PATENT DOCUMENT

Publication Number: US-10355339-B2
Application Number: US-201615085095-A
Country: US
Kind Code: B2

Title: Tunable antenna with slot-based parasitic element

Abstract:
Electronic devices may be provided that contain wireless communications circuitry. The wireless communications circuitry may include radio-frequency transceiver circuitry and antenna structures. The antenna structures may form a dual arm inverted-F antenna. The antenna may have a resonating element formed from portions of a peripheral conductive electronic device housing member and may have an antenna ground that is separated from the antenna resonating element by a gap. A short circuit path may bridge the gap. An antenna feed may be coupled across the gap in parallel with the short circuit path. Low band tuning may be provided using an adjustable inductor that bridges the gap. The antenna may have a slot-based parasitic antenna resonating element with a slot formed between portions of the peripheral conductive electronic device housing member and the antenna ground. An adjustable capacitor may bridge the slot to provide high band tuning.

Claims:
What is claimed is: 
     
       1. An electronic device, comprising:
 a housing having peripheral conductive structures; 
 first and second dielectric gaps formed on opposing sides of the electronic device that divide the peripheral conductive housing structures; 
 an antenna resonating element formed from a segment of the peripheral conductive structures located between the first and second dielectric gaps; 
 an antenna ground; 
 an antenna feed having a first antenna feed terminal coupled to the segment and a second antenna feed terminal coupled to the antenna ground; 
 a parasitic antenna resonating element formed between the segment of the peripheral conductive structures and the antenna ground; and 
 an adjustable component that is coupled to the segment and the antenna ground and that overlaps the parasitic antenna resonating element. 
 
     
     
       2. The electronic device defined in  claim 1 , wherein the parasitic antenna resonating element resonates in a first frequency band, the antenna resonating element comprising:
 a first arm that resonates in a second frequency band that is lower than the first frequency band; and 
 a second arm that resonates in a third frequency band that is lower than the second frequency band. 
 
     
     
       3. The electronic device defined in  claim 2 , wherein the parasitic antenna resonating element is formed between the second arm of the antenna resonating element and the antenna ground. 
     
     
       4. The electronic device defined in  claim 3 ,
 wherein the adjustable component is coupled to the second arm of the antenna resonating element. 
 
     
     
       5. The electronic device defined in  claim 1 , wherein the parasitic antenna resonating element is located between the antenna feed and the first dielectric gap and the antenna feed is located between the parasitic antenna resonating element and the second dielectric gap. 
     
     
       6. The electronic device defined in  claim 1 , further comprising:
 an additional adjustable component coupled to the segment of the peripheral conductive structures and the antenna ground. 
 
     
     
       7. The electronic device defined in  claim 1 , wherein the adjustable component comprises an adjustable inductor. 
     
     
       8. The electronic device defined in  claim 1 , wherein the parasitic antenna resonating element has a first portion that extends along a first longitudinal axis and a second portion that extends from an end of the first portion and along a second longitudinal axis that is substantially perpendicular to the first longitudinal axis. 
     
     
       9. The electronic device defined in  claim 8 , wherein the parasitic antenna resonating element further comprises a third portion that extends along a third longitudinal axis that is substantially parallel to the first longitudinal axis. 
     
     
       10. An antenna, comprising:
 an antenna resonating element formed from a metal electronic device housing structure that has a first arm that resonates in a first frequency band and a second arm that resonates in a second frequency band that is greater than the first frequency band; 
 an antenna ground that is separated from the antenna resonating element; 
 a parasitic antenna resonating element that resonates in a third frequency band that is greater than the second frequency band; and 
 an adjustable component that is coupled to the first arm and the antenna ground, that bridges and overlaps the parasitic antenna resonating element, and that is configured to adjust the first frequency band in which the first arm resonates. 
 
     
     
       11. The antenna defined in  claim 10 , wherein the parasitic antenna resonating element has a first portion that extends along a first longitudinal axis and a second portion that extends along a second longitudinal axis that is substantially perpendicular to the first longitudinal axis. 
     
     
       12. The antenna defined in  claim 10 , wherein the parasitic antenna resonating element is interposed between the first arm and the antenna ground. 
     
     
       13. The antenna defined in  claim 10 , wherein the parasitic antenna resonating element comprises a slot that resonates in the third frequency band and the adjustable component bridges the slot. 
     
     
       14. An electronic device, comprising:
 an antenna ground; 
 an antenna resonating element formed from a metal electronic device housing structure that extends across a width of the electronic device, wherein the antenna resonating element has a low band arm that resonates in a first frequency band and a high band arm that resonates in a second frequency band that is greater than the first frequency band; 
 an antenna feed having a first antenna feed terminal coupled to the antenna resonating element and a second antenna feed terminal coupled to the antenna ground; and 
 a parasitic antenna resonating element formed between the low band arm and the antenna ground, wherein the parasitic antenna resonating element is indirectly fed by the antenna resonating element via near-field electromagnetic coupling. 
 
     
     
       15. The electronic device defined in  claim 14 , wherein the parasitic antenna resonating element resonates in a third frequency band that is greater than the second frequency band. 
     
     
       16. The electronic device defined in  claim 14 , wherein the parasitic antenna resonating element comprises a slot having a first edge defined by the antenna ground and an opposing second edge defined by the low band arm. 
     
     
       17. The electronic device defined in  claim 14 , wherein the electronic device has a length and a height, and the width is less than the length and greater than the height. 
     
     
       18. The electronic device defined in  claim 14 , wherein the parasitic antenna resonating element is indirectly fed by the low band arm. 
     
     
       19. The electronic device defined in  claim 14 , further comprising an adjustable component that is coupled to the low band arm and the antenna ground and that overlaps the parasitic antenna resonating element.

Description:
This application is a continuation of U.S. patent application Ser. No. 13/846,471, filed Mar. 18, 2013. This application claims the benefit of and claims priority to U.S. patent application Ser. No. 13/846,471, filed Mar. 18, 2013, which is hereby incorporated by reference herein in its entirety. 
    
    
     BACKGROUND 
     This relates generally to electronic devices, and more particularly, to antennas for electronic devices with wireless communications circuitry. 
     Electronic devices such as portable computers and cellular telephones are often provided with wireless communications capabilities. For example, electronic devices may use long-range wireless communications circuitry such as cellular telephone circuitry to communicate using cellular telephone bands. Electronic devices may use short-range wireless communications circuitry such as wireless local area network communications circuitry to handle communications with nearby equipment. Electronic devices may also be provided with satellite navigation system receivers and other wireless circuitry. 
     To satisfy consumer demand for small form factor wireless devices, manufacturers are continually striving to implement wireless communications circuitry such as antenna components using compact structures. At the same time, it may be desirable to include conductive structures in an electronic device such as metal device housing components. Because conductive components can affect radio-frequency performance, care must be taken when incorporating antennas into an electronic device that includes conductive structures. Moreover, care must be taken to ensure that the antennas and wireless circuitry in a device are able to exhibit satisfactory performance over a range of operating frequencies. 
     It would therefore be desirable to be able to provide improved wireless communications circuitry for wireless electronic devices. 
     SUMMARY 
     Electronic devices may be provided that contain wireless communications circuitry. The wireless communications circuitry may include radio-frequency transceiver circuitry and antenna structures. The antenna structures may form a dual arm inverted-F antenna. The transceiver circuitry may be coupled to the dual arm inverted-F antenna by a transmission line. 
     The antenna may have a dual arm inverted-F antenna resonating element formed from portions of a peripheral conductive electronic device housing structure and may have an antenna ground that is separated from the antenna resonating element by a gap. A short circuit path may bridge the gap. An antenna feed may be coupled across the gap in parallel with the short circuit path. 
     Low band tuning may be provided using an adjustable inductor that bridges the gap. The adjustable inductor may include a series of fixed inductors and switching circuitry that is configured to tune the antenna by switching a selected one of the fixed inductors into use. 
     The antenna may have a slot-based parasitic antenna resonating element with a slot that is formed between portions of the peripheral conductive electronic device housing member and the antenna ground. An adjustable capacitor may bridge the slot to provide high band tuning. 
     Further features of the invention, its nature and various advantages will be more apparent from the accompanying drawings and the following detailed description of the preferred embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an illustrative electronic device with wireless communications circuitry in accordance with an embodiment of the present invention. 
         FIG. 2  is a schematic diagram of an illustrative electronic device with wireless communications circuitry in accordance with an embodiment of the present invention. 
         FIG. 3  is a diagram of an illustrative tunable antenna in accordance with an embodiment of the present invention. 
         FIG. 4  is a diagram of an illustrative adjustable capacitor of the type that may be used in tuning an antenna in an electronic device in accordance with an embodiment of the present invention. 
         FIG. 5  is a diagram of an illustrative adjustable single-element inductor that may be used in tuning an antenna in an electronic device in accordance with an embodiment of the present invention. 
         FIG. 6  is a diagram of an illustrative adjustable multi-element inductor in accordance with an embodiment of the present invention. 
         FIG. 7  is a diagram of an illustrative tunable electronic device antenna having an antenna resonating element that is formed from a portion of a peripheral conductive housing member and having a slot-based parasitic resonating element and tuning capabilities provided by adjustable inductor and adjustable capacitor circuitry in accordance with an embodiment of the present invention. 
         FIG. 8  is a graph of antenna performance as a function of frequency for a tunable antenna of the type shown in  FIG. 7  in accordance with an embodiment of the present invention. 
         FIG. 9  is a diagram of an illustrative tunable electronic device antenna having an antenna resonating element that is formed from a portion of a peripheral conductive housing member and having tuning capabilities provided by an adjustable inductor in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Electronic devices such as electronic device  10  of  FIG. 1  may be provided with wireless communications circuitry. The wireless communications circuitry may be used to support wireless communications in multiple wireless communications bands. The wireless communications circuitry may include one or more antennas. 
     The antennas 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 a peripheral conductive member that runs around the periphery of an electronic device. The peripheral conductive member may serve as a bezel for a planar structure such as a display, may serve as sidewall structures for a device housing, and/or may form other housing structures. Gaps in the peripheral conductive member may be associated with the antennas. 
     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 cellular telephone, or a media player. 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, for example, be a touch screen that incorporates capacitive touch electrodes. 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 cover glass layer may cover the surface of display  14 . Buttons such as button  19  may pass through openings in the cover glass. The cover glass 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, structures  16  may be implemented using a peripheral housing member have a rectangular ring shape (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 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, 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. If desired, 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 ). In the example of  FIG. 1 , peripheral housing structures  16  have substantially straight vertical sidewalls. This is merely illustrative. The sidewalls formed by peripheral housing structures  16  may be 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 left and right 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. 
     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 may be located in the center of housing  12  under display  14  (as an example). 
     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 structures such as conductive housing midplate or rear housing wall structures, a conductive ground plane associated with a printed circuit board, and conductive electrical components in 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  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 . 
     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, 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 such 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 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 . 
     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 of an illustrative configuration that may be used for electronic device  10  is shown in  FIG. 2 . As shown in  FIG. 2 , electronic device  10  may include control circuitry such as storage and processing circuitry  28 . Storage and processing circuitry  28  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  28  may be used to control the operation of device  10 . The processing circuitry may be based on one or more microprocessors, microcontrollers, digital signal processors, baseband processors, power management units, audio codec chips, application specific integrated circuits, etc. 
     Storage and processing circuitry  28  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  28  may be used in implementing communications protocols. Communications protocols that may be implemented using storage and processing circuitry  28  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, etc. 
     Circuitry  28  may be configured to implement control algorithms that control the use of antennas in device  10 . For example, circuitry  28  may perform signal quality monitoring operations, sensor monitoring operations, and other data gathering operations and may, in response to the gathered data and information on which communications bands are to be used in device  10 , control which antenna structures within device  10  are being used to receive and process data and/or may adjust one or more switches, tunable elements, or other adjustable circuits in device  10  to adjust antenna performance. As an example, circuitry  28  may control which of two or more antennas is being used to receive incoming radio-frequency signals, may control which of two or more antennas is being used to transmit radio-frequency signals, may control the process of routing incoming data streams over two or more antennas in device  10  in parallel, may tune an antenna to cover a desired communications band, etc. In performing these control operations, circuitry  28  may open and close switches, may turn on and off receivers and transmitters, may adjust impedance matching circuits, may configure switches in front-end-module (FEM) radio-frequency circuits that are interposed between radio-frequency transceiver circuitry and antenna structures (e.g., filtering and switching circuits used for impedance matching and signal routing), may adjust switches, tunable circuits, and other adjustable circuit elements that are formed as part of an antenna or that are coupled to an antenna or a signal path associated with an antenna, and may otherwise control and adjust the components of device  10 . 
     Input-output circuitry  30  may be used to allow data to be supplied to device  10  and to allow data to be provided from device  10  to external devices. Input-output circuitry  30  may include input-output devices  32 . Input-output devices  32  may include touch screens, buttons, joysticks, click wheels, scrolling wheels, touch pads, key pads, keyboards, microphones, speakers, tone generators, vibrators, cameras, sensors, light-emitting diodes and other status indicators, data ports, etc. A user can control the operation of device  10  by supplying commands through input-output devices  32  and may receive status information and other output from device  10  using the output resources of input-output devices  32 . 
     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, 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 satellite navigation system receiver circuitry such as Global Positioning System (GPS) receiver circuitry  35  (e.g., for receiving satellite positioning signals at 1575 MHz) or satellite navigation system receiver circuitry associated with other satellite navigation systems. Wireless local area network transceiver circuitry such as 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 cellular telephone bands such as bands in frequency ranges of about 700 MHz to about 2700 MHz or bands at higher or lower frequencies. 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. Near field communications may also be supported (e.g., at 13.56 MHz). 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 one or more 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, dual arm inverted-F antenna structures, closed and open slot antenna structures, planar inverted-F antenna structures, helical antenna structures, strip antennas, monopoles, dipoles, 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 structures in device  10  such as one or more of antennas  40  may be provided with one or more antenna feeds, fixed and/or adjustable components, and optional parasitic antenna resonating elements so that the antenna structures cover desired communications bands. 
     An illustrative antenna of the type that may be used in device  10  (e.g., in region  20  and/or region  22 ) is shown in  FIG. 3 . The illustrative antenna of  FIG. 3  uses a design of the type that is sometimes referred to as a dual arm inverted-F antenna or T antenna. As shown in  FIG. 3 , antenna  40  may have conductive antenna structures such as dual arm inverted-F antenna resonating element  50 , optional parasitic antenna resonating element  54 , and antenna ground  52 . The conductive structures that form antenna resonating element  50 , parasitic antenna resonating element  54 , and antenna ground  52  may be formed from parts of conductive housing structures, from parts of electrical device components in device  10 , from printed circuit board traces, from strips of conductor such as strips of wire and metal foil, or other conductive materials. 
     As shown in  FIG. 3 , transceiver circuitry  90  may be coupled to antenna  40  using transmission line structures such as transmission line  92 . Transmission line  92  may have positive signal path  92 A and ground signal path  92 B. Paths  92 A and  92 B may be formed from metal traces on rigid printed circuit boards, may be formed from metal traces on flexible printed circuits, may be formed on dielectric support structures such as plastic, glass, and ceramic members, may be formed as part of a cable, etc. Transmission line  92  may be formed using one or more microstrip transmission lines, stripline transmission lines, edge coupled microstrip transmission lines, edge coupled stripline transmission lines, coaxial cables, or other suitable transmission line structures. Circuits such as impedance mating circuits, filters, switches, duplexers, diplexers, and other circuitry may, if desired, be interposed in transmission line path  92 . 
     Transmission line  92  may be coupled to an antenna feed formed from antenna feed terminals such as positive antenna feed terminal  94  and ground antenna feed terminal  96 . Antenna resonating element  50  may include a short circuit branch such as branch  98  that couples resonating element arm structures such as arms  100  and  102  to antenna ground  52 . Dielectric gap  101  separates arms  100  and  102  from antenna ground  52 . Antenna ground  52  may be formed from housing structures such as a metal midplate member, printed circuit traces, metal portions of electronic components, or other conductive ground structures. Gap  101  may be formed by air, plastic, and other dielectric materials. Feed path  104  contains the antenna feed formed from feed terminals  94  and  96  and is coupled between the resonating element arm structures and antenna ground  52  in parallel with short circuit path  98 . Resonating element arms  100  and  102  may have one or more bends. The illustrative arrangement of  FIG. 3  in which arms  100  and  102  run parallel to ground  52  is merely illustrative. 
     Low-band arm  100  may allow antenna  40  to exhibit an antenna resonance at low band (LB) frequencies (e.g., 700 MHz to 960 MHz or other suitable frequencies). High-band arm  102  may allow antenna  40  to exhibit one or more antenna resonances at high band (HB) frequencies (e.g., resonances at frequencies between 960 MHz to 2700 MHz or other suitable frequencies). 
     If desired, antenna  40  may include optional parasitic antenna resonating elements such as parasitic antenna resonating element  54 . Parasitic antenna resonating element  54  is coupled to antenna resonating element  50  by near-field electromagnetic coupling and is used to modify the frequency response of antenna  40  so that antenna  40  operates at desired frequencies. 
     In the example of  FIG. 3 , parasitic antenna resonating element  54  is based on a slot antenna resonating element structure. Slot-type resonating element structures may include open slot structures (i.e., slots with one open end and one closed end) and closed slot structures (i.e., slots that are completely surrounded by metal). Slots for a slot-based parasitic antenna resonating element may be formed between opposing metal structures in antenna resonating element  50  and/or antenna ground  52 . Plastic, air, or other dielectric may fill the interior of a slot. Slots are typically elongated (i.e., their lengths are substantially longer than their widths). Metal surrounds the periphery of the slot. In an open slot, one of the ends of the slot is open to surrounding dielectric. 
     To provide antenna  40  with tuning capabilities, antenna  40  may include adjustable circuitry. The adjustable circuitry may form part of antenna resonating element  50 , optional parasitic elements such as parasitic antenna resonating element  54 , or the structures of antenna ground  52 . 
     As shown in  FIG. 3 , for example, parasitic antenna resonating element  54  may be a tunable parasitic resonating element that includes adjustable circuitry such as adjustable capacitor  106 . The adjustable circuitry of tunable slot-based parasitic antenna resonating element  54  such as adjustable capacitor  106  may be tuned using control signals from control circuitry  28  ( FIG. 2 ). Control signals may from control circuitry  28  may, for example, be provided to tunable slot-based parasitic antenna resonating element using control input path  108  to adjust the capacitance exhibited by adjustable capacitor  106 . By selecting a desired capacitance value for capacitor  106  using control signals on path  108 , antenna  40  can be tuned to cover operating frequencies of interest. 
     If desired, the adjustable circuitry of antenna  40  may include one or more adjustable circuits that are coupled to antenna resonating element structures  50  such as arms  102  and  100  in antenna resonating element  50 . As shown in  FIG. 3 , for example, adjustable inductor  110  may be coupled between antenna resonating element arm structures in antenna  40  such as arm  100  (or arm  102 ) and antenna ground  52  (i.e., inductor  110  may bridge gap  101 ). Adjustable inductor  110  may exhibit an inductance value that is adjusted in response to control signals provided to control input  112  of adjustable inductor  110  from control circuitry  28 . 
     During operation of device  10 , control circuitry such as storage and processing circuitry  28  of  FIG. 2  may make antenna adjustments by providing control signals to adjustable components such as adjustable inductors, adjustable capacitors, adjustable resistors, switches, switches in adjustable inductors, adjustable capacitors, and adjustable resistors, adjustable components such as variable inductors, varactors, and variable resistors, adjustable circuits that include combinations of two or more of these components and/or fixed inductors, capacitors, and resistors, or by providing control signals to other adjustable circuitry. Antenna frequency response adjustments may be made in real time in response to information identifying which communications bands are active, in response to feedback related to signal quality or other performance metrics, sensor information, or other information. 
       FIG. 4  is a schematic diagram of an illustrative adjustable capacitor circuit. Adjustable capacitor  106  of  FIG. 4  produces an adjustable amount of capacitance between terminals  114  and  116  in response to control signals provided to input path  108 . Switching circuitry  118  has two terminals coupled respectively to capacitors C 1  and C 2  and has another terminal coupled to terminal  116  of adjustable capacitor  106 . Capacitor C 1  is coupled between terminal  114  and one of the terminals of switching circuitry  118 . Capacitor C 2  is coupled between terminal  114  and the other terminal of switching circuitry  118  in parallel with capacitor C 1 . By controlling the value of the control signals supplied to control input  108 , switching circuitry  118  may be configured to produce a desired capacitance value. For example, switching circuitry  118  may be configured to switch capacitor C 1  into use or may be configured to switch capacitor C 2  into use. 
     If desired, switching circuitry  118  may include one or more switches or other switching resources that selectively decouple capacitors C 1  and C 2  (e.g., by forming an open circuit so that the path between terminals  114  and  116  is an open circuit and both capacitors are switched out of use). Switching circuitry  118  may also be configured (if desired) so that both capacitors C 1  and C 2  can be simultaneously switched into use. Other types of switching circuitry  118  such as switching circuitry that exhibits fewer switching states or more switching states may be used if desired. Adjustable capacitors such as adjustable capacitor  106  may also be implemented using variable capacitor devices (sometimes referred to as varactors). The configuration of  FIG. 4  is merely illustrative. 
       FIG. 5  is a schematic diagram of adjustable inductor circuitry  110 . In the  FIG. 5  example, adjustable indictor circuitry  110  can be adjusted to produce different amounts of inductance between terminals  112  and  124 . Switch  120  is controlled by control signals on control input  112 . When switch  120  is placed in a closed state, inductor L is switched into use and adjustable inductor  110  exhibits an inductance L between terminals  122  and  124 . When switch  120  is placed in an open state, inductor L is switched out of use and adjustable inductor  110  exhibits an essentially infinite amount of inductance between terminals  122  and  124 . 
       FIG. 6  is a schematic diagram of adjustable inductor circuitry  110  in a configuration in which multiple inductors are used in providing an adjustable amount of inductance. Adjustable inductor circuitry  110  of  FIG. 6  can be adjusted to produce different amounts of inductance between terminals  112  and  124  by controlling the state of switching circuitry such as switch  120  (e.g., a single pole double throw switch) using control signals on control input  112 . For example, control signals on path  112  may be used to switch inductor L 1  into use between terminals  122  and  124  while switching inductor L 2  out of use, may be used to switch inductor L 2  into use between terminals  122  and  124  while switching inductor L 1  out of use, may be used to switch both inductors L 1  and L 2  into use in parallel between terminals  122  and  124 , or may be used to switch both inductors L 1  and L 2  out of use. The switching circuitry arrangement of adjustable inductor  110  of  FIG. 6  is therefore able to produce one or more different inductance values, two or more different inductance values, three or more different inductance values, or, if desired, four different inductance values (e.g., L 1 , L 2 , L 1  and L 2  in parallel, or infinite inductance when L 1  and L 2  are switched out of use simultaneously). 
       FIG. 7  is a diagram of an illustrative antenna of the type that may be implemented using conductive housing structures in electronic device  10 . As shown in  FIG. 7 , dual arm inverted-F antenna resonating element  50  may be formed from portions of peripheral conductive housing structures  16 . In particular, resonating element arm portion  102  for producing an antenna response in a high band (HB) frequency range and resonating element arm portion  100  for producing an antenna response in a low band (LB) frequency range may be formed from respective portions of peripheral conductive housing structures  16 . Antenna ground  52  may be formed from sheet metal (e.g., one or more housing midplate members and/or a rear housing wall in housing  12 ), may be formed from portions of printed circuits, may be formed from conductive device components, or may be formed from other metal portions of device  10 . 
     Antenna  40  may be fed by an antenna feed coupled in feed path  104 . Feed path  104  may include an antenna feed formed from antenna feed terminals such as positive antenna feed terminal  94  and ground antenna feed terminal  96 . Transmission line  92  ( FIG. 3 ) may have a positive signal line coupled to terminal  94  and a ground signal line coupled to terminal  96 . Impedance matching circuits such as matching circuit  130  and other circuitry (e.g., filters, switches, etc.) may be incorporated into feed path  104  or transmission line  92  if desired). 
     Slot-based parasitic antenna resonating element  54  is formed from slot  132 . Slot  132  is surrounded by conductive structures such as metal housing structures  16  and other housing structures  12  (e.g., metal parts that form antenna ground  52 ), printed circuit traces, and electrical components and is filled with dielectric (e.g., air, plastic, glass, and/or other dielectric materials). Inner edge  134  of slot  132  may, for example, be formed from portions of antenna ground  52 . Outer edge  136  of slot  132  may be formed from portions of peripheral conductive housing structures  16  (e.g., portions of resonating element arm  100 ). 
     As shown in  FIG. 7 , slot  132  has an elongated shape in which its width (i.e., the distance between edges  134  and  136 ) is substantially less than its length. Dashed line  142  shows how slot  132  extends from closed slot end  138  where slot  132  is bordered by conductive portions of antenna ground  52  to open slot end  140  where slot  132  is open to surrounding dielectric. With this type of configuration, slot  132  is characterized by bend  144  where slot  132  wraps around corner  144  of device  10  and is characterized by bend  146  where slot  132  departs from the periphery of device  10  and extends between opposing edges of antenna ground  52  towards closed end  138 . 
     The length of slot  132 , which affects the resonant frequency associated with slot  132 , may be about 1-5 cm (as examples). With one suitable arrangement, the length of slot  132  is selected to create a resonant peak for slot  132  at about 3.5 GHz. This peak is located at a higher frequency range than typically desired for wireless communications in device  10 . However, in the presence of adjustable capacitor  106  bridging slot  132  between peripheral conductive housing structures  16  and antenna ground  52 , the resonant peak associated with parasitic resonating element slot  132  is shifted from 3.5 GHz to lower frequencies (e.g., frequencies in the range of about 2300 MHz to 2700 MHz). Adjustable capacitor  106  can be adjusted to tune the resonant frequency of the slot-based parasitic resonating element so that antenna  40  covers all frequencies of interest in the vicinity of the shifted resonance from slot-based parasitic antenna resonating element  54 . Adjustable inductor  110  affects primarily low band performance for antenna  40  and can be adjusted to ensure that antenna  40  covers all low band frequencies of interest. 
     The presence of slot-based parasitic antenna resonating element  54  may help spatially distribute radio-frequency energy across the entire width of device  10  during operation of device  10  at high band frequencies. Spatially distributing radio-frequency signals in this way may help ensure that device  10  complies with regulatory limits on emitted radiation levels. In the absence of element  54 , emitted energy at high frequencies may be concentrated in the vicinity of high band resonating element arm  102 . In the presence of slot-based parasitic antenna resonating element  54 , energy tends to be concentrated near arm  102  at lower high band frequencies and at element  54  at higher high band frequencies, so that emitted energy is distributed across the width of device  10  when averaged over high band frequencies. 
       FIG. 8  is a graph in which antenna performance (i.e., standing wave ratio SWR) has been plotted as a function of operating frequency f. As shown in  FIG. 8 , antenna  40  may exhibit resonance  200 . Slot-based parasitic antenna resonating element  54  may produce a resonant contribution at a relatively high frequency (e.g. 3.5 GHz). When adjustable capacitor  106  bridges slot  54  to couple edge  134  of antenna ground  52  to arm  100  (i.e., when arm  100  is coupled to ground  52  by adjustable capacitor  106 ), the resonance from slot-based parasitic antenna resonating element  54  may be shifted to the position shown in  FIG. 8  (e.g., a position such as position  200  that covers frequencies such as frequencies from 2500 MHz to 2700 MHz for supporting operations in communications bands such as Long Term Evolution (LTE) band  38 ). In this position, capacitor  106  may exhibit a first capacitance (e.g., a capacitance C 1  of 0.6 pF). 
     When it is desired to operate at lower frequencies such as frequencies associated with resonant peak position  202  of  FIG. 8  (e.g., frequencies such as frequencies from 2300 MHz to 2500 MHz to cover communications bands such as LTE band  40 ), adjustable capacitor  106  may be adjusted to exhibit a second capacitance (e.g., a capacitance C 2  of 0.8 pF). When capacitor  106  is adjusted to produce a capacitance of 0.8 pF (in this example), resonant peak  200  shifts to the position of resonant peak  202 . Adjustable capacitor  106  therefore provides sufficient tuning to allow the slot-based parasitic antenna resonating element resonance from slot  54  to cover a range of frequencies from about 2300 MHz to about 2700 MHz (in this example). 
     High band resonance HB (e.g., frequencies from about 1710 MHz to 2000 MHz) may be covered by an antenna resonance contribution produced by high band arm  102  of antenna  40 . Low band arm  100  may produce a resonance that is used in covering low band frequencies LB. Adjustable inductor  110  is coupled across gap  101  between low band resonating element arm  100  and antenna ground  52 . The value of inductance produced by an adjustable inductor that bridges gap  101  such as adjustable inductor  110  is used in tuning antenna  40  in low band LB. 
     In the illustrative arrangement of  FIG. 8 , inductor  110  is being adjusted between three different states each associated with a different corresponding inductance value. Inductor  110  may be, for example, an adjustable inductor of the type shown in  FIG. 6  in which L 1  has a value of 12 nH and in which L 2  has a value of 51 nH. 
     When switching circuitry  120  of  FIG. 6  is placed in a position in which L 1  and L 2  are both switched into use in parallel, the inductance of inductor  110  will be about 10 nH. In this situation, antenna  40  (e.g., arm  100 ) will produce resonance peak  208 . When switching circuitry  120  of  FIG. 6  is placed in a configuration in which L 2  is switched into use and L 1  is switched out of use, inductor  110  will exhibit an inductance of about 51 nH and antenna  40  will produce resonance peak  206  (which is peak  208  shifted to a lower frequency). Switching circuitry  120  of  FIG. 6  can also be adjusted so that both inductors L 1  and L 2  are switched out of use. In this situation, the inductance of inductor  110  will be high (effectively infinite) and antenna  40  will exhibit resonance peak  204  (which is peak  206  shifted to a lower frequency). The ability to tune the antenna resonance exhibited by low band antenna resonating element arm  100  allows antenna  40  to cover all desired frequencies of interested in low band LB (e.g., all frequencies of interest from about 700 MHz to about 960 MHz, as an example). 
     In situations in which it is not desired to cover communications frequencies in the range of 2300 to 2700 MHz, slot-based parasitic antenna resonating element  54  may be omitted from antenna  40 , as shown in  FIG. 9 . In this configuration, antenna  40  may exhibit the resonances of low band LB and high band HB that are shown in  FIG. 8  without exhibiting resonances  200  and  202  associated with slot-based parasitic antenna resonating element  54 . 
     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: 20160330
Publication Date: 20190716
Grant Date: 20190716
Priority Date: 20130318
Inventors: JIN, NANBO
OUYANG, Yuehui
ZHOU, YIJUN
AYALA VAZQUEZ, ENRIQUE
LAKSHMANAN, ANAND
SCHLUB, ROBERT W.
PASCOLINI, MATTIA
MOW, MATTHEW A.
Assignee: APPLE INC
CPC Classifications: [{"code": "H01Q21/28", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q1/24", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01Q5/15", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q5/314", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q1/243", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q9/06", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q13/10", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01Q5/10", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q1/243", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01Q5/10", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q21/28", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q13/10", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01Q1/24", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01Q5/314", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q5/15", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q5/10", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q1/243", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q9/06", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 50069286