PATENT DOCUMENT

Publication Number: US-9270012-B2
Application Number: US-201213363743-A
Country: US
Kind Code: B2

Title: Electronic device with calibrated tunable antenna

Abstract:
An electronic device may have tunable antenna structures. A tunable antenna may have an antenna resonating element and an antenna ground. An adjustable electronic component such as an adjustable capacitor, adjustable inductor, or adjustable phase-shift element may be used in tuning the antenna. An impedance matching circuit may be coupled between the tunable antenna and a radio-frequency transceiver. The adjustable electronic component may be coupled to the antenna resonating element or other structures in the antenna or may form part of the impedance matching circuit, a transmission line, a parasitic antenna element, or other antenna structures. During manufacturing, manufacturing variations may cause the performance of the tunable antenna to deviate from desired specifications. Calibration operations may be performed to identify compensating adjustments to be made with the adjustable electronic component. Calibration data for the adjustable component may be stored in control circuitry in the electronic device.

Claims:
What is claimed is: 
     
       1. An electronic device, comprising:
 a tunable antenna having an adjustable component that is operable to tune the antenna and that has multiple control lines; and 
 control circuitry that is configured to provide digital control signals over the multiple control lines to tune the antenna, wherein the control circuitry produces the digital control signals by modifying calibration settings for the adjustable component using information that compensates for manufacturing variations in the electronic device. 
 
     
     
       2. The electronic device defined in  claim 1  wherein the tunable antenna comprises an antenna resonating element and wherein the adjustable component is coupled to the antenna resonating element. 
     
     
       3. The electronic device defined in  claim 1  further comprising:
 radio-frequency transceiver circuitry; and 
 an impedance matching circuit interposed between the tunable antenna and the radio-frequency transceiver circuitry, wherein the impedance matching circuit includes the adjustable component. 
 
     
     
       4. The electronic device defined in  claim 1  wherein the adjustable component comprises an adjustable component selected from the group consisting of: an adjustable phase shift element, an adjustable capacitor, and an adjustable inductor. 
     
     
       5. The electronic device defined in  claim 4  further comprising:
 a peripheral conductive housing member, wherein at least part of the peripheral conductive housing member forms at least part of the tunable antenna. 
 
     
     
       6. The electronic device defined in  claim 1  wherein the adjustable component comprises an adjustable phase-shift element. 
     
     
       7. The electronic device defined in  claim 1  wherein the adjustable component comprises an adjustable capacitor. 
     
     
       8. The electronic device defined in  claim 1  wherein the adjustable component comprises:
 a digital control signal input configured to receive a digital control signal from the control circuitry; and 
 a switch that is configured to receive the digital control signal from the digital control signal input; and 
 a plurality of capacitors coupled to the switch. 
 
     
     
       9. The electronic device defined in  claim 8  further comprising:
 a peripheral conductive housing member, wherein at least part of the peripheral conductive housing member forms at least part of the tunable antenna. 
 
     
     
       10. The electronic device defined in  claim 9  wherein the tunable antenna comprises an inverted-F antenna having at least one resonating element arm formed from the peripheral conductive housing member. 
     
     
       11. The electronic device defined in  claim 10  wherein the adjustable component is coupled to the resonating element arm. 
     
     
       12. The electronic device defined in  claim 10  further comprising:
 radio-frequency transceiver circuitry; and 
 an impedance matching circuit interposed between the tunable antenna and the radio-frequency transceiver circuitry, wherein the impedance matching circuit includes the adjustable component. 
 
     
     
       13. The electronic device defined in  claim 1 , wherein the information that compensates for manufacturing variations in the electronic device comprises a formula and the digital control signals are computed in real time based on the formula and the calibration settings for the adjustable component. 
     
     
       14. The electronic device defined in  claim 1 , wherein the adjustable component comprises:
 multiplexing circuitry that receives the digital control signals and that adjusts a phase shift provided by the adjustable component based on the digital control signals. 
 
     
     
       15. The electronic device defined in  claim 1 , wherein the control circuitry adjusts raw calibration settings using the information that compensates for manufacturing variations to produce the digital control signals, the information that compensates for manufacturing variations comprises an offset, and the digital control signals are generated by applying the offset of the information that compensates for manufacturing variations to the raw calibration settings. 
     
     
       16. The electronic device defined in  claim 1 , wherein the adjustable component comprises:
 multiplexing circuitry that receives the digital control signals and that adjusts an impedance of the adjustable component based on the digital control signals. 
 
     
     
       17. The electronic device defined in  claim 1 , wherein the tunable antenna comprises:
 an antenna ground; 
 an antenna resonating arm; and 
 an antenna feed branch coupled between the antenna resonating arm and the antenna ground, wherein the adjustable component is coupled in the antenna feed branch. 
 
     
     
       18. The electronic device defined in  claim 17 , further comprising:
 a peripheral conductive housing member, wherein the antenna resonating arm of the tunable antenna is at least partially formed from a portion of the peripheral conductive housing member. 
 
     
     
       19. The electronic device defined in  claim 1 , wherein the adjustable component comprises:
 an adjustable capacitor having a switch that adjusts a capacitance exhibited by the adjustable capacitor.

Description:
BACKGROUND 
     This relates generally to manufacturing, and more particularly, to calibrating electronic device antenna performance during manufacturing. 
     Electronic devices such as portable computers and cellular telephones are often provided with wireless communications capabilities. For example, electronic devices may use long-range wireless communications circuitry such as cellular telephone circuitry and short-range wireless communications circuitry such as wireless local area network circuitry. To handle wireless communications, electronic devices may be provided with one or more antennas. In some configurations, antennas may include tunable circuitry. 
     Due to manufacturing variations, antennas may not initially perform according to desired specifications. This may lead to costly rework or may require that antennas be discarded on the manufacturing line. In situations in which antennas are formed using conductive parts of an electronic device housing and situations in which there are multiple antennas in a device, antenna faults due to manufacturing variations may have a significant adverse impact to device yields. 
     It would therefore be desirable to be able to provide improved ways of manufacturing antennas and electronic devices with antennas. 
     SUMMARY 
     An electronic device may have tunable antenna structures. Adjustable components may be used to tune the tunable antenna structures. 
     Manufacturing variations may cause antenna performance to deviate from design specifications. During manufacturing, wireless test equipment may be used to characterize antenna performance. Antenna performance measurements may be made while using a variety of different settings for the adjustable components that tune the antennas. Antenna performance measurements for each set of settings may be compared to desired performance limits to determine whether compensating adjustments should be made to the adjustable components in an electronic device. Calibration data for the adjustable components in the device may be stored in control circuitry in the device. 
     A tunable antenna may have an antenna resonating element and an antenna ground. An adjustable electronic component such as an adjustable capacitor, adjustable inductor, or adjustable phase-shift element may be used in tuning the antenna. An impedance matching circuit may be coupled between the tunable antenna and a radio-frequency transceiver. The adjustable electronic component may be coupled to the antenna resonating element or may form part of the impedance matching circuit, a transmission line, a parasitic antenna element, or other antenna structures. 
     Further features of the invention, its nature and various advantages will be more apparent from the accompanying drawings and the following detailed description of the preferred embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an illustrative electronic device of the type that may include wireless circuitry with antenna structures that may be calibrated in accordance with an embodiment of the present invention. 
         FIG. 2  is a schematic diagram of an illustrative electronic device of the type that may include wireless circuitry with antenna structures that may be calibrated in accordance with an embodiment of the present invention. 
         FIG. 3  is a top view of an electronic device having conductive housing structures such as a segmented peripheral conductive member and planar mid-plate structures that may be used in forming antenna structures in accordance with an embodiment of the present invention. 
         FIG. 4  is a circuit diagram showing how radio-frequency transceiver circuitry may be coupled to antenna structures using an impedance matching circuit such as impedance mating circuitry that includes one or more adjustable components in accordance with an embodiment of the present invention. 
         FIG. 5  is a diagram of an illustrative antenna having adjustable circuits with adjustable capacitors in accordance with an embodiment of the present invention. 
         FIG. 6  is a diagram of an illustrative antenna having adjustable circuits with adjustable inductors in accordance with an embodiment of the present invention. 
         FIG. 7  is a graph showing how adjustable impedance matching circuitry and adjustable antenna components may be used in tuning antenna performance by adjusting low band and high band antenna resonance peaks in accordance with an embodiment of the present invention. 
         FIG. 8  is a diagram of an adjustable capacitor in accordance with an embodiment of the present invention. 
         FIG. 9  is a diagram of an adjustable inductor in accordance with an embodiment of the present invention. 
         FIG. 10  is a diagram of an illustrative adjustable phase-shift element that may be used in a matching circuit, transmission line, or other wireless circuit to tune antenna performance in accordance with an embodiment of the present invention. 
         FIG. 11  is a diagram of an illustrative system that may be used in calibrating wireless electronic devices and antenna structures in accordance with an embodiment of the present invention. 
         FIG. 12  is a graph showing how antenna performance may vary in response to the use of different adjustable component settings and how antenna performance may be compared to predefined performance limits to determine whether calibrating adjustments should be made in accordance with an embodiment of the present invention. 
         FIG. 13  is a flow chart of illustrative steps involved in manufacturing devices with calibrated wireless circuitry in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Electronic devices such as electronic device  10  of  FIG. 1  may be provided with wireless communications circuitry. The wireless communications circuitry may have one or more antennas and may be used to support wireless communications in one or more wireless communications bands. 
     Device  10  of  FIG. 1  may be a computer monitor with an integrated computer, a desktop computer, a television, a notebook computer, other portable electronic equipment such as a cellular telephone, a tablet computer, a media player, a wrist-watch device, a pendant device, an earpiece device, other compact portable devices, or other electronic equipment. 
     Device  10  may include antenna structures 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. The housing structures may include a peripheral conductive member that runs around the periphery of an electronic device. The peripheral conductive member may serve as a bezel for a planar structure such as a display, may serve as sidewall structures for a device housing, or may form other housing structures. Gaps in the peripheral conductive member may be associated with the antennas. 
     The size of the gaps that are produced during manufacturing, the size and shapes of the peripheral conductive member and internal ground plane structures formed from parts of an electronic device housing or other conductive structures (e.g., printed circuit board structures), the size and shapes of printed circuit traces that are used in forming antenna structure, impedance matching circuit component variations, transmission line variations, and other manufacturing variations can influence the electrical properties of the antennas that are formed in device  10 . For example, manufacturing variations may cause an antenna to exhibit a resonant peak at a different frequency than desired. 
     To ensure that device  10  performs properly, device  10  and/or antenna structures in device  10  may be tested during manufacturing. The test measurements may reveal undesired antenna performance variations. Compensating calibration adjustments may then be made to adjustable circuitry in device  10 . For example, settings for adjustable components in impedance matching circuits and/or antennas may be identified for calibrating the wireless performance of the antenna structures and device  10 . Using this approach, each device (and the antenna structures for that device) may be individually calibrated to ensure that its wireless circuitry is satisfying desired performance criteria. 
     Device  10  of  FIG. 1  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, electronic ink elements, liquid crystal display (LCD) components, or other suitable image pixel structures. A cover glass layer may cover the surface of display  14 . Buttons and speaker port openings may pass through openings in the cover glass. 
     Housing  12  may include structures such as housing member  16 . Member  16  may run around the rectangular periphery of device  10  and display  14 . Member  16  or part of member  16  may serve as a bezel for display  14  (e.g., a cosmetic trim that surrounds all four sides of display  14  and/or helps hold display  14  to device  10 ). Member  16  may also, if desired, form sidewall structures for device  10 . 
     Member  16  may be formed of a conductive material and may therefore sometimes be referred to as a peripheral conductive housing member, conductive housing structures, or peripheral conductive member. Member  16  may be formed from a metal such as stainless steel, aluminum, or other suitable materials. One, two, or more than two separate structures may be used in forming member  16 . 
     It is not necessary for member  16  to have a uniform cross-section. For example, the top portion of member  16  may, if desired, have an inwardly protruding lip that helps hold display  14  in place. If desired, the bottom portion of member  16  may also have an enlarged lip (e.g., in the plane of the rear surface of device  10 ). In the example of  FIG. 1 , member  16  has substantially straight vertical sidewalls. This is merely illustrative. The sidewalls of member  16  may be curved or may have any other suitable shape. In some configurations (e.g., when member  16  serves as a bezel for display  14 ), member  16  may run around the lip of housing  12  (i.e., member  16  may cover only the edge of housing  12  that surrounds display  14  and not the rear edge of the sidewalls of housing  12 ). 
     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 sheet metal structure formed from one or more sections that are welded or otherwise connected between the opposing right and left sides of member  16 ), printed circuit boards, and other internal conductive structures. These conductive structures may be located in center of housing  12  (as an example). 
     In regions  20  and  22 , openings may be formed between the conductive housing structures and conductive electrical components that make up device  10 . These openings may be filled with air, plastic, and other dielectrics. Conductive housing structures and other conductive structures in device  10  may serve as a ground plane for the antennas in device  10 . The openings in regions  20  and  22  may serve as slots in open or closed slot antennas, may serve as a central dielectric region that is surrounded by a conductive path of materials in a loop antenna, may serve as a space that separates an antenna resonating element such as a strip antenna resonating element or an inverted-F antenna resonating element from the ground plane, or may otherwise serve as part of antenna structures formed in regions  20  and  22 . 
     Portions of member  16  may be provided with gap structures  18 . Gaps  18  may be filled with dielectric such as polymer, ceramic, glass, etc. Gaps  18  may divide member  16  into one or more peripheral conductive member segments. There may be, for example, two segments of member  16  (e.g., in an arrangement with two gaps), three segments of member  16  (e.g., in an arrangement with three gaps), four segments of member  16  (e.g., in an arrangement with four gaps, etc.). The segments of peripheral conductive member  16  that are formed in this way may form parts of antennas in device  10 . 
     A schematic diagram of electronic device  10  is shown in  FIG. 2 . As shown in  FIG. 2 , electronic device  10  may include control circuitry such as storage and processing circuitry  28 . Storage and processing circuitry  28  may include storage such as hard disk drive storage, nonvolatile memory (e.g., flash memory or other electrically-programmable-read-only memory configured to form a solid state drive), volatile memory (e.g., static or dynamic random-access-memory), etc. Processing circuitry in storage and processing circuitry  28  may be used to control the operation of device  10 . This processing circuitry may be based on one or more system on chip (SoC) integrated circuits, microprocessors, microcontrollers, digital signal processors, baseband processors, power management units, audio codec chips, application specific integrated circuits, memory controllers, timing controllers, etc. 
     Storage and processing circuitry  28  may be used to run software on device  10 , such as internet browsing applications, voice-over-internet-protocol (VoIP) telephone call applications, email applications, media playback applications, operating system functions, etc. To support interactions with external equipment, storage and processing circuitry  28  may be used in implementing communications protocols. Communications protocols that may be implemented using storage and processing circuitry  28  include internet protocols, wireless local area network protocols (e.g., IEEE 802.11 protocols—sometimes referred to as WiFi®), protocols for other short-range wireless communications links such as the Bluetooth® protocol, cellular telephone protocols, etc. 
     To support manufacturing operations, circuitry  28  may be configured to implement test and calibration algorithms. For example, circuitry  28  may be configured to direct radio-frequency transceiver circuitry in device  10  to transmit or receive signals at particular frequencies while making power measurements (as an example). 
     Adjustable components in device  10  may be used to tune antenna performance. For example, device  10  may include tunable impedance matching circuitry, tunable antennas, or other tunable circuitry that can be adjusted to modify the frequency response of the wireless circuitry of device  10 . Circuitry  28  may be configured to implement a control algorithm that adjusts components such as adjustable capacitors, adjustable inductors, adjustable phase shifters, and other adjustable circuitry. 
     Input-output circuitry  30  may be used to allow data to be supplied to device  10  and to allow data to be provided from device  10  to external devices. Input-output circuitry  30  may include input-output devices  32 . Input-output devices  32  may include touch screens, buttons, joysticks, click wheels, scrolling wheels, touch pads, key pads, keyboards, microphones, speakers, tone generators, vibrators, cameras, sensors, light-emitting diodes and other status indicators, transceiver circuits associated with data ports, etc. A user can control the operation of device  10  by supplying commands through input-output devices  32  and may receive status information and other output from device  10  using the output resources of input-output devices  32 . 
     Wireless communications circuitry  34  may include radio-frequency (RF) transceiver circuitry formed from one or more integrated circuits, power amplifier circuitry, low-noise input amplifiers, passive RF components, one or more antennas, impedance matching circuits, switches, filters, and other circuitry for handling RF wireless signals. Wireless signals can also be sent using light (e.g., using infrared communications). 
     Wireless communications circuitry  34  may include satellite navigation system receiver circuitry  35  such as Global Positioning System (GPS) receiver circuitry operating at 1575 MHz and/or receiver circuitry using the Global Navigation System (GLONASS) at 1605 MHz or other satellite navigation systems. Wireless local area network transceiver circuitry  36  may handle 2.4 GHz and 5 GHz bands for WiFi® (IEEE 802.11) communications and may handle the 2.4 GHz Bluetooth® communications band. Circuitry  34  may use cellular telephone transceiver circuitry  38  for handling wireless communications in cellular telephone bands such as bands at about 700 MHz to about 2200 MHz or other cellular telephone bands of interest. Wireless communications circuitry  34  can include circuitry for other short-range and long-range wireless links if desired. For example, wireless communications circuitry  34  may include wireless circuitry for receiving radio and television signals, paging circuits, near field communications circuitry, 60 GHz communications circuitry, etc. In WiFi® and Bluetooth® links and other short-range wireless links, wireless signals are typically used to convey data over tens or hundreds of feet. In cellular telephone links and other long-range links, wireless signals are typically used to convey data over thousands of feet or miles. 
     Wireless communications circuitry  34  may include one or more antennas  40 . Antennas  40  may be formed using any suitable antenna types. For example, antennas  40  may include antennas with resonating elements that are formed from loop antenna structure, patch antenna structures, inverted-F antenna structures, closed and open slot antenna structures, planar inverted-F antenna structures, helical antenna structures, strip antennas, monopoles, dipoles, hybrids of these designs, etc. Different types of antennas may be used for different bands and combinations of bands. For example, one type of antenna may be used in forming a local wireless link antenna and another type of antenna may be used in forming a remote wireless link. If desired, a single antenna with one or more feeds may be used to handle multiple types of signals. For example, a single antenna may be used to handle wireless local area network traffic at 2.4 GHz, satellite navigation signals, and cellular telephone signals (as an example). 
     A top view of an interior portion of device  10  is shown in  FIG. 3 . If desired, device  10  may have upper and lower antennas (as an example). An upper antenna such as antenna  40 U may, for example, be formed at the upper end of device  10  in region  22 . A lower antenna such as antenna  40 L may, for example, be formed at the lower end of device  10  in region  20 . The antennas may be used separately to cover separate communications bands of interest or may be used together to implement an antenna diversity scheme or a multiple-input-multiple-output (MIMO) antenna scheme. 
     Antenna  40 L may be formed from the portions of midplate  58  and peripheral conductive housing member  16  that surround dielectric-filled opening  56 . Antenna  40 L may be fed by transmission line  50 , which is coupled to positive feed terminal  54  and ground feed terminal  52 . Other feed arrangements may be used if desired. The arrangement of  FIG. 3  is merely illustrative. 
     Antenna  40 U may be formed from the portions of midplate  58  and peripheral conductive housing member  16  that surround dielectric-filled opening  60 . Member  16  may have a low-band segment LBA that terminates at one of gaps  18  and a high-band segment HBA that terminates at another one of gaps  18 . Antenna  40 U may be fed using transmission line  62 . Transmission line  62  may be coupled to positive antenna feed terminal  66  and ground antenna feed terminal  64  (as an example). Conductive member  68  may span opening  60  to form an inverted-F antenna short-circuit path. Segments LBA and HBA may form low-band and high-band cellular telephone inverted-F antennas (as an example). 
     If desired, the positions of antennas  40 U and  40 L may be reversed (i.e., antenna  40 U may be formed in region  20  and antenna  40 L may be formed in region  22 . Configurations in which antennas  40  are formed in other portions of device  10  may also be used. 
     As shown in  FIG. 4 , wireless circuitry  34  may include impedance matching circuitry such as impedance matching circuitry  70  (e.g., for each antenna and/or each antenna feed in device  10 ). Matching circuitry  70  may include a network of one or more switches, filters, discrete components such as inductors, resistors, and capacitors, and one or more adjustable components such as adjustable components  74 . One or more adjustable components  74  may also be incorporated into other portions of wireless circuitry  34  such as antenna  40 , part of a transmission line, part of a parasitic antenna element, etc. 
     The performance of antenna  40  may be tuned by adjusting adjustable components  74  in impedance matching circuitry  70  and/or antenna  40 . Tuning may be used in real time during the operation of antenna  40  to allow antenna  40  to cover desired communications bands of interest. To accommodate manufacturing variations, adjustable component  74  may be controlled using calibration data. The calibration data may include, for example, compensating offset settings to be used when adjusting an adjustable component. By applying the calibration data (e.g., compensating offsets) when adjusting adjustable components  74 , the wireless performance of device  10  may be assured of meeting design specifications. 
     Transmission lines such as transmission line  72  may be used to couple transceiver circuitry  76  (e.g., transceiver circuitry such as transceiver circuitry  35 ,  36 , and/or  38  of  FIG. 2 ) to antenna structures such as antenna  40 . Transmission line  72  may be formed from coaxial cable, a microstrip transmission line structure, a stripline transmission line structure, transmission line structures that are formed from other structures or combinations of these structures. Transmission line  72  may include a positive signal conductor such as signal line  72 P and a ground signal conductor such as ground signal line  72 N. Matching circuitry  70  may be interposed within transmission line  72  between radio-frequency transceiver circuitry  76  and antenna  40 . Antenna  40  may have an antenna feed made up of a positive antenna feed terminal (+) to which positive signal lines  72 P is coupled and a ground antenna feed terminal (−) to which ground signal lines  72 N is coupled (i.e., antenna feed terminals such as terminals  66 ,  64 ,  54 , and  52  of  FIG. 3 ). 
     Antennas such as antenna  40  may be located at upper end  22  or lower end  20  of device housing  12  or may be located at other portions of device housing  12  (e.g., along a device edge, in the center of a rear housing wall, etc.). 
     Each antenna  40  may, if desired, be provide with adjustable components such as adjustable components  74 . Adjustable components  74  may also be incorporated into a matching circuit such as matching circuit  70 . Adjustable components  74  may include varactors, variable resistors, switch-based components such as variable capacitors and inductors that respectively exhibit multiple discrete capacitance or inductance values, adjustable phase shift components, or other adjustable circuitry. Adjustable components  74  may be controlled using analog or digital control signals. For example, a 32 bit digital control signal may be used to place an adjustable component in a desired state out of 32 available states. Digital control signals with other bit widths may be used for controlling adjustable components with other numbers of states. Digital control signals may, in general, be a one bit signal, a two bit signal, a signal with more than two bits, a signal with two to 128 bits, a signal with 32, 64, or 128 bits, etc. 
     During calibration operations, the wireless performance of device  10  can be measured using test equipment and corresponding calibration adjustments may be made using adjustable components  74 , so that device  10  exhibits desired wireless performance. 
       FIG. 5  is a schematic diagram of an illustrative antenna such as antenna  40  of  FIG. 4 . Antenna  40  may be located at the upper or lower end of device  10  or may be mounted in other suitable locations within device housing  12 . Antenna  40  may have an antenna feed with a positive antenna feed terminal (+) and a ground antenna feed terminal (−). Transmission line  72  ( FIG. 4 ) may have respective positive and ground conductors that are coupled to the positive and ground antenna feed terminals. 
     In the illustrative configuration of  FIG. 5 , antenna  40  has antenna resonating element  78  and antenna ground  80 . Antenna resonating element  78  may be, for example, an inverted-F antenna resonating element. Resonating element  78  may include a main resonating element arm such as arm  84 . Short circuit branch  82  may be coupled between main resonating element arm  84  and ground  80 . Antenna resonating element  78  may have a feed branch such as feed branch  86  that is coupled in parallel with short circuit branch  82  between main resonating element arm  84  and ground  80 . Some or all of the conductive structures in antenna  40  such as arm  84  and branch  82  may be formed from conductive housing structures. For example, arm  84  and branch  82  may be formed from a segment of peripheral conductive member  16  at the upper or lower end of housing  12  in  FIG. 3 . The end of arm  84  may be separated from ground  80  by a gap such as gap  18  ( FIG. 3 ). 
     Antenna  40  may have one or more adjustable components such as components in adjustable circuit  88  and adjustable circuit  90 . As shown in  FIG. 5 , adjustable circuit  88  may be interposed in antenna feed branch  86  between the antenna feed and main antenna resonating element arm  84 . Adjustable circuit  90  may be coupled in parallel with the antenna feed (i.e., circuit  90  may be bridge the (+) and (−) antenna feed terminals). If desired, control circuitry  28  ( FIG. 2 ) may issue digital or analog control signals to adjustable circuit  88  and/or adjustable circuit  90  in real time during the operation of device  10  to dynamically tune antenna  40  to cover desired communications bands of interest. Control circuitry  28  may also apply an offset or other calibration data when adjusting circuits  88  and  90 , so that antenna  40  and device  10  performs according to design specifications. As shown in the example of  FIG. 5 , adjustable circuits  88  and  90  may be adjustable capacitors or may contain adjustable capacitors. As shown in the example of  FIG. 6 , adjustable circuits  88  and  90  may be adjustable inductors or may contain adjustable inductors. These are merely illustrative examples. Adjustable circuits  88  and  90  may be formed from any suitable network of adjustable components. 
     In the examples of  FIGS. 5 and 6 , antenna  40  is based on an inverted-F design having a single main resonating element arm. If desired, antenna  40  may be an inverted-F antenna that has a main resonating element arm with multiple branches each of which covers a separate communications band (see, e.g., arm segments LBA and HBA in the illustrative T-shaped dual band inverted-F antenna of  FIG. 3 ) or may be implemented using other types of antenna (e.g., a loop antenna design, a planar inverted-F antenna, etc.). 
       FIG. 7  is an antenna performance graph for an illustrative adjustable dual band antenna (e.g., an antenna of the type shown in  FIG. 3  that has a low band segment LBA that resonates in a low communications band and that has a high band segment HBA that resonates in a high communications band). Adjustable components such as adjustable components  74  of  FIG. 4  (e.g., adjustable capacitors, adjustable inductors, adjustable phase shifters, or other adjustable circuitry) may be used in the antenna to provide the antenna with adjustability. 
     In the graph of  FIG. 7 , antenna performance (standing wave ratio SWR) has been plotted as a function of operating frequency f. As shown by curve  92 , when operating with its nominal settings for its adjustable circuits, the antenna may exhibit a first antenna resonance peak such as peak  94  at resonant frequency f 1  and may exhibit a second antenna resonance peak such as peak  98  at resonant frequency f 2 . Frequency f 1  may be associated with a low communication band and frequency f 2  may be associated with a high communications band (as an example). 
     Due to manufacturing variations, not all antennas will satisfy desired operating criteria. For example, variations in the size and shape of conductive housing structures such as peripheral conductive housing member  16  and midplate  58 , variations in circuit components in device  10 , variations in conductive antenna traces on a flexible printed circuit, rigid printed circuit, or other substrate, variations in transmission line structures, or other manufacturing variations may cause the antenna to exhibit a frequency response in which curve  94  is undesirably shifted to frequency f 1 ′ and in which curve  98  is undesirably shifted to frequency f 2 ′. 
     To compensate for this undesired variation in the performance of antenna  40  and device  10  from design specifications, device  10  may be calibrated during manufacturing. For example, after device  10  has been assembled, radio-frequency test measurements may be made to characterize the locations of peaks  96  and  100 . Suitable offsets for use in operating adjustable components  74  or other calibration data may then be provided to device  10 . Device  10  may maintain the calibration data in storage and processing circuitry  28 . During operation, device  10  may apply the calibration data so that antenna  40  exhibits the performance characteristic given by line  92  (e.g., resonance peak  94  rather than erroneous resonance peak  96  and resonance peak  98  rather than erroneous resonance peak  100 ), as desired. If desired, device  10  may also dynamically adjust the calibrated antenna (e.g., to switch different frequency bands into and out of use during different modes of operation). Each band in this type of multiband antenna may be calibrated using appropriate calibration data. 
     Because adjustable component calibration data can be used to compensate for manufacturing variations that affect antenna performance, product yields may be increased, particularly in devices with multiple antennas and/or communications bands that are sensitive to performance variations. 
       FIG. 8  is a circuit diagram of an illustrative adjustable component  74 . In the example of  FIG. 8 , adjustable component  74  is based on multiple capacitors having respective capacitances (i.e., capacitances C 1 , C 2 , C 3 , etc.). Switch  102  may receive analog and/or digital control signals on one or more control lines in control path  104 . Switch  102  may have a terminal that is coupled to terminal A of adjustable component  74  and may have multiple terminals that are connected respectively to the different capacitors in component  74 . By adjusting the state of switch  102 , a desired, capacitance (C 1 , C 2 , C 3 , etc.) may be switched into place between terminals A and B. If desired, an adjustable capacitor may be implemented using a continuously variable adjustable capacitor. The example of  FIG. 8  in which adjustable component  74  has been implemented using a switch-based adjustable capacitor that exhibits a plurality of different capacitances (C 1 , C 2 , C 3 , etc.) is merely illustrative. 
     As shown in the illustrative configuration of FIG.  9 , adjustable component  74  may be based on multiple inductors having respective inductances (L 1 , L 2 , L 3 , etc.). Switch  102  may receive analog and/or digital control signals on one or more control lines in control input path  104 . Switch  102  may have a terminal that is coupled to terminal A of adjustable component  74  and may have multiple terminals that are connected respectively to the different inductors in component  74 . By adjusting the state of switch  102 , a desired, inductance (L 1 , L 2 , L 3 , etc.) may be switched into place between terminals A and B. If desired, an adjustable inductor, adjustable resistor, or other adjustable component may be implemented using a continuously variable adjustable component. The example of  FIG. 9  in which adjustable component  74  has been implemented using a switch-based adjustable inductor that exhibits a plurality of different inductances L 1 , L 2 , L 3 , etc. is merely illustrative. 
     Adjustable switch circuitry  102  may be formed from a single switch (e.g., a switch with multiple terminals each of which is coupled to a respective component such as a capacitor or inductor). Alternatively, adjustable component  74  may be implemented using a network of switches (i.e., switch  102  may include multiple sub-switches). The use of a network of switches connected in series and/or in parallel with capacitors, inductors, or other components within adjustable component  74  may allow component  74  to efficiently produce a relatively large number of parameter values (e.g., separate capacitances, inductances, etc.). 
     Adjustable components  74  may be implemented using microelectromechanical systems (MEMS) devices, using solid state devices (e.g., one or more integrated circuits), using devices packaged using surface mount technology (i.e., SMT adjustable components), or other suitable parts. 
     If desired, adjustable components such as adjustable phase shifters may be used in antenna  40 , in antenna matching circuit  70 , or in other antenna structures (e.g., in part of a transmission line, etc.). An illustrative circuit configuration that may be used for an adjustable phase shifter is shown in  FIG. 10 . With an arrangement of the type shown in  FIG. 10 , variable components such as series-connected inductors L and/or shunt-connected capacitors C may be adjusted to produce desired amounts of phase shift along the path made up of parallel signal lines P and G, thereby tuning the performance of antenna  40 , as described in connection with  FIG. 7 . Inductors L may be, for example, switch-based inductors of the type shown in  FIG. 9  that exhibit two or more switchable inductance values. Capacitors C may be, for example, switch-based capacitors of the type shown in  FIG. 8  that exhibit two or more switchable capacitance values. Control inputs  104  may receive control signals from control circuitry  28  that adjust the amount of phase shift that is produced. If desired, combinations of fixed and adjustable components may be used in the phase shift circuit of  FIG. 10 . 
     Control circuitry  28  may maintain information on how to adjust adjustable component(s)  74  to produce desired antenna performance characteristics for device  10 . For example, control circuitry  28  may maintain tables or other data structures that indicate how each adjustable component should be configured to produce each of a plurality of desired frequency responses for antenna structures  40 . If, for example, device  10  desires to transmit and/or receive signals in a first communications band, control circuitry  28  may use a first set of settings for adjustable components  74  to ensure that the antenna is configured properly to operate in the first communications band. If device  10  desires to transmit and/or receive signals in a second communications band, control circuitry  28  may use a second set of settings for adjustable components  74  to ensure that the antenna is tuned to operate in the second communications band. Any suitable number of communications bands may be covered using antenna tuning techniques such as these (e.g., one or more, two or more, three or more, etc.). Moreover, any suitable number of antennas  40  in device  10  may be tuned (e.g., one or more two or more, three or more, etc.). 
     To make accurate adjustments to antenna structures (and/or associated impedance matching circuits or other circuitry that tunes antenna performance), device  10  and its associated antenna structures  40  and other wireless circuitry  34  can be calibrated during manufacturing. Calibration operations may be performed on a lot-to-lot basis, or, for enhanced accuracy, on a device-to-device (or antenna-to-antenna) basis. 
     An illustrative system that may be used in performing calibration operations is shown in  FIG. 11 . As shown in  FIG. 11 , system  144  may include test equipment for testing device  10  and antenna structures  40 . Device  10  and antenna structures  40  may be tested in fully assembled form or antenna structures  40  and/or device  10  may be tested in other states. For example, antenna structures  40  may be wirelessly tested before being installed in a completed device housing (e.g., in situations in which antenna structures  40  are not formed from conductive device housing members). As another example, antenna structures  40  may include a conductive device housing member and may be tested following formation of a partly complete device (e.g., a device that includes all of the relevant conductive housing members for forming antenna structures  40 , but which does not yet include some portions of a fully completed device). The testing of antenna structures  40  and device  10  using a fully formed device may tend to be more accurate than the testing of antenna structures in partly completed devices or other incomplete device configurations, so examples in which wireless antenna performance testing for device  10  is performed on device  10  after the structures of device  10  have been assembled to form a full device are sometimes described herein as an example. 
     To reduce radio-frequency interference, wireless testing of device  10  may be performed in a test chamber such as test chamber  130  (e.g., a metal enclosure). Test host  132  (e.g., computing equipment such as one or more computers) may be coupled to device  10  using cable  134 . Test antenna  138  may be located within test chamber  130  and may be coupled to wireless test equipment such as a spectrum analyzer, power meter, network analyzer, or other test equipment. As shown in  FIG. 11 , for example, test antenna  138  may be coupled to vector network analyzer  140  by cable  136 . Path  134  may be a digital signal bus formed from one or more parallel lines. Path  136  may be a transmission line such as a coaxial cable for handing radio-frequency test signals. One or more paths such as path  142  may be used to interconnect pieces of test equipment in system  130  such as test host  132  and vector network analyzer  140 . 
     Test system  144  may be used to make wireless radio-frequency test measurements that characterize the wireless performance of device  10 . For example, vector network analyzer  140  may use test antenna  138  to transmit radio-frequency test signals to device  10  while antenna structures  40  and receiver circuitry in device  10  are being used to receive these signals. Information on which signals are being transmitted by vector network analyzer  140  may be provided to host  132  via path  142 . Information on which corresponding signals are received by device  10  may be provided by device  10  to host  132  by path  134 . 
     Vector network analyzer  140  may also use test antenna  138  to receive wireless test signals that are being transmitted by device  10  using antenna(s)  40 . Information on which signals are being transmitted by device  10  may be provided to host  132  via path  134 . Information on which corresponding signals are received by vector network analyzer  140  may be provided by vector network analyzer  140  to host  132  by path  142 . Using information on transmitted and received signals, host  132  can determine the performance of antenna(s)  40  in device  10  as a function of operating frequency. Performance can be quantified using any suitable antenna performance metric (e.g., S 11  parameter data or standing wave ratio data, etc.). 
     After making wireless antenna performance measurements to characterize the wireless performance of device  10 , host  132  or other computing equipment may analyze the wireless antenna performance measurements. As shown in  FIG. 12 , for example, antenna performance measurements (e.g., standing-wave-ratio measurements or other performance measurement) such as measurements  200 ,  202 ,  204 , and  206  may be compared to predefined acceptable performance criteria such as upper limit  208  and lower limit  210 . In the example of  FIG. 12 , performance measurements have been made in a frequency range that covers a single antenna resonance peak. If desired, antenna performance measurements may be made that cover multiple antenna resonance peaks (and corresponding communications bands of interest). The data that is acquired need not be captured in the form of continuous curves of data, but may, if desired, be made up of a limited number of discrete points. The use of measurement curves and corresponding upper and lower threshold limits that have been plotted as curves on the graph of  FIG. 12  is merely illustrative. 
     The upper and lower satisfactory performance limits of  FIG. 12  define maximum and minimum acceptable values for the antenna performance measurements (in the  FIG. 12  example). An antenna that exhibits measurements  200  or  206  would not be acceptable, because these performance characteristics do not fall within the acceptable performance limits (limits  208  and  210 ). 
     In some situations, device  10  will perform within acceptable performance limits using default settings for adjustable components  74 . In this type of scenario, device  10  may be said to “pass” wireless performance testing and can be allowed to proceed to further test stations (if any) before being finalized as a device to ship to a user using the default settings. 
     In other situations, however, device  10  may initially exhibit unacceptable performance but may, with use of appropriate calibration settings for adjustable components  74 , be able to perform satisfactorily. As an example, an antenna might initially be characterized as exhibiting performance characteristic  206  of  FIG. 12 . This performance does not satisfy performance criteria  208  and  210 , so the antenna may be retested using different settings for one or more adjustable components  74  until a satisfactory calibration setting is found. 
     If, as an example, the frequency band in  FIG. 12  corresponds to a low band in a dual-band antenna of the type shown in  FIG. 5 , the adjustable capacitor in adjustable circuit  88  may be used to adjust the frequency peak associated with the low band antenna resonance. Adjustments to the adjustable capacitor in circuit  90  may be used to make high band adjustments in a dual-band antenna (as an example). In an antenna configuration of the type shown in  FIG. 6 , the adjustments to the adjustable inductor in adjustable circuit  88  may be used to make high-band antenna performance adjustments and adjustments to the adjustable inductor in adjustable circuit  90  may be used to make low-band antenna performance adjustments (as examples). Adjustable phase shift elements such as element  10  may also be used to make antenna performance adjustments. In general, adjustable components  74  for making antenna performance adjustments may form part of an antenna (e.g., part of an antenna resonating element, part of an antenna ground, etc.), may form part of an impedance matching circuit, may form part of a transmission line structure, may form part of a parasitic antenna resonating element, or may form part of any other conductive structures that affect antenna performance. 
     A flow chart of illustrative operations associated with manufacturing an electronic device such as device  10  that includes antenna structures  40  with one or more adjustable components such as adjustable components  74  is shown in  FIG. 13 . 
     At step  212 , device  10  may be programmed with initial (default) settings for adjustable components  74 . The initial settings may be loaded into storage in storage and processing circuitry  28  using computing equipment such as a test system computer (e.g., host  132  or a computer associated with another test station that is used in manufacturing device  10 ). 
     At step  214 , device  10  and test system  144  may cooperate to wirelessly test antenna structures  40  in device  10 . For example, host  132  may direct device  10  to begin transmitting radio-frequency signals of a particular power across a range of frequencies while directing vector network analyzer  140  to measure corresponding received antenna signals or device  10  may be directed to measure received signals while vector network analyzer  140  is directed to transmit test signals. The antenna performance measurement data that is acquired during the operations of step  214  may be gathered by host  132  and stored in a results database on host  132  (as an example). 
     After gathering antenna performance measurements with system  144  during the operations of step  214 , host  132  or other computing equipment may evaluate the antenna performance measurements to determine whether or not calibration data should be loaded into device  10 . For example, a set of measurement data such as curve  200 ,  202 ,  204 , or  206  in the example of  FIG. 12  may be compared to satisfactory performance limits such as limits  208  and  210 . 
     If the measured antenna performance data over all communications bands of interest satisfies desired limits and is therefore satisfactory for use in a finished device, device  10  may be considered to have passed testing. When device  10  passes testing at step  214 , additional manufacturing operations may be performed, if desired (step  216 ). For example, software may be loaded onto device  10  by host  132  or other computing equipment, pieces of device housing  12  and/or internal electronic components may be used in completing device  10 , or other manufacturing operations associated with completing device  10  may be performed. The finished device may be shipped to an end user. 
     If, however, the measured antenna performance data from the operations of step  214  is not satisfactory (i.e., because some or all of the measurements from step  214  exceed desired performance limits), device  10  may be considered to have failed testing with the initial antenna tuning settings. Accordingly, one or more additional antenna performance settings may be evaluated using the operations of step  218 . Each antenna performance setting may correspond to a different setting for one or more adjustable components  74  (e.g., adjustable antenna components, adjustable matching circuit components, etc.). 
     If desired, an antenna may be placed in one or more configurations (e.g., tuned to operate in a low band mode, tuned to operate in a high band mode, etc.) during calibration, so that the antenna is calibrated over all desired communications bands of interest (e.g., with corresponding settings for adjustable components  74  in each band of interest). 
     Host  132  may provide device  10  with each trial set of adjustable component settings using path  134 . If antenna performance with the new settings is not satisfactory, another set of trial settings may be used, as indicated by line  224 . If antenna performance has been evaluated for all desired combinations of adjustable component settings, system  144  can conclude that settings adjustments through the use of calibration data will not be successful at restoring proper function to the antenna. Accordingly, the device may be removed from system  144  and discarded or reworked (step  222 ). 
     If, however, a set of satisfactory additional settings for adjustable components  74  can be identified during the operations of step  218 , device  10  may be considered to have “passed” wireless testing. Processing may then continue to step  220 . During the operations of step  220 , device  10  may be instructed to use the satisfactory device settings for normal operation of device  10  in a wireless network. If the settings are presently loaded into storage and processing circuitry  28 , those settings may be retained. With this approach, the calibration data may be stored in the storage of storage and processing circuitry  28  in response to having identified the appropriate calibration data during testing by virtue of retaining the calibration data and not overwriting the retained calibration data. If desired, the appropriately calibrated settings may be loaded during the operations of step  222  (i.e., in response to identifying the calibration data needed to properly calibrate device  10 , the calibration data may be stored in the storage of storage and processing circuitry  28  by reloading the calibration data into the storage over path  134 ). 
     Calibration information may be provided to device  10  in the form of raw calibrated settings for adjustable components  74 , in the form of offset values or formulas for use in computing calibrated settings for adjustable components  74  from raw settings in real time, using a combination of these approaches, or using any other suitable technique for ensuring that device  10  uses calibrated settings for one or more adjustable components  74  when operating tunable antenna structures  40  in device  10 . 
     If device  10  has not been completely manufactured, final manufacturing operations may be performed at step  220  such as loading software onto device  10  from host  132  or other computing equipment, attaching pieces of device housing  12  and/or internal electronic components to device  10 , or performing other manufacturing operations associated with completing device  10 . The finished device may then be shipped to an end user. 
     Antenna calibration operations such as the operations of  FIG. 13  may be performed for each tunable antenna in device  10 . 
     The foregoing is merely illustrative of the principles of this invention and various modifications can be made by those skilled in the art without departing from the scope and spirit of the invention.

Metadata:
Filing Date: 20120201
Publication Date: 20160223
Grant Date: 20160223
Priority Date: 20120201
Inventors: NICKEL JOSHUA G.
PASCOLINI MATTIA
Assignee: APPLE INC
CPC Classifications: [{"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": "H01Q9/42", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q1/243", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01Q5/328", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 48869753