curve  126 . At lower frequencies such as frequencies in low band LB, antenna resonating element L 2  serves at the primary radiating element in structures  102  and antenna resonating element L 1  serves as a secondary radiating element in structures  102 . At higher frequencies such as frequencies in high band HB, antenna resonating element L 1  serves as the primary radiating element in antenna structures  102  and antenna resonating element L 2  serves as a secondary radiating element. 
     A dielectric carrier for antenna structures  102  may be formed from plastic. As an example, a hollow plastic structure may be used to serve as a carrier for antenna structures  102 . If desired, a hollow plastic antenna carrier structure may be used to form a speaker enclosure (sometimes referred to as a speaker box). A speaker driver may be mounted within the speaker box to produce sound. 
       FIG. 9  is a diagram of an illustrative speaker driver. As shown in  FIG. 9 , speaker driver  128  may have a speaker driver housing such as housing  130 . Housing  130  may be formed from plastic, metal, or other suitable materials. An opening such as speaker driver port  132  may be formed in housing  130  to allow sound to exit driver  128 . 
     Speaker driver  128  may have electrical terminals such as terminals  134  and  136 . Wires such as wires  138  and  140  may be coupled to terminals  134  and  136 . For example, wire  138  may be used to couple one of the outputs of audio amplifier  142  to terminal  134  and wire  140  may be used to couple another of the outputs of audio amplifier  142  to terminal  136 . During operation, audio amplifier  142  may receive audio signals via input  144  (e.g., from control circuitry  29 ) and may drive corresponding analog audio signals onto lines  138  and  140 . Speaker driver  128  may respond by creating sound that exits driver  128  through port  132 . 
     It may be desirable to insulate conductive portions of speaker driver  128  to help ensure that antenna currents do not flow through speaker driver  128 . If speaker driver  128  is not insulated, there is a potential for speaker driver  128  to couple to antenna structures  102 , which could adversely affect antenna performance. 
     As shown in the cross-sectional side view of  FIG. 10 , speaker driver  128  may have a coating such as coating  146  on housing  130 . Housing  130  or parts of housing  130  may be formed from a conductive material such as metal. Coating  146  may be formed from plastic or other insulating material. As shown in  FIG. 10 , coating  146  may cover potentially conductive portions of speaker driver  128  such as housing  130  and terminals  134  and  136 , thereby helping to ensure that speaker driver  128  is electrically isolated from surrounding structures. Insulating coating  146  may be used to help allow speaker driver  128  to electrically float with respect to ground (and antenna structures  102 ) and thereby minimize coupling with antenna structures  102 . 
       FIG. 11  is a top view of an illustrative dielectric carrier of the type that may serve as both an antenna carrier for the conductive structures of antenna structures  102  and as a speaker enclosure for speaker driver  128 . As shown in  FIG. 11 , dielectric carrier  150  may have an elongated shape that extends along longitudinal axis  120 . Conductive structures for antenna structures  102  may be formed in regions  154  and  152 . For example, conductive structures  116  associated with antenna resonating element loop L 2  may be formed in region  152  and conductive structures  114  associated with antenna resonating element loop L 1  may be formed in region  154 . Dielectric carrier  150  may have a hollow interior that serves as an acoustic cavity for a speaker. Speaker driver  128  may be mounted within the hollow interior of carrier  150  under loop element L 1 . The distributed loop design of  FIG. 11  may help ensure that electric field strength is minimized in the vicinity of speaker driver  128  during operation of antenna structures  102 , thereby minimizing electrical coupling between antenna structures  102  and speaker driver  128 . 
       FIG. 12  is a perspective view of antenna structures  102  showing how conductive structures for antenna structures  102  may be formed on and around a speaker enclosure or other dielectric carrier  150 . As shown in  FIG. 12 , antenna resonating element loop L 1  may be formed from metal traces  114  on the upper surface of speaker enclosure  150  (or other dielectric carrier). Antenna resonating element loop L 2  may be formed from a strip of metal traces  116  of width W on the surfaces of speaker enclosure  150 . During operation, antenna currents may flow in loop L 2  such as currents  164  and  166 . 
     If desired, antenna resonating element loop traces  114  may be mounted in a ground cavity (i.e., loop L 1  may be mounted in a cavity-backed antenna environment). For example, metal traces may be formed on the sidewalls of carrier  150  to the front, rear, side, and beneath traces  114  (see, e.g., cavity sidewalls  115  of  FIG. 12 ). By placing traces  114  within antenna cavity  115 , loop antenna resonating element can be decoupled from surrounding metal structures in device  10  (i.e., the performance of loop antenna L 1  will not be affected by variations in the distance between carrier  150  and nearby conductive structures due to the isolation afforded by antenna cavity  115 ). 
     A gap may be formed between opposing edges  160  and  162  of traces  116  on the upper surface of enclosure  150 . The layout of this gap may be configured to produce a desired value for capacitance C ( FIG. 7 ). If, for example, a large value of C is desired, edges  160  and  162  may be placed closer together and/or the paths that edges  160  and  162  follow may be implemented using a meandering pattern that maximizes the lengths of edges  160  and  162 . 
     Traces  116  may form a strip of material of width W that wraps around axis  120  on the surface of enclosure  150 . Inductance L may be produced by forming openings  168  in a portion of traces  116  such as portion  116 E. Openings  168  may have the shapes of slots or other openings that run parallel to each other, giving rise to narrow metal line segments such as segments  172  through which antenna currents  166  pass. Segments  172  may be relatively long and thin and may therefore serve as inductive elements. Segments  172  may collectively produce inductance L in loop L 2 . 
     Enclosure  150  may contain speaker driver  128 . To ensure that sound can escape from enclosure  150  when playing audio with speaker driver  128 , enclosure  150  may be provided with openings such as speaker enclosure openings  170 . Openings  170  may be formed in the shape of circular holes, oval holes, rectangular slots, or openings of other shapes. Enclosure  150  may have walls with a thickness of 0.2 to 2 mm (as an example). Rectangular slot openings  170  may have lengths of 3-4 mm or 1-8 mm and widths of 0.2 to 1 mm (as examples). Segments  172  may have lengths of 3-4 mm or 1-8 mm and widths of 0.2 to 1 mm (as examples). As shown in  FIG. 12 , enclosure openings  170  and metal trace openings  168  may overlap each other (e.g., openings  168  may be aligned with openings  170  and may be sufficiently large to ensure that portions of metal traces  116  do not block enclosure openings  170 ). This allows sound to exit the hollow interior of enclosure  150  when speaker driver  128  is in use. 
       FIG. 13  is a cross-sectional side view of a portion of electronic device  10  showing how antenna structures  102  may be mounted along an edge of housing  12 . As shown in  FIG. 13 , electronic device  10  may have a display such as display  14  that has an associated display module  176  and display cover layer  174 . Display module  176  may be a liquid crystal display module, an organic light-emitting diode display, or other suitable display for producing images for a user. Display cover layer  174  may be a clear sheet of glass, a transparent layer of plastic, or other transparent member. If desired, display cover layer  174  may form a portion of display module  176 . 
     In inactive display border region IA, the inner surface of display cover layer  174  may be coated with a layer of black ink or other opaque masking layer  178  to hide internal device structures from view by a user. Antenna structures  102  may be mounted within housing  12  under opaque masking layer  178 . During operation, antenna signals may be transmitted and received through portion  182  of display cover layer  174  and, if desired, through dielectric portions of housing  12 . 
     Housing  12  in the configuration of  FIG. 13  has been formed from metal. Openings  180  in housing  12  may serve as speaker openings. Openings  170  in speaker enclosure  150  and openings  168  in loop antenna traces  116  may be aligned with housing openings  180 . During operation of speaker driver  128 , sound may escape from the interior of speaker enclosure  150  through openings  170 ,  168 , and  180 . 
       FIG. 14  is a perspective view of an exterior portion of device  10  in the vicinity of speaker openings  180 . Speaker openings  180  may be organized in an array having rows and columns (as an example). Each column of speaker openings  180  in device  10  of  FIG. 14  may be aligned with a respective one of the slot-shaped trace openings  168  and enclosure openings  170  of  FIG. 12 . 
     If desired, housing speaker openings  180  may have other shapes. As shown in  FIG. 15 , for example, speaker openings  180  may have rectangular slot shapes. 
       FIG. 16  is a cross-sectional side view of device  10  showing how antenna structures  102  may have a non-rectangular cross-sectional shape. Antenna structures  102  may be formed, for example, from traces  116  on a speaker enclosure or other dielectric carrier  150  that has a curved wall. Curved wall  182  of speaker enclosure  150  may have a shape that matches the curved shape of wall portion  184  of electronic device housing  12 . 
     Conductive structures such as conductive structures  186  may be used to electrically couple traces  116  to metal housing  12 . When traces  116  are shorted to housing  12  in this way, a portion of the loop antenna currents in loop L 2  may pass through housing  12  in parallel with underlying antenna traces  116  or, if desired, some of traces  116  may be omitted so that all of the loop antenna currents in a portion of loop L 2  pass through housing  12  in parallel with enclosure  150 . Structures  186  may be formed from metal tape, metal paint, conductive adhesive, solder, welds, fasteners such as screws, or other conductive structures. 
       FIG. 17  is a cross-sectional side view of device  10  in a configuration in which dielectric carrier  150  (e.g., a speaker enclosure) in antenna structures  102  has been provided with a recess such as recess  188  to accommodate edge  190  of display structures  176 . If desired, antenna structures  102  may have other shapes to accommodate other electrical or mechanical components in interior portions of device  10 . 
     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.