PATENT DOCUMENT

Publication Number: US-9502750-B2
Application Number: US-201313855568-A
Country: US
Kind Code: B2

Title: Electronic device with reduced emitted radiation during loaded antenna operating conditions

Abstract:
An electronic device may have an antenna for providing coverage in wireless communications bands of interest. The wireless communications bands may include a communications band at a first frequency. The antenna may have a parasitic antenna resonating element that supports a low efficiency resonance. In response to operation of the electronic device in free space, the low efficiency resonance will be located at a second frequency that is greater than the first frequency. In response to operation of the electronic device in proximity to a user&#39;s body or other external object, the antenna will be loaded and the low efficiency resonance associated with the parasitic antenna resonating element will shift to the communications band at the first frequency. The antenna may include a resonating element formed on a flexible printed circuit or a dielectric carrier such as a plastic support structure.

Claims:
What is claimed is: 
     
       1. An antenna operable in a communications band at a first frequency, comprising:
 an antenna ground; 
 antenna resonating element, wherein the antenna resonating element comprises an inverted-F antenna resonating element; 
 a parasitic antenna resonating element, wherein the parasitic antenna resonating element exhibits a resonance at a second frequency greater than the first frequency when the antenna is operated in free space, the resonance shifts to overlap the communications band at the first frequency when the antenna is loaded due to proximity to an object, and the shifted resonance reduces antenna efficiency in the communications band at the first frequency when the antenna is loaded relative to when the antenna is operated in free space; and 
 a flexible printed circuit having opposing first and second surfaces, wherein the antenna resonating element is formed on the first surface and wherein the parasitic antenna resonating element is formed on the second surface. 
 
     
     
       2. The antenna defined in  claim 1  wherein the parasitic antenna resonating element comprises an L-shaped parasitic antenna resonating element. 
     
     
       3. The antenna defined in  claim 1  further comprising a molded plastic carrier, wherein the antenna resonating element comprises metal traces formed on the plastic carrier, and the parasitic antenna resonating element comprises metal traces formed on the molded plastic carrier. 
     
     
       4. The antenna defined in  claim 1  wherein the antenna ground comprises a metal electronic device housing. 
     
     
       5. The antenna defined in  claim 1  further comprising capacitive proximity sensor circuitry that is electrically coupled to the antenna resonating element. 
     
     
       6. An antenna operable in a communications band at a first frequency, comprising:
 an antenna ground; 
 antenna resonating element, wherein the antenna resonating element comprises an inverted-F antenna resonating element; 
 a parasitic antenna resonating element, wherein the parasitic antenna resonating element exhibits a resonance at a second frequency greater than the first frequency when the antenna is operated in free space, the resonance shifts to overlap the communications band at the first frequency when the antenna is loaded due to proximity to an object, the shifted resonance reduces antenna efficiency in the communications band at the first frequency when the antenna is loaded relative to when the antenna is operated in free space, and the parasitic antenna resonating element comprises a metal trace; and 
 an inductor coupled between the metal trace and the antenna ground. 
 
     
     
       7. An antenna operable in a communications band at a first frequency, comprising:
 an antenna ground; 
 antenna resonating element, wherein the antenna resonating element comprises an inverted-F antenna resonating element; 
 a parasitic antenna resonating element, wherein the parasitic antenna resonating element exhibits a resonance at a second frequency greater than the first frequency when the antenna is operated in free space, the resonance shifts to overlap the communications band at the first frequency when the antenna is loaded due to proximity to an object, the shifted resonance reduces antenna efficiency in the communications band at the first frequency when the antenna is loaded relative to when the antenna is operated in free space, and the parasitic antenna resonating element comprises a metal trace; and 
 a capacitor coupled between the metal trace and the antenna ground.

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. 
     To satisfy consumer demand for small form factor wireless devices, manufacturers are continually striving to reduce the size of components that are used in these devices while providing enhanced functionality. It is generally impractical to completely shield a user of a compact handheld device from transmitted radio-frequency signals. For example, conventional cellular telephone handsets generally emit signals in the vicinity of a user&#39;s head during telephone calls. Government regulations limit radio-frequency signal powers. In particular, so-called specific absorption rate (SAR) standards are in place that impose maximum energy absorption limits on handset manufacturers. At the same time, wireless carriers require that the handsets that are used in their networks be capable of producing certain minimum radio-frequency powers so as to ensure satisfactory operation of the handsets. 
     The manufacturers of electronic devices such as wireless handheld devices therefore face challenges in producing devices with adequate radio-frequency signal strengths that are compliant with applicable government regulations. 
     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. The wireless communications bands may include a communications band at a first frequency. The antenna may have a parasitic antenna resonating element that supports a resonance associated with lowered antenna efficiency. 
     When operating the electronic device in free space, the low efficiency resonance is located at a second frequency that is greater than the first frequency. Wireless communications signals may therefore be transmitted and received with the antenna in the communications band at the first frequency without reduction in the efficiency of the antenna due to the resonance from the parasitic antenna resonating element. When operating the electronic device in proximity to a user&#39;s body or other external object, the antenna will be loaded. This will cause the low efficiency resonance associated with the parasitic antenna resonating element to shift to the communications band at the first frequency, thereby reducing transmitted radio-frequency signal power and helping to ensure that regulatory limits on transmitted power levels are satisfied. 
     The antenna may include a resonating element formed on a flexible printed circuit or a dielectric carrier such as a plastic support structure. Antenna ground for the antenna may be formed by a metal housing for the electronic device. A capacitor or inductor may be used to couple the parasitic antenna resonating element to the antenna ground. The antenna may have a curved shape overlapping an inactive display area and an antenna window in the housing. Capacitive proximity sensor circuitry may be coupled to the antenna. 
     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 parasitic antenna resonating element that may be used in an electronic device in accordance with an embodiment of the present invention. 
         FIG. 6  is a graph in which antenna performance (standing-wave ratio) for an antenna of the type shown in  FIG. 5  has been plotted as a function of operating frequency for loaded and unloaded operating conditions in accordance with an embodiment of the present invention. 
         FIG. 7  is a graph in which antenna efficiency for an antenna of the type shown in  FIG. 5  has been plotted as a function of operating frequency for loaded and unloaded operating conditions in accordance with an embodiment of the present invention. 
         FIG. 8  is a perspective view of an illustrative antenna with a parasitic element mounted to the opposing side of a flexible printed circuit substrate from an antenna resonating element in accordance with an embodiment of the present invention. 
         FIG. 9  is a perspective view of an illustrative antenna with a parasitic element formed from metal traces on a plastic carrier substrate in accordance with an embodiment of the present invention. 
         FIG. 10  is a perspective view of an illustrative antenna in which a parasitic element is coupled to ground using a circuit element such as an inductor in accordance with an embodiment of the present invention. 
         FIG. 11  is a perspective view of an illustrative antenna in which a parasitic element is coupled to ground using a circuit element such as a capacitor in accordance with an embodiment of the present invention. 
         FIGS. 12 and 13  are cross-sectional side views of illustrative electronic device antennas mounted in an electronic device 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 an 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 solid plastic member, a hollow plastic member, or other dielectric carrier structures. 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  30  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 dual band inverted-F antenna are sometimes described herein as an example. 
     If desired, 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). 
     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 or inductor coupled to metal traces in antenna structures  204 ) may also be formed using these arrangements. If desired, antenna structures  204  may omit tunable circuitry  208  (i.e., antenna structures  204  may be implemented using only fixed components). 
     Wireless carriers typically require that wireless devices that are to be used in their networks pass certification testing. Typical tests involve ascertaining whether a device under test can satisfy wireless performance criteria when tested in free space. Government regulations impose limits on emitted radiation levels from devices such as device  10 . These regulations, which are sometimes referred to as specific absorption rate (SAR) standards, impose maximum energy absorption limits on devices that are used in the vicinity of a user&#39;s body. There is therefore a tension between ensuring adequate wireless performance to satisfy carrier requirements and satisfying SAR standards. 
     To provide antenna structures  204  with the ability to cover communications frequencies of interest with desired performance while satisfying SAR limits when a device is placed in the vicinity of an external object such as a user&#39;s head or other body part, antenna structures  204  may be provided with an antenna resonating element and near-field coupled parasitic antenna structures such parasitic antenna resonating element  250 . Parasitic antenna resonating element  250  may be electromagnetically coupled to the antenna resonating element through near field coupling, whereas the antenna resonating element may be fed using an antenna feed such as the feed formed from positive antenna feed terminal  218  and ground antenna feed  220 . The presence of parasitic antenna resonating element  250  may help reduce emitted radiation levels in a given communications band when device  10  is operated in the vicinity of an external object that loads the antenna(s) in device  10  without adversely affecting the free space performance of device  10  in the given communications band. The given communications band may be, for example, a cellular telephone band. 
     It is often most challenging to satisfy SAR standards when operating a device in high frequency communications bands (e.g., at high band cellular telephone frequencies). With one suitable arrangement, parasitic antenna resonating element  250  may be configured to resonate at a frequency range just above these high communications bands of interest for antenna structures  204 . The resonant mode supported by the parasitic antenna resonating element may exhibit a lower efficiency than that of the antenna resonating element due to current concentration in the parasitic element, so the presence of the parasitic antenna resonating element in the antenna may reduce antenna performance at the resonant frequency associated with the parasitic antenna resonating element. 
     The position of the parasitic antenna resonating element resonance depends on antenna loading. During normal free space operation in which the antenna is unloaded by the presence of a user&#39;s head or other external object, the resonant frequency of the parasitic antenna resonating element (and therefore the frequency of reduced antenna efficiency) is generally located outside of the operating frequencies of device  10  (i.e., above the highest cellular telephone bands of interest). During operation in the vicinity of a user&#39;s head or other external object that loads the antenna, the resonant frequency of the parasitic antenna resonating element (and therefore the frequency of reduced antenna efficiency) will be shifted to lower frequencies, overlapping the highest cellular telephone bands of interest. Because of the reduced efficiency of the antenna during loaded operating conditions, less radiation will be emitted from device  10  whenever device  10  is operated in proximity to the user&#39;s body, thereby helping to ensure that device  10  satisfies SAR limits. 
       FIG. 5  is a perspective view 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  228  also has parasitic antenna resonating element  250 . Antenna resonating element  244  and parasitic antenna resonating element  250  may be formed from metal traces (see, e.g., metal trace  232  for element  244 ) on curved dielectric support  230  (as an example). Dielectric support  230  may be a flexible printed circuit (as an example). 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  218  coupled to arm  252  and ground antenna feed terminal  220  coupled to antenna ground  246 . 
     Antenna  228  may, if desired, have a curved shape of the type shown in  FIG. 5 . This type of layout may allow antenna  228  to be mounted within the edge of housing  12  in a configuration of the type shown in  FIG. 3  where part of the antenna overlaps inactive region  54  of display  50  and part of the antenna overlaps antenna window  58 . Other layouts for antenna  228  may be used, if desired. 
     Antenna ground  246  may be formed from housing  12  and/or other conductive structures in device  10 . Antenna resonating element trace  232  and metal traces for parasitic antenna resonating element  250  may be formed from patterned metal traces in a flexible printed circuit that is supported by a dielectric support structure or may be formed from patterned metal traces on the surface of a molded plastic member or other dielectric carrier. Laser processing techniques may be used in forming metal traces on plastic carriers, if desired. 
     Antenna  228  may be fed using an antenna feed that includes positive antenna feed terminal  218  coupled to arm  252  and ground antenna feed terminal  220  on antenna ground  246 . Parasitic antenna resonating element  250  may be located at the opposing end of arm  252 . As shown in  FIG. 5 , parasitic antenna resonating element  250  may have an L shape (as an example). Elongated portion  260  of L-shaped parasitic resonating element  250  may run parallel to the edge of trace  232  and may be separated from trace  232  of antenna resonating element  244  by a dielectric gap such as gap  262 . 
     Short circuit path  248  may couple antenna resonating element  244  to antenna ground  246  at a location between the antenna feed and parasitic antenna resonating element  250  (as an example). Electrical connections  268  such as welds, solder joints, screws or other structures may be used in coupling parasitic antenna resonating element  250  and short circuit path  248  to ground  246 . 
     There may be one or more layers of metal traces such as the metal traces of element  250  and traces  232  in antenna  228 . If desired, traces  232  may be used in forming capacitive proximity sensor electrodes for a capacitive proximity sensor. Proximity sensor circuitry  224  ( FIG. 4 ) may be coupled to metal traces  232  using path  226  ( FIG. 4 ) via a pair of inductors or other signal isolating circuitry for preventing radio-frequency antenna signals from antenna resonating element trace  232  from reaching circuitry  224  of  FIG. 4 . 
       FIG. 6  is a graph in which antenna performance (standing wave ratio SWR) has been plotted as a function of operating frequency for an illustrative antenna such as antenna  228  of  FIG. 5 . As shown in  FIG. 6 , illustrative antenna  228  of  FIG. 5  has been configured to operate in low frequency band f 1 , middle frequency band f 2 , and high frequency band f 3 . The communications bands associated with frequencies f 1 , f 2 , and f 3  may be, for example, cellular telephone bands at frequencies between about 700 MHz to 2700 MHz (as examples). 
     Solid line curve  280  corresponds to operation of antenna  228  in free space when antenna  228  is not loaded due to the presence of a user&#39;s head or other external object in proximity to device  10 . Dashed line curve  282  corresponds to operation of antenna  228  when device  10  and antenna  228  have been placed in the vicinity of a user&#39;s head or other external object that loads antenna  228 . Due to the presence of parasitic antenna resonating element  250  ( FIG. 5 ), curve  280  is characterized by a reduced-efficiency resonance such as resonance  284  (i.e., a resonant mode associated with currents flowing within parasitic antenna resonating element  250 ). 
     During normal unloaded operation of antenna  228 , resonance  284  lies at a frequency f 4  that is above the frequencies associated with desired operation of device  10  (i.e., signals at frequency f 4  lie above the communications bands at frequencies f 2  and f 3 ). The presence of parasitic antenna resonating element  250  in antenna  228  and the resulting parasitic resonant mode that is supported by the parasitic antenna resonating element will therefore not adversely affect antenna performance during unloaded operations. 
     When device  10  and antenna  228  are brought into proximity of an external object such as a user&#39;s head or other body part, antenna  228  will be loaded by the presence of the external object. This will cause the response curve for antenna  228  to shift from that shown by curve  280  to that shown by curve  282 . As shown in  FIG. 6 , for example, resonance  284  will shift to the position shown by resonance  286 , overlapping high frequency communications bands such as the high frequency communications bands at frequencies f 2  and f 3 . The overlap of resonance  286  with the communications bands at f 2  and f 3  will decrease antenna efficiency in the bands at frequencies f 2  and f 3 . Because antenna efficiency is decreased in the bands at frequencies f 2  and f 3  when antenna  228  is loaded, the amount of emitted power at frequencies f 2  and f 3  will be reduced when antenna  228  is loaded, thereby helping to ensure that SAR regulations and SAR compliance tests (which are performed when device  10  is in the vicinity of a phantom) are satisfied. 
     The graph of  FIG. 7  shows how antenna efficiency in the communications bands at frequencies f 2  and f 3  decreases when antenna  228  is loaded due to operation of device  10  at the head of a user or in the vicinity of other external objects that load antenna  228 . Curve  280 ′ corresponds to unloaded operation, where antenna efficiency at frequencies f 2  and f 3  is relatively high, because parasitic resonance  284 ′ lies out of band. Curve  282 ′ corresponds to loaded operation, where parasitic resonance  284 ′ has shifted to the position shown by resonance  286 ′ and antenna efficiency has been reduced. 
     As shown in  FIG. 8 , parasitic antenna resonating element  250  may, if desired, be implemented using traces  290  on the opposing side of a flexible printed circuit substrate or other dielectric carrier  230  from traces  232 . Gap  262  may be sufficiently small to allow traces  290  to be electromagnetically near field coupled to traces  232  of antenna resonating element  244 . 
       FIG. 9  is a perspective view of antenna  228  in a configuration in which antenna resonating element  244  has been formed from metal traces  232  that have been formed on the surface of a hollow or solid molded plastic member or other dielectric carrier  296 . In this type of configuration, it may be desirable to form parasitic antenna resonating element  250  from metal traces such as metal traces  292  that have been formed directly on carrier  296 . Laser processing techniques such as those involving light illumination to selectively activate surface regions on carrier  296  followed by electroplating may be used in forming patterned metal traces such as metal traces  292  and  232  of  FIG. 9 . Metal traces in flexible printed circuits  294  or other conductive paths may be used in coupling parasitic element  250  and short circuit path  248  to antenna ground  246 . 
     If desired, an electrical component such as inductor  293  may be coupled between parasitic antenna resonating element trace  260  in parasitic antenna resonating element  250  and antenna ground  246 , as shown in  FIG. 10 . With this type of hybrid parasitic antenna element configuration, the length of elongated parasitic antenna resonating element trace  260  may be reduced (relative to the length of trace  260  of  FIG. 5 ) for a given parasitic antenna resonating element resonance frequency. 
       FIG. 11  is a perspective view of antenna  228  showing an illustrative configuration that may be used for antenna  228  in which an electrical component such as capacitor  295  has been coupled between parasitic antenna resonating element trace  260  in parasitic antenna resonating element  250  (i.e., tip portion  260 ′ of trace  260 ) and antenna ground  246 . The opposing end of trace  260  may be coupled to ground  246 . As with the configuration of  FIG. 10 , the configuration of  FIG. 11  allows the length of elongated parasitic antenna resonating element trace  260  to be reduced relative to the length of trace  260  of  FIG. 5  while maintain a desired parasitic antenna resonating element resonance frequency. 
       FIG. 12  is a cross-sectional side view of device  10  showing how antenna  228  may be formed from a flexible printed circuit substrate (flexible printed circuit  230 ) on dielectric carrier  300 . Component  304  (e.g., inductor  292  or capacitor  294 ) may be coupled to traces on flexible printed circuit  230 . A conductive structure such as screw  306  may be used to electrically connect traces on printed circuit  230  to antenna ground (e.g., portion  12 ′ of metal housing  12 ). As shown in the illustrative configuration of  FIG. 13 , screw  306  or other electrical connection structures may be used to couple traces on printed circuit  302  to housing  12 . Using configurations of the type shown in  FIGS. 12 and 13 , antenna  228  may be curved so as to overlap inactive portion  54  of display  50  and antenna window  58 , allowing antenna signals to be transmitted and received through antenna window  58  and/or inactive portion  54  of display  50  (e.g., area  54  in display cover layer  60 ). 
     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: 20130402
Publication Date: 20161122
Grant Date: 20161122
Priority Date: 20130402
Inventors: YARGA SALIH
LI QINGXIANG
SCHLUB ROBERT W.
Assignee: APPLE INC
CPC Classifications: [{"code": "H01Q5/378", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q9/0421", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q1/243", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01Q1/245", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q1/38", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q1/38", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q1/243", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01Q5/378", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q9/0421", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q1/245", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 51620257