PATENT DOCUMENT

Publication Number: US-9461674-B2
Application Number: US-201314050023-A
Country: US
Kind Code: B2

Title: Electronic device with antennas isolated using phase shifter

Abstract:
An electronic device may be provided with a primary antenna that is used for transmitting and receiving signals and a secondary antenna that is used for receiving signals. The primary and secondary antennas may be used together in a diversity arrangement when receiving signals. The electronic device may have a transceiver. A phase shifter may be interposed between the transceiver and the secondary antenna. Control circuitry may select a communications band of interest for transmitting signals with the primary antenna. The control circuitry can adjust the phase shifter in real time based on which communications band of interest has been selected for transmission with the primary antenna. The phase shifter may impose a phase shift on signals carried between the secondary antenna and the transceiver that ensures that primary antenna efficiency degradation associated with the presence of the secondary antenna in the vicinity of the primary antenna is avoided.

Claims:
What is claimed is: 
     
       1. An electronic device, comprising:
 a first antenna; 
 a second antenna; 
 radio-frequency transceiver circuitry coupled to the first and second antennas by respective first and second transmission lines; 
 a phase shifter interposed in the second transmission line; 
 control circuitry configured to adjust the phase shifter in response to transmission of signals in a communications band of interest with the first antenna; and 
 an electronic device housing, wherein the first and second antenna share a common ground plane that is formed from the electronic device housing, and the first and second antennas are surrounded on all but a single side by the common ground plane. 
 
     
     
       2. The electronic device defined in  claim 1  wherein the first and second antennas are located along an edge of the electronic device housing. 
     
     
       3. The electronic device defined in  claim 2  wherein the first and second antennas overlap a dielectric window in the electronic device housing. 
     
     
       4. The electronic device defined in  claim 1  wherein the radio-frequency transceiver comprises a transmitter-receiver coupled to the first transmission line that is configured to operate in cellular telephone bands. 
     
     
       5. The electronic device defined in  claim 4  wherein the radio-frequency transceiver comprises a receiver coupled to the second transmission line. 
     
     
       6. The electronic device defined in  claim 5  wherein the communications band of interest includes a band in the frequency range of 700 MHz to 960 MHz. 
     
     
       7. The electronic device defined in  claim 6  wherein the phase shifter includes an adjustable capacitor. 
     
     
       8. The electronic device defined in  claim 6  wherein the phase shifter includes an adjustable inductor. 
     
     
       9. A method of operating an electric device having primary and secondary antennas, comprising:
 selecting a communications band of interest for transmitting radio-frequency signals with the primary antenna; 
 adjusting a phase shifter to maintain a desired antenna efficiency when transmitting the radio-frequency signals in the communications band of interest, wherein the phase shifter is interposed in a transmission line path that couples the secondary antenna to a radio-frequency transceiver having a plurality of receiver ports; and 
 controlling switching circuitry interposed between the phase shifter and the radio-frequency transceiver to couple the phase shifter to a selected receiver port of the plurality of receiver ports, wherein the radio-frequency transceiver is mounted to a printed circuit board and the phase shifter is mounted to a flexible printed circuit board that is coupled to the printed circuit board. 
 
     
     
       10. The method defined in  claim 9  wherein adjusting the phase shifter comprises imposing a phase shift on antenna signals from the secondary antenna. 
     
     
       11. The method defined in  claim 10  wherein the radio-frequency transceiver comprises a receiver, the method further comprising receiving antenna signals with the receiver from the secondary antenna through the phase shifter. 
     
     
       12. The method defined in  claim 11  wherein the radio-frequency transceiver comprises a transmitter-receiver, the method further comprising using the transmitter-receiver to transmit the radio-frequency signals in the communications band of interest. 
     
     
       13. The method defined in  claim 12  wherein using the transmitter-receiver comprises transmitting the radio-frequency signals in a communications band between 700 MHz and 960 MHz. 
     
     
       14. An electronic device, comprising:
 a first antenna; 
 a second antenna; 
 a radio-frequency receiver; 
 a variable phase shifter; 
 control circuitry that adjusts the variable phase shifter when transmitting signals with the first antenna to avoid antenna efficiency degradation for the first antenna due to presence of the second antenna; 
 a housing in which the first and second antennas are mounted, wherein the first and second antennas comprise patterned metal on a flexible printed circuit; 
 a display in the housing that is covered by a display cover layer, wherein the flexible printed circuit is overlapped by a portion of the display cover layer and radio-frequency signals for the first and second antennas pass through the display cover layer; and 
 a printed circuit board coupled to the flexible printed circuit, wherein the radio-frequency receiver is mounted to the printed circuit board and the variable phase shifter is mounted to the flexible printed circuit. 
 
     
     
       15. The electronic device defined in  claim 14  wherein the housing comprises metal that forms a common antenna ground plane for the first and second antennas. 
     
     
       16. The electronic device defined in  claim 15  wherein the radio-frequency receiver is coupled to the second antenna by a signal path, and the variable phase shifter is interposed in the signal path. 
     
     
       17. The electronic device defined in  claim 15  further comprising a radio-frequency transmitter-receiver coupled to the first antenna that transmits signals in cellular telephone bands. 
     
     
       18. The method defined in  claim 9 , wherein each receiver port of the plurality of receiver ports is associated with a different respective communications band and controlling the switching circuitry comprises:
 controlling the switching circuitry to couple the phase shifter to a selected receiver port of the plurality of receiver ports that is associated with the communications band of interest used by the primary antenna for transmitting the radio-frequency signals. 
 
     
     
       19. The method defined in  claim 10 , wherein adjusting the phase shifter comprising:
 controlling the phase shifter to exhibit a different corresponding phase shift on the antenna signals from the secondary antenna based on which receiver port of the plurality of receiver ports is coupled to the phase shifter by the switching circuitry.

Description:
BACKGROUND 
     This relates generally to electronic devices and, more particularly, to electronic devices with antennas. 
     Electronic devices often include antennas. For example, cellular telephones, computers, and other devices often contain antennas for supporting wireless communications. 
     It can be challenging to form electronic device antenna structures with desired attributes. In some wireless devices, wireless communications are handled using multiple antennas. This can pose challenges. If care is not taken, the presence of one antenna can adversely affect the performance of another antenna. Antennas can be isolated from each other by separating the antennas by large distances, but this leads to bulky devices. Antennas can also be isolated from each other by designing the antennas to reduce coupling. Such designs may not be effective over a desired range of frequencies. 
     It would therefore be desirable to be able to provide improved wireless circuitry for electronic devices that contain multiple antennas. 
     SUMMARY 
     An electronic device may be provided with multiple antennas such as a primary antenna that is used for transmitting and receiving signals and a secondary antenna that is used for receiving signals. The electronic device may be provided with a housing such as a metal housing. The primary and secondary antennas may be located adjacent to each other along an edge of an electronic device housing. The primary and secondary antennas may be formed from antenna resonating elements such as inverted-F antenna resonating elements that share a common ground plane. The ground plane may be formed from portions of the metal electronic device housing. 
     The primary and secondary antennas may be used together in a diversity arrangement when receiving signals. Signals may be transmitted by the primary antenna in a communications band of interest. Transceiver circuitry may be coupled to the primary and secondary antennas using respective transmission line paths. 
     A phase shifter may be interposed in a transmission line path between the transceiver circuitry and the secondary antenna. Control circuitry may be used to select the communications band of interest for transmitting signals with the primary antenna. The control circuitry can adjust the phase shifter based on information on which communications band of interest has been selected for transmission with the primary antenna. The phase shifter may impose a phase shift on signals carried between the secondary antenna and the transceiver that avoids primary antenna efficiency degradation associated with the presence of the secondary antenna in the vicinity of the primary antenna. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an illustrative electronic device such as a laptop computer with wireless circuitry in accordance with an embodiment. 
         FIG. 2  is a perspective view of an illustrative electronic device such as a handheld electronic device with wireless circuitry in accordance with an embodiment. 
         FIG. 3  is a perspective view of an illustrative electronic device such as a tablet computer with wireless circuitry in accordance with an embodiment. 
         FIG. 4  is a perspective view of an illustrative electronic device such as a display for a computer or television with wireless circuitry in accordance with an embodiment. 
         FIG. 5  is a cross-sectional side view of an electronic device with wireless circuitry in accordance with an embodiment. 
         FIG. 6  is a schematic diagram of an illustrative electronic device in accordance with an embodiment. 
         FIG. 7  is a diagram showing how antenna ground plane currents associated with two adjacent antennas may combine in an additive fashion that enhances antenna efficiency in accordance with an embodiment. 
         FIG. 8  is a diagram showing how antenna ground plane currents associated with two adjacent antennas may tend to cancel each other and thereby reduce antenna efficiency in accordance with an embodiment. 
         FIG. 9  is a diagram of an illustrative pair of adjacent antennas and associated wireless circuitry having a phase shifter in accordance with an embodiment. 
         FIG. 10  is a graph in which antenna efficiency has been plotted as a function of operating frequency for a primary antenna in the pair of antennas of  FIG. 9  under two different phase shifter settings in accordance with an embodiment. 
         FIG. 11  is a circuit diagram of an illustrative variable phase shifter in accordance with an embodiment. 
         FIG. 12  is a circuit diagram of transceiver and phase shifter circuitry that may be used in an electronic device in accordance with an embodiment. 
         FIG. 13  is a perspective view of a printed circuit board coupled to a flexible printed circuit that includes antenna resonating element traces for an antenna in accordance with an embodiment. 
         FIG. 14  is a flow chart of illustrative steps involved in operating an electronic device with wireless circuitry in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Electronic devices may be provided with antennas. There may be multiple antennas mounted in the vicinity of each other in a device. For example, a pair of antennas may be used in a device. A first of the antennas, which may sometimes be referred to as a primary antenna, may be used in transmitting and receiving wireless signals. A second of the antennas, which may sometimes be referred to as a secondary antenna, may be used in receiving wireless signals. An electronic device may use a phase shifter to ensure that the impedance of the transmission line path and transceiver circuitry that serve to terminate the secondary antenna is appropriately mismatched with respect to the primary antenna, so that antenna efficiency for the primary antenna is not degraded by the presence of the secondary antenna while operating in a frequency band of interest. The phase shifter may be adjusted to support operation in a variety of different communications bands without primary antenna performance degradation. 
     Illustrative electronic devices that have wireless circuitry with phase shifter circuitry to ensure efficient antenna operation over a variety of communications bands are shown in  FIGS. 1, 2, 3, and 4 . 
     Electronic device  10  of  FIG. 1  has the shape of a laptop computer and has upper housing  12 A and lower housing  12 B with components such as keyboard  16  and touchpad  18 . Device  10  has hinge structures  20  (sometimes referred to as a clutch barrel) to allow upper housing  12 A to rotate in directions  22  about rotational axis  24  relative to lower housing  12 B. Display  14  is mounted in housing  12 A. Upper housing  12 A, which may sometimes referred to as a display housing or lid, is placed in a closed position by rotating upper housing  12 A towards lower housing  12 B about rotational axis  24 . Antenna structures may be located in housing  12 A, in housing  12 B, and in hinge structures  20 . 
       FIG. 2  shows an illustrative configuration for electronic device  10  based on a handheld device such as a cellular telephone, music player, gaming device, navigation unit, or other compact device. In this type of configuration for device  10 , housing  12  has opposing front and rear surfaces. Display  14  is mounted on a front face of housing  12 . Display  14  may have an exterior layer that includes openings for components such as button  26  and speaker port  28 . Antennas in device  10  of  FIG. 2  may be located at locations in housing  12  such as upper end  32  and lower end  34 . 
     In the example of  FIG. 3 , electronic device  10  is a tablet computer. In electronic device  10  of  FIG. 3 , housing  12  has opposing planar front and rear surfaces. Display  14  is mounted on the front surface of housing  12 . As shown in  FIG. 3 , display  14  has an external layer with an opening to accommodate button  26 . Antennas may be located in regions such as one or more regions  36  along the edge of housing  12  and display  14 . 
       FIG. 4  shows an illustrative configuration for electronic device  10  in which device  10  is a computer display, a computer that has an integrated computer display, or a television. Display  14  is mounted on a front face of housing  12 . With this type of arrangement, housing  12  for device  10  may be mounted on a wall or may have an optional structure such as support stand  30  to support device  10  on a flat surface such as a table top or desk. Antennas for device  10  of  FIG. 4  may be located along one or more of the edges of display  14 , on the rear surface of housing  12 , an in stand  30 . 
     Antennas may be provided in other electronic devices if desired. In general, device  10  may be computing device such as a laptop computer, a computer monitor containing an embedded computer, a tablet computer, a cellular telephone, a media player, or other handheld or portable electronic device, a smaller device such as a wrist-watch device, a pendant device, a headphone or earpiece device, or other wearable or miniature device, a television, a computer display that does not contain an embedded computer, a gaming device, a navigation device, an embedded system such as a system in which electronic equipment with a display is mounted in a kiosk or automobile, equipment that implements the functionality of two or more of these devices, or other electronic equipment. The illustrative configurations for device  10  that are shown in  FIGS. 1, 2, 3, and 4  are merely illustrative. 
     Housing  12  of device  10 , which is sometimes referred to as a case, may be formed of materials such as plastic, glass, ceramics, carbon-fiber composites and other fiber-based composites, metal (e.g., machined aluminum, stainless steel, or other metals), other materials, or a combination of these materials. Device  10  may be formed using a unibody construction in which most or all of housing  12  is formed from a single structural element (e.g., a piece of machined metal or a piece of molded plastic) or may be formed from multiple housing structures (e.g., outer housing structures that have been mounted to internal frame elements or other internal housing structures). 
     Display  14  of device  10  may be a touch sensitive display that includes a touch sensor or may be insensitive to touch. Touch sensors for display  14  may be formed from an array of capacitive touch sensor electrodes, a resistive touch array, touch sensor structures based on acoustic touch, optical touch, or force-based touch technologies, or other suitable touch sensor components. 
     A cross-sectional side view of an illustrative electronic device of the type that may be provided with antenna structures is shown in  FIG. 5 . As shown in  FIG. 5 , display  14  in device  10  may have display cover layer  40  and display module  42 . Display layers in display module  42  may include display pixels formed from liquid crystal display (LCD) components or other suitable display pixel structures such as organic light-emitting diode display pixels, electrophoretic display pixels, plasma display pixels, etc. The display pixels may be arranged in an array having numerous rows and columns to form a rectangular active area AA that is surrounded by an inactive border region such as inactive area IA. When viewed from the front of display  14 , inactive area IA may have the shape of a rectangular ring. 
     Display cover layer  40  may cover the surface of display  14  or a display layer such as a color filter layer (e.g., a layer formed from a clear substrate covered with patterned color filter elements) or other portion of a display may be used as the outermost (or nearly outermost) layer in display  14 . The outermost display layer may be formed from a transparent glass sheet, a clear plastic layer, or other transparent member. To hide internal components from view, the underside of the outermost display layer or other display layer surface in inactive area IA may be coated with opaque masking layer  52  (e.g., a layer of opaque ink such as a layer of black ink). 
     Antenna structures  50  may be mounted under inactive area IA. Antenna structures  50  may include one or more antennas for device  10 . Antenna structures  50  may include antennas with resonating elements that are formed from loop antenna structures, patch antenna structures, inverted-F antenna structures, closed and open slot antenna structures, planar inverted-F antenna structures, helical antenna structures, strip antennas, monopoles, dipoles, hybrids of these designs, etc. Different types of antennas may be used for different bands and combinations of bands. 
     If desired, antenna structures  50  may be provided with tunable circuitry. The tunable circuitry may include switching circuitry based on one or more switches. The switching circuitry may, for example, include a switch that can be placed in an open or closed position. When control circuitry in device  10  places the switch in its open position, an antenna may exhibit a first frequency response. When the control circuitry places the switch in its closed position, the antenna may exhibit a second frequency response. Tunable circuitry for one or more antennas in antenna structures  50  may also be based on switching circuitry that can switch selected circuit components into use. For example, an adjustable inductor may operate in a first mode in which a first inductor is switched into use and a second mode in which a second inductor is switched into use. An adjustable inductor may optionally also be switched into a configuration in which a short circuit is switched into use or in which an open circuit is formed. 
     Opaque masking layer  52  and display cover layer  40  may be radio-transparent, so that radio-frequency antenna signals can be transmitted and received through display cover layer  40  in inactive area IA and opaque masking layer  52 . Housing  12  may be formed from a dielectric such as plastic that is transparent to radio-frequency signals or may be formed from a material such as metal in which an antenna window such as antenna window  56  has been formed. Antenna window  56  may be formed from a dielectric such as plastic, so that antenna window  56  is transparent to radio-frequency signals. During operation, antenna signals associated with antenna structures  50  may pass through the portions of display  14  in inactive area IA that overlap antenna structures  50  and/or through antenna window  56  and/or other dielectric portions of housing  12 . 
     Device  10  may contain electrical components  46 . Components  46  may be mounted on one or more substrates such as printed circuit  44 . Printed circuit  44  may be a rigid printed circuit board (e.g., a printed circuit formed from a rigid printed circuit board material such as fiberglass-filled epoxy) or a flexible printed circuit (e.g., a flex circuit formed from a sheet of polyimide or other layer of flexible polymer). Electrical components  46  may include integrated circuits, connectors, sensors, light-emitting components, audio components, discrete devices such as inductors, capacitors, and resistors, switches, and other electrical devices. Paths such as path  48  may be used to couple antenna structures  50  to wireless circuitry on substrates such as printed circuit  44 . Paths such as path  48  may include transmission line paths such as stripline transmission lines, microstrip transmission lines, coplanar transmission lines, coaxial cable transmission lines, transmission lines formed on flexible printed circuits, transmission lines formed on rigid printed circuit boards, or other signal paths. 
       FIG. 6  is a diagram showing how antenna structures  50  may include multiple antennas. As shown in  FIG. 6 , electronic device  10  may include wireless circuitry  60 . Wireless circuitry  60  may include antenna structures  50 , radio-frequency transceiver circuitry  68 , and phase shifter  66 . 
     Antenna structures  50  may include multiple antennas such as antenna  76  and antenna  74 . Antenna  76 , which may sometimes be referred to as a primary antenna, may be used for transmitting and receiving wireless signals (as an example). Antenna  74 , which may sometimes be referred to as a secondary antenna, may be used for receiving wireless signals (as an example). Other antenna configurations may be used in device  10  if desired (e.g., configurations with different numbers of antennas, configurations in which each antenna is used for both transmitting and receiving antenna signals, etc.). The configuration of  FIG. 6  is merely illustrative. 
     Transceiver circuitry  68  may include transmitters and receivers for transmitting and receiving antenna signals through antenna structures  50 . For example, transceiver circuitry  68  may have a transmitter-receiver  72  for transmitting and receiving antenna signals and a receiver such as receiver  70  for receiving antenna signals. Receiver  70  may, as an example, be configured to receive signals at the same communications frequencies as the receiver circuitry in transmitter receiver  72 . Transmission line  212 A may be used to route signals between transceiver circuitry  68  (e.g., transmitter-receiver  72 ) and a first antenna feed formed from positive antenna feed terminal  218 A and ground antenna feed terminal  220 A. Transmission line  212 B may be used in conveying signals between a second antenna feed that is formed from positive antenna feed terminal  218 B and ground antenna feed terminal  220 B and transceiver circuitry  68  (e.g., receiver  70 ). 
     Phase shifter  66  may be interposed within transmission line  212 B and may be used to control the phase of signals being conveyed between the second antenna feed and transceiver circuitry  68 . These phase adjustments may help ensure that the antenna efficiency of primary antenna  76  is not adversely affected due to the presence of secondary antenna  74 . Primary antenna  76  may be coupled to the antenna feed formed from positive antenna feed terminal  218 A and ground antenna feed  220 A and may be coupled to transmitter-receiver  72  by transmission line  212 A. Secondary antenna  74  may be coupled to the antenna feed formed from positive antenna feed terminal  218 B and ground antenna feed terminal  220 B and may be coupled to receiver  70  by transmission line  212 B. 
     The 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. With one suitable arrangement, secondary antenna  74  serves as a diversity antenna. Outgoing wireless signals are transmitted using primary antenna  76 . Incoming signals are received by primary antenna  76  and/or secondary antenna  74  in an antenna diversity arrangement. 
     As shown in  FIG. 6 , electronic device  10  may include control circuitry  62 . Control circuitry  62  may include storage and processing circuitry for supporting the operation of device  10 . The storage and processing circuitry 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 control circuitry  62  may be used to control the operation of device  10 . The processing circuitry may be based on one or more microprocessors, microcontrollers, digital signal processors, baseband processors, power management units, audio codec chips, application specific integrated circuits, etc. 
     Control circuitry  62  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, control circuitry  62  may be used in implementing communications protocols. Communications protocols that may be implemented using the storage and processing circuitry of control circuitry  62  include internet protocols, wireless local area network protocols (e.g., IEEE 802.11 protocols—sometimes referred to as WiFi®), protocols for other short-range wireless communications links such as the Bluetooth® protocol, cellular telephone protocols, etc. 
     Circuitry  62  may be configured to implement control algorithms that control the use of antennas in device  10 . For example, circuitry  62  may perform signal quality monitoring operations, sensor monitoring operations, and other data gathering operations and may, in response to the gathered data and/or information on which communications bands are to be used in device  10 , control which antenna structures within device  10  are being used to receive and process data and/or may adjust one or more switches, tunable elements, or other adjustable circuits in device  10  to adjust antenna performance. As an example, circuitry  62  may control the operation of phase shifter  66  to help ensure that antenna structures  50  perform optimally when handling signals in various communications bands. Adjustments to phase shifter  66  may be made, for example, based on information on which frequency band(s) transmitter-receiver  72  is currently using to transmit and receive antenna signals through primary antenna  76 . Control circuitry  62  may also select which of antennas  76  and  74  to use in receiving signals in real time based on received signal strength information, based on sensor data, based on information on which communications band(s) are being used, etc. 
     Control circuitry  62  may use paths such as path  224  to issue control signals to phase shifter  66  in real time. Control circuitry  62  may use path  222  to provide signals to transceiver circuitry  68  for transmission over antenna  76  and may use path  222  to receive signals from transceiver circuitry  68  that transceiver circuitry  68  has wirelessly received using antenna  76 . 
     In performing control operations on wireless circuitry  60 , circuitry  62  may open and close switches, may turn on and off receivers and transmitters, may adjust impedance matching circuits, may make phase adjustments using phase shifter  66 , may configure switches in front-end-module (FEM) radio-frequency circuits that are interposed between radio-frequency transceiver circuitry  68  and antenna structures  50  (e.g., filtering and switching circuits used for impedance matching and signal routing), may adjust switches, tunable circuits, and other adjustable circuit elements that are formed as part of an antenna or that are coupled to an antenna or a signal path associated with an antenna, and may otherwise control and adjust the components of device  10 . 
     Input-output circuitry in device  10  such as input-output devices  64  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  64  may include touch screens, buttons, joysticks, click wheels, scrolling wheels, touch pads, key pads, keyboards, microphones, speakers, tone generators, vibrators, cameras, sensors, light-emitting diodes and other status indicators, data ports, etc. A user can control the operation of device  10  by supplying commands through input-output devices  64  and may receive status information and other output from device  10  using the output resources of input-output devices  64 . 
     The presence of antenna  74  in the vicinity of antenna  76  gives rise to the potential for electromagnetic signal coupling between antennas  76  and  74 . Antennas  76  and  74  are terminated with respective impedances Z 1  and Z 2 , as shown in  FIG. 6 . The impedance Z 2  of the path and transceiver that are coupled to secondary antenna  74  and that therefore serve as a termination for the secondary antenna can influence currents in antenna ground structures for antennas  76  and  74  that ultimately affect primary antenna performance. As an example, consider a scenario in which transceiver  68  is used to cover cellular telephone communications bands such as LTE band 20, band 13, band 17, band 8, etc. (i.e., various 700 MHz to 960 MHz communications bands). When transmitting at frequencies such as these using primary antenna  76 , the presence of secondary antenna  74  in the vicinity of antenna  76  (e.g., within 10 cm or less, within 5 cm or less, within 3 cm or less, etc.) can lead to additive ground plane currents that do not adversely affect the efficiency of primary antenna  76  or can lead to cancelling ground plane currents that tend to reduce the efficiency of primary antenna  76 . Phase shifter  66  can be adjusted by control circuitry  62  to ensure that the cancelling ground plane current scenario arises only at out-of-band frequencies (i.e., frequencies out of the communications band in which transmitter circuitry in transmitter-receiver  72  is transmitting signals with primary antenna  76 ). The use of phase shifter  66  therefore helps avoid primary antenna efficiency degradation due to the presence of antenna  74 . 
     As shown in  FIG. 7 , antennas  76  and  74  may be formed from first and second antenna resonating elements (e.g., first and second respective inverted-F antenna resonating elements or antenna resonating elements of other designs) coupled to common ground plane  100 . Antennas  76  and  74  may be located along an edge of housing  12  (e.g., in a position that overlaps antenna window  56  or other radio-transparent structures). Ground plane  100  may be formed from portions of housing  12  (e.g., metal housing structures such as a metal rear housing wall, a side wall, or other housing wall structures and/or internal metal structures), may be formed from ground plane traces on a printed circuit board, may be formed form conductive structures in electrical components in device  10 , or may be formed form other conductive structures. 
     The impact of a secondary antenna such as secondary antenna  74  of  FIG. 7  that is adjacent to primary antenna  76  depends on the impedance Z 2  with which secondary antenna  74  is terminated. In the scenario of  FIG. 7 , impedance Z 2  is matched to impedance Z 1  (e.g., Z 1  and Z 2  may both be 50 ohms). During operation of antenna  76  in this situation, currents IA that flow in antenna  76  are coupled into antenna  74  in a way that leads to induced currents IB that are in phase with currents IA. As a result, ground plane currents IAG associated with antenna  76  and ground plane currents IBG associated with antenna  74  tend to add to each other. The additive nature of the ground plane currents of antennas  74  and  76  in the  FIG. 7  scenario leads to good efficiency for antenna  76 . This configuration may, however, be difficult to achieve in practice, because it may be desirable to form the transmission line paths that are coupled to the feeds for antennas  74  and  76 , respectively, so that these transmission line paths (i.e., the terminations for antennas  74  and  76 ) have different impedances and thereby reduced crosstalk and coupling. 
     The scenario depicted in  FIG. 8  involves an impedance Z 2  that is mismatched with respect to impedance Z 1 . In this scenario, antenna ground plane currents IBG of antenna  74  and antenna ground plane currents IAG of antenna  76  tend to cancel each other at some operating frequencies, thereby decreasing the efficiency of antenna  76  at those operating frequencies. It may be desirable to configure transmission line  212 B to exhibit a different impedance from path  212 A to prevent coupling and crosstalk on the printed circuit board or other substrate on which transmission lines  212 A and  212 B are formed. Impedance mismatches can reduce crosstalk and coupling, but, if care is not taken, can lead to an undesired drop in efficiency for primary antenna  76  when operating in a communications band of interest. 
     To ensure that a desired efficiency is maintained in the communications band of interest for transmitting antennas with primary antenna  76 , phase shifter  66  may be used to adjust the phase of the signals traveling between secondary antenna  74  and transceiver circuitry  68  when primary antenna  76  is handling signals in the communications band of interest. These phase adjustments may move efficiency losses out of the communications band of interest, thereby preserving a desired antenna efficiency for primary antenna  76 . 
       FIG. 9  is a diagram of illustrative inverted-F antenna resonating element structures that may be used in forming antennas  76  and  74 . As shown in  FIG. 9 , antenna  76  may have an inverted-F antenna resonating element  124 . Inverted-F antenna resonating element  124  may have one or more arms such as long arm (low band arm)  106  and short arm (high band arm)  108 . Positive feed terminal  218 A may be coupled to feed arm  110  of resonating element  124 , which runs parallel to return path  112 . Antenna  74  may have an inverted-F antenna resonating element  122 . Inverted-F antenna resonating element  122  may have one or more arms such as long arm (low band arm)  114  and short arm (high band arm)  116 . Positive feed terminal  218 B may be coupled to feed arm  118  of resonating element  124 , which runs parallel to return path  120 . Phase shifter  66  may be interposed in transmission line signal path  212 B between antenna  74  and transceiver circuitry  68 . 
       FIG. 10  is a graph in which antenna efficiency for primary antenna  76  has been plotted as a function of operating frequency f. It may be desired to operate antenna  76  in a communications band extending from frequency fa to frequency fb (e.g., a low band cellular telephone band or other suitable communications band of interest). Phase shifter  66  imparts a phase shift to antenna signals carried between secondary antenna  74  and transceiver circuitry  68 . Phase shifter  66  may be a variable phase shifter that is controlled in real time by control circuitry  62 . Control circuitry  62  may, for example, determine which communications band is being actively used by transceiver  68  and primary antenna  76  to transmit and receive wireless signals. In response to determining which communications band is currently active, control circuitry  62  can issue control signals on path  224  that adjust phase shifter  66  so that a desired amount of phase shift is imparted to path  212 B. The amount of phase shift to be used when operating in each communications band may be determined empirically (e.g., by calibrating device  10  during manufacturing). 
     In the absence of an appropriate phase shift from phase shifter  66 , antenna  76  may be characterized by antenna efficiency curve  300 . As shown in  FIG. 10 , curve  300  may be characterized by a decrease in efficiency (decrease  302 ) at frequencies that lie within the communications band of interest (i.e., the band extending from fa to fb in the example of  FIG. 10 ). This decrease in antenna efficiency would degrade wireless performance (e.g., the decrease in efficiency would require larger transmit powers to be used when transmitting signals, thereby depleting battery energy unnecessarily). 
     When, however, the phase of phase shifter  66  is adjusted to impart a 180° phase shift or other appropriate phase (e.g., a phase determined through calibrating device  10  during manufacturing) to the signals traveling on path  212 B, primary antenna  76  may be characterized by antenna efficiency curve  304 . As shown in  FIG. 10 , the efficiency drop associated with dip  306  of curve  304  is effectively shifted to frequencies below the communications band of interest (i.e., efficiency drop  302  at frequencies between fa and fb is shifted to the position occupied by efficiency drop  306  of  FIG. 10 , below frequency fa at the lower end of the communications band of interest). By shifting the low efficiency characteristic (dip  306 ) out of the communications band being used by primary antenna  76  (i.e., to a frequency below the communications band of interest), antenna efficiency for primary antenna  76  when operating within the communications band of interest may be maintained. 
     An illustrative adjustable phase shifter circuit that may be used in implementing phase shifter  66  is shown in  FIG. 11 . As shown in  FIG. 11 , phase shifter  66  may have a positive signal path P and a ground signal path G. Capacitor C may be coupled in series in path P between port  400  and port  402  of phase shifter  66 . Inductor L may be coupled in a shunt configuration between positive signal line P and ground line G. Capacitor C may be a variable capacitor and/or inductor L may be a variable inductor to provide phase shifter  66  with the ability to be adjusted by control signals from control circuitry  62 . During operation, port  400  may be coupled to antenna  74  and port  402  may be coupled to transceiver  68  (as an example). Other phase shifter circuits may be used to implement phase shifter  66  if desired. The configuration of  FIG. 11  is provided as an example. 
     In the illustrative configuration of  FIG. 12 , phase shifter  66  has been coupled to switch  404  in transceiver circuitry  68 . Switch  404  may receive control signals on input  408  (e.g., control signals from control circuitry  62 ). Switch  404  may be adjusted to couple port  402  of adjustable phase shifter  66  to a selected one of paths  406 . Each of paths  406  may be coupled to a respective port of receiver  70 . Each receiver port may be associated with a different respective communications band of interest. During operation, control circuitry  62  can adjust switch  404  to switch a desired communications band into use by receiver  70  (e.g., to receive signals via secondary antenna  74 ). Control circuitry  62  can also adjust circuitry associated with transmitter-receiver  72  to ensure that the receiver circuitry of transmitter-receiver  72  is receiving signals in the same communications band. The transmitter circuitry of transmitter-receiver  72  may be set to an appropriate associated transmit band. For each switch state of switch  404 , phase shifter  66  may be directed to produce a corresponding phase shift appropriate for ensuring that antenna efficiency drops are shifted out of band and therefore do not overlap with the communications band being used by primary antenna  76  to transmit signals. 
       FIG. 13  is a perspective view of an illustrative transceiver  68  mounted on an illustrative rigid printed circuit board  44 . Antenna  74  (and, if desired, antenna  76 ) may be formed from traces such as patterned metal layer  502  on printed circuit  500 . Printed circuit  500  may be coupled to printed circuit board  44  using solder or other conductive connections. Printed circuit  500  may be a flexible printed circuit (as an example). Phase shifter  66  may be implemented using phase shifter circuitry on printed circuit  500  such as phase shifter  66 - 2  and/or phase shifter circuitry on printed circuit board  44  such as phase shifter  66 - 1 . Phase shifter circuitry can also be implemented using fixed length transmission line structures, circuitry on an integrated circuit such as portions of transceiver  68 , discrete components (e.g., surface mount technology components), or other circuits. 
     Illustrative steps involved in operating device  10  are shown in  FIG. 14 . 
     At step  600 , control circuitry  62  (e.g., a microprocessor, a baseband processor integrated circuit, and/or other processing circuitry) can select a desired transmit frequency for primary antenna  76 . The transmit frequency may fall within a communications band of interest such as the frequency band extending from frequency fa to frequency fb in the example of  FIG. 10 . Examples of frequency bands of interest include bands 13, 17, 5, 20, 8, etc. for LTE/UMTS. 
     At step  602 , control circuitry  62  uses information on the current operating frequency and currently selected communications band to adjust phase shifter  66  so that any antenna efficiency reductions are moved out of band. 
     At step  604 , device  10  can use antennas  74  and  76  in a diversity arrangement to receive signals (i.e., device  10  can dynamically switch between antennas  74  and  76  so that an optimum antenna is always maintained in use) and can use primary antenna  76  to transmit signals in the communications band of interest without loss of antenna efficiency due to the presence of secondary antenna  74 . 
     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: 20131009
Publication Date: 20161004
Grant Date: 20161004
Priority Date: 20131009
Inventors: YARGA SALIH
SAMARDZIJA MIROSLAV
LI QINGXIANG
SCHLUB ROBERT W.
Assignee: APPLE INC
CPC Classifications: [{"code": "H01Q5/371", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q9/42", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B1/0064", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01Q1/243", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q1/521", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q1/2266", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q21/28", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B1/0064", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01Q1/2266", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q5/371", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q1/243", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q9/42", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q1/521", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q1/2266", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01Q21/28", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q5/371", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q1/521", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q1/243", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q9/42", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q21/28", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 52777337