PATENT DOCUMENT

Publication Number: US-7705795-B2
Application Number: US-95882407-A
Country: US
Kind Code: B2

Title: Antennas with periodic shunt inductors

Abstract:
An antenna may be formed from conductive regions that define a gap that is bridged by shunt inductors. The inductors may have equal inductances and may be located equidistant from each other to form a scatter-type antenna structure. The inductors may also have unequal inductances and may be located along the length of the gap with unequal inductor-to-inductor spacings, thereby creating a decreasing shunt inductance at increasing distances from a feed for the antenna. This type of antenna structure functions as a horn-type antenna. One or more scatter-type antenna structures may be cascaded to form a multiband antenna. Antenna gaps may be formed in conductive device housings.

Claims:
1. An antenna comprising:
 first and second coplanar conductive regions that are spaced apart to form a gap; 
 first and second antenna terminals that are connected to the conductive regions and that form an antenna feed for the antenna, wherein the gap supports a zero-order transverse electric field (TE 0 ) mode; and 
 a plurality of fixed shunt inductors each of which bridges the gap. 
 
   
   
     2. The antenna defined in  claim 1  wherein the gap has a longitudinal axis and wherein the inductors are separated by equal spacings along the longitudinal axis. 
   
   
     3. The antenna defined in  claim 1  wherein the gap has a longitudinal axis and wherein the inductors are separated by unequal spacings along the longitudinal axis. 
   
   
     4. The antenna defined in  claim 1  wherein the gap has a longitudinal axis, wherein the inductors are separated by equal spacings along the longitudinal axis, and wherein the inductors each have the same inductance. 
   
   
     5. The antenna defined in  claim 1  wherein the gap has a longitudinal axis, wherein the inductors are separated by unequal spacings along the longitudinal axis, and wherein the inductors each have the same inductance. 
   
   
     6. The antenna defined in  claim 1 , wherein the inductors each have the same inductance. 
   
   
     7. The antenna defined in  claim 1 , wherein the inductors are arranged at multiple distances from the antenna feed and wherein the inductors have decreasing inductances as distance from the feed increases. 
   
   
     8. The antenna defined in  claim 1  wherein a first set of the inductors forms a scatter-type antenna having inductors of a first inductance value and wherein a second set of the inductors forms a scatter-type antenna having inductors of a second inductance value that is different from the first inductance value. 
   
   
     9. The antenna defined in  claim 1  wherein a first set of the inductors forms a scatter-type antenna structure and wherein a second set of the inductors forms a horn-type antenna structure. 
   
   
     10. The antenna defined in  claim 1  wherein both ends of the gap are open. 
   
   
     11. The antenna defined in  claim 1  wherein both ends of the gap are closed. 
   
   
     12. The antenna defined in  claim 1  wherein one end of the gap is open and one end of the gap is closed. 
   
   
     13. An antenna comprising:
 conductive regions that form a gap; 
 first and second antenna terminals that are connected to the conductive regions and that form an antenna feed for the antenna, wherein the gap supports a zero-order transverse electric field (TE 0 ) mode; and 
 a plurality of fixed shunt inductors each of which bridges the gap, wherein at least some of the inductors have unequal inductor-to-inductor spacings along the gap and have equal inductances and wherein at least some of the inductors have equal inductances and equal inductor-to-inductor spacings along the gap. 
 
   
   
     14. An open structure transmission line antenna, comprising:
 a first antenna pole; 
 a second antenna pole that is separated from the first antenna pole by a gap; and 
 a plurality of fixed surface-mount shunt inductors that bridge the gap. 
 
   
   
     15. The open-structure transmission line antenna defined in  claim 14  wherein the first antenna pole comprises a strip of conductor and wherein the second antenna pole comprises a ground plane, the antenna further comprising a dielectric interposed between the first antenna pole and the second antenna pole, wherein the first antenna pole and the second antenna pole form a microstrip transmission line antenna. 
   
   
     16. The open-structure transmission line antenna defined in  claim 14  wherein the first antenna pole comprises a strip of conductor and wherein the second antenna pole comprises first and second parallel ground strips on opposing sides of the first antenna pole that form a coplanar waveguide antenna, wherein the first antenna pole and the first ground strip form the gap, wherein the first antenna pole and the second ground strip form a second gap, the antenna further comprising a plurality of surface-mount shunt inductors that bridge the second gap. 
   
   
     17. The open-structure transmission line antenna defined in  claim 14  wherein the first and second antenna poles are formed from conductive material in the housing of an electronic device. 
   
   
     18. An antenna comprising:
 conductive regions that define a gap; 
 a first plurality of fixed shunt inductors of a first inductance that bridge the gap and that form a first antenna structure that emits electromagnetic radiation for the antenna; and 
 a second plurality of fixed shunt inductors of a second inductance that bridge the gap and that form a second antenna structure cascaded with the first antenna structure that emits electromagnetic radiation for the antenna, wherein the first and second inductances are different. 
 
   
   
     19. The antenna defined in  claim 18  wherein the first and second plurality of shunt inductors are formed from surface-mount components. 
   
   
     20. The antenna defined in  claim 18  wherein the conductive regions are formed in portions of a conductive housing of a portable electronic device. 
   
   
     21. The antenna defined in  claim 18  wherein the conductive regions are formed in portions of a laptop computer housing. 
   
   
     22. The antenna defined in  claim 18  wherein the conductive regions are formed in portions of an electronic device housing, wherein the first and second plurality of shunt inductors are formed from surface-mount components, and wherein the antenna supports a zero-order transverse electric field mode.

Description:
BACKGROUND 
   This invention relates to antennas, and more particularly, to antennas that have shunt inductors at intervals along their lengths. 
   Antennas are widely used in modern electronic devices. For example, antennas are often used in portable electronic devices such as laptop computers and cellular telephones. Particularly in environments such as these, there is a premium placed on small size and high radiation efficiency. Antennas that are compact take up less space in a portable device than bulkier antennas, which allows a designer to enhance the portability of a device. Highly efficient antennas reduce the amount of battery drain that is imposed on a portable device. 
   It is sometimes desirable for an antenna to cover multiple frequency bands. This allows antenna hardware to be shared among multiple radio-frequency transceivers without providing too much antenna hardware in a device. Multiband antenna designs generally require antenna resonating structures that radiate over a wide range of frequencies or multiple radiators. 
   It would therefore be desirable to be able to provide antennas that cover one or more communications band without consuming too much space in an electronic device such as a portable electronic device. 
   SUMMARY 
   Antennas may be provided for electronic devices. The electronic devices may be portable electronic devices such as laptop computers. The antennas may have conductive regions that form positive and negative antenna poles. The poles may be separated by a dielectric-filled gap. For example, the poles may be planar strips or regions of metal or metal alloy that are separated by a gap of air several microns in width. The conductive regions that form the antenna poles may be part of a conductive housing for an electronic device. Because the gap is small, the gap may be invisible to the naked eye, allowing the antenna to be formed on an exterior housing surface. 
   Shunt inductors may bridge the antenna gap at various locations along the length of the antenna. The shunt inductors may be provided in the form of surface-mount devices (SMD). 
   The antenna may be fed using positive and negative antenna feed terminals. The shunt inductors may have equal inductances and may be located equidistant from each other to form a scatter-type antenna structure. The inductors may also have unequal inductances and/or may be located along the length of the gap with unequal inductor-to-inductor spacings, thereby creating a decreasing shunt inductance at increasing distances from the antenna feed terminals. This type of antenna structure functions as a horn-type antenna. 
   One or more scatter-type antenna structures may be cascaded to form a multiband antenna. A horn-type antenna structure may also be cascaded to add to the multiband nature of the antenna. Hybrid antennas may be thus formed from one or more scatter-type antenna structures and a horn-type antenna structure. 
   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 antenna in accordance with an embodiment of the present invention. 
       FIG. 2  is a cross-sectional side view of an antenna in accordance with an embodiment of the present invention. 
       FIG. 3  is a perspective view of an illustrative portable electronic device containing an antenna in accordance with an embodiment of the present invention. 
       FIG. 4  is a top view of an illustrative antenna showing how the antenna may be formed from a slot with two open ends that is bridged by inductors and that forms a gap in accordance with an embodiment of the present invention. 
       FIG. 5  is a top view of an illustrative antenna showing how the antenna may be formed from a slot with one open end that is bridged by inductors and that forms a gap in accordance with an embodiment of the present invention. 
       FIG. 6  is a top view of an illustrative antenna showing how the antenna may be formed from a slot with closed ends that is bridged by inductors and that forms a gap in accordance with an embodiment of the present invention. 
       FIG. 7  is a sectional perspective end view of an illustrative microstrip antenna with shunt inductors in accordance with an embodiment of the present invention. 
       FIG. 8  is a cross-sectional side view of an antenna of the type shown in  FIG. 7  in accordance with an embodiment of the present invention. 
       FIG. 9  is a perspective view of an illustrative coplanar waveguide antenna with shunt inductors in accordance with an embodiment of the present invention. 
       FIG. 10  is an equivalent circuit of an illustrative antenna such as a microstrip or coplanar waveguide antenna that supports operation in a transverse electromagnetic (TEM) propagation mode in accordance with an embodiment of the present invention. 
       FIG. 11  is an equivalent circuit of an illustrative antenna such as a gap antenna that supports operation in a zero-order transverse electric field mode (TE 0 ) in accordance with an embodiment of the present invention. 
       FIG. 12A  is a top view of an antenna showing how the antenna may be fed at antenna feed terminals in accordance with an embodiment of the present invention. 
       FIG. 12B  is a top view of an antenna showing how the antenna may be fed using a matching network that includes a balun and/or an impedance transformer in accordance with an embodiment of the present invention. 
       FIG. 13  is a circuit diagram of a portion of an illustrative antenna with a shunt inductance in accordance with an embodiment of the present invention. 
       FIG. 14  is a graph of the reactance of the circuit of  FIG. 13  plotted as a function of frequency in accordance with an embodiment of the present invention. 
       FIG. 15  is a top view of an illustrative antenna with shunt inductors showing how inductors with the same inductance value may be placed at even intervals along the length of the antenna in accordance with an embodiment of the present invention. 
       FIG. 16  is a top view of an illustrative antenna with shunt inductors showing how shunt inductors having different inductance values may be placed at even intervals along the length of the antenna in accordance with an embodiment of the present invention. 
       FIG. 17  is a graph showing the reactance of an antenna of the type shown in  FIG. 16  as a function of signal frequency in accordance with an embodiment of the present invention. 
       FIG. 18  is a graph in which the reflection coefficient of an illustrative antenna with shunt inductors has been plotted as a function of frequency in accordance with an embodiment of the present invention. 
       FIG. 19  is a top view of an illustrative antenna having shunt inductors placed at unequally separated locations along the length of the antenna in accordance with an embodiment of the present invention. 
       FIG. 20  is a top view of an illustrative antenna having a first portion in which shunt inductors of a first value are placed at equally spaced locations along the antenna length and having a second portion in which shunt inductors of a second value are placed at equally spaced locations along the antenna length in accordance with an embodiment of the present invention. 
       FIG. 21  is a top view of an illustrative antenna having a first portion in which shunt inductors of potentially different values are placed along the antenna&#39;s length at potentially unequally spaced locations and having a second portion in which shunt inductors of potentially different values are placed along the antenna&#39;s length at potentially unequally spaced locations. 
       FIG. 22  is a graph in which the reactance of an antenna of the type shown in  FIG. 21  is plotted as a function of frequency in accordance with an embodiment of the present invention. 
       FIG. 23  is a top view of an illustrative antenna having a first portion in which shunt inductors of potentially equal values are placed along the antenna&#39;s length at potentially equally spaced locations and having a second portion in which shunt inductors of potentially equal values are placed along the antenna&#39;s length at potentially equally spaced locations so that the antenna may handle multiple communications bands in accordance with an embodiment of the present invention. 
       FIG. 24  is a graph in which the reactance of an antenna of the type shown in  FIG. 21  is plotted as a function of frequency in accordance with an embodiment of the present invention. 
   

   DETAILED DESCRIPTION 
   The present invention relates to antennas for electronic devices. The electronic devices in which the antennas are used may be any suitable type of electronic equipment. For example, the electronic devices may include computers such as laptop computers, desktop computers, computers that are integrated into computer monitors, processing equipment that is part of a set-top box, handheld computers, etc. The antennas may be used in any suitable wireless communications circuitry in a wireless electronic device such as cellular telephone wireless communications circuitry or wireless communications circuitry for implementing local wireless data links (as examples). 
   The wireless electronic devices in which the antennas are used may or may not be portable. An example of a wireless electronic device that may not be considered portable is a large computer. Examples of wireless electronic devices that may be considered portable are 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 such as handheld electronic devices. Examples of smaller portable electronic devices include wrist-watch devices, pendant devices, headphone and earpiece devices, and other wearable and miniature devices. Typical handheld devices may be, for example, cellular telephones, media players with wireless communications capabilities, handheld computers (also sometimes called personal digital assistants), remote controllers, global positioning system (GPS) devices, and handheld gaming devices. If desired, the antennas may be incorporated into hybrid devices that combine the functionality of multiple devices of these types. Examples of hybrid handheld 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. 
   The antennas in these devices may support communications over any suitable wireless communications bands. For example, the antennas may be used to cover communications frequency bands such as the cellular telephone bands at 850 MHz, 900 MHz, 1800 MHz, and 1900 MHz, data service bands such as the 3G data communications band at 2170 MHz (commonly referred to as the UMTS or Universal Mobile Telecommunications System band), the Wi-Fi® (IEEE 802.11) bands at 2.4 GHz and 5.0 GHz (also sometimes referred to as wireless local area network or WLAN bands), the Bluetooth® band at 2.4 GHz, and the global positioning system (GPS) band at 1575 MHz. The 850 MHz band is sometimes referred to as the Global System for Mobile (GSM) communications band. The 900 MHz communications band is sometimes referred to as the Extended GSM (EGSM) band. The 1800 MHz band is sometimes referred to as the Digital Cellular System (DCS) band. The 1900 MHz band is sometimes referred to as the Personal Communications Service (PCS) band. Single band antennas may be used to cover individual bands. For example, a single band antenna may be used to cover the Wi-Fi® band at 2.4 GHz. Multiband antennas may be used to cover multiple communications bands. For example, a multiband antenna may be used to cover a Wi-Fi® band at 2.4 GHz and a Wi-Fi® band at 5.0 GHz. 
   Antennas in accordance with embodiments of the present invention may be very narrow (e.g., microns in width) and may be electrically very short (e.g., having a length less than a quarter of a wavelength at their operating frequency). An antenna of this type may be suitable form multiple antenna applications such as in multiple in multiple out (MIMO) high throughput communications systems, and phased arrays for high gain, steerable beam, adaptive beam systems. 
   The antenna may have a slot. The slot may be suitable for integration into conductor skins (e.g., thin metal housing walls) of various platforms, and may be integrated with other electronics to form skin-like complete systems. Its small aperture (slot area) may allow the antenna to be invisible at short distances, so it may blend into its immediate environment for cosmetic or covert applications. 
   The antenna may be used to provide communications and remote control capabilities for any metallic-skin-enclosed device (e.g., a valuable device) such as a device that might otherwise be cut off from the environment. For example, it may be desirable to enclose a computer in a metal enclosure for security or electromagnetic pulse (EMP) protection. The antenna can be placed in the enclosure wall to permit wireless communications through the enclosure. 
   An illustrative antenna in accordance with an embodiment of the present invention is shown in  FIG. 1 . As shown in  FIG. 1 , antenna  10  may have a gap  14  that is formed between two opposing conductive regions  12 . In the example of  FIG. 1 , conductive regions  12  are planar and are formed on a substrate  22 . Conductive regions  12  may be formed from any suitable conductive materials. Illustrative conductive materials from which conductive regions  12  may be formed include elemental metals such as gold and copper. Conductive regions  12  may also be formed from alloys such as metal alloys. Conductive materials that are formed from non-metal substances (e.g., semiconductors, conductive plastics, conductive ceramics, etc.) may also be used. The use of metallic conductive structures is sometimes described herein as an example. This is, however, merely illustrative. Conductive regions  12  may be formed from any suitable materials. 
   In a typical arrangement, a thin film or thin sheet of metal or metal alloy may be deposited on a substrate such as substrate  22  that is formed from dielectric. Illustrative dielectric materials that may be used for forming substrate  22  include glass, ceramic, and plastic. These are, however, merely illustrative examples. Any suitable substrate material may be used for antenna  10  if desired. If desired, antennas such as antenna  10  may be formed without using dielectric substrate  22 . For example, gap  14  may be formed in a piece of conductive material that does not require a dielectric support. Antennas of this type and antennas with dielectric substrates may be coated with coatings (e.g., protective dielectric coatings). 
   Gap  14  may have an equal width W along its length or may be tapered. In tapered antenna arrangements, the electrical properties of the antenna may vary as a function of location along longitudinal axis  16 . For example, the impedance of the antenna is generally affected by the inherent (parasitic) shunt capacitance associated with the opposing conductive regions  12 . Conductive regions  12  may be considered to form a parallel plate capacitor. Because the capacitance of this type of structure is dependent on the separation between the plates, the capacitance of antenna  10  per unit length will generally be constant in arrangements in which width W is constant along the antenna&#39;s length and will generally vary in arrangements in which width W varies along the antenna&#39;s length. 
   Antenna  10  may have a number of shunt inductors  20  that bridge gap  14 . Inductors  20  may be formed from patterned conductor (e.g., metal or metal alloys that have been pattered using semiconductor fabrication techniques). In one particularly suitable arrangement, inductors  20  are formed from discrete surface-mount components. Surface mount components are compact (e.g., less than a millimeter in their largest lateral dimension) and may be assembled using machine-assisted manufacturing techniques (if desired). The values of inductors  20  are typically in the nH range (e.g., 1-1000 nH). Inductors  20  may also be bonded beneath or to the underside of conductive regions  12 , which, for this illustrative example, would be in substrate  22 . 
   Electromagnetic radiation may be emitted from antenna  10  when antenna  10  is being used to transmit radio-frequency (RF) signals. In this type of configuration, electromagnetic waves may travel along gap  14  in direction  18 . Electromagnetic radiation may also be received by antenna  10  (e.g., when antenna  10  is being used to receive incoming RF signals) due to the reciprocity of linear electrical components. It is not necessary for antenna  10  to operate in both transmitting and receiving modes. For example, an antenna may be used to receive global positioning system (GPS) signals without transmitting any signals. In a typical arrangement, however, antenna  10  may be used to transmit and receive RF signals (e.g., for cellular telephone or data communications). 
   Antennas such as the illustrative antenna of  FIG. 1  support a zero-order transverse electric field mode (sometimes referred to as the TE 0  mode) as in slot lines and slot antennas. The configuration of the electric field E and magnetic field H in this mode are shown in  FIG. 2 .  FIG. 2  contains a cross-sectional side view of an antenna of the type shown in  FIG. 1  taken along longitudinal axis  16  and viewed in direction  26 . Inductors  20  are not shown in  FIG. 2  to avoid over-complicating the drawing. As shown in  FIG. 2 , electric field E extends directly across gap  14  and magnetic field H forms loops in the plane of gap  12  (i.e., in the page in the orientation of  FIG. 2 ). The TE 0  mode is distinct from the TEM mode, so the treatment of slot lines and conventional transmission lines are also different. 
   A typical antenna is on the order of millimeters in length (e.g., a fractional wavelength to several wavelengths). A typical width W for gap  14  may be on the order of microns. Gaps that are of this size may be invisible to the naked eye. As a result, antennas such as antenna  10  of  FIG. 1  may be formed in plain sight of a user of an electronic device without actually being visible (or at least being unnoticeable under normal observation). This allows antenna  10  to be formed in locations that would otherwise be obtrusive if antenna  10  were larger and visible. For example, antenna  10  may be formed as an integral part of a conductive housing in an electronic device. If the electronic device has a conductive housing (e.g., a metal case or stand), the gap for the antenna may be formed directly in the conductive housing (or other such conductive structure). 
   An example is shown in  FIG. 3 . As shown in  FIG. 3 , antenna  10  may be formed in housing  28  of laptop computer  30 . Antenna  10  may be formed in any suitable portion of housing  28 . For example, antenna  10  may be formed in the top lid of laptop computer  30  (e.g., on outer surface  29  of the top lid), may be formed as part of or adjacent to a conductive logo structure, may be formed as part of a sidewall or lower housing portion of laptop computer  30 , etc. If laptop computer  30  or other electronic device has a conductive housing such as a thin sheet of metal or metal alloy, inductors  20  ( FIG. 1 ) may be mounted on the inside of the housing. 
   As shown in  FIG. 4 , antenna  10  may be constructed from a slot that has open ends  32  and  34 . In this type of arrangement, gap  14  may be bridged by inductors  20  (which are shown schematically) at intervals along its length. Because the slot of antenna  10  forms gap  14 , antennas of the type shown in  FIG. 4  are sometimes referred to as slot antennas or gap antennas (regardless of whether gap  14  has open ends). 
   As shown in  FIG. 5 , the slot from which gap  14  is formed may have one open end (end  34 ) and one closed end (end  36 ). 
   In the illustrative arrangement shown in  FIG. 6 , antenna  10  has two closed ends (ends  38  and  40 ). 
   Regardless of the type of gap or slot that is used to form antenna  10 , antenna  10  may still be considered to have two poles. For example, in the arrangement of  FIG. 1 , one pole (e.g., a ground or negative pole) of antenna  10  may be formed by one of conductive regions  12  and another pole (e.g., a positive pole) of antenna  10  may be formed by the other one of conductive regions  12 . This nomenclature may be used for regions  12  of other antenna arrangements, including slot antenna arrangements of the types shown in  FIGS. 5 and 6  in which one or both ends of the slot are closed. 
   If desired, antennas with shunt inductors may be formed from waveguides that support transverse electromagnetic (TEM) field modes. Examples of this type of structure are shown in  FIGS. 7-9 . 
     FIG. 7  shows an illustrative microstrip antenna  10  that is formed from a positive strip-shaped conductive region (pole)  12 A formed on a planar ground conductive region (pole)  12 B. Interposing dielectric layer  22  may be used to separate poles  12 A and  12 B. In this type of configuration, conductive vias may be used to form inductors  20 . Conductive vias, which are shown in cross-section in  FIG. 8 , may be formed from metal or metal alloys. The holes for the vias may be formed by semiconductor fabrication techniques (e.g., etching). The via conductors may be deposited by sputter deposition (as an example). 
     FIG. 9  shows an illustrative coplanar waveguide antenna  10  that is formed from a strip-shaped center conductor  12 A and two planar side conductors  12 B. Shunt inductors  20 , which may be formed from surface mounted components as described in connection with  FIG. 1 , may be mounted on the conductive regions of antenna  10  so that gaps  14 A and  14 B are both bridged. Antenna  10  of  FIG. 9  may have a dielectric support structure  22  or may be formed without dielectric  22  (e.g., by forming dual gaps  14 A and  14 B as an integral portion of a conductive device housing. 
   Microstrip antenna  10  of  FIG. 8  and coplanar waveguide antenna  10  of  FIG. 9  are examples of TEM-type waveguides, whereas the gap antennas of  FIGS. 4 ,  5 , and  6  are examples of TE 0 -type antennas. An equivalent circuit for a TEM-type antenna is shown in  FIG. 10 . An equivalent circuit for a TE 0 -type antenna is shown in  FIG. 11 . As shown in the equivalent circuits of  FIGS. 10 and 11 , there is generally a parasitic capacitance C associated with a unit length of either antenna type. TEM-type antennas typically exhibit a series inductance LS per unit length. In contrast, TE 0 -type antennas have zero (negligible) amounts of series inductance. Each shunt inductor  20 , in combination with the parasitic capacitance C per unit length in the antenna, creates an impedance discontinuity that generates radiative scattering. At this impedance discontinuity, the impedance of the shunt inductor-capacitor combination tends to infinity. The abruptness of this impedance discontinuity can be used to efficiently scatter antenna radiation. 
   An advantage of the TE 0 -type antenna configuration of  FIG. 11  is that it does not exhibit significant series inductance. In TEM antennas of the type shown in  FIG. 10 , the inductances LS produce a phase delay between successive inductors  20 . This phase delay causes the radiation scattering pattern to exhibit a less omnidirectional behavior than in TE 0  antenna arrangements of the type shown in  FIG. 11 . Although either type of antenna or combinations of these antenna types may be used in forming antenna  10 , arrangements in which antenna  10  is based on a TE 0  configuration are sometimes described herein as an example. 
   Antennas  10  (either TEM or TE 0 ) are preferably open structure transmission line antennas in which signals are fed to opposing positive and negative (ground) poles of the antenna and in which the positive pole is not encircled by the ground poles so as to prevent radiation. 
   Any suitable feed arrangement may be used for antenna  10 . An illustrative feed arrangement is shown in  FIG. 12A . As shown in the example of  FIG. 12A , a transmission line such as coaxial transmission line  46  may be used to convey radio-frequency signals between antenna  10  and a radio-frequency transceiver such as radio-frequency transceiver  48 . Transceiver  48  may include one or more transceiver circuits for handling communications in one or more discrete communications bands. For example, transceiver  48  may be used to handle communications for one or more cellular telephone or 3G data bands and/or one or more local data bands such as Bluetooth, Wi-Fi, etc. 
   Transmission line  46  may be coupled to antenna  12  at feed terminals such as feed terminals  44  and  42 . Feed terminal  44  may be referred to as a ground or negative feed terminal and may be shorted to the outer (ground) conductor of transmission line  46 . Feed terminal  42  may be referred to as the positive antenna terminal. 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 in  FIG. 12B , the feed arrangement for antenna  10  may include a matching network such as matching network  43 . Matching network  43  may include a balun (to match an unbalanced transmission line to a balanced antenna) and/or an impedance transformer (to help match the impedance of the transmission line to the impedance of the antenna). 
   A circuit diagram of a unit cell of antenna  10  is shown in  FIG. 13 . Inductor  20  may be formed by a component such as a surface-mounted component. Capacitor C may be the parasitic capacitance associated with a segment of the antenna (i.e., the capacitance formed by a length of the opposing portions of conductor across gap  14 ). 
   The circuit of  FIG. 13  forms a resonant circuit. The reactance X of a circuit of the type shown in  FIG. 13  as a function of signal frequency is shown in  FIG. 14 . Reactance X is positive for signal frequencies f below resonant frequency fr and is negative for signal frequencies f above resonant frequency fr. Graphs of the type shown in  FIG. 14  may be used to analyze the radiative properties of antennas  10  that are formed with inductors  20  in different configurations. 
   One suitable configuration for inductors  20  is shown in  FIG. 15 . In this type of arrangement, inductors  20  of inductance L are located along the length of gap  14  at equally spaced positions. Each inductor  20  may be separated by a distance D from adjacent inductors  20 . Distance D may be, for example, a fraction of a millimeter. As waves pass each shunt inductor, electromagnetic radiation is scattered from the impedance discontinuity that is formed by the inductor. Antenna structures with this type of configurations are sometimes referred to as scatter-type antenna structures. These antennas tend to exhibit broad bandwidths and high efficiencies. 
   A single communications band or multiple communications bands may be supported using antennas of the type shown in  FIG. 15 . There are only four inductors in the example of  FIG. 15 , but this is merely illustrative. Antennas  10  may have any suitable number of inductors  20 . 
   Another suitable configuration for conductors  20  is shown in  FIG. 16 . In the arrangement of  FIG. 16 , antenna  10  has three shunt inductors  20 , having respective inductance values of L 1 , L 2 , and L 3 . These inductors may be evenly spaced along the gap  14  (e.g., with spacing D). The values of L 1 , L 2 , and L 3  may decrease in the direction of travel  18  of a transmitted electromagnetic wave. For example, the values of L 1 , L 2 , and L 3  may respectively be 64 mH, 32 mH, and 16 mH. 
   A graph of the reactance of each inductor  20  as a function of frequency is shown in  FIG. 17 . As shown in  FIG. 17 , inductor L 1  may be characterized by reactance curve  50 , inductor L 2  may be characterized by reactance curve  52 , and inductor L 3  may be characterized by reactance curve  54 . At a given operating frequency (e.g., frequency f 4  in the  FIG. 17  example), the reactance X of signals in antenna  10  may increase in direction  18  along gap  14 . In particular, the reactance of signals in antenna  10  may vary as a function of position along gap  14  at frequency f 4  as shown by reactance values  56 ,  58 , and  60 . This increase of reactance value X as a function of position along the length of antenna  10  shows that antenna  10  has the characteristics of a horn antenna (e.g., a Vivaldi horn antenna). A horn antenna (which could also be formed by increasing the width W of gap  14  as a function of distance in direction  18 ) may exhibit increased efficiency, because the flare in the horn helps to impedance match transmission line  46  to free space. Antennas structures for antenna  10  in which the inductance values of inductors  20  vary as a function of length to create a horn-type antenna characteristic are sometimes referred to herein as horn-type antenna structures. 
   Reflectance coefficient calculations have been performed for horn-type antennas  10 . As shown by the illustrative reflectance coefficient graph of  FIG. 18 , there may be only a relatively small amount of reflection at operating frequency f 4 , indicating that horn-type antennas can perform efficiently, as with the scatter-type antennas such as the antenna of  FIG. 15 . 
   If desired, a horn-type antenna can be implemented by varying the spacing between shunt inductors  20  along the length of antenna gap  14 . This type of arrangement is shown in  FIG. 19 . As shown in  FIG. 19 , antenna  10  may have shunt inductors  20  that are spaced unequally from each other. In the example of  FIG. 19 , the longitudinal separation D 2  between the second and third inductors  20  of antenna  10  may be greater than the longitudinal separation D 1  between the first and second inductors  20 . Similarly, the longitudinal separation D 3  between the third and fourth inductors  20  of antenna  10  may be greater than the longitudinal separation D 2 . The antenna feed may be located across terminals  42  and  44 . Because the distances between respective inductive elements increases with increasing distance from the antenna feed terminals, the shunt inductance per unit length is effectively decreasing with increasing distance along the longitudinal axis of gap  14  away from the feed terminals. Even if inductances L 1 , L 2 , L 3 , and L 4  are all equal in value, the increasing inductor-to-inductor spacing has the effect of decreasing the shunt inductance value, as with the horn-type arrangement described in connection with  FIG. 16 . The use of increasing spacing arrangements of the type shown in  FIG. 19  therefore represents an alternative technique for forming horn-type antennas. 
   In a horn-type arrangement of the type shown in  FIG. 19 , the inductance values L 1 , L 2 , L 3 , and L 4  may be equal. An arrangement of this type may be advantageous, because it can be relatively straightforward to match inductance values in a batch of inductors. The properties of antenna  10  may then be precisely controlled by controlling the spacings D 1 , D 2 , and D 3 . 
   If desired, a horn-type antenna structure may be formed in which inductance values L 1 , L 2 , L 3 , and L 4  decrease and in which some or all of the inductor-to-inductor lateral spacings D 1 , D 2 , and D 3  vary as described in connection with  FIG. 19 . 
   Hybrid layouts are also possible in which a mixture of spacings are used (increasing, decreasing, or equal) and a mixture of inductance values (increasing, decreasing, or equal) are used. When the effective shunt inductance per unit length decreases with increasing distance from the antenna feed, a horn-type antenna structure is produced. When the effective shunt inductance per unit length is equal, a scatter-type antenna structure is produced. 
   Antenna  10  may contain a single antenna type (e.g., a single scatter-type structure or a single horn-type structure) or may contain multiple such structures (e.g., two or more scatter-type structures, two or more horn-type structures, or a mixture of one or more scatter-type structures and one or more horn-type structures. 
   An illustrative configuration is shown in  FIG. 20 . In the example of  FIG. 20 , antenna  10  has a first portion and a second portion. First portion  62  may be a scatter-type antenna having shunt inductances of inductance L 1 . Second portion  64  may be a horn-type antenna having successively decreasing shunt inductances L 1 , L 2 , L 3 , and L 4  or may be a horn-type antenna having equal inductance values L with increasing inductor-to-inductor spacings or may be a hybrid device with a mixture of different inductance values and a mixture of inductor-to-inductor spacings resulting in a decreasing effective shunt inductance with increasing distance from the antenna feed terminals. 
   In configurations such as the illustrative configuration of  FIG. 20  the scatter-type portion may handle communications in one frequency band and the horn-type portion may handle communications in second communications band. The first band may have a higher or lower center frequency than the second band. The antenna may also be used to handle communications in a single frequency band with increased efficiency relative to a shorter antenna (e.g., an antenna having only a horn type antenna structure or only a scatter-type antenna structure). 
   In the illustrative configuration of  FIG. 21 , antenna  10  has a first portion H 1  and a second portion H 2 . Portions H 1  and H 2  may be horn-type antenna structures with different efficiencies in different communications bands. In horn antenna structure H 1 , inductance L 2  may be less than inductance L 1 . In horn antenna structure H 2 , inductance L 4  may be less than inductance L 3 . Inductance L 3  may be less than inductance L 2  (as an example). 
   In multiband antennas  10  such as antenna  10  of  FIG. 21  and the other antennas  10  described herein, a diplexer such as diplexer  47  may be used to couple two separate transceivers to the antenna. For example, a first transmission line such as transmission line  49 A of  FIG. 21  may be used to couple transceiver  51 A to diplexer  47  and a second transmission line such as transmission line  49 B of  FIG. 21  may be used to couple transceiver  51 B to diplexer  47 . Transmission line  46  may be coupled to gap  14  using antenna terminals  42  and  44 . Transmission line  49 A, associated transceiver  51 A, and antenna structure H 1  may be used to handle communications in a first communications band. Transmission line  49 B, associated transceiver  51 B, and antenna structure H 2  may be used to handle communications in a second communications band. The center frequency of the first communications band may be less than or more than the center frequency of the second communications band. Structures of the type shown in  FIG. 21  may also be used to handle communications in a single band. 
   A graph showing the predicted reactance X of antenna structures H 1  and H 2  as a function of frequency is shown in  FIG. 22 . As shown in  FIG. 22 , at frequency f 1  (e.g., the center of the first communications band), the magnitude of the reactance X may increase from the value at point  66  to the value at point  68 . These values may correspond to the characteristics of horn-type antenna H 1 . At frequency f 2  (e.g., the center of the second communications band), the magnitude of the reactance X may increase from the value at point  70  to the value at point  72 . These values may correspond to the characteristics of horn-type antenna H 2 . Although two cascaded horn antenna structures H 1  and H 2  are shown in the example of  FIG. 22 , in general any suitable number of horn antenna structures may be cascaded if desired. 
   Antenna  10  may also be formed by cascading two or more scatter-type antenna structures. An antenna  10  of this type is shown in  FIG. 23 . In the example of  FIG. 23 , antenna  10  has a first portion and a second portion. First portion S 1  and second portion S 2  each have four shunt inductors  20 . The inductors  20  in first portion S 1  may have an inductance value of L 1 . The inductance values of inductors  20  in second portion S 2  may have an inductance value of L 2 . Inductance L 1  may be greater than or less than inductance L 2 . For example, inductance L 1  may be greater than inductance L 2 . 
   Scatter-type antenna structure S 1  may be used to handle communications in a first communications band (e.g., 2.4 GHz), whereas scatter-type antenna structure S 2  may be used to handle communications in a second communications band (e.g., 5.4 GHz). Each band may be fed using a corresponding transceiver through transmission line  46 . For example, a first transceiver may be used for a first communications band and a second transceiver may be used for a second communications band. 
   A graph of the reactance X of antenna  10  as a function of frequency is shown in  FIG. 24 . As shown in  FIG. 24 , scatter-type antenna structure S 1  (with shunt inductors of value L 1 ) may be characterized by the reactance of point  74  at frequency f 1  (e.g., at 2.4 GHz), whereas scatter-type antenna structure S 2  (with shunt inductors of value L 2 ) may be characterized by the reactance of point  76  at frequency f 2  (e.g., at 5.4 GHz). These reactance values may allow scatter-type antenna structure S 1  to efficiently handle communications in the first communications band (e.g., the band centered at 2.4 GHz) while scatter-type antenna structure S 2  may efficiently handle communications in the second communications band (e.g, the band centered at 5.4 GHz). 
   As these examples demonstrate, hybrid antennas may be formed from combinations of one or more scatter-type and one or more horn type antenna structures. Non-hybrid antennas may be formed from one or more scatter-type antenna structures or may be formed from one or more horn-type antenna structures. The use of multiple such structures in a single antenna may allow the antenna to cover multiple communications bands of interest or may support improved antenna efficiency in a given communications band. 
   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: 20100427
Grant Date: 20100427
Priority Date: 20071218
Inventors: CHIANG BING
SPRINGER GREGORY ALLEN
KOUGH DOUGLAS B.
AYALA ENRIQUE
MCDONALD MATTHEW IAN
Assignee: APPLE INC
CPC Classifications: [{"code": "H01Q1/2283", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q1/2266", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01Q13/10", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q5/321", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q13/10", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q1/2266", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01Q1/2283", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q5/321", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 40752508