Patent Publication Number: US-9853364-B2

Title: Multiple-antenna system and mobile terminal

Description:
This application is a continuation of International Patent Application No. PCT/CN2014/073023, filed on Mar. 7, 2014, which claims priority to Chinese Patent Application No. 201310270549.8, filed on Jun. 28, 2013, both of which are hereby incorporated by reference in their entireties. 
    
    
     TECHNICAL FIELD 
     The present invention relates to the field of wireless communications technologies, and in particular, to a multiple-antenna system and a mobile terminal. 
     BACKGROUND 
     With rapid development of mobile communications technologies, application of small-sized mobile terminals, for example, mobile phones, is becoming increasingly popular. An air interface used by a small-sized mobile terminal to communicate with a base station and to receive and transmit a radio frequency signal is an antenna, and power of the small-sized mobile terminal is transmitted to the base station in a form of an electromagnetic wave by using the antenna. Therefore, the antenna plays a key role in the mobile communications technologies. 
     A planar inverted-F antenna (PIFA) is a common antenna used on a mobile phone and is increasingly widely applied to a mobile terminal because of advantages of the PIFA, such as a small size, a light weight, a low profile, a simple structure, and ease of integration. 
     A PIFA includes four parts: a metallic ground plane, a radiation patch, a short-circuit structure, and a feeding network, where the radiation patch may be in any shape. The PIFA has a resonant length that is only one fourth of an operating wavelength of an antenna, is small in size, and is in a plane structure, and therefore, can be applied to a small-sized portable mobile terminal such as a mobile phone. 
     However, as functions of a mobile terminal increase continuously, a multi-input multi-output (MIMO) technology emerges, which requires the mobile terminal to use multiple antennas to implement reception and transmission of data and information. However, multiple PIFAs are limited to such a cramped and complex electromagnetic environment as a mobile terminal, and therefore, a requirement for high isolation between multiple frequency bands cannot be met. 
     SUMMARY 
     In view of this, embodiments of the present invention provide a multiple-antenna system and a mobile terminal, so as to meet a requirement for high isolation between multiple frequency bands. 
     According to a first aspect, an embodiment of the present invention provides a multiple-antenna system. A planar inverted-F antenna PIFA of a first type includes a metallic ground plane, a dielectric plate, a radiation patch, a probe-type feeding unit, and a metallic shorting pin. The radiation patch is located on an upper surface of the dielectric plate and is connected to the metallic ground plane by using the probe-type feeding unit and the metallic shorting pin. A PIFA of a second type is perpendicular to the PIFA of the first type and includes a metallic ground plane, a radiation patch, a feeding unit, and a metallic shorted patch. The radiation patch is connected to the metallic ground plane by using the feeding unit and metallic shorted patch. In isolation stub is located on an edge of a side, close to the PIFA of the second type, of an upper surface of the dielectric plate of the PIFA of the first type. 
     With reference to the first aspect, in a first possible implementation manner of the first aspect, a distance from the PIFA of the first type to the PIFA of the second type is greater than or equal to a preset threshold. 
     With reference to the first possible implementation manner of the first aspect, in a second possible implementation manner of the first aspect, the preset threshold is 7 mm. 
     With reference to the first aspect or the first or the second possible implementation manner of the first aspect, in a third possible implementation manner of the first aspect, a U-shaped groove is etched on the radiation patch of the PIFA of the first type. 
     With reference to the first aspect or any one of the first to the third possible implementation manners of the first aspect, in a fourth possible implementation manner of the first aspect, an L-shaped slot is etched on the radiation patch of the PIFA of the second type. 
     With reference to the first aspect or any one of the first to the fourth possible implementation manners of the first aspect, in a fifth possible implementation manner of the first aspect, the feeding unit of the PIFA of the second type is an L-shaped coaxial feeding unit. 
     With reference to the first aspect or any one of the first to the fifth possible implementation manners of the first aspect, in a sixth possible implementation manner of the first aspect, the PIFA of the second type further includes an L-shaped folded metallic ground plane, where the L-shaped folded metallic ground plane is disposed on an edge of the metallic ground plane of the PIFA of the second type. 
     With reference to the first aspect or any one of the first to the sixth possible implementation manners of the first aspect, in a seventh possible implementation manner of the first aspect, there are four PIFAs of the first type and four PIFAs of the second type, where the four PIFAs of the first type are located at four corners of a quadrangle, two of the PIFAs of the second type are located outside a first side of the quadrangle, and the other two PIFAs of the second type are located outside a second side of the quadrangle, the first side is opposite to the second side, and a distance from any one of the PIFAs of the first type to a nearest PIFA of the second type is greater than or equal to 7 mm. 
     With reference to the seventh possible implementation manner of the first aspect, in an eighth possible implementation manner of the first aspect, a slot is etched on the radiation patch of the PIFA of the second type, and the radiation patch is in a shape obtained by cutting off three corners from a rectangular. 
     With reference to the first aspect or any one of the first to the eighth possible implementation manners of the first aspect, in a ninth possible implementation manner of the first aspect, a dielectric constant of the dielectric plate is between 1 and 10. 
     According to a second aspect, an embodiment of the present invention provides a mobile terminal, including a mobile terminal body and any one of the foregoing multiple-antenna systems, where the multiple-antenna system is connected to the mobile terminal body and is used to receive and transmit a signal for the mobile terminal body. 
     According to the multiple-antenna system and the mobile terminal that are provided in the foregoing embodiments, two different operating frequency bands may be provided by using two PIFAs. The two antennas are perpendicular to each other, and a distance between the two antennas is greater than or equal to a preset threshold, so that isolation between the antennas and isolation between the operating frequency bands meet an operating requirement of the multiple-antenna system. In addition, on a premise of meeting high isolation between multiple frequency bands, the multiple-antenna system occupies less space. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       To describe the technical solutions in the embodiments of the present invention more clearly, the following briefly introduces the accompanying drawings required for describing the embodiments. Apparently, the accompanying drawings in the following description show merely some embodiments of the present invention, and persons of ordinary skill in the art may still derive other drawings from these accompanying drawings without creative efforts. 
         FIG. 1  is a three-dimensional schematic diagram of a multiple-antenna system according to an embodiment of the present invention; 
         FIG. 2  is a three-dimensional schematic diagram of a multiple-antenna system according to another embodiment of the present invention; 
         FIG. 3  is a schematic diagram of the multiple-antenna system shown in  FIG. 2  on an azimuth plane; 
         FIG. 4 a    is a front view of a PIFA  10  of a first type in  FIG. 2 ; 
         FIG. 4 b    is a side view of the PIFA  10  of the first type; 
         FIG. 5 a    is a front view of a PIFA  80  of a second type in  FIG. 2 ; 
         FIG. 5 b    is a side view of the PIFA  80  of the second type; 
         FIG. 6 a    to  FIG. 6 d    are simulation diagrams of a parameter S of the multiple-antenna system shown in  FIG. 2  in a frequency band of 2.631 GHz-2.722 GHz; 
         FIG. 7 a    to  FIG. 7 d    are simulation diagrams of a parameter S of the multiple-antenna system shown in  FIG. 2  in a frequency band of 3.440 GHz-3.529 GHz; 
         FIG. 8 a    is a diagram of a normalized radiation direction of a PIFA  10  of a first type that operates at 2.7 GHz; 
         FIG. 8 b    is a diagram of a normalized radiation direction of a PIFA  10  of a first type that operates at 3.5 GHz; 
         FIG. 9 a    is a diagram of a normalized radiation direction of a PIFA  80  of a second type that operates at 2.7 GHz; 
         FIG. 9 b    is a diagram of a normalized radiation direction of a PIFA  80  of a second type that operates at 3.5 GHz; and 
         FIG. 10  is a schematic structural diagram of a mobile terminal according to another embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS 
     To make the objectives, technical solutions, and advantages of the present invention clearer, the following further describes the present invention in detail with reference to the accompanying drawings. Apparently, the described embodiments are merely some but not all of the embodiments of the present invention. All other embodiments obtained by persons of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention. 
       FIG. 1  is a three-dimensional schematic diagram of a multiple-antenna system according to an embodiment of the present invention. In this embodiment, the multiple-antenna system includes a PIFA  10  of a first type, a PIFA  30  of a second type, and an isolation stub  2 . 
     The PIFA  10  of the first type is located on an azimuth plane (for example, an xoy coordinate plane in  FIG. 1 ) and includes a metallic ground plane  11 , a dielectric plate  12 , a radiation patch  13 , a probe-type feeding unit  15 , and a metallic shorting pin  16 . 
     The radiation patch  13  is disposed on an upper surface of the dielectric plate  12  and is connected to the metallic ground plane  11  by using the probe-type feeding unit  15  and the metallic shorting pin  16 . 
     The isolation stub  2  is a patch and is disposed on an edge, close to the PIFA  30  of the second type, of the upper surface of the dielectric plate  12 , to improve isolation between the PIFA  10  of the first type and the PIFA  30  of the second type. 
     The PIFA  30  of the second type is located on a side view plane (for example, an xoz coordinate plane in  FIG. 1 ) perpendicular to the azimuth plane. That is, the PIFA  10  of the first type and the PIFA  30  of the second type are mutually orthogonal, thereby reducing coupling between the antennas and improving isolation between the antennas. The PIFA  30  of the second type includes a metallic ground plane  31 , a radiation patch  33 , a feeding unit  36 , and a metallic shorted patch  34 . The radiation patch  33  is connected to the metallic ground plane  31  by using the feeding unit  36  and the metallic shorted patch  34 . 
     A distance from the PIFA  10  of the first type to the PIFA  30  of the second type is set to be greater than or equal to a preset threshold (for example, 7 mm), which can further improve the isolation between the antennas. 
     According to the multiple-antenna system provided in this embodiment, two different operating frequency bands may be provided by using two PIFAs. The two antennas are perpendicular to each other, a distance between the two antennas is greater than or equal to a preset threshold, and the two antennas are isolated by an isolation stub, so that isolation between the antennas and isolation between the operating frequency bands meet an operating requirement of the multiple-antenna system. In addition, the PIFAs are small in size, so that the multiple-antenna system occupies less space, which facilitates further increase in a quantity of antennas and makes further reduction in a volume of a mobile terminal possible. 
     Further, a U-shaped groove  14  may be disposed on the radiation patch  13  of the PIFA  10  of the first type, so that the PIFA  10  of the first type can generate two different current paths, thereby enabling the PIFA  10  of the first type to implement two operating frequency bands. 
     Further, the feeding unit  36  may be an L-shaped coaxial feeding unit. An L-shaped slot  35  may be disposed on the radiation patch  33  of the PIFA  30  of the second type, so that the PIFA  30  of the second type can generate two different current paths, thereby enabling the PIFA  30  of the second type to implement two operating frequency bands. 
     Further, if there are multiple PIFAs of the second type on the side view plane, a straight-line-shaped slot  37  may be disposed on the radiation patch  33  of the PIFA  30  of the second type and three corners of the radiation patch  33  are cut off, which changes a flow direction of a current on the radiation patch of the PIFA  30  of the second type that operates in a high frequency band, thereby improving isolation, on the side view plane, between the PIFAs of the second type in the high frequency band. 
     Further, the PIFA  30  of the second type may further include an L-shaped folded metallic ground plane  32 , which can further improve isolation between the multiple PIFAs  30  of the second type. 
       FIG. 2  is a three-dimensional schematic diagram of a multiple-antenna system according to another embodiment of the present invention. In this embodiment, the multiple-antenna system includes four PIFAs of a first type: a PIFA  10  of the first type, a PIFA  20  of the first type, a PIFA  50  of the first type, and a PIFA  60  of the first type; and four PIFAs of a second type: a PIFA  30  of the second type, a PIFA  40  of the second type, a PIFA  70  of the second type, and a PIFA  80  of the second type. 
     The PIFA  10  of the first type, the PIFA  20  of the first type, the PIFA  50  of the first type, and the PIFA  60  of the first type are located on an azimuth plane (for example, a plane where an x-axis and a y-axis are located in  FIG. 1 ). A distance, in a direction of the y-axis, between the PIFA  10  of the first type and the PIFA  20  of the first type is: W 1 =30 mm. A distance, in a direction of the x-axis, between the PIFA  20  of the first type and the PIFA  60  of the first type is: L 1 =20 mm. The PIFA  10  of the first type and the PIFA  20  of the first type are connected to the PIFA  50  of the first type and the PIFA  60  of the first type by using a dielectric plate whose dielectric constant ∈ r =4.4. It should be noted that, the distance, in the direction of the y-axis, between the PIFA  10  of the first type and the PIFA  20  of the first type may be less than 30 mm or may be greater than 30 mm, provided that the distance can meet a requirement for isolation between the PIFA  10  of the first type and the PIFA  20  of the first type. The distance, in the direction of the x-axis, between the PIFA  20  of the first type and the PIFA  60  of the first type may be less than 20 mm or may be greater than 20 mm, provided that the distance can meet a requirement for isolation between the PIFA  60  of the first type and the PIFA  20  of the first type. The foregoing dielectric constant may be set to another value. 
     The PIFA  30  of the second type, the PIFA  40  of the second type, the PIFA  70  of the second type, and the PIFA  80  of the second type are located on a side view plane. A distance, in a direction of the y-axis, between the PIFA  70  of the second type and the PIFA  80  of the second type is : W 2 =10 mm. 
     The side view plane is perpendicular to the azimuth plane. Distances, in a direction of the x-axis, between the PIFA  60  of the first type and the PIFA  80  of the second type, between the PIFA  50  of the first type and the PIFA  70  of the second type, between the PIFA  10  of the first type and the PIFA  30  of the second type, and between the PIFA  20  of the first type and the PIFA  40  of the second type are all: L 1 ≧7 mm. The PIFA  30  of the second type, the PIFA  10  of the first type, the PIFA  50  of the first type, and the PIFA  70  of the second type are respectively symmetrical to the PIFA  40  of the second type, the PIFA  20  of the first type, the PIFA  60  of the first type, and the PIFA  80  of the second type with respect to an xoz coordinate plane. The PIFA  30  of the second type, the PIFA  40  of the second type, the PIFA  10  of the first type, and the PIFA  20  of the first type are respectively symmetrical to the PIFA  70  of the second type, the PIFA  80  of the second type, the PIFA  50  of the first type, and the PIFA  60  of the first type with respect to a yoz coordinate plane. That is, the four antennas, namely, the PIFA  10  of the first type, the PIFA  20  of the first type, the PIFA  50  of the first type, and the PIFA  60  of the first type, on the azimuth plane have an orthogonal polarization relationship with the four antennas, namely, the PIFA  30  of the second type, the PIFA  40  of the second type, the PIFA  70  of the second type, and the PIFA  80  of the second type, on the side view plane. 
     The PIFA  10  of the first type, the PIFA  20  of the first type, the PIFA  50  of the first type, and the PIFA  60  of the first type are in a same structure and all include a metallic ground plane, a dielectric plate, a radiation patch, a probe-type feeding unit, and a metallic shorting pin. 
     The following uses the PIFA  10  of the first type to describe the structure of the PIFAs of the first type. 
     The PIFA  10  of the first type includes a metallic ground plane  11 , a dielectric plate  12 , a radiation patch  13 , a probe-type feeding unit  15 , and a metallic shorting pin  16 . 
     As shown in  FIG. 4 a    and  FIG. 4 b   , a length of the metallic ground plane  11  is: a 1 =45 mm, and a width of the metallic ground plane  11  is: a w =20 mm. A length of the dielectric plate  12  is: b 1 =40 mm, a width of the dielectric plate  12  is: b w =20 mm, and a height of the dielectric plate  12  is: h 1 =0.9 mm. A length of the radiation patch  13  is: c 1 =11.9 mm, a width of the radiation patch  13  is: c w =10 mm, a horizontal distance from the radiation patch  13  to a narrow side of the metallic ground plane  11  is: g=8.3 mm, and a horizontal distance from the radiation patch  13  to a wide side of the metallic ground plane  11  is: i=8 mm. 
     The radiation patch  13  is printed on an upper surface of the dielectric plate  12  and is connected to the metallic ground plane  11  by using the metallic shorting pin  16 . A foam support  9  is used as a support between the dielectric plate  12  and the metallic ground plane  11 . 
     A U-shaped groove  14  is etched on the radiation patch  13 . For example, a length of the U-shaped groove  14  is: d 1 =10.55 mm, a width of the U-shaped groove  14  is: d w =9.4 mm, a line width of the U-shaped groove  14  is: W=0.3 mm, a distance from a base side of the U-shaped groove  14  to a base side of the radiation patch  13  is: v=0.4 mm, and a distance from a right side of the U-shaped groove  14  to a right side of the radiation patch  13  and a distance from a left side of the U-shaped groove  14  to a left side of the radiation patch  13  are both 0.3 mm. After the U-shaped groove  14  is etched, the PIFA  10  of the first type is enabled to operate in two frequency bands: 2.558 GHz-2.801 GHz and 3.387 GHz-3.666 GHz. The PIFA  10  of the first type may be enabled to operate in another two frequency bands by adjusting values of c 1  and c w  and values of d 1  and d w , so as to meet a requirement for different operating frequency bands of the PIFA of the first type. 
     A radius of the probe-type feeding unit  15  is 0.7 mm, a height of the probe-type feeding unit  15  is 9.55 mm, and a distance from a center of the probe-type feeding unit  15  to the base side of the radiation patch  13  is 7.2 mm. 
     A radius of the metallic shorting pin  16  is 0.5 mm, a height of the metallic shorting pin  16  is 9.55 mm, and a distance from a center of the metallic shorting pin  16  to the center of the probe-type feeding unit  15  is 3.8 mm. 
     An operating bandwidth and an impedance matching feature of the PIFA  10  of the first type can be adjusted by adjusting the radiuses, locations, and the heights of the probe-type feeding unit  15  and the metallic shorting pin  16 . 
     An isolation stub  3  is printed on the upper surface of the dielectric plate  12 . The isolation stub  3  is a rectangular metallic patch with a length of 70 mm and a width of 1.5 mm and is located between the PIFA of the first type and the PIFA of the second type. It can be seen from  FIG. 2  that, the dielectric plate of the PIFA  10  of the first type and the dielectric plate of the PIFA  20  of the first type are connected at a side close to the PIFA  30  of the second type and the PIFA  40  of the second type, where a width of a connection part is the same as the width of the isolation stub  3 . 
     The isolation stub  3  resonates at a range around 2.7 GHz, which can increase isolation between the antennas by approximately 2.5 dB when the antennas operate in a frequency band of 2.675 GHz-2.762 GHz. 
     The PIFA  30  of the second type, the PIFA  40  of the second type, the PIFA  70  of the second type, and the PIFA  80  of the second type are in a same structure and all include a metallic ground plane, an L-shaped folded metallic ground plane, an L-shaped coaxial feeding unit, a metallic shorted patch, and a radiation patch. 
     The following uses the PIFA  80  of the second type to describe the structure of the PIFAs of the second type. 
     The PIFA  80  of the second type includes a metallic ground plane  81 , an L-shaped folded metallic ground plane  82 , an L-shaped coaxial feeding unit  86 , a metallic shorted patch  84 , and a radiation patch  83 . 
     As shown in  FIG. 5 a   , a length of the metallic ground plane  81  is: a 1l =30 mm, and a width of the metallic ground plane  81  is: a 1w =8.6 mm. The L-shaped folded metallic ground plane  82  is disposed on an edge of the metallic ground plane  81 . A height of the L-shaped folded metallic ground plane  82  is h 8 =8 mm, and a length and a width of the L-shaped folded metallic ground plane  82  are respectively: b 1l =3 mm and b 1w =5 mm. The L-shaped folded metallic ground plane  82  can implement miniaturization of the PIFA  80  of the second type, thereby reducing space occupied by antennas. 
     The radiation patch  83  is connected to the metallic ground plane  81  by using the metallic shorted patch  84 . 
     The radiation patch  83  is a metallic patch that is etched with an L-shaped slot  85  and disposed with a straight-line-shaped slot  87  and that is in a shape obtained by cutting off three corners from a rectangular metallic patch. 
     A length of the radiation patch  83  is: c 1l =22.8 mm, and a width of the radiation patch  83  is: c 1w =8.4 mm, and a horizontal distance from the radiation patch  83  to a wide side of the metallic ground plane  81  is: 1=0.2 mm, and a horizontal distance from the radiation patch  83  to a narrow side of the metallic ground plane  81  is: m=4.5 mm. 
     A length of the L-shaped slot  85  is: e l =15.3 mm, and a width of the L-shaped slot  85  is: e w =5.5 mm. A slot width of the L-shaped slot  85  is 1 mm. A distance from a base side of the L-shaped slot  85  to a base side of the radiation patch  83  is 3.1 mm. A distance from a left side of the L-shaped slot  85  to a left side of the radiation patch  83  is 2.9 mm. After the L-shaped slot  85  is etched, the PIFA  80  of the second type is enabled to operate in two frequency bands: 2.631 GHz-2.722 GHz and 3.440 GHz-3.529 GHz. Two operating frequency bands required by the PIFA  80  of the second type can be obtained by adjusting values of c 1l  and c 1w  and values of e l  and e w . 
     Among the three corners that are cut off, two corners have a side length of 2 mm and the other corner has a side length of 1 mm. 
     A width of the straight-line-shaped slot  87  is 0.1 mm, and a length of the straight-line-shaped slot  87  is 6.5 mm. Cutting off three corners from a rectangular metallic patch and disposing a slot on a remaining metallic patch can improve isolation between the PIFAs of the second type when the PIFAs of the second type operate in a high frequency band. 
     A width of the L-shaped coaxial feeding unit  86  is 7.5 mm, and a height of the L-shaped coaxial feeding unit  86  is 6 mm. The L-shaped coaxial feeding unit  86  is in a shape of a rectangle obtained by cutting off a rectangle on a corner, where a length of the rectangle that is cut off is 3 mm, and a width of the rectangle that is cut off 4 mm. 
     Because the PIFA  30  of the second type, the PIFA  40  of the second type, the PIFA  70  of the second type, and the PIFA  80  of the second type are in the same structure, cutting off the rectangle can effectively improve isolation, in a frequency band of 3.466 GHz-3.546 GHz, between the PIFA  70  of the second type and PIFA  80  of the second type and between the PIFA  30  of the second type and PIFA  40  of the second type. 
     A distance from the metallic shorted patch  84  to the L-shaped coaxial feeding unit  86  is 4.5 mm. A width of the metallic shorted patch  84  is 0.9 mm, and a height of the metallic shorted patch  84  is 8 mm. 
     An operating frequency band and an impedance matching feature of the antenna can be adjusted by setting locations, the widths, and the heights of the L-shaped coaxial feeding unit  86  and the metallic shorted patch  84 . 
     The multiple-antenna system provided in this embodiment includes four PIFAs of the first type and four PIFAs of the second type. A distance from an antenna on an azimuth plane to a nearest antenna on a side view plane is equal to 7 mm. Each of the eight antennas has its own independent metallic ground plane, which improves isolation between the antennas to some extent when the antennas operate in two frequency bands. In addition, an orthogonal polarization relationship between four antennas on the azimuth plane and four antennas on the side view plane further improves the isolation between the antennas in two frequency bands. Because L-shaped slots are etched on radiation patches of the four antennas on the side view plane, the antennas are enabled to operate in two frequency bands: 2.631 GHz-2.722 GHz and 3.440 GHz-3.529 GHz. Because the four antennas on the side view plane use L-shaped coaxial feeding units, flow directions of currents on the feeding units of the antennas in a high frequency band present included angles of 90 degrees, which greatly improves isolation between the antennas in a high frequency band. Because slots are etched on radiation patches of the four antennas on the side view plane and three right triangles are cut off from the radiation patch, flow directions of currents on the radiation patches in a high frequency band are changed, thereby improving isolation between the antennas in a high frequency band. Simple isolation stubs are used, so that the antennas generate resonance at the isolation stubs, which greatly improves isolation, in a low frequency band, between the four antennas on the azimuth plane and the four antennas on the side plane. Folded metallic ground planes are used, which further improves isolation between multiple antennas of the second type. Because PIFAs are used, the multiple-antenna system features a simple, small, and compact structure, easy fabrication, and low costs, and is easy integrated with a radio frequency front-end microwave circuit. In addition, a resonance operating point of an antenna can be adjusted by changing sizes and locations of a radiation patch, a U-shaped groove, an L-shaped slot, a coaxial feeding unit, a short-circuit unit, and an isolation stub, so as to meet different application requirements. 
     Simulation results of a parameter S of the multiple-antenna system shown in  FIG. 2  are shown in  FIG. 6 a    to  FIG. 6 d    and  FIG. 7 a    to  FIG. 7   d.    
     In  FIG. 6 a   , S 11  indicates an impedance matching feature of the PIFA  10  of the first type, S 22  indicates an impedance matching feature of the PIFA  20  of the first type, S 33  indicates an impedance matching feature of the PIFA  30  of the second type, and S 44  indicates an impedance matching feature of the PIFA  40  of the second type. It can be seen that, an operating frequency range of the PIFA  10  of the first type and the PIFA  20  of the first type is 2.558 GHz-2.801 GHz, and an operating frequency range of the PIFA  30  of the second type and the PIFA  40  of the second type is 2.631 GHz-2.722 GHz. 
     In  FIG. 6 b   , S 12  indicates isolation between the PIFA  10  of the first type and the PIFA  20  of the first type, S 13  indicates isolation between the PIFA  10  of the first type and the PIFA  30  of the second type, S 14  indicates isolation between the PIFA  10  of the first type and the PIFA  40  of the second type, and S 34  indicates isolation between the PIFA  30  of the second type and the PIFA  40  of the second type. It can be seen that, S 12 , S 13 , S 14 , and S 34  are all less than −20 dB. 
     In  FIG. 6 c   , S 15  indicates isolation between the PIFA  10  of the first type and the PIFA  50  of the first type, S 16  indicates isolation between the PIFA  10  of the first type and the PIFA  60  of the first type, S 17  indicates isolation between the PIFA  10  of the first type and the PIFA  70  of the second type, and S 18  indicates isolation between the PIFA  10  of the first type and the PIFA  80  of the second type. It can be seen that, S 15 , S 16 , S 17 , and S 18  are all less than −20 dB. 
     In  FIG. 6 d   , S 35  indicates isolation between the PIFA  30  of the second type and the PIFA  50  of the first type, S 36  indicates isolation between the PIFA  30  of the second type and the PIFA  60  of the first type, S 37  indicates isolation between the PIFA  30  of the second type and the PIFA  70  of the second type, and S 38  indicates isolation between the PIFA  30  of the second type and the PIFA  80  of the second type. It can be seen that, S 35 , S 36 , S 37 , and S 38  are all less than −25 dB. 
     In  FIG. 7 a   , it can be seen that, an operating frequency range of the PIFA  10  of the first type and the PIFA  20  of the first type is 3.387 GHz-3.666 GHz, and an operating frequency range of the PIFA  30  of the second type and the PIFA  40  of the second type is 3.440 GHz-3.529 GHz. 
     In  FIGS. 7 b   , S 12 , S 13 , S 14 , and S 34  are all less than −20 dB. 
     In  FIGS. 7 c   , S 15 , S 16 , S 17 , and S 18  are all less than −25 dB. 
     In  FIGS. 7 d   , S 35 , S 36 , S 37 , and S 38  are all less than −25 dB. 
     The multiple-antenna system shown in  FIG. 2  operates in two frequency bands: 2.631 GHz-2.722 GHz and 3.440 GHz-3.529 GHz. A bandwidth at 2.7 GHz is 91 MHz, and an impedance bandwidth at 3.5 GHz is 89 MHz. It can be further seen from  FIG. 6 b    to  FIG. 6 d    and from  FIG. 7 b    to  FIG. 7 d    that isolation between the antennas in the multiple-antenna system shown in  FIG. 2  is relatively high (less than −20 dB) in two frequency bands: 2.631 GHz-2.722 GHz and 3.440 GHz-3.529 GHz. 
     Simulation results of normalized radiation directions of the multiple-antenna system shown in  FIG. 2  are shown in  FIG. 8 a   ,  FIG. 8 b   ,  FIG. 9 a   , and  FIG. 9   b.    
       FIG. 8 a    is a diagram of a normalized radiation direction of the PIFA  10  of the first type that operates at 2.7 GHz, showing radiation of the PIFA  10  of the first type. 
       FIG. 8 b    is a diagram of a normalized radiation direction of the PIFA  10  of the first type that operates at 3.5 GHz. 
       FIG. 9 a    is a diagram of a normalized radiation direction of the PIFA  80  of the second type that operates at 2.7 GHz. 
       FIG. 9 b    is a diagram of a normalized radiation direction of the PIFA  80  of the second type that operates at 3.5 GHz. It can be seen that the PIFA  10  of the first type and the PIFA  80  of the second type have a better isotropic radiation feature. 
     The multiple-antenna system shown in  FIG. 2  is symmetrical with respect to both the xoz coordinate plane and the yoz coordinate plane. Therefore, simulation results of a parameter S and a diagram of a normalized radiation direction of another antenna are the same as the foregoing simulation results, and details are not described herein again. 
     Therefore, the multiple-antenna system shown in  FIG. 2  is a multiple-antenna system that is of a small-sized mobile phone terminal and that can meet requirements for dual frequency bands, high isolation, and easy fabrication. For the multiple-antenna system shown in  FIG. 2 , an impedance matching value less than −10 dB in both a frequency band of 2.631 GHz-2.722 GHz and a frequency band of 3.440 GHz-3.529 GHz, and has relatively high isolation (less than −20 dB) respectively in the frequency band of 2.631 GHz-2.722 GHz and the frequency band of 3.440 GHz-3.529 GHz, requirements of a next-generation mobile communications system are satisfied. 
       FIG. 10  is a schematic structural diagram of a mobile terminal according to another embodiment of the present invention. The mobile terminal provided in this embodiment includes a mobile terminal body  101  and an antenna system  102 , where the mobile terminal body  101  includes basic functional components, such as a processor and a memory, of a mobile terminal. The antenna system  102  may be any one of multiple-antenna systems provided in the foregoing embodiments, and is used to receive and transmit a signal for the mobile terminal body  101 . The mobile terminal body  101  processes a signal received by the antenna system  102 , generates a signal, and transmits the signal by using the antenna system  102 . 
     The mobile terminal provided in this embodiment uses the foregoing multiple-antenna system, which can not only achieve a smaller volume, but also further improve communication performance of the mobile terminal because as many antennas as possible can be disposed in relatively small space. 
     Finally, it should be noted that the foregoing embodiments are merely intended for describing the technical solutions of the present invention, but not for limiting the present invention. Although the present invention is described in detail with reference to the foregoing embodiments, persons of ordinary skill in the art should understand that they may still make modifications to the technical solutions described in the foregoing embodiments or make equivalent replacements to some or all technical features thereof, without departing from the scope of the technical solutions of the embodiments of the present invention.