Abstract:
A microstrip antenna is provided. The microstrip antenna includes a first substrate with a first surface and a second surface paralleled to each other, a metal ground plane with an aperture disposed on the first surface and exposing parts of the first substrate via the aperture and a metal feed line disposed on the second surface, the metal feed line has at least two intersections with the aperture on a horizontal projection plane, in order to feed a signal received or transmitted by the microstrip antenna.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a microstrip antenna. In particular, the present invention relates to an aperture coupled microstrip antenna. 
     BACKGROUND OF THE INVENTION 
     One Antenna is a coupling element or a conductive system interchanging electromagnetic energy of the circuit. When transmitting the signal, the electricity of the radio frequency is transferred by the antenna to the electromagnetic energy and is radiated to the surroundings. When receiving the signal, the electromagnetic energy received by the antenna is transferred to the electricity of the radio frequency which is provided and accessed to the processor. Generally speaking, the characteristic and the efficiency of the antenna are obtained from the parameters, such as operation frequency, radiation pattern, return loss, and antenna gain, etc., wherein the radiation pattern resulting from the antenna radiate energy in all directions is the characteristic of the antenna radiation described as the space function by the figure. 
     Due to the different communication products have different restriction or function, the antenna design for radiant or received signals have diversities, such as dipole antenna, monopole antenna, traveling-wave wire antenna, helical antenna, spiral antenna, ring antenna, microstrip antenna, and print antenna, etc. In the wireless network application, the products having excellent covering range on the horizontal plane are needed, so the dipole antenna is generally used to obtain the omnidirectional radiation pattern. However, the drawbacks of the dipole antenna lies in that the dipole antenna is protruded from the product and the product volume and the difficulty of the design are increased. The microstrip antenna has the advantages of small volume, light weight, low cost and easy production. Therefore, for further minimizing the product volume, the microstrip antenna is an adoptable means. 
     The current microstrip antenna includes many feeding methods, such as coaxial cable feed, microstrip feed, and coplanar waveguide (CPW) feed, etc., wherein the method of using coaxial cable feed is more common. Please refer to  FIG. 1 , which is a structural diagram showing a coaxial cable fed (ring-shaped) microstrip antenna according to the prior art. In  FIG. 1 , a microstrip antenna  10  includes a plane-shaped dielectric substrate  101 , a radiant metal sheet  102 , a metal ground plane  105 , and a coaxial cable  103 . The radiant metal sheet  102  is disposed on one side of the dielectric substrate  101 , and the metal ground plane  105  is stuck on another side of the dielectric substrate  101 . The coaxial cable  103  passes through the metal ground plane  105  and is connected to radiant metal sheet  102 . When receiving the signal, the electromagnetic energy radiation received by the radiant metal sheet  102  is transferred to a current of the radio frequency transmitted and accessed to the receptor by the coaxial cable  103 . In the same way, when transmitting the signal, the current signal of the radio frequency transmitted from the coaxial cable  103  is transferred by the radiant metal sheet  102  to the electromagnetic energy radiation. The drawback of the microstrip antenna fed into the coaxial cable is the narrow bandwidth, and it is generally used in the mobile phone with the narrower bandwidth demand, such as GSM system. However, the bandwidth is about 3% in the 2.4 GHz application, which is insufficient to provide enough bandwidth in the standard of 802.11b/g in the presently mainstreamed wireless network. 
     In order to increase the effective bandwidth of the microstrip antenna, another current feed method is achieved by using aperture couple. Please refer to  FIG. 2 , which is a structural diagram showing an aperture coupled microstrip antenna according to the prior art. In  FIG. 2 , the aperture coupled microstrip antenna  20  includes two substrates  2011  and  2012 , a radiant metal sheet  202  with a spectacular shape stuck on one side of the first substrate  2011 , and a metal ground plane  205  stuck on one side of the second substrate  2012  arranged near to the first substrate  2011 . The metal ground metal  205  includes an aperture  203  exposing the second substrate  2012 , and a metal feed line  204  exposing on another side of the second substrate  2012  which received and transmitted the current signal with a specific frequency through the aperture  203 . The bandwidth is increased about 6% by using microstrip antenna coupled with an aperture, but the present ring antennas in general all are the fundamental mode of the excited antenna. Moreover, the radiation pattern of the ring antenna is provided as a single direction in the fundamental mode and restricted in the application. At the same time, it remains to be insufficient for the progressive wireless surroundings. 
     It is therefore attempted by the applicant to deal with the above situation encountered in the prior art. 
     SUMMARY OF THE INVENTION 
     According to one aspect of the present invention, the microstrip antenna includes a first substrate with a first surface and a second surface paralleled to each other, a metal ground plane with an aperture disposed on the first surface and exposing parts of the first substrate via the aperture, and a metal feed line disposed on the second surface, the metal feed line has at least two intersections with the aperture on a horizontal projection plane, in order to feed a signal received or transmitted by the microstrip antenna. 
     According to another aspect of the present invention, the aperture is a rectangular aperture with a longer side and a shorter side, and the metal feed line having a first and a second intersections with the longer side of the rectangular aperture on the horizontal projection plane has an endpoint and a current feeding point, wherein the first intersection is arranged near to the endpoint, the second intersection is arranged near to the current feeding point, and the length from the endpoint to the second intersection ranged between 
                   (       2   ×   n     -   1     )     2     ×   L   ⁢           ⁢   and   ⁢           ⁢   n   ×   L     ,         
wherein n is a positive integer, L is a wavelength of an applied frequency of the microstrip antenna.
 
     According to further another aspect of the present invention, the microstrip antenna further includes a second substrate paralleled to the first substrate, wherein the second substrate has a radiant metal sheet with a ring shape. 
     According to further another aspect of the present invention, the rectangular aperture passes through the radiant metal sheet on the horizontal projection plane and lies in a radial direction of the ring shape. 
     According to further another aspect of the present invention, the metal feed line is a continuous bending segment including a first segment and a second segment, wherein the first segment passes through the endpoint and the first intersection, the second segment passes through the current feeding point and the second intersection, and the first segment and the second segment are arranged near to the inner edge and the outer edge of the ring shape, respectively. 
     According to further another aspect of the present invention, the first and the second segment are perpendicular to the longer side of the rectangular aperture on the horizontal projection plane. 
     According to further another aspect of the present invention, at least one of the first substrate and the second substrate is a dielectric substrate. 
     According to further another aspect of the present invention, the metal feed line further includes a third segment connected the first segment and the second segment. 
     According to further another aspect of the present invention, the third segment is parallel to the longer side of the rectangular aperture on the horizontal projection plane. 
     According to further another aspect of the present invention, the microstrip antenna includes a metal ground plane disposed on a first plane and having an aperture formed thereon, and a feed line disposed in a second plane paralleled to the first plane, wherein the feed line has at least two intersections with the aperture on a horizontal projection plane, in order to feed a signal received and transmitted by the microstrip antenna. 
     According to further another aspect of the present invention, the feed line is formed by a metal material. 
     According to further another aspect of the present invention, the first plane and the second plane are disposed on a dielectric substrate with a first surface and a second surface, where the first plane and the second plane are carried by the first surface and the second surface, respectively. 
     According to further another aspect of the present invention, the microstrip antenna further includes a radiant metal sheet with a ring shape formed in a third plane paralleled to the first plane, and the third plane is arranged in an opposite side of the first plane with respect to the second plane. 
     According to further another aspect of the present invention, the aperture is a rectangular aperture with a longer side and a shorter side, the longer side of the rectangular aperture is formed in a radial direction of the radiant metal sheet on the horizontal projection plane, and an extension line of the longer side passes through a center point of the radiant metal sheet. 
     According to further another aspect of the present invention, the radiant metal sheet is formed on a dielectric substrate. 
     According to further another aspect of the present invention, the first plane and the second plane are insulated by an air medium, so are the second plane and the third plane. 
     According to further another aspect of the present invention, the feed line is a continuous bending segment including a first segment and a second segment, wherein the feed line further includes a curved segment connected the first segment and the second segment. 
     According to further another aspect of the present invention, the curved fragment is an arc. 
     According to the modulation method for a microstrip antenna couple with an aperture of the present invention, the microstrip antenna includes one metal ground plane, one feed line, and one radiant metal sheet, wherein the metal ground plane is formed on a first plane, the feed line is formed on a second plane paralleled to the first plane, the radiant metal sheet is formed on a third plane paralleled to the first plane, and the second plane and the third plane are arranged on different sides of the first plane. The modulation method includes the steps of: (a) performing a simulation of the microstrip antenna in a relatively higher order operation mode, in order to obtain a current distribution of the radiant metal sheet in the relatively higher order operation mode, (b) adjusting a location and a shape of the feed line, in order that a current distribution of the feed line and the current distribution of the radiant metal sheet in the same phase area have their respective maximum values, and (c) obtaining a matched impedance by adjusting the feed line, in order to excite the microstrip antenna operated in the relatively higher order operation mode and obtain an omnidirectional radiation pattern of the microstrip antenna. 
     According to another aspect of the modulation method for a microstrip antenna coupled with an aperture of the present invention, the abovementioned step (b) further includes a step of adjusting the feed line passing through the aperture at least two times on the horizontal projection plane. 
     The above objects and advantages of the present invention will become more readily apparent to those ordinarily skilled in the art after reviewing the following detailed descriptions and accompanying drawings, in which: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a structural diagram showing a coaxial cable fed microstrip antenna according to the prior art; 
         FIG. 2  is a structural diagram showing an aperture coupled microstrip antenna according to the prior art; 
         FIG. 3  is a structural diagram showing a microstrip antenna in accordance with a first preferred embodiment of the present invention; 
         FIG. 4  is a current distribution diagram showing a relatively higher order operation mode (TM21) of the microstrip antenna on the ring-shaped radiant metal sheet in accordance with a first preferred embodiment of the present invention; 
         FIG. 5  is a current distribution diagram showing a metal feed line of the microstrip antenna satisfied the length condition in accordance with a first preferred embodiment of the present invention; 
         FIG. 6  is a data simulating diagram showing the radiation pattern result of the relatively higher order operation mode of the microstrip antenna in accordance with a first preferred embodiment of the present invention; 
         FIG. 7  is the diagram showing the frequency and the return loss of the first segment of different metal feed lines of the microstrip antenna in accordance with the a first preferred embodiment of the present invention; 
         FIG. 8  is a structural diagram showing the microstrip antenna in accordance with a second preferred embodiment of the present invention; 
         FIG. 9  is the diagram showing the frequency and the return loss of the relatively higher order operation mode of the microstrip antenna in accordance with a second embodiment of the present invention; 
         FIG. 10  is a structural diagram showing the microstrip antenna in accordance with a third preferred embodiment of the present invention; 
         FIG. 11  is a data simulating diagram showing the radiation pattern result of the relatively higher order operation mode of the microstrip antenna in accordance with the a third preferred embodiment of the present invention; and 
         FIG. 12  is the diagram showing the frequency and the return loss of the relatively higher order operation mode of the microstrip antenna with 7.5 mm of the radius (R) of the arc and 8.5 mm of the first segment (L1) 8.5 mm in accordance with a third preferred embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present invention will now be described more specifically with reference to the following embodiments. It is to be noted that the following descriptions of preferred embodiments of this invention are presented herein for purpose of illustration and description only; it is not intended to be exhaustive or to be limited to the precise form disclosed. 
     The present invention is considered to excite the relatively higher order operation mode of the ring antenna by using the aperture couple, so as to improve the single-directional radiation pattern of the aperture coupled microstrip antenna in the present fundamental mode. However, the aperture couple method according to the prior art can not always achieve the efficient impedance in the relatively higher order operation mode of the excited ring antenna. In order to overcome the difficulty, the feed line is adjusted in the present invention, the current phase distribution of the feed line is matched to the current distribution of the ring antenna. Therefore, the relatively higher order operation mode of the efficient excited ring antenna is obtained and the boardband result is successfully reached. 
     Please refer to  FIG. 3 , which is a structural diagram showing a microstrip antenna in accordance with a first preferred embodiment of the present invention. In  FIG. 3 , a microstrip antenna  30  includes a first substrate  3011  and a second substrate  3012 , wherein the second substrate  3012  is disposed and paralleled to the first substrate  3011  and the gap is reserved within two substrates, a ring-shaped radiant metal sheet  302  formed on the upper surface of the second substrate  3012 , a metal ground plane  305  stuck on the upper surface of the first substrate  3011  arranged near to the second substrate  3012 , a rectangular aperture  303  formed in the middle of the metal ground plane  305  in order to expose parts of the first substrate  3011 , and a metal feed line  304  formed in the lower surface of the first substrate  3011  fed the signal received or transmitted by the microstrip antenna. The metal feed line  304  includes a endpoint C and a feeding point F linked to a signal processor (not shown in the figure), and a bending shape is formed on the horizontal projection plane. The metal feed line  304  passes through one side of the rectangular aperture  303 , bends and passes through the opposite side of the rectangular aperture  303  on the horizontal projection plane. Then an intersection A and another intersection B are formed on the horizontal projection plane, wherein the intersection A is arranged near to the feeding point F in the metal feed line  304  and the intersection B is arranged near to the endpoint C. 
     The metal feed line  304  arranged near to the inner edge and the outer edge of the ring-shaped radiant metal sheet  320  is linear, including a first segment (L1)  3041  arranged near to the outer edge and a second segment (L2)  3043  arranged near to the inner edge, wherein the first segment (L1)  3041  passes through the intersection B and the endpoint C and the second segment (L2)  3043  passes through the intersection A and the feeding point F. 
     Please refer to  FIG. 4 , which is a current distribution diagram showing a relatively higher order operation mode (TM21) of the microstrip antenna on the ring-shaped radiant metal sheet in accordance with a first preferred embodiment of the present invention. In this figure, when operating the ring-shaped microstrip antenna in the relatively higher order operation mode, the current of the ring-shaped radiant metal sheet  302  mainly distributed in the inner edge and the outer edge of the ring is obtained, and the current direction of the inner edge and the out edge of the ring are identical. 
     Therefore, the first segment  3401  and the second segment  3403  of the metal feed line  304  are arranged and distributed in the inner edge and the outer edge of the ring-shaped radiant metal sheet  302  respectively. At the same time, if the length of the metal feed line  304  passing from the intersection A to the endpoint C is a length Ls, the current of the metal feed line  304  passing through the intersection A and the intersection B are the identical phase, and the current distribution of the ring-shaped radiant metal sheet  302  is matched successfully in the relatively higher order operation mode. 
     The abovementioned first length Ls is satisfies the relationship below: 
                     (       2   ×   n     -   1     )     2     ×   L     &lt;     L   ⁢           ⁢   s     &lt;     n   ×   L       ,         
n is a positive integer and L is a wavelength of the applied frequency of the microstrip antenna.
 
     Please refer to  FIG. 5 , which is a current distribution diagram showing a metal feed line of the microstrip antenna satisfied the length condition in accordance with a first preferred embodiment of the present invention. Here, the relatively higher order operation mode of the microstrip antenna  30  is excited successfully, and the omnidirectional radiation pattern on the horizontal projection plane is obtained. As shown in  FIG. 6 , which is a data simulating diagram showing the radiation pattern result of the relatively higher order operation mode of the microstrip antenna in accordance with a first preferred embodiment of the present invention. In the figure, the omnidirectional radiation pattern is obvious on the horizontal plane (X-Y plane), and the excellent coverage is obtained on the vertical plane (Y-Z plane and X-Z plane). 
     Please refer to  FIG. 7 , which is the diagram showing the frequency and the return loss of the first segment of different metal feed lines of the microstrip antenna in accordance with the a first preferred embodiment of the present invention. The excellent impedance in particular is obtained with about 12.5 mm or 47.5 mm of the first segment length. The bandwidth of the antenna is about 220 MHz (9%), and the biggest antenna gain is 5 dBi. Therefore, the operation efficiency of the wireless network is achieved. 
     Please refer to  FIG. 8 , which is the structural diagram showing the microstrip antenna in accordance with a second preferred embodiment of the present invention. In  FIG. 8 , a microstrip antenna  40  includes a first substrate  4011  and a second substrate  4012 , wherein the second substrate  4012  is disposed and paralleled to the first substrate  4011 , a ring-shaped radiant metal sheet  402  formed on the upper surface of the second substrate  4012 , a metal ground plane  405  stuck on the upper surface of the first substrate  4011  arranged near to the second substrate  4012 , a rectangular aperture  403  formed in the middle of the metal ground plane  405  in order to expose parts of the first substrate  4011 , and a feed line  404  is in the lower surface of the first substrate  4011 , and the feed line  404  formed on the lower surface. The feed line  404  is generally formed by a metal material in order to feed the signal received or transmitted by the microstrip antenna. The feed line  404  includes a endpoint C and a feeding point F linked to a signal processor (not shown in the figure), and a bending shape is formed on the horizontal projection plane. 
     The feed line  404  passes through one side of the rectangular aperture  403 , bends and passes through the opposite side of the rectangular aperture  403  on the horizontal projection plane. Then an intersection A and an intersection B are formed on the horizontal projection plane, wherein the intersection A is arranged near to the feeding point F in the feed line  404  and the intersection B is arranged near to the endpoint C in the feed line  404 . 
     The difference between the microstrip antenna  40  and the microstrip antenna  30  of the first embodiment simply lies in that the arrangement of the feed line  404  is the mirror image of the feed line  304  on the horizontal projection plane. The feed line  404  arranged near to the inner edge and the outer edge of ring-shaped radiant metal sheet  402  is linear, including a first segment (L1)  4041  arranged near to the inner edge of the ring-shaped radiant metal sheet  402  and a second segment (L2)  4043  arranged near to the outer edge of the ring-shape radiant metal sheet  402 , wherein the first segment (L1)  4041  passes through the intersection B and the endpoint C and the second segment (L2)  4043  passes through the intersection A and feeding point F. 
     When the length of the feed line  404  from the intersection A to the endpoint C is the length Ls, the current distribution of the ring-shaped radiant metal sheet  402  also matches successfully with that in the relatively higher order operation mode, the relatively higher order operation mode of the microstrip antenna  40  is excited successfully, and the omnidirectional radiation pattern of the microstrip antenna is obtained on the horizontal projection plane. Please refer to  FIG. 9 , wherein is the diagram showing the frequency and the return loss of the relatively higher order operation mode of the microstrip antenna in accordance with a second embodiment of the present invention. It is recognized that the bandwidth of the microstrip antenna is about 200 MHz (9%), and the biggest antenna gain is also 5 dBi. Therefore, the obvious operation efficiency of the wireless network is achieved. 
     Please refer to  FIG. 10 , which is a structural diagram showing the microstrip antenna in accordance with the third preferred embodiment of the present invention. In  FIG. 10 , a microstrip antenna  50  includes a metal ground plane  505 , a feed line  504  and a radiant metal sheet  502 , wherein the metal ground plane  505  is disposed on the first plane  5011 , the feed line  504  is disposed on the second plane  5012  paralleled to the first plane  5011 , the radiant metal sheet  502  is disposed on the third plane  5013  paralleled to the first plane  5011  and the second plane  5012  and is arranged in the opposite side of the first plane  5011  with respect to the second plane  5012 . The radiant metal sheet  502  is a ring shape, and a rectangular aperture  503  is disposed on the metal ground plane  505 . The rectangular aperture  503  passes through the ring-shaped radiant metal sheet  502  and lies in the radial direction of the ring shape on the horizontal projection plane. 
     The feed line  504  feeding the signal received or transmitted by the microstrip antenna is generally formed by a metal material. The feed line  504  includes a endpoint C and a feeding point F linked to a signal processor (not shown in the figure), and a bending shape is formed on the horizontal projection plane. The feed line  504  passes through one side of the rectangular aperture  503 , bends and passes through the opposite side of the rectangular aperture  503  on the horizontal projection plane. Then an intersection A and an intersection B are formed on the horizontal projection plane, wherein the intersection A is arranged near to the feeding point F in the feed line  504  and the intersection B is arranged near to the endpoint C in the feed line  504 . The feed line  504  arranged near to the inner edge and the outer edge of ring-shaped radiant metal sheet  502  is linear, including a first segment (L1)  5041  arranged near to the outer edge and a second segment (L2)  5043  arranged near to the inner edge, wherein the first segment (L1)  5041  passes through the intersection B and the endpoint C and the second segment (L2)  5043  passes through the intersection A and feeding point F. The first segment (L1)  5041  and the second segment (L2)  5043  are connected with a curved segment  5042  with a radius R. 
     With regard to the length Ls satisfies the relationship below: 
                     (       2   ×   n     -   1     )     2     ×   L     &lt;     L   ⁢           ⁢   s     &lt;     n   ×   L       ,         
n is a positive integer and L is a wavelength of the applied frequency of the microstrip antenna. When the length of the feed line  504  from the intersection A to the endpoint C is the length Ls, the currents of the feed line  504  between the intersection A and the intersection B have the same phase. The current distribution of the ring-shaped radiant metal sheet  502  is matched successfully in the relatively higher order operation mode, and the relatively higher order operation mode of the microstrip antenna  50  is excited successfully. Please refer to  FIG. 11 , which is the data simulating diagram showing the radiation pattern result of the relatively higher order operation mode of the microstrip antenna in accordance with a third preferred embodiment of the present invention. In the figure, the omnidirectional radiation pattern is significant on the horizontal plane (X-Y plane), and the excellent coverage is also obtained on the vertical plane (Y-Z plane and X-Z plane).
 
     Preferably, the excellent impedance in particular is obtained with 7.5 mm of the radius of the curved segment  5012  and 8.5 mm of the length of the first segment. Please refer to  FIG. 12 , which is the diagram showing the frequency and the return loss of the relatively higher order operation mode of the microstrip antenna in accordance with a third preferred embodiment of the present invention. It is known that the bandwidth of the microstrip antenna is about 200 MHz (9%), and the biggest antenna gain is 5 dBi. Therefore, the obvious operation efficiency of the wireless network is achieved. 
     In conclusion, the present invention is to arrange skillfully the feed line of the aperture coupled microtstrip antenna, so that an excellent impedance is obtained in order to excite the relatively higher order operation mode of the microstrip antenna, an excellent radiation pattern is maintained, and the bandwidth of the wireless network in the 2.4 GHz application is increased efficiently. 
     While the invention has been described in terms of what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention needs not be limited to the disclosed embodiments. On the contrary, it is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims, which are to be accorded with the broadest interpretation so as to encompass all such modifications and similar structures.