Patent Publication Number: US-7586448-B2

Title: Multi-frequency antenna

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a multi-frequency antenna, and more particularly, to a multi-frequency antenna for use in a wireless local area network system. 
   2. Description of the Prior Art 
   An antenna is utilized to radiate or receive electromagnetic waves for transmission or reception of radio frequency signals. For an electronic product with communications functions of a wireless local area network (WLAN), such as a notebook, there is commonly a built-in antenna utilized to access the WLAN system. With the advance of the wireless communication technologies, various wireless communications systems may adopt different operating frequencies. For example, the wireless LAN standard IEEE 802.11a developed by the Institute of Electrical and Electronics Engineers (IEEE) adopts a central frequency of about 5 GHz, and the evolution of the standard IEEE 802.11, IEEE 802.11b, adopts a central frequency of about 2.4 GHz. Therefore, for the purpose of convenience for users to access a WLAN, an ideal, single antenna should be able to operate for multi-frequency bands utilized by different WLAN systems. In addition, the size of the antenna should be designed as small size as possible to catch up with the tendency of miniaturization in wireless communications facilities. 
   Please refer to  FIG. 1 , which is a schematic diagram of an inverted-F planar multi-frequency antenna  10  according to the prior art. The planar multi-frequency antenna  10  includes an interconnecting element  12 , a planar radiating element  14  and a planar grounding element  16 . The interconnecting element  12  has a connecting terminal  20  coupled to a feeding wire  18 , for feeding signals into the planar radiating element  14 . The planar radiating element  14  and the planar grounding element  16  generate electromagnetic waves, and thereby a metal bar P 1  of the planar radiating element  14  is utilized to radiate higher frequency electromagnetic waves and a metal bar P 2  thereof radiates lower frequency electromagnetic waves. 
   As known well in the art, a conducting path of an antenna is preferred to be longer than or approximate to ¼ wavelength of the radiating wave. With the ¼ wavelength limitation, the planar radiating element  14  mostly occupies a certain planar space such that the planar multi-frequency antenna  10  cannot be reduced in size effectively, which is inadequate for requirements of miniaturization. 
   SUMMARY OF THE INVENTION 
   It is therefore a primary object of the present invention to provide a multi-frequency antenna. 
   The present invention discloses a multi-frequency antenna. The multi-frequency antenna includes a feeding element, a first U-shaped radiator, a second U-shaped radiator, a grounding element and a coupling element. The first U-shaped radiator is coupled to the feeding element and forms a first gap toward the feeding element. The second U-shaped radiator is coupled to the feeding element and forms a second gap toward the first U-shaped radiator. The grounding element is coupled to a ground end. The coupling element is coupled between the feeding element and the grounding element. 
   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 THE DRAWINGS 
       FIG. 1  is a schematic diagram of an inverted-F planar multi-frequency antenna according to the prior art. 
       FIG. 2  is a schematic diagram of a multi-frequency antenna according to an embodiment of the present invention. 
       FIG. 3  is a schematic diagram of the multi-frequency antenna according to  FIG. 2  from a different view. 
       FIG. 4  is a measured result of a VSWR experiment using the multi-frequency antenna according to  FIG. 2 . 
       FIG. 5  is a measured result of a VSWR experiment using the planar multi-frequency antenna according to  FIG. 1 . 
       FIG. 6  is a radiation pattern of the multi-frequency antenna according to  FIG. 2 . 
       FIG. 7  is a radiation pattern of the planar multi-frequency antenna according to  FIG. 1 . 
       FIG. 8  is a measured result of the multi-frequency antenna according to  FIG. 2  for average gain in a horizontal plane. 
       FIG. 9  is a measured result of the planar multi-frequency antenna according to  FIG. 1  for average gain in a horizontal plane. 
       FIGS. 10-13  are schematic diagrams of different architectures of the first U-shaped radiator of the multi-frequency antenna according to  FIG. 2 . 
       FIG. 14  is a vertical view of the first U-shaped radiator and the second U-shaped radiator in a specific architecture. 
       FIG. 15  is a vertical view of the first U-shaped radiator and the second U-shaped radiator in another architecture. 
       FIG. 16  is a schematic diagram of a multi-frequency antenna according to an embodiment of the present invention. 
   

   DETAILED DESCRIPTION 
   Please refer to  FIG. 2  and  FIG. 3 , which are schematic diagrams of a multi-frequency antenna  20  from different views according to an embodiment of the present invention. The multi-frequency antenna  20  includes a feeding element  22 , a first U-shaped radiator  24 , a second U-shaped radiator  26 , a grounding element  28  and a coupling element  29 . The feeding element  22  can be a bow-tie shape. The first U-shaped radiator  24  is coupled to the feeding element  22  and forms a first gap  242  toward the feeding element  22 . The second U-shaped radiator  26  is coupled to the feeding element  22 , and forms a second gap  262  toward the first gap  242 . The grounding element  28  is coupled to a feeding point  282  of the feeding element  22  by a feeding wire  284  feeding signals into the first U-shaped radiator  24  and the second U-shaped radiator  26 . The multi-frequency antenna  20  can further include a conduction tape  30  fittingly coupled to the bottom of the grounding element  28 . 
   In  FIG. 2 , the first U-shaped radiator  24  is formed by bending a metal bar or by coupling multiple metal bars jointly, seen as a combination of metal bars M 1 , M 2  and M 3 . The metal bar M 1 , M 2  and the metal bar M 2 , M 3  form an angle of 90°, respectively. That is, the metal bar M 2  and the metal bar M 1  are set perpendicularly to each other, and the metal bar M 3  and the metal bar M 1  are parallel. Similarly, the second U-shaped radiator  26  can be considered as a combination of metal bars M 4 , M 5  and M 6 . The metal bar M 4 , M 5  and the metal bar M 5 , M 6  also form a angle of 90°, respectively, indicating that the metal bar M 5  is perpendicular to the metal bar M 4 , and the metal bar M 6  is parallel to the metal bar M 4 . Thus, as can be seen in  FIG. 2 , the first gap  242  and the second gap  262  stretch in parallel and face-to-face directions. The multi-frequency antenna  20  can simultaneously be applied to the wireless LAN standards IEEE 802.11a and IEEE 802.11b. The first U-shaped radiator  24  is utilized to transmit signals conforming to the wireless LAN standard IEEE 802.11b adopting a central frequency of about 2.4 GHz, and the second U-shaped radiator  26  is utilized to transmit signals conforming to the wireless LAN standard IEEE 802.11a adopting a central frequency of about 5 GHz. 
     FIG. 4-13  are measured results of the multi-frequency antenna  20  and the planar multi-frequency antenna  10  for four different experiments. For the multi-frequency antenna  20  in the following experiments, the metal bars M 1 -M 3  of the first U-shaped radiator  24  is implemented as being 16 mm, 2.5 mm and 10 mm long, respectively. In addition, the metal bars M 4 -M 6  of the second U-shaped radiator  24  respectively have lengths of 4 mm, 2.5 mm and 5 mm. All of the metal bars M 1 -M 6  have a width of 2 mm. Please refer to  FIG. 4  and  FIG. 5 , which are charts of voltage standing wave ratio (VSWR) performance according to the multi-frequency antenna  20  and the planar multi-frequency antenna  10 . As can be seen from the frequency band of 2.4 GHz in  FIG. 4  and  FIG. 5 , the multi-frequency antenna  20  has a lower frequency bandwidth of about 380 MHz, and the planar multi-frequency antenna  10  has a lower frequency bandwidth of about 250 MHz in a condition of 2:1 VSWR. As for the frequency band of 5 GHz, the multi-frequency antenna  20  has a higher frequency bandwidth of about 1500 MHz, whereas the planar multi-frequency antenna  10  has a higher frequency bandwidth of about 1160 MHz in a condition of 2.5:1 VSWR. Obviously, regardless of the frequency band of 2.4 GHz or 5 GHz, the multi-frequency antenna  20  has wider bandwidths than the planar multi-frequency antenna  10  does. 
   Please refer to  FIG. 6  and  FIG. 7 , which are measured results of the multi-frequency antenna  20  and the planar multi-frequency antenna  10  for radiation efficiency. As experimented in the lower frequency band between 2.4 GHz and 2.5 GHz, the radiation efficiency of the multi-frequency antenna  20  is measured between 51%-55%, and the radiation efficiency of the planar multi-frequency antenna  10  is measured between 40%-44%. As for the higher frequency band between 4.9 GHz and 5.875 GHz, the radiation efficiency of the multi-frequency antenna  20  is approximately between 44%-50%, while the radiation efficiency of the planar multi-frequency antenna  10  is approximately between 40%-49%. Thus, the multi-frequency antenna  20  has better performance in the radiation efficiency than the planar multi-frequency antenna  10  does. 
   Please continue by referring to  FIG. 8  and  FIG. 9 , which are measured results of the multi-frequency antenna  20  and the planar multi-frequency antenna  10  for average gain in the horizontal plane (as known θ=90°). From the two tables in  FIG. 8 and 9 , at the same frequencies, the average gain of the multi-frequency antenna  20  is larger by about 1-2 dB than that of the planar multi-frequency antenna  10 . 
   Note that the first U-shaped radiator  24  and the second U-shaped radiator  26  in  FIG. 2  are just considered as an embodiment of the present invention. Those skills in the art can do modifications if necessary. Any modifications making the first gap  242  and the second gap  262  face-to-face or parallel in opposite directions fall within the concept of the present invention. For instance, please refer to  FIG. 14-17 , which are schematic diagrams of different architectures of the first U-shaped radiator  24 . In  FIG. 14 , the metal bars M 1  and M 2  form an angle of 180°, and so do the metal bars M 2  and M 3 . As a result, the metal bar M 2  is parallel to the metal bar M 1 , and the metal bar M 3  is also parallel to the metal bar M 1 . In  FIG. 15 , the metal bars M 1  and M 2  form an angle of 90°, and the metal bars M 2  and M 3  form an angle of 180°. That is, the metal bar M 2  is perpendicular to the metal bar M 1 , and the metal bar M 3  is parallel to the metal bar M 1 . In  FIG. 16 , on the contrary, the metal bars M 1  and M 2  form an angle of 180°, and the metal bars M 2  and M 3  form an angle of 90°. In this situation, the metal bar M 2  is parallel to the metal bar M 1 , and the metal bar M 3  is perpendicular to the metal bar M 1 . In  FIG. 17 , the first U-shaped radiator  24  further includes a metal bar M 7  coupled to the metal bar M 3  so that the metal bars M 3  and M 7  form a U-shape. Please note that the modifications above can also be applied to the second U-shaped radiator  26 . 
   Please refer to  FIGS. 18 and 19 , which are vertical views of different architectures of the first U-shaped radiator  24  and the second U-shaped radiator  26 . In  FIG. 18 , a metal bar formed by the metal bars M 1  and M 4  can be considered a boundary. Thus, the metal bars M 2  and M 3  of the first U-shaped radiator  24  form a gap at one side of the boundary, and the metal bars M 5  and M 6  of the second U-shaped radiator  26  form another gap at the same side of the boundary. For the first U-shaped radiator  24 , the metal bars M 2  and M 3  form an angle of 135°, and the metal bars M 2  and M 1  form an angle of 45°, thereby paralleling the metal bars M 3  and M 1 . On the contrary, for the second U-shaped radiator  26 , the metal bars M 5  and M 6  form an angle of 45°, and the metal bars M 5  and M 4  form an angle of 135°, thereby paralleling the metal bars M 6  and M 4 . Unlike  FIG. 18 , in  FIG. 19 , the metal bars M 2 , M 3  and the metal bars M 5 , M 6  form a gap respectively at the opposite sides of the boundary. The first U-shaped radiator  24  shown in  FIG. 19  is the same as that shown in  FIG. 18 , while the second U-shaped radiator  26  shown in  FIG. 19  is constructed with an angle of 135° formed by the metal bars M 5  and M 6  and an angle of 45° formed by the metal bars M 5  and M 4 . Therefore, as can be known from the above, the gaps of the first U-shaped radiator  24  and the second U-shaped radiator  26  may be formed face-to-face in parallel or in two opposite, parallel directions. 
   Please refer to  FIG. 20 , which is a schematic diagram of a multi-frequency antenna  200  according to another embodiment of the present invention. The multi-frequency antenna  200  has similar architecture to the multi-frequency antenna  20  shown in  FIG. 2 , and thereby the same elements are labeled with the same symbols. Different from the multi-frequency antenna  20 , the multi-frequency antenna  200  utilizes the first U-shaped radiator  24  shown in  FIG. 14 . Thus, the first gap  242  lies above the metal bar M 1 , and the second gap  262  lies at a side of the metal bar M 4 . That is, the first gap  242  and the second gap  262  of the multi-frequency antenna  200  are parallel and opposite, but not on the same plane. Therefore, in the present invention, the two gaps of the two U-shaped radiators are not limited to be opposite face-to-face. The two gaps can also be setup opposite in parallel. 
   The multi-frequency antenna of the present invention adopts a architecture in order to reduce sizes of the U-shaped radiators and the grounding element for the requirement of low space occupation. In conclusion, the multi-frequency antenna is simple, light and easily-made and besides applied to various wireless LAN standards, such as IEEE 802.11a and IEEE 802.11b. Therefore, the multi-frequency antenna of the present invention has high commercialization value. 
   Those skilled in the art will readily observe that numerous modifications and alterations of the device and method 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.