PATENT DOCUMENT

Publication Number: US-8922443-B2
Application Number: US-201213629005-A
Country: US
Kind Code: B2

Title: Distributed loop antenna with multiple subloops

Abstract:
An electronic device may be provided with antenna structures. The antenna structures may be formed using a dielectric carrier structure. The antenna structures may have first and second loop antenna resonating elements. The first loop antenna resonating element may indirectly feed the second loop antenna resonating element. The second loop antenna resonating element may be a distributed loop element formed from multiple antenna resonating element subloops. The second loop antenna resonating element may be formed from a strip of metal with a width that loops around the dielectric carrier. An opening in the metal may separate first and second subloop antenna resonating elements from each other in the second loop antenna resonating element. Openings in the metal may form metal segments that collectively form an inductance for the first subloop. Antenna currents may flow through metal traces on the carrier and portions of an electronic device housing wall.

Claims:
What is claimed is: 
     
       1. An antenna, comprising:
 a dielectric carrier having a longitudinal axis; and 
 a loop antenna resonating element that extends around the longitudinal axis and surrounds at least part of the dielectric carrier, wherein the loop antenna resonating element includes at least first and second parallel subloops, wherein the first subloop includes metal traces on the dielectric carrier, the metal traces are configured to form a plurality of parallel openings, metal segment structures are formed between the parallel openings, and the metal segment structures collectively produce an inductance in the first subloop. 
 
     
     
       2. The antenna defined in  claim 1  wherein the first subloop includes a first strip of conductive structures wrapped around the longitudinal axis and wherein the second subloop includes a second strip of conductive structures wrapped around the longitudinal axis. 
     
     
       3. The antenna defined in  claim 2  wherein the first strip of conductive structures includes the metal traces on the dielectric carrier. 
     
     
       4. The antenna defined in  claim 3  wherein the first strip of conductive structures includes a gap that produces a capacitance in the first subloop. 
     
     
       5. The antenna defined in  claim 4  wherein at least part of the first strip of conductive structures is separated from at least part of the second strip of conductive structures by an opening in the loop antenna resonating element. 
     
     
       6. The antenna defined in  claim 1  wherein the dielectric carrier has a hollow interior and wherein the antenna further comprises a speaker driver in the hollow interior. 
     
     
       7. The antenna defined in  claim 1  wherein the dielectric carrier has a recess configured to receive a portion of a display module. 
     
     
       8. The antenna defined in  claim 1  wherein the dielectric carrier has a curved portion without antenna traces that is configured to run parallel to a curved portion of a metal electronic device housing wall that forms at least part of the loop antenna resonating element. 
     
     
       9. An antenna, comprising:
 a dielectric carrier having a longitudinal axis; and 
 a loop antenna resonating element that extends around the longitudinal axis and surrounds at least part of the dielectric carrier, wherein the loop antenna resonating element includes at least first and second parallel subloops, wherein the antenna loop resonating element comprises metal traces on the dielectric carrier and wherein an opening in the metal traces separates at least part of the first subloop from at least part of the second subloop. 
 
     
     
       10. The antenna defined in  claim 9  further comprising an indirect feeding loop antenna element formed from metal on the dielectric carrier. 
     
     
       11. The antenna defined in  claim 10  wherein the indirect feeding loop antenna element has positive and ground antenna feed terminals and wherein at least the first subloop includes a gap that produces a capacitance for the first subloop. 
     
     
       12. The antenna defined in  claim 11  wherein the first subloop includes a plurality of parallel metal segments that collectively provide the first subloop with an inductance. 
     
     
       13. A distributed loop antenna, comprising:
 an antenna feed; and 
 an antenna resonating element formed from first and second antenna resonating element loops that run parallel to each other around an axis, wherein the antenna resonating element includes metal traces on a dielectric carrier and includes portions of a metal electronic device housing wall. 
 
     
     
       14. The antenna defined in  claim 13  further comprising a screw for attaching the metal traces to the metal electronic device housing wall. 
     
     
       15. The distributed loop antenna defined in  claim 13  wherein the first antenna resonating element loop includes a capacitance and an inductance. 
     
     
       16. The distributed loop antenna defined in  claim 15  wherein the second antenna resonating element loop includes a capacitance. 
     
     
       17. The distributed loop antenna defined in  claim 15  further comprising an elongated dielectric carrier that extends along the axis, wherein the first antenna resonating element loop includes metal traces on the elongated dielectric carrier that extend in a strip around the axis. 
     
     
       18. The distributed loop antenna defined in  claim 13  wherein the first antenna resonating element loop is characterized by an antenna resonance at a first operating frequency and wherein the second antenna resonating element loop is characterized by an antenna resonance at a second operating frequency that is different than the first operating frequency. 
     
     
       19. Apparatus, comprising:
 an electronic device housing having an edge; 
 an elongated dielectric carrier that extends along a longitudinal axis parallel to the edge; and 
 metal structures on the elongated dielectric carrier that form a distributed loop antenna having a loop antenna resonating element that has a width and that extends around the longitudinal axis, wherein the loop antenna resonating element includes first and second parallel subloops, wherein the metal structures include metal traces on the dielectric carrier and wherein the metal traces include a slot that separates at least part of the first subloop from at least part of the second subloop. 
 
     
     
       20. The apparatus defined in  claim 19  wherein the metal structures includes parallel elongated openings that form segments of metal that collectively produce an inductance for the first subloop. 
     
     
       21. The apparatus defined in  claim 20  wherein the first subloop includes a capacitance formed from a gap in the metal traces.

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. The dielectric carrier may have an elongated shape that extends along a longitudinal axis. The longitudinal axis of the dielectric carrier may run parallel to an edge of the electronic device. 
     The antenna structures may have first and second loop antenna resonating elements. The first loop antenna resonating element may indirectly feed the second loop antenna resonating element. The second loop antenna resonating element may be a distributed loop element formed from multiple antenna resonating element subloops. 
     The antenna resonating element subloops may include a first antenna resonating element subloop that extends around the longitudinal axis and that surrounds at least some of the dielectric carrier structure and may include a second antenna resonating element subloop that extends around the longitudinal axis in parallel with the first subloop and that surrounds at least some of the dielectric carrier structure. 
     The second loop antenna resonating element may be formed from a strip of metal with a width that loops around the dielectric carrier. An opening in the metal may separate the first and second subloop antenna resonating elements from each other by helping to divide antenna currents between the first and second subloops. Openings in the metal may form metal segments that collectively form an inductance for the first subloop. Inductances formed from parallel metal segments may also be formed in other subloops. Antenna currents may flow through metal traces on the carrier and portions of an electronic device housing wall. 
     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 diagram of an illustrative loop antenna having multiple parallel subloops in accordance with an embodiment of the present invention. 
         FIG. 10  is a graph of antenna performance as a function of operating frequency for an illustrative antenna of the type shown in  FIG. 9  in accordance with an embodiment of the present invention. 
         FIG. 11  is a perspective view of an illustrative distributed loop antenna formed using conductive traces on a dielectric antenna carrier in accordance with an embodiment of the present invention. 
         FIG. 12  is a diagram showing where a loop in a distributed loop antenna may be provided with current dividing structures to form multiple subloops 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. 
     
    
    
     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 hollow 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  and/or the longitudinal axis of a dielectric carrier used to support conductive loop structures. 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. 
     To broaden the bandwidth of antenna structures, it may be desirable to form antenna resonating element L 2  from multiple loop elements (i.e., loop L 2  may be formed form multiple parallel subloops). In general, loop L 2  may be formed form one antenna loop resonating element, two antenna loop resonating elements, three antenna loop resonating elements, or four antenna loop resonating elements. Illustrative configurations in which antenna structures  102  are formed from two parallel subloops may sometimes be described as an example. 
     As shown in  FIG. 9 , antenna structures  102  may have a loop antenna resonating element L 2  that is formed from subloops such as loop antenna resonating element L 2 A and loop antenna resonating element L 2 B. Subloops L 2 A and L 2 B may both be electromagnetically coupled to feed loop L 1 . 
     Loop L 2 A may include structures such as conductive structures  116 A that form capacitance C 1  and inductance LA. Loop L 2 B may include structures such as conductive structures  116 B that form capacitance C 2  and inductance LB. Capacitances C 1  and C 2  may be formed using discrete capacitors and/or using conductive antenna loop resonating element conductive structures to form gaps that give rise to capacitances C 1  and C 2 . Inductances LA and LB may be formed using discrete inductors and/or using conductive antenna loop resonating element conductive structures to form current paths that give rise to inductances LA and LB. If desired, each subloop in loop L 2  may include multiple capacitances and/or multiple inductances. The configuration of  FIG. 9  in which each loop includes a capacitance and an inductance is merely illustrative. 
     Loops L 2 A and L 2 B may both extend around longitudinal axis  120 . For example, the conductive materials of loop L 2 A may extend around axis  120  so that loop L 2 A surrounds at least part of a dielectric carrier, whereas the conductive materials of loop L 2 B may likewise extend around axis  120 , running parallel with loop L 2 A and surrounding at least part of the dielectric carrier. 
     By forming loop L 2  from multiple parallel subloops such as loops L 2 A and L 2 B, the performance of antenna structures  102  may be enhanced. For example, the bandwidth of antenna structures  102  in one or more communications bands can be increased.  FIG. 10  is a graph in which antenna performance (standing-wave ratio) has been plotted for antenna structures  102  of  FIG. 9  in a communications band of interest (e.g., low band LB of  FIG. 8 ). As described in connection with  FIG. 8 , antenna structures  102  may also resonate in other bands (e.g., high band HB). 
     As shown in  FIG. 10 , each subloop in loop L 2  may contribute to a resonance at a potentially different frequency. For example, antenna resonating element loop L 2 A may be configured to exhibit a resonance at frequency f 1 , as illustrated by curve  128  in  FIG. 10 , whereas antenna resonating element loop L 2  may be configured to exhibit a resonance at frequency f 2 , as illustrated by curve  130  in  FIG. 10 . By selecting locations of frequencies f 1  and f 2  so that the resonances at F 1  and f 2  overlap, the overall response curve for antenna structures  102  may be broadened, as illustrated by total response curve  132  of  FIG. 10 . In particular, loop L 2 A operating alone might exhibit a bandwidth of BW 1  and loop L 2 B operating alone might exhibit a bandwidth of BW 2 . By configuring loops L 2 A and L 2 B so that frequencies f 1  and f 2  are adjacent but not equal, response curves  128  and  130  will overlap so that the resulting bandwidth BW 3  of antenna structures  102  in low band LB is greater than BW 1  and BW 2 . By using two or more subloops with different respective resonant frequencies in this way, the overall bandwidth of antenna structures  102  due to the contribution of antenna loop resonating element L 2  may be enhanced. 
       FIG. 11  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. 11 , antenna resonating element loop L 1  may be formed from metal traces  114  on the upper surface of carrier  150 . 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 ). 
     Antenna resonating element loop L 2  may be formed from antenna resonating element loops such as parallel subloops L 2 A and L 2 B. Conductive structures such as metal traces on the surface of carrier  150  may extend around axis  120  to form loop L 2 . The metal of loop L 2  may form a strip of width W. 
     An opening such as opening  138  may be formed in the metal of loop L 2 . For example, in a configuration in which the metal of loop L 2  is formed from metal traces on the surface of carrier  150 , a slot-shaped opening or other opening such as opening  138  may be formed by patterning the metal traces. The presence of opening  138  may at least partly divide the currents that flow in loop L 2  into two parallel paths. Currents  136 A may flow around axis  120  in conductive structures such as metal traces  116 A, whereas currents  136 B may tend to flow around axis  120  in in conductive structures such as metal traces  116 B. Metal traces  116 A may have the shape of a metal strip of width W 1  that forms loop L 2 A. Metal traces  116 B may have the shape of a metal strip of width W 2  that forms loop L 2 B. If desired, other types of current dividing structures may be used (e.g., openings with shapes other than the rectangular slot shape of opening  138 , openings with meandering paths, openings with curved edges, openings with combinations of curved and straight edges, multiple openings that are aligned in a line such as a series of slots or circular openings), etc. The shape of opening  138  that is shown in  FIG. 11  is merely illustrative. 
     Metal traces  116 A may be patterned to form capacitance C 1  and inductance LA of  FIG. 9 . Metal traces  116 B may be patterned to form capacitance C 2  and inductance LB of  FIG. 9 . Capacitances such as capacitances C 1  and C 2  may be formed by creating gaps in the metal traces of loop L 2 . For example, a gap such as gap G 1  may be formed between opposing edges  170  and  172  of traces  116 A and a gap such as gap G 2  may be formed between opposing edges  174  and  176  of traces  116 B. Gap G 1  may be characterized by capacitance C 1 . Gap G 2  may be characterized by a capacitance C 2 . The values of C 1  and C 2  may be the same or may be different. 
     The layout of gaps such as gaps G 1  and G 2  may be configured to produce desired values for capacitances C 1  and C 2 . If, for example, a large value of capacitance is desired in an antenna loop element, the edges of the gap in the loop element (e.g., edges  170  and  172  in loop L 2 A or edges  174  and  176  in loop L 2 B) may be placed closer together and/or the paths that the gap edges follow may be implemented using a meandering pattern that maximizes the lengths of the edges. If desired, one or both of gaps G 1  and G 2  and corresponding capacitances C 1  and C 2  may be omitted. 
     The conductive material of traces  116 A and  116 B may be configured to produce inductances such as inductances L 1  and L 2  of  FIG. 9 . For example, traces  116 A may be provided with openings such as openings  142 . As shown in  FIG. 11 , openings  142  may be slots or other openings of other elongated shapes that run parallel to each other. The shapes of openings  142  form metal segment structures between respective openings  142 . In particular, the presence of openings  142  may give rise to narrow metal line segments such as segments  144  through which antenna currents  136 A pass, as illustrated by current  146 . 
     Segments  146  may be relatively long and thin and may therefore serve as inductive elements. Segments  146  may collectively produce inductance LA in loop L 2 A. Traces  116 B may be provided with one or more openings such as openings  142  so as to increase the value of inductance LB in loop L 2 B or may, as shown in the example of  FIG. 11 , be provided with no openings so that portion  180  of traces  116 B may form a single solid strip of metal characterized by a low or negligible value of inductance. In general, LA may be present and LB may be omitted, LB may be present and LA may be omitted, both LA and LB may be present using respective sets of parallel metal segments, or both LA and LB may be omitted. 
     Openings  142  in traces  116 A of loop L 2 A may, if desired, overlap corresponding openings in carrier  150  (e.g., when carrier  150  is a hollow structure that is serving as a speaker box and when openings in carrier  150  are used to allow sound to exit the interior of the speaker box). Openings  142  may be formed on face  148  of carrier  150  or on other suitable carrier surfaces. Capacitor gaps G 1  and G 2  and current dividing openings such as opening  138  may be formed on upper surface  140  of carrier  150  (e.g., in a location that lies under a display cover glass or other dielectric rather than immediately under metal structures that could interfere with gaps G 1  and G 2  and opening  138 ) or may be formed on other carrier surfaces. 
       FIG. 12  is a schematic diagram of an antenna loop resonating element such as loop L 2  showing how antenna loop resonating element L 2  may be mounted in device  10  under dielectric layer  184 . Dielectric layer  184  may be a display cover layer such as a layer of glass or plastic covering the face of display  14 . The portion of layer  184  under which antenna loop resonating element L 2  is mounted may correspond to an inactive region of display  14 . 
     To provide adequate current separation between traces  116 A and  116 B and thereby effectively form loop antenna resonating elements L 2 A and L 2 B with distinct resonances as described in connection with  FIG. 10  while ensuring that the current separator structures in loop L 2  are not covered with metal structures that might interfere with their operation, it may be desirable to form current separator structures such as opening  138  in region  182  between capacitor C (i.e., C 1  and C 2 ) and inductance L (i.e., inductances L 1  and L 2 ) under dielectric layer  184 . 
     If desired, loop L 2  may be provided with one or more discrete components (e.g., capacitors or inductors packaged in surface mount technology packages, etc.). These components may be combined with switches or other circuits to form tunable components. Optional components  186  in loop L 2  of  FIG. 12  are interposed in loop L 2  in illustrative locations where circuitry such as tunable circuitry, fixed circuitry, discrete inductors, discrete capacitors, and/or switches or other electronic devices may optionally be used. 
       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  198  and display cover layer  184 . Display module  198  may be a liquid crystal display module, an organic light-emitting diode display, or other display for producing images for a user. Display cover layer  184  may be a clear sheet of glass, a transparent layer of plastic, or other transparent member. If desired, display cover layer  184  may form a portion of display module  198 . 
     In active area AA, an array of display pixels associated with display structures such as display module  198  may present images to a user of device  10 . In inactive display border region IA, the inner surface of display cover layer  184  may be coated with a layer of black ink or other opaque masking layer  190  to hide internal device structures from view by a user. Antenna structures  102  may be mounted within housing  12  under opaque masking layer  190 . During operation, antenna signals may be transmitted and received through portion  206  of display cover layer  184  and, if desired, through dielectric portions of housing  12 . 
     Housing  12  in the configuration of  FIG. 13  has been formed from metal. Openings  194  in housing  12  may serve as speaker openings. Dielectric carrier  150  may be hollow and may contain components such as speaker driver  192 . In this type of configuration, dielectric carrier  150  may serve as a speaker enclosure (speaker box) for speaker driver  192 . Openings  196  in speaker enclosure  150  and openings  142  ( FIG. 11 ) in loop antenna traces  116  (e.g., traces  116 A) may be aligned with housing openings  194 . During operation of speaker driver  192 , sound may escape from the interior of speaker enclosure  150  through in enclosure  150 , openings  142  in traces  116 A, and openings  194  in housing wall  12 . If desired, carrier  150  may be solid or may be a hollow structure that does not include a speaker driver. 
     As illustrated by curved portion  208  of carrier  150 , antenna structures  102  may have a non-rectangular cross-sectional shape. Curved surface portion  208  may, for example, have a shape that matches the curved inner surface of housing wall  12 . 
     The conductive structures that form antenna structures  102  such as the metal that forms loops L 1  and L 2  may be formed from conductive traces that are formed on the surface of carrier  150  and/or other conductive structures in device  10 . As shown in  FIG. 13 , antenna currents  204  may, if desired, flow through conductive housing wall  12  in the portion of housing  12  that overlaps curved surface  208  of dielectric carrier  150 . Other portions of dielectric carrier  150  may be covered with metal traces  116  (e.g., traces  116 A and  116 B of  FIG. 11 ). Traces  114  of loop L 1  ( FIG. 11 ) may also be formed on carrier  150 . 
     Conductive structures such as conductive structures  202  and  200  may be used to electrically couple traces  116  to metal housing  12  at either end of curved portion  208 . When traces  116  are shorted to housing  12  in this way, loop antenna currents in loop L 2  will pass through traces  116  on portions of carrier  150  other than curved surface  108  and will pass through housing  12  (as shown by currents  204 ) in the portions of housing  12  adjacent to curved surface  208  (i.e., the portion of housing  12  between conductive structure  200  and conductive structure  202 ). In the vicinity of curved surface  208  of carrier  150 , the loop antenna currents in loop L 2  will therefore pass through curved portions of housing  12  rather than through underlying antenna traces on carrier  150 . Because housing  12  effectively forms part of antenna loop L 2  in the vicinity of surface  208  in this type of configuration for antenna structures  102 , conductive traces  116  can be omitted from surface  208  in the vicinity of surface  208  (i.e., surface  208  of carrier  150  may be free of metal traces). 
     Conductive structure  200  and  202  may include screws or other fasteners, welds, solder joints, conductive adhesive, connectors, conductive paint such as silver paint or other metal paint, other conductive structures, or combinations of these structures. As an example, structures  200  may include one or more screws and structures  202  may include metal tape. 
     As shown in  FIG. 13 , carrier  150  may be provided with a recess such as recess  210  to accommodate end portion  212  of display module  198 . If desired, antenna structures  102  may have other shapes to accommodate other electrical or mechanical components in interior portions of device  10 . 
     Gaps such as gap G of  FIG. 13  (e.g., gaps G 1  and/or G 2  of  FIG. 11 ) may be formed on the upper surface of carrier  150 . During operation, antenna signals may tend to be concentrated around the upper surface of carrier  150 . Because fewer signals are associated with other portions of carrier  150 , relatively small gaps may be used so separate traces  116  on other portions of carrier  150  from surrounding conductive structures. For example, a gap D of about 0.5 mm to 1.5 mm or less may be used to separate metal trace portion  116 ′ from display module portion  212  of display module  198 . Insulating (dielectric) material such as material  216  may be used to help electrically isolate antenna traces  116  from display module  198 . Material  216  may be, for example, insulating foam that is attached to traces  116  and/or display module  198  using adhesive. 
     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: 20120927
Publication Date: 20141230
Grant Date: 20141230
Priority Date: 20120927
Inventors: ZHU JIANG
LI QINGXIANG
SCHLUB ROBERT W.
CABALLERO RUBEN
Assignee: APPLE INC
CPC Classifications: [{"code": "H01Q7/00", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01Q1/243", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q5/378", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q7/00", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01Q5/378", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q1/243", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 50338324