Abstract:
A planner inverted-F antenna (PIFA) includes a ground plane, a rib-shaped radiation plate installed approximately in parallel with the ground plane, a feeding line installed on the rib-shaped radiation plate, a feeding contact installed on an end of the feeding line, and a ground contact electrically connected to the ground plane.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a planner inverted-F antenna (PIFA), and more particularly, to a PIFA having a rib-shaped radiation plate.  
         [0003]     2. Description of the Prior Art  
         [0004]     The quality of an antenna is very important for a wireless communication system. A desirable installation of a proper and well-designed antenna on the wireless communication device can raise the value of the signal-to-noise ratio (SNR) of wireless signals, and can improve the bit error rate (BER) of the wireless signals.  
         [0005]     Along with the development of wireless communication technologies, the integration of its device can be more and more compact. Accordingly, an embedded micro antenna has to be made as compact as possible so that can be successfully embedded into the wireless communication device. For example, a chip antenna and a planner antenna are two of the most popular micro antennas in the market. Both of the micro antennas have the characteristics of low profile and compact size. The planner antenna can be designed to have a variety of design patterns, such as a microstrip antenna, a printed antenna, and a planner inverted-F antenna (PIFA). Since the planner antenna has a strong sense of direction and a compact size and can be installed on a printed circuit board of the wireless communications device, the wireless communications device, with the planner antenna installed, is cheap.  
         [0006]     Please refer to  FIG. 1 , which is a schematic diagram of a PIFA  10  according to the prior art. The PIFA  10  comprises a ground plane  12 , a planner radiation plate  14  installed approximately in parallel with the ground plane  12 , a feeding line  16  installed on the radiation plate  14 , a feeding contact  18  located on an end of the feeding line  16 , and a ground contact  20  electrically connected to the ground plane  12 .  
         [0007]     The PIFA  10  has a voltage standing wave ratio and a return loss changing in close relation with a position (f x ,f y ) at which the feeding contact  18  feeds the ground plane  12 , a width w of the radiation plate  14 , and a distance h between the radiation plate  14  and the ground plane  12 . Thus, most of the researches of the PIFA  10  focus on the adjustment of the position (f x ,f y ), the width w, the distance h, or the shape of the radiation plate  14  so as to obtain an optimized receiving quality of the wireless signals.  
         [0008]     Since the ground plane  12  and the radiation plate  14  are both thin metal plates of 0.3 mm only, an insulating material such as a sponge is inserted between the ground plane  12  and the radiation plate  14  to prevent the deformation of the radiation plate  14  by gravity or external force such that the distance h and the gain of the PIFA  10  can be constant.  
         [0009]     However, the sponge will melt in the environment of high temperature due to the operation of the wireless communications device. In statistics, the sponge can survive one and a half years only. Moreover, since the sponge cannot survive in the high temperature environment, the high temperature reflow processes of a surface mount technology (SMT) or a wave soldering process cannot be utilized to install the PIFA  10  onto a printed circuit board but a soldering process by solder iron after the high temperature reflow process. Therefore, the manufacturing time and the cost are increased.  
       SUMMARY OF INVENTION  
       [0010]     It is therefore a primary objective of the claimed invention to provide a PIFA with a rib-shaped radiation plate, which has a rigidity stronger than that of a planner radiation plate, and is not deformed even after a long time of use.  
         [0011]     Another objective of the claimed invention is to provide a PIFA with a rib-shaped radiation plate. A high temperature reflow processes of a surface mount technology (SMT) or a wave soldering process can therefore be utilized to install the PIFA onto a printed circuit board instead of a soldering process by solder iron after the high temperature reflow process. Therefore, the manufacturing time and the cost are decreased.  
         [0012]     According to the claimed invention, the PIFA includes a ground plane, a rib-shaped radiation plate installed approximately in parallel with the ground plane, the rib-shaped radiation plate comprising a rib, a feeding line installed on the rib-shaped radiation plate, a feeding contact located on an end of the feeding line, and a ground contact electrically connected to the ground plane.  
         [0013]     According to the preferred embodiment, the ground plane is electrically connected to a ground area in a printed circuit board, the rib-shaped radiation plate has a line-shaped rib, the line-shaped rib extends from one edge to the other of the rib-shaped radiation plate, and the rib-shaped radiation plate has a cross section having the shape of an open rectangle, a “V” character, or a semicircle.  
         [0014]     It is an advantage of the claimed invention that a PIFA with the rib-shaped radiation plate is not easy to be deformed by gravity or external force. Moreover, the installation of the rib does not degrade but improve the average gains of the PIFA. Further, the PIFA according to the present invention can be installed onto a printed circuit board through an SMT or a wave soldering processes, and the time and the cost of manufacturing a PIFA is therefore reduced.  
         [0015]     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  
       [0016]      FIG. 1  is a schematic diagram of a PIFA according to the prior art;  
         [0017]      FIG. 2  is a schematic diagram of a PIFA of the preferred embodiment according to the present invention;  
         [0018]      FIG. 3  is a side view of the PIFA shown in  FIG. 1  when a 100 gw external force is applied on an end of the PIFA;  
         [0019]      FIG. 4  is a side view of the PIFA shown in  FIG. 2  when the 100 gw external force is applied on an end of the PIFA;  
         [0020]      FIG. 5  is a characteristic curve for S 11  values corresponding to the operating frequencies of the PIFA shown in  FIG. 2 ;  
         [0021]      FIG. 6  to  FIG. 8  are three cross sectional diagrams of a rib-shaped radiation plate of the PIFA shown in  FIG. 2 ;  
         [0022]      FIG. 9  is a comparison diagram of horizontal average gains of the PIFAs shown in  FIG. 1  and  FIG. 2  toward an X-Z, a Y-Z, and an X-Y direction respectively when operating in 2440 MHz; and  
         [0023]      FIG. 10  is a comparison diagram of vertical average gains of the PIFAs shown in  FIG. 1  and  FIG. 2  toward an X-Z, a Y-Z, and an X-Y direction respectively when operating in 2440 MHz. 
     
    
     DETAILED DESCRIPTION  
       [0024]     Please refer to  FIG. 2 , which is a schematic diagram of a PIFA  50  of the preferred embodiment according to the present invention. In addition to the ground plane  12 , the feeding line  16 , the feeding contact  18 , and the ground contact  20 , the PIFA  50  further comprises a rib-shaped radiation plate  54 . In contrast with the planner radiation plate  14  described in the prior art, the rib-shaped radiation plate  54  has a non-planner structure. In detail, the rib-shaped radiation plate  54  comprises a rib  52 . Through the molding of the rib  52  on the radiation plate, a better rigidity of the shaped radiation plate is performed.  
         [0025]     Please refer to  FIG. 1  and  FIG. 2 . The distance h between the planner radiation plate  14  and the ground plane  12 , and the distance h between the rib-shaped radiation plate  54  and the ground plane  12  are both equal to 6 mm. After an 100 gw external force is applied on an end indicated by arrow E 1  of the planner radiation plate  14 , as shown  FIG. 3 , the end of the planner radiation plate  14  is fallen by 5 mm and the distance h is reduced to 1 mm. Similarly, as shown in  FIG. 4 , after the 100 gw external force is applied on an end indicated by arrow E 2  of the rib-shaped radiation plate  54 , the end of the rib-shaped radiation plate  54  is fallen by 2.5 mm and the distance h is reduced to 3.5 mm. It is apparent that the rib-shaped radiation plate  54  of the PIFA  50  has a better rigidity than that of the prior art.  
         [0026]     Please refer to  FIG. 9  and  FIG. 10 , which show the comparison diagrams of the horizontal and vertical average gains of the PIFA  10  and the PIFA  50  toward an X-Z, a Y-Z, and an X-Y direction respectively when operating in 2440 MHz. As shown in  FIG. 9  and  FIG. 10 , the average gains of the PIFA  50  are all higher than that of the prior art except the X-Z directional vertical average gain. In conclusion, in addition to the improvement of rigidity, the installation of the rib  52  on a planner radiation plate to form the rib-shaped radiation plate  54  does not degrade but improve the average gains of the PIFA  50 .  
         [0027]     Besides the average gains, the S 11  VS. frequency characteristic curve is also very important to the performance of an antenna. Please refer to  FIG. 5 , which is a characteristic curve of the operating frequencies and the antenna S 11  values, where the Y-axis is the S 11  values and the X-axis is the frequencies. As shown in  FIG. 5 , when the PIFA  50  is operating in a channel of 2.3975 GHz, 2.4475 GHz, and 2.4975 GHz, which is within WLAN 802.11b and 802.11g band, the S 11  values are −14.65 dB, −18.66 dB, and −15.56 dB respectively. And all are better than acceptable level, −10 dB.  
         [0028]     According to the preferred embodiment, the rib-shaped radiation plate  54  can have a cross section of a variety of shapes, for example the shapes of an open rectangle shown in  FIG. 6 , of a “V” character shown in  FIG. 7 , and of a semicircle shown in  FIG. 8 . The rib  52  can be of any shape, for example a straight line shown in  FIG. 2 , and the two ends of the rib  52  can selectively contact to the edges of the rib-shaped radiation plate  54 , for example, as shown in  FIG. 2 , the length of the rib  52  is equal to that of the radiation plate  54 .  
         [0029]     As mentioned previously, since the PIFA  50  can be installed onto a printed circuit board, the PIFA  50  can be grounded to the grounded area of the printed circuit board.  
         [0030]     In contrast to the prior art, the present invention can provide a PIFA with a rib-shaped radiation plate. Without the need of any additional processes, the rib-shaped radiation plate manufactured through a molding of a rib on a planner radiation plate has a better rigidity than that of the prior art. Moreover, the installation of the rib does not degrade but improve the average gains of the PIFA. Further, the PIFA according to the present invention can be installed onto a printed circuit board through an SMT or a wave soldering process, and the time and the cost of manufacturing a PIFA is therefore reduced.  
         [0031]     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.