Patent Publication Number: US-8115694-B2

Title: Dual-polarized coupling device comprising annular groove fed by first and second feed conductors

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a coupling device, and more particularly to a coupling device with improved isolation. 
     2. Description of the Related Art 
       FIG. 1  shows a conventional coupling antenna  1  comprising a substrate  10 , a ground element  20 , a first feed conductor  30  and a second feed conductor  40 . The substrate  10  comprises a first surface  11  and a second surface  12 . The ground element  20  is disposed on the second surface  12 , which comprises a first portion  21 , a second portion  22  and an annular groove  23 . The annular groove  23  is located between the first portion  21  and the second portion  22  enclosing the first portion  21 . The first feed conductor  30  is disposed on the first surface  11  corresponding to the first portion  21  and the annular groove  23 . The second feed conductor  40  is disposed on the first surface  11  corresponding to the first portion  21  and the annular groove  23 . 
     When a conventional coupling antenna  1  is utilized for transmitting wireless signal, noise is generated due to poor isolation between the first feed conductor  30  and the second feed conductor  40 . 
     SUMMARY OF THE INVENTION 
     A detailed description is given in the following embodiments with reference to the accompanying drawings. 
     A coupling device is provided, comprising a substrate, a ground element, a first feed conductor and a second feed conductor. The substrate comprises a first surface and a second surface. The ground element is disposed on the second surface, wherein the ground element comprises a first portion, a second portion, an annular groove and a feed slot, the annular groove is located between the first portion and the second portion, enclosing the first portion, and a first end of the feed slot is connected to the annular groove. The first feed conductor is disposed on the first surface corresponding to the annular groove, wherein the first feed conductor couples the ground element to feed a current signal. The second feed conductor is disposed on the first surface corresponding to the feed slot, wherein second feed conductor couples the feed slot to feed a magnetic current. 
     The coupling device of the invention provides improved port isolation and polarization isolation. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein: 
         FIG. 1  shows a conventional coupling antenna; 
         FIG. 2  shows a coupling device of the invention; 
         FIG. 3  is a top view of the coupling device of the invention; 
         FIG. 4   a  shows location of a first radiation area of the invention; 
         FIG. 4   b  shows location of a second radiation area of the invention; 
         FIG. 5  shows signal reflection of the coupling device of the invention; 
         FIG. 6   a  shows divergence field on x-z plane of the first feed conductor of the invention; 
         FIG. 6   b  shows divergence field on y-z plane of the first feed conductor of the invention; 
         FIG. 7   a  shows divergence field on x-z plane of the second feed conductor of the invention; and 
         FIG. 7   b  shows divergence field on y-z plane of the second feed conductor of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following description is of the best-contemplated mode of carrying out the invention. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims. 
       FIG. 2  shows a coupling device  100  of the invention which comprises a substrate  110 , a ground element  120 , a first feed conductor  130  and a second feed conductor  140 . The substrate  110  comprises a first surface  111  and a second surface  112 . The ground element  120  is disposed on the second surface  112 . The first feed conductor  130  and the second feed conductor  140  are disposed on the first surface  111  corresponding to the ground element  120 . 
     The ground element  120  comprises a first portion  121 , a second portion  122 , an annular groove  123 , a feed slot  124  and a short circuit slot  125 . The annular groove  123  is located between the first portion  121  and the second portion  122  enclosing the first portion  121 . The first portion  121  is rectangular. The annular groove  123  defines a rectangular area. A first end  1241  of the feed slot  124  is connected to the annular groove  123 . A second end  1242  of the feed slot  124  is connected to the short circuit slot  125 . The short circuit slot  125  is circular. 
     With reference to  FIG. 3 , the substrate  110  further comprises a first side  113  and a second side  114 . The first side  113  is perpendicular to the second side  114 . The feed conductor  130  extends in a first direction y from the first side  113 . The second feed conductor  140  extends in a second direction x from the second side  114 . The first direction y is perpendicular to the second direction x. 
     The first feed conductor  130  is T-shaped, comprising a first conductive portion  131  and a first feed portion  132 . The first feed portion  132  corresponds to the annular groove  123 . The first conductive portion  131  extends in the first direction y from the first side  113  connected to the first feed portion  132 . The first conductive portion  131  is perpendicular to the first feed portion  132 . 
     With reference to  FIGS. 2 and 3 , the second feed conductor  140  comprises a second conductive portion  141 , a second feed portion  142  and a matching element  143 . The second feed portion  142  corresponds to the feed slot  124 . The second conductive portion  141  extends in the second direction x from the second side  114  connected to the second feed portion  142 . The second feed portion  142  is substantially sector-shaped, and comprises a convergent end  144  ( FIG. 3 ). The second conductive portion  141  is connected to the convergent end  144 , and the convergent end  144  corresponds to the second end  1242  ( FIG. 2 ) of the feed slot  124 . An included angle nearing the convergent end  144  is between 0° to 90°. The matching element  143  connects the second conductive portion  141  and is perpendicular thereto. 
     When the coupling device  100  ( FIG. 2 ) transmits a wireless signal, the first feed conductor  130  couples the ground element  120  ( FIG. 2 ) to feed a current signal, and the second feed conductor  140  couples the feed slot  124  to feed a magnetic current. With reference to  FIG. 4   a , after the first feed conductor  130  couples the ground  120  ( FIG. 2 ) to feed the current signal, the coupling device  100  ( FIG. 2 ) transmits a first wireless signal via a first radiation area  151  ( FIG. 4   a ). With reference to  FIG. 4   b , after the second feed conductor  140  couples the feed slot  124  to feed the magnetic current, the coupling device  100  ( FIG. 2 ) transmits a second wireless signal via a second radiation area  152  ( FIG. 4   b ). A polarization mode of the first radiation area  151  ( FIG. 4   a ) is perpendicular to a polarization mode of the second radiation area  152  ( FIG. 4   b ). A polarization direction of the first wireless signal is perpendicular to a polarization direction of the second wireless signal. 
       FIG. 5  shows signal reflection of the coupling device  100  ( FIG. 2 ) of the invention, wherein curve  301  shows a return loss (S 11 ) of a first output port, curve  302  shows a return loss (S 22 ) of a second output port, and curve  303  shows isolation (S 21 ) between the first output port and the second output port. In  FIG. 5 , the cross axle represents frequency with unit GHz, and the vertical axle represents Scattering Parameters with unit dB. As shown in  FIG. 5 , scattering parameter of the curve  303  is substantially lower than −25 dB. The coupling device  100  ( FIG. 2 ) of the invention provides improved port isolation. 
       FIG. 6   a  shows divergence field on x-z plane of the first feed conductor  130  (e.g.  FIG. 2 ) of the invention,  FIG. 6   b  shows divergence field on y-z plane of the first feed conductor  130  (e.g.  FIG. 2 ) of the invention,  FIG. 7   a  shows divergence field on x-z plane of the second feed conductor  140  (e.g.  FIG. 2 ) of the invention, and  FIG. 7   b  shows divergence field on y-z plane of the second feed conductor  140  (e.g.  FIG. 2 ) of the invention. As shown in  FIGS. 6   a ,  6   b ,  7   a  and  7   b , the coupling device  100  of the invention also provides improved polarization isolation. In  FIGS. 6   a ,  6   b ,  7   a  and  7   b , “Meas. C-pol” means “Measured co-polarized”, “Meas. X-pol” means “Measured cross-polarized”, “Sim. C-pol” means “Simulated co-polarized”, and “Sim. X-pol” means “Simulated cross-polarized”. 
     In the embodiment of the invention, the shape and location of the first feed conductor  130  (e.g.  FIG. 2 ) and the second feed conductor  140  (e.g.  FIG. 2 ) can be modified according to matching requirement. 
     The coupling device of the invention can be a feed assembly mechanism of a dual-polarized antenna or an orthomode transducer of a wave guide. 
     While the invention has been described by way of example and in terms of preferred embodiment, it is to be understood that the invention is not limited thereto. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.