PATENT DOCUMENT

Publication Number: US-9594147-B2
Application Number: US-201414506123-A
Country: US
Kind Code: B2

Title: Wireless electronic device with calibrated reflectometer

Abstract:
An electronic device may have control circuitry that uses a reflectometer to measure antenna impedance during operation. The reflectometer may have a directional coupler that is coupled between radio-frequency transceiver circuitry and an antenna. A calibration circuit may be coupled between the directional coupler and the antenna. The calibration circuit may have a first port coupled to the antenna, a second port coupled to the directional coupler, and a third port that is coupled to a calibration resistance. The reflectometer may have terminations of identical impedance that are coupled to ground. Switching circuitry in the reflectometer may be used to route signals from the directional coupler to a feedback receiver for measurement by the control circuitry or to ground through the terminations. Calibrated antenna reflection coefficient measurements may be used in dynamically adjusting the antenna.

Claims:
What is claimed is: 
     
       1. An electronic device, comprising:
 radio-frequency transceiver circuitry; 
 an antenna; 
 a transmission line path that couples the antenna to the radio-frequency transceiver circuitry; 
 a reflectometer coupled in the transmission line path between the antenna and the radio-frequency transceiver circuitry; and 
 a calibration circuit coupled between the reflectometer and the antenna, wherein the reflectometer comprises:
 a feedback receiver; 
 first and second terminations of identical impedance that are coupled to ground; 
 a directional coupler with first and second ports; 
 a first switch that couples the first port to the first termination in a first configuration and couples the first port to the feedback receiver in a second configuration; and 
 a second switch that couples the second port to the second termination in a first configuration and couples the second port to and the feedback receiver in a second configuration. 
 
 
     
     
       2. The electronic device defined in  claim 1  wherein the first and second terminations are characterized by a reflection coefficient and the electronic device comprises control circuitry that stores the reflection coefficient to calibrate the reflectometer. 
     
     
       3. The electronic device defined in  claim 2  wherein the calibration circuit has a first state in which a calibration resistance is switched into use and is coupled to the reflectometer and a second state in which the calibration resistance is switched out of use and the antenna is coupled to the reflectometer and the reflection coefficient is determined by the control circuitry using forward path and reverse path measurements made using the directional coupler, the switching circuitry, and the feedback receiver. 
     
     
       4. The electronic device defined in  claim 3  wherein the calibration circuit comprises a 50 ohm resistor that provides the calibration resistance. 
     
     
       5. The electronic device defined in  claim 4  wherein the calibration circuit further comprises a switch controlled by the control circuitry that selectively couples the reflectometer to one of: the 50 ohm resistor and the antenna. 
     
     
       6. The electronic device defined in  claim 4  further comprising peripheral conductive housing structures, wherein the antenna comprises an inverted-F antenna resonating element that is formed from the peripheral conductive housing structures. 
     
     
       7. The electronic device defined in  claim 3  wherein the calibration circuit comprises a switch connector. 
     
     
       8. The electronic device defined in  claim 2  wherein the antenna comprises a hybrid inverted-F slot antenna. 
     
     
       9. The electronic device defined in  claim 2  wherein the control circuitry is configured to calibrate the reflectometer and store the reflection coefficient by gathering both forward path measurements and reverse path measurements with the reflectometer. 
     
     
       10. A method of operating an electronic device having radio-frequency transceiver circuitry coupled to an antenna with a transmission line path, wherein the antenna includes adjustable circuitry, the method comprising:
 with control circuitry in the electronic device, controlling a reflectometer interposed in the transmission line path to gather a calibrated reflection coefficient measurement for the antenna; and 
 adjusting the adjustable circuitry of the antenna based on the calibrated reflection coefficient measurement for the antenna. 
 
     
     
       11. The method defined in  claim 10  wherein the reflectometer comprises a feedback receiver, first and second terminations of identical impedance that are coupled to ground, a directional coupler, and switching circuitry that is used in routing signals from the directional coupler to the feedback receiver and to ground and controlling the reflectometer comprises controlling the switching circuitry while measuring signals with the feedback receiver. 
     
     
       12. The method defined in  claim 11  wherein a calibration circuit is coupled between the reflectometer and the antenna, the method further comprising:
 transmitting and receiving signals with the radio-frequency transceiver circuitry and the antenna while the calibration circuit couples the directional coupler to the antenna. 
 
     
     
       13. The method defined in  claim 12  further comprising:
 performing calibration operations for the reflectometer by transmitting and receiving signals with the radio-frequency transceiver circuitry while the calibration circuit couples the directional coupler to a calibration resistor. 
 
     
     
       14. The method defined in  claim 13  wherein the antenna has an inverted-F antenna resonating element separated from an antenna ground by a gap and the adjustable circuitry bridges the gap. 
     
     
       15. An electronic device, comprising:
 a housing; 
 control circuitry in the housing; 
 radio-frequency transceiver circuitry; 
 an antenna; 
 a transmission line path that couples the antenna to the radio-frequency transceiver circuitry; 
 a reflectometer coupled in the transmission line path between the antenna and the radio-frequency transceiver circuitry, wherein the reflectometer is controlled by the control circuitry; and 
 a calibration circuit coupled between the reflectometer and the antenna, wherein the calibration circuit comprises:
 a calibration resistor; and 
 a switch having a first port coupled to the antenna, a second port coupled to the reflectometer, and a third port coupled to the calibration resistor. 
 
 
     
     
       16. The electronic device defined in  claim 15  wherein the reflectometer comprises:
 first and second terminations of identical impedance that are coupled to ground; 
 a directional coupler; and 
 switching circuitry that coupled between the directional coupler and the first and second terminations, wherein the switching circuitry is controlled by the control circuitry. 
 
     
     
       17. The electronic device defined in  claim 16  wherein the antenna includes adjustable circuitry that is adjusted by the control circuitry based on calibrated reflection coefficient measurements made on the antenna with the reflectometer. 
     
     
       18. The electronic device defined in  claim 17  wherein the control circuitry stores a reflection coefficient for the terminations and the electronic device housing comprises peripheral conductive structures that form part of the antenna. 
     
     
       19. The electronic device defined in  claim 1 , wherein the feedback receiver is configured to make phase and magnitude measurements on signals received from the directional coupler. 
     
     
       20. The electronic device defined in  claim 1 , further comprising:
 a housing; and 
 a display in the housing, wherein the radio-frequency transceiver circuitry, the antenna, the transmission line path, the reflectometer, and the calibration circuit are formed in the housing. 
 
     
     
       21. The electronic device defined in  claim 1 , wherein the first and second terminations comprise resistors. 
     
     
       22. The method defined in  claim 10 , wherein the adjustable circuitry comprises an adjustable inductor.

Description:
BACKGROUND 
     This relates generally to electronic devices and, more particularly, to wireless electronic devices. 
     Electronic devices often include wireless circuitry. For example, cellular telephones, computers, tablet computers, and other devices often contain antennas for supporting wireless communications. 
     It can be challenging to form wireless circuitry in electronic devices that is completely immune to environmental effects. As a result, antennas and other wireless circuits may experience variations in performance under different operating conditions. If, for example, an electronic device is resting against a metal table top, an antenna in that device may be loaded differently than when the electronic device is operated in free space. 
     It would therefore be desirable to be able to provide electronic devices with wireless circuitry that that can better accommodate changes in operating environment. 
     SUMMARY 
     An electronic device may have control circuitry that uses a reflectometer to measure antenna reflection coefficients and therefore monitor antenna impedance during operation. The reflectometer may have a directional coupler that is coupled between radio-frequency transceiver circuitry and an antenna. The directional coupler may also include a pair of terminations that are coupled to ground. The terminations may have identical impedance values. A feedback receiver with vector signal analyzer capabilities may be used in the reflectometer to gather signals from the directional coupler. Switching circuitry in the reflectometer may be used to route signals from the directional coupler to a feedback receiver for measurement by the control circuitry or to ground through the termination resistors. 
     A calibration circuit may be coupled between the directional coupler and the antenna. The calibration circuit may have a first port coupled to the antenna, a second port coupled to the directional coupler, and a third port that is coupled to a calibration resistance. The value of the calibration resistance is known, which allows the reflectometer to be calibrated. 
     During calibration operations, the reflection coefficients for the termination resistors can be obtained while the calibration resistor is switched into use. These reflection coefficients may then be stored in the control circuitry to calibrate the reflectometer. 
     During normal operation, calibrated reflection coefficient measurements may be made for the antenna by using the stored reflection coefficient values. The calibrated reflection coefficient measurements may be used by the control circuitry in determining how to adjust circuitry in the antenna. For example, control circuitry may make real time antenna adjustments to compensate for antenna detuning due to changes in antenna loading from contact of a body part or other external object with the antenna or other changes in the operating environment for the antenna. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an illustrative electronic device in accordance with an embodiment. 
         FIG. 2  is a schematic diagram of illustrative circuitry in an electronic device in accordance with an embodiment. 
         FIG. 3  is a top interior view of a portion of an electronic device having an antenna in accordance with an embodiment. 
         FIG. 4  is a diagram of a reflectometer of the type that may be used in monitoring the antenna of  FIG. 3  or other wireless electronic device circuitry in accordance with an embodiment. 
         FIG. 5  is a diagram showing variable names for signals associated with paths in the reflectometer of  FIG. 5  during forward path measurements in accordance with an embodiment of the present invention. 
         FIGS. 6, 7, and 8  show equations that may be used in analyzing forward path measurements made on an antenna using the reflectometer of  FIG. 5  in accordance with an embodiment. 
         FIG. 9  is a flow chart of illustrative operations involved in calibrating a reflectometer in an electronic device in accordance with an embodiment. 
         FIG. 10  is a flow chart of illustrative operations involved in using an electronic device with an antenna and a calibrated reflectometer that monitors the antenna in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Electronic devices such as electronic device  10  of  FIG. 1  may be provided with circuitry such as wireless communications circuitry. The wireless circuitry may include one or more antennas for transmitting and receiving wireless signals. An antenna or other wireless circuitry may be monitored in real time using a reflectometer. A calibration procedure may be used to ensure that measurements from the reflectometer will be accurate. 
     Device  10  may include one or more antennas such as 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 and internal structures (e.g., brackets, metal members that are formed using techniques such as stamping, machining, laser cutting, etc.), and other conductive electronic device structures. The housing structures may include peripheral structures such as peripheral conductive structures that run around the periphery of an electronic device. The peripheral conductive structure may serve as a bezel for a planar structure such as a display, may serve as sidewall structures for a device housing, may have portions that extend upwards from an integral planar rear housing (e.g., to form vertical planar sidewalls or curved sidewalls), and/or may form other housing structures. Gaps may be formed in the peripheral conductive structures that divide the peripheral conductive structures into peripheral segments. One or more of the segments may be used in forming one or more antennas for electronic device  10 . Antennas may also be formed using an antenna ground plane formed from conductive housing structures such as metal housing midplate structures and other internal device structures. Rear housing wall structures may be used in forming antenna structures such as an antenna ground. 
     Electronic device  10  may be a portable electronic device or other suitable electronic device. For example, electronic device  10  may be a laptop computer, a tablet computer, a somewhat smaller device such as a wristwatch device, pendant device, headphone device, earpiece device, or other wearable or miniature device, a handheld device such as a cellular telephone, a media player, an electronic stylus, 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. 
     The rear face of housing  12  may have a planar housing wall. The rear housing wall may be formed from metal with one or more regions that are filled with plastic or other dielectric. Portions of the rear housing wall that are separated by dielectric in this way may be coupled together using conductive structures (e.g., internal conductive structures) and/or may be electrically isolated from each other. 
     Device  10  may, if desired, have a display such as display  14 . Display  14  may be mounted on the opposing front face of device  10  from the rear housing wall. Display  14  may be a touch screen that incorporates capacitive touch electrodes or may be insensitive to touch. 
     Display  14  may include image pixels formed from light-emitting diodes (LEDs), organic LEDs (OLEDs), plasma cells, electrowetting pixels, electrophoretic pixels, liquid crystal display (LCD) components, or other suitable image pixel structures. A display cover layer such as a layer of clear glass or plastic, a layer of sapphire, a transparent dielectric such as clear ceramic, fused silica, transparent crystalline material, or other materials or combinations of these materials may cover the surface of display  14 . Buttons such as button  24  may pass through openings in the cover layer. The cover layer may also have other openings such as an opening for speaker port  26 . 
     Housing  12  may include peripheral housing structures such as structures  16 . Structures  16  may run around the periphery of device  10  and display  14 . In configurations in which device  10  and display  14  have a rectangular shape with four edges, structures  16  may be implemented using peripheral housing structures that have a rectangular ring shape with four corresponding edges (as an example). Peripheral structures  16  or part of peripheral structures  16  may serve as a bezel for display  14  (e.g., a cosmetic trim that surrounds all four sides of display  14  and/or that helps hold display  14  to device  10 ). Peripheral structures  16  may also, if desired, form sidewall structures for device  10  (e.g., by forming a metal band with vertical sidewalls, by curved sidewalls that extend upwards as integral portions of a rear housing wall, etc.). 
     Peripheral housing structures  16  may be formed of a conductive material such as metal and may therefore sometimes be referred to as peripheral conductive housing structures, conductive housing structures, peripheral metal structures, or a peripheral conductive housing member (as examples). Peripheral housing structures  16  may be formed from a metal such as stainless steel, aluminum, or other suitable materials. One, two, or more than two separate structures may be used in forming peripheral housing structures  16 . 
     It is not necessary for peripheral housing structures  16  to have a uniform cross-section. For example, the top portion of peripheral housing structures  16  may, if desired, have an inwardly protruding lip that helps hold display  14  in place. The bottom portion of peripheral housing structures  16  may also have an enlarged lip (e.g., in the plane of the rear surface of device  10 ). Peripheral housing structures  16  may have substantially straight vertical sidewalls, may have sidewalls that are curved, or may have other suitable shapes. In some configurations (e.g., when peripheral housing structures  16  serve as a bezel for display  14 ), peripheral housing structures  16  may run around the lip of housing  12  (i.e., peripheral housing structures  16  may cover only the edge of housing  12  that surrounds display  14  and not the rest of the sidewalls of housing  12 ). 
     If desired, housing  12  may have a conductive rear surface. For example, housing  12  may be formed from a metal such as stainless steel or aluminum. The rear surface of housing  12  may lie in a plane that is parallel to display  14 . In configurations for device  10  in which the rear surface of housing  12  is formed from metal, it may be desirable to form parts of peripheral conductive housing structures  16  as integral portions of the housing structures forming the rear surface of housing  12 . For example, a rear housing wall of device  10  may be formed from a planar metal structure and portions of peripheral housing structures  16  on the sides of housing  12  may be formed as vertically extending integral metal portions of the planar metal structure. Housing structures such as these may, if desired, be machined from a block of metal and/or may include multiple metal pieces that are assembled together to form housing  12 . The planar rear wall of housing  12  may have one or more, two or more, or three or more portions. 
     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 a display module for displaying images). 
     In regions such as 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 and/or solid dielectrics such as plastic, glass, ceramic, polymers with fiber filler material (e.g., fiber composites), sapphire, etc. 
     Conductive housing structures and other conductive structures in device  10  such as a midplate, traces on a printed circuit board, display  14 , and conductive electronic components may serve as a ground plane for the antennas in device  10 . The openings in regions  20  and  22  may serve as slots in open or closed slot antennas, may serve as a central dielectric region that is surrounded by a conductive path of materials in a loop antenna, may serve as a space that separates an antenna resonating element such as a strip antenna resonating element or an inverted-F antenna resonating element from the ground plane, may contribute to the performance of a parasitic antenna resonating element, or may otherwise serve as part of antenna structures formed in regions  20  and  22 . If desired, the ground plane that is under active area AA of display  14  and/or other metal structures in device  10  may have portions that extend into parts of the ends of device  10  (e.g., the ground may extend towards the dielectric-filled openings in regions  20  and  22 ). 
     In general, device  10  may include any suitable number of antennas (e.g., one or more, two or more, three or more, four or more, etc.). The antennas in device  10  may be located at opposing first and second ends of an elongated device housing (e.g., at ends  20  and  22  of device  10  of  FIG. 1 ), along one or more edges of a device housing, in the center of a device housing, in other suitable locations, or in one or more of these locations. The arrangement of  FIG. 1  is merely illustrative. 
     Portions of peripheral housing structures  16  may be provided with gap structures. For example, peripheral housing structures  16  may be provided with one or more peripheral 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 . If desired, gaps may extend across the width of the rear wall of housing  12  and may penetrate through the rear wall of housing  12  to divide the rear wall into different portions. Polymer or other dielectric may fill these housing gaps (grooves). 
     In a typical scenario, device  10  may have upper and lower antennas (as an example). An upper antenna may, for example, be formed at the upper end of device  10  in region  22 . A lower antenna may, for example, be formed at the lower end of device  10  in region  20 . The antennas may be used separately to cover identical communications bands, overlapping communications bands, or separate communications bands. The antennas may be used to implement an antenna diversity scheme or a multiple-input-multiple-output (MIMO) antenna scheme. 
     Antennas in device  10  may be used to support any communications bands of interest. For example, device  10  may include antenna structures for supporting local area network communications, voice and data cellular telephone communications, global positioning system (GPS) communications or other satellite navigation system communications, Bluetooth® communications, etc. 
     A schematic diagram showing illustrative components that may be used in device  10  of  FIG. 1  is shown in  FIG. 2 . As shown in  FIG. 2 , device  10  may include control circuitry such as storage and processing circuitry  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. Storage and processing circuitry  28  may, if desired, control the operation of adjustable antenna components to dynamically tune antennas in device  10 . 
     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, scrolling wheels, touch pads, key pads, keyboards, microphones, cameras, buttons, speakers, status indicators, light sources, audio jacks and other audio port components, digital data port devices, light sensors, motion sensors (accelerometers), capacitance sensors, proximity sensors, fingerprint sensors (e.g., a fingerprint sensor integrated with a button such as button  24  of  FIG. 1 ), etc. 
     Input-output circuitry  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 one or more antennas such as 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. 
     An interior top view of an illustrative antenna of the type that may be formed in device  10  is shown in  FIG. 3 . Antenna  40  of  FIG. 3  may be formed at end  20 , end  22 , or other portion of device  10 . The configuration for antenna  40  of  FIG. 3  is based on an inverted-F antenna design with a slot resonating element (i.e., antenna  40  of  FIG. 3  is a hybrid inverted-F slot antenna). This is merely illustrative. Antenna  40  may be any suitable type of antenna. 
     As shown in  FIG. 3 , antenna  40  may be coupled to transceiver circuitry  90 , so that transceiver circuitry  90  may transmit antenna signals through antenna  40  and may receive antenna signals through antenna  40 . 
     Transceiver circuitry  90  may be coupled to antenna  40  using paths such as transmission line path  92 . Transmission line  92  may include positive signal line (path)  94  and ground signal line (path)  96 . Transmission line  92  may be coupled to an antenna feed for antenna  40  that is formed from positive antenna feed terminal  98  and ground antenna feed terminal  100 . Positive signal line  94  may be coupled to positive antenna feed terminal  98  and ground signal line  96  may be coupled to ground antenna feed terminal  100 . If desired, impedance matching circuitry, switching circuitry, filter circuitry, reflectometer circuitry, and other circuits may be interposed in the path between transceiver circuitry  90  and antenna  40 . 
     Antenna  40  of  FIG. 3  includes inverted-F antenna resonating element  106  and antenna ground  104 . Ground  104  may be formed from metal portions of housing  12  (e.g., portions of the rear wall of housing  12 , a housing midplate, etc.), conductive structures such as display components and other electrical components, ground traces in printed circuits, etc. For example, ground  104  may include portions such as portions  104 ′ that are formed from metal housing walls, a metal band or bezel, or other peripheral conductive housing structures. 
     Antenna resonating element  106  may be formed from conductive structure  108 . Structure  108  may be formed from peripheral conductive housing structure in device  10  (e.g., a segment of structures  16  of  FIG. 1 ) or other conductive structure. Structure  108  may form a main resonating element arm for inverted-F antenna resonating element  106  and may have left and right ends that are separate from ground structure  104 ′ by peripheral gaps  18 . Components such as inductors  130  may, if desired, span gaps  18  to help tune antenna  40 . 
     Conductive structure  108  may have long and short branches (to the opposing sides of the antenna feed in the orientation of  FIG. 3 ) that support respective lower and higher frequency antenna resonances (e.g., low band and mid-band resonances). Inverted-F antennas that have opposing branches such as these may sometimes be referred to as T antennas or multi-branch inverted-F antennas. 
     Dielectric  114  may form a gap that separates structure  108  from ground  104 . The shape of the dielectric gap associated with dielectric  114  may form a slot antenna resonating element (i.e., the conductive structures surrounding dielectric  114  may form a slot antenna). The slot antenna resonating element may support an antenna resonance at higher frequencies (e.g., a high band resonance). Higher frequency antenna performance may also be supported by harmonics of the lower-frequency resonances associated with the longer and shorter branches of structure  108 . 
     One or more electrical components such as components  102  may span dielectric gap  114 . Components  102  may include resistors, capacitors, inductors, switches and other structures to provide tuning capabilities, etc. For example, components  102  may include an adjustable inductor that may be controlled by control circuitry  28  to produce a selected inductance value (e.g., a value selected form two possible inductances, a value selected from three or more possible inductances, etc.). The adjustable inductor may be adjusted using an electrically controlled switch or other circuitry. Adjustable circuitry such as the circuitry of components  102  may be used to tune the performance of antenna  40  dynamically during antenna operation. Fixed components may be included in components  102  to ensure that antenna  40  operates at desired frequencies. 
     Return path  110  may be coupled between the main inverted-F resonating element arm formed from structure  108  and antenna ground  104  in parallel with the antenna feed formed by feed terminals  98  and  100 . Return path  110  may be formed from a metal member having opposing first and second ends. In the example of  FIG. 3 , return path  110  is formed from a metal structure that has a first end with a terminal  120  coupled to structure  108  of inverted-F antenna resonating element  106  (e.g., on a housing sidewall or other peripheral conductive structure) and has a second end with a terminal  122  coupled to antenna ground  104 . Return path  110  may have other shapes and sizes, as illustrated, for example, by dashed line  110 ′ and illustrative terminal  122 ′. 
     Antenna  40  may become detuned as device  10  and antenna  40  are exposed to different operating environments. For example, antenna  40  may be detuned when placed in a removable case, when rested on a table top such as a metal or insulating table top, when held in a user&#39;s hand or operated in the vicinity of other body parts, etc. By monitoring the condition of antenna  40 , antenna  40  can be dynamically retuned by making adjustments to adjustable circuitry such as components  102  of  FIG. 3 . 
     With one suitable arrangement, antenna  40  or other wireless circuitry in device  10  (e.g., part of a transmission line, part of an antenna, etc.) may be monitored using an on-board reflectometer. As shown in  FIG. 4 , for example, device  10  may include a reflectometer such as reflectometer  200 . Reflectometer  200  may be interposed within transmission line path  92  between transceiver circuitry  90  and antenna  40 . Reflectometer  200  may include directional coupler  202 . Directional coupler  202  may have a first port (P 1 ) coupled to transceiver circuitry  90 , a second port (P 2 ) coupled to antenna  40 , and third and fourth ports (P 3  and P 4 ) that are coupled to terminations  208  (e.g., terminating circuits such as resistors and/or other electrical components) and feedback receiver  206  using switching circuitry  204 . Terminations  208  may be coupled to ground. Feedback receiver  206  may be a vector receiver (sometimes referred to as a vector signal analyzer or vector analyzer). Feedback receiver  206  may make phase and magnitude measurements on signals from directional coupler  202 . Feedback receiver  206  may be implemented at a stand-alone circuit or may be incorporated into transceiver circuitry  90  (as examples). 
     Switching circuitry  204  may be used to route signals from port P 3  or P 4  to feedback receiver  206 . When switch SW 1  is routing signals to receiver  206  from port P 3 , port P 4  may be terminated to ground using one of terminations  208  (i.e., switch SW 2  may couple port P 4  to the termination  208  that is coupled to switch SW 2 ). When switching circuitry  204  is configured so that switch SW 2  couples port P 4  to receiver  206 , switch SW 1  couples port P 3  to one of terminations  208 . 
     Terminations  208  and switching circuitry  204  may be implemented using an integrated circuit or other circuitry. Due to manufacturing variations, the precise resistance (impedance) of terminations  208  is not initially known, although it is accurate to assume that terminations  208  are well matched to each other and have identical impedance values. Because the impedances of terminations  208  are not initially known, the reflection coefficients Γ of terminations  208  are not initially known. 
     By using calibration circuit  210 , the impedances and reflection coefficients Γ of terminations  208  may be measured by control circuitry  28  and these measured values retained in storage in control circuitry  28 , thereby calibrating reflectometer  200  and device  10 . During subsequent operation of device  10 , reflectometer  200  may be used to make real time measurements on antenna  40  (e.g., measurements of antenna reflection coefficient Taut and therefore antenna impedance). 
     During normal operation, calibration circuit  210  is placed in a first state and couples port P 2  and antenna  40  together, so that transceiver circuitry  90  may transmit and receive antenna signals using antenna  40 . When it is desired to calibrate reflectometer  200 , switch S 3  is configured to temporarily place calibration circuit  210  in a second state in which calibration circuit  210  switches calibration resistor  212  into use. Calibration resistor  212  may be a grounded 50 ohm resistor or other resistor with an accurately known resistance such as a resistor that is calibrated using test equipment before installation into device  10 . When calibration circuit  210  is placed in its temporary second state, calibration resistor  212  will be coupled to directional coupler  202  in reflectometer  200  in place of antenna  40 . The switch of switch SW 3  in this type of scenario may be controlled by control signals from control circuitry  28 . If desired, calibration circuit  210  may be implemented using a switch connector. During normal operation of the switch connector, port P 2  and antenna  40  will be coupled to each other. When a probe is inserted into the switch connector during calibration operations, a calibrated 50 ohm resistance will be momentarily interposed within transmission line path  92  between port P 2  of directional coupler  202  and antenna  40 . In general, calibration circuit  210  may use an electrically controllable switch to switch calibration resistance  212  into use, may use a switch connector to momentarily switch calibration resistance  212  into use, or may use any other suitable switching circuitry to selectively couple port P 2  of directional coupler  202  to either resistor  212  or antenna  40 . 
     Reflectometer  200  may be configured to make forward path measurements and reverse path measurements. During calibration operations, which may be performed on a device-by-device basis or other suitable basis within a manufacturing facility during manufacturing, reflectometer  200  may be used in both the forward path and reverse path configurations while the known 50 ohm load of resistor  212  is switched into use to terminate port P 2  to ground. After gathering signals from reflectometer  200  for both the forward and reverse path configurations using feedback receiver  206 , network analysis may be performed on the gathered measurements using control circuitry  28 . The network analysis operations performed by circuitry  28  may be used to extract reflection coefficient Γ. Reflection coefficient Γ (which is related to the impedance of terminations  208 ) may be stored in memory within circuitry  28 . Knowing the value of Γ and retaining this value in device  10  serves to calibrate reflectometer  200 . Device  10  can then be shipped to a user and used normally to transmit and receive wireless signals. 
     During normal operation, control circuitry  28  may use reflectometer  200  to make measurements on antenna  40  (e.g., measurements of the reflection coefficient Γaut for antenna  40 , which are related to antenna impedance). The value of Γaut may be gathered using either forward path measurements or reverse path measurements. By measuring antenna impedance in real time, control circuitry  28  can determine whether antenna  40  is being detuned or is otherwise being affected by the presence of nearby objects. If antenna  40  is being detuned, control circuitry  28  can take corrective action. For example, components  102  or other adjustable circuitry may be used to adjust antenna  40  so that antenna  40  performs as desired. The corrective actions to take in response to different measured antenna impedance values (i.e., different measured reflection coefficients) can be characterized for device  10  (e.g., one or more sample devices, etc.) during characterization operations made in advance. Antenna characterization results may be stored in memory in storage  28  and used in determining how to adjust antenna  40  in response to different measured values of Γaut. For example, antenna characterization tests may reveal that whenever the impedance of antenna  40  lies within a given range, an adjustable inductor in components  102  should have a particular corresponding inductance value. A component adjustment function based on a look-up table or other data structure may be used to determine how control circuitry  28  should adjust components  102  during operation as a function of measured antenna impedance (reflection coefficient Γaut) to ensure that antenna  40  operates satisfactorily. 
     During calibration, network analysis operations may be performed to determine Γ (and therefore the impedance) of terminations  208 . Calibration operations involve using directional coupler measurements from reflectometer  200  and the known value of the impedance (and reflection coefficient) for calibration (reference) resistor  212  to determine Γ of terminations  208 . The network analysis operations performed during calibration involve processing the measurements taken by feedback receiver  206  when reflectometer  200  is in both the forward path and reverse path configurations and assume that the value of Γ is the same for both of terminations  208 . Terminations  208  are generally fabricated as part of a common integrated circuit (e.g., an integrated circuit on which directional coupler  202  is formed), so the assumption that terminations  208  have identical resistance will be valid. 
     During normal operation, either forward or reverse path measurements may be made to determine Γaut (and therefore the impedance of antenna  40 ).  FIGS. 5, 6, 7, and 8  illustrate how Γaut may be determined based on network analysis of forward path measurements made during normal operation. If desired, network analysis computations of Γaut such as these may be based on reverse path measurements with reflectometer  200  and these types of computations can be used when determining Γ during calibration. The example of  FIGS. 5, 6, 7, and 8  (pertaining to network analysis of forward path measurements) is merely illustrative. 
       FIG. 5  is a diagram showing the signal notation that is used in equations  6 ,  7 , and  8 . Signal af 1  is the signal injected at port  1  from transceiver  90  and is known, signal b 3   f  is the signal being measured by feedback receiver  206  and is known. The other signals are not initially known. The value of Γ, which is the reflection coefficient of terminations  208 , was obtained during calibration and is stored in circuitry  28 . The variables Sijk (i, j=1 to 4, k=f or b) are the S-parameters for directional coupler  202 . In the equation of  FIG. 6 , the value of a 4   f  is calculated as a function of the known S-parameters, the known injected signal a 1   f , the known measured signal b 3   f , and the known value of Γ. In the equation of  FIG. 7 , the value of a 4   f  that was calculated using the equation of  FIG. 6  is used (along with the known values of b 3   f  and a 1   f  and the known S-parameter values) to compute a 2   f . As shown in the equation of  FIG. 8 , the value of reflection coefficient Γaut for antenna  40  may then be calculated based on the value of a 2   f  from the equation of  FIG. 7  and the known values of a 1   f  and a 4   f  from the equation of  FIG. 6 . The value of Γaut (or the related antenna impedance of antenna  40  that is a function of Γaut) may be used in making antenna adjustment decisions or other decisions involving the operation of device  10 . 
       FIG. 9  is a flow chart of illustrative steps involved in performing calibration operations to calibrate reflectometer  200 . The operations of  FIG. 9  may be performed during manufacturing or at any other suitable time. 
     At step  300 , control circuitry  28  may use reflectometer  200 , calibration circuit  210 , and feedback receiver  206  to make forward path measurements. Calibration circuit  210  may be configured to switch reference (calibration) resistor  212  into use by coupling resistor  212  to port P 2  of directional coupler  202 . This switches antenna  40  temporarily out of use and substitutes the known load of resistor  212 . Switching circuitry  204  of reflectometer  200  may be used to route forward path signals from port P 3  to receiver  206  through switch SW 1  while switch SW 2  grounds port P 4  via the termination  208  that is coupled to switch SW 2 . Measurements from receiver  206  are then gathered by control circuitry  28 . 
     At step  302 , control circuitry  28  may use reflectometer  200 , calibration circuit  210 , and feedback receiver  206  to make reverse path measurements. During these measurements, calibration circuit  210  is still configured to switch reference resistors  212  into use, but the states of switches SW 1  and SW 2  are reversed, so that port P 3  is grounded via the right-hand termination  208  in  FIG. 4  while signals from port P 4  are measured by receiver  206 . Circuitry  28  gathers measurements from receiver  206 . 
     During the operations of step  304 , control circuitry  28  may extract the value of Γ (i.e., the reflection coefficient for each of terminations  208 ) from the measurements gathered at steps  300  and  302  using network analysis. The value of Γ serves as calibration information for reflectometer  200  and may be stored in memory in circuitry  28  for future use in calibrating antenna impedance measurements (reflection coefficient measurements) that are made using reflectometer  200 . 
     Illustrative steps involved in operating device  10  during normal operation (i.e., after reflectometer  200  in device  10  has been calibrated by gathering Γ) are shown in  FIG. 10 . 
     At step  306 , control circuitry  28  may perform either forward or reverse path measurements on antenna  40  using reflectometer  200  and feedback receiver  206 . During these measurements, calibration circuit  210  is configured to switch reference resistor  212  out of use and is configured to couple port P 2  to antenna  40  so that antenna  40  may be used normally by transceiver circuitry  90 . As described in connection with  FIGS. 5, 6, 7, and 8 , the measurements of step  306  allow control circuitry  28  to compute the reflection coefficient Γaut of antenna  40  (i.e., the impedance of antenna  40 ) at step  308 . Once Γaut is known, control circuitry  28  can take suitable action in controlling the operation of device  10  at step  310 . For example, control circuitry  28  can compare the value of Γaut (reflection coefficient or antenna impedance) to a table or other data structure that includes corresponding antenna settings for antenna  40  that are to be used to ensure that antenna  40  performs satisfactorily. The table or other data structure may, for example, be a look-up table that provides control circuitry  28  with appropriate settings to use for components  102  as a function of measured reflection coefficient (antenna impedance). Upon obtaining the appropriate settings for components  102  or other adjustable antenna circuitry for antenna  40 , control circuitry  28  can adjust antenna  40  by adjusting components  102  accordingly. Wireless signals may then be transmitted and received normally using transceiver  90  and antenna  40 . The antenna monitoring and adjustment operations of steps  306  and  308 , and  310  may be periodically repeated, as illustrated by line  312  (e.g., according to a schedule, when predetermined criteria have been satisfied, when a measurement command is received from external equipment, etc.). 
     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: 20141003
Publication Date: 20170314
Grant Date: 20170314
Priority Date: 20141003
Inventors: HAN LIANG
MOW MATTHEW A.
BIEDKA THOMAS E.
PASCOLINI MATTIA
TSAI MING-JU
JUDKINS JAMES G.
LEE VICTOR
SCHLUB ROBERT W.
Assignee: APPLE INC
CPC Classifications: [{"code": "H04B17/14", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B17/103", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q13/10", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01Q1/243", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01R29/0878", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q9/42", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01Q1/243", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B17/14", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01R35/005", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01Q1/243", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01R35/005", "inventive": true, "first": true, "tree": "[]"}, {"code": "G01R29/0878", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B17/14", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B17/103", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B17/103", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01Q13/10", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01Q9/42", "inventive": false, "first": false, "tree": "[]"}]
Family ID: 54251750