Patent Publication Number: US-9413058-B1

Title: Loop-feeding wireless area network (WAN) antenna for metal back cover

Description:
BACKGROUND 
     A large and growing population of users is enjoying entertainment through the consumption of digital media items, such as music, movies, images, electronic books, and so on. The users employ various electronic devices to consume such media items. Among these electronic devices (referred to herein as user devices) are electronic book readers, cellular telephones, personal digital assistants (PDAs), portable media players, tablet computers, netbooks, laptops and the like. These electronic devices wirelessly communicate with a communications infrastructure to enable the consumption of the digital media items. In order to wirelessly communicate with other devices, these electronic devices include one or more antennas. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The present inventions will be understood more fully from the detailed description given below and from the accompanying drawings of various embodiments of the present invention, which, however, should not be taken to limit the present invention to the specific embodiments, but are for explanation and understanding only. 
         FIG. 1A  is a diagram of an antenna architecture of a user device with a low-band feeding structure and a high-band parasitic structure according to one embodiment. 
         FIG. 1B  is a diagram of a metal cover of the user device with the low-band feeding structure and the high-band parasitic structure according to one embodiment. 
         FIG. 2A  shows an expanded view of the low-band feeding structure according to one embodiment. 
         FIG. 2B  shows an expanded view of the high-band parasitic structure according to one embodiment. 
         FIG. 3A  illustrates current flows of the low-band feeding structure according to one embodiment. 
         FIG. 3B  illustrates current flows of the low-band feeding structure according to one embodiment. 
         FIG. 4A  is a Smith chart of an input impedance of the low-band feeding structure according to one embodiment. 
         FIG. 4B  is a Smith chart of an input impedance of the low-band feeding structure according to one embodiment. 
         FIG. 5  is a schematic diagram of an impedance matching circuit according to one embodiment. 
         FIG. 6A  is a graph of S 11  parameter of the antenna structure of  FIG. 1A  according to one embodiment. 
         FIG. 6B  is a graph of efficiencies of the antenna structure of  FIG. 1A  according to one embodiment. 
         FIG. 7  is a block diagram of a user device in which embodiments of an antenna structure with a low-band feeding element and a high-band parasitic element may be implemented. 
     
    
    
     DETAILED DESCRIPTION 
     Antenna structures and methods of operating the same are described. One apparatus includes a metal cover having a first corner portion, a second corner portion, and an elongated portion. The elongated portion is physically separated from the first corner portion by a first cutout in the metal cover and the elongated portion is physically separated from the second corner portion by a second cutout in the metal cover. A radio frequency (RF) circuit is coupled to a feeding element that is coupled to the elongated portion. A capacitor is coupled between the feeding element and the first corner portion near the distal end of the feeding element. The RF circuit is operable to cause the feeding element, the elongated portion, and the first corner portion to radiate electromagnetic energy as a first radiator in a first frequency range with dual resonance. As described herein, the first radiator has a first resonant mode and a second resonant mode, resulting in the dual resonance. 
     The embodiments described herein are directed to WAN antennas that can use the metal cover, such as back cover. Mobile devices with a metal back cover typically cannot use both corner areas for efficient radiation. These conventional antennas require slot cutouts nearby the corners. The embodiments described herein can utilize the corners of the metal cover as low band and high band radiators, respectively without cutouts nearby the corners as done conventionally. With the preservation of the connected corners, consequently, the metal structure enhances the reliability of the mobile devices. The low band feeding structure can have a unique loop ground feeding structure, as described in more detail below. This feeding structure utilizes the corner ground element to cause a loop curve that goes inward in the smith chart described and illustrated herein. This cause a dual resonance for the low band radiator. The dual resonance causes a wideband dual resonance at the low band in a limited antenna volume without matching components as described herein. The embodiments described herein utilize the corners to give effective radiation and provide bandwidth without matching components. The embodiments described herein can also utilize a middle strip of the low band resonator as a long isolated bar for a proximity sensor. That is, the elongated portion of the antenna structure can be repurposed as a proximity sensor. The elongated structure can be considered a capacitor of which the capacitance can be measured by proximity sensing circuitry. This permits a proximity sensor and an antenna to be integrated into the same structure of the user device. 
     Several topologies of 2G/3G WAN antenna structures are contemplated herein. One antenna structure involves a two-cutout design with a middle portion (also described herein as an elongated portion) and two corner areas that are robustly connected to a chassis of the metal cover. This design can also reuse the antenna structure as a proximity sensor. The antenna structure exhibits good efficiency and may account for lossy materials such as inductors, caps, plastic, touch traces, ink, indium-tin-oxide (ITO) traces, or the like. 
     The antenna structures described herein can be used for wireless area network (WAN) technologies, such as cellular technologies including Long Term Evolution (LTE) frequency bands, third generation (3G) frequency bands, Wi-Fi® and Bluetooth® frequency bands or other wireless local area network (WLAN) frequency bands, global navigation satellite system (GNSS) frequency bands (e.g., positioning system (GPS) frequency bands, or the like. 
       FIG. 1A  is a diagram of an antenna architecture of a user device  100  with a low-band feeding structure  101  and a high-band parasitic structure  103  according to one embodiment. The user device  100  includes a RF circuit  140  (also referred to herein as RF chipset and RF circuitry), a single RF feed  102 , the low-band feeding structure  101 , and the high-band parasitic structure  103 . The low-band feeding structure  101  includes a feeding element  104 , a middle strip element  106 , and a first corner ground element  108 . A capacitor  116  is disposed between the first corner ground element  108  and the feeding element  104 . The low-band feeding structure  101  is a dual-resonance structure in a first frequency range (e.g., low band). 
     The user device  100  includes a metal cover  105  that operates as a ground plane. One corner of the metal cover  105  is the first corner ground element  108  and another corner of the metal cover  105  is a second corner ground element  110  disposed at a periphery of the metal cover  105 . The middle strip element  106 , also referred to herein as an elongated portion, is physically separated from the first corner ground element  108  by a first cutout  118  in the metal cover  105  and the middle strip element  106  is physically separated from the second corner ground element  110  by a second cutout  120  in the metal cover  105 . The middle strip element  106  is also disposed at the periphery of the metal cover  105 . In one embodiment, the first cutout  118  and second cutout  120  measure 1.8 mm in width. In another embodiment, the first cutout  118  and second cutout  120  measure 2.0 mm in width. Alternatively, other widths may be used. The middle strip element  106  can operate as part of the metal cover  105  in a structural manner. The middle strip element  106  can also be operational in an antenna mode of the user device  100 , as well as in a proximity sensing mode of the user device  100 . In particular, the middle strip element  106  can operate as an electrode of a proximity sensing circuit. A capacitance of the electrode can be measured by a proximity sensing circuit  150 . The proximity sensing circuit  150  can be coupled to the RF feed  102 . A switch can control the coupling of the RF circuit  140  and the proximity sensing circuit  150  to the RF feed. Alternatively, matching components can be used to permit both the proximity sensing circuit  150  and the RF circuit  140  to be coupled to the RF feed. It should be noted that the first corner ground element  108  and the second corner ground element  110  can be separate parts or can be integrated with the rest of the metal cover  105 . 
     The low-band feeding structure  101  is made up of the ground plane of the metal cover  105 , the feeding element  104 , the middle strip element  106  and the first corner ground element  108 . The low-band feeding structure  101  with the capacitor  116  operates a first radiator with dual resonance. The high-band parasitic structure  103  is made up of the ground plane of the metal cover  105 , a grounding line  122  and the second corner ground element  110 . 
     In the depicted embodiment, the feeding element  104  includes a first section that extends from a feeding point  112  at the RF feed  102  along a first path, a second section that extends from a distal end of the first section along a second path, and a third section that extends from a distal end of the second section along a third path and couples to a first end of the middle strip element  106 . In the depicted embodiment, the first path is a first direction, the second path is a second direction that is perpendicular to the first direction, and the third path is the first direction. Alternatively, the first, second and third paths may not be perpendicular and may not be linear. The middle strip element  106  extends from the first end along a fourth path (e.g., second direction in the depicted embodiment) to a second end of the middle strip element. The first corner ground element  108  includes a first section that extends from the ground plane along a fifth path that follows a direction of the first path to form a first gap (illustrated in  FIG. 2A ) between the feeding element  104  and the first corner ground element  108 . In the depicted embodiment, the first section extends from the ground plane in the second direction to the second end of the middle strip element. A second section of the first corner ground element  108  extends from a distal end of the first section of the first corner ground element  108  along a sixth path that follows a direction of the second path to form a second gap (illustrated in  FIG. 2A ) between the feeding element  104  and the first corner ground element  108 . In the depicted embodiment, the second section extends from the distal end of the first section in the second direction to form the second gap. 
     In one embodiment, as illustrated in  FIG. 1A , the capacitor  116  is disposed between the feeding element  104  and the first corner ground element  108  at the distal end of the feeding element  104 , near an end of the first corner ground element  108 . 
     In the depicted embodiment, the second corner ground element  110  is coupled to the ground plane at a grounding point  114  via the grounding line  122 . The grounding line  122  may include a first section that extends out from the grounding point in a first path, a second section that extends form a distal end of the first section in a second path, and a third section that extends from a distal end of the second section in a third path to couple to the second corner ground element  110 . 
     In one embodiment, the RF circuit  140  includes a wireless area network (WAN) module. The WAN module is operable to cause the feeding element  104 , the middle strip element  106  and the first corner ground element  108  to radiate electromagnetic energy in a first frequency range in a first resonant mode and a second resonant mode. In another embodiment, the RF circuit  140  may include other modules, such as a wireless local area network (WLAN) module, a personal area network (PAN) module, global navigation satellite system (GNSS) module (e.g., global positioning system (GPS) module), or the like. The low-band feeding structure  101  can be designed to be self-resonant at 800 MHz and 950 MHz for the dual resonance. These modes can be further matched to desired working bands of interest. Alternatively, other resonant modes can be achieved, such as for WLAN frequency bands. For example, in dual-band Wi-Fi® networks, the low-band feeding structure  101  and high-band parasitic structure  102  can be matched in the two modes to cover the 2.4 GHz band and the 5 GHz band. For example, the WLAN module may include a WLAN RF transceiver for communications on one or more Wi-Fi® bands (e.g., 2.4 GHz and 5 GHz). It should be noted that the Wi-Fi® technology is the industry name for wireless local area network communication technology related to the IEEE 802.11 family of wireless networking standards by Wi-Fi Alliance. For example, a dual-band WLAN RF transceiver allows an electronic device to exchange data or connection to the Internet wireless using radio waves in two WLAN bands (2.4 GHz band, 5 GHz band) via one or multiple antennas. For example, a dual-band WLAN RF transceiver includes a 5 GHz WLAN channel and a 2.4 GHz WLAN channel. In other embodiments, the antenna architecture may include additional RF modules and/or other communication modules, such as a wireless local area network (WLAN) module, a GPS receiver, a near field communication (NFC) module, an amplitude modulation (AM) radio receiver, a frequency modulation (FM) radio receiver, a personal area network (PAN) module (e.g., Bluetooth® module, Zigbee® module), a Global Navigation Satellite System (GNSS) receiver, or the like. The RF circuit  140  may include one or multiple RFFE (also referred to as RF circuitry). The RFFEs may include receivers and/or transceivers, filters, amplifiers, mixers, switches, and/or other electrical components. The RF circuit  140  may be coupled to a modem that allows the user device  100  to handle both voice and non-voice communications (such as communications for text messages, multimedia messages, media downloads, web browsing, etc.) with a wireless communication system. The modem may provide network connectivity using any type of digital mobile network technology including, for example, LTE, LTE advanced (4G), CDPD, GPRS, EDGE, UMTS, 1×RTT, EVDO, HSDPA, WLAN (e.g., Wi-Fi® network), etc. In the depicted embodiment, the modem can use the RF circuit  140  to radiate electromagnetic energy on the antennas to communication data to and from the user device  100  in the respective frequency ranges. In other embodiments, the modem may communicate according to different communication types (e.g., WCDMA, GSM, LTE, CDMA, WiMAX, etc.) in different cellular networks. 
     Additional details regarding the current follow for the dual resonance are described below with respect to  FIG. 3B . In short, the capacitor  116  increases the radiation by changing the current flow on the first corner ground element to be the same direction as the current flow along the feeding element  104 . This cause the low-band feeding structure  101  to have dual resonance. The capacitor  116  may be a discrete component with a capacitive value or may be conductive traces with the corresponding capacitance value. In one embodiment, the capacitor  116  has a capacitance value of 2 pF. This type of capacitance value gives a very small loading effect when in the proximity sensing mode, but provides the looping current effect in the antenna mode as described herein. The feeding element  104 , the middle strip element  106 , and the first corner ground element  108  (collectively the low-band feeding structure  101 ) are operable to cause the second corner ground element  110  to radiate electromagnetic energy in a second frequency range in a third resonant mode. It should be noted that radiation enables functionality of both transmission and receiving data using reciprocity. That is there is a high-band coupling between the middle strip element  106  and the second corner ground element  110  via the second cutout  120 . In one embodiment, the first frequency range is between approximately 770 MHz and approximately 1.0 GHz and the second frequency range is between approximately 1.7 GHz and 2.2 GHz. It should be noted that if the device scales up, the S 11  parameter  602  could be extended to lower frequencies, e.g., 700 MHz. 
     The user device  100  (also referred to herein as an electronic device) may be any content rendering device that includes a modem for connecting the user device to a network. Examples of such electronic devices include electronic book readers, portable digital assistants, mobile phones, laptop computers, portable media players, tablet computers, cameras, video cameras, netbooks, notebooks, desktop computers, gaming consoles, Blu-ray® or DVD players, media centers, drones, speech-based personal data assistants, and the like. The user device may connect to a network to obtain content from a server computing system (e.g., an item providing system) or to perform other activities. The user device may connect to one or more different types of cellular networks. 
     In one embodiment, the user device  100  includes a single radio frequency (RF) feed, RF circuitry coupled to the single RF feed, and a metal cover. The metal cover includes a middle strip element, a first corner ground element, and a second corner ground element. The middle strip element is physically separated from the first corner ground element by a first cutout in the metal cover and the middle strip element is physically separated from the second corner ground element by a second cutout in the metal cover. The antenna structure is coupled to the RF feed and includes a ground plane (e.g., chassis of the user device  100  or metal back cover), a first antenna formed by a feeding element, the middle strip element and the first corner ground element and a second parasitic antenna formed by the second corner ground element. 
     In one embodiment, the feeding element includes a first section, a second section, and a third section. The first section extends from a feeding point at the RF feed along a first path. The second section extends from a distal end of the first section along a second path. The third section extends from a distal end of the second section along a third path and couples to a first end of the middle strip element. The middle strip element extends from the first end along a fourth path to a second end. 
     In a further embodiment, the first corner ground element includes a first section and a second section. The first section extends from the ground plane along a fifth path that follows a direction of the first path to form a first gap between the feeding element and the first corner ground element. The second section extends from a distal end of the first section of the first corner ground element along a sixth path that follows a direction of the second path to form a second gap between the feeding element and the first corner ground element. 
     In a further embodiment, a capacitor disposed between the feeding element and the first corner ground element at the distal end of the feeding element. The second corner ground element is coupled to the ground plane at a grounding point via a grounding line. 
     In a further embodiment, the RF circuitry comprises a WAN module that is operable to cause the feeding element, the middle strip element and the first corner ground element to radiate electromagnetic energy in a first frequency range in a first resonant mode and a second resonant mode. The feeding element, the middle strip element and the first corner ground element are operable to cause the second corner ground element to radiate electromagnetic energy in a second frequency range in a third resonant mode. In one embodiment, the first frequency range is between approximately 770 MHz and approximately 1.0 GHz, and wherein the second frequency range is between approximately 1.7 GHz and 2.2 GHz. Alternatively, other frequency ranges may be achieved. 
     In another embodiment, an electronic device includes a metal cover with a first corner part, a second corner part, and an elongated part disposed between the first corner part and the second corner part. The elongated part is physically separated from the first corner part by a first cutout in the metal cover and the elongated part is physically separated from the second corner part by a second cutout in the metal cover. A RF circuit is coupled to a RF feed and the RF feed is coupled to a feeding element at a feeding point. The feeding element is coupled to the elongated part at a distal end, the distal end being farthest from the feeding point. A capacitor is coupled between the feeding element and the first corner part near the distal end of the feeding element. The RF circuit is operable to cause the feeding element, the elongated part, and the first corner part to radiate electromagnetic energy as a first radiator in a first frequency range with dual resonance. 
     In a further embodiment, the first radiator is operable to cause the second corner part to radiate electromagnetic energy as a parasitic ground element in a second frequency range, the second frequency range being higher than the first frequency range. 
     In a further embodiment, the RF circuit is operable to apply a signal at the feeding point. The signal causes a first current flow along the feeding element towards the elongated part and causes a second current flow along the first corner part towards the first cutout in the same direction as the first current flow. 
     In one embodiment, the first cutout and the second cutout are disposed at symmetric locations on a first side of the electronic device relative to a center point on the first side of the electronic device. 
     In another embodiment, the electronic device includes a switch coupled between the RF circuit and the RF feed, the first switch switching the electronic device between an antenna mode and a proximity sensing mode. The electronic device further includes a proximity sensing circuit coupled to the switch. The proximity sensing circuitry is operable to measure a capacitance of the elongated part in the proximity sensing mode. It should be noted that the elongated part is operable to radiate the electromagnetic energy as part of the first radiator in the antenna mode. In another embodiment, the electronic device does not switch between modes, but uses an inductor as an RF choke between the RF feed and the proximity sensing circuitry as described herein. 
     In a further embodiment, the feeding element includes a first section, a second section, and a third section. The first section extends from the feeding point along a first path. The second section that extends from a distal end of the first section along a second path. The third section extends from a distal end of the second section along a third path and couples to the middle strip element at a first end. The middle strip element extends along a fourth path to a second end. The first corner part includes a first section and a second section. The first section extends along a fifth path that follows a direction of the first path to form a first gap between the feeding element and the first corner part. The second section extends from a distal end of the first section of the first corner part along a sixth path that follows a direction of the second path to form a second gap between the feeding element and the first corner part. 
     In a further embodiment, the antenna structure includes a grounding line coupled to the second corner part and coupled to a ground plane at a grounding point. In another embodiment, the first corner part is an L-shape that starts at a first side of the metal cover and bends to a second side of the electronic device (e.g., bends around a first corner of the electronic device to the second side). The first side and the second side of the metal cover may be curved or rounded on one or more edges. 
     In another embodiment, the antenna structure includes a grounding line coupled between a distal end of the second corner part and a grounding point at the ground plane. The second corner part is a second L-shape that starts at a third side of the metal cover and bends to the second side (e.g., bends around a second corner of the user device to the second side. The third side of the metal cover may be curved or otherwise rounded as described herein. 
     In one embodiment, the RF circuit includes a WAN module to cause the feeding element, the elongated part and the first corner part to radiate electromagnetic energy in the first frequency range in two resonant modes. The feeding element, the elongated part and the first corner part are operable to cause the second corner part to radiate electromagnetic energy in the second frequency range in a third resonant mode. In one embodiment, the first frequency range is between approximately 770 MHz and approximately 1.0 GHz, and the second frequency range is between approximately 1.7 GHz and 2.2 GHz. Alternatively, other frequencies may be achieved with similar antenna structures. 
     During operation of the user device  100 , RF circuit applies a signal to cause a first radiator to radiate electromagnetic energy in a first frequency range in an antenna mode. As described herein, the first radiator may be similar to the low-band feeding element  101 , including a feeding element, a first corner part of the metal cover, an elongated part of the metal cover, and a capacitor. The feeding element is coupled to the elongated part. The elongated part is coupled to a distal end of the feeding element, and the first corner part is physically separated from the elongated part by a first cutout in the metal cover. The capacitor is disposed between the first corner part and the feeding element at a distal end of the feeding element. The signal causes a first current to flow along the feeding element towards the elongated part. The capacitor causes a second current to flow from a ground plane, around the first corner part and towards the first cutout, the first current and the second current causing a dual resonance by the first radiator. In addition, the feeding element parasitically induces a third current on a second radiator to radiate electromagnetic energy in a second frequency range in the antenna mode. As described herein, the second radiator may be similar to the high-band parasitic element  103 . The second radiator may include a second corner part of the metal cover with a grounding line coupled between a grounding point at the ground plane and a distal end of the second corner part. 
     In a further embodiment, the user device switches from the antenna mode to a proximity sensing mode and a proximity sensing circuit measures a capacitance of the elongated part to detect an object proximate to the elongated part in a proximity sensing mode. 
     In a further embodiment, the signal is applied by a WAN module to cause the feeding element, the elongated part and the first corner part to radiate electromagnetic energy in the first frequency range in two resonant modes. The feeding element, the elongated part and the first corner part are operable to cause the second corner part to radiate electromagnetic energy in the second frequency range in a third resonant mode. In one embodiment, the first frequency range is between approximately 770 MHz and approximately 1.0 GHz, and the second frequency range is between approximately 1.7 GHz and 2.2 GHz. 
     It should be noted that the diagram of  FIG. 1B  does not illustrate the entire metal cover  105  to show the low-band feeding structure  101  and the high-band parasitic structure  103 .  FIG. 1B  shows the metal cover  105  cover the entire back of the user device  100 . 
       FIG. 1B  is a diagram of a metal cover  105  of the user device  100  with the low-band feeding structure  101  and the high-band parasitic structure  103  according to one embodiment. In particular, the middle strip element  106  is shown as being separated from the first corner ground element  108  by the first cutout  118  in the metal cover  105  and the middle strip element  106  is physically separated from the second corner ground element  110  by the second cutout  120  in the metal cover  105 . 
       FIG. 2A  shows an expanded view of the low-band feeding structure  101  according to one embodiment. As described above, the feeding element  104  includes a first section  202  that extends from the feeding point  112  at the RF feed  102  along a first path, a second section  204  that extends from a distal end of the first section  202  along a second path, and a third section  206  that extends from a distal end of the second section  204  along a third path and couples to a first end  208  of the middle strip element  106 . The middle strip element  106  extends from the first end  208  along a fourth path to a second end  210  illustrated in  FIG. 2B . The first corner ground element  108  includes a first section  214  that extends from the ground plane along a fifth path that follows a direction of the first path to form a first gap  216  between the feeding element  104  (first section  202 ) and the first corner ground element  108  (first section  214 ). A second section  218  of the first corner ground element  108  extends from a distal end of the first section  214  of the first corner ground element  108  along a sixth path that follows a direction of the second path to form a second gap  220  between the feeding element  104  (second section  204 ) and the first corner ground element  108  (second section  218 ). 
     In the depicted embodiment, the first corner ground element  108  connects in an L-shape above the chassis of the metal cover  105  as depicted. Also, in the depicted embodiment, the sides of the metal cover are curved or otherwise rounded. In other embodiments, the sides may have different shapes. 
     In the depicted embodiment, the capacitor  116  is disposed between the second section  204  of the feeding element  104  and the second section  218  of the first corner ground element  108  at the distal end of the feeding element  104 , near an end of the first corner ground element  108  that is closest to the first cutout  118 . 
       FIG. 2B  shows an expanded view of the high-band parasitic structure  103  according to one embodiment. The high-band parasitic structure  103  is coupled to the ground plane at the grounding point  114  via the grounding line  122 . The grounding line  122  may include a first section  232  that extends out from the grounding point in a first path, a second section  234  that extends form a distal end of the first section  232  in a second path, and a third section  236  that extends from a distal end of the second section  234  in a third path to couple to the second corner ground element  110 . The second corner ground element  110  includes a first section  238  that extends from the ground plane along a fourth path that follows a direction of the first path to form a first gap  240  between the grounding line  122  (first section  232 ) and the second corner ground element  110  (first section  238 ). A second section  242  of the second corner ground element  110  extends from a distal end of the first section  238  of the second corner ground element  110  along a fifth path that follows a direction of the second path to form a second gap  244  between the grounding line  122  (second section  234 ) and the second corner ground element  110  (second section  242 ). In one embodiment, the high-band parasitic structure  103  operates as a parasitic loop antenna. This parasitic loop antenna may enhance reliability of the antenna structure. 
     In the depicted embodiment, the second corner ground element  110  connects in an L-shape above the chassis of the metal cover  105  as depicted. Also, in the depicted embodiment, the sides of the metal cover are curved or otherwise rounded. In other embodiments, the sides may have different shapes. 
       FIG. 3A  illustrates current flows of the low-band feeding structure  101  according to one embodiment. In  FIG. 3A , a first current  302  flows from the RF feed  102  along the feeding element  104  and through the middle strip element  106 . A second current  304  flows from a distal end of the first corner ground element  108  towards the ground plane. This may cause the radiation to be reduced in that the first current  302  and second current  304  tend to cancel out due to the currents flowing in different directions relative to the RF feed  102 . 
       FIG. 3B  illustrates current flows of the low-band feeding structure  101  according to one embodiment. In  FIG. 3B , a first current  352  flows from the RF feed  102  along the feeding element  104  and through the middle strip element  106 . A second current  354  flows from a proximal end of the first corner ground element  108  towards the distal end of the first corner ground element  108 . This may cause the radiation to be enhanced as current flows in the same direction. The capacitor  116  can be used to match the RF circuit  140  and block direct current to keep the proximity sensor signal quality high. For example, the capacitor  116  may be 2 pF in value to match the RF circuit  140 . The current flowing in the same direction causes the low-band feeding structure  101  to operate as a loop feeding element. The low-band feeding structure  101  parasitically induces another current on the high-band parasitic structure  103  (not illustrated in  FIG. 3B ). 
       FIG. 4A  is a Smith chart  400  of an input impedance of the low-band feeding structure  101  according to one embodiment. The Smith chart  400  illustrates how the impedance and reactance behave at one or more frequencies for the low-band feeding structure  101 . In particular, the line  402  corresponds to the impedance of the low-band feeding structure  101  without the capacitor  116  of  FIG. 1A . The Smith chart  400  illustrates the low-band feeding structure  101  as having two resonant modes, one in the low band and one in the high band, as the locus of antenna input impedance on the Smith chart as identified as the two loops. As illustrated in Smith chart  400 , the low-band feeding structure  101  generates a single low-band resonance and the low-band feeding structure  101  is not well matched for the high-band parasitic structure  103 . 
       FIG. 4B  is a Smith chart  450  of an input impedance of the low-band feeding structure  101  according to one embodiment. The Smith chart  450  illustrates how the impedance and reactance behave at one or more frequencies for the low-band feeding structure  101 . In particular, the line  402  corresponds to the impedance of the low-band feeding structure  101  with the capacitor  116  of  FIG. 1A . The Smith chart  450  illustrates the low-band feeding structure  101  as having three resonant modes, two in the low band and one in the high band, as the locus of antenna input impedance on the Smith chart as identified as the three loops. As illustrated in Smith chart  450 , the low-band feeding structure  101  with the capacitor  116  generates double resonance and the low-band feeding structure is better matched for the high-band parasitic structure  103 . 
     As noted above, the low-band feeding structure  101  with the capacitor  116  can achieve dual resonance without impedance matching circuits. In other embodiments, an impedance matching circuit can be used. The impedance matching circuit can be used to further enlarge the bandwidth in the low band. 
       FIG. 5  is a schematic diagram of an impedance matching circuit  500  according to one embodiment. In this embodiment, the impedance matching circuit  500  is disposed in-line with the RF feed  102  and the low-band feeding structure  101 . The impedance matching circuit  500  can also be disposed before the RF feed  102  on the circuit board where the RF circuit resides. In this embodiment, the impedance matching circuit  500  includes two series capacitors  502 ,  504  and a shunt inductor  506 . The first series capacitor  502  is coupled to the RF feed  102  and an intermediate node  508 . The second series capacitor  504  is coupled between the intermediate node  508  and the low-band feeding structure  101 . The shunt inductor  506  is coupled between the intermediate node  508  and a ground potential. In another embodiment, the output of the impedance matching circuit  500  is coupled to the RF feed  142 . The input of the impedance matching circuit  500  may be coupled to an output of the modem or other antenna circuitry. In one embodiment, the impedance matching circuit  500  is disposed on a PCB. In the depicted embodiment, the impedance matching circuit  500  is a simple matching T circuit and can be used to further enlarge the bandwidth. Alternatively, other components and other configurations of components may be used for matching the low-band feeding structure  101  in other ways. 
     In some embodiments, a proximity sensing circuit  150  is coupled to the low-band feeding structure  101  via an inductor  510 . Alternatively, the proximity sensing circuit  150  can be coupled to the low-band feeding structure  101  without an inductor. The inductor  510  may operate to filter signals from the RF circuitry driven at RF feed  102 . Alternatively, other configurations of the RF circuitry and proximity sensing circuitry may be utilized for the two modes of the low-band feeding structure  101 . In one embodiment, the low-band feeding structure  101  can be switched between an antenna mode and a proximity sensing mode. In another embodiment, the low-band feeding structure  101  can operate concurrently in the antenna mode and the proximity sensing mode because the proximity sensing mode operates at a much lower frequency than the antenna mode. 
       FIG. 6A  is a graph  600  of the S 11  parameter  602  of the antenna structure of  FIG. 1A  according to one embodiment. The graph  600  shows the S 11  parameter  602  of the antenna structure in a low band (LB)  604  and in a high band (HB)  606 . The S 11  parameter  602  is measured in dB. In one embodiment, the LB  604  covers a frequency range between approximately 770 MHz and approximately 1.0 GHz, such as for GSM850/900 bands. Alternatively, other frequencies in the LB  604  may be covered by the low-band feeding element  101 . In one embodiment, the HB  606  covers a frequency range between approximately 1.7 GHz and 2.2 GHz. Alternatively, other frequencies in the HB  606  may be covered by the high-band parasitic element  103 . 
       FIG. 6B  is a graph  650  of efficiencies of the antenna structure of  FIG. 1A  according to one embodiment. The total efficiency of the antenna structure can be measured by including the loss of the structure and mismatch loss. The graph  650  shows the measured efficiencies  652  of the antenna structure in the LB  604  and the HB  606 . In the depicted embodiment, the measured efficiencies  652  are good between approximately 770 MHz and approximately 1.0 GHz in the LB  604  and between 1.71 GHz and 2.2. GHZ in the HB  606 . 
       FIG. 7  is a block diagram of a user device  705  in which embodiments of an antenna structure  700  with a low-band feeding element  101  and a high-band parasitic element  103  may be implemented. The user device  705  may correspond to the user device  100  of  FIG. 1A . The user device  705  may be any type of computing device such as an electronic book reader, a PDA, a mobile phone, a laptop computer, a portable media player, a tablet computer, a camera, a video camera, a netbook, a desktop computer, a gaming console, a DVD player, a Bluray®, a computing pad, a media center, a voice-based personal data assistant, and the like. The user device  705  may be any portable or stationary user device. For example, the user device  705  may be an intelligent voice control and speaker system. Alternatively, the user device  705  can be any other device used in a WLAN network (e.g., Wi-Fi® network), a WAN network, or the like. 
     The user device  705  includes one or more processor(s)  730 , such as one or more CPUs, microcontrollers, field programmable gate arrays, or other types of processors. The user device  705  also includes system memory  706 , which may correspond to any combination of volatile and/or non-volatile storage mechanisms. The system memory  706  stores information that provides operating system component  708 , various program modules  710 , program data  712 , and/or other components. In one embodiment, the system memory  706  stores instructions of the methods as described herein. The user device  705  performs functions by using the processor(s)  730  to execute instructions provided by the system memory  706 . 
     The user device  705  also includes a data storage device  714  that may be composed of one or more types of removable storage and/or one or more types of non-removable storage. The data storage device  714  includes a computer-readable storage medium  716  on which is stored one or more sets of instructions embodying any of the methodologies or functions described herein. Instructions for the program modules  710  may reside, completely or at least partially, within the computer-readable storage medium  716 , system memory  706  and/or within the processor(s)  730  during execution thereof by the user device  705 , the system memory  706  and the processor(s)  730  also constituting computer-readable media. The user device  705  may also include one or more input devices  718  (keyboard, mouse device, specialized selection keys, etc.) and one or more output devices  720  (displays, printers, audio output mechanisms, etc.). 
     The user device  705  further includes a modem  722  to allow the user device  705  to communicate via a wireless network (e.g., such as provided by the wireless communication system) with other computing devices, such as remote computers, an item providing system, and so forth. The modem  722  can be connected to RF circuitry  783  and zero or more RF modules  786 . The RF circuitry  783  may be a WLAN module, a WAN module, PAN module, or the like. Antennas  788  are coupled to the RF circuitry  783 , which is coupled to the modem  722 . Zero or more antennas  784  can be coupled to one or more RF modules  786 , which are also connected to the modem  722 . The zero or more antennas  784  may be GPS antennas, NFC antennas, other WAN antennas, WLAN or PAN antennas, or the like. The modem  722  allows the user device  705  to handle both voice and non-voice communications (such as communications for text messages, multimedia messages, media downloads, web browsing, etc.) with a wireless communication system. The modem  722  may provide network connectivity using any type of mobile network technology including, for example, cellular digital packet data (CDPD), general packet radio service (GPRS), EDGE, universal mobile telecommunications system (UMTS), 1 times radio transmission technology (1×RTT), evaluation data optimized (EVDO), high-speed down-link packet access (HSDPA), Wi-Fi®, Long Term Evolution (LTE) and LTE Advanced (sometimes generally referred to as 4G), etc. 
     The modem  722  may generate signals and send these signals to antenna  788 , and  784  via RF circuitry  783 , and RF module(s)  786  as descried herein. User device  705  may additionally include a WLAN module, a GPS receiver, a PAN transceiver and/or other RF modules. These RF modules may additionally or alternatively be connected to one or more of antennas  784 ,  788 . Antennas  784 ,  788  may be configured to transmit in different frequency bands and/or using different wireless communication protocols. The antennas  784 ,  788  may be directional, omnidirectional, or non-directional antennas. In addition to sending data, antennas  784 ,  788  may also receive data, which is sent to appropriate RF modules connected to the antennas. 
     In one embodiment, the user device  705  establishes a first connection using a first wireless communication protocol, and a second connection using a different wireless communication protocol. The first wireless connection and second wireless connection may be active concurrently, for example, if a user device is downloading a media item from a server (e.g., via the first connection) and transferring a file to another user device (e.g., via the second connection) at the same time. Alternatively, the two connections may be active concurrently during a handoff between wireless connections to maintain an active session (e.g., for a telephone conversation). Such a handoff may be performed, for example, between a connection to a WLAN hotspot and a connection to a wireless carrier system. In one embodiment, the first wireless connection is associated with a first resonant mode of an antenna structure that operates at a first frequency band and the second wireless connection is associated with a second resonant mode of the antenna structure that operates at a second frequency band. In another embodiment, the first wireless connection is associated with a first antenna element and the second wireless connection is associated with a second antenna element. In other embodiments, the first wireless connection may be associated with a media purchase application (e.g., for downloading electronic books), while the second wireless connection may be associated with a wireless ad hoc network application. Other applications that may be associated with one of the wireless connections include, for example, a game, a telephony application, an Internet browsing application, a file transfer application, a global positioning system (GPS) application, and so forth. 
     Though a modem  722  is shown to control transmission and reception via antenna ( 784 ,  788 ), the user device  705  may alternatively include multiple modems, each of which is configured to transmit/receive data via a different antenna and/or wireless transmission protocol. 
     The user device  705  delivers and/or receives items, upgrades, and/or other information via the network. For example, the user device  705  may download or receive items from an item providing system. The item providing system receives various requests, instructions and other data from the user device  705  via the network. The item providing system may include one or more machines (e.g., one or more server computer systems, routers, gateways, etc.) that have processing and storage capabilities to provide the above functionality. Communication between the item providing system and the user device  705  may be enabled via any communication infrastructure. One example of such an infrastructure includes a combination of a wide area network (WAN) and wireless infrastructure, which allows a user to use the user device  705  to purchase items and consume items without being tethered to the item providing system via hardwired links. The wireless infrastructure may be provided by one or multiple wireless communications systems, such as one or more wireless communications systems. One of the wireless communication systems may be a wireless local area network (WLAN) hotspot connected with the network. The WLAN hotspots can be created by products using the Wi-Fi® technology based on IEEE 802.11x standards by Wi-Fi Alliance. Another of the wireless communication systems may be a wireless carrier system that can be implemented using various data processing equipment, communication towers, etc. Alternatively, or in addition, the wireless carrier system may rely on satellite technology to exchange information with the user device  705 . 
     The communication infrastructure may also include a communication-enabling system that serves as an intermediary in passing information between the item providing system and the wireless communication system. The communication-enabling system may communicate with the wireless communication system (e.g., a wireless carrier) via a dedicated channel, and may communicate with the item providing system via a non-dedicated communication mechanism, e.g., a public Wide Area Network (WAN) such as the Internet. 
     The user devices  705  are variously configured with different functionality to enable consumption of one or more types of media items. The media items may be any type of format of digital content, including, for example, electronic texts (e.g., eBooks, electronic magazines, digital newspapers, etc.), digital audio (e.g., music, audible books, etc.), digital video (e.g., movies, television, short clips, etc.), images (e.g., art, photographs, etc.), and multi-media content. The user devices  705  may include any type of content rendering devices such as electronic book readers, portable digital assistants, mobile phones, laptop computers, portable media players, tablet computers, cameras, video cameras, netbooks, notebooks, desktop computers, gaming consoles, DVD players, media centers, and the like. 
     In the above description, numerous details are set forth. It will be apparent, however, to one of ordinary skill in the art having the benefit of this disclosure, that embodiments may be practiced without these specific details. In some instances, well-known structures and devices are shown in block diagram form, rather than in detail, in order to avoid obscuring the description. 
     Some portions of the detailed description are presented in terms of algorithms and symbolic representations of operations on data bits within a computer memory. These algorithmic descriptions and representations are the means used by those skilled in the data processing arts to most effectively convey the substance of their work to others skilled in the art. An algorithm is here, and generally, conceived to be a self-consistent sequence of steps leading to a desired result. The steps are those requiring physical manipulations of physical quantities. Usually, though not necessarily, these quantities take the form of electrical or magnetic signals capable of being stored, transferred, combined, compared, and otherwise manipulated. It has proven convenient at times, principally for reasons of common usage, to refer to these signals as bits, values, elements, symbols, characters, terms, numbers or the like. 
     It should be borne in mind, however, that all of these and similar terms are to be associated with the appropriate physical quantities and are merely convenient labels applied to these quantities. Unless specifically stated otherwise as apparent from the above discussion, it is appreciated that throughout the description, discussions utilizing terms such as “inducing,” “parasitically inducing,” “radiating,” “detecting,” determining,” “generating,” “communicating,” “receiving,” “disabling,” or the like, refer to the actions and processes of a computer system, or similar electronic computing device, that manipulates and transforms data represented as physical (e.g., electronic) quantities within the computer system&#39;s registers and memories into other data similarly represented as physical quantities within the computer system memories or registers or other such information storage, transmission or display devices. 
     Embodiments also relate to an apparatus for performing the operations herein. This apparatus may be specially constructed for the required purposes, or it may comprise a general-purpose computer selectively activated or reconfigured by a computer program stored in the computer. Such a computer program may be stored in a computer readable storage medium, such as, but not limited to, any type of disk including floppy disks, optical disks, CD-ROMs and magnetic-optical disks, read-only memories (ROMs), random access memories (RAMs), EPROMs, EEPROMs, magnetic or optical cards, or any type of media suitable for storing electronic instructions. 
     The algorithms and displays presented herein are not inherently related to any particular computer or other apparatus. Various general-purpose systems may be used with programs in accordance with the teachings herein, or it may prove convenient to construct a more specialized apparatus to perform the required method steps. The required structure for a variety of these systems will appear from the description below. In addition, the present embodiments are not described with reference to any particular programming language. It will be appreciated that a variety of programming languages may be used to implement the teachings of the present invention as described herein. It should also be noted that the terms “when” or the phrase “in response to,” as used herein, should be understood to indicate that there may be intervening time, intervening events, or both before the identified operation is performed. 
     It is to be understood that the above description is intended to be illustrative, and not restrictive. Many other embodiments will be apparent to those of skill in the art upon reading and understanding the above description. The scope of the present embodiments should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.