Patent Publication Number: US-2009237311-A1

Title: Single-plate dual-band antenna and wireless network device having the same

Description:
BACKGROUND OF INVENTION 
     1. Field of the Invention 
     The present invention relates to a single-plate dual-band antenna, and more particularly, to an integrally formed, resilient, single-plate dual-band antenna for use with a wireless network device, and a wireless network device having such antenna. 
     2. Description of the Prior Art 
       FIG. 1  is a perspective view of a conventional wireless network device  10  of a wireless network card, for example. The wireless network device  10  usually includes a main body  11 , an internal circuit device  12  located inside the main body  11 , a connector portion  13  located at one end of the main body  11  for connecting an external mainframe (not shown), and an antenna signal receiving/transmitting portion  14  located at another end of the main body  11  opposing the connector portion  13 . Generally, the antenna signal receiving/transmitting portion  14  is provided with a housing that is made of a non-metal material. When the wireless network device  10  is connected to the external mainframe, the antenna signal receiving/transmitting portion  14  must be exposed outside of the external mainframe so as to effectively receive and transmit wireless signals. 
       FIG. 2  is a schematic view of a conventional internal circuit device  20  of wireless network device. The conventional internal circuit device  20  of the wireless network device includes a substrate  21 , a control circuit  22  located on the substrate  21 , a ground portion  23  covering a predetermined area of the substrate  21 , and an antenna unit  24  electrically connected to the control circuit  22 . The conventional antenna unit  24 , as illustrated in  FIG. 2 , includes a first antenna  241  and a second antenna  242  located at two lateral sides of the substrate  21 , respectively. Since the antenna unit of this conventional internal circuit device  20  is designed as printed monopole antenna printed on the substrate  21 . Due to limitation in height difference along a vertical direction, this type of printed antenna can achieve a better radiation pattern and higher gain on an X-Y plane (horizontal plane) only by designing different shapes of the first antenna  241  and the second antenna  242 ; but there is almost no further improvement of antenna gain along the vertical Z direction. However, the design of current wireless network device tends to be a vertical stand type, so as to reduce the space occupied by the wireless network device, as well as to make the appearance of the wireless network device more modern and high-tech. It is obvious that the conventional printed antenna cannot meet the requirement for the vertical stand type wireless network device due to the poor gain along the vertical Z direction. 
       FIG. 3  is a chart showing a radiation pattern measured on an X-Y plane of the first antenna of the conventional printed antenna unit  24  as shown in  FIG. 2 . From the radiation pattern of  FIG. 3 , it can be seen that the peak gain value of the first antenna  241  along the vertical direction is only −15.89 dBi, which is apparently lower than the minimum standard acceptable by consumers (a general requirement is that the gain value should be at least higher than −10 dBi). Thus, there are still rooms for improvement regarding to the design of antenna, which is also critically important for meeting consumer&#39;s need for high performance antenna. 
     SUMMARY OF INVENTION 
     A first objective of the present invention is to provide a single-plate dual-band antenna having a three-dimensional single-plate antenna structure, which can be integrally formed by stamping, so that the antenna can be easily manufactured at a lower cost. 
     A second objective of the present invention is to provide an antenna for a wireless network device, wherein the antenna can be rapidly assembled with the wireless network device by being embedded therein and has an improved antenna radiation pattern for increasing a vertical gain of the antenna, eliminating dead spots and broadening an operating bandwidth of the antenna. 
     In order to achieve the aforementioned objectives, the present invention discloses a single-plate dual-band antenna which comprises a base portion, a ground portion, a radiating portion and a signal portion. The base portion is combined with a wireless network device. The ground portion has an end connected with the base portion and extends upwards from the base portion to a certain height. The signal portion is generally perpendicular to the radiating portion, the ground portion and the base portion, respectively. The signal portion has an upper side and a lower end, wherein the upper side is formed with a connecting edge connected with the radiating portion while the lower end is formed with a feed pin, so that the signal portion generally has a downwardly tapered, inverted triangular structure. The radiating portion further comprises a first radiating section and a second radiating section, wherein the first radiating section extends a first length from an upper end of the ground portion along the connecting edge of the signal portion while the second radiating section extends a second length sinuously from an end of the first radiating section distal from the ground portion. The different extension lengths of the first and second radiating sections provide two frequency bands for wireless communication, such as a band from 4.9 to 5.85 GHz and another band from 2.4 to 2.5 GHz. On the other hand, the inverted triangular structure of the signal portion broadens an operating bandwidth of the antenna. The antenna is a one-piece element integrally formed by stamping a thin, electrically conductive metal plate, which allows easy and rapid manufacture. In addition, the antenna can be conveniently assembled onto a substrate of a wireless network device and serves to increase a gain in a vertical direction as well as a bandwidth of the wireless network device. 
     In a preferred embodiment, the second radiating section stemming from the end of the first radiating section distal from the ground portion extends initially a distance in a same plane as the first radiating section and perpendicular to the connecting edge, and then extends another distance sinuously towards the ground portion in a shape resembling a continuous square wave, in which a total distance extended by the second radiating section is the second length, and the sinuous extension of the second radiating section is spaced from the first radiating section by a predetermined spacing. 
     In a preferred embodiment, the predetermined height is between 7 mm and 10 mm and the first length is between 15 mm and 17 mm while the second length is between 25 mm and 35 mm and the predetermined spacing is between 0.4 mm and 0.7 mm. 
     When the antenna of the present invention is utilized in a wireless network device, the wireless network device generally includes a substrate, a control circuit and at least one feed line. The substrate may be made of a dielectric material and may have at least one aperture defined thereon. The control circuit is formed on the substrate and may provide a wireless network transmitting function. The feed line is coupled to the control circuit. When the antenna assembles onto the wireless network device, a ground pin of a base portion of the antenna is inserted into the aperture, and the base portion is closely contact with a ground zone of the substrate. A feed pin of a signal portion of the antenna is coupled to the feed line. The wireless network device can thus be provided with an improved radiation pattern and a higher gain in the vertical direction as well as a significantly increased the antenna performance. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention as well as a preferred mode of use, further objectives and advantages thereof will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings, wherein: 
         FIG. 1  is a perspective view of a typical wireless network device; 
         FIG. 2  is a schematic view of a conventional internal circuit device of the wireless network device; 
         FIG. 3  is a chart showing a radiation pattern measured on an X-Y plane of the first antenna of the conventional antenna unit as shown in  FIG. 2 ; 
         FIG. 4  is a perspective structural drawing of a single-plate dual-band antenna according to a preferred embodiment of the present invention; 
         FIG. 5A  is a top view of the antenna in  FIG. 4 ; 
         FIG. 5B  is a right view of the antenna in  FIG. 4 ; 
         FIG. 5C  is a front view of the antenna in  FIG. 4 ; 
         FIG. 6  is a schematic structural drawing of a preferred embodiment of a wireless network device having the antenna according to the present invention; 
         FIG. 7A  illustrates a radiation pattern in an X-Y plane at an applicable frequency band of  2 . 45  GHz for a left antenna in  FIG. 6 ; 
         FIG. 7B  illustrates a radiation pattern in the X-Y plane at an applicable frequency band of  4 . 9  GHz for the left antenna in  FIG. 6 ; 
         FIG. 7C  illustrates a radiation pattern in the X-Y plane at an applicable frequency band of  5 . 35  GHz for the left antenna in  FIG. 6 ; 
         FIG. 7D  illustrates a radiation pattern in the X-Y plane at an applicable frequency band of 5.85 GHz for the left antenna in  FIG. 6 ; and 
         FIG. 8  is a plot showing return loss versus frequency for the single-plate dual-band antenna of the present invention shown in  FIG. 6 . 
     
    
    
     DETAILED DESCRIPTION 
     A single-plate dual-band antenna according to the present invention and a wireless network device having the same are based on the principle that a three-dimensional antenna structure integrally formed by stamping allows the antenna to be rapidly assembled onto a substrate of the wireless network device. Therein, a height difference between a radiating portion and a base portion of the single-plate dual-band antenna according to the present invention effectively increases a gain in a vertical direction, while a unique, downwardly tapered structure of a signal portion broadens an operating bandwidth. In addition, the radiating portion comprises a first radiating section and a second radiating section whose lengths are different. These two radiating sections provide two different frequency bands for wireless communication, such as a band from 4.9 to 5.85 GHz and another band from 2.4 to 2.5 GHz. Furthermore, the first and second radiating sections are spaced by a predetermined spacing which can be adjusted to modify an applicable frequency band of the antenna and increase a gain in a horizontal direction. Therefore, not only a greater gain in the vertical direction and a broader operating bandwidth can be obtained, but also the antenna can be manufactured and assembled with some other devices more conveniently and cost-effectively. 
       FIGS. 4 and 5A  to  5 C are a perspective structural drawing and schematic views from three different viewing angles of a single-plate dual-band antenna  5  according to a preferred embodiment of the present invention, respectively. The single-plate dual-band antenna  5  is a three-dimensional resilient single-plate element integrally formed by stamping and bending a thin, electrically conductive metal plate of, for example, copper, iron, aluminum, tin, nickel, silver, chromium, gold or an alloy of the above-mentioned metals. As a result, the antenna has a uniform thickness generally throughout the entire structure except where it is bent. In this embodiment, the antenna  5  is a planar inverted-F antenna (PIFA) comprising a base portion  51 , a ground portion  52 , a radiating portion  53  and a signal portion  54 . 
     The base portion  51  has an upper surface  511  in a generally rectangular shape and a connecting edge  512  adjacent to where the base portion  51  is connected with the ground portion  52 . The base portion  51  further has a connecting pin  513  formed at the connecting edge  512  and a ground pin  514  formed at a side of the base portion  51  distal from the ground portion  52  for electrical connection with an external ground, such as a ground zone  63  on a substrate  61  of a wireless network device  6 , as shown in  FIG. 6 . According to the present invention, the connecting pin  513  can be a downward protrusion from an end of the connecting edge  512  as shown in  FIG. 4 , or a soldering point located near the ground portion  52  (without protruding downwards). Furthermore, the base portion  51  has a cut  515  whose location on the base portion  51  corresponds to a feed pin  542  formed at a lower end of the signal portion  54 , so that the feed pin  542  can extend below the base portion  51  without contacting the base portion  51 . 
     The ground portion  52  has an end connected with the upper surface  511  of the base portion  51  and extends generally vertically upwards from the base portion  51  to a predetermined height H, wherein 7 mm&lt;H&lt;10 mm. The value of the predetermined height H can be controlled and adjusted to increase a gain of the single-plate dual-band antenna  5  according to the present invention in a vertical direction and reduce dead spots. 
     The radiating portion  53  has a lateral end connected with an upper end  521  of the ground portion  52  distal from the base portion  51 . Furthermore, the radiating portion  53  extends a predetermined length generally horizontally from the upper end  521  of the ground portion  52  to form a predetermined shape. As a result, the radiating portion  53  is generally perpendicular to the ground portion  52  and generally parallel to the upper surface  511  of the base portion  51 . Moreover, the radiating portion  53  has a vertically projected area generally encompassed by the upper surface  511  of the base portion  51 . 
     In this embodiment of the present invention, the radiating portion  53  further comprises a first radiating section  531  and a second radiating section  532 . The first radiating section  531  extends a first length L 1  from the upper end  521  of the ground portion  52  along the connecting edge  541  connecting the signal portion  54  and the radiating portion  53  while the second radiating section  532  extends a second length L 2  (not designated in the figures) sinuously from an end of the first radiating section  531  distal from the ground portion  52 . In this embodiment, the second radiating section  532  stemming from the end of the first radiating section  531  distal from the ground portion  52  extends initially a distance in a same plane as the first radiating section  531  and perpendicular to the connecting edge  541  of the signal portion  54 , and then extends another distance sinuously towards the ground portion  52  in a shape resembling a continuous square wave, wherein a total distance extended by the second radiating section  532  is the second length L 2  (not designated in the figures). In addition, the sinuous extension of the second radiating section  532  is spaced from the first radiating section  531  by a predetermined spacing s. In this embodiment, 15 mm&lt;L 1 &lt;17 mm, 25 mm&lt;L 2 &lt;35 mm and 0.4 mm&lt;s&lt;0.7 mm. The first radiating section  531  allows the wireless network device  6  to conduct wireless communication in a first frequency band (such as from 4.9 to 5.85 GHz, and usually a frequency band for wireless communication in conformity with IEEE 802.11a or Ultra-Wideband (UWB) specifications) whereas the second radiating section  532  allows the wireless network device  6  to conduct wireless communication in a second frequency band (such as from 2.4 to 2.5 GHz, and usually a frequency band for wireless communication in conformity with IEEE 802.11b/g specifications). Therefore, the single-plate dual-band antenna  5  according to the present invention is applicable to two different frequency bands, i.e., 2.4˜2.5 GHz and 4.9˜5.85 GHz. Besides, the operating frequency band of the antenna  5  can be adjusted and a gain in the horizontal direction increased by adjusting the spacing s. 
     While the connecting edge  541  formed at an upper side of the signal portion  54  is connected with the first radiating section  531  of the radiating portion  53 , the signal portion  54  itself extends a predetermined height downwards from the radiating portion  53  so that the feed pin  542  formed at the lower end of the signal portion  54  (i.e., an end of the signal portion  54  distal from the radiating portion  53 ) is slightly lower than the base portion  51 . As a result, the signal portion  54  is generally perpendicular to the radiating portion  53 , the ground portion  52  and the base portion  51 , respectively. A width of the connecting edge  541  connecting the signal portion  54  with the radiating portion  53  is greater than a width of the end of the signal portion  54  distal from the radiating portion  53  (i.e., the feed pin  542 ) so that the signal portion  54  generally has an inverted triangular structure. This downwardly tapered structure of the signal portion  54  contributes to increasing an operating bandwidth of the single-plate dual-band antenna  5  according to the present invention. 
       FIG. 6  is a schematic drawing of a preferred embodiment of an internal circuit layout of the wireless network device  6  having the single-plate dual-band antenna according to the present invention. The wireless network device  6  according to the present invention comprises the substrate  61 , a control circuit  62 , a ground zone  63 , at least one feed line  64  and at least one single-plate dual-band antenna  5 ,  5   a  of the present invention. The substrate  61  is made of a dielectric material and has a generally flat and rectangular shape. The substrate  61  is further provided with a plurality of apertures  611 . The ground zone  63  provides electrical connection to a ground (GND) and generally covers an area where the single-plate dual-band antennas  5 ,  5   a  are installed. The control circuit  62  is disposed on the substrate  61  and comprises a circuit layout, a number of integrated circuit elements and a number of electronic elements. The control circuit  62  provides wireless transmission functions in conformity with 802.11a, 802.11b, 802.11g, 802.11n and/or UWB communication protocols. Since the control circuit  62  can be selected from prior art devices and does not constitute a major technical feature of the present invention, a detailed description of its structure is herein omitted. 
     As most components of the antennas  5  and  5   a  in this embodiment are the same as or similar to those of the foregoing embodiment, said same components are designated by same names and reference numerals. The two antennas  5  and  5   a  are mounted on two lateral sides of a front end of the substrate  61  in a mirroring manner. However, it is understood that there can be only one or more than two antennas  5  mounted at predetermined locations on the substrate  61  as needed, and the antenna(s) may be arranged in a predetermined way other than described above. The number and arrangement of the antenna  5  are not major technical features of the present invention and therefore will not be explained further. In addition, the connecting pin  513 , the ground pin  514  and the feed pin  542  are located on the antenna  5  in such a way that each of the pins  513 ,  514  and  542  has a corresponding aperture  611  on the substrate  61 . Therefore, when the pins  513 ,  514  and  542  are connected with the corresponding apertures  611 , respectively, a lower surface of the base portion  51  will be in contact with an upper surface of the substrate  61 . As a result, the feed pin  542  is connected with the feed line  64 , which in turn is connected with the control circuit  62 , to enable signal transmission. 
       FIGS. 7A to 7D  illustrate radiation patterns in an X-Y plane at applicable frequency bands of 2.45, 4.9, 5.35 and 5.85 GHz, respectively, for the left antenna  5  in  FIG. 6 . It is shown in the radiation pattern in  FIG. 7A  that the left antenna  5  according to the present invention has a gain as high as −1.72 dBi in a vertical direction at the applicable frequency band of 2.45 GHz. At the applicable frequency band of 4.9 GHz, the antenna  5  has a gain in the vertical direction as high as 1.85 dBi as shown in the radiation pattern in  FIG. 7B . At the applicable frequency band of 5.35 GHz, as shown in the radiation pattern in  FIG. 7C , the antenna  5  has a vertical gain as high as 3.15 dBi. At the applicable frequency band of 5.85 GHz, the antenna  5  has a vertical gain as high as 3.35 dBi as shown in the radiation pattern in  FIG. 7D . According to  FIGS. 7A to 7D , the single-plate dual-band antenna  5  of the present invention has a vertical gain much higher than that of the conventional antenna in  FIG. 3 , i.e., −15.89 dBi. Furthermore, it can also be seen in  FIGS. 7B to 7D  that the vertical gain of the antenna  5  according to the present invention is presented in the radiation patterns as having a generally circular shape, meaning that radiation is emitted more evenly at different angles and in different directions with no dead spots, so that the quality of communication is improved. 
       FIG. 8  is a plot showing test results of return loss of the antenna according to the present invention as shown in  FIG. 6 . It is shown in  FIG. 8  that the antenna according to the present invention has a return loss generally between −11.48 and −13.03 dBi at a frequency band between 2.4 and 2.5 GHz, and a return loss of −14.37 dBi and −10.96 dBi at 4.9 GHz and 5.85 GHz, respectively. These values of return loss, which are all smaller than −10 dBi, already meet the market&#39;s demands of a high performance antenna design. Compared with conventional techniques, the antenna  5  according to the present invention not only provides a higher quality in wireless communication and better transmission efficiency in the vertical direction, but also offers a much wider operating bandwidth comprising two different frequency bands, i.e., 2.4˜2.5 GHz and 4.9˜5.85 GHz. Moreover, the antenna  5  according to the present invention has a resilient three-dimensional single-plate PIFA structure that can be integrally formed by stamping, which contributes to convenience in manufacture as well as a lower cost. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.