PATENT DOCUMENT

Publication Number: US-10498011-B2
Application Number: US-201615255770-A
Country: US
Kind Code: B2

Title: Electronic devices having closed-loop antenna adjustment capabilities

Abstract:
An electronic device may be provided with wireless circuitry that includes an antenna. Control circuitry may perform closed loop tuning adjustments on the antenna. For example, the control circuitry may adjust a tunable component to tune the antenna to a first tuning setting. The control circuitry may gather impedance values from the antenna while tuned to the first tuning setting and may process the impedance values to determine whether to tune the antenna to a second tuning setting. If the impedance values lie within a predetermined complex impedance region, the control circuitry may tune the antenna to the second setting. If the impedance values lie outside of the region, the control circuitry may continue to gather impedance values using the first setting. These operations may compensate for detuning of the antenna due to proximity of a user regardless of how the electronic device is held during operation.

Claims:
What is claimed is: 
     
       1. A method of adjusting an antenna in an electronic device having opposing first and second ends and comprising an ear speaker located at the first end of the electronic device and the antenna is located at the second end of the electronic device, the method comprising:
 with control circuitry in the electronic device, determining whether the ear speaker is playing audio signals; 
 with the control circuitry, determining whether the electronic device is located on a body based on sensor signals generated by sensor circuitry in the electronic device and at least partly in response to determining that the ear speaker is not playing audio signals; 
 with the control circuitry, controlling the antenna to transmit radio-frequency signals below a maximum transmit power level and adjusting a tunable component to tune the antenna to a first tuning setting in response to determining that the electronic device is located on the body; 
 with the control circuitry, gathering a first set of antenna impedance information from the antenna while the antenna is tuned to the first tuning setting; 
 with the control circuitry, determining whether an operating environment of the electronic device has changed based on the first set of antenna impedance information; 
 with the control circuitry, in response to determining that the operating environment has changed, adjusting the tunable component to tune the antenna to a second tuning setting and gathering a second set of antenna impedance information from the antenna while the antenna is tuned to the second tuning setting; and 
 with the control circuitry, in response to determining that the operating environment has not changed, gathering a third set of antenna impedance information from the antenna while the antenna is tuned to the first tuning setting. 
 
     
     
       2. The method defined in  claim 1 , wherein the first tuning setting is a grip tuning setting that compensates for detuning of the antenna generated by presence of a hand adjacent to the antenna and the second tuning setting is a free-space tuning setting that is different from the grip tuning setting. 
     
     
       3. The method defined in  claim 1 , wherein determining whether the operating environment of the electronic device has changed comprises determining whether the electronic device has entered a second operating environment from a first operating environment based on the first set of antenna impedance information, the method further comprising:
 with the control circuitry, determining whether the electronic device has entered the first operating environment from the second operating environment based on the second set of antenna impedance information. 
 
     
     
       4. The method defined in  claim 3 , further comprising:
 with the control circuitry, in response to determining that the electronic device has entered the first operating environment from the second operating environment, adjusting the tunable component to tune the antenna to the first tuning setting and gathering a fourth set of antenna impedance information from the antenna while the antenna is tuned to the first tuning setting. 
 
     
     
       5. The method defined in  claim 1 , wherein the first set of antenna impedance information comprises a complex impedance value and determining whether the operating environment of the electronic device has changed comprises:
 identifying boundaries of a complex impedance region from data stored on the electronic device; and 
 determining whether the complex impedance value lies within the identified complex impedance region by comparing the complex impedance value to the identified boundaries of the complex impedance region. 
 
     
     
       6. The method defined in  claim 5 , wherein determining whether the operating environment of the electronic device has changed further comprises:
 in response to determining that the complex impedance value lies within the complex impedance region, determining that the operating environment of the electronic device has changed; and 
 in response to determining that the complex impedance value lies outside of the complex impedance region, determining that the operating environment of the electronic device has not changed. 
 
     
     
       7. The method defined in  claim 1 , wherein gathering the first set of antenna impedance information from the antenna while the antenna is tuned to the first tuning setting comprises:
 receiving reflected radio-frequency signals from the antenna over a radio-frequency coupler; and 
 generating a set of complex scattering parameter values based on the received reflected radio-frequency signals. 
 
     
     
       8. The method defined in  claim 7 , wherein gathering the first set of antenna impedance information from the antenna while the antenna is tuned to the first tuning setting further comprises:
 averaging a plurality of complex scattering parameter values in the set of complex scattering parameter values to generate an average complex scattering parameter value, wherein determining whether the operating environment of the electronic device has changed based on the first set of antenna impedance information comprises determining whether the operating environment of the electronic device has changed based on the generated average complex scattering parameter value. 
 
     
     
       9. The method defined in  claim 7 , wherein the generated set of complex scattering parameter values comprises a plurality of complex scattering parameter values and determining whether the operating environment of the electronic device has changed based on the first set of antenna impedance information comprises performing a voting operation on the plurality of complex scattering parameter values. 
     
     
       10. The method defined in  claim 7 , wherein determining whether the operating environment of the electronic device has changed based on the first set of antenna impedance information comprises:
 determining whether magnitudes of complex scattering parameter values in the set of complex scattering parameter values have decreased over time; and 
 in response to determining that the magnitudes have not decreased over time, determining that the operating environment of the electronic device has not changed. 
 
     
     
       11. A method of adjusting an antenna in an electronic device, the method comprising:
 with control circuitry in the electronic device, adjusting a tunable component to tune the antenna to a first tuning setting; 
 with the control circuitry, gathering a first set of antenna impedance information from the antenna while the antenna is tuned to the first tuning setting, wherein gathering the first set of antenna impedance information from the antenna while the antenna is tuned to the first tuning setting comprises:
 receiving reflected radio-frequency signals from the antenna over a radio-frequency coupler; and 
 generating a set of complex scattering parameter values based on the received reflected radio-frequency signals; 
 
 with the control circuitry, determining whether an operating environment of the electronic device has changed based on the first set of antenna impedance information; 
 with the control circuitry, in response to determining that the operating environment has changed, adjusting the tunable component to tune the antenna to a second tuning setting and gathering a second set of antenna impedance information from the antenna while the antenna is tuned to the second tuning setting; and 
 with the control circuitry, in response to determining that the operating environment has not changed, gathering a third set of antenna impedance information from the antenna while the antenna is tuned to the first tuning setting. 
 
     
     
       12. The method defined in  claim 11 , wherein gathering the first set of antenna impedance information from the antenna while the antenna is tuned to the first tuning setting further comprises:
 averaging a plurality of complex scattering parameter values in the set of complex scattering parameter values to generate an average complex scattering parameter value, wherein determining whether the operating environment of the electronic device has changed based on the first set of antenna impedance information comprises determining whether the operating environment of the electronic device has changed based on the generated average complex scattering parameter value. 
 
     
     
       13. The method defined in  claim 11 , wherein the generated set of complex scattering parameter values comprises a plurality of complex scattering parameter values and determining whether the operating environment of the electronic device has changed based on the first set of antenna impedance information comprises performing a voting operation on the plurality of complex scattering parameter values. 
     
     
       14. The method defined in  claim 11 , wherein determining whether the operating environment of the electronic device has changed based on the first set of antenna impedance information comprises:
 determining whether magnitudes of complex scattering parameter values in the set of complex scattering parameter values have decreased over time; and 
 in response to determining that the magnitudes have not decreased over time, determining that the operating environment of the electronic device has not changed. 
 
     
     
       15. The method defined in  claim 14 , wherein determining whether the operating environment of the electronic device has changed based on the first set of antenna impedance information further comprises:
 in response to determining that the magnitudes have decreased over time, determining whether the set of complex scattering parameter values lies within a predetermined complex impedance region; 
 in response to determining that the set of complex scattering parameter values lies within the predetermined complex impedance region, determining that the operating environment of the electronic device has changed; and 
 in response to determining that the set of complex scattering parameter values lies outside of the predetermined complex impedance region, determining that the operating environment of the electronic device has not changed. 
 
     
     
       16. A method of adjusting an antenna in an electronic device, the method comprising:
 with control circuitry in the electronic device, adjusting a tunable component to tune the antenna to a first tuning setting; 
 with the control circuitry, gathering a first set of antenna impedance information from the antenna while the antenna is tuned to the first tuning setting; 
 with the control circuitry, determining whether an operating environment of the electronic device has changed based on the first set of antenna impedance information, wherein determining whether the operating environment of the electronic device has changed comprises determining whether the electronic device has entered a second operating environment from a first operating environment based on the first set of antenna impedance information; 
 with the control circuitry, in response to determining that the operating environment has changed, adjusting the tunable component to tune the antenna to a second tuning setting and gathering a second set of antenna impedance information from the antenna while the antenna is tuned to the second tuning setting; and 
 with the control circuitry, in response to determining that the operating environment has not changed, gathering a third set of antenna impedance information from the antenna while the antenna is tuned to the first tuning setting; 
 with the control circuitry, determining whether the electronic device has entered the first operating environment from the second operating environment based on the second set of antenna impedance information; and 
 with the control circuitry, in response to determining that the electronic device has entered the first operating environment from the second operating environment, adjusting the tunable component to tune the antenna to the first tuning setting and gathering a fourth set of antenna impedance information from the antenna while the antenna is tuned to the first tuning setting. 
 
     
     
       17. The method defined in  claim 16 , further comprising:
 with the control circuitry, in response to determining that the electronic device has not entered the first operating environment from the second operating environment, gathering a fifth set of antenna impedance information while the antenna is tuned to the second antenna tuning setting.

Description:
BACKGROUND 
     This relates generally to electronic devices and, more particularly, to electronic devices with wireless communications circuitry. 
     Electronic devices often include wireless communications circuitry. For example, cellular telephones, computers, and other devices often contain antennas and wireless transceivers for supporting wireless communications. 
     It can be challenging to form electronic device antenna structures with desired attributes. In some wireless devices, antennas are bulky. In other devices, antennas are compact, but are sensitive to the position of the antennas relative to external objects. If care is not taken, antennas may become detuned, may emit wireless signals with a power that is more or less than desired, or may otherwise not perform as expected. 
     It would therefore be desirable to be able to provide improved wireless circuitry for electronic devices. 
     SUMMARY 
     An electronic device may be provided with wireless circuitry. The wireless circuitry may include one or more antennas and radio-frequency transceiver circuitry. The electronic device may have a housing in which control circuitry, the radio-frequency transceiver circuitry, and other wireless circuitry are mounted. The transceiver circuitry may be used to transmit and receive radio-frequency signals using the antennas. 
     The control circuitry may perform closed loop antenna tuning adjustments on a given one of the antennas. The closed loop antenna tuning adjustments may be performed based on antenna impedance information gathered from the given one of the antennas. For example, the control circuitry may adjust a tunable component coupled to the antenna to tune the antenna to a first tuning setting. The first tuning setting may be, for example, a grip tuning setting that compensates for detuning of the antenna caused by the presence of a user&#39;s hand adjacent to the antenna. 
     The control circuitry may gather a first set of antenna impedance information (e.g., complex impedance values such as complex scattering parameter values) from the antenna while the antenna is tuned to the first tuning setting. The control circuitry may determine whether an operating environment of the electronic device has changed based on the first set of antenna impedance information. 
     The control circuitry may adjust the tunable component to tune the antenna to a second tuning setting (e.g., a free-space tuning setting) in response to determining that the operating environment has changed. Once tuned to the second tuning setting, the control circuitry may gather a second set of antenna impedance information from the antenna. The second set of impedance information may be used to identify subsequent changes in the operating environment of the device. The control circuitry may continue to gather antenna impedance information using the first tuning setting in response to determining that the operating environment has not changed. 
     While the device is in a first operating environment, the control circuitry may determine whether the operating environment has changed by identifying a complex impedance region associated with a second operating environment from calibration data stored in memory. The control circuitry may compare the gathered impedance information to the complex impedance region to determine whether the operating environment has changed. If the complex impedance information lies within the complex impedance region, then the control circuitry may identify that the operating environment has changed and a tuning adjustment may be performed. If the information lies outside of the complex impedance region, the control circuitry may identify that the operating environment has not changed. 
     If desired, the electronic device may include speaker components such as an ear speaker and sensor circuitry such as an accelerometer. The electronic device may include a second antenna located at an opposite end of the electronic device from the first antenna. The control circuitry may impose different maximum transmit power levels on both antennas based on whether audio signals are being played through the ear speaker and based on whether the accelerometer detects that the device is on the body of a user. The control circuitry may perform the closed loop tuning adjustments on one of the antennas when the control circuitry determines that audio is being played through the ear speaker or the device is on the body of the user. In this way, the control circuitry may actively compensate for any detuning of the antennas due to proximity of the user to the antennas while also ensuring that regulatory limits on signal absorption are satisfied, regardless of how the user holds the electronic device during operation. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an illustrative electronic device with wireless communications circuitry in accordance with an embodiment. 
         FIG. 2  is a schematic diagram of an illustrative electronic device with wireless communications circuitry in accordance with an embodiment. 
         FIG. 3  is a diagram of illustrative wireless communications circuitry in accordance with an embodiment. 
         FIG. 4  is a diagram of a portion of an electronic device with circuitry that may be used to gather antenna signals and other signals to help determine how to adjust wireless circuitry in accordance with an embodiment. 
         FIG. 5  is a circuit diagram of illustrative tuning circuitry that may be adjusted to tune the resonating frequency of an antenna in accordance with an embodiment. 
         FIG. 6  is a diagram showing examples of different wireless operating environments of an illustrative electronic device in accordance with an embodiment. 
         FIG. 7  is a Smith chart showing illustrative impedances associated with operation of an antenna in an electronic device when operated by different groups of users in accordance with an embodiment. 
         FIG. 8  is a table of illustrative maximum transmit power level settings that may be stored on an electronic device for use during wireless communications in accordance with an embodiment. 
         FIG. 9  is a table of illustrative antenna tuning settings that may be stored on an electronic device for use during wireless communications in accordance with an embodiment. 
         FIG. 10  is a flow chart of illustrative steps involved in adjusting antenna tuning settings and maximum transmit power level settings while performing wireless communications using an electronic device in accordance with an embodiment. 
         FIG. 11  is a flow chart of illustrative steps involved in performing wireless communications using an electronic device while the electronic device is in a free-space operating environment in accordance with an embodiment. 
         FIG. 12  is a flow chart of illustrative steps that may be performed by an electronic device to adjust maximum transmit power level and antenna tuning settings during wireless communications while the electronic device is located near to a user&#39;s head in accordance with an embodiment. 
         FIG. 13  is a flow chart of illustrative steps that may be performed by an electronic device to adjust maximum transmit power level and antenna tuning settings during wireless communications using while the electronic device is located near to a user&#39;s body in accordance with an embodiment. 
         FIG. 14  is a flow chart of illustrative steps involved in using an electronic device to perform closed loop antenna tuning adjustments during wireless communications in accordance with an embodiment. 
         FIG. 15  is a flow chart of illustrative steps that may be performed by an electronic device to determine when to change antenna tuning settings based on gathered impedance information in accordance with an embodiment. 
         FIG. 16  is a plot of complex impedance values for an illustrative antenna while the antenna is tuned using a free-space tuning setting in accordance with an embodiment. 
         FIG. 17  is a plot of complex impedance values for an illustrative antenna while the antenna is tuned using a grip tuning setting in accordance with an embodiment. 
         FIG. 18  is a table of illustrative calibration data that may be stored on an electronic device and processed to determine when to change antenna tuning settings in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Electronic devices such as electronic device  10  of  FIG. 1  may contain wireless communications circuitry. The wireless communications circuitry may be used to support wireless communications in multiple wireless communications bands. 
     The wireless communications circuitry of device  10  may include a Global Position System (GPS) receiver that handles GPS satellite navigation system signals at 1575 MHz or a GLONASS receiver that handles GLONASS signals at 1609 MHz. Device  10  may also contain wireless communications circuitry that operates in communications bands such as cellular telephone bands and wireless circuitry that operates in communications bands such as the 2.4 GHz Bluetooth® band and the 2.4 GHz and 5 GHz WiFi® wireless local area network bands (sometimes referred to as IEEE 802.11 bands or wireless local area network communications bands). If desired, device  10  may also contain wireless communications circuitry for implementing near-field communications, light-based wireless communications, or other wireless communications (e.g., millimeter wave communications at 60 GHz or other extremely high frequencies, etc.). 
     The wireless communications circuitry may include one more antennas. The antennas of the wireless communications circuitry can include loop antennas, inverted-F antennas, strip antennas, planar inverted-F antennas, slot antennas, hybrid antennas that include antenna structures of more than one type, or other suitable antennas. Conductive structures for the antennas may, if desired, be formed from conductive electronic device structures. 
     The conductive electronic device structures may include conductive housing structures. The housing structures may include peripheral structures such as 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 wrist-watch device, pendant device, headphone device, earpiece device, or other wearable or miniature device, a handheld device such as a cellular telephone, a media player, or other small portable device. Device  10  may also be a set-top box, a desktop computer, a display into which a computer or other processing circuitry has been integrated, a display without an integrated computer, or other suitable electronic equipment. 
     Device  10  may include a housing such as housing  12 . Housing  12 , which may sometimes be referred to as a case, may be formed of plastic, glass, ceramics, fiber composites, metal (e.g., stainless steel, aluminum, etc.), other suitable materials, or a combination of these materials. In some situations, parts of housing  12  may be formed from dielectric or other low-conductivity material. In other situations, housing  12  or at least some of the structures that make up housing  12  may be formed from metal elements. 
     Device  10  may, if desired, have a display such as display  14 . Display  14  may be mounted on the front face of device  10 . Display  14  may be a touch screen that incorporates capacitive touch electrodes or may be insensitive to touch. The rear face of housing  12  (i.e., the face of device  10  opposing the front face of device  10 ) may have a planar housing wall. The rear housing wall may be have slots that pass entirely through the rear housing wall and that therefore separate housing wall portions (and/or sidewall portions) of housing  12  from each other. Housing  12  (e.g., the rear housing wall, sidewalls, etc.) may also have shallow grooves that do not pass entirely through housing  12 . The slots and grooves may be filled with plastic or other dielectric. If desired, portions of housing  12  that have been separated from each other (e.g., by a through slot) may be joined by internal conductive structures (e.g., sheet metal or other metal members that bridge the slot). 
     Display  14  may include pixels formed from light-emitting diodes (LEDs), organic LEDs (OLEDs), plasma cells, electrowetting pixels, electrophoretic pixels, liquid crystal display (LCD) components, or other suitable pixel structures. A display cover layer such as a layer of clear glass or plastic may cover the surface of display  14  or the outermost layer of display  14  may be formed from a color filter layer, thin-film transistor layer, or other display layer. 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 . Speaker port  26  may allow audio signals (sound) to be heard by a user of device  10  (e.g., while the user holds device  10  and speaker port  26  to their ear). Speaker port  26  may therefore sometimes be referred to herein as ear speaker port  26  or ear speaker  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, curved sidewalls, etc.). 
     Peripheral housing structures  16  may be formed of a conductive material such as metal and may therefore sometimes be referred to as peripheral conductive housing structures, conductive housing structures, peripheral metal structures, or a peripheral conductive housing member (as examples). Peripheral housing structures  16  may be formed from a metal such as stainless steel, aluminum, or other suitable materials. One, two, or more than two separate structures may be used in forming peripheral housing structures  16 . If desired, holes such as holes  17  may be provided in peripheral structures  16  or in a rear surface of housing  12 . Speakers within device  10  may transmit sound to the exterior of device  10  through holes  17  and/or through ear speaker  26 . If desired, microphones may be placed adjacent to holes  17  or any other desired locations within device  10  on to generate audio signals from sound received by device  10 . 
     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 flat or curved 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. 
     Housing  12  may include internal conductive structures such as metal frame members and a planar conductive 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 ). Device  10  may also include conductive structures such as printed circuit boards, components mounted on 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 . 
     In regions  22  and  20 , openings may be formed within the conductive structures of device  10  (e.g., between peripheral conductive housing structures  16  and opposing conductive ground structures such as conductive housing midplate or rear housing wall structures, a printed circuit board, and conductive electrical components in display  14  and device  10 ). These openings, which may sometimes be referred to as gaps, may be filled with air, plastic, and other dielectrics and may be used in forming slot antenna resonating elements for one or more antennas in device  10 . 
     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 . 
     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.). In the example of  FIG. 1 , device  10  includes a first antenna  40 L and a second antenna  40 U formed on opposing sides of device  10 . For example, antenna  40 L may be formed within region  20  at the lower end of device  10  (e.g., the end of device  10  adjacent to microphone holes  17 ) and may therefore sometimes be referred to herein as lower antenna  40 L. Similarly, antenna  40 U may be formed within region  22  at the upper end of device  10  (e.g., the end of device  10  adjacent to ear speaker  26 ) and may therefore sometimes be referred to herein as upper antenna  40 U. Antennas  40 L and  40 U may, if desired, 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. 
     The arrangement of  FIG. 1  is merely illustrative. In general, 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. 
     Portions of peripheral housing structures  16  may be provided with peripheral gap structures. For example, peripheral conductive housing structures  16  may be provided with one or more gaps such as gaps  18 , as shown in  FIG. 1 . The gaps in peripheral housing structures  16  may be filled with dielectric such as polymer, ceramic, glass, air, other dielectric materials, or combinations of these materials. Gaps  18  may divide peripheral housing structures  16  into one or more peripheral conductive segments. There may be, for example, two peripheral conductive segments in peripheral housing structures  16  (e.g., in an arrangement with two of gaps  18 ), three peripheral conductive segments (e.g., in an arrangement with three of gaps  18 ), four peripheral conductive segments (e.g., in an arrangement with four gaps  18 , etc.). 
     The segments of peripheral conductive housing structures  16  that are formed in this way may form parts of antennas in device  10 . For example, the segment of peripheral conductive housing structures  16  that is located between the two gaps  18  in region  20  may form some or all of an antenna resonating element for lower antenna  40 L (e.g., one or more resonating element arms of an inverted-F antenna resonating element in scenarios where lower antenna  40 L is an inverted-F antenna, a portion of a loop antenna resonating element in scenarios where lower antenna  40 L is a loop antenna, a conductive portion that defines an edge of a slot antenna resonating element in scenarios where lower antenna  40 L is a slot antenna, combinations of these, or any other desired antenna resonating element structures). Similarly, the segment of peripheral conductive housing structures  16  that is located between the two gaps  18  in region  22  may form some or all of an antenna resonating element for upper antenna  40 U. This example is merely illustrative. If desired, antennas  40 L and  40 U may not include any portion of peripheral conductive housing structures  16  or segments of structures  16  may form part of an antenna ground plane for antennas  40 L and  40 U. 
     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  is shown in  FIG. 2 . As shown in  FIG. 2 , device  10  may include control circuitry such as storage and processing circuitry  30 . Storage and processing circuitry  30  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  30  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, baseband processor integrated circuits, application specific integrated circuits, etc. 
     Storage and processing circuitry  30  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  30  may be used in implementing communications protocols. Communications protocols that may be implemented using storage and processing circuitry  30  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, satellite navigation system protocols, etc. If desired, circuitry  30  may be used in tuning antennas, adjusting wireless transmit powers for transceivers in device  10  (e.g., transmit powers may be adjusted up and down in response to transmit power commands from wireless base stations while observing an established overall maximum allowed transmit power), and/or in otherwise controlling the wireless operation of device  10 . 
     Device  10  may include input-output circuitry  44 . Input-output circuitry  44  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, speakers, status indicators, light sources, audio jacks and other audio port components, digital data port devices, light sensors, gyroscopes, compasses, accelerometers or other components that can detect motion and device orientation relative to the Earth, capacitance sensors, proximity sensors (e.g., a capacitive proximity sensor and/or an infrared proximity sensor), touch sensors, magnetic sensors, a connector port sensor or other sensor that determines whether device  10  is mounted in a dock, radio-frequency sensors, and other sensors and input-output components. 
     Input-output circuitry  44  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  40 , 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  36  for handling various radio-frequency communications bands. For example, circuitry  36  may include wireless local area network transceiver circuitry that may handle 2.4 GHz and 5 GHz bands for WiFi® (IEEE 802.11) communications and that may handle the 2.4 GHz Bluetooth® communications band, may include cellular telephone transceiver circuitry 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), and may include circuitry for other short-range and long-range wireless links if desired. If desired, wireless transceiver circuitry  36  may include 60 GHz transceiver circuitry, circuitry for receiving television and radio signals, paging system transceivers, near field communications (NFC) circuitry, etc. Wireless transceiver circuitry  36  may also include satellite navigation system circuitry such as global positioning system (GPS) receiver circuitry for receiving GPS signals at 1575 MHz or for handling other satellite positioning data (e.g., GLONASS signals at 1609 MHz). In WiFi® and Bluetooth® links and other short-range wireless links, wireless signals are typically used to convey data over tens or hundreds of feet. In cellular telephone links and other long-range links, wireless signals are typically used to convey data over thousands of feet or miles. 
     Antennas  40  in wireless communications circuitry  34  (e.g., antennas such as antennas  40 U and  40 L of  FIG. 1 ) 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. If desired, one or more of antennas  40  may be cavity-backed antennas. 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. Dedicated antennas may be used for transmitting and/or receiving signals in a particular band or, if desired, antennas  40  can be configured to receive signals for multiple communications bands. 
     Device  10  may contain multiple antennas  40 . The antennas may be used together or one of the antennas may be switched into use while the other antenna(s) may be switched out of use. If desired, control circuitry  30  may be used to select an optimum antenna to use in device  10  in real time and/or an optimum setting for tunable wireless circuitry associated with one or more of antennas  40 . Storage and processing circuitry  30 , input-output circuitry  44 , and other components of device  10  may be mounted in device housing  12 . 
     As shown in  FIG. 3 , transceiver circuitry  36  in wireless circuitry  34  may be coupled to antenna structures  40  using paths such as path  92 . Transmission line paths in device  10  such as transmission line  92  may include coaxial cable paths, microstrip transmission lines, stripline transmission lines, edge-coupled microstrip transmission lines, edge-coupled stripline transmission lines, transmission lines formed from combinations of transmission lines of these types, etc. A separate respective transmission line  92  may be used in routing signals between each antenna  40  in device  10  and transceiver circuitry  36  (as an example). 
     Filter circuitry, switching circuitry, impedance matching circuitry, and other circuitry may be interposed within the transmission lines, if desired (see, e.g., impedance matching and filter circuitry  106 - 3  interposed on transmission line  92 ). 
     Wireless circuitry  34  may be coupled to control circuitry  30 . Control circuitry  30  may be coupled to input-output devices  32 . Input-output devices  32  may supply output from device  10  and may receive input from sources that are external to device  10 . Control circuitry  30  may use wireless circuitry  34  to transmit and receive wireless signals. 
     To provide antenna structures  40  with the ability to cover communications frequencies of interest, antenna structures  40  may be provided with circuitry such as filter circuitry (e.g., one or more passive filters and/or one or more tunable circuits). If desired, antenna structures  40  may be provided with adjustable circuits such as tunable components  106  to tune antennas over communications bands of interest. Tunable components  106  may include tunable inductors, tunable capacitors, or other tunable components. Tunable components such as these may be based on switches and networks of fixed components, distributed metal structures that produce associated distributed capacitances and inductances, variable solid state devices for producing variable capacitance and inductance values, tunable filters, or other suitable tunable structures. 
     During operation of device  10 , control circuitry  30  may issue control signals on one or more paths such as path  88  that adjust inductance values, capacitance values, or other parameters associated with tunable components  106 , thereby tuning antenna structures  40  to cover desired communications bands. Configurations in which antennas  40  are fixed (not tunable) and configurations in which tunable components  106  are incorporated into circuits such as filter and matching circuits (e.g., circuit  106 , which may contain tunable components controlled using signals on path  122 ), in which tunable components  106  are incorporated into parasitic antenna elements (e.g., parasitics in structures  40 ), and other arrangements in which wireless circuitry  34  includes adjustable components may also be used. 
     Path  92  may include one or more transmission lines. As an example, signal path  92  of  FIG. 3  may be a transmission line having a positive signal conductor such as line  94  and a ground signal conductor such as line  96 . Lines  94  and  96  may form parts of a coaxial cable or a microstrip transmission line (as examples). A tunable impedance matching network (matching circuit) such as matching circuit  106 - 3  that is formed from components such as inductors, resistors, and capacitors may be used in matching the impedance of antenna structures  40  to the impedance of transmission line  92  and may, if desired, incorporate a band pass filter, band stop filter, high pass filter, and/or low pass filter. Matching network components may be provided as discrete components (e.g., surface mount technology components) or may be formed from housing structures, printed circuit board structures, traces on plastic supports, etc. Components such as these may also be used in forming filter circuitry in antenna structures  40 . As shown in  FIG. 3 , control circuitry  30  may adjust circuitry such as circuitry  106 - 3  (e.g., tunable components in circuitry  106 - 3 ) by issuing control signals on paths such as path  104 . 
     Transmission line  92  may be coupled to antenna feed structures associated with antenna structures  40 . As an example, antenna structures  40  may form an inverted-F antenna, a slot antenna, a hybrid inverted-F slot antenna or other antenna having an antenna feed with a positive antenna feed terminal such as terminal  98  and a ground antenna feed terminal such as ground antenna feed terminal  100 . Positive transmission line conductor  94  may be coupled to positive antenna feed terminal  98  and ground transmission line conductor  96  may be coupled to ground antenna feed terminal  92 . Other types of antenna feed arrangements may be used if desired. The illustrative feeding configuration of  FIG. 3  is merely illustrative. 
       FIG. 4  is a diagram of wireless circuitry in an illustrative configuration for electronic device  10 . In the example of  FIG. 4 , lower antenna  40 L is based on an inverted-F antenna. This is merely illustrative. In general, antenna  40 L may be based on any suitable antenna type (slot, inverted-F, planar inverted-F, loop, hybrid slot and inverted-F, other types of antennas, and hybrids based on multiple antenna structures such as these). Similar structures to those shown in  FIG. 4  may be used to form upper antenna  40 U, if desired, or upper antenna  40 U may be formed using different structures. 
     As shown in  FIG. 4 , lower antenna  40 L includes antenna resonating element  150  and antenna ground (ground plane)  152 . Antenna resonating element  150  may have a main resonating element arm such as arm  154 . Arm  154  may have multiple branches (e.g., a short branch for supporting a high band resonance and a long branch for supporting a low band resonance). Arm  154  may, for example, be formed using a segment of peripheral conductive housing structures  16  ( FIG. 1 ). Arm  154  may be separated from ground plane  152  by opening  153  (e.g., an opening between peripheral conductive structures  16  and ground plane  152 ). The size of arm  154  (e.g., the lengths of the branches of arm  154 ) may be selected so that antenna  40 L resonates at desired operating frequencies. 
     Main resonating element arm  154  may be coupled to ground  152  by return path  156 . Antenna feed  158  may include positive antenna feed terminal  98  and ground antenna feed terminal  100  and may run parallel to return path  156  between arm  154  and ground  152 . 
     If desired, antenna  40 L may have tunable components (e.g., tunable components such as components  106 - 3  and  106  of  FIG. 3 ). For example, antenna  40 L may have tunable components  106 - 1  in return path  156 , tunable components  106 - 2  in feed path  158 , tunable components  106 - 3  in a matching network interposed in transmission line path  92 , and/or tunable components  106 - 4  in an additional antenna path such as illustrative path  160  coupled between resonating element arm  154  and ground  152 . Tunable component(s)  106 - 1 ,  106 - 2 ,  106 - 3 , and  106 - 4  may include adjustable inductors, adjustable capacitors, and/or other adjustable components. By adjusting components  106 - 1 ,  106 - 2 ,  106 - 3 , and  106 - 4 , the impedance of antenna  40 L and matching circuit  106 - 3  and therefore the frequency response of antenna  40 L may be tuned. 
     Antennas such as antenna  40 L of  FIG. 4  may be affected by the presence of nearby objects. For example, an antenna may exhibit an expected frequency response when device  10  is operated in free space in the absence of nearby external objects such as external object  162 , but may exhibit a different frequency response when device  10  is operated in the presence of external object  162 . The magnitude of the distance between external object  162  and antenna  40 L and the type of object  162  may also influence antenna performance. 
     External objects such as object  162  may include a user&#39;s body (e.g., a user&#39;s head, a user&#39;s leg, a user&#39;s hand, or other user body part), may include a table or other inanimate object on which device  10  is resting, may include dielectric objects, may include a user&#39;s clothing, may include conductive objects, and/or may include other objects that affect wireless performance (e.g., by loading antenna  40 L in device  10  and thereby affecting antenna impedance for antenna  40 L). 
     When an external object such as object  162  is brought into the vicinity of antenna  40 L (e.g., when object  162  is within 10 cm of antenna  40 L, when object  162  is within 1 cm of antenna  40 L, when object  162  is within 1 mm of antenna  40 L, or when the distance between antenna  40 L and object  162  has other suitable values), antenna  40 L may exhibit an altered frequency response (e.g., antenna  40 L may be detuned because the impedance of the antenna has been changed due to loading from object  162 ). In addition, different types of object  162  may detune antenna  40 L by differing amounts (e.g., because different materials will load antenna  40 L differently). For example, a user&#39;s hand, a user&#39;s head, and other parts of a user&#39;s body may each detune antenna  40 L by a different respective amount when in the vicinity of antenna  40 L. 
     Antenna adjustments can be made by control circuitry  30  based on knowledge of the current operating state of device  10  and based on knowledge of the operating environment of device  10 . Information about the current operating state of device  10  may include information about what transmit power levels are used to transmit radio-frequency signals, information about what frequencies are used for communications, information about which antennas  40  are active, information about a task being performed by device  10  (e.g., information identifying whether device  10  is being used to make a telephone call, check email, send a text message, browse the internet, etc.), information about what input/output components on device  10  are active, information about whether audio of different types is being played be device  10 , information about whether device  10  is currently being used for a telephone call or to communicate data signals, or any other desired information. 
     Information about the operating environment of device  10  may be provided to control circuitry  30  using sensor data and/or based on antenna feedback from radio-frequency coupler  164 . The information about the operating environment of device  10  may include information about any external objects  162  that may be present and/or the effects of external objects  162  on antennas  40 , information about whether device  10  is in motion, information about the orientation of device  10  relative to the earth, etc. 
     Coupler  164  may be used to tap antenna signals flowing to and from antenna  40 L. Tapped antenna signals from coupler  164  may be conveyed to control circuitry  30  over coupler path  166 . In the example of  FIG. 4 , coupler  164  is coupled between adjustable component  106 - 3  and transceiver  36 . If desired, coupler  164  may be coupled between adjustable component  106 - 3  and feed terminals  98 / 100 . The tapped antenna signals may be processed using receiver circuitry or other circuitry associated with control circuitry  30 . Control circuitry  30  may gather phase and magnitude information from the tapped antenna signals on path  166 . Control circuitry  30  may use the gathered phase and magnitude information to determine the impedance of antenna  40 L during the operation of wireless circuitry  34 . 
     For example, control circuitry  30  may convert the measured phase and magnitude values to complex impedance data points. The complex impedance data points may include, for example, scattering parameter (so-called “S-parameters”) values that are indicative of the complex impedance of antenna  40 . Measurements of the S-parameters may include measured reflection coefficient parameter values (S11 values) that are indicative of the amount of radio-frequency signals that is reflected back towards coupler  164  from antenna  40 L during signal transmission. 
     Control circuitry  30  may use the impedance of antenna  40 L (e.g., the complex impedance data points or S11 values measured for antenna  40 L) to determine whether the behavior of antenna  40 L is being influenced by the presence of external object  162 . Circuitry  30  may use the complex impedance values to determine the extent to which the behavior of antenna  40 L is being influenced by the presence of external object  162 . 
     For example, as external object  162  approaches and influences antenna  40 L (e.g., by loading antenna  40 L), the amount of transmitted radio-frequency signals that are reflected back towards coupler  164  may change. This change in signal reflection may change the S11 values that are measured over coupler  164 . Similarly, different materials that are present in object  162  may affect the S11 values that are measured over coupler  164 . Control circuitry  30  may use measurements of the S11 values to obtain knowledge of the operating environment of device  10  over time. Control circuitry  30  may use this information to adjust antenna  40 L to correct for any detuning caused by the presence of external object  162 . 
     In this way, antenna impedance information associated with antenna  40 L (e.g., as measured using signals tapped by coupler  164 ) may be used to at least partially determine the operating environment of device  10 . If desired, other components such as sensors  168  and/or accelerometer  170  may also be used by device  10  to help determine the operating environment of device  10 . 
     Sensors  168  may, for example, include proximity sensors such as capacitive proximity sensors or light-based proximity sensors. Proximity sensors in sensor circuitry  168  may provide data to control circuitry  30  indicating that external object  162  is within a predetermined distance of antenna  40 L or otherwise indicating that is nearby to antenna  40 L. If desired, sensors  168  may include connector sensors or accessory sensors that provide data to control circuitry  30  identifying when an accessory is connected to device  10  and/or what type of accessory is connected to device  10 . Sensors  168  may, if desired, include audio sensors that measure sound signals and provide data identifying the sound signals to control circuitry  30 . Sensors  168  may include any other desired sensors such as temperature sensors, magnetic sensors, visual sensors such as light detectors and image sensors (e.g., camera sensors for front and/or rear cameras), etc. 
     Accelerometer  170  may be used to gather signals on the motion of device  10 . Accelerometer  170  may provide data that indicates whether device  10  is in motion and/or that indicates an amount of motion that device  10  is experiencing to control circuitry  30 . For example, if a user of device  10  is carrying device  10  in a pocket or in the user&#39;s hand, device  10  may jiggle at a characteristic frequency. Device  10  may exhibit different accelerometer signals when at rest on a table. Control circuitry  30  may process data from sensors  168 , data from accelerometer  170 , and/or phase and magnitude measurements from coupler  164  to determine the current operating environment of device  10  (e.g., to determine whether device  10  is being used by a user or is resting on an inanimate object, how device  10  is being held, or to determine other information about the presence of external objects  162  in the vicinity of device  10 ). 
     During operation of device  10 , control circuitry  30  can use this information on the current operating environment of device  10  to determine how to adjust tunable antenna components (e.g., components such as components  106 - 1 ,  106 - 2 ,  106 - 3 , and/or  106 - 4 ) to compensate for any detuning of antennas  40  due to the presence of external objects  162 . If desired, this information may also be used to determine how to adjust the maximum permissible transmit power levels of antennas  40 . 
     For example, there may be regulatory standards such as government or industry regulations that limit radio-frequency signal powers for electronic devices. In many jurisdictions, regulatory standards impose maximum energy absorption limits on manufactures of electronic devices. Such maximum energy absorption limits typically include specific absorption rate (SAR) limits and other absorption limits. These standards place restrictions on the amount of transmitted wireless power that can be absorbed by users or other entities in the vicinity of wireless electronic devices. 
     In order to ensure that such standards are satisfied (e.g., to limit absorption of wireless power by sensitive objects), control circuit  30  may limit the maximum transmit power levels that are provided by antennas  40 . For example, control circuitry  30  may control amplifier circuitry interposed between transceiver  36  and antenna  40  (not shown) that amplifies radio-frequency signals to be transmitted by antenna  40  to a desired transmit power level. The transmit power level may be adjusted to ensure satisfactory link quality while also minimizing power consumption in the device. By imposing a maximum transmit power level, control circuitry  30  may control the amplifier circuitry to only transmit radio-frequency signals at transmit power levels that are below the maximum transmit power level, for example. 
     If desired, control circuitry  30  may use information about the current operating state of device  10  in addition to information about the current operating environment of device  10  to determine how to adjust the tunable antenna components and/or to adjust the maximum transmit power levels of antennas  40 . The information about the current operating state may include information about which antenna is active, what frequencies are being used for communication, a task that is being performed by device  10  (e.g., information about whether the device is being used to make a telephone call, being used to browse the internet, being used to check email, being used to send a text message, etc.), information about audio that is being played by speakers  172 , or any other desired information. 
     Control circuitry  30  may provide audio signals to speakers  172 . Speakers  172  may include ear speaker  26  ( FIG. 1 ), speakers adjacent to holes  17 , or any other desired speakers. If desired, control circuitry  30  may use information about whether audio is being played over speakers  172  when determining the current operating state of device  10 . 
     If desired, switching circuitry such as switching circuitry  174  may be interposed on transmission line  92 . Switching circuitry  174  may be used so that only a given one of antennas  40 L and antenna  40 U is used to transmit radio-frequency signals at a given time. For example, switching circuitry  174  may have a first state in which radio-frequency signals are transmitted from transceiver  36  to lower antenna  40 L. Switch  174  may have a second state in which radio-frequency signals are transmitted from transceiver  36  to upper antenna  40 U. Control circuitry  30  may provide control signals to switch  174  over path  178  that control the state of switch  174  (e.g., to selectively activate a given antenna for transmission. Control circuitry  30  may use information about which antenna  40  is transmitting radio-frequency signals at a given time when determining the current operating state of device  10 . 
     The example of  FIG. 4  is merely illustrative. If desired, switch  174  may be omitted. Other switching circuitry may be used to select a given antenna  40  for signal transmission if desired. In another suitable arrangement, a given antenna  40  may be selected for transmission by selectively activating and deactivating transmitter circuits coupled to each antenna. 
     Control circuitry  30  may combine this information about the current operating state of device  10  with the information about the current operating environment of device  10  to determine how to adjust antennas  40  to compensate for detuning and to determine how to adjust maximum transmit power levels imposed on antennas  40  (e.g., to establish an appropriate maximum transmit power for transceiver circuitry  36 , to tune antenna  40 L, etc.). 
     Consider, as an example, a scenario in which a user of device  10  is making a voice telephone call while pressing device housing  12  against the user&#39;s head. In this scenario, it may be desirable to limit the maximum transmit power from transceiver circuitry  36  (e.g., to ensure that regulatory standards that impose maximum energy absorption limits are satisfied). By determining whether the user is using ear speaker  26  ( FIG. 1 ), control circuitry  30  can determine whether or not transmit power should be limited. Coupler  164  and/or other sensors on device  10  may be used to determine whether antenna detuning due to the user holding device  10  needs to be compensated for by adjusting tunable components  106 . 
     When making antenna adjustments, sensors such a sensors  168  and  170  and information about the current operating state of device  10  may be used in an open loop fashion to predict how much antenna  40 L should be adjusted to compensate for detuning. Feedback from coupler  166  may be used in real time in a closed loop fashion to measure antenna detuning. This may allow control circuitry  30  to adjust antennas  40  to compensate for any measured antenna detuning as it occurs. If desired, both sensor data and antenna impedance data from coupler  164  may be used. 
     The example of  FIG. 4  is merely illustrative. In general, antenna  40 L may include any desired circuitry. Antenna  40 L may be any type of antenna arranged in any desired manner. Any desired number of antennas  40  may be coupled to control circuitry  30 . If desired, similar structures may be used by upper antenna  40 U or by other antennas  40  in device  10 . 
       FIG. 5  is a circuit diagram showing one possible circuit that may be used to form adjustable matching circuitry  106 - 3  of  FIGS. 3 and 4 . As shown in  FIG. 5 , adjustable matching circuitry  106 - 3  may include a first inductor  182  connected in series with first switch  184  between signal conductor  94  of transmission line  92  and ground  152 . Matching circuitry  106 - 3  may include a second inductor  186  connected in series with second switch  188  between signal conductor  94  and ground. Switches  184  and  188  may be single-pole single-throw (SPST) switches, for example. Circuitry  106 - 3  in this example of  FIG. 5  may therefore sometimes be referred to herein as shunt SPST circuitry. 
     Inductor  182  may have a first inductance value and inductor  186  may have a second inductance value that is equal to or different from the first inductance value. Control circuitry  30  may provide control signals  104  to selectively open and close switches  184  and  188 . Opening and closing switches  184  and  188  may be performed to adjust the tuning of antenna  40 L (e.g., to compensate for detuning due to the presence of object  162 ). 
     For example, control circuitry  30  may compensate for a first amount of detuning in lower antenna  40 L by opening switch  184  and closing switch  188  (e.g., when device  10  is in a free-space environment). Control circuitry  30  may compensate for a second amount of detuning in lower antenna  40 L by opening switch  188  and closing switch  184  (e.g., when device  10  is being held or gripped by a user such that the user&#39;s hand serves as external object  162  adjacent to lower antenna  40 L). If desired, additional matching circuitry  190  may be interposed on line  94  between feed  98  and the connection to inductor  182  and/or additional matching circuitry  192  may be interposed on line  94  between the connection to inductor  186  and transceiver  36 . 
     The example of  FIG. 5  is merely illustrative. If desired, circuitry  106 - 3  may include any desired resistive, inductive, capacitive, and/or switching components arranged in any desired manner. Any other desired switches such as single pole four-throw (SP4T) switches may be formed in circuitry  106 - 3 . Circuitry  106 - 3  or other tunable circuits such as circuits  106 - 1 ,  106 - 2 , and/or  106 - 4  may be adjusted using control signals  104  and/or control signals  88  ( FIG. 3 ) to compensate for detuning of antenna  40 L due to the presence of external object  162 . 
       FIG. 6  is a diagram showing different possible operating environments for device  10 . As shown in  FIG. 6 , device  10  may be operated in a free-space environment such as free-space environment  200 . Free-space environment  200  may be any environment in which external objects such as object  162  of  FIG. 4  are not located in the vicinity of antennas  40  or any environment in which external objects adjacent to antennas  40  do not significantly impact the performance of antennas  40 . For example, when located in free-space environment  200 , device  10  may be resting on a tabletop or other surface that does not significantly detune antennas  40 . 
     In free-space environment  200 , upper antenna  40 U and lower antenna  40 L of device  10  may transmit radio-frequency signals without being detuned by external objects. As device  10  is not in the vicinity of a body in scenario  200 , control circuitry  30  need not limit the maximum transmit power levels of antennas  40  (or the maximum transmit power levels may be relatively high). 
     During normal operation, a user may hold device  10  in their hand (e.g., to interact with device  10 ). In scenarios where the user is making a telephone call with device  10 , the user may also hold device  10  up to their head (e.g., so that the ear of the user is adjacent to ear speaker  26 ). Environments  202  and  204  of  FIG. 6  illustrate two possible scenarios where the user holds device  10  up to their head. In practice, there may also be other scenarios where the user holds device  10  up to their head such as to listen to audio, take photographs, or to perform any other desired operations. 
     When the user holds device  10  to their head as shown in operating environments  202  and  204 , upper antenna  40 U may be adjacent to the user&#39;s head. Some of the signals transmitted by upper antenna  40 U may be absorbed by the user&#39;s head. In order to satisfy regulatory requirements on maximum energy absorption, the maximum transmit power level of antenna  40 U and/or antenna  40 L may be limited when device  10  is operated in environments  202  and  204  to ensure that the amount of signal absorption by the user&#39;s head meets the regulatory requirements. 
     In other scenarios, the user may hold device  10  away from their head such as in operating environments  208  and  206  of  FIG. 6 . In environments  206  and  208 , the user&#39;s hand may be adjacent to antennas  40  and may potentially detune antennas  40  during wireless communications. As examples, device  10  may be located in environments  208  and  206  when the user is text messaging with device  10 , browsing the internet with device  10 , interacting with software applications on device  10 , conducting a speakerphone telephone call with device  10 , or at any other time while the user holds device  10  in their hands. 
     Lower antenna  40 L of device  10  may have at least two discrete tuning settings or states (e.g., tunable components  106  may have two discrete settings or states). The two tuning settings may compensate for any potential detuning of lower antenna  40 L due to proximity of the user&#39;s body or other objects to lower antenna  40 L. 
     For example, lower antenna  40 L may have a first tuning setting that compensates for antenna detuning when the user holds device  10  (e.g., when device is in operating environment  202 ,  204 ,  206 , or  208 ). Lower antenna  40 L may have a second tuning setting for when the user is not holding device  10  (e.g., when the device is in free-space environment  200 ). The second tuning setting may allow antenna  40 L to be well matched with transmission line  92  in the absence of external objects  192 , thereby allowing antenna  40 L to be properly tuned in the free-space environment. The first tuning setting may sometimes be referred to herein as a grip tuning setting or state (e.g., because the first setting is used to compensate for detuning caused by the user gripping the device). The second tuning setting may sometimes be referred to herein as a free-space tuning setting or state. 
     In scenarios where tuning circuit  106 - 3  of  FIG. 5  is used, the first tuning setting may be a setting in which switch  184  is open and switch  188  is closed whereas the second tuning setting is a setting in which switch  184  is closed and switch  188  is open, for example. When control circuitry  30  determines that the user&#39;s body is in the vicinity of antenna  40 L, control circuitry  30  may control tuning circuitry  106  to place antenna  40 L in the first tuning state. Otherwise, control circuitry  30  may control tuning circuitry  106  to place antenna  40 L in the second tuning state. In this way, antenna  40 L may be well matched to its surroundings so that the antenna remains properly tuned during operation. 
     In practice, when interacting with device  10 , different users may hold the device in different positions. For example, a first group of users may hold device  10  along the lower edge of housing  12  as shown in operating environments  208  and  204 . A second group of users may hold device  10  elsewhere along housing  12  (e.g., along the middle of housing  12 ) as shown in operating environments  206  and  202 . 
     The performance of antennas  40  may depend on how the user holds device  10 . For example, lower antenna  40 L may be detuned by a greater amount when held as shown in environments  208  and  204  than when held as shown in environments  206  and  202 . This may be due to the user&#39;s hand loading lower antenna  40 L more when holding device  10  along the bottom of housing  12  than when holding device  10  along the middle of housing  12 . If care is not taken, switching antenna  40 L between the first and second tuning states may properly compensate for antenna detuning for one group of users while deteriorating antenna performance or further detuning the antenna for another group of users. 
       FIG. 7  is a Smith chart showing how switching antenna  40 L between the first and second antenna tuning states may affect antenna performance differently between two different groups of users. In the Smith chart of  FIG. 7 , antenna impedances for lower antenna  40 L are measured as a function of different operating conditions. A fifty ohm antenna impedance is characterized by impedance point  220  in the chart of  FIG. 7 . An antenna with an impedance close to point  220  may be considered well matched to a fifty ohm transmission line in device  10  (e.g., transmission line  92 ). 
     Antenna  40 L may exhibit an impedance within region  222  of  FIG. 7  when tuned to the free-space tuning setting while device  10  is being held by a first group of users (e.g., users who hold or tend to hold device  10  at the bottom of housing  12  as shown in environments  204  and  208  of  FIG. 6 ). Region  222  is relatively far from point  220 , indicating a relatively high level of antenna detuning. In order to compensate for this detuning, control circuitry  30  may control tuning circuitry  106  to tune antenna  40 L to the grip tuning setting as shown by arrow  224 . After being tuned to the grip tuning setting, antenna  40 L may exhibit an impedance within region  226 . Region  226  is closer to point  220  than region  222 , indicating a lower level of antenna detuning than when operated under the free-space tuning setting associated with region  222 . In this way, control circuitry  30  may compensate for the detuning of lower antenna  40 L caused by the hand of users in the first group. 
     However, antenna  40 L may exhibit different impedances in the grip and free-space tuning settings when held by the second group of users (e.g., users who hold or tend to hold device  10  along the middle of housing  12  as shown in environments  206  and  202  of  FIG. 6 ). For example, antenna  40 L may exhibit an impedance within region  228  when tuned to the free-space tuning setting while device  10  is being held by the second group of users. Region  228  is very close to point  220 , indicating a relatively low (e.g., negligible) level of antenna detuning. 
     If antenna  40 L were to be blindly adjusted to the grip tuning settings in this scenario (e.g., because control circuitry  30  may still detect that a user is holding device  10 ), the impedance of antenna  40 L would shift to region  230  as shown by arrow  232 . However, region  230  is farther away from point  220  than region  228 , indicating that antenna  40 L would be more significantly detuned if such an adjustment were to be made while device  10  is being held by the second group of users. It would therefore be desirable for device  10  to be able to compensate for detuning of antenna  40 L regardless of which group of users is operating device  10  (e.g., regardless of how the user holds the device), while also ensuring that regulations on energy absorption by the user are satisfied. 
     The example of  FIGS. 6 and 7  is merely illustrative. In general, device  10  may be operated in any desired number of different operating environments. For example, device  10  may be placed on a user&#39;s leg or in a user&#39;s pocket. The user may hold device  10  in other positions, with a different hand, with both hands, or in any other desired manner. Each operating environment may affect the antenna impedance ways other than as shown in  FIG. 7 . In general, there may be any desired number of groups of users that use device  10  who may affect antenna performance differently. Care must be taken when adjusting antenna  40 L to ensure that detuning is mitigated for antenna  40 L regardless of the group of user that uses device  10 . 
     Control circuitry  30  may control the maximum transmit power level of antennas  40  in order to ensure that device  10  satisfies regulations on energy absorption regardless of the operating environment and operating state of device  10 .  FIG. 8  shows a table  240  of different maximum transmit power level settings that may be imposed on antennas  40  by control circuitry  30 . Table  240  may, for example, be stored on storage circuitry associated with controller  30 . 
     As shown in  FIG. 8 , control circuitry  30  may impose maximum transmit power levels P 1 , P 2 , P 3 , and P 4  on antennas  40 . Maximum power level P 1  may be a maximum power level for lower antenna  40 L when device  10  is in the vicinity of a user&#39;s head (e.g., in environments  202  and  204  of  FIG. 6 ). Maximum power level P 1  may therefore sometimes be referred to herein as lower antenna head power level P 1 . Maximum power level P 2  may be a maximum power level for lower antenna  40 L when device  10  is not in the vicinity of the user&#39;s head (e.g., in environments  208  and  206 ). If desired, maximum power level P 2  may be used when device  10  is adjacent to a part of the user&#39;s body other than the user&#39;s head (e.g., the user&#39;s hand, leg, etc.). Maximum power level P 2  may therefore sometimes be referred to herein as lower antenna body power level P 2 . If desired, when operating in free-space environment  200  of  FIG. 6 , the higher of power levels P 1  and P 2  may be imposed on lower antenna  40 L and the higher of power levels P 3  and P 4  may be imposed on upper antenna  40 U. 
     In one suitable arrangement, lower antenna head power level P 1  may be greater than lower antenna body power level P 2 . When control circuitry  30  determines that device  10  is adjacent to a user&#39;s head or in free-space environment  200 , control circuitry  30  may impose maximum power level P 1  on lower antenna  40 L. Otherwise (e.g., when control circuitry  30  determines that device  10  is adjacent to other parts of the user&#39;s body), control circuitry  30  may impose maximum power level P 2  on lower antenna  40 L. 
     Maximum power level P 3  may be a maximum power level for upper antenna  40 U when device  10  is in the vicinity of a user&#39;s head (e.g., as in environments  202  and  204 ). Maximum power level P 3  may therefore sometimes be referred to herein as upper antenna head power level P 3 . Maximum power level P 4  may be a maximum power level for upper antenna  40 U when device  10  is not in the vicinity of the user&#39;s head (e.g., as in environments  208  and  206 ). If desired, maximum power level P 4  may be used when device  10  is adjacent to a part of the user&#39;s body other than the user&#39;s head (e.g., the user&#39;s hand, leg, etc.). Maximum power level P 4  may therefore sometimes be referred to herein as upper antenna body power level P 4 . 
     Upper antenna head power level P 3  may be lower than upper antenna body power level P 4 . When control circuitry  30  determines that device  10  is adjacent to a user&#39;s head, control circuitry  30  may impose maximum power level P 3  on upper antenna  40 U. Otherwise, control circuitry  30  may impose maximum power level P 4  on upper antenna  40 U. 
     The example of  FIG. 8  is merely illustrative. Lower antenna body power level P 2  may be less than, greater than, or equal to upper antenna head power level P 3 . If desired, lower antenna head power level P 1  may be greater than lower antenna body power P 2  (e.g., because the bottom side of device  10  may still be held sufficiently far away from the user&#39;s head when the user holds device  10  to their head). In general, any desired number of maximum transmit power levels may be imposed on upper antenna  40 U and lower antenna  40 L (e.g., three maximum power levels, four maximum power levels, more than four maximum power levels, etc.). Similar maximum power levels may be imposed on other antennas  40  within device  10  if desired. 
     Control circuitry  30  may control the tuning of antennas  40 U and  40 L in order to ensure that the antennas operate properly in both the presence and absence of external objects such as a user&#39;s head or hand. Antenna  40 U and antenna  40 L may each have two respective tuning settings so that antennas  40 U and  40 L collectively exhibit four different tuning settings, for example. 
       FIG. 9  shows a table  250  of different tuning settings (states) of antennas  40 U and  40 L that may be controlled by control circuitry  30 . Table  250  may, for example, be stored on storage circuitry associated with controller  30 . 
     As shown in  FIG. 9 , lower antenna  40 L may have a grip tuning setting and a free-space tuning setting. Upper antenna  40 U may have two settings such as a free-space tuning setting and a head tuning setting. Control circuitry  30  may, for example, configure upper antenna  40 U using the head tuning setting when device  10  is being held adjacent to the user&#39;s head. The head tuning setting of upper antenna  40 U may mitigate any detuning of upper antenna  40 U caused by loading of antenna  40 U by the user&#39;s head. Control circuitry  30  may configure upper antenna  40 U using the upper antenna free-space tuning setting when device  10  is not being held to a user&#39;s head. Control circuitry  30  may adjust the tuning setting of upper antenna  40 U by, for example, controlling switching circuitry in tuning circuits such as tuning circuits  106  coupled to upper antenna  40 U. 
     In scenarios where upper antenna  40 U and lower antenna  40 L each have two tuning settings, antennas  40 U and  40 L may collectively have four different tuning states T 1 , T 2 , T 3 , and T 4 . Control circuitry  30  may place device  10  in first tuning state T 1  by applying the upper antenna free-space tuning setting to antenna  40 U and the lower antenna free-space tuning setting to lower antenna  40 L. Control circuitry  30  may place device  10  in first tuning state T 1  when device  10  is located in free space environment  200  of  FIG. 6 , for example. 
     Control circuitry  30  may place device  10  in second tuning state T 2  by applying the upper antenna free-space tuning setting to upper antenna  40 U and the grip tuning setting to lower antenna  40 L. Control circuitry  30  may place device  10  in third tuning state T 3  by applying the head tuning setting to upper antenna  40 U and the lower antenna free-space tuning setting to lower antenna  40 L. Control circuitry may place device  10  in fourth tuning state T 4  by applying the head tuning setting to upper antenna  40 U and the grip tuning setting to lower antenna  40 L. 
     The example of  FIG. 9  is merely illustrative. In general, each antenna  40  may have any desired number of tuning settings or states (e.g., antenna  40 L may have one tuning setting, two tuning settings, three tuning settings, four tuning settings, more than four tuning settings, etc.). If desired, upper antenna  40 U may have a different number of tuning settings than lower antenna  40 L. 
     Control circuitry  30  may process information about the operating environment of device  10  and the operating state of device  10  to select appropriate tuning settings (e.g., tuning settings such as those in table  250  of  FIG. 9 ) and maximum transmit power level settings (e.g., settings such as those shown in table  240  of  FIG. 9 ) for antennas  40 . Control circuitry  30  may, for example, operate in a closed loop manner to actively update the tuning settings based on continuously or semi-continuously gathered impedance information associated with antenna  40 L. 
       FIG. 10  is a flow chart of illustrative steps that may be performed by device  10  to adjust antenna tuning and maximum transmit power level settings for antennas  40  while performing wireless communications operations. 
     At step  260 , control circuitry  30  may identify a change in the operational state of device  10  (e.g., any desired change in device state that may require adjustment to antennas  40  to ensure satisfactory antenna performance and compliance with absorption regulations). For example, control circuitry  30  may identify that a telephone call has been received, that a user of device  10  is using device  10  to browse the internet, send email, send a text message, etc. In general, control circuitry  30  may identify any desired triggering condition associated with the operation of device  10 . 
     At step  262 , control circuitry  30  may determine whether audio is being played through ear speaker  26  ( FIG. 1 ). Audio being played through ear speaker  26  may be, for example, an indication that device  10  is being held up to the ear of a user (e.g., so that the user can hear the audio being played from the ear speaker, as shown in scenarios  202  and  204  of  FIG. 6 ). If audio is being played through ear speaker  26 , processing may proceed to step  266  as shown by path  264 . 
     At step  266 , control circuitry  30  may control upper antenna  40 U and lower antenna  40 L to perform wireless communications using head-adjacent maximum transmit power level settings. For example, control circuitry  30  may impose maximum transmit power level P 1  on lower antenna  40 L and may impose maximum transmit power level P 3  on upper antenna  40 U ( FIG. 8 ). This may help to ensure that the amount of radio-frequency signals absorbed by the user&#39;s head is limited, thereby ensuring that energy absorption regulations are satisfied. 
     Control circuitry  30  may set upper antenna  40 U to a first upper antenna tuning setting such as the upper antenna head tuning setting (e.g., as shown in  FIG. 9 ). This may mitigate any detuning of upper antenna  40 U caused by the presence of a user&#39;s head adjacent to upper antenna  40 U (e.g., as may be required to hear audio through ear speaker  26 ). Control circuitry  30  may set and actively update the tuning settings of lower antenna  40 L based on real time measurements of the impedance of antenna  40 L (e.g., using closed loop tuning adjustments). 
     If no audio is being played through ear speaker  26 , processing may proceed to step  270  as shown by path  268 . This may, for example, occur if device  10  is being used in a speakerphone mode (e.g., if audio is being played from speakers on device  10  other than ear speaker  26 ), if the user of device  10  is using device  10  to browse the internet, send email, interact with software applications, etc. 
     At step  270 , control circuitry  30  may determine whether device  10  is near to (adjacent to) or in contact with a body (e.g., the body of the user of device  10 ). For example, control circuitry  30  may use sensors  168  or accelerometer  170  to identify when device  10  is currently on the body of a user. As an example, accelerometer  170  may measure motion signals that are processed by control circuitry  30 . Control circuitry  30  may determine that device  10  is on the body of the user when the measured motion signals have a frequency that is characteristic of device  10  being on the body of the user (e.g., being held by the user, placed on the body of the user, in a pocket of the user, etc.). Control circuitry  30  may determine that device  10  is not on the body of the user when the measured motion signals do not have this characteristic frequency. When device  10  is next to the body of the user, antennas  40  may need to be limited and tuned differently than when device  10  is not near the user&#39;s body. 
     If control circuitry  30  determines that device  10  is near to a body (e.g., on, in contact with, or adjacent to the body of the user), processing may proceed to step  278  as shown by path  276 . At step  278 , control circuitry  30  may control upper antenna  40 U and lower antenna  40 L to perform wireless communications using body-adjacent maximum transmit power level settings. For example, control circuitry  30  may impose maximum transmit power level P 2  on lower antenna  40 L and may impose maximum transmit power level P 4  on upper antenna  40 U ( FIG. 8 ). This may help to ensure that the amount of radio-frequency signals absorbed by the user&#39;s body is limited, thereby ensuring that energy absorption regulations are satisfied. 
     Control circuitry  30  may set upper antenna  40 U to a second upper antenna tuning setting such as the upper antenna free-space tuning setting shown in  FIG. 9 . Control circuitry  30  may set and actively update the tuning setting of lower antenna  40 L based on real time measurements of the impedance of antenna  40 L (e.g., using closed loop tuning adjustments). 
     If control circuitry  30  determines that device  10  is not near to a body, processing may proceed to step  274  as shown by path  272 . At step  274 , control circuitry  30  may control upper antenna  40 U and lower antenna  40 L to perform wireless communications using free-space antenna tuning settings. For example, control circuitry  30  may place antennas  40 U and  40 L in tuning state T 1  of  FIG. 9  (e.g., so that upper antenna  40 U conveys radio-frequency signals using the upper antenna free-space tuning setting and lower antenna  40 L conveys radio-frequency signals using the lower antenna free-space tuning setting). 
     If desired, the steps of  FIG. 10  may be repeated or halted when device  10  changes its operational state. For example, the steps of  FIG. 10  may be halted or repeated when the telephone call is ended, when the user stops browsing the internet using device  10 , when radio-frequency data is no longer being conveyed to a base station, etc. In general, the steps of  FIG. 10  may be performed whenever data needs to be transmitted and/or received using antennas  40 . In this way, the tuning and maximum transmit power levels of antennas  40  may be updated as needed to ensure that satisfactory wireless communication is performed without violating any signal absorption regulations. 
       FIG. 11  is a flow chart of illustrative steps that may be performed by control circuitry  30  to control antennas  40  when device  10  is in a free-space environment. The steps of  FIG. 11  may, for example, be performed while processing step  274  of  FIG. 10  (e.g., while device  10  is in a free-space or static device environment as shown by environment  200  of  FIG. 6 ). 
     At step  290 , control circuitry  30  may determine whether upper antenna  40 U or lower antenna  40 L is transmitting radio-frequency signals. For example, antennas  40  may be configured so that only a given one of antennas  40 L and  40 U is transmitting radio-frequency signals at a given time. One of the antennas may receive radio-frequency signals while the other antenna transmits radio-frequency signals if desired. The maximum transmit power level and tuning settings that are used for antennas  40  may depend on which of the antennas is currently being used for transmission. 
     If upper antenna  40 U is being used for transmission, processing may proceed to step  298  as shown by path  294 . At step  298 , control circuitry  30  may set the maximum transmit power level of upper antenna  40 U to upper antenna body power level P 4  ( FIG. 8 ). In another suitable arrangement, control circuitry  30  may impose a different maximum transmit power level or may not impose any maximum power level on antenna  40 U. Transmission at relatively high power level P 4  may ensure that a satisfactory wireless link quality is maintained for antenna  40 U. Signal transmission in this configuration may still satisfy regulations on signal absorption because antenna  40 U is not adjacent to the user&#39;s body. Processing may subsequently proceed to step  300 . 
     If lower antenna  40 L is being used for transmission, processing may proceed to step  296  as shown by path  292 . At step  296 , control circuitry  30  may set the maximum transmit power level of lower antenna  40 L to lower antenna head power level P 1 . In another suitable arrangement, control circuitry  30  may impose a different maximum transmit power level on antenna  40 L or may not impose any maximum power level on antenna  40 L. Signal transmission in this configuration may still satisfy regulations on signal absorption because antenna  40 L is not adjacent to the user&#39;s body. Processing may subsequently proceed to step  300 . 
     At step  300 , control circuitry  30  may set antennas  40  to free-space tuning state T 1 . For example, control circuitry  30  may set lower antenna  40 L to the lower antenna free-space tuning setting and may set upper antenna  40 U to the upper antenna free-space tuning setting. When operating in tuning state T 1 , antennas  40  may convey radio-frequency signals with high efficiency and without any detuning due to the presence of external objects (e.g., because antennas  40  are well matched to a free-space environment and device  10  is located in a free-space environment in this scenario). 
     Processing may loop back to step  290  as shown by optional path  301 , if desired. For example, the steps of  FIG. 11  may be repeated if the transmit antenna is changed during communications. The example of  FIG. 11  is merely illustrative. If desired, step  300  may be performed prior to or concurrently with steps  296  and  298 . 
       FIG. 12  is a flow chart of illustrative steps that may be performed by control circuitry  30  to control antennas  40  when device  10  is determined to be in the vicinity of a user&#39;s head. The steps of  FIG. 12  may, for example, be performed while processing step  266  of  FIG. 10  (e.g., while device  10  is being held by a user to their head as shown in environments  202  or  204  of  FIG. 6 ). 
     At step  310 , control circuitry  30  may set the maximum transmit power level of lower antenna  40 L to lower antenna head power level P 1 . Control circuitry  30  may set the maximum transmit power level of upper antenna  40 U to upper antenna head power level P 3 . By configuring antennas  40  using head transmit power levels P 1  and P 3 , signal absorption by the user&#39;s head may be limited, thereby satisfying signal absorption regulations. 
     At step  312 , device  10  may determine whether upper antenna  40 U or lower antenna  40 L is being used to transmit radio-frequency signals. If upper antenna  40 U is being used to transmit signals, processing may proceed to step  316  as shown by path  314 . 
     At step  316 , control circuitry  30  may set upper antenna  40 U to the head tuning setting ( FIG. 9 ). This may mitigate any detuning of upper antenna  40 U caused by loading of antenna  40 U by the user&#39;s head. Control circuitry  30  may set lower antenna  40 L to the grip tuning setting. This may mitigate any detuning of lower antenna  40 L caused by the user holding device  10  up to their head (e.g., so that reception of radio-frequency signals over lower antenna  40 L is satisfactory). In other words, control circuitry  30  may place antennas  40  in tuning state T 4  of  FIG. 9 . If desired, processing may loop back to step  312  as shown by optional path  317  if the transmit antenna changes during communications. 
     If lower antenna  40 L is being used to transmit signals, processing may proceed to step  320  as shown by path  318 . At step  320 , control circuitry  30  may set upper antenna  40 U to the head tuning setting and may set lower antenna  40 L to the grip tuning setting (e.g., as reflected by tuning state T 4  of  FIG. 9 ). Processing may subsequently proceed to step  322 . 
     At step  322 , control circuitry  30  may perform closed-loop tuning adjustments for lower antenna  40 L based on impedance information measured from lower antenna  40 L and based on predetermined calibration data stored on device  10 . For example, control circuitry  30  may actively gather phase and magnitude information in the form of complex S11 values using signals routed by coupler  164  ( FIG. 4 ) during communications. 
     Control circuitry  30  may process the actively gathered S11 values to determine whether the tuning setting of antenna  40 L needs to be updated (e.g., to compensate for any change in the operating environment of device  10 ). By updating the tuning settings of antenna  40 L using the gathered S11 values, control circuitry  30  may ensure that any detuning of lower antenna  40 L is mitigated during communications regardless of changes in the operating environment of device  10 . 
     For example, by initially setting antenna  40 L to the grip tuning setting at step  320 , control circuitry  30  initially assumes that the user potentially belongs to the group of users that holds the device  10  along the bottom side of housing  12  (e.g., as shown in scenarios  208  and  204  of  FIG. 6 ). However, the closed loop tuning adjustments may allow control circuitry  30  to actively determine if the user actually belongs to that group of users or if the user belongs to the group of users that holds the phone elsewhere on housing  12  (e.g., as shown in scenarios  202  and  206 ). In this way, control circuitry  30  may actively perform the appropriate tuning adjustments (or lack thereof) for antenna  40 L to mitigate any potential detuning regardless of how the user holds the device. The closed loop tuning adjustments may allow control circuitry  30  to update the tuning adjustments if the user changes how they are holding device  10  over time. Processing may loop back to step  312  as shown by optional path  323 , if desired. For example, steps  312 - 322  may be repeated if the transmit antenna is changed during communications. 
       FIG. 13  is a flow chart of illustrative steps that may be performed by control circuitry  30  to control antennas  40  when device  10  is determined to be in the vicinity of a body. The steps of  FIG. 13  may, for example, be performed while processing step  278  of  FIG. 10  (e.g., while device  10  is being held by a user but not near their head, such as is in operating environments  208  or  206  of  FIG. 6 ). 
     At step  330 , control circuitry  30  may set the maximum transmit power level of lower antenna  40 L to lower antenna body power level P 2 . Control circuitry  30  may set the maximum transmit power level of upper antenna  40 U to upper antenna body power level P 4 . By configuring antennas  40  using body transmit power levels P 2  and P 4 , a high quality wireless link can be established without violating signal absorption regulations. 
     At step  332 , device  10  may determine whether upper antenna  40 U or lower antenna  40 L is being used to transmit radio-frequency signals. If upper antenna  40 U is transmitting signals, processing may proceed to step  336  as shown by path  334 . 
     At step  336 , control circuitry  30  may set upper antenna  40 U to the free-space tuning setting (e.g., because users do not typically hold device  10  by the top half of housing  12 , so antenna  40 U may effectively operate in a free-space environment). Control circuitry  30  may set lower antenna  40 L to the grip tuning setting. This may mitigate any detuning of lower antenna  40 L caused by the user holding device  10  (e.g., so that reception of radio-frequency signals over lower antenna  40 L is satisfactory). In other words, control circuitry  30  may place antennas  40  in tuning state T 2  of  FIG. 9 . If the transmit antenna changes during communications, processing may loop back to step  332  as shown by optional path  337 , if desired. 
     If lower antenna  40 L is transmitting signals, processing may proceed to step  340  as shown by path  338 . At step  340 , control circuitry  30  may set upper antenna  40 U to the free-space tuning setting and may set lower antenna  40 L to the grip tuning setting (e.g., as shown by tuning state T 2  of  FIG. 9 ). Processing may subsequently proceed to step  342 . 
     At step  342 , control circuitry  30  may perform closed-loop tuning adjustments for lower antenna  40 L based on impedance information measured from lower antenna  40 L and based on predetermined calibration data stored on device  10 . For example, control circuitry  30  may actively gather phase and magnitude information in the form of complex S11 values from coupler  164  during communications. 
     Control circuitry  30  may process the gathered S11 values to determine whether the tuning setting of antenna  40 L needs to be updated (e.g., to compensate for any change in the operating environment of device  10 ). By updating the tuning settings of antenna  40 L using the gathered S11 values, control circuitry  30  may ensure that any detuning of lower antenna  40 L is mitigated during communications regardless of changes in the operating environment of device  10 . Processing may loop back to step  332  as shown by optional path  337 , if desired. For example, steps  332 - 342  may be repeated if the transmit antenna is changed during communications. 
       FIG. 14  is a flow chart of illustrative steps that may be processed by control circuitry  30  to perform closed-loop tuning adjustments on lower antenna  40 L (e.g., based on impedance information measured using lower antenna  40 L and predetermined calibration data stored on device  10 ). The steps of  FIG. 14  may, for example, be performed by control circuitry  30  while processing step  322  of  FIG. 12  or step  342  of  FIG. 13 . 
     At step  350 , control circuitry  30  may obtain antenna impedance information from lower antenna  40 L. For example, control circuitry  30  may measure phase and magnitude information from signals transmitted on transmission line  92  and from reflected versions of the transmitted signals that are received via coupler  164  ( FIG. 4 ). Control circuitry  30  may obtain complex impedance values such as S11 values from the measured phase and magnitude information. 
     Control circuitry  30  may measure any desired number of S11 values at step  350 . For example, control circuitry  30  may measure a single S11 value, two S11 values, three or more S11 values, etc. If desired, control circuitry  30  may perform S11 measurements at regular updating time intervals (e.g., every 10 ms, every 1 second, every 10 seconds, etc.). If desired, control circuitry  30  may combine multiple S11 values to generate a final S11 value that is used for subsequent processing. For example, control circuitry  30  may generate the final S11 value as a linear combination or average of any desired number of measured S11 values. Performing more S11 measurements may increase the reliability of the final S11 measurement at the expense of increasing processing time. 
     At step  352 , control circuitry  30  may process the gathered lower antenna impedance information to determine whether antenna  40 L has entered a free-space environment. For example, control circuitry  30  may compare the S11 values (or the final S11 value in scenarios where multiple S11 measurements are performed at step  350 ) to predetermined calibration data to determine whether antenna  40 L has entered the free-space environment. 
     If control circuitry  30  determines that device  10  has not entered a free-space environment, processing may loop back to step  350  as shown by path  354  to continue to gather additional S11 values. For example, if device  10  remains in an environment such as environment  208  or  206  of  FIG. 6 , the S11 values obtained by control circuitry  30  may indicate that device  10  has not yet entered a free-space environment. 
     If control circuitry  30  determines that device  10  has entered a free-space environment, processing may proceed to step  358  as shown by path  356 . For example, if device  10  enters environment  200  from environments  208  or  206  of  FIG. 6 , the S11 values obtained by control circuitry  30  may indicate that device  10  (or at least lower antenna  40 L) has entered a free-space environment. Entering the free-space environment may cause an impedance mismatch at antenna  40 L that detunes antenna  40 L, which was previously set to the grip tuning setting (e.g., at step  320  of  FIG. 12  or step  340  of  FIG. 13 ). 
     At step  358 , control circuitry  30  may adjust lower antenna  40 L to the lower antenna free-space tuning setting. For example, circuitry  30  may place antennas  40  in tuning state T 3  ( FIG. 9 ) in scenarios where the steps of  FIG. 14  are performed while processing step  322  of  FIG. 12 . Circuitry  30  may place antennas  40  in tuning state T 1  in scenarios where the steps of  FIG. 14  are performed while processing step  342  of  FIG. 13 . Adjusting lower antenna  40 L may ensure that lower antenna  40 L is well matched to the environment surrounding antenna  40 L, thereby mitigating any antenna detuning that would have been caused by the antenna being set to the grip tuning setting in a free-space environment (e.g., so that reception of radio-frequency signals over lower antenna  40 L is satisfactory). 
     Antenna  40 L may continue to transmit signals using the free-space tuning setting. If desired, control circuitry  30  may concurrently obtain additional antenna impedance information from lower antenna  40 L. For example, control circuitry  30  may gather additional S11 values from lower antenna  40 L. 
     Control circuitry  30  may measure any desired number of S11 values at step  360 . For example, control circuitry  30  may measure a single S11 value, two S11 values, three or more S11 values, etc. If desired, control circuitry  30  may perform S11 measurements at regular time intervals (e.g., every 10 seconds, every 1 second, etc.). If desired, control circuitry  30  may combine multiple S11 values to generate a final S11 value that is used for subsequent processing. For example, control circuitry  30  may generate the final S11 value as a linear combination or average of any desired number of S11 values. Control circuitry  30  may gather the same number of S11 values as when performing step  350  or may gather a different number of S11 values than when performing step  350 . 
     At step  362 , control circuitry  30  may process the gathered additional impedance information to determine whether antenna  40 L has returned to a grip environment (e.g., an environment in which the user is holding device  10  or in which the user&#39;s body is otherwise adjacent to antenna  40 L). For example, control circuitry  30  may compare the measured additional S11 values (or the final S11 value in scenarios where multiple S11 measurements are performed at step  360 ) to predetermined calibration data to determine whether antenna  40 L has entered the grip environment. 
     If control circuitry  30  determines that device  10  has not returned to the grip environment, processing may loop back to step  360  as shown by path  364  to continue to gather additional S11 values. For example, if device  10  remains in an environment such as environment  200  of  FIG. 6  or another environment in which the user&#39;s hand is not adjacent to lower antenna  40 L, the additional S11 values obtained by control circuitry  30  may indicate that device  10  has not yet returned to the grip environment. 
     If control circuitry  30  determines that device  10  has returned to the grip environment, processing may proceed to step  368  as shown by path  366 . For example, if device  10  enters environment  208  or  206  from environments  200  of  FIG. 6 , the S11 values obtained by control circuitry  30  may indicate that device  10  (or at least lower antenna  40 L) has returned to the grip environment. Entering the grip environment may detune antenna  40 L, which was previously set to the free-space tuning setting (e.g., at step  358 ). 
     At step  368 , control circuitry  30  may adjust lower antenna  40 L to the grip tuning setting. For example, circuitry  30  may place antennas  40  in tuning state T 4  ( FIG. 9 ) in scenarios where the steps of  FIG. 14  are performed while processing step  322  of  FIG. 12 . Circuitry  30  may place antennas  40  in tuning state T 2  in scenarios where the steps of  FIG. 14  are performed while processing step  342  of  FIG. 13 . Adjusting lower antenna  40 L may ensure that lower antenna  40 L is well matched to the environment surrounding antenna  40 L, thereby mitigating any antenna detuning that would have been caused by the antenna being set to the free-space tuning setting in a grip environment (e.g., so that reception of radio-frequency signals over lower antenna  40 L is satisfactory). 
     Processing may subsequently loop back to step  350  to obtain additional impedance measurements and update the tuning settings of lower antenna  40 L as necessary. If audio is played through ear speaker  26  at any time while processing the steps of  FIG. 11  or  FIG. 13 , processing may, if desired, jump to step  266  of  FIG. 10 . For example, when a user switches from speaker phone mode to ear speaker mode during a telephone call, processing may be updated to perform head-adjacent power and antenna tuning adjustment operations. If audio stops being played through ear speaker  26  at any time while processing the steps of  FIG. 11 , processing may, if desired, jump to step  270  of  FIG. 10 . For example, when a user switches from ear speaker mode to speaker phone mode during a telephone call, processing may be updated to perform body-adjacent or free-space antenna tuning and power adjustment operations. If the operational state of device  10  changes (e.g., if the call is ended) during processing of the steps of  FIGS. 10-14 , the processing operations of  FIGS. 10-14  may halt or processing may return to step  260 , if desired. 
     In this way, control circuitry  30  may perform closed-loop tuning adjustments (e.g., by looping back to steps  350  and  360  to continually and actively updating tuning based on S11 measurements over time). This is in contrast with open loop processing in which control circuitry  30  adjusts antennas  40  using only settings that are stored in look up tables on device  10 . 
     By performing closed-loop antenna adjustments in this way, antenna  40 L can be actively adjusted based on the current operating environment so that the antenna is provided with proper tuning regardless of the group of users that is operating antenna  40  (e.g., regardless of whether the user holds the device as shown in environments  208  and  204  or as shown in environments  206  and  202  of  FIG. 6 ). In other words, performing these operations may allow control circuitry  30  to adjust the impedance of antenna  40 L from region  222  to region  226  for users that hold device  10  as shown in scenarios  208  and  204  without adjusting the impedance of antenna  40 L from region  228  to region  230  for users that hold device  10  as shown in scenarios  206  and  202 . 
     If desired, steps  332 - 342  of  FIG. 13  and steps  312 - 322  of  FIG. 12  may be omitted if the desired transmit power level for antennas  40  drops below a threshold transmit power level. For example, a cellular base station or other access point equipment may instruct device  10  to operate at a transmit power level that is below the threshold (e.g., if link quality is satisfactory enough so that transmit power may be limited without affecting call quality). In these scenarios, it may not be necessary to perform closed loop antenna tuning adjustment operations. In addition, measurement of S11 values may, in practice, become less reliable at transmit power levels below the threshold level. Omission of such processing steps may therefore prevent any unreliable measurement of S11 in such a scenario, for example. 
     If desired, control circuitry  30  may additionally or alternatively perform open-loop antenna tuning and maximum transmit power adjustment operations using lookup tables. For example, control circuitry  30  may perform open loop look up table operations to determine antenna settings to use for changes in carrier frequency, handover operations, measurement gap operations, paging operations, or any other desired operations. 
       FIG. 15  is a flow chart of illustrative steps that may be performed by control circuitry  30  to determine whether lower antenna  40 L has changed operating environments (e.g., to a free-space environment from a grip environment or from a grip environment to a free-space environment). The steps of  FIG. 15  may, for example, be performed while processing step  352  or  362  of  FIG. 14  (e.g., after obtaining a complex S11 value from lower antenna  40 L). 
     At step  380 , control circuitry  30  may determine whether the magnitude of the measured S11 value(s) (“|S11|”) has decreased while antenna  40 L is tuned using a first tuning setting (e.g., using the grip tuning setting while processing step  352  or using the free-space tuning setting while processing step  362 ). 
     In scenarios where multiple S11 values are obtained, circuitry  30  may determine whether the magnitude of the final S11 value (e.g., the magnitude of the average of multiple S11 values) has decreased over time. For example, control circuitry  30  may compare the final S11 value to one or more previously-stored S11 measurements made with the current lower antenna tuning setting to determine whether the magnitude of S11 has decreased. 
     If the magnitude of the final S11 value has not decreased, processing may proceed to step  384  as shown by path  382 . At step  384 , control circuitry  30  may continue to gather antenna impedance information. In scenarios where the steps of  FIG. 15  are performed while processing step  352  of  FIG. 14 , step  384  may involve looping back to step  350  as shown by path  354  of  FIG. 14 . In scenarios where the steps of  FIG. 15  are performed while processing step  362  of  FIG. 14 , step  384  may involve looping back to step  360  as shown by path  364  of  FIG. 14 . 
     In general, a decrease in the magnitude of S11 may be indicative of fewer reflected signals being received at coupler  164 , a better impedance match between lower antenna  40 L and its immediate surroundings, and less antenna detuning caused by external objects  162 . An increase in the magnitude of S11 (or if the magnitude of S11 is unchanged) may be indicative of more reflected signals being received at coupler  164 , a poorer impedance match, and more antenna detuning. By continuing to gather impedance data when the magnitude of S11 has not decreased, control circuitry  30  may ensure that any change in the tuning setting of lower antenna  40 L actually improves antenna tuning and performance before changing the tuning setting. 
     If the magnitude of the final S11 value has decreased, processing may proceed to step  386  as shown by path  381 . At step  386 , control circuitry  30  may determine whether the final S11 value falls within an expected complex impedance region (e.g., a complex impedance region associated with a free-space environment when antenna  40 L is set using the grip tuning setting or a complex impedance region associated with a grip environment when antenna  40 L is set using the free-space tuning setting). The boundaries of the expected complex impedance region may vary based on the current tuning settings for antenna  40 L and based on the frequency of operation. The boundaries of the expected complex impedance region may be defined by calibration data stored on device  10  (e.g., the boundaries may be predetermined and stored on device  10  during a calibration of device  10 ). 
     If the S11 value is outside of the expected complex impedance region, processing may proceed to step  384  and additional S11 data may be gathered. The value of S11 being outside of the expected region may be indicative of lower antenna  40 L having not yet changed operating environments. As such, the antenna tuning setting need not be updated. 
     If the final S11 is within the expected complex impedance region, processing may proceed to step  392  as shown by path  390 . At step  392 , control circuitry  30  may proceed with the appropriate lower antenna tuning adjustment. For example, in scenarios where step  352  of  FIG. 14  is performed, processing may proceed to step  358 . In scenarios where step  362  is performed, processing may proceed to step  368  of  FIG. 14 . 
     If desired, control circuitry  30  may process multiple S11 measurements at step  386 . For example, control circuitry  30  may perform a voting process to determine whether to proceed along path  390  or  388 . To perform the voting process, control circuitry  30  may determine whether a predetermined number of S11 measurements agrees or falls within the expected region. For example, control circuitry  30  may advance to step  392  if a predetermined ratio of sequentially measured S11 measurements are the same or if a predetermined ratio of sequentially measured S11 measurements fall within the expected region (e.g., if four out of five S11 measurements are the same or fall within the expected region, if seven out of ten S11 measurements fall within the expected region, etc.). If the predetermined ratio of S11 measurements disagree or do not fall within the expected region, processing may advance to step  384 . Performing a voting process during this determination may help to eliminate false positive signals, noise, or other outliers from impacting the decision making performed by control circuitry  30 . 
     If desired, control circuitry  30  may ignore S11 measurements that are excessively old in performing step  386 . For example, control circuitry  30  may include a buffer for storing sequentially measured S11 values. Control circuitry  30  may remove S11 measurements from the buffer that are older than a predetermined threshold time (e.g., a so-called “forgetting factor”). This may prevent outdated or inaccurate S11 measurements from affecting the decision making performed by control circuitry  30  at step  386 . If recent S11 measurements are not available, antenna tuning adjustments may be omitted or open loop antenna adjustments may be performed, if desired. 
       FIG. 16  shows a plot  399  of complex impedance values (e.g., with the real component of the complex impedance values on the horizontal axis and the imaginary component of the complex impedance values on the vertical axis) for antenna  40 L while tuned using the free-space tuning setting. Plot  399  may, for example, be indicative of the impedance of antenna  40 L while control circuitry  30  gathers S11 values from antenna  40 L when processing step  360  of  FIG. 14 . 
     As shown in  FIG. 16 , calibration data stored on device  10  may identify a free-space complex impedance region  400 . Region  400  may be defined by an upper radius threshold ρ MAX1 , a lower radius threshold ρ MIN1 , a lower angular threshold θ MIN1 , and an upper angular threshold θ MIN2 . Control circuitry  30  may identify the region of plot  399  outside of region  400  as the expected region while processing step  386  of  FIG. 15 . 
     If the measured S11 value falls within the expected region, such as at point  404 , control circuitry  30  may determine that the measured S11 value is within the expected region and the tuning of lower antenna  40 L may be adjusted to the grip tuning setting (e.g., as shown by step  392  of  FIG. 15  and step  368  of  FIG. 14 ). An S11 value at point  404  may, for example, be indicative of a user holding device  10  as shown in scenarios  208  and  204  of  FIG. 6  (e.g., a user from a group of users that hold device  10  along the bottom of housing  12 ). 
     If the measured S11 value falls outside of the expected region, such as at point  402 , control circuitry  30  may determine that the measured S11 value is outside of the expected region and circuitry  30  may continue to gather impedance information using the free-space tuning setting for lower antenna  40 L (e.g., as shown by step  384  of  FIG. 15  and loop  364  of  FIG. 14 ). An S11 value at point  402  may, for example, be indicative of a user holding device  10  as shown in scenarios  206  and  202  of  FIG. 6  (e.g., a user from a group of users that hold device  10  along the middle of housing  12 ). 
       FIG. 17  shows a plot  409  of complex impedance values for antenna  40 L while tuned using the grip tuning setting. Plot  409  may, for example, be indicative of the antenna impedance of antenna  40 L while control circuitry  30  gathers S11 values from antenna  40 L when processing step  352  of  FIG. 14 . 
     As shown in  FIG. 17 , calibration data stored on device  10  may identify a free-space complex impedance region  406 . Region  406  may be defined by an upper radius threshold ρ MAX2 , a lower radius threshold ρ MIN2 , a lower angular threshold θ MIN2 , and an upper angular threshold θ MAX2 . Control circuitry  30  may identify region  406  of plot  409  as the expected region while processing step  386  of  FIG. 15 , for example. 
     If the measured S11 value falls within the expected region, such as at point  408 , control circuitry  30  may determine that the measured S11 value is within the expected region and the tuning of lower antenna  40 L may be adjusted to the free-space tuning setting. An S11 value at point  408  may, for example, be indicative of a user holding device  10  as shown in scenarios  206  and  202  of  FIG. 6  (e.g., a user from a group of users that hold device  10  along the middle of housing  12 ). 
     If the measured S11 value falls outside of the expected region, such as at point  410 , control circuitry  30  may determine that the measured S11 value is outside of the expected region and circuitry  30  may continue to gather impedance information using the grip tuning setting for lower antenna  40 L. An S11 value at point  408  may, for example, be indicative of a user holding device  10  as shown in scenarios  208  and  204  of  FIG. 6  (e.g., a user from a group of users that hold device  10  along the bottom of housing  12 ). 
     In the example of  FIGS. 16 and 17 , S11 values  404  and  410  may be gathered for the group of users that hold device  10  along the bottom of housing  12 , whereas S11 values  410  and  408  are gathered for the group of users that hold device  10  along the middle of housing  12 . By performing the operations of  FIGS. 10-15 , adjustments of antenna  40 L from impedance region  228  to impedance region  230  of  FIG. 7  may be avoided, whereas adjustments of antenna  40 L from region  222  to  226  are performed. This may mitigate detuning of antenna  40 L for the group of users that hold device  10  along the bottom of housing  12  without detuning antenna  40 L for the group of users that hold device  10  along the middle of housing  12 . 
     The example of  FIGS. 16 and 17  are merely illustrative. In general, regions  400  and  406  may be located at any desired location in plots  399  and  409 , respectively. Regions  400  and  406  may have any desired shape (e.g., as determined by factory or design calibration of device  10 ). Regions  400  and  406  may be defined by any desired boundaries. If desired, plots  399  and  409  may each have multiple continuous and/or discontinuous regions  400 . 
       FIG. 18  is a table of calibration data that may be stored on device  10  for determining when to adjust tuning settings for lower antenna  40 L. As shown in  FIG. 18 , table  420  may store threshold values ρ MAX1 , ρ MIN1 , θ MAX1 , and θ MIN1  defining free-space region  400  when antenna  40 L is set to the free-space tuning setting ( FIG. 16 ). Table  420  may also store threshold values ρ MAX2 , ρ MIN2 , θ MAX2 , and θ MIN2  defining free-space region  406  when antenna  40 L is set to the grip tuning setting ( FIG. 17 ). 
     Table  420  may store different values of these thresholds (e.g., ρ 1 , ρ 2 , θ 1 , θ 2 , etc.) for different operating frequencies F of antenna  40 L (e.g., a first frequency F 1 , a second frequency F 2 , etc.). This may allow different regions to be defined for different frequencies of operation (e.g., because antenna impedance of antenna  40 L may be dependent upon the operating frequency). Control circuitry  30  may select the appropriate row of table  420  for use in comparing with measured S11 values (e.g., while processing step  386  of  FIG. 15 ) based on the operating frequency of antenna  40 L. 
     If desired, steps  312 - 322  of  FIG. 12  and steps  332 - 342  of  FIG. 13  may be omitted for some frequencies of operation (e.g., closed loop antenna tuning may be performed for some frequencies of operation and may be omitted for other frequencies of operation). As an example, control circuitry  30  may perform closed loop tuning of lower antenna  40 L when operating at a low band cellular telephone frequency such as between 700 and 960 MHz whereas circuitry  30  performs open loop adjustments at midband cellular telephone frequencies between 1710 and 2170 MHz and high band cellular telephone frequencies between 2300 and 2700 MHz. In this example, lower antenna  40 L may be particularly susceptible to detuning due to the presence of the user&#39;s hand at frequencies between 700 and 960 MHz and less susceptible at other frequencies. Calibration data  420  for these frequencies may be omitted if desired. 
     The example of  FIGS. 10-18  described in connection with upper and lower antennas  40 U and  40 L is merely illustrative. If desired, the methods of  FIGS. 10-18  may be extended to any number of antennas placed at any desired locations on device  10 . 
     These threshold values may be loaded onto device  10  before normal operation of device  10  by an end user of device  10 . For example, these values may be generated during design or factory calibration of device  10 . Table  420  may include data stored in any desired format or data structure. 
     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: 20160902
Publication Date: 20191203
Grant Date: 20191203
Priority Date: 20160902
Inventors: HAN, LIANG
MOW, MATTHEW A.
BIEDKA, THOMAS E.
Assignee: APPLE INC
CPC Classifications: [{"code": "H01Q1/243", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04W52/42", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W52/367", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q1/243", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01Q9/42", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q1/245", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W52/367", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q5/371", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q5/328", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W52/42", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q9/42", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W52/367", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q5/328", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q1/243", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01Q5/371", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q1/245", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 61280739