PATENT DOCUMENT

Publication Number: US-9337537-B2
Application Number: US-201313890013-A
Country: US
Kind Code: B2

Title: Antenna with tunable high band parasitic element

Abstract:
Electronic devices may be provided that include radio-frequency transceiver circuitry and antennas. An antenna may be formed from an antenna resonating element and an antenna ground. The antenna resonating element may have a shorter portion that resonates at higher communications band frequencies and a longer portion that resonates at lower communications band frequencies. The resonating element may be formed from a peripheral conductive electronic device housing structure that is separated from the antenna ground by an opening. A parasitic monopole antenna resonating element or parasitic loop antenna resonating element may be located in the opening. Antenna tuning in the higher communications band may be implemented using an adjustable inductor in the parasitic element. Antenna tuning in the lower communications band may be implemented using an adjustable inductor that couples the antenna resonating element to the antenna ground.

Claims:
What is claimed is: 
     
       1. An electronic device, comprising:
 control circuitry; 
 an antenna that is tuned by the control circuitry, wherein the antenna has an antenna resonating element and an antenna ground configured to resonate in at least a first communications band and a second communications band that is higher in frequency than the first communications band, and the antenna has a parasitic monopole antenna resonating element; and 
 a peripheral conductive housing member, wherein the antenna resonating element comprises a portion of the peripheral conductive housing member. 
 
     
     
       2. The electronic device defined in  claim 1  further comprising an adjustable electrical component in the parasitic monopole antenna resonating element that is adjusted by the control circuitry. 
     
     
       3. The electronic device defined in  claim 2  wherein the adjustable electrical component comprises an adjustable inductor. 
     
     
       4. The electronic device defined in  claim 1  wherein the peripheral conductive housing member is separated from the antenna ground by an opening and wherein the parasitic monopole antenna resonating element is located in the opening. 
     
     
       5. The electronic device defined in  claim 4  wherein the parasitic monopole antenna resonating element comprises an L-shaped resonating element having a first end coupled to the antenna ground and an opposing second end that is floating in the opening. 
     
     
       6. An electronic device, comprising:
 control circuitry; 
 an antenna that is tuned by the control circuitry, wherein the antenna has an antenna resonating element and an antenna ground configured to resonate in at least a first communications band and a second communications band that is higher in frequency than the first communications band, and the antenna has a parasitic monopole antenna resonating element; 
 an adjustable electrical component in the parasitic monopole antenna resonating element that is adjusted by the control circuitry, wherein the adjustable electrical component comprises an adjustable inductor; and 
 an additional adjustable inductor coupled between the antenna resonating element and the antenna ground, wherein the adjustable inductor tunes the antenna in the second communications band and the additional adjustable inductor tunes the antenna in the first communications band. 
 
     
     
       7. The electronic device defined in  claim 6  further comprising:
 a first gap between the antenna resonating element and the antenna ground that is associated with a first capacitance; 
 a first inductor coupled across the first gap; 
 a second gap between the antenna resonating element and the antenna ground that is associated with a second capacitance; and 
 a second inductor that is coupled across the second gap. 
 
     
     
       8. The electronic device defined in  claim 7  wherein the antenna resonating element comprises a dual arm inverted-F antenna resonating element, the electronic device further comprising an antenna feed coupled between the antenna ground and the dual arm inverted-F antenna resonating element. 
     
     
       9. An electronic device, comprising:
 control circuitry; and 
 an antenna that is tuned by the control circuitry, wherein the antenna has an antenna resonating element and an antenna ground configured to resonate in at least a first communications band and a second communications band that is higher in frequency than the first communications band, the antenna has a parasitic loop antenna resonating element, and the parasitic loop antenna resonating element has a first end that is coupled to the antenna ground and a second end that is coupled to the antenna ground. 
 
     
     
       10. The electronic device defined in  claim 9  further comprising an adjustable inductor in the parasitic loop antenna resonating element that is adjusted by the control circuitry to tune the antenna. 
     
     
       11. The electronic device defined in  claim 10  further comprising a peripheral conductive housing member, wherein the antenna resonating element comprises a portion of the peripheral conductive housing member. 
     
     
       12. An electronic device, comprising:
 control circuitry; 
 an antenna that is tuned by the control circuitry, wherein the antenna has an antenna resonating element and an antenna ground configured to resonate in at least a first communications band and a second communications band that is higher in frequency than the first communications band, and the antenna has a parasitic loop antenna resonating element; and 
 a peripheral conductive housing member that is separated from the antenna ground by an opening, wherein the antenna resonating element is formed from a segment of the peripheral conductive housing member, and the loop antenna resonating element is located in the opening. 
 
     
     
       13. The electronic device defined in  claim 12  further comprising:
 a first adjustable inductor in the parasitic loop antenna resonating element that is adjusted by the control circuitry to tune the antenna in the second communications band; and 
 a second adjustable inductor that couples the peripheral conductive housing member to the antenna ground and that is adjusted by the control circuitry to tune the antenna in the first communications band. 
 
     
     
       14. The electronic device defined in  claim 13  wherein the peripheral conductive housing member has at least one end that is separated from the antenna ground by a gap, the electronic device further comprising an inductor that is coupled across the gap. 
     
     
       15. An antenna, comprising:
 an inverted-F antenna resonating element; 
 an antenna ground; 
 a parasitic antenna resonating element; and 
 an adjustable inductor in the parasitic antenna resonating element that tunes the antenna, wherein the inverted-F antenna resonating element comprises a portion of a peripheral conductive electronic device housing structure. 
 
     
     
       16. The antenna defined in  claim 15  wherein the antenna is configured to operate in a first communications band and a second communications band at higher frequencies than the first communications band, wherein the parasitic antenna resonating element comprises a parasitic monopole antenna resonating element, and wherein the adjustable inductor tunes the antenna in the second communications band. 
     
     
       17. The antenna defined in  claim 15  wherein the antenna is configured to operate in a first communications band and a second communications band at higher frequencies than the first communications band, wherein the parasitic antenna resonating element comprises a parasitic loop antenna resonating element, and wherein the adjustable inductor tunes the antenna in the second communications band.

Description:
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 structures 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 antennas. An antenna may be formed from an antenna resonating element arm and an antenna ground. The antenna resonating element arm may have a shorter portion that resonates at higher communications band frequencies and a longer portion that resonates at lower communications band frequencies. The resonating element arm may be formed from a peripheral conductive electronic device housing structure that is separated from the antenna ground by an opening. 
     A parasitic monopole antenna resonating element or parasitic loop antenna resonating element may be located in the opening. Antenna tuning in the higher communications band may be implemented using an adjustable inductor in the parasitic element. Antenna tuning in the lower communications band may be implemented using an adjustable inductor that couples the antenna resonating element to the antenna ground. 
     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 top view of an illustrative electronic device of the type shown in  FIG. 1  in which antennas may be formed using conductive housing structures such as portions of a peripheral conductive housing member in accordance with an embodiment of the present invention. 
         FIG. 4  is a circuit diagram showing how an antenna in the electronic device of  FIG. 1  may be coupled to radio-frequency transceiver circuitry in accordance with an embodiment of the present invention. 
         FIG. 5  is a diagram of an illustrative antenna having an antenna resonating element of the type that may be formed from a segment of a peripheral conductive housing member and that has portions that support communications in low and high bands in accordance with an embodiment of the present invention. 
         FIG. 6  is a graph in which antenna performance for a dual band inverted-F antenna has been plotted as a function of operating frequency in accordance with an embodiment of the present invention. 
         FIG. 7  is a diagram of an illustrative adjustable inductor based on a single fixed inductor that may be used in a tunable antenna in accordance with an embodiment of the present invention. 
         FIG. 8  is a diagram of an illustrative adjustable inductor based on multiple fixed inductors that may be used in a tunable antenna in accordance with an embodiment of the present invention. 
         FIG. 9  is a diagram of an illustrative antenna having a parasitic monopole antenna resonating element and adjustable components for providing the antenna with tunable low and high band responses in accordance with an embodiment of the present invention. 
         FIG. 10  is a diagram of an illustrative antenna having a parasitic loop antenna resonating element and adjustable components for providing the antenna with tunable low and high band responses 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 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 display cover layer formed from clear glass, transparent plastic, or other transparent dielectric may cover the surface of display  14 . Buttons such as button  19  may pass through openings in the display cover layer. The cover layer may also have other openings such as an opening for speaker port  26 . 
     Housing  12  may include a peripheral member such as member  16 . Member  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, member  16  may have a rectangular ring shape (as an example). Member  16  or part of member  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 ). Member  16  may also, if desired, form sidewall structures for device  10  (e.g., by forming a metal band with vertical sidewalls surrounding the periphery of device  10 , etc.). 
     Member  16  may be formed of a conductive material and may therefore sometimes be referred to as a peripheral conductive member, peripheral conductive housing member, or conductive housing structures. Member  16  may be formed from a metal such as stainless steel, aluminum, or other suitable materials. One, two, or more than two separate structures (e.g., segments) may be used in forming member  16 . 
     It is not necessary for member  16  to have a uniform cross-section. For example, the top portion of member  16  may, if desired, have an inwardly protruding lip that helps hold display  14  in place. If desired, the bottom portion of member  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 , member  16  has substantially straight vertical sidewalls. This is merely illustrative. The sidewalls of member  16  may be curved or may have any other suitable shape. In some configurations (e.g., when member  16  serves as a bezel for display  14 ), member  16  may run around the lip of housing  12  (i.e., member  16  may cover only the edge of housing  12  that surrounds display  14  and not the rear edge of housing  12  of the sidewalls of housing  12 ). Integral portions of the metal structure that forms member  16  may, if desired, extend across the rear of device  10  (e.g., housing  12  may have a planar rear portion and portions of peripheral conductive member  16  may be formed from sidewall portions of that extend vertically upwards from the planar rear portion). 
     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 member 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 member  16  and opposing conductive structures such as conductive housing structures, a conductive ground plane associated with a printed circuit board, and conductive electrical components in device  10 ). These openings 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, 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 member  16  may be provided with gap structures. For example, member  16  may be provided with one or more gaps such as gaps  18 , as shown in  FIG. 1 . The gaps may be filled with dielectric such as polymer, ceramic, glass, air, other dielectric materials, or combinations of these materials. Gaps  18  may divide member  16  into one or more peripheral conductive member segments. There may be, for example, two segments of member  16  (e.g., in an arrangement with two gaps), three segments of member  16  (e.g., in an arrangement with three gaps), four segments of member  16  (e.g., in an arrangement with four gaps, etc.). The segments of peripheral conductive member  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. Transceiver circuitry  36  may handle wireless local area network communications. For example, 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. 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 structure, patch antenna structures, 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. 
     If desired, one or more of antennas  40  may be provided with tunable circuitry. The tunable circuitry may include switching circuitry based on one or more switches. The switching circuitry may, for example, include a switch that can be placed in an open or closed position. When control circuitry  28  of device  10  places the switch in its open position, an antenna may exhibit a first frequency response. When control circuitry  28  of device  10  places the switch in its closed position, the antenna may exhibit a second frequency response. Tunable circuitry for one or more of antennas  40  may also be based on switching circuitry that can switch selected circuit components into use. For example, an adjustable inductor may operate in a first mode in which a first inductor is switched into use and a second mode in which a second inductor is switched into use. An adjustable inductor may optionally also be switched into a mode in which a short circuit is switched into use or in which an open circuit is formed. 
     Using adjustable inductors such as these or other adjustable circuit components, the performance of antenna  40  may be adjusted in real time to cover operating frequencies of interest. 
     Antenna  40  may exhibit both a low band response and a high band response. As an example, antenna  40  may operate at low band communications frequencies from 700 MHz to 960 MHz and may operate at high band communications frequencies above 1710 MHz (e.g., from 1710-2700 MHz). Adjustment of the state of adjustable inductors or other adjustable circuit components may be used to tune the low band response of the antenna without appreciably affecting the high band response and may be used to tune the high band response of the antenna without appreciably affecting the low band response. The ability to adjust the low and/or high band responses of the antenna may allow the antenna to cover communications frequencies of interest. 
     A top interior view of device  10  in a configuration in which device  10  has a peripheral conductive housing member such as housing member  16  of  FIG. 1  with one or more gaps  18  is shown in  FIG. 3 . As shown in  FIG. 3 , device  10  may have an antenna ground plane such as antenna ground plane  52 . Ground plane  52  may be formed from traces on printed circuit boards (e.g., rigid printed circuit boards and flexible printed circuit boards), from conductive planar support structures in the interior of device  10 , from conductive structures that form exterior parts of housing  12 , from conductive structures that are part of one or more electrical components in device  10  (e.g., parts of connectors, switches, cameras, speakers, microphones, displays, buttons, etc.), or other conductive device structures. Gaps such as gaps (openings)  82  may be filled with air, plastic, or other dielectric. 
     One or more segments of peripheral conductive member  16  may serve as antenna resonating elements for an antenna in device  10 . For example, the uppermost segment of peripheral conductive member  16  in region  22  may serve as an antenna resonating element for an upper antenna in device  10  and the lowermost segment of peripheral conductive member  16  in region  20  (i.e., segment  16 ′, which extends between gap  18 A and gap  18 B) may serve as an antenna resonating element for a lower antenna in device  10 . The conductive materials of peripheral conductive member  16 , the conductive materials of ground plane  52 , and dielectric openings  82  (and gaps  18 ) may be used in forming one or more antennas in device  10  such as an upper antenna in region  22  and a lower antenna in region  20 . Configurations in which an antenna in lower region  20  is implemented using a tunable frequency response configuration are sometimes described herein as an example. 
       FIG. 4  is a diagram showing how a radio-frequency signal path such as path  44  may be used to convey radio-frequency signals between antenna  40  and radio-frequency transceiver  42 . Antenna  40  may be one of antennas  40  of  FIG. 2 . Radio-frequency transceiver  42  may be a receiver and/or transmitter in wireless communications circuitry  34  ( FIG. 3 ) such as receiver  35 , wireless local area network transceiver  36  (e.g., a transceiver operating at 2.4 GHz, 5 GHz, 60 GHz, or other suitable frequency), cellular telephone transceiver  38 , or other radio-frequency transceiver circuitry for receiving and/or transmitting radio-frequency signals. 
     Signal path  44  may include one or more transmission lines such as one or more segments of coaxial cable, one or more segments of microstrip transmission line, one or more segments of stripline transmission line, or other transmission line structures. Signal path  44  may include a positive conductor such as positive signal line  44 A and may include a ground conductor such as ground signal line  44 B. Antenna  40  may have an antenna feed such as feed  92  with a positive antenna feed terminal (+) and a ground antenna feed terminal (−). If desired, circuitry such as filters, impedance matching circuits, switches, amplifiers, and other circuits may be interposed within path  44 . 
       FIG. 5  is a diagram showing how structures such as peripheral conductive member segment  16 ′ of  FIG. 3  may be used in forming antenna  40 . In the illustrative configuration of  FIG. 5 , antenna  40  includes antenna resonating element  90  and antenna ground  52 . Antenna resonating element  90  may have a main resonating element arm portion formed from peripheral conductive member  16 ′ (e.g., a segment of peripheral conductive member  16  of  FIG. 1 ). Gaps such as gaps  18 A and  18 B may be interposed between the ends of resonating element arm structure  16 ′ and ground  52  and may be associated with respective capacitances C 1  and C 2 . Short circuit branch  94  (sometimes referred to as a return path for antenna  40 ) may be coupled between arm structure  16 ′ and ground  52 . Antenna feed branch (antenna feed)  92  may be coupled between arm structure  16 ′ and ground  52  in parallel with short circuit branch  94 . Antenna feed branch  92  may include a positive antenna feed terminal (+) and a ground antenna feed terminal (−). As described in connection with  FIG. 4 , lines  44 A and  44 B in signal path  44  may be respectively coupled to terminals (+) and (−) in antenna feed  92 . 
     Resonating element arm structure  16 ′ may have a longer portion (arm) that is associated with a low band resonance LB and that can be used for handling low band wireless communications. Resonating element arm  16 ′ may also have a shorter portion (arm) that is associated with a high band resonance HB and that can be used for handling high band wireless communications. The low band portion of resonating element arm structure  16 ′ may, for example, be used in handling signals at frequencies of 700 MHz to 960 MHz (as an example). The high band portion of arm structure  16 ′ may, for example, be used in handling signals at frequencies of 1710 MHz to 2700 MHz (as an example). 
     A graph in which antenna performance (e.g., standing wave ratio SWR) for antenna  40  has been plotted as a function of operating frequency f is shown in  FIG. 6 . As shown in  FIG. 6 , antenna  40  may exhibit a low band resonance LB and a high band resonance HB. As indicated by arrows  100 , antenna tuning may be used to ensure that antenna  40  covers low band LB and/or high band HB. Low band LB may lie in a frequency range of about 700 MHz to 960 MHz and high band HB may lie in a frequency range of about 1710 MHz to 2700 MHz. These are merely illustrative low band and high band frequencies of operation for antenna  40 . In general, antenna  40  may be configured to handle any suitable frequencies of interest for device  10 . If desired, one or more adjustable inductors or other tunable circuit elements may be incorporated into antenna  40  to help antenna  40  cover bands LB and HB (e.g., to tune antenna  40  as indicated by arrows  100 ). 
     When tuning is used, antenna  40  may exhibit an antenna resonance that is narrower than the desired frequency band of interest. For example, the resonance in band LB may be narrower than the width of band LB. Tuning of the LB resonance may then be used to ensure that antenna  40  can handle all desired frequencies in band LB. Similarly, the bandwidth of the antenna resonance in band HB may be narrower than band HB, but antenna tuning may be used to move the antenna resonance in band HB as needed during operation to ensure that antenna  40  can cover all frequencies of interest in band HB. 
     Adjustable components may be controlled by control circuitry such as storage and processing circuitry  28  of  FIG. 2 . During operation of device  10 , control circuitry  28  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. 
     Antenna  40  may, if desired, include one or more adjustable inductor circuits that are controlled by control circuitry  28 .  FIG. 7  is a schematic diagram of illustrative adjustable inductor circuitry  110  of the type that may be used in tuning antenna  40 . In the  FIG. 7  example, adjustable inductor circuitry  110  can be adjusted to produce different amounts of inductance between terminals  122  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 open circuit between terminals  122  and  124 . 
       FIG. 8  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. 8  can be adjusted to produce different amounts of inductance between terminals  122  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. 8  is therefore able to produce inductance values such as L 1 , L 2 , an inductance value associated with operating L 1  and L 2  in parallel, and an open circuit (when L 1  and L 2  are switched out of use simultaneously). 
     Antenna  40  may include a parasitic antenna resonating element. The parasitic antenna element may, for example, be used to enhance the frequency response of antenna  40  in high band HB (as an example). Tuning circuitry may be used to tune the resonant behavior of the parasitic antenna resonating element and thereby tune the performance of antenna  40  in high band HB. 
       FIG. 9  is a diagram of an illustrative antenna of the type that may be implemented using a parasitic antenna resonating element. As shown in  FIG. 9 , dual arm inverted-F antenna resonating element  90  may be formed from portions of peripheral conductive housing structures  16 . In particular, resonating element arm portion (arm)  202  for producing an antenna response in a high band (HB) frequency range and resonating element arm portion (arm)  200  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  92 . Feed path  92  may include an antenna feed formed from antenna feed terminals such as positive antenna feed terminal (+) and ground antenna feed terminal (−). Transmission line  44  ( FIG. 4 ) may have a positive signal line coupled to terminal (+) and a ground signal line coupled to terminal (−). Impedance matching circuits and other circuitry (e.g., filters, switches, etc.) may be incorporated into feed path  92  or transmission line  44 , if desired. 
     Optional inductors such as inductors L′ and L″ (e.g., fixed inductors or tunable inductors) may be coupled across gaps  18 A and  18 B to counteract the capacitances (C 1  and C 2 ) associated with gaps  18 A and  18 B and thereby ensure that antenna  40  operates at frequencies of interest (i.e., so that antenna  40  exhibits a low band response above 690 MHz). Short circuit path  94  may be used to short resonating element arm  202  to ground  52  or may be omitted (e.g., in a configuration in which inductor L″ is used to form a return path for antenna  40 ). 
     Adjustable inductor  110 - 1  may have switching circuitry such as switch  120 - 1  that receives control signals from control circuitry  28  on input  112 - 1 . When inductor L is switched into use, antenna  40  may be configured so that the low band resonance of antenna  40  covers an upper portion of low band LB (e.g., frequencies up to 960 MHz). When inductor L is switched out of use, antenna  40  may be configured so that the low band resonance of antenna  40  covers a lower portion of low band LB (e.g., frequencies down to about 700 MHz). If desired, other types of tunable circuitry may be used in adjusting the low band performance of antenna  40 . The use of an inductor such as adjustable inductor  110 - 1  that is coupled between resonating element  90  and ground  52  to tune the performance of antenna  40  in low band LB is merely illustrative. 
     Parasitic antenna resonating element  204  may have an L-shape or other suitable shape. Parasitic antenna resonating element  204  may be, for example, a parasitic monopole antenna resonating element having a first end such as end  206  that is coupled to ground  52  and a second end such as end  208  that is floating in opening  82 . The length of monopole antenna resonating element  204  may be approximately a quarter of a wavelength at frequencies of interest (i.e., frequencies in band HB where it is desired to use the antenna resonance associated with parasitic antenna resonating element  204  to enhance antenna performance). 
     Parasitic antenna resonating element  204  may have tunable circuitry such as adjustable inductor  110 - 2 . Inductor  110 - 2  may be adjusted by commands on input  112 - 2 . Adjustable inductor  110 - 2  may have multiple inductors and switching circuitry that can be configured to selectively switch the inductors in and out of use to produce a desired amount of inductance between terminals  122 - 2  and  124 - 2 . Adjustable inductor  110 - 2  may, for example, have switching circuitry such as switching circuitry  120  of  FIG. 8  and a pair of inductors such as inductors L 1  and L 2  of  FIG. 8  (as an example). 
     Adjustments to inductor  110 - 2  may be used to adjust the performance of antenna  40 . For example, adjusting the inductance value produced by adjustable inductor  110 - 2  in parasitic antenna resonating element  204  may adjust the position of a high band antenna resonance located in high band HB of  FIG. 6 , as indicated by arrow  100  in high band HB. Inductors such as inductor  110 - 2  and/or inductor  110 - 1  may be implemented using fixed inductors or other types of adjustable circuitry can be used to tune antenna  40 . The use of adjustable inductors to tune antenna  40  of  FIG. 9  is merely illustrative. 
     If desired, antenna  40  may contain a parasitic loop antenna resonating element, as indicated by illustrative antenna  40  of  FIG. 10 . A shown in  FIG. 10 , antenna  40  may have parasitic loop antenna resonating element  220 . Parasitic loop antenna resonating element  220  may have a first end such as end  224  that is coupled to ground  52  at a first location and may have a second end such as end  226  that is coupled to ground  52  at a second end such as end  226 . Parasitic loop antenna resonating element  220  may be electromagnetically coupled (near field coupled) to antenna resonating element  90 , as indicated by coupled electromagnetic fields  222  in  FIG. 10 . 
     Antenna  40  of  FIG. 10  may have a resonating element such as dual arm inverted-F antenna resonating element  90  that is formed from portions of peripheral conductive housing structures  16 . Resonating element arm portion  202  may produce an antenna response in high band HB and resonating element arm portion  200  may produce an antenna response in a low band LB. Antenna  40  may also have antenna ground  52 . 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  92 . Feed path  92  may include an antenna feed formed from antenna feed terminals such as positive antenna feed terminal (+) and ground antenna feed terminal (−). Transmission line  44  ( FIG. 4 ) may have a positive signal line coupled to terminal (+) and a ground signal line coupled to terminal (−). Impedance matching circuits and other circuitry (e.g., filters, switches, etc.) may be incorporated into feed path  92  or transmission line  44 , if desired. 
     As with inductors L′ and L″ in antenna  40  of  FIG. 9 , optional inductors in antenna  40  of  FIG. 10  such as inductors L′ and L″ may be coupled across gaps  18 A and  18 B to counteract the capacitances (C 1  and C 2 ) associated with gaps  18 A and  18 B and thereby ensure that antenna  40  operates at frequencies of interest (i.e., so that antenna  40  exhibits a low band response above 690 MHz). Short circuit path  94  may be used to short resonating element arm  202  to ground  52  or may be omitted (e.g., in a configuration in which inductor L″ is used to form a return path for antenna  40 ). 
     Low band tuning for antenna  40  of  FIG. 10  may be implemented using tunable circuitry such as adjustable inductor  110 - 1 . Adjustable inductor  110 - 1  may have switching circuitry such as switch  120 - 1  that receives control signals from control circuitry  28  on input  112 - 1 . When inductor L is switched into use, antenna  40  may be configured so that the low band resonance of antenna  40  covers an upper portion of low band LB (e.g., frequencies up to 960 MHz). When inductor L is switched out of use, antenna  40  may be configured so that the low band resonance of antenna  40  moves to lower frequencies and covers a lower portion of low band LB (e.g., frequencies down to about 700 MHz). If desired, other types of tunable circuitry may be used in adjusting low band performance. The use of adjustable inductor  110 - 1  to tune the performance of antenna  40  of  FIG. 10  in low band LB is merely illustrative. 
     The length of parasitic loop antenna resonating element  220  may be configured to exhibit an antenna resonance at frequencies of interest (i.e., frequencies in band HB where it is desired to use the antenna resonance associated with parasitic loop antenna resonating element  220  to enhance antenna performance). 
     Parasitic loop antenna resonating element  220  may have tunable circuitry such as adjustable inductor  110 - 2 . Control signals from control circuitry  28  may be applied to input  112 - 2  to adjust inductor  110 - 2 . Adjustable inductor  110 - 2  may have multiple inductors and switching circuitry that can be configured to selectively switch the inductors in and out of use to produce a desired amount of inductance between terminals  122 - 2  and  124 - 2 . Adjustable inductor  110 - 2  may, for example, have switching circuitry such as switching circuitry  120  of  FIG. 8  and a pair of inductors such as inductors L 1  and L 2  of  FIG. 8  (as an example). Adjustments to inductor  110 - 2  may be used to adjust the performance of antenna  40  of  FIG. 10 . For example, adjusting the inductance value produced by adjustable inductor  110 - 2  in parasitic loop antenna resonating element  220  may tune the position of a high band antenna resonance located in high band HB of  FIG. 6 , as indicated by arrow  100  in high band HB. Inductors such as inductor  122 - 2  and/or inductor  110 - 1  may be implemented using fixed inductors or other types of adjustable circuitry can be used to tune antenna  40 . The use of adjustable inductors to tune antenna  40  of  FIG. 10  is merely illustrative. 
     The foregoing is merely illustrative of the principles of this invention and various modifications can be made by those skilled in the art without departing from the scope and spirit of the invention.

Metadata:
Filing Date: 20130508
Publication Date: 20160510
Grant Date: 20160510
Priority Date: 20130508
Inventors: HU HONGFEI
PASCOLINI MATTIA
VAZQUEZ ENRIQUE AYALA
MOW MATTHEW A.
DARNELL DEAN F.
TSAI MING-JU
SCHLUB ROBERT W.
JIN NANBO
OUYANG YUEHUI
HAN LIANG
PRATT DAVID
Assignee: APPLE INC
CPC Classifications: [{"code": "H01Q5/378", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q5/321", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q9/0421", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q1/243", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q5/30", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01Q5/30", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01Q9/0421", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q5/321", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q5/378", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q1/243", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q5/0024", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01Q5/30", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q5/321", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q9/0421", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q5/378", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q1/243", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 50736173