Patent Document

BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to antennas, and more particularly to antennas used with wireless communication devices. 
     2. Description of the Related Art 
     Wireless devices typically include an antenna for transmitting and/or receiving wireless communications signals. Historically, monopole and dipole antennas have been employed in various radiotelephone applications, due to their simplicity, wideband response, broad radiation pattern, and low cost. 
     However, wireless communications devices are undergoing miniaturization and low cost. As a result, there is increasing interest in small antennas that can be utilized as internally-mounted antennas for wireless devices at minimum cost. 
     Conventional inverted-F antennas, by design, is a single port antenna. Most antennas for wireless devices are one-port antennas. When the device is sending or receiving, it uses the same port. With one-port antennas, the antenna connection must be switched between transmit and receive. To achieve high frequency switching a PIN diode switch is often used. A PIN diode switch is very expensive and has failure potential. 
     In addition, wireless devices may also incorporate Bluetooth wireless technology. Bluetooth technology provides a universal radio interface in the 2.45 GHz frequency band that enables portable electronic devices to connect and communicate wirelessly via short-range ad hoc networks. Accordingly, wireless devices incorporating these technologies may require additional antennas tuned for the particular frequencies Bluetooth. 
     SUMMARY OF THE INVENTION 
     A double F antenna is disclosed. In one embodiment, an antenna, comprises a conductive member having a center between a first end and a second end of the member; a first port connected perpendicularly to the conductive member between the center and the first end; a second port connected perpendicularly to the conductive member between the center and the second end; and a ground port connected perpendicularly to the conductive member, wherein the ground port is connected to the center. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A better understanding of the present invention can be obtained from the following detailed description in conjunction with the following drawings, in which: 
     FIG. 1 illustrates an exemplary wireless device (PDA) within which an antenna according to the present invention may be incorporated. 
     FIG. 2 schematically illustrates a double F antenna according to an embodiment of the present invention. 
     FIG. 3 schematically illustrates a top view of a double F antenna according to an embodiment of the present invention. 
     FIG. 4 schematically illustrates a front view of a double F antenna according to an embodiment of the present invention. 
     FIG. 5 schematically illustrates a side view of a double F antenna according to an embodiment of the present invention. 
     FIG. 6 schematically illustrates a front angle view of a double F antenna according to an embodiment of the present invention. 
     FIG. 7 schematically illustrates a back angle view of a double F antenna according to an embodiment of the present invention. 
     FIG. 8 illustrates the frequency response of a double F antenna when receiving communication signals according to an embodiment of the present invention. 
     FIG. 9 illustrates the frequency response of a double F antenna when transmitting communication signals according to an embodiment of the present invention. 
     FIG. 10 is a Smith chart illustrating impedance characteristics of a double F antenna according to an embodiment of the present invention. 
     FIG. 11 illustrates the radiation pattern of a double F antenna according to an embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION 
     In the following description, for the purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent, however, to one skilled in the art that the present invention may be practiced without some of these specific details. In other instances, well-known structures and devices are shown in block diagram form to avoid obscuring the underlying principles of the invention. 
     Referring now to FIG. 1, an exemplary wireless device  100  is illustrated within which a double F antenna according to the present invention may be incorporated. Although FIG. 1 illustrates a Person Digital Assistant (PDA), the present double F antenna, may be used on any wireless or Bluetooth enabled device, such as a computer keyboard, mouse, digital camera or cordless phone. 
     A double F antenna according to one embodiment of the present invention is within device  100 . FIG. 2 schematically illustrates an integrated circuit  200  having double F antenna  299  with supporting circuitry  250  according to one embodiment of the present invention. Antenna  299  has two ports, Transmit Port  204  and Receive Port  203 . Antenna  299  is symmetrical in one embodiment; although non-symmetrical embodiments are also considered to be within the scope of the present invention. In one embodiment, the height (h port    207 ) of ports  203 ,  204  are 5 mm, and the width (w port    206 ) of ports  203 ,  204  are 1.6 mm. Antenna  299  also includes a grounding port and via  202  which connects ground plane  214  to antenna  299 . The width (w via    205 ) of grounding port and via  202  may be 1 millimeter in one embodiment. The length (l ant    209 ) of antenna  299  can be 42 mm. The height (h ant    211 ) can be 1 mm in one embodiment. The length (l 1    208 ) of one end of antenna  299  to ground port and via  202  can be 20.5 mm and the length (l 2    210 ) of one end of antenna  299  to port  203  can be 16.8 mm. 
     In one embodiment, antenna  299  is made from one ounce copper, with conductivity 58,000,000 and permeability 1, although other conductive metals are considered to be within the scope of the present invention. Because antenna  299  is symmetrical either port  203 , or  204  may be configured to transmit or receive via the radiative portion of antenna  299 . Substrate  213  may be FR4 material having relative permittivity of 4.5 and electric loss tangent of 0.03 or other material with similar dielectric properties. In one embodiment, the height of substrate  213  can be 36 mm. A top side ground plane  215  is also included in circuit  200 . 
     FIG. 2 also illustrates supporting circuitry  250  for use with antenna  299 . Circuitry  250  is connected to antenna  299  via ports  203 ,  204 . Matching circuits  264  and  265  match the impedance of antenna  299  with supporting circuitry  250 . Transmit port  204  is connected to transceiver  260  via matching circuit  264 . Receive port  203  is connected to transceiver  260  via matching circuit  265 . 
     Transceiver  260  includes a transmitter  262  for providing signals for broadcast on antenna  299 . A receiver  263  receives signals from antenna  299 , such as signals in the 2.4 GHz frequency range, using Bluetooth technology. Transmit and receive signals may be (de)modulated or mixed at baseband processor  261 . Circuit  200  communicates with the rest of device  100  via interface  251  which may be a universal serial bus (USB), serial port or Joint Test Action Group (JTAG) connector. Interface  251  is connected to transceiver  260 . Although circuitry  250  is shown to be a simplified transceiver scheme, other configurations are also considered to be within the spirit and scope of the present invention. 
     FIG. 3 schematically illustrates a top view  300  of antenna  299  (support circuitry  250  is not shown). FIG. 4 schematically illustrates a front view  400  of antenna  299  (support circuitry  250  is not shown). FIG. 5 schematically illustrates a side view  500  of antenna  299  (support circuitry  250  is not shown). FIG. 6 schematically illustrates a front-angle view  600  of antenna  299  (support circuitry  250  is not shown). Also shown in FIG. 6 are vias  601  for connecting bottom side ground plane  214  with top side ground plane  215 . FIG. 7 schematically illustrates a back-angle view  700  of antenna  299  (support circuitry  250  is not shown). 
     FIG. 8 illustrates a graph  800  displaying the frequency response  801  of antenna  299  when receiving signals. At 2.45 GHz, antenna  299  shows approximately −10.5 dB gain. The shape of graph  800  indicates that energy from other devices broadcasting at frequencies other than 2.45 GHZ will be rejected by antenna  299 . Although, the present example was that of a Bluetooth device operating at 2.45 GHz, antenna  299  can be tuned to provide a similar frequency response as shown in FIG. 8, for other operational frequencies. 
     FIG. 9 illustrates a graph  900  displaying the frequency response  901  of antenna  299  when transmitting signals. A high performance antenna has little reflection of the energy transmitted or received through it, as is evidenced by the shape of graph  800 . In the present example at 2.45 GHZ, the gain of antenna  299  is approximately −15 dBm, which is only approximately 10% loss of power passed through transmit port  204 . Although, the present example was that of a Bluetooth device operating at 2.45 GHz, antenna  299  can be tuned to provide a similar frequency response as shown in FIG. 9, for other operational frequencies. 
     FIG. 10 is a Smith chart  1000  illustrating the impedance characteristics of antenna  299  according to one embodiment of the present invention. According to graph  1001 , a 4.7 pF capacitor may be used to perfectly match the input impedance of antenna  299  to 50 ohms. This capacitor may be placed within matching circuits  264 ,  265 . 
     FIG. 11 illustrates the radiation pattern  1100  of antenna  299 . Thus, in free space, antenna  299  radiation graph  1101  is consistent with a −20 dBm loss of energy, due to imperfect isolation between ports  203  and  204 . The radiation pattern  1100  is at 2.45 GHz although other frequencies are also within the scope of the present design. 
     Throughout the foregoing description, for the purpose of explanation, numerous specific details were set forth in order to provide a thorough understanding of the invention. It will be apparent, however, to one skilled in the art that the invention may be practiced without some of these specific details. For example, while the embodiments described above focused on the Bluetooth protocol, many of the underlying principles of the invention may practiced using various other types of wireless and terrestrial protocols. Accordingly, the scope and spirit of the invention should be judged in terms of the claims which follow.

Technology Category: 5