Patent Publication Number: US-2011063174-A1

Title: Patch antenna and wireless communications module

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the priority of Korean Patent Application No. 10-2009-0086099 filed on Sep. 11, 2009, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a patch antenna and a wireless communications module, and more particularly, to a patch antenna capable of improving antenna characteristics and achieving a reduction in the size of an antenna, and a wireless communications module. 
     2. Description of the Related Art 
     Recently, wireless communications systems have been developed to achieve a size reduction by integrating a signal creation component with a signal reception/transmission component. In order that several components are integrated so as to constitute a wireless communications system, a multilayer ceramic substrate technology is used as an integration technology. 
     However, a planar microstrip patch antenna, implemented using a multilayer ceramic substrate, suffers from limitations such as surface waves, narrow bandwidth and low efficiency due to a high dielectric constant of a dielectric body constituting the multilayer ceramic substrate. For this reason, in order to form an antenna in a multilayer ceramic substrate, studies focused on improving antenna characteristics by lowering the dielectric constant of the substrate are being conducted. 
     On the other hand, there is the need for the substrate to maintain a sufficient level of dielectric constant to form other integrated components. Therefore, research directed towards forming a substrate that can satisfy both antenna characteristics and other component characteristics is ongoing. 
     SUMMARY OF THE INVENTION 
     An aspect of the present invention provides a patch antenna capable of enhancing antenna characteristics and achieving a size reduction, and a wireless communications module. 
     According to an aspect of the present invention, there is provided a patch antenna including: a high dielectric constant substrate having a cavity; a radiator disposed on a portion of one surface of the high dielectric constant substrate corresponding to the cavity; a feeder line disposed on the high dielectric constant substrate and supplying a signal to the radiator; and a ground part disposed on the high dielectric constant substrate. 
     The cavity may have an enclosed structure. 
     The high dielectric constant substrate may be a low temperature co-fired ceramic (LTCC) multilayer substrate. 
     The feeder line may be formed in the cavity. 
     The ground part may be disposed on the other surface of the high dielectric constant substrate. 
     According to another aspect of the present invention, there is provided a wireless communications module including: a low temperature co-fired ceramic (LTCC) multilayer substrate having an enclosed cavity; a radiator disposed on a portion of one surface of the LTCC multilayer substrate corresponding to the cavity; a feeder line disposed on the LTCC multilayer substrate and supplying a signal to the radiator; a ground part disposed on the LTCC multilayer substrate; and at least one electronic device mounted on the LTCC multilayer substrate. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a cross-sectional view illustrating a patch antenna according to an exemplary embodiment of the present invention; 
         FIG. 2  is a cross-sectional view illustrating a wireless communications module according to another exemplary embodiment of the present invention; and 
         FIGS. 3A through 3F  are cross-sectional views illustrating an example of manufacturing a patch antenna according to an exemplary embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Exemplary embodiments of the present invention will now be described in detail with reference to the accompanying drawings. The invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. In the drawings, the thicknesses of layers and regions are exaggerated for clarity. Like reference numerals in the drawings denote like elements, and thus their description will be omitted. 
       FIG. 1  is a cross-sectional view illustrating a patch antenna according to an exemplary embodiment of the present invention. 
     Referring to  FIG. 1 , the patch antenna, according to this embodiment, may include a high dielectric constant substrate  110 , a radiator  120 , a feeder line  130  and a ground part  140 . 
     The high dielectric constant substrate  110  has a cavity  101  to provide a space in which the radiator  120 , the feeder line  130  and the ground part  140  may be formed. According to this embodiment, the high dielectric constant substrate  110  may be a low temperature co-fired ceramic (LTCC) multilayer substrate, and the cavity  101  may have an enclosed structure within the multilayer substrate. 
     The LTCC multilayer substrate  110  may be formed by stacking a plurality of green sheets and firing a stack of the plurality of green sheets at a low temperature. In order to form the enclosed cavity  101  inside the substrate as in this embodiment, a plurality of green sheets may be stacked, and a green sheet for covering the cavity may then be stacked thereon. According to this embodiment, the dielectric constant of the green sheets for forming the LTCC multilayer substrate may range from approximately 7 to 8. 
     The radiator  120  may be disposed on one surface of the high dielectric constant substrate  110 . Here, the location of the radiator  120  may correspond to the cavity  101 . Antenna characteristics may be significantly affected by the dielectric constant of a substrate where a radiator is formed. As in this embodiment, if the LTCC multilayer substrate is used as an antenna board, it may achieve a reduction in antenna size; however, antenna characteristics may be impaired when a radiator is formed on a printed circuit board (PCB) having a low dielectric constant. Therefore, this embodiment provides the cavity  101  inside the LTCC multilayer substrate on which the radiator  120  is formed, thereby lowering the dielectric constant of the entire substrate. Considering that the dielectric constant of air is approximately 1 in general, the dielectric constant in the cavity  101  therefore becomes 1, so that the dielectric constant of the entire LTCC multilayer substrate having the cavity  101  can be lowered as compared to the dielectric constant of an LTCC multilayer substrate without the cavity. Accordingly, the transmission characteristics of the radiator can be improved. 
     The feeder line  130  may supply a signal to the radiator  120 . The feeder line  130  may be connected directly to the radiator  120 . However, according to this embodiment, the feeder line  130  may be separated from the radiator  120  at a predetermined interval. The feeder line  130  and the radiator  120 , separated from each other at predetermined interval, may be electromagnetically coupled with each other so that a signal can flow in the radiator  120 . According to this embodiment, the feeder line  130  may be formed within the cavity  101  in the LTCC multilayer substrate  110 . 
     The radiator  120  is connected to the ground part  140  to send radio waves to the radiator  120 . According to this embodiment, the ground part  140  may be formed on the bottom surface of the LTCC multilayer substrate. 
     As described above, since the patch antenna employs the LTCC multilayer substrate, a reduction in antenna size can be achieved, and the cavity provided inside the LTCC multilayer substrate may contribute to improving the bandwidth and radiation characteristics of the antenna. 
       FIG. 2  is a cross-sectional view illustrating a wireless communications module according to another exemplary embodiment of the present invention. 
     Referring to  FIG. 2 , the wireless communications module, according to this embodiment, may include a high dielectric constant substrate  210 , a radiator  220 , a feeder line  230 , a ground part  240  and electronic devices  251  and  252 . 
     The high dielectric constant substrate  210  has a cavity  210  therein to thereby provide a space where the radiator  220 , the feeder line  230  and the ground part  240  may be formed. In this embodiment, the high dielectric constant substrate  210  may be an LTCC multilayer substrate, and the cavity  201  may be enclosed inside the multilayer substrate. 
     The LTCC multilayer substrate  210  may be formed by stacking a plurality of green sheets and firing a stack of the plurality of green sheets at a low temperature. In order to form the enclosed cavity  201  inside the substrate as in this embodiment, a plurality of green sheets may be stacked, and a green sheet for covering the cavity may then be stacked thereon. According to this embodiment, the dielectric constant of the green sheets for forming the LTCC multilayer substrate may range from approximately 7 to 8. 
     Circuit patterns, connecting the electronic devices  251  and  252  mounted on the LTCC multilayer substrate  210 , may be formed between the stacked surfaces of the stacked green sheets. The circuit patterns may be electrically connected by conductive vias penetrating the stacked green sheets. In the drawing, the detailed illustrations of the circuit patterns and the conductive vias are omitted. Furthermore, an electrode constituting a capacitor may be formed on the stacked surface of the multilayer substrate. 
     The radiator  220  may be disposed on one surface of the high dielectric constant substrate  210 . Here, the location of the radiator  220  may correspond to the cavity  201 . Antenna characteristics may be significantly affected by the dielectric constant of a substrate where a radiator is formed. If the LTCC multilayer substrate is used as an antenna board as in this embodiment, it may achieve a reduction in antenna size; however, antenna characteristics may be impaired when the radiator is formed on a printed circuit board (PCB) having a low dielectric constant. Therefore, this embodiment provides the cavity  201  inside the LTCC multilayer substrate on which the radiator  220  is formed, thereby lowering the dielectric constant of the entire substrate. Considering that the dielectric constant of air is approximately 1 in general, the dielectric constant in the cavity  201  therefore becomes 1, so that the dielectric constant of the entire LTCC multilayer substrate having the cavity  201  can be lowered as compared to the dielectric constant of an LTCC multilayer substrate without the cavity. Accordingly, the transmission characteristics of the radiator can be improved. 
     The feeder line  230  may supply a signal to the radiator  220 . The feeder line  230  may be connected directly to the radiator  220 . However, according to this embodiment, the feeder line  230  is separated from the radiator  220  at a predetermined interval. The feeder line  230  and the radiator  220 , separated from each other at predetermined interval, may be electromagnetically coupled with each other so that a signal can flow in the radiator  220 . According to this embodiment, the feeder line  230  may be formed within the cavity  201  in the LTCC multilayer substrate  210 . 
     The radiator  220  is connected to the ground part  240  to send radio waves to the radiator  220 . According to this embodiment, the ground part  240  may be formed on the bottom surface of the LTCC multilayer substrate. 
     The electronic devices  251  and  252  may be mounted on the LTCC multilayer substrate. The electronic devices may be electrically connected by the circuit patterns and the conductive vias formed in the multilayer substrate, and perform desired functions. 
     As described above, in the wireless communications modules according to this embodiment, a patch antenna is formed using a part of an LTCC multilayer substrate, and electronic devices are mounted on another part of the LTCC multilayer substrate, so that the miniaturization of the wireless communications module can be achieved. This wireless communications module may experience the deterioration in antenna characteristics due to the high dielectric constant of the LTCC multilayer substrate. In order to prevent this deterioration, this embodiment provides the cavity at a location corresponding to that of the radiator. The use of the LTCC multilayer substrate having the cavity can achieve the miniaturization of the LTCC multilayer substrate and enhance the antenna characteristics. 
       FIGS. 3A through 3F  are views illustrating an example of a process of manufacturing a patch antenna according to an exemplary embodiment of the present invention. 
       FIG. 3A  illustrates a process of stacking a first green sheet  311  and a second green sheet  312  in order to form an LTCC multilayer substrate. The first and second green sheets  311  and  322  may be made from a ceramic slurry containing ceramic powder and glass components. After a conductive pattern and a conductive via hole are formed in each of the first and second sheets  311  and  312 , the plurality of green sheets may then be stacked. Furthermore, the first green sheet  311  and the second green sheet  312  may be formed using a slurry containing tabular ceramic powder and glass components. 
       FIG. 3B  illustrates a process of stacking a third green sheet  313  and a fourth green sheet  314  in order to form the LTCC multilayer substrate. According to this embodiment, in order to provide an enclosed cavity  301  in the LTCC multilayer substrate, the third and fourth green sheets  313  and  314 , before being stacked, may be punched to form a cavity region, and then stacked. Alternatively, the cavity region may be formed by punching the third and fourth green sheets  313  and  314  after stacking the third and fourth green sheets  313  and  134 . The third and fourth green sheets  313  and  314  may be produced using a slurry of ceramic powder and glass components. 
       FIG. 3C  is a process of forming a feeder line  330  in the cavity. In this process, the feeder line  330  may be formed by using a printing process. Namely, a feeder line having a desired pattern is printed using conductive paste, and is then dried. According to this embodiment, the feeder line  330 , sullying current to a radiator, may be formed in this process in order to place it inside the cavity  301 . To place the feeder line  330  at a different location, the order of the actions of the process may be changed. For example, if the feeder line  330  is formed outside the LTCC multilayer substrate, rather than within the cavity region, the process of forming a feeder line may be performed after a process of forming a resultant stack. The feeder line may be formed by a sputtering or deposition process, other than the printing process. 
       FIG. 3D  illustrates a process of stacking a fifth green sheet  315  covering the cavity region. By this process, a stack  310   a  of the plurality of green sheets may be formed. In this embodiment, five stacked green sheets are illustrated. However, the number of green sheets being stacked may be varied according to electronic devices and circuit patterns formed inside the green sheets, provided that an enclosed cavity is provided inside the stack  310   a.    
     A process of pressing the stack  310   a  at a constant temperature and under constant pressure may be included. The pressing process may include a first preliminary pressing process and a subsequent second isostatic pressing process. The isostatic pressing process may apply pressure to the stack  310   a  within water or oil in all directions. 
       FIG. 3E  illustrates a process of firing the stack to form the LTCC multilayer substrate. The stack  310   a  formed by the process depicted in  FIG. 3D  may be co-fired at a firing temperature of the stacked green sheets. The firing process may be performed at a low temperature ranging from approximately 800° C. to 1000° C. A jig for firing may be maintained at the top and bottom of the stack. The low temperature firing process may cause the stack  310   a  of the green sheets to experience horizontal shrinkage and deformation. In order to prevent deformation caused by the firing process, the jigs for firing may be maintained under constant pressure at the uppermost layer and the lowermost layer of the stack  310   a . The stack  310   a  fixed to the jig is prevented from shrinking in the horizontal direction (i.e., X-direction and Y-direction) and shrinks only in a vertical direction (i.e., Z-direction), namely, a thickness direction. The process of co-firing the green sheets with the jigs placed at the upper and lower layers thereof to prevent the green sheets from shrinking in the horizontal direction is called a non-shrinkage process. For the non-shrinkage process, a sheet for high-temperature firing, which is not fired at a low temperature, may be used instead of the jig, and this sheet may be removed after the firing process. 
       FIG. 3F  illustrates a process of forming a radiator and a ground part on the LTCC multilayer substrate. In this process, a radiator  320  and a ground part  340  are printed using conductive paste on the sintered LTCC multilayer substrate  310 , and are then dried. The radiator  320  and the ground part  340  may be formed by a sputtering or deposition process, other than the printing process. 
     As set forth above, according to exemplary embodiments of the invention, the patch antenna and the wireless communications modules can be reduced in size, and the radiation characteristics of the antenna can be improved. 
     The present invention is not limited to the above embodiments and accompanying drawings. Namely, the thickness of a stack and the components of green sheets may be implemented variously. While the present invention has been shown and described in connection with the exemplary embodiments, it will be apparent to those skilled in the art that modifications and variations can be made without departing from the spirit and scope of the invention as defined by the appended claims.