Patent Publication Number: US-8542151-B2

Title: Antenna module and antenna unit thereof

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an antenna module, and in particular relates to an antenna module and cavity-backed stacked planar antenna unit thereof. 
     2. Description of the Related Art 
       FIG. 1  shows a conventional antenna  1 , including an antenna substrate  10 , a feed substrate  20 , a microstrip patch  30 , a ground plane  40  and a microstrip feed line  50 . The antenna substrate  10  includes a first surface  11  and a second surface  12 . The feed substrate  20  includes a third surface  21  and a fourth surface  22 . The microstrip patch  30  is disposed on the first surface  11 . The ground plane  40  is disposed on the third surface  21 . The second surface  12  is connected to the ground plane  40 . A coupling aperture  41  is formed on the ground plane  40 . The microstrip feed line  50  is disposed on the fourth surface  22 . The microstrip feed line  50  feeds wireless signals via the coupling aperture  41  to the microstrip patch  30 . Conventional antennas typically have small bandwidths, unignored back radiation and unwanted surface wave radiation issues. 
     BRIEF SUMMARY OF THE INVENTION 
     An antenna unit is provided. The antenna unit includes a first substrate, a first conductive layer, a second conductive layer, a plurality of conductive vias, a feed conductor and a patch. The first substrate includes a first surface and a second surface, wherein the first surface is opposite to the second surface. The first conductive layer is disposed on the first surface. The second conductive layer is disposed on the second surface, wherein an opening is formed on the second conductive layer, and the opening has an opening edge. The conductive vias are formed in the first substrate and connect the first conductive layer to the second conductive layer, wherein the conductive vias surround the opening to define a cavity. The feed conductor extends above the opening to feed a wireless signal to the antenna unit. The patch is disposed above the opening and is separated from the feed conductor. 
     Utilizing the antenna unit of the embodiment of the invention, an electric field Ē is formed between the patch, the feed conductor and the opening edge of the second conductive layer to enhance the oblique resonant directions. With the oblique resonant directions, the antenna unit of the embodiment of the invention has broader beamwidth. Additionally, the antenna unit or antenna array module of the embodiments of the invention can be easily mass produced by a standard low-cost PCB process. 
     A detailed description is given in the following embodiments with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present 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 antenna; 
         FIG. 2  shows an antenna unit of an embodiment of the invention; 
         FIG. 3  is a sectional view along direction III-III of  FIG. 2 ; 
         FIG. 4  is a top view of the antenna unit; 
         FIG. 5  shows the input impedance (S 11 ) of the antenna unit; 
         FIG. 6   a  shows the E and H plane antenna patterns at 57 GHz of the antenna unit; 
         FIG. 6   b  shows the small back radiation characteristic at 57 GHz of the antenna unit; 
         FIG. 7   a  shows the E and H plane antenna patterns at 66 GHz of the antenna unit; 
         FIG. 7   b  shows the small back radiation characteristic at 66 GHz of the antenna unit; and 
         FIG. 8  shows an antenna array module of an embodiment 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 an antenna unit  100  of an embodiment of the invention. The antenna unit  100  includes a first substrate  110 , a second substrate  120 , a first conductive layer  130 , a second conductive layer  140 , a plurality of conductive vias  150 , a feed conductor  160  and a patch  170 . The first substrate  110  includes a first surface  111  and a second surface  112 , wherein the first surface  111  is opposite to the second surface  112 . The second substrate  120  includes a third surface  121  and a fourth surface  122 , the third surface  121  is opposite to the fourth surface  122 . The first conductive layer  130  is disposed on the first surface  111 . The second conductive layer  140  is disposed on the second surface  112 , wherein an opening  141  is formed on the second conductive layer  140 , and the opening  141  has an opening edge  142 . The conductive vias  150  are formed in the first substrate  110  and connect the first conductive layer  130  to the second conductive layer  140 , wherein the conductive vias  150  surrounds the opening  141  to define a cavity  151 . The cavity  151  is formed by the conductive vias  150  and the first conductive layer  130 . The feed conductor  160  extends above the opening  141  to feed a wireless signal to the antenna unit  100 . The patch  170  is disposed above the opening  141  and is separated from the feed conductor  160 . In this embodiment, the first conductive layer  130  and the second conductive layer  140  are ground layers. 
       FIG. 3  is a sectional view along direction III-III of  FIG. 2 . As shown in  FIG. 3 , the patch  170  is disposed on the fourth surface  122 , and the third surface  121  contacts the second conductive layer  140 . In this embodiment, the feed conductor  160  is embedded in the second substrate  120 . 
       FIG. 4  is a top view of the antenna unit  100 . The feed conductor  160  is T shaped, and includes a first section  161  and a second section  162 , wherein an end of the second section  162  is connected to the first section  161 . The patch  170  is rectangular, and has a major axis  171 , and the first section  161  of the feed conductor  160  is parallel to the major axis  171 . The opening  141  is rectangular. A space d 1  between the first section  161  and the patch  170  is about 0.15λ, and λ is a wavelength of the wireless signal. By changing the space d 1  or the width of the opening  141  which is parallel to axis  171 , the impedance matching may be modified. By changing the length of the opening  141  which is perpendicular to axis  171 , the resonated center frequency of the antenna may be shifted. By changing the distance between the patch  170  and the opening edge  142 , the bandwidth of the antenna unit may be modified. With further reference to  FIG. 3 , a height h between the first conductive layer  130  and the second conductive layer  140  is about 0.25λ. A gap g between each two conductive vias is designed smaller than λ/8. The height h and gap g may also be modified. 
     With reference to  FIG. 3 , an electric field Ē is formed between the patch  170  and the opening edge  142 , the electric field Ē has oblique resonant direction relative to the second conductive layer  140 . With the oblique resonant direction, the antenna unit of the embodiment of the invention has broader beamwidth.  FIG. 5  shows the input return loss (S 11 ) of the antenna unit  100 , wherein the antenna unit  100  has an ultra-large fractional bandwidth which is near 25%.  FIG. 6   a  shows the E and H plane antenna patterns at 57 GHz of the antenna unit  100 .  FIG. 6   b  shows the small back radiation characteristic at 57 GHz of the antenna unit  100 .  FIG. 7   a  shows the E and H plane antenna patterns at 66 GHz of the antenna unit  100 .  FIG. 7   b  shows the small back radiation characteristic at 66 GHz of the antenna unit  100 . As shown in  FIGS. 6   a ,  6   b ,  7   a  and  7   b , the antenna unit of the invention provides a peak gain which is higher than 6 dBi. 
     In the embodiment above, the cavity  151  and the opening  141  are rectangular. However, the invention is not limited thereto. The rectangular cavity  151  and opening  141  may also be implemented by circular, elliptic and other opening shapes. 
     In the embodiment above, the feed conductor  160  is T shaped. However, the invention is not limited thereto. The feed conductor  160  here is embedded in the second substrate  120 , strip-line structure. However, the invention is not limited thereby and other transmission line structures may also be implemented. Additionally, the extending direction or shape of the second section  162  may also be modified. 
     In the embodiment above, the patch  170  is disposed on the fourth surface  122 . However, the invention is not limited thereby. The patch  170  and the feed conductor  160  may also be located on a same plane. For example, both the patch  170  and the feed conductor  160  may be disposed on the fourth surface  122 . Or, the patch  170  may be disposed on the third surface  121 , and the feed conductor  160  is placed on the fourth surface  122 . 
       FIG. 8  shows an antenna array module  200  of an embodiment of the invention, wherein the antenna units  100  of the embodiment of the invention are formed on a same first substrate  110 , second substrate  120 , first conductive layer  130  and second conductive layer  140 . The antenna array module  200  of the embodiment of the invention provides improved isolation between the antenna units  100  (more than 15 dB). In this embodiment, spaces between the antenna units  100  are nearly 0.5λ. The antenna unit  100  or the antenna array module  200  of the embodiments of the invention may be easily mass produced by a standard low-cost PCB process. 
     Use of ordinal terms such as “first”, “second”, “third”, etc., in the claims to modify a claim element does not by itself connote any priority, precedence, or order of one claim element over another or the temporal order in which acts of a method are performed, but are used merely as labels to distinguish one claim element having a certain name from another element having a same name (but for use of the ordinal term) to distinguish the claim elements. 
     While the invention has been described by way of example and in terms of the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. 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.