Patent Publication Number: US-11658401-B2

Title: Antenna apparatus and terminal

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a U.S. National Stage of International Patent Application No. PCT/CN2019/086635 filed on May 13, 2019, which claims priority to Chinese Patent Application No. 201810481642.6 filed on May 18, 2018. Both of the aforementioned applications are hereby incorporated by reference in their entireties. 
     TECHNICAL FIELD 
     The present invention relates to the field of communications antenna technologies, and in particular, to an antenna apparatus and a terminal. 
     BACKGROUND 
     Different from a personal mobile communications terminal, for a vehicle-mounted communications terminal product, a horizontal plane gain index of an antenna is a main index for measuring a vehicle-mounted antenna. In a known monopole antenna solution, when a size of the floor is infinite, a maximum radiation direction of the antenna is on a floor plane (referred to as a horizontal plane below). In actual application, the size of the floor cannot be infinite, therefore the maximum radiation direction of the antenna is tilted, and a gain on the horizontal plane is worse than that on the infinite floor. 
     SUMMARY 
     Embodiments of this application provide an antenna apparatus, to improve a radiation pattern of an antenna and increase a horizontal plane gain. 
     According to a first aspect, an embodiment of this application provides an antenna apparatus, including a ground plate, a radiator, and a signal source, where the radiator is disposed on the ground plate, the signal source is configured to feed an electromagnetic wave signal of a first frequency band into the radiator, a first slot and a second slot are disposed on the ground plate, both the first slot and the second slot are closed slots and surround the radiator, and the first slot and the second slot are used to restrain current distribution on the ground plate, so that a current generated by the electromagnetic wave signal of the first frequency band is confined in and around the first slot and the second slot. 
     The first slot and the second slot surrounding the radiator are disposed to prevent a current from flowing to an edge of the ground plate, and the current is confined in and around the first slot and the second slot, to change a radiation pattern of the radiator, so that a maximum radiation direction of the radiator moves towards a horizontal plane. This improves a horizontal plane gain of the radiator. 
     The first slot and the second slot are symmetrically disposed by using a joint between the radiator and the ground plate as a center. The first slot and the second slot that are symmetrically centered may enable that current distribution almost the same is generated on the ground plate around the radiator, so that shapes of radiation patterns of an antenna in all directions around the radiator are almost the same. 
     A radial distance from the radiator to the first slot ranges from 0.2xλ 1  to 0.3xλ 1 , and λ 1  is a wavelength of the electromagnetic wave signal of the first frequency band. The distance between the first slot and the radiator is set to 0.2xλ 1  to 0.3xλ 1 , and a current flows from the radiator to the first slot. When the current flows through the distance of 0.2xλ 1  to 0.3xλ 1 , the current is relatively weak, an electric field is relatively strong, resonance is generated, and the current is confined in and around the first slot, so that resonance is generated at the first slot after a current of the electromagnetic wave signal of the first frequency band flows through the path, and the current is confined in and around the first slot. 
     The first slot is arc shaped, a distance between an inner side of the first slot and a center of the radiator is a first radius, and the first radius is 0.25xλ 1 . The first radius is 0.25xλ 1 , so that resonance can be generated at the first slot after the current of the electromagnetic wave signal of the first frequency band flows through the path. Because at 0.25xλ 1 , the current is the smallest, the electric field is the strongest, and a resonance effect is the best, the current is confined in and around the first slot. 
     A length of the first slot extending in a circumference direction is a first electrical length, and the first electrical length is 0.5xλ 1 . The first electrical length is set to 0.5xλ 1 , so that resonance is generated at the first slot when the current of the electromagnetic wave signal of the first frequency band flows to the first slot. 
     A length of the first slot in a radial direction is a first width, the first width is 0.05xλ 1 , and the first frequency band is 5.9 GHz. The first width is set to 0.05xλ 1 , to obtain the first frequency band 5.9 GHz meeting an operating frequency band range of the antenna. 
     In an embodiment, the signal source is further configured to feed an electromagnetic wave signal of a second frequency band into the radiator, the second frequency band is lower than the first frequency band, the antenna apparatus further includes a third slot and a fourth slot that are located on peripheries of the first slot and the second slot, both the third slot and the fourth slot are closed slots, and the third slot and the fourth slot are used to restrain current distribution on the ground plate, so that a current generated by the electromagnetic wave signal of the second frequency band is confined in and around the third slot and the fourth slot. 
     The signal source feeds the electromagnetic wave signal of the second frequency band, so that the antenna apparatus may be further configured to radiate the electromagnetic wave signal of the second frequency band, and the antenna apparatus may be used for a multi-frequency terminal. In addition, the current generated by the electromagnetic wave signal of the second frequency band is confined to the third slot and the fourth slot, so that a horizontal plane gain of the electromagnetic wave signal of the second frequency band can be improved. 
     The third slot and the fourth slot are symmetrically disposed by using the joint between the radiator and the ground plate as the center. The third slot and the fourth slot that are symmetrically centered may enable that current distribution almost the same is generated on the ground plate around the radiator, so that the shapes of the radiation patterns of the antenna in all the directions around the radiator are almost the same. 
     A radial distance from the radiator to the third slot ranges from 0.2xλ 2  to 0.3xλ 2 , and λ 2  is a wavelength of the electromagnetic wave signal of the second frequency band. The distance between the third slot and the radiator is set to 0.2xλ 2  to 0.3xλ 2 , and a current flows from the radiator to the third slot. When flowing through the distance of 0.2xλ 2  to 0.3xλ 2 , the current is relatively weak, an electric field is relatively strong, resonance is generated, and the current is confined in and around the third slot, so that resonance is generated at the third slot after a current of the electromagnetic wave signal of the second frequency band flows through the path, and the current is confined in and around the third slot. 
     The third slot is arc shaped, a distance between an inner side of the third slot and the center of the radiator is a second radius, and the second radius is 0.25xλ 2 . The second radius is 0.25xλ 2 , so that resonance can be generated at the third slot after the current of the electromagnetic wave signal of the second frequency band flows through the path. Because at 0.25xλ 2 , the current is the smallest, the electric field is the strongest, and a resonance effect is the best, the current is confined in and around the third slot. 
     A length of the third slot extending in the circumference direction is a second electrical length, and the second electrical length is 0.5xλ 2 . The second electrical length is set to 0.5xλ 2 , so that resonance is generated at the third slot when the current of the electromagnetic wave signal of the second frequency band flows to the third slot. 
     A length of the third slot in the radial direction is a second width, the second width is equal to the first width, and the second frequency band is 2.45 GHz. The first width and the second width are set to be the same, to obtain the second frequency band 2.45 GHz meeting the operating frequency band range of the antenna. 
     According to a second aspect, an embodiment of this application provides an antenna apparatus, including a ground plate, a radiator, a signal source, a first filter, and a second filter, where the radiator is disposed on the ground plate, the signal source is configured to feed electromagnetic wave signals of a first frequency band and a second frequency band into the radiator, and the second frequency band is lower than the first frequency band, a third slot and a fourth slot are disposed on the ground plate, both the third slot and the fourth slot are closed slots and surround the radiator, the first filter is disposed in the third slot and divides the third slot into two slots, the second filter is disposed in the fourth slot and divides the fourth slot into two slots, and the first filter and the second filter enable the third slot and the fourth slot to each form two different electrical lengths, so that currents generated by the electromagnetic wave signals of the first frequency band and the second frequency band can be confined in and around the third slot and the fourth slot. 
     The third slot and the fourth slot surrounding the radiator are disposed to prevent the current from flowing to an edge of the ground plate. The first filter and the second filter are disposed, so that two different electrical lengths are generated in the third slot and two different electrical lengths are generated in the fourth slot. Therefore, the radiator generates resonance in two modalities the first frequency band and the second frequency band, to meet a multi-frequency communication requirement. In addition, because the current is confined to the third slot and the fourth slot, horizontal plane gains of the electromagnetic wave signals of the first frequency band and the second frequency band are increased. 
     Both the first filter and the second filter are band-pass filters in which an inductor and a capacitor are connected in series, and are configured to enable the current generated by the electromagnetic wave signal of the second frequency band to pass and block the current generated by the electromagnetic wave signal of the first frequency band, so that an electrical length of the electromagnetic wave signal of the second frequency band is greater than an electrical length of the electromagnetic wave signal of the first frequency band. The first filter and the second filter are disposed as the band-pass filters, so that two electrical lengths are generated in the third slot, two electrical lengths are generated in the fourth slot, the entire third slot is the electrical length of the second frequency band with a lower frequency, and a part of the third slot is the electrical length of the first frequency band with a higher frequency. The other part is not used to confine the electromagnetic wave signal of the first frequency band because no current flows through the other part due to a blocking effect of the first filter. 
     A specific location of the first filter disposed in the third slot and a specific location of the second filter disposed in the fourth slot are related to a wavelength λ 1  of the electromagnetic wave signal of the first frequency band. The first filter is disposed at 0.5xλ 1  away from an endpoint of the third slot, and the second filter is disposed at 0.5xλ 1  away from an endpoint of the fourth slot. Through the foregoing settings, 0.5xλ 1  is a first electrical length of the electromagnetic wave signal of the first frequency band, and 0.5xλ 2  is a second electrical length of the electromagnetic wave signal of the second frequency band, where λ 1  is the wavelength of the electromagnetic wave signal of the first frequency band, and λ 2  is a wavelength of the electromagnetic wave signal of the second frequency band. 
     The third slot and the fourth slot are symmetrically disposed by using a joint between the radiator and the ground plate as a center. The third slot and the fourth slot that are symmetrically centered may enable that current distribution almost the same is generated on the ground plate around the radiator, so that shapes of radiation patterns of an antenna in all directions around the radiator are almost the same. 
     A radial distance from the radiator to the third slot ranges from 0.2xλ 2  to 0.3xλ 2 , and λ 2  is the wavelength of the electromagnetic wave signal of the second frequency band. The distance between the third slot and the radiator is set to 0.2xλ 2  to 0.3xλ 2 , and a current flows from the radiator to the third slot. When flowing through the distance of 0.2xλ 2  to 0.3xλ 2 , the current is relatively weak, an electric field is relatively strong, resonance is generated, and the current is confined in and around the third slot, so that resonance is generated at the third slot after the currents of the electromagnetic wave signals of the first frequency band and the second frequency band flow through the path, and the current is confined in and around the third slot. 
     The third slot is arc shaped, a distance between an inner side of the third slot and a center of the radiator is a first radius, and the first radius is 0.25xλ 2 . The first radius is 0.25xλ 2 , so that resonance can be generated at the third slot after the current of the electromagnetic wave signal of the first frequency band flows through the path. Because at 0.25xλ 2 , the current is the smallest, the electric field is the strongest, and a resonance effect is the best, the current is confined in and around the third slot. 
     A length of the third slot extending in a circumference direction is a first electrical length, and the first electrical length is 0.5xλ 2 . The first electrical length is set to 0.5xλ 2 , so that resonance is generated at the third slot when the current of the electromagnetic wave signal of the second frequency band flows to the third slot. 
     A length of the third slot in a radial direction is a first width, the first width is 0.05xλ 1 , λ 1  is the wavelength of the electromagnetic wave signal of the first frequency band, the first frequency band is 5.9 GHz, and the second frequency band is 2.45 GHz. The first width is set to 0.05xλ 1 , to obtain the first frequency band 5.9 GHz and the second frequency band 2.45 GHz meeting an operating frequency band range of the antenna. 
     According to a third aspect, an embodiment of this application provides a terminal, including a PCB board and the antenna apparatus, where the radiator of the antenna apparatus is disposed on the PCB board, the ground plate is a part of the PCB board, the signal source configured for feeding is disposed on the PCB board, and the signal source feeds power to the radiator. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       To describe the technical solutions in some of the embodiments of this application more clearly, the following briefly describes the accompanying drawings describing some of the embodiments. It is clear that the accompanying drawings in the following description show some embodiments of the present disclosure, and a person of ordinary skill in the art may still derive other drawings from these accompanying drawings without creative efforts. 
         FIG.  1   a    is a schematic structural diagram of a terminal according to an embodiment; 
         FIG.  1   b    is a schematic structural diagram of an antenna apparatus of the terminal in  FIG.  1     a;    
         FIG.  2   a    is a schematic structural diagram of an antenna apparatus according to an embodiment; 
         FIG.  2   b    is a schematic diagram of a partially enlarged structure at A in  FIG.  2     a;    
         FIG.  2   c    is a schematic simulation diagram of a return loss (S  11 ) of an antenna apparatus according to an embodiment; 
         FIG.  2   d    is a schematic simulation diagram of current distribution on a ground plate before and after there is a slot according to an embodiment, where in the figure, a left diagram shows a simulation result of the current distribution on the ground plate without a slot, and a right diagram shows a simulation result of the current distribution on the ground plate with a slot; 
         FIG.  2   e   - 1  to  FIG.  2   e   - 3  are simulation directivity diagrams of an antenna apparatus without a slot according to an embodiment, where in the figures,  FIG.  2   e   - 1  is a top view of the simulation directivity diagram,  FIG.  2   e   - 2  is a side view of the simulation directivity diagram, and  FIG.  2   e   - 3  is a side view of the simulation directivity diagram (vertical to a view angle of  FIG.  2   e   - 2 ); 
         FIG.  2   f   - 1  to  FIG.  2   f   - 3  are simulation directivity diagrams of an antenna apparatus with a slot according to an embodiment, where in the figures,  FIG.  2   f   - 1  is a top view of the simulation directivity diagram.  FIG.  2   f   - 2  is a side view of the simulation directivity diagram, and  FIG.  2   f   - 3  is a side view of the simulation directivity diagram (vertical to a view angle of  FIG.  2   f   - 2 ); 
         FIG.  2   g    is a schematic comparison diagram of a horizontal plane gain of an antenna apparatus before and after there is a slot according to an embodiment; 
         FIG.  3   a    is a schematic structural diagram of an antenna apparatus according to another embodiment, where a signal source and a matching circuit are omitted in the figure; 
         FIG.  3   b    is a schematic diagram of a partially enlarged structure at A in  FIG.  3     a;    
         FIG.  3   c    is a schematic simulation diagram of a return loss (S11) of an antenna apparatus according to another embodiment; 
         FIG.  3   d    is a schematic simulation diagram of current distribution on a ground plate without a slot according to another embodiment, where in the figure, a left figure is a simulation result of current distribution on the ground plate without a slot in a 2.45 GHz modal, and a right figure is a simulation result of current distribution on the ground plate without a slot in a 5.9 GHz modal; 
         FIG.  3   e    is a schematic simulation diagram of current distribution on a ground plate with a slot according to another embodiment, where in the figure, a left figure is a simulation result of current distribution on the ground plate with a slot in a 2.45 GHz modal, and a right figure is a simulation result of current distribution on the ground plate with a slot in a 5.9 GHz modal. 
         FIG.  3   f   - 1  to  FIG.  3   f   - 3  are simulation directivity diagrams of an antenna apparatus without a slot in a 2.45 GHz modal according to another embodiment, where in the figures,  FIG.  3   f   - 1  is a top view of the simulation directivity diagram,  FIG.  3   f   - 2  is a side view of the simulation directivity diagram, and  FIG.  3   f   - 3  is a side view of the simulation directivity diagram (vertical to a view angle of  FIG.  3   f   - 2 ); 
         FIG.  3   g   - 1  to  FIG.  3   g   - 3  are simulation directivity diagrams of an antenna apparatus without a slot in a 5.9 GHz modal according to another embodiment, where in the figures.  FIG.  3   g   - 1  is a top view of the simulation directivity diagram,  FIG.  3   g   - 2  is a side view of the simulation directivity diagram, and  FIG.  3   g   - 3  is a side view of the simulation directivity diagram (vertical to a view angle of  FIG.  3   g   - 2 ); 
         FIG.  3   h   - 1  to  FIG.  3   h   - 3  are simulation directivity diagrams of an antenna apparatus with a slot in a 2.45 GHz modal according to another embodiment, where in the figures,  FIG.  3   h   - 1  is a top view of the simulation directivity diagram,  FIG.  3   h   - 2  is a side view of the simulation directivity diagram, and  FIG.  3   h   - 3  is a side view of the simulation directivity diagram (vertical to a view angle of  FIG.  3   h   - 2 ); 
         FIG.  3   i   - 1  to  FIG.  3   i   - 3  are simulation directivity diagrams of an antenna apparatus with a slot in a 5.9 GHz modal according to another embodiment, where in the figures,  FIG.  3   i   - 1  is a top view of the simulation directivity diagram,  FIG.  3   i   - 2  is a side view of the simulation directivity diagram, and  FIG.  3   i   - 3  is a side view of the simulation directivity diagram (vertical to a view angle of  FIG.  3   i   - 2 ); 
         FIG.  3   j    is a schematic comparison diagram of a horizontal plane gain of an antenna apparatus before and after there is a slot in each of a 2.45 GHz modal and a 5.9 GHz modal according to another embodiment; 
         FIG.  4   a    is a schematic structural diagram of an antenna apparatus according to another embodiment; 
         FIG.  4   b    is a schematic diagram of a partially enlarged structure at A in  FIG.  4     a;    
         FIG.  4   c    is a schematic simulation diagram of a return loss (S  11 ) of an antenna apparatus according to another embodiment; 
         FIG.  4   d    is a schematic simulation diagram of current distribution on a ground plate without a slot according to another embodiment, where in the figure, a left figure is a simulation result of current distribution on the ground plate without a slot in a 2.45 GHz modal, and a right figure is a simulation result of current distribution on the ground plate without a slot in a 5.9 GHz modal; 
         FIG.  4   e    is a schematic simulation diagram of current distribution on a ground plate with a slot according to another embodiment, where in the figure, a left figure is a simulation result of current distribution on the ground plate with a slot in a 2.45 GHz modal, and a right figure is a simulation result of current distribution on the ground plate with a slot in a 5.9 GHz modal; 
         FIG.  4   f   - 1  to  FIG.  4   f   - 3  are simulation directivity diagrams of an antenna apparatus without a slot in a 2.45 GHz modal according to another embodiment, where in the figures,  FIG.  4   f   - 1  is a top view of the simulation directivity diagram,  FIG.  4   f   - 2  is a side view of the simulation directivity diagram, and  FIG.  4   f   - 3  is a side view of the simulation directivity diagram (vertical to a view angle of  FIG.  4   f   - 2 ); 
         FIG.  4   g   - 1  to  FIG.  4   g   - 3  are simulation directivity diagrams of an antenna apparatus without a slot in a 5.9 GHz modal according to another embodiment, where in the figures,  FIG.  4   g   - 1  is a top view of the simulation directivity diagram.  FIG.  4   g   - 2  is a side view of the simulation directivity diagram, and  FIG.  4   g   - 3  is a side view of the simulation directivity diagram (vertical to a view angle of  FIG.  4   g   - 2 ); 
         FIG.  4   h   - 1  to  FIG.  4   h   - 3  are simulation directivity diagrams of an antenna apparatus added with a filter with a slot in a 2.45 GHz modal according to another embodiment, where in the figures,  FIG.  4   h   - 1  is a top view of the simulation directivity diagram.  FIG.  4   h   - 2  is a side view of the simulation directivity diagram, and  FIG.  4   h   - 3  is a side view of the simulation directivity diagram (vertical to a view angle of  FIG.  4   h   - 2 ); 
         FIG.  4   i   - 1  to  FIG.  4   i   - 3  are simulation directivity diagrams of an antenna apparatus added with a filter with a slot in a 5.9 GHz modal according to another embodiment, where in the figures,  FIG.  4   i   - 1  is a top view of the simulation directivity diagram,  FIG.  4   i   - 2  is a side view of the simulation directivity diagram, and  FIG.  4   i   - 3  is a side view of the simulation directivity diagram (vertical to a view angle of  FIG.  4   i   - 2 ); and 
         FIG.  4   j    is a schematic comparison diagram of a horizontal plane gain of an antenna apparatus added with a filter, before and after there is a slot in each of a 2.45 GHz modal and a 5.9 GHz modal according to another embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Referring to  FIG.  1   a   , an embodiment of this application provides a terminal. The terminal may be a mobile transportation vehicle such as a car or an airplane. A horizontal plane gain of an antenna apparatus of the terminal is improved, so that a wireless communication effect of the terminal is better. For example, the terminal is a car. The antenna apparatus of the terminal may be a vehicle-mounted external antenna or a vehicle-mounted T-Box, and the antenna apparatus of the terminal may be disposed at a location such as the top of the car or an engine cover. 
     Referring to  FIG.  1   b   , a housing is omitted in the figure. The terminal includes a PCB board and the antenna apparatus provided in this embodiment of this application. A radiator  20  of the antenna apparatus is connected to the PCB board, the ground plate  10  is a part of the PCB board, a signal source configured for feeding is disposed on the PCB board, and the signal source feeds power to the radiator  20 . 
     Because the PCB board  10  on the terminal cannot be infinitely large, a radiation pattern of the radiator  20  on the PCB board  10  is tilted, causing a decrease in a horizontal plane gain. However, the radiation pattern of the radiator  20  may be pulled down by disposing a slot on the PCB board  10 . In this way, a maximum radiation direction of the radiator  20  is close to a horizontal plane. This increases a horizontal plane gain of an antenna and improves a wireless communication effect of the terminal. 
     Referring to  FIG.  2   a    and  FIG.  2   b   , an embodiment of this application provides an antenna apparatus, including a ground plate  10 , a radiator  20 , and a signal source  30 . The radiator  20  is disposed on the ground plate  10 , and the signal source  30  is configured to feed an electromagnetic wave signal of a first frequency band into the radiator  20 . The antenna apparatus may further include a matching circuit  40 , where the matching circuit  40  is electrically connected between the radiator  20  and the signal source  30 , and is configured to adjust a resonance state of the radiator  20 . A first slot  11  and a second slot  12  are disposed on the ground plate  10 , both the first slot  11  and the second slot  12  are closed slots and surround the radiator  20 , and the first slot  11  and the second slot  12  are configured to restrain current distribution on the ground plate  10 , so that a current generated by the electromagnetic wave signal of the first frequency band is confined in and around the first slot  11  and the second slot  12 . 
     The first slot  11  and the second slot  12  surrounding the radiator  20  are disposed to prevent a current from flowing to an edge of the ground plate  10 , and the current is confined in and around the first slot  11  and the second slot  12 , to change a radiation pattern of the radiator  20 , so that a maximum radiation direction of the radiator  20  moves towards a horizontal plane. This improves a horizontal plane gain of the radiator  20 . 
     Similar to the terminal shown in  FIG.  1   , the ground plate  10  may be a PCB board, a copper-clad surface is disposed on the PCB board, and the radiator  20  is connected to the copper-clad surface to implement grounding. A size of the ground plate  10  may be set to be much greater than a size of the radiator  20 , so that the ground plate  10  simulates an infinite ground as much as possible. This facilitates antenna design by referring to an antenna radiation theory of the infinite ground, and a difference between the ground plate  10  and the infinite ground is relatively small. The ground plate  10  may be in any shape such as a circle, a square, or a triangle, provided that a conductive surface that is approximately a plane can be provided as a horizontal plane of the ground plate  10 . 
     Both the first slot  11  and the second slot  12  disposed on the ground plate  10  are closed slots. To be specific, the first slot  11  and the second slot  12  do not intersect, and are not connected to the edge of the ground plate  10 , but are located in a middle part of the ground plate  10 . Preferably, both the first slot  11  and the second slot  12  are disposed around a center point of the ground plate  10 . 
     Specifically, a form in which the first slot  11  and the second slot  12  are disposed around the radiator  20  on the ground plate  10  may be that the first slot  11  is disposed around one side of the radiator  20 , the second slot  12  is disposed around another side of the radiator  20  opposite to the first slot  11 , and an angle formed by connection lines connecting the radiator  20  and two ends of each of the first slot  11  and the second slot  12  is less than 180°. In another disposing form, the first slot  11  and the second slot  12  are nested structures, the first slot  11  is located on an inner side of the second slot  12 , that is, an included angle between connection lines connecting the radiator  20  and the two ends of the first slot  11  is greater than 180°, the second slot  12  is located on a side towards which an opening of the first slot  11  faces and does not overlap the first slot  11 , and at least a part of the second slot  12  and at least a part of the first slot  11  at least partially encircle the radiator  20 . Regardless of a disposing form, the ground plate  10  is enabled to have at least a partially connected area within and outside a slot area, to provide a support structure for the radiator  20 . In addition, a current on the radiator  20  can flow from an inner part the slot area to an inner area of the first slot  11  and the second slot  12  and a surrounding area outside the slot area. 
     The first slot  11  and the second slot  12  may be in an arc shape, a wave shape, a rectangle (that is, the first slot  11  and the second slot  12  each have a straight line segment and a corner, so that the two are combined to form the rectangle), a sawtooth shape, or the like. It should be understood that, the first slot  11  and the second slot  12  need to be disposed around the radiator  20 , and therefore the shapes of the first slot  11  and the second slot  12  cannot be two straight lines. The first slot  11  and the second slot  12  may be disposed by using a machining technology. Through grooves penetrating through an upper surface and a lower surface of the ground plate  10  are dug in the ground plate  10 , to form the first slot  11  and the second slot  12 . 
     The radiator  20  may be an antenna structure such as a monopole antenna, an inverted F antenna (IFA), or a loop antenna. The radiator  20  may be vertical to the ground plate  10 . In other words, a main body of the radiator  20  is a standing structure, and is not attached to a surface of the ground plate  10 , and an extension direction of the main body of the radiator  20  may be perpendicular to a plane (that is, a ground or a horizontal plane) on which the ground plate  10  is located, or may have a relatively small tilt angle. For example, an included angle between the extension direction of the radiator  20  and the plane on which the ground plate  10  is located ranges from 45° to 90°. In this way, an area occupied by a connection point between the radiator  20  and the ground plate  10  is the smallest, and the radiator  20  extends in a direction away from the ground plate  10 , to simulate a radiation characteristic of the antenna in an ideal state (that is, on the infinite ground) as much as possible to obtain an approximate antenna radiation pattern. 
     The first slot  11  and the second slot  12  are symmetrically disposed by using a joint between the radiator  20  and the ground plate  10  as a center. The first slot  11  and the second slot  12  that are centrally symmetric may enable current distribution on the ground plate  10  around the radiator  20  to be almost the same, so that shapes of radiation patterns of the antenna in all directions around the radiator  20  are almost the same. 
     A radial distance from the radiator  20  to the first slot  11  ranges from 0.2xλ 1  to 0.3xλ 1 , and λ 1  is a wavelength of the electromagnetic wave signal of the first frequency band. The distance between the first slot  11  and the radiator  20  is set to 0.2xλ 1  to 0.3xλ 1 , and a current flows from the radiator  20  to the first slot  11 . When the current flows through the distance of 0.2xλ 1  to 0.3xλ 1 , the current is relatively weak, an electric field is relatively strong, resonance is generated, and the current is confined in and around the first slot  11 , so that resonance is generated at the first slot  11  after the current of the electromagnetic wave signal of the first frequency band flows through the path, and the current is confined in and around the first slot  11 . 
     The first slot  11  is arc shaped, a distance between an inner side of the first slot  11  and a center of the radiator  20  is a first radius R 1 , and the first radius R 1  is 0.25xλ 1 . The first radius R 1  is 0.25xλ 1 , so that resonance can be generated at the first slot  11  after the current of the electromagnetic wave signal of the first frequency band flows through the path. Because at 0.25xλ 1 , the current is the smallest, the electric field is the strongest, and a resonance effect is the best, the current is confined in and around the first slot  11 . 
     A length of the first slot  11  extending in a circumference direction is a first electrical length, and the first electrical length is 0.5xλ 1 . The first electrical length is set to 0.5xλ 1 , so that resonance is generated at the first slot  11  when the current of the electromagnetic wave signal of the first frequency band flows to the first slot  11 . A length of the first slot  11  in a radial direction is a first width W 1 , the first width W 1  is 0.05xλ 1 , and the first frequency band is 5.9 GHz. The first width W 1  is set to 0.05xλ 1 , to obtain the first frequency band 5.9 GHz meeting an operating frequency band range of the antenna. 
     In the field of antenna communications, there are frequency bands preferred in various application scenarios. Some of these frequency bands are included in standards and are mandatory for use, and relevant qualifications and applications are required to obtain the right to use the relevant frequency bands. Some of these frequency bands are industry practices. For example, frequency bands used by a smartphone are a low frequency, an intermediate frequency, and a high frequency, and there is an upper limit and a lower limit of each frequency band. An antenna of the smartphone needs to work in these frequency bands. Likewise, a vehicle-mounted antenna also has a dedicated operating frequency band. In conclusion, when the structure of the antenna apparatus is designed, it needs to be ensured that the antenna works within a specified frequency band range. In this embodiment, the first frequency band is within the specified frequency band range. For example, in the field of terminals such as a vehicle-mounted antenna, the frequency 5.9 GHz is a common communication frequency, and the frequency 5.9 GHz obtained through the foregoing settings is within a preferred frequency band range of the vehicle-mounted antenna, so that a relatively good wireless communication effect can be implemented. Structures of the first slot  11  and the second slot  12  need to be disposed to obtain the first frequency band. More specifically, sizes of the first slot  11  and the second slot  12  need to be limited, and the sizes are related to the wavelength λ 1  of the electromagnetic wave signal that is of the first frequency band and that is fed into the radiator  20 . Therefore, when resonance of the first frequency band is achieved, different sizes of the first slot  11  and the second slot  12  may be obtained based on different λ 1 , to meet arrangement requirements of antenna apparatuses of various terminals. 
     In this embodiment, the radiator  20  preferably uses a monopole antenna, and a height of the radiator  20  is preferably 0.25xλ 1 . The monopole antenna has a dual feature. In an ideal state (that is, the ground plane is an infinite plane), a maximum radiation direction of the monopole antenna is a horizontal plane. However, when the monopole antenna is applied to a terminal, a size of the ground plane  10  cannot be infinite. Therefore, the first slot  11  and the second slot  12  are disposed to change a directivity pattern of the antenna. Specifically, a height of radiator  20  is 0.25xλ 1 , the first radius R 1  ranges from 0.2xλ 1  to 0.3xλ 1 , and is preferably 0.25xλ 1 . In this way, a total length of a path through which the current flows on the radiator  20  and the ground plate  10  is 0.5xλ 1 . In this case, the radiation pattern of the antenna is the closest to a radiation form of a dipole antenna, and a horizontal plane gain obtained is the highest. In addition, the first electrical length of the first slot  11  is set to 0.5xλ 1 , and the signal source  30  feeds power to the radiator  20  and feeds power to the first slot  11 , so that a resonance modal excited in the first slot  11  is the same as that of the radiator  20 . When the current on the ground plate  10  flows to the first slot  11 , the resonance is generated at the first slot  11 , and the current no longer flows further. Compared with a structure in which no slot is disposed on the ground plate  10 , the structure in this embodiment changes current distribution on the ground plate  10 , so that the maximum radiation direction of the antenna moves towards the horizontal plane. This improves the horizontal plane gain. 
     With reference to  FIG.  2   a    and  FIG.  2   b   , a specific embodiment is provided. The ground plate  10  is a circle, a radius R ground  of the ground plate  10  is 65 mm, the radiator  20  is a monopole antenna, a height H of the radiator  20  is 10 mm, a first radius R 1  is 10 mm, a first electrical length is 20 mm, and a first width W 1  is 2 mm. The antenna apparatus is simulated, and for a simulation result, refer to subsequent descriptions. 
     Referring to  FIG.  2   c   , a diagram of an antenna return loss S11 shows that when there is no slot, no clear resonance point is included in an antenna return loss curve (shown by a dashed line), but in an antenna return loss curve (shown by a solid line) after the first slot  11  and the second slot  12  are disposed, it can be clearly seen that a resonance frequency is near a 6 GHz location, and the resonance is the first frequency band needed to be obtained in this embodiment. An emulation result is basically the same as an expected resonance point 5.9 GHz. In this way, the antenna apparatus is designed. 
     Referring to  FIG.  2   d   , in the figure, a left figure is a current distribution diagram when there is no slot, and a right figure is a current distribution diagram after a slot is disposed. When there is no slot, current distribution on the ground plate  10  extends to an edge of the plate. After the slot is added, most current on the ground plate is “confined” in and around the slot, a current outside the slot is relatively weak, and the slot changes the current distribution on the ground plate  10 . This changes a directivity pattern and a horizontal plane gain of an antenna. 
     Referring to  FIG.  2   e   - 1  to  FIG.  2   e   - 3 , in the figures,  FIG.  2   e   - 1  is a top view of a simulation directivity diagram,  FIG.  2   e   - 2  is a side view of the simulation directivity diagram, and  FIG.  2   e   - 3  is a side view of the simulation directivity diagram (vertical to a view angle of  FIG.  2   e   - 2 ). When there is no slot, a maximum radiation direction of an antenna is tilted. Therefore, the maximum radiation direction deviates from a horizontal plane relatively far and a horizontal plane gain decreases. 
     Referring to  FIG.  2   f   - 1  to  FIG.  2   f   - 3 , in the figures,  FIG.  2   f   - 1  is a top view of a simulation directivity diagram.  FIG.  2   f   - 2  is a side view of the simulation directivity diagram, and  FIG.  2   f   - 3  is a side view of the simulation directivity diagram (vertical to a view angle of  FIG.  2   f   - 2 ). After a slot is disposed, a change of current distribution on the ground plate  10  brings a change of a radiation pattern of an antenna, and the radiation pattern of the antenna is pulled down, so that a degree of deviation of a maximum radiation direction of the antenna from a horizontal plane is reduced, and the maximum radiation direction of the antenna is closer to the horizontal plane. This increases a horizontal plane gain. 
     Referring to  FIG.  2   g   , a connection line of dots of an inner circle in the figure is a horizontal plane gain when there is no slot, and a connection line of dots of an outer circle in the figure is a horizontal plane gain after a slot is disposed. It can be seen that the horizontal plane gain is increased by more than 2 dB after the slot is disposed. 
     In an embodiment, referring to  FIG.  3   a    and  FIG.  3   b   , a signal source  30  and a matching circuit  40  are omitted in the figure. Similar to the foregoing embodiment, a difference lies in that the signal source  30  is further configured to feed an electromagnetic wave signal of a second frequency band into the radiator  20 , where the second frequency band is lower than the first frequency band, the antenna apparatus further includes a third slot  13  and a fourth slot  14  that are located on peripheries of the first slot  11  and the second slot  12 , both the third slot  13  and the fourth slot  14  are closed slots, and the third slot  13  and the fourth slot  14  are used to restrain current distribution on the ground plate  10 , so that a current generated by the electromagnetic wave signal of the second frequency band is confined in and around the third slot  13  and the fourth slot  14 . 
     The signal source  30  feeds the electromagnetic wave signal of the second frequency band, so that the antenna apparatus may be further configured to radiate the electromagnetic wave signal of the second frequency band, and the antenna apparatus may be used for a multi-frequency terminal. In addition, the current generated by the electromagnetic wave signal of the second frequency band is confined to the third slot  13  and the fourth slot  14 , so that a horizontal plane gain of the electromagnetic wave signal of the second frequency band can be improved. 
     In this embodiment, both the first frequency band and the second frequency band are within specified frequency band ranges, and the specified frequency bands are two frequency ranges with different ranges, and the two frequency ranges do not overlap. 
     The third slot  13  and the fourth slot  14  are symmetrically disposed by using a joint between the radiator  20  and the ground plate  10  as a center. The third slot  13  and the fourth slot  14  that are symmetrically centered may enable that current distribution almost the same is generated on the ground plate  10  around the radiator  20 , so that shapes of radiation patterns of an antenna in all directions around the radiator  20  are almost the same. 
     A radial distance from the radiator  20  to the third slot  13  ranges from 0.2xλ 2  to 0.3xλ 2 , and λ 2  is a wavelength of the electromagnetic wave signal of the second frequency band. The distance between the third slot  13  and the radiator  20  is set to 0.2xλ 2  to 0.3xλ 2 , and a current flows from the radiator  20  to the third slot  13 . When flowing through the distance of 0.2xλ 2  to 0.3xλ 2 , the current is relatively weak, an electric field is relatively strong, resonance is generated, and the current is confined in and around the third slot  13 , so that resonance is generated at the third slot  13  after the current of the electromagnetic wave signal of the second frequency band flows through the path, and the current is confined in and around the third slot  13 . 
     The third slot  13  is arc shaped, a distance between an inner side of the third slot  13  and a center of the radiator  20  is a second radius R 2 , and the second radius R 2  is 0.25xλ 2 . The second radius R 2  is 0.25xλ 2 , so that resonance can be generated at the third slot  13  after the current of the electromagnetic wave signal of the second frequency band flows through the path. Because at 0.25xλ 2 , the current is the smallest, the electric field is the strongest, and a resonance effect is the best, the current is confined in and around the third slot  13 . 
     A length of the third slot  13  extending in the circumference direction is a second electrical length, and the second electrical length is 0.5xλ 2 . The second electrical length is set to 0.5xλ 2 , so that resonance is generated at the third slot  13  when the current of the electromagnetic wave signal of the second frequency band flows to the third slot  13 . 
     A length of the third slot  13  in the radial direction is a second width W 2 , the second width W 2  is equal to the first width W 1 , and the second frequency band is 2.45 GHz. The first width W 1  and the second width W 2  are set to be the same, to obtain the second frequency band 2.45 GHz meeting the operating frequency band range of the antenna. In the field of terminals such as a vehicle-mounted antenna, the frequency 2.45 GHz is a common communication frequency, and the frequency 2.45 GHz obtained through the foregoing settings is within a preferred frequency band range of the vehicle-mounted antenna, so that a relatively good wireless communication effect can be implemented. 
     In this embodiment, the radiator  20  preferably uses a monopole antenna, and a height of the radiator  20  is preferably 0.25xλ 2 . Sizes of the first slot  11 , the second slot  12 , the third slot  13 , and the fourth slot  14  are limited, and the sizes are set to be related to the wavelength λ 1  of the electromagnetic wave signal of the first frequency band and the wavelength λ 2  of the electromagnetic wave signal of the second frequency band that are fed into the radiator  20 . Therefore, the first slot  11  and the second slot  12  are used to generate resonance of the electromagnetic wave signal of the first frequency band, and the third slot  13  and the fourth slot  14  are used to generate resonance of the electromagnetic wave signal of the second frequency band. Different sizes of the radiator  20 , the first slot  11 , the second slot  12 , the third slot  13 , and the fourth slot  14  may be obtained based on different λ to meet arrangement requirements of antenna apparatuses of various terminals. 
     With reference to  FIG.  3   a    and  FIG.  3   b   , a specific embodiment is provided. The ground plate  10  is a circle, a radius R ground  of the ground plate  10  is 100 mm, the radiator  20  is a monopole antenna, a height H of the radiator  20  is 20 mm, a first radius R 1  is 8 mm, and a first electrical length is 20 mm, a first width W 1  and a second width W 2  are 2 mm, a second radius R 2  is 20 mm, and a second electrical length is 40 mm. The antenna apparatus is simulated, and for a simulation result, refer to subsequent descriptions. 
     Referring to  FIG.  3   c   , a diagram of an antenna return loss S11 shows resonance points in an antenna return loss curve (shown by a solid line) when there is no slot, however, in an antenna return loss curve (shown by a dashed line) after the first slot  11 , the second slot  12 , the third slot  13 , and the fourth slot  14  are disposed, it can be clearly seen that two resonance points are generated near locations of 2.5 GHz and 5.9 GHz. The resonance point near 2.5 GHz is the first frequency band expected to be obtained in this embodiment, and the resonance point near 5.9 GHz is the second frequency band expected to be obtained in this embodiment. An emulation result is basically the same as preset resonance points of 2.45 GHz and 5.9 GHz. In this way, the antenna apparatus is designed. It should be noted that resonance near a 4.5 GHz location is further generated, the resonance is generated by resonance of the first slot  11  and the second slot  12 , and is different from a purpose of this embodiment and may be ignored. 
     Referring to  FIG.  3   d   , in the figure, a left figure is a current distribution diagram in a 2.45 GHz modal when there is no slot, and a right figure is a current distribution diagram in a 5.9 GHz modal when there is no slot. It can be seen that, when there is no slot, current distribution on the ground plate  10  extends to an edge of the plate. 
     Referring to  FIG.  3   e   , in the figure, a left figure is a current distribution diagram in a 2.45 GHz modal after a slot is disposed, and a right figure is a current distribution diagram in a 5.9 GHz modal after a slot is disposed. It can be seen that most currents on the ground plate  10  are “confined” in and around the slot, a current outside the slot is relatively weak, the slot changes current distribution on the ground plate  10 , and further changes a directivity pattern and a horizontal plane gain of the antenna. 
     Referring to  FIG.  3   f   - 1  to  FIG.  3   f   - 3 , in the figures,  FIG.  3   f   - 1  is a top view of a simulation directivity diagram.  FIG.  3   f   - 2  is a side view of the simulation directivity diagram, and  FIG.  3   f   - 3  is a side view of the simulation directivity diagram (vertical to a view angle of  FIG.  3   f   - 2 ). When there is no slot, a maximum radiation direction in a 2.45 GHz modal is tilted. Therefore, the maximum radiation direction deviates from a horizontal plane relatively far and a horizontal plane gain decreases. 
     Referring to  FIG.  3   g   - 1  to  FIG.  3   g   - 3 , in the figures,  FIG.  3   g   - 1  is a top view of a simulation directivity diagram,  FIG.  3   g   - 2  is a side view of the simulation directivity diagram, and  FIG.  3   g   - 3  is a side view of the simulation directivity diagram (vertical to a view angle of  FIG.  3   g   - 2 ). When there is no slot, a maximum radiation direction in a 5.9 GHz modal is tilted. Therefore, the maximum radiation direction deviates from a horizontal plane relatively far and a horizontal plane gain decreases. 
     Referring to  FIG.  3   h   - 1  to  FIG.  3   h   - 3 , in the figures,  FIG.  3   h   - 1  is a top view of a simulation directivity diagram,  FIG.  3   h   - 2  is a side view of the simulation directivity diagram, and  FIG.  3   h   - 3  is a side view of the simulation directivity diagram (vertical to a view angle of  FIG.  3   h   - 2 ). After a slot is disposed, a change of current distribution on the ground plate  10  brings a change of a radiation pattern of an antenna in a 2.45 GHz modal, and the radiation pattern of the antenna is pulled down, so that a degree of deviation of a maximum radiation direction of the antenna from a horizontal plane is reduced, and the maximum radiation direction of the antenna is closer to the horizontal plane. This increases a horizontal plane gain. 
     Referring to  FIG.  3   i   - 1  to  FIG.  3   i   - 3 , in the figures,  FIG.  3   i   - 1  is a top view of a simulation directivity diagram,  FIG.  3   i   - 2  is a side view of the simulation directivity diagram, and  FIG.  3   i   - 3  is a side view of the simulation directivity diagram (vertical to a view angle of  FIG.  3   i   - 2 ). After a slot is disposed, a change of current distribution on the ground plate  10  brings a change of a radiation pattern of an antenna in a 5.9 GHz modal, and the radiation pattern of the antenna is pulled down, so that a degree of deviation of a maximum radiation direction of the antenna from a horizontal plane is reduced, and the maximum radiation direction of the antenna is closer to the horizontal plane. This increases a horizontal plane gain. 
     Referring to  FIG.  3   j   , in the figure, a connection line between dots of an inner circle indicates a horizontal plane gain in a 2.45 GHz modal when there is no slot, a connection line between dots of an outer circle indicates a horizontal plane gain in the 2.45 GHz modal after a slot is disposed, a solid line of an inner circle indicates a horizontal plane gain in a 5.9 GHz modal when there is no slot, and a dashed line of an outer circle indicates a horizontal plane gain in the 5.9 GHz modal after a slot is disposed. It can be seen that the horizontal plane gain in each of the two modalities is increased by more than 2 dB after the slot is disposed. 
     Referring to  FIG.  4   a    and  FIG.  4   b   , another embodiment of the present invention provides an antenna apparatus, including a ground plate  10 , a radiator  20 , and a signal source  30 , where the radiator  20  is disposed on the ground plate  10 . The antenna apparatus may further include a matching circuit  40 , where the matching circuit  40  is electrically connected between the radiator  20  and the signal source  30 , and is configured to adjust a resonance state of the radiator  20 . The signal source  30  is configured to feed electromagnetic wave signals of a first frequency band and a second frequency band into the radiator  20 , where the second frequency band is lower than the first frequency band, a third slot  13  and a fourth slot  14  are disposed on the ground plate  10 , and both the third slot  13  and the fourth slot  14  are closed slots and surround the radiator  20 . The antenna apparatus further includes a first filter  131  and a second filter  141 , where the first filter  131  is disposed in the third slot  13  and divides the third slot  13  into two slots, the second filter  141  is disposed in the fourth slot  14  and divides the fourth slot  14  into two slots, and the first filter  131  and the second filter  141  enable the third slot  13  and the fourth slot  14  to each form two different electrical lengths, so that currents generated by the electromagnetic wave signals of the first frequency band and the second frequency band can be confined in and around the third slot  13  and the fourth slot  14 . 
     The third slot  13  and the fourth slot  14  surrounding the radiator  20  are disposed to prevent the current from flowing to an edge of the ground plate  10 . The first filter  131  and the second filter  141  are disposed, so that two different electrical lengths are generated in the third slot  13  and two different electrical lengths are generated in the fourth slot  14 . Therefore, the radiator  20  generates resonance in two modalities of the first frequency band and the second frequency band, to meet a multi-frequency communication requirement. In addition, because the current is confined to the third slot  13  and the fourth slot  14 , horizontal plane gains of the electromagnetic wave signals of the first frequency band and the second frequency band are increased. The complete third slot  13  and the complete fourth slot  14  are used to confine the current generated by the electromagnetic wave signal of the second frequency band, and the first filter  131  and the second filter  141  are added, so that the current generated by the electromagnetic wave signal of the first frequency band can be also restrained by the antenna apparatus, and is confined to a part of the third slot  13  and a part of the fourth slot  14 . 
     The third slot  13  and the fourth slot  14  in this embodiment are basically the same as those in the embodiment shown in  FIG.  3   a    and  FIG.  3   b   . This is equivalent to canceling the first slot  11  and the second slot  12  in  FIG.  3   a    and  FIG.  3   b   , and the first filter  131  and the second filter  141  are added to the third slot  13  and the fourth slot  14 . 
     Both the first filter  131  and the second filter  141  are band-pass filters in which an inductor and a capacitor are connected in series, and are configured to enable the current generated by the electromagnetic wave signal of the second frequency band to pass and block the current generated by the electromagnetic wave signal of the first frequency band, so that an electrical length of the electromagnetic wave signal of the second frequency band is greater than an electrical length of the electromagnetic wave signal of the first frequency band. The first filter  131  and the second filter  141  are disposed as the band-pass filters, so that the two electrical lengths are generated in the third slot  13 , the two electrical lengths are generated in the fourth slot  14 , the entire third slot  13  is the electrical length of the second frequency band with a lower frequency, and a part of the third slot  13  is the electrical length of the first frequency band with a higher frequency. The other part is not used to confine the electromagnetic wave signal of the first frequency band because no current flows through the other part due to a blocking effect of the first filter  131 . The fourth slot  14  is similar to this, and details are not described. 
     A specific location of the first filter  131  disposed in the third slot  13  and a specific location of the second filter  141  disposed in the fourth slot  14  are related to a wavelength λ 1  of the electromagnetic wave signal of the first frequency band. Specifically, the first filter  131  is disposed at 0.5xλ 1  away from an endpoint of the third slot  13 , and the second filter  141  is disposed 0.5xλ 1  away from an endpoint of the fourth slot  14 . Through the foregoing settings, 0.5xλ 1  is the first electrical length of the electromagnetic wave signal of the first frequency band, and 0.5xλ 2  is the second electrical length of the electromagnetic wave signal of the second frequency band, where λ 1  is the wavelength of the electromagnetic wave signal of the first frequency band, and λ 2  is the wavelength of the electromagnetic wave signal of the second frequency band. 
     The third slot  13  and the fourth slot  14  are symmetrically disposed by using a joint between the radiator  20  and the ground plate  10  as a center. The third slot  13  and the fourth slot  14  that are symmetrically centered may enable that current distribution almost the same is generated on the ground plate  10  around the radiator  20 , so that shapes of radiation patterns of an antenna in all directions around the radiator  20  are almost the same. 
     A radial distance from the radiator  20  to the third slot  13  ranges from 0.2xλ 2  to 0.3xλ 2 , and λ 2  is the wavelength of the electromagnetic wave signal of the second frequency band. The distance between the third slot  13  and the radiator  20  is set to 0.2xλ 2  to 0.3xλ 2 , and a current flows from the radiator  20  to the third slot  13 . When flowing through the distance of 0.2xλ 2  to 0.3xλ 2 , the current is relatively weak, an electric field is relatively strong, resonance is generated, and the current is confined in and around the third slot  13 , so that resonance is generated at the third slot  13  after currents of the electromagnetic wave signals of the first frequency band and the second frequency band flow through the path, and the current is confined in and around the third slot  13 . 
     The third slot  13  is arc shaped, a distance between an inner side of the third slot  13  and a center of the radiator  20  is a first radius R 1 , and the first radius is 0.25xλ 2 . The first radius R 1  is 0.25xλ 2 , so that resonance can be generated at the third slot  13  after the current of the electromagnetic wave signal of the first frequency band flows through the path. Because at 0.25xλ 2 , the current is the smallest, the electric field is the strongest, and a resonance effect is the best, the current is confined in and around the third slot  13 . 
     A length of the third slot  13  extending in a circumference direction is a first electrical length, and the first electrical length is 0.5xλ 2 . The first electrical length is set to 0.5xλ 2 , so that resonance is generated at the third slot  13  when the current of the electromagnetic wave signal of the second frequency band flows to the third slot  13 . 
     A length of the third slot  13  in a radial direction is a first width W 1 , the first width W 1  is 0.05xλ 1 , λ 1  is the wavelength of the electromagnetic wave signal of the first frequency band, the first frequency band is 5.9 GHz, and the second frequency band is 2.45 GHz. The first width W 1  is set to 0.05xλ 1 , to obtain the first frequency band 5.9 GHz and the second frequency band 2.45 GHz meeting an operating frequency band range of the antenna. In the field of terminals such as a vehicle-mounted antenna, the frequencies 2.45 GHz and 5.9 GHz are both common communication frequencies, and the frequencies 2.45 GHz and 5.9 GHz obtained through the foregoing settings are both within a preferred frequency band range of the vehicle-mounted antenna, so that a relatively good wireless communication effect can be implemented. 
     In this embodiment, the radiator  20  preferably uses a monopole antenna, and a height of the radiator  20  is preferably 0.25xλ 2 . 
     With reference to  FIG.  4   a    and  FIG.  4   b   , a specific embodiment is provided. The ground plate  10  is a circle, a radius R ground  of the ground plate  10  is 100 mm, the radiator  20  is a monopole antenna, a height H of the radiator  20  is 20 mm, a first radius R 1  is 20 mm, and a first electrical length is 40 mm, a first width W 1  is 2 mm. Both the first filter  131  and the second filter  141  are band-pass filters in which an inductor of 3.6 nH and a capacitor of 0.2 pF are connected in series. The antenna apparatus is simulated, and for a simulation result, refer to subsequent descriptions. 
     Referring to  FIG.  4   c   , in the figure, a solid line is an S11 curve of an antenna when there is no slot, and a dashed line is an S11 curve of an antenna added with a filter after a slot is disposed. It can be seen that, after the slot is disposed and the filter is added, locations of two generated resonance points are close to the expected first frequency band 2.45 GHz and the expected second frequency band 5.9 GHz. In this way, the antenna apparatus is disposed. 
     Referring to  FIG.  4   d   , a left figure in the figure is a current distribution diagram in a 2.45 GHz modal when there is no slot, and a right figure in the figure is a current distribution diagram in a 5.9 GHz modal when there is no slot. It can be seen that, when there is no slot, current distribution on the ground plate  10  extends to an edge of the plate. 
     Referring to  FIG.  4   e   , in the figure, a left figure is a current distribution diagram in a 2.45 GHz modal after a slot is disposed and a filter is added, and a right figure is a current distribution diagram in a 5.9 GHz modal after a slot is disposed and a filter is added. It can be seen that, after the slot is added and the filter is added, a current on the ground plate  10  is “confined” to some extent in and around the slot, and a current outside the slot becomes weak. The slot can improve current distribution of 2.45 GHz, and the filter added at a specific location of the slot enables a current of 5.9 GHz to generate resonance at the slot, in other words, after the filter is added to the same slot, currents in two modalities generate resonance around the slot. This changes current distribution on the ground plate  10 , and further changes a directivity pattern and a horizontal plane gain of the antenna. 
     Referring to  FIG.  4   f   - 1  to  FIG.  4   f   - 3 , in the figures,  FIG.  4   f   - 1  is a top view of a simulation directivity diagram.  FIG.  4   f   - 2  is a side view of the simulation directivity diagram, and  FIG.  4   f   - 3  is a side view of the simulation directivity diagram (vertical to a view angle of  FIG.  4   f   - 2 ). When there is no slot, a maximum radiation direction in a 2.45 GHz modal is tilted. Therefore, the maximum radiation direction deviates from a horizontal plane relatively far and a horizontal plane gain decreases. 
     Referring to  FIG.  4   g   - 1  to  FIG.  4   g   - 3 , in the figures,  FIG.  4   g   - 1  is a top view of a simulation directivity diagram.  FIG.  4   g   - 2  is a side view of the simulation directivity diagram, and  FIG.  4   g   - 3  is a side view of the simulation directivity diagram (vertical to a view angle of  FIG.  4   g   - 2 ). When there is no slot, a maximum radiation direction in a 5.9 GHz modal is tilted. Therefore, the maximum radiation direction deviates from a horizontal plane relatively far and a horizontal plane gain decreases. 
     Referring to  FIG.  4   h   - 1  to  FIG.  4   h   - 3 , in the figures,  FIG.  4   h   - 1  is a top view of a simulation directivity diagram,  FIG.  4   h   - 2  is a side view of the simulation directivity diagram, and  FIG.  4   h   - 3  is a side view of the simulation directivity diagram (vertical to a view angle of  FIG.  4   h   - 2 ). After a slot is disposed and a filter is added, a change of current distribution on the ground plate  10  brings a change of a radiation pattern of an antenna in a 2.45 GHz modal, and the radiation pattern of the antenna is pulled down, so that a degree of deviation of a maximum radiation direction of the antenna from a horizontal plane is reduced, and the maximum radiation direction of the antenna is closer to the horizontal plane. This increases a horizontal plane gain. 
     Referring to  FIG.  4   i   - 1  to  FIG.  4   i   - 3 , in the figures,  FIG.  4   i   - 1  is a top view of the simulation directivity diagram,  FIG.  4   i   - 2  is a side view of the simulation directivity diagram, and  FIG.  4   i   - 3  is a side view of the simulation directivity diagram (vertical to the view of  FIG.  4   i   - 2 ). After a slot is disposed and a filter is added, because of a change of current distribution on the ground plate  10 , in this way, the 5.9 GHz modal pattern of the antenna is changed, and the pattern of the antenna is pulled down, so that a degree of deviation of the maximum radiation direction of the antenna from the horizontal plane is reduced, and the maximum radiation direction of the antenna is closer to the horizontal plane, thereby increasing a horizontal plane gain. 
     Referring to  FIG.  4   j   , in the figure, a connection line between dots of an inner circle indicates a horizontal plane gain in a 2.45 GHz modal when there is no slot, a connection line between dots of an outer circle indicates a horizontal plane gain in the 2.45 GHz modal after a slot is disposed, a solid line of an inner circle indicates a horizontal plane gain in a 5.9 GHz modal when there is no slot, and a dashed line of an outer circle indicates a horizontal plane gain in the 5.9 GHz modal after a slot is disposed. It can be seen that after the slot is disposed and a filter is added, the horizontal plane gain in the 2.45 GHz modal increases by about 1.3 dB and the horizontal plane gain in the 5.9 GHz modal increases by about 0.5 dB. 
     What is disclosed above is merely several example embodiments of the present invention, and certainly is not intended to limit the protection scope of the present invention. A person of ordinary skill in the art may understand that all or some of processes that implement the foregoing embodiments and equivalent modifications made in accordance with the claims of the present invention shall fall within the scope of the present invention.