Abstract:
A feeding apparatus includes a substrate, an annular grounded metal sheet having a first opening and a second opening, a rectangular grounded metal sheet extending from the annular grounded metal sheet toward an interior according to a configuration of a septum polarizer of a waveguide, a first parasitic grounded metal sheet extending from a side of the rectangular grounded metal sheet along a first direction, a second parasitic grounded metal sheet extending from another side of the rectangular grounded metal sheet along a second direction, a first feeding metal sheet extending from the first opening toward the interior and including a first portion, a second portion and a third portion and a second feeding metal sheet extending from the second opening toward the interior and including a fourth portion, a fifth portion and a sixth portion.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a feeding apparatus and a low noise block down-converter for a waveguide, and more particularly, to a feeding apparatus and a low noise block down-converter, which can simultaneously modify impedance matching at high frequencies and low frequencies and reduce return loss. 
         [0003]    2. Description of the Prior Art 
         [0004]    Satellite communication has the advantage of wide communication coverage and being free from interference from ground environment, and is widely used for military communication, exploration and business communication services such as satellite navigation, satellite voice broadcast and satellite television broadcast. A conventional satellite communication receiving device consists of a dish reflector and a low noise block down-converter. The low noise block down-converter is disposed at the focus of the dish reflector. After the low noise block down-converter receives radio signals reflected from dish reflector, the low noise block down-converter converts the radio signals down to middle band, and then transmits the radio signals to a back-end radio frequency processing unit for signal processing, thereby providing satellite television programs to users. 
         [0005]    Please refer to  FIG. 1A  that is a schematic diagram illustrating a conventional low noise block down-converter  10  for satellite communication. The low noise block down-converter  10  can be disposed at the focus of a dish reflector to collect radio signals reflected by the dish reflector. As shown in  FIG. 1A , the low noise block down-converter  10  consists of a feedhorn  12 , a waveguide  14 , a septum polarizer  16  and a feeding apparatus  100 . The septum polarizer  16  is fixed in the waveguide  14  with a cylindrical shape, and divides the interior of the waveguide  14  in half.  FIG. 1B  is a schematic diagram illustrating a top view of a front surface of the conventional feeding apparatus  100 . The feeding apparatus  100  is utilized to transmit the radio signals received by the feedhorn  12  to a back-end radio frequency processing unit, and consists of a substrate  110 , an annular grounded metal sheet  120 , a rectangular grounded metal sheet  130 , feeding metal sheets  140   a ,  140   b  and signal wires  150   a ,  150   b.    
         [0006]    Conventionally, in order to adjust operating frequency range of the low noise block down-converter  10 , lengths of the feeding metal sheets  140   a ,  140   b  are modified to control impedance of the feeding apparatus  100  so that impedance matching may be achieved with sufficient bandwidth. In practice, however, failures frequently occur—there exists a tradeoff among frequencies. Specifically, please refer to  FIG. 1C , which is a schematic diagram illustrating return loss of the feeding apparatus  100  in Ku band (10.7 GHz-12.75 GHz). As shown in  FIG. 1C , the return loss of the feeding apparatus  100  is low, merely in a range of 11.00 GHz to 12.00 GHz, while the return loss of the feeding apparatus  100  from 10.7 GHz to 11.00 GHz and from 12.00 GHz to 12.75 GHz is quite high and grows rapidly. Therefore, the feeding apparatus  100  cannot optimize return loss at high frequencies and low frequencies at the same time. Along with the growing needs for satellite television, the number of frequency bands covered by direct broadcast satellites is increasing; as a result, there is an urgent need for improvement in the field. 
       SUMMARY OF THE INVENTION 
       [0007]    It is therefore one of the objectives of the present invention to provide a feeding apparatus and a low noise block down-converter to effectively modify impedance matching at high frequencies and low frequencies and reduce return loss. 
         [0008]    An embodiment of the invention provides a feeding apparatus adapted to a waveguide. The feeding apparatus comprises a substrate; an annular grounded metal sheet, disposed on the substrate, substantially in a shape of an annularity, and having a first opening and a second opening; a rectangular grounded metal sheet, disposed on the substrate, extending from the annular grounded metal sheet across an interior of the annularity and corresponding to a configuration of a polarizer of the waveguide; a first parasitic grounded metal sheet, extending from a side of the rectangular grounded metal sheet along a first direction; a second parasitic grounded metal sheet, extending from another side of the rectangular grounded metal sheet along a second direction, wherein the second direction is substantially opposite to the first direction; a first feeding metal sheet, extending from the first opening toward the interior of the annularity and comprising a first portion, a second portion and a third portion, wherein a width of the first portion is different from a width of the second portion, and the width of the second portion is different from a width of the third portion; and a second feeding metal sheet, extending from the second opening toward the interior of the annularity and comprising a fourth portion, a fifth portion and a sixth portion, wherein a width of the fourth portion is different from a width of the fifth portion, and the width of the fifth portion is different from a width of the sixth portion. 
         [0009]    Another embodiment of the invention provides a low noise block down-converter adapted to a communication receiving device. The low noise block down-converter comprises a feedhorn, a waveguide, a polarizer, and a feeding apparatus. The feeding apparatus comprises a substrate; an annular grounded metal sheet, disposed on the substrate, substantially in a shape of an annularity, and having a first opening and a second opening; a rectangular grounded metal sheet, disposed on the substrate, extending from the annular grounded metal sheet across an interior of the annularity and corresponding to a configuration of a polarizer of the waveguide; a first parasitic grounded metal sheet, extending from a side of the rectangular grounded metal sheet along a first direction; a second parasitic grounded metal sheet, extending from another side of the rectangular grounded metal sheet along a second direction, wherein the second direction is substantially opposite to the first direction; a first feeding metal sheet, extending from the first opening toward the interior of the annularity and comprising a first portion, a second portion and a third portion, wherein a width of the first portion is different from a width of the second portion, and the width of the second portion is different from a width of the third portion; and a second feeding metal sheet, extending from the second opening toward the interior of the annularity and comprising a fourth portion, a fifth portion and a sixth portion, wherein a width of the fourth portion is different from a width of the fifth portion, and the width of the fifth portion is different from a width of the sixth portion. 
         [0010]    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 
         [0011]      FIG. 1A  is a schematic diagram illustrating a conventional low noise block down-converter for satellite communication. 
           [0012]      FIG. 1B  is a schematic diagram illustrating a top view of a front surface of the conventional feeding apparatus in  FIG. 1A . 
           [0013]      FIG. 1C  is a schematic diagram illustrating return loss of the feeding apparatus in  FIG. 1A  in Ku band. 
           [0014]      FIG. 2  is a schematic diagram illustrating a top view of a front surface of a feeding apparatus according to an embodiment of the present invention. 
           [0015]      FIG. 3A  is a schematic diagram illustrating a top view of a front surface of the feeding apparatus according to an embodiment of the present invention. 
           [0016]      FIG. 3B  is a schematic diagram illustrating a top view of a front surface of the feeding apparatus according to an embodiment of the present invention. 
           [0017]      FIG. 4A  is a schematic diagram illustrating how impedance of feeding apparatuses varies with frequencies. 
           [0018]      FIG. 4B  is a schematic diagram illustrating return loss of feeding apparatuses. 
           [0019]      FIG. 4C  is a schematic diagram illustrating feeding apparatuses in a Smith chart. 
           [0020]      FIG. 5A  is a schematic diagram illustrating return loss of feeding apparatuses. 
           [0021]      FIG. 5B  is a schematic diagram illustrating feeding apparatuses in a Smith chart. 
           [0022]      FIG. 6  is a schematic diagram illustrating a top view of a front surface of a feeding apparatus according to an embodiment of the present invention. 
           [0023]      FIG. 7A  is a schematic diagram illustrating a feeding metal sheet according to an embodiment of the present invention. 
           [0024]      FIG. 7B  is a schematic diagram illustrating a feeding metal sheet according to an embodiment of the present invention. 
           [0025]      FIG. 7C  is a schematic diagram illustrating a feeding metal sheet according to an embodiment of the present invention. 
           [0026]      FIG. 8  is a schematic diagram illustrating a top view of a front surface of a feeding apparatus according to an embodiment of the present invention. 
           [0027]      FIG. 9A  is a schematic diagram illustrating a locally enlarged view of a rectangular grounded metal sheet and parasitic grounded metal sheets according to an embodiment of the present invention. 
           [0028]      FIG. 9B  is a schematic diagram illustrating a locally enlarged view of a rectangular grounded metal sheet and parasitic grounded metal sheets according to an embodiment of the present invention. 
           [0029]      FIG. 9C  is a schematic diagram illustrating a locally enlarged view of a rectangular grounded metal sheet and parasitic grounded metal sheets according to an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0030]    Please refer to  FIG. 2 .  FIG. 2  is a schematic diagram illustrating a top view of a front surface of a feeding apparatus  20  according to an embodiment of the present invention. The feeding apparatus  20  may replace the feeding apparatus  100  in  FIGS. 1A and 1B  and be implemented in the low noise block down-converter  10  to transmit radio frequency signals received by the feedhorn  12  to the back-end radio frequency processing unit. The feeding apparatus  20  comprises a substrate  200 , an annular grounded metal sheet  202 , a rectangular grounded metal sheet  204 , feeding metal sheets  206 ,  208 , signal wires  210 ,  212  and parasitic grounded metal sheets  214 ,  216 . The annular grounded metal sheet  202 , the rectangular grounded metal sheet  204 , the feeding metal sheets  206 ,  208 , the signal wires  210 ,  212  and the parasitic grounded metal sheets  214 ,  216  are disposed on the substrate  200 . The annular grounded metal sheet  202  is substantially in a shape of an annularity with two openings that break an enclosed circle in half, and therefore the annular grounded metal sheet  202  is divided into two separate portions  2020 ,  2022 . The rectangular grounded metal sheet  204  is disposed inside the annular grounded metal sheet and connects the portions  2020  and  2022  of the annular grounded metal sheet  202 ; the portions  2020 ,  2022  are respectively symmetric with respect to the rectangular grounded metal sheet  204 . The size and shape of the annular grounded metal sheet  202  and the rectangular grounded metal sheet  204  are respectively designed according to the size and shape of the waveguide  14  and the septum polarizer  16 , so that they match with each other. Moreover, the rectangular grounded metal sheet  204  extends from the annular grounded metal sheet  202  across the interior of the annularity in a way corresponding to a configuration of the septum polarizer  16  of the waveguide  14 . Therefore, by lining up the annular grounded metal sheet  202  with the waveguide  14  and by lining up the rectangular grounded metal sheet  204  with the septum polarizer  16 , the waveguide  14 , the septum polarizer  16  and the feeding apparatus  20  are put together to assemble the low noise block down-converter  10  as shown in  FIG. 1 . The parasitic grounded metal sheets  214 ,  216  of the feeding apparatus  20  are extended outward from each side of the rectangular grounded metal sheet  204  oppositely, and the parasitic grounded metal sheets  214  and  216  are respectively symmetric with respect to the rectangular grounded metal sheet  204 . In addition, the feeding metal sheets  206  and  208  are respectively symmetric with respect to the rectangular grounded metal sheet  204 , and extend from the two openings of the annular grounded metal sheet  202  toward the interior of the annularity. The signal wires  210  and  212  are respectively connected to the feeding metal sheets  206  and  208  through the two openings of the annular grounded metal sheet  202 , and extend out (of the annularity) from the feeding metal sheets  206  and  208 . The signal wires  210 ,  212  and the feeding metal sheets  206 ,  208  do not come into contact with the annular grounded metal sheet  202 , and extending centerlines  220 ,  222  of the feeding metal sheets  206 ,  208  are respectively perpendicular to the rectangular grounded metal sheet  204 . 
         [0031]    With the parasitic grounded metal sheets  214 ,  216  and the feeding metal sheets  206 ,  208 , the feeding apparatus  20  can simultaneously affect impedance and return loss at high frequencies and low frequencies. 
         [0032]    Basically, the parasitic grounded metal sheets  214 ,  216  of the feeding apparatus  20  are extended outward from each side of the rectangular grounded metal sheet  204  oppositely, and a extending centerline  224  of the parasitic grounded metal sheet  214  and a extending centerline  226  of the parasitic grounded metal sheet  216  are respectively extended to the center of the rectangular grounded metal sheet  204 ; therefore, the parasitic grounded metal sheets  214 ,  216  are vertically aligned to a center of the rectangular grounded metal sheets  204 . In addition, in this embodiment, the extending centerlines  220 ,  222 ,  224 ,  226  overlap as shown in  FIG. 2 , because the feeding metal sheets  206 ,  208  and the parasitic grounded metal sheets  214 ,  216  may be all vertically aligned to the center of the rectangular grounded metal sheet  204 . However, in other embodiments, the extending centerlines  220 ,  222 ,  224 ,  226  may be shifted to form different lines, and the parasitic grounded metal sheets  214  and  216 , for example, may be disposed close to one end of the rectangular grounded metal sheet  204  in such a situation. The parasitic grounded metal sheets  214  and  216  can ensure impedance matching at low frequencies, and have the impedance of the feeding apparatus  20  in operating frequency range to match better toward the low frequency end, thereby improving return loss at low frequencies. 
         [0033]    On the other hand, because the feeding metal sheets  206  and  208  are symmetric, and because the widths of the feeding metal sheets  206  and  208  may vary respectively, the feeding metal sheet  206  (or, the feeding metal sheet  208 ) may include several segments. In particular, the feeding metal sheet  206  comprises portions  2060 ,  2062 ,  2064 . The portion  2060  is electrically connected to the signal wire  210 ; the portion  2062  and the portion  2064  extend toward the interior of the annularity of the annular grounded metal sheet  202  in sequence. The width of the portion  2060  may be substantially about the same size as that of the signal wire  210 , while the width of the portion  2062  is preferably less than that of the portion  2060  and that of the portion  2064 . Moreover, the structure of the feeding metal sheet  208  is identical and symmetrical to that of the feeding metal sheet  206 . The feeding metal sheet  208  comprises portions  2080 ,  2082 ,  2084 . The portion  2080  is electrically connected to the signal wire  212 ; the portion  2082  and the portion  2084  extend toward the interior of the annularity of the annular grounded metal sheet  202  in sequence. The width of the portion  2080  may be substantially about the same size as that of the signal wire  212 , while the width of the portion  2082  is preferably less than that of the portion  2080  and that of the portion  2084 . Moreover, the width of the portion  2060  may be either equal to or distinct from that of the portion  2064 ; the width of the portion  2080  may be either equal to or distinct from that of the portion  2084 . By modifying the widths of the feeding metal sheet  206 ,  208 , the impedance can thus be changed, such that the impedance of the feeding apparatus  20  in operating frequency range tends to match better toward the high frequency end, thereby improving return loss at high frequencies. 
         [0034]    In order to point out the improvement on return loss at low frequencies and high frequencies by means of the parasitic grounded metal sheets  214 ,  216  and the feeding metal sheets  206 ,  208 , respectively, please refer to  FIG. 3A  and  FIG. 3B , which are schematic diagrams respectively illustrating a top view of a front surface of the feeding apparatus  30  and that of the feeding apparatus  32  according to embodiments of the present invention. Since the structure of the feeding apparatuses  30 ,  32  is similar to that of the feeding apparatus  20  shown in  FIG. 2 , the similar parts are not detailed redundantly. Unlike the feeding apparatus  20 , the widths of the feeding metal sheets  306 ,  308  of the feeding apparatus  30  respectively keep fixed, such that the effect of the parasitic grounded metal sheets  214 ,  216  at low frequencies in Ku band (i.e., 10.7 GHz-11.7 GHz) is easy to tell. Moreover, the parasitic grounded metal sheets  214 ,  216  of the feeding apparatus  20  are removed in the feeding apparatus  32 , and thus the effect of the feeding metal sheets  206 ,  208  at high frequencies in Ku band (i.e., 11.7 GHz-12.75 GHz) is distinguishable. 
         [0035]    Please refer to  FIGS. 4A ,  4 B,  4 C.  FIG. 4A  is a schematic diagram illustrating how impedance of the feeding apparatuses  20 ,  30 ,  32  varies with frequencies.  FIG. 4B  is a schematic diagram illustrating return loss of the feeding apparatuses  20 ,  30 ,  32 .  FIG. 4C  is a schematic diagram illustrating the feeding apparatuses  20 ,  30 ,  32  in a Smith chart. In  FIGS. 4A ,  4 B,  4 C, the long dashed line indicates the feeding apparatus  30 , the short dashed line indicates the feeding apparatus  32 , and the solid line indicates the feeding apparatus  20 . As shown in  FIG. 4A , with the parasitic grounded metal sheets  214 ,  216 , the feeding apparatus  30  achieves an impedance match at low frequencies in Ku band (i.e., 10.7 GHz-11.7 GHz), meaning that the impedance is around 50 ohms (Ω). With the feeding metal sheets  206 ,  208 , the feeding apparatus  32  achieves an impedance match at high frequencies in Ku band (i.e., 11.7 GHz-12.75 GHz), meaning that the impedance is around 50 ohms (Ω). As a result, by integrating the parasitic grounded metal sheets  214 ,  216  into the feeding metal sheets  206 ,  208 , the feeding apparatus  20  can achieve impedance matching from 10.7 GHz to 12.75 GHz, thereby boosting transmission efficiency. 
         [0036]    As shown in  FIG. 4B , the return loss of the feeding apparatus  30  at low frequencies (10.7 GHz-11.7 GHz) is lower, while the return loss of the feeding apparatus  32  at high frequencies (11.7 GHz-12.75 GHz) is lower. Accordingly, the feeding apparatus  20 , which combines with the parasitic grounded metal sheets  214 ,  216  and the feeding metal sheets  206 ,  208 , has lower return loss from 10.7 GHz to 12.75 GHz. Therefore, the return loss at high frequencies and low frequencies in Ku band can all meet requirements, which benefits signal transmission. In addition, as shown in  FIG. 4C , the feeding apparatus  30  at high frequencies is distributed further from the center of the Smith chart, while the feeding apparatus  32  at low frequencies is distributed further from the center of the Smith chart. In comparison, the feeding apparatus  20  is distributed closer to the center of the Smith chart within Ku band (10.7 GHz-12.75 GHz), and reflection coefficient is therefore smaller. 
         [0037]    As shown in  FIGS. 4A to 4C , with the parasitic grounded metal sheets  214 ,  216  and the feeding metal sheets  206 ,  208 , the impedance of the feeding apparatus  20  matches the characteristic impedance of transmission lines, such that a good impedance match is simultaneously achieved at high frequencies and low frequencies, and reflection coefficient is reduced to increase transmission efficiency. 
         [0038]    Please refer to  FIGS. 5A and 5B .  FIG. 5A  is a schematic diagram illustrating return loss of the feeding apparatuses  100  and  20 .  FIG. 5B  is a schematic diagram illustrating the feeding apparatuses  100  and  20  in a Smith chart. In  FIGS. 5A and 5B , the dashed line indicates the feeding apparatus  100 , and the solid line indicates the feeding apparatus  20 . As shown in  FIG. 5A , the return loss of the feeding apparatus  100  within Ku band (10.7 GHz-12.75 GHz) is higher than that of the feeding apparatus  20 , such that transmission efficiency of the feeding apparatus  100  is worse than that of the feeding apparatus  20  of the present invention. Besides, as shown in  FIG. 5B , the feeding apparatus  20  is distributed closer to the center of the Smith chart within Ku band (10.7 GHz-12.75 GHz) than the feeding apparatus  100  is; thus, the reflection coefficient of the feeding apparatus  20  is smaller than that of the feeding apparatus  100 , and the impedance of the feeding apparatus  20  matches the characteristic impedance of transmission lines more. In other words, comparing to the feeding apparatus  100 , the feeding apparatus  20  achieves impedance matching at high frequencies and low frequencies. As set forth above, by modifying the widths of the feeding metal sheets  206 ,  208 , disposing the parasitic grounded metal sheets  214 ,  216 , and properly adjusting the distance between the parasitic grounded metal sheet  214  and the feeding metal sheet  206  and between the parasitic grounded metal sheet  216  and the feeding metal sheet  208 , impedance matching at high frequencies and low frequencies can be effectively improved and return loss is also reduced. 
         [0039]    Please note that the feeding apparatus  20  is an exemplary embodiment of the invention, and those skilled in the art can make alternations and modifications accordingly. For example, any kind or material of substrate on which layout can be drawn can be served as the substrate  200 . Preferably, the lengths of the feeding metal sheets  206 ,  208  are substantially one quarter of the wavelength of received signals, but appropriate adjustments are also feasible. The back-end radio frequency processing unit coupled to the signal wires  210 ,  212  may be a low noise amplifier, an intermediate frequency (IF) filter, an IF amplifier, other radio frequency circuits, or any combination thereof, but not limited thereto. Besides, the feedhorn  12 , the waveguide  14  and the septum polarizer  16  of the low noise block down-converter  10  here aim to illustrate the feeding apparatus  20 , and hence those skilled in the art might appropriately modify them according to different design considerations and system requirements. For example, the feedhorn  12  can be applied into different shapes of the opening, such as a square, circle, rectangle, rhombus and ellipse. Moreover, the feedhorn  12  may have corrugations inside to improve a radiation pattern of the feedhorn, such that the radiation pattern may be more symmetric and centralized to decrease a spillover loss of the feedhorn. 
         [0040]    On the other hand, in the feeding apparatus  20 , extending centerlines  220 ,  222  of the feeding metal sheets  206 ,  208  are respectively perpendicular to the rectangular grounded metal sheet  204 ; however, in other embodiments, there may be an included angle between the extending centerline of a feeding metal sheet and the rectangular grounded metal sheet  204 . Specifically, please refer to  FIG. 6 , which is a schematic diagram illustrating a top view of a front surface of a feeding apparatus  60  according to an embodiment of the present invention. The feeding apparatus  60  comprises a substrate  600 , an annular grounded metal sheet  602 , a rectangular grounded metal sheet  604 , feeding metal sheets  606 ,  608 , signal wires  610 ,  612  and parasitic grounded metal sheets  614 ,  616 . Comparing the feeding apparatus  20  shown in  FIG. 2  and the feeding apparatus  60  shown in  FIG. 6 , although the structure of the feeding apparatus  60  is similar to that of the feeding apparatus  20  shown in  FIG. 2 , openings of the annular grounded metal sheet  602  locate differently from the openings of the annular grounded metal sheet  202 . The annular grounded metal sheet  602  is also in a shape of an annularity substantially with two openings that break an enclosed circle, and therefore the annular grounded metal sheet  602  is divided into two separate portions  6020 ,  6022  of different sizes. The two openings are respectively at angles θ 1  and θ 2  with respect to the vertical. The feeding metal sheets  606 ,  608  extend from the two openings of the annular grounded metal sheet  602  toward the interior of the annularity. That is to say, there is an included angle θ 1  between the extension of the rectangular grounded metal sheet  604  and the extending centerline of the feeding metal sheet  606 , and there is an included angle θ 2  between the extension of the rectangular grounded metal sheet  604  and the extending centerline of the feeding metal sheet  608 . Additionally, the feeding apparatus  60  may be operated in a way similar to the feeding apparatus  20  shown in  FIG. 2 ; therefore, related details can be found from the aforementioned illustrations. 
         [0041]    In  FIG. 6 , the included angles θ 1 , θ 2  may be in a range of 0° (degrees) to 90°, but not limited thereto. Since the effective length of the substrate  600  in the horizontal direction (i.e., the direction perpendicular to the rectangular grounded metal sheet  604 ) depends on the orientation of the feeding metal sheets  606 ,  608 , the effective length of the substrate  600  in the horizontal direction can effectively shrink by minimizing the included angles θ 1 , θ 2 . As a result, density of the back-end radio frequency processing unit increases, circuit layout area of the substrate  200  is saved, and fewer screws are required, thereby reducing product volume, product weight, and manufacturing cost. 
         [0042]    Apart from location of the feeding metal sheets and location of the openings of the annular grounded metal sheet, branches may be added in each portion, and the shape of the feeding metal sheet may be modified. Please refer to  FIGS. 7A to 7C , which are schematic diagrams respectively illustrating feeding metal sheets  706 ,  716 ,  726  according to embodiments of the present invention. The feeding metal sheets  706 ,  716 ,  726  can replace the feeding metal sheets  206 ,  208  shown in  FIG. 2  (or the feeding metal sheets  606 ,  608  shown in  FIG. 6 ). As shown in  FIG. 7A , the feeding metal sheet  706  comprises portions  7060 ,  7062 ,  7064  and branches  7066 ,  7068 . When the feeding metal sheet  706  is utilized to replace the feeding metal sheets in previous embodiments, the portion  7060  is electrically connected to a signal wire (e.g., one of the signal wires  210 ,  212 ,  610 ,  612 ), the portion  7062  and the portion  7064  extend toward the interior of the annularity of the annular grounded metal sheet in sequence, and the branches  7066  and  7068  extends oppositely from two sides of the portion  7062 . As shown in  FIG. 7B , the feeding metal sheet  716  comprises portions  7160 ,  7162 ,  7164 ,  7166 . The portion  7160  is electrically connected to a signal wire, and the portions  7162 ,  7164  and  7166  extend toward the interior of the annular of the annular grounded metal sheet in sequence. As shown in  FIG. 7C , the feeding metal sheet  726  comprises portions  7260 ,  7262 ,  7264 ,  7266 . The portion  7260  is electrically connected to a signal wire, the portions  7262 ,  7264 ,  7266  extend toward the interior of the annularity of the annular grounded metal sheet in sequence, and the portion  7260 ,  7262 ,  7264 ,  7266  are in the shape of a curve. 
         [0043]    In  FIG. 7A , the branches  7066 ,  7068  are disposed on the sides of the portion  7062 , but in other embodiments, branches may be designed on the sides of the portion  7060  or the portion  7064 , and the number of branches may be modified according different considerations. In  FIG. 7B , the feeding metal sheet  716  is divided into four portions. The widths of the portion  7162  and the portion  7166  are greater than that of the portion  7160  and that of the portion  7164 , but not limited thereto. In other words, the widths of the portions can vary without following a specific rule and may not increase gradually. Moreover, the number of portions of the feeding metal sheet  716  is not limited to a specific value, but may be several portions. Consequently, with the number, relative width and shape of the portions properly adjusted and branches disposed, the impedance of the feeding apparatus can be changed as one would wish. 
         [0044]    Apart from adjusting the structure of feeding metal sheets, location of parasitic grounded metal sheets with respect to the rectangular grounded metal sheet may be appropriately modified to meet the desired impedance. Please refer to  FIG. 8 , which is a schematic diagram illustrating a top view of a front surface of a feeding apparatus  80  according to an embodiment of the present invention. The feeding apparatus  80  comprises a substrate  800 , an annular grounded metal sheet  802 , a rectangular grounded metal sheet  804 , feeding metal sheets  806 ,  808 , signal wires  810 ,  812  and parasitic grounded metal sheets  814 ,  816 . Comparing the feeding apparatus  80  to the feeding apparatus  20  shown in  FIG. 2 , although the structure of the feeding apparatus  80  is similar to that of the feeding apparatus  20  shown in  FIG. 2 , the parasitic grounded metal sheets  814 ,  816 , with respect to the rectangular grounded metal sheet  804 , locate differently from the feeding apparatus  20 . As shown in  FIG. 8 , the parasitic grounded metal sheets  814 ,  816  on opposite sides of the rectangular grounded metal sheet  804  may be disposed along the rectangular grounded metal sheet  804  but at different locations, and hence the cross shape formed by the rectangular grounded metal sheet  804  and the parasitic grounded metal sheets  814 ,  816  varies. Additionally, the feeding apparatus  80  may be operated in a way similar to the feeding apparatus  20  shown in  FIG. 2 ; therefore, related details can be found from the aforementioned illustrations. 
         [0045]    The shape of the parasitic grounded metal sheets may be adjusted as the number of the portions increases. Please refer to  FIGS. 9A to 9C .  FIG. 9A  is a schematic diagram illustrating a locally enlarged view of a rectangular grounded metal sheet  902  and parasitic grounded metal sheets  904 ,  906  according to an embodiment of the present invention.  FIG. 9B  is a schematic diagram illustrating a locally enlarged view of a rectangular grounded metal sheet  912  and parasitic grounded metal sheets  914 ,  916  according to an embodiment of the present invention.  FIG. 9C  is a schematic diagram illustrating a locally enlarged view of a rectangular grounded metal sheet  922  and parasitic grounded metal sheets  924 ,  926  according to an embodiment of the present invention. The rectangular grounded metal sheets  902 ,  912 ,  922  and the associated parasitic grounded metal sheets  904 ,  906 ,  914 ,  916 ,  924 ,  926  can replace the rectangular grounded metal sheet  204  and the parasitic grounded metal sheets  214 ,  216  shown in  FIG. 2  (or other embodiments). As shown in  FIG. 9A , the parasitic grounded metal sheets  904 ,  906  respectively extend from two opposite sides of the rectangular grounded metal sheet  902 , and the parasitic grounded metal sheets  904 ,  906  are in the shape of a curve. As shown in  FIG. 9B , the parasitic grounded metal sheets  914 ,  916  respectively extend from two opposite sides of the rectangular grounded metal sheet  912 . The parasitic grounded metal sheet  914  comprises portions  9140 ,  9142  of different widths; the parasitic grounded metal sheet  916  comprises portions  9160 ,  916  of different widths. The variation of the widths may be further modified according to different system requirements. As shown in  FIG. 9C , the parasitic grounded metal sheet  924 ,  926  respectively extend from two opposite sides of the rectangular grounded metal sheet  922 . The parasitic grounded metal sheet  924  comprises portions  9240 ,  9242 ; the parasitic grounded metal sheet  926  comprises portions  9260 ,  9262 . The variation of the widths of the portions  9240 ,  9242  and the portions  9260 ,  9262  may also be modified according to different system requirements. It is worth noting that the number of portions of the parasitic grounded metal sheets  914 ,  916 ,  924 ,  926  shown in  FIGS. 9B and 9C  is not limited to a specific value, but may be several portions. Moreover, the widths of the portions can vary without following a specific rule and may not increase gradually. Consequently, as the number, relative width and shape of the portions are properly adjusted, the impedance of the feeding apparatus can be changed as one would wish. 
         [0046]    To sum up, by modifying widths of feeding metal sheets, disposing parasitic grounded metal sheets, and properly adjusting the distance between the parasitic grounded metal sheet and the feeding metal sheet, impedance of the feeding apparatus in operating frequency range match more toward both the low frequency end and the high frequency end, thereby improving return loss at high frequencies and low frequencies. In other words, a good impedance matching is achieved and return loss is reduced with the designed pattern of the feeding apparatus, and design freedom diverges while it is still easy to manufacture. 
         [0047]    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.