PATENT DOCUMENT

Publication Number: US-9531061-B2
Application Number: US-201414476490-A
Country: US
Kind Code: B2

Title: Electronic device antenna with reduced lossy mode

Abstract:
An electronic device may be provided with an antenna. The antenna may have an antenna resonating element and an antenna ground. An adjustable inductor may be coupled between the antenna resonating element and the antenna ground. An antenna feed may have a positive feed terminal coupled to the antenna resonating element and a ground antenna feed coupled to the antenna ground. The adjustable inductor may have first and second inductors coupled to respective first and second ports of a switch. The switch may have a third port coupled to the antenna ground. A capacitor may have a first terminal coupled to ground and a second terminal coupled to the first inductor at the first port of the switch. An inductor may be coupled between the antenna resonating element and antenna ground at a location between the adjustable inductor and the antenna feed.

Claims:
What is claimed is: 
     
       1. Apparatus, comprising:
 an antenna resonating element; 
 an antenna ground; 
 an adjustable inductor coupled between the antenna resonating element and the antenna ground, wherein the adjustable inductor has a plurality of fixed inductors and a switch; 
 an inductor coupled between the antenna resonating element and the antenna ground in parallel with the adjustable inductor; and 
 at least one capacitor having a first terminal coupled to one of the fixed inductors at a node between that one of the fixed inductors and the switch and a second terminal coupled to the antenna ground. 
 
     
     
       2. The apparatus defined in  claim 1  wherein the antenna resonating element and antenna ground form an antenna having an antenna feed with a positive antenna feed terminal and a ground antenna feed terminal and wherein the inductor is coupled between the antenna resonating element and the antenna ground at a location between the adjustable inductor and the antenna feed. 
     
     
       3. The apparatus defined in  claim 2  wherein the plurality of fixed inductors includes first and second inductors coupled to respective first and second ports in the switch, wherein the switch has a third port, and wherein the switch operates in a first mode in which the first and second inductors are switched out of use, a second mode in which the first inductor is switched out of use and the second inductor is switched into use, a third mode in which the first inductor is switched into use and the second inductor is switched out of use, and a fourth mode in which the first and second inductors are switched into use. 
     
     
       4. The apparatus defined in  claim 3  wherein the one of the fixed inductors to which the capacitor is coupled is the first inductor, wherein the first inductor has a first terminal coupled to the antenna resonating element, wherein the first inductor has a second terminal coupled to the first port at the node, and wherein the first terminal of the capacitor is coupled to the second terminal of the first inductor. 
     
     
       5. The apparatus defined in  claim 4  further comprising an electronic device housing having peripheral conductive structures, wherein the antenna resonating element is formed from at least part of the peripheral conductive structures. 
     
     
       6. The apparatus defined in  claim 5  wherein the resonating element comprises an inverted-F antenna resonating element. 
     
     
       7. The apparatus defined in  claim 6  wherein the antenna comprises a hybrid inverted-F slot antenna having a slot antenna resonating element. 
     
     
       8. The apparatus defined in  claim 4  wherein the first inductor and the second inductor have different respective inductance values. 
     
     
       9. The apparatus defined in  claim 8  wherein the antenna resonating element comprises a peripheral conductive electronic device housing structure running along at least one peripheral edge of an electronic device. 
     
     
       10. The apparatus defined in  claim 1  wherein the antenna resonating element has first and second branches, wherein the adjustable inductor is coupled between the second branch and the antenna ground, wherein an antenna feed is coupled to the antenna resonating element, and wherein the inductor is coupled between the antenna resonating element and the antenna ground at a location that is between the antenna feed and the adjustable inductor. 
     
     
       11. The apparatus defined in  claim 10  further comprising control circuitry that issues control signals to adjustable inductor to tune the antenna when the antenna is operating at a frequency between 700 and 960 MHz. 
     
     
       12. An antenna, comprising:
 an antenna ground; 
 an antenna resonating element separated from the antenna ground by a gap; 
 an antenna feed having a positive antenna feed terminal coupled to the antenna resonating element and a ground antenna feed terminal coupled to the antenna ground; 
 an adjustable inductor circuit having first and second inductors and a switch coupled to the first and second inductors at respective first and second ports, wherein the adjustable inductor circuit is coupled between the antenna resonating element and the antenna ground; and 
 a capacitor having a first terminal coupled to the first inductor at the first port of the switch. 
 
     
     
       13. The antenna defined in  claim 12  wherein the capacitor has a second terminal coupled to the antenna ground, the antenna further comprising an inductor coupled between the antenna resonating element and the antenna ground in parallel with the adjustable inductor circuit at a location between the antenna feed and the adjustable inductor circuit. 
     
     
       14. The antenna defined in  claim 13  wherein the switch has a third port that is coupled to the antenna ground. 
     
     
       15. The antenna defined in  claim 14  wherein the antenna resonating element includes metal electronic device housing structures. 
     
     
       16. The antenna defined in  claim 15  wherein the metal electronic device housing structures comprise peripheral housing structures that run along at least one edge of an electronic device housing. 
     
     
       17. An electronic device, comprising:
 peripheral conductive housing structures; 
 a hybrid inverted-F slot antenna, wherein the hybrid inverted-F slot antenna has an inverted-F antenna portion formed from an inverted-F antenna resonating element and an antenna ground, wherein the inverted-F antenna resonating element is formed from the peripheral conductive housing structures, wherein the hybrid inverted-F slot antenna has a slot antenna portion formed from an opening between the inverted-F antenna resonating element and the antenna ground, and wherein the hybrid inverted-F antenna has an antenna feed that feeds both the inverted-F antenna portion and the slot antenna portion; 
 an adjustable inductor having at least first and second inductors coupled to first and second ports of a switch, wherein the adjustable inductor is coupled between the inverted-F antenna resonating element and the antenna ground; and 
 a capacitor having a first terminal coupled to the antenna ground and a second terminal coupled to the first inductor at the first port of the switch. 
 
     
     
       18. The electronic device defined in  claim 17  further comprising an inductor that is coupled between the inverted-F antenna resonating element and the antenna ground in parallel with the adjustable inductor. 
     
     
       19. The electronic device defined in  claim 18  wherein the inductor is coupled between the inverted-F antenna resonating element and the antenna ground at a location that is between the adjustable inductor and the antenna feed. 
     
     
       20. The electronic device defined in  claim 19  wherein the first and second inductors have different first and second inductor values and wherein adjustments to the adjustable inductor tune the antenna.

Description:
BACKGROUND 
     This relates generally to electronic devices and, more particularly, to electronic devices with antennas. 
     Electronic devices often include antennas. For example, cellular telephones, computers, and other devices often contain antennas for supporting wireless communications. 
     It can be challenging to form electronic device antenna structures with desired attributes. In some wireless devices, the presence of conductive housing structures can influence antenna performance. Antenna performance may not be satisfactory if the housing structures are not configured properly and interfere with antenna operation. Device size can also affect performance. It can be difficult to achieve desired performance levels in a compact device, particularly when the compact device has conductive housing structures. 
     It would therefore be desirable to be able to provide improved wireless circuitry for electronic devices such as electronic devices that include conductive housing structures. 
     SUMMARY 
     An electronic device may be provided with an antenna. The antenna may have an antenna resonating element and an antenna ground. An adjustable inductor may be coupled between the antenna resonating element and the antenna ground to tune the antenna. An antenna feed may have a positive feed terminal coupled to the antenna resonating element and a ground antenna feed coupled to the antenna ground. The adjustable inductor may have first and second inductors coupled to respective first and second ports of a switch. The switch may have a third port coupled to the antenna ground. A capacitor may have a first terminal coupled to ground and a second terminal coupled to the first inductor at the first port of the switch. An inductor may be coupled between the antenna resonating element and antenna ground in parallel with the adjustable inductor at a location between the adjustable inductor and the antenna feed. 
     The electronic device may have a housing. The housing may have a periphery that is surrounded by peripheral conductive housing structures. The antenna resonating element may be formed from at least some of the peripheral conductive housing structures. The antenna may be a hybrid inverted-F slot antenna or other suitable antenna. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an illustrative electronic device with wireless circuitry in accordance with an embodiment. 
         FIG. 2  is a schematic diagram of illustrative circuitry in an electronic device in accordance with an embodiment. 
         FIG. 3  is a schematic diagram of illustrative wireless circuitry in accordance with an embodiment. 
         FIG. 4  is a schematic diagram of an illustrative inverted-F antenna in accordance with an embodiment. 
         FIG. 5  is a schematic diagram of an illustrative inverted-F antenna with an inductor to tune the antenna to cover desired operating frequencies in accordance with an embodiment. 
         FIG. 6  is a schematic diagram of an illustrative inverted-F antenna with a capacitor to tune the antenna to cover desired operating frequencies in accordance with an embodiment. 
         FIG. 7  is a diagram of an illustrative slot antenna in accordance with an embodiment of the present invention. 
         FIG. 8  is a diagram of an illustrative hybrid inverted-F slot antenna in accordance with an embodiment. 
         FIG. 9  is a diagram of illustrative circuitry that may be used in an antenna such as the antenna of  FIG. 8  or other suitable antenna to reduce lossy mode operation and thereby enhance performance over a range of operating frequencies in accordance with an embodiment. 
         FIG. 10  is a graph in which antenna performance (antenna efficiency) has been plotted as a function of operating frequency for various operating conditions and antenna configurations for an illustrative antenna in accordance with an embodiment. 
     
    
    
     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 may be formed in the peripheral conductive member that divide the peripheral conductive member into segments. One or more of the segments may be used in forming one or more antennas for electronic device  10 . 
     Electronic device  10  may be a portable electronic device or other suitable electronic device. For example, electronic device  10  may be a laptop computer, a tablet computer, a somewhat smaller device such as a wrist-watch device, pendant device, headphone device, earpiece device, or other wearable or miniature device, a handheld device such as a cellular telephone, a media player, or other small portable device. Device  10  may also be a television, a set-top box, a desktop computer, a computer monitor into which a computer has been integrated, or other suitable electronic equipment. 
     Device  10  may include a housing such as housing  12 . Housing  12 , which may sometimes be referred to as a case, may be formed of plastic, glass, ceramics, fiber composites, metal (e.g., stainless steel, aluminum, etc.), other suitable materials, or a combination of these materials. In some situations, parts of housing  12  may be formed from dielectric or other low-conductivity material. In other situations, housing  12  or at least some of the structures that make up housing  12  may be formed from metal elements. 
     Device  10  may, if desired, have a display such as display  14 . Display  14  may, 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 such as a layer of clear glass or plastic may cover the surface of display  14 . Buttons such as button  24  may pass through openings in the cover layer. The cover layer may also have other openings such as an opening for speaker port  26 . 
     Housing  12  may include peripheral housing structures such as structures  16 . Structures  16  may run around the periphery of device  10  and display  14 . In configurations in which device  10  and display  14  have a rectangular shape with four edges, structures  16  may be implemented using a peripheral housing member have a rectangular ring shape with four corresponding edges (as an example). Peripheral structures  16  or part of peripheral structures  16  may serve as a bezel for display  14  (e.g., a cosmetic trim that surrounds all four sides of display  14  and/or 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, which may be used in forming a ground plane in device  10 , may be located in the center of housing  12  under active area AA of display  14  (e.g., the portion of display  14  that contains circuitry and other structures for displaying images). 
     In regions  22  and  20 , openings may be formed within the conductive structures of device  10  (e.g., between peripheral conductive housing structures  16  and opposing conductive ground structures such as conductive housing midplate or rear housing wall structures, a printed circuit board, and conductive electrical components in display  14  and device  10 ). These openings, which may sometimes be referred to as gaps, may be filled with air, plastic, and other dielectrics. 
     Conductive housing structures and other conductive structures in device  10  such as a midplate, traces on a printed circuit board, display  14 , and conductive electronic components may serve as a ground plane for the antennas in device  10 . The openings in regions  20  and  22  may serve as slots in open or closed slot antennas, may serve as a central dielectric region that is surrounded by a conductive path of materials in a loop antenna, may serve as a space that separates an antenna resonating element such as a strip antenna resonating element or an inverted-F antenna resonating element from the ground plane, may contribute to the performance of a parasitic antenna resonating element, or may otherwise serve as part of antenna structures formed in regions  20  and  22 . If desired, extensions of the ground plane under active area AA of display  14  and/or other metal structures in device  10  may have portions that extend into parts of the dielectric-filled openings in regions  20  and  22 . 
     In general, device  10  may include any suitable number of antennas (e.g., one or more, two or more, three or more, four or more, etc.). The antennas in device  10  may be located at opposing first and second ends of an elongated device housing (e.g., at ends  20  and  22  of device  10  of  FIG. 1 ), along one or more edges of a device housing, in the center of a device housing, in other suitable locations, or in one or more of 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 showing illustrative components that may be used in device  10  of  FIG. 1  is shown in  FIG. 2 . As shown in  FIG. 2 , device  10  may include control circuitry such as storage and processing circuitry  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 . This processing circuitry may be based on one or more microprocessors, microcontrollers, digital signal processors, 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, MIMO protocols, antenna diversity protocols, etc. 
     Input-output circuitry  30  may include input-output devices  32 . Input-output devices  32  may be used to allow data to be supplied to device  10  and to allow data to be provided from device  10  to external devices. Input-output devices  32  may include user interface devices, data port devices, and other input-output components. For example, input-output devices may include touch screens, displays without touch sensor capabilities, buttons, joysticks, click wheels, scrolling wheels, touch pads, key pads, keyboards, microphones, cameras, buttons, speakers, status indicators, light sources, audio jacks and other audio port components, digital data port devices, light sensors, motion sensors (accelerometers), capacitance sensors, proximity sensors, etc. 
     Input-output circuitry  30  may include wireless communications circuitry  34  for communicating wirelessly with external equipment. Wireless communications circuitry  34  may include radio-frequency (RF) transceiver circuitry formed from one or more integrated circuits, power amplifier circuitry, low-noise input amplifiers, passive RF components, one or more antennas, transmission lines, and other circuitry for handling RF wireless signals. Wireless signals can also be sent using light (e.g., using infrared communications). 
     Wireless communications circuitry  34  may include radio-frequency transceiver circuitry  90  for handling various radio-frequency communications bands. For example, circuitry  34  may include transceiver circuitry  36 ,  38 , and  42 . Transceiver circuitry  36  may handle 2.4 GHz and 5 GHz bands for WiFi® (IEEE 802.11) communications and may handle the 2.4 GHz Bluetooth® communications band. Circuitry  34  may use cellular telephone transceiver circuitry  38  for handling wireless communications in frequency ranges such as a low communications band from 700 to 960 MHz, a midband from 1710 to 2170 MHz, and a high band from 2300 to 2700 MHz or other communications bands between 700 MHz and 2700 MHz or other suitable frequencies (as examples). Circuitry  38  may handle voice data and non-voice data. Wireless communications circuitry  34  can include circuitry for other short-range and long-range wireless links if desired. For example, wireless communications circuitry  34  may include 60 GHz transceiver circuitry, circuitry for receiving television and radio signals, paging system transceivers, near field communications (NFC) circuitry, etc. Wireless communications circuitry  34  may include global positioning system (GPS) receiver equipment such as GPS receiver circuitry  42  for receiving GPS signals at 1575 MHz or for handling other satellite positioning data. In WiFi® and Bluetooth® links and other short-range wireless links, wireless signals are typically used to convey data over tens or hundreds of feet. In cellular telephone links and other long-range links, wireless signals are typically used to convey data over thousands of feet or miles. 
     Wireless communications circuitry  34  may include antennas  40 . Antennas  40  may be formed using any suitable antenna types. For example, antennas  40  may include antennas with resonating elements that are formed from loop antenna structures, patch antenna structures, inverted-F antenna structures, slot antenna structures, planar inverted-F antenna structures, helical antenna structures, hybrids of these designs, etc. Different types of antennas may be used for different bands and combinations of bands. For example, one type of antenna may be used in forming a local wireless link antenna and another type of antenna may be used in forming a remote wireless link antenna. 
     As shown in  FIG. 3 , transceiver circuitry  90  in wireless circuitry  34  may be coupled to antenna structures  40  using paths such as path  92 . Wireless circuitry  34  may be coupled to control circuitry  28 . Control circuitry  28  may be coupled to input-output devices  32 . Input-output devices  32  may supply output from device  10  and may receive input from sources that are external to device  10 . 
     To provide antenna structures  40  with the ability to cover communications frequencies of interest, antenna structures  40  may be provided with circuitry such as filter circuitry (e.g., one or more passive filters and/or one or more tunable filter circuits). Discrete components such as capacitors, inductors, and resistors may be incorporated into the filter circuitry. Capacitive structures, inductive structures, and resistive structures may also be formed from patterned metal structures (e.g., part of an antenna). If desired, antenna structures  26  may be provided with adjustable circuits such as tunable components  102  to tune antennas over communications bands of interest. Tunable components  102  may include tunable inductors, tunable capacitors, or other tunable components. Tunable components such as these may be based on switches and networks of fixed components, distributed metal structures that produce associated distributed capacitances and inductances, variable solid state devices for producing variable capacitance and inductance values, tunable filters, or other suitable tunable structures. During operation of device  10 , control circuitry  28  may issue control signals on one or more paths such as path  93  that adjust inductance values, capacitance values, or other parameters associated with tunable components  102 , thereby tuning antenna structures  40  to cover desired communications bands. 
     Path  92  may include one or more transmission lines. As an example, signal path  92  of  FIG. 3  may be a transmission line having a positive signal conductor such as line  94  and a ground signal conductor such as line  96 . Lines  94  and  96  may form parts of a coaxial cable or a microstrip transmission line (as examples). A matching network formed from components such as inductors, resistors, and capacitors may be used in matching the impedance of antenna structures  40  to the impedance of transmission line  92 . Matching network components may be provided as discrete components (e.g., surface mount technology components) or may be formed from housing structures, printed circuit board structures, traces on plastic supports, etc. Components such as these may also be used in forming filter circuitry in antenna structures  40 . 
     Transmission line  92  may be coupled to antenna feed structures associated with antenna structures  40 . As an example, antenna structures  40  may form an inverted-F antenna, a slot antenna, a hybrid inverted-F slot antenna or other antenna having an antenna feed with a positive antenna feed terminal such as terminal  98  and a ground antenna feed terminal such as ground antenna feed terminal  100 . Positive transmission line conductor  94  may be coupled to positive antenna feed terminal  98  and ground transmission line conductor  96  may be coupled to ground antenna feed terminal  92 . Other types of antenna feed arrangements may be used if desired. The illustrative feeding configuration of  FIG. 3  is merely illustrative. 
       FIG. 4  is a diagram of illustrative inverted-F antenna structures that may be used in implementing antenna  40  for device  10 . Inverted-F antenna  40  of  FIG. 4  has antenna resonating element  106  and antenna ground (ground plane)  104 . Antenna resonating element  106  may have a main resonating element arm such as arm  108 . The length of arm  108  may be selected so that antenna  40  resonates at desired operating frequencies. For example, if the length of arm  108  may be a quarter of a wavelength at a desired operating frequency for antenna  40 . Antenna  40  may also exhibit resonances at harmonic frequencies. 
     Main resonating element arm  108  may be coupled to ground  104  by return path  110 . Antenna feed  112  may include positive antenna feed terminal  98  and ground antenna feed terminal  100  and may run in parallel to return path  110  between arm  108  and ground  104 . If desired, inverted-F antennas such as illustrative antenna  40  of  FIG. 4  may have more than one resonating arm branch (e.g., to create multiple frequency resonances to support operations in multiple communications bands) or may have other antenna structures (e.g., parasitic antenna resonating elements, tunable components to support antenna tuning, etc.). 
       FIG. 5  is a diagram of an illustrative inverted-F antenna configuration of the type that may be used to implement a tunable antenna. As shown in  FIG. 5 , antenna  40  may be provided with an inductor L that couples a portion of antenna resonating element arm  108  (e.g., a tip of arm  108 ) in resonating element  106  to antenna ground  104 . Inductor L may be a variable inductor. For example, inductor L may be an adjustable inductor that is formed from one or more transistor or other switching circuitry and a set of fixed inductors. During operation of device  10 , control circuitry  28  can issue control signals that adjust the switching circuitry (e.g., that open and close transistor switches in the switching circuitry), thereby switching desired patterns of the set of fixed inductors into and out of use to adjust the inductance value of inductor L. Adjustments such as these may be made to vary the inductance of inductor L when it is desired to tune the frequency response of antenna  40  (e.g., when it is desired to tune the low band resonance of antenna  40 , when it is desired to tune a mid-band resonance of antenna  40 , etc.). For example, increases to the value of L may be made to increase the frequency of the communications band(s) in which antenna  40  is operating (e.g., to increase a low-band resonant frequency or a mid-band resonant frequency). One or more inductors such as inductor L may be coupled between arm  108  and ground  104  at one or more locations along the length of arm  108 . The configuration of  FIG. 5  is illustrative. 
       FIG. 6  is a diagram of an illustrative inverted-F antenna structure with a capacitor that may be used to implement a tunable antenna. As shown in  FIG. 6 , antenna  40  may be provided with a capacitor C that couples a tip portion of antenna resonating element arm  108  in resonating element  106  to antenna ground  104 . Capacitors such as capacitor C may also be coupled to arm  108  at other locations. Capacitor C may be a fixed capacitor or may be a variable capacitor. For example, capacitor C may be formed from one or more switches or other switching circuitry and a set of fixed capacitors (e.g., a programmable capacitor) or a varactor. During operation of device  10 , control circuitry  28  can issue control signals that open and close switches in the switching circuitry to switch desired capacitors into and out of use or that otherwise make adjustments to capacitor C, thereby varying the capacitance value exhibited by capacitor C. Adjustments such as these may be made to vary the capacitance of capacitance C when it is desired to tune the frequency response of antenna  40  (e.g., when it is desired to tune the low band resonance of antenna  40 , when it is desired to tune a mid-band resonance of antenna  40 , or when it is desired to tune a high band resonance of antenna  40 ). For example, increases to the value of C may be made to decrease the frequency range of the communications band(s) in which antenna  40  is operating (e.g., to decrease a high-band resonant frequency). Capacitor C need not be located at the tip of arm  108 . For example, the resonant frequency decrease associated with inclusion of capacitor C in antenna  40  can be enhanced by locating capacitor C closer to feed  112 . If desired, antenna  40  can be implemented using a pair of fixed capacitances C (e.g., fixed capacitances associated with gaps  18  at either end of a two-branch inverted-F antenna resonating element formed from a peripheral conductive structure such as a segment of peripheral structure  16 ) and variable capacitors can be omitted (as an example). 
     In general, antenna  40  may have one or more adjustable components (adjustable inductors, adjustable capacitors, etc.). The configurations of  FIGS. 5 and 6  are merely illustrative. 
     Antenna  40  may include a slot antenna resonating element. As shown in  FIG. 7 , for example, antenna  40  may be a slot antenna having an opening such as slot  114  that is formed within antenna ground  104 . Slot  114  may be filled with air, plastic, and/or other dielectric. The shape of slot  114  may be straight or may have one or more bends (i.e., slot  114  may have an elongated shape follow a meandering path). The antenna feed for antenna  40  may include positive antenna feed terminal  98  and ground antenna feed terminal  100 . Feed terminals  98  and  100  may, for example, be located on opposing sides of slot  114  (e.g., on opposing long sides). Slot-based antenna resonating elements such as slot antenna resonating element  114  of  FIG. 7  may give rise to an antenna resonance at frequencies in which the wavelength of the antenna signals is equal to the perimeter of the slot. In narrow slots, the resonant frequency of a slot antenna resonating element is associated with signal frequencies at which the slot length is equal to a half of a wavelength. Slot antenna frequency response can be tuned using one or more tunable components such as tunable inductors or tunable capacitors. These components may have terminals that are coupled to opposing sides of the slot (i.e., the tunable components may bridge the slot). If desired, tunable components may have terminals that are coupled to respective locations along the length of one of the sides of slot  114 . Combinations of these arrangements may also be used. 
     If desired, antenna  40  may incorporate conductive device structures such as portions of housing  12 . As an example, peripheral conductive housing structures  16  may include multiple segments such as segments  16 - 1 ,  16 - 2 , and  16 - 3  of  FIG. 8  that are separated from each other by gaps  18  (e.g., spaces between the adjoining ends of the segments that are filled with plastic or other dielectric). In antenna  40  of  FIG. 8 , segment  16 - 1  may be formed from a strip of stainless steel or other metal that forms a segment of a peripheral conductive housing member (e.g., a stainless steel member or other peripheral metal housing structure) that runs around the entire periphery of device  10 . 
     Segment  16 - 1  may form antenna resonating arm  108  for an inverted-F antenna. For example, segment  16 - 1  may form a dual-band inverted-F antenna resonating element having a longer branch that contributes an antenna response in a low frequency communications band (low band LB) and having a shorter branch that contributes an antenna response in a middle frequency communications band (middle band MB). Dual-band inverted-F antenna structures of this type may sometimes be referred to as T-shaped antennas or T-antennas. A return path conductor such as a strip of metal may be used to form return path  110  between peripheral conductive segment  16 - 1  (i.e., the main resonating element arm of the T-antenna resonating element) and antenna ground  104 . 
     Antenna ground  104  may have ground structures such as a substantially rectangular antenna ground plane portion in the center of device  10  (e.g., the portion of device underlying active area AA of display  14  of  FIG. 1 ). Antenna ground  104  may also have a portion such as ground plane extension  104 E that extends outwards from the main antenna ground region in device  10 . Ground plane extension  104 E may protrude into an end region of device  10  such as lower end region  20 . Ground plane extension  104 E of antenna ground  104  may be separated from the main portion of antenna ground  104  and peripheral segment  16 - 1  by an opening that forms antenna slot  114 . Antenna slot  114  may be fed using antenna feed  112  (i.e., using antenna feed terminals on opposing sides of slot  114  such as positive antenna feed terminal  98  and ground antenna feed terminal  100 ). The magnitude of the periphery of antenna slot  114  may determine the frequency at which slot  114  resonances and may therefore be used to produce a desired resonance for antenna (e.g., a high band resonance HB that complements low band resonance LB and midband resonance MB associated with the T-antenna formed from segment  16 - 1 ). 
     When operating antenna  40  in device  10 , both the T-antenna formed from segment  16 - 1  of peripheral conductive housing structures  16  (i.e., the inverted-F antenna) and the slot antenna formed from slot  114  may contribute to the overall response of the antenna. Because two different types of antenna contribute to the operation of antenna  40  (i.e., the inverted-F antenna portion and the slot antenna portion), antenna  40  may sometimes be referred to as a hybrid inverted-F slot antenna or hybrid antenna. 
     If desired, optional electrical components such as inductors and/or capacitors may be coupled to antenna  40 . For example, one or more inductors such as inductors L 1 , L 2 , and L 3  may bridge slot  114  or may be coupled to different locations along the periphery of slot  114  and/or one or more capacitors may bridge slot  114  or may be coupled to different locations along the periphery of slot  114 . Capacitances may be formed by discrete components (capacitors) or may be produced by the metal structures of  FIG. 8 . For example, the metal portions of peripheral conductive structures  16  that are separated by gaps  18  from ground  104  may produce capacitances at the left and right ends of resonating element  108 . Inductor L 1  may bridge the left-hand gap  18  and may help compensate for the capacitance associated with the left-hand gap  18 . Inductor L 3  may bridge the right-hand gap  18  and may help compensate for the capacitance associated with the right-hand gap  18 . 
     Inductor L 2  may be an adjustable inductor that can be adjusted by control circuitry  28  to produce various different inductance values. For example, inductor L 2  may include two parallel inductors and an associated silicon-on-insulator (SOI) high speed silicon metal oxide-semiconductor switch (e.g., a switch with a pair of field-effect transistors). In response to control signals on path  93 , the switch of inductor L 2  may switch both inductors into use, may switch a selected one of the inductors into use, or may switch both inductors out of use. Configurations with larger numbers of fixed inductors and corresponding larger numbers of transistors to perform switching operations for the switch may also be used. 
     Device  10  may include connectors for data ports and other electrical components. One or more of these electrical components may be mounted in housing  12  in a position that minimizes interference with antenna  40 . For example, a data port connector or other electrical component may be mounted in device  10  in a location such as location  116  that overlaps ground plane extension  104 E. 
     The size and shape of conductive antenna structures such as inverted-F antenna resonating element  108 , slot antenna resonating element  114  and ground  104  affect the frequency response of antenna  40 . 
     With one suitable arrangement, antenna  40  may exhibit low band (LB), midband (MB), and high band (HB) antenna resonances. The antenna resonance that is associated with low band LB may be generated by the longer of the two branches of inverted-F resonating element arm  108 , the antenna resonance that is associated with middle band MB may be produced partly by the shorter branch of inverted-F arm  108  and partly by slot  114  (or just by the shorter branch), and the antenna resonance that is associated with high band HB may be produced partly by slot antenna  114  and partly by a harmonic of low band LB. Tunable inductor L 2  may be used to tune low band LB. Other inductors and/or capacitors (see, e.g., inductors L 1  and L 3 , etc.) may, if desired, be adjusted to tune antenna performance. 
     Tunable inductor L 2  may have multiple states. For example, tunable inductor L 2  may include a switch that allows inductor L 2  to be placed in multiple states so that antenna  40  exhibits four corresponding frequency responses or other suitable number of frequency responses. 
     Consider, as an example, inductor L 2  of  FIG. 9 . As shown in  FIG. 9 , inductor L 2  may contain two inductors coupled in parallel: inductor L 2 A and inductor L 2 B. Adjustable inductor L 2  may also have switching circuitry such as switch  120 . Switch  120  may be a semiconductor switch (e.g., a switch having two silicon-on-insulator field-effect transistors S 1  and S 2  or other suitable transistor-based switch). Inductor L 2  may be coupled between resonating element  108  and antenna ground  104 . For example, inductor L 2 A may be coupled between a first port of switch  120  and resonating element  108  (e.g., node  122  on peripheral conductive structures  16 - 1 ). Inductor L 2 B may be coupled between a second port of switch  120  and resonating element  108  (e.g., node  122  on peripheral conductive structures  16 - 1 ). Switch  120  has a third port that is coupled to antenna ground  104  at node  124 . 
     During operation, control signals (e.g., control signals on a path such as path  93  of  FIG. 3 ) may be used to adjust the state of switch  120 . Inductor L 2 A may have a value of 12 nH or other suitable value (e.g., less than 20 nH, 5-20 nH, more than 3 nH, etc.). Inductor L 2 B may have a value of 51 nH or other suitable value (e.g., less than 60 nH, less than 100 nH, more than 20 nH, more than 40 nH, between 40-100 nH, etc.). 
     Switch  120  may be placed in one of four different modes, corresponding to four different tunings for antenna  40 . In the first mode, the transistor switches S 1  and S 2  of switch  120  are both open, so that the first and second switch ports are isolated from the third switch port. In this scenario, both inductors L 2 A and L 2 B are switched out of use and the impedance of adjustable inductor L 2  between nodes  122  and  124  is ideally infinite. In a second mode, transistor S 1  is open and transistor S 2  is closed. In this scenario, the inductance of inductor L 2  may be about 51 nH. In a third mode, the transistors in switch  120  are configured so that S 1  is closed and S 2  is open to switch inductor L 2 A into use and switch inductor L 2 B out of use. In this scenario, the inductance of inductor L 2  may be about 12 nH. In a fourth mode, the transistors in switch  120  are configured to switch both inductor L 2 A and inductor L 2 B into use (i.e., both S 1  and S 2  are closed), so the impedance of adjustable inductor L 2  has a fourth value (about 9.7 nH). 
     Switch  120  may be characterized by parasitics such as a capacitance Coff when the first and second ports are isolated from the third port and such as an “on resistance” Ron when the first and second ports are connected to the third port. The product of Coff and Ron may be about 200 fs. 
     The parasitic characteristics of switch  120  can influence antenna performance. Modelling results have shown that an antenna such as antenna  40  of  FIG. 8  that includes a tunable inductor such as inductor L 2  (e.g., an adjustable inductor with a field-effect transistor switch such as switch  120 ) will be prone to losses (lossy mode operation) in the two modes of operation in which inductor L 2 A is switched into use. These losses reduce antenna efficiency. The reduction in antenna efficiency, which may appear, for example, at operating frequencies of about 2 to 2.4 GHz, can be reduced or even eliminated by including capacitor C and inductor L 4  in antenna  40 , as shown in  FIG. 9 . Capacitor C may be coupled to inductor L 2 A. Inductor L 4  may be coupled in parallel with inductor L 2  between antenna resonating element  108  and ground  104 . Inductor L 4  and may be located between inductor L 2  and the antenna feed formed from positive feed terminal  98  and ground antenna feed terminal  100 . 
     As shown in  FIG. 9 , capacitor C may be coupled between one of the terminals of the lossy mode inductor (L 2 A) and ground. Capacitor C may, for example, have a first terminal that is coupled to inductor L 2 A at one of the ports of switch  120  (node  126 ) and may have a second terminal that is coupled to antenna ground  104  (node  128 ). The value of capacitor C may be about 0.3 pF (or other suitable value from 0.1 to 1 pF, more than 0.05 pF, more than 0.2 pF, less than 0.4 pF, less than 1 pF, etc.). Inductor L 4  may be coupled between antenna resonating element  108  (e.g., node  130  on peripheral conductive structure  16 - 1 ) and antenna ground  104  (e.g., node  132 ) in parallel with adjustable inductor L 2 . The value of inductor L 4  may be 36 nH or other suitable value (e.g., 10-60 nH, 20-45 nH, more than 5 nH, more than 30 nH, less than 50 nH, less than 60 nH, etc.). Circuit components such as inductor L 4  and capacitor C form circuit  134 . Circuit  134  may be used to ensure that antenna  40  of  FIG. 8  or other suitable antennas with adjustable inductors such as inductor L 2  will perform satisfactorily over a range of operating frequencies and will avoid performance degradation due to lossy mode operation. If desired, multiple capacitors may be used to eliminate multiple lossy modes. The example of  FIG. 9  is merely illustrative. 
       FIG. 10  is a graph in which antenna performance (antenna efficiency) has been plotted as a function of operating frequency for an illustrative antenna such as antenna  40  of  FIG. 8 . As shown in  FIG. 9 , antenna  40  may be configured to cover operating frequencies in a low band (e.g., frequencies from about 700 to 960 MHz) as well as midband and high band frequencies from 1500 to 2700 MHz (as examples). 
     During operation of device  10 , control circuitry may adjust switch  120  to place adjustable inductor L 2  in a desired mode, exhibiting inductance values of La (infinite impedance), Lb (51 nH in this example), Lc (12 nH in this example), or Lc (9.7 nH in this example). Each different tuning for adjustable inductor L 2  results in a different low band frequency response, as indicated by the antenna resonances labeled La, Lb, Lc, and Ld that are shown in the 700-960 MHz portion of the graph of  FIG. 10 . 
     In the Lc and Ld modes, the antenna response of antenna  40  between frequencies 1500 and 2700 MHz is given by solid line  140 . This is the normal expected response for antenna  40 . In the absence of circuit  134 , antenna  40  with adjustable inductor L 2  may exhibit undesired reductions in antenna performance at midband frequencies when operated in the La and Lb modes, as indicated by dashed line  142 . In the presence of circuit  134 , however, antenna  40  performs satisfactorily in the La and Lb modes as well as in the Lc and Ld modes. When circuit  134  is present, antenna performance will therefore be characterized by solid line  140  for all modes La, Lb, Lc, and Ld. 
     The foregoing is merely illustrative and various modifications can be made by those skilled in the art without departing from the scope and spirit of the described embodiments. The foregoing embodiments may be implemented individually or in any combination.

Metadata:
Filing Date: 20140903
Publication Date: 20161227
Grant Date: 20161227
Priority Date: 20140903
Inventors: HAN LIANG
MOW MATTHEW A.
TSAI MING-JU
ZHOU YIJUN
HU HONGFEI
YARGA SALIH
PASCOLINI MATTIA
OUYANG YUEHUI
IRCI ERDINC
AYALA VAZQUEZ ENRIQUE
SCHLUB ROBERT W.
Assignee: APPLE INC
CPC Classifications: [{"code": "H01Q13/10", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q9/42", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q5/328", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q1/243", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01Q5/328", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q1/243", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01Q9/42", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q13/10", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 55403578