Patent Publication Number: US-6992631-B2

Title: Dual-band antenna

Description:
BACKGROUND OF INVENTION 
   1. Field of the Invention 
   The present invention relates to a dual-band antenna, and more particularly, to a dual-band antenna distributed on the printed circuit board. 
   2. Description of the Prior Art 
   As communication technology is increasingly improved, the weight, volume, cost, performance, and complexity of a communication system also become more important, so antennas that transmit and receive signals in a wireless communication system especially “draw designers” attention. In a wireless local area network (WLAN), because the space for setting up an antenna is limited and the antenna should transmit a large amount of data, the antenna should be carefully designed. The ordinary antennas used in a WLAN are flat printed antennas, which have the following characteristics: 1. a small volume, weight, and thickness due to being one single device; 2. low cost and simple to be manufactured by using a printed circuit; 3. easy adjustment of the resonant frequency, pattern, impedance, and polarization of the antenna by changing the structure and size and of the circuit. The flat printed antennas also have the following disadvantages: 1. low radiation efficiency and low gain; 2. narrow bandwidth (the bandwidth is about 5% of the center frequency). Because the signals of WLAN bands, 802.11b(2.4 GHz) and 802.11a(5.2 GHz), are easily influenced by surface features in the area. Since the printed antennas have the above disadvantages, how to improve the gain and bandwidth of the antenna at high frequency (5.2 GH) needs to be overcome by designers. 
   Please refer to the  FIG. 1  and  FIG. 2 . Because WLANs operate in the bands 802.11b and 802.11a for receiving the dual bands by the antenna, a dual-band antenna  2  is disclosed by Taiwan patent 557603, which has a first horizontal wire  21 , a second horizontal wire  22 , and a vertical radiation wire  23  disposed on the top surface  26  of an interface substrate  24 . A ground  28  is disposed on the bottom surface  26  of the interface substrate  24 . The first horizontal wire  21  and the second horizontal wire  22  cooperate with the vertical radiation wire  23  to produce the high operation frequency and low operation frequency of the dual-band monopole antenna  2 . A micro-strip  25  transmits the RF signals generated by the antenna. Therefore, when designers adjust the length or the width of the wire  21  or the wire  22  to change the behavior of one band of the antenna, the behavior of the other band will also be changed, making it difficult to design this kind of antenna. 
   SUMMARY OF INVENTION 
   Therefore, the purpose of the present invention is to provide a dual-band antenna, which has larger gain and bandwidth and is easier to design. 
   The dual-band antenna of the present invention includes a substrate, an emitting unit, a transmission line, and a ground pad. The emitting unit and the ground pad are on the opposite sides of the substrate. The transmission line coupled to the emitting unit is used to transmit the received or emitted RF signals. 
   The substrate has a first edge, and a first surface and a second surface that is on the opposite side of the substrate from the first surface. The emitting unit has a first wire and a second wire and is disposed on the first surface substantially between the first edge and a feeding point. The first wire and the second wire are crossed at the feeding point and the transmission line is coupled to the feeding point transmitting RF signals. The ground pad disposed on the second surface of the substrate includes a base and an extension. The base is extended from the substrate toward feeding point. The extension is adjacent to the emitting unit and extends from the base toward the first edge. The combination of the base and the extension forms an “L” shape. 
   These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
       FIG. 1  illustrates a dual-band antenna of the prior art. 
       FIG. 2  illustrates the dual-band antenna in  FIG. 1  in another view. 
       FIG. 3  illustrates the preferred embodiment of the present invention dual-band antenna. 
       FIG. 4  illustrates the preferred embodiment of the present invention dual-band antenna from another view. 
       FIG. 5  illustrates the measured return loss in the preferred embodiment of the present invention. 
       FIG. 6  illustrates the measured VSWR in the preferred embodiment of the present invention. 
       FIG. 7  illustrates the measured gain in two bands of 2.4 GHz and 5.2 GHz in the preferred embodiment of the present invention. 
       FIG. 8  illustrates the measured radiation pattern in the H-Plane at 2.4 GHz in the preferred embodiment of the present invention. 
       FIG. 9  illustrates the measured radiation pattern in the H-Plane at 2.45 GHz in the preferred embodiment of the present invention. 
       FIG. 10  illustrates the measured radiation pattern in the H-Plane at 2.5 GHz in the preferred embodiment of the present invention. 
       FIG. 11  illustrates the measured radiation pattern in the E-Plane at 2.4 GHz in the preferred embodiment of the present invention. 
       FIG. 12  illustrates the measured radiation pattern in the E-Plane at 2.45 GHz in the preferred embodiment of the present invention. 
       FIG. 13  illustrates the measured radiation pattern in the E-Plane at 2.5 GHz in the preferred embodiment of the present invention. 
       FIG. 14  illustrates the measured radiation pattern in the H-Plane at 5.15 GHz in the preferred embodiment of the present invention. 
       FIG. 15  illustrates the measured radiation pattern in the H-Plane at 5.25 GHz in the preferred embodiment of the present invention. 
       FIG. 16  illustrates the measured radiation pattern in the H-Plane at 5.35 GHz in the preferred embodiment of the present invention. 
       FIG. 17  illustrates the measured radiation pattern in the H-Plane at 5.75 GHz in the preferred embodiment of the present invention. 
       FIG. 18  illustrates the measured radiation pattern in the H-Plane at 5.85 GHz in the preferred embodiment of the present invention. 
       FIG. 19  illustrates the measured radiation pattern in the E-Plane at 5.15 GHz in the preferred embodiment of the present invention. 
       FIG. 20  illustrates the measured radiation pattern in the E-Plane at 5.25 GHz in the preferred embodiment of the present invention. 
       FIG. 21  illustrates the measured radiation pattern in the E-Plane at 5.35 GHz in the preferred embodiment of the present invention. 
       FIG. 22  illustrates the measured radiation pattern in the E-Plane at 5.75 GHz in the preferred embodiment of the present invention. 
       FIG. 23  illustrates the measured radiation pattern in the E-Plane at 5.85 GHz in the preferred embodiment of the present invention. 
   

   DETAILED DESCRIPTION 
   The content, the characteristics, and the advantages of the present invention are clearly described in the following preferred embodiment and the figures. 
   Please refer to  FIG. 3  and  FIG. 4 . The dual-band antenna of the present invention comprises a substrate  11 , an emitting unit  12 , a transmission line  13 , and a ground pad  14 . 
   The emitting unit  12  and the ground pad  14  are on opposite sides of the substrate. The transmission line  13  coupled to the emitting unit is used to transfer the RF signals received or emitted by emitting unit  12 . In the present invention, the transmission line  13  is a microstrip line. In other embodiment, it can be coaxial cable or a coplanar waveguide, and not to be limited by this disclosure. 
   The substrate  11  is a printed circuit board made of fiberglass reinforced epoxy resin and has a first surface  111  and a second surface  112  that is on the opposite side of the printed circuit board from the first surface  111 . The printed circuit board also has a first edge shown at the top of  FIG. 3 . The emitting unit  12  and the transmission line  13  are printed on the first surface  111  of the substrate  11 . The emitting unit  12  has a first wire  121  and a second wire  122 . The first wire  121 , the second wire  122 , and the transmission line  13  are crossed at a feeding point  123  used to emit the RF signals from the transmission line  13  or receive the RF signals from the air. The first wire  121  and the second wire  122  are extended away from the feeding point  123  and bent at some angle, resulting in the emitting unit  12  being substantially between the feeding point  123  and the first edge of the substrate  11 . The end portions of the wire  121  and the wire  122  are substantially parallel and form a mouth  124 . The first wire  121  is longer than the second wire  122  and is used to decide the low operating frequency of the dual-band antenna  1 . The second wire  122  is used to decide the high operating frequency of the dual-band antenna  1 . Because the wire  121  and the wire  122  do not have a common part, designers can adjust two bands of the dual-band antenna  1  respectively without affecting each other. It is help for shortening the lag-time. 
   Transmission line  13  extending from the feeding point  123  to the downside of the substrate  11  is combined with the emitting unit  12  to form a similar “F” shape. 
   The ground pad  14  disposed on the second surface  112  of thee substrate  11  comprises a base  141  and an extension  142 . The base  141  extends toward the feeding point  123  from the first edge of the substrate  11 . The extension is adjacent to the emitting unit and extends from the base  141  toward the first edge of the substrate  11 . The combination of the base and the extension makes an “L” shape, which generates electromagnetic coupling effects with the emitting unit  12  on the first surface  111  so that the first wire  121  and the second wire  122  can shorten the length corresponding to the operation frequency (one fourth wavelength of the electromagnetic signal, λ/4) as well as improve gain and bandwidth. 
   Please refer to  FIGS. 5–23 , which are the measurement results of the dual-band antenna.  FIG. 5  and  FIG. 6  illustrate the reflection coefficient under −10 dB. The low frequency bandwidth in the dual-band antenna  1  is 560 MHz (2410 MHz˜2970 MHz), and the high frequency bandwidth in the dual-band antenna  1  is 730 MHz (5100 MHz˜5845 MHz).  FIGS. 5–23  also disclose the corresponding VSWR(voltage standing wave ratio). From the results, it is found that the operation frequency of the dual-band antenna  1  covers 2.4 GHz (2.4 GHz˜2.484 GHz) and 5.2 GHz (5.15 GHz˜5.35 GHz), which meet the specification of dual-band WLAN.  FIGS. 7–23  illustrate the radiation pattern and gain of the experimental results in the preferred embodiment of the present invention operating at the frequencies of 2.4, 2.45, 2.5 GHz and 5.15, 5.25, 5.35, 5.75, 5.85 GHz. From the preferred embodiment of the present invention, it demonstrates that besides the characteristic of the dual-band operation, it have a characteristic of higher gain when operating at high frequency (5.2 GHz). 
   In summary, the dual-band antenna  1  of the present invention utilizes the ground pad  14  similar to an “L” shape and the electromagnetic coupling effect generated by the emitting unit  12  to effectively reduce the length of the first wire  121  and the second wire  122  corresponding to the operation frequency. Moreover, because of the special shapes of the first wire  121  and the second wire  122  of the emitting unit  12  and no common part between the first wire  121  and the second wire  122 , the first wire  121  and the second wire  122  have a better degree of isolation. It is easier for the designers to adjust each wire independently to change the properties of the antenna, shortening the product lag-time and improving the high frequency gain as well as the bandwidth of the dual-band antenna. 
   Those skilled in the art will readily observe that numerous modifications and alterations of the device may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.