PATENT DOCUMENT

Publication Number: US-9084124-B2
Application Number: US-201213725769-A
Country: US
Kind Code: B2

Title: Methods and apparatus for performing passive antenna testing with active antenna tuning device control

Abstract:
A wireless electronic device may contain at least one adjustable antenna tuning element for use in tuning the operating frequency range of the device. The antenna tuning element may include radio-frequency switches, continuously/semi-continuously adjustable components such as tunable resistors, inductors, and capacitors, and other load circuits that provide desired impedance characteristics. A test system that is used for performing passive radio-frequency (RF) testing on antenna tuning elements in partially assembled devices is provided. The test system may include an RF tester and a test host. The tester may be used to gather scattering parameter measurements from the antenna tuning element. The test host may be used to ensure that power and appropriate control signals are being supplied to the antenna tuning element so that the antenna tuning element is placed in desired tuning states during testing.

Claims:
What is claimed is: 
     
       1. A method for using a radio-frequency test system to test an electronic device under test that contains transceiver circuitry and a tunable antenna having an adjustable antenna tuning element, the method comprising:
 placing the adjustable antenna tuning element in a plurality of tuning states to tune the tunable antenna; 
 while the adjustable antenna tuning element is being placed in each of the plurality of states and while the transceiver circuitry is deactivated, gathering test data from the electronic device under test with the radio-frequency test system; and 
 with the radio-frequency test system, gathering baseline test data by performing radio-frequency calibration on a plurality of reference electronic devices under test, wherein the adjustable antenna tuning element comprises at least one adjustable circuit selected from the group consisting of: a radio-frequency switch, a tunable resistive component, a tunable capacitive component, and a tunable inductive component. 
 
     
     
       2. The method defined in  claim 1 , further comprising:
 with the radio-frequency test system, comparing the test data to the baseline radio-frequency test data to determine whether the tunable antenna satisfies design criteria. 
 
     
     
       3. The method defined in  claim 1 , wherein gathering the test data and the baseline test data comprises obtaining multiport scattering parameter measurements. 
     
     
       4. The method defined in  claim 1 , wherein placing the adjustable antenna tuning element in the plurality of tuning states comprises controlling the adjustable antenna tuning element using the radio-frequency test system. 
     
     
       5. The method defined in  claim 1 , wherein placing the adjustable antenna tuning element in the plurality of tuning states comprises configuring the adjustable antenna tuning element to exhibit different impedance values in the respective tuning states. 
     
     
       6. The method defined in  claim 1 , wherein the radio-frequency test system comprises a radio-frequency tester, and wherein gathering the test data from the electronic device under test comprises:
 sending radio-frequency test signals to the electronic device under test with the radio-frequency tester; and 
 receiving corresponding radio-frequency test signals from the electronic device under test with the radio-frequency tester. 
 
     
     
       7. The method defined in  claim 6 , wherein gathering the test data from the electronic device under test comprises gathering scattering parameter measurements. 
     
     
       8. The method defined in  claim 1 , wherein the electronic device under test comprises a partially assembled wireless electronic device. 
     
     
       9. The method defined in  claim 8 , wherein gathering test data from the electronic device under test with the radio-frequency test system comprises gathering scattering parameter measurements from the electronic device under test while the transceiver circuitry in the electronic device under test is idle. 
     
     
       10. The method defined in  claim 9 , wherein gathering the scattering parameter measurements comprises coupling the adjustable antenna tuning element to the radio-frequency test system using a contact test probe. 
     
     
       11. The method defined in  claim 9 , wherein gathering the scattering parameter measurements comprises coupling the adjustable antenna tuning element to the radio-frequency test system using a wireless test probe.

Description:
BACKGROUND 
     This relates generally to wireless communications circuitry, and more particularly, to electronic devices having wireless communications circuitry. 
     Electronic devices such as portable computers and cellular telephones are often provided with wireless communications capabilities. For example, electronic devices may use long-range wireless communications circuitry such as cellular telephone circuitry to communicate using cellular telephone bands. Electronic devices may use short-range wireless communications circuitry such as wireless local area network communications circuitry to handle communications with nearby equipment. Electronic devices may also be provided with satellite navigation system receivers and other wireless circuitry. 
     To satisfy consumer demand for small form factor wireless devices, manufacturers are continually striving to implement wireless communications circuitry such as antenna components using compact structures. However, it can be difficult to fit conventional antenna structures into small devices. For example, antennas that are confined to small volumes often exhibit narrower operating bandwidths than antennas that are implemented in larger volumes. If the bandwidth of an antenna becomes too narrow, the antenna will not be able to cover all communications bands of interest. 
     In view of these considerations, it would be desirable to provide antenna tuning elements that allow the antenna to cover a wider range of frequency bands. Antenna tuning elements are adjustable components that can be placed in various tuning states during wireless operation of an electronic device. In order for the antenna to be able to cover the desired range of frequency bands, the antenna tuning elements would have to be able to switch among the different tuning states and to provide appropriate loading in the different respective tuning states. 
     During device assembly, workers and automated assembly machines may be used to solder the antenna tuning elements to various antenna structures and to otherwise form connections to other wireless circuitry. If care is not taken, however, faults may result that can impact the performance of a final assembled device. For example, an antenna tuning element may not be properly mounted within the electronic device. As another example, an antenna tuning element may be damaged during assembly due to overheating, electrical stress (i.e., from excessive amounts of electrostatic discharge), and mechanical stress (i.e., from being dropped or otherwise mishandled), or may exhibit manufacturing defects that result in the antenna tuning element being unable to switch from one state to another or exhibiting unsatisfactory loading in the different states. In some situations, it can be difficult or impossible to detect and identify these defects, if at all, until assembly is complete and a finished device is available for testing. Detection of defects only after assembly is complete can result in costly device scrapping or extensive reworking. 
     It would therefore be desirable to be able to provide improved ways in which to characterize the performance and to detect faults associated with antenna tuning elements during the manufacturing of electronic devices. 
     SUMMARY 
     A wireless electronic device may include storage and processing circuitry and wireless communications circuitry. The wireless communications circuitry may include a baseband processor, transceiver circuitry, and at least one tunable antenna. The tunable antenna may be provided with at least one adjustable antenna tuning element. The adjustable antenna tuning element may be used to help the tunable antenna cover a wider range of communications frequencies than would otherwise be possible. 
     The adjustable antenna tuning element may include radio-frequency switches, continuously or semi-continuously tunable resistive/inductive/capacitive components forming using integrated circuits, discrete surface mount components, or other suitable conductive structures, and other load circuits configured to provide desired impedance characteristics for the tunable antenna at selected frequencies. 
     In accordance with an embodiment of the present invention, a radio-frequency test system may be provided that includes a test host, a radio-frequency tester for generating radio-frequency test signals (e.g., vector network analyzer, a spectrum analyzer, etc.) and for gathering radio-frequency measurements, a test fixture on which a wireless electronic device under test (DUT) that contains an adjustable antenna tuning element may be mounted during testing, and other test equipment. The radio-frequency test system may be used to test partially assembled wireless electronic devices so that defects in the DUT can be detected at a relatively early assembly stage. 
     Power may be supplied to the antenna tuning element. As an example, power supply voltages may be directly supplied to the antenna tuning element from the test host. As another example, the test host may send commands to the DUT that direct a power supply circuit with the DUT to provide power supply voltages to the adjustable antenna tuning element. 
     While power is being supplied to the antenna tuning element, the antenna tuning element may be placed in a variety of different tuning states during testing to tune the tunable antenna. As an example, the test host may directly send control signals to the antenna tuning element to configure the antenna tuning element in the different respective tuning states. As another example, the test host may send commands that direct processing circuitry (e.g., the baseband processor) within the DUT to provide appropriate control signals to the antenna tuning element that configure the antenna tuning element in the different respective tuning states. 
     While the adjustable antenna tuning element is being placed in each of the different tuning states, the RF tester may be used to gather radio-frequency test data from the wireless DUT. For example, single-port or multiport scattering parameter measurements may be obtained using the RF tester by sending RF test signals to the DUT and by receiving corresponding RF test signals emitted/reflected from the DUT. The RF test signals may be applied and detected using contact test probes (e.g., pogo-pin test probes, coaxial test probes, etc.) or wireless test probes sometimes referred to as antenna probes. During passive test operations of this type, the transceiver circuitry within the DUT may be deactivated so that only radio-frequency characteristics associated with the adjustable antenna tuning element in its different tuning states are being measured. 
     Further features of the present invention, its nature and various advantages will be more apparent from the accompanying drawings and the following detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of an illustrative electronic device with wireless communications circuitry in accordance with an embodiment of the present invention. 
         FIG. 2  is a diagram showing how radio-frequency transceiver circuitry may be coupled to one or more antennas within an electronic device of the type shown in  FIG. 1  in accordance with an embodiment of the present invention. 
         FIG. 3  is a circuit diagram showing how wireless communications circuitry in the electronic device of  FIG. 1  may be provided with adjustable antenna tuning elements in accordance with an embodiment of the present invention. 
         FIGS. 4 and 5  are plots showing how antennas containing tuning elements may be used to cover multiple communications bands of interest in accordance with an embodiment of the present invention. 
         FIGS. 6A ,  6 B, and  6 C are circuit diagrams of illustrative switchable load circuits and continuously tunable load circuits that may be used as antenna tuning elements in accordance with an embodiment of the present invention. 
         FIGS. 7 and 8  are diagrams of illustrative radio-frequency test systems for characterizing an antenna tuning element in accordance with an embodiment of the present invention. 
         FIG. 9  is a cross-sectional side view showing how a conducted test probe having signal and ground pins may be coupled to an antenna tuning element in accordance with an embodiment of the present invention. 
         FIG. 10  is a cross-sectional side view showing how a coaxial test probe may be coupled to an antenna tuning element in accordance with an embodiment of the present invention. 
         FIG. 11  is a cross-sectional side view showing how a wireless test probe may be used in testing an antenna tuning element in accordance with an embodiment of the present invention. 
         FIG. 12  is a diagram of an illustrative radio-frequency test system that can be used to gather multiport scattering parameter measurements from an antenna tuning element in accordance with an embodiment of the present invention. 
         FIG. 13  is a graph in which reflection coefficient magnitude data that has been gathered using a test system of the type shown in  FIG. 7  or  FIG. 8  has been plotted as a function of applied signal frequency in accordance with an embodiment of the present invention. 
         FIG. 14  is a flow chart of illustrative steps involved in testing antenna tuning element(s) in a partially assembled electronic device using a radio-frequency test system in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Electronic devices such as device  10  of  FIG. 1  may be provided with wireless communications circuitry. The wireless communications circuitry may be used to support long-range wireless communications such as communications in cellular telephone bands. Examples of long-range (cellular telephone) bands that may be handled by device  10  include the 700 MHz band, the 800 MHz band, the 850 MHz band, the 900 MHz band, the 1800 MHz band, the 1900 MHz band, the 2100 MHz band, and other bands. The long-range bands used by device  10  may include the so-called LTE (Long Term Evolution) bands. The LTE bands are numbered (e.g., 1, 2, 3, etc.) and are sometimes referred to as E-UTRA operating bands. Long-range signals such as signals associated with satellite navigation bands may be received by the wireless communications circuitry of device  10 . For example, device  10  may use wireless circuitry to receive signals in the 1575 MHz band associated with Global Positioning System (GPS) communications. Short-range wireless communications may also be supported by the wireless circuitry of device  10 . For example, device  10  may include wireless circuitry for handling local area network links such as WiFi® links at 2.4 GHz and 5 GHz, Bluetooth® links at 2.4 GHz, etc. 
     As shown in  FIG. 1 , device  10  may include storage and processing circuitry  28 . Storage and processing circuitry  28  may include storage such as hard disk drive storage, nonvolatile memory (e.g., flash memory or other electrically-programmable-read-only memory configured to form a solid state drive), volatile memory (e.g., static or dynamic random-access-memory), etc. Processing circuitry in storage and processing circuitry  28  may be used to control the operation of device  10 . This processing circuitry may be based on one or more microprocessors, microcontrollers, digital signal processors, application specific integrated circuits, etc. 
     Storage and processing circuitry  28  may be used to run software on device  10 , such as internet browsing applications, voice-over-internet-protocol (VOIP) telephone call applications, email applications, media playback applications, operating system functions, functions related to communications band selection during radio-frequency transmission and reception operations, etc. To support interactions with external equipment such as base station  21 , storage and processing circuitry  28  may be used in implementing communications protocols. Communications protocols that may be implemented using storage and processing circuitry  28  include internet protocols, wireless local area network protocols (e.g., IEEE 802.11 protocols—sometimes referred to as WiFi®), protocols for other short-range wireless communications links such as the Bluetooth® protocol, IEEE 802.16 (WiMax) protocols, cellular telephone protocols such as the “2G” Global System for Mobile Communications (GSM) protocol, the “2G” Code Division Multiple Access (CDMA) protocol, the “3G” Universal Mobile Telecommunications System (UMTS) protocol, and the “4G” Long Term Evolution (LTE) protocol, MIMO (multiple input multiple output) protocols, antenna diversity protocols, etc. Wireless communications operations such as communications band selection operations may be controlled using software stored and running on device  10  (i.e., stored and running on storage and processing circuitry  28  and/or input-output circuitry  30 ). 
     Input-output circuitry  30  may include input-output devices  32 . Input-output devices  32  may be used to allow data to be supplied to device  10  and to allow data to be provided from device  10  to external devices. Input-output devices  32  may include user interface devices, data port devices, and other input-output components. For example, input-output devices may include touch screens, displays without touch sensor capabilities, buttons, joysticks, click wheels, scrolling wheels, touch pads, key pads, keyboards, microphones, cameras, buttons, speakers, status indicators, light sources, audio jacks and other audio port components, digital data port devices, light sensors, motion sensors (accelerometers), capacitance sensors, proximity sensors, etc. 
     Input-output circuitry  30  may include wireless communications circuitry  34  for communicating wirelessly with external equipment. Wireless communications circuitry  34  may include radio-frequency (RF) transceiver circuitry formed from one or more integrated circuits, power amplifier circuitry, low-noise input amplifiers, passive RF components, one or more antennas, transmission lines, and other circuitry for handling RF wireless signals. Wireless signals can also be sent using light (e.g., using infrared communications). 
     Wireless communications circuitry  34  may include radio-frequency transceiver circuitry  90  for handling various radio-frequency communications bands. For example, circuitry  90  may include transceiver circuitry  36 ,  38 , and  42 . Transceiver circuitry  36  may handle 2.4 GHz and 5 GHz bands for WiFi® (IEEE 802.11) communications and may handle the 2.4 GHz Bluetooth® communications band. Circuitry  34  may use cellular telephone transceiver circuitry  38  for handling wireless communications in cellular telephone bands such as at 850 MHz, 900 MHz, 1800 MHz, 1900 MHz, and 2100 MHz and/or the LTE bands and other bands (as examples). Circuitry  38  may handle voice data and non-voice data traffic. 
     Transceiver circuitry  90  may include global positioning system (GPS) receiver equipment such as GPS receiver circuitry  42  for receiving GPS signals at 1575 MHz or for handling other satellite positioning data. In WiFi® and Bluetooth® links and other short-range wireless links, wireless signals are typically used to convey data over tens or hundreds of feet. In cellular telephone links and other long-range links, wireless signals are typically used to convey data over thousands of feet or miles. 
     Wireless communications circuitry  34  may include one or more antennas  40 . Antennas  40  may be formed using any suitable antenna types. For example, antennas  40  may include antennas with resonating elements that are formed from loop antenna structure, patch antenna structures, inverted-F antenna structures, slot antenna structures, planar inverted-F antenna structures, helical antenna structures, hybrids of these designs, etc. Different types of antennas may be used for different bands and combinations of bands. For example, one type of antenna may be used in forming a local wireless link antenna and another type of antenna may be used in forming a remote wireless link antenna. 
     As shown in  FIG. 1 , wireless communications circuitry  34  may also include baseband processor  88 . Baseband processor  88  may include memory and processing circuits and may also be considered to form part of storage and processing circuitry  28  of device  10 . 
     Baseband processor  88  may be used to provide data to storage and processing circuitry  28 . Data that is conveyed to circuitry  28  from baseband processor  88  may include raw and processed data associated with wireless (antenna) performance metrics for received signals such as received power, transmitted power, frame error rate, bit error rate, channel quality measurements based on received signal strength indicator (RSSI) information, channel quality measurements based on received signal code power (RSCP) information, channel quality measurements based on reference symbol received power (RSRP) information, channel quality measurements based on signal-to-interference ratio (SINR) and signal-to-noise ratio (SNR) information, channel quality measurements based on signal quality data such as Ec/Io or Ec/No data, information on whether responses (acknowledgements) are being received from a cellular telephone tower corresponding to requests from the electronic device, information on whether a network access procedure has succeeded, information on how many re-transmissions are being requested over a cellular link between the electronic device and a cellular tower, information on whether a loss of signaling message has been received, information on whether paging signals have been successfully received, and other information that is reflective of the performance of wireless circuitry  34 . This information may be analyzed by storage and processing circuitry  28  and/or processor  88  and, in response, storage and processing circuitry  28  (or, if desired, baseband processor  88 ) may issue control commands for controlling wireless circuitry  34 . For example, baseband processor  88  may issue commands that direct transceiver circuitry  90  to switch into use desired transmitters/receivers and antennas. 
     Antenna diversity schemes may be implemented in which multiple redundant antennas are used in handling communications for a particular band or bands of interest. In an antenna diversity scheme, storage and processing circuitry  28  may select which antenna to use in real time based on signal strength measurements or other data. In multiple-input-multiple-output (MIMO) schemes, multiple antennas may be used in transmitting and receiving multiple data streams, thereby enhancing data throughput. 
     Illustrative locations in which antennas  40  may be formed in device  10  are shown in  FIG. 2 . As shown in  FIG. 2 , electronic device  10  may have a housing such as housing  12 . Housing  12  may include plastic walls, metal housing structures, structures formed from carbon-fiber materials or other composites, glass, ceramics, or other suitable materials. Housing  12  may be formed using a single piece of material (e.g., using a unibody configuration) or may be formed from a frame, housing walls, and other individual parts that are assembled to form a completed housing structure. The components of device  10  that are shown in  FIG. 1  may be mounted within housing  12 . Antenna structures  40  may be mounted within housing  12  and may, if desired, be formed using parts of housing  12 . For example, housing  12  may include metal housing sidewalls, peripheral conductive members such as band-shaped members (with or without dielectric gaps), conductive bezels, and other conductive structures that may be used in forming antenna structures  40 . 
     As shown in  FIG. 2 , antenna structures  40  may be coupled to transceiver circuitry  90  by paths such as paths  45 . Paths  45  may include transmission line structures such as coaxial cables, microstrip transmission lines, stripline transmission lines, etc. Impedance matching circuitry, filter circuitry, and switching circuitry may be interposed in paths  45  (as examples). Impedance matching circuitry may be used to ensure that antennas  40  are efficiently coupled to transceiver circuitry  90  in desired frequency bands of interest. Filter circuitry may be used to implement frequency-based multiplexing circuits such as diplexers, duplexers, and triplexers. Switching circuitry may be used to selectively couple antennas  40  to desired ports of transceiver circuitry  90 . For example, a switch may be configured to route one of paths  45  to a given antenna in one operating mode. In another operating mode, the switch may be configured to route a different one of paths  45  to the given antenna. The use of switching circuitry between transceiver circuitry  90  and antennas  40  allows device  10  to switch particular antennas  40  in and out of use depending on the current performance associated with each of the antennas. 
     In a device such as a cellular telephone that has an elongated rectangular outline, it may be desirable to place antennas  40  at one or both ends of the device. As shown in  FIG. 2 , for example, some of antennas  40  may be placed in upper end region  42  of housing  12  and some of antennas  40  may be placed in lower end region  44  of housing  12 . The antenna structures in device  10  may include a single antenna in region  42 , a single antenna in region  44 , multiple antennas in region  42 , multiple antennas in region  44 , or may include one or more antennas located elsewhere in housing  12 . 
     Antenna structures  40  may be formed within some or all of regions such as regions  42  and  44 . For example, an antenna such as antenna  40 T- 1  may be located within region  42 - 1  or an antenna such as antenna  40 T- 2  may be formed that fills some or all of region  42 - 2 . Similarly, an antenna such as antenna  40 B- 1  may fill some or all of region  44 - 2  or an antenna such as antenna  40 B- 2  may be formed in region  44 - 1 . These types of arrangements need not be mutually exclusive. For example, region  44  may contain a first antenna such as antenna  40 B- 1  and a second antenna such as antenna  40 B- 2 . 
     Transceiver circuitry  90  may contain transmitters such as radio-frequency transmitters  48  and receivers such as radio-frequency receivers  50 . Transmitters  48  and receivers  50  may be implemented using one or more integrated circuits (e.g., cellular telephone communications circuits, wireless local area network communications circuits, circuits for Bluetooth® communications, circuits for receiving satellite navigation system signals, other suitable wireless communications circuits, and combinations of these circuits). 
       FIG. 3  is a diagram showing how radio-frequency path  45  may be used to convey radio-frequency signals between radio-frequency transceiver  90  and antenna structures  40 ′ (e.g., antenna resonating structures and associated grounding structures formed within device  10  or formed as part of housing  12  of device  10 ). Antenna structures  40 ′ may be part of the antennas of  FIG. 2  (e.g., antenna  40 T- 1 ,  40 T- 2 ,  40 B- 1 ,  40 B- 2 , or other antennas). 
     As shown in  FIG. 3 , radio-frequency front-end circuitry such as front-end circuitry  102  may be interposed in the transmission line path between transceiver  90  and antenna structures  40 ′. Uplink signals may be provided from transceiver  90  to front-end circuitry  102  via transmit (TX) port  104 , whereas downlink signals may be provided from front-end circuitry  102  to transceiver  90  via receive (RX) port  106 . Radio-frequency front-end circuitry  102  may include power amplifiers for amplifying transmit radio-frequency signals, low noise amplifiers for amplifying received radio-frequency signals, filters for applying desired frequency-based selection, matching circuits for providing desired impedance between different radio-frequency components, radio-frequency splitters/combiners, etc. 
     Radio-frequency front-end circuitry  102  may be coupled to antenna structures  40 ′ via conductive path  45 . Conductive path  45  may include one or more transmission lines such as one or more segments of coaxial cable, one or more segments of microstrip transmission line, one or more segments of stripline transmission line, or other transmission line structures. Path  45  may include a first conductor such as signal line  45 A and may include a second conductor such as ground line  45 B. Antenna  40  may have an antenna feed with a positive (+) antenna feed terminal  58  that is coupled to signal path  45 A and a ground (−) antenna feed terminal  54  that is coupled to ground path  45 B. In practice, front-end circuitry  102  may be interposed in path  45  and may sometimes be considered as an integral part of path  45 . 
     As described above, antenna structures  40 ′ may be 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. 
     In general, it is desirable for device  10  to be able to exhibit wide band coverage (e.g., for device  10  to be able to support operation in multiple frequency bands corresponding to different radio access technologies). For example, it may be desirable for antenna  40  to be capable of operating in a higher frequency band that covers the GSM sub-bands at 1800 MHz and 1900 MHz and the data sub-band at 2100 MHz, a first lower frequency band that covers the GSM sub-bands at 850 MHz and 900 MHz, and a second lower frequency band that covers the LTE band at 700 MHz, the GSM sub-bands at 710 MHz and 750 MHz, the UMTS sub-band at 700 MHz, and other desired wireless communications bands. 
     The band coverage of antenna  40  may be limited by its volume (i.e., the amount of space that is occupied by antenna  40  within housing  12 ). For an antenna having a given volume, a higher band coverage (or bandwidth) results in a decrease in gain (e.g., the product of maximum gain and bandwidth is constant). As a result, increasing the volume of antenna  40  will generally increase its band coverage. Increasing the volume of antennas, however, may not always be feasible if a small form factor is desired. 
     To satisfy consumer demand for small form factor wireless devices, one or more of antennas  40  in device  10  may be provided with antenna tuning circuitry. The antenna tuning circuitry may include a tunable radio-frequency component such as tunable component (sometimes referred to as an adjustable antenna tuning element)  100 . Tunable element  100  may sometimes be formed as an integral part of or as a separate discrete surface-mount component that is attached to parts of antenna structures  40 ′ and/or RF front-end circuitry  102  (see, e.g.,  FIG. 3 ). 
     For example, antenna tuning element  100  may include switching circuitry based on one or more radio-frequency switches or continuously tunable load components. Antenna tuning elements  100  may include active components configured to receive power supply voltages. Device  10  may therefore include a power supply circuit such as power supply  108  that is operable to supply antenna tuning elements  100  with power supply voltage Vsup via power supply line  110  during normal operation of device  10 . 
     Baseband processor  88  (or other control circuitry within storage and processing circuitry  28 ) may be used to place tunable elements  100  in their desired tuning states by sending appropriate control signals Vc via path  112 . The example of  FIG. 3  in which antenna tuning elements  100  receive power supply signals Vsup from power supply  108  and receive control signals Vc from baseband processor  88  is merely illustrative and does not serve to limit the scope of the present invention. If desired, antenna tuning elements  100  may receive power supply voltage signals and control signals from any suitable circuitry within device  10  during normal operation. 
     Antenna tuning element  100  may, for example, include a switch that can be dynamically placed in an open or closed position. When the switch is placed in its open position (e.g., when control signal Vc has a first value), antenna  40  may exhibit a first frequency response. When the switch is placed in its closed position (e.g., when control signal Vc has a second value that is different than the first value), antenna  40  may exhibit a second frequency response. By using an antenna tuning scheme of this type, a relatively narrow bandwidth (and potentially compact) design can be used for antenna  40 , if desired. The use of antenna tuning circuitry may therefore help device  10  cover a wider range of communications frequencies than would otherwise be possible. 
     By dynamically controlling antenna tuning elements  100 , antenna  40  may be able to cover a wider range of radio-frequency communications frequencies than would otherwise be possible. A standing-wave-ratio (SWR) versus frequency plot such as SWR plot of  FIG. 4  illustrates the band tuning capability for antenna  40 . As shown in  FIG. 4 , solid SWR frequency characteristic curve  124  corresponds to a first antenna tuning mode in which antenna  40  exhibits satisfactory resonant peaks at low-band frequency f A  (e.g., to cover the 850 MHz band) and high-band frequency f B  (e.g., to cover the 1900 MHz band). In the first antenna tuning mode, the antenna tuning elements  100  of antenna  40  may be placed in a first configuration (e.g., antenna tuning elements  100  may be provided with a first set of control signals Vc). 
     Dotted SWR frequency characteristic curve  126  corresponds to a second antenna tuning mode in which the antennas of device  10  exhibits satisfactory resonant peaks at low-band frequency f A ′ (e.g., to cover the 750 MHz band) and high-band frequency f B ′ (e.g., to cover the 2100 MHz band). In the second antenna tuning mode, the antenna tuning elements  100  may be placed in a second configuration that is different than the first configuration (e.g., antenna tuning circuits  100  may be provided with a second set of control signals Vc that is different than the first set of control signals). 
     If desired, antenna  40  may be placed in a third antenna tuning mode in which antenna  40  exhibits satisfactory resonant peaks at both low-band frequencies f A ′ and f A  (e.g., to cover both the 750 and 850 MHz bands) and at high-band frequencies f B  and f B ′ (e.g., to cover both the 1900 and 2100 MHz bands), as shown by SWR characteristic curve  128 . In the third antenna tuning mode, the antenna tuning elements  100  may be placed in a third configuration that is different than the first and second configurations (e.g., antenna tuning elements  100  may be provided with a third set of control signals Vc that is different than the first and second sets of control signals). A combination of tuning methods may be used so that the resonance curve  128  exhibits broader frequency ranges than curves  124  and  126 . 
     In another suitable arrangement, antenna  40  may be placed in a fourth antenna tuning mode in which antenna  40  exhibits satisfactory resonant peaks at mid-band frequencies f C  and f D  (e.g., to cover frequencies between the low and high bands), as shown by SWR characteristic curve  130  of  FIG. 5 . In the fourth antenna tuning mode, the antenna tuning circuits  100  may yet be placed in another different configuration. The SWR curves of  FIGS. 4 and 5  are merely illustrative and do not serve to limit the scope of the present invention. In general, antenna(s)  40  may include antenna tuning circuits  100  that enable device  10  to transmit and receive wireless signals in any suitable number of radio-frequency communications bands. 
     Antenna tuning element  100  may be any switchable or tunable electrical component that can be adjusted in real time. Antenna tuning element  100  may have a first terminal A and a second terminal B that are coupled to desired locations in antenna structures  40 ′ or RF front-end circuitry  102 , a power supply terminal operable to receive Vsup from path  110  (and optionally ground power supply voltage), and a control terminal operable to receive control signal Vc from path  112 . 
       FIG. 6A  shows one suitable circuit implementation of tunable element  100 . As shown in  FIG. 6A , element  100  may include a load circuit  150  and a radio-frequency switch  152  coupled in series between terminals A and B. Switch  152  may be implemented using a p-i-n diode, a gallium arsenide field-effect transistor (FET), a microelectromechanical systems (MEMS) switch, a metal-oxide-semiconductor field-effect transistor (MOSFET), a high-electron mobility transistor (HEMT), a pseudomorphic HEMT (PHEMT), a transistor formed on a silicon-on-insulator (SOI) substrate, etc. Switch  152  may be powered using Vsup provided over path  110 . The state of the switch can be controlled using signal Vc provided from baseband processor  88  (see,  FIG. 3 ). For example, a high Vc will turn on or close switch  152  whereas a low Vc will turn off or open switch  152 . 
     Load circuit  150  may be formed from one or more electrical components. Components that may be used as all or part of circuit  150  include resistors, inductors, capacitors, and/or other electrical components. Desired resistances, inductances, and capacitances for circuit  150  may be formed using integrated circuits, using discrete components (e.g., a surface mount technology inductor) and/or using dielectric and conductive structures that are not part of a discrete component or an integrated circuit. For example, a resistance can be formed using thin lines of a resistive metal alloy, capacitance can be formed by spacing two conductive pads close to each other that are separated by a dielectric, and an inductance can be formed by creating a conductive path (e.g., a transmission line) on a printed circuit board. 
     In another suitable arrangement, tunable element  100  may include a switch  154  (e.g., a single-pole triple-throw radio-frequency switch) and multiple load circuits  150 - 1 ,  150 - 2 , and  150 - 3 . As shown in  FIG. 6B , switch  154  may have ports P 1 , P 2 , P 3 , and P 4 . Terminal B of tunable element  100  may be coupled to port P 1  while terminal A of tunable element  100  may be coupled to port P 2  via circuit  150 - 1 , to port P 3  via circuit  150 - 2 , and to port P 4  via circuit  150 - 3 . As described in connection with  FIG. 6A , load circuits  150 - 1 ,  150 - 2 , and  150 - 3  may include any desired combination of resistive components, inductive components, and capacitive components formed using integrated circuits, discrete components, or other suitable electrical structures. Switch  154  may be powered using Vsup provide over path  110  and may be controlled using signal Vc provided over path  112 . For example, switch  154  may be configured to couple port P 1  to P 2  when Vc is at a first value, to couple port P 1  to P 3  when Vc is at a second value that is different than the first value, and to couple port P 1  to P 4  when Vc is at a third value that is different than the first and second values. 
     The example of  FIG. 6B  in which tunable element  100  is operable in three different states is merely illustrative and does not serve to limit the scope of the present invention. If desired, tunable element  100  may include a radio-frequency switch having any number of ports configured to support switching among any desired number of loading circuits. If desired, switch  154  may be configured such that more than one of the multiple loading circuits  150  may be coupled to port P 1  in parallel. 
     In arrangements in which tunable element  100  includes multiple capacitors  150  coupled to a single-pole multi-throw switch such as switch  154 , tunable element  100  may be used to provide different capacitance values in each of its respective states and may therefore sometimes be referred to as a programmable array of capacitors (PAC). Other arrangements in which antenna tuning element  100  is configured as a programmable array of inductors (PAI), a programmable array of resistors (PAR), or other programmable circuits with different combinations of passive electrical components may also be used in device  10 . 
     In another suitable arrangement, tunable element  100  may include a continuously tunable element such as a variable capacitor circuit  156  (sometimes referred to as a varactor). As shown in  FIG. 6C , varactor  156  may have first terminal A, second terminal B, and a control terminal operable to receive signal Vsup and Vc. A continuously tunable element need not always receive power supply voltage Vsup. Control signal Vc that is provided to continuously tunable element  100  may be a digital control signal or an analog control signal that adjusts the capacitance of varactor  156  to the desired amount. Varactor  156  may be formed using integrated circuits, one or more discrete components (e.g., SMT components), etc. In general, antenna tuning element  100  may be a continuously tunable component or semi-continuously tunable component. 
     Having antenna tuning element  100  as part of wireless circuitry  34  introduces an additional component that needs to be tested, because the performance of antenna tuning element  100  can substantially impact the wireless operation of device  10 . For example, it may be desirable to test whether tunable element  100  can switch among multiple tuning states in response to application of control signals Vc and to test whether tunable element  100  exhibits the desired impedance in each of the different states. It is generally desirable to have a way of testing the performance of antenna tuning element  100  during manufacturing prior to complete assembly of a finished device, because detection of defects only after assembly is complete can result in costly device scrapping or extensive reworking. 
       FIG. 7  is a diagram of a test system  200  that can be used to test antenna tuning element(s)  100  in a completed or partially assembled electronic device  10 . In a completed device, a display layer such as a display cover layer may be mounted to device housing  12 . In a partially assembled device, the display cover layer may not yet be assembled and at least parts of wireless communications circuitry  34  may be exposed to test equipment during production testing. 
     An electronic device (whether completely assembled or partially assembled) that is being tested using test system  200  may sometimes be referred to as a device under test (DUT) or as device structures under test. As shown in  FIG. 7 , test system  200  may include a test host such as test host  202  (e.g., a personal computer), a radio-frequency tester such as radio-frequency tester  204 , a test fixture such as test fixture  210 , control circuitry, network circuitry, cabling, and other test equipment. 
     DUT  100  may be mounted on test fixture  210  during testing. Test fixture  210  may be formed from plastic support structures, a rigid printed circuit board substrate such as a fiberglass-filled epoxy substrate (e.g., FR4), a flexible printed circuit (“flex circuit”) formed from a sheet of polyimide or other flexible polymer, or other dielectric material. 
     In the example of  FIG. 7 , antenna tuning element  100  may receive power supply voltage Vsup and control signal Vc from test host  202 . In particular, antenna tuning element  100  may be coupled to test contacts  228  and  230  via paths  110  and  112 , respectively. Test host  202  may supply signal Vsup to test contact  228  via path  224  and signals Vc to test contact  230  via path  226 . When contacts  228  and  230  are mated to test host  202  via paths  224  and  226 , signals provided from baseband processor  88  (if any) may be bypassed (see,  FIG. 3 ). 
     Connected in this way, test host  202  may be used to directly power antenna tuning element(s)  100  on device  10  and may be used to place antenna tuning element(s)  100  in desired tuning states during testing. In particular, the control signals conveyed over path  226  may serve to place antenna tuning element  100  in the desired state for testing. For example, consider a scenario in which antenna tuning element  100  is a programmable array of capacitors of the type shown in  FIG. 6B . During a first test iteration, test host  202  may send control signals to antenna tuning element  100  via path  226  that configure switch  154  to connect ports P 1  and P 2 . During a second test iteration, test host  202  may send control signals to antenna tuning element  100  via path  226  that configure switch  154  to connect ports P 1  and P 3 . During a third test iteration, test host  202  may send control signals to DUT  100  via path  226  that configure switch  154  to connect ports P 1  and P 4 . 
     Radio-frequency tester  204  may be a vector network analyzer (as an example). Tester  204  may have at least one test port to which a test cable  220  is connected. Radio-frequency cable  220  may, for example, be a coaxial cable. In particular, cable  220  may have a first end that is connected to the tester port and a second end terminating at a radio-frequency test probe  222 . During testing, test probe  222  may be coupled to antenna tuning element  100  via a wired path or a wireless path. If desired, tester  204  include multiple ports (e.g., at least two test ports, at least three test ports, at least four test ports, etc.) through which radio-frequency test signals may be transmitted to DUT  10  during testing. Radio-frequency tester  204  may receive commands from test host  202  via path  206  that direct tester  204  to gather desired radio-frequency measurements. If desired, test data can be provided from tester  204  to test host  202  via path  206 . 
     Radio-frequency tester  204  may be configured to produce radio-frequency test signals that are applied to antenna tuning element  100  via cables  220 . Radio-frequency transceiver  90  need not be active during testing of antenna tuning element  100 . Even without receiving active radio-frequency signals from transceiver  90 , antenna tuning element  100  may emit radio-frequency signals when being energized by the test signals generated using tester  204 . As electromagnetic test signals are transmitted by tester  204  and applied to antenna tuning element  100  through test cable  220 , corresponding reflected electromagnetic test signals may be received through test cable  220 . The reflected signals gathered in this way may be used to compute a reflection coefficient (sometimes referred to as an S 11  parameter or S 11  scattering parameter). The S 11  may include magnitude and phase components. Radio-frequency testing using this approach in which radio-frequency transceiver  90  is idle and is not transmitting or receiving wireless signals via antenna(s)  40  may be referred to as “passive” testing, passive radio-frequency testing, or passive antenna testing. 
     In another suitable arrangement, test host  202  may provide commands to DUT  10  during passive radio-frequency testing (see, e.g.,  FIG. 8 ). As shown in  FIG. 8 , test host  202  may provide test commands to DUT  10  via path  240 . The connection represented by line  240  may be a Universal Serial Bus (USB) based connection, a Universal Asynchronous Receiver/Transmitter (UART) based connection, or other suitable types of data connection. 
     In the arrangement of  FIG. 8 , DUT  10  may be placed in a test mode in which baseband processor  88  and power supply unit  108  are active while transceiver circuitry  90  may still be inactive. Commands received from test host  202  via connection  240  may be processed using storage and processing circuitry  28 . In response to DUT  10  receiving the commands from test host  202 , power supply  108  may be configured to provide suitable power supply voltage signals Vsup to antenna tuning element  100  while baseband processor  88  may be configured to provide appropriate control signals Vc to antenna tuning element  100  so that antenna tuning element  100  can be placed in a desired tuning state for testing. The configuration of  FIG. 7  in which test host  202  directly accesses and controls tunable element  100  by bypassing baseband processor  88  and the configuration of  FIG. 8  in which test host  202  provides commands to DUT  10  that direct circuitry on DUT  10  (e.g., baseband processor  88 , power supply circuit  108 , storage and processor circuitry  28 , etc.) to provide desired control signals to tunable elements  100  are merely illustrative. If desired, other suitable ways of providing power and control signals to antenna tuning element(s)  100  on DUT  10  can be implemented. 
     In some arrangements, antenna tuning element  100  may be mounted on a substrate such as semiconductor substrate  300  (see, e.g.,  FIG. 9 ). Substrate  300  may be a rigid printed circuit board, a flexible printed circuit board (e.g., a flex circuit), a rigid-flex circuit, or other suitable types of dielectric material. As shown in  FIG. 9 , antenna tuning element  100  may be coupled to a signal contact pad  302  and a ground contact pad  304  that are formed on the surface of substrate  300 . Signal contact pad  302  may be coupled to at least one of terminals A and B of antenna tuning element  100  via conductive trace  306 , whereas ground contact pad  304  may be coupled to a ground plane  308  within substrate  300  though conductive via or trace  310 . Antenna tuning element  100  may be coupled to ground plane  308  through a conductive trace  350 . The configuration of  FIG. 9  is merely illustrative. If desired, contact pads  302  and  304  may be coupled to respective terminals of tunable element  100 . In yet other suitable configurations, tunable element  100  may be mounted on plastic device housing structures, conductive device housing structures, and/or other types of device structures. 
     In the example of  FIG. 9 , a contact test probe  320  may be placed in physical contact with conductive pads  302  and  304  during test operations (e.g., to perform conducted radio-frequency testing). Test probe  320  may be one type of test probe component  222  that is coupled to RF tester  204  via cable  220  and that is used for testing antenna tuning element(s)  100  (see,  FIG. 8 ). Test probe  320  may include first and second probe pins  322  and  324  configured to make contact with pads  302  and  304 , respectively, or with other circuitry associated with antenna tuning element  100 . Pins  322  and  324  may serve as signal and ground pins, respectively. At least one of pins  322  and  324  may be spring-loaded to reduce the chance of damaging the test equipment and any of the device structures under test. Test probe  320  of this type may sometimes be referred to as a pogo-pin test probe. If desired, test probes such as alligator clip probes, tweezer probes, shielded-lead probes, or other types of test probes may be used in test system  200 . 
       FIG. 10  shows another suitable configuration in which antenna tuning element  100  is coupled to a radio-frequency connector such as coaxial radio-frequency connector  330 . Connector  330  may have a signal terminal that is coupled to antenna tuning element  100  via trace  332  and a ground terminal that is coupled to ground plane  308  through via  334 . 
     In the example of  FIG. 10 , a test probe such as coaxial test probe  340  may be mated with connector  330  during test operations to perform conducted RF testing. Test probe  340  may include an inner signal conductor  346  surrounded by a cylindrical shielding ground conductor. Test probe  340  may be another type of conducted test probe component  222  that is coupled to RF tester  204  via cable  220  and that is used for testing antenna tuning element(s)  100  (see,  FIG. 8 ). Signal conductor  346  and the associated ground conductor may share a common geometric axis and may be respectively coupled to the signal and ground terminals of connector  330  when probe  340  is mated with connector  330 . Test probe  340  may be a type of test probe suitable for mating with a corresponding U.FL connector, W.FL connector, SubMiniature version A (SMA) connector, SubMiniature version B (SMB) connector, or other types of coaxial radio-frequency connectors (as examples). 
       FIG. 11  shows another suitable configuration in which a non-contact test probe such as antenna probe  360  is used to test antenna tuning element  100  (e.g., antenna tuning element  100  may be coupled to other wireless circuitry via traces  352  and  354 ). Antenna probe  360 , which may sometimes be referred to as a wireless probe, may include one or more antennas. Antenna probe  360  may be used to transmit radio-frequency signals  364  to the device structures under test and may be used to receive corresponding radio-frequency signals  366  from the device structures under test. The antennas in antenna probe  360 , which are sometimes referred to herein as test antennas or probe antennas, may be implemented using any suitable antenna type (e.g., loop antennas, patch antennas, dipole antennas, monopole antennas, inverted-F antennas, planar inverted-F antennas, coil antennas, open-ended waveguides, horn antennas, etc.). 
     During testing, antenna probe  360  may be placed in the vicinity of antenna tuning element  100  or associated device structures under test. For example, antenna probe  360  may be placed within 10 cm or less of tunable element  100 , within 2 cm or less of tunable element  100 , or within 1 cm or less of tunable element  100  (as examples). These distances may be sufficiently small to place antenna probe  360  within the “near field” of antenna tuning element  100  (i.e., a location at which signals are received by an antenna that is located within about one or two wavelengths from element  100  or less). 
     The different test probes that are described in connection with  FIGS. 9-11  are merely illustrative and do not serve to limit the scope of the present invention. In general, any type of conducted and/or wireless test probe can be used to transmit RF test signals to and receive RF test signals from device structures under test within a partially assembled or a completed device  10 . 
       FIG. 12  shows another suitable embodiment of the present invention in which tester  204  sends and receives radio-frequency test signals via more than one test port. As shown in  FIG. 12 , RF tester  204  may have a first test port P 1  that is coupled to a first test probe  222 - 1  via a first RF cable  220 - 1  and a second test port P 2  that is coupled to a second test probe  222 - 2  via a second RF cable  220 - 2 . Test probes  222 - 1  and  222 - 2  may be test probes of the type described in connection with  FIGS. 9-11  or other types of radio-frequency test probes. 
     As electromagnetic test signals are transmitted by tester  204  and applied to antenna tuning element  100  through test probe  222 - 1 , corresponding emitted electromagnetic test signals may be received using test probe  222 - 2  (as an example). Tester  204  may also receive reflected signals via probe  222 - 1  (i.e., signals that were reflected from tunable element  100  in response to the signals transmitted through test cable  220 - 1 ). 
     The reflected signals gathered in this way may be used to compute a reflection coefficient (sometimes referred to as an S 11  parameter or S 11  scattering parameter). The transmitted signals on cable  220 - 1  and corresponding received signals on cable  220 - 2  may be used to compute a forward transfer coefficient (sometimes referred to as an S 21  parameter or S 21  scattering parameter). The S 11  and S 21  data may include magnitude and phase components. 
     Similarly, tester  204  may also transmit test signals to element  100  via test probe  222 - 2 . As test electromagnetic signals are transmitted by tester  204  and applied to DUT  100  using test probe  222 - 2 , corresponding emitted electromagnetic test signals may be received using test probe  222 - 1 . Tester  204  may also receive reflected signals via probe  222 - 2  (i.e., signals that were reflected from element  100  in response to the signals transmitted through test cable  220 - 2 ). The emitted and reflected signals gathered in this way may be used to compute reflection coefficient data (sometimes referred to as an S 22  scattering parameter) and forward transfer coefficient data (sometimes referred to as an S 12  scattering parameter). 
     The S 11 , S 12 , S 21 , and S 22  parameters (collectively referred to as scattering parameters or S-parameters) measured using tester  204  may be used as test data representative of radio-frequency characteristics associated with antenna tuning element  100 . For example, in situations in which antenna tuning element  100  is operating in a desired state and exhibits desired loading, S-parameter measurements will have values that are relatively close to baseline measurements on fault-free structures (sometimes referred to as reference structures in a “gold” reference unit). In situations in which antenna tuning element  100  has a defect that affects the electromagnetic properties of the device structures under test (i.e., when an antenna tuning element is unable to switch states or when an antenna tuning element exhibits improper loading), the S-parameter measurements will exceed normal tolerances. 
     When tester  204  determines that the gathered test data has deviated from normal baseline measurements by more than predetermined limits, tester  204  can alert an operator that antenna tuning element  100  within device  10  and other associated wireless circuitry likely contain a defect and/or other appropriate action can be taken. If desired, test system  200  may include any number of RF testers  204  each of which includes at least one active test port (for measuring reflection coefficient data), at least two active test ports (for measuring two-port scattering parameter data), at least three active test ports (for measuring three-port scattering parameter data), at least four active test ports (for measuring four-port scattering parameter data), etc. 
     Illustrative test data gathered using test system  200  of  FIG. 8  is shown in  FIG. 12 . In  FIG. 12 , the magnitude of reflection coefficient S 11  has been plotted as a function of test signal frequency. Curve  400  corresponds to test data gathered from an antenna tuning element  100  placed in a first state, whereas curve  402  corresponds to test data gathered from antenna tuning element  100  placed in a second state that is different than the first state. 
     When antenna tuning element  100  is placed in the first state, it may be desirable for the magnitude of S 11  to be within predetermined lower and upper limits  404 L and  404 U at frequency fx. When antenna tuning element  100  is placed in the second state, it may be desirable for the magnitude of S 11  to be within predetermined lower and upper limits  406 L and  406 U at frequency fy. These predetermined limits may be violated in scenarios in which antenna tuning element  100  is incapable of switching states, in which antenna tuning element  100  presents incorrect impedance/loading, and/or in which antenna tuning element  100  exhibits other types of defect. 
     The predetermined limits may be determined via calibration operations. Initially, during calibration operations, test unit  204  may, for example, gather S 11  measurements from antenna tuning element  100  and device structures under test that are known to be free of defects. Data gathered from fault-free devices may therefore represent a baseline (calibration) response to which other measured test data may be compared (e.g., the baseline response serves as a reference that can be used to determine when measurements results are meeting expectations or are deviating from expectations). The upper and lower limits may, for example, represent upper and lower bounds that deviate from the baseline response by a predetermined statistical variance. 
     The test data of  FIG. 13  is merely illustrative. In general, magnitude and phase data may be gathered from one or more test ports to provide single-port S-parameter measurements, two-port S-parameter measurements, three-port S-parameter measurements, or other suitable measurement data to help determine whether antenna tuning element  100  and other associated wireless circuitry are capable of operating correct at desired frequencies. 
     Illustrative steps involved in performing radio-frequency testing on devices  10  with antenna tuning elements  100  using test system  200  are shown in  FIG. 14 . 
     At step  500 , calibration operations may be performed on reference devices  10  with antenna tuning element(s) that are free of defects. The reference devices that are being tested during calibration should be in a similar form as that of devices being tested by system  200  during production testing (e.g., if test system  200  tests devices  10  in the partially assembled state, calibration data should be gathered from similar partially assembled reference devices). 
     During calibration, tester  204  may use a test probe to transmit and receive radio-frequency signals in a desired frequency range (e.g., from 0 Hz to 3 GHz, from 3-14 GHz, a subset of one of these frequency ranges, or another suitable frequency range). Signals corresponding to the transmitted signals may be received from the device structures under test and processed with the transmitted signals to obtain scattering parameter measurements or other suitable test data. The S-parameter measurements or other test measurements that are made on the properly manufactured device structures may be stored in storage in tester  204  (e.g., in storage on a vector network analyzer, in storage on computing equipment such as a computer or network of computers that are associated with the vector network analyzer, etc.). If desired, antenna tuning elements  100  that are tested during the calibration operations of step  500  may be “limit samples” (i.e., components that have parameters on the edge or limit of the characteristic being tested). Device structures of this type are marginally acceptable and can therefore be used in establishing limits (e.g., upper and lower bound limits) on acceptable device performance during calibration operations. 
     At step  502 , a partially assembled production DUT  10  may be placed within test fixture  210 . At step  504 , tester  204  may be electrically coupled to antenna tuning element  100  via one or more conducted and/or wireless test probes. 
     At step  506 , test host  202  may be used to place selected antenna tuning element  100  within DUT  10  in a desired state for testing. As an example, test host  202  may directly send power and control signals to antenna tuning element  100  ( FIG. 7 ). As another example, test host  202  may send test commands to storage and processing circuitry  28  of device  10  that direct the storage and processing circuitry of device  10  to send appropriate power and control signals to antenna tuning element  100  ( FIG. 8 ). 
     At step  508 , tester  204  may use one or more test probes  222  to gather test data. During the operations of step  508 , tester  204  may use test probe(s)  222  to transmit and receive radio-frequency signals in a desired frequency range (e.g., from 0 Hz to 3 GHz, 3 GHz to 14 GHz, or other suitable frequency range, preferably matching the frequency range used in obtaining the calibration measurements of step  500 ). Wireless test data such as S 11 , S 21 , S 12 , and S 22  measurements or other suitable test data may be gathered. The S-parameter measurements (phase and magnitude measurements for impedance and forward transfer coefficient) may be stored in storage in tester  204 . Processing may loop back to step  506  to test other states of antenna tuning element  100 , as indicated by path  510  (e.g., to ensure that antenna tuning element  100  is capable of switching to another state and is operable to provide the desired impedance characteristic in each of the different respective states). 
     When test data from a sufficient number of antenna tuning states have been gathered, the radio-frequency test data may be analyzed (at step  512 ). For example, the test data that was gathered during the operations of step  508  may be compared to the baseline (calibration) data obtained during the operations of step  500  (e.g., by calculating the difference between these sets of data and determining whether the calculated difference exceeds predetermined threshold amounts, by comparing test data to calibration data from limit samples that represents limits on acceptable device structure performance, or by otherwise determining whether the test data deviates by more than a desired amount from acceptable data values). 
     After computing the difference between the test data and the calibration data at one or more frequencies to determine whether the difference exceeds predetermined threshold values, appropriate actions may be taken. For example, if the test data and the calibration data differ by more than a predetermined amount, tester  204  may conclude that antenna tuning element  100  current being tested contains a fault and appropriate actions may be taken at step  516  (e.g., by issuing an alert, by informing an operator that additional testing is required, by displaying information instructing an operator to rework or scrap the device structures, etc.). 
     In response to a determination that the test data and the calibration data differ by less than the predetermined amount, tester  204  may conclude that the device structures under test (including antenna tuning element  100  currently being tested) have been manufactured properly and appropriate actions may be taken at step  514  (e.g., by issuing an alert that the structures have passed testing, by completing the assembly of the structures to form a finished electronic device, by shipping the final assembled electronic device to a customer, etc.). 
     The foregoing is merely illustrative of the principles of this invention and various modifications can be made by those skilled in the art without departing from the scope and spirit of the invention. The foregoing embodiments may be implemented individually or in any combination.

Metadata:
Filing Date: 20121221
Publication Date: 20150714
Grant Date: 20150714
Priority Date: 20121221
Inventors: NICKEL JOSHUA G.
SHEN JR-YI
LAKSHMANAN ANAND
NATH JAYESH
MOW MATTHEW A.
PASCOLINI MATTIA
VENKATARAMAN VISHWANATH
BEVELACQUA PETER
CUI XIN
Assignee: APPLE INC
CPC Classifications: [{"code": "G01R27/26", "inventive": false, "first": false, "tree": "[]"}, {"code": "G01R27/28", "inventive": false, "first": false, "tree": "[]"}, {"code": "G01R29/08", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04B17/12", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W24/00", "inventive": true, "first": true, "tree": "[]"}, {"code": "G01R29/10", "inventive": false, "first": false, "tree": "[]"}, {"code": "G01R31/2822", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01R29/08", "inventive": false, "first": false, "tree": "[]"}, {"code": "G01R31/2822", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01R27/26", "inventive": false, "first": false, "tree": "[]"}, {"code": "G01R31/2822", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04W24/00", "inventive": true, "first": true, "tree": "[]"}, {"code": "G01R29/10", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04B17/12", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B17/12", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01R27/28", "inventive": false, "first": false, "tree": "[]"}]
Family ID: 50975159