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.

Abstract: Electronic devices may be provided that contain wireless communications circuitry. The wireless communications circuitry may include radio-frequency transceiver circuitry coupled to an adjustable antenna. The adjustable antenna may contain conductive antenna structure such as conductive electronic device housing structures. Electrical components such as switches and resonant circuits may be used in configuring the antenna to operate in two or more different antenna modes at different respective communications bands. Control circuitry may be used in controlling the switches. The antenna may be configured to operate as an inverted-F antenna in one mode of operation and a slot antenna in a second mode of operation.

Abstract: Electronic devices may be provided that contain wireless communications circuitry. The wireless communications circuitry may include radio-frequency transceiver circuitry coupled to an adjustable antenna. The adjustable antenna may contain conductive antenna structure such as conductive electronic device housing structures. Electrical components such as switches and resonant circuits may be used in configuring the antenna to operate in two or more different antenna modes at different respective communications bands. Control circuitry may be used in controlling the switches. The antenna may be configured to operate as an inverted-F antenna in one mode of operation and a slot antenna in a second mode of operation.

Abstract: A test system for characterizing an antenna tuning element is provided. The test system may include a test host, a radio-frequency tester, and a test fixture. The test system may calibrate the radio-frequency tester using known coaxial standards. The test system may then calibrate transmission line effects associated with the test fixture using a THRU-REFLECT-LINE calibration algorithm. The antenna tuning element may be mounted on a test socket that is part of the test fixture. While the antenna tuning element is mounted on the test socket, scattering parameter measurements may be obtained using the radio-frequency tester. An equivalent circuit model for the test socket can be obtained based on the measured scattering parameters and known characteristics of the antenna tuning element. Once the test socket has been characterized, an equivalent circuit model for the antenna tuning element can be obtained by extracting suitable modeling parameters from the measured scattering parameters.

Abstract: Electronic devices may include antenna structures. The antenna structures may form an antenna having first and second feeds at different locations. A first transceiver may be coupled to the first feed using a first circuit. A second transceiver may be coupled to the second feed using a second circuit. The first and second feeds may be isolated from each other using the first and second circuits. The second circuit may have a notch filter that isolates the second feed from the first feed at operating frequencies associated with the first transceiver. The first circuit may include an adjustable component such as an adjustable capacitor. The adjustable component may be placed in different states depending on the mode of operation of the second transceiver to ensure that the first feed is isolated from the second feed.

Abstract: Custom antenna structures may be used to improve antenna performance and to compensate for manufacturing variations in electronic device antennas. An electronic device antenna may include an antenna tuning element and conductive structures formed from portions of a peripheral conductive housing member and other conductive antenna structures. The antenna tuning element may be connected across a gap in the peripheral conductive housing member. The custom antenna structures may be used to couple the antenna tuning element to a fixed custom location on the peripheral conductive housing member to help satisfy design criteria and to compensate for manufacturing variations in the conductive antenna structures that could potentially lead to undesired variations in antenna performance. Custom antenna structures may include springs and custom paths on dielectric supports.

Abstract: Electronic devices may include radio-frequency transceiver circuitry and antenna structures. The antenna structures may form a dual arm inverted-F antenna and an additional antenna such as a monopole antenna sharing a common antenna ground. The antenna structures may have three ports. A first antenna port may be coupled to an inverted-F antenna resonating element at a first location and a second antenna port may be coupled to the inverted-F antenna resonating element at a second location. A third antenna port may be coupled to the additional antenna. An adjustable component may be coupled to the first antenna port to tune the inverted-F antenna. The inverted-F antenna may be near-field coupled to the additional antenna so that the inverted-F antenna may serve as a tunable parasitic antenna resonating element that tunes the additional antenna.

Abstract: Electronic devices may be provided that contain wireless communications circuitry. The wireless communications circuitry may include radio-frequency transceiver circuitry and antenna structures. The antenna structures may form an antenna having first and second feeds at different locations. The transceiver circuit may have a first circuit that handles communications using the first feed and may have a second circuit that handles communications using the second feed. A first filter may be interposed between the first feed and the first circuit and a second filter may be interposed between the second feed and the second circuit. The first and second filters and the antenna may be configured so that the first circuit can use the first feed without being adversely affected by the presence of the second feed and so that the second circuit can use the second feed without being adversely affected by the presence of the first feed.

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.

Abstract: A manufacturing system for assembling wireless electronic devices is provided. The manufacturing system may include test stations for testing the radio-frequency performance of components that are to be assembled within the electronic devices. A reference test station may be calibrated using calibration coupons having known radio-frequency characteristics. The calibration coupons may include transmission line structures. The reference test station may measure verification standards to establish baseline measurement data. The verification standards may include circuitry having electrical components with given impedance values. Many verification coupons may be measured to enable testing for a wide range of impedance values. Test stations in the manufacturing system may subsequently measure the verification standards to generate test measurement data.

Abstract: A test system may include test stations for testing the radio-frequency performance of wireless electronic devices. A reference test station may perform test measurements on a group of wireless electronic devices under test (DUTs) to select a reference DUT. The reference test station may gather radio-frequency measurements at a number of test frequencies from the group of DUTs. The reference test station may compute statistical data associated with the gathered measurements. The reference test station may compute weight values associated with each test frequency based on the statistical parameters. The reference test station may compute a weighted mean square error value for each DUT based on the weight values and the statistical data. The reference test station may select a DUT having a minimum weighted mean square error value to serve as the reference DUT, which may be used to calibrate test stations in the test system.

Abstract: A test system for testing a device under test (DUT) is provided. The test system may include a DUT receiving structure configured to receive the DUT during testing and a DUT retention structure that is configured to press the DUT against the DUT receiving structure so that DUT cannot inadvertently shift around during testing. The DUT retention structure may include a pressure sensor operable to detect an amount of pressure that is applied to the DUT. The DUT retention structure may be raised and lowered vertically using a manually-controlled or a computer-controlled positioner. The positioner may be adjusted using a coarse tuning knob and a fine tuning knob. The positioner may be calibrated such that the DUT retention structure applies a sufficient amount of pressure on the DUT during production testing.

Abstract: Electronic devices may be provided with antennas. The antennas may include conductive antenna cavities. Antenna resonating elements may be mounted in the antenna cavities to form cavity antennas. An antenna cavity may be formed from metal structures with curved edges that define a curved cavity opening. A flexible printed circuit substrate may be coated with a layer of metal. Slot antenna structures such as a directly fed antenna slot and a parasitic antenna slot may be formed from openings in the metal layer. The flexible printed circuit substrate may be flexed so that the antenna resonating element forms a non-planar curved shape that mates with the opening of the antenna cavity. A ring of solder may be used to electrically seal the edges of the cavity opening to the metal layer in the antenna resonating element. The curved opening may be aligned with curved housing walls in an electronic device.

Abstract: A test system for characterizing an antenna tuning element is provided. The test system may include a test host, a radio-frequency tester, and a test fixture. The test system may calibrate the radio-frequency tester using known coaxial standards. The test system may then calibrate transmission line effects associated with the test fixture using a THRU-REFLECT-LINE calibration algorithm. The antenna tuning element may be mounted on a test socket that is part of the test fixture. While the antenna tuning element is mounted on the test socket, scattering parameter measurements may be obtained using the radio-frequency tester. An equivalent circuit model for the test socket can be obtained based on the measured scattering parameters and known characteristics of the antenna tuning element. Once the test socket has been characterized, an equivalent circuit model for the antenna tuning element can be obtained by extracting suitable modeling parameters from the measured scattering parameters.

Abstract: Calibration equipment for calibrating multiple test stations in a test system is provided. Each test station may include a test unit, a test chamber with multiple antennas, and radio-frequency (RF) cables that connect the test unit to the multiple antennas within the test chamber. Reference devices under test (DUTs) may be used to calibrate the OTA path loss of each test station while switching one of the multiple antennas into use one at a time at desired frequencies. A preferred antenna list indicating the preferred antenna that provides the optimal path loss for each desired frequency may be generated. Once calibrated, the test stations may be used during product testing to test factory DUTs to determine whether a particular production DUT satisfies pass/fail criteria. During product testing, a selected one of the multiple antennas is enabled based on the preferred antenna list to perform desired measurements.

Abstract: Electronic devices may be provided that contain wireless communications circuitry. The wireless communications circuitry may include radio-frequency transceiver circuitry and antenna structures. The antenna structures may form an antenna having first and second feeds at different locations. The transceiver circuit may have a first circuit that handles communications using the first feed and may have a second circuit that handles communications using the second feed. A first filter may be interposed between the first feed and the first circuit and a second filter may be interposed between the second feed and the second circuit. The first and second filters and the antenna may be configured so that the first circuit can use the first feed without being adversely affected by the presence of the second feed and so that the second circuit can use the second feed without being adversely affected by the presence of the first feed.

Abstract: Electronic devices may be provided with antenna structures. The antenna structures may be used in wirelessly transmitting and receiving radio-frequency signals. Antenna structures may be formed from molded dielectric substrates. Patterned conductive material may be formed on the dielectric substrates. The dielectric substrates may be formed from molded materials such as glass or ceramic. Sheets of dielectric or dielectric powder may be compressed to form a dielectric substrate of a desired shape. The patterned conductive material may be formed from metallic paint or other conductors. A hollow antenna chamber may be formed by joining molded dielectric structures. An antenna such as an indirectly-fed loop antenna or other antennas may be formed from the molded dielectric substrates and patterned conductors.

Abstract: Cavity antennas may be provided for electronic devices. A cavity antenna may have a conductive antenna cavity with an opening. An antenna resonating element may be soldered within the cavity opening. An electronic device may have a display that is covered by a display cover layer. A cavity antenna may be mounted so that the cavity opening is located under a portion of the display cover layer outside of the active display region. An antenna cavity for a cavity antenna may have one or more bends. A curved antenna cavity or a cavity antenna with one or more angled branches may have a portion that extends between a conductive housing wall and internal device components such as a display. A speaker may be formed using the interior volume within a cavity antenna.

Abstract: Electronic devices may be provided that contain wireless communications circuitry. The wireless communications circuitry may include radio-frequency transceiver circuitry coupled to an adjustable antenna. The adjustable antenna may contain conductive antenna structure such as conductive electronic device housing structures. Electrical components such as switches and resonant circuits may be used in configuring the antenna to operate in two or more different antenna modes at different respective communications bands. Control circuitry may be used in controlling the switches. The antenna may be configured to operate as an inverted-F antenna in one mode of operation and a slot antenna in a second mode of operation.

Abstract: Calibration equipment for calibrating multiple test stations in a test system is provided. Each test station may include a test unit, a test chamber with multiple antennas, and radio-frequency (RF) cables that connect the test unit to the multiple antennas within the test chamber. Reference devices under test (DUTs) may be used to calibrate the OTA path loss of each test station while switching one of the multiple antennas into use one at a time at desired frequencies. A preferred antenna list indicating the preferred antenna that provides the optimal path loss for each desired frequency may be generated. Once calibrated, the test stations may be used during product testing to test factory DUTs to determine whether a particular production DUT satisfies pass/fail criteria. During product testing, a selected one of the multiple antennas is enabled based on the preferred antenna list to perform desired measurements.