Abstract:
The present invention relates to a partially reflective surface antenna and, more particularly, to a partially reflective surface antenna including a reflective board composed of arrays of microstrip antennas, and has advantages of low side lobe and high gain. It comprises: a substrate with an upper surface having a signal transmitting notch for transmitting and receiving a high frequency signal; a reflective board for partially reflecting the high frequency signal; and a plurality of supporting elements for supporting the reflective board on the substrate. The reflective board has a second antenna array and a first antenna array surrounded by the second antenna array, wherein the first and the second antenna array are composed of a plurality of first microstrip reflective units and a plurality of second microstrip reflective units, respectively. Besides, the distance between the first microstrip reflective units is smaller than the distance between the second microstrip reflective units.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a partially reflective surface antenna and, more particularly, to a partially reflective surface antenna that includes a reflective board composed of arrays of microstrip antennas, and has the advantages of low side lobe and high gain.  
         [0003]     2. Description of Related Art  
         [0004]     Recently, in the military or civil application fields, a partially reflective surface antenna having a partially reflective surface (PRS), which is composed of arrays of microstrip antenna, has been used frequently. These partially reflective surface antennas have low profile, and can be manufactured by using printed circuit boards (PCB).  
         [0005]     However, the high frequency signals transmitted by these partially reflective surface antennas still have obvious levels of the side lobe portion, and the ratio of the side lobe portion to the whole waveform cannot be further decreased. This drawback prevents the partially reflective surface antenna from providing high frequency signals whose energy is centralized at the portion in the main beam direction, and thus limits the transmission distance of the high frequency signals. Furthermore, the gain of the partially reflective surface antenna cannot be continuously increased as the area of the reflective board increases. Namely, when the area of the reflective board is larger than an optimum value, the efficiency (the gain of a unit area) of the partially reflective surface antenna contrarily decreases as the area of the reflective board increases. Currently, the best available efficiency of the conventional partially reflective surface antenna is only about 50%.  
         [0006]      FIG. 1  is a schematic drawing of the conventional partially reflective surface antenna, wherein the partially reflective surface antenna  1  comprises a substrate  11  and a reflective board  12 . Both of them are composed of microwave substrates made of the FR-4 materials. The reflective board  12  is supported by the first supporting rod  141 , the second supporting rod  142 , the third supporting rod  143 , and the fourth supporting rod  144 . As a result, a resonant distance between the reflective board  12  and the upper surface  111  of the substrate  11  is maintained. The length of the resonant distance is determined with relation to the design frequency of the partially reflective surface antenna  1 . Besides, a rectangular notch (not shown) is formed near the center position of the substrate  21 , and the rectangular notch is electrically connected to a coaxial cable (not shown) in order to transmit or receive the high frequency signal.  
         [0007]     When the partially reflective surface antenna is in the “transmitting state”, the high frequency signal is reflected back and forth between the substrate  11  and the reflective board  12 . Later, due to the “partially reflection” effect of the reflective board  12 , the high frequency signal eventually passes through the reflective board  12  and then the high frequency signal will pass through the reflective board  12  and will be transmitted outwardly by the partially reflective surface antenna  1 . The length and width of the reflective board  12  are both 12.9 cm, and a plurality of microstrip reflective units  13  are disposed evenly on the upper surface  121  of the reflective board  12 . The length and width of the microstrip reflective units are both 12 mm, and the distance between two adjacent microstrip reflective units is 1.1 mm.  
         [0008]     As depicted above, even though the conventional partially reflective surface antenna  1  can properly adjust the arrangement of the microstrip reflective units  13  disposed on the upper surface  121  of the reflective board  12  (i.e. adjust the distance between two adjacent microstrip reflective units  13 ) to improve the signal to noise ratio (S/N ration) and the directivity of the high frequency signal it transmits. However, the ratio of the side lobe portion of the high frequency signal transmitted by the conventional partially reflective surface antenna  1  cannot be further decreased and the gain of the conventional partially reflective surface antenna  1  cannot be further increased, either.  
         [0009]     Therefore, it is desired to have a partially reflective surface antenna being able to provide the advantages of low side lobe portion ratio and high gain, in order to improve the efficiency of antenna module in a wireless communication system.  
       SUMMARY OF THE INVENTION  
       [0010]     The partially reflective surface antenna of the present invention comprises: a substrate with an upper surface having a signal transmitting notch for transmitting and receiving a high frequency signal; a reflective board for partially reflecting the high frequency signal; and a plurality of supporting elements for supporting the reflective board on the upper surface of the substrate and to maintain a specific distance between the reflective board and the substrate. Wherein a first antenna array and a second antenna array are disposed on the surface of the reflective board, and the first antenna array is surrounded by the second antenna array. The first antenna array is composed of a plurality of the first microstrip reflective units, and the second antenna array is composed of a plurality of the second microstrip reflective units, wherein the distance between the first microstrip reflective units is smaller than the distance between the second microstrip reflective units.  
         [0011]     Therefore, by having two different kinds of arrangement of the antenna array disposed on the surface of the reflective board, the partially reflective surface antenna of the present invention can reduce the energy ratio of the side lobe portion of the transmitted high frequency signals and centralize the energy of the transmitted high frequency signals into its main lobe portion, in order to elongate the distance that the high frequency signal can be transmitted and minimize the possibility of the high frequency signal suffering interference. Furthermore, the gain of the partially reflective surface antenna of the present invention is raised higher than that of the conventional partially reflective antenna, so the antenna module having the partially reflective surface antenna of the present invention can have optimum operation efficiency.  
         [0012]     The material of the printed circuit board which composes the substrate of the partially reflective surface antenna of the present invention is not limited; the substrate is preferably made of a microwave substrate of the FR-4 material, a microwave substrate of the Duroid material, or a microwave substrate of the Teflon material. The material of the printed circuit board which composes the reflective board of the partially reflective surface antenna of the present invention is not limited; the reflective board is preferably made of a microwave substrate of the FR-4 material, a microwave substrate of the Duroid material, or a microwave substrate of the Teflon material. The shape of the reflective board of the partially reflective surface antenna of the present invention is not limited; the shape is preferable square, rectangular, or circular. The shape of the first microstrip reflective units of the partially reflective surface antenna of the present invention is not limited; the shape is preferably square or strip-like. The shape of the second microstrip reflective units of the partially reflective surface antenna of the present invention is not limited; the shape is preferably square or strip-like. The material of the supporting elements of the partially reflective surface antenna of the present invention is not limited; it is preferably made of an insulating material. The frequency range of the high frequency signal transmitted or received by the partially reflective surface antenna of the present invention is not limited; the frequency range is preferably between 8 GHz and 26 GHz. The distance between the reflective board and the substrate of the partially reflective surface antenna of the present invention is not restricted; it is preferably one-third to two-thirds of the wavelength of the high frequency signal, and it is more preferably one-half of the wavelength of the high frequency signal. The form of the signal transmitting notch of the substrate of the partially reflective surface antenna of the present invention is not limited; it is preferably a square notch or a rectangular notch. The form of the signal wire being electrically connected to the signal transmitting notch of the substrate of the partially reflective surface antenna of the present invention is not limited; it is preferably a coaxial cable or a copper wire.  
         [0013]     Other objects, advantages, and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]      FIG. 1  is a schematic drawing of the conventional partially reflective surface antenna;  
         [0015]      FIG. 2A  is a perspective schematic drawing of the partially reflective surface antenna according to the first preferred embodiment of the present invention;  
         [0016]      FIG. 2B  is a schematic drawing of the reflective board of the partially reflective surface antenna according to the first preferred embodiment of the present invention;  
         [0017]      FIG. 2C  is a schematic drawing showing the two kinds of the arrangements of the first antenna array and the second antenna array disposed on the surface of the reflective board of the partially reflective surface antenna according to the first preferred embodiment of the present invention;  
         [0018]      FIG. 3A  is a schematic drawing of the reflective board of the first kind of the conventional partially reflective surface antenna;  
         [0019]      FIG. 3B  is a schematic drawing showing the arrangement of the microstrip reflective units disposed on the surface of the reflective board displayed in  FIG. 3A ;  
         [0020]      FIG. 4A  is a waveform diagram at the magnetic field plane showing the waveforms of the high frequency signals transmitted by the first kind of the conventional partially reflective surface antenna and by the partially reflective surface antenna according to the first preferred embodiment of the present invention;  
         [0021]      FIG. 4B  is a waveform diagram at the electric field plane showing the waveforms of the high frequency signals transmitted by the first kind of the conventional partially reflective surface antenna and by the partially reflective surface antenna according to the first preferred embodiment of the present invention;  
         [0022]      FIG. 4C  is a schematic diagram showing the gain distribution curves of the first kind of the conventional partially reflective surface antenna and the partially reflective surface antenna according to the first preferred embodiment of the present invention;  
         [0023]      FIG. 5A  is a schematic drawing of the reflective board of the second kind of the conventional partially reflective surface antenna;  
         [0024]      FIG. 5B  is a schematic drawing showing the arrangements of the microstrip reflective units disposed on the surface of reflective board displayed in  FIG. 5A ;  
         [0025]      FIG. 6A  is a waveform diagram at the magnetic field plane showing the waveforms of the high frequency signals transmitted by the second kind of the conventional partially reflective surface antenna and by the partially reflective surface antenna according to the first preferred embodiment of the present invention;  
         [0026]      FIG. 6B  is a waveform diagram at the electric field plane showing the waveforms of the high frequency signals transmitted by the second kind of the conventional partially reflective surface antenna and by the partially reflective surface antenna according to the first preferred embodiment of the present invention;  
         [0027]      FIG. 6C  is a schematic diagram showing the gain distribution curves of the second kind of the conventional partially reflective surface antenna and the partially reflective surface antenna according to the first preferred embodiment of the present invention;  
         [0028]      FIG. 7A  is a schematic diagram of the reflective board of the partially reflective surface antenna according to the second preferred embodiment of the present invention; and  
         [0029]      FIG. 7B  is a schematic drawing showing the two kinds of the arrangements of the first antenna array and the second antenna array disposed on the surface of the reflective board of the partially reflective surface antenna according to the second preferred embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0030]      FIG. 2A  is a perspective schematic drawing of the partially reflective surface antenna according to the first preferred embodiment of the present invention, wherein the partially reflective surface antenna  2  comprises a substrate  21  and a reflective board  22 . Both of them are composed of microwave substrates made of the FR-4 materials with a thickness of 0.8 mm. The reflective board  22  is supported by a first supporting rod  241 , a second supporting rod  242 , a third supporting rod  243 , and a fourth supporting rod  244 . As a result, a resonant distance between the reflective board  22  and an upper surface  211  of the substrate  21  is maintained. The length of the resonant distance is determined with relation to the design frequency of the partially reflective surface antenna  2  of the present invention. That is, when the design frequency of the partially reflective surface antenna  2  of the present invention is 9.3 GHz, the resonant distance is about 1.68 cm; and when the design frequency of the partially reflective surface antenna  2  of the present invention is 9.5 GHz, the resonant distance is about 1.65 cm.  
         [0031]     Besides, there is a rectangular notch (not shown) near the center position of the substrate  21 , and the rectangular notch is electrically connected to a coaxial cable (not shown) in order to transmit or receive a high frequency signal the frequency range of which is between 9.25 GHz and 9.55 GHz. When the partially reflective surface antenna of the first preferred embodiment of the present invention is in the “transmitting state”, the high frequency signal is reflected back and forth between the substrate  21  and the reflective board  22  of the partially reflective surface antenna  2  of the invention. Later, due to the “partial reflection” effect of the reflective board  22 , the high frequency signals eventually pass through the reflective board  22  and will be transmitted outwardly by the partially reflective surface antenna  2 .  
         [0032]     As shown in  FIG. 2B  and  FIG. 2C , both the length and width of the reflective board  22  are 17.8 cm, and the surface area of the reflective board  22  is 316.94 cm 2 . There are two kinds of antenna arrays disposed on the upper surface  211  of the reflective board  22 , i.e. the first antenna array and the second antenna array, with different pitches. In these two kinds of the antenna arrays, the length (L) and width (W) of the composing first microstrip reflective units  231  and each of the composing second microstrip reflective units  232  are both 12 mm. However, the distance between each of the first microstrip reflective units  231  is different from the distance between each one of the second microstrip reflective units  232 . Namely, in the first antenna array, the distances between two adjacent first microstrip reflective units  231  in the X-axis direction (Dx  1 ) and in the Y-axis direction (Dy 1 ) are both 1.1 mm (Dx 1 =Dy 1 =1.1 mm). On the other hand, in the second antenna array, the distances between two adjacent first microstrip reflective units  231  in the X-axis direction (Dx 2 ) and in the Y-axis direction (Dy 2 ) are both 3.14 mm (Dx 2 =Dy 2 =3.14 mm).  
         [0033]      FIG. 3A  is a schematic drawing of the reflective board of the first kind of the conventional partially reflective surface antenna, while  FIG. 3B  is a schematic drawing showing the arrangement of the microstrip reflective unit disposed on the surface of the reflective board displayed in  FIG. 3A . The reflective board  31  is composed of a microwave substrate made of the FR-4 materials with a thickness of 0.8 mm. The length and width of the reflective board  31  are both 12.9 cm, and the surface area of the reflective board  31  is 166.41 cm 2 . There is a plurality of microstrip reflective units  33  evenly disposed on the upper surface  32  of the reflective board  31 , while both the length (L) and width (W) of the microstrip reflective unit  33  are 12 mm. The distance between two adjacent microstrip reflective units  33  in the x-axis direction and the y-axis direction are both 1.1 mm (Dx 1 =Dy 1 =1.1 mm).  
         [0034]     After comparing the features (i.e. side lobe level ratio, gain, etc.) of the high frequency signal transmitted by the first kind of the conventional partially reflective surface antenna to those of the high frequency signal transmitted by the partially reflective surface antenna according to the first preferred embodiment of the invention, it is obvious that the high frequency signal transmitted by the partially reflective surface antenna according to the first preferred embodiment of the invention has lower side lobe level and better gain.  
         [0035]     In  FIG. 4A ,  FIG. 4B , and  FIG. 4C , the features of the high frequency signals transmitted by the partially reflective surface antenna according to the first preferred embodiment of the present invention are represented by the curve of “the third PRS”. On the other hand, the features of the high frequency signals transmitted by the first kind of the conventional partially reflective surface antenna are represented by the curve of “the first PRS”.  
         [0036]      FIG. 4A  is a waveform diagram at the magnetic field plane (H-plane) showing the waveforms of the high frequency signals (9.3 GHz) transmitted by the first kind of the conventional partially reflective surface antenna and by the partially reflective surface antenna according to the first preferred embodiment of the present invention.  FIG. 4B  is a waveform diagram at the electric field plane (E-plane) showing the high frequency signals (9.3 GHz) transmitted by the first kind of the conventional partially reflective surface antenna and by the partially reflective surface antenna according to the first preferred embodiment of the present invention.  
         [0037]     Referring to  FIG. 4A  and  FIG. 4B , the waveform of the third PRS curve is more centralized than the waveform of the first PRS curve, especially in the magnetic field plane (H-plane). Therefore, as compared to the high frequency signal transmitted by the first kind of the partially reflective surface antenna, the ratio of the side lobes portion of the high frequency signal transmitted by the partially reflective surface antenna according to the first preferred embodiment of the invention is lowered. Besides, the energy of the high frequency signal is more centralized into the main lobe portion of the high frequency signal. Thus, the distance that the high frequency signal can be transmitted is elongated, and the possibility of the high frequency signal being subjected to interference is minimized.  
         [0038]      FIG. 4C  is a schematic diagram showing the gain distribution curves of the first kind of the conventional partially reflective surface antenna and the partially reflective surface antenna according to the first preferred embodiment of the present invention. As shown in  FIG. 4C , the frequencies of the maximum gain of the two partially reflective surface antennas are both close to 9300 MHz (9.3 GHz).  
         [0039]     As also shown in  FIG. 4C , in the whole frequency range between 8800 MHz and 10300 MHz, the gain curve (the third PRS) of the high frequency signal transmitted by the partially reflective surface antenna according to the first preferred embodiment of the present invention is always larger than the gain curve (the first PRS) of the high frequency signal transmitted by the first kind of the conventional partially reflective surface antenna. After executing certain calculating processes, the efficiency (the gain per area) of the partially reflective surface antenna according to the first preferred embodiment of the present invention is about 51%, which is the same as that the efficiency of the first kind of the conventional partially reflective surface antenna.  
         [0040]     Moreover, the area of the reflective board of the first kind of the conventional partially reflective surface antenna is identical to the area covered by the first antenna array on the surface of the reflective board of the partially reflective surface antenna according to the first preferred embodiment of the present invention. Namely, the reflective board of the partially reflective surface antenna according to the first preferred embodiment of the present invention can be formed by adding the second antenna array with larger pitches surrounding the reflective board of the first kind of the conventional partially reflective surface antenna. Thus, by adding the area having the second antenna array on it, the side lobe portion of the high frequency signal transmitted by the partially reflective surface antenna according to the first preferred embodiment of the present invention is decreased, and the gain of the high frequency signal is increased. To be more specific, the wastages of the substrates and the conductive materials do not reduce the efficiency of the partially reflective antenna with its increased area, i.e. even with the reflective board having the larger area, the efficiency of the partially reflective surface antenna according the first preferred embodiment of the present invention does not change, it is maintained at 51%.  
         [0041]     As shown in  FIG. 4A  and  FIG. 4C , by adding the area having the second antenna array to the reflective board of the first kind of the conventional partially reflective surface antenna to form the reflective board of the partially reflective surface antenna according to the first preferred embodiment of the present invention, the ratio side lobe portion of the high frequency signal is obviously decreased, and the energy of the high frequency signal is more centralized in the main lobe portion thereof. Besides, the efficiency of the partially reflective surface antenna according to the first preferred embodiment of the present invention is maintained (still about 51%).  
         [0042]     Later, the reflective board of the second kind of the partially reflective surface antenna is described, in order to prove that even with the reflective board having the same size, the partially reflective surface antenna of the present invention can still have better performance in transmitting high frequency signals (e.g. the efficiency of the partially reflective surface antenna), comparing to the second kind of the conventional partially reflective surface antenna.  
         [0043]      FIG. 5A  is a schematic drawing of the reflective board of the second kind of the conventional partially reflective surface antenna;  FIG. 5B  is a schematic drawing showing the arrangements of the microstrip reflective units disposed on the surface of reflective board displayed in  FIG. 5A . The reflective board  51  is composed of a microwave substrate made of the FR-4 materials with the thickness of 0.8 mm. The length and width of the reflective board  51  are 19.4 cm and 16.9 cm, respectively. Thus, the surface area of the reflective board  51  is 327.86 cm 2 . There is a plurality of microstrip reflective units  53  evenly disposed on the upper surface  52  of the reflective board  51 , while both the length (L) and width (W) of the microstrip reflective unit  53  are 12 mm. The distance between two adjacent microstrip reflective units  53  in the x-axis direction and the y-axis direction are both 1.1 mm (Dx 1 =Dy 1 =1.1 mm).  
         [0044]     After comparing the features (i.e. side lobe level ratio, gain, etc.) of the high frequency signal transmitted by the second kind of the conventional partially reflective surface antenna to those of the high frequency signal transmitted by the partially reflective surface antenna according to the first preferred embodiment of the invention, it is obvious that the high frequency signal transmitted by the partially reflective surface antenna according to the first preferred embodiment of the invention has lower side lobe level and better gain.  
         [0045]     In  FIG. 6A ,  FIG. 6B , and  FIG. 6C , the features of the high frequency signals transmitted by the partially reflective surface antenna according to the first preferred embodiment of the present invention are represented by the curve of “the third PRS”. On the other hand, the features of the high frequency signals transmitted by the second kind of the conventional partially reflective surface antenna are represented by the curve of “the second PRS”.  
         [0046]      FIG. 6A  is a waveform diagram at the magnetic field plane (H-plane) showing the waveforms of the high frequency signals (9.3 GHz) transmitted by the second kind of the conventional partially reflective surface antenna and by the partially reflective surface antenna according to the first preferred embodiment of the present invention.  FIG. 6B  is a waveform diagram at the electric field plane (E-plane) showing the high frequency signals (9.3 GHz) transmitted by the second kind of the conventional partially reflective surface antenna and by the partially reflective surface antenna according to the first preferred embodiment of the present invention.  
         [0047]     With reference to  FIG. 6A  and  FIG. 6B , the waveform of the third PRS curve is more centralized than the waveform of the second PRS curve, especially in the magnetic field plane (H-plane). Therefore, as compared to the high frequency signal transmitted by the second kind of the partially reflective surface antenna, the ratio of the side lobes portion of the high frequency signal transmitted by the partially reflective surface antenna according to the first preferred embodiment of the invention is lowered. Besides, the energy of the high frequency signal is more centralized into the main lobe portion of the high frequency signal. Thus, the distance that the high frequency signals can be transmitted is elongated, and the possibility of the high frequency signal being subjected to interference is minimized.  
         [0048]      FIG. 6C  is a schematic diagram showing the gain distribution curves of the second kind of the conventional partially reflective surface antenna and the partially reflective surface antenna according to the first preferred embodiment of the present invention. As shown in  FIG. 6C , the frequencies of the maximum gain of this two partially reflective surface antenna are both close to 9300 MHz (9.3 GHz).  
         [0049]     As also shown in  FIG. 6C , in the whole frequency range between 8800 MHz and 10300 MHz, the gain curve (the third PRS) of the high frequency signal transmitted by the partially reflective surface antenna according to the first preferred embodiment of the present invention is always larger than the gain curve (the second PRS) of the high frequency signal transmitted by the second kind of the conventional partially reflective surface antenna.  
         [0050]     After executing certain calculating processes, the efficiency (the gain per area) of the second kind of the partially reflective surface antenna is around 41%, which is far less than the efficiency of the partially reflective surface antenna according to the first preferred embodiment of the present invention (which is about 51%). That is, although the surface area of the reflective board of the partially reflective surface antenna according to the first preferred embodiment of the present invention (316.84 cm 2 ) is smaller than the surface area of the reflective board of the second kind of the conventional partially reflective surface antenna (327.86 cm 2 ), the gain curve (the third PRS) of the high frequency signal transmitted by the partially reflective surface antenna according to the first preferred embodiment of the present invention is still larger than the gain curve (the second PRS) of the high frequency signal transmitted by the second kind of the conventional partially reflective surface antenna.  
         [0051]     As described above, referring to  FIG. 6A  through  FIG. 6C , the gain of the partially reflective surface antenna according to the first preferred embodiment of the present invention is larger than the gain of the second kind of the conventional partially reflective surface antenna.  
         [0052]      FIG. 7A  is a schematic diagram of the reflective board of the partially reflective surface antenna according to the second preferred embodiment of the present invention.  FIG. 7B  is a schematic drawing showing the two kinds of the arrangements of the first antenna array and the second antenna array disposed on the surface of the reflective board of the partially reflective surface antenna according to the second preferred embodiment of the present invention. The reflective board  71  is composed of a microwave substrate made of the FR-4 materials with a thickness of 0.8 mm; wherein the length and width of the reflective board  71  are 16.8 cm and 16.5 cm, respectively. There are two kinds of antenna array disposed on the upper surface  72  of the reflective board  71 , i.e. the first antenna array and the second antenna array, with different pitches. In these two kinds of the antenna arrays, the length (L) and width (W) of the first microstrip reflective units  731  and the second microstrip reflective units  732  are 17.25 mm and 0.75 mm, respectively. However, the distance between two adjacent first microstrip reflective units  731  in X-axis direction is different from the distance between two neighboring second microstrip reflective units  732  in X-axis direction. Namely, the distances between two adjacent first microstrip reflective units  731  in the X-axis direction (Dx 1 ) and in the Y-axis direction (Dy 1 ) are both 0.75 mm (Dx 1 =Dy 1 =0.75 mm). However, the distance between two adjacent second microstrip reflective units  732  in the X-axis direction (Dx 2 ) is 2.25 mm, while the distance between two adjacent second microstrip reflective units  732  in the Y-axis direction (Dy 2 ) is 1.6 mm.  
         [0053]     Besides, the 3-D structure of the partially reflective surface antenna according to the second preferred embodiment of the present invention is similar to the one shown in  FIG. 2A , and its operation mechanism is the same as the partially reflective surface antenna according to the first preferred embodiment of the present invention. The differences between these two kinds of the partially reflective surface antenna of the present invention are the dimension of the reflective boards, the shape of the first microstrip reflective units and the second microstrip reflective units (i.e. square vs. rectangular), and the location of the rectangular notch on the substrate. Therefore, the 3-D structure of the partially reflective surface antenna according to the second embodiment of the present invention and the operational mechanism are omitted. As described above, after comparing the features (i.e. side lobe level ratio, gain, etc.) of the high frequency signal transmitted by the conventional partially reflective surface antenna to those of the high frequency signal transmitted by the partially reflective surface antenna according to the second preferred embodiment of the invention, it is obvious that the high frequency signal transmitted by the partially reflective surface antenna according to the second preferred embodiment of the invention has lower side lobe level and better gain.  
         [0054]     Therefore, by having two different kinds of arrangement of the antenna array disposed on the surface of the reflective board, the partially reflective surface antenna of the present invention can reduce the energy ratio of the side lobe portion of the transmitted high frequency signals and centralize the energy of the transmitted high frequency signals into its main lobe portion, in order to elongate the distance that the high frequency signal can be transmitted and minimize the possibility of the high frequency signal being subjected to interference. Furthermore, the gain of the partially reflective surface antenna of the present invention is raised higher than that of the conventional partially reflective antenna, so the antenna module having the partially reflective surface antenna of the present invention can has optimum operation efficiency.  
         [0055]     Although the present invention has been explained in relation to its preferred embodiment, it is to be understood that many other possible modifications and variations can be made without departing from the scope of the invention as hereinafter claimed.