Patent Publication Number: US-11394118-B2

Title: Loop-like dual-antenna system

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority benefit of Taiwan applications serial No. 108138316, filed on Oct. 23, 2019. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of specification. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The invention relates to a loop-like dual-antenna system. 
     Description of the Related Art 
     With the development trend of 5G communication, future 5G communication requires higher data rate and more stable signal quality. Therefore, Multiple Input Multiple Output (MIMO) has become one of the cores of 5G technology. The antenna design space also continues to shrink. Multiple antennas need to be housed in a limited space, which also causes degradation of isolation and affects radiation efficiency. 
     Taking the dual-antenna structure as an example, in order to improve the isolation between the dual antennas, the spacing of the dual-antenna unit is generally increased, or a decoupling element is added between the dual-antenna unit, such as resistive connecting elements or capacitive connecting elements to improve the isolation between the dual-antenna units. These dual-antenna structures can all be planar structures, and the end of the dual-antenna unit usually maintains an open structure without any components attached. In the design of the decoupling element, the decoupling element is still separate from the main radiator of the antenna unit. In addition to the low degree of integration with the dual-antenna unit, the distance between the dual-antenna units will also increase the overall size of the dual-antenna structure due to the additional decoupling element. 
     BRIEF SUMMARY OF THE INVENTION 
     According to an aspect, a loop-like dual-antenna system is provided. The loop-like dual-antenna system comprises: a dielectric substrate, includes a first surface and a second surface opposite to each other; a loop radiating element, disposed on the first surface of the dielectric substrate, the loop radiating element includes a first radiating part with two ends and a second radiating part opposite to the first radiating part; a first signal source, disposed on the first surface of the dielectric substrate and electrically connected to two ends of the first radiating part; a grounding part, disposed on the second surface of the dielectric substrate and disposed on one side of the dielectric substrate away from the first signal source; a coupling matching element, disposed on the second surface of the dielectric substrate and adjacent to the grounding part, for coupling to and exciting the second radiating part; and a second signal source, disposed on the second surface of the dielectric substrate, and electrically connected to the coupling matching element and the grounding part. 
     In summary, the loop-like dual-antenna system in the embodiments uses the structural design that two signal sources share the loop radiating element, which effectively reduces the overall size of the loop-like dual-antenna system. The position of current null excited by one of the signal sources is located at the maximum current areas excited by the other signal source, therefore, the isolation between the antennas is enhanced, and the loop-like dual-antenna system has advantages in a single antenna size and good radiation characteristics at the same time. 
     These and other features, aspects and advantages of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic structural diagram of a loop-like dual-antenna system according to an embodiment. 
         FIG. 2  is a top view of the loop-like dual-antenna system according to an embodiment. 
         FIG. 3  is a bottom view of the loop-like dual-antenna system according to an embodiment. 
         FIG. 4  is a schematic structural diagram of the loop-like dual-antenna system disposed on a system ground plane according to an embodiment. 
         FIG. 5  is a schematic diagram of current distribution of a first signal source of the loop-like dual-antenna system according to an embodiment. 
         FIG. 6  is a schematic diagram of current distribution of a second signal source of the loop-like dual-antenna system according to an embodiment. 
         FIG. 7  is a schematic structural diagram of a loop-like dual-antenna system according to another embodiment. 
         FIG. 8  is an S-parameter simulation schematic diagram of the loop-like dual-antenna system according to an embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       FIG. 1  is a schematic structural diagram of a loop-like dual-antenna system according to an embodiment.  FIG. 2  is a top view of the loop-like dual-antenna system according to an embodiment.  FIG. 3  is a bottom view of the loop-like dual-antenna system according to an embodiment. Please refer to  FIG. 1 ,  FIG. 2  and  FIG. 3 . A loop-like dual-antenna system  10  includes a dielectric substrate  12 , a loop radiating element  14 , a first signal source  16 , a grounding part  18 , a coupling matching element  20 , and a second signal source  22 . The dielectric substrate  12  includes a first surface  121  and a second surface  122 . The loop radiating element  14  and the first signal source  16  are disposed on the first surface  121  of the dielectric substrate  12 , and the grounding part  18 , the coupling matching element  20  and the second signal source  22  are disposed on the second surface  122  of the dielectric substrate  12 . 
     In the loop-like dual-antenna system  10 , the dielectric substrate  12  has a first long side  123  and a second long side  124 . The loop radiating element  14  includes a first radiating part  141  with two ends  143 ,  144  and a second radiating part  142  opposite to the first radiating part  141 . The first radiating part  141  is close to the first long side  123  of the dielectric substrate  12 , the second radiating part  142  is close to the second long side  124  of the dielectric substrate  12 , and the first radiating part  141  and the second radiating part  142  form a loop shape together. In one embodiment, the loop shape is a rectangular structure designed integrally. 
     The first signal source  16  is located on the first surface  121  of the dielectric substrate  12 , and is electrically connected between two ends  143  and  144  of the first radiating part  141 . In one embodiment, since the two ends  143  and  144  are at the geometric center of the first radiating part  141 , the first signal source  16  is located at the center of the first radiating part  141 . 
     The grounding part  18  is located on the second surface  122  of the dielectric substrate  12 , and disposed on one side of the dielectric substrate  12  away from the first signal source  16 . In one embodiment, the sides of the dielectric substrate  12  include the first long side  123  and the second long side  124 , and the grounding part  18  is located on the edge of the second long side  124  of the dielectric substrate  12 . The coupling matching element  20  is located on the second surface  122  of the dielectric substrate  12  and adjacent to the grounding part  18 . The length direction of the coupling matching element  20  is parallel to the second long side  124 , so that an appropriate interval always exists between the coupling matching element  20  and the grounding part  18 . The second signal source  22  on the second surface  122  of the dielectric substrate  12  is electrically connected to the coupling matching element  20  and the grounding part  18 , and then the second signal source  22  is coupled to and excites the second radiating part  142  through the coupling matching element  20 . 
     In an embodiment, the first signal source  16  is located in the first radiating part  141 , the first signal source  16  is adjacent to the second signal source  22 , and the position of the first signal source  16  is the position of the current null excited by the second signal source  22 . In detail, the first signal source  16  is located at the center position of the first radiating part  141 , and the center position of the first radiating part  141  is the position of the current null excited by the second signal source  22 . At least a part of the second signal source  22  overlaps with the vertical projection of the second radiating part  142  on the second surface  122  of the dielectric substrate  12 , and the position of the second signal source  22  is the maximum current area excited by the first signal source  16 . 
     In an embodiment, the overall antenna height of the loop-like dual-antenna system  10  is between 0.024 times to 0.056 times the wavelength of the operating frequencies of the antenna system (0.024λ to 0.056λ). 
     In the loop-like dual-antenna system  10  of an embodiment, when taking the connection line between the first signal source  16  and the second signal source  22  as a central axis, the loop radiating element  14  on the first surface  121  of the dielectric substrate  12 , the coupling matching element  20  on the second surface  122  of the dielectric substrate  12 , and the grounding part  18  are designed to be left-right symmetrical structure. 
     In an embodiment, the loop radiating element  14 , the coupling matching element  20 , and the grounding part  18  are made of a conductive material, such as copper, silver, aluminum, iron, or an alloy thereof, but are not limited herein. 
       FIG. 4  is a schematic structural diagram of the loop-like dual-antenna system disposed on a system ground plane according to an embodiment. Please refer to  FIG. 1  to  FIG. 4 . The grounding part  18  is further electrically connected to a system ground plane  32 , which is located on a side of the second long side  124  of the dielectric substrate  12 . In an embodiment, the system ground plane  32  is an independent metal piece or a metal plane attached to an electronic device. For example, the system ground plane  32  is a grounding part of a metal case of an electronic device or a metal part inside the plastic case of the electronic device, which is not limited herein. The size of the system ground plane  32  drawn is for illustration only, which is adjustable according to the application of the loop-like dual-antenna system  10 . 
     The first signal source  16  and the second signal source  22  adjacent to each other are respectively located on the first surface  121  and the second surface  122  of the dielectric substrate  12 , and share the loop radiating element  14 . The first signal source  16  is directly electrically connected to the loop radiating element  14  to directly feed the signal to the loop radiating element  14 . The second signal source  22  is a distributed capacitive coupling signal source formed by the coupling matching element  20  and the loop radiating element  14  when the signal of the first signal source  16  is fed into the loop radiating element  14 . Therefore, it can be known from the above that the first signal source  16  and the second signal source  22  share the same loop radiating element  14 , and each of the first signal source  16  and the second signal source  22  generates a resonant mode of about one wavelength at the operating frequencies. In an embodiment, the aforementioned operating frequency band is an operating frequency band covering 2.4 GHz to 2.5 GHz. 
     When the first signal source  16  and the second signal source  22  are excited, the loop-like dual-antenna system  10  generates the resonant mode of about one wavelength and generates two current nulls on the resonant path. In detail, please referring to  FIG. 5 , when the first signal source  16  is excited, the surface currents of the loop radiating element  14  generates two current nulls  24  and  24 ′, which are respectively located at two sides where the first radiating part  141  and the second radiating part  142  are connected. Please refer to  FIG. 6 . When the second signal source  22  is excited, the surface current of the loop radiating element  14  also generates two current nulls  26  and  26 ′, which are respectively located on the geometric center position of the first radiating part  141  and the second radiating part  142 . Please refer to  FIG. 5  and  FIG. 6  at the same time, the positions of the current nulls  24  and  24 ′ excited by the first signal source  16  are located at two maximum current areas  30 ,  30 ′ excited by the second signal source  22 , and the positions of the two current nulls  26 ,  26 ′ excited by the second signal source  22  are located at two maximum current areas  28 ,  28 ′ excited by the first signal source  16 . Thereby, the isolation of the loop-like dual-antenna system  10  is greatly improved. At the same time, the two radiation fields of the loop-like dual-antenna system  10  also achieves orthogonal polarization characteristics. 
       FIG. 7  is a schematic structural diagram of a loop-like dual-antenna system according to another embodiment. Please refer to  FIG. 7 . In the loop-like dual-antenna system  10 , the loop radiating element  14  has different implementations. The loop radiating element  14  on the first surface  121  of the dielectric substrate  12  is an elliptical loop design. The loop radiating element  14  includes the first radiating part  141  with two ends  143 ,  144  and the second radiating part  142  opposite to the first radiating part  141 . The first radiating part  141  is near the first long side  123  of the dielectric substrate  12 , the second radiating part  142  is near the second long side  124  of the dielectric substrate  12 , and the first signal source  16  is electrically connected between the two ends  143  and  144  of the first radiating part  141 . Except that the shape design of the loop radiating element  14  is different, the rest of the structure and the actuation system are the same as those in the embodiment shown in  FIG. 1 . The loop shape of the loop radiating element  14  can be designed in different shapes according to actual needs, and is not limited to the rectangle shape shown in  FIG. 2  and the ellipse shape shown in  FIG. 7 . 
     Please refer to  FIG. 1  to  FIG. 4 . The actual overall size of the loop-like dual-antenna system  10  is 40 mm in length, 5 mm in width, and the antenna area is 200 square millimeters, which is smaller than the 300-320 square millimeters of a single antenna commonly used in the industry, therefore, a dual-antenna system is achieved by using only a single antenna space, which is actually a structural design of a small-sized dual-antenna system. Specifically, the loop radiating element  14  formed by the first radiating part  141  and the second radiating part  142  has a length of 40 mm, a height of 4.5 mm. In an embodiment, the coupling matching element  20  has a length of 10 mm and is used to optimize the impedance matching of the antenna in 2.4 GHz frequency band. The distance between the first signal source  16  and the second signal source  22  is 2 mm. 
       FIG. 8  is an S-parameter simulation schematic diagram of the loop-like dual-antenna system according to an embodiment. Please refer to  FIG. 1  to  FIG. 4  and  FIG. 8  at the same time. In order to prove that the loop-like dual-antenna system  10  does have a good isolation effect, the loop-like dual-antenna system  10  of the aforementioned size is used to simulate S-parameters. In the operating band (2.4 GHz), the S-parameter results are shown in  FIG. 8 . The isolation curve (S 21 ) is better than 30 dB in the operating band, and the reflection coefficients (S 11 , S 22 ) of the antenna operating band is less than −10 dB, so it has good isolation in the 2.4 GHz band. Therefore, the loop-like dual-antenna system  10  in the embodiments has good isolation in the single frequency band. 
     In summary, in order to solve the problem of isolation between dual antennas, the loop-like dual-antenna system in the disclosure uses the structural design that the first signal source and the second signal source share the loop radiating element, effectively reduce the overall size of the loop-like dual-antenna system, and the position of the current null excited by the first signal source is located at the maximum current area excited by the second signal source, and vice versa. Therefore, the isolation between antennas is enhanced, so that the loop-like dual-antenna system has the advantages of a single antenna size and good radiation characteristics at the same time, which is very suitable for application in electronic devices with small antennas and multiple antennas. 
     Although the present invention has been described in considerable detail with reference to certain preferred embodiments thereof, the disclosure is not for limiting the scope. Persons having ordinary skill in the art may make various modifications and changes without departing from the scope. Therefore, the scope of the appended claims should not be limited to the description of the preferred embodiments described above.