Patent Publication Number: US-6903693-B1

Title: Bifurcated inverted F antenna

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates generally to radio communication systems. More specifically, a system and method for small built-in antennas that can be incorporated into short range communication devices such as cordless headsets are disclosed. 
   2. Description of Related Art 
   It is often desirable to provide wireless communication rather than wired communication using cables between related pairs of devices separated by a short distance. Devices that communicate using cables often require the devices to be located in close proximity to each other as dictated in part by the length of the cables. In contrast, wireless communication decreases the amount of cabling between devices and thus increases the ease of use and convenience for the user, is more aesthetic, and may provide added safety. With wireless communication, the distance between the related devices is generally only limited by the limits of the wireless signal transmission and receive systems. Examples of related pairs of devices include a cordless headset on the one hand and a telephone, computer, television, VCR, DVD player, video game player, stereo receiver, CD player, and MP3 player on the other hand. Other examples of related pairs of devices include a computer and its various external devices such as a monitor, printer, keyboard, mouse, telephone and speakers, for example. 
   A cordless headset requires an internal antenna to permit a radio in the headset to communicate with a radio in a corresponding base unit. In general, it is desirable to minimize the size of the headset so as to provide a headset that is as discrete as practicable. The volume within the headset is governed by industrial design and may place restrictions on both the size of the antenna and the size of the ground plane. However, the dimensions of the antenna residing within the headset are dictated by the wavelengths of the signals that the antenna is to receive and transmit as well as the form of the antenna. Thus, the antenna and the headset are designed with mutual considerations in order to accommodate the antenna within the headset. 
   Many types of antenna technologies may be chosen for the internal antenna of the headset. The selection depends upon the size and shape of the headset volume into which the antenna must fit and the system electrical and performance requirements of the antenna. An Inverted F Antenna (IFA) is often utilized for headsets operating in the 1900 MHz radio frequency band. However, the need for the IFA to occupy the centerline of the headset undesirably restricts placement of various switches and/or buttons of the headset. In addition, the IFA has a relatively high profile, e.g., approximately 5 mm. Thus, the dimensions and the positioning of the IFA within the headset negatively impacts the industrial design of the headset by increasing the height of and restricting the placement of switches and buttons on the headset. 
   To overcome the increased height and the restricted placement of switches and buttons, some headsets utilize a quarter-wave dipole antenna, e.g., a 1.6″ single wire housed within a boom of the headset. However, the quarter-wave dipole antenna increases the assembly cost and introduces interference to wires of the microphone housed within the boom due to the proximity of the microphone wires to the antenna, resulting in performance degradation. 
   Thus, what is needed is an antenna for use in a communication headset that meets required RF performance without or with minimized performance degradation resulting from interference with the microphone wires. The antenna is preferably low profile and configured to allow better placement of controls switches and/or buttons of the headset. Ideally, the antenna is also cost-effective to manufacture and to assemble. 
   SUMMARY OF THE INVENTION 
   A system and method for small built-in antennas that can be incorporated into short range communication devices such as cordless headsets are disclosed. It should be appreciated that the present invention can be implemented in numerous ways, including as a process, an apparatus, a system, a device, a method, or a computer readable medium such as a computer readable storage medium or a computer network wherein program instructions are sent over optical or electronic communication lines. Several inventive embodiments of the present invention are described below. 
   The antenna is a built-in bifurcated inverted F antenna. The antenna generally includes two signal radiating and receiving arms of substantially equal electrical length extending generally parallel to each other along a longitudinal length of the antenna, the arms defining an opening therebetween extending along the longitudinal length of the antenna, a signal component in communication with the two arms for transmitting and receiving signals between the two arms and a signal contact of the wireless communication device, and a grounding component in contact with a grounding plane for grounding the antenna. The antenna may include an extension sloped relative to the grounding plane and extending between the grounding component and the arms to minimize the profile of the antenna. The antenna may be supported by the signal and the grounding components such that the two arms are suspended in free space. The antenna is tuned for a 1900 MHz or scaled and tuned for a 2400 MHz frequency band, for example. 
   The communication device may further include a signal converter such as a printed circuit board onto which the antenna is secured. The printed circuit board includes the signal contact and the grounding plane and converts signals received and/or signals to be output by the antenna. 
   The wireless device may also include a user interface disposed within the opening between the antenna arms. For example, the user interface may be a control such as a switch in communication with the printed circuit board extending through the opening such that the switch is symmetrically arranged relative to the two arms, approximately on a center line extending the longitudinal length of the device. 
   According to another preferred embodiment, a wireless communication headset generally comprises a bifurcated antenna for receiving signals, a speaker for outputting information received by the antenna, and a signal converter for converting signals received by the antenna for output by the speaker. The antenna has two signal receiving arms extending generally parallel to each other and defining an open space therebetween extending along a longitudinal length of the antenna The wireless communication headset may also include a microphone for receiving signals converted by the signal converter for output by the antenna. 
   These and other features and advantages of the present invention will be presented in more detail in the following detailed description and the accompanying figures which illustrate by way of example the principles of the invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be readily understood by the following detailed description in conjunction with the accompanying drawings, wherein like reference numerals designate like structural elements, and in which: 
       FIG. 1  is a perspective view illustrating an exemplary embodiment of a bifurcated inverted F antenna; 
       FIG. 2  is a perspective view of the exemplary embodiment bifurcated inverted F antenna of  FIG. 1  secured to and in communication with a printed circuit board of a cordless headset device; and 
       FIG. 3  is a partial broken away perspective view of a top portion of a chassis for an exemplary cordless headset in which the bifurcated inverted F antenna and the printed circuit board may be employed. 
   

   DESCRIPTION OF SPECIFIC EMBODIMENTS 
   A system and method for small built-in antennas that can be incorporated into short range communication devices such as cordless headsets are disclosed. The following description is presented to enable any person skilled in the art to make and use the invention. Descriptions of specific embodiments and applications are provided only as examples and various modifications will be readily apparent to those skilled in the art. The general principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the invention. Thus, the present invention is to be accorded the widest scope encompassing numerous alternatives, modifications and equivalents consistent with the principles and features disclosed herein. For purpose of clarity, details relating to technical material that is known in the technical fields related to the invention have not been described in detail so as not to unnecessarily obscure the present invention. 
     FIG. 1  is a perspective view illustrating an exemplary embodiment of a bifurcated inverted F antenna  10  and  FIG. 2  is a perspective view of the bifurcated inverted F antenna  10  secured to and in communication with a printed circuit board (PCB)  50  of, for example, a cordless or wireless communication headset device. As shown, the bifurcated inverted F antenna  10  is divided along its length to form two arms  12 . The arms  12  act as radiating and receiving elements for the antenna  10  and are of substantially equal electrical length. In other words, the antenna  10  is used in the cordless headset as both a radiator and a receiver of signals within a specified frequency range or band. Although the arms  12  are shown to be approximately identical in physical dimensions, as is preferred, it is noted that the arms  12  may be of different physical dimensions but tuned to be of substantially equal electrical length such that the antenna  10  is configured to be a single frequency band antenna. 
   The bifurcated inverted F antenna  10  also includes a signal feed component  14  disposed between the bifurcated arms  12 . The signal feed component  14  transmits and/or receives signals between the antenna  10  and a signal contact on the PCB  50 . The bifurcated inverted F antenna  10  further includes a sloped extension  16  extending between the signal transmit/receive component  14  and a solder pad  18  serving as a feed point to ground. The feed to ground solder pad  18  grounds the bifurcated inverted F antenna  10  while the signal transmit/receive component  14  enables signal transmission and/or facilitates electrical contact between the bifurcated inverted F antenna  10  and the PCB  50 . 
   The sloped extension  16  is sloped relative to the bifurcated arms  12 , e.g., at approximately 17°. The sloped extension  16  extends between the PCB  50  via the solder pad  18  at one end and the bifurcated arms  12  and the signal component  14  at the other end. As is well known with inverted F antennas, the antenna  10  contacts the PCB  50  only at the solder pad  18  and the signal component  14  while elevating the bifurcated arms  12  relative to the PCB  50 . Thus, being sloped, the extension  16  allows the antenna  10  to require less volume within the headset. 
   The signal transmission component  14  is in contact with the PCB  50  to enable signal transmission therebetween and to support the bifurcated arms  12  in free space in an elevated position relative to the PCB  50 . The signal transmission component  14  generally extends perpendicularly between the bifurcated arms  12  and the PCB  50 . 
   Preferably, the signal transmit/receive component  14  and/or the solder pad  18  include one or more tabs that extend into corresponding openings provided in the PCB  50  in order to facilitate accurate placement, alignment, and securing of the bifurcated inverted F antenna  10  onto the PCB  50  during assembly of the headset device. As one example, the solder pad  18  may be divided to form two tabs  18   a ,  18   b  that extend into corresponding openings  54   a ,  54   b  provided in the PCB  50 . In addition, the signal transmit/receive component  14  may also be divided into two tabs  14   a ,  14   b  where tab  14   a  extends into a corresponding opening  52  provided in the PCB  50 . Typically, solder is applied to tab  18   c  of the solder pad  18  as well as to tab  14   b  of the signal component  14  in order to secure the bifurcated inverted F antenna  10  to the PCB  50 . Typically tab  14 a of the signal component  14  and tabs  18   a ,  18   b  of the solder pad  18  are not soldered to the PCB  50 . 
   As is evident, tabs  18   a ,  18   b  are appropriately bent relative to the sloped extension  16  in order for the tabs  18   a ,  18   b  to extend into the corresponding openings  54   a ,  54   b  in the PCB  50 . The solder pad  18  also provides a tab  18   c  that is preferably slightly bent relative to the sloped extension  16  to provide better contact between the solder pad  18  and the PCB  50  as the slope of the sloped extension  16  would otherwise minimize the contact between tab  18   c  and the PCB  50 . In addition, tab  14   b  of the signal component  14  is bent relative to the remainder of the component  14  such that tab  14   b  generally rests on and is soldered to the PCB  50 . 
   As shown in  FIG. 2 , the bifurcated arms  12  are elevated relative to the PCB  50  and thus suspended in free space above the PCB  50 . In addition, the bifurcation of the arms  12  allows an open space  20  to be defined between the arms  12  generally centered and along a center line extending along the length of the antenna  10 . Thus, the bifurcated arms  12  and the open space  20  are symmetrically arranged relative to the longitudinal center line of the antenna  10 . The arms  12  are preferably arranged such that there is sufficient field separation therebetween in the space  20  such that a user interface may be located within the space  20 . For example, the center line space  20  allows control switches, buttons, and/or LEDs of the cordless headset device to be disposed on the PCB  50 , for example, along the longitudinal center line along the length of the cordless headset device. An example of a control switch or button is an on/off switch  60  although other controls such as for volume, treble boost, bass boost, etc. may be provided. Such central and symmetrical placement of the control switches and/or buttons allows the cordless headset device to be symmetrically arranged such that a user may easily and intuitively use the cordless headset device and controls provided thereon on either the left or the right ear. It is noted that the PCB  50  may also provide such controls along the longitudinal center line of the device but away from the open space  20  defined by the arms  12  of the antenna  10 , such as an LED  62 , and/or in other areas of the PCB  50 . The LED  62  may light to indicate an on status and is off to indicate an off status for the cordless headset. 
   The bifurcated inverted F antenna  10  is scalable to be used in any suitable frequency band. As is known in the art, a smaller antenna corresponds to a higher frequency band and vice versa. The bifurcated inverted F antenna  10  is particularly suitable for use as an 1900 MHz antenna in a cordless DECT (Digitally Enhanced Cordless Telephony) headset or a 2400 MHz antenna in a cordless telephone headset using preferably Bluetooth™ standard or optionally the IEEE 802.11 standard. 
   The bifurcated inverted F antenna  10  may be made of any suitable material. In one preferred embodiment, the antenna  10  is made of phosphorus bronze. Preferably, the phosphorus bronze is approximately 0.25 mm in thickness with a nickel undercoating and a tin finish. A preplated material may be used from which the bifurcated inverted F antenna  10  is cut and bent. It is noted that by cutting from a preplated material, the cut edges of the antenna  10  would not have the nickel undercoating. 
   In the preferred embodiment for a 1900 MHz antenna as shown in  FIGS. 1 and 2 , each arm  12  is 34.5 mm in length  30  and 2.5 mm in width  22 . The arms are separated by 7 mm in width  32 . The remainder of the antenna  10  is 11.4 mm in length  24 . The sloped extension  16  and solder pad  18  are 6.5 mm in width  26  and the tab  18   c  is 3.5 mm in width  28 . The signal feed component  14  is also 2.5 mm in width  34 . The sloped extension  16  is sloped  170  relative to the arms  12  such that the arms  12  are elevated or suspended above the PCB  50  by approximately 3 mm and are at a slight angle of 4° relative to the PCB  50 . As noted above, the sloped extension  16  maximizes the separation between the PCB  50  and the free end of the antenna  10 , i.e., the free end of the arms  12 , and minimizes the height at the fixed end of the antenna, i.e., the solder pad  18 . Thus, the profile of the antenna  10  is minimized making for a smaller, sleeker, and less conspicuous cordless headset. 
   As is evident, the configuration of the bifurcated inverted F antenna  10  allows controls to be placed along the longitudinal center line of the antenna  10  and the headset while maintaining a low profile and meeting RF requirements. Such central placement of the controls allows the cordless headset device to be symmetrically arranged such that a user may easily and intuitively use the cordless headset on either ear. The bifurcated inverted F antenna  10  also maintains the balance from an RF point of view as the antenna  10  works with the PCB  50 . Such balance enables better tuning and thus greater range for the antenna  10 . 
     FIG. 3  is a partial broken away perspective view of a top portion  70  of a chassis of an exemplary cordless headset in which the bifurcated inverted F antenna and the printed circuit board (not shown) may be employed. The top chassis  70  includes heat stake posts  72  which support a lever  74 . The lever  74  acts as a spring for the switch  60  that the user depresses to turn on/off the headset. In addition, the top chassis  70  provides a window  78  for allowing light from the LED to be visible to the user. The top chassis  70  also includes a microphone opening  80  for a microphone/transmitter. Although not shown, the headset typically also includes a speaker/receiver. Both the microphone/transmitter and the speaker/receiver are preferably in communication with the antenna via the PCB for transmitting and receiving signals to and from a base unit corresponding to the cordless headset. 
   While the preferred embodiments of the present invention are described and illustrated herein, it will be appreciated that they are merely illustrative and that modifications can be made to these embodiments without departing from the spirit and scope of the invention. Thus, the invention is intended to be defined only in terms of the following claims.