PATENT DOCUMENT

Publication Number: US-9093752-B2
Application Number: US-201313790549-A
Country: US
Kind Code: B2

Title: Electronic device with capacitively loaded antenna

Abstract:
An electronic device may have an antenna for providing coverage in wireless communications bands of interest such as a low frequency communications band, a middle frequency communications band, and a high frequency communications band. Slot structures in the antenna that might reduce efficiency in the high frequency communications band may be avoided by capacitively loading the antenna and omitting meandering paths in the antenna. A capacitor may be coupled between an antenna ground formed from a metal housing structure and an antenna resonating element having a curved shape that conforms to the shape of the edge of the electronic device. The capacitor may have interdigitated fingers and may be adjustable to tune the antenna. The antenna may transmit and receive radio-frequency signals through a display cover layer in a display and a dielectric antenna window portion of the housing.

Claims:
What is claimed is: 
     
       1. An antenna, comprising:
 an inverted-F antenna resonating element; and 
 an antenna ground; 
 an antenna feed coupled between the inverted-F antenna resonating element and the antenna ground at one end of the inverted-F antenna resonating element; and 
 a capacitor that is coupled between the inverted-F antenna resonating element and the antenna ground at an opposing end of the inverted-F antenna resonating element, wherein the inverted-F antenna resonating element is formed from a metal trace without a meandering path, the capacitor comprises interdigitated metal fingers, and the interdigitated metal fingers include at least part of the metal trace. 
 
     
     
       2. The antenna defined in  claim 1  wherein the inverted-F antenna resonating element has a curved surface. 
     
     
       3. The antenna defined in  claim 1  wherein the capacitor comprises an adjustable capacitor. 
     
     
       4. The antenna defined in  claim 3  wherein the adjustable capacitor comprises a plurality of capacitors and corresponding switches, wherein the adjustable capacitor has a first terminal coupled to the metal trace and has a second terminal coupled to the antenna ground, and wherein the capacitors and switches are coupled between the first and second terminals. 
     
     
       5. The antenna defined in  claim 1  further comprising a short circuit path that is coupled between the antenna resonating element and the antenna ground at a location between the antenna feed and the capacitor. 
     
     
       6. An electronic device, comprising:
 a housing; 
 a display mounted in the housing, wherein the display has a display cover layer; 
 a dielectric portion of the housing; and 
 a capacitively loaded inverted-F antenna having an antenna resonating element, an antenna ground, and a capacitor coupled between the antenna resonating element and the antenna ground, wherein the capacitively loaded inverted-F antenna has a curved shape with a first region that faces the display cover layer and a second region that faces the dielectric portion of the housing, the antenna resonating element has a first edge adjacent to the first region and a second edge adjacent to the second region, the capacitor is coupled between the first edge and a portion of the housing that serves as the antenna ground, and the portion of the housing comprises a vertical metal wall that extends between opposing front and rear surfaces of the electronic device. 
 
     
     
       7. The electronic device defined in  claim 6  wherein the antenna resonating element has an inverted-F antenna resonating element arm formed without a meandering path. 
     
     
       8. The electronic device defined in  claim 7  wherein the capacitor comprises interdigitated fingers formed at least partly from the antenna resonating element. 
     
     
       9. The electronic device defined in  claim 7  wherein the capacitor comprises an adjustable capacitor configured to exhibit at least first and second capacitance values. 
     
     
       10. The electronic device defined in  claim 7  further comprising proximity sensor circuitry coupled to the inverted-F antenna resonating element arm. 
     
     
       11. An electronic device, comprising:
 a capacitively loaded inverted-F antenna having an inverted-F antenna resonating element, an antenna ground, and a capacitor coupled between the inverted-F antenna resonating element and the antenna ground; 
 a display module; 
 a display cover layer that covers the display module; 
 a metal housing that forms at least part of the antenna ground; and 
 a dielectric antenna window in the metal housing, wherein the capacitively loaded inverted-F antenna is mounted adjacent to the dielectric antenna window, the capacitively loaded inverted-F antenna has a curved shape with a first region that faces the display cover layer and a second region that faces the dielectric antenna window, the inverted-F antenna resonating element has a first edge adjacent to the first region and a second edge adjacent to the second region, and the capacitor is coupled between the second edge and a portion of the metal housing that serves as the antenna ground. 
 
     
     
       12. The electronic device defined in  claim 11  wherein the capacitor comprises an adjustable capacitor that is adjusted to tune the capacitively loaded inverted-F antenna. 
     
     
       13. The electronic device defined in  claim 12  wherein the display cover layer has an inactive area that is uncovered by the display module, the electronic device further comprising:
 a layer of opaque masking material in the inactive area, wherein the inverted-F antenna resonating element is mounted adjacent to the layer of opaque masking material; and 
 a screw that electrically couples the capacitor to the portion of the metal housing that serves as the antenna ground. 
 
     
     
       14. The electronic device defined in  claim 11 , wherein the display module is mounted on a front surface of the metal housing and the portion of the metal housing comprises a metal rear surface of the metal housing.

Description:
BACKGROUND 
     This relates generally to electronic devices, and, more particularly, to antennas in electronic devices. 
     Electronic devices such as portable computers and handheld electronic devices are often provided with wireless communications capabilities. For example, electronic devices may have wireless communications circuitry to communicate using cellular telephone bands and to support communications with satellite navigation systems and wireless local area networks. 
     It can be difficult to incorporate antennas and other electrical components successfully into an electronic device. Some electronic devices are manufactured with small form factors, so space for components is limited. In many electronic devices, the presence of conductive structures can influence the performance of electronic components, further restricting potential mounting arrangements for components such as antennas. 
     It would therefore be desirable to be able to provide improved electronic device antennas. 
     SUMMARY 
     An electronic device may have an antenna for providing coverage in wireless communications bands of interest such as a low frequency communications band, a middle frequency communications band, and a high frequency communications band. Slot structures in the antenna that might reduce efficiency in the high frequency communications band may be avoided while maintain a compact antenna size by capacitively loading the antenna and omitting meandering paths in the antenna. 
     A capacitor may be coupled between an antenna ground formed from a metal housing structure and an antenna resonating element having a curved shape that conforms to the shape of the edge of the electronic device. The capacitor may have interdigitated fingers that are formed from a metal trace that forms the antenna resonating element. The capacitor may be an adjustable capacitor that includes multiple fixed capacitors and switching circuitry for configuring which capacitors are switched into use. Adjustments to the adjustable capacitor may be used to tune the antenna. 
     The electronic device may have a housing. A display may be mounted on a front portion of the housing. A rear surface of the housing may have metal housing walls that form part of the antenna ground. The display may be covered by a display cover layer. An interior surface of an inactive portion of the display cover layer may be coated with an opaque masking material. The antenna may transmit and receive radio-frequency signals through the opaque masking material on the display cover layer and may transmit and receive radio-frequency signals through a dielectric portion of the housing such as a plastic antenna window in the metal housing walls. Portions of the antenna may be used to form capacitive proximity sensor electrode structures. 
     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 front perspective view of an illustrative electronic device of the type that may be provided with antenna structures in accordance with an embodiment of the present invention. 
         FIG. 2  is a rear perspective view of an illustrative electronic device such as the electronic device of  FIG. 1  in accordance with an embodiment of the present invention. 
         FIG. 3  is a cross-sectional side view of a portion of an electronic device having antenna structures in accordance with an embodiment of the present invention. 
         FIG. 4  is a diagram of illustrative antenna structures and other wireless circuitry in accordance with an embodiment of the present invention. 
         FIG. 5  is a perspective view of an antenna with a antenna resonating element having a meandering path that may be used in an electronic device in accordance with an embodiment of the present invention. 
         FIG. 6  is a perspective view of an antenna with a capacitively loaded antenna resonating element without a meandering path in accordance with an embodiment of the present invention. 
         FIG. 7  is a graph in which antenna performance (standing-wave ratio) for antennas of the types shown in  FIGS. 5 and 6  has been plotted as a function of operating frequency in accordance with an embodiment of the present invention. 
         FIG. 8  is a graph in which antenna efficiency has been plotted as a function of operating frequency for antennas of the types shown in  FIGS. 5 and 6  in accordance with an embodiment of the present invention. 
         FIG. 9  is a top view of an edge portion of a illustrative electronic device of the type that may be provided with multiple capacitively loaded inverted-F antennas in accordance with an embodiment of the present invention. 
         FIG. 10  is a circuit diagram of an illustrative tunable component based on multiple components such as capacitors and associated switches coupled in parallel between first and second terminals in accordance with an embodiment of the present invention. 
         FIG. 11  is a graph in which antenna performance (standing wave ratio) has been plotted as a function of frequency for three corresponding settings of a tunable component such as a tunable capacitor in a capacitively loaded inverted-F antenna in accordance with an embodiment of the present invention. 
         FIG. 12  is a diagram of a portion of a capacitively loaded inverted-F antenna having interdigitated capacitor fingers for forming a capacitor in accordance with an embodiment of the present invention. 
         FIG. 13  is a perspective view of an illustrative capacitively loaded inverted-F antenna resonating element formed in a curved shape in accordance with an embodiment of the present invention. 
         FIG. 14  is a cross-sectional side view of an illustrative electronic device with an antenna formed from a curved antenna resonating element of the type shown in  FIG. 13  in accordance with an embodiment of the present invention. 
         FIG. 15  is a perspective view of another illustrative capacitively loaded inverted-F antenna resonating element formed in a curved shape in accordance with an embodiment of the present invention. 
         FIG. 16  is a cross-sectional side view of an illustrative electronic device with an antenna formed from a curved antenna resonating element of the type shown in  FIG. 15  in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Electronic devices may be provided with antennas, and other electronic components. An illustrative electronic device in which electronic components such as antenna structures may be used is shown in  FIG. 1 . As shown in  FIG. 1 , device  10  may have a display such as display  50 . Display  50  may be mounted on a front (top) surface of device  10  or may be mounted elsewhere in device  10 . Device  10  may have a housing such as housing  12 . Housing  12  may have curved, angled, or vertical sidewall portions that form the edges of device  10  and a relatively planar portion that forms the rear surface of device  10  (as an example). Housing  12  may also have other shapes, if desired. 
     Housing  12  may be formed from conductive materials such as metal (e.g., aluminum, stainless steel, etc.), carbon-fiber composite material or other fiber-based composites, glass, ceramic, plastic, or other materials. A radio-frequency-transparent window such as window  58  may be formed in housing  12  (e.g., in a configuration in which the rest of housing  12  is formed from conductive structures). Window  58  may be formed from plastic, glass, ceramic, or other dielectric material. Antenna structures, and, if desired, proximity sensor structures for use in determining whether external objects are present in the vicinity of the antenna structures may be formed in the vicinity of window  58 . If desired, antenna structures and proximity sensor structures may be mounted behind a dielectric portion of housing  12  (e.g., in a configuration in which housing  12  is formed from plastic or other dielectric material). 
     Device  10  may have user input-output devices such as button  59 . Display  50  may be a touch screen display that is used in gathering user touch input. The surface of display  50  may be covered using a display cover layer such as a planar cover glass member or a clear layer of plastic. The central portion of display  50  (shown as region  56  in  FIG. 1 ) may be an active region that displays images and that is sensitive to touch input. Peripheral portions of display  50  such as region  54  may form an inactive region that is free from touch sensor electrodes and that does not display images. 
     An opaque masking layer such as opaque ink or plastic may be placed on the underside of display  50  in peripheral region  54  (e.g., on the underside of the display cover layer). This layer may be transparent to radio-frequency signals. The conductive touch sensor electrodes and display pixel structures and other conductive structures in region  56  tend to block radio-frequency signals. However, radio-frequency signals may pass through the display cover layer (e.g., through a cover glass layer) and opaque masking layer in inactive display region  54  (as an example). Radio-frequency signals may also pass through antenna window  58  or dielectric housing walls in a housing formed from dielectric material. Lower-frequency electromagnetic fields may also pass through window  58  or other dielectric housing structures, so capacitance measurements for a proximity sensor may be made through antenna window  58  or other dielectric housing structures, if desired. 
     With one suitable arrangement, housing  12  may be formed from a metal such as aluminum. Portions of housing  12  in the vicinity of antenna window  58  may be used as antenna ground. Antenna window  58  may be formed from a dielectric material such as polycarbonate (PC), acrylonitrile butadiene styrene (ABS), a PC/ABS blend, or other plastics (as examples). Window  58  may be attached to housing  12  using adhesive, fasteners, or other suitable attachment mechanisms. To ensure that device  10  has an attractive appearance, it may be desirable to form window  58  so that the exterior surfaces of window  58  conform to the edge profile exhibited by housing  12  in other portions of device  10 . For example, if housing  12  has straight edges  12 A and a flat bottom surface, window  58  may be formed with a right-angle bend and vertical sidewalls. If housing  12  has curved edges  12 A, window  58  may have a similarly curved exterior surface along the edge of device  10 . 
       FIG. 2  is a rear perspective view of device  10  of  FIG. 1  showing how device  10  may have a relatively planar rear surface  12 B and showing how antenna window  58  may be rectangular in shape with portions that match the shape of housing edges  12 A. Antenna window  58  may have curved walls, planar walls, or walls of other shapes, if desired. Display  50  may be mounted on the opposing front surface of housing  12  of device  10 . 
     A cross-sectional view of device  10  taken along line  1300  of  FIG. 2  and viewed in direction  1302  is shown in  FIG. 3 . As shown in  FIG. 3 , antenna structures  204  may be mounted within device  10  in the vicinity of antenna window  58 . Structures  204  may include conductive material that serves as an antenna resonating element for an antenna. The antenna may be fed using transmission line  212 . Transmission line  212  may have a positive signal conductor that is coupled to a positive antenna feed terminal (e.g., a feed terminal associated with a metal antenna resonating element trace on a dielectric support in structures  204 ) and a ground signal conductor that is coupled to a ground antenna feed terminal (i.e., antenna ground formed from conductive ground traces on a dielectric carrier in antenna structures  204  and/or grounded structures such as grounded portions of housing  12 ). 
     The antenna resonating element formed from structures  204  may be based on any suitable antenna resonating element design (e.g., structures  204  may form a patch antenna resonating element, a single arm inverted-F antenna structure, a dual-arm inverted-F antenna structure, other suitable multi-arm or single arm inverted-F antenna structures, a closed and/or open slot antenna structure, a loop antenna structure, a monopole, a dipole, a planar inverted-F antenna structure, a hybrid of any two or more of these designs, etc.). Configurations in which antenna structures  204  form a capacitively loaded inverted-F antenna are sometimes described herein as an example. 
     Housing  12  may serve as antenna ground for an antenna formed from structure  204  and/or other conductive structures within device  10  and antenna structures  204  may serve as ground (e.g., conductive components, traces on printed circuits, etc.). 
     Structures  204  may include patterned conductive structures such as patterned metal structures. The patterned conductive structures may, if desired, be supported by a dielectric carrier. The conductive structures may be formed from a coating, from metal traces on a flexible printed circuit, or from metal traces formed on a plastic carrier using laser-processing techniques or other patterning techniques. Structures  204  may also be formed from stamped metal foil or other metal structures. In configurations for antenna structures  204  that include a dielectric carrier, metal layers may be formed directly on the surface of the dielectric carrier and/or a flexible printed circuit that includes patterned metal traces may be attached to the surface of the dielectric carrier. If desired, conductive material in structures  204  may also form one or more proximity sensor capacitor electrodes. 
     During operation of the antenna formed from structures  204 , radio-frequency antenna signals can be conveyed through dielectric window  58 . Radio-frequency antenna signals associated with structures  204  may also be conveyed through a display cover member such as cover layer  60 . Display cover layer  60  may be formed from one or more clear layers of glass, plastic, or other materials. Display  50  may have an active region such as region  56  in which cover layer  60  has underlying conductive structure such as display module  64 . The structures in display module  64  such as touch sensor electrodes and active display pixel circuitry may be conductive and may therefore attenuate radio-frequency signals. In region  54 , however, display  50  may be inactive (i.e., module  64  may be absent). An opaque masking layer such as plastic or ink  62  may be formed on the underside of transparent cover glass  60  in region  54  to block antenna structures  204  from view by a user of device  10 . Opaque material  62  and the dielectric material of cover layer  60  in region  54  may be sufficiently transparent to radio-frequency signals that radio-frequency signals can be conveyed through these structures during operation of device  10 . 
     Device  10  may include one or more internal electrical components such as components  23 . Components  23  may include storage and processing circuitry such as microprocessors, digital signal processors, application specific integrated circuits, memory chips, and other control circuitry. Components  23  may be mounted on one or more substrates such as substrate  79  (e.g., rigid printed circuit boards such as boards formed from fiberglass-filled epoxy, flexible printed circuits, molded plastic substrates, etc.). Components  23  may include input-output circuitry such as sensor circuitry (e.g., capacitive proximity sensor circuitry), wireless circuitry such as radio-frequency transceiver circuitry (e.g., circuitry for cellular telephone communications, wireless local area network communications, satellite navigation system communications, near field communications, and other wireless communications), amplifier circuitry, and other circuits. Connectors such as connector  81  may be used in interconnecting circuitry  23  to communications paths such as transmission line path  212 . 
     Conductive structures for antenna structures  204  may be supported by a dielectric carrier. Antenna structures  204  may, for example, have conductive structures such as metal structures that are supported by a hollow plastic member or other dielectric carrier. The conductive structures may be metal traces that are formed on the surface of a dielectric carrier using laser-based deposition techniques, physical vapor deposition techniques, electrochemical deposition, blanket metal deposition followed by photolithographic patterning, ink-jet printing deposition techniques, etc. The conductive structures may also be metal traces that are formed on a rigid printed circuit board (e.g., a printed circuit board formed from a substrate such as fiberglass-filled epoxy), metal traces that are formed on a flexible printed circuit (e.g., a printed circuit formed from a layer of polyimide or a sheet of other polymer) that is mounted on a dielectric carrier (e.g., a carrier formed from molded plastic or other material), may be other metal structures supported by a carrier (e.g., patterned metal foil), or may be other conductive structures. 
     Dielectric carriers for supporting metal antenna traces or a flexible printed circuit or other structure that includes metal antenna traces may be formed from a dielectric material such as glass, ceramic, or plastic. As an example, a dielectric carrier for antenna(s) in device  10  may be formed from plastic parts that are molded and/or machined into a desired shape such as a rectangular prism shape (rectangular box shape), a three-dimensional solid shape with one or more curved surfaces (e.g., a box shape with a curved outer surface that matches a corresponding curved housing edge  12 A, or other shapes. In general, dielectric carrier shapes such as box or prism shapes with different numbers of sides and/or one or more curved surfaces or other three-dimensional carrier shapes may be used for antenna structures  204 . The illustrative configuration of  FIG. 3  in which antenna structures  204  have a rectangular cross-sectional shape is merely illustrative. 
     A schematic diagram of an illustrative configuration that may be used for electronic device  10  is shown in  FIG. 4 . As shown in  FIG. 4 , 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, for example, transmit and receive wireless data, tune antennas to cover communications bands of interest, and perform other functions related to the operation of device  10 . 
     Input-output devices  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 such as wired communications circuitry. Device  10  may also use wireless circuitry such as transceiver circuitry  206  and antenna structures  204  to communicate over one or more wireless communications bands. 
     Input-output devices  30  may also include input-output components with which a user can control the operation of device  10 . A user may, for example, supply commands through input-output devices  30  and may receive status information and other output from device  10  using the output resources of input-output devices  30 . 
     Input-output devices  30  may include proximity sensor circuitry  224  such as capacitive proximity sensor circuitry that uses portions of antenna structures  204  or other conductive structures in device  10  as capacitive proximity sensor electrodes. Proximity sensor circuitry  224  may be coupled to proximity sensor electrode structures in antenna structures  204  or elsewhere in device  10  using paths such as path  226 . A capacitive proximity sensor may, for example, be used to determine when a user&#39;s body or other external object is in the vicinity of antenna structures  204 . Proximity sensors for device  10  may also be formed using light-based proximity sensor structures, acoustic proximity sensor structures, etc. 
     Input-output devices  10  may also include sensors and status indicators such as an ambient light 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 in devices  30  may include speakers and tone generators for presenting sound to a user of device  10  and microphones for gathering user audio input. 
     Devices  30  may include one or more displays such as display  50  of  FIG. 1 . Displays may be used to present images for a user such as text, video, and still images. Sensors in devices  30  may include a touch sensor array that is formed as one of the layers in display  14 . During operation, user input may be gathered using buttons and other input-output components in devices  30  such as touch pad sensors, buttons, joysticks, click wheels, scrolling wheels, touch sensors such as a touch sensor array in a touch screen display or a touch pad, key pads, keyboards, vibrators, cameras, and other input-output components. 
     Wireless communications circuitry  34  may include radio-frequency (RF) transceiver circuitry such as transceiver circuitry  206  that is formed from one or more integrated circuits, power amplifier circuitry, low-noise input amplifiers, passive RF components, one or more antennas such as antenna structures  204 , 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 radio-frequency transceiver circuits for handling multiple radio-frequency communications bands. For example, circuitry  34  may include transceiver circuitry  206  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  206  may handle 2.4 GHz and 5 GHz bands for WiFi® (IEEE 802.11) communications or other wireless local area network communications and may handle the 2.4 GHz Bluetooth® communications band. Circuitry  206  may use 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). 
     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, 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 also include circuitry for handing near field communications. 
     Wireless communications circuitry  34  may include antenna structures  204 . Antenna structures  204  may include one or more antennas. Antenna structures  204  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 from an inverted-F antenna structure such as a capacitively loaded dual band inverted-F antenna are sometimes described herein as an example. 
     To provide antenna structures  204  with the ability to cover communications frequencies of interest, antenna structures  204  may be provided with one or more tunable components or other tunable circuitry. Discrete components such as capacitors, inductors, and resistors may be incorporated into the tunable circuitry. Capacitive structures, inductive structures, and resistive structures may also be formed from patterned metal structures (e.g., part of an antenna). 
     If desired, antenna structures  204  may be provided with adjustable circuits such as tunable circuitry  208  of  FIG. 4 . Tunable circuitry  208  may be controlled by control signals from control circuitry  29 . For example, control circuitry  29  may supply control signals to tunable circuitry  208  via control path  210  during operation of device  10  whenever it is desired to tune antenna structures  204  to cover a desired communications band. Path  222  may be used to convey data between control circuitry  29  and wireless communications circuitry  34  (e.g., when transmitting wireless data or when receiving and processing wireless data). 
     A fixed or adjustable component such as a capacitor (e.g., a fixed capacitor coupled to antenna structures  204  and/or a tunable capacitor in tunable circuitry  208 ) may be used to help antenna structures  204  exhibit antenna resonances in communications bands of interest with desired antenna efficiencies. 
     Transceiver circuitry  206  may be coupled to antenna structures  204  by signal paths such as signal path  212 . Signal path  212  may include one or more transmission lines. As an example, signal path  212  of  FIG. 4  may be a transmission line having a positive signal conductor such as line  214  and a ground signal conductor such as line  216 . Lines  214  and  216  may form parts of a coaxial cable or a microstrip transmission line (as examples). A matching network formed from components such as inductors, resistors, and capacitors may be used in matching the impedance of antenna structures  204  to the impedance of transmission line  212 . 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. Components such as these may also be used in forming fixed circuit elements such as a fixed capacitor coupled to an antenna resonating element trace in antenna structures  204  and/or a tunable element such as a tunable capacitor in tunable circuitry  208  in antenna structures  204 . 
     Transmission line  212  may be coupled to antenna feed structures associated with antenna structures  204 . As an example, antenna structures  204  may form an inverted-F antenna having an antenna feed with a positive antenna feed terminal such as terminal  218  and a ground antenna feed terminal such as ground antenna feed terminal  220 . Positive transmission line conductor  214  may be coupled to positive antenna feed terminal  218  and ground transmission line conductor  216  may be coupled to ground antenna feed terminal  220 . Other types of antenna feed arrangements may be used if desired. The illustrative feeding configuration of  FIG. 4  is merely illustrative. 
     Tunable circuitry  208  may be formed from one or more tunable circuits such as circuits based on capacitors, resistors, inductors, and switches. Tunable circuitry  208  may be implemented using discrete components mounted to a printed circuit such as a rigid printed circuit board (e.g., a printed circuit board formed from glass-filled epoxy) or a flexible printed circuit formed from a sheet of polyimide or a layer of other flexible polymer, a plastic carrier, a glass carrier, a ceramic carrier, or other dielectric substrate. As an example, tunable circuitry  208  may be coupled to a dielectric carrier of the type that may be used in supporting antenna resonating element traces for antenna structures  204  ( FIG. 3 ). Fixed circuit components (e.g., a fixed capacitor coupled to antenna structures  204 ) may also be formed using these arrangements. 
       FIG. 5  is a diagram of an illustrative antenna of the type that may be used in an electronic device such as device  10 . Antenna  228  has antenna resonating element  244  and antenna ground  246 . Antenna resonating element  244  may be formed from antenna resonating element trace  232  on curved dielectric support  230 . Antenna  228  may have an inverted-F configuration having main resonating element arm  252 , short circuit path  248  to couple main resonating element arm  252  to antenna ground  246 , and an antenna feed having positive antenna feed terminal  240  and ground antenna feed terminal  242 . 
     Arm  252  may be characterized by length  234  (e.g., a length extending from the antenna feed formed from terminals  240  and  242  at one end of arm  252  to the opposing end of arm  252 ). A fundamental antenna resonant peak may be associated with a signal frequency where a quarter of a wavelength is equal to length  234 . To help implement antenna  228  in a compact size, antenna resonating element arm  252  of  FIG. 5  has a meandering path. The meandering layout of arm  252  in antenna resonating element trace  232  gives rise to opposing currents such as currents  236  and  238  in some modes of operation, which can reduce antenna efficiency. The meandering layout of arm  252  also gives rise to slot  250 , which can exhibit undesired slot resonances (e.g., slot resonances where the length of the slot is equal to about a quarter of a wavelength). 
     An antenna design for device  10  that can be used to avoid the use of the meandering path configuration of  FIG. 5  is shown in  FIG. 6 . Antenna  204  of  FIG. 6  may have an inverted-F antenna resonating element such as antenna resonating element  254  and an antenna ground such as antenna ground  264 . Antenna ground  264  may be formed from housing  12  and/or other conductive structures in device  10 . Antenna resonating element  254  may have a main antenna resonating element arm formed from metal trace  256  on dielectric support  258  (e.g., a plastic carrier or a printed circuit mounted to a plastic carrier, etc.). Antenna  204  may be fed using an antenna feed that includes positive antenna feed terminal  218  coupled to trace  256  and ground antenna feed terminal  220  on antenna ground  264 . The antenna feed may be located at one end of the main resonating element arm (e.g., the right-hand end in the orientation of  FIG. 6 ). Capacitor  262  may be coupled to the opposing (left-hand) end of the resonating element arm. Short circuit path  270  may couple the main antenna resonating element arm to antenna ground  264  at a location between the antenna feed and capacitor  262  (as an example). An electrical connection such as a weld, solder joint, or screw  268  may be used in coupling short circuit path  270  to ground  264 . 
     There may be one or more layers of metal traces  256  in antenna  204 . If desired, proximity sensor circuitry  224  ( FIG. 4 ) may be coupled to metal traces  256  via path  226  and isolating circuitry  274  (e.g., a pair of inductors for preventing radio-frequency antenna signals from antenna resonating element trace  256  from reaching circuitry  224  through a pair of respective signal lines in path  226 ). 
     Inverted-F antenna resonating element  254  may avoid the use of meandering paths of the type shown in  FIG. 5 , so antenna currents  266  may flow in antenna resonating element  254  without cancelling each other and without being subjected to undesired slot-based resonances. The layout of antenna resonating element  254  of  FIG. 6  may thereby enhance antenna performance in desired communications bands. 
     Capacitor  262  (or other suitable coupling circuit) may couple tip portion  276  to antenna ground  264 , thereby capacitively loading antenna  204 . Capacitor  262  may be, for example, a surface mount technology component that exhibits a fixed or a tunable capacitance value. One terminal of capacitor  262  may be connected to portion  276  of metal trace  256 . The other terminal of capacitor  262  may be coupled to trace segment  272 , which is coupled to antenna ground  264  by electrical connections  268  (e.g., a weld, solder, a screw, or other fastener). 
     With a capacitively loaded inverted-F antenna resonating element configuration of the type shown in  FIG. 6 , antenna resonating element  254  may be characterized by electrical length  260 . Length  260  may have a first portion based on the physical size of metal trace  256  and may have a second portion based on capacitive loading from capacitor  262 . Because of the presence of capacitor  262 , antenna  204  may be implemented in a compact size (e.g., approximately the same antenna volume as the antenna of  FIG. 5 ) without using a meandering resonating element arm layout of the type shown in  FIG. 5  and without including resonating slot structure  250  of  FIG. 5 . 
       FIG. 7  is a graph in which antenna performance (standing wave ratio SWR) has been plotted as a function of operating frequency for an antenna with a meandering path of the type shown in  FIG. 5  (curve  280 ) and a capacitively loaded antenna of the type shown in  FIG. 6  that has a main resonating element arm without meandering portions (curve  282 ). As shown in  FIG. 7 , in low frequency band f1 and middle frequency band f2, curves  280  and  282  may exhibit satisfactory performance. Performance for antenna  204  of  FIG. 6  (curve  282 ) may be superior to performance for antenna  228  of  FIG. 5 , because antenna  204  does not generally experience nullification of antenna currents due to a meandering path. Antenna resonating element traces  256  may be relatively large due to the absence of slot  250 , thereby enhancing the ability of traces  256  to serve as a capacitive proximity sensor electrode for a proximity sensor in device  10 . The absence of slot  250  may also prevent undesired operation of antenna  204  in an inefficient slot antenna mode, thereby improving antenna performance at high frequency communications band f3 as illustrated by the separation between curves  280  and  282  at frequency band f3. With one illustrative configuration, communications bands f1, f2, and f3 may cover cellular bands and other antenna signals ranging from 700 MHz (bottom of band f1) to 2700 MHz (top of band f3). 
     In  FIG. 8 , antenna efficiency has been plotted as a function of operating frequency for an antenna with a meandering path of the type shown in  FIG. 5  (curve  280 ′) and a capacitively loaded antenna of the type shown in  FIG. 6  that has a main resonating element arm without meandering portions (curve  282 ′). At operating frequencies associated with low frequency band f1 and middle frequency band f2, curves  280 ′ and  282 ′ may exhibit satisfactory efficiency. The efficiency of antenna  204  of  FIG. 6  (curve  282 ′) may be greater than the efficiency of antenna  228  of  FIG. 5 , because antenna  204  does not generally experience nullification of antenna currents due to a meandering path. The absence of slot  250  may also prevent undesired operation of antenna  204  in an inefficient slot antenna mode, thereby improving antenna performance at high frequency communications band f3, as illustrated by the greater efficiency of antenna  204  (curve  282 ′) than the efficiency of meandering path antenna of  FIG. 5  (curve  280 ′). 
       FIG. 9  is a top view of an edge portion of device  10  showing how device  10  may be provided with multiple antennas such as antenna  204 A and antenna  204 B. Conductive structures  284  (e.g., metal housing structures, traces on printed circuit boards, antenna structures such as a Global Positioning System antenna, metal portions of device components such as a camera and other conductive structures) may be interposed between antennas  204 A and  204 B. Antennas  204 A and  204 B may each be an antenna of the type shown in  FIG. 6 . If desired, additional antennas such as antenna  204  of  FIG. 6  may be mounted within device  10 . The illustrative configuration of  FIG. 9  in which device  10  has been provided with a pair of antennas  204  is merely illustrative. 
     Capacitor  262  of antenna  204  of  FIG. 6  may be implemented using a fixed capacitor or an adjustable capacitor.  FIG. 10  is a circuit diagram of an illustrative configuration that may be used for implementing capacitor  262  as an adjustable capacitor. Adjustable capacitor  262  of  FIG. 10  has three fixed capacitors C 1 , C 2 , and C 3  coupled respectively to three respective switches SW 1 , SW 2 , and SW 3 . The switches and respective fixed capacitors of  FIG. 10  may be coupled in parallel between adjustable capacitor terminals  286  and  288 . 
     Various capacitor values may be achieved by adjusting switches SW 1 , SW 2 , and SW 3  using control signals from control circuitry  29 . When switches SW 1 , SW 2 , and SW 3  are all closed, the capacitance of capacitor  262  will be maximized (C 1 +C 2 +C 3 ). When switches SW 1 , SW 2 , and SW 3  are all open, the capacitance of capacitor  262  will be zero. Intermediate values of capacitance may be produced with other switch settings. For example, when one of the switches such as switch SW 1  is closed while the other switches are opened, a single capacitor (e.g., capacitor C 1 ) will be switched into use while the other capacitors (C 2  and C 3 ) will be switched out of use. 
     If desired, other numbers of fixed capacitors may be used in adjustable capacitor  262 . The example of  FIG. 10  in which three capacitors are selectively switched into or out of use by switching circuitry such as switches SW 1 , SW 2 , and SW 3  is merely illustrative. In operation in antenna  204 , terminal  286  of adjustable capacitor  262  may be coupled to portion  276  of metal trace  256  and terminal  288  of adjustable capacitor  262  may be coupled to metal structure  272  and antenna ground  264 . 
       FIG. 11  is a graph in which antenna performance (standing wave ratio SWR) for antenna  204  has been plotted in a given communications band (e.g., low band f1 or other suitable band) as a function of operating frequency. Adjustments to the capacitance exhibited by adjustable capacitor  262  will tune antenna  204  and thereby shift the position of the antenna resonance exhibited by antenna  204 . In the  FIG. 11  example, adjustable capacitor  262  has been adjusted between three different capacitance settings. Curve  290  corresponds to a first state of capacitor  262  in which capacitor  262  has been configured to exhibit a first capacitance value and antenna  204  therefore exhibits an antenna resonance centered on frequency fa. Curve  292  corresponds to a second state of capacitor  262  in which capacitor  262  has been configured to exhibit a second capacitance value that is different than the first capacitance value so that antenna  204  exhibits an antenna resonance centered on frequency fb. In the configuration of curve  294 , adjustable capacitor  262  has a third capacitance value that differs from the first and second capacitance values so that antenna  204  exhibits an antenna resonance centered on frequency fc. By adjusting the value of capacitor  262  in this way, a desired range of operating frequencies (i.e., a desired communications bandwidth) may be covered by antenna  204 . 
     It may be desirable to implement capacitor  262  using metal structures separated by a gap. The metal structures may be, for example, metal traces such as portions of metal trace  256  and  272  of  FIG. 6 . To enhance the amount of capacitance that is produced within a given volume, metal traces  256  and  272  may have interdigitated portions such as interdigitated fingers  256 ′ and  272 ′ of  FIG. 12 . The use of interdigitated structures may increase capacitance without significantly increasing the amount of space consumed by the adjustable capacitor. 
     Antenna  204  may be implemented using a curved flexible printed circuit substrate that is supported by a plastic carrier with a curved surface or other surface shape and/or using metal traces formed directly on the surface of a plastic carrier with a curved surface or other surface shape (e.g., metal traces deposited using electrochemical deposition techniques or other metal deposition techniques). 
       FIG. 13  shows how capacitor  262  may be coupled to edge  296  of antenna structures  204  (i.e., the edge of metal trace  256  that includes positive antenna feed terminal  218  and short circuit path  270 ). Antenna  204  is curved, so that surface I faces out of the page of  FIG. 13  and so that surface II faces into the page of  FIG. 13 .  FIG. 14  is a cross-sectional side view of device  10  showing how terminal  288  of capacitor  262  may be coupled to metal housing portion  12 ′ (e.g., a vertical metal wall that serves as antenna ground  264  and that extends between opposing front and rear surfaces of device  10 ) via an electrical connection structure such as screw  300 . Antenna  204  may be mounted on a dielectric support such as plastic support structure  298  so that surface I of antenna  204  lies under inactive region  54  of display cover layer  60  and faces inactive region  54  of display cover layer  60  and so that surface II of antenna  204  faces antenna window  58 . 
       FIG. 15  shows how capacitor  262  may be coupled to edge  304  of antenna structures  204  (i.e., the edge of metal trace  256  opposing edge  296  that includes positive antenna feed terminal  218  and short circuit path  270 ). Antenna  204  is curved, so that surface I′ faces out of the page of  FIG. 15  and so that surface II′ faces into the page of  FIG. 15 .  FIG. 16  is a cross-sectional side view of device  10  showing how terminal  288  of capacitor  262  may be coupled to metal housing portion  12  (which may serve as antenna ground  264 ) using an electrical connection structure such as screw  304 . Antenna  204  may be mounted on a dielectric support such as plastic support structure  298  so that surface I′ of antenna  204  faces inactive region  54  of display cover layer  60  and so that surface II′ of antenna  204  faces antenna window  58 . 
     If desired, other types of mounting arrangements may be used for antennas  204  in device  10 . The configurations of  FIGS. 13 ,  14 ,  15 , and  16  in which antenna  204  is curved to fit within the curved edge portion of housing  12  and device  10  is merely illustrative. 
     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: 20130308
Publication Date: 20150728
Grant Date: 20150728
Priority Date: 20130308
Inventors: YARGA SALIH
LI QINGXIANG
SCHLUB ROBERT W.
Assignee: APPLE INC
CPC Classifications: [{"code": "H01Q1/36", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01Q5/335", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q1/243", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q5/371", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q5/328", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q5/335", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q5/328", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q5/335", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q5/371", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q1/243", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01Q5/371", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q1/36", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01Q5/328", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q1/243", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 51487217