Abstract:
A planar inverted-F antenna comprises an antenna coupled to an antenna ground plane having a ground plane extension that is at least partially perpendicular to the plane of the antenna. The antenna structure comprises a modular unit that may be installed in a plurality of disparate devices without unduly changing the performance profile of the antenna at the desired operating frequencies.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to a modular inverted-F antenna well suited for deployment in Bluetooth modules.  
           [0002]    Wireless communication devices have proliferated throughout modern society. Pagers and cell phones are now ubiquitous. Wireless enabled personal digital assistants are also becoming common. A new standard, known as the Bluetooth standard, has been propounded and would allow many disparate devices to communicate with one another. For example, the Bluetooth standard would allow mobile terminals to communicate wirelessly with printers, scanners, computers, and household appliances.  
           [0003]    Wireless communication devices require antennas that radiate and receive electromagnetic signals. By their very nature, antennas are susceptible to many factors that affect the performance of the antenna. Exemplary factors include electromagnetic interference (EMI or crosstalk), impedance matching concerns, and the like. Additionally, the antenna is often placed into close proximity with a circuit board on which other electronic components and a ground plane are located. The electronic circuits and ground plane of the host device interact with the antenna structure and may degrade performance of the antenna. Typically, antenna designs for electronic devices are application specific and Bluetooth devices, in particular, may require significant development time to design a suitable antenna for each application to accommodate printed circuit board layout, component positioning, and other factors. This design and redesign process is inefficient and wasteful.  
         BRIEF SUMMARY OF THE INVENTION  
         [0004]    The present invention relates to antennas and more particular to planar inverted-F antennas for use in wireless communication devices. A planar inverted-F antenna is coupled to an antenna ground plane that is at least partially perpendicular to the plane in which the antenna lies. Another portion of the antenna ground plane is generally coplanar with the plane in which the antenna lies. Together the antenna and the antenna ground plane, with perpendicular extension, form a modular unit. This modular unit may be installed in a plurality of devices without unduly changing the performance profile of the antenna at the desired operating frequencies. In effect, the perpendicular portion of the antenna ground plane helps reduce interference that may be caused by components on the primary printed circuit board of the host device into which the antenna is placed. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0005]    [0005]FIG. 1 illustrates a schematic diagram of a Bluetooth enabled mobile terminal;  
         [0006]    [0006]FIG. 2 illustrates a mobile terminal with an exemplary embodiment of an antenna according to the present invention installed therein;  
         [0007]    [0007]FIG. 3 illustrates a top plan view of one embodiment of the planar inverted-F antenna of the present invention removed from a Bluetooth enabled device; and  
         [0008]    [0008]FIG. 4 illustrates a partial side elevational view of the antenna of FIG. 3.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0009]    The present invention is directed to a modular antenna structure that can be placed in any of a plurality of host devices without the need to redesign the antenna structure to compensate for interference caused by electronic components within the host device. In particular, the present invention is well suited for use in Bluetooth devices.  
         [0010]    The Bluetooth standard enables seamless communication of data and voice over short-range wireless links between both mobile devices and fixed devices. The Bluetooth standard permits ad hoc networking of devices equipped with a Bluetooth interface. Bluetooth devices operate in the Industrial-Scientific-Medical (ISM) frequency band at approximately 2.45 GHz. Different Bluetooth devices can automatically connect and link up with one another when they come into range to form an ad hoc network, generally referred to as a piconet. The Bluetooth standard specifies how mobile devices, such as phones, personal digital assistants (PDAs), and wireless information devices (WIDS), can interconnect with one another and with stationary devices, such as desktop computers, printers, scanners, and stationary phones.  
         [0011]    As used herein, the term “Bluetooth device” means a device capable of communicating with other devices via short-range wireless link. Bluetooth devices may comprise many disparate types of devices, such as desktop or laptop computers, printers, scanners, computer input devices, other computer peripheral devices, mobile radiotelephones, other mobile terminals, or household appliances. Bluetooth devices may be fixed devices or mobile devices.  
         [0012]    [0012]FIG. 1 is a block diagram of a mobile terminal  10  with a Bluetooth interface, which is one example of a Bluetooth device. It should be noted that the term “mobile terminal”  10  as used herein may include a cellular radiotelephone with or without a multi-line display; a Personal Communications System (PCS) terminal that may combine a cellular radiotelephone with data processing, facsimile and data communications capabilities; a Personal Digital Assistant (PDA) may include a radiotelephone, pager, Internet/intranet access, Web browser, organizer, calendar and/or a global positioning system (GPS) receiver; and a conventional laptop and/or palmtop receiver or other appliance that includes a radiotelephone transceiver. Mobile terminals  10  may also be referred to as “pervasive computing” devices.  
         [0013]    Mobile terminal  10  comprises a main control unit  12  for controlling the operation of the mobile terminal  10  and memory  14  for storing control programs and data used by the mobile terminal  10  during operation. Memory  14  may be contained in a removable smart card if desired. Input/output circuits  16  interface the control unit  12  with a keypad  18 , display  20 , audio processing circuits  22 , receiver  28 , and transmitter  30 . The keypad  18  allows the operator to dial numbers, enter commands, and select options. The display  20  allows the operator to see dialed digits, stored information, and call status information. The audio processing circuits  22  provide basic analog audio outputs to a speaker  24  and accept analog audio inputs from a microphone  26 . The receiver  28  and transmitter  30  receive and transmit signals using shared antenna  32 . The mobile terminal  10  further includes a Bluetooth module  34  operating as previously described and having an antenna structure  50  operating in the ISM band according to the present invention.  
         [0014]    [0014]FIG. 2 illustrates an antenna structure  50  according to an exemplary embodiment of the present invention in a mobile terminal  10  (i.e., host device). The exact positioning of the antenna structure  50  will depend on the physical geometry of the circuit board layout and other factors and other positions internal to the mobile terminal  10  (or other host device) are contemplated. Note that this does not require the antenna structure  50  to be redesigned, but the actual positioning within the host device will of course, to some extent, be contingent upon the space available within the host device. As illustrated, mobile terminal  10  includes a printed circuit board  40  with ground plane  42  and various electronic components  44  disposed thereon. Electronic components  44  may comprise the Bluetooth module  34 , control unit  12 , memory  14 , or other RF circuitry.  
         [0015]    Antenna structure  50  is illustrated in more detail in FIGS. 3 and 4. In particular, antenna structure  50  is constructed as a unitary module that can be inserted into a host device, such as mobile terminal  10 . Antenna structure  50  comprises a printed circuit board  51  with an antenna ground plane  52  disposed on a top surface and a bottom surface thereof. Antenna  54  is disposed on the top surface of printed circuit board  51  . Antenna  54  forms a planar inverted-F antenna, wherein the distance of L+H (FIG. 3) approximates a quarter wavelength of the operative frequency of the antenna structure  50 . Antenna  54  may be terminated by launch  58  that acts as an electrical lead for the antenna  54 . Planar inverted-F antenna  54  may be formed from conventional microstrip materials as is well understood.  
         [0016]    Appropriate electrical connections may extend between electronic components  44  or circuit board  40  and antenna structure  50  as is well understood. For example, a coaxial cable (not illustrated) may be soldered with one lead to launch  58 , and a second lead to ground plane  52 . Alternatively, a surface mount device (SMA) may be soldered to the launch  58  and the coaxial cable connected thereto. Other devices, such as a snap may also be used. To the extent that launch  58  is a lead for the antenna  54 , there is an open circuit between launch  58  and the ground plane  52 .  
         [0017]    As illustrated in FIG. 4, antenna ground plane  52  covers a substantial portion of the top and bottom surfaces of the printed circuit board  51 . Antenna ground plane  52  includes an extension portion  56  that is perpendicular to planar inverted-F antenna  54  while other portions of antenna ground plane  52  are generally coplanar or parallel to the plane of the planar inverted-F antenna  54 . In the disclosed embodiment, extension portion  56  extends the entire length of the antenna ground plane  52 . Extension portion  56  may be realized in various manners, such as a metal component that is soldered to the printed circuit board  51 , a small ground plane printed circuit board structure that is inserted into slots on the printed circuit board  51 , or the like. In one embodiment, the extension portion  56  begins at the  50  ohm launch  58  to the planar inverted-F antenna  54 .  
         [0018]    The addition of extension portion  56  helps reduce interference that may be caused by other components within the host device. In use, the antenna structure  50  is positioned proximate the main printed circuit board  40  and ground plane  42  of the host device. Appropriate connections to electronic components  44 , printed circuit board  40 , and/or the host device ground plane  42  are made. The distance of antenna structure  50  from the host device ground plane  42  will vary depending upon the operating frequency and circuit board layout. This distance may, for example, be a quarter wavelength at the desired operating frequency. Because of its modular design, the antenna structure  50  need not be redesigned for each application. That is, the same modular antenna structure  50  may be effective in a broad range of applications.  
         [0019]    The present invention may, of course, be carried out in other specific ways than those herein set forth without departing from the scope and the essential characteristics of the invention. The present embodiments are therefore to be construed in all aspects as illustrative and not restrictive and all changes coming within the meaning and equivalency range of the appended claims are intended to be embraced therein.