Patent Publication Number: US-8525743-B2

Title: Antenna with near-field radiation control

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 13/529,531, which was filed on Jun. 21, 2012, which is a continuation of U.S. application Ser. No. 13/358,126, which was filed on Jan. 25, 2012 (now U.S. Pat. No. 8,223,078), which is a continuation of U.S. application Ser. No. 13/156,728, which was filed on Jun. 9, 2011 (now U.S. Pat. No. 8,125,397), which is a continuation of U.S. application Ser. No. 12/474,075, which was filed on May 28, 2009 (now U.S. Pat. No. 7,961,154), which is a continuation of U.S. application Ser. No. 11/774,383, which was filed on Jul. 6, 2007 (now U.S. Pat. No. 7,541,991), which is a continuation of U.S. application Ser. No. 10/940,869, which was filed on Sep. 14, 2004 (now U.S. Pat. No. 7,253,775), which is a continuation of U.S. application Ser. No. 10/317,659, which was filed on Dec. 12, 2002 (now U.S. Pat. No. 6,791,500). The entire disclosure and the drawing figures of these prior applications are hereby incorporated by reference. 
    
    
     FIELD 
     This document relates generally to the field of antennas. More specifically, an antenna: is provided that is particularly well-suited for use in wireless mobile communication devices, generally referred to herein as “mobile devices”, such as Personal Digital Assistants, cellular telephones, and wireless two-way email communication devices. 
     BACKGROUND 
     Many different types of antenna for mobile devices are known, including helix, “inverted F”, folded dipole, and retractable antenna structures. Helix and retractable antennas are typically installed outside of a mobile device, and inverted F and folded dipole antennas are typically embedded inside of a mobile device case or housing. Generally, embedded antennas are preferred over external antennas for mobile devices for mechanical and ergonomic reasons. Embedded antennas are protected by the mobile device case or housing and therefore tend to be more durable than external antennas. Although external antennas may physically interfere with the surroundings of a mobile device and make a mobile device difficult to use, particularly in limited-space environments, embedded antennas present fewer such challenges. However, established standards and limitations on near-field radiation tend to be more difficult to satisfy for embedded antennas without significantly degrading antenna performance. 
     SUMMARY 
     According to an example implementation, an antenna comprises a first conductor section electrically coupled to a first feeding point, a second conductor section electrically coupled to a second feeding point, and a near-field radiation control structure adapted to control characteristics of near-field radiation generated by the antenna. 
     In accordance with another example implementation, a wireless mobile communication device comprises a receiver configured to receive communication signals, a transmitter configured to transmit communication signals, and an antenna having a first feeding point and a second feeding point connected to the receiver and the transmitter. The antenna comprises a first conductor section connected to the first feeding point, a parasitic element positioned adjacent the first conductor section and configured to control characteristics of near-field radiation generated by the first conductor section, and a second conductor section connected to the second feeding point and comprising a diffuser configured to diffuse near-field radiation into a plurality of directions. 
     Further features and examples will be described or will become apparent in the course of the following detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a top view of an example antenna. 
         FIGS. 2(   a )- 2 ( f ) are top views of alternative parasitic elements; 
         FIG. 3  is a top view of an alternative diffusing element; 
         FIG. 4  is an orthogonal view of the antenna shown in  FIG. 1  mounted in a mobile device; and 
         FIG. 5  is a block diagram of a mobile device. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a top view of an antenna. The antenna  10  includes a first conductor section  12  and a second conductor section  14 . The first and second conductor sections  12  and  14  are positioned to define a gap  16 , thus forming an open-loop structure known as an open folded dipole antenna. 
     The antenna  10  also includes two feeding points  18  and  20 , one connected to the first conductor section  12  and the other connected to the second conductor section  14 . The feeding points  18  and  20  are offset from the gap  16  between the conductor sections  12  and  14 , resulting in a structure commonly referred to as an “offset feed” open folded dipole antenna. The feeding points  18  and  20  are configured to couple the antenna  10  to communications circuitry. For example, the feeding points  18  and  20  couple the antenna  10  to a transceiver in a mobile device, as illustrated in  FIG. 4  and described below. 
     Operating frequency of the antenna  10  is determined by the electrical length of the first conductor section  12 , the second conductor section  14 , and the position of the gap  16  relative to the feeding points  18  and  20 . For example, decreasing the electrical length of the first conductor section  12  and the second conductor section  14  increases the operating frequency band of the antenna  10 . Although the conductor sections  12  and  14  are electromagnetically coupled through the gap  16 , the first conductor section  12  is the main radiator of the antenna  10 . 
     As those familiar with antenna design will appreciate, the second conductor section  14  in the folded dipole antenna  10  is provided primarily to improve the efficiency of the antenna  10 . Environments in which antennas are implemented are typically complicated. The second conductor section  14  significantly increases the overall size of the antenna  10  and thus reduces the antenna dependency on its surrounding environment, which improves antenna efficiency. 
     Operation of an offset feed open folded dipole antenna is well known to those skilled in the art. The conductor sections  12  and  14  are folded so that directional components of far-field radiation, which enable communications in a wireless communication network, generated by currents in different parts of the conductor sections interfere constructively in at least one of the conductor sections. For example, the first conductor section  12  includes two arms  22  and  24  connected as shown at  26 . Current in the first conductor section  12  generates both near- and far-field radiation in each of the arms  22  and  24 . The arms  22  and  24  are sized and positioned, by adjusting the location and dimensions of the fold  26 , so that the components of the generated far-field radiation constructively interfere, thereby improving the operating characteristics of the antenna  10 . The location of the gap  16  in the antenna  10  is adjusted to effectively tune the phase of current in the arms  22  and  24 , to thereby improve constructive interference of far-field radiation generated in the first conductor section  12 . Since the first conductor section  12  is the primary far-field radiation element in the antenna  10 , maintaining the same phase of current in the arms  22  and  24  also improves antenna gain. 
     The first and second conductor sections  12  and  14  generate not only far-field radiation, but also near-field radiation. From an operational standpoint, the far-field radiation is the most important for communication functions. Near-field radiation tends to be confined within a relatively limited range of distance from an antenna, and as such does not significantly contribute to antenna performance in communication networks. As described briefly above, however, mobile devices must also satisfy various standards and regulations relating to near-field radiation. 
     Although antennas generate near-field radiation in addition to desired far-field radiation, near-field radiation tends to be much more difficult to analyze in antenna design. Far-field radiation patterns and polarizations for many types of antenna are known and predictable, whereas strong near-field radiation effects can be localized in an antenna. Generally, the near-field region of an antenna is proportional to the largest dimension of the antenna. However, simulation and other techniques that are often effective for predicting far-field radiation characteristics of an antenna have proven less reliable for determining near-field radiation patterns and polarizations. 
     A common scheme for reducing strong near-field radiation to acceptable levels involves installing a shield in a mobile device to at least partially block near-field radiation. Localized shielding required to reduce strong near-field radiation to acceptable levels also have more significant effects on far-field radiation, and thereby degrade the performance of the antenna. In this example, the antenna  10  includes near-field radiation control structures. These structures, labeled  34  and  36  in  FIG. 1 , provide another control mechanism for localized near-field radiation. 
     The structure  34  is a parasitic element comprising a conductor and a connection that electrically couples the conductor to the first conductor section of the antenna  10 . The length of the conductor in a parasitic element determines whether the parasitic element is a director or deflector. As those skilled in the art will appreciate, a parasitic deflector deflects near-field radiation. Although the near-field radiation pattern changes with a parasitic director, the direction of energy of such near-field radiation can be enhanced toward the direction of a parasitic director, generally to a greater degree than for a parasitic deflector. Near-field radiation is deflected or directed by the parasitic element  34  to reduce near-field radiation in particular directions. 
     As described above, near-field radiation tends to be more difficult to predict and analyze than far-field radiation. For far-field radiation, the length of a parasitic element is dependent upon the wavelength of the radiation to be directed or deflected, which is related to the operating frequency band of an antenna. Parasitic elements having a length greater than half the wavelength act as deflectors, and shorter elements act as directors. However, near-field radiation characteristics are also affected by mutual coupling between elements of an antenna. As such, near-field radiation directors and deflectors in accordance with this example are preferably adjusted as required during an antenna design and testing process in order to achieve the desired effects. When the dimensions and position of a parasitic element have been optimized for a particular antenna structure, and its effects confirmed by testing and measurement, then the parasitic element is effective for near-field radiation control in other antennas having the same structure. 
     In a preferred embodiment, the antenna  10  is mounted on the sides of a mobile device housing, with the feeding points  18  and  20  positioned toward a rear of the housing. Since near-field radiation restrictions generally relate to a direction out of the front of such devices, the parasitic element  34  is a deflector in this example, and deflects near-field radiation toward the rear of the device. Depending upon the desired effect in an antenna, which is often related to the location of the antenna in a mobile device, the parasitic element  34  is configured as either a deflector or a director in alternate embodiments. 
     The first conductor section  12  is the primary far-field radiating element in the antenna  10 . As such, introducing the parasitic element  34  also affects the operating characteristics of the antenna  10 . The parasitic element  34 , another conductor, electromagnetically couples to both arms  22  and  24  of the first conductor section  12 , and, to a lesser degree, to the second conductor section  14 . The impact of the parasitic element  34  on far-field radiation can be minimized, for example, by adjusting the shape and dimensions of the first and second conductor sections  12  and  14 , the size of the gap  16 , and the offset between the gap  16  and the feeding points  18  and  20 . It has also been found by the inventors that the parasitic element  34  can be connected to the first conductor section  12  with relatively little effect on far-field radiation. 
     The structure  36  in the second conductor section  14  includes a first diffuser  38  in the arm  28  and a second diffuser  40  in the arm  30 . Each diffuser  38  and  40  diffuses relatively strong near-field radiation into a plurality of directions. In the absence of the structure  36 , the second conductor section  14  generates near-field radiation in a direction substantially perpendicular to the arms  28  and  30 . In the above example in which the antenna  10  is mounted along side walls of a mobile device housing with the feeding points  18  and  20  toward the back of the mobile device, this near-field radiation propagates outward from the front of the mobile device. The diffusers  38  and  40  similarly generate near-field radiation, but not in a direction perpendicular to the arms  28  and  30 . Instead, the near-field radiation becomes isotropic in nature. The diffusers  38  and  40  reduce the gain of near-field radiation in a direction perpendicular to the arms  28  and  30 . Each diffuser comprises multiple conductor sections which extend in different directions, to thereby diffuse near-field radiation into multiple directions perpendicular to the conductor sections. Those skilled in the art will appreciate that the diffusers  38  and  40  also diffuse far-field radiation. However, the first conductor section  12  is the main radiator of the antenna  10 , such that diffusing the far-field radiation generated by the second conductor section  14  does not significantly impact antenna performance. 
     The antenna  10  shown in  FIG. 1  is intended for illustrative purposes. The invention is in no way limited to the particular structures  34  and  36 .  FIGS. 2(   a )- 2 ( f ) are top views of alternative parasitic elements. As described above, a parasitic element is configured as a director or deflector, depending upon its desired effect on near-field radiation. 
     The T-shaped parasitic element  42  in  FIG. 2(   a ) is substantially the same as the element  34  in  FIG. 1 , except that the conductor in the parasitic element, that is, the “top” of the T, is not perpendicular to the connection  43  which electrically couples the conductor to the first conductor section  12 . In  FIG. 2(   a ), the arms  22  and  24  of the conductor section  12  are not parallel, and the conductor in the parasitic element  42  is parallel to the arm  24 . Alternatively, the conductor may be parallel to the arm  22 , or not parallel to either of the arms, whether or not the arms themselves are parallel to each other. 
     In a further alternative embodiment, the parasitic element comprises multiple conductor sections, each conductor section being parallel to one of the arms of a folded dipole antenna. Thus, the conductor of a parasitic element need not necessarily be straight. For example, the parasitic element  44  comprises a sawtooth-shaped conductor, as shown in  FIG. 2(   b ). 
     Not only the shape of a conductor in a parasitic element, but also its connection point to the conductor section  12 , can be changed in alternate embodiments. In  FIG. 2(   c ), the parasitic element  46  comprises a conductor which is coupled to the conductor section  12  at one if its ends, to form an L-shaped parasitic element. 
     As those familiar with antennas appreciate, the conductor in any of the parasitic elements described above electromagnetically couples with other parts of an antenna. Therefore, near-field radiation control using parasitic elements can also be achieved without electrically connecting the conductor in a parasitic element to an antenna. Such a parasitic element is shown in  FIG. 2(   d ). The parasitic element  48  either directs or defects near-field radiation into desired directions, preferably away from the front of a mobile device. 
     The position of a parasitic element relative to the arms of a folded conductor section can also be different in alternate embodiments. For example, the parasitic element  47  in  FIG. 2(   e ) is located at one side of the first conductor section  12  adjacent the arm  22 , and the parasitic element  49  in  FIG. 2(   f ) is positioned at the other side of the first conductor section  12 , adjacent the arm  24 , instead of between the arms  22  and  24  as in  FIGS. 2(   a )- 2 ( d ). Where physical limitations permit, more than one parasitic element may be provided. 
     Diffusing elements can similarly be implemented having shapes other than the generally V-shaped elements shown in  FIG. 1 .  FIG. 3  is a top view of an alternative diffusing element, comprising a pair of curved diffusers  50  and  52  in the arms  28  and  30  of the second conductor section  14 . As described above, a diffuser includes multiple conductor sections extending in different directions to diffuse near-field radiation into directions perpendicular to the conductor sections. Although curved diffusers are shown in  FIG. 3 , other shapes of diffusers, having straight and/or curved conductor sections, are also contemplated. 
       FIG. 4  is an orthogonal view of the antenna shown in  FIG. 1  mounted in a mobile device. Those skilled in the art will appreciate that a front housing wall and a majority of internal components of the mobile device  100 , which would obscure the view of the antenna  10 , have not been shown in  FIG. 4 . In an assembled mobile device, an embedded antenna such as the antenna  10  is not visible. 
     The mobile device  100  comprises a case or housing having a front wall (not shown), a rear wall  68 , a top wall  62 , a bottom wall  66 , and side walls, one of which is shown at  64 . The view in  FIG. 4  shows the interior of the mobile device housing, looking toward the rear and bottom walls  68  and  66  of the mobile device  100 . 
     The antenna  10  is fabricated on a flexible dielectric substrate  60 , with a copper conductor and using known copper etching techniques, for example. This fabrication technique facilitates handling of the antenna  10  before and during installation in the mobile device  100 . The antenna  10  and the dielectric substrate  60  are mounted to the inside of the housing of the mobile device  100 . The substrate  60  and thus the antenna  10  are folded from an original, flat configuration illustrated in  FIG. 1 , such that they extend around the inside surface of the mobile device housing to orient the antenna  10  in multiple planes. The first conductor section  12  of the antenna  10  is mounted along the side wall  64  of the housing and extends from the side wall  64  around a front corner  65  to the top wall  62 . The feeding point  18  is mounted toward the rear wall  68  and connected to the transceiver  70 . In this embodiment, the parasitic element  34  is preferably a parasitic deflector, to deflect near-field radiation toward the rear wall  68 , and thus away from the front of the mobile device  100 . 
     The second conductor section  14  of the antenna  10  is folded and mounted across the side wall  64 , around the corner  67 , and along the bottom wall  66  of the housing. The feeding point  20  is mounted adjacent the feeding point  18  toward the rear wall  68  and is also connected to the transceiver  70 . The structure  36 , as described above, diffuses near-field radiation into multiple directions, and thereby reduces the amount of near-field radiation in a direction out of the front of the mobile device  100 . 
     Although  FIG. 4  shows the orientation of the antenna  10  within the mobile device  100 , it should be appreciated that the antenna  10  may be mounted in different ways, depending upon the type of housing, for example. In a mobile device with substantially continuous top, side, and bottom walls, the antenna  10  may be mounted directly to the housing. Many mobile device housings are fabricated in separate parts that are attached together when internal components of the mobile device have been placed. Often, the housing sections include a front section and a rear section, each including a portion of the top, side and bottom walls of the housing. Unless the portion of the top, side, and bottom walls in the rear housing section is of sufficient size to accommodate the antenna  10  and the substrate  60 , then mounting of the antenna  10  directly to the housing might not be practical. In such mobile devices, the antenna  10  is preferably attached to an antenna frame that is integral with or adapted to be mounted inside the mobile device, a structural member in the mobile device, or another component of the mobile device. Where the antenna  10  is fabricated on a substrate  60 , as shown, mounting or attachment of the antenna  10  is preferably accomplished using an adhesive provided on or applied to the substrate  60 , the component to which the antenna  10  is mounted or attached, or both. 
     The mounting of the antenna  10  as shown in  FIG. 4  is intended for illustrative purposes only. The antenna  10  or other similar antenna structures may be mounted on different surfaces of a mobile device or mobile device housing. For example, housing surfaces on which an antenna is mounted need not necessarily be flat, perpendicular, or any particular shape. An antenna may also extend onto fewer or further surfaces or planes than the antenna  10  shown in  FIG. 4 . 
     The feeding points  18  and  20  of the antenna  10  are coupled to the transceiver  70 . The operation of the mobile communication device  100 , along with the transceiver  70 , is described in more detail below with reference to  FIG. 5 . 
     The mobile device  100 , in alternative embodiments, is a data communication device, a voice communication device, a dual-mode communication device such as a mobile telephone having data communications functionality, a personal digital assistant (PDA) enabled for wireless communications, a wireless email communication device, or a wireless modem. 
     In  FIG. 5 , the mobile device  100  is a dual-mode and dual-band mobile device and includes a transceiver module  70 , a microprocessor  538 , a display  522 , a non-volatile memory  524 , a random access memory (RAM)  526 , one or more auxiliary input/output (I/O) devices  528 , a serial port  530 , a keyboard  532 , a speaker  534 , a microphone  536 , a short-range wireless communications sub-system  540 , and other device sub-systems  542 . 
     Within the non-volatile memory  524 , the device  100  preferably includes a plurality of software modules  524 A- 524 N that can be executed by the microprocessor  538  (and/or the DSP  520 ), including a voice communication module  524 A, a data communication module  524 B, and a plurality of other operational modules  524 N for carrying out a plurality of other functions. 
     The mobile device  100  is preferably a two-way communication device having voice and data communication capabilities. Thus, for example, the mobile device  100  may communicate over a voice network, such as any of the analog or digital cellular networks, and may also communicate over a data network. The voice and data networks are depicted in  FIG. 5  by the communication tower  519 . These voice and data networks may be separate communication networks using separate infrastructure, such as base stations, network controllers, etc., or they may be integrated into a single wireless network. 
     The transceiver module  70  is used to communicate with the networks  519 , and includes a receiver  516 , a transmitter  514 , one or more local oscillators  513 , and a DSP  520 . The DSP  520  is used to receive communication signals from the receiver  514  and send communication signals to the transmitter  516 , and provides control information to the receiver  514  and the transmitter  516 . If the voice and data communications occur at a single frequency, or closely-spaced sets of frequencies, then a single local oscillator  513  may be used in conjunction with the receiver  516  and the transmitter  514 . Alternatively, if different frequencies are utilized for voice communications versus data communications for example, then a plurality of local oscillators  513  can be used to generate a plurality of frequencies corresponding to the voice and data networks  519 . Information, which includes both voice and data information, is communicated to and from the transceiver module  70  via a link between the DSP  520  and the microprocessor  538 . 
     The detailed design of the transceiver module  70 , such as frequency bands, component selection, power level etc., is dependent upon the communication networks  519  in which the mobile device  100  is intended to operate. For example, the transceiver module  70  may be designed to operate with any of a variety of communication networks, such as the Mobitex™ or DataTAC™ mobile data communication networks, AMPS, TDMA, CDMA, PCS, and GSM. Other types of data and voice networks, both separate and integrated, may also be utilized where the mobile device  100  includes a corresponding transceiver module  70 . 
     Depending upon the type of network  519 , the access requirements for the mobile device  100  may also vary. For example, in the Mobitex and DataTAC data networks, mobile devices are registered on the network using a unique identification number associated with each mobile device. In GPRS data networks, however, network access is associated with a subscriber or user of a mobile device. A GPRS device typically requires a subscriber identity module (“SIM”), which is required in order to operate a mobile device on a GPRS network. Local or non-network communication functions (if any) may be operable, without the SIM device, but a mobile device will be unable to carry out any functions involving communications over the data network  519 , other than any legally required operations, such as ‘911’ emergency calling. 
     After any required network registration or activation procedures have been completed, the mobile device  100  may then send and receive communication signals, including both voice and data signals, over the networks  519 . Signals received by the antenna  10  from the communication network  519  are routed to the receiver  516 , which provides for signal amplification, frequency down conversion, filtering, channel selection, for example, as well as analog to digital conversion. Analog to digital conversion of the received signal allows more complex communication functions, such as digital demodulation and decoding to be performed using the DSP  520 . In a similar manner, signals to be transmitted to the network  519  are processed, including modulation and encoding, for example, by the DSP  520 , and are then provided to the transmitter  514  for digital to analog conversion, frequency up conversion, filtering, amplification and transmission to the communication network  519  via the antenna  10 . 
     In addition to processing the communication signals, the DSP  520  also provides for transceiver control. For example, the gain levels applied to communication signals in the receiver  516  and the transmitter  514  may be adaptively controlled through automatic gain control algorithms implemented in the DSP  520 . Other transceiver control algorithms could also be implemented in the DSP  520  in order to provide more sophisticated control of the transceiver module  70 . 
     The microprocessor  538  preferably manages and controls the overall operation of the dual-mode mobile device  100 . Many types of microprocessors or microcontrollers could be used here, or, alternatively, a single DSP  520  could be used to carry out the functions of the microprocessor  538 . Low-level communication functions, including at least data and voice communications, are performed through the DSP  520  in the transceiver module  70 . Other, high-level communication applications, such as a voice communication application  524 A, and a data communication application  524 B may be stored in the non-volatile memory  524  for execution by the microprocessor  538 . For example, the voice communication module  524 A may provide a high-level user interface operable to transmit and receive voice calls between the mobile device  100  and a plurality of other voice or dual-mode devices via the network  519 . Similarly, the data communication module  524 B may provide a high-level user interface operable for sending and receiving data, such as e-mail messages, files, organizer information, short text messages, etc., between the mobile device  100  and a plurality of other data devices via the networks  519 . 
     The microprocessor  538  also interacts with other device subsystems, such as the display  522 , the non-volatile memory  524 , the RAM  526 , the auxiliary input/output (I/O) subsystems  528 , the serial port  530 , the keyboard  532 , the speaker  534 , the microphone  536 , the short-range communications subsystem  540 , and any other device subsystems generally designated as  542 . 
     Some of the subsystems shown in  FIG. 5  perform communication-related functions, whereas other subsystems may provide “resident” or on-device functions. Notably, some subsystems, such as keyboard  532  and display  522  may be used for both communication-related functions, such as entering a text message for transmission over a data communication network, and device-resident functions such as a calculator or task list or other PDA type functions. 
     Operating system software used by the microprocessor  538  is preferably stored in a persistent store such as non-volatile memory  524 . In addition to the operation system, which controls all of the low-level functions of the mobile device  100 , the non-volatile memory  524  may include a plurality of high-level software application programs, or modules, such as a voice communication module  524 A, a data communication module  524 B, an organizer module (not shown), or any other type of software module  524 N. The non-volatile memory  524  also may include a file system for storing data. These modules are executed by the microprocessor  538  and provide a high-level interface between a user and the mobile device  100 . This interface typically includes a graphical component provided through the display  522 , and an input/output component provided through the auxiliary I/O  528 , the keyboard  532 , the speaker  534 , and the microphone  536 . The operating system, specific device applications or modules, or part thereof, may be temporarily loaded into a volatile store, such as RAM  526  for faster operation. Moreover, received communication signals may also be temporarily stored to RAM  526 , before permanently writing them to a file system located in a persistent store such as the non-volatile memory  524 . The non-volatile memory  524  may be implemented, for example, as a Flash memory component, or a battery backed-up RAM. 
     An exemplary application module  524 N that may be loaded onto the mobile device  100  is a personal information manager (PIM) application providing PDA functionality, such as calendar events, appointments, and task items. This module  524 N may also interact with the voice communication module  524 A for managing phone calls, voice mails, etc., and may also interact with the data communication module for managing e-mail communications and other data transmissions. Alternatively, all of the functionality of the voice communication module  524 A and the data communication module  524 B may be integrated into the PIM module. 
     The non-volatile memory  524  preferably provides a file system to facilitate storage of PIM data items on the device. The PIM application preferably includes the ability to send and receive data items, either by itself, or in conjunction with the voice and data communication modules  524 A,  524 B, via the wireless networks  519 . The PIM data items are preferably seamlessly integrated, synchronized and updated, via the wireless networks  519 , with a corresponding set of data items stored or associated with a host computer system, thereby creating a mirrored system for data items associated with a particular user. 
     The mobile device  100  may also be manually synchronize with a host system by placing the device  100  in an interface cradle, which couples the serial port  530  of the mobile device  100  to the serial port of the host system. The serial port  530  may also be used to enable a user to set preferences through an external device or software application, or to download other application modules  524 N for installation. This wired download path may be used to load an encryption key onto the device, which is a more secure method than exchanging encryption information via the wireless network  519 . Interfaces for other wired download paths may be provided in the mobile device  100 , in addition to or instead of the serial port  530 . For example, a USB port would provide an interface to a similarly equipped personal computer. 
     Additional application modules  524 N may be loaded onto the mobile device  100  through the networks  519 , through an auxiliary I/O subsystem  528 , through the serial port  530 , through the short-range communications subsystem  540 , or through any other suitable subsystem  542 , and installed by a user in the non-volatile memory  524  or RAM  526 . Such flexibility in application installation increases the functionality of the mobile device  100  and may provide enhanced on-device functions, communication-related functions, or both. For example, secure communication applications enable electronic commerce functions and other such financial transactions to be performed using the mobile device  100 . 
     When the mobile device  100  is operating in a data communication mode, a received signal, such as a text message or a web page download, is processed by the transceiver module  70  and provided to the microprocessor  538 , which preferably further processes the received signal for output to the display  522 , or, alternatively, to an auxiliary I/O device  528 . A user of mobile device  100  may also compose data items, such as email messages, using the keyboard  532 , which is preferably a complete alphanumeric keyboard laid out in the QWERTY style, although other styles of complete alphanumeric keyboards such as the known DVORAK style may also be used. User input to the mobile device  100  is further enhanced with a plurality of auxiliary I/O devices  528 , which may include a thumbwheel input device, a touchpad, a variety of switches, a rocker input switch, etc. The composed data items input by the user are then stored in the non-volatile memory  524  or the RAM  526  and/or transmitted over the communication network  519  via the transceiver module  70 . 
     When the mobile device  100  is operating in a voice communication mode, the overall operation of the mobile device is substantially similar to the data mode, except that received signals are preferably output to the speaker  534  and voice signals for transmission are generated by a microphone  536 . Alternative voice or audio I/O subsystems, such as a voice message recording subsystem, may also be implemented on the mobile device  100 . Although voice or audio signal output is preferably accomplished primarily through the speaker  534 , the display  522  may also be used to provide an indication of the identity of a calling party, the duration of a voice call, or other voice call related information. For example, the microprocessor  538 , in conjunction with the voice communication module and the operating system software, may detect the caller identification information of an incoming voice call and display it on the display  522 . 
     A short-range communications subsystem  540  is also included in the mobile device  100 . For example, the subsystem  540  may include an infrared device and associated circuits and components, or a short-range RF communication module such as a Bluetooth™ module or an 802.11 module to provide for communication with similarly-enabled systems and devices. Those skilled in the art will appreciate that “Bluetooth” and “ 802 . 11 ” refer to sets of specifications, available from the Institute of Electrical and Electronics Engineers, relating to wireless personal area networks and wireless local area networks, respectively. 
     This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to make and use the invention. The invention may include other examples that occur to those skilled in the art. 
     For example, although described above primarily in the context of a single-band antenna, an antenna with near-field radiation control structures may also include further antenna elements to provide for operation in more than one frequency band. 
     In alternative embodiments, other antenna designs may be utilized, such as a closed folded dipole structure, for example. Similarly, in an open loop structure, the feeding points  18  and  20  need not necessarily be offset from the gap  16 , and may be positioned to provide space for or so as not to physically interfere with other components of a mobile device in which the second antenna element is implemented. 
     Near-field radiation control structures preferably do not preclude such antenna structures as loading structures and meander structures that are commonly used to control operating characteristics of an antenna. Open folded dipole antennas such as  10  also often include a stability patch on one or both conductor sections, which affects the electromagnetic coupling between the conductor sections.