PATENT DOCUMENT

Publication Number: US-9537219-B2
Application Number: US-201414500819-A
Country: US
Kind Code: B2

Title: Electronic device with passive antenna retuning circuitry

Abstract:
An electronic device may have wireless circuitry with antennas. An antenna may have an inverted-F antenna resonating element, an antenna ground, and other resonating element structures. A tip of the antenna resonating element and the antenna ground may be separated by a peripheral housing gap filled with plastic. The antenna may be sensitive to capacitance changes induced by the presence of a user&#39;s hand overlapping the gap or other portions of the antenna. A hand capacitance sensing electrode may be mounted in the plastic of the gap or elsewhere in the vicinity of the antenna. A transmission line may couple the hand capacitance sensing electrode to the antenna to retune the antenna in the event that the user&#39;s hand overlaps the antenna.

Claims:
What is claimed is: 
     
       1. An electronic device, comprising:
 an antenna having an antenna feed; 
 a transceiver circuit coupled to the antenna; 
 a hand capacitance sensing electrode; 
 a radio-frequency transmission line that couples the hand capacitance sensing electrode to the antenna; and 
 a capacitor coupled between the radio-frequency transmission line and the antenna feed. 
 
     
     
       2. The electronic device defined in  claim 1  wherein the antenna feed is coupled to a first end of the radio-frequency transmission line and wherein the hand capacitance sensing electrode is coupled to an opposing second end of the radio-frequency transmission line. 
     
     
       3. The electronic device defined in  claim 2  wherein the antenna comprises:
 an inverted-F antenna resonating element; and 
 an antenna ground, wherein a tip portion of the inverted-F antenna resonating element is separated from the antenna ground by a gap. 
 
     
     
       4. The electronic device defined in  claim 3  further comprising:
 a housing, wherein the gap is formed on a peripheral edge of the housing. 
 
     
     
       5. The electronic device defined in  claim 4  wherein the hand capacitance sensing electrode is located at the gap. 
     
     
       6. The electronic device defined in  claim 5  wherein the gap is filled with plastic and wherein the electrode is embedded within the plastic. 
     
     
       7. The electronic device defined in  claim 6  wherein the housing has peripheral conductive housing structures and wherein the inverted-F antenna resonating element is formed from the peripheral conductive housing structures. 
     
     
       8. The electronic device defined in  claim 1  wherein the radio-frequency transmission line has an inner conductor and an outer conductor and wherein the capacitor is coupled between the inner conductor and an inner conductor of an additional radio-frequency transmission line that is coupled between the transceiver circuit and the antenna. 
     
     
       9. The electronic device defined in  claim 1  further comprising:
 a housing having first and second ends, wherein the antenna is located at the first end. 
 
     
     
       10. The electronic device defined in  claim 9  wherein the antenna comprises:
 an inverted-F antenna resonating element; and 
 an antenna ground. 
 
     
     
       11. The electronic device defined in  claim 10  wherein the inverted-F antenna resonating element has a resonating element arm formed from peripheral conductive housing structures in the housing. 
     
     
       12. The electronic device defined in  claim 11  wherein a tip portion of the inverted-F antenna resonating element is separated from the antenna ground by a gap. 
     
     
       13. The electronic device defined in  claim 12  wherein the hand capacitance sensing electrode is mounted at the gap. 
     
     
       14. The electronic device defined in  claim 1  further comprising:
 a metal housing, wherein the antenna comprises an antenna resonating element formed from at least part of the metal housing and an antenna ground formed from at least part of the metal housing. 
 
     
     
       15. The electronic device defined in  claim 14  wherein the metal housing has peripheral conductive structures, wherein a gap separates the peripheral conductive structures from the antenna ground, wherein the hand capacitance sensing electrode is mounted adjacent to the gap and detects a capacitance change when a hand covers the gap, and wherein the capacitance change is conveyed to the antenna by the radio-frequency transmission line to retune the antenna and maintain antenna performance while the hand covers the gap. 
     
     
       16. An electronic device that is configured to be held in a hand of a user, comprising:
 an antenna; 
 a radio-frequency transceiver circuit; 
 a hand capacitance sensing electrode that is not grounded along its length; 
 a first radio-frequency transmission line that couples the radio-frequency transceiver circuit to the antenna; and 
 a second radio-frequency transmission line that couples the hand capacitance sensing electrode to the antenna. 
 
     
     
       17. The electronic device defined in  claim 16  further comprising a housing having an exterior surface, wherein the hand capacitance sensing electrode is mounted adjacent to the exterior surface and senses capacitance changes due to presence and absence of the hand of the user overlapping a given part of the antenna. 
     
     
       18. The electronic device defined in  claim 17  wherein the capacitance changes are conveyed to a feed of the antenna by the second radio-frequency transmission line to retune the antenna when the hand of the user is present adjacent to the given part of the antenna. 
     
     
       19. An electronic device, comprising:
 peripheral conductive housing structures that extend around a periphery of the electronic device, wherein a gap is formed in the peripheral conductive housing structures at the periphery of the electronic device, and the gap is filled with dielectric; 
 an antenna that is sensitive to detuning from contact by a user&#39;s hand; and 
 an electrode that is coupled to the antenna by a conductor in a radio-frequency transmission line, wherein contact with the electrode changes a capacitance at the antenna that compensates for the detuning and the electrode is at least partially embedded within the dielectric at the gap. 
 
     
     
       20. The electronic device defined in  claim 19  further comprising:
 an additional radio-frequency transmission line; and 
 a radio-frequency transceiver that is coupled to the antenna by the additional radio-frequency transmission line, wherein the additional radio-frequency transmission line has a signal line that is coupled to the conductor in the radio-frequency transmission line. 
 
     
     
       21. The electronic device defined in  claim 1  wherein the radio-frequency transmission line is coupled between the antenna feed and the hand capacitance sensing electrode. 
     
     
       22. The electronic device defined in  claim 21 , wherein the radio-frequency transmission line is directly connected to the hand capacitance sensing electrode.

Description:
BACKGROUND 
     This relates generally to electronic devices and, more particularly, to electronic devices with antennas and other wireless circuitry. 
     Electronic devices often include wireless circuitry with antennas. For example, cellular telephones, computers, and other devices often contain antennas for supporting wireless communications. 
     It can be challenging to form electronic device antenna structures with desired attributes. In large electronic devices, antennas can sometimes be isolated from the surrounding environment. This makes the antennas relatively immune to environmental effects, but is not feasible in smaller devices. In a compact electronic device, antenna structures may be formed on or near the external surfaces of the device. This may make antenna performance subject to environmental influence. If, for example, a portion of an antenna is touched by a user&#39;s hand, the antenna can be detuned. Antenna detuning has the potential to adversely impact wireless communications performance. 
     It would therefore be desirable to be able to provide wireless circuitry and electrical components for electronic devices that exhibit enhanced immunity to environmental detuning. 
     SUMMARY 
     An electronic device may have wireless circuitry. The wireless circuitry may include a radio-frequency transceiver circuit coupled to one or more antennas. The electronic device may have a housing. Peripheral conductive housing structures in the housing may be used to form an inverted-F antenna resonating element and an antenna ground. 
     An antenna may be formed from the inverted-F antenna resonating element, the antenna ground, and other antenna structures. A tip of the antenna resonating element and the antenna ground may be separated by a peripheral housing gap filled with plastic. The antenna may be sensitive to capacitance changes induced by the presence of a user&#39;s hand overlapping the gap or other portions of the antenna. A hand capacitance sensing electrode may be mounted in the plastic of the gap or elsewhere in the vicinity of the antenna. 
     A transmission line may couple the radio-frequency transceiver circuit to the antenna. Another transmission line may couple the hand capacitance sensing electrode to the antenna to retune the antenna in the event that the user&#39;s hand overlaps the antenna. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an illustrative electronic device in accordance with an embodiment. 
         FIG. 2  is a schematic diagram of illustrative circuitry in an electronic device in accordance with an embodiment. 
         FIG. 3  is a schematic diagram of illustrative wireless circuitry in accordance with an embodiment. 
         FIG. 4  is a schematic diagram of an illustrative inverted-F antenna showing how the antenna may be influenced by the presence of a user&#39;s body or other external object in accordance with an embodiment. 
         FIG. 5  is a Smith chart showing illustrative impedances associated with operation of an antenna in accordance with an embodiment. 
         FIG. 6  is a top interior view of an illustrative electronic device with a passively retuned antenna in accordance with an embodiment. 
         FIG. 7  is a diagram in which antenna performance (standing wave ratio) has been plotted as a function of frequency during free-space operation and when loaded by an external object in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Electronic devices such as electronic device  10  of  FIG. 1  may be provided with electrical components and wireless communications circuitry. The wireless communications circuitry may include one or more antennas and may be used to support wireless communications in multiple wireless communications bands. Passive returning circuitry may be used to ensure that the antennas remain adequately tuned and performs as desired, even when users&#39; hands or other external objects are adjacent to the antennas. 
     The antennas of the wireless communications circuitry can include loop antennas, inverted-F antennas, strip antennas, planar inverted-F antennas, slot antennas, hybrid antennas that include antenna structures of more than one type, or other suitable antennas. Conductive structures for the antennas may, if desired, be formed from conductive electronic device structures. The conductive electronic device structures may include conductive housing structures. The housing structures may include peripheral structures such as peripheral conductive structures that run around the periphery of an electronic device. The peripheral conductive structure may serve as a bezel for a planar structure such as a display, may serve as sidewall structures for a device housing, may have portions that extend upwards from an integral planar rear housing (e.g., to form vertical planar sidewalls or curved sidewalls), and/or may form other housing structures. Gaps may be formed in the peripheral conductive structures that divide the peripheral conductive structures into peripheral segments. One or more of the segments may be used in forming one or more antennas for electronic device  10 . Antennas may also be formed using an antenna ground plane formed from conductive housing structures such as metal housing midplate structures and other internal device structures. Rear housing wall structures may be used in forming antenna structures such as an antenna ground. 
     Electronic device  10  may be a portable electronic device or other suitable electronic device. For example, electronic device  10  may be a laptop computer, a tablet computer, a somewhat smaller device such as a wrist-watch device, pendant device, headphone device, earpiece device, or other wearable or miniature device, a handheld device such as a cellular telephone, a media player, or other small portable device. Device  10  may also be a television, a set-top box, a desktop computer, a computer monitor into which a computer has been integrated, or other suitable electronic equipment. 
     Device  10  may include a housing such as housing  12 . Housing  12 , which may sometimes be referred to as a case, may be formed of plastic, glass, ceramics, fiber composites, metal (e.g., stainless steel, aluminum, etc.), other suitable materials, or a combination of these materials. In some situations, parts of housing  12  may be formed from dielectric or other low-conductivity material. In other situations, housing  12  or at least some of the structures that make up housing  12  may be formed from metal elements. 
     Device  10  may, if desired, have a display such as display  14 . Display  14  may be mounted on the front face of device  10 . The rear face of device  10  may be formed from a planar rear housing wall in housing  12 . Display  14  may be a touch screen that incorporates capacitive touch electrodes or may be insensitive to touch. 
     Display  14  may include image pixels formed from light-emitting diodes (LEDs), organic LEDs (OLEDs), plasma cells, electrowetting pixels, electrophoretic pixels, liquid crystal display (LCD) components, or other suitable image pixel structures. A display cover layer such as a layer of clear glass or plastic may cover the surface of display  14 . Buttons such as button  24  may pass through openings in the cover layer. The cover layer may also have other openings such as an opening for speaker port  26 . 
     Housing  12  may include peripheral housing structures such as structures  16 . Structures  16  may run around the periphery of device  10  and display  14 . In configurations in which device  10  and display  14  have a rectangular shape with four edges, structures  16  may be implemented using peripheral housing structures that have a rectangular ring shape with four corresponding edges (as an example). Peripheral structures  16  or part of peripheral structures  16  may serve as a bezel for display  14  (e.g., a cosmetic trim that surrounds all four sides of display  14  and/or that helps hold display  14  to device  10 ). Peripheral structures  16  may also, if desired, form sidewall structures for device  10  (e.g., by forming a metal band with vertical sidewalls, curved sidewalls, etc.). 
     Peripheral housing structures  16  may be formed of a conductive material such as metal and may therefore sometimes be referred to as peripheral conductive housing structures, conductive housing structures, peripheral metal structures, or a peripheral conductive housing member (as examples). Peripheral housing structures  16  may be formed from a metal such as stainless steel, aluminum, or other suitable materials. One, two, or more than two separate structures may be used in forming peripheral housing structures  16 . 
     It is not necessary for peripheral housing structures  16  to have a uniform cross-section. For example, the top portion of peripheral housing structures  16  may, if desired, have an inwardly protruding lip that helps hold display  14  in place. The bottom portion of peripheral housing structures  16  may also have an enlarged lip (e.g., in the plane of the rear surface of device  10 ). Peripheral housing structures  16  may have substantially straight vertical sidewalls, may have sidewalls that are curved, or may have other suitable shapes. In some configurations (e.g., when peripheral housing structures  16  serve as a bezel for display  14 ), peripheral housing structures  16  may run around the lip of housing  12  (i.e., peripheral housing structures  16  may cover only the edge of housing  12  that surrounds display  14  and not the rest of the sidewalls of housing  12 ). 
     If desired, housing  12  may have a conductive rear surface. For example, housing  12  may be formed from a metal such as stainless steel or aluminum. The rear surface of housing  12  may lie in a plane that is parallel to display  14 . In configurations for device  10  in which the rear surface of housing  12  is formed from metal, it may be desirable to form parts of peripheral conductive housing structures  16  as integral portions of the housing structures forming the rear surface of housing  12 . For example, a rear housing wall of device  10  may be formed from a planar metal structure and portions of peripheral housing structures  16  on the sides of housing  12  may be formed as vertically extending integral metal portions of the planar metal structure. Housing structures such as these may, if desired, be machined from a block of metal and may include one or more separate pieces. 
     Display  14  may include conductive structures such as an array of capacitive electrodes, conductive lines for addressing pixel elements, driver circuits, etc. Housing  12  may include internal structures such as metal frame members, a planar housing member (sometimes referred to as a midplate) that spans the walls of housing  12  (i.e., a substantially rectangular sheet formed from one or more parts that is welded or otherwise connected between opposing sides of member  16 ), printed circuit boards, and other internal conductive structures. These conductive structures, which may be used in forming a ground plane in device  10 , may be located in the center of housing  12  (e.g., the portion of display  14  that contains a display module for displaying images and that lie between end regions  22  and  20 ). 
     In regions  22  and  20 , openings may be formed within the conductive structures of device  10  (e.g., between peripheral conductive housing structures  16  and opposing conductive ground structures such as conductive housing midplate or rear housing wall structures, a printed circuit board, and conductive electrical components in display  14  and device  10 ). These openings, which may sometimes be referred to as gaps, may be filled with air, plastic, and other dielectrics. 
     Conductive housing structures and other conductive structures in device  10  such as a midplate, traces on a printed circuit board, display  14 , and conductive electronic components may serve as a ground plane for the antennas in device  10 . The openings in regions  20  and  22  may serve as slots in open or closed slot antennas, may serve as a central dielectric region that is surrounded by a conductive path of materials in a loop antenna, may serve as a space that separates an antenna resonating element such as a strip antenna resonating element or an inverted-F antenna resonating element from the ground plane, may contribute to the performance of a parasitic antenna resonating element, or may otherwise serve as part of antenna structures formed in regions  20  and  22 . If desired, the ground plane that is under the active area of display  14  and/or other metal structures in device  10  may have portions that extend into parts of the ends of device  10  (e.g., the ground may extend towards the dielectric-filled openings in regions  20  and  22 ). 
     In general, device  10  may include any suitable number of antennas (e.g., one or more, two or more, three or more, four or more, etc.). The antennas in device  10  may be located at opposing first and second ends of an elongated device housing (e.g., at ends  20  and  22  of device  10  of  FIG. 1 ), along one or more edges of a device housing, in the center of a device housing, in other suitable locations, or in one or more of these locations. The arrangement of  FIG. 1  is merely illustrative. 
     Portions of peripheral housing structures  16  may be provided with gap structures. For example, peripheral housing structures  16  may be provided with one or more gaps such as peripheral gaps  18 , as shown in  FIG. 1 . The gaps in peripheral housing structures  16  may be filled with dielectric such as polymer, ceramic, glass, air, other dielectric materials, or combinations of these materials. Gaps  18  may divide peripheral housing structures  16  into one or more peripheral conductive segments. There may be, for example, two peripheral conductive segments in peripheral housing structures  16  (e.g., in an arrangement with two gaps), three peripheral conductive segments (e.g., in an arrangement with three gaps), four peripheral conductive segments (e.g., in an arrangement with four gaps, etc.). The segments of peripheral conductive housing structures  16  that are formed in this way may form parts of antennas in device  10 . If desired, gaps may extend across the width of the rear wall of housing  12  and may penetrate through the rear wall of housing  12  to divide the rear wall into different portions. Polymer or other dielectric may fill these housing gaps (grooves). 
     In a typical scenario, device  10  may have upper and lower antennas (as an example). An upper antenna may, for example, be formed at the upper end of device  10  in region  22 . A lower antenna may, for example, be formed at the lower end of device  10  in region  20 . The antennas may be used separately to cover identical communications bands, overlapping communications bands, or separate communications bands. The antennas may be used to implement an antenna diversity scheme or a multiple-input-multiple-output (MIMO) antenna scheme. 
     Antennas in device  10  may be used to support any communications bands of interest. For example, device  10  may include antenna structures for supporting local area network communications, voice and data cellular telephone communications, global positioning system (GPS) communications or other satellite navigation system communications, Bluetooth® communications, etc. 
     A schematic diagram showing illustrative components that may be used in device  10  of  FIG. 1  is shown in  FIG. 2 . As shown in  FIG. 2 , device  10  may include control circuitry such as storage and processing circuitry  30 . Storage and processing circuitry  30  may include storage such as hard disk drive storage, nonvolatile memory (e.g., flash memory or other electrically-programmable-read-only memory configured to form a solid state drive), volatile memory (e.g., static or dynamic random-access-memory), etc. Processing circuitry in storage and processing circuitry  30  may be used to control the operation of device  10 . This processing circuitry may be based on one or more microprocessors, microcontrollers, digital signal processors, application specific integrated circuits, etc. 
     Storage and processing circuitry  30  may be used to run software on device  10 , such as internet browsing applications, voice-over-internet-protocol (VOIP) telephone call applications, email applications, media playback applications, operating system functions, etc. To support interactions with external equipment, storage and processing circuitry  30  may be used in implementing communications protocols. Communications protocols that may be implemented using storage and processing circuitry  30  include internet protocols, wireless local area network protocols (e.g., IEEE 802.11 protocols—sometimes referred to as WiFi®), protocols for other short-range wireless communications links such as the Bluetooth® protocol, cellular telephone protocols, MIMO protocols, antenna diversity protocols, etc. 
     Input-output circuitry  44  may include input-output devices  32 . Input-output devices  32  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 devices  32  may include user interface devices, data port devices, and other input-output components. For example, input-output devices may include touch screens, displays without touch sensor capabilities, buttons, joysticks, scrolling wheels, touch pads, key pads, keyboards, microphones, cameras, buttons, speakers, status indicators, light sources, audio jacks and other audio port components, digital data port devices, light sensors, motion sensors (accelerometers), capacitance sensors, proximity sensors, fingerprint sensors (e.g., a fingerprint sensor integrated with a button such as button  24  of  FIG. 1 ), etc. 
     Input-output circuitry  44  may include wireless communications circuitry  34  for communicating wirelessly with external equipment. Wireless communications circuitry  34  may include radio-frequency (RF) transceiver circuitry formed from one or more integrated circuits, power amplifier circuitry, low-noise input amplifiers, passive RF components, one or more antennas, transmission lines, 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 circuitry  90  for handling various radio-frequency communications bands. For example, circuitry  34  may include transceiver circuitry  36 ,  38 , and  42 . Transceiver circuitry  36  may handle 2.4 GHz and 5 GHz bands for WiFi® (IEEE 802.11) communications and may handle the 2.4 GHz Bluetooth® communications band. Circuitry  34  may use cellular telephone transceiver circuitry  38  for handling wireless communications in frequency ranges such as a low communications band from 700 to 960 MHz, a midband from 1710 to 2170 MHz, and a high band from 2300 to 2700 MHz or other communications bands between 700 MHz and 2700 MHz or other suitable frequencies (as examples). Circuitry  38  may handle voice data and non-voice data. 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 60 GHz transceiver circuitry, circuitry for receiving television and radio signals, paging system transceivers, near field communications (NFC) circuitry, etc. Wireless communications circuitry  34  may include global positioning system (GPS) receiver equipment such as GPS receiver circuitry  42  for receiving GPS signals at 1575 MHz or for handling other satellite positioning data. In WiFi® and Bluetooth® links and other short-range wireless links, wireless signals are typically used to convey data over tens or hundreds of feet. In cellular telephone links and other long-range links, wireless signals are typically used to convey data over thousands of feet or miles. 
     Wireless communications circuitry  34  may include antennas  40 . Antennas  40  may be formed using any suitable antenna types. For example, antennas  40  may include antennas with resonating elements that are formed from loop antenna structures, patch antenna structures, inverted-F antenna structures, slot antenna structures, planar inverted-F antenna structures, helical antenna structures, hybrids of these designs, etc. Different types of antennas may be used for different bands and combinations of bands. For example, one type of antenna may be used in forming a local wireless link antenna and another type of antenna may be used in forming a remote wireless link antenna. 
     As shown in  FIG. 3 , transceiver circuitry  90  in wireless circuitry  34  may be coupled to antenna structures  40  using paths such as path  92 . Wireless circuitry  34  may be coupled to control circuitry  30 . Control circuitry  30  may be coupled to input-output devices  32 . Input-output devices  32  may supply output from device  10  and may receive input from sources that are external to device  10 . 
     To provide antenna structures such as antenna(s)  40  with the ability to cover communications frequencies of interest, antenna(s)  40  may be provided with circuitry such as filter circuitry (e.g., one or more passive filters and/or one or more tunable filter circuits). Discrete components such as capacitors, inductors, and resistors may be incorporated into the filter 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(s)  40  may be provided with adjustable circuits such as tunable components  102  to tune antennas over communications bands of interest. Tunable components  102  may be part of a tunable filter or tunable impedance matching network, may be part of an antenna resonating element, may span a gap between an antenna resonating element and antenna ground, etc. Tunable components  102  may include tunable inductors, tunable capacitors, or other tunable components. Tunable components such as these may be based on switches and networks of fixed components, distributed metal structures that produce associated distributed capacitances and inductances, variable solid state devices for producing variable capacitance and inductance values, tunable filters, or other suitable tunable structures. During operation of device  10 , control circuitry  30  may issue control signals on one or more paths such as path  88  that adjust inductance values, capacitance values, or other parameters associated with tunable components  102 , thereby tuning antenna structures  40  to cover desired communications bands. 
     Path  92  may include one or more transmission lines. As an example, signal path  92  of  FIG. 3  may be a transmission line having a positive signal conductor such as line  94  and a ground signal conductor such as line  96 . Lines  94  and  96  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(s)  40  to the impedance of transmission line  92 . 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 filter circuitry in antenna(s)  40  and may be tunable and/or fixed components. 
     Transmission line  92  may be coupled to antenna feed structures associated with antenna structures  40 . As an example, antenna structures  40  may form an inverted-F antenna, a slot antenna, a hybrid inverted-F slot antenna or other antenna having an antenna feed with a positive antenna feed terminal such as terminal  98  and a ground antenna feed terminal such as ground antenna feed terminal  100 . Positive transmission line conductor  94  may be coupled to positive antenna feed terminal  98  and ground transmission line conductor  96  may be coupled to ground antenna feed terminal  100 . Other types of antenna feed arrangements may be used if desired. The illustrative feeding configuration of  FIG. 3  is merely illustrative. 
     A directional coupler may be interposed in transmission line path  92 . Control circuitry  30  and transceiver circuitry  90  may gather phase and magnitude information on the impedance of antenna  40  (or part of antenna  40 ) using the directional coupler. By using the coupler or other circuitry to gather real time information on the impedance of antenna  40 , control circuitry  30  can determine when antenna  40  is being loaded by external objects (e.g., when a user&#39;s hand is in the vicinity of antenna  40  and is therefore affecting the impedance of antenna  40 ). If desired, control circuitry  30  may use information from a proximity sensor (see. e.g., sensors  32  of  FIG. 2 ), received signal strength information, or other information in determining when antenna  40  is being affected by the presence of nearby external objects. In response to detecting that a user&#39;s hand or other external object is adjacent to antenna  40 , control circuitry  30  may take corrective action. For example, control circuitry  30  can issue commands to adjustable circuitry such as tunable components  102  of  FIG. 3  or other tunable circuitry that affects the operation of antenna  40 . 
     Passive retuning circuitry may also be provided in device  10  to help prevent antenna  40  from being detuned due to the presence of an external object such as a user&#39;s hand or other body part. In a passive retuning arrangement, a capacitance change or other change that is produced by the user&#39;s hand (or other external object) is used to adjust antenna  40  in a way that prevents antenna  40  from exhibiting undesired detuning effects. By using passive retuning structures, the need to implement active tuning control for components  102  may be reduced or may even be eliminated (if desired). 
     The potential of an external object to influence antenna performance is illustrated in connection with the illustrative antenna of  FIG. 4 .  FIG. 4  is a diagram of illustrative inverted-F antenna structures that may be used in implementing antenna  40  for device  10 . Other types of antenna (e.g., slot antennas, hybrid inverted-F slot antennas, etc.) may be used in forming antenna  40  if desired. 
     As shown in  FIG. 4 , inverted-F antenna  40  may have antenna resonating element  106  and antenna ground (ground plane)  104 . Antenna resonating element  106  may have a main resonating element arm such as arm  108 . The length of arm  108  and/or portions of arm  108  may be selected so that antenna  40  resonates at desired operating frequencies. For example, the length of arm  108  or a portion of arm  108  may be a quarter of a wavelength at a desired operating frequency for antenna  40 . Antenna  40  may also exhibit resonances at harmonic frequencies. As illustrated by illustrative resonating element arm branch  108 ′, resonating element arm  108  may have two or more branches. For example, arm  108  may have a longer portion that extends to the right (in  FIG. 4 ) and that handles lower frequency communications and may have a shorter portion (see, e.g., branch portion  108 ′ of arm  108 ) that extends to the left (in  FIG. 4 ) and that handles higher frequency communications. If desired, additional structures may be combined with the antenna structures of  FIG. 4  so that antenna  40  covers communications bands of interest. For example, a slot antenna resonating element may be added to antenna  40  that supports antenna operation in a higher frequency band than that covered using the longer and shorter portions of arm  108 . 
     Main resonating element arm  108  may be coupled to ground  104  by return path  110 . Antenna feed  112  may include positive antenna feed terminal  98  and ground antenna feed terminal  100  and may run in parallel to return path  110  between arm  108  and ground  104 . The antenna feed for antenna  40  may include positive antenna feed terminal  98  and ground antenna feed terminal  100 . 
     Antenna  40  may be implemented using conductive structures in device  10  such as conductive housing structures, metal traces on a plastic carrier or printed circuit, etc. With one suitable arrangement, arm  108  and/or portions of ground  104  may be formed from peripheral conductive housing structures  16 . Gap  18  may separate tip portion  120  of arm  108  from nearby portion  122  of ground  104  (and a corresponding gap  18  on an opposing side of device  10  may separate the tip of branch  108 ′ of arm  108  from a corresponding adjacent portion of ground  104 ). 
     Resonating element arm portion  120  and antenna ground portion  122  form electrodes in a capacitor (i.e., gap  18  is associated with a capacitance C). The value of the capacitance between portion  120  and portion  122  is influenced by the operating environment of antenna  40 . In particular, the value of capacitance C associated with gap  18  may be influenced by whether or not an external object such as user hand  124  is adjacent to gap  18  of antenna  40 . Electric fields such as electric fields E 1  and E 2  may develop between portions  120  and  122 . The change in capacitance C results from the varying environments of the electric fields between portions  120  and  122 . In some situations such as the illustrative scenario shown in  FIG. 4 , some of these electric fields (see, e.g., field E 2 ) may pass through external object  124  (e.g., a user&#39;s hand), whereas in other scenarios, electric fields pass through air. The dielectric constant of flesh is greater than the dielectric constant of air, so the value of C will rise in the presence of an external object such as a user&#39;s hand and will fall in the presence of air (i.e., in the absence of the hand). Unless care is taken, fluctuations in the value of capacitance C may have an undesired impact on antenna performance. 
     The location of the portion of antenna  40  that experiences a change in capacitance or other impedance change due to the presence of a user&#39;s hand in the vicinity of antenna  40  affects the results of the capacitance change. In an inverted-F antenna of the type shown in  FIG. 4 , for example, an increase in capacitance C at the tip of arm  108  between portions  120  and  122  will tend to reduce antenna efficiency and will tend to shift the antenna resonance associated with arm  108  (e.g., a low band resonance) to lower frequencies. The shift of the low band to lower frequencies and the decrease in antenna efficiency associated with the operation of antenna  40  may disrupt desired antenna operation (e.g., communications in a low band frequency range may be disrupted). If, on the other hand, capacitance increases at feed  112  of antenna  40 , the frequency of the low band resonance may be increased or at least maintained at a constant value. Antenna efficiency may also improve or at least may not decrease when the capacitance at the feed is increased. 
     To help passively counteract the undesired effects of increasing capacitance C between portions  120  and  122  due to contact between a user&#39;s hand and antenna  40  in the vicinity of gap  18 , a transmission line may be used to transfer the influence of the presence of the user&#39;s hand from the vicinity of gap  18  or other suitable location on device  10  to the vicinity of feed  112 . The transmission line may be, for example, a coaxial cable transmission line, a microstrip transmission line, or other transmission line. An electrode may be used to register the presence of the user&#39;s hand. When the user&#39;s hand touches the electrode, a rise in capacitance is produced. This rise in capacitance is transferred to feed  112  to counteract the expected detuning influence of hand  124  in the vicinity of gap  18  at the tip of arm  108 . 
     Consider, as an example, the illustrative impedances for antenna  40  that are plotted in  FIG. 5 .  FIG. 5  is a Smith chart illustrating the impact of using a coaxial cable or other circuitry to transfer capacitance increases (or other impedance changes) from an electrode that is contacted by the user&#39;s hand to a portion of antenna  40  where the capacitance increase will help improve antenna performance (e.g., feed  112 ). 
     In the Smith chart of  FIG. 5 , transmission line  92  may have an impedance of 50 ohms (as an example), as illustrated by impedance  140 . When antenna  40  is operating normally (across a range of frequencies between 700 MHz and 2700 MHz or other frequency range), antenna  40  may exhibit an impedance such as illustrative impedance  142 . Impedance  142  may be associated with the use of device  10  in free space. In this configuration, tip  120  and portion  122  of ground  104  serve as capacitor electrodes for a capacitor of capacitance C at the tip of arm  108 . Because of the absence of the user&#39;s hand, antenna  40  will operate normally (i.e., antenna impedance  142  will be sufficiently matched to transmission line impedance  140  to allow antenna  40  to function as desired). 
     If the user&#39;s hand or other external object is placed in the presence of gap(s)  18  (i.e., adjacent to antenna  40 ), antenna impedance  142  has the potential be detuned to impedance  146  (e.g., a value that is at mismatched with respect to transmission line impedance  140  and which therefore may cause antenna  40  to operate with unsatisfactory performance). 
     To prevent this detuning from adversely affecting antenna operation, antenna  40  may be passively retuned. In particular, an electrode may be provided near the external surface of device  10  in the vicinity of antenna  40  (e.g., near gap  18 ). Impedance changes in the vicinity of this electrode due to the presence of the user&#39;s hand may be conveyed to a suitable location in antenna  40  such as antenna feed  112  by a transmission line to counteract the potential antenna detuning associated with impedance  146 . As shown in  FIG. 5 , for example, antenna  40  may exhibit satisfactory impedance  148  in the presence of passive retuning. Impedance  148  may be as well matched to transmission line impedance  140  as impedance  142  or may (as shown in  FIG. 5 ) be more closely matched to impedance  140  than free space impedance  142 . Configurations in which passive antenna retuning is used to make antenna detuning from hand contact less severe than the detuning associated with detuned impedance  146  but that do not completely eliminate detuning effects may also be used. 
       FIG. 6  is a top interior view of device  10  in an illustrative configuration in which passive antenna retuning is being used for antenna  40 . As shown in  FIG. 6 , antenna  40  may include an inverted-F antenna resonating element formed from peripheral conductive housing structures such as inverted-F antenna resonating element  108 . Resonating element  108  may be separated from antenna ground  104  by opening  150 . Opening  150  may be filled with dielectric such as air and/or plastic. The shape of opening  150  may be selected to form a slot antenna resonating element. Antenna resonating element  108  may be a two-branch inverted-F antenna resonating element that resonates in first and second communications bands (e.g., a low band and a middle band) and slot  105  may be a slot antenna resonating element that contributes an antenna resonance in a high band (as an example). Return path  110  may couple resonating element  108  to ground  104  and may bridge slot  150 . Feed  112  may be formed in parallel with return path  110 . 
     Transceiver circuitry  90  may be coupled to antenna feed terminals  98  and  100  using transmission line  92 . Impedance matching circuit  166  may be coupled between terminals  98  and  100  to help match the impedance of transmission line  92  to the impedance of antenna  40 . Gaps  18  in the peripheral conductive housing structures of housing  12  may separate the ends of inverted-F antenna resonating element  108  from grounded portions of housing  12  (i.e., antenna ground). Gaps  18  may be filled with polymer or other dielectric. For example, right-hand gap  18  of  FIG. 6  may be filled with plastic  152 . 
     An electrode such as electrode  154  may be located on or near the external surface of antenna  40  in the vicinity of gap  18  or may be mounted in device  10  in another location that allows electrode  154  to sense capacitance changes associated with the presence and absence of the user&#39;s hand or other external object. In the example of  FIG. 6 , electrode  154  has been embedded within plastic  152  in peripheral gap  18 . This is merely illustrative. Electrode  154  may be mounted in device  10  using any suitable mounting arrangement. Because electrode  154  senses capacitance changes associated with the presence or absence of a user&#39;s hand or other external object, electrode  154  may sometimes be referred to as a hand capacitance sensing electrode. 
     A transmission line such as coaxial cable  160  may be coupled between electrode  154  and feed  112 . Cable  160  may have a positive inner conductor such as center conductor  156  that is coupled to electrode  154  and may have an outer ground conductor that is shorted to ground  104  at node  158 . At end  162  of cable  160 , center conductor  156  may be coupled to center conductor  94  of coaxial cable  92  (or other transmission line) through capacitor  164  or other coupling circuitry. The outer ground conductor of cable  160  at end  162  may be coupled to ground antenna feed terminal  100 . Positive antenna feed terminal  98  in feed  112  may be coupled to resonating element  108  (e.g., the segment of peripheral conductive housing structure that stretches between the left-hand and right-hand peripheral gaps  18  of  FIG. 6 ). 
     The response of antenna  40  when device  10  is held in the hand of a user is shown in  FIG. 7 . In the graph of  FIG. 7 , antenna performance for antenna  40  (e.g., standing wave ratio SWR) has been plotted as a function of operating frequency f. As shown in  FIG. 7 , antenna  40  operates in a low band at frequency f 1 , a midband at frequency f 2 , and a high band at frequency f 3 . Low band operation is most influenced by the presence or absence of contact between the user&#39;s hand and device  10  (e.g., hand contact overlapping gap  18  of antenna  40 , etc.). In free space, low band performance of antenna  40  may be characterized by curve  170 . When a user holds device  10 , there is a potential for the user&#39;s hand to load antenna  40  and thereby detune antenna  40 , as described in connection with  FIG. 4 . Due to the presence of electrode  154 , however, the capacitance rise or other impedance change that is produced when the user&#39;s hand overlaps gap  18 , is conveyed from electrode  154  to feed  112  by cable  160 . As a result, antenna performance improves rather than being adversely affected by the presence of the user&#39;s hand. Antenna  40  is effectively retuned and detuning is prevented as shown by curve  172  ( FIG. 7 ). The ability of the configuration of  FIG. 6  to convey the increase in capacitance (or other effects) due to the user&#39;s hand from hand capacitance sensing electrode  154  to antenna feed  112  and thereby retune the antenna allows device  10  to maintain a desired level of antenna performance or to improve antenna performance when the user&#39;s hand is adjacent to antenna  40  (i.e., gap  18  and electrode  154 ). 
     The foregoing is merely illustrative and various modifications can be made by those skilled in the art without departing from the scope and spirit of the described embodiments. The foregoing embodiments may be implemented individually or in any combination.

Metadata:
Filing Date: 20140929
Publication Date: 20170103
Grant Date: 20170103
Priority Date: 20140929
Inventors: AYALA VAZQUEZ ENRIQUE
PASCOLINI MATTIA
HU HONGFEI
IRCI ERDINC
OUYANG YUEHUI
EDWARDS JENNIFER M.
NATH JAYESH
YARGA SALIH
ZHOU YIJUN
XU HAO
Assignee: APPLE INC
CPC Classifications: [{"code": "H01Q5/328", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q9/42", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q9/0442", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01Q1/243", "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": "H01Q1/243", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q9/42", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q9/0442", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 55585447