Patent Publication Number: US-2023163466-A1

Title: Antenna Unit and Electronic Device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a national stage of International Application No. PCT/CN2021/082974, filed on Mar. 25, 2021, which claims priority to Chinese Patent Application No. 202010323918.5, filed on Apr. 22, 2020. Both of the aforementioned applications are hereby incorporated by reference in their entireties. 
    
    
     TECHNICAL FIELD 
     This application relates to the field of electronic technologies, and in particular, to an antenna unit and an electronic device. 
     BACKGROUND 
     With development of a full screen of an electronic device, a strain is increasingly put on space of an antenna. In addition, to meet various user requirements, there are an increasingly large quantity of antennas. Therefore, how to place a larger quantity of antennas in limited space and ensure that each antenna has good isolation and a low envelope correlation coefficient ECC is an urgent problem that needs to be resolved currently. 
     SUMMARY 
     This application provides an antenna unit and an electronic device, to implement two antennas with high isolation and a low envelope correlation coefficient ECC based on a same loop antenna. In this way, good antenna performance is ensured, and utilization of antenna space is improved. 
     According to a first aspect, this application provides an antenna unit, including a first loop branch, a first feed, and a second feed. The first loop branch includes a first radiation section, a second radiation section, and a third radiation section. The first radiation section is in a ring shape, and the first radiation section is not closed. One end of the first radiation section is connected to the second radiation section, and the other end of the first radiation section is connected to the third radiation section. The second radiation section and the third radiation section are symmetrically disposed in a first direction. There is an opening between the second radiation section and the third radiation section, and both the second radiation section and the third radiation section are grounded. The first feed is symmetrically connected to the first radiation section in the first direction. A second contact point and a third contact point are symmetrical in the first direction, and a distance between the second contact point and the third contact point falls within a first preset range. The second contact point is a contact point between the second feed and the second radiation section. The third contact point is a contact point between the second feed and the third radiation section. 
     According to the antenna unit provided in the first aspect, based on a symmetrical arrangement of a same loop antenna (namely, the first loop branch), the antenna unit respectively excites a signal at a C-mode port and a signal at a D-mode port of the loop antenna by using two feeds, so that the signal at the C-mode port is self-canceled at the D-mode port, and the signal at the D-mode port is self-canceled at the C-mode port, to implement signal isolation between the two ports, and the signal at the C-mode port and the signal at the D-mode port are complementary to each other in different radiation directions, to implement two antennas with high isolation and a low ECC. In this way, good antenna performance can be ensured, so that an electronic device can fully use the antenna unit in limited space to implement various scenarios. In addition, the electronic device can include a larger quantity of antennas in the limited space, to improve utilization of antenna space. 
     In a possible design, the second radiation section and the third radiation section are disposed inside the first radiation section in the first direction, to help arrange the antenna unit in relatively small space, so as to improve space utilization of the antenna unit; the second radiation section and the third radiation section are disposed outside the first radiation section in the first direction, to provide a possibility for implementing the antenna unit, so that the antenna unit can meet a space requirement in an actual situation; the second radiation section and the third radiation section are disposed to extend from an inside of the first radiation section to an outside of the first radiation section in the first direction, to provide a possibility for implementing the antenna unit, so that the antenna unit can meet a space requirement in an actual situation; or the second radiation section and the third radiation section are disposed to extend from an inside of the first radiation section to an outside of the first radiation section in a direction opposite to the first direction, to provide a possibility for implementing the antenna unit, so that the antenna unit can meet a space requirement in an actual situation. 
     In a possible design, the second radiation section is connected to N first ground points of the electronic device, and the third radiation section is connected to N second ground points of the electronic device, where N is a positive integer. 
     In a possible design, when the second radiation section and the third radiation section are disposed on a bracket, the first ground point and the second ground point are disposed on the bracket. In this case, each of the first ground point and the second ground point needs to be connected to a ground of a printed circuit board by using a spring on the bracket, and no trace needs to be arranged on the bracket. Alternatively, the first ground point and the second ground point are disposed on a printed circuit board in the electronic device. In this way, a spring is saved, and this solution is simple and easy to implement. 
     In a possible design, both the second radiation section and the third radiation section are connected to a ground region of the electronic device, and the ground region is symmetrically disposed in the first direction. 
     In a possible design, there is one first contact point between the first feed and the first radiation section, and the first contact point is a symmetry point of the first radiation section, and is located on the first radiation section. 
     In a possible design, there are P (an even number) first contact points between the first feed and the first radiation section, the P (an even number) first contact points are symmetrically disposed in the first direction, and the P (an even number) first contact points are located on a radiation section, in the first radiation section, on which a symmetry point of the first radiation section is located. 
     In a possible design, there are Q (an odd number) first contact points between the first feed and the first radiation section, where the odd number Q is greater than or equal to 3, the Q (an odd number) first contact points include one first contact point and P (an even number) first contact points, the one first contact point is a symmetry point of the first radiation section, and is located on the first radiation section, the P (an even number) first contact points are symmetrically disposed in the first direction, and the P (an even number) first contact points are located on a radiation section, in the first radiation section, on which the symmetry point of the first radiation section is located. 
     In a possible design, a first matching component is disposed between the first feed and the first contact point, to adjust a frequency band of the antenna unit, so that the first feed can obtain a better pattern and better cross polarization performance, to improve performance of the antenna unit. 
     In a possible design, a second matching component is disposed between the second feed and the second contact point, and/or a second matching component is disposed between the second feed and the third contact point, to adjust the frequency band of the antenna unit, so that the second feed can obtain a better pattern and better cross polarization performance, to improve the performance of the antenna unit. 
     In a possible design, the antenna unit further includes a first non-conductive support member, a first conductive member, and a second conductive member; and the first conductive member and the second conductive member are suspended by using the first non-conductive support member, the first conductive member and the second conductive member are symmetrically disposed in the first direction, a length of the first conductive member is a ½ wavelength, a length of the second conductive member is a ½ wavelength, and the wavelength is a wavelength corresponding to any frequency in an operating frequency band of the antenna unit. Therefore, the first conductive member and the second conductive member can extend a bandwidth of the antenna unit, to improve the performance of the antenna unit. Usually, larger widths of the first conductive member and the second conductive member indicate better performance of the antenna unit. 
     In a possible design, the first conductive member and the second conductive member are disposed outside or inside the first radiation section. 
     In a possible design, the first non-conductive support member includes at least one of a glass battery cover, a plastic battery cover, or an explosion-proof film in the electronic device. 
     According to a second aspect, this application provides an antenna unit, including a second loop branch, a feeding branch, a third feed, and a fourth feed. The second loop branch includes a fourth radiation section, a fifth radiation section, and a sixth radiation section. The fourth radiation section is in a ring shape, and the fourth radiation section is not closed. One end of the fourth radiation section is connected to the fifth radiation section, and the other end of the fourth radiation section is connected to the sixth radiation section. The fifth radiation section and the sixth radiation section are symmetrically disposed in a second direction. There is an opening between the fifth radiation section and the sixth radiation section, and both the fifth radiation section and the sixth radiation section are grounded. The feeding branch is symmetrically disposed in the second direction, and an area of a part that is of the feeding branch and that faces the fifth radiation section is equal to an area of a part that is of the feeding branch and that faces the sixth radiation section. The third feed is symmetrically connected to the feeding branch in the second direction. A fifth contact point and a sixth contact point are symmetrical in the second direction, and a distance between the fifth contact point and the sixth contact point falls within a second preset range. The fifth contact point is a contact point between the fourth feed and the fifth radiation section. The sixth contact point is a contact point between the fourth feed and the sixth radiation section. 
     According to the antenna unit provided in the second aspect, based on a symmetrical arrangement of a same loop antenna (namely, the second loop branch and the feeding branch), the antenna unit respectively excites a signal at a C-mode port and a signal at a D-mode port of the loop antenna by using two feeds, so that the signal at the C-mode port is self-canceled at the D-mode port, and the signal at the D-mode port is self-canceled at the C-mode port, to implement signal isolation between the two ports, and the signal at the C-mode port and the signal at the D-mode port are complementary to each other in different radiation directions, to implement two antennas with high isolation and a low ECC. In this way, good antenna performance can be ensured, so that an electronic device can fully use the antenna unit in limited space to implement various scenarios. In addition, the electronic device can include a larger quantity of antennas in the limited space, to improve utilization of antenna space. 
     In a possible design, the fifth radiation section and the sixth radiation section are disposed inside the fourth radiation section in the second direction, to help arrange the antenna unit in relatively small space, so as to improve space utilization of the antenna unit; the fifth radiation section and the sixth radiation section are disposed outside the fourth radiation section in the second direction, to provide a possibility for implementing the antenna unit, so that the antenna unit can meet a space requirement in an actual situation; the fifth radiation section and the sixth radiation section are disposed to extend from an inside of the fourth radiation section to an outside of the fourth radiation section in the second direction, to provide a possibility for implementing the antenna unit, so that the antenna unit can meet a space requirement in an actual situation; or the fifth radiation section and the sixth radiation section are disposed to extend from an inside of the fourth radiation section to an outside of the fourth radiation section in a direction opposite to the second direction, to provide a possibility for implementing the antenna unit, so that the antenna unit can meet a space requirement in an actual situation. 
     In a possible design, the fifth radiation section is connected to M third ground points of the electronic device, and the sixth radiation section is connected to M fourth ground points of the electronic device, where M is a positive integer. 
     In a possible design, when the fifth radiation section and the sixth radiation section are disposed on a bracket, the third ground point and the fourth ground point are disposed on the bracket. In this case, each of the third ground point and the fourth ground point needs to be connected to a ground of a printed circuit board by using a spring on the bracket, and no trace needs to be arranged on the bracket. Alternatively, the third ground point and the fourth ground point are disposed on a printed circuit board in the electronic device. In this way, a spring is saved, and this solution is simple and easy to implement. 
     In a possible design, both the fifth radiation section and the sixth radiation section are connected to a ground region of the electronic device, and the ground region is symmetrically disposed in the second direction. 
     In a possible design, the feeding branch is disposed inside the fourth radiation section in the second direction, so that inner space of the fourth radiation section can be fully used to dispose the feeding branch, the fifth radiation section, and the sixth radiation section, to help arrange the antenna unit in relatively small space, so as to improve space utilization of the antenna unit; the feeding branch is disposed outside the fourth radiation section in the second direction, to provide a possibility for implementing the antenna unit, so that the antenna unit can meet a space requirement in an actual situation; or the feeding branch is disposed to extend from an inside of the fourth radiation section to an outside of the fourth radiation section in the second direction, to provide a possibility for implementing the antenna unit, so that the antenna unit can meet a space requirement in an actual situation. 
     In a possible design, an area of a part that is of the feeding branch and that faces the fifth radiation section in the second direction is equal to an area of a part that is of the feeding branch and that faces the sixth radiation section in the second direction; or an area of a part that is of the feeding branch and that faces the fifth radiation section in a direction perpendicular to the second direction is equal to an area of a part that is of the feeding branch and that faces the sixth radiation section in the direction perpendicular to the second direction, to ensure symmetry of the feeding branch. 
     In a possible design, there is at least one fourth contact point between the third feed and the feeding branch. 
     In a possible design, a third matching component is disposed between the third feed and the fourth contact point, to adjust a frequency band of the antenna unit, so that the third feed can obtain a better pattern and better cross polarization performance, to improve performance of the antenna unit. 
     In a possible design, a fourth matching component is disposed between the fourth feed and the fifth contact point, and/or a fourth matching component is disposed between the fourth feed and the sixth contact point, to adjust the frequency band of the antenna unit, so that the fourth feed can obtain a better pattern and better cross polarization performance, to improve the performance of the antenna unit. 
     In a possible design, the antenna unit further includes a second non-conductive support member, a third conductive member, and a fourth conductive member; and the third conductive member and the fourth conductive member are suspended by using the second non-conductive support member, the third conductive member and the fourth conductive member are symmetrically disposed in the second direction, a length of the third conductive member is a ½ wavelength, a length of the fourth conductive member is a ½ wavelength, and the wavelength is a wavelength corresponding to any frequency in an operating frequency band of the antenna unit. Therefore, the third conductive member and the fourth conductive member can extend a bandwidth of the antenna unit, to improve the performance of the antenna unit. Usually, larger widths of the third conductive member and the fourth conductive member indicate better performance of the antenna unit. 
     In a possible design, the third conductive member and the fourth conductive member are disposed outside or inside the fourth radiation section. 
     In a possible design, the second non-conductive support member includes at least one of a glass battery cover, a plastic battery cover, or an explosion-proof film in the electronic device. 
     According to a third aspect, this application provides an electronic device, including a printed circuit board and the antenna unit in any one of the first aspect and the possible designs of the first aspect, and/or a printed circuit board and the antenna unit in any one of the second aspect and the possible designs of the second aspect. A feed point, a tuned circuit, and a matching circuit in the antenna unit are disposed on the printed circuit board, and a ground point in the antenna unit and the printed circuit board share a ground. 
     For beneficial effects of the electronic device provided in the third aspect and the possible designs of the third aspect, refer to the first aspect and the possible implementations of the first aspect, and/or for beneficial effects of the electronic device provided in the third aspect and the possible designs of the third aspect, refer to the beneficial effects brought by the second aspect and the possible implementations of the second aspect. Details are not described herein. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a diagram of current distribution of a loop antenna whose circumference is one wavelength λ; 
         FIG.  2    is a schematic diagram of waveforms of input reflection coefficients S 11  of the loop antenna in  FIG.  1    on different operating frequency bands; 
         FIG.  3   a    is a schematic diagram of a shape of a first radiation section/a fourth radiation section in an antenna unit according to an embodiment of this application; 
         FIG.  3   b    is a schematic diagram of a shape of a first radiation section/a fourth radiation section in an antenna unit according to an embodiment of this application; 
         FIG.  3   c    is a schematic diagram of a shape of a first radiation section/a fourth radiation section in an antenna unit according to an embodiment of this application; 
         FIG.  3   d    is a schematic diagram of a shape of a first radiation section/a fourth radiation section in an antenna unit according to an embodiment of this application; 
         FIG.  3   e    is a schematic diagram of a shape of a first radiation section/a fourth radiation section in an antenna unit according to an embodiment of this application; 
         FIG.  4   a    is a schematic diagram of a second radiation section and a third radiation section or a fifth radiation section and a sixth radiation section in an antenna unit according to an embodiment of this application; 
         FIG.  4   b    is a schematic diagram of a second radiation section and a third radiation section or a fifth radiation section and a sixth radiation section in an antenna unit according to an embodiment of this application; 
         FIG.  4   c    is a schematic diagram of a second radiation section and a third radiation section or a fifth radiation section and a sixth radiation section in an antenna unit according to an embodiment of this application; 
         FIG.  4   d    is a schematic diagram of a second radiation section and a third radiation section or a fifth radiation section and a sixth radiation section in an antenna unit according to an embodiment of this application; 
         FIG.  4   e    is a schematic diagram of a second radiation section and a third radiation section or a fifth radiation section and a sixth radiation section in an antenna unit according to an embodiment of this application; 
         FIG.  4   f    is a schematic diagram of a second radiation section and a third radiation section or a fifth radiation section and a sixth radiation section in an antenna unit according to an embodiment of this application; 
         FIG.  5   a    is a schematic diagram of grounding manners of a second radiation section and a third radiation section or a fifth radiation section and a sixth radiation section in an antenna unit according to an embodiment of this application; 
         FIG.  5   b    is a schematic diagram of grounding manners of a second radiation section and a third radiation section or a fifth radiation section and a sixth radiation section in an antenna unit according to an embodiment of this application; 
         FIG.  5   c    is a schematic diagram of grounding manners of a second radiation section and a third radiation section or a fifth radiation section and a sixth radiation section in an antenna unit according to an embodiment of this application; 
         FIG.  6   a    is a schematic diagram in which a first feed is connected to a first radiation section in a first direction in an antenna unit according to an embodiment of this application; 
         FIG.  6   b    is a schematic diagram in which a first feed is connected to a first radiation section in a first direction in an antenna unit according to an embodiment of this application; 
         FIG.  6   c    is a schematic diagram in which a first feed is connected to a first radiation section in a first direction in an antenna unit according to an embodiment of this application; 
         FIG.  7   a    is a schematic diagram in which a second feed is separately connected to a second radiation section and a third radiation section in an antenna unit according to an embodiment of this application; 
         FIG.  7   b    is a schematic diagram in which a second feed is separately connected to a second radiation section and a third radiation section in an antenna unit according to an embodiment of this application; 
         FIG.  8   a    is a schematic diagram of a shape of a first conductive member, a second conductive member, a third conductive member, or a fourth conductive member in an antenna unit according to an embodiment of this application; 
         FIG.  8   b    is a schematic diagram of a shape of a first conductive member, a second conductive member, a third conductive member, or a fourth conductive member in an antenna unit according to an embodiment of this application; 
         FIG.  8   c    is a schematic diagram of a shape of a first conductive member, a second conductive member, a third conductive member, or a fourth conductive member in an antenna unit according to an embodiment of this application; 
         FIG.  9   a    is a schematic diagram of a shape of a first conductive member, a second conductive member, a third conductive member, or a fourth conductive member in an antenna unit according to an embodiment of this application; 
         FIG.  9   b    is a schematic diagram of a shape of a first conductive member, a second conductive member, a third conductive member, or a fourth conductive member in an antenna unit according to an embodiment of this application; 
         FIG.  9   c    is a schematic diagram of a shape of a first conductive member, a second conductive member, a third conductive member, or a fourth conductive member in an antenna unit according to an embodiment of this application; 
         FIG.  10   a    is a schematic diagram of positions of a first conductive member and a second conductive member in an antenna unit according to an embodiment of this application; 
         FIG.  10   b    is a schematic diagram of positions of a first conductive member and a second conductive member in an antenna unit according to an embodiment of this application; 
         FIG.  10   c    is a schematic diagram of positions of a first conductive member and a second conductive member in an antenna unit according to an embodiment of this application; 
         FIG.  10   d    is a schematic diagram of positions of a first conductive member and a second conductive member in an antenna unit according to an embodiment of this application; 
         FIG.  10   e    is a schematic diagram of positions of a first conductive member and a second conductive member in an antenna unit according to an embodiment of this application; 
         FIG.  10   f    is a schematic diagram of positions of a first conductive member and a second conductive member in an antenna unit according to an embodiment of this application; 
         FIG.  11   a    is a schematic diagram of an overall structure of an electronic device; 
         FIG.  11   b    is a schematic diagram of a topology of an antenna unit according to an embodiment of this application; 
         FIG.  11   c    is a schematic diagram of a topology of an antenna unit according to an embodiment of this application; 
         FIG.  11   d    is a schematic diagram of waveforms of S parameters of a first feed and a second feed in  FIG.  11   b    and  FIG.  11   c    on different operating frequency bands; 
         FIG.  11   e    is a schematic diagram of waveforms of system efficiency and radiation efficiency of each of a first feed and a second feed in  FIG.  11   b    and  FIG.  11   c   ; 
         FIG.  12   a    is a schematic diagram of a feeding branch in an antenna unit according to an embodiment of this application; 
         FIG.  12   b    is a schematic diagram of a feeding branch in an antenna unit according to an embodiment of this application; 
         FIG.  12   c    is a schematic diagram of a feeding branch in an antenna unit according to an embodiment of this application; 
         FIG.  12   d    is a schematic diagram of a feeding branch in an antenna unit according to an embodiment of this application; 
         FIG.  12   e    is a schematic diagram of a feeding branch in an antenna unit according to an embodiment of this application; 
         FIG.  12   f    is a schematic diagram of a feeding branch in an antenna unit according to an embodiment of this application; 
         FIG.  13   a    is a schematic diagram of a feeding branch in an antenna unit according to an embodiment of this application; 
         FIG.  13   b    is a schematic diagram of a feeding branch in an antenna unit according to an embodiment of this application; 
         FIG.  13   c    is a schematic diagram of a feeding branch in an antenna unit according to an embodiment of this application; 
         FIG.  13   d    is a schematic diagram of a feeding branch in an antenna unit according to an embodiment of this application; 
         FIG.  13   e    is a schematic diagram of a feeding branch in an antenna unit according to an embodiment of this application; 
         FIG.  13   f    is a schematic diagram of a feeding branch in an antenna unit according to an embodiment of this application; 
         FIG.  14   a    is a schematic diagram of a feeding branch in an antenna unit according to an embodiment of this application; 
         FIG.  14   b    is a schematic diagram of a feeding branch in an antenna unit according to an embodiment of this application; 
         FIG.  14   c    is a schematic diagram of a feeding branch in an antenna unit according to an embodiment of this application; 
         FIG.  14   d    is a schematic diagram of a feeding branch in an antenna unit according to an embodiment of this application; 
         FIG.  14   e    is a schematic diagram of a feeding branch in an antenna unit according to an embodiment of this application; 
         FIG.  14   f    is a schematic diagram of a feeding branch in an antenna unit according to an embodiment of this application; 
         FIG.  15   a    is a schematic diagram in which a third feed is symmetrically connected to a feeding branch in a second direction in an antenna unit according to an embodiment of this application; 
         FIG.  15   b    is a schematic diagram in which a third feed is symmetrically connected to a feeding branch in a second direction in an antenna unit according to an embodiment of this application; 
         FIG.  16   a    is a schematic diagram in which a fourth feed is separately connected to a fifth radiation section and a sixth radiation section in an antenna unit according to an embodiment of this application; 
         FIG.  16   b    is a schematic diagram in which a fourth feed is separately connected to a fifth radiation section and a sixth radiation section in an antenna unit according to an embodiment of this application; 
         FIG.  17   a    is a schematic diagram of positions of a third conductive member and a fourth conductive member in an antenna unit according to an embodiment of this application; 
         FIG.  17   b    is a schematic diagram of positions of a third conductive member and a fourth conductive member in an antenna unit according to an embodiment of this application; 
         FIG.  17   c    is a schematic diagram of positions of a third conductive member and a fourth conductive member in an antenna unit according to an embodiment of this application; 
         FIG.  17   d    is a schematic diagram of positions of a third conductive member and a fourth conductive member in an antenna unit according to an embodiment of this application; 
         FIG.  17   e    is a schematic diagram of positions of a third conductive member and a fourth conductive member in an antenna unit according to an embodiment of this application; 
         FIG.  17   f    is a schematic diagram of positions of a third conductive member and a fourth conductive member in an antenna unit according to an embodiment of this application; 
         FIG.  18   a    is a schematic diagram of a topology of an antenna unit according to an embodiment of this application; 
         FIG.  18   b    is a schematic diagram of waveforms of S parameters of a third feed and a fourth feed in  FIG.  18   a    on different operating frequency bands; 
         FIG.  18   c    is a schematic diagram of waveforms of system efficiency and radiation efficiency of each of a third feed and a fourth feed in  FIG.  18   a   ; 
         FIG.  18   d    is a diagram of current distribution of the antenna unit in  FIG.  18   a   ; 
         FIG.  18   e    is a diagram of current distribution of the antenna unit in  FIG.  18   a   ; 
         FIG.  18   f    is a diagram of current distribution of the antenna unit in  FIG.  18   a   ; 
         FIG.  18   g    is a diagram of current distribution of the antenna unit in  FIG.  18   a   ; 
         FIG.  18   h    is a diagram of current distribution of the antenna unit in  FIG.  18   a   ; 
         FIG.  18   i    is a diagram of current distribution of the antenna unit in  FIG.  18   a   ; 
         FIG.  19   a    is a schematic diagram of a topology of an antenna unit according to an embodiment of this application; 
         FIG.  19   b    is a schematic diagram of waveforms of S parameters of a third feed and a fourth feed in  FIG.  19   a    on different operating frequency bands; 
         FIG.  19   c    is a schematic diagram of waveforms of system efficiency and radiation efficiency of each of a third feed and a fourth feed in  FIG.  19   a   ; 
         FIG.  19   d    is a diagram of current distribution of the antenna unit in  FIG.  19   a   ; 
         FIG.  19   e    is a diagram of current distribution of the antenna unit in  FIG.  19   a   ; 
         FIG.  19   f    is a diagram of current distribution of the antenna unit in  FIG.  19   a   ; 
         FIG.  19   g    is a diagram of current distribution of the antenna unit in  FIG.  19   a   ; 
         FIG.  19   h    is a diagram of current distribution of the antenna unit in  FIG.  19   a   ; 
         FIG.  19   i    is a diagram of current distribution of the antenna unit in  FIG.  19   a   ; 
         FIG.  19   j    is a diagram of current distribution of the antenna unit in  FIG.  19   a   ; 
         FIG.  20   a    is a schematic diagram of a topology of an antenna unit according to an embodiment of this application; 
         FIG.  20   b    is a schematic diagram of waveforms of S parameters of a third feed and a fourth feed in  FIG.  20   a    on different operating frequency bands; 
         FIG.  20   c    is a schematic diagram of waveforms of system efficiency and radiation efficiency of each of a third feed and a fourth feed in  FIG.  20   a   ; 
         FIG.  20   d    is a diagram of current distribution of the antenna unit in  FIG.  20   a   ; 
         FIG.  20   e    is a diagram of current distribution of the antenna unit in  FIG.  20   a   ; 
         FIG.  20   f    is a diagram of current distribution of the antenna unit in  FIG.  20   a   ; 
         FIG.  20   g    is a diagram of current distribution of the antenna unit in  FIG.  20   a   ; 
         FIG.  20   h    is a diagram of current distribution of the antenna unit in  FIG.  20   a   ; 
         FIG.  20   i    is a diagram of current distribution of the antenna unit in  FIG.  20   a   ; 
         FIG.  21   a    is a schematic diagram of a topology of an antenna unit according to an embodiment of this application; 
         FIG.  21   b    is a schematic diagram of waveforms of S parameters of a third feed and a fourth feed in  FIG.  21   a    on different operating frequency bands; and 
         FIG.  21   c    is a schematic diagram of waveforms of system efficiency and radiation efficiency of each of a third feed and a fourth feed in  FIG.  21   a   . 
     
    
    
     Description of reference numerals:
       10 : First loop branch;  11 : First radiation section;  12 : Second radiation section;  13 : Third radiation section;  14 : First non-conductive support member;  15 : First conductive member;  16 : Second conductive member; F 1 : First feed; F 2 : Second feed; and X 1 : First direction; and     20 : Second loop branch;  21 : Fourth radiation section;  22 : Fifth radiation section;  23 : Sixth radiation section;  24 : Second non-conductive support member;  25 : Third conductive member;  26 : Fourth conductive member;  27 : Feeding branch; F 3 : Third feed; F 4 : Fourth feed; and X 2 : Second direction.   

     DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS 
     Some terms in this application are first described, to help persons skilled in the art have a better understanding. 
     1. A loop antenna (loop antenna) is a structure in which a metal wire is wound into a specific shape such as a circular shape, a square shape, a triangular shape, or a diamond shape, and two ends of a conductor are used as output ends. 
       FIG.  1    is a diagram of current distribution of a loop antenna whose circumference is one wavelength λ. For ease of description, in  FIG.  1   , an example in which the loop antenna is in a square shape is used for illustration. As shown in  FIG.  1   , a thick black line represents the loop antenna. One end of the loop antenna is connected to a feed (feed), and the other end of the loop antenna is connected to a ground point. Each arrow represents current distribution of the loop antenna at a frequency corresponding to one wavelength λ. The loop antenna has a lowest current at a position of a triangle, and the loop antenna has a highest current at a position of a solid circle. 
       FIG.  2    is a schematic diagram of waveforms of input reflection coefficients S 11  of the loop antenna in  FIG.  1    on different operating frequency bands. As shown in  FIG.  2   , a curve  1  and a curve  2  respectively represent S 11  of the loop antenna in  FIG.  1    on different operating frequency bands. The loop antenna has rich higher order modes in the curve  1  and the curve  2 , and therefore the loop antenna has advantages such as easy to tune and capable of covering a very wide medium and high frequency bandwidth. 
     In  FIG.  2   , a horizontal coordinate is a frequency in a unit of GHz, and a vertical coordinate is an input reflection coefficient S 11  in a unit of dB. The input reflection coefficient S 11  is one of S parameters (namely, scattering parameters), and represents a return loss characteristic. A loss value in dB and an impedance characteristic are usually obtained by using a network analyzer. This parameter represents a matching degree between an antenna and a front-end circuit. A larger value of the reflection coefficient S 11  indicates a larger amount of energy reflected by the antenna, which indicates a lower matching degree of the antenna. For example, if a value of S 11  of an antenna A at a specific frequency is -1, and a value of S 11  of an antenna B at the same frequency is -3, the antenna B has a higher matching degree than the antenna A. 
     2. Antenna isolation refers to a ratio of power of a signal transmitted by an antenna to power of a signal received by another antenna. A reverse transmission coefficient S12 is usually used to represent the antenna isolation. The reverse transmission coefficient S12 is one of S parameters. 
     3. An envelope correlation coefficient ECC is used to represent coupling between different antennas. The coupling herein may include current coupling, free space coupling, and surface wave coupling. A person skilled in the art may understand that isolation is an important indicator for measuring coupling between antennas. Usually, the three coupling effects are alleviated, to improve the isolation between the antennas, ensure a low enough ECC, and maintain relatively good antenna performance. 
     A person skilled in the art may understand that an antenna may be fed separately to generate currents with an equal amplitude and a same phase, namely, a signal at a common mode (common mode, C mode) port. An antenna may be fed separately to generate currents with an equal amplitude and opposite phases, namely, a signal at a differential mode (differential mode, D mode) port. However, when there is a relatively short distance between two antennas, as the distance continuously decreases, a coupling effect between the two antennas continuously increases because there is coupling capacitance between the two antennas. Therefore, when there is a relatively short distance between the two antennas, there is a relatively strong coupling effect between the two antennas. Consequently, isolation between the two antennas is reduced, and there is a relatively high ECC between the two antennas. 
     To resolve the foregoing problem, this application provides an antenna unit and an electronic device. A signal at a C-mode port and a signal at a D-mode port of a same loop antenna in any antenna unit are respectively excited by using two feeds, and the antenna unit is electrically symmetrically disposed, so that the signal at the C-mode port is self-cancelled at the D-mode port, and the signal at the D-mode port is self-cancelled at the C-mode port, to implement signal isolation between the two ports, and the signal at the C-mode port and the signal at the D-mode port can be complementary to each other in different radiation directions, to implement two antennas with high isolation and a low envelope correlation coefficient ECC based on the same loop antenna. In this way, good antenna performance is ensured, so that the electronic device can fully use the antenna unit in limited space to implement various scenarios, for example, implement application to a multi-antenna scenario such as a diversity antenna or a multiple-input multiple-output (multiple-input multiple-output, MIMO) antenna, a scenario of obtaining a pattern through combination, and a pattern switching scenario such as switching between a horizontal direction and a vertical direction. In addition, the electronic device can include a larger quantity of antennas in the limited space, to improve utilization of antenna space. 
     The electronic device in this application may include but is not limited to a device such as a mobile phone, a headset, a tablet computer, a portable computer, a wearable device, or a data card. 
     The antenna unit is electrically symmetrically disposed. That the antenna unit is electrically symmetrically disposed may be understood as that the antenna unit has an electrical symmetry center that usually corresponds to a physical symmetry center, and electrical sizes on two sides of the antenna unit relative to the electrical symmetry center are approximately equal. If a surrounding environment of the antenna unit is ideally symmetrical, electrical symmetry of the antenna unit is physical symmetry. If an asymmetrical device is introduced in the surrounding environment of the antenna unit, the antenna unit needs to be disposed as an asymmetrical structure to cancel asymmetry introduced by the device, so as to implement electrical symmetry of the antenna unit. For ease of description, in this application, an example in which the antenna unit is structurally symmetrical and the surrounding environment of the antenna unit is also structurally symmetrically disposed is used for illustration. 
     A feeding manner of exciting the loop antenna by the feed is not limited in this application. Therefore, in this application, a scenario in which the feed excites the loop antenna in a direct feeding manner may be set as Embodiment 1, and a scenario in which the feed excites the loop antenna in a feeding manner similar to a manner of using a coplanar waveguide (coplanar waveguide, CPW) may be set as Embodiment 2. 
     For ease of description, a specific implementation process of implementing two antennas by using a same loop antenna in this application is described by using an example in which the electronic device is a mobile phone, with reference to the embodiments of this application and the accompanying drawings of this application, and by using Embodiment 1 and Embodiment 2. 
     Embodiment 1 
     In Embodiment 1, the antenna unit in this application may include a first loop branch  10 , a first feed F 1 , and a second feed F 2 . 
     A process of manufacturing the first loop branch  10  is not limited in this application. For example, the first loop branch  10  may be manufactured by using a flexible printed circuit board (flexible printed circuit board, FPC), may be manufactured through laser direct structuring, or may be manufactured by using a spraying process. In addition, a position at which the first loop branch  10  is disposed is also not limited in this application. For example, the first loop branch  10  may be disposed on a metal frame of an electronic device such as a mobile phone, may be disposed on a printed circuit board in an electronic device, or may be disposed on a printed circuit board in an electronic device by using a bracket. 
     In this application, the first loop branch  10  may include a first radiation section  11 , a second radiation section  12 , and a third radiation section  13 . 
     The first radiation section  11  is in a ring shape. Optionally, the first radiation section  11  may be in a circular shape shown in  FIG.  3   a   , may be in a square shape shown in  FIG.  3   b   , may be in an irregular shape shown in  FIG.  3   c    to  FIG.  3   e   , or may be in a triangular shape. A specific shape of the first radiation section  11  is not limited in this application provided that it is met that the first radiation section  11  is symmetrically disposed in a first direction X 1 . The first direction X 1  is a direction in which a symmetry axis of the first loop branch  10  is located, and may be any direction that varies with a direction in which the first loop branch  10  is placed. For ease of description, in this application, an example in which the first direction X 1  is a positive direction of an X axis is used for illustration. It should be noted that the first loop branch  10  may be completely structurally symmetrically disposed, that is, the first direction X 1  is the direction in which the symmetry axis of the first loop branch  10  is located. Alternatively, the first loop branch  10  may be allowed to be structurally asymmetrically disposed within an error range. Asymmetry herein is intended to eliminate electrical asymmetry introduced by a component other than the first loop branch  10 , that is, the first direction X 1  is a direction in which a symmetry axis of the first loop branch  10  that exists after correction is located. 
     In addition, the first radiation section  11  is not closed, and includes two ends. One end of the first radiation section  11  is connected to the second radiation section  12 , and the other end of the first radiation section  11  is connected to the third radiation section  13 . The second radiation section  12  and the third radiation section  13  are symmetrically disposed in the first direction X 1 , and there is an opening between the second radiation section  12  and the third radiation section  13 . 
     Parameters such as shapes, widths, or lengths of the second radiation section  12  and the third radiation section  13  are also not limited in this application. A size of the opening between the second radiation section  12  and the third radiation section  13  is not limited. In addition, a relative position relationship between the first radiation section  11  and each of the second radiation section  12  and the third radiation section  13  is not limited in this application. 
     Based on the first radiation section  11  in the square shape shown in  FIG.  3   b   , disposing of the second radiation section  12  and the third radiation section  13  is described below with reference to  FIG.  4   a    to  FIG.  4   f   . 
     Optionally, the second radiation section  12  and the third radiation section  13  may be disposed inside the first radiation section  11  in the first direction X 1 , so that inner space of the first radiation section  11  can be fully used to dispose the second radiation section  12  and the third radiation section  13 , to help arrange the antenna unit in relatively small space, so as to improve space utilization of the antenna unit. Based on the foregoing description, the second radiation section  12  and the third radiation section  13  may be in a plurality of shapes.  FIG.  4   a   ,  FIG.  6   b   , and  FIG.  6   c    are used as examples for description. For ease of description, the second radiation section  12  and the third radiation section  13  shown in  FIG.  4   a    are in long strip shapes, and the second radiation section  12  and the third radiation section  13  shown in  FIG.  4   b    and  FIG.  4   c    are in different irregular shapes. 
     Optionally, the second radiation section  12  and the third radiation section  13  may be disposed outside the first radiation section  11  in the first direction X 1 , to provide a possibility for implementing the antenna unit, so that the antenna unit can meet a space requirement in an actual situation. Based on the foregoing description, the second radiation section  12  and the third radiation section  13  may be in a plurality of shapes.  FIG.  4   d    is used as an example for description. For ease of description, the second radiation section  12  and the third radiation section  13  shown in  FIG.  4   d    are in long strip shapes. 
     Optionally, the second radiation section  12  and the third radiation section  13  may be disposed to extend from an inside of the first radiation section  11  to an outside of the first radiation section  11  in the first direction X 1 , to provide another possibility for implementing the antenna unit, so that the antenna unit can meet a space requirement in an actual situation. Based on the foregoing description, the second radiation section  12  and the third radiation section  13  may be in a plurality of shapes.  FIG.  4   e    is used as an example for description. The second radiation section  12  and the third radiation section  13  shown in  FIG.  4   e    are in long strip shapes. 
     Optionally, the second radiation section  12  and the third radiation section  13  may be disposed to extend from an inside of the first radiation section  11  to an outside of the first radiation section  11  in a direction opposite to the first direction X 1 , to provide another possibility for implementing the antenna unit, so that the antenna unit can meet a space requirement in an actual situation. Based on the foregoing description, the second radiation section  12  and the third radiation section  13  may be in a plurality of shapes.  FIG.  4   f    is used as an example for description. The second radiation section  12  and the third radiation section  13  shown in  FIG.  4   f    are in long strip shapes. 
     In addition, both the second radiation section  12  and the third radiation section  13  are grounded. Grounding manners of the second radiation section  12  and the third radiation section  13  are not limited in this application. The grounding manners of the second radiation section  12  and the third radiation section  13  are described below with reference to  FIG.  5   a    to  FIG.  5   c   . 
     Optionally, the second radiation section  12  is connected to N first ground points of an electronic device, and the third radiation section  13  is connected to N second ground points of the electronic device, where N is a positive integer. A specific value of N is not limited in this application. For ease of description, in  FIG.  5   a    to  FIG.  5   c   , the first ground point and the second ground point are illustrated by using a ground symbol. 
     For example, N=1. In this case, based on the first loop branch  10  shown in  FIG.  4   b   , it is shown in  FIG.  5   a    that the second radiation section  12  is connected to one first ground point, and the third radiation section  13  is connected to one second ground point. 
     For example, N=2. In this case, based on the first loop branch  10  shown in  FIG.  4   c   , it is shown in  FIG.  5   b    that the second radiation section  12  is connected to two first ground points, and the third radiation section  13  is connected to two second ground points. It should be noted that based on the first loop branch  10  shown in  FIG.  4   c   , the second radiation section  12  may alternatively be connected to one first ground point, and the third radiation section  13  may be connected to one second ground point. 
     Specific implementations of the first ground point and the second ground point of the electronic device are not limited in this application. A person skilled in the art may understand that components in the electronic device need to share a ground. Therefore, the first ground point and the second ground point need to be connected to a ground of a printed circuit board in the electronic device. 
     When the antenna unit in this application is manufactured by using a bracket, the second radiation section  12  and the third radiation section  13  are disposed on the bracket, and the first ground point and the second ground point may be disposed in a plurality of manners. Two feasible implementations are used as examples below for illustration. 
     In a feasible implementation, the first ground point and the second ground point may be disposed on the printed circuit board. The first ground point and the second ground point may be the ground of the printed circuit board, and do not need to be separately disposed. Alternatively, the first ground point and the second ground point may be separately disposed, and connected to the ground of the printed circuit board by using traces on the printed circuit board. Therefore, the second radiation section  12  and the third radiation section  13  are respectively connected to the first ground point and the second ground point on the printed circuit board by using different traces on the bracket. The different traces on the bracket are usually symmetrically disposed in the first direction X 1 . In this way, a spring is saved, and this solution is simple and easy to implement. 
     In another feasible implementation, the first ground point and the second ground point may be disposed on the bracket, so that the second radiation section  12  is connected to the first ground point, and the third radiation section  13  is connected to the second ground point. In addition, each of the first ground point and the second ground point needs to be connected to the ground of the printed circuit board by using a spring on the bracket, and no trace needs to be arranged on the bracket. 
     Optionally, both the second radiation section  12  and the third radiation section  13  may be connected to a ground region of the electronic device, and the ground region is symmetrically disposed in the first direction X 1 . For ease of description, based on the first loop branch  10  shown in  FIG.  4   f   , it is shown in  FIG.  5   c    that both the second radiation section  12  and the third radiation section  13  are connected to the ground region (the ground region is illustrated by using GG in  FIG.  5   c   ). 
     A specific size and position of the ground region are not limited in this application. The ground region may be disposed on the printed circuit board in the electronic device, may be disposed as a conductive fabric connected to a ground of the electronic device, or may be disposed as a conductive plate that is connected to a ground of the electronic device and that is below a screen of the electronic device. This is not limited in this application. 
     In this application, the first feed F 1  is symmetrically connected to the first radiation section  11  in the first direction X 1 , so that there are one or more first contact points between the first feed F 1  and the first radiation section  11 . A quantity and a position of first contact points are not limited in this application provided that it is met that all the first contact points are symmetrical in the first direction X 1 . 
     Based on the first loop branch  10  shown in  FIG.  5   b    and with reference to  FIG.  6   a    to  FIG.  6   c   , three feasible implementations are used as examples below to illustrate a case in which the first feed F 1  is connected to the first radiation section  11  in the first direction X 1 . In  FIG.  6   a    to  FIG.  6   c   , the first radiation section  11  is symmetrical in the first direction X 1 , and therefore a symmetry axis of the first radiation section  11  overlaps the first direction X 1 . 
     In a feasible implementation, there is one first contact point between the first feed F 1  and the first radiation section  11 , and the first contact point is a symmetry point of the first radiation section  11 , and is located on the first radiation section  11 , in other words, a point A in  FIG.  6   a    is the first contact point. 
     In another feasible implementation, there are P (an even number) first contact points between the first feed F 1  and the first radiation section  11 , the P (an even number) first contact points are symmetrically disposed in the first direction X 1 , and the P (an even number) first contact points are located on a radiation section, in the first radiation section  11 , on which a symmetry point of the first radiation section  11  is located. 
     A specific value of the even number P is not limited in this application, and a distance between any two first contact points is not limited in this application. For ease of description, when the even number P is equal to 2, as shown in  FIG.  6   b   , a point A1 and a point A2 are two first contact points, and the point A1 and the point A2 are symmetrical in the first direction X 1 . 
     In another feasible implementation, with reference to the foregoing two implementations, there are Q (an odd number) first contact points between the first feed F 1  and the first radiation section  11 . The odd number Q is greater than or equal to 3. The Q (an odd number) first contact points include one first contact point and P (an even number) first contact points. The one first contact point is a symmetry point of the first radiation section  11 , and is located on the first radiation section  11 . The P (an even number) first contact points are symmetrically disposed in the first direction X 1 , and the P (an even number) first contact points are located on a radiation section, in the first radiation section  11 , on which the symmetry point of the first radiation section  11  is located. Therefore, the Q (an odd number) first contact points are symmetrically disposed in the first direction X 1 . 
     A specific value of the odd number Q is not limited in this application, and a distance between any two first contact points is not limited in this application. For ease of description, when the odd number Q is equal to 3, as shown in  FIG.  6   c   , a point A1, a point A2, and a point A3 are three first contact points, and the point A1, the point A2, and the point A3 are symmetrical in the first direction X 1 . 
     In addition, a first matching component may be disposed between the first feed F 1  and the first contact point, to adjust a frequency band of the antenna unit, so that the first feed F 1  can obtain a better pattern and better cross polarization performance, to improve performance of the antenna unit. A specific implementation form of the first matching component is not limited in this application. For example, the first matching component may be a capacitor, an inductor, a capacitor and an inductor, a capacitor and a switch, an inductor and a switch, or a capacitor, an inductor, and a switch. In this application, no limitation is imposed on a capacitance value and a quantity of capacitors, an inductance value and a quantity of inductors, a type and a quantity of switches, or a connection relationship between any two of the capacitor, the inductor, and the switch. 
     In this application, the second feed F 2  is separately connected to the second radiation section  12  and the third radiation section  13 . In this application, a contact point between the second feed F 2  and the second radiation section  12  is referred to as a second contact point, and a contact point between the second feed F 2  and the second radiation section  12  is referred to as a third contact point. The second contact point and the third contact point are symmetrical in the first direction X 1 . 
     In addition, the second contact point is disposed at any position on a side that is of the second radiation section  12  and that is opposite to the third radiation section  13 , the third contact point is disposed at any position on a side that is of the third radiation section  13  and that is opposite to the second radiation section  12 , and a distance between the second contact point and the third contact point falls within a first preset range, to ensure the performance of the antenna unit. 
     A specific magnitude of the first preset range is not limited in this application provided that the distance between the second contact point and the third contact point can ensure that the antenna unit has good performance. 
     With reference to  FIG.  7   a    and  FIG.  7   b   , a specific implementation in which the second feed F 2  is separately connected to the second radiation section  12  and the third radiation section  13  is illustrated below. 
     Based on the first loop branch  10  shown in  FIG.  6   a   , as shown in  FIG.  7   a   , there is a same distance between the second radiation section  12  and the third radiation section  13 , the distance is aa, and the distance aa falls within the first preset range. Therefore, the second feed F 2  may be disposed at any position between the second radiation section  12  and the third radiation section  13 . For ease of description, in  FIG.  7   a   , an example in which the second feed F 2  is disposed at each of a position corresponding to a solid line and a position corresponding to a dashed line is used for illustration. 
     Based on the first loop branch  10  shown in  FIG.  5   b    and the fact that there is one first contact point between the first feed F 1  and the first radiator, as shown in  FIG.  7   b   , a minimum distance and a maximum distance between the second radiation section  12  and the third radiation section  13  are respectively a distance aa1 and a distance aa2. The first preset range is set to be less than or equal to a distance aa3, and the distance aa3 is less than the distance aa2 and greater than the distance aa1. Therefore, the second feed F 2  may be disposed at any position corresponding to a distance that is greater than or equal to the distance aa1 and less than or equal to the distance aa3. For ease of description, in  FIG.  7   b   , an example in which the second feed F 2  is disposed at each of a position corresponding to the distance aa1 and a position corresponding to the distance aa3 is used for illustration. 
     In addition, a second matching component may be disposed between the second feed F 2  and the second contact point and/or between the second feed F 2  and the third contact point, to adjust the frequency band of the antenna unit, so that the second feed F 2  can obtain a better pattern and better cross polarization performance, to improve the performance of the antenna unit. A specific implementation form of the second matching component is not limited in this application. For example, the second matching component may be a capacitor, an inductor, a capacitor and an inductor, a capacitor and a switch, an inductor and a switch, or a capacitor, an inductor, and a switch. In this application, no limitation is imposed on a capacitance value and a quantity of capacitors, an inductance value and a quantity of inductors, a type and a quantity of switches, or a connection relationship between any two of the capacitor, the inductor, and the switch. 
     Based on the foregoing embodiment, the antenna unit may further include a first non-conductive support member  14 , a first conductive member  15 , and a second conductive member  16 . The first conductive member  15  and the second conductive member  16  are suspended by using the first non-conductive support member  14 , and the first conductive member  15  and the second conductive member  16  are symmetrically disposed in the first direction X 1 . A length of the first conductive member  15  is a ½ wavelength, and a length of the second conductive member  16  is a ½ wavelength. The wavelength is a wavelength corresponding to any frequency in an operating frequency band of the antenna unit. 
     In this application, the first conductive member  15  and the second conductive member  16  are made of conductive materials, and may be suspended by using the first non-conductive support member  14  in a manner such as a manner of using a surface-mount technology or etching. Therefore, the first conductive member  15  and the second conductive member  16  can extend a bandwidth of the antenna unit, to improve the performance of the antenna unit. Usually, larger widths of the first conductive member  15  and the second conductive member  16  indicate better performance of the antenna unit. 
     The first conductive member  15  or the second conductive member  16  may be in a plurality of shapes. Optionally, the first conductive member  15  or the second conductive member  16  may be in a regular patch shape (patch) shown in  FIG.  8   a    to  FIG.  8   c   , may be in an irregular patch shape, may be in a regular closed ring shape shown in  FIG.  9   a    to  FIG.  9   c   , or may be in an irregular closed ring shape. A specific shape of the first conductive member  15  or the second conductive member  16  is not limited in this application provided that it is met that the first conductive member  15  and the second conductive member  16  are symmetrically disposed in the first direction X 1 . 
     In addition, parameters such as widths, quantities, and positions of first conductive members  15  and second conductive members  16  are also not limited in this application. Based on the antenna unit shown in  FIG.  7   a    and with reference to  FIG.  10   a    to  FIG.  10   f   , the positions of the first conductive member  15  and the second conductive member  16  are described below by using examples. For ease of description, in  FIG.  10   a    to  FIG.  10   c   , an example in which the first conductive member  15  and the second conductive member  16  are in rectangular cross-sectional shapes is used for illustration, and in  FIG.  10   d    to  FIG.  10   f   , an example in which the first conductive member  15  and the second conductive member  16  are rectangular closed rings is used for illustration. 
     Optionally, the first conductive member  15  and the second conductive member  16  may be disposed outside the first radiation section  11 . For example, the first conductive member  15  and the second conductive member  16  may be horizontally symmetrically disposed outside the first radiation section  11  in the first direction X 1 , as shown in  FIG.  10   a    and  FIG.  10   b   . In  FIG.  10   a   , a direction of placing the first conductive member  15  and the second conductive member  16  is perpendicular to the first direction X 1 , and in  FIG.  10   b   , a direction of placing the first conductive member  15  and the second conductive member  16  is not perpendicular to the first direction X 1 . For another example, the first conductive member  15  and the second conductive member  16  may be vertically symmetrically disposed outside the first radiation section  11  in the first direction X 1 , as shown in  FIG.  10   c   . 
     Optionally, the first conductive member  15  and the second conductive member  16  may be disposed inside the first radiation section  11 . For example, the first conductive member  15  and the second conductive member  16  may be horizontally symmetrically disposed inside the first radiation section  11  in the first direction X 1 , as shown in  FIG.  10   d    and  FIG.  10   e   . In  FIG.  10   d   , a direction of placing the first conductive member  15  and the second conductive member  16  is perpendicular to the first direction X 1 , and in  FIG.  10   e   , a direction of placing the first conductive member  15  and the second conductive member  16  is not perpendicular to the first direction X 1 . For another example, the first conductive member  15  and the second conductive member  16  may be vertically symmetrically disposed inside the first radiation section  11  in the first direction X 1 , as shown in  FIG.  10   f   . 
     It should be noted that the positions of the first conductive member  15  and the second conductive member  16  are not limited to the foregoing implementations. 
     In addition, the first non-conductive support member  14  is made of a non-conductive material. Parameters such as a quantity, a material, and a position of first non-conductive support members  14  are not limited in this application. Optionally, the first non-conductive support member  14  may be a glass battery cover, a plastic battery cover, or an explosion-proof film. This is not limited in this application. 
     In a specific embodiment, based on the antenna unit shown in  FIG.  5   c    and with reference to  FIG.  11   a    to  FIG.  11   d   , a structure and the performance of the antenna unit in this application are described in detail. 
       FIG.  11   a    is a schematic diagram of an overall structure of an electronic device. As shown in  FIG.  11   a   , the electronic device may include the printed circuit board, a middle frame, and the antenna unit shown in  FIG.  5   c   . As shown in  FIG.  11   a    and  FIG.  5   c   , the second radiation section  12  may be connected to the ground region GG of the electronic device, and the ground region GG of the electronic device is connected to the ground of the printed circuit board by using a spring foot  1  on the middle frame of the electronic device. The third radiation section  13  may be connected to the ground region GG of the electronic device, and the ground region GG of the electronic device is connected to the ground of the printed circuit board by using a spring foot  2  on the middle frame of the electronic device. 
     The middle frame may be used as a structural support of the printed circuit board, and may be further used to be connected to the spring, so that the ground region GG, the first ground point, and the second ground point of the electronic device may be connected to the ground of the printed circuit board. A quantity and a position of springs on the middle frame are not limited in this application. For ease of description, in  FIG.  11   a   , an example in which the electronic device is a mobile phone is used for illustration, and the middle frame, the spring foot  1 , and the spring foot  2  are not illustrated. 
       FIG.  11   b    and  FIG.  11   c    respectively show schematic diagrams of topologies of the antenna units in  FIG.  11   a    and  FIG.  5   c   . As shown in  FIG.  11   b   , the first feed F 1  is connected to one first contact point in the first direction X 1 , and the first contact point is the symmetry point of the first radiation section  11 , and is located on the first radiation section  11 , to implement symmetrical feeding of the antenna unit, so as to excite a signal at a C-mode port of the first loop branch  10 . As shown in  FIG.  11   c   , the second feed F 2  is separately connected to the second radiation section  12  and the third radiation section  13 , to implement anti-symmetrical feeding of the antenna unit, so as to excite a signal at a D-mode port of the first loop branch  10 . 
       FIG.  11   d    is a schematic diagram of waveforms of S parameters of the first feed F 1  and the second feed F 2  in  FIG.  11   b    and  FIG.  11   c    on different operating frequency bands. In  FIG.  11   d   , a horizontal coordinate is a frequency in a unit of GHz, and a vertical coordinate is an input reflection coefficient S 11 , a reverse transmission coefficient S12/a forward transmission coefficient S21, and an output reflection coefficient S22 in S parameters, and is in a unit of dB. As shown in  FIG.  11   d   , a curve  1  represents an input reflection coefficient S 11  of the first feed F 1 , a curve  2  represents reverse transmission coefficients S12/forward transmission coefficients S21 of the first feed F 1  and the second feed F 2 , and a curve  3  represents an output reflection coefficient S22 of the second feed F 2 . 
       FIG.  11   e    is a schematic diagram of waveforms of system efficiency and radiation efficiency of each of the first feed F 1  and the second feed F 2  in  FIG.  11   b    and  FIG.  11   c   . In  FIG.  11   e   , a horizontal coordinate is a frequency in a unit of GHz, and a vertical coordinate is system efficiency in a unit of dB. As shown in  FIG.  11   e   , a curve  1  represents system efficiency of the first feed F 1 , a curve  2  represents radiation efficiency of the first feed F 1 , a curve  3  represents system efficiency of the second feed F 2 , and a curve  4  represents radiation efficiency of the second feed F 2 . 
     In Embodiment 1, based on a symmetrical arrangement of a same loop antenna (namely, the first loop branch), the antenna unit respectively excites the signal at the C-mode port and the signal at the D-mode port of the loop antenna by using two feeds, so that the signal at the C-mode port is self-canceled at the D-mode port, and the signal at the D-mode port is self-canceled at the C-mode port, to implement signal isolation between the two ports, and the signal at the C-mode port and the signal at the D-mode port are complementary to each other in different radiation directions, to implement two antennas with high isolation and a low ECC. In this way, good antenna performance can be ensured, so that the electronic device can fully use the antenna unit in limited space to implement various scenarios. In addition, the electronic device can include a larger quantity of antennas in the limited space, to improve utilization of antenna space. 
     Embodiment 2 
     A similarity between Embodiment 1 and Embodiment 2 in structure is that the antenna unit includes a loop antenna and two feeds, and there is a same specific implementation of the loop antenna. A difference between Embodiment 1 and Embodiment 2 is that in comparison with the antenna unit in Embodiment 1, a branch is newly added to the antenna unit in Embodiment 2. 
     In terms of connection manner, a similarity between Embodiment 1 and Embodiment 2 is that there is a same connection manner of one of the two feeds, and the feed is connected to the loop antenna. A difference between Embodiment 1 and Embodiment 2 is that there is a different connection manner of the other feed in the two feeds. In Embodiment 1, the feed is connected to the loop branch, and in Embodiment 2, the feed is connected to the newly added branch. 
     In Embodiment 2, the antenna unit in this application may include a second loop branch  20 , a feeding branch  27 , a third feed F 3 , and a fourth feed F 4 . 
     For a specific implementation of the second loop branch  20 , refer to the description content of the first loop branch in Embodiment  1 . Details are not described herein. 
     In this application, the second loop branch  20  may include a fourth radiation section  21 , a fifth radiation section  22 , and a sixth radiation section  23 . 
     The fourth radiation section  21  is in a ring shape. For a specific shape of the fourth radiation section  21 , refer to the description content of the shape of the first radiation section in Embodiment  1 . Details are not described herein. For example, for the shape of the fourth radiation section  21 , refer to the shape of the first radiation section shown in  FIG.  3   a    to  FIG.  3   e   . 
     In addition, the fourth radiation section  21  is not closed, and includes two ends. One end of the fourth radiation section  21  is connected to the fifth radiation section  22 , and the other end of the fourth radiation section  21  is connected to the sixth radiation section  23 . The fifth radiation section  22  and the sixth radiation section  23  are symmetrically disposed in a second direction X 2 , and there is an opening between the fifth radiation section  22  and the sixth radiation section  23 . 
     Parameters such as shapes, widths, or lengths of the fourth radiation section  21  and the fifth radiation section  22  are also not limited in this application. A size of the opening between the fourth radiation section  21  and the fifth radiation section  22  is not limited. In addition, a relative position relationship between the third radiation section and each of the fourth radiation section  21  and the fifth radiation section  22  is not limited in this application. 
     For a specific implementation of the fifth radiation section  22 , refer to the description content of the second radiation section in Embodiment 1. For a specific implementation of the sixth radiation section  23 , refer to the description content of the third radiation section in Embodiment 1. Details are not described herein. For example, for disposing of the fifth radiation section  22  and the sixth radiation section  23 , refer to the description content of the disposing of the second radiation section and the third radiation section shown in  FIG.  4   a    to  FIG.  4   f    in Embodiment 1. 
     In addition, both the fifth radiation section  22  and the sixth radiation section  23  are grounded. For grounding manners of the fifth radiation section  22  and the sixth radiation section  23 , refer to the description content of the grounding manners of the second radiation section and the third radiation section in Embodiment  1 . Details are not described herein. For example, for the grounding manners of the fifth radiation section  22  and the sixth radiation section  23 , refer to the description content of the grounding manners of the second radiation section and the third radiation section shown in  FIG.  5   a    to  FIG.  5   c    in Embodiment  1 . 
     Optionally, the fifth radiation section  22  is connected to M third ground points of an electronic device, and the sixth radiation section  23  is connected to M fourth ground points of the electronic device, where M is a positive integer. A specific value of M is not limited in this application. For the third ground point, refer to the description content of the first ground point shown in  FIG.  5   a    and  FIG.  5   b    in Embodiment 1. For the fourth ground point, refer to the description content of the second ground point shown in  FIG.  5   a    and  FIG.  5   b    in Embodiment 1. 
     When the antenna unit in this application is manufactured by using a bracket, the fifth radiation section  22  and the sixth radiation section  23  are disposed on the bracket, and the third ground point and the fourth ground point may be disposed in a plurality of manners. Two feasible implementations are used as examples below for illustration. 
     In a feasible implementation, the third ground point and the fourth ground point may be disposed on a printed circuit board. The third ground point and the fourth ground point may be a ground of the printed circuit board, and do not need to be separately disposed. Alternatively, the third ground point and the fourth ground point may be separately disposed, and connected to a ground of the printed circuit board by using traces on the printed circuit board. Therefore, the fifth radiation section  22  and the sixth radiation section  23  are respectively connected to the third ground point and the fourth ground point on the printed circuit board by using different traces on the bracket. The different traces on the bracket are usually symmetrically disposed in the second direction X 2 . In this way, a spring is saved, and this solution is simple and easy to implement. 
     In another feasible implementation, the third ground point and the fourth ground point may be disposed on the bracket, so that the fifth radiation section  22  is connected to the third ground point, and the sixth radiation section  23  is connected to the fourth ground point. In addition, each of the third ground point and the fourth ground point needs to be connected to a ground of a printed circuit board by using a spring on the bracket, and no trace needs to be arranged on the bracket. 
     Optionally, both the fifth radiation section  22  and the sixth radiation section  23  may be connected to a ground region of the electronic device, and the ground region is symmetrically disposed in the second direction X 2 . For the foregoing implementation, refer to the description content in the embodiment shown in  FIG.  5   c    in Embodiment  1 . 
     The second direction X 2  is a direction in which a symmetry axis of the second loop branch  20  is located, and may be any direction that varies with a direction of placing the second loop branch  20 . It should be noted that the second loop branch  20  may be completely structurally symmetrically disposed, that is, the second direction is the direction in which the symmetry axis of the second loop branch  20  is located. Alternatively, the second loop branch  20  may be allowed to be structurally asymmetrically disposed within an error range. Asymmetry herein is intended to eliminate electrical asymmetry introduced by a component other than the second loop branch  20 , that is, the second direction is a direction in which a symmetry axis of the second loop branch  20  that exists after correction is located. For specific content of the second direction X 2 , refer to the description content of the first direction X 1  in Embodiment 1. Details are not described herein. For ease of description, in this application, an example in which the second direction X 2  is a positive direction of an X axis is used for illustration. 
     In this application, the feeding branch  27  is symmetrically disposed in the second direction X 2 , and an area of a part that is of the feeding branch  27  and that faces the fifth radiation section  22  is equal to an area of a part that is of the feeding branch  27  and that faces the sixth radiation section  23 , to ensure symmetry of the feeding branch  27 . 
     A process of manufacturing the feeding branch  27  is not limited in this application. For example, the feeding branch  27  may be manufactured by using a flexible printed circuit board (flexible printed circuit board, FPC), may be manufactured through laser direct structuring, or may be manufactured by using a spraying process. In addition, a parameter such as a shape, a width, or a length and a position of the feeding branch  27  are not limited in this application. 
     Disposing of the feeding branch  27  is described below by using an example and with reference to  FIG.  12   a    to  FIG.  12   f   ,  FIG.  13   a    to  FIG.  13   f   , and  FIG.  14   a    to  FIG.  14   f   . For ease of description, in  FIG.  12   a    to  FIG.  12   f   ,  FIG.  13   a    to  FIG.  13   f   , and  FIG.  14   a    to  FIG.  14   f   , an example in which the fourth radiation section  21  is in a square shape is used for illustration. 
     Optionally, the feeding branch  27  may be disposed inside the fourth radiation section  21  in the second direction X 2 , so that inner space of the fourth radiation section  21  can be fully used to dispose the feeding branch  27 , the fifth radiation section  22 , and the sixth radiation section  23 , to help arrange the antenna unit in relatively small space, so as to improve space utilization of the antenna unit. 
     The feeding branch  27  in the foregoing description manner is illustrated by using  FIG.  12   a    to  FIG.  12   f    as examples. 
     As shown in  FIG.  12   a   , the feeding branch  27  is in a long strip shape, is located between the fifth radiation section  22  and the sixth radiation section  23 , and is located inside the fourth radiation section  21  (a solid line is used for illustration in  FIG.  12   a   ); or the feeding branch  27  is in a long strip shape, and is located on a side that is of the fifth radiation section  22  and the sixth radiation section  23  and that is close to an inside of the fourth radiation section  21  (a dashed line is used for illustration in  FIG.  12   a   ). For disposing of the fifth radiation section  22  in  FIG.  12   a   , refer to the second radiation section shown in  FIG.  4   a    in Embodiment 1. For disposing of the sixth radiation section  23  in  FIG.  12   a   , refer to the third radiation section shown in  FIG.  4   a    in Embodiment 1. 
     As shown in  FIG.  12   b   , the feeding branch  27  is in a long strip shape, is located between the fifth radiation section  22  and the sixth radiation section  23 , and is located inside the fourth radiation section  21  (a solid line is used for illustration in  FIG.  12   b   ); or the feeding branch  27  is in a long strip shape, and is located on a side that is of the fifth radiation section  22  and the sixth radiation section  23  and that is close to an inside of the fourth radiation section  21  (a dashed line is used for illustration in  FIG.  12   b   ). For disposing of the fifth radiation section  22  in  FIG.  12   b   , refer to the second radiation section shown in  FIG.  4   b    in Embodiment 1. For disposing of the sixth radiation section  23  in  FIG.  12   b   , refer to the third radiation section shown in  FIG.  4   b    in Embodiment 1. 
     As shown in  FIG.  12   c   , the feeding branch  27  is in a long strip shape, is located between the fifth radiation section  22  and the sixth radiation section  23 , and is located inside the fourth radiation section  21  (a solid line is used for illustration in  FIG.  12   c   ); or the feeding branch  27  is in a long strip shape, and is located on a side that is of the fifth radiation section  22  and the sixth radiation section  23  and that is close to an inside of the fourth radiation section  21  (a dashed line is used for illustration in  FIG.  12   c   ). For disposing of the fifth radiation section  22  in  FIG.  12   c   , refer to the second radiation section shown in  FIG.  4   c    in Embodiment 1. For disposing of the sixth radiation section  23  in  FIG.  12   c   , refer to the third radiation section shown in  FIG.  4   c    in Embodiment 1. 
     As shown in  FIG.  12   d   , the feeding branch  27  is in a long strip shape, and is located on a side that is of the fifth radiation section  22  and the sixth radiation section  23  and that is close to an inside of the fourth radiation section  21 . For disposing of the fifth radiation section  22  in  FIG.  12   d   , refer to the second radiation section shown in  FIG.  4   d    in Embodiment 1. For disposing of the sixth radiation section  23  in  FIG.  12   d   , refer to the third radiation section shown in  FIG.  4   d    in Embodiment 1. 
     As shown in  FIG.  12   e   , the feeding branch  27  is in a long strip shape, is located between the fifth radiation section  22  and the sixth radiation section  23 , and is located inside the fourth radiation section  21  (a solid line is used for illustration in  FIG.  12   e   ); or the feeding branch  27  is in a long strip shape, and is located on a side that is of the fifth radiation section  22  and the sixth radiation section  23  and that is close to an inside of the fourth radiation section  21  (a dashed line is used for illustration in  FIG.  12   e   ). For disposing of the fifth radiation section  22  in  FIG.  12   e   , refer to the second radiation section shown in  FIG.  4   e    in Embodiment 1. For disposing of the sixth radiation section  23  in  FIG.  12   e   , refer to the third radiation section shown in  FIG.  4   e    in Embodiment 1. 
     As shown in  FIG.  12   f   , the feeding branch  27  is in a long strip shape, is located between the fifth radiation section  22  and the sixth radiation section  23 , and is located inside the fourth radiation section  21 . For disposing of the fifth radiation section  22  in  FIG.  12   f   , refer to the second radiation section shown in  FIG.  4   f    in Embodiment 1. For disposing of the sixth radiation section  23  in  FIG.  12   f   , refer to the third radiation section shown in  FIG.  4   f    in Embodiment 1. 
     Optionally, the feeding branch  27  may be disposed outside the fourth radiation section  21  in the second direction X 2 , to provide a possibility for implementing the antenna unit, so that the antenna unit can meet a space requirement in an actual situation. 
     The feeding branch  27  described above is illustrated by using  FIG.  13   a    to  FIG.  13   f    as examples. 
     As shown in  FIG.  13   a   , the feeding branch  27  is in a long strip shape, and is located on a side that is of the fifth radiation section  22  and the sixth radiation section  23  and that is close to an outside of the fourth radiation section  21 . For disposing of the fifth radiation section  22  in  FIG.  13   a   , refer to the second radiation section shown in  FIG.  4   a    in Embodiment 1. For disposing of the sixth radiation section  23  in  FIG.  13   a   , refer to the third radiation section shown in  FIG.  4   a    in Embodiment 1. 
     As shown in  FIG.  13   b   , the feeding branch  27  is in a long strip shape, and is located on a side that is of the fifth radiation section  22  and the sixth radiation section  23  and that is close to an outside of the fourth radiation section  21 . For disposing of the fifth radiation section  22  in  FIG.  13   b   , refer to the second radiation section shown in  FIG.  4   b    in Embodiment 1. For disposing of the sixth radiation section  23  in  FIG.  13   b   , refer to the third radiation section shown in  FIG.  4   b    in Embodiment 1. 
     As shown in  FIG.  13   c   , the feeding branch  27  is in a long strip shape, and is located on a side that is of the fifth radiation section  22  and the sixth radiation section  23  and that is close to an outside of the fourth radiation section  21 . For disposing of the fifth radiation section  22  in  FIG.  13   c   , refer to the second radiation section shown in  FIG.  4   c    in Embodiment 1. For disposing of the sixth radiation section  23  in  FIG.  13   c   , refer to the third radiation section shown in  FIG.  4   c    in Embodiment 1. 
     As shown in  FIG.  13   d   , the feeding branch  27  is in a long strip shape, is located between the fifth radiation section  22  and the sixth radiation section  23 , and is located outside the fourth radiation section  21  (a solid line is used for illustration in  FIG.  13   d   ); or the feeding branch  27  is in a long strip shape, and is located on a side that is of the fifth radiation section  22  and the sixth radiation section  23  and that is close to an outside of the fourth radiation section  21  (a dashed line is used for illustration in  FIG.  13   d   ). For disposing of the fifth radiation section  22  in  FIG.  13   d   , refer to the second radiation section shown in  FIG.  4   d    in Embodiment 1. For disposing of the sixth radiation section  23  in  FIG.  13   d   , refer to the third radiation section shown in  FIG.  4   d    in Embodiment 1. 
     As shown in  FIG.  13   e   , the feeding branch  27  is in a long strip shape, is located between the fifth radiation section  22  and the sixth radiation section  23 , and is located outside the fourth radiation section  21  (a solid line is used for illustration in  FIG.  13   e   ); or the feeding branch  27  is in a long strip shape, and is located on a side that is of the fifth radiation section  22  and the sixth radiation section  23  and that is close to an outside of the fourth radiation section  21  (a dashed line is used for illustration in  FIG.  13   e   ). For disposing of the fifth radiation section  22  in  FIG.  13   e   , refer to the second radiation section shown in  FIG.  4   e    in Embodiment 1. For disposing of the sixth radiation section  23  in  FIG.  13   e   , refer to the third radiation section shown in  FIG.  4   e    in Embodiment 1. 
     As shown in  FIG.  13   f   , the feeding branch  27  is in a long strip shape, and is located on a side that is of the fifth radiation section  22  and the sixth radiation section  23  and that is close to an outside of the fourth radiation section  21 . For disposing of the fifth radiation section  22  in  FIG.  13   f   , refer to the second radiation section shown in  FIG.  4   f    in Embodiment 1. For disposing of the sixth radiation section  23  in  FIG.  13   f   , refer to the third radiation section shown in  FIG.  4   f    in Embodiment 1. 
     Optionally, the feeding branch  27  may be disposed to extend from an inside of the fourth radiation section  21  to an outside the fourth radiation section  21  in the second direction X 2 , to provide another possibility for implementing the antenna unit, so that the antenna unit can meet a space requirement in an actual situation. 
     The feeding branch  27  described above is illustrated by using  FIG.  14   a    to  FIG.  14   f    as examples. 
     As shown in  FIG.  14   a   , the feeding branch  27  is in a long strip shape, and is located between the fifth radiation section  22  and the sixth radiation section  23 , and the feeding branch  27  is disposed to extend from the inside of the fourth radiation section  21  to the outside of the fourth radiation section  21  in the second direction X 2 . For disposing of the fifth radiation section  22  in  FIG.  14   a   , refer to the second radiation section shown in  FIG.  4   a    in Embodiment 1. For disposing of the sixth radiation section  23  in  FIG.  14   a   , refer to the third radiation section shown in  FIG.  4   a    in Embodiment 1. 
     As shown in  FIG.  14   b   , the feeding branch  27  is in a long strip shape, and is located between the fifth radiation section  22  and the sixth radiation section  23 , and the feeding branch  27  is disposed to extend from the inside of the fourth radiation section  21  to the outside of the fourth radiation section  21  in the second direction X 2 . For disposing of the fifth radiation section  22  in  FIG.  14   b   , refer to the second radiation section shown in  FIG.  4   b    in Embodiment 1. For disposing of the sixth radiation section  23  in  FIG.  14   b   , refer to the third radiation section shown in  FIG.  4   b    in Embodiment 1. 
     As shown in  FIG.  14   c   , the feeding branch  27  is in a long strip shape, and is located between the fifth radiation section  22  and the sixth radiation section  23 , and the feeding branch  27  extends from the inside of the fourth radiation section  21  to the outside of the fourth radiation section  21  in the second direction X 2 . For disposing of the fifth radiation section  22  in  FIG.  14   c   , refer to the second radiation section shown in  FIG.  4   c    in Embodiment 1. For disposing of the sixth radiation section  23  in  FIG.  14   c   , refer to the third radiation section shown in  FIG.  4   c    in Embodiment 1. 
     As shown in  FIG.  14   d   , the feeding branch  27  is in a long strip shape, and is located between the fifth radiation section  22  and the sixth radiation section  23 , and the feeding branch  27  extends from the inside of the fourth radiation section  21  to the outside of the fourth radiation section  21  in the second direction X 2 . For disposing of the fifth radiation section  22  in  FIG.  14   d   , refer to the second radiation section shown in  FIG.  4   d    in Embodiment 1. For disposing of the sixth radiation section  23  in  FIG.  14   d   , refer to the third radiation section shown in  FIG.  4   d    in Embodiment 1. 
     As shown in  FIG.  14   e   , the feeding branch  27  is in a long strip shape, and is located between the fifth radiation section  22  and the sixth radiation section  23 , and the feeding branch  27  extends from the inside of the fourth radiation section  21  to the outside of the fourth radiation section  21  in the second direction X 2 . For disposing of the fifth radiation section  22  in  FIG.  14   e   , refer to the second radiation section shown in  FIG.  4   e    in Embodiment 1. For disposing of the sixth radiation section  23  in  FIG.  14   e   , refer to the third radiation section shown in  FIG.  4   e    in Embodiment 1. 
     As shown in  FIG.  14   f   , the feeding branch  27  is in a long strip shape, and is located between the fifth radiation section  22  and the sixth radiation section  23 , and the feeding branch  27  extends from the inside of the fourth radiation section  21  to the outside of the fourth radiation section  21  in the second direction X 2 . For disposing of the fifth radiation section  22  in  FIG.  14   f   , refer to the second radiation section shown in  FIG.  4   f    in Embodiment 1. For disposing of the sixth radiation section  23  in  FIG.  14   f   , refer to the third radiation section shown in  FIG.  4   f    in Embodiment 1. 
     In conclusion, an area of a part that is of the feeding branch  27  and that faces the fifth radiation section  22  in the second direction X 2  is equal to an area of a part that is of the feeding branch  27  and that faces the sixth radiation section  23  in the second direction X 2 , or an area of a part that is of the feeding branch  27  and that faces the fifth radiation section  22  in a direction perpendicular to the second direction X 2  is equal to an area of a part that is of the feeding branch  27  and that faces the sixth radiation section  23  in the direction perpendicular to the second direction X 2 , to ensure symmetry of the feeding branch  27 . 
     In this application, the third feed F 3  is symmetrically connected to the feeding branch  27  in the second direction X 2 , which is different from the manner in which the first feed is symmetrically connected to the first radiation section in the first direction X 1  in Embodiment 1. In addition, in this application, there are one or more fourth contact points between the third feed F 3  and the feeding branch  27 . The fourth contact point is a symmetry point of the feeding branch  27  in the second direction X 2 . A quantity and a position of fourth contact points are not limited in this application provided that it is met that the fourth contact point is symmetrical in the second direction X 2 . 
     A case in which the third feed F 3  is symmetrically connected to the feeding branch  27  in the second direction X 2  is illustrated by using an example in which there is one fourth contact point and with reference to  FIG.  15   a    and  FIG.  15   b   . 
     Based on the second loop branch  20  shown in  FIG.  12   b   , as shown in  FIG.  15   a   , the third feed F 3  is fed from the fourth contact point in the second direction X 2 , and the fourth contact point is located on one side of the feeding branch  27  inside the fourth radiation section  21 . The fifth radiation section  22  is connected to one third ground point, and the sixth radiation section  23  is connected to one fourth ground point. In  FIG.  15   a   , an example in which the third ground point and the fourth ground point are ground symbols is used for illustration. 
     Based on the second loop branch  20  shown in  FIG.  12   c   , as shown in  FIG.  15   b   , the third feed F 3  is fed from the fourth contact point in the second direction X 2 , and the fourth contact point is located on one side of the feeding branch  27  inside the fourth radiation section  21 . The fifth radiation section  22  is connected to two third ground points, and the sixth radiation section  23  is connected to two fourth ground points. In  FIG.  15   b   , an example in which the third ground point and the fourth ground point are ground symbols is used for illustration. 
     In addition, a third matching component may be disposed between the third feed F 3  and the fourth contact point, to adjust a frequency band of the antenna unit, so that the third feed F 3  can obtain a better pattern and better cross polarization performance, to improve performance of the antenna unit. A specific implementation form of the third matching component is not limited in this application. For example, the third matching component may be a capacitor, an inductor, a capacitor and an inductor, a capacitor and a switch, an inductor and a switch, or a capacitor, an inductor, and a switch. In this application, no limitation is imposed on a capacitance value and a quantity of capacitors, an inductance value and a quantity of inductors, a type and a quantity of switches, or a connection relationship between any two of the capacitor, the inductor, and the switch. 
     In this application, the fourth feed F 4  is separately connected to the fifth radiation section  22  and the sixth radiation section  23 , which is the same as the manner in which the second feed is separately connected to the second radiation section and the third radiation section in Embodiment 1. In addition, in this application, a contact point between the fourth feed F 4  and the fifth radiation section  22  is referred to as a fifth contact point, and a contact point between the fourth feed F 4  and the sixth radiation section  23  is referred to as a sixth contact point. The fifth contact point and the sixth contact point are symmetrical in the second direction X 2 . 
     In addition, the fifth contact point is disposed at any position on a side that is of the fifth radiation section  22  and that is opposite to the sixth radiation section  23 , the sixth contact point is disposed at any position on a side that is of the sixth radiation section  23  and that is opposite to the fifth radiation section  22 , and a distance between the fifth contact point and the sixth contact point falls within a second preset range, to ensure the performance of the antenna unit. 
     A specific magnitude of the second preset range is not limited in this application provided that the distance between the fifth contact point and the sixth contact point can ensure that the antenna unit has good performance. 
     With reference to  FIG.  16   a    and  FIG.  16   b   , a specific implementation in which the fourth feed F 4  is separately connected to the fifth radiation section  22  and the sixth radiation section  23  is illustrated below. 
     Based on the second loop branch  20  shown in  FIG.  15   a   , as shown in  FIG.  16   a   , there is a same distance between the fifth radiation section  22  and the sixth radiation section  23 , the distance is aa, and the distance aa falls within the second preset range. Therefore, the fourth feed F 4  may be disposed at any position between the fifth radiation section  22  and the sixth radiation section  23 . For ease of description, in  FIG.  16   a   , an example in which the fourth feed F 4  is disposed at each of a position corresponding to a solid line and a position corresponding to a dashed line is used for illustration. 
     Based on the second loop branch  20  shown in  FIG.  15   b   , as shown in  FIG.  16   b   , a minimum distance and a maximum distance between the fifth radiation section  22  and the sixth radiation section  23  are respectively a distance aa1 and a distance aa2, the second preset range is set to be less than or equal to a distance aa3, and the distance aa3 is less than the distance aa2 and greater than the distance aa1. Therefore, the fourth feed F 4  may be disposed at any position corresponding to a distance that is greater than or equal to the distance aa1 and less than or equal to the distance aa3. For ease of description, in  FIG.  16   b   , an example in which the fourth feed F 4  is disposed at each of a position corresponding to the distance aa1 and a position corresponding to the distance aa3 is used for illustration. 
     In addition, a fourth matching component may be disposed between the fourth feed F 4  and the fifth contact point and/or between the fourth feed F 4  and the sixth contact point, to adjust the frequency band of the antenna unit, so that the fourth feed F 4  can obtain a better pattern and better cross polarization performance, to improve the performance of the antenna unit. A specific implementation form of the fourth matching component is not limited in this application. For example, the fourth matching component may be a capacitor, an inductor, a capacitor and an inductor, a capacitor and a switch, an inductor and a switch, or a capacitor, an inductor, and a switch. In this application, no limitation is imposed on a capacitance value and a quantity of capacitors, an inductance value and a quantity of inductors, a type and a quantity of switches, or a connection relationship between any two of the capacitor, the inductor, and the switch. 
     Based on the foregoing embodiment, the antenna unit may further include a second non-conductive support member  24 , a third conductive member  25 , and a fourth conductive member  26 . The third conductive member  25  and the fourth conductive member  26  are suspended by using the second non-conductive support member  24 , and the third conductive member  25  and the fourth conductive member  26  are symmetrically disposed in the second direction X 2 . A length of the third conductive member  25  is a ½ wavelength, and a length of the fourth conductive member  26  is a ½ wavelength. The wavelength is a wavelength corresponding to any frequency in an operating frequency band of the antenna unit. 
     In this application, the third conductive member  25  and the fourth conductive member  26  are made of conductive materials, and may be suspended by using the second non-conductive support member  24  in a manner such as a manner of using a surface-mount technology or etching. Therefore, the third conductive member  25  and the fourth conductive member  26  can extend a bandwidth of the antenna unit, to improve the performance of the antenna unit. Usually, larger widths of the third conductive member  25  and the fourth conductive member  26  indicate better performance of the antenna unit. 
     The third conductive member  25  or the fourth conductive member  26  may be in a plurality of shapes. For a shape of the third conductive member  25  or the fourth conductive member  26 , refer to the description content of the shape of the first conductive member or the second conductive member in Embodiment 1. Details are not described herein. For example, for the shape of the third conductive member  25  or the fourth conductive member  26 , refer to the patch (patch) shape shown in  FIG.  8   a    to  FIG.  8   c    or the closed ring shape shown in  FIG.  9   a    to  FIG.  9   c    in Embodiment 1. A specific shape of the third conductive member  25  or the fourth conductive member  26  is not limited in this application provided that it is met that the third conductive member  25  and the fourth conductive member  26  are symmetrically disposed in the second direction X 2 . 
     In addition, parameters such as widths, quantities, and positions of third conductive members  25  and fourth conductive members  26  are also not limited in this application. Based on the antenna unit shown in  FIG.  16   a    and with reference to  FIG.  17   a    to  FIG.  17   f   , the positions of the third conductive member  25  and the fourth conductive member  26  are described below by using examples. For ease of description, in  FIG.  17   a    to  FIG.  17   c   , an example in which the third conductive member  25  and the fourth second conductive member  26  are in rectangular crosssectional shapes is used for illustration, and in  FIG.  17   d    to  FIG.  17   f   , an example in which the third conductive member  25  and the fourth conductive member  26  are rectangular closed rings is used for illustration. 
     Optionally, the third conductive member  25  and the fourth conductive member  26  may be disposed outside the fourth radiation section  21 . For example, the third conductive member  25  and the fourth conductive member  26  may be horizontally symmetrically disposed outside the fourth radiation section  21  in the second direction X 2 , as shown in  FIG.  17   a    and  FIG.  17   b   . In  FIG.  17   a   , a direction of placing the third conductive member  25  and the fourth conductive member  26  is perpendicular to the second direction X 2 , and in  FIG.  17   b   , a direction of placing the first conductive member and the second conductive member is not perpendicular to the second direction X 2 . For another example, the third conductive member  25  and the fourth conductive member  26  may be vertically symmetrically disposed outside the fourth radiation section  21  in the second direction X 2 , as shown in  FIG.  17   c   . 
     Optionally, the third conductive member  25  and the fourth conductive member  26  may be disposed inside the fourth radiation section  21 . For example, the third conductive member  25  and the fourth conductive member  26  may be horizontally symmetrically disposed inside the fourth radiation section  21  in the second direction X 2 , as shown in  FIG.  17   d    and  FIG.  17   e   . In  FIG.  17   b   , a direction of placing the third conductive member  25  and the fourth conductive member  26  is perpendicular to the second direction X 2 , and in  FIG.  17   e   , a direction of placing the third conductive member  25  and the fourth conductive member  26  is not perpendicular to the second direction X 2 . For another example, the third conductive member  25  and the fourth conductive member  26  may be vertically symmetrically disposed inside the fourth radiation section  21  in the second direction X 2 , as shown in  FIG.  17   f   . 
     It should be noted that the positions of the third conductive member  25  and the fourth conductive member  26  are not limited to the foregoing implementations. 
     In addition, the second non-conductive support member  24  is made of a non-conductive material. Parameters such as a quantity, a material, and a position of second non-conductive support members  24  are not limited in this application. Optionally, the second non-conductive support member  24  may be a glass battery cover, a plastic battery cover, or an explosion-proof film. This is not limited in this application. 
     In a specific embodiment, based on the antenna unit shown in  FIG.  16   a    and with reference to  FIG.  18   a    to  FIG.  18   i   , a structure, the performance, and current distribution of the antenna unit in this application are described in detail. 
       FIG.  18   a    is a schematic diagram of a topology of the antenna unit shown in  FIG.  16   a   . As shown in  FIG.  18   a   , the antenna unit may include a second loop antenna (ABGHIJKLCD), the feeding branch  27  (EF), the third feed F 3 , and the fourth feed F 4 . The third feed F 3  is coupled and fed through a fourth contact point E, and the fourth feed F 4  is fed through a fifth contact point B and a sixth contact point C. A point A and a point D are ground points, and are jointly used as a ground of a microstrip line of the fourth feed F 4 . The third matching component of the third feed F 3  is a 0.6 pF capacitor connected in series, and the fourth matching component of the fourth feed F 4  is a 1.5 nH inductor connected in series. The third feed F 3  excites a signal at a C-mode port of the second loop antenna (ABGHIJKLCD), and a specific absorption rate (specific absorption rate, SAR) value is not greater than 0.75. The fourth feed F 4  excites a signal at a D-mode port of the second loop antenna (ABGHIJKLCD). A maximum SAR value is 4.23, and a second resonant SAR is relatively low, and is 1.2. 
     In conclusion, the signal at the C-mode port of the second loop antenna (ABGHIJKLCD) enables the antenna unit to form an antenna  1 , and the signal at the D-mode port of the second loop antenna (ABGHIJKLCD) enables the antenna unit to form an antenna  2 . Therefore, the antenna unit can form two antennas. 
     Table 1 shows an SAR simulation value of the antenna  1 , where backside (backside) is a posture in which an SAR probe is located at a back of the electronic device and that is in a region 5 mm away from the antenna. Table 2 shows an SAR simulation value of the antenna  2 . An ECC between the antenna  1  and the antenna  2  varies with a frequency. For details, refer to Table 3. Isolation between the antenna  1  and the antenna  2  is greater than 19.5 dB, and the ECC is less than 0.007. The third feed F 3  may cover frequency bands N77 and N79, and in-band efficiency is -3 dB. The fourth feed F 4  may cover a frequency band N77, and in-band efficiency is -5 dB. 
     
       
         
          TABLE 1
           
               
               
               
               
               
               
               
               
             
               
                 SAR simulation value of the antenna 1 
               
               
                 Antenna 1 
                 3 GHz 
                 3.64 GHz 
                 4.42 GHz 
               
               
                 Input power 24 dBm 
                 Resonant frequency 
                 1 g 
                 10 g 
                 1 g 
                 10 g 
                 1 g 
                 10 g 
               
             
            
               
                   
                 Free space (free space, FS) simulation efficiency 
                 -2.2 
                 -2.2 
                 -2.8 
                 -2.8 
                 -2.3 
                 -2.3 
               
               
                 Body specific absorption rate (body specific absorption rate, body SAR) 
                 5 mm backside 
                 2.99 
                 1.43 
                 1.78 
                 0.80 
                 2.62 
                 1.07 
               
               
                 Normalized efficiency 
                   
                 -5 
                 -5 
                 -5 
                 -5 
                 -5 
                 -5 
               
               
                 Normalized 5 mm body SAR 
                 5 mm backside 
                   
                 0.75 
                   
                 0.48 
                   
                 0.57 
               
            
           
         
       
     
     
       
         
          TABLE 2
           
               
               
               
               
               
               
             
               
                 SAR simulation value of the antenna 2 
               
               
                 Antenna 2 
                 3.13 GHz 
                 4.22 GHz 
               
               
                 Input power 24 dBm 
                 Resonant frequency 
                 1 g 
                 10 g 
                 1 g 
                 10 g 
               
             
            
               
                   
                 FS simulation efficiency 
                 -4.1 
                 -4.1 
                 -2.8 
                 -2.8 
               
               
                 Body SAR 
                 5 mm backside 
                 16.80 
                 5.20 
                 6.25 
                 2.01 
               
               
                 Normalized efficiency 
                   
                 -5 
                 -5 
                 -5 
                 -5 
               
               
                 Antenna 2 
                 3.13 GHz 
                 4.22 GHz 
               
               
                 Normalized 5 mm body SAR 
                 5 mm backside 
                   
                 4.23 
                   
                 1.21 
               
            
           
         
       
     
     
       
         
          TABLE 3
           
               
               
               
               
             
               
                 ECC between the antenna 1 and the antenna 2 
               
             
            
               
                 Frequency 
                 3.3 
                 3.6 
                 4.2 
               
               
                 ECC 
                 0.002 
                 0.0001 
                 0.007 
               
            
           
         
       
     
       FIG.  18   b    is a schematic diagram of waveforms of S parameters of the third feed F 3  and the fourth feed F 4  in  FIG.  18   a    on different operating frequency bands. In  FIG.  18   b   , a horizontal coordinate is a frequency in a unit of GHz, and a vertical coordinate is an input reflection coefficient S 11 , a reverse transmission coefficient S12/a forward transmission coefficient S21, and an output reflection coefficient S22 in S parameters, and is in a unit of dB. As shown in  FIG.  18   b   , a curve  1  represents an input reflection coefficient S11 of the third feed F 3 , there is a resonant point in the curve  1  (a signal at a D-mode port of a corresponding first feed), a curve  2  represents reverse transmission coefficients S12/forward transmission coefficients S21 of the third feed F 3  and the fourth feed F 4 , and a curve  3  represents an output reflection coefficient S22 of the fourth feed F 4 . 
       FIG.  18   c    is a diagram of waveforms of system efficiency and radiation efficiency of each of the third feed F 3  and the fourth feed F 4  in  FIG.  18   a   . In  FIG.  18   c   , a horizontal coordinate is a frequency in a unit of GHz, and a vertical coordinate is system efficiency in a unit of dB. As shown in  FIG.  18   c   , a curve  1  represents system efficiency of the third feed F 3 , a curve  2  represents radiation efficiency of the third feed F 3 , a curve  3  represents system efficiency of the fourth feed F 4 , and a curve  4  represents radiation efficiency of the fourth feed F 4 . 
     Based on the foregoing description and with reference to  FIG.  18   d    to  FIG.  18   i   , circuit direction distribution of the antenna unit is described below by using an example. 
       FIG.  18   d    is a diagram of current distribution of the antenna unit that exists when the third feed F 3  excites a half wavelength mode of the second loop branch  20  at 1.4 GHz.  FIG.  18   e    is a diagram of current distribution of the antenna unit that exists when the third feed F 3  excites a two-thirds wavelength mode of the second loop branch  20  at 3 GHz.  FIG.  18   f    is a diagram of current distribution of the antenna unit that exists when the third feed F 3  excites a two-thirds wavelength mode of the second loop branch  20  at 3.6 GHz.  FIG.  18   g    is a diagram of current distribution of the antenna unit that exists when the third feed F 3  excites a two-thirds wavelength mode of the second loop branch  20  at 4 GHz and a quarter wavelength mode of the feeding branch  27  EF. 
       FIG.  18   h    is a diagram of current distribution of the antenna unit that exists when the fourth feed F 4  excites a single wavelength mode of the second loop branch  20  at 3.2 GHz.  FIG.  18   i    is a diagram of current distribution of the antenna unit that exists when the fourth feed F 4  excites a double wavelength mode of the second loop branch  20  at 4.2 GHz (the fourth matching component, namely, a 1.5 nH inductor, is connected in series, and a radiation section AB and a radiation section CD function as parallel inductors). 
     In another specific embodiment, based on the antenna unit shown in  FIG.  16   a    and with reference to  FIG.  19   a    to  FIG.  19   j   , a structure, the performance, and current distribution of the antenna unit in this application are described in detail. A difference from the foregoing embodiment is that the third feed F 3  is connected to a different third matching component, and the fourth feed F 4  is connected to a different fourth matching component. 
       FIG.  19   a    is a schematic diagram of a topology of the antenna unit shown in  FIG.  16   a   . As shown in  FIG.  19   a   , the antenna unit includes a second loop antenna (ABGHIJKLCD), the feeding branch  27  (EF), the third feed F 3 , and the fourth feed F 4 . The third feed F 3  is coupled and fed through a fourth contact point E, and the fourth feed F 4  is fed through a fifth contact point B and a sixth contact point C. A point A and a point D are ground points, and are jointly used as a ground of a microstrip line of the fourth feed F 4 . The third matching component of the third feed F 3  is a 1 pF capacitor connected in series, and the fourth matching component of the fourth feed F 4  is a 0.3 pF capacitor and a 4 nH inductor connected in series. The third feed F 3  excites a signal at a C-mode port of the second loop antenna (ABGHIJKLCD). The fourth feed F 4  excites a signal at a D-mode port of the second loop antenna ABGHIJKLCD. The third feed F 3  may cover frequency bands Wi-Fi 2.4G, N77, N79, and Wi-Fi 5G. In-band efficiency at Wi-Fi 2.4G is -3.2 dB, in-band efficiency at N77 is -5.7 dB, in-band efficiency at N79 is -4.2 dB, and in-band efficiency at Wi-Fi 5G is -3.4 dB. The fourth feed F 4  may cover frequency bands Wi-Fi 2.4G and Wi-Fi 5G. In-band efficiency at Wi-Fi 2.4G is -3.2 dB, and in-band efficiency at Wi-Fi 5G is -3.7 dB. Maximum directivity of two antennas at Wi-Fi 2.4G is 3.7 dBi. 
     In conclusion, the signal at the C-mode port of the second loop antenna (ABGHIJKLCD) enables the antenna unit to form an antenna  1 , and the signal at the D-mode port of the second loop antenna (ABGHIJKLCD) enables the antenna unit to form an antenna  2 . Therefore, the antenna unit can form two antennas. Table 4 shows an SAR simulation value of the antenna  1 , and Table 5 shows an SAR simulation value of the antenna  2 . An ECC between the antenna  1  and the antenna  2  varies with a frequency. For details, refer to Table 6. Isolation between the antenna  1  and the antenna  2  is greater than 12.1 dB, and the ECC is less than 0.04. At Wi-Fi 2.4G, an SAR value of the signal at the C-mode port is 0.6, and an SAR value of the signal at the D-mode port is 2.86. At Wi-Fi 5G, an SAR value of the signal at the C-mode port is 1.7, and an SAR value of the signal at the D-mode port is 0.5. At N77 or N79, an SAR value of the signal at the C-mode port is 0.7. 
     
       
         
          TABLE 4
           
               
               
               
               
               
               
               
               
               
               
             
               
                 SAR simulation value of the antenna 1 
               
               
                 Antenna 1 
                 2.4 GHz 
                 3.7 GHz 
                 4.7 GHz 
                 5.8 GHz 
               
               
                 Input power 24 dBm 
                 Resonant frequency 
                 1 g 
                 10 g 
                 1 g 
                 10 g 
                 1 g 
                 10 g 
                 1 g 
                 10 g 
               
             
            
               
                   
                 FS simulation efficiency 
                 -2.3 
                 -2.3 
                 -5 
                 -5 
                 -1.5 
                 -1.5 
                 -2.3 
                 -2.3 
               
               
                 Body SAR 
                 5 mm backside 
                 2.48 
                 1.12 
                 1.49 
                 0.57 
                 6.02 
                 1.60 
                 9.48 
                 3.22 
               
               
                 Normalized efficiency 
                   
                 -5 
                 -5 
                 -5 
                 -5 
                 -5 
                 -5 
                 -5 
                 -5 
               
               
                 Normalized 5 mm body SAR 
                 5 mm backside 
                   
                 0.60 
                   
                 0.57 
                   
                 0.71 
                   
                 1.73 
               
            
           
         
       
     
     
       
         
          TABLE 5
           
               
               
               
               
               
               
             
               
                 SAR simulation value of the antenna 2 
               
               
                 Antenna 2 
                 2.4 GHz 
                 5.5 GHz 
               
               
                 Input power 24 dBm 
                 Resonant frequency 
                 1 g 
                 10 g 
                 1 g 
                 10 g 
               
             
            
               
                   
                 FS simulation efficiency 
                 -2.4 
                 -2.4 
                 -1.5 
                 -1.5 
               
               
                 Body SAR 
                 5 mm backside 
                 13.40 
                 5.21 
                 4.39 
                 1.32 
               
               
                 Normalized efficiency 
                   
                 -5 
                 -5 
                 -5 
                 -5 
               
               
                 Normalized 5 mm body SAR 
                 5 mm backside 
                   
                 2.86 
                   
                 0.59 
               
            
           
         
       
     
     
       
         
          TABLE 6
           
               
               
               
               
               
             
               
                 ECC between the antenna 1 and the antenna 2 
               
             
            
               
                 Frequency 
                 2.4 
                 3.6 
                 4.7 
                 5.5 
               
               
                 ECC 
                 0.0007 
                 0.004 
                 0.04 
                 0.007 
               
            
           
         
       
     
       FIG.  19   b    is a schematic diagram of waveforms of S parameters of the third feed F 3  and the fourth feed F 4  in  FIG.  19   a    on different operating frequency bands. In  FIG.  19   b   , a horizontal coordinate is a frequency in a unit of GHz, and a vertical coordinate is an input reflection coefficient S11, a reverse transmission coefficient S12/a forward transmission coefficient S21, and an output reflection coefficient S22 in S parameters, and is in a unit of dB. As shown in  FIG.  19   b   , a curve  1  represents an input reflection coefficient S11 of the third feed F 3 , a curve  2  represents reverse transmission coefficients S12/forward transmission coefficients S21 of the third feed F 3  and the fourth feed F 4 , and a curve  3  represents an output reflection coefficient S22 of the fourth feed F 4 . 
       FIG.  190    is a diagram of waveforms of system efficiency and radiation efficiency of each of the third feed F 3  and the fourth feed F 4  in  FIG.  19   a   . In  FIG.  19   c   , a horizontal coordinate is a frequency in a unit of GHz, and a vertical coordinate is system efficiency in a unit of dB. As shown in  FIG.  19   c   , a curve  1  represents system efficiency of the third feed F 3 , a curve  2  represents radiation efficiency of the third feed F 3 , a curve  3  represents system efficiency of the fourth feed F 4 , and a curve  4  represents radiation efficiency of the fourth feed F 4 . 
     Based on the foregoing description and with reference to  FIG.  19   d    to  FIG.  19   j   , circuit direction distribution of the antenna unit is described below by using an example. 
       FIG.  19   d    is a diagram of current distribution of the antenna unit that exists when the third feed F 3  excites a two-thirds wavelength mode of the second loop branch  20  at 2.4 GHz.  FIG.  190    is a diagram of current distribution of the antenna unit that exists when the third feed F 3  excites a two-thirds wavelength mode of the second loop branch  20  at 3.6 GHz (a radiation section AB and a radiation section CD function as parallel inductors).  FIG.  19   f    is a diagram of current distribution of the antenna unit that exists when the third feed F 3  excites a two-fifths wavelength mode of the second loop branch  20  at 4.7 GHz.  FIG.  19   g    is a diagram of current distribution of the antenna unit that exists when the third feed F 3  excites a two-thirds wavelength mode of the second loop branch  20  at 5.8 GHz. 
       FIG.  19   h    is a diagram of current distribution of the antenna unit that exists when the fourth feed F 4  excites a single wavelength mode of the second loop branch  20  at 2.4 GHz.  FIG.  19   i    is a diagram of current distribution of the antenna unit that exists when the fourth feed F 4  excites a double wavelength mode of the second loop branch  20  at 4 GHz.  FIG.  19   j    is a diagram of current distribution of the antenna unit that exists when the fourth feed F 4  excites a triple wavelength mode of the second loop branch  20  at 5.6 GHz. 
     In another specific embodiment, based on the antenna unit shown in  FIG.  17   a    and with reference to  FIG.  20   a    to  FIG.  20   i   , a structure, the performance, and current distribution of the antenna unit in this application are described in detail. A difference from the first specific embodiment is that the second non-conductive support member  24 , the third conductive member 25 MN, and the fourth conductive member  26  OP are added. 
       FIG.  20   a    is a schematic diagram of a topology of the antenna unit shown in  FIG.  17   a   . As shown in  FIG.  20   a   , the antenna unit includes a second loop antenna (ABGHIJKLCD), the feeding branch  27  (EF), the third feed F 3 , the fourth feed F 4 , the second non-conductive support member  24  (not shown in  FIG.  20   a   ), the third conductive member 25 MN, and the fourth conductive member  26  OP. The third feed F 3  is coupled and fed through a fourth contact point E, and the fourth feed F 4  is fed through a fifth contact point B and a sixth contact point C. A point A and a point D are ground points, and are jointly used as a ground of a microstrip line of the fourth feed F 4 . The third conductive member  25  (MN) and the fourth conductive member  26  (OP) are used to extend the bandwidth of the antenna unit. The third matching component of the third feed F 3  is a 0.6 pF capacitor connected in series, and the fourth matching component of the fourth feed F 4  is a 1.5 nH inductor connected in series. The third feed F 3  excites a signal at a C-mode port of the second loop antenna (ABGHIJKLCD). The fourth feed F 4  excites a signal at a D-mode port of the second loop antenna (ABGHIJKLCD). 
     In conclusion, the signal at the C-mode port of the second loop antenna (ABGHIJKLCD) enables the antenna unit to form an antenna  1 , and the signal at the D-mode port of the second loop antenna (ABGHIJKLCD) enables the antenna unit to form an antenna  2 . Therefore, the antenna unit can form two antennas. Table 7 shows SAR simulation values of the antenna  1 , the third conductive member  25  (MN), and the fourth conductive member  26  (OP), and Table 8 shows SAR simulation values of the antenna  2 , the third conductive member 25 MN, and the fourth conductive member  26  OP. An ECC between the antenna  1  and the antenna  2  varies with a frequency. For details, refer to Table 9. Isolation between the antenna  1  and the antenna  2  is greater than 12 dB, and the ECC is less than 0.09. The third conductive member  25  (MN) and the fourth conductive member  26  (OP) are used, and therefore both the third feed F 3  and the fourth feed F 4  may cover frequency bands N77 and N79. In-band efficiency of the third feed F 3  is -3 dB, and in-band efficiency of the fourth feed F 4  is -4 dB. In addition, the third conductive member 25 MN and the fourth conductive member  26  OP are used, and therefore a maximum SAR value of the antenna  2  is 1.89 and a maximum SAR value of the antenna  1  is 1.18. 
     
       
         
          TABLE 7
           
               
               
               
               
               
               
               
               
               
               
               
               
             
               
                 SAR simulation values of the antenna 1, the third conductive member 25 (MN), and the fourth conductive member 26 (OP) 
               
               
                 Antenna 1, third conductive member 25 (MN), and fourth conductive member 26 (OP) 
                 2.98 GHz 
                 3.3 GHz 
                 3.73 GHz 
                 4.52 GHz 
                 5 GHz 
               
             
            
               
                 Input power 24 dBm 
                 Resonant frequency 
                 1 g 
                 10 g 
                 1 g 
                 10 g 
                 1 g 
                 10 g 
                 1 g 
                 10 g 
                 1 g 
                 10 g 
               
               
                   
                 FS simulation efficiency 
                 -1.9 
                 -1.9 
                 -2 
                 -2 
                 -1 
                 -1 
                 -1 
                 -1 
                 -4 
                 -4 
               
               
                 Body SAR 
                 5 mm backside 
                 3.25 
                 1.50 
                 3.14 
                 1.41 
                 3.42 
                 1.32 
                 9.41 
                 2.35 
                 6.60 
                 1.49 
               
               
                 Normalized efficiency 
                   
                 -5 
                 -5 
                 -5 
                 -5 
                 -5 
                 -5 
                 -5 
                 -5 
                 -5 
                 -5 
               
               
                 Normalized 5 mm body SAR 
                 5 mm backside 
                   
                 0.73 
                   
                 0.71 
                   
                 0.53 
                   
                 0.94 
                   
                 1.18 
               
            
           
         
       
     
     
       
         
          TABLE 8
           
               
               
               
               
               
               
               
               
               
               
               
               
             
               
                 SAR simulation values of the antenna 2, the third conductive member 25 (MN), and the fourth conductive member 26 (OP) 
               
               
                 Antenna 2, third conductive member 25 (MN), and fourth conductive member 26 (OP) 
                 2.85 GHz 
                 3.32 GHz 
                 4 GHz 
                 4.52 GHz 
                 5 GHz 
               
               
                 Input power 24 dBm 
                 Resonant frequency 
                 1 g 
                 10 g 
                 1 g 
                 10 g 
                 1 g 
                 10 g 
                 1 g 
                 10 g 
                 1 g 
                 10 g 
               
             
            
               
                   
                 FS simulation efficiency 
                 -1.9 
                 -1.9 
                 4.74 
                 4.74 
                 -3.4 
                 -3.4 
                 -4.7 
                 -4.7 
                 -2 
                 -2 
               
               
                 Body SAR 
                 5 mm backside 
                 21.07 
                 7.31 
                 5.80 
                 2.01 
                 6.40 
                 2.18 
                 4.43 
                 1.30 
                 10.57 
                 2.52 
               
               
                 Normalized efficiency 
                   
                 -5 
                 -5 
                 -5 
                 -5 
                 -5 
                 -5 
                 -5 
                 -5 
                 -5 
                 -5 
               
               
                 Normalized 5 mm body SAR 
                 5 mm backside 
                   
                 3.58 
                   
                 1.89 
                   
                 1.51 
                   
                 1.21 
                   
                 1.26 
               
            
           
         
       
     
     
       
         
          TABLE 9
           
               
               
               
               
               
             
               
                 ECC between the antenna 1 and the antenna 2 
               
             
            
               
                 Frequency 
                 3.3 
                 3.6 
                 4.2 
                 5 
               
               
                 ECC 
                 0.005 
                 0.004 
                 0.01 
                 0.09 
               
            
           
         
       
     
       FIG.  20   b    is a schematic diagram of waveforms of S parameters of the third feed F 3  and the fourth feed F 4  in  FIG.  20   a    on different operating frequency bands. In  FIGS.  20   b ,  a    horizontal coordinate is a frequency in a unit of GHz, and a vertical coordinate is an input reflection coefficient S11, a reverse transmission coefficient S12/a forward transmission coefficient S21, and an output reflection coefficient S22 in S parameters, and is in a unit of dB. As shown in  FIG.  20   b   , a curve  1  represents an input reflection coefficient S11 of the third feed F 3 , a curve 2represents reverse transmission coefficients S12/forward transmission coefficients S21 of the third feed F 3  and the fourth feed F 4 , and a curve  3  represents an output reflection coefficient S22 of the fourth feed F 4 . 
       FIG.  20   c    is a diagram of waveforms of system efficiency and radiation efficiency of each of the third feed F 3  and the fourth feed F 4  in  FIG.  20   a   . In  FIG.  20   c   , a horizontal coordinate is a frequency in a unit of GHz, and a vertical coordinate is system efficiency in a unit of dB. As shown in  FIG.  20   c   , a curve  1  represents system efficiency of the third feed F 3 , a curve  2  represents radiation efficiency of the third feed F 3 , a curve  3  represents system efficiency of the fourth feed F 4 , and a curve  4  represents radiation efficiency of the fourth feed F 4 . 
     Based on the foregoing description and with reference to  FIG.  20   d    to  FIG.  20   i    circuit direction distribution of the antenna unit is described below by using an example. 
       FIG.  20   d    is a diagram of current distribution of the antenna unit that exists when the third feed F 3  excites a two-thirds wavelength mode of the second loop branch  20  at 3 GHz.  FIG.  20   e    is a diagram of current distribution of the antenna unit that exists when the third feed F 3  excites a two-thirds wavelength mode of the second loop branch  20  at 3.7 GHz.  FIG.  20   f    is a diagram of current distribution of the antenna unit that exists when the third feed F 3  excites a two-fifths wavelength mode of the second loop branch  20  at 4.5 GHz.  FIG.  20   g    is a diagram of current distribution of the antenna unit that exists when the third feed F 3  excites a two-thirds wavelength mode of the second loop branch  20  at 2.9 GHz. 
       FIG.  20   h    is a diagram of current distribution of the antenna unit that exists when the fourth feed F 4  excites a single wavelength mode of the second loop branch  20  at 4 GHz.  FIG.  20   i    is a diagram of current distribution of the antenna unit that exists when the fourth feed F 4  excites a double wavelength mode of the second loop branch  20  at 2.5 GHz. 
     In another specific embodiment, based on the antenna unit shown in  FIG.  16   b    and with reference to  FIG.  21   a    to  FIG.  21   c   , a structure, the performance, and current distribution of the antenna unit in this application are described in detail. A difference from the first specific embodiment is that there is a different specific implementation form of the antenna unit. 
       FIG.  21   a    is a schematic diagram of a topology of the antenna unit shown in  FIG.  16   b   . As shown in  FIG.  21   a   , the antenna unit includes a second loop antenna (ABGHIJKLCD+MNO+PQR), the feeding branch  27  (EF), the third feed F 3 , and the fourth feed F 4 . The third feed F 3  is coupled and fed through a fourth contact point E, and the fourth feed F 4  is fed through a fifth contact point O and a sixth contact point P. A point M, a point N, a point Q, and a point R are ground points. The third matching component of the third feed F 3  is a 0.7 pF capacitor connected in series, and the fourth matching component of the fourth feed F 4  is a 0.3 pF capacitor connected in series. The third feed F 3  excites a signal at a C-mode port of the second loop antenna (ABGHIJKLCD+MNO+PQR). The fourth feed F 4  excites a signal at a D-mode port of the second loop antenna (ABGHIJKLCD+MNO+PQR). 
     In conclusion, the signal at the C-mode port of the second loop antenna (ABGHIJKLCD+MNO+PQR) enables the antenna unit to form an antenna  1 , and the signal at the D-mode port of the second loop antenna (ABGHIJKLCD+MNO+PQR) enables the antenna unit to form an antenna  2 . Therefore, the antenna unit can form two antennas. An ECC between the antenna  1  and the antenna  2  varies with a frequency. For details, refer to Table 10. Isolation between the antenna  1  and the antenna  2  is greater than 24.5 dB, and the ECC is less than 0.0077. The third feed F 3  may cover frequency bands N77 and N79, and in-band efficiency is -3 dB. The fourth feed F 4  may cover a frequency band N77, and in-band efficiency is -3.5 dB.  
     
       
         
          TABLE 10
           
               
               
               
               
             
               
                 ECC between the antenna 1 and the antenna 2 
               
             
            
               
                 Frequency 
                 4.4 
                 4.7 
                 5 
               
               
                 Frequency 
                 4.4 
                 4.7 
                 5 
               
               
                 ECC 
                 0.0002 
                 0.0035 
                 0.0077 
               
            
           
         
       
     
       FIG.  21   b    is a schematic diagram of waveforms of S parameters of the third feed F 3  and the fourth feed F 4  in  FIG.  21   a    on different operating frequency bands. In  FIG.  21   b   , a horizontal coordinate is a frequency in a unit of GHz, and a vertical coordinate is an input reflection coefficient S 11 , a reverse transmission coefficient S12/a forward transmission coefficient S21, and an output reflection coefficient S22 in S parameters, and is in a unit of dB. As shown in  FIG.  21   b   , a curve  1  represents an input reflection coefficient S11 of the third feed F 3 , a curve  2  represents reverse transmission coefficients S12/forward transmission coefficients S21 of the third feed F 3  and the fourth feed F 4 , and a curve  3  represents an output reflection coefficient S22 of the fourth feed F 4 . 
       FIG.  21 C  is a diagram of waveforms of system efficiency and radiation efficiency of each of the third feed F 3  and the fourth feed F 4  in  FIG.  21   a   . In  FIG.  21   c   , a horizontal coordinate is a frequency in a unit of GHz, and a vertical coordinate is system efficiency in a unit of dB. As shown in  FIG.  21   c   , a curve  1  represents system efficiency of the third feed F 3 , a curve  2  represents radiation efficiency of the third feed F 3 , a curve  3  represents system efficiency of the fourth feed F 4 , and a curve  4  represents radiation efficiency of the fourth feed F 4 . 
     In conclusion, it may be learned from the foregoing four embodiments that based on the same second loop branch  20 , the antenna unit in this application can implement two antennas with high isolation and a low envelope correlation coefficient ECC under excitation of the third feed F 3  and the fourth feed F 4 . 
     In Embodiment 2, based on a symmetrical arrangement of a same loop antenna (namely, the second loop branch and the feeding branch), the antenna unit respectively excites the signal at the C-mode port and the signal at the D-mode port of the loop antenna by using two feeds, so that the signal at the C-mode port is self-canceled at the D-mode port, and the signal at the D-mode port is self-canceled at the C-mode port, to implement signal isolation between the two ports, and the signal at the C-mode port and the signal at the D-mode port are complementary to each other in different radiation directions, to implement two antennas with high isolation and a low ECC. In this way, good antenna performance can be ensured, so that the electronic device can fully use the antenna unit in limited space to implement various scenarios. In addition, the electronic device can include a larger quantity of antennas in the limited space, to improve utilization of antenna space. 
     For example, this application further provides an electronic device. The electronic device in this application may include a printed circuit board and at least one antenna unit. The electronic device includes but is not limited to a device such as a mobile phone, a headset, a tablet computer, a portable computer, a wearable device, or a data card. 
     In this application, any antenna unit and the printed circuit board share a ground. The specific implementation in any one of the embodiments in  FIG.  1    to  FIG.  21   c    may be used for the antenna unit. For example, the electronic device may include an antenna unit implemented based on the description content in Embodiment 1, may include an antenna unit implemented based on the description content in Embodiment 2, or may include an antenna unit implemented based on the description content in Embodiment 1 and an antenna unit implemented based on the description content in Embodiment 2. This is not limited in this application. In addition, the any antenna unit may be disposed on a frame of the electronic device, may be disposed on the printed circuit board, or may be disposed by using a bracket. This is not limited in this application. 
     The electronic device in this application includes at least one antenna unit. A signal at a C-mode port and a signal at a D-mode port of a same loop antenna in any antenna unit are respectively excited by using two feeds, and the antenna unit is electrically symmetrically disposed, so that the signal at the C-mode port is self-cancelled at the D-mode port, and the signal at the D-mode port is self-cancelled at the C-mode port, to implement signal isolation between the two ports, and the signal at the C-mode port and the signal at the D-mode port can be complementary to each other in different radiation directions, to implement two antennas with high isolation and a low envelope correlation coefficient ECC based on the same loop antenna. In this way, good antenna performance is ensured, so that the electronic device can fully use the antenna unit in limited space to implement various scenarios, for example, implement application to a multi-antenna scenario such as a diversity antenna or a multiple-input multiple-output (multiple-input multiple-output, MIMO) antenna, a scenario of obtaining a pattern through combination, and a pattern switching scenario such as switching between a horizontal direction and a vertical direction. In addition, the electronic device can include a larger quantity of antennas in the limited space, to improve utilization of antenna space.