PATENT DOCUMENT

Publication Number: US-11309628-B2
Application Number: US-202017079284-A
Country: US
Kind Code: B2

Title: Multiple-input and multiple-output antenna structures

Abstract:
An electronic device may include a housing and four antennas at respective corners of the housing. Cellular telephone transceiver circuitry may concurrently convey signals at one or more of the same frequencies over one or more of the four antennas using a multiple-input multiple-output (MIMO) scheme. In order to isolate adjacent antennas, dielectric-filled openings may be formed in conductive walls of the housing to divide the walls into segments that are used to form resonating element arms for the antennas. If desired, first and second antennas may include resonating element arms formed from a wall without any gaps. The first and second antennas may include adjacent return paths. A magnetic field associated with currents for the first antenna may cancel out with a magnetic field associated with currents for the second antenna at the adjacent return paths, thereby serving to electromagnetically isolate the first and second antennas.

Claims:
What is claimed is: 
     
       1. A portable electronic device, comprising:
 a housing having a peripheral conductive wall and having opposing first and second ends; 
 a first antenna resonating element formed from the peripheral conductive wall, and having a first end at a first dielectric-filled opening in the housing and a second end at a second dielectric-filled opening in the housing; 
 a second antenna resonating element formed from the peripheral conductive wall, and having a first end at the second dielectric-filled opening in the housing and a second end at a third dielectric-filled opening in the housing; 
 a third antenna resonating element formed from the peripheral conductive wall, and having a first end at a fourth dielectric-filled opening in the housing and a second end at a fifth dielectric-filled opening in the housing; 
 a fourth antenna resonating element formed from the peripheral conductive wall, and having a first end at the fifth dielectric-filled opening in the housing and a second end at a sixth dielectric-filled opening in the housing; and 
 radio-frequency transceiver circuitry configured to concurrently convey radio-frequency signals at a given frequency using the first and fourth antenna resonating elements. 
 
     
     
       2. The portable electronic device defined in  claim 1  further comprising:
 an antenna ground; 
 a first antenna feed coupled between the antenna ground and the first antenna resonating element; and 
 a second antenna feed coupled between the antenna ground and the second antenna resonating element. 
 
     
     
       3. The portable electronic device defined in  claim 2  further comprising:
 first and second adjustable components coupled between the antenna ground and the first antenna resonating element, wherein the first antenna feed is interposed between the first and second adjustable components. 
 
     
     
       4. The portable electronic device defined in  claim 3  wherein the second adjustable component is interposed between the first antenna feed and the first dielectric-filled opening and the second adjustable component is configured to tune the first antenna resonating element in a first frequency band. 
     
     
       5. The portable electronic device defined in  claim 4  wherein the first adjustable component is configured to tune the first antenna resonating element in a second frequency band that is lower than the first frequency band. 
     
     
       6. The portable electronic device defined in  claim 5  wherein the given frequency is in the second frequency band. 
     
     
       7. The portable electronic device defined in  claim 5  wherein the radio-frequency transceiver circuitry is configured to concurrently convey radio-frequency signals at an additional frequency using the first, second, third, and fourth antenna resonating elements, and the additional frequency is in the first frequency band. 
     
     
       8. The portable electronic device defined in  claim 3  further comprising:
 an additional adjustable component coupled between the first and second antenna resonating elements. 
 
     
     
       9. The portable electronic device defined in  claim 8  wherein the additional adjustable component comprises switching circuitry, the switching circuitry has a first state at which the second antenna resonating element is shorted to the antenna ground along an antenna return path and the switching circuitry has a second state at which the antenna return path forms an open circuit between the second antenna resonating element and the antenna ground. 
     
     
       10. The portable electronic device defined in  claim 3  wherein the first and second adjustable components each comprise inductors. 
     
     
       11. The portable electronic device defined in  claim 10  wherein the first and second adjustable components form adjustable return paths. 
     
     
       12. The portable electronic device defined in  claim 3 , further comprising:
 a third antenna feed coupled between the antenna ground and the third antenna resonating element; 
 a fourth antenna feed coupled between the antenna ground and the fourth antenna resonating element; and 
 third and fourth adjustable components coupled between the antenna ground and the fourth antenna resonating element, wherein the fourth antenna feed is interposed between the third and fourth adjustable components. 
 
     
     
       13. The portable electronic device defined in  claim 1  wherein the housing has first and second sides with a first length and third and fourth sides perpendicular to the first and second sides with a second length that is less than the first length, the second dielectric-filled opening is in the third side, and the fifth dielectric-filled opening is in the fourth side. 
     
     
       14. The portable electronic device defined in  claim 13  wherein the first and fourth dielectric-filled openings are in the first side and the third and sixth dielectric-filled openings are in the second side. 
     
     
       15. An electronic device, comprising:
 a housing having a peripheral conductive wall; 
 a dielectric-filled opening in the housing that divides the peripheral conductive wall into first and second segments, wherein dielectric material in the dielectric-filled opening extends from the first segment to the second segment; 
 an antenna ground that is separated from the first and second segments by a slot; 
 a first antenna having a first resonating element arm formed from the first segment and a first antenna feed coupled between a first location on the first segment and the antenna ground across the slot; 
 a second antenna having a second resonating element arm formed from the second segment and a second antenna feed coupled between the second segment and the antenna ground across the slot; 
 a first adjustable component that is coupled between a second location on the first segment and the antenna ground; 
 a second adjustable component coupled between a third location on the first segment and the antenna ground, wherein the first location is interposed between the second and third locations; 
 control circuitry coupled to the first and second adjustable components, wherein the control circuitry is configured to tune a resonant frequency of the first antenna. 
 
     
     
       16. The electronic device defined in  claim 15  further comprising:
 a second dielectric-filled opening in the housing that divides the peripheral conductive wall into third and fourth segments, wherein dielectric material in the second dielectric-filled opening extends from the third segment to the fourth segment; 
 a third antenna having a third resonating element arm formed from the third segment; and 
 a fourth antenna having a fourth resonating element arm formed from the fourth segment. 
 
     
     
       17. The electronic device defined in  claim 15  wherein the third location is interposed between the first location and the dielectric-filled opening, and the second adjustable component is configured to tune the first antenna at a first frequency. 
     
     
       18. The electronic device defined in  claim 17  wherein the first adjustable component is configured to tune the first antenna at a second frequency that is higher than the first frequency. 
     
     
       19. An electronic device, comprising:
 a housing having peripheral conductive structures and having a rectangular periphery with first and second corners at a first end of the housing and third and fourth corners at a second end of the housing; 
 a first antenna element at the first corner having first and second opposing ends that each terminate at dielectric material in the rectangular periphery at the first end of the housing; 
 a second antenna element at the second corner having first and second opposing ends that each terminate at dielectric material in the rectangular periphery at the first end of the housing; 
 a third antenna element at the third corner having first and second opposing ends that each terminate at dielectric material in the rectangular periphery at the second end of the housing; and 
 a fourth antenna element at the fourth corner having first and second opposing ends that each terminate at dielectric material in the rectangular periphery at the second end of the housing. 
 
     
     
       20. The electronic device defined in  claim 19  wherein dielectric material in the rectangular periphery extends from the first end of the first antenna to the first end of the second antenna and from the first end of the third antenna to the first end of the fourth antenna.

Description:
This application is a continuation of patent application Ser. No. 15/657,001, filed Jul. 21, 2017, which is hereby incorporated by reference herein in its entirety. 
    
    
     BACKGROUND 
     This relates generally to electronic devices and, more particularly, to electronic devices with wireless communications circuitry. 
     Electronic devices often include wireless circuitry with 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, antennas are bulky. In other devices, antennas are compact, but are sensitive to the position of the antennas relative to external objects. It is often difficult to perform wireless communications with a satisfactory data rate (data throughput) using a single antenna in a wireless device, especially as software applications performed by wireless devices become increasingly data hungry. In order to increase the possible data rate for the wireless device, wireless devices can include multiple antennas that convey radio-frequency signals at the same frequency. However, it can be difficult to electromagnetically isolate multiple antennas operating at the same frequency, potentially leading to interference between the radio-frequency signals conveyed by each of the antennas and deterioration in the radio-frequency performance of the wireless device. 
     It would therefore be desirable to be able to provide improved wireless circuitry for electronic devices such as electronic devices that include multiple antennas. 
     SUMMARY 
     An electronic device may be provided with wireless circuitry. The wireless circuitry may include multiple antennas and transceiver circuitry. The electronic device may include a housing having opposing first and second ends and a rectangular periphery with first and second corners at the first end and third and fourth corners at the second end. 
     The antennas may include a first antenna at the first corner, a second antenna at the second corner, a third antenna at the third corner, and a fourth antenna at the fourth corner. The first and fourth antennas may occupy a greater spatial volume than the first and second antennas. Transceiver circuitry such as cellular telephone transceiver circuitry may concurrently convey radio-frequency signals at one or more of the same frequencies over the first, second, third, and/or fourth antennas using a multiple-input multiple-output (MIMO) scheme. For example, the transceiver circuitry may convey radio-frequency signals at a first frequency using the first and fourth antennas and at a second frequency that is greater than the first frequency using the first, second, third, and fourth antennas. If desired, the transceiver circuitry may also concurrently convey radio-frequency signals at a third frequency that is greater than the second frequency using the first and fourth antennas or using all of the first, second, third, and fourth antennas. 
     The housing may include peripheral conductive housing walls. The antennas may each include resonating element arms that are formed from the peripheral conductive housing walls. In order to ensure that adjacent antennas are electromagnetically isolated when operating at the same frequency, a dielectric-filled opening in a given peripheral conductive wall may divide the wall into first and second segments that are used to form resonating element arms for the first and second antennas, respectively. Similarly, a dielectric-filled opening may be formed in an additional conductive wall that divides the additional wall into third and fourth segments that are used to form resonating element arms for the third and fourth antennas, respectively. If desired, switching circuitry may be coupled between the first and second antennas and the third and fourth antennas. The switching circuitry may have a state at which the first and second antennas are configured to form a single fifth antenna and the third and fourth antennas are configured to form a single sixth antenna. The transceiver circuitry may concurrently convey radio-frequency signals over the fifth and sixth antennas at one or more of the same frequencies using a MIMO scheme if desired. 
     In another suitable arrangement, the first and second antennas may include resonating element arms that are formed from portions of a conductive housing wall without any dielectric-filled gaps. In this example, the first and second antennas may include adjacent return paths coupled between the housing wall and an internal ground plane. A magnetic field associated with currents for the first antenna may cancel out with a magnetic field associated with currents for the second antenna as the currents flow over the adjacent return paths, thereby serving to electromagnetically isolate the first and second antennas even though the first and second antennas are both formed from a single continuous housing wall. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of illustrative circuitry in an electronic device in accordance with an embodiment. 
         FIG. 2  is a schematic diagram of illustrative wireless circuitry in accordance with an embodiment. 
         FIG. 3  is a diagram of illustrative wireless circuitry including multiple antennas for performing multiple-input and multiple-output (MIMO) communications in accordance with an embodiment. 
         FIG. 4  is a plot showing how illustrative antennas of the type shown in  FIG. 3  may perform wireless communications in multiple frequency bands in accordance with an embodiment. 
         FIG. 5  is a perspective view of an illustrative electronic device in accordance with an embodiment. 
         FIG. 6  is a schematic diagram of an illustrative inverted-F antenna in accordance with an embodiment. 
         FIG. 7  is a schematic diagram of an illustrative slot antenna in accordance with an embodiment. 
         FIG. 8  is a schematic diagram of illustrative first and second antennas having adjacent return paths for performing MIMO communications in accordance with an embodiment. 
         FIG. 9  is a diagram of illustrative first and second antennas having adjacent return paths for performing MIMO communications and having resonating elements formed from a continuous conductive electronic device housing wall in accordance with an embodiment. 
         FIG. 10  is a diagram showing how illustrative antennas of the type shown in  FIGS. 8 and 9  may be electromagnetically isolated from each other while performing MIMO communications in accordance with an embodiment. 
         FIG. 11  is a schematic diagram of illustrative first and second antennas having mechanically separated resonating elements for performing MIMO communications in accordance with an embodiment. 
         FIG. 12  is a diagram of illustrative first and second antennas having mechanically separated resonating elements formed from a conductive electronic device housing wall and having switching circuitry for switching between first and second MIMO modes in accordance with an embodiment. 
         FIG. 13  is a diagram of switching circuitry that may be used to toggle antennas of the type shown in  FIGS. 11 and 12  between first and second MIMO modes in accordance with an embodiment. 
         FIG. 14  is a graph of antenna performance (antenna efficiency) for illustrative antenna structures of the types shown in  FIGS. 8-13  in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Electronic devices such as electronic device  10  of  FIG. 1  may be provided with wireless communications circuitry. The wireless communications circuitry may be used to support wireless communications in multiple wireless communications bands. 
     The wireless communications circuitry may include one or more antennas. The antennas of the wireless communications circuitry can include loop antennas, inverted-F antennas, strip antennas, planar inverted-F antennas, slot antennas, dipole antennas, monopole antennas, helical antennas, patch antennas, hybrid antennas that include antenna structures of more than one type, or other suitable antennas. Conductive structures for the antennas may, if desired, be formed from conductive electronic device structures. 
     The conductive electronic device structures may include conductive housing structures. The housing structures may include peripheral structures such as peripheral conductive structures that run around the periphery of an electronic device. The peripheral conductive structures may serve as a bezel for a planar structure such as a display, may serve as sidewall structures for a device housing, may have portions that extend upwards from an integral planar rear housing (e.g., to form vertical planar sidewalls or curved sidewalls), and/or may form other housing structures. 
     Gaps may be formed in the peripheral conductive structures that divide the peripheral conductive structures into peripheral segments. One or more of the segments may be used in forming one or more antennas for electronic device  10 . Antennas may also be formed using an antenna ground plane formed from conductive housing structures such as metal housing midplate structures and other internal device structures. Rear housing wall structures may be used in forming antenna structures such as an antenna ground. 
     Electronic device  10  may be a portable electronic device or other suitable electronic device. For example, electronic device  10  may be a portable electronic device such as a laptop computer, a tablet computer, a cellular telephone, a media player, a remote control device, a wearable device such as a wristwatch device, pendant device, headphone or earpiece device, virtual or augmented reality headset device, device embedded in eyeglasses or other equipment worn on a user&#39;s head, or other wearable or miniature device, gaming controller, computer mouse, keyboard, mousepad, a navigation device, or trackpad or touchpad device, or electronic device  10  may be a larger device such as a television, a computer monitor containing an embedded computer, a computer display that does not contain an embedded computer, a gaming device, an embedded system such as a system in which electronic equipment is mounted in a kiosk, building, vehicle, or automobile, a wireless access point or base station, a desktop computer, equipment that implements the functionality of two or more of these devices, or other electronic equipment. Other configurations may be used for device  10  if desired. The example of  FIG. 1  is merely illustrative. 
     Device  10  may include a housing such as housing  12 . Housing  12 , which may sometimes be referred to as a case, may be formed of plastic, glass, ceramics, fiber composites, metal (e.g., stainless steel, aluminum, etc.), other suitable materials, or a combination of these materials. In some situations, parts of housing  12  may be formed from dielectric or other low-conductivity material. In other situations, housing  12  or at least some of the structures that make up housing  12  may be formed from metal elements. 
       FIG. 1  is a schematic diagram showing illustrative components that may be used in device  10 . As shown in  FIG. 1 , device  10  may include control circuitry such as storage and processing circuitry  28 . Storage and processing circuitry  28  may include storage such as hard disk drive storage, nonvolatile memory (e.g., flash memory or other electrically-programmable-read-only memory configured to form a solid state drive), volatile memory (e.g., static or dynamic random-access-memory), etc. Processing circuitry in storage and processing circuitry  28  may be used to control the operation of device  10 . This processing circuitry may be based on one or more 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, etc. To support interactions with external equipment, storage and processing circuitry  28  may be used in implementing communications protocols. Communications protocols that may be implemented using storage and processing circuitry  28  include internet protocols, wireless local area network protocols (e.g., IEEE 802.11 protocols—sometimes referred to as WiFi®), protocols for other short-range wireless communications links such as the Bluetooth® protocol, cellular telephone protocols (e.g., Long-Term Evolution (LTE) protocols, LTE Advanced protocols, Global System for Mobile Communications (GSM) protocols, Universal Mobile Telecommunications System (UMTS) protocols, or other mobile telephone protocols), multiple-input and multiple-output (MIMO) protocols, antenna diversity protocols, combinations of these, etc. 
     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  32  may include touch screens, displays without touch sensor capabilities, buttons, joysticks, 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, fingerprint sensors (e.g., a fingerprint sensor integrated with a button such as button  24  of  FIG. 1  or a fingerprint sensor that takes the place of button  24 ), 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  42  for handling various radio-frequency communications bands. For example, circuitry  34  may include transceiver circuitry  44 ,  46 , and  48 . Transceiver circuitry  46  may handle 2.4 GHz and 5 GHz bands for WiFi® (IEEE 802.11) communications or other wireless local area network (WLAN) bands and may handle the 2.4 GHz Bluetooth® communications band or other wireless personal area network (WPAN) bands. Circuitry  34  may use cellular telephone transceiver circuitry  48  for handling wireless communications in frequency ranges such as a low communications band from 700 to 960 MHz, a low midband from 1400-1520 MHz, a midband from 1710 to 2170 MHz, and a high band from 2300 to 2700 MHz or other communications bands between 700 MHz and 4000 MHz or other suitable frequencies (as examples). Circuitry  48  may handle voice data and non-voice data using one or more cellular telephone protocols (e.g., Long-Term Evolution (LTE) protocols, LTE Advanced protocols, Global System for Mobile Communications (GSM) protocols, Universal Mobile Telecommunications System (UMTS) protocols, other mobile telephone protocols, etc.). 
     Wireless communications circuitry  34  can include circuitry for other short-range and long-range wireless links if desired. For example, wireless communications circuitry  34  may include 60 GHz transceiver circuitry, circuitry for receiving television and radio signals, paging system transceivers, near field communications (NFC) circuitry, etc. Wireless communications circuitry  34  may include global positioning system (GPS) receiver equipment such as GPS receiver circuitry  44  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 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 structures, patch antenna structures, inverted-F antenna structures, slot antenna structures, planar inverted-F antenna structures, helical antenna structures, monopole antenna structures, dipole 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. 2 , transceiver circuitry  42  in wireless circuitry  34  may be coupled to antenna structures  40  using paths such as path  50 . Wireless circuitry  34  may be coupled to control circuitry  28 . Control circuitry  28  may be coupled to input-output devices  32 . Input-output devices  32  may supply output from device  10  and may receive input from sources that are external to device  10 . 
     To provide antenna structures such as antenna(s)  40  with the ability to cover communications frequencies of interest, antenna(s)  40  may be provided with circuitry such as filter circuitry (e.g., one or more passive filters and/or one or more tunable filter circuits). Discrete components such as capacitors, inductors, and resistors may be incorporated into the filter circuitry. Capacitive structures, inductive structures, and resistive structures may also be formed from patterned metal structures (e.g., part of an antenna). If desired, antenna(s)  40  may be provided with adjustable circuits such as tunable components  60  to tune antennas over communications bands of interest. Tunable components  60  may be part of a tunable filter or tunable impedance matching network, may be part of an antenna resonating element, may span a gap between an antenna resonating element and antenna ground, etc. Tunable components  60  may include tunable inductors, tunable capacitors, or other tunable components. Tunable components such as these may be based on switches and networks of fixed components, distributed metal structures that produce associated distributed capacitances and inductances, variable solid state devices for producing variable capacitance and inductance values, tunable filters, or other suitable tunable structures. During operation of device  10 , control circuitry  28  may issue control signals on one or more paths such as path  62  that adjust inductance values, capacitance values, or other parameters associated with tunable components  60 , thereby tuning antenna structures  40  to cover desired communications bands. If desired, components  60  may include fixed (non-adjustable) tuning components such as capacitors, resistors, and/or inductors. 
     Path  50  may include one or more transmission lines. As an example, signal path  50  of  FIG. 2  may be a transmission line having a positive signal conductor such as line  52  and a ground signal conductor such as line  54 . Lines  52  and  54  may form parts of a coaxial cable, a stripline transmission line, or a microstrip transmission line (as examples). A matching network formed from components such as fixed or tunable inductors, resistors, and capacitors may be used in matching the impedance of antenna(s)  40  to the impedance of transmission line  50 . Matching network components may be provided as discrete components (e.g., surface mount technology components) or may be formed from housing structures, printed circuit board structures, traces on plastic supports, etc. Components such as these may also be used in forming filter circuitry in antenna(s)  40  and may be tunable and/or fixed components (e.g., components  60 ). 
     Transmission line  50  may be coupled to antenna feed structures such as antenna feed  55  associated with antenna structures  40 . As an example, antenna structures  40  may form an inverted-F antenna, a slot antenna, a hybrid inverted-F slot antenna or other antenna having an antenna feed with a positive antenna feed terminal such as terminal  56  and a ground antenna feed terminal such as ground antenna feed terminal  58 . Positive transmission line conductor  52  may be coupled to positive antenna feed terminal  56  and ground transmission line conductor  54  may be coupled to ground antenna feed terminal  58 . Other types of antenna feed arrangements may be used if desired. For example, antenna structures  40  may be fed using multiple feeds. The illustrative feeding configuration of  FIG. 2  is merely illustrative. 
     Antenna structures  40  may include resonating element structures, antenna ground plane structures, an antenna feed such as feed  55 , and other components (e.g., tunable components  60 ). Antenna structures  40  may be configured to form any suitable types of antenna. With one suitable arrangement, which is sometimes described herein as an example, antenna structures  40  are used to implement a hybrid inverted-F-slot antenna that includes both inverted-F and slot antenna resonating elements. 
     If desired, multiple antennas  40  may be formed in device  10 . Each antenna  40  may be coupled to transceiver circuitry  42  over respective transmission lines  50 . If desired, two or more antennas  40  may share the same transmission line structures  50 .  FIG. 3  is a diagram showing how device  10  may include multiple antennas  40  for performing wireless communications. 
     As shown in  FIG. 3 , device  10  may include two or more antennas  40  such as a first antenna  40 - 1 , a second antenna  40 - 2 , a third antenna  40 - 3 , and a fourth antenna  40 - 4 . Antennas  40  may be provided at different locations within housing  12  of device  10 . For example, antennas  40 - 1  and  40 - 2  may be formed within region  66  at a first (upper) end of housing  12  whereas antennas  40 - 3  and  40 - 4  are formed within region  68  at an opposing second (lower) end of housing  12 . In the example of  FIG. 3 , housing  12  has a rectangular periphery (e.g., a periphery having four corners) and each antenna  40  is formed at a respective corner of housing  12 . This example is merely illustrative and, in general, antennas  40  may be formed at any desired location within housing  12 . 
     Wireless circuitry  34  may include input-output ports such as port  74  for interfacing with digital data circuits in storage and processing circuitry  28  ( FIG. 1 ). Wireless circuitry  34  may include baseband circuitry such as baseband (BB) processor  70  and radio-frequency transceiver circuitry such as transceiver circuitry  42 . 
     Port  74  may receive digital data from storage and processing circuitry  28  that is to be transmitted by transceiver circuitry  42 . Incoming data that has been received by transceiver circuitry  42  and baseband processor  70  may be supplied to storage and processing circuitry  28  via port  74 . 
     Transceiver circuitry  42  may include one or more transmitters and one or more receivers. For example, transceiver circuitry  42  may include multiple remote wireless transceiver circuits  48  ( FIG. 1 ) such as a first transceiver  48 - 1 , a second transceiver  48 - 2 , a third transceiver  48 - 3 , and a fourth transceiver  48 - 4  (e.g., transceivers for handling voice and non-voice cellular telephone communications in cellular telephone communications bands). Each transceiver  48  may be coupled to a respective antenna  40  over a corresponding transmission line  50 . For example, first transceiver  48 - 1  may be coupled to antenna  40 - 1  over transmission line  50 - 1 , second transceiver  48 - 2  may be coupled to antenna  40 - 2  over transmission line  50 - 2 , third transceiver  48 - 3  may be coupled to antenna  40 - 3  over transmission line  50 - 3 , and fourth transceiver  48 - 4  may be coupled to antenna  40 - 4  over transmission line  50 - 4 . 
     Radio-frequency front end circuitry  76  may be interposed on each transmission line  50  (e.g., first front end circuits  76 - 1  may be interposed on line  50 - 1 , second front end circuits  76 - 2  may be interposed on line  50 - 2 , third front end circuits  76 - 3  may be interposed on line  50 - 3 , etc.). Front end circuitry  76  may each include switching circuitry, filter circuitry (e.g., duplexer and/or diplexer circuitry, notch filter circuitry, low pass filter circuitry, high pass filter circuitry, bandpass filter circuitry, etc.), impedance matching circuitry for matching the impedance of transmission line  50  to the corresponding antenna  40 , networks of active and/or passive components such as components  60  of  FIG. 2 , radio-frequency coupler circuitry for gathering antenna impedance measurements, or any other desired radio-frequency circuitry. If desired, front end circuitry  76  may include switching circuitry that is configured to selectively couple antennas  40 - 1 ,  40 - 2 ,  40 - 3 , and  40 - 4  to different respective transceivers  48 - 1 ,  48 - 2 ,  48 - 3 , and  48 - 4  (e.g., so that each antenna can handle communications for different transceivers  48  over time based on the state of the switching circuits in front end circuitry  76 ). 
     If desired, front end circuits  76  may include filtering circuitry (e.g., duplexers and/or diplexers) that allow the corresponding antenna  40  to transmit and receive radio-frequency signals at the same time (e.g., using a frequency domain duplexing (FDD) scheme). Antennas  40 - 1 ,  40 - 2 ,  40 - 3 , and  40 - 4  may transmit and/or receive radio-frequency signals in respective time slots or two or more of antennas  40 - 1 ,  40 - 2 ,  40 - 3 , and  40 - 4  may transmit and/or receive radio-frequency signals concurrently. In general, any desired combination of transceivers  48 - 1 ,  48 - 2 ,  48 - 3 , and  48 - 4  may transmit and/or receive radio-frequency signals using the corresponding antenna  40  at a given time. In one suitable arrangement, each of transceivers  48 - 1 ,  48 - 2 ,  48 - 3 , and  48 - 4  may receive radio-frequency signals while a given one of transceivers  48 - 1 ,  48 - 2 ,  48 - 3 , and  48 - 4  transmits radio-frequency signals at a given time. 
     Amplifier circuitry such as one or more power amplifiers may be interposed on transmission lines  50  and/or formed within transceiver circuitry  42  for amplifying radio-frequency signals output by transceivers  48  prior to transmission over antennas  40 . Amplifier circuitry such as one or more low noise amplifiers may be interposed on transmission lines  50  and/or formed within transceiver circuitry  42  for amplifying radio-frequency signals received by antennas  40  prior to conveying the received signals to transceivers  48 . 
     In the example of  FIG. 3 , separate front end circuits  76  are formed on each transmission line  50 . This is merely illustrative. If desired, two or more transmission lines  50  may share the same front end circuits  76  (e.g., front end circuits  76  may be formed on the same substrate, module, or integrated circuit). 
     Each of transceivers  48  may, for example, include circuitry for converting baseband signals received from baseband processor  70  over path  72  into corresponding radio-frequency signals. For example, transceivers  48  may each include mixer circuitry for up-converting the baseband signals to radio-frequencies prior to transmission over antennas  40 . Transceivers  48  may include digital to analog converter (DAC) and/or analog to digital converter (ADC) circuitry for converting signals between digital and analog domains. Each of transceivers  48  may include circuitry for converting radio-frequency signals received from antennas  40  over paths  50  into corresponding baseband signals. For example, transceivers  48  may each include mixer circuitry for down-converting the radio-frequency signals to baseband frequencies prior to conveying the baseband signals to baseband processor  70  over paths  72 . 
     Each transceiver  48  may be formed on the same substrate, integrated circuit, or module (e.g., transceiver circuitry  42  may be a transceiver module having a substrate or integrated circuit on which each of transceivers  48  are formed) or two or more transceivers  48  may be formed on separate substrates, integrated circuits, or modules. Baseband circuitry  70  and front end circuits  76  may be formed on the same substrate, integrated circuit, or module as transceiver circuits  48  or may be formed on separate substrates, integrated circuits, or modules from transceiver circuits  48 . In another suitable arrangement, transceiver circuitry  42  may include a single transceiver  48  having four ports, each of which is coupled to a respective transmission line  50 , if desired. Each transceiver  48  may include transmitter and receiver circuitry for both transmitting and receiving radio-frequency signals. In another suitable arrangement, one or more transceivers  48  may perform only signal transmission or signal reception (e.g., one or more of circuits  48  may be a dedicated transmitter or dedicated receiver). 
     In the example of  FIG. 3 , antennas  40 - 1  and  40 - 4  may occupy a larger space (e.g., a larger area or volume within device  10 ) than antennas  40 - 2  and  40 - 3 . This may allow antennas  40 - 1  and  40 - 4  to support communications at longer wavelengths (i.e., lower frequencies) than antennas  40 - 2  and  40 - 3 . This is merely illustrative and, if desired, each of antennas  40 - 1 ,  40 - 2 ,  40 - 3 , and  40 - 4  may occupy the same volume or may occupy different volumes. Antennas  40 - 1 ,  40 - 2 ,  40 - 3 , and  40 - 4  may be configured to convey radio-frequency signals in at least one common frequency band. If desired, one or more of antennas  40 - 1 ,  40 - 2 ,  40 - 3 , and  40 - 4  may handle radio-frequency signals in at least one frequency band that is not covered by one or more of the other antennas in device  10 . 
     If desired, each antenna  40  and each transceiver  48  may handle radio-frequency communications in multiple frequency bands (e.g., multiple cellular telephone communications bands). For example, transceiver  48 - 1 , antenna  40 - 1 , transceiver  48 - 4 , and antenna  40 - 4 , may handle radio-frequency signals in a first frequency band such as a low band between 700 and 960 MHz, a second frequency band such as a midband between 1700 and 2200 MHz, and a third frequency band such as a high band between 2300 and 2700 MHz. Transceiver  48 - 2 , antenna  40 - 2 , transceiver  48 - 3 , and antenna  40 - 3  may handle radio-frequency signals in the second frequency band between 1700 and 2200 MHz and the third frequency band between 2300 and 2700 MHz (e.g., antennas  40 - 2  and  40 - 3  may not occupy sufficient volume to support signals within the low band). 
     The example of  FIG. 3  is merely illustrative. In general, antennas  40  may cover any desired frequency bands. Transceiver circuitry  42  may include other transceiver circuits such as one or more circuits  36  of  FIG. 1  coupled to one or more antennas  40 . Housing  12  may have any desired shape. Forming each of antennas  40 - 1  through  40 - 4  at different corners of housing  12  may, for example, maximize the multi-path propagation of wireless data conveyed by antennas  40  to optimize overall data throughput for wireless circuitry  34 . 
     When operating using a single antenna  40 , a single stream of wireless data may be conveyed between device  10  and external communications equipment (e.g., one or more other wireless devices such as wireless base stations, access points, cellular telephones, computers, etc.). This may impose an upper limit on the data rate (data throughput) obtainable by wireless communications circuitry  34  in communicating with the external communications equipment. As software applications and other device operations increase in complexity over time, the amount of data that needs to be conveyed between device  10  and the external communications equipment typically increases, such that a single antenna  40  may not be capable of providing sufficient data throughput for handling the desired device operations. 
     In order to increase the overall data throughput of wireless circuitry  34 , multiple antennas  40  may be operated using a multiple-input and multiple-output (MIMO) scheme. When operating using a MIMO scheme, two or more antennas  40  on device  10  may be used to convey multiple independent streams of wireless data at the same frequency. This may significantly increase the overall data throughput between device  10  and the external communications equipment relative to scenarios where only a single antenna  40  is used. In general, the greater the number of antennas  40  that are used for conveying wireless data under the MIMO scheme, the greater the overall throughput of circuitry  34 . 
     However, if care is not taken, radio-frequency signals conveyed in the same frequency band by multiple antennas  40  may interfere with each other, serving to deteriorate the overall wireless performance of circuitry  34 . Ensuring that antennas operating at the same frequency are electromagnetically isolated from each other can be particularly challenging for adjacent antennas  40  (e.g., antennas  40 - 1  and  40 - 2 , antennas  40 - 3  and  40 - 4 , etc.) and for antennas  40  that have common (shared) structures (e.g., that have resonating elements formed from adjacent or shared conductive portions of housing  12 ). 
     In order to perform wireless communications under a MIMO scheme, antennas  40  need to convey data at the same frequencies. If desired, wireless circuitry  34  may perform so-called two-stream (2×) MIMO operations (sometimes referred to herein as 2×MIMO communications or communications using a 2×MIMO scheme) in which two antennas  40  are used to convey two independent streams of radio-frequency signals at the same frequency. Wireless circuitry  34  may perform so-called four-stream (4×) MIMO operations (sometimes referred to herein as 4×MIMO communications or communications using a 4×MIMO scheme) in which four antennas  40  are used to convey four independent streams of radio-frequency signals at the same frequency. Performing 4×MIMO operations may support higher overall data throughput than 2×MIMO operations because 4×MIMO operations involve four independent wireless data streams whereas 2×MIMO operations involve only two independent wireless data streams. If desired, antennas  40 - 1 ,  40 - 2 ,  40 - 3 , and  40 - 4  may perform 2×MIMO operations in some frequency bands and may perform 4×MIMO operations in other frequency bands (e.g., depending on which bands are handled by which antennas). Antennas  40 - 1 ,  40 - 2 ,  40 - 3 , and  40 - 4  may perform 2×MIMO operations in some bands concurrently with performing 4×MIMO operations in other bands, for example. 
     As one example, antennas  40 - 1  and  40 - 4  (and the corresponding transceivers  48 - 1  and  48 - 4 ) may perform 2×MIMO operations by conveying radio-frequency signals at the same frequency in a low band between 600 MHz and 960 MHz. At the same time, antennas  40 - 1 ,  40 - 2 ,  40 - 3 , and  40 - 4  may collectively perform 4×MIMO operations by conveying radio-frequency signals at the same frequency in a midband between 1700 and 2200 MHz and/or at the same frequency in a high band between 2300 and 2700 MHz (e.g., antennas  40 - 1  and  40 - 4  may perform 2×MIMO operations in the low band concurrently with performing 4×MIMO operations in the midband and/or high band). 
     If desired, antennas  40 - 1  and  40 - 2  may include switching circuitry that is adjusted by control circuitry  28 . Control circuitry  28  may control the switching circuitry in antennas  40 - 1  and  40 - 2  to configure antenna structures in antennas  40 - 1  and  40 - 2  to form a single antenna  40 U in region  66  of device  10 . Similarly, antennas  40 - 3  and  40 - 4  may include switching circuitry that is adjusted by control circuitry  28 . Control circuitry  28  may control the switching circuitry in antennas  40 - 3  and  40 - 4  to form a single antenna  40 L (e.g., an antenna  40 L that includes antenna structures from antennas  40 - 3  and  40 - 4 ) in region  68  of device  10 . Antenna  40 U may, for example, be formed at an upper end of housing  12  and may therefore sometimes be referred to herein as upper antenna  40 U. Antenna  40 L may be formed at an opposing lower end of housing  12  and may therefore sometimes be referred to herein as lower antenna  40 L. 
     When antennas  40 - 1  and  40 - 2  are configured to form upper antenna  40 U and antennas  40 - 3  and  40 - 4  are configured to form lower antenna  40 L, wireless circuitry  34  may perform 2×MIMO operations using antennas  40 U and  40 L in one, two, or each of the low band, midband, and high band, for example. If desired, control circuitry  28  may toggle the switching circuitry over time to switch wireless circuitry  34  between a first mode in which antennas  40 - 1 ,  40 - 2 ,  40 - 3 , and  40 - 4  perform 2×MIMO operations in the low band and 4×MIMO operations in the midband and/or high band and a second mode in which antennas  40 - 1 ,  40 - 2 ,  40 - 3 , and  40 - 4  are configured to form antennas  40 U and  40 L that perform 2×MIMO operations in the low band, midband, and/or high band. 
       FIG. 4  is a diagram showing how antennas  40 - 1 ,  40 - 2 ,  40 - 3 , and  40 - 4  may cover multiple frequency bands for performing MIMO operations. As shown in  FIG. 4 , frequency is plotted on the horizontal axis. Coverage blocks  80  represent frequency bands that may be covered by antennas  40 - 1 ,  40 - 2 ,  40 - 3 , or  40 - 4  in performing MIMO operations. Transceivers  48  and antennas  40  may perform wireless communications in a first (low) band LB (e.g., a cellular telephone band between 600 and 960 MHz), a second band (midband) MB (e.g., a cellular telephone band between 1700 and 2200 MHz), and/or a third (high) band HB (e.g., a cellular telephone band between 2300 and 2700 MHz). 
     First antenna  40 - 1  and fourth antenna  40 - 4  may cover low band LB, midband MB, and high band HB (e.g., antennas  40 - 1  and  40 - 4  may each transmit and/or receive wireless signals in one, two, or each of bands LB, MB, and HB). First antenna  40 - 1  and fourth antenna  40 - 4  may perform 2×MIMO operations at the same frequency in low band LB (e.g., because both antennas  40 - 1  and  40 - 4  have sufficient volume and are configured to handle signals in low band LB). Second antenna  40 - 2  and third antenna  40 - 3  may each cover midband MB and optionally high band HB (e.g., antennas  40 - 2  and  40 - 3  may each transmit and/or receive wireless signals in one or both of bands MB and HB). First antenna  40 - 1 , second antenna  40 - 2 , third antenna  40 - 3 , and fourth antenna  40 - 4  may each perform 4×MIMO operations at the same frequency in midband MB. First antenna  40 - 1  and fourth antenna  40 - 4  may perform 2×MIMO operations at the same frequency in high band HB or, in scenarios where antennas  40 - 2  and  40 - 3  are configured to cover high band HB, antennas  40 - 1 ,  40 - 2 ,  40 - 3 , and  40 - 4  may perform 4×MIMO operations at the same frequency in high band HB. 
     Antennas  40  may contribute a corresponding amount of data throughput to wireless circuitry  34  in communicating with external communications equipment for each frequency that is covered by each antenna (e.g., each coverage block  80  may represent data throughput capability that is added to wireless circuitry  34  by the corresponding antenna). For example, each antenna  40  may contribute a data throughput of 40 MB/s for each coverage block  80 . In this scenario, antennas  40  may exhibit a data throughput of 320 MB/s if antennas  40 - 2  and  40 - 3  do not cover high band HB (e.g., with antennas  40 - 1  and  40 - 2  performing 2×MIMO operations in low band LB and high band HB and antennas  40 - 1  through  40 - 4  performing 4×MIMO operations in midband MB) and may exhibit a data throughput of 400 MB/s if antennas  40 - 2  and  40 - 3  cover high band HB (e.g., with antennas  40 - 1  through  40 - 4  performing 4×MIMO operations in both midband MB and high band HB and antennas  40 - 1  and  40 - 4  performing 2×MIMO operations in low band LB). 
     If desired, wireless communications circuitry  34  may convey wireless data with multiple antennas on one or more external devices (e.g., multiple wireless base stations) in a scheme sometimes referred to as carrier aggregation. When operating using a carrier aggregation scheme, the same antenna  40  may convey radio-frequency signals with multiple antennas (e.g., antennas on different wireless base stations) at different respective frequencies (sometimes referred to herein as carrier frequencies, channels, carrier channels, or carriers). For example, antenna  40 - 1  may receive radio-frequency signals from a first wireless base station at a first frequency (e.g., a frequency in low band LB), from a second wireless base station at a second frequency (e.g., a frequency in midband MB), and a from a third base station at a third frequency (e.g., a frequency in high band HB). The received signals at different frequencies may be simultaneously processed (e.g., by transceiver  48 - 1 ) to increase the communications bandwidth of transceiver  48 - 1 , thereby increasing the data rate of transceiver  48 - 1 . If desired, antenna  40 - 1  may convey radio-frequency signals with more than three base stations (e.g., using more than one frequency in low band LB, midband MB, and/or high band HB). Similarly, antenna  40 - 4  may perform carrier aggregation at two, three, or more than three frequencies within bands LB, MB, and/or HB, and antennas  40 - 2  and  40 - 3  may perform carrier aggregation at two or more frequencies within bands MB and/or HB. This may serve to further increase the overall data throughput of wireless circuitry  34  relative to scenarios where no carrier aggregation is performed. For example, the data throughput of circuitry  34  may increase for each carrier frequency (e.g., each carrier frequency within bands LB, MB, and HB) that is used (e.g., for each wireless base station that communicates with each of antennas  40 - 1 ,  40 - 2 ,  40 - 3 , and  40 - 4 ). 
     By performing communications using both a MIMO scheme and a carrier aggregation scheme, the data throughput of wireless circuitry  34  may be even greater than in scenarios where either a MIMO scheme or a carrier aggregation scheme is used. The data throughput of circuitry  34  may, for example, increase for each carrier frequency that is used by antennas  40  (e.g., each carrier frequency may contribute 40 MB/s or some other throughput to the total throughput of circuitry  34 ). As one example, antennas  40 - 1  and  40 - 4  may perform carrier aggregation across three frequencies within each of bands LB, MB, and HB and antennas  40 - 3  and  40 - 4  may perform carrier aggregation across three frequencies within each of bands MB and HB. At the same time, antennas  40 - 1  and  40 - 4  may perform 2×MIMO operations in low band LB using and antennas  40 - 1 ,  40 - 2 ,  40 - 3 , and  40 - 4  may perform 4×MIMO operations in one of bands MB and HB. In this scenario, with an exemplary throughput of 40 MB/s per carrier frequency, wireless circuitry  34  may exhibit a throughput of approximately 960 MB/s. If 4×MIMO operations are performed in both bands MB and HB by antennas  40 - 1 ,  40 - 2 ,  40 - 3 , and  40 - 4 , circuitry  34  may exhibit an even greater throughput of approximately 1200 MB/s. In other words, the data throughput of wireless circuitry  34  may be increased from the 40 MB/s associated with conveying signals at a single frequency with a single antenna to approximately 1 GB/s by performing communications using MIMO and carrier aggregation schemes using four antennas  40 - 1 ,  40 - 2 ,  40 - 3 , and  40 - 4 . These examples are merely illustrative and, if desired, carrier aggregation may be performed in fewer than three carriers per band, may be performed across different bands, or may be omitted for one or more of antennas  40 - 1  through  40 - 4 . If desired, pairs of antennas  40 - 1 ,  40 - 2 ,  40 - 3 , and  40 - 4  may perform 2×MIMO operations in bands MB or HB or antennas  40 - 1  through  40 - 4  may not perform MIMO operations in one of bands LB, MB, and HB (e.g., antennas  40 - 1 ,  40 - 2 ,  40 - 3 , and  40 - 4  need not utilize their full throughput capacity if desired). 
     When antennas  40 - 1  and  40 - 2  are configured to form antenna  40 U and antennas  40 - 3  and  40 - 4  are configured to form antenna  40 L, antennas  40 U and  40 L may each perform 2×MIMO operations in none, one, two, or all three of bands LB, MB, and HB. If desired, antennas  40 U and  40 L may perform communications using a carrier aggregation scheme using one more carrier frequencies in bands LB, MB, and/or HB. Control circuitry  28  may toggle antennas  40 - 1 ,  40 - 2 ,  40 - 3 , and  40 - 4  between a first mode in which antennas  40 - 1 ,  40 - 2 ,  40 - 3 , and  40 - 4  perform 2×MIMO operations in some bands and 4×MIMO operations in other bands and a second mode in which antennas  40 U and  40 L perform 2×MIMO operations in one or more bands over time to further increase the overall data throughput of circuitry  34  if desired. Control circuitry  28  may also switch between the first and second mode to meet desired antenna efficiency or data throughput requirements. The example of  FIG. 4  is merely illustrative. If desired, antennas  40  may cover any desired number of frequency bands at any desired frequencies. More than four antennas  40  or fewer than four antennas  40  may perform MIMO and/or carrier aggregation operations if desired. 
       FIG. 5  is a perspective view of device  10  having multiple antennas for performing MIMO communications. As shown in  FIG. 5 , device  10  may, if desired, have a display such as display  92 . Display  92  may be mounted on the front face of device  10 . Display  92  may be a touch screen that incorporates capacitive touch electrodes or may be insensitive to touch. 
     Display  92  may include pixels formed from light-emitting diodes (LEDs), organic LEDs (OLEDs), plasma cells, electrowetting pixels, electrophoretic pixels, liquid crystal display (LCD) components, or other suitable pixel structures. A display cover layer such as a layer of clear glass or plastic may cover the surface of display  92  or the outermost layer of display  92  may be formed from a color filter layer, thin-film transistor layer, or other display layer. Buttons such as button  86  may pass through openings in the cover layer or may be formed under the cover layer if desired. The cover layer may include openings such as an opening for speaker port  90  if desired. 
     Housing  12  may include peripheral housing structures such as structures  88 . Structures  88  may run around the periphery of device  10  and display  92 . In configurations in which device  10  and display  92  have a rectangular shape with four edges, structures  88  may be implemented using peripheral housing structures that have a rectangular ring shape with four corresponding edges (as an example). Peripheral structures  88  or part of peripheral structures  88  may serve as a bezel for display  92  (e.g., a cosmetic trim that surrounds all four sides of display  92  and/or that helps hold display  92  to device  10 ). Peripheral structures  88  may also, if desired, form sidewall structures for device  10  (e.g., by forming a metal band with vertical sidewalls, curved sidewalls, etc.). 
     Peripheral housing structures  88  may be formed of a conductive material such as metal and may therefore sometimes be referred to as peripheral conductive housing structures, conductive housing structures, peripheral metal structures, or a peripheral conductive housing member (as examples). Peripheral housing structures  88  may be formed from a metal such as stainless steel, aluminum, or other suitable materials. One, two, or more than two separate structures may be used in forming peripheral housing structures  88 . 
     It is not necessary for peripheral housing structures  88  to have a uniform cross-section. For example, the top portion of peripheral housing structures  88  may, if desired, have an inwardly protruding lip that helps hold display  92  in place. The bottom portion of peripheral housing structures  88  may also have an enlarged lip (e.g., in the plane of the rear surface of device  10 ). Peripheral housing structures  88  may have substantially straight vertical sidewalls, may have sidewalls that are curved, or may have other suitable shapes. In some configurations (e.g., when peripheral housing structures  88  serve as a bezel for display  92 ), peripheral housing structures  88  may run around the lip of housing  12  (i.e., peripheral housing structures  88  may cover only the edge of housing  12  that surrounds display  92  and not the rest of the sidewalls of housing  12 ). 
     If desired, housing  12  may have a conductive rear surface. For example, housing  12  may be formed from a metal such as stainless steel or aluminum. The rear surface of housing  12  may lie in a plane that is parallel to display  92 . In configurations for device  10  in which the rear surface of housing  12  is formed from metal, it may be desirable to form parts of peripheral conductive housing structures  88  as integral portions of the housing structures forming the rear surface of housing  12 . For example, a rear housing wall of device  10  may be formed from a planar metal structure and portions of peripheral housing structures  88  on the sides of housing  12  may be formed as vertically extending integral metal portions of the planar metal structure. Housing structures such as these may, if desired, be machined from a block of metal and/or may include multiple metal pieces that are assembled together to form housing  12 . The planar rear wall of housing  12  may have one or more, two or more, or three or more portions. Peripheral conductive housing structures  88  and/or the conductive rear wall of housing  12  may form one or more exterior surfaces of device  10  (e.g., surfaces that are visible to a user of device  10 ) and/or may be implemented using internal structures that do not form exterior surfaces of device  10  (e.g., conductive housing structures that are not visible to a user of device  10  such as conductive structures that are covered with layers of dielectric such as glass, ceramic, plastic, or other structures that form the exterior surfaces of device  10  and serve to hide structures  88  from view of the user). 
     Display  92  may have an array of pixels that form an active area that displays images for a user of device  10 . An inactive border region may run along one or more of the peripheral edges of active area if desired. Display  92  may include conductive structures such as an array of capacitive electrodes for a touch sensor, conductive lines for addressing pixels, driver circuits, etc. 
     Housing  12  may include internal conductive structures such as metal frame members and a planar conductive housing member (sometimes referred to as a midplate) that spans the walls of housing  12  (i.e., a substantially rectangular sheet formed from one or more parts that is welded or otherwise connected between opposing sides of member  88  or other sheet metal parts that provide housing  12  with structural support). Device  10  may also include conductive structures such as printed circuit boards, components mounted on printed circuit boards, and other internal conductive structures. These conductive structures, which may be used in forming a ground plane in device  10 , may be located in the center of housing  12 , may extend under inactive or active areas display  92 , etc. 
     In regions  66  and  68 , openings may be formed within the conductive structures of device  10  (e.g., between peripheral conductive housing structures  88  and opposing conductive ground structures such as conductive housing midplate or rear housing wall structures, a printed circuit board, and conductive electrical components in display  92  and device  10 ). These openings, which may sometimes be referred to as gaps, may be filled with air, plastic, and other dielectrics and may be used in forming slot antenna resonating elements for one or more antennas in device  10 . 
     Conductive housing structures and other conductive structures in device  10  such as a midplate, traces on a printed circuit board, display  92 , and conductive electronic components may serve as a ground plane for the antennas in device  10 . The openings in regions  66  and  68  may serve as slots in open or closed slot antennas, may serve as a central dielectric region that is surrounded by a conductive path of materials in a loop antenna, may serve as a space that separates an antenna resonating element such as a strip antenna resonating element or an inverted-F antenna resonating element from the ground plane, may contribute to the performance of a parasitic antenna resonating element, or may otherwise serve as part of antenna structures formed in regions  66  and  68 . If desired, the ground plane that is under display  92  and/or other metal structures in device  10  may have portions that extend into parts of the ends of device  10  (e.g., the ground may extend towards the dielectric-filled openings in regions  66  and  68 ), thereby narrowing the slots in regions  66  and  68 . In configurations for device  10  with narrow U-shaped openings or other openings that run along the edges of device  10 , the ground plane of device  10  can be enlarged to accommodate additional electrical components (integrated circuits, sensors, etc.) 
     Antennas  40  in device  10  may be located at opposing first and second ends of an elongated device housing  12  (e.g., at ends  66  and  68  of device  10  as shown in  FIGS. 3 and 5 ), along one or more edges of a device housing, in the center of a device housing, in other suitable locations, or in one or more of these locations. The arrangement of  FIG. 5  is merely illustrative. 
     Portions of peripheral housing structures  88  may be provided with peripheral gap structures. For example, peripheral conductive housing structures  88  may be provided with one or more gaps such as gaps  84 , as shown in  FIG. 5 . The gaps in peripheral housing structures  88  may be filled with dielectric such as polymer, ceramic, glass, air, other dielectric materials, or combinations of these materials. Gaps  84  may divide peripheral housing structures  88  into one or more peripheral conductive segments. There may be, for example, two peripheral conductive segments in peripheral housing structures  88  (e.g., in an arrangement with two of gaps  84 ), three peripheral conductive segments (e.g., in an arrangement with three of gaps  84 ), four peripheral conductive segments (e.g., in an arrangement with four gaps  84 , etc.). The segments of peripheral conductive housing structures  88  that are formed in this way may form parts of antennas  40  in device  10 . 
     If desired, openings in housing  12  such as grooves that extend partway or completely through housing  12  may extend across the width of the rear wall of housing  12  and may penetrate through the rear wall of housing  12  to divide the rear wall into different portions. These grooves may also extend into peripheral housing structures  88  and may form antenna slots, gaps  84 , and other structures in device  10 . Polymer or other dielectric may fill these grooves and other housing openings. In some situations, housing openings that form antenna slots and other structure may be filled with a dielectric such as air. 
     In a typical scenario, device  10  may have upper and lower antennas (as an example). An upper antenna such as antennas  40 - 1 ,  40 - 2 , and  40 U of  FIG. 3  may, for example, be formed at the upper end of device  10  in region  66 . A lower antenna may such as antennas  40 - 3 ,  40 - 4 , and  40 L of  FIG. 3  may, for example, be formed at the lower end of device  10  in region  68 . The antennas may be used separately to cover identical communications bands, overlapping communications bands, or separate communications bands. For example, the antennas may be used to implement a MIMO antenna scheme (e.g., a 2×MIMO scheme and/or a 4×MIMO scheme) in which two or more of the antennas cover the same frequencies. 
     When forming antennas such as antennas  40 - 1 ,  40 - 2 ,  40 - 3 , and  40 - 4  for communicating using a MIMO scheme, care should be taken to ensure that antennas operating at the same frequencies are sufficiently isolated from each other. For example, in scenarios where portions of housing  12  are used to form portions of antennas  40 - 1 ,  40 - 2 ,  40 - 3 , and  40 - 4 , if care is not taken, it can be difficult to ensure that antennas operating at the same frequencies have satisfactory electromagnetic isolation from each other. Insufficient isolation may decrease the overall antenna efficiency for one or more antennas  40 , may reduce the overall data throughput, may introduce errors into transmitted and received data, and may result in a wireless connection with external communications equipment being dropped, as examples. 
     Antennas  40  in device  10  may be formed using any desired antenna type. For example, an antenna  40  may include an antenna with a resonating element that is formed from loop antenna structures, patch antenna structures, inverted-F antenna structures, slot antenna structures, planar inverted-F antenna structures, helical antenna structures, monopole antenna structures, dipole antenna structures, hybrids of these designs, etc.  FIG. 6  is a diagram of illustrative inverted-F antenna structures that may be used in implementing an antenna  40  for device  10 . 
     As shown in  FIG. 6 , antenna  40  may include inverted-F antenna resonating element  102  and antenna ground (ground plane)  100 . Antenna resonating element  102  may have a main resonating element arm such as arm  104 . The length of arm  104  and/or portions of arm  104  may be selected so that antenna  40  resonates at desired operating frequencies. For example, the length of arm  104  may be a quarter of a wavelength at a desired operating frequency for antenna  40 . Antenna  40  may also exhibit resonances at harmonic frequencies. 
     Main resonating element arm  104  may be coupled to ground  100  by return path  106 . An inductor or other component may be interposed in path  106  and/or tunable components  60  ( FIG. 2 ) may be interposed in path  106 . If desired, tunable components  60  may be coupled in parallel with path  106  between arm  104  and ground  100 . Additional return paths  106  may be coupled between arm  108  and ground  100  if desired. 
     Antenna  40  may be fed using one or more antenna feeds. For example, antenna  40  may be fed using antenna feed  55 . Antenna feed  55  may include positive antenna feed terminal  56  and ground antenna feed terminal  58  and may run in parallel to return path  106  between arm  104  and ground  100 . If desired, inverted-F antennas such as illustrative antenna  40  of  FIG. 6  may have more than one resonating arm branch (e.g., to create multiple frequency resonances to support operations in multiple communications bands) or may have other antenna structures (e.g., parasitic antenna resonating elements, tunable components to support antenna tuning, etc.). For example, arm  104  may have left and right branches that extend outwardly from feed  55  and return path  106 . Multiple feeds may be used to feed antennas such as antenna  40 . 
     Antenna  40  may be a hybrid antenna that includes one or more slot antenna resonating elements. As shown in  FIG. 7 , for example, antenna  40  may be based on a slot antenna configuration having an opening such as slot  108  that is formed within conductive structures such as antenna ground  100 . Slot  108  may be filled with air, plastic, and/or other dielectric. The shape of slot  108  may be straight or may have one or more bends (i.e., slot  108  may have an elongated shape following a meandering path). Feed terminals  56  and  58  may, for example, be located on opposing sides of slot  108  (e.g., on opposing long sides). Slot-based antenna resonating elements such as slot antenna resonating element  108  of  FIG. 7  may give rise to an antenna resonance at frequencies in which the wavelength of the antenna signals is equal to the perimeter of the slot. In narrow slots, the resonant frequency of a slot antenna resonating element is associated with signal frequencies at which the slot length is equal to a half of a wavelength. 
     Slot antenna frequency response can be tuned using one or more tuning components (e.g., components  60  of  FIG. 2 ). These components may have terminals that are coupled to opposing sides of the slot (i.e., the tunable components may bridge the slot). If desired, tunable components may have terminals that are coupled to respective locations along the length of one of the sides of slot  108 . Combinations of these arrangements may also be used. If desired, antenna  40  may be a hybrid slot-inverted-F antenna that includes resonating elements of the type shown in both  FIG. 6  and  FIG. 7  (e.g., having resonances given by both a resonating element arm such as arm  104  of  FIG. 6  and a slot such as slot  108  of  FIG. 7 ). 
     While the examples of  FIGS. 6 and 7  show only a single antenna  40 , multiple antennas  40  may be formed from these structures within device  10 .  FIG. 8  is a schematic diagram of a pair of adjacent antennas such as antennas  40 - 1  and  40 - 2  of  FIG. 3  that may be used for performing MIMO operations. 
     As shown in  FIG. 8 , antennas  40 - 1  and  40 - 2  may include inverted-F antenna structures (e.g., as shown in  FIG. 6 ). Antenna  40 - 1  may include a resonating element arm  104 - 1  coupled to ground  100  by short path  106 - 1 . Antenna  40 - 1  may be fed using a first antenna feed  55 - 1 . Antenna feed  55 - 1  may have a first feed terminal  56 - 1  coupled to resonating element arm  104 - 1  and a second feed terminal  58 - 1  coupled to ground  100 . Antenna  40 - 2  may include a resonating element arm  104 - 2  coupled to ground  100  by short path  106 - 2 . Antenna  40 - 2  may be fed using a second antenna feed  55 - 2  having a first feed terminal  56 - 2  coupled to resonating element arm  104 - 2  and a second feed terminal  58 - 2  coupled to ground  100 . 
     In the example of  FIG. 8 , return path  106 - 1  of antenna  40 - 1  may be interposed between the location of feed  55 - 1  and return path  106 - 2  of antenna  40 - 2 . Similarly, return path  106 - 2  of antenna  40 - 2  may be interposed between return path  106 - 1  of antenna  40 - 1  and feed  55 - 2 . Radio-frequency signals may be conveyed to and from antenna  40 - 1  over feed  55 - 1  and may be conveyed to and from antenna  40 - 2  over feed  55 - 2 . Corresponding antenna currents for antenna  40 - 1  may flow through main resonating element arm  104 - 1  of antenna  40 - 1  and are shorted to ground  100  over path  106 - 1 . Similarly, antenna currents for antenna  40 - 2  may flow through main resonating element arm  104 - 2  of antenna  40 - 2  and are shorted to ground  100  over path  106 - 2 . 
     When performing MIMO operations (e.g., 4×MIMO operations) within the same frequency band (e.g., within midband MB or high band HB), if care is not taken, antenna currents from antenna  40 - 1  can electromagnetically interact with antenna currents from antenna  40 - 2 , thereby deteriorating radio-frequency performance by both antennas. However, by forming short path  106 - 1  adjacent to antenna  106 - 2 , the magnetic fields of antenna currents from both antennas  40 - 1  and  40 - 2  may cancel out, serving to effectively isolate antenna  40 - 1  from  40 - 2 . While arms  104 - 1  and  104 - 2  are shown as being electrically separated in the electrical schematic of  FIG. 8  (e.g., due to the electromagnetic isolation between arms  104 - 1  and  104 - 2 ), in one suitable arrangement, arms  104 - 1  and  104 - 2  may be formed from a single continuous conductor (e.g., a single housing wall  88  of device  10 ) and/or short paths  106 - 1  and  106 - 2  may be formed from a single continuous conductor between arms  104 - 1  and  104 - 2  and ground  100  (e.g., without affecting the isolation between antennas  40 - 1  and  40 - 2 ). While the example of  FIG. 8  describes adjacent antennas  40 - 1  and  40 - 2 , similar antenna structures may be used in forming antennas  40 - 2  and  40 - 3  of  FIG. 3  (e.g., where antenna  40 - 4  replaces antenna  40 - 1  and antenna  40 - 3  replaces antenna  40 - 2  in  FIG. 8 ) 
     If desired, an opening between arms  104 - 1  and  104 - 2  and ground  100  may contribute a slot antenna resonance to antennas  40 - 1  and  40 - 2  (e.g., antennas  40 - 1  and  40 - 2  may be hybrid slot-inverted-F antennas including resonating elements of the types shown in both  FIGS. 6 and 7 ).  FIG. 9  is a diagram showing how antennas  40 - 1  and  40 - 2  may include both slot and inverted-F antenna structures and may be formed from portions of device housing  12 . 
     As shown in  FIG. 9 , resonating element arm  104 - 1  of antenna  40 - 1  and resonating element arm  104 - 2  of antenna  40 - 2  may be formed from a segment of peripheral conductive housing structures  88 . The segment of peripheral conductive housing structures  88  forming resonating element arms  104 - 1  and  104 - 2  may extend between a first dielectric gap  84 - 1  at a first side of device  10  and a second dielectric gap  84 - 2  at an opposing second side of device  10 . For example, the segment of structures  88  may include a peripheral conductive wall (e.g., sidewall) of device  10 . Resonating element arm  104 - 1  may be formed from a first portion of the peripheral conductive wall and resonating element arm  104 - 2  may be formed from a second portion of the peripheral conductive wall that extends from an end of the first portion (e.g., the first and second portions may be directly connected and formed from the same conductive sidewall of device  10 ). 
     The segment of peripheral conductive housing structures  88  (e.g., resonating element arms  104 - 1  and  104 - 2 ) may be separated from ground  100  by slot  108 . Slot  108  may be formed from an elongated opening extending from gap  84 - 1  to gap  84 - 2  (e.g., the ends of slot  108 , which may sometimes be referred to as open ends, may be formed by gaps  84 - 1  and  84 - 2 ). Slot  108  may have an elongated shape having any suitable length (e.g., about 4-20 cm, more than 2 cm, more than 4 cm, more than 8 cm, more than 12 cm, less than 25 cm, less than 10 cm, etc.) and any suitable width (e.g., approximately 2 mm, less than 2 mm, less than 3 mm, less than 4 mm, 1-3 mm, etc.). Slot  108  may be filled with dielectric such as air or plastic. For example, plastic may be inserted into portions of slot  108  and this plastic may be flush with the outside of housing  12 . Ground  100  may be formed from a conductive layer within device  10 , a midplate member for device  10 , a rear wall of housing  12 , portions of peripheral conductive structures  88 , and/or any other desired conductive structures within device  10 . 
     Antenna feed  55 - 1  for antenna  40 - 1  may include a first feed terminal  56 - 1  coupled to peripheral structures  88  and a second feed terminal  58 - 1  coupled to ground  100 . Antenna feed  55 - 2  may include a first feed terminal  56 - 2  coupled to peripheral structures  88  and a second feed terminal  58 - 2  coupled to ground  100 . Feed  55 - 1  may be fed by transceiver circuitry  48 - 1  using transmission line  50 - 1  ( FIG. 3 ) and feed  55 - 2  may be fed by transceiver circuitry  48 - 2  using transmission line  50 - 2 , for example. 
     Return path  106 - 1  for antenna  40 - 1  may be coupled between peripheral structures  88  and ground  100 . Return path  106 - 2  for antenna  40 - 2  may be coupled between peripheral structures  88  and ground  100  adjacent to return path  106 - 1 . In one suitable arrangement, return paths  106 - 1  and  106 - 2  may be formed from the same conductive structure (e.g., an elongated conductive strip, a conductive wire, conductive spring structures, a metal trace on a rigid or flexible printed circuit, a metal screw or fastener, etc.) coupled between segment  88  and ground  100 . 
     Portions of slot  108  may contribute slot antenna resonances to antennas  40 - 1  and/or  40 - 2 . For example, a portion of slot  108  between arm  104 - 1  and ground  100  (e.g., between feed  55 - 1  and gap  84 - 1 ) may contribute a resonance in high band HB for antenna  40 - 1  and a portion of slot  108  between arm  104 - 2  and ground  100  may contribute a high band resonance HB for antenna  40 - 2 . 
     In the example of  FIG. 9 , antenna  40 - 1  occupies a greater volume than antenna  40 - 2  and arm  104 - 1  is longer than arm  104 - 2 . The length of antenna resonating element arms  104  may be selected so that antennas  40 - 1  and  40 - 2  resonate at desired frequencies. For example, the resonance of antenna  40 - 1  in midband MB may be associated with the distance along peripheral conductive structures  88  between feed terminal  56 - 1  and gap  14 - 1 . The resonance of antenna  40 - 1  in low band LB may be associated with the distance along peripheral conductive structures  88  between feed terminal  56 - 1  and return path  106 - 1 . Arm  104 - 2  of antenna  40 - 2  may be too short to support a frequency in low band LB. However, the resonance of antenna  40 - 2  in midband MB may be associated with the distance along peripheral conductive structures  88  between return path  106 - 2  and gap  84 - 2 , for example. 
     The example of  FIG. 9  is merely illustrative. If desired, adjustable components (e.g., tuning components  60  of  FIG. 2 ) such as switches, capacitors, resistors, and/or inductors may be coupled between different locations along peripheral structures  88  and ground  100 . The adjustable components may, for example, tune the midband and/or low band resonance of antennas  40 - 1  and  40 - 2  to different desired frequencies. Peripheral conductive structures  88  may have any desired shape following the periphery of device  10 . 
     When configured in this way, both antennas  40 - 1  and  40 - 2  may support communications in midband MB and high band HB whereas antenna  40 - 1  also supports communications in low band LB. Antennas  40 - 1  and  40 - 2  may therefore both perform communications using a MIMO scheme in midband MB and/or high band HB (e.g., a 2×MIMO scheme in midband MB and/or high band HB using only antennas  40 - 1  and  40 - 2  or a 4×MIMO scheme in midband MB and/or high band HB together with antennas  40 - 3  and  40 - 4  of  FIG. 3 ). When performing communications in this way at the same frequency, antenna currents in antenna  40 - 1  may be susceptible to interference with antenna currents  40 - 2 . However, the arrangement of antenna structures within antennas  40 - 1  and  40 - 2  may configure antennas  40 - 1  and  40 - 2  to be sufficiently isolated from one another, even though resonating element arms  104 - 1  and  104 - 2  are both formed from the same continuous piece of conductive material (i.e., peripheral structures  88 ). At the same time, antenna  40 - 1  may, if desired, perform 2×MIMO operations in low band LB with antenna  40 - 4  ( FIG. 3 ). 
       FIG. 10  is a diagram of return paths  106 - 1  and  106 - 2  (e.g., within dashed region  105  of  FIG. 9 ) showing how antennas  40 - 1  and  40 - 2  may be sufficiently isolated despite having resonating element arms  104 - 1  and  104 - 2  formed from a continuous conductor. As shown in  FIG. 10 , radio-frequency antenna currents I1 may flow through ground plane  100 , over return path  106 - 1 , and over arm  104 - 1  between the feed terminals of antenna  40 - 1 . Similarly, radio-frequency antenna currents I2 may flow through ground plane  100 , over return path  106 - 2 , and over arm  104 - 2  between the feed terminals of antenna  40 - 2 . 
     Antenna currents I1 for antenna  40 - 1  may produce a magnetic field B1 that points into the page of  FIG. 10  at the exterior of peripheral housing structures  88  and out of the page between structures  88  and ground plane  100  (e.g., at the interior of device  10 ). At the same time, antenna currents I2 for antenna  40 - 2  may produce a magnetic field B2 that points out of the page at the exterior of peripheral housing structures  88  and into the page between structures  88  and ground plane  100 . In this way, magnetic field B1 outside of structures  88  may cancel out with magnetic field B2 outside of structures  88  and magnetic field B1 between structures  88  and ground  100  may cancel out with magnetic field B2 between structures  88  and ground  100 . This may result in the magnetic field produced by current I1 canceling out with the magnetic field produced by current I2 at the location of return paths  106 - 1  and  106 - 2 , thereby serving to electromagnetically isolate antenna  40 - 1  from antenna  40 - 2 , even though arms  104 - 1  and  104 - 2  are both formed from a continuous structure  88 . Forming both arms  104 - 1  and  104 - 2  from a continuous conductor (e.g., without any gaps such as gaps  84 ) may, for example, enhance the aesthetic appearance of device  10  to a user and/or may enhance the structural (mechanical) integrity of device  10  relative to scenarios where gaps are used to isolate antenna  40 - 1  and  40 - 2 . In addition, as shown in  FIG. 10 , return paths  106 - 1  and  106 - 2  may both be formed using the same conductive structure  107  (e.g., a conductive trace on a substrate, a metal wire, a conductive pin, a solder joint, weld, etc.) extending between peripheral structures  88  and ground  100  without affecting the isolation between antennas  40 - 1  and  40 - 2 . 
     While the example of  FIGS. 8-10  describes adjacent antennas  40 - 1  and  40 - 2 , similar antenna structures may be used in forming antennas  40 - 2  and  40 - 3  at lower end  68  of device  10  as shown in  FIG. 3  (e.g., where antenna  40 - 4  replaces antenna  40 - 1  and antenna  40 - 3  replaces antenna  40 - 2  in  FIG. 10 ). While the arrangement of  FIGS. 8-10  may provide a satisfactory amount of isolation between antennas  40 - 1  and  40 - 2 , in another suitable arrangement, antennas  40 - 1  and  40 - 2  may be further isolated by mechanically separating arm  104 - 1  of antenna  40 - 1  from arm  104 - 2  of antenna  40 - 2 . 
       FIG. 11  is a schematic diagram of a pair of adjacent antennas such as antennas  40 - 1  and  40 - 2  of  FIG. 3  having mechanically separated (isolated) resonating elements. As shown in  FIG. 11 , resonating element arm  104 - 1  of antenna  40 - 1  may be mechanically separated from resonating element arm  104 - 2  of antenna  40 - 2  by gap  109 . Gap  109  may, for example, be formed from a gap  84  in peripheral conductive structures  88 . Feed  55 - 1  of antenna  40 - 1  may be interposed between gap  109  and return path  106 - 1 . Return path  106 - 1  may be coupled to resonating element arm  104 - 1  at a location that is interposed between the end of arm  104 - 1  opposing gap  109  and terminal  56 - 1  of feed  55 - 1 . 
     Return path  106 - 2  of antenna  40 - 2  may be coupled between an end of arm  104 - 2  that is adjacent to gap  109  and ground  100 . This is merely illustrative. If desired, return path  106 - 2  may be coupled between ground  100  and any desired location on arm  104 - 2  that is between feed terminal  56 - 2  and gap  109 . Feed  55 - 2  of antenna  40 - 2  may be interposed between return path  106 - 2  and the end of arm  104 - 2  that opposes gap  109 . When configured in this way, gap  109  may both mechanically separate arm  104 - 1  from arm  104 - 2  and serve to electromagnetically isolate antenna  40 - 1  from antenna  40 - 2  (e.g., by preventing the electromagnetic fields from antenna currents handled by feed  55 - 1  from significantly interacting with the electromagnetic fields from antenna currents handled by feed  55 - 2 ). 
       FIG. 12  is a diagram showing how antennas  40 - 1  and  40 - 2  may be formed from slot and inverted-F antenna structures and from mechanically separated portions of device housing  12 . Antennas  40 - 1  and  40 - 2  may be hybrid slot-inverted-F antennas that include resonating elements of the type shown in both  FIGS. 6 and 7 . 
     As shown in  FIG. 12 , an opening  84  ( FIG. 5 ) such as opening  84 - 3  may separate peripheral conductive housing structures  88  into a first segment  88 - 1  and a second segment  88 - 1 . Resonating element arm  104 - 1  of antenna  40 - 1  may be formed from segment  88 - 1 . Resonating element arm  104 - 2  of antenna  40 - 2  may be formed from segment  88 - 2 . 
     Segment  88 - 1  may extend between gap  84 - 3  and gap  84 - 1 . Segment  88 - 2  may extend between gap  84 - 3  and gap  84 - 2 . Feed  55 - 1  of antenna  40 - 1  may be coupled across slot  108  between segment  88 - 1  and ground  100  whereas feed  55 - 2  of antenna  40 - 2  is coupled across slot  108  between segment  88 - 2  and ground  100 . A portion of slot  108  between segment  88 - 1  and ground  100  may contribute a slot antenna resonance such as a resonance in high band HB for antenna  40 - 1 . A portion of slot  108  between segment  88 - 2  and ground  100  may contribute a slot antenna resonance such as a resonance in high band HB for antenna  40 - 2 . 
     Return paths such as paths  106 - 1  and  106 - 2  of  FIG. 11  may be formed by fixed conductive paths bridging slot  108  or by adjustable components such as components  110  and  114  (e.g., adjustable components  60  of  FIG. 2 ) bridging slot  108 . Adjustable components  110  and  114  may both be coupled between segment  88 - 1  and ground  100  across slot  108  and may form adjustable return paths (e.g., return path  106 - 1  of  FIG. 11 ) for antenna  40 - 1 . Adjustable components  114  and  110  may sometimes be referred to herein as tuning components, tunable components, tunable circuits, or adjustable tuning components. Return path  106 - 2  may be coupled between segment  88 - 2  and ground  100 . Return path  106 - 2  may include adjustable components such as switches or may be free from adjustable components. Antenna feed terminal  56 - 2  of antenna  40 - 2  may be coupled to segment  88 - 2  at a location that is interposed between return path  106 - 2  and gap  84 - 2 . 
     Adjustable component  114  may bridge slot  108  at a first location along slot  108 . For example, adjustable component  114  may be coupled to segment  88 - 1  at a location that is interposed between feed terminal  56 - 1  and gap  84 - 1 . Adjustable component  110  may bridge slot  108  at a second location along slot  108 . For example, adjustable component  110  may be coupled to segment  88 - 1  at one or more locations that are interposed between gap  84 - 3  and feed terminal  56 - 1 . 
     Components  110  and  114  may include switches (SW) coupled to fixed components such as inductors for providing adjustable amounts of inductance or an open circuit between ground  100  and segment  88 - 1 . The switches in component  114  may include, for example, a single-pole double-throw (SP2T) switch and two inductors. The switches in component  110  may include, for example, a single-pole four-throw (SP4T) switch coupled to four inductors. This example is merely illustrative and, in general, components  110  and  114  may include other components such as adjustable return path switches, switches coupled to capacitors, or any other desired components. Components  110  and  114  may include any desired number of inductors. If desired, components  110  and/or  114  may include paths without any inductors that may be selectively coupled between segment  88 - 1  and ground  100 . Components  110  and  114  (e.g., the states of the corresponding switches) may be controlled by control circuitry  28  ( FIG. 1 ), for example. Components  110  and  114  may, for example, form return paths for antenna  40 - 1  (e.g., one or more return paths  106 - 1  as shown in  FIG. 11 ). 
     The length of antenna resonating element arms  104  may be selected so that antennas  40 - 1  and  40 - 2  resonate at desired frequencies. For example, the resonance of antenna  40 - 1  in midband MB may be associated with the distance along segment  88 - 1  between component  114  and gap  84 - 1 . The resonance of antenna  40 - 1  in low band LB may be associated with the distance along segment  88 - 1  between component  114  and gap  84 - 3 , for example. The resonance of antenna  40 - 2  in midband MB may be associated with the distance along segment  88 - 2  between return path  106 - 2  and gap  84 - 2 , for example. Adjustable components such as components  60  of  FIG. 2  may bridge slot  108  between segment  88 - 2  and ground  100  if desired. 
     Control circuitry  28  ( FIG. 1 ) may adjust components  114  and  110  to tune the frequency response of antenna  40 - 1  if desired. For example, control circuitry  28  may adjust component  114  (e.g., by switching one of the corresponding inductors into use) to tune the resonant frequency of antenna  40 - 1  within midband MB. Control circuitry  28  may adjust component  110  to tune the resonant frequency of antenna  40 - 1  within low band LB. 
     Antennas  40 - 1  and  40 - 2  may perform communications using a MIMO scheme in midband MB and/or high band HB. The mechanical separation between arms  104 - 1  and  104 - 2  provided by gap  84 - 3  may serve to isolate antenna  40 - 1  from antenna  40 - 2  when antennas  40  operate at the same frequency (e.g., while performing communications using a MIMO scheme). While the example of  FIGS. 11 and 12  describe adjacent antennas  40 - 1  and  40 - 2 , similar antenna structures may be used in forming antennas  40 - 2  and  40 - 3  at lower end  68  of device  10  as shown in  FIG. 3  (e.g., where antenna  40 - 4  replaces antenna  40 - 1  and antenna  40 - 3  replaces antenna  40 - 2  in  FIGS. 11 and 12 ). 
     Antennas  40 - 1  and  40 - 2  as shown in  FIG. 12  may, if desired, perform communications using a 2×MIMO scheme in midband MB and/or high band HB (e.g., without MIMO contributions from antennas  40 - 3  and  40 - 4 ) or a 4×MIMO scheme with antennas  40 - 3  and  40 - 4  in midband MB and/or high band HB (e.g., as shown in  FIG. 4 ). When performing MIMO operations in midband MB and/or high band HB, antennas  40 - 1 ,  40 - 2 ,  40 - 3 , and  40 - 4  may transmit and/or receive independent data streams at the same frequencies (e.g., in midband MB and/or high band HB). The presence of gap  84 - 3  may ensure that antenna  40 - 1  is sufficiently isolated from antenna  40 - 2  despite both antennas operating at the same frequency. At the same time, antenna  40 - 1  may, if desired, perform 2×MIMO operations in low band LB with antenna  40 - 4  ( FIG. 3 ). 
     In some scenarios, the high data throughput achievable using a 4×MIMO scheme may not be necessary for communications between device  10  and the external communications equipment. In these scenarios, device  10  may perform 2×MIMO communications in which two antennas are used for performing communications at the same frequencies (e.g., without performing any 4×MIMO communications). In order to maximize isolation between the two antennas in these scenarios, the two antennas for performing the 2×MIMO operations may be located at opposing sides (e.g., sides  66  and  68 ) of device  10 . In order to further increase the antenna efficiency of the two antennas in these scenarios (e.g., by utilizing as much antenna volume as possible), antennas  40 - 1 ,  40 - 2 ,  40 - 3 , and  40 - 4  may be configured to form upper antenna  40 U and lower antenna  40 L ( FIG. 3 ) for performing the 2×MIMO operations. 
     As shown in  FIG. 12 , if desired, antennas  40 - 1  and  40 - 2  may include switching circuitry that is controlled by control circuitry  28  ( FIG. 1 ) to place antennas  40 - 1  and  40 - 2  in a selected one of a first operating mode and a second operating mode. In the first operating mode (sometimes referred to herein as a 4×MIMO mode or first MIMO mode), antennas  40 - 1  and  40 - 2  are isolated by gap  84 - 3  and convey separate data streams at the same frequency (e.g., so that antennas  40 - 1  and  40 - 2  can perform 4×MIMO operations with antennas  40 - 3  and  40 - 4 ). In the second operating mode (sometimes referred to herein as a 2×MIMO mode or second MIMO mode), antennas  40 - 1  and  40 - 2  are configured to form a single antenna such as upper antenna  40 U (e.g., a single antenna  40  including structures from both antennas  40 - 1  and  40 - 2 ). 
     In the second operating mode, segment  88 - 1  may be shorted to segment  88 - 2 , return path  106 - 2  may be decoupled from ground  100 , and feed  55 - 2  may be disabled. Antenna  40 U may subsequently be fed using antenna feed  55 - 1 . The distance between feed  55 - 1  and gap  84 - 2  may support a resonance in low band LB (as shown by arrow  118 ) and the distance between feed  55 - 1  and gap  84 - 1  may support resonance in midband MB (as shown by arrow  116 ) for antenna  40 U (e.g., both segments  88 - 1  and  88 - 2  may form part of a single resonating element arm  106  for antenna  40 U). Slot  108  between the resonating element arm of antenna  40 U and ground  110  may support a resonance in high band HB. 
     In this example, similar structures may be used to form antennas  40 - 3  and  40 - 4  (e.g., with antenna  40 - 4  replacing antenna  40 - 1  and antenna  40 - 3  replacing antenna  40 - 2  in  FIG. 12 ). Antennas  40 - 3  and  40 - 4  may thereby be toggled between the first operating mode where antennas  40 - 3  and  40 - 4  independently convey two separate data streams at the same frequencies for performing 4×MIMO operations with antennas  40 - 1  and  40 - 2  and the second operating mode where antennas  40 - 3  and  40 - 4  form a single lower antenna  40 L ( FIG. 3 ). When antennas  40 - 1 ,  40 - 2 ,  40 - 3 , and  40 - 4  are placed in the second operating mode to form antennas  40 U and  40 L, antennas  40 U and  40 L may perform 2×MIMO operations by both transmitting and/or receiving independent data streams at the same frequencies in low band LB, midband MB, and/or high band HB. 
       FIG. 13  is a diagram of switching circuitry that may be formed in device  10  for toggling antennas  40 - 1  and  40 - 2  between the first operating mode and the second operating mode (e.g., within dashed region  112  of  FIG. 12 ). As shown in  FIG. 13 , switching circuitry  120  may be coupled between antenna  40 - 1  and antenna  40 - 2 . The state of switching circuitry  120  may be controlled by control signals  122  received from control circuitry  28 . 
     Switching circuitry  120  may include a first switch  120 - 1  coupled between resonating element arm  104 - 1  (segment  88 - 1 ) and resonating element arm  104 - 2  (segment  88 - 2 ) across gap  84 - 3 . When switch  120 - 1  is closed (turned on), arm  104 - 1  of antenna  40 - 1  may be shorted to arm  104 - 2  of antenna  40 - 2  to form a single resonating element arm  106  for antenna  40 U. 
     Switching circuitry  120  may include a second switch  120 - 2  interposed on return path  106 - 2  of antenna  40 - 2  (e.g., switch  106 - 2  may be coupled between arm  104 - 2  of antenna  40 - 2  and ground  100 ). When switch  120 - 2  is closed, arm  104 - 2  of antenna  40 - 2  may be shorted to ground  100  (e.g., for supporting a resonance in midband MB for antenna  40 - 2 ). When switch  120 - 2  is open, an open circuit may be formed between arm  104 - 2  and ground  100  (e.g., so that the resonating element arm of antenna  40 U is not shorted to ground between feed  55 - 1  and gap  84 - 2 ). 
     Switching circuitry  120  may include a third switch  120 - 3  interposed between feed terminal  56 - 2  of antenna feed  55 - 2  and resonating element arm  104 - 2 . When switch  120 - 3  is closed, feed  56 - 2  is coupled to arm  104 - 2  and radio-frequency antenna signals for antenna  40 - 2  may be conveyed by antenna  40 - 2 . When switch  120 - 3  is open, feed  55 - 2  is disabled by decoupling feed terminal  56 - 2  from arm  104 - 2 . 
     Control circuitry  28  may place switching circuitry  120  in a first state (e.g., a 4×MIMO state or first MIMO state) in which switch  120 - 1  is open and switches  120 - 2  and  120 - 3  are closed. When switching circuitry  120  is in the first state, antennas  40 - 1  and  40 - 2  are placed in the first operating mode. In the first operating mode, arm  104 - 1  of antenna  40 - 1  may be isolated from arm  104 - 2  of antenna  40 - 2  by gap  84 - 3 , return path  106 - 2  of antenna  40 - 2  may be coupled between arm  104 - 2  and ground  100 , and feed  55 - 2  may be active (e.g., feed terminal  56 - 2  may be coupled to arm  104 - 2 ). Antennas  40 - 1  and  40 - 2  may subsequently perform 4×MIMO operations by conveying separate data streams at the same frequencies as antennas  40 - 3  and  40 - 4  ( FIG. 3 ). 
     Control circuitry  28  may place switching circuitry  120  in a second state (e.g., a 2×MIMO state or second MIMO state) in which switch  120 - 1  is closed and switches  120 - 2  and  120 - 3  are open. When switching circuitry  120  is in the second state, antennas  40 - 1  and  40 - 2  are placed in the second operating mode in which structures in antennas  40 - 1  and  40 - 2  form a single antenna  40 U. In the second operating mode, arm  104 - 1  of antenna  40 - 1  may be shorted to arm  104 - 2  of antenna  40 - 2  across gap  84 - 3  to form the resonating element arm of antenna  40 U, return path  106 - 2  may form an open circuit between peripheral structures  88  and ground  100 , and feed  55 - 2  may be deactivated (e.g., feed terminal  56 - 2  may be decoupled from arm  104 - 2 ). Antenna  40 U may subsequently perform 2×MIMO operations by conveying data streams at the same frequencies as antenna  40 L ( FIG. 3 ). 
     The example of  FIG. 13  is merely illustrative. If desired, one or more of switches  120 - 1 ,  120 - 2 , and  120 - 3  may be omitted or additional switches may be formed within switching circuitry  120 . In the example of  FIG. 13 , switches  120 - 1 ,  120 - 2 , and  120 - 3  are SP2T switches. However, in general, any desired switches may be used and the switches in switching circuitry  120  may be arranged in any desired manner between antennas  40 - 1  and  40 - 2 . 
     Performing 2×MIMO operations (e.g., while switching circuitry  120  is in the second state) may involve a lower throughput than performing 4×MIMO operations (e.g., while switching circuitry  120  is in the first state). However, performing 2×MIMO operations may involve higher antenna efficiency than performing 4×MIMO operations (e.g., because antennas  40 U and  40 L are formed at opposing ends of device  10  and are therefore isolated from each other and because antennas  40 U and  40 L occupy larger volumes than antennas  40 - 1 ,  40 - 2 ,  40 - 3 , or  40 - 4 ). If desired, control circuitry  28  may place antennas  40 - 1 ,  40 - 2 ,  40 - 3 , and  40 - 4  in the first operating mode when the processing operations of device  10  call for relatively high data throughput (e.g., for streaming high definition video, performing computationally intensive cloud computing algorithms, etc.) and may configure antennas  40 - 1 ,  40 - 2 ,  40 - 3 , and  40 - 4  to form antennas  40 U and  40 L in the second operating mode when the processing operations of device  10  call for relatively high antenna efficiency (e.g., when there is a low wireless link quality between device  10  and external wireless equipment). 
       FIG. 14  is a graph in which antenna performance (antenna efficiency) has been plotted as a function of operating frequency f for antennas  40 - 1 ,  40 - 2 , and/or  40 U of  FIGS. 11-13  (e.g., including switching circuitry  120 ). As shown in  FIG. 14 , curve  130  plots the antenna efficiency of antenna  40 U when placed in the second operating mode (e.g., when switching circuitry  120  is placed in the second state). When operating in the second mode, antenna  40 U may exhibit peak efficiencies E1 in low band LB, midband MB, and high band HB (e.g., peak efficiencies of approximately −3 dB). The peak in low band LB may be generated by a resonance of antenna  40 U associated with the path length  118  of  FIG. 12 , the peak in midband MB may be generated by a resonance of antenna  40 U associated with path length  116 , and the peak in high band HB may be generated by a resonance of antenna  40 U associated with a portion of slot  108  between path  116  and ground  100 , for example. The frequency response of antenna  40 U within low band LB may be adjusted by adjusting component  110  of  FIG. 12  if desired. The frequency response of antenna  40 L within midband MB may be adjusted by adjusting component  114  of  FIG. 12  if desired. 
     Curve  132  plots the antenna efficiency of antenna  40 - 1  when operated in the first operating mode (e.g., when switching circuitry  120  is placed in the first state). When operating in the first operating mode, antenna  40 - 1  may exhibit peak efficiencies E2 in low band LB, midband MB, and high band HB that are less than efficiencies E1 associated with curve  130  (e.g., due to the decrease in isolation between each active antenna and the decrease in spatial volume for each antenna). As an example, peak efficiencies E2 may be approximately −6 dB. The peak in low band LB may be generated by a resonance of antenna  40 - 1  associated with the path between component  114  and gap  84 - 3  of  FIG. 12 , the peak in midband MB may be generated by a resonance of antenna  40 - 1  associated with the path between component  114  and gap  84 - 1 , and the peak in high band HB may be generated by a resonance of slot  108  between segment  88 - 1  and ground  100 , for example. The frequency response of curve  132  within low band LB may be adjusted by adjusting component  110  of  FIG. 12 . The frequency response of curve  130  within midband MB may be adjusted by adjusting component  114 . 
     Curve  134  plots the antenna efficiency of antenna  40 - 2  when placed in the first operating mode (e.g., when switching circuitry  120  is placed in the first state). When operating in the first mode, antenna  40 - 2  may exhibit peak efficiencies E2 in low midband MB and high band HB. The peak in midband MB may be generated by a resonance of antenna  40 - 2  associated with the distance between return path  106 - 2  and gap  84 - 2  and the peak in high band HB may be generated by a resonance of slot  108  between segment  88 - 2  and ground  100 , for example. While operating in the first mode reduces the overall antenna efficiency from E1 to E2, data throughput for wireless circuitry  34  is also greater than in the first mode than in the second mode. 
     When placed in the first operating mode, antennas  40 - 1  and  40 - 2  may perform 4×MIMO operations with antennas  40 - 3  and  40 - 4  in one or both of midband MB and high band HB and may additionally or alternatively perform 2×MIMO operations in low band LB with antenna  40 - 4  (e.g., as shown by coverage blocks  80  for antennas  40 - 1  through  40 - 4  in  FIG. 4 ). If desired, antennas  40 - 1 ,  40 - 2 ,  40 - 3 , and  40 - 4  may perform carrier aggregation in which multiple carrier frequencies in one or more of bands LB, MB, and HB are used to further increase data throughput. 
     When placed in the second operating mode, antennas  40 U and  40 L may perform 2×MIMO operations in one, two, or all of bands LB, MB, and HB. If desired, antennas  40 U and  40 L may perform carrier aggregation in which multiple carrier frequencies in one or more of bands LB, MB, and HB are used to further increase data throughput (e.g., where each of antennas  40 U and  40 L covers the same carrier frequencies so that 2×MIMO operations are performed for each carrier frequency in the carrier aggregation scheme). 
     While antennas  40 - 1  and  40 - 4  may perform 2×MIMO operations in low band LB while placed in the first operating mode, none of the antennas may perform 4×MIMO operations when the antennas are placed in the second operating mode, for example. In this way, four or more antennas  40  may be used to perform MIMO operations to increase overall data throughput relative to scenarios where only a single antenna is used, while also ensuring that there is satisfactory electromagnetic isolation between antennas operating at the same frequencies and, in the example of  FIGS. 11-13 , while also allowing for the antennas to be dynamically adjusted between different modes depending on antenna efficiency and data throughput requirements for device  10 . 
     The example of  FIG. 14  is merely illustrative. In general, efficiency curves  130 ,  132 , and  134  may have any desired shape. Curves  130 ,  132 , and  134  may exhibit peaks in efficiency in more than three frequency bands, in fewer than three frequency bands, or in any other desired frequency bands if desired. Similar efficiency curves may also be used to characterize antennas  40 - 3 ,  40 - 4 , and  40 L of  FIG. 3  if desired. 
     A curve such as curve  132  of  FIG. 14  (or a similar curve that follows the path of curve  132  at slightly lower efficiencies) may be used to characterize the performance of antennas  40 - 1  and  40 - 4  in scenarios where antennas  40 - 1  and  40 - 2  are formed from a continuous conductor and antennas  40 - 3  and  40 - 4  are formed from a continuous conductor ( FIGS. 8-10 ). Similarly, a curve such as curve  134  (or a similar curve that follows the path of curve  134  at slightly lower efficiencies) may be used to characterize the performance of antennas  40 - 2  and  40 - 3  in the arrangement of  FIGS. 8-10 . Antennas  40 - 1 ,  40 - 2 ,  40 - 3 , and  40 - 4  may perform 4×MIMO operations in midband MB and/or high band HB and/or may perform 2×MIMO operations in low band LB whether antennas  40 - 1  and  40 - 2  have resonating elements formed from a continuous conductor ( FIGS. 8-10 ) or whether gap  84 - 3  is formed in housing wall  88  ( FIGS. 11-13 ). If desired, any pair of antennas  40 - 1 ,  40 - 2 ,  40 - 3 , and  40 - 4  may perform 2×MIMO operations in one or more of bands LB, MB, and/or HB (e.g., antennas  40  need not utilize their full data throughput capacity). 
     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: 20201023
Publication Date: 20220419
Grant Date: 20220419
Priority Date: 20170721
Inventors: AYALA VAZQUEZ, ENRIQUE
HU, HONGFEI
PASCOLINI, MATTIA
JIN, NANBO
MOW, MATTHEW A.
IRCI, Erdinc
TONG, ERICA J.
WANG, HAN
Assignee: APPLE INC
CPC Classifications: [{"code": "H04B7/0404", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B1/40", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01Q1/42", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q5/321", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01Q1/523", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01Q1/44", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q1/243", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q21/28", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q5/35", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01Q21/28", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q5/321", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01Q1/243", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01Q1/523", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01Q9/42", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B7/0404", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q1/243", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q21/06", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q9/42", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q1/42", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q21/28", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q5/35", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q1/44", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q9/42", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B1/40", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q5/321", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q21/06", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B7/0404", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q1/42", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q1/242", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q5/35", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01Q1/44", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q1/242", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B1/40", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01Q1/42", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q1/523", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01Q21/28", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q5/321", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01Q21/06", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q1/44", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B7/0404", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q5/35", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01Q9/42", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q1/243", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 62952406