PATENT DOCUMENT

Publication Number: US-8854266-B2
Application Number: US-201113216012-A
Country: US
Kind Code: B2

Title: Antenna isolation elements

Abstract:
Electronic devices may be provided with antenna structures and antenna isolation element structures. An antenna array may be located within an electronic device. The antenna array may have multiple antennas and interposed antenna isolation element structures for isolating the antennas from each other. An antenna isolation element structure may have a dielectric carrier with a longitudinal axis. A sheet of conductive material may extend around the longitudinal axis to form a conductive loop structure. The loop structure in the antenna isolation element may have a gap that spans the sheet of conductive material parallel to the longitudinal axis. Electronic components may bridge the gap. Control circuitry may adjust the electronic components to tune the antenna isolation element.

Claims:
What is claimed is: 
     
       1. An antenna array, comprising:
 at least first and second antennas; and 
 an antenna isolation element formed from a loop of conductor that is configured to isolate the first and second antennas from each other, wherein the antenna isolation element is formed from a sheet of conductive material that extends around an axis to form the loop of conductor, wherein the loop of conductor has a gap, wherein the sheet of conductive material has a first dimension that spans the sheet of conductive material parallel to the axis and has a second dimension associated with a peripheral length of the sheet of conductive material around the axis, and wherein the first dimension is 1-10 cm and the second dimension is 1.5 to 3.5 cm. 
 
     
     
       2. The antenna array defined in  claim 1  wherein the antenna isolation element is interposed between the first and second antennas. 
     
     
       3. The antenna array defined in  claim 2  wherein the antenna isolation element comprises a dielectric carrier and wherein the sheet of conductive material comprises metal on the dielectric carrier. 
     
     
       4. The antenna array defined in  claim 3  wherein the gap spans the sheet of conductive material. 
     
     
       5. The antenna array defined in  claim 4  wherein the gap is configured to form a meandering path across the sheet of conductive material. 
     
     
       6. The antenna array defined in  claim 5  wherein the first and second antennas comprise loop antennas. 
     
     
       7. The antenna array defined in  claim 6  wherein the first and second antennas each have a sheet of conductive material configured to form a loop antenna resonating element. 
     
     
       8. The antenna array defined in  claim 4  wherein the first and second antennas each comprise a loop-shaped antenna resonating element and a loop-shaped antenna feed structure, wherein the loop-shaped antenna feed structure in the first antenna indirectly feeds the loop antenna resonating element in the first antenna, and wherein the loop-shaped antenna feed structure in the second antenna indirectly feeds the loop antenna resonating element in the second antenna. 
     
     
       9. The antenna array defined in  claim 1  wherein the first and second antennas comprise distributed loop antennas. 
     
     
       10. The antenna array defined in  claim 9  wherein the first and second antennas comprise strips of conductive material that each extend around the axis and that are each configured to form a respective loop with a gap. 
     
     
       11. An electronic device, comprising:
 a housing; 
 a display in the housing; and 
 an antenna array mounted in the housing along an edge of the display, wherein the antenna array includes at least first and second antennas and an antenna isolation element formed from a loop of conductor with a gap and wherein the loop of conductor is configured to isolate the first and second antennas from each other. 
 
     
     
       12. The electronic device defined in  claim 11  wherein the antenna isolation element is interposed between the first and second antennas and comprises a sheet of conductive material that extends around an axis to form the loop of conductor with the gap. 
     
     
       13. The electronic device defined in  claim 12  wherein the sheet of material has a dimension that spans the sheet of material parallel to the axis and wherein the first and second antennas are located along the axis. 
     
     
       14. The electronic device defined in  claim 13  further comprising at least one electrical component that bridges the gap. 
     
     
       15. The electronic device defined in  claim 14  further comprising control circuitry that supplies control signals that adjust the electrical component to tune the antenna isolation element. 
     
     
       16. An antenna isolation element configured to isolate first and second antennas in an electronic device from each other, comprising:
 a dielectric carrier; and 
 conductive material on the dielectric carrier that forms a loop, wherein the conductive material comprises a sheet of conductive material that extends around the dielectric carrier and that has a gap, wherein the dielectric carrier has a longitudinal axis, wherein the sheet of conductive material has a first dimension that spans the sheet of conductive material parallel to the longitudinal axis and has a second dimension associated with a periphery of the sheet around the longitudinal axis, and wherein the first dimension is 1-10 cm and the second dimension is 1.5 to 3.5 cm.

Description:
BACKGROUND 
     This relates generally to electronic devices and, more particularly, to electronic devices with antennas. 
     Electronic devices such as computers are often provided with antennas. For example, a computer monitor with an integrated computer may be provided with antennas that are located along an edge of the monitor. 
     Challenges can arise in mounting antennas within an electronic device, particularly in applications in which it is desired to form an array of multiple antennas. For example, the relative position between antennas in an array can affect coupling between antennas. If care is not taken, antennas may not be sufficiently well isolated from one another, which may degrade wireless performance. 
     It would therefore be desirable to be able to provide improved arrangements for isolating antennas in electronic devices. 
     SUMMARY 
     An electronic device may be provided with an array of multiple antennas. To isolate the antennas from each other, one or more antenna isolation elements may be provided. The antenna isolation elements may be interposed in the array between respective pairs of antennas. 
     The antennas in an antenna array may be, for example, distributed loop antennas. The antenna isolation elements may be based on loop-shaped parasitic structures. 
     An antenna isolation element may have a dielectric carrier with a longitudinal axis. A sheet of conductive material may extend around the longitudinal axis to form a conductive loop structure. The loop structure in the antenna isolation element may have a gap that spans the sheet of conductive material parallel to the longitudinal axis. Electronic components may bridge the gap. Control circuitry may adjust the electronic components to tune the antenna isolation element. 
     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 antennas and antenna isolation structures in accordance with an embodiment of the present invention. 
         FIG. 2  is a top view of a portion of an illustrative electronic device containing a pair of antennas and an antenna isolation element in accordance with an embodiment of the present invention. 
         FIG. 3  is a top view of a portion of an illustrative electronic device containing an array of three antennas with two interposed antenna isolation elements in accordance with an embodiment of the present invention. 
         FIG. 4  is a diagram showing how antennas may be coupled to radio-frequency transceiver circuitry and how optional control circuitry may be used in controlling antennas and isolation element structures in accordance with an embodiment of the present invention. 
         FIG. 5  is a perspective view of an illustrative loop antenna of the type that may be used in an antenna array in accordance with an embodiment of the present invention. 
         FIG. 6  is a graph of antenna performance for an illustrative indirectly fed distributed loop antenna showing respective contributions to performance that may be made by a loop-shaped indirect feeding structure and a loop antenna resonating element structure in accordance with the present invention. 
         FIG. 7  is a perspective view of an illustrative cavity-backed inverted-F antenna of the type that may be used in an antenna array in accordance with an embodiment of the present invention. 
         FIG. 8  is a schematic diagram of an illustrative loop-based antenna isolation element in accordance with an embodiment of the present invention. 
         FIG. 9  is a perspective view of an illustrative loop-based antenna isolation element in accordance with an embodiment of the present invention. 
         FIG. 10  is a cross-sectional end view of an illustrative loop-based antenna isolation element in an electronic device in accordance with an embodiment of the present invention. 
         FIG. 11  is a cross-sectional end view of an illustrative loop-based antenna isolation element having an oval cross-sectional shape in accordance with an embodiment of the present invention. 
         FIG. 12  is a cross-sectional end view of an illustrative loop-based antenna isolation element having a rectangular cross-sectional shape in accordance with an embodiment of the present invention. 
         FIG. 13  is a cross-sectional end view of an illustrative loop-based antenna isolation element having a cross-sectional shape with an angled side in accordance with an embodiment of the present invention. 
         FIG. 14  is a cross-sectional end view of an illustrative loop-based antenna isolation element having a cross-sectional shape with a combination of straight and curved sides in accordance with an embodiment of the present invention. 
         FIG. 15  is a cross-sectional end view of an illustrative loop-based antenna isolation element having a cross-sectional shape with straight edges that form a recessed portion in accordance with an embodiment of the present invention. 
         FIG. 16  is a perspective view of an illustrative loop-based antenna isolation element having electrical components that bridge a gap in a sheet of conductive material that forms the loop-based antenna isolation element in accordance with an embodiment of the present invention. 
         FIG. 17  is a diagram of an illustrative antenna isolation element formed from multiple L-shaped parasitic elements in accordance with an embodiment of the present invention. 
         FIG. 18  is a graph comparing how coupling between a pair of antennas may be reduced using different types of antenna isolation elements in accordance with embodiments of the present invention. 
         FIG. 19  is a diagram showing how an antenna may have a first loop antenna structure for indirectly feeding a second loop antenna structure and showing how the structures of the antenna may be oriented relative to an X-Y-Z coordinate system in accordance with an embodiment of the present invention. 
         FIG. 20  is a diagram showing how an antenna isolation element may be oriented relative to an X-Y-Z coordinate system in accordance with an embodiment of the present invention. 
         FIG. 21  is a diagram showing how an array of antennas and an interposed antenna isolation element may be oriented relative to one another to enhance antenna isolation in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Electronic devices may be provided with antennas and other wireless communications circuitry. The wireless communications circuitry may be used to support wireless communications in multiple wireless communications bands. One or more antennas may be provided in an electronic device. For example, antennas may be used to form an antenna array to support communications with a communications protocol such as the IEEE 802.11(n) protocol that uses multiple antennas. 
     An illustrative electronic device of the type that may be provided with one or more antennas is shown in  FIG. 1 . Electronic device  10  may be a computer such as a computer that is integrated into a display such as a computer monitor. Electronic device  10  may also be a laptop computer, a tablet computer, a somewhat smaller portable device such as a wrist-watch device, pendant device, headphone device, earpiece device, or other wearable or miniature device, a cellular telephone, a media player, or other electronic equipment. Illustrative configurations in which electronic device  10  is a computer formed from a computer monitor are sometimes described herein as an example. In general, electronic device  10  may be any suitable electronic equipment. 
     Device  10  may include one or more antenna isolation elements. The antenna isolation elements, which are sometimes referred to as parasitic elements, may be used to reduce coupling between antennas. For example, an isolation element may be placed between a pair of antennas in device  10  to help isolate the antennas from each other. Enhancing antenna isolation may help to improve the performance of wireless circuits such as 802.11(n) circuits during operation. The isolation elements may be formed from loop-based structures (e.g., distributed loop-based structures) or other parasitic antenna element structures. 
     Antennas and antenna isolation elements may be formed in device  10  in any suitable location such as locations along the edge of device  10 . For example, antennas and antenna isolation elements may be formed in one or more locations such as locations  26  in device  10 . The antennas in device  10  may include loop antennas, inverted-F antennas, strip antennas, planar inverted-F antennas, slot antennas, cavity antennas, monopoles, dipoles, patch antennas, hybrid antennas that include antenna structures of more than one type, or other suitable antennas. Antenna isolation elements may also be formed using structures such as these. The antennas may cover cellular network communications bands, wireless local area network communications bands (e.g., the 2.4 and 5 GHz bands associated with protocols such as the Bluetooth® and IEEE 802.11 protocols), and other communications bands. The antennas may support single band and/or multiband operation. For example, the antennas may be dual band antennas that cover the 2.4 and 5 GHz bands. The antennas may also cover more than two bands (e.g., by covering three or more bands or by covering four or more bands). Antenna isolation elements may operate to isolate antenna in one or more bands, two or more bands (e.g., 2.4 and/or 5 GHz bands), three or more bands, etc. 
     Conductive structures for the antennas and antenna isolation elements may, if desired, be formed from conductive electronic device structures such as conductive housing structures, from conductive structures such as metal traces on plastic carriers, from metal traces in flexible printed circuits and rigid printed circuits, from metal foil supported by dielectric carrier structures, from wires, and from other conductive materials. 
     Device  10  may include a display such as display  18 . Display  18  may be mounted in a housing such as electronic device housing  12 . Housing  12  may be supported using a stand such as stand  14  or other support structure. 
     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. 
     Display  18  may be a touch screen that incorporates capacitive touch electrodes or other touch sensor components or may be a display that is not touch sensitive. Display  18  may include image pixels formed from light-emitting diodes (LEDs), organic LEDs (OLEDs), plasma cells, electronic ink elements, liquid crystal display (LCD) components, or other suitable image pixel structures. 
     A cover glass layer may cover the surface of display  18 . Rectangular active region  22  of display  18  may lie within rectangular boundary  24 . Active region  22  may contain an array of image pixels that display images for a user. Active region  22  may be surrounded by an inactive peripheral region such as rectangular ring-shaped inactive region  20 . The inactive portions of display  18  such as inactive region  20  are devoid of active image pixels. Display driver circuits, antennas and antenna isolation elements (e.g., antennas and antenna isolation elements in regions such as regions  26 ), and other components that do not generate images may be located under inactive region  20 . 
     The cover glass for display  18  may cover both active region  22  and inactive region  20 . The inner surface of the cover glass in inactive region  20  may be coated with a layer of an opaque masking material such as opaque plastic (e.g., a dark polyester film) or black ink. The opaque masking layer may help hide internal components in device  10  such as antennas, driver circuits, housing structures, mounting structures, and other structures from view. 
     The cover layer for display  18 , which is sometimes referred to as a cover glass, may be formed from a dielectric such as glass or plastic. Antennas and antenna isolation elements may be mounted in regions such as regions  26  under an inactive portion of the cover glass. The antennas may transmit and receive signals through the cover glass. This allows the antennas to operate, even when some or all of the structures in housing  12  are formed from conductive materials. For example, mounting the antenna structures of device  10  under part of inactive region  20  may allow the antennas to operate even in arrangements in which some or all of the walls of housing  12  are formed from a metal such as aluminum or stainless steel (as examples). 
     A top (front) view of a portion of device  10  in the vicinity of an array of antennas mounted under region  26  of a display cover glass is shown in  FIG. 2 . As shown in  FIG. 2 , antenna array  72  may include antennas  74  and antenna isolation element  76 . In the arrangement shown in  FIG. 2 , antenna isolation element  76  is interposed between a first of antennas  74  (antenna ANT 1 ) and a second of antennas  74  (antenna ANT 2 ). If desired, antenna isolation elements (i.e., parasitic elements) may be located in other locations within device  10  (e.g., in a location that is not interposed between antennas  74  such as to the left of antenna ANT 1  or to the right of antenna ANT 2  or elsewhere in device  10 ). The configuration of  FIG. 2  is merely illustrative. 
     If desired, device  10  may include multiple antenna isolation elements. As shown in  FIG. 3 , for example, antenna array  72  may include three antennas  74  and two antenna isolation elements  76 . Antenna isolation element ISO 1  may be interposed between antennas ANT 1  and ANT 2  and antenna isolation element ISO 2  may be interposed between antennas ANT 2  and ANT 3  (as an example). Antenna arrays with more than three antennas and two or more antenna isolation elements may also be used in device  10 . 
       FIG. 4  is a circuit diagram showing how radio-frequency transceiver circuitry such as transceiver circuitry  78  may be coupled to antennas  74  in antenna array  72 . Respective transmission lines  80  may be used in coupling transceiver circuitry  78  to each antenna  74 . Transmission lines  80  may each include one or more portions of transmission line structures such as coaxial cable transmission lines, microstrip transmission lines, stripline transmission lines, edge coupled microstrip transmission lines, edge coupled stripline transmission lines, or other suitable transmission lines. Each transmission line  80  may include one or more portions of different types of transmission line structures (e.g., a segment of coaxial cable, a segment of a microstrip transmission line formed on a printed circuit board, etc.). Transmission lines  80  may each may contain a positive conductor (+) and a ground conductor (−). The conductors in transmission lines  80  may be formed from wires, braided wires, strips of metal, conductive traces on substrates, planar metal structures, housing structures, or other conductive structures. 
     Antennas  74  and isolation elements  76  may, if desired, contain tunable components such as tunable capacitors and other tunable circuitry. The tunable circuitry in antennas  74  and isolation elements  76  may be used to adjust the performance of antenna array  72  to cover various communications bands of interest during operation of device  10 . As shown in  FIG. 4 , control circuitry  82  may supply control signals to the antennas and antenna isolation elements of antenna array  72  using communications paths such as paths  84 . Control circuitry  82  may include baseband processor integrated circuits, microprocessors, microcontrollers, memory, application specific integrated circuits, and other storage and processing circuitry for device  10 . Paths  84  may serve as control paths that convey control signals from control circuitry  82  to adjustable circuits in antennas  74  and/or isolation elements  76 . 
     An illustrative antenna of the type that may be used to implement antennas in antenna array  72  in device  10  is shown in  FIG. 5 . As shown in  FIG. 5 , antenna  74  may have two loop-based portions (L 1  and L 2 ). In particular, antenna  74  may have a first portion formed from antenna resonating element structure L 2  and a second portion formed from antenna feed structure L 1 . In structure L 2 , current may loop within conductive material  52  in directions  94  about axis  40 . In structure L 1 , current  60  may loop within conductive structures  56 . 
     Feed structure L 1  may be a loop antenna structure that is directly fed by transmission line  80  at a positive antenna feed terminal (+) and ground antenna feed terminal (−). Antenna resonating element structure L 2  may be a loop antenna structure having conductive material  52  that extends around longitudinal axis  40  of structure L 2  and that is distributed across dimension ZD of structure L 2  (i.e., a sheet of conductive material that is distributed along longitudinal axis  40 ). Antenna feed structure L 1  may be formed from conductive structures  56 . 
     Conductive structures  52  and  56  may be formed from metal, conductive materials that contain metal, or other conductive substances. One or more support structures such as support structures  58  may be used to support conductive structures  52  and  56  of antenna structures L 1  and L 2  in antenna  74 . Support structures  58  may be formed from a dielectric such as plastic. Conductive structures  52  and  56  may be, for example, metal traces formed on a plastic carrier or metal traces formed on a flex circuit substrate or other substrate that is attached to support structures  58  (as examples). 
     In the illustrative configuration for antenna  74  that is shown in  FIG. 5 , support structures  58  have parallel left and right surfaces LS and RS and have a bottom surface BS that is angled with respect to top surface TS. Directly fed antenna feed structure L 1  may be directly fed by a transmission line  80  using an antenna feed formed a positive antenna feed terminal (+) and a ground antenna feed terminal (−). During operation, currents in structure L 1  may circulate within structure L 1  as indicated by loop  60 . The current circulating within structure L 1  produces electromagnetic fields that are coupled to structure L 2  (i.e., structure L 2  is indirectly fed by structure L 1 ). 
     Indirectly fed antenna resonating element structure L 2  may be formed from conductive structures  52  that are looped around longitudinal axis  40  of antenna  74 . Gap  50  or other suitable structures or components that are interposed in the loop of structure L 2  may be used to create a capacitance within the loop of structure L 2  (as an example). 
     As shown in  FIG. 5 , some of the conductive structures of antenna structures L 1  and L 2  may be electrically coupled to each other. For example, some of the metal structures on surfaces LS, RS, and BS (sometimes referred to as ground plane structures) may extend into parts of structure L 1  and parts of structure L 2 . 
     The coupling between structures L 1  and L 2  is affected both by electromagnetic near field coupling and by electrical coupling through shared conductive structures. Electromagnetic coupling occurs when electromagnetic fields that are generated by one loop pass through the other loop. Electric coupling occurs when current is generated in a shared conductor such as a portion of a shared ground plane structure. Consider, as an example, current flowing in portion  68  of loop L 1  in direction  64 . This current may electromagnetically induce a current in direction  66  in structures  62 . Because structure  62  is electrically connected to structures  52  (because structure  62  is a longitudinal extension of structures  52 ), the flow of induced current  66  tends to result in currents in structures  52 . The presence of portion  62  in antenna  28  may therefore enhance coupling between antenna structures L 1  and L 2 . 
     A graph corresponding to an illustrative antenna  74  in which both structures L 1  and L 2  contribute to antenna performance (for at least some frequencies of operation) is shown in  FIG. 6 . In  FIG. 6 , standing wave ratio (SWR) for a loop antenna that includes both antenna structure L 1  and antenna structure L 2  (e.g., in an arrangement of the type shown in  FIG. 5 ) is plotted as a function of operating frequency f. Frequency f 1  may correspond to the center frequency of a first band of interest such as an IEEE 802.11 band of 2.4 GHz (as an example). Frequency f 2  may correspond to the center frequency of a second band of interest such as an IEEE 802.11 band of 5 GHz (as an example). Antennas that cover more than two bands, fewer than two bands, and/or other bands of interest may use a distributed loop configuration. The example of  FIG. 6  is merely illustrative. 
     Curve L 2  of  FIG. 6  corresponds to the contribution to antenna  74  from antenna resonating element L 2 . As shown in  FIG. 6 , there are performance contributions from L 2  at frequency f 1  and a frequency that is equal to about 2 times f 1  (i.e., at 2f 1 , which is the second harmonic of frequency f 1 ). The antenna performance contribution from antenna structure L 2  at the second harmonic of frequency f 1  may lie close to upper band center frequency f 2 . 
     Curve L 1  corresponds to the contribution to antenna  74  from antenna resonating element L 1 . There may be relatively little contribution to antenna performance from L 1  at frequencies in the vicinity of low band frequency f 1 . However, at frequencies in the vicinity of f 2 , L 1  may exhibit a resonance that broadens the bandwidth of antenna  74  from L 2  and helps antenna  28  adequately cover the upper band at f 2 . 
     If desired, other types of antenna may be used in implementing antennas  74  in antenna array  72 . Examples of other types of antenna that may be used for antennas  74  include inverted-F antennas, strip antennas, planar inverted-F antennas, slot antennas, cavity antennas, patch antennas, monopoles, dipoles, hybrid antennas that include antenna structures of more than one type, or other suitable antennas.  FIG. 7  is a perspective view of an illustrative configuration for antenna  74  based on a cavity-backed inverted-F antenna design. As shown in  FIG. 7 , antenna  74  may have a support structure such as dielectric support structure  58 . Metal or other conductive material  86  may be used to cover the bottom and sidewall surfaces of structure  58  and thereby form an antenna cavity for cavity-backed antenna  74 . Inverted-F antenna resonating element  88  or other suitable antenna resonating element structures may be mounted in an opening that is formed at the upper surface of the cavity to form antenna  74 . The antenna may be fed using an antenna feed formed from a positive antenna feed terminal (terminal +) and a ground antenna feed terminal (terminal −). 
     An illustrative loop-based antenna isolation element (parasitic element) that may be used for antenna isolation element  76  of antenna array  72  is shown in  FIG. 8 . As shown in  FIG. 8 , antenna isolation element  76  may have conductive structures that form a loop-shaped conductive path (loop-shaped path  90  encircling axis  104 ). A gap may be interposed in the conductive materials that form the loop and/or components may be interposed within the loop to introduce capacitance  92 . The inclusion of capacitance  92  (e.g., from a gap in conductive structures  90 ) may help antenna isolation element  76  resonate (and perform isolation functions) at a frequency that is lower than would otherwise be possible. This may allow antenna isolation element  76  to be used in isolating antennas in a desired communications band without requiring the use of excessively large structures  90  (i.e., without enlarging perimeter P of path  90  excessively to create a desired reduction in operating frequency). The resonant frequency for isolation element  76  (i.e., the frequency at which isolation element  76  is effective at isolating antennas  74  from each other) for a loop-based structure of the type shown in  FIG. 8  that includes capacitance  92  will tend to decrease as the value of capacitance  92  is increased. 
     Loop path  90  may be implemented using a wire, using metal traces or other conductive traces on a flexible printed circuit (e.g., a “flex circuit” formed from a flexible sheet of polymer such as a sheet of polyimide), using metal traces on a rigid printed circuit board, using metal foil, using portions of conductive housing structures in housing  12 , or using other suitable conductive structures. 
     An illustrative configuration that may be used for antenna isolation element  76  is shown in  FIG. 9 . As shown in  FIG. 9 , antenna isolation element  76  may have conductive structures  90  that form a loop shape. Conductive structures  90  may be formed from a sheet (strip) of conductive material that extends around longitudinal axis  104  of antenna isolation element  76 . Conductive structures  90  may be formed on dielectric support structures  102  (e.g., plastic or other suitable material). The dimension L of isolation element  76  along longitudinal axis  104  (i.e., the dimension across the strip of conductor  90  that is wrapped around support structure  102  and axis  104 ) may be, for example, about 1-5 cm, about 1-10 cm, about 2-10 cm, about 2-5 cm, more than 1 cm, less than 10 cm, or other suitable size. Peripheral dimension P (i.e., the length of the loop of metal  90  or other conductor that is wrapped around support  102 ) may be about 1.5 to 2.5 cm, about 2.5 cm, 1.5 to 3.5 cm, 1 to 4 cm, more than 1 cm, less than 4 cm, or other suitable size. 
     Capacitance  92  of loop-based antenna isolation element  76  may be formed from a gap in conductive structures  90  that spans the sheet of material that is looped around axis  104 . The gap may, for example, have a width WD. In the  FIG. 9  example, the gap in conductive loop structures  90  is formed from a straight split in structures  90  that runs in a lateral dimension across structures  90  parallel to longitudinal axis  104 . The gap in structures  90  may have other shapes such as a meandering path shape (e.g., illustrative meandering gap  92 ′ of  FIG. 9 ). Use of a meandering path shape for the gap in conductive structures  90  may help to increase the magnitude of capacitance  92 . 
     A cross-sectional end view of an illustrative antenna isolation element  76  mounted within electronic device  10  is shown in  FIG. 10 . As shown in  FIG. 10 , antenna isolation element  76  may be mounted under a region such as region  26  ( FIG. 1 ) between respective antennas  74  (not shown in  FIG. 10 ). Antenna isolation element  76  may have a support structure such as support structure  102  with a rectangular cross-sectional shape to accommodate rectangular sidewalls and rear housing structures in housing  12  (as an example). Conductive structures  90  may form a loop that extends around longitudinal axis  104  of antenna isolation element  76 . Gap  92  may be interposed in the path of the loop to form a capacitance, as described in connection with  FIG. 8 . 
     In the illustrative configuration of  FIG. 10 , the cross-sectional shape of support structure  102  and antenna isolation element  76  is rectangular. If desired, other cross-sectional shapes may be used for antenna isolation element  76 . In general, antenna isolation element  76  may have any suitable cross-sectional shape that forms a loop of radio-frequency currents around axis  104  in response to the operation of antennas  74  in antenna array  72 . 
     As shown in  FIG. 11 , for example, conductive layer  90  may have an oval cross-sectional shape when viewed along longitudinal axis  104 . In the  FIG. 12  example, conductive layer  90  of antenna isolation element  76  has a rectangular cross-sectional shape. In the example of  FIG. 13 , conductive layer  90  forms a rectangular cross-sectional shape for antenna isolation element  76  with an angled sidewall. In particular, the upper and lower surfaces of antenna isolation element  76  of  FIG. 13  are parallel to each other and are perpendicular to the right surface of antenna isolation element  76 . The left surface of antenna isolation element  76  in  FIG. 13  is angled at a non-orthogonal angle with respect to the upper and lower surfaces and does not lie parallel to the right surface of antenna isolation element  76 . If desired, some of the surfaces of antenna isolation element  76  may be planar and other surfaces of antenna isolation element  76  may be non-planar, so that the cross-sectional shape of antenna isolation element  76  when viewed along longitudinal axis  104  has a combination of straight and curved sides, as shown in  FIG. 14 .  FIG. 15  shows how the shape of antenna isolation element  76  may have a recessed portion such as recessed portion  108 . Recesses such as recessed portion  108  may be configured so that antenna isolation element  76  can accommodate protruding housing structures in housing  12 , internal components in device  10 , and other structures in device  10 . 
     The examples of  FIGS. 11 ,  12 ,  13 ,  14 , and  15  are merely illustrative. In general, conductive structures  90  of antenna isolation element  76  may have any suitable shape that causes currents to flow around axis  104  during operation in antenna array  72 . 
       FIG. 16  shows how gap capacitance  92  in antenna isolation element  76  can be configured using electrical components  110 . Gap  92  in conductive structures  90  may have a built-in capacitance due to its shape (i.e., whether meandering or straight) and size (e.g., gap width WD). In addition to the capacitance due to the layout of gap  92 , the capacitance that is interposed within the loop formed by structures  90  may be affected by the capacitance of electrical components  110  that bridge gap  92 . Electrical components  110  may be capacitors or components that exhibit a capacitance. Electrical components  110  may be, for example, surface mount technology (SMT) components that are attached to the conductive material of conductive structures  90  using solder. Electronic components  110  may include one or more integrated circuits, one or more components such as capacitors, resistors, inductors, etc. that are packaged within a common SMT package, radio-frequency filter components, or other suitable circuit components. If desired, antennas  74  may incorporate electronic components such as components  110  (e.g., components that bridge gap  50  of conductive structures  52  in loop structure L 2  of antenna  74  of  FIG. 5 ). 
     Components such as one or more of electronic components  110  or other components associated with one or more antenna isolation elements  76  and/or antennas  74  in antenna array  72  may be implemented using tunable components. Tunable components may be controlled in real time using control circuitry in device  10  such as control circuitry  82  of  FIG. 4  (e.g., to produce desired amounts of capacitance). This allows device  10  to tune the frequency response of antennas  74  and/or antenna isolation elements  76  and therefore allows device  10  to tune the overall performance of antenna array  72 . Device  10  may, for example, tune antennas  74  and/or antenna isolation elements  76  when it is desired to cover a particular frequency band or bands of interest (e.g., when switching from one type of wireless communications mode to another, when device  10  is moved into a new geographical region that uses a different set of wireless communications frequencies, etc.). 
       FIG. 17  shows how antenna isolation element  76  may be implemented using L-shaped parasitic elements extending from a common ground plane structure such as ground conductor  118 . As shown in  FIG. 17 , antenna isolation element  76  may include two or more L-shaped conductive elements such as L-shaped parasitic element  112 , L-shaped parasitic element  114 , and L-shaped parasitic element  116 . Each L-shaped element in antenna isolation element  76  may have a different length so that each L-shaped parasitic element contributes a resonance peak (and a corresponding antenna isolation contribution) at a different corresponding frequency. If desired, other types of conductive structures may be used in forming a parasitic antenna element (e.g., structures with more than one conductive branch such as T-shaped structures, structures formed from strips of conductive material that form planar L-shaped elements, structures with other shapes, etc.). The example of  FIG. 17  is merely illustrative. 
       FIG. 18  is a graph comparing antenna isolation performance for an antenna isolation element of the type shown in  FIG. 17  (curve  120 ) and an antenna isolation element of the type shown in  FIG. 9  (curve  122 ). In the configuration shown in  FIG. 17 , antenna isolation element  76  has three individual L-shaped resonating structures that resonate in response to radio-frequency signals from antennas  74  in array  72 . The presences of the three separate L-shaped elements in antenna isolation element  76  of  FIG. 17  gives rise to three corresponding decreases in coupling (S 21 ) between a pair of antennas  74  in array  72  (shown as isolation resonances P 1 , P 2 , and P 3 ). Each resonance P 1 , P 2 , and P 3  is associated with a different frequency f, because each of elements  112 ,  114 , and  116  in antenna isolation element  76  of  FIG. 17  has a different corresponding length and therefore a different resonance behavior. Collectively, resonances P 1 , P 2 , and P 3  may serve to isolate a pair of antennas  74  in array  72  in a communications band centered at operating frequency fa. 
     Curve  122  of  FIG. 18  corresponds to an isolation element of the type shown in  FIG. 9  in which conductive loop structures  90  have a dimension L along longitudinal axis  104 . The size of L (e.g., 1-10 cm), helps to broaden the bandwidth of isolation element  76 , so that curve  122  (in the  FIG. 18  example) is broader and deeper than curve  120 . In general, increases in dimension L of antenna isolation element  76  may be used to increase the amount of isolation (isolation bandwidth) exhibited by antenna isolation element  76 . 
     When using an isolation element of the type shown in  FIG. 9 , common ground currents from antennas in the antenna array (i.e., induced currents flowing along dimension Z) tend to be drawn into current path  98  ( FIG. 9 ) in the isolation element and do not couple significantly further along the array. The configuration of loop-based isolation element  76  of  FIG. 9  may therefore help suppress antenna-to-antenna coupling through shared ground currents. 
     Elements  112 ,  114 , and  116  of isolation element  76  in  FIG. 17  serve as parasitic elements that tend to create virtual open circuits to the common ground currents traveling along the Z axis that lower coupling between antennas in the array that share common ground plane  118 . 
       FIG. 19  is a diagram showing how antenna feed structure L 1  may be used to indirectly feed antenna resonating element L 2  in an antenna of the type described in connection with antenna  74  of  FIG. 5 . The antenna feed structure for antenna  74  of  FIG. 19  is formed from a directly fed loop antenna structure (antenna structure L 1 ) and the antenna resonating element structure is formed from a loop antenna structure (e.g., antenna structure L 2  of  FIG. 5 ). Directly fed loop antenna structure L 1  may include a loop of conductive material  56  that is directly fed by transmission line  80 . The positive conductor in transmission line  80  may be connected to positive antenna feed terminal (+) and the ground conductor in transmission line  80  may be connected to ground antenna feed terminal (−). Loop antenna L 2  may be formed using conductive structures such as conductive structures  52  that are distributed along the length of longitudinal axis  40 . To avoid over-complicating the drawings, the distributed shape of conductive structures  52  in antenna resonating element L 2  is not depicted in  FIG. 19 . Electromagnetic fields that may be coupled between structures L 1  and L 2  during operation of antenna  74  are represented by lines  54 . In configurations of the type shown in  FIG. 19 , the plane that contains antenna feed structure L 1  lies perpendicular to the plane that contains antenna resonating element structure L 2 . Other relative orientations between structures L 1  and L 2  may be used if desired. 
     In antenna  74  of  FIG. 19 , loop L 2  lies in the X-Y plane and longitudinal axis  40  of antenna resonating element L 2  is parallel to the Z axis.  FIG. 20  is a diagram showing how antenna isolation element  76  may be oriented so that loop-shaped path  90  lies in the X-Y plane and so that longitudinal axis  104  extends parallel to the Z-axis. 
     Antenna isolation may be enhanced by aligning antenna structures such as antenna structure  74  of  FIG. 19  and antenna isolation elements such as antenna isolation element  20  so that longitudinal axis  40  of each antenna  74  lies along a common axis (i.e., the Z-axis) with longitudinal axis  104  of antenna isolation element  76 , as shown in the example of  FIG. 21 . In the  FIG. 21  example, antennas ANT 1  and ANT 2  are being isolated using interposed antenna isolation element ISO, each of which is aligned along a common axis (axis Z). 
     In this configuration, currents in each antenna  74  travel along the conductive path of loop L 2  rather than towards an adjacent antenna, which minimizes the amount of current that is induced in one of antennas  74  when operating another of antennas  74  through common ground plane currents. The Z-axis tends to be associated with a null in the radiation pattern for antennas  74  of the type shown in  FIG. 19 , so aligning each axis  40  along a common axis also may enhance isolation by reducing electromagnetic near-field coupling. 
     The antennas and antenna isolation elements of antenna array  72  of  FIG. 21  may, if desired, be mounted within device  10  in a region such as one of regions  26  of  FIG. 1 . Other suitable antenna arrays may be formed if desired (e.g., to place multiple antennas within the hinge of a laptop computer, to place multiple antennas along the edge of a tablet computer or other portable device, etc.). In configurations such as these in which antennas are mounted along a common ground plane structure (e.g., shared traces on a printed circuit board, shared conductive electronic device housing structures  12 , or other common ground plane structures), there is a potential for the antennas to couple through shared ground plane currents. When one or more or two or more antennas in an antenna array are formed using loop-antenna structures, antenna coupling through shared ground plane currents can be reduced by orienting the antenna resonating element loops perpendicular to the dimension along which common ground plane currents have the potential to flow. 
     In the antenna array of  FIG. 21 , for example, loop currents in loop antenna resonating elements L 2  flow in the X-Y plane, perpendicular to dimension Z. Common ground plane currents associated with antenna-to-antenna coupling would flow in dimension Z, past each antenna in the array. When using loop antennas, however, currents in the loop antenna resonating elements flow in the X-Y plane, not along dimension Z. Common ground currents between antennas (i.e., shared ground plane currents along dimension Z) are therefore suppressed when the loop antenna resonating elements are configured so that loop currents flow in the X-Y plane, providing additional isolation to that provided by the antenna isolation element. 
     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.

Metadata:
Filing Date: 20110823
Publication Date: 20141007
Grant Date: 20141007
Priority Date: 20110823
Inventors: ZHU JIANG
GUTERMAN JERZY
PASCOLINI MATTIA
NATH JAYESH
SCHLUB ROBERT W.
Assignee: APPLE INC
CPC Classifications: [{"code": "H01Q1/2266", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q1/2266", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q13/18", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01Q1/523", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01Q1/523", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01Q1/523", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 46750443