PATENT DOCUMENT

Publication Number: US-8441404-B2
Application Number: US-95916507-A
Country: US
Kind Code: B2

Title: Feed networks for slot antennas in electronic devices

Abstract:
Electronic devices and antennas for electronic devices are provided. The antennas may have ground plane elements with dielectric-filled openings. The dielectric-filled openings may be configured to form one or more rectangular slots. The antennas may be fed using transmission lines having first and second conductors. The first conductor of a given transmission line may be coupled to the ground plane element on one side of the slots. The second conductor of the transmission line may be coupled to a planar conductive element. The planar conductive element may couple to the ground plane element on the other side of the slots. The slots may be separated by a portion of the ground plane element. The planar conductive element may bridge at least one of the slots and may overlap the portion of the ground plane element that separates the slots without electrically contacting that portion of the ground plane element.

Claims:
What is claimed is: 
     
       1. An antenna that has an impedance and that is fed by a transmission line that has a first conductor and a second conductor, wherein the transmission line has an impedance, comprising:
 a ground plane element connected to the first conductor; 
 at least one antenna resonating element opening formed in the ground plane element; and 
 a planar conductive structure that bridges at least part of the antenna resonating element opening and that is connected to the second conductor, wherein the planar conductive structure has an area and is operable to, together with the ground plane element, create a feed capacitance to match the impedance of the transmission line to the impedance of the antenna, wherein the at least one antenna resonating element opening comprises first and second antenna resonating element slots, wherein the planar conductive structure overlaps a first part of the first slot, and wherein the second conductor overlaps the second slot and overlaps a second part of the first slot. 
 
     
     
       2. The antenna defined in  claim 1  wherein the at least one antenna resonating element opening comprises a third antenna resonating element slot, wherein the planar conductive structure overlaps the third slot. 
     
     
       3. The antenna defined in  claim 1  wherein a ground plane portion of the ground plane element lies between the first and second antenna resonating element slots and wherein at least some of the planar conductive structure overlaps part of the ground plane portion without contacting that part of the ground plane portion. 
     
     
       4. The antenna defined in  claim 3  wherein a solid dielectric lies between the planar conductive structure and the ground plane portion. 
     
     
       5. The antenna defined in  claim 1  wherein the ground plane element is formed from a portion of a conductive electronic device housing. 
     
     
       6. The antenna defined in  claim 1  wherein the ground plane element is formed from a portion of a printed circuit board conductor. 
     
     
       7. The antenna defined in  claim 1  further comprising solid dielectric that fills the first and second antenna resonating element slots. 
     
     
       8. An antenna that has an impedance and that is fed by a transmission line that has a first conductor and a second conductor, wherein the transmission line has an impedance, comprising:
 a ground plane element connected to the first conductor; 
 at least one antenna resonating element opening formed in the ground plane element; and 
 a planar conductive structure that bridges at least part of the antenna resonating element opening and that is connected to the second conductor, wherein the planar conductive structure has an area and is operable to, together with the ground plane element, create a feed capacitance to match the impedance of the transmission line to the impedance of the antenna, wherein the at least one antenna resonating element opening comprises at least first and second antenna resonating element slots, wherein the first and second antenna resonating element slots are aligned along a common longitudinal axis, wherein the planar conductive structure overlaps the first antenna resonating element slot at a first longitudinal position, wherein the planar conductive structure overlaps the second antenna resonating element slot at a second longitudinal position, and wherein the first and second longitudinal positions are different. 
 
     
     
       9. The antenna defined in  claim 8  wherein at least one of the first and second antenna resonating element slots comprises a rectangular slot portion. 
     
     
       10. The antenna defined in  claim 8  wherein a ground plane portion of the ground plane element lies between the first and second antenna resonating element slots and wherein the planar conductive structure comprises a metal strap that covers part of the ground plane portion. 
     
     
       11. The antenna defined in  claim 8  wherein a ground plane portion of the ground plane element lies between the first and second antenna resonating element slots and wherein the planar conductive structure comprises a substantially rectangular metal strap that covers part of the ground plane portion. 
     
     
       12. The antenna defined in  claim 8  wherein the antenna resonating element slots each have a first end and a second end, and wherein the first ends are aligned. 
     
     
       13. The antenna defined in  claim 8  wherein the antenna resonating element slots each have a first end and a second end, and wherein the first ends are offset with respect to each other so that they are not aligned. 
     
     
       14. The antenna defined in  claim 8  wherein the second conductor bridges at least a part of the antenna resonating element opening. 
     
     
       15. An antenna that is fed by a transmission line having a first conductor and a second conductor, comprising:
 a ground plane; 
 at least first and second slots in the ground plane that are separated by a portion of the ground plane; 
 a conductive planar structure that bridges the first slot, that is electrically coupled to the ground plane element, and that overlaps at least a first part of the portion of the ground plane separating the first and second slots, wherein there is a gap between the conductive planar structure and the part of the ground plane that is overlapped by the conductive planar structure, wherein the first conductor is connected to the ground plane, wherein the second conductor is connected to the conductive planar structure, and wherein the second conductor overlaps at least a first part of the second slot; and 
 a solid dielectric in the gap. 
 
     
     
       16. The antenna defined in  claim 15  wherein the first slot is shorter than the second slot and wherein the first and second slots are configured to handle radio-frequency signals for respective first and second communications bands. 
     
     
       17. The antenna defined in  claim 16  wherein the first slot is configured to handle radio-frequency signals for a 2.4 GHz communications band and wherein the second slot is configured to handle radio-frequency signals for a 5.0 communications band. 
     
     
       18. The antenna defined in  claim 15  further comprising a solid dielectric that fills the first and second slots. 
     
     
       19. The antenna defined in  claim 15  wherein the conductive planar structure bridges the portion of the ground plane separating the first and second slots and overlaps at least a second part of the second slot. 
     
     
       20. A portable electronic device, comprising:
 circuitry that handles radio-frequency signals; 
 a transmission line coupled to the circuitry, wherein the transmission line has first and second conductors; and 
 an antenna, wherein the antenna has:
 a ground plane element; 
 at least first and second slots in the ground plane that are separated by a portion of the ground plane element and that serve as antenna resonating elements for the antenna; and 
 a conductive planar structure that overlaps at least part of the slots, wherein the second conductor is connected to the conductive planar structure, wherein the first conductor is connected to the ground plane element on one side of the first and second slots without electrically contacting any of the portion of the ground plane element between the slots, wherein the conductive planar structure is connected to an opposing side of the first and second slots without electrically contacting any of the portion of the ground plane element between the slots, wherein the conductive planar structure bridges the first slot and overlaps at least a first part of the portion of the ground plane element between the slots, wherein the first slot has a width, wherein the second slot has a width, and wherein the conductive planar structure has a width that is greater than the width of the first slot and that is greater than the width of the second slot. 
 
 
     
     
       21. The portable electronic device defined in  claim 20  wherein the ground plane element comprises a portion of a conductive housing for the portable electronic device. 
     
     
       22. The portable electronic device defined in  claim 20  wherein the conductive planar structure overlaps the portion of the ground plane element between the slots without contacting any of that portion of the ground plane element, and wherein the antenna further comprises a solid dielectric between the conductive planar structure and some of the portion of the ground plane element that is between the slots. 
     
     
       23. The portable electronic device defined in  claim 20  wherein the first slot is configured to handle radio-frequency signals for a first communications band and wherein the second slot is configured to handle radio-frequency signals for a second communications band, wherein the first and second communications bands do not overlap. 
     
     
       24. The portable electronic device defined in  claim 20  further comprising a solid dielectric in the first and second slots. 
     
     
       25. The portable electronic device defined in  claim 20  wherein the second conductor overlaps at least a first part of the second slot. 
     
     
       26. The portable electronic device defined in  claim 25  wherein the second conductor bridges the second slot and overlaps at least a second part of the portion of the ground plane element between the slots. 
     
     
       27. The portable electronic device defined in  claim 25  wherein the conductive planar structure bridges the portion of the ground plane element between the slots and overlaps at least a second part of the second slot. 
     
     
       28. An antenna that is fed by a transmission line having a first conductor and a second conductor, comprising:
 a ground plane; 
 at least first and second slots in the ground plane that are separated by a portion of the ground plane; and 
 a conductive planar structure that bridges the first slot, that is electrically coupled to the ground plane element, and that overlaps at least a first part of the portion of the ground plane separating the first and second slots, wherein there is a gap between the conductive planar structure and the part of the ground plane that is overlapped by the conductive planar structure, wherein the first conductor is connected to the ground plane, wherein the second conductor is connected to the conductive planar structure, wherein the second conductor overlaps at least a first part of the second slot, and wherein the second conductor bridges the second slot and overlaps at least a second part of the portion of the ground plane separating the first and second slots.

Description:
BACKGROUND 
     This invention relates to antennas, and more particularly, to feed networks for slot antennas in electronic devices. 
     Due in part to their mobile nature, portable electronic devices are often provided with wireless communications capabilities. Portable electronic devices may use wireless communications to communicate with wireless base stations. For example, cellular telephones may communicate using cellular telephone bands at 850 MHz, 900 MHz, 1800 MHz, and 1900 MHz (e.g., the main Global System for Mobile Communications or GSM cellular telephone bands). Portable electronic devices may also use other types of communications links. For example, portable electronic devices may communicate using the Wi-Fi® (IEEE 802.11) bands at 2.4 GHz and 5.0 GHz and the Bluetooth® band at 2.4 GHz. Communications are also possible in data service bands such as the 3 G data communications band at 2100 MHz band (commonly referred to as UMTS or Universal Mobile Telecommunications System). 
     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 portable 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. These techniques can be used to produce internal antennas that fit within the tight confines of a compact portable device such as a handheld electronic device. With conventional portable electronic devices, however, design compromises are made to accommodate such antennas. These design compromises may include, for example, compromises related to antenna efficiency and antenna bandwidth. It can therefore be difficult to integrate conventional antennas into electrical devices while maintaining satisfactory performance. 
     It would therefore be desirable to be able to provide improved antenna structures for electronic devices such as portable electronic devices. 
     SUMMARY 
     Electronic devices and antennas for electronic devices are provided. The electronic devices may be desktop computers or other computing equipment, portable electronic devices such as laptop or tablet computers, or handheld electronic devices such as devices with music player and wireless communications capabilities. 
     The electronic devices may have ground plane elements. The ground plane elements may be formed from a portion of a conductive device housing or from internal structures such as conductive layers on printed circuit boards. 
     Antennas may be formed from one or more dielectric-filled openings in the ground plane elements. For example, an antenna may be formed from one or more dielectric-filled rectangular slots in a ground plane element. The dielectric-filled slots may have lengths that are configured so that the slots serve as antenna resonating elements for the antenna in communications bands of interest. For example, one slot may be configured to have a length that is suitable for handling communications in a first communications band whereas another slot may be configured to have a length that is suitable for handling communications in a second communications band. 
     An antenna may be fed using a coaxial cable or other transmission line that has first and second conductors. The first conductor of a given transmission line may be coupled to the ground plane element on one side of the slots. The second conductor of the transmission line may be coupled to a planar conductive element. The planar conductive element may couple to the ground plane element on the other side of the slots. The slots may be separated by a portion of the ground plane element. The planar conductive element may bridge at least one of the slots and may overlap the portion of the ground plane element that separates the slots without electrically contacting that portion of the ground plane 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 such as a portable electronic device that may be provided with slot antennas in accordance with an embodiment of the present invention. 
         FIG. 2  is a perspective view of an illustrative slot antenna that has been formed in a conductive housing wall of an electrical device in accordance with an embodiment of the present invention. 
         FIG. 3  is a perspective view of an illustrative slot antenna that has been mounted within an electrical device adjacent to an antenna window in a housing wall in accordance with an embodiment of the present invention. 
         FIG. 4  is a perspective view of an illustrative dual-slot antenna in accordance with an embodiment of the present invention. 
         FIG. 5  is a graph showing how an antenna such as an antenna of the type shown in  FIG. 4  may be used to cover multiple communications bands in accordance with an embodiment of the present invention. 
         FIG. 6  is a top view of an illustrative dual-slot antenna showing an alternative position for antenna feed terminals relative to the slots in a dual-slot antenna configuration of the type shown in  FIG. 4  in accordance with an embodiment of the present invention. 
         FIG. 7  is a top view of an illustrative multislot antenna having more than two slots in accordance with an embodiment of the present invention. 
         FIG. 8  is a top view of an illustrative alternative feed arrangement for a multislot antenna of the type shown in  FIG. 7  in accordance with an embodiment of the present invention. 
         FIG. 9  is a top view of another illustrative feed arrangement for a multislot antenna of the type shown in  FIG. 7  in accordance with an embodiment of the present invention. 
         FIG. 10  is a perspective view of an illustrative slot antenna with a matching network formed from a conductive planar element in accordance with an embodiment of the present invention. 
         FIG. 11  is a cross-sectional side view of an illustrative slot antenna and matching network of the type shown in  FIG. 10  in accordance with an embodiment of the present invention. 
         FIG. 12  is a top view of an illustrative slot antenna having two slots and an impedance matching network structure in accordance with an embodiment of the present invention. 
         FIG. 13  is a top view of an illustrative single-slot antenna having an impedance matching network structure that substantially covers the width of the antenna slot in accordance with an embodiment of the present invention. 
         FIG. 14  is a top view of an illustrative single-slot antenna having an impedance matching network structure that partially covers the width of the antenna slot in accordance with an embodiment of the present invention. 
         FIG. 15  is a top view of an illustrative dual-slot antenna having an impedance matching network structure that substantially covers the width of one of the antenna slots in accordance with an embodiment of the present invention. 
         FIG. 16  is a top view of an illustrative dual-slot antenna having an impedance matching network structure that substantially covers the widths of both of the antenna slots in accordance with an embodiment of the present invention. 
         FIG. 17  is a top view of an illustrative dual-slot antenna having an impedance matching network structure that partially covers the width of one of the antenna slots in accordance with an embodiment of the present invention. 
         FIG. 18  is a top view of an illustrative slot antenna having three slots and having an impedance matching network structure that spans the widths of at least two of the slots in accordance with an embodiment of the present invention. 
         FIG. 19  is a top view of an illustrative slot antenna having an impedance matching network structure that is configured to provide various amount of impedance matching to each slot in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     The present invention relates generally to antennas and antenna feed arrangements for wireless electronic devices. 
     The wireless electronic devices may be any suitable electronic devices. As an example, the wireless electronic devices may be desktop computers or other computer equipment. The wireless electronic devices may also 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 may be handheld electronic devices. 
     Examples of portable and handheld electronic devices include cellular telephones, media players with wireless communications capabilities, handheld computers (also sometimes called personal digital assistants), remote controls, global positioning system (GPS) devices, and handheld gaming devices. The devices may also be hybrid devices that combine the functionality of multiple conventional devices. Examples of hybrid 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 handheld device that receives email, supports mobile telephone calls, has music player functionality and supports web browsing. These are merely illustrative examples. 
     An illustrative electronic device such as a portable electronic device in accordance with an embodiment of the present invention is shown in  FIG. 1 . Device  10  may be any suitable electronic device. As an example, device  10  may be a laptop computer. 
     Device  10  may handle communications over one or more communications bands. For example, wireless communications circuitry in device  10  may be used to handle cellular telephone communications in one or more frequency bands and data communications in one or more communications bands. Typical data communications bands that may be handled by the wireless communications circuitry in device  10  include the 2.4 GHz band that is sometimes used for Wi-Fi® (IEEE 802.11) and Bluetooth® communications, the 5.0 GHz band that is sometimes used for Wi-Fi communications, the 1575 MHz Global Positioning System band, and 3 G data bands (e.g., the UMTS band at 1920-2170). These bands may be covered using single-band and multiband antennas. For example, cellular telephone communications can be handled using a multiband cellular telephone antenna and local area network data communications can be handled using a multiband wireless local area network antenna. As another example, device  10  may have a single multiband antenna for handling communications in two or more data bands (e.g., at 2.4 GHz and at 5.0 GHz). 
     Device  10  may have housing  12 . Housing  12 , which is sometimes referred to as a case, may be formed of any suitable materials including plastic, glass, ceramics, metal, other suitable materials, or a combination of these materials. In some situations, portions of housing  12  may be formed from a dielectric or other low-conductivity material, so as not to disturb the operation of conductive antenna elements that are located in proximity to housing  12 . 
     In other situations, housing  12  will be partly or entirely formed from conductive materials such as metal. An illustrative conductive 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 conductive materials 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 conductive elements, one or more of the conductive elements may be used as part of the antenna in device  10 . For example, metal portions of housing  12  and metal components in housing  12  may be shorted together to form a ground plane in device  10  or to expand a ground plane structure that is formed from a planar circuit structure such as a printed circuit board structure (e.g., a printed circuit board structure used in forming antenna structures for device  10 ). The ground plane may be used in forming the antenna. 
     Device  10  may have one or more buttons such as buttons  14 . Buttons  14  may be formed on any suitable surface of device  10 . In the example of  FIG. 1 , buttons  14  have been formed on the top surface of device  10 . Buttons  14  may form a keyboard on a laptop computer (as an example). 
     If desired, device  10  may have a display such as display  16 . Display  16  may be a liquid crystal diode (LCD) display, an organic light emitting diode (OLED) display, a plasma 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 . Device  10  may also have a separate touch pad device such as touch pad  26 . 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. Buttons  14  may, if desired, be arranged adjacent to display  16 . With this type of arrangement, the buttons may be aligned with on-screen options that are presented on display  16 . A user may press a desired button to select a corresponding one of the displayed options. 
     Device  10  may have circuitry  18 . Circuitry  18  may include storage, processing circuitry, and input-output components. Wireless transceiver circuitry in circuitry  18  may be used to transmit and receive radio-frequency (RF) signals. Transmission lines such as coaxial transmission lines and microstrip transmission lines may be used to convey radio-frequency signals between transceiver circuitry and antenna structures in device  10 . As shown in  FIG. 1 , for example, transmission line  22  may be used to convey signals between antenna  20  and circuitry  18 . Transmission line  22  may be, for example, a coaxial cable that is connected between an RF transceiver (sometimes called a radio) and an antenna. 
     Antennas such as antenna  20  may be located adjacent to keys  14  as shown in  FIG. 1  or may be located in other suitable locations (e.g., top cover surface  24  of housing  12 ). These are merely illustrative locations for antenna  20 . Antenna  20  may be formed on any suitable portion of an electronic device if desired. 
     Antenna  20  and the wireless communications circuitry of device  10  may support communications over any suitable wireless communications bands. For example, wireless communications circuitry in device  10  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 3 G data communications band at 2100 MHz band (commonly referred to as UMTS or Universal Mobile Telecommunications System), Wi-Fi® (IEEE 802.11) bands (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 1575 MHz. Wi-Fi bands that may be supported include the 2.4 GHz band and the 5.0 GHz bands. The 2.4 GHz Wi-Fi band extends from 2.412 to 2.484 GHz. Commonly-used channels in the 5.0 GHz Wi-Fi band extend from 5.15-5.85 GHz, so the 5.0 GHz band is sometimes referred to by the 5.4 GHz approximate center frequency for this range (i.e., these communications frequencies are sometimes referred to as making up a 5.4 GHz communications band). Device  10  can cover these communications bands and/or other suitable communications bands with proper configuration of antennas such as antenna  20 . 
     Antenna  20  may be formed from a conductive surface that has one or more dielectric-filled openings. These openings, which may sometimes be referred to as slots, may serve as resonating elements for antenna  20 . The conductive surface from which antenna  20  is formed may sometimes be referred to as a ground plane element or ground plane and is typically coupled to an antenna ground terminal. In this type of configuration, one antenna pole may be formed by a dielectric-filled antenna resonating element slot and one antenna pole may be formed by the ground plane. 
     A slotted antenna of this type may be formed from any suitable conductive surface. For example, antenna  20  may be formed from a conductive surface that makes up a portion of a conductive housing for device  10 . Antenna  20  may also be formed from a conductive surface that is located on an interior component of device  10  such as a conductive surface on a printed circuit board. Combinations of these arrangements or other suitable arrangements may also be used. 
     An illustrative embodiment of antenna  20  in which antenna  20  has been formed from an exterior housing surface of device  10  is shown in  FIG. 2 . As shown in  FIG. 2 , antenna  20  may have a ground plane element formed from conductive housing  12 . Slots  28  may be formed in housing  12 . In the example of  FIG. 2 , there are two slots  28 . This is merely illustrative. Antenna  20  may have one slot, two slots, three slots, more than three slots, or any other suitable number of slots. 
     Any suitable feed arrangement may be used for antenna  20 . For example, a transmission line may be connected to antenna terminals  34  and  36 . If desired, an impedance matching network may be coupled to the antenna (e.g., at terminals such as terminals  34  and  36 ). 
     In antenna  20  of  FIG. 2 , conductive surface  12  may be any conductive external surface associated with electronic equipment such as electronic device  10  (e.g., a handle surface, a surface associated with a base or other support structure, etc.). In a typical scenario, conductive surface  12  is a substantially planar conductive housing surface. Such conductive structures are sometimes referred to as device housings, devices cases, housing or case walls, housing or case surfaces, etc. 
     Slots  28  may be filled with a dielectric such as air or a solid dielectric such as plastic or epoxy. An advantage of filling slots  28  with a solid dielectric material is that this may help prevent intrusion of dust, liquids, or other foreign matter into the interior of device  10 . 
     In general, slots  28  may have any suitable shape. For example, slots  28  may have shapes with curved sides, shapes with bends, circular or oval shapes, non-rectangular polygonal shapes, combinations of these shapes, etc. In a typical arrangement, which is described herein as an example, slots  28  may be substantially rectangular in shape and may have narrower dimensions (i.e., widths measured parallel to lateral dimension  30 ) and longer dimensions (e.g., lengths L measured parallel to longitudinal dimension  32 ). This is merely illustrative. Slots  28  may have any suitable non-rectangular shapes (e.g., shapes with non-perpendicular edges, shapes with curved edges, shapes with bends, etc.). The use of rectangular slot configurations is only described herein as an example. 
     Whether straight, curved, or having shapes with bends, the widths (i.e., the narrowest lateral dimensions) of slots  28  are typically much less than their lengths. For example, the widths of slots  28  may be 5-5000 times less than the lengths of slots  28  (as an example). Slots  28  may be narrow or wide. Narrow slot configurations may be characterized by slot widths of less than about 200 microns (as an example). Wide slot configurations may be characterized by slot widths that are greater than about 200 microns (as an example). 
     Illustrative widths that may be used for narrow slots are on the order of microns, tens of microns, or hundreds of microns (e.g., 5-200 microns, 10-30 omicrons, less than 100 microns, less than 50 microns, less than 30 microns, etc.). Illustrative widths for larger slots are on the order of fractions of a millimeter, a millimeter, more than one millimeter, etc. 
     Slots  28  that have particularly small widths (e.g., tens of microns) are generally invisible to the naked eye under normal observation. Slots  28  that have somewhat larger widths (e.g., hundreds of microns) may be barely visible, but will generally be unnoticeable under normal observation. For example, on a shiny metallic surface of a laptop computer, slots such as slots  28  of antenna  20  in  FIG. 2  may be barely visible in the form of a slight change in the sheen of the surface when viewed from an oblique angle. The use of narrow slots  28  to form an antenna on a housing surface therefore allows the antenna to be located in prominent device locations without becoming obtrusive. For example, antenna  20  may be formed on normally exposed portions of housing  12 . Examples of normally exposed housing portions include the exterior surfaces of a laptop computer or other device  10 , surfaces of a laptop computer such as the housing surface adjacent to the keyboard or display (e.g., when the cover of a laptop computer has been opened for use), or housing sidewalls. 
     Slots that are larger (e.g., fractions of a millimeter or a millimeter or larger) may be large enough to form a visible pattern on the surface of device  12  (e.g., to form a logo or other desirable antenna window pattern). 
     The lengths of slots  28  may be on the order of millimeters or centimeters (e.g., 10 mm or more) or may be any other suitable length. With one suitable arrangement, both ends of the slots are surrounded by conductor (i.e., the slots are close-ended) and the lengths of slots  28  are selected so that the slots are about half of a wavelength at a desired antenna operating frequency. If desired, slots  28  may have open ends. If a slot has an open end, the slot may be configured to have a length that is equal to about a quarter of a wavelength at its desired antenna operating frequency. 
     Slots  28  may be spaced apart by any suitable amount. As an example, there may be about 1 to 1.5 mm, 0.5 to 2 mm, or 0.25 to 3 mm of lateral separation between adjacent pairs of slots. These are merely illustrative examples. Slots  28  may be separated by any suitable distance (e.g., less than 0.5 mm, less than 1 mm, less than 2 mm, more than 2 mm, etc.). 
     The spacings between the slots in a given antenna  20  need not be uniform. For example, in arrangements where there three or more slots  28 , some slots  28  may be spaced apart by 1 mm lateral separations and other slots may be spaced apart by 1.5 mm lateral separations. In other suitable configurations, each pair of adjacent slots may be separated by a different distance. Combinations of these slot spacing schemes may also be used. 
     The slots in antenna  20  may have the same lengths or may have different lengths. For example, each slot  28  may have a different length. Alternatively, some slots may have the same length and other slots may have different lengths. Slots  28  may also have different widths. The use of different combinations of slot widths, slot lengths, slot spacings, and slots shapes may be helpful in designing antennas  20  with desired performance characteristics. 
     Slots  28  may be formed using any suitable technique. For example, slots may be machined in metal walls or other conductive wall structures in housing  12  using laser cutting, plasma arc cutting, micromachining (e.g., using grinding tools), or other suitable techniques. 
     If desired, slotted antennas  20  may be used as internal antennas in device  10 . This type of arrangement is shown in  FIG. 3 . In the example of  FIG. 3 , antenna  20  has two slots  28  in a conductive ground plane element  38 . Ground plane  38  may be formed from a conductive layer on a rigid or flexible printed circuit board, from a conductive layer that is part of an electrical component housing, from other suitable conductive structures in device  10 , or from a combination of such structures. An example of a rigid printed circuit board substrate is fiberglass-filled epoxy. An example of a flexible printed circuit board material is polyimide. 
     To allow radio-frequency signals from antenna  20  to be conveyed satisfactorily through housing wall  12 , housing wall  12  may be constructed from a dielectric material such as plastic. If desired, a conductive housing wall  12  may be provided with a window  40  that is transparent to radio-frequency signals. In this type of situation, antenna  20  may be mounted within device  10  in the proximity of window  40 , as shown in  FIG. 3 . 
     As shown in  FIG. 4 , a coaxial cable or other suitable transmission line  22  may be coupled to antenna  20  at feed terminals such as feed terminals  34  and  36 . In antenna  20  of  FIG. 4 , slots  28  are formed from dielectric-filled openings in ground plane element  42 . Feed terminal  34  may be referred to as a ground or negative feed terminal and may be connected to the outer (ground) conductor of transmission line  22  and ground plane  42 . Feed terminal  36  may be referred to as the positive antenna terminal. Transmission line center conductor  44  may be used to connect transmission line  22  to positive feed terminal  36 . If desired, other types of antenna coupling arrangements may be used (e.g., based on near-field coupling, using impedance matching networks, etc.). 
     As shown schematically by dashed line  46  in  FIG. 4 , the feed arrangement for antenna  20  may include a matching network. Matching network  46  may include a balun (to match an unbalanced transmission line to a balanced antenna or to match a balanced transmission line to an unbalanced antenna) and/or an impedance transformer (to help match the impedance of the transmission line to the impedance of the antenna). 
     An illustrative performance graph for an antenna such as antenna  20  of  FIG. 4  is shown in  FIG. 5 . As shown in  FIG. 5 , a slotted antenna such as antenna  20  of  FIG. 4  may cover multiple communications bands of interest. In particular, antenna  20  of  FIG. 4  may cover a first communications band at frequency f 1  and a second communications band at frequency f 2 . The first band may be (for example) the 2.4 GHz IEEE 802.11 band and the second band may be (for example) the 5.0 GHz IEEE 802.11 band (sometimes referred to by its approximate center frequency of 5.4 GHz). In a dual-slot configuration for antenna  20 , a shorter of the two slots may be configured to resonate in the communications band at frequency f 2  and a longer of the two slots may be configured to resonate in the communications band at f 1 . Additional slots (or slot shapes) may be provided to widen the bandwidth of the antenna in a given band. 
     The impedance of a slot antenna may be influenced by the location of the antenna feed relative to slots  28 . When adjusting the impedance of the slots in a given antenna, the position and shapes of the slots may be adjusted. The locations of the feed terminals may also be adjusted. Consider, for example, a situation of the type shown in  FIG. 4 . In the  FIG. 4  example, antenna  20  has two slots. The left-most ends of slots  28  in  FIG. 4  are aligned with one another and feed terminals  34  and  36  (and optional matching network  46 ) are located roughly in the center of the length of the shorter slot  28 . The impedance of each slot may be adjusted by adjusting the positions of each slot  28  independently relative to feed terminals  34  and  36  (and optional matching network  46 ). 
     For example, if the shorter slot  28  of  FIG. 4  is moved to the right and if antenna terminals  34  and  36  are moved to the left, antenna  20  may have a configuration of the type shown in  FIG. 6 . If it is desired to adjust the impedance of the shorter slot without adjusting the impedance of the longer slot, the shorter slot can be moved to the left or right (in the orientation of  FIG. 6 ), while terminals  34  and  36  are held stationary relative to the longer slot. Alternatively, the position of the longer slot may be adjusted while maintaining the shorter slot in a fixed position. Impedance adjustments may also be made by moving the position of antenna feed terminals  34  and  36  (and optional matching network  46 ) relative to both the shorter and longer slots. Using adjustments such as these, it may be possible to improve impedance matching between transmission line  22  and slots  28 , thereby improving antenna efficiency. 
     If desired, impedance adjustments such as these may be made in antenna configurations that have more than two slots. For example, consider the situation of  FIG. 7 . In this configuration, each slot  28  is positioned so that its leftmost end (as viewed in the orientation of  FIG. 7 ) is aligned with that of the other slots  28 . As shown in  FIG. 8 , impedance adjustments may be made to each of the slots  28  independently, resulting in an antenna arrangement of the type shown in  FIG. 8 , in which the leftmost ends of slots  28  are no longer aligned. 
     Antenna impedance adjustments may also be made by changing the angle at which the feed terminals bridge the antenna slots. This type of arrangement is shown in  FIG. 9 . As shown in  FIG. 9 , it is not necessary for antenna terminals  34  and  36  to bridge slots  28  at a perpendicular angle. Rather, terminals  34  and  36  (and optional matching network  46 ) may be positioned at an angle relative to slots  28 . This approach may be used when it is desirable to make independent impedance adjustments for slots  28  without changing the relative positions of slots  28  to each other (e.g., to accommodate an antenna layout in which slots  28  are aligned with each other at one end as shown in the  FIG. 9  example). In angled feed arrangements of the type shown in  FIG. 9 , coupling efficiency may be somewhat lower than when perpendicular feed arrangements are used. 
     Nevertheless, angled feed arrangements may be desirable in situations in which geometric constraints make it difficult or impossible to use a perpendicular feed configuration. 
     Matching network  46  may be formed from any suitable components. Examples of components that may be used include surface mount components and components formed from circuit board traces. With one suitable arrangement, which is described herein as an example, a capacitive feed arrangement is formed using a planar conductive element. This type of element, which is sometimes referred to as a conductive strip or conductive strap may be formed from metal, metal alloys, conductive elements with a dielectric backing (e.g., metal or metal alloy layers on a flex circuit or rigid printed circuit board substrate), other conductive materials, combinations of such materials, etc. 
     An illustrative matching network  46  formed from a layer of conductive material is shown in  FIG. 10 . As shown in  FIG. 10 , coaxial cable transmission line  22  may be configured so that its outer ground conductor is connected to ground plane  42  at ground terminal  34 . Center conductor  44  may be connected to planar conductive element  50  at a location such as location  48 . In the configuration illustrated in  FIG. 10 , antenna  20  has two slots  28  formed in ground plane  42 . Planar conductive element  50  is configured to span the shorter of the two slots. Part of conductive planar element  50  is connected to ground plane  42  and forms positive antenna feed terminal  36 . The other portions of conductive planar element  50  are preferably not shorted to ground plane  42 . 
     The slots of  FIG. 10  are separated by a portion of ground plane  42  (i.e., ground plane portion  52 ). If desired, planar conductive element  50  can overlap a portion of ground plane portion  52  as shown in  FIG. 10 . 
     Using an arrangement of the type shown in  FIG. 10 , an antenna designer can adjust a variety of parameters to optimize an antenna design. For example, slot length typically affects resonant frequency, so a designer can select the length of a slot along its longitudinal dimension to adjust the frequency at which the antenna will operate. The width of an antenna slot affects antenna bandwidth. Antenna slots that have larger widths will generally exhibit larger bandwidths than narrower slots. There is a practical limit to the amount that an antenna&#39;s bandwidth can be increased by increasing slot width, so in some situations it may be desirable to construct antennas from multiple parallel slots. Each slot in this type of configuration may have a different length and therefore a different resonant frequency. By combining the response of multiple parallel slots, each of which has a different resonant frequency, the bandwidth of the antenna in a particular communications band may be enhanced or coverage for one or more additional communications bands may be added. 
     In matching networks formed from planar conductive elements such as conductive element  50 , adjustments to the size and shape of element  50  and the position of the feed terminals may be used to help match the impedance of transmission line  22  to the impedance of the antenna slot structures. An antenna slot may have an impedance that is larger or smaller than that of transmission line  22 . In general, good matching may be obtained by determining optimum real and imaginary impedance values for the matching network. Put another way, both the magnitude and phase of the matching network impedance should be adjusted correctly to ensure that transmission line  22  will be efficiently coupled to the antenna slots. In arrangements of the type shown in  FIG. 10 , it is possible to achieve good matching, because there are several independently adjustable parameters associated with the structures of antenna  20  and its matching network, each of which has a different type of impact on the magnitude and phase of the matching network impedance. 
     For example, an antenna designer may make adjustments to the position of the antenna feed. If the feed is positioned near to the end of the slot, the magnitude of the impedance of the matching network will tend to be low. If the feed is positioned in the middle of the slot, the impedance magnitude will be higher. The position of the feed along the length of the slot may therefore be used to make impedance magnitude adjustments. These adjustments affect mostly the magnitude of the matching network impedance, rather than its phase. 
     Adjustments can also be made to conductive planar structure  50 . Adjustments in the length of structure  50  (i.e., adjustments in the lateral dimension of structure  50  measured along direction  51 ) tend to affect primarily the phase or reactive (imaginary) component of the matching network impedance. Adjustments in the width of structure  50  (i.e., adjustments in the longitudinal dimension of structure  50  measured along direction  53 ) tend to affect primarily the magnitude of the impedance. When the impedance of the slot is high, it may be desirable to use a relatively narrower width for conductive planar structure  50 , because narrower widths result in higher impedance values for the matching network. When the impedance of the slot is low, it may be desirable to use a relatively wider width for conductive planar structure  50 . 
     The way in which length adjustments for structure  50  affect primarily the real component of the impedance whereas width adjustments affect primarily the imaginary component of the impedance allows an antenna designer to create a matching network with a desired balance of real and imaginary impedance components. The position of the feed along the slot length provides an additional degree of freedom. Further adjustability is provided by varying the dielectric constant of the material in the slot (or in the vicinity of the slot). The dielectric constant of air is less from that of epoxy, so when it is desired to increase the dielectric constant in the vicinity of the antenna slot, the slot can be filled with epoxy (as an example). The antenna&#39;s resonant frequency and bandwidth can be adjusted by making dielectric loading adjustments of this type, by making adjustments to the slot length, by changing the slot width, by selecting an appropriate number of slots, etc. The availability of these independently adjustable parameters makes it possible to design matching networks and slot antennas such as antenna  20  of  FIG. 10  in which coupling between transmission line  22  and slots  28  is optimized and in which the antenna covers desired communications frequencies. 
     A cross-sectional diagram of antenna  20  of  FIG. 10  taken along dashed line  56  and viewed in direction  54  is shown in  FIG. 11 . As shown in  FIG. 11 , there is preferably a dielectric-filled gap  58  between planar conductive structure  50  and ground plane portion  52  of ground plane  42 . Dielectric-filled gap  58  may be filled with air or a solid dielectric such as plastic, epoxy, polyimide, or other suitable dielectric. The dielectric and the separation between conductive planar element  50  and ground plane portion  52  create a feed capacitance that can help match the impedance of transmission line  22  to the impedance of slots  28 . Because dielectric  58  is not conductive, planar conductive element  50  is not electrically connected to the underlying ground plane portion  52 . 
     In a typical situation, transmission line  22  may have an impedance (e.g., 50 ohms) that is larger than the impedance of slots such as slots  28  (e.g., 20 ohms). Conductive planar structure  50  may be used to form an impedance matching network (e.g., a matching network such as optional matching network  46  of  FIG. 4 ) that helps to alleviate undesirable impedance mismatch discontinuities between slots  28  and transmission line  22  that might reduce antenna coupling efficiency. If desired, other matching network components (e.g., surface mount or discrete components such as resistors, capacitors, and inductors) may be combined with a matching network structure formed from planar elements such as conductive planar element  50 . 
     Any suitable sizes and shapes may be used for slots  28  and planar conductive element  50  if desired. An example is shown in  FIG. 12 . As shown in  FIG. 12 , antenna  20  may have a larger slot of length L 1  and width W 1  and may have a shorter slot of length L 2  and width W 2 . The lengths L 1  and L 2  may be selected to be about a half of a wavelength at signal frequencies associated with communications bands of interest (e.g., the 2.4 GHz band for length L 1  and the 5.0 GHz band for length L 2 ). Length L 1  may be 61 mm. Width W 1  may be 0.8 mm. Length L 2  may be 23.5 mm. Width W 2  may be 0.82 mm. There may be a lateral separation of 1.43 mm between slots  28 . The left end of the smaller slot may be offset from the left end of the longer slot by an offset distance D 1  of 1.5 mm. Planar conductive element  50  may have a length L 3  of 8.65 mm. Distances D 2  and D 3  may be equal to 4.55 mm and 10.3 mm, respectively. Distances such as distance D 1  and the dimensions of the structures in  FIG. 12  may be adjusted to tune the impedance matching capabilities of the matching network formed using planar conductive element  50 . 
     As shown in  FIG. 13 , the size of planar conductive element  50  may be selected so that planar conductive element  50  just spans the width of antenna slot  28 . In the example of  FIG. 14 , planar conductive element  50  only partially bridges the width of slot  28 . 
     Another illustrative configuration is shown in the dual-slot antenna of  FIG. 15 . As shown in  FIG. 15 , planar conductive element  50  may completely bridge an antenna slot and may partially overlap the region of ground plane  42  that lies between slots  28  (i.e., region  52 ). 
     If desired, planar conductive element  50  may span the widths of both slots  28  in a dual-slot antenna. This type of arrangement is shown in  FIG. 16 . As shown in  FIG. 16 , planar conductive region  50  may cover the width of the shorter of the two slots  28 , may cover the width of the larger of the two slots  28 , and may span the width of region  52  of ground plane  42 . 
     It is not necessary for planar conductive element  50  to completely bridge the shorter slot in a two-slot antenna. As shown in  FIG. 17 , for example, planar conductive element  50  in dual-slot antenna  20  may only partially bridge the shorter of the two slots in antenna  20 . 
     The size of planar conductive element  50  may also be adjusted in slotted antennas having more than two slots. As shown in  FIG. 18 , for example, planar conductive element  50  may be configured to overlap two slots  28  and two ground plane slot separation regions  52 . Dashed line  54  illustrates how planar conductive element  50  may, if desired, partially span the third of the three slots in antenna  20  of  FIG. 18 . Other arrangements in a three-slot antenna are also possible. For example, planar conductive element  50  may bridge all three slots completely, may partially bridge either of regions  52 , may partially bridge either of the shorter two slots, etc. 
     Planar conductive elements such as planar conductive element  50  need not be rectangular in shape. An example of a planar conductive element  50  that has a non-rectangular shape is shown in  FIG. 19 . As shown in the  FIG. 19  example, the area of element  50  that overlaps each slot may be different and may be adjusted independently. The longitudinal position at which planar conductive element  50  crosses each slot  28  may also be adjusted independently. The shape of planar conductive element  50  may be individually tailored wherever conductive element  50  crosses ground plane slot separation regions such as regions  52 . The amount of spacing between planar conductive element  50  and underlying regions  52  and the shape and size of the overlap between planar conductive element  50  and slots  28  are additional adjustable parameters associated with antennas of the type shown in  FIG. 19 . These parameters and other suitable parameters may be selected to enhanced impedance matching and/or to perform other desired matching functions (e.g., the functions of a balun when it is desired to match an unbalanced transmission line to a balanced slot antenna or when it is desired to match a balanced transmission line to an unbalanced slot antenna). The configuration of  FIG. 19  and the other configurations shown in the FIGS. are merely illustrative. 
     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: 20071218
Publication Date: 20130514
Grant Date: 20130514
Priority Date: 20071218
Inventors: CHIANG BING
SPRINGER GREGORY ALLEN
KOUGH DOUGLAS B.
AYALA ENRIQUE
MCDONALD MATTHEW IAN
Assignee: APPLE INC
CPC Classifications: [{"code": "H01Q5/40", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q13/10", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q21/30", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q13/10", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q21/30", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q13/08", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01Q5/40", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q13/08", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 40752499