Patent Publication Number: US-8531341-B2

Title: Antenna isolation for portable electronic devices

Description:
This application is a continuation of patent application Ser. No. 13/073,872, filed Mar. 28, 2011, now U.S. Pat. No. 8,144,063 which is a continuation of patent application Ser. No. 11/969,684, filed Jan. 4, 2008, now U.S. Pat. No. 7,916,089, which are hereby incorporated by referenced herein in their entireties. This application claims the benefit of and claims priority to patent application Ser. No. 13/073,872, filed Mar. 28, 2011 and patent application Ser. No. 11/969,684, filed Jan. 4, 2008, now U.S. Pat. No. 7,916,089. 
    
    
     BACKGROUND 
     This invention relates generally to wireless communications circuitry, and more particularly, to wireless communications circuitry with antenna isolation for electronic devices such as portable electronic devices. 
     Handheld electronic devices and other portable electronic devices are becoming increasingly popular. Examples of handheld devices include handheld computers, cellular telephones, media players, and hybrid devices that include the functionality of multiple devices of this type. Popular portable electronic devices that are somewhat larger than traditional handheld electronic devices include laptop computers and tablet computers. 
     Due in part to their mobile nature, portable electronic devices are often provided with wireless communications capabilities. For example, handheld electronic devices may use long-range wireless communications to communicate with wireless base stations. Cellular telephones and other devices with cellular capabilities may communicate using cellular telephone bands at 850 MHz, 900 MHz, 1800 MHz, and 1900 MHz. Portable electronic devices may also use short-range wireless communications links. For example, portable electronic devices may communicate using the Wi-Fi® (IEEE 802.11) band at 2.4 GHz and the Bluetooth® band at 2.4 GHz. Communications are also possible in data service bands such as the 3G data communications band at 2170 MHz band (commonly referred to as UMTS or Universal Mobile Telecommunications System band). 
     To satisfy consumer demand for small form factor wireless devices, manufacturers are continually striving to reduce the size of components that are used in these devices. For example, manufacturers have made attempts to miniaturize the antennas used in handheld electronic devices. 
     A typical antenna may be fabricated by patterning a metal layer on a circuit board substrate or may be formed from a sheet of thin metal using a foil stamping process. Antennas such as planar inverted-F antennas (PIFAs) and antennas based on L-shaped resonating elements can be fabricated in this way. Antennas such as PIFA antennas and antennas with L-shaped resonating elements can be used in handheld devices. 
     Although modern portable electronic devices often use multiple antennas, it is challenging to produce successful antenna arrangements in which multiple antennas operate in close proximity to each other without experiencing undesirable interference. 
     It would therefore be desirable to be able to provide improved antenna structures for wireless electronic devices. 
     SUMMARY 
     A portable electronic device such as a handheld electronic device is provided with wireless communications circuitry that includes antennas and antenna isolation elements. The antenna isolation elements may be interposed between respective antennas to reduce radio-frequency interference between the antennas and thereby improve antenna isolation. 
     With one suitable arrangement, there are at least three antennas in the wireless communications circuitry. The three antennas may each have a respective antenna resonating element. The antenna resonating elements may be formed from conductive structures such as traces on a flex circuit or stamped metal foil structures (as examples). Each antenna resonating element may have at least one antenna resonating element arm. The arms may be aligned along a common axis. 
     The antenna isolation elements may be formed from antenna isolation resonating elements such as L-shaped strips of conductor. The L-shaped conductive strips may have arms that are aligned with the common axis. 
     The antennas and the antenna isolation elements may share a common ground plane. With this type of configuration, a first antenna resonating element and the ground plane form a first antenna, a second antenna resonating element and the ground plane form a second antenna, a third antenna resonating element and a ground plane form a third antenna, a first antenna isolation resonating element and the ground plane form a first antenna isolation element, and a second antenna isolation resonating element and the ground plane form a second antenna isolation element. 
     If desired, some of the antennas and resonating elements may have multiple arms. For example, the first and third antenna resonating elements may have arms that are aligned with the common axis and arms that are perpendicular to the common axis. 
     The first and third antennas may be used to implement an antenna diversity scheme. With one suitable arrangement, a Wi-Fi transceiver that operates at 2.4 GHz and 5.1 GHz is coupled to the first and third antennas, whereas a Bluetooth transceiver that operates at 2.4 GHz is coupled to the second antenna. Antenna isolation elements that operate at 2.4 GHz may be placed between the first and second antennas and between the second and third antennas, thereby isolating the first antenna from the third antenna at 2.4 GHz and isolating the first and third antennas from the second antenna at 2.4 GHz. 
     Further features of the invention, its nature and various advantages will be more apparent from the accompanying drawings and the following detailed description of the preferred embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an illustrative electronic device with isolated antenna structures in accordance with an embodiment of the present invention. 
         FIG. 2  is a perspective view of another illustrative electronic device with isolated antenna structures in accordance with an embodiment of the present invention. 
         FIG. 3  is a schematic diagram of an illustrative portable electronic device with isolated antenna structures in accordance with an embodiment of the present invention. 
         FIG. 4  is a schematic diagram of illustrative portable electronic device isolated antenna structures in accordance with an embodiment of the present invention. 
         FIG. 5  is a perspective view of an illustrative electronic device antenna in accordance with an embodiment of the present invention. 
         FIG. 6  is a perspective view of an illustrative portable electronic device antenna that has been mounted on a support structure and that is being fed by a transmission line in accordance with an embodiment of the present invention. 
         FIG. 7  is a perspective view of an illustrative portable electronic device antenna having a ground plane and first and second antenna resonating element arms including a longer arm that is located nearer to the ground plane than a shorter arm in accordance with an embodiment of the present invention. 
         FIG. 8  is a perspective view of an illustrative portable electronic device antenna having short and long arms that are oriented so that they are orthogonal to each other while lying in a plane parallel to a ground plane in accordance with an embodiment of the present invention. 
         FIG. 9  is a perspective view of an illustrative portable electronic device antenna structure having three antennas isolated by two antenna isolation structures in accordance with an embodiment of the present invention. 
         FIG. 10  is a perspective view of a portable electronic device antenna structure in which antennas are isolated by isolation elements that extend in a vertical direction that is perpendicular to a ground plane in accordance with the present invention. 
         FIG. 11  is a perspective view of a portable electronic device antenna structure with antennas and antenna isolation elements in which the antenna isolation elements each have a bent portion that runs perpendicular to the longitudinal axis of the antennas in accordance with an embodiment of the present invention. 
         FIG. 12  is a perspective view of an illustrative portable electronic device antenna resonating element and an associated antenna isolation element showing possible locations for the associated antenna isolation element relative to the portable electronic device antenna resonating element in accordance with an embodiment of the present invention. 
         FIG. 13  is a perspective view of an illustrative portable electronic device antenna resonating element and an associated antenna isolation element showing possible angular orientations for the associated antenna isolation element relative to the longitudinal axis of the electronic device antenna resonating element in accordance with an embodiment of the present invention. 
         FIG. 14  is a perspective view of two illustrative portable electronic device antennas separated by an antenna isolation element having multiple antenna isolation element structures in accordance with an embodiment of the present invention. 
         FIG. 15  is a perspective view of two illustrative portable electronic device antennas separated by an antenna isolation element having multiple orthogonal antenna isolation element arms in accordance with an embodiment of the present invention. 
         FIG. 16  is a perspective view of three illustrative portable electronic device antennas, two of which are isolated by an antenna isolation element having multiple parallel antenna isolation element arms and two of which are isolated by an antenna isolation element having two individual L-shaped isolation element structures in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     The present invention relates generally to wireless communications, and more particularly, to wireless electronic devices and antennas for wireless electronic devices. 
     The wireless electronic devices may be portable electronic devices such as laptop computers or small portable computers of the type that are sometimes referred to as ultraportables. Portable electronic devices may also be somewhat smaller devices. Examples of smaller portable electronic devices include wrist-watch devices, pendant devices, headphone and earpiece devices, and other wearable and miniature devices. With one suitable arrangement, the portable electronic devices are handheld electronic devices. 
     The wireless electronic devices may be, for example, cellular telephones, media players with wireless communications capabilities, handheld computers (also sometimes called personal digital assistants), remote controllers, global positioning system (GPS) devices, and handheld gaming devices. The wireless electronic devices may also be hybrid devices that combine the functionality of multiple conventional devices. Examples of hybrid portable electronic devices include a cellular telephone that includes media player functionality, a gaming device that includes a wireless communications capability, a cellular telephone that includes game and email functions, and a portable device that receives email, supports mobile telephone calls, has music player functionality and supports web browsing. These are merely illustrative examples. 
     An illustrative portable electronic device in accordance with an embodiment of the present invention is shown in  FIG. 1 . Device  10  of  FIG. 1  may be, for example, a handheld electronic device. 
     Device  10  may have housing  12 . Antennas for handling wireless communications may be housed within housing  12  (as an example). 
     Housing  12 , which is sometimes referred to as a case, may be formed of any suitable materials including, plastic, glass, ceramics, metal, or other suitable materials, or a combination of these materials. In some situations, housing  12  or portions of housing  12  may be formed from a dielectric or other low-conductivity material, so that the operation of conductive antenna elements that are located in proximity to housing  12  is not disrupted. Housing  12  or portions of housing  12  may also be formed from conductive materials such as metal. An illustrative housing material that may be used is anodized aluminum. Aluminum is relatively light in weight and, when anodized, has an attractive insulating and scratch-resistant surface. If desired, other metals can be used for the housing of device  10 , such as stainless steel, magnesium, titanium, alloys of these metals and other metals, etc. In scenarios in which housing  12  is formed from metal elements, one or more of the metal elements may be used as part of the antennas in device  10 . For example, metal portions of housing  12  may be shorted to an internal ground plane in device  10  to create a larger ground plane element for that device  10 . To facilitate electrical contact between an anodized aluminum housing and other metal components in device  10 , portions of the anodized surface layer of the anodized aluminum housing may be selectively removed during the manufacturing process (e.g., by laser etching). 
     Housing  12  may have a bezel  14 . The bezel  14  may be formed from a conductive material and may serve to hold a display or other device with a planar surface in place on device  10 . As shown in  FIG. 1 , for example, bezel  14  may be used to hold display  16  in place by attaching display  16  to housing  12 . 
     Display  16  may be a liquid crystal diode (LCD) display, an organic light emitting diode (OLED) display, or any other suitable display. The outermost surface of display  16  may be formed from one or more plastic or glass layers. If desired, touch screen functionality may be integrated into display  16  or may be provided using a separate touch pad device. An advantage of integrating a touch screen into display  16  to make display  16  touch sensitive is that this type of arrangement can save space and reduce visual clutter. 
     Display screen  16  (e.g., a touch screen) is merely one example of an input-output device that may be used with electronic device  10 . If desired, electronic device  10  may have other input-output devices. For example, electronic device  10  may have user input control devices such as button  19 , and input-output components such as port  20  and one or more input-output jacks (e.g., for audio and/or video). Button  19  may be, for example, a menu button. Port  20  may contain a 30-pin data connector (as an example). Openings  24  and  22  may, if desired, form microphone and speaker ports. In the example of  FIG. 1 , display screen  16  is shown as being mounted on the front face of handheld electronic device  10 , but display screen  16  may, if desired, be mounted on the rear face of handheld electronic device  10 , on a side of device  10 , on a flip-up portion of device  10  that is attached to a main body portion of device  10  by a hinge (for example), or using any other suitable mounting arrangement. 
     A user of electronic device  10  may supply input commands using user input interface devices such as button  19  and touch screen  16 . Suitable user input interface devices for electronic device  10  include buttons (e.g., alphanumeric keys, power on-off, power-on, power-off, and other specialized buttons, etc.), a touch pad, pointing stick, or other cursor control device, a microphone for supplying voice commands, or any other suitable interface for controlling device  10 . Although shown schematically as being formed on the top face of electronic device  10  in the example of  FIG. 1 , buttons such as button  19  and other user input interface devices may generally be formed on any suitable portion of electronic device  10 . For example, a button such as button  19  or other user interface control may be formed on the side of electronic device  10 . Buttons and other user interface controls can also be located on the top face, rear face, or other portion of device  10 . If desired, device  10  can be controlled remotely (e.g., using an infrared remote control, a radio-frequency remote control such as a Bluetooth remote control, etc.). 
     Electronic device  10  may have ports such as port  20 . Port  20 , which may sometimes be referred to as a dock connector, 30-pin data port connector, input-output port, or bus connector, may be used as an input-output port (e.g., when connecting device  10  to a mating dock connected to a computer or other electronic device). Device  10  may also have audio and video jacks that allow device  10  to interface with external components. Typical ports include power jacks to recharge a battery within device  10  or to operate device  10  from a direct current (DC) power supply, data ports to exchange data with external components such as a personal computer or peripheral, audio-visual jacks to drive headphones, a monitor, or other external audio-video equipment, a subscriber identity module (SIM) card port to authorize cellular telephone service, a memory card slot, etc. The functions of some or all of these devices and the internal circuitry of electronic device  10  can be controlled using input interface devices such as touch screen display  16 . 
     Components such as display  16  and other user input interface devices may cover most of the available surface area on the front face of device  10  (as shown in the example of  FIG. 1 ) or may occupy only a small portion of the front face of device  10 . Because electronic components such as display  16  often contain large amounts of metal (e.g., as radio-frequency shielding), the location of these components relative to the antenna elements in device  10  should generally be taken into consideration. Suitably chosen locations for the antenna elements and electronic components of the device will allow the antennas of electronic device  10  to function properly without being disrupted by the electronic components. 
     Examples of locations in which antenna structures may be located in device  10  include region  18  and region  21 . These are merely illustrative examples. Any suitable portion of device  10  may be used to house antenna structures for device  10  if desired. 
     If desired, electronic device  10  may be a portable electronic device such as a laptop or other portable computer. For example, electronic device  10  may be an ultraportable computer, a tablet computer, or other suitable portable computing device. An illustrative portable electronic device  10  of this type is shown in  FIG. 2 . As shown in  FIG. 2 , such portable electronic devices may have a screen  16  on a housing  12 . Antennas may be placed at any suitable location within device  10 . For example, antenna structures may be located along the right-hand edge of housing  12  (e.g., in region  18  of  FIG. 2 ) or may be located along the upper edge of housing  12  (e.g., in region  21  of  FIG. 2 ). These are merely illustrative examples. If desired, antenna structures may be placed along a left-hand edge, a bottom edge, or in portions of housing  12  other than a housing edge (e.g., in the middle of housing  12  or on an extendable structure that is connected to device  10 ). An advantage of locating antenna structures along a device edge is that this generally allows the antennas to be placed in a location that is separated somewhat from conductive structures that might otherwise impede the operation of the antenna structures. 
     A schematic diagram of an embodiment of an illustrative portable electronic device is shown in  FIG. 3 . Portable device  10  may be a mobile telephone, a mobile telephone with media player capabilities, a handheld computer, a remote control, a game player, a global positioning system (GPS) device, a laptop computer, a tablet computer, an ultraportable computer, a combination of such devices, or any other suitable portable electronic device. 
     As shown in  FIG. 3 , device  10  may include storage  34 . Storage  34  may include one or more different types of storage such as hard disk drive storage, nonvolatile memory (e.g., flash memory or other electrically-programmable-read-only memory), volatile memory (e.g., battery-based static or dynamic random-access-memory), etc. 
     Processing circuitry  36  may be used to control the operation of device  10 . Processing circuitry  36  may be based on a processor such as a microprocessor and other suitable integrated circuits. With one suitable arrangement, processing circuitry  36  and storage  34  are 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. Processing circuitry  36  and storage  34  may be used in implementing suitable communications protocols. Communications protocols that may be implemented using processing circuitry  36  and storage  34  include internet protocols, wireless local area network protocols (e.g., IEEE 802.11 protocols—sometimes referred to as Wi-Fi®), protocols for other short-range wireless communications links such as the Bluetooth® protocol, protocols for handling 3G data services such as UMTS, cellular telephone communications protocols, etc. 
     Input-output devices  38  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. Display screen  16 , button  19 , microphone port  24 , speaker port  22 , and dock connector port  20  are examples of input-output devices  38 . 
     Input-output devices  38  can include user input-output devices  40  such as buttons, touch screens, joysticks, click wheels, scrolling wheels, touch pads, key pads, keyboards, microphones, cameras, etc. A user can control the operation of device  10  by supplying commands through user input devices  40 . Display and audio devices  42  may include liquid-crystal display (LCD) screens or other screens, light-emitting diodes (LEDs), and other components that present visual information and status data. Display and audio devices  42  may also include audio equipment such as speakers and other devices for creating sound. Display and audio devices  42  may contain audio-video interface equipment such as jacks and other connectors for external headphones and monitors. 
     Wireless communications devices  44  may include communications circuitry such as radio-frequency (RF) transceiver circuitry formed from one or more integrated circuits, power amplifier circuitry, passive RF components, antennas, and other circuitry for handling RF wireless signals. Wireless signals can also be sent using light (e.g., using infrared communications). 
     Device  10  can communicate with external devices such as accessories  46  and computing equipment  48 , as shown by paths  50 . Paths  50  may include wired and wireless paths. Accessories  46  may include headphones (e.g., a wireless cellular headset or audio headphones) and audio-video equipment (e.g., wireless speakers, a game controller, or other equipment that receives and plays audio and video content), a peripheral such as a wireless printer or camera, etc. 
     Computing equipment  48  may be any suitable computer. With one suitable arrangement, computing equipment  48  is a computer that has an associated wireless access point (router) or an internal or external wireless card that establishes a wireless connection with device  10 . The computer may be a server (e.g., an internet server), a local area network computer with or without internet access, a user&#39;s own personal computer, a peer device (e.g., another portable electronic device  10 ), or any other suitable computing equipment. 
     The antenna structures and wireless communications devices of device  10  may support communications over any suitable wireless communications bands. For example, wireless communications devices  44  may be used to cover communications frequency bands such as the cellular telephone bands at 850 MHz, 900 MHz, 1800 MHz, and 1900 MHz, data service bands such as the 3G data communications band at 2170 MHz band (commonly referred to as UMTS or Universal Mobile Telecommunications System), the Wi-Fi® (IEEE 802.11) bands at 2.4 GHz and 5.0 GHz (also sometimes referred to as wireless local area network or WLAN bands), the Bluetooth® band at 2.4 GHz, and the global positioning system (GPS) band at 1550 MHz. The 850 MHz band is sometimes referred to as the Global System for Mobile (GSM) communications band. The 900 MHz communications band is sometimes referred to as the Extended GSM (EGSM) band. The 1800 MHz band is sometimes referred to as the Digital Cellular System (DCS) band. The 1900 MHz band is sometimes referred to as the Personal Communications Service (PCS) band. 
     Device  10  can cover these communications bands and/or other suitable communications bands with proper configuration of the antenna structures in wireless communications circuitry  44 . 
     With one suitable arrangement, which is sometimes described herein as an example, the wireless communications circuitry of device  10  may have at least two antennas that are used in a diversity arrangement to handle communications in a first communications band. Antenna diversity arrangements use multiple antennas in parallel to obtain improved immunity to proximity effects and improved throughput. The antennas may operate in any suitable frequency band. For example, the antennas may be used to handle local area network (LAN) communications in a communications band that is centered at 2.4 GHz (e.g., the 2.4 GHz IEEE 802.11 frequency band sometimes referred to as Wi-Fi®). If desired, antenna diversity arrangements may be implemented using more than two antennas (e.g., three or more antennas). For clarity, examples with two antennas are sometimes described herein as an example. 
     At least one additional antenna may be placed in close proximity to the diversity scheme antennas. The additional antenna may, for example, be placed in the vicinity of the other antennas to conserve space in electronic device  10 . For example, the additional antenna may be placed between the other antennas. With one suitable arrangement, the antennas have resonating element structures with longitudinal axis that are all aligned. 
     The additional antenna may operate at the same frequency as the other antennas. For example, the additional antenna may operate at 2.4 GHz (e.g., to handle Bluetooth® communications). Because the antennas operate in the same communications band, care should be taken to avoid undesirable interference between the antennas. 
     The amount of isolation that is required between the antennas depends on the particular requirements of the system in which the antennas are being used. For example, the designers of portable electronic device  10  may require that the two diversity scheme antennas exhibit greater than 25 dB of isolation from each other and may require that the additional antenna exhibit greater than 15 dB of isolation relative to the other two antennas. These isolation criteria may be applied to antenna structures that exhibit a three-dimensional antenna efficiency of about 25-50%. 
     To achieve these levels of isolation, antenna isolation elements may be provided in the vicinity of the antennas. The structures that make up the antenna isolation elements may, for example, be interposed between the antenna resonating elements of the antennas. The antennas and the antenna isolation elements may share a common ground plane. 
     An illustrative antenna arrangement of this type is shown in  FIG. 4 . As shown in  FIG. 4 , wireless communications circuitry  44  may include first and second radio-frequency transceivers such as radio-frequency transceiver  52  and radio-frequency transceiver  54  (sometimes referred to as “radios”). Transceiver  54  may be, for example, a Bluetooth transceiver that is connected to antenna  60  by transmission line  68 . Transceiver  52  may be, for example, a Wi-Fi transceiver that is connected to antennas  56  and  64  by transmission lines  70  and  72 . Transmission lines  68 ,  70 , and  72  may be any transmission lines suitable for carrying radio-frequency signals between radio-frequency transceivers and antennas. For example, transmission lines  68 ,  70 , and  72  may be coaxial cable transmission lines, microstrip transmission lines, etc. 
     Transceiver  52  or other circuitry in device  10  may monitor the status of antennas  56  and  64  to implement an antenna diversity scheme. With this type of arrangement, transceiver  52  may use both antennas simultaneously or may opt to use primarily or exclusively antenna  56  or antenna  64  depending on which antenna has a higher associated signal strength or is less affected by proximity effects (e.g., from the close proximity of a user&#39;s hand or other part of a user&#39;s body), etc. Transceiver  52  may include coupling circuitry that routes radio-frequency signals to antenna  56  and/or antenna  64  from a transmitter in transceiver  52  during radio-frequency transmissions and that routes radio-frequency signals from antenna  56  and/or antenna  64  to a receiver in transceiver  52  during reception of radio-frequency signals. Transceiver  54  may include radio-frequency transmitter circuitry for transmitting radio-frequency signals and may include receiver circuitry for receiving radio-frequency signals. 
     During operation of device  10 , it may be desirable to use transceiver  54  and transceiver  52  at the same time. The ability to operate transceivers  54  and  52  asynchronously may allow, for example, a user to use a Bluetooth headset to use device  10  to make a voice-over-internet-protocol (VOIP) telephone call. Transceiver  54  may be used to establish a wireless Bluetooth link with the Bluetooth headset. At the same time, transceiver  52  may be used to establish an IEEE 802.11(n) Wi-Fi link with a wireless access point connected to the Internet. Because both links may be used simultaneously, both links may carry data traffic without interruption. 
     The IEEE 802.11(n) protocol is an example of a protocol that may use antenna diversity to improve performance. This type of arrangement uses two antennas (e.g., antennas  56  and  64 ) to carry Wi-Fi traffic. In general, any suitable number of antennas such as antennas  56  and  64  may be used in an antenna diversity scheme. For example, there may be three or more antennas coupled to transceiver  52 . The use of an arrangement with two diversity antennas is described herein as an example. Moreover, the Bluetooth link or other communications link that is established between transceiver  54  and antenna  60  is merely illustrative. There may be more than one antenna  60  and there may be more than one associated transceiver  54  that is coupled to that antenna if desired. 
     As shown in  FIG. 4 , antennas  56 ,  60 , and  64  may share a common ground plane (e.g., ground plane  66 ). With this type of arrangement, each of antennas  56 ,  60 , and  64  may have an associated antenna resonating element. These antenna resonating elements may be formed using inverted-F structures, planar inverted-F structures, L-shaped monopole structures, or any other suitable antenna resonating element configuration. The antenna resonating element portions of antennas  56 ,  60 , and  64  are generally spaced somewhat above common ground  66 . Common ground  66  may be formed from conductive elements in device  10  such as housing  12 , printed circuit boards, conductive packages for integrated circuits in device  10 , conductive components that are electrically connected to printed circuit boards or other grounded elements, etc. In a typical arrangement, some or all of these grounded structures are substantially planar. Accordingly, common ground structure  66  is sometimes referred to as a ground plane and is sometimes depicted schematically as an ideal plane. In practice, however, some non-planar structures may protrude slightly from portions of the ground plane. To ensure good efficiency for antennas  56 ,  60 , and  64 , sufficient clearance may be provided between such protruding conductive structures and the antenna resonating elements of antennas  56 ,  60 , and  64 . 
     Antenna  60  is generally located between antennas  56  and  64 , as shown in  FIG. 4 . If there were an unlimited amount of space in device  10 , it might be possible to place antenna  60  at a remote location, thereby ensuring adequate isolation between antenna  60  and antennas  56  and  64  based on physical separation. In real-world configurations for device  10 , this type of layout may not be practical. Accordingly, antenna  60  may be located between antennas  56  and  64 . This may provide a compact layout arrangement that fits within the potentially tight confines of housing  12 . 
     Because the printed circuit board and other conductive elements of ground plane  66  are electrically connected to form a common ground plane structure for antennas  56 ,  60 , and  64 , it may not be possible to create electrical gaps in ground plane  66  to help isolate antennas  56 ,  60 , and  64  from each other. Particularly in situations such as these, it may be advantageous to use antenna isolation elements. As shown in  FIG. 4 , for example, radio-frequency isolation between antennas  56 ,  60 , and  64  may be enhanced using antenna isolation elements  58  and  62 . Antenna isolation elements  58  and  62  may be formed from antenna resonating element structures that are similar to the antenna resonating element structures used in antennas  56 ,  60 , and  64 . For example, antenna isolation elements  58  and  62  may be formed using inverted-F structures, planar inverted-F structures, L-shaped structures, etc. Unlike antennas  56 ,  60 , and  64 , however, the antenna isolation elements  58  do not have antenna feed terminals that are coupled to transmission lines such as transmission lines  68  and  70 . Rather, antenna isolation elements  58  and  62  serve to provide enhanced levels of radio-frequency isolation between antennas  56 ,  60 , and  64 . In effect, isolation elements  58  and  62  may serve as radio-frequency chokes that prevent undesirable near-field electromagnetic coupling between antennas  56 ,  60 , and  64  at the frequency of interest (e.g., in the common communications frequency band of 2.4 GHz in this example). 
     For example, with antenna isolation elements  58  and  62  in place, antennas  56  and  64  may exhibit greater than 25 dB of isolation from each other, whereas antenna  60  may exhibit greater than 15 dB of isolation relative to antennas  58  and  64 . These isolation specifications may be achieved for antennas  56 ,  60 , and  64  that exhibit three-dimensional antenna efficiencies of about 25-50% (as an example). Moreover, these isolation specification (or other suitable specifications) may be achieved when operating all antennas  56 ,  60 , and  64  in the same frequency band (e.g., at 2.4 GHz or other suitable resonant frequency). 
     To enhance the capabilities of antennas  56 ,  60 , and  64 , some or all of antennas  56 ,  60 , and  64  may operate in multiple communications bands. For example, antennas  56  and  64  may be configured to handle communications at both 2.4 Hz and 5.1 GHz (e.g., to handle additional Wi-Fi bands). In this type of configuration, radio-frequency transceiver (or an associated transceiver) may be used to convey signals at 5.1 GHz to and from antennas  56  and  64  over communications paths such as transmission lines  70  and  72  in addition to the 2.4 GHz signals that are being conveyed between the antennas and transceiver  52 . Antenna  60  may be a single band antenna or may be a multiband antenna. 
     In a typical configuration, the resonating element structures of antennas  56 ,  60 , and  64  and of antenna isolation elements  58  and  62  may have lateral dimensions on the order of a quarter of a wavelength at each frequency of interest (e.g., on the order of a couple of centimeters for 2.4 GHz communications). Antennas  56  and  64  may be separated by about 14 centimeters (as an example). Antenna  60  may be located midway between antennas  56  and  64 . With one suitable arrangement, antennas  56 ,  60 , and  64  and antenna isolation elements  58  and  62  are arranged in a line (i.e., along a common axis that is aligned with the longitudinal axis of each of the resonating elements in antennas  56 ,  60 , and  64  and antenna isolation elements  58  and  62 ). Collinear arrangements such as these are illustrative. Other configurations (e.g., with different antenna resonating element sizes and/or different spacings and relative positions for the antennas) may be used if desired. 
     An illustrative configuration for an antenna such as antenna  56  or  64  is shown in  FIG. 5 . This type of configuration may also be used for antenna  60  (e.g., when antenna  60  is a dual-band antenna). 
     As shown in  FIG. 5 , antenna  74  may have an antenna resonating element  76  and ground plane portion  66 . Together, antenna resonating element  76  and ground plane  66  make up the two poles in antenna  74 . Ground plane  66  is preferably shared by other antennas in device  10  as shown in  FIG. 4 . These other antennas are not shown in  FIG. 5  to avoid over-complicating the drawing. 
     Antenna resonating element  76 , ground plane  66  and the other antenna structures in device  10  (including the resonating element structures associated with isolation elements  58  and  62 ) may be formed from any suitable conductive materials (e.g., copper, gold, metal alloys, other conductors, or combinations of such conductive materials). Such structures may be formed from stamped foils, from screen-printed structures, from conductive traces formed on flexible printed circuit substrates (so-called flex circuits) or using any other suitable arrangement. 
     In the example of  FIG. 5 , antenna resonating element  76  has multiple branches formed by first arm  78  and second arm  80 . These branches each form a resonant structure with a different effective length. A longer length L 1  is associated with longer arm  78  of antenna resonating element  76 . A shorter length L 2  is associated with shorter arm  80  of antenna resonating element  76 . The length L 1  may be equal to about a quarter of a wavelength at a first operating frequency. The length L 2  may be equal to about a quarter of a wavelength at a second operating frequency. For example, the length L 1  may be equal to a quarter of a wavelength at 2.4 GHz and the length L 2  may be equal to a quarter of a wavelength at 5.1 GHz. As shown in  FIG. 5 , resonating element  76  may include a vertical portion  94  that extends parallel to vertical axis  90 . Vertical axis  90  is perpendicular to ground plane  66 . Resonating element  76  also generally includes horizontal portions such as arms  78  and  80  in the  FIG. 5  example. 
     The horizontal portions of antenna resonating element  76  run parallel to ground plane  66 . Antenna  74  of  FIG. 5  has a longitudinal axis  92  that is defined by the main portions of antenna resonating element  76  (e.g., by arm  78  in the example of  FIG. 5 ). Arms such as arm  78  and arm  80  may run parallel to longitudinal axis  92 . With one suitable arrangement, antennas  56 ,  60 , and  64  and antenna isolation elements  58  and  62  are substantially collinear with axis  92  and each other. 
     If desired, some or all of the antennas and isolation elements can be located off of axis  92  (e.g., by a small offset amount such as by a few millimeters or by a relatively larger distance such as centimeter or more), but in general, such off-axis locations may not be highly favored because locating isolation elements  58  and  62  off of the longitudinal axis that runs through antennas  56 ,  60 , and  64  will generally tend to reduce the effectiveness of isolation elements  58  and  62  in isolating the antennas from each other. Locating antennas  56 ,  60 , and  64  at off-axis positions also tends to increase the overall footprint for the antennas, which makes it more difficult to fit the desired antenna structures into a device with a compact form factor. 
     The antennas in device  10  may be fed directly using feed terminals that are connected to portions of the antenna or indirectly through near-field coupling arrangements. In the illustrative example of  FIG. 5 , antenna  74  is fed using positive antenna feed terminal  86  and negative (ground) antenna feed terminal  84 . A transmission line such as coaxial cable  82  may be used to convey signals to and from feed terminals  86  and  84 . Transmission line center conductor  88  may be used to convey signals to and from positive antenna feed terminal  86 . The outer ground conductor of transmission line  82  is connected to terminal  84 . The outer ground conductor of transmission line  82  to terminal  84 . The antenna feed arrangement of  FIG. 5  is merely illustrative. Any suitable feed arrangement may be used. For example, antenna feed terminals  86  and  84  may be located at other portions of antenna  74  (e.g., so that the positive terminal is coupled to long arm  78  or so that the horizontal position of the feed point is adjusted for impedance matching). Moreover, a tuning network (e.g., a circuit formed from capacitors, inductors, etc.) may be coupled to antenna  74  or may be used as part of a feed network. 
     The antennas and isolation elements of device  10  may have dielectric support structures. An example of this type of arrangement is shown in  FIG. 6 . As shown in  FIG. 6 , antenna  74  may have an antenna resonating element such as element  76  that is supported by a dielectric support structure such as dielectric support structure  96 . Resonating element  76  may be formed from conductive traces on a flex circuit substrate or other suitable conductive materials. Dielectric support structure  96  may be formed from plastic or other suitable dielectric materials. In the example of  FIG. 6 , antenna  74  is being fed using a positive feed terminal  86  that is connected to antenna resonating element arm  78 . Antenna ground terminal  84  is connected to ground plane  66 . Arrangements of the type shown in  FIG. 6  may be used for antennas  56  and  64  (e.g., when antennas  56  and  64  are dual-band antennas). Arrangements of the type shown in  FIG. 6  may also be used for antenna  60  (e.g., when antenna  60  is a dual-band antenna). If one of arms  78  and  80  is omitted, antenna resonating element  76  will have an L-shape configuration. In this type of configuration, resonating element  76  may be used for a single-band antenna  60 . When feed terminals  86  and  84  are omitted, single-arm or multi-arm resonating elements such as element  76  of  FIG. 6  may serve as antenna isolation elements  58  and  62 . 
     As shown in  FIG. 7 , it is not necessary for the longer arm of a resonating element (in either an antenna or an antenna isolation element) to be located farther from the ground plane than the shorter arm of the resonating element. In the  FIG. 7  example, shorter resonating element arm  78  in resonating element  76  is located farther from ground plane  66  than longer resonating element arm  80 . 
     Antenna feed terminals for antennas such as antenna  74  of  FIG. 7  may be placed at any suitable location. For example, positive antenna feed terminal  86  may be connected to arm  80  and ground antenna feed terminal  84  may be connected to ground conductor  66 . 
     The bandwidth of an antenna such as the antenna of  FIG. 7  is in part determined by the vertical position of its arms. Antennas with antenna resonating element arms that are located relatively farther from ground plane  66  tend to exhibit relatively more bandwidth than antennas with resonating element structures that are located near to ground plane  66 . An illustrative antenna resonating element configuration in which both antenna resonating element arms are located at substantially the same vertical distance from ground plane  66  (and which therefore both produce antenna resonances with maximum bandwidth) is shown in  FIG. 8 . As shown in  FIG. 8 , antenna  74  may have a longer arm such as long arm  78  that is aligned with longitudinal axis  92  and a shorter arm such as short arm  80  that lies perpendicular to arm  78 . Both arm  78  and arm  80  lie parallel to ground plane  66 . 
     Particularly in situations in which it is desirable to provide the higher-frequency band of a multi-band antenna with a maximized bandwidth (e.g., when handling the 5.1 GHz band of a 2.4 GHz/5.1 GHz dual-band Wi-Fi antenna), it may be advantageous to use an arrangement of the type shown in  FIG. 8  or  FIG. 7 , because these configurations for antenna resonating element  76  place shorter antenna resonating element arm  80  at a relatively large vertical position relative to ground plane  66  than would otherwise be possible. An advantage of the  FIG. 8  arrangement is that the enhanced vertical spacing associated with arm  80  is achieved without adversely affecting the vertical spacing associated with arm  78 . 
     A perspective view of an illustrative antenna configuration of the type that is shown schematically in  FIG. 4  is shown in  FIG. 9 . As shown in  FIG. 9 , antennas  56 ,  60 , and  64  may be arranged in a line on common ground plane  66  (i.e., aligned in a collinear fashion with axis  92 ). Each antenna may have a longitudinal axis defined by its longest arm. Each such longitudinal axis may, if desired, be aligned with axis  92  as shown in  FIG. 9 . Similarly, isolation elements  58  and  62  may be configured so that they each have a longitudinal axis that is aligned with axis  92 . Antennas  56  and  64  may be dual-band antennas each having two respective resonating element arms. Antenna  60  may be a single band antenna (as an example). Antenna  60  may be formed from an L-shaped resonating element, as shown in  FIG. 9 . Antenna isolation elements  58  and  62  may be formed from any suitable antenna resonating element structures. For example, antenna isolation elements  58  and  62  may be formed from L-shaped resonating elements, as shown in  FIG. 9 . 
     To ensure that isolation elements  58  and  62  provide satisfactory radio-frequency isolation for antennas  56 ,  60 , and  64 , the resonating element structures that make up antenna isolation elements  58  and  62  may be tuned to resonate at the frequency at which isolation is desired. For example, if antennas  56  and  64  resonate at 2.4 GHz and 5.1 GHz and antenna  60  resonates at 2.4 GHz, and if isolation is desired at 2.4 GHz, antenna isolation elements  58  and  62  may have L-shaped resonating elements of length L, where L is equal to a quarter of a wavelength at 2.4 GHz. 
     As shown in  FIG. 9 , the antenna isolation elements may have termination points such as termination points  98 . L-shaped conductive elements such as elements  100  may have lengths L that are selected to provide isolation between antennas  56  and  64  and between antenna  60  and antennas  56  and  64 . Antennas  56  and  64  may have antenna resonating elements  104  that are connected to ground plane  66  at points  102 . Antenna  60  may have an antenna resonating element such as resonating element  108  that is connected to ground plane  66  at point  106 . 
     In the example of  FIG. 9 , resonating elements  104  and  108  of antennas  56 ,  60 , and  64  extend upwards and to the right (in the orientation shown in  FIG. 9 ). Similarly, antenna isolation elements  58  and  62  have resonating elements  100  that extend upwards and to the right from points  98 . This configuration is merely illustrative. Antennas  56 ,  60 , and  64  and antenna isolation elements  58  and  62  may extend upwards and to the left and/or upwards and to the right in any suitable combination (e.g., all facing to the right, all facing to the left, the antennas facing to the right and the isolation elements facing to the left, the antennas facing to the left and the isolation elements facing to the right, some of the antennas facing to the right and some to the left, some of the isolation elements facing to the right and some to the left, or combinations of these arrangements). 
       FIG. 10  shows an illustrative antenna configuration in which antennas  56 ,  60 , and  64  have resonating elements that extend upwards and to the right (i.e., elements that face to the right) and in which isolation elements  58  and  62  face to the left. In this type of configuration, points  98  are located in the vicinity of points  106  and  102 . 
     An alternative configuration for the antennas of device  10  is shown in  FIG. 11 . In the arrangement of  FIG. 11 , antenna isolation elements  58  and  62  have resonating elements with perpendicular conductive portions such as portion  112  of element  58 . Resonating element  100  is connected to ground conductive structure  66  at point  98 . Vertical portion  108  extends vertically in vertical direction  110 , perpendicular to the plane of ground conductor  66 . Horizontal perpendicular section  112  extends in direction  114 . Direction  114  is parallel to ground plane  66  and is perpendicular to vertical direction  110  and longitudinal axis  92 . Horizontal portion  116  of resonating element  100  extends parallel to longitudinal axis  92 , perpendicular to horizontal direction  114 , and perpendicular to vertical direction  110 . If desired, antennas  56 ,  60 , and  64  may have bends (e.g., perpendicular sections such as perpendicular portion  112  and/or U-shaped portions or serpentine paths). Isolation elements  58  and  62  may also have bends of different shapes and orientations. The arrangement of  FIG. 11  is merely illustrative. 
     If desired, the antenna isolation elements may be located at positions that are offset somewhat from axis  92 .  FIG. 12  shows potential offset positions in which isolation element  58  may be placed relative to antenna  56 . 
     Isolation element  58  may be located so that it contacts ground plane  66  at point  118 . In this type of situation, the resonant element of isolation element  58  will be positioned where indicated by solid line  120 . As indicated by dashed line  122 , in this configuration, the resonating element of antenna  56  is collinear with the resonating element of antenna isolation element  58 . Because point  118  lies on line  122 , there is no lateral offset between the location of resonating element  58  and the longitudinal axis of the antennas in device  10  (e.g., antenna  56  and the antennas that are not shown in  FIG. 12 ). 
     If desired, isolation element  58  may be located so that it contacts ground plane  66  at point  132 . In this configuration, antenna isolation element  58  will be positioned where indicated by dashed line  134 . Contact point  132  is offset from dashed line  122  by lateral offset distance  136 . Provided that lateral offset  136  is not too large, antenna isolation element  58  may still provide sufficient isolation for the antennas of device  10 . For example, a lateral offset of a fraction of a millimeter or a few millimeters may be acceptable for antennas that are a few centimeters in length. 
     Isolation element  58  may be provided with both a lateral and longitudinal offset with respect to antenna  56 . This type of configuration is illustrated by dashed line  126 . When the resonating element of antenna isolation element  58  is aligned with the position indicated by dashed line  126 , the resonating element contacts ground plane  66  at point  124 . As shown in  FIG. 12 , point  124  is laterally offset from dashed line  122  by lateral offset distance  128  and is longitudinally offset from point  118  (which is substantially vertically aligned with the tip of the longer resonating element arm of antenna  56 ) by longitudinal offset distance  130 . Provided that the magnitudes of the longitudinal offset and lateral offset are not too large (e.g., several millimeters as an example), isolation element  58  may provide sufficient radio-frequency isolation for the antennas of device  10 . 
     One isolation element, two isolation elements, or more than two isolation elements (e.g., in arrangements with four or more antennas) may be offset as shown in  FIG. 12 . If desired, mixed arrangements may be used (e.g., in which some isolation elements are laterally and/or longitudinally offset and in which some isolation elements are not offset). Moreover, antennas such as antennas  56 ,  60 , and  64  may be longitudinally and/or laterally offset with respect to each other and with respect to the isolation elements. 
     The arms of the antenna isolation elements and/or antennas in device  10  may also be oriented at non-zero angles with respect to longitudinal axis  92  if desired. An example of this type of arrangement is shown in  FIG. 13 . As shown in  FIG. 13 , antenna  56  has a longitudinal axis  92 . The other antennas of device  10  (e.g., antennas  60  and  64 ) may be aligned with axis  92 . Isolation elements such as isolation element  58  may be interposed between adjacent antennas to provide enhanced levels of radio-frequency signal isolation. Antenna isolation element  58  may have an L-shaped resonating element conductor. Arm  138  of the resonating element may be oriented at a non-zero angle α with respect to axis  92 . Any suitable angle α may be used. For example, isolation element  58  may have a resonating element arm  138  that is oriented at an angle α of about 1-10° with respect to axis  92  (as an example). 
     Non-zero resonating element arm orientations of the type illustrated by the orientation of isolation element arm  138  of  FIG. 13  may be used for antenna resonating elements and/or isolation element resonating elements. None of the elements, one or more of the elements, or all of the elements may be angled with respect to axis  92  if desired. Moreover, angled resonating element arrangements such as these may be used in configurations in which the resonating elements are longitudinally and/or laterally offset from axis  92 . 
     If desired, one or more of the antenna isolation elements may be implemented using multiple resonating element structures. As shown in  FIG. 14 , for example, antenna isolation element  56  may be implemented using three L-shaped conductive resonating elements: resonating element  140 , resonating element  142 , and resonating element  144 . Each of these conductive structures may be oriented at a zero angle with respect to longitudinal axis  92  of antennas  56  and  60  or at a non-zero angle with respect to longitudinal axis  92  of antennas  56  and  60  (as described in connection with  FIG. 13 ). Lateral and longitudinal offsets may be used in positioning resonating elements  140 ,  142 , and  144  as described in connection with  FIG. 12 . Moreover, different numbers of resonating element structures may be used. For example, antenna isolation element  58  may have more than three L-shaped conductive structures, or may have two L-shaped conductive structures. 
     The conductors of antenna isolation element  58  may have any suitable shape (e.g., L-shaped, multi-branched, shapes with bends, shapes with U-shaped and/or serpentine layouts, structures with combinations of these configurations, etc.). One of the antenna isolation elements may use multiple conductive structures, two of the antenna isolation elements may use multiple conductive structures, or (in arrangements using more than three antennas) three or more of the antenna isolation elements may use multiple conductive structures. The conductive structures in a given antenna isolation element may be substantially similar in shape or may have different shapes and sizes. 
     Antenna isolation elements  58  and  62  may be formed using multi-arm configurations. When the antenna isolation elements have multiple arms, the frequency response of the antenna isolation elements may be broadened to help enhance radio-frequency signal isolation effectiveness. An illustrative configuration in which antenna isolation element  58  is provided with multiple arms is shown in  FIG. 15 . As shown in  FIG. 15 , antenna isolation element  58  may have a first arm such as arm  146  and a second arm such as arm  148 . Additional arms may be used if desired. 
     Arm  146  may be longer than arm  148  (as an example). Arm  146  may be oriented so that it is parallel to longitudinal axis  92  of antennas such as antennas  56  and  60 . Arm  148  may be oriented perpendicular to axis  92  and parallel to ground plane  66 . 
     Additional suitable multi-arm configurations for the antenna isolation elements are shown in  FIG. 16 . In the example of  FIG. 16 , antenna isolation element  58  has two arms. Arm  152  is longer than arm  150 . Both arm  150  and arm  152  lie parallel to axis  92  (which is aligned with the longitudinal axis of each antenna and isolation structure in the  FIG. 16  arrangement). Antenna isolation element  62  is formed from multiple free-standing structures. One resonating element structure in antenna isolation element  62  is formed from L-shaped conductive strip  156 . Another resonating element structure in antenna isolation element  62  is formed from smaller L-shaped conductive strip  160 . As shown in  FIG. 16 , arm  158  of resonating element  156  may be larger than arm  162  of element  160 . If desired, structures such as resonating element  160  may be laterally or longitudinally offset, so that their attachment points to ground plane  66  are shifted with respect to the position shown for element  160 . For example, the position of a resonating element such as resonating element  160  may be longitudinally shifted so that it is aligned with the position indicated by dashed line  164 . 
     In general, the antenna isolation elements may have one or more individual resonating element structures. The structures may have the same shapes and sizes or may have different shapes and sizes. The structures may have one arm (e.g., in an L-shaped conductive strip) or may have multiple arms. The structures may be aligned with the longitudinal axis of the antenna structures or may be oriented at a non-zero angle. Lateral and longitudinal offsets may be used in positioning the resonating element structures. Combinations of these arrangements may be used in forming antenna isolation elements. 
     Antennas such as antennas  56 ,  60 , and  64  may also use these types of resonating element structures. For example, antenna  56  may be formed from two closely spaced resonating elements such as elements  156  and  160  of  FIG. 16 , provided that these elements are fed using appropriate antenna feed terminals such as feed terminals  86  and  84  of  FIG. 5 . In this type of arrangement, one of the antenna resonating elements may be directly fed using antenna feed terminals that are connected to the resonating element arm and ground plane as shown for arm  80  of antenna  74  in  FIG. 5 . The other antenna resonating element may be indirectly fed through near-field electromagnetic coupling (as an example). 
     The foregoing is merely illustrative of the principles of this invention and various modifications can be made by those skilled in the art without departing from the scope and spirit of the invention.