Patent Publication Number: US-2018048051-A1

Title: Multi-Band Antenna and Terminal Device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a U.S. National Stage of International Patent Application No. PCT/CN2015/072782 filed on Feb. 11, 2015, which is hereby incorporated by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     Embodiments of the present disclosure relate to antenna technologies, and in particular, to a multi-band antenna and a terminal device. 
     BACKGROUND 
     With development of wireless communications technologies, portable terminal devices such as a smartphone or a tablet computer are increasingly used. To attract consumers to make a purchase, a manufacturer of portable terminal devices needs to continuously improve the portable terminal devices. 
     An appearance is a first impression that a consumer has on a portable terminal device. Therefore, to attract a consumer to purchase a portable terminal device, in addition to continuous improvement of software and hardware performance of the portable terminal device, appearance factors such as an appearance of the portable terminal device and holding feeling have become increasingly important. Currently, a portable terminal device such as a high-end smartphone or tablet computer is developing towards a trend of lightness and thinness. In addition, to increase product texture, a metallic material is used as a main element in design of an appearance part (for example, a rear housing of a mobile phone) of the portable terminal device. 
     However, currently, all portable terminal devices support wireless communication functions of multiple standards, for example, mobile communication of various standards such as WI-FI, Global Positioning System (GPS), BLUETOOTH, Code Division Multiple Access (CDMA), Global System for Mobiles (GSM), and Long-Term Evolution (LTE). A multi-band antenna needs to be configured for the portable terminal device, and to improve an appearance of the portable terminal device, built-in design needs to be used for the antenna. A length of a built-in antenna is generally a quarter of a wavelength corresponding to a resonance frequency. How to reduce an antenna size to better apply an antenna to a terminal device is a problem to be urgently resolved at present. 
     SUMMARY 
     Embodiments of the present disclosure provide a multi-band antenna and a terminal device, which can reduce an antenna size. 
     A first aspect provides a multi-band antenna, including a feeding matching circuit, a feeding part, a capacitor component, a radiation part, and a grounding part, where the feeding part is connected to the capacitor component to form a feeding circuit, and the feeding matching circuit is electrically connected between a feeding radio frequency circuit and the feeding circuit, and the radiation part is electrically connected both to the feeding circuit and the grounding part, the grounding part is electrically connected to a ground plane, a first resonant circuit is formed from the feeding circuit to an end that is of the radiation part and that is away from the grounding part, the first resonant circuit generates a first resonance frequency and a second resonance frequency, the first resonance frequency is a GPS frequency, the second resonance frequency is a multiplied frequency of the first resonance frequency, a length of the first resonant circuit ranges from 0.12 times to 0.18 times as great as a wavelength corresponding to the first resonance frequency, and a width of the grounding part ranges from 0.5 millimeter (mm) to 2.5 mm. 
     With reference to the first aspect, in a first possible implementation manner of the first aspect, a groove is disposed on the radiation part, the groove extends to the grounding part from the end that is of the radiation part and that is away from the grounding part, the groove is configured to form a second resonant circuit on the radiation part, the second resonant circuit generates a third resonance frequency, and the third resonance frequency is different from the first resonance frequency and the second resonance frequency. 
     With reference to the first aspect or the first possible implementation manner of the first aspect, in a second possible implementation manner of the first aspect, a capacitance value of the capacitor component is inversely proportional to the first resonance frequency. 
     With reference to any one of the first aspect to the second possible implementation manner of the first aspect, in a third possible implementation manner of the first aspect, the width of the grounding part is inversely proportional to the second resonance frequency. 
     With reference to any one of the first aspect to the third possible implementation manner of the first aspect, in a fourth possible implementation manner of the first aspect, the ground plane is a copper layer of a circuit board. 
     A second aspect provides a terminal device, including a housing, a baseband processing circuit, a frequency mixing circuit, a feeding radio frequency circuit, and a multi-band antenna, where the baseband processing circuit, the frequency mixing circuit, the feeding radio frequency circuit, and the multi-band antenna are located inside the housing, the baseband processing circuit and the frequency mixing circuit are connected to the feeding radio frequency circuit, and the multi-band antenna includes a feeding matching circuit, a feeding part, a capacitor component, a radiation part, and a grounding part, where the feeding part is connected to the capacitor component to form a feeding circuit, and the feeding matching circuit is electrically connected between the feeding radio frequency circuit and the feeding circuit, and the radiation part is electrically connected both to the feeding circuit and the grounding part, the grounding part is electrically connected to a ground plane, a first resonant circuit is formed from the feeding circuit to an end that is of the radiation part and that is away from the grounding part, the first resonant circuit generates a first resonance frequency and a second resonance frequency, the first resonance frequency is a GPS frequency, the second resonance frequency is a multiplied frequency of the first resonance frequency, a length of the first resonant circuit ranges from 0.12 times to 0.18 times as great as a wavelength corresponding to the first resonance frequency, and a width of the grounding part ranges from 0.5 mm to 2.5 mm. 
     With reference to the second aspect, in a first possible implementation manner of the second aspect, a groove is disposed on the radiation part, the groove extends to the grounding part from the end that is of the radiation part and that is away from the grounding part, the groove is configured to form a second resonant circuit on the radiation part, the second resonant circuit generates a third resonance frequency, and the third resonance frequency is different from the first resonance frequency and the second resonance frequency. 
     With reference to the second aspect or the first possible implementation manner of the second aspect, in a second possible implementation manner of the second aspect, a capacitance value of the capacitor component is inversely proportional to the first resonance frequency. 
     With reference to any one of the second aspect to the second possible implementation manner of the second aspect, in a third possible implementation manner of the second aspect, the width of the grounding part is inversely proportional to the second resonance frequency. 
     With reference to any one of the second aspect to the third possible implementation manner of the second aspect, in a fourth possible implementation manner of the second aspect, the ground plane is a copper layer of a circuit board in the terminal device. 
     A third aspect provides a multi-band antenna, including a feeding matching circuit, a feeding part, a capacitor component, a radiation part, and a grounding part, where the feeding part is connected to the capacitor component to form a feeding circuit, and the feeding matching circuit is electrically connected between a feeding radio frequency circuit and the feeding circuit, and the radiation part is electrically connected both to the feeding circuit and the grounding part, the grounding part is electrically connected to a ground plane, a first resonant circuit is formed from the feeding circuit to an end that is of the radiation part and that is away from the grounding part, the first resonant circuit generates a first resonance frequency and a second resonance frequency, and the second resonance frequency is a multiplied frequency of the first resonance frequency. 
     With reference to the third aspect, in a first possible implementation manner of the third aspect, a groove is disposed on the radiation part, the groove extends to the grounding part from the end that is of the radiation part and that is away from the grounding part, the groove is configured to form a second resonant circuit on the radiation part, the second resonant circuit generates a third resonance frequency, and the third resonance frequency is different from the first resonance frequency and the second resonance frequency. 
     With reference to the third aspect or the first possible implementation manner of the third aspect, in a second possible implementation manner of the third aspect, a length of the groove is inversely proportional to the third resonance frequency. 
     With reference to any one of the third aspect to the second possible implementation manner of the third aspect, in a third possible implementation manner of the third aspect, a width of the grounding part is inversely proportional to the second resonance frequency. 
     With reference to any one of the third aspect to the third possible implementation manner of the third aspect, in a fourth possible implementation manner of the third aspect, the ground plane is a copper layer of a circuit board. 
     A fourth aspect provides a terminal device, including a housing, a baseband processing circuit, a frequency mixing circuit, a feeding radio frequency circuit, and a multi-band antenna, where the baseband processing circuit, the frequency mixing circuit, the feeding radio frequency circuit, and the multi-band antenna are located inside the housing, the baseband processing circuit and the frequency mixing circuit are connected to the feeding radio frequency circuit, and the multi-band antenna includes a feeding matching circuit, a feeding part, a capacitor component, a radiation part, and a grounding part, where the feeding part is connected to the capacitor component to form a feeding circuit, and the feeding matching circuit is electrically connected between the feeding radio frequency circuit and the feeding circuit, and the radiation part is electrically connected both to the feeding circuit and the grounding part, the grounding part is electrically connected to a ground plane, a first resonant circuit is formed from the feeding circuit to an end that is of the radiation part and that is away from the grounding part, the first resonant circuit generates a first resonance frequency and a second resonance frequency, and the second resonance frequency is a multiplied frequency of the first resonance frequency. 
     With reference to the fourth aspect, in a first possible implementation manner of the fourth aspect, a groove is disposed on the radiation part, the groove extends to the grounding part from the end that is of the radiation part and that is away from the grounding part, the groove is configured to form a second resonant circuit on the radiation part, the second resonant circuit generates a third resonance frequency, and the third resonance frequency is different from the first resonance frequency and the second resonance frequency. 
     With reference to the fourth aspect, in a first possible implementation manner of the fourth aspect, a length of the groove is inversely proportional to the third resonance frequency. 
     With reference to any one of the fourth aspect to the second possible implementation manner of the fourth aspect, in a third possible implementation manner of the fourth aspect, a width of the grounding part is inversely proportional to the second resonance frequency. 
     With reference to any one of the fourth aspect to the third possible implementation manner of the fourth aspect, in a fourth possible implementation manner of the fourth aspect, the ground plane is a copper layer of a circuit board in the terminal device. 
     According to the multi-band antenna and the terminal device provided in the embodiments of the present disclosure, disposing a capacitor component between a feeding part and a radiation part is equivalent to disposing a series resistor for the radiation part of the antenna, and a path between a grounding part and the feeding part that are of the antenna is equivalent to a parallel inductor. The feeding part, the series resistor, and the parallel inductor form a multi-band antenna that complies with a composite right/left handed (CRLH) principle, which can reduce an antenna size. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       To describe the technical solutions in the embodiments of the present disclosure more clearly, the following briefly describes the accompanying drawings required for describing the embodiments. The accompanying drawings in the following description show some embodiments of the present disclosure, and persons of ordinary skill in the art may still derive other drawings from these accompanying drawings without creative efforts. 
         FIG. 1  is a multi-band antenna; 
         FIG. 2  is a schematic structural diagram of Embodiment 1 of a multi-band antenna according to an embodiment; 
         FIG. 3  is a schematic diagram of spectrums of a first resonance frequency corresponding to different capacitance values of a capacitor component; 
         FIG. 4  is a schematic diagram of spectrums of a first resonance frequency corresponding to different widths of a grounding part; 
         FIG. 5  is a schematic structural diagram of Embodiment 2 of a multi-band antenna according to an embodiment of the present disclosure; 
         FIG. 6  is a schematic structural diagram of Embodiment 3 of a multi-band antenna according to an embodiment of the present disclosure; 
         FIG. 7  is a schematic structural diagram of Embodiment 4 of a multi-band antenna according to an embodiment of the present disclosure; 
         FIG. 8  is a schematic structural diagram of Embodiment 5 of a multi-band antenna according to an embodiment of the present disclosure; 
         FIG. 9  is a schematic structural diagram of Embodiment 6 of a multi-band antenna according to an embodiment of the present disclosure; 
         FIG. 10  is a diagram of antenna radiation efficiency of the multi-band antenna in the embodiment shown in  FIG. 9 ; 
         FIG. 11  is a schematic structural diagram of Embodiment 7 of a multi-band antenna according to an embodiment of the present disclosure; 
         FIG. 12A ,  FIG. 12B , and  FIG. 12C  are schematic diagrams of surface current distribution and electric field distribution of the multi-band antenna shown in  FIG. 11 ; 
         FIG. 13  is a schematic structural diagram of Embodiment 1 of a terminal device according to an embodiment of the present disclosure; 
         FIG. 14  is a schematic structural diagram of Embodiment 8 of a multi-band antenna according to an embodiment; 
         FIG. 15  is a schematic structural diagram of Embodiment 9 of a multi-band antenna according to an embodiment of the present disclosure; and 
         FIG. 16  is a schematic structural diagram of Embodiment 2 of a terminal device according to an embodiment of the present disclosure. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     To make the objectives, technical solutions, and advantages of the embodiments of the present disclosure clearer, the following clearly and completely describes the technical solutions in the embodiments of the present disclosure with reference to the accompanying drawings in the embodiments of the present disclosure. The described embodiments are some but not all of the embodiments of the present disclosure. All other embodiments obtained by persons of ordinary skill in the art based on the embodiments of the present disclosure without creative efforts shall fall within the protection scope of the present disclosure. 
     Because a portable terminal device integrates more functions, a multi-band antenna that can provide multiple resonance frequencies needs to be configured for the portable terminal device. Currently, antennas in portable terminal devices are designed mainly based on an architecture of an inverted F antenna (IFA) or an architecture of a planar inverted F antenna (PIFA). The multi-band antenna is designed mainly using an architecture of multiple resonant circuits plus a parasitic circuit. 
       FIG. 1  is a multi-band antenna. A technical implementation manner of the multi-band antenna is that different resonant modes may be simultaneously generated by means of excitation using the multiple resonant circuits of different lengths in the antenna. In  FIG. 1 , on an antenna  11 , a point A is a feed point, a path AB and a path AC are two different resonant circuits, and a section of a grounding parasitic circuit  12  is added near the feed point or a grounding point of the antenna. In the parasitic circuit  12 , a point D is a grounding point, and an extra resonant mode may be generated on a path DE. By adjusting sizes of the antenna  11  and the parasitic circuit  12 , the antenna  11  shown in  FIG. 1  may generate three resonant modes of different frequencies. In addition, according to a principle of the antenna  11  shown in  FIG. 1 , an antenna that may generate more than three resonant modes of different frequencies can be designed. The antenna  11  shown in  FIG. 1  is still based on the IFA architecture, and a size of a resonant circuit of the antenna  11  that generates a fundamental frequency is generally a quarter of a wavelength. If the antenna  11  includes multiple resonant circuits and parasitic circuits, an overall size of the antenna  11  is increased based on a quarter of a wavelength of the fundamental frequency. However, for a design trend of an increasingly miniaturized portable terminal, the antenna  11  of such a size is still relatively large. In addition, when the antenna based on the IFA or PIFA architecture works at the fundamental frequency, surface currents mainly concentrate on a radiation part of the antenna (that is, near a point B in  FIG. 1 ). If there is a ground terminal near the antenna, such design causes significant reduction of bandwidth and radiation efficiency of the antenna. Therefore, the antenna  11  that is based on the IFA or PIFA architecture and that is shown in  FIG. 1  is hardly applied to a portable device with an all-metal back cover. 
     To resolve problems that the size of the multi-band antenna is relatively large in the foregoing portable terminal device, and that a solution in  FIG. 1  is hardly applied to a portable device with an all-metal back cover, the embodiments of the present disclosure provide a multi-band antenna that is based on CRLH design and a terminal device that uses the CRLH-based antenna. 
       FIG. 2  is a schematic structural diagram of Embodiment 1 of a multi-band antenna according to an embodiment. As shown in  FIG. 2 , the multi-band antenna in this embodiment includes a feeding matching circuit  21 , a feeding part  22 , a capacitor component  23 , a radiation part  24 , and a grounding part  25 . 
     The feeding part  22  is connected to the capacitor component  23  to form a feeding circuit  26 , the feeding matching circuit  21  is electrically connected between a feeding radio frequency circuit  27  and the feeding part  22 , and the capacitor component  23  is connected to the radiation part  24 . The feeding matching circuit  21  is configured to match a radio frequency signal in the feeding radio frequency circuit  27 , and transmit the signal to the feeding circuit  26 . The feeding part  22  is configured to feed a radio frequency signal generated by the feeding radio frequency circuit  27  into the radiation part  24 , or feed a radio frequency signal generated by the radiation part  24  into the feeding radio frequency circuit  27 . The radiation part  24  is electrically connected both to the capacitor component  23  and the grounding part  25 , the grounding part  25  is electrically connected to a ground plane  28 , a first resonant circuit (that is, a path from a point F to a point G in  FIG. 2 ) is formed from the feeding circuit  26  to an end that is of the radiation part  24  and that is away from the grounding part  25 , and the first resonant circuit generates a first resonance frequency and a second resonance frequency. Generally, the grounding part  25  and the radiation part  24  may be an integrated metal plate, that is, a part of the radiation part  24  extending to the ground plane  28  is the grounding part  25 . A width of the grounding part  25  may be W. 
     The feeding part  22 , the radiation part  24 , and the grounding part  25  form a basic antenna structure. In addition, impedance does not match between the feeding radio frequency circuit  27  and the feeding part  22 . Therefore, the feeding matching circuit  21  is further electrically connected between the feeding radio frequency circuit  27  and the feeding part  22 . The feeding matching circuit  21  is configured to match a radio frequency signal in the feeding radio frequency circuit  27  and the feeding part  22 , including matching a signal transmitted by the feeding radio frequency circuit  27  and transmitting the matched signal to the feeding circuit  26 , and then radiating the matched signal using the radiation part  24 , or matching a signal that is transmitted by the feeding circuit  26  and that is received by the radiation part  24 , and then transmitting the matched signal to the feeding radio frequency circuit  27 . The capacitor component  23  is further disposed between the feeding part  22  and the radiation part  24 , where the capacitor component  23  and the feeding part  22  form the feeding circuit  26 . The capacitor component  23  may be a lumped capacitor, or may be a distributed capacitor. If the capacitor component  23  is a lumped capacitor, the lumped capacitor device whose capacitance value is determined is connected (for example, in a welding manner) between the feeding part  22  and the radiation part  24 . If the capacitor component  23  is a distributed capacitor, a specific gap may be reserved between the feeding part  22  and the radiation part  24 . The gap presents a characteristic of the distributed capacitor, and the capacitance value of the distributed capacitor may be adjusted by adjusting a width of the gap between the feeding part  22  and the radiation part  24 . For example, when the width of the gap between the feeding part  22  and the radiation part  24  is 0.3 mm, the capacitance value of the distributed capacitor may be equivalent to a 0.4 picofarads (pF) capacitance value of the lumped capacitor. 
     In the multi-band antenna provided in this embodiment, the first resonance frequency may be a GPS frequency. The GPS frequency is divided into three frequency bands L1, L2, and L3, whose frequencies are respectively 1.57542 gigahertz (GHz) for the L1 frequency band, 1.22760 GHz for the L2 frequency band, and 1.38105 GHz for the L3 frequency band. In this embodiment, the L1 frequency band of the GPS is used as an example, that is, the first resonance frequency is 1.57542 GHz. A length of the first resonant circuit (that is, the path from the point F to the point G) ranges from 0.12 times to 0.18 times as great as a wavelength corresponding to the first resonance frequency. If the first resonance frequency is 1.57542 GHz, the calculated length of the first resonant circuit may approximately range from 30.5 mm to 34.3 mm. The second resonance frequency is a multiplied frequency of the first resonance frequency. Further, the second resonance frequency may be 1.5 times of the first resonance frequency, the second resonance frequency may be 2.5 times of the first resonance frequency, or the second resonance frequency may be 3 times of the first resonance frequency. In this embodiment, the second resonance frequency may be 3.5 times of the first resonance frequency. For example, the first resonance frequency is 1.57542 GHz, and the second resonance frequency is approximately 5.5 GHz, which is a WI-FI frequency. The width W of the grounding part  25  may range from 0.5 mm to 2.5 mm, for example, the width W of the grounding part may be equal to 1 mm. Certainly, the width of the grounding part  25  may alternatively be 0.8 mm, 2 mm, or 2.2 mm. 
     The multi-band antenna provided in this embodiment is disposed in a terminal device that needs to work in multiple wireless frequency bands. The feeding radio frequency circuit  27  is disposed in the terminal device, where the feeding radio frequency circuit  27  is configured to process a radio frequency signal received using the multi-band antenna or transmit a generated radio frequency signal using the multi-band antenna. The ground plane  28  for grounding is further disposed in the terminal device. The ground plane  28  is generally a copper cover on a circuit board in the terminal device, for example, a copper layer of the circuit board. 
     In the multi-band antenna shown in  FIG. 2 , a part from a connection point H between the grounding part  25  and the ground plane  28  to a connection point I between the feeding circuit  26  and the radiation part  24  forms an inductor that is in parallel with the radiation part  24 . The capacitor component  23  and the radiation part  24  are in a serial connection relationship, which is equivalent to a series resistor. According to the principle of the CRLH antenna, the parallel inductor and the series resistor form a core component that complies with a principle of a right/left handed transmission line, and the path from the point G that is of the radiation part  24  of the multi-band antenna and that is away from the grounding part  25  to the point F connected between the feeding part  22  and the feeding radio frequency circuit  27  forms the first resonant circuit. The first resonant circuit generates the first resonance frequency, where the first resonance frequency is a fundamental frequency of the multi-band antenna. In addition, according to the CRLH principle, the first resonant circuit further generates the second resonance frequency, where the second resonance frequency is a multiplied frequency of the first resonance frequency. The first resonance frequency complies with a left handed rule, and the length of the first resonant circuit ranges from 0.12 times to 0.18 times as great as a wavelength corresponding to the first resonance frequency. For example, the length of the first resonant circuit is 0.125 times as great as the wavelength corresponding to the first resonance frequency. The second resonance frequency complies with a right handed rule. Therefore, the multi-band antenna shown in  FIG. 2  generates two resonance frequencies, and the first resonance frequency and the second frequency may be adjusted by adjusting sizes and parameters of various parts in the multi-band antenna. By adjusting a length of the path from the point G to the point F, the length of the first resonant circuit may be adjusted, that is, a magnitude of the first resonance frequency is adjusted, and a magnitude of the second resonance frequency also changes. By adjusting a capacitance value of the capacitor component  23 , a resonance frequency may be adjusted for the first resonant circuit, where the capacitance value of the capacitor component  23  is inversely proportional to the first resonance frequency. By adjusting a width W of the grounding part  25 , the second resonance frequency may also be adjusted, where the width W of the grounding part  25  is inversely proportional to the second resonance frequency. Increasing the width W of the grounding part  25  is equivalent to increasing an equivalent inductance value of the inductor that is in parallel with the first resonant circuit. 
     It can be learned from the principle of the CRLH antenna that, for the antenna based on the CRLH principle, a length of a resonant circuit that generates a fundamental frequency approximately ranges from 0.12 times to 0.18 times as great as a wavelength corresponding to the fundamental frequency. In contrast, for the antenna (for example, the antenna shown in  FIG. 1 ) designed based on the IFA or PIFA principle, a length of a resonant circuit that generates a fundamental frequency is approximately 0.25 times as great as a wavelength corresponding to the fundamental frequency. Therefore, the wavelength corresponding to the fundamental frequency for the multi-band antenna provided in this embodiment may be 0.09 times shorter than that for the antenna based on the IFA or PIFA principle, which is quite important to a terminal device of increasingly miniaturized design. Because the fundamental frequency of the multi-band antenna in this embodiment is designed at a GPS frequency, in an L1 frequency band of GPS, a center frequency of the fundamental frequency of the multi-band antenna is 1575 megahertz (MHz), and a wavelength corresponding to 1575 MHz is approximately 190 mm. If the antenna designed based on the IFA or PIFA principle is used, a length of the antenna is approximately 47.6 mm. If the antenna provided in this embodiment is used, a length of the antenna ranges approximately from 30.5 mm to 34.3 mm. A length difference between the two antennas reaches 17.1 mm. Considering that an existing mainstream portable terminal device such as an IPHONE 4 smartphone of Apple has outline dimensions of only 115.2×58.6×9.3 cubic millimeters (mm 3 ), the difference of 17.1 mm is quite considerable for a current portable terminal device. Therefore, if a terminal device uses the multi-band antenna provided in this embodiment, space of the terminal device may be saved such that a size of the terminal device may be reduced or space may be reserved for another device for use, thereby enhancing a function of the terminal device. 
     In addition, for the multi-band antenna designed based on the CRLH principle in this embodiment, when the multi-band antenna works at a fundamental frequency, surface currents on the radiation part  24  of the multi-band antenna mainly concentrate near the grounding part  25 . For the antenna that is designed based on the IFA or PIFA architecture and that is shown in  FIG. 1 , when the antenna works at a fundamental frequency, surface current distribution on the antenna  11  at the fundamental frequency mainly concentrates on an end that is of the antenna  11  and that is close to the point B. If currents mainly concentrate near the point B on the antenna  11 , when there is a ground terminal near the point B, currents on the antenna  11  are affected by the ground terminal. Consequently, a capacitance effect is generated, thereby severely affecting antenna performance. In contrast, in the multi-band antenna shown in  FIG. 2 , currents mainly concentrate near the grounding part  25 . In this case, if there is a ground terminal near the radiation part  24  or the grounding part  25 , because current distribution at a location that is of the radiation part  24  and that is away from the ground terminal is relatively small, a capacitance effect generated by the current distribution has relatively little impact on antenna performance. Current distribution is relatively large at the grounding part  25 , but the grounding part  25  is electrically connected to the ground plane. Therefore, a capacitance effect generated between the ground terminal near the grounding part  25  and the radiation part  24  also has relatively little impact on antenna performance. In this way, using the terminal device configured with the multi-band antenna provided in this embodiment, design of an all-metal back cover or another all-metal appearance part may be used, and performance of the multi-band antenna is not affected greatly. 
       FIG. 3  is a schematic diagram of spectrums of a first resonance frequency corresponding to different capacitance values of a capacitor component. In  FIG. 3 , the horizontal axis indicates a frequency measured in GHz, and the vertical axis indicates a return loss measured in decibels (dB). As shown in  FIG. 3 , in the multi-band antenna in the embodiment shown in  FIG. 2 , it is assumed that the capacitor component  23  is a distributed capacitor, that is, a gap of a specific width is disposed between the feeding part  22  and the radiation part  24 . A curve  31  is a corresponding spectrum curve of the first resonance frequency when a gap width is 0.1 mm, a curve  32  is a corresponding spectrum curve of the first resonance frequency when a gap width is 0.3 mm, and a curve  33  is a corresponding spectrum curve of the first resonance frequency when a gap width is 0.5 mm. A smaller gap between the feeding part  22  and the radiation part  24  indicates a larger capacitance value of the equivalent capacitor component  23 . It can be seen from  FIG. 3  that, when the capacitance value of the capacitor component  23  increases, the first resonance frequency moves to a low frequency. 
       FIG. 4  is a schematic diagram of spectrums of a first resonance frequency corresponding to different widths of a grounding part. In  FIG. 4 , the horizontal axis indicates a frequency measured in GHz, and the vertical axis indicates a return loss measured in dB. As shown in  FIG. 4 , in the multi-band antenna in the embodiment shown in  FIG. 2 , a curve  41  is a corresponding spectrum curve of the first resonance frequency when a width W of the grounding part  25  is 0.5 mm, a curve  42  is a corresponding spectrum curve of the first resonance frequency when a width W of the grounding part  25  is 1 mm, and a curve  43  is a corresponding spectrum curve of the first resonance frequency when a width W of the grounding part  25  is 1.5 mm. A smaller width W of the grounding part  25  indicates a larger equivalent inductance value of a path from the grounding point H to the point I. It can be seen from  FIG. 4  that, when the width W of the grounding part  25  increases, the first resonance frequency moves to a high frequency. 
     According to the multi-band antenna provided in this embodiment, disposing a capacitor component between a feeding part and a radiation part is equivalent to disposing a series resistor for the radiation part of the antenna, and a path between a grounding part and the feeding part that are of the antenna is equivalent to a parallel inductor. The feeding part, the series resistor, and the parallel inductor form a multi-band antenna that complies with a CRLH principle, which reduces an antenna size, and enables the antenna to be applied to a terminal device with an all-metal appearance part because surface current distribution of the antenna is changed. 
       FIG. 5  is a schematic structural diagram of Embodiment 2 of a multi-band antenna according to an embodiment of the present disclosure. As shown in  FIG. 5 , a difference between the multi-band antenna in this embodiment and the multi-band antenna shown in  FIG. 2  lies in that, in the multi-band antenna shown in  FIG. 5 , a capacitor component  23  is disposed between a feeding part  22  and a feeding matching circuit  21 , where the feeding part  22  is electrically connected to a radiation part  24 , and the capacitor component  23  is electrically connected to the feeding matching circuit  21 . In the multi-band antenna shown in this embodiment, a feeding circuit  26  is still formed by the capacitor component  23  and the feeding part  22 . Likewise, an antenna that complies with a CRLH principle may be formed by the capacitor component  23  and a path from a grounding part  25  to the feeding part  22 . 
     In the embodiments shown in  FIG. 2  and  FIG. 5 , the capacitor component  23  may be implemented using a lumped capacitor or a distributed capacitor. However, when design of a distributed capacitor is used, a gap between the feeding part  22  and the radiation part  24  needs to be controlled in order to control the capacitance value of the capacitor component  23 . 
       FIG. 6  is a schematic structural diagram of Embodiment 3 of a multi-band antenna according to an embodiment of the present disclosure. As shown in  FIG. 6 , the multi-band antenna in this embodiment may be based on the multi-band antenna shown in  FIG. 2 , and a groove  29  is disposed on the radiation part  24 , where the groove  29  extends to the grounding part  25  from the end (that is, the point G) that is of the radiation part  24  and that is away from the grounding part  25 . 
     The groove  29  is disposed on the radiation part  24 , where the groove  29  on the radiation part  24  changes electric field distribution on the radiation part  24 . The electric field distribution in the groove  29  may generate a new resonance frequency on the radiation part  24 , that is, the groove  29  may form a second resonant circuit on the radiation part  24 . The second resonant circuit generates a third resonance frequency, and the third resonance frequency may be adjusted by adjusting a position, a length, and a width of the groove  29  on the radiation part  24 . Generally, the length of the groove  29  is 0.25 times as great as a wavelength corresponding to the third resonance frequency. When the length or the width of the groove  29  increases, the third resonance frequency moves to a low frequency. 
     Likewise, as shown in  FIG. 7 , the groove  29  in the embodiment shown in  FIG. 6  may alternatively be disposed based on the embodiment shown in  FIG. 5 .  FIG. 7  is a schematic structural diagram of Embodiment 4 of a multi-band antenna according to an embodiment of the present disclosure. As shown in  FIG. 7 , a difference between the multi-band antenna in this embodiment and the multi-band antenna shown in  FIG. 6  lies in that, in the multi-band antenna shown in  FIG. 7 , the capacitor component  23  is disposed between the feeding part  22  and the feeding matching circuit  21 , where the feeding part  22  is electrically connected to the radiation part  24 , and the capacitor component  23  is electrically connected to the feeding matching circuit  21 . 
     The multi-band antenna that is based on the CRLH principle and that is shown in  FIG. 2  or  FIG. 5  may provide two resonance frequencies. After the groove shown in  FIG. 6  or  FIG. 7  is added, the multi-band antenna that is based on the CRLH principle and that is provided in this embodiment of the present disclosure may provide three resonance frequencies. By adjusting sizes and parameters of various parts in the multi-band antenna, the multi-band antenna may work in three different frequency bands. 
       FIG. 8  is a schematic structural diagram of Embodiment 5 of a multi-band antenna according to an embodiment of the present disclosure. As shown in  FIG. 8 , a difference between the multi-band antenna in this embodiment and the multi-band antenna shown in  FIG. 6  lies in that the groove  29  in  FIG. 6  is in a “-” shape, while the groove  29  in  FIG. 8  is in an “L” shape. Setting the groove  29  to the “L” shape is mainly to increase the length of the groove  29  and to lower the third resonance frequency. For example, in the embodiment shown in  FIG. 8 , a center of the first resonance frequency is set to 1575 MHz, and a length of a path from a point G to a point F is approximately 30.5 mm. If a center of the third resonance frequency needs to be set to 2442 MHz (which is 2.4 GHz of a WI-FI frequency), the length of the groove  29  is approximately 30.7 mm. It can be learned that, if the groove  29  is set to the “-” shape, the length of the radiation part  24  may be insufficient. Therefore, the groove  29  may be set to the “L” shape such that the center of the third resonance frequency may be set to 2442 MHz. 
       FIG. 9  is a schematic structural diagram of Embodiment 6 of a multi-band antenna according to an embodiment of the present disclosure. As shown in  FIG. 9 , on the basis of the multi-band antenna shown in  FIG. 8 , the multi-band antenna in this embodiment further includes a matching capacitor  30 . The matching capacitor  30  is disposed between the feeding matching circuit  21  and the ground plane  28 . The matching capacitor  30  is configured to match a second resonance frequency. When the second resonance frequency is in a 5 GHz frequency band (5150 MHz to 5850 MHz, such as a frequency band of WI-FI), the matching capacitor  30  may be set to 0.4 pF. Likewise, the matching capacitor  30  shown in this embodiment may alternatively be disposed on multi-band antennas provided in other embodiments of the present disclosure. 
       FIG. 10  is a diagram of antenna radiation efficiency of the multi-band antenna in the embodiment shown in  FIG. 9 . In the figure, the horizontal axis indicates a frequency measured in GHz, and the vertical axis indicates efficiency measured in dB. In the multi-band antenna in the embodiment shown in  FIG. 10 , a center of the first resonance frequency is set to 1575 MHz (a GPS frequency), a center of the second resonance frequency is set to 5500 MHz (5 GHz of a WI-FI frequency), and a center of the third resonance frequency is set to 2442 MHz (2.4 GHz of a WI-FI frequency). In  FIG. 10 , a curve  101  is an efficiency curve of the multi-band antenna in the embodiment shown in  FIG. 9 . It can be seen from the curve  101  that, efficiency of the multi-band antenna in the embodiment shown in  FIG. 9  in the GPS frequency approximately ranges from −2.36 dB to −2.92 dB, efficiency in 5 GHz of the WI-FI frequency approximately ranges from −2.24 dB to −3.73 dB, and efficiency in 2.4 GHz of the WI-FI frequency approximately ranges from −2.74 dB to −3.93 dB. It can be learned that, the multi-band antenna in the embodiment shown in  FIG. 9  meets an actual working requirement. 
       FIG. 11  is a schematic structural diagram of Embodiment 7 of a multi-band antenna according to an embodiment of the present disclosure. As shown in  FIG. 11 , a difference between the multi-band antenna in this embodiment and the multi-band antenna shown in  FIG. 7  lies in that various parts in the multi-band antenna shown in  FIG. 7  may be all located on a same plane, for example, the plane may be the ground plane  28  on which the multi-band antenna is disposed. For example, the multi-band antenna may be a microstrip structure. In contrast, in the multi-band antenna shown in  FIG. 11 , the feeding matching circuit  21 , the feeding part  22 , the capacitor component  23 , and the grounding part  25  are located on a same plane, and the radiation part  24  may be disposed on a plane that is perpendicular to the plane. For example, the plane may be the ground plane  28  on which the multi-band antenna is disposed, and the radiation part  24  may be disposed on a plane that is perpendicular to the ground plane  28 . 
     Generally, in a terminal device configured with a multi-band antenna, to ensure a radiation effect of the multi-band antenna, the multi-band antenna is disposed on an edge of the terminal device. Therefore, in the multi-band antenna in the embodiment shown in  FIG. 11 , the radiation part  24  may be disposed on a side of the terminal device, to ensure the radiation effect of the multi-band antenna. Compared with the multi-band antenna shown in  FIG. 7 , the multi-band antenna shown in the  FIG. 11  can further save space of the terminal device. 
     In the multi-band antenna shown in  FIG. 11 , there is a gap between the feeding part  22  and the radiation part  24 , where the gap presents a capacitor characteristic, and the gap may be the capacitor component  23 . 
       FIG. 12A  to  FIG. 12C  are schematic diagrams of surface current distribution and electric field distribution of the multi-band antenna shown in  FIG. 11 . It is assumed that in the multi-band antenna shown in  FIG. 11 , the first resonance frequency is 1575 MHz, the second resonance frequency is 5500 MHz, and the third resonance frequency is 2442 MHz. In  FIG. 12A , a density degree of surface filling of the radiation part  24  is used to indicate a status of surface current distribution of the radiation part  24 , where denser filling indicates a stronger current, and sparser filling indicates a weaker current. As shown in  FIG. 12A , when the multi-band antenna works in the first resonance frequency 1575 MHz, the surface current distribution of the multi-band antenna mainly concentrates near a point H connected between the grounding part  25  and the ground plane  28 , while the lowest surface current is distributed near a point G that is of the radiation part  24  and that is away from the grounding part. In  FIG. 12A , after the surface current density of the radiation part  24  is quantized, a current density near the point H is approximately 500 ampere per meter (A/m), while a current density near the point G is only approximately 10 A/m. In  FIG. 12B , a density degree of surface filling of the radiation part  24  is used to indicate a status of surface current distribution of the radiation part  24 , where denser filling indicates a stronger current, and sparser filling indicates a weaker current. As shown in  FIG. 12B , when the multi-band antenna works in the second resonance frequency 5500 MHz, the surface current distribution of the multi-band antenna mainly concentrates near the point H connected between the grounding part  25  and the ground plane  28 , while the lowest surface current is distributed near the point G that is of the radiation part  24  and that is away from the grounding part. In  FIG. 12B , after the surface current density of the radiation part  24  is quantized, a current density near the point G is approximately 10 A/m, while a current density near the point H is approximately 70-100 A/m. In  FIG. 12C , a density degree of filling inside the groove  29  is used to indicate a change status of electric field strength inside the groove  29 , where denser filling indicates stronger electric field strength, and sparser filling indicates weaker electric field strength. As shown in  FIG. 12C , when the multi-band antenna works in the third resonance frequency 2442 MHz, an electric field in the groove  29  is relatively strong on a side of the point G that is close to the radiation part  24  and that is away from the grounding part, while an electric field is relatively weak near a point I connected between the feeding circuit  26  and the radiation part  24 . After the electric field strength of the groove  29  in  FIG. 12C  is quantized, an electric field on a side near the point G is approximately 10000 volt per meter (V/m), and an electric field on a side near the point I is approximately 2000 V/m. 
     It can be learned based on  FIG. 12A  to  FIG. 12C  that, when the multi-band antenna works in the first resonance frequency and the second resonance frequency, the current of the multi-band antenna concentrates on the surface of the radiation part  24  and near the point H, while the current near the point G is relatively weak. Therefore, if a metal back cover is installed near the multi-band antenna, the surface current on the radiation part  24  and a capacitance effect generated by the metal back cover are relatively small. In this case, working of the multi-band antenna is not affected. However, when the multi-band antenna works in the third resonance frequency, the electric field concentrates on the groove  29  rather than on the surface of the radiation part  24 . Therefore, the metal back cover near the multi-band antenna does not affect the multi-band antenna greatly. 
       FIG. 13  is a schematic structural diagram of Embodiment 1 of a terminal device according to an embodiment of the present disclosure. As shown in  FIG. 13 , the terminal device provided in this embodiment includes a housing  131 , a feeding radio frequency circuit  27 , a multi-band antenna  133 , a frequency mixing circuit  135 , and a baseband processing circuit  134 , where the feeding radio frequency circuit  27 , the multi-band antenna  133 , the frequency mixing circuit  135 , and the baseband processing circuit  134  are located inside the housing  131 . The housing  131  may further include another device  136 . 
     The feeding radio frequency circuit  27  is configured to process a radio frequency signal received using the multi-band antenna  133  and send a processed signal to the frequency mixing circuit  135  for down-conversion processing. The frequency mixing circuit  135  sends an intermediate frequency signal obtained by means of down-conversion to the baseband processing circuit  134  for processing, or the baseband processing circuit  134  sends a baseband signal to the frequency mixing circuit  135  for up-conversion to obtain a radio frequency signal, and then the frequency mixing circuit  135  sends the radio frequency signal to the feeding radio frequency circuit  27  and the radio frequency signal is transmitted using the multi-band antenna  133 . 
     The terminal device shown in this embodiment may be any type of portable terminal device that needs to perform wireless communication, such as a mobile phone and a tablet computer. The multi-band antenna  133  may be any type of multi-band antenna in the embodiments shown in  FIG. 2 ,  FIG. 5 ,  FIG. 6 ,  FIG. 7 ,  FIG. 8 ,  FIG. 9 , or  FIG. 11 . For a specific structure and an implementation principle of the multi-band antenna  133 , reference may be made to the multi-band antenna in the embodiments shown in  FIG. 2 ,  FIG. 5 ,  FIG. 6 ,  FIG. 7 ,  FIG. 8 ,  FIG. 9 , or  FIG. 11 , and details are not described herein again. 
     In the terminal device provided in this embodiment, overall dimensions of the terminal device are 140×70×7 mm 3 , but the multi-band antenna  133  occupies only 20×6×7 mm 3 . 
     In the terminal device shown in this embodiment, the multi-band antenna shown in  FIG. 2 ,  FIG. 5 ,  FIG. 6 ,  FIG. 7 ,  FIG. 8 ,  FIG. 9 , or  FIG. 11  is used, and a size of the multi-band antenna is relatively small. Therefore, a size of an entire terminal device may be further reduced, which meets a miniaturized design trend of a current terminal device. On the premise of not changing outline dimensions of the terminal device, the saved space may be used for installing more functional devices for the terminal device. In addition, because the multi-band antenna complies with the CRLH principle, the housing  131  of the multi-band antenna may be produced using an all-metal appearance part, without affecting performance of the multi-band antenna. Generally, the housing  131  of the terminal device may be made of a metal material, which can improve an appearance of the terminal device and enhance holding feeling of the terminal device, thereby attracting consumers to make a purchase. 
       FIG. 14  is a schematic structural diagram of Embodiment 8 of a multi-band antenna according to an embodiment. As shown in  FIG. 14 , the multi-band antenna in this embodiment includes a feeding matching circuit  141 , a feeding part  142 , a capacitor component  143 , a radiation part  144 , and a grounding part  145 . 
     The feeding part  142  is connected to the capacitor component  143  to form a feeding circuit  146 . The feeding matching circuit  141  is electrically connected between a feeding radio frequency circuit  147  and the feeding part  142 , and the capacitor component  143  is connected to the radiation part  144 . The feeding matching circuit  141  is configured to match a radio frequency signal in the feeding radio frequency circuit  147  and the feeding circuit  146 . The feeding part  142  is configured to feed a radio frequency signal generated by the feeding radio frequency circuit  147  into the radiation part  144 , or feed a radio frequency signal generated by the radiation part  144  into the feeding radio frequency circuit  147 . The radiation part  144  is electrically connected both to the capacitor component  143  and the grounding part  145 , the grounding part  145  is electrically connected to a ground plane  148 , a first resonant circuit (that is, a path from a point F to a point G in  FIG. 14 ) is formed from the feeding circuit  146  to an end that is of the radiation part  144  and that is away from the grounding part  145 , and the first resonant circuit generates a first resonance frequency and a second resonance frequency. Generally, the grounding part  145  and the radiation part  144  are an integrated metal plate, that is, a part of the radiation part  144  extending to the ground plane  148  is the grounding part  145 . A width of the grounding part  145  may be W. 
     The feeding part  142 , the radiation part  144 , and the grounding part  145  form a basic antenna structure. In addition, impedance does not match between the feeding radio frequency circuit  147  and the feeding part  142 . Therefore, the feeding matching circuit  141  is electrically connected between the feeding radio frequency circuit  147  and the feeding part  142 . The feeding matching circuit  141  is configured to match a radio frequency signal in the feeding radio frequency circuit  147  and the feeding part  142 , including matching a signal transmitted by the feeding radio frequency circuit  147  and transmitting the matched signal to the feeding circuit  146 , and then radiating the matched signal using the radiation part  144 , or matching a signal that is transmitted by the feeding circuit  146  and that is received by the radiation part  144 , and then transmitting the matched signal to the feeding radio frequency circuit  147 . The capacitor component  143  is further disposed between the feeding part  142  and the radiation part  144 , where the capacitor component  143  and the feeding part  142  form the feeding circuit  146 . The capacitor component  143  may be a lumped capacitor, or may be a distributed capacitor. If the capacitor component  143  is a lumped capacitor, the lumped capacitor device whose capacitance value is determined is connected (for example, in a welding manner) between the feeding part  142  and the radiation part  144 . If the capacitor component  143  is a distributed capacitor, a specific gap may be reserved between the feeding part  142  and the radiation part  144 . The gap presents a characteristic of the distributed capacitor, and the capacitance value of the distributed capacitor may be adjusted by adjusting a width of the gap between the feeding part  142  and the radiation part  144 . For example, when the width of the gap between the feeding part  142  and the radiation part  144  is 0.3 mm, the capacitance value of the distributed capacitor may be equivalent to a 0.4 pF capacitance value of the lumped capacitor. 
     Optionally, a groove  149  is disposed on the radiation part  144 , where the groove  149  extends to the grounding part  145  from the end (that is, the point G) that is of the radiation part  144  and that is away from the grounding part  145 . 
     A part from a connection point H between the grounding part  145  and the ground plane  148  to a connection point I between the feeding circuit  146  and the radiation part  144  forms an inductor that is in parallel with the radiation part  144 . The capacitor component  143  and the radiation part  144  are in a serial connection relationship, which is equivalent to a series resistor. According to the principle of the CRLH antenna, the parallel inductor and the series resistor form a core component that complies with a principle of a right/left handed transmission line, and the path from the point G that is of the radiation part  144  of the multi-band antenna and that is away from the grounding part  145  to the point F connected between the feeding part  142  and the feeding radio frequency circuit  147  forms the first resonant circuit. The first resonant circuit generates the first resonance frequency, where the first resonance frequency is a fundamental frequency of the multi-band antenna. In addition, according to the CRLH principle, the first resonant circuit further generates the second resonance frequency, where the second resonance frequency is a multiplied frequency of the first resonance frequency. The first resonance frequency complies with a left handed rule, and the second resonance frequency complies with a right handed rule. The groove  149  is disposed on the radiation part  144 , where the groove  149  on the radiation part  144  changes electric field distribution on the radiation part  144 . The electric field distribution in the groove  149  may generate a new resonance frequency on the radiation part  144 , that is, the groove  149  may form a second resonant circuit on the radiation part  144 , and the second resonant circuit generates a third resonance frequency. 
     Therefore, the multi-band antenna shown in  FIG. 14  generates three resonance frequencies, and the first resonance frequency, the second frequency, and the third resonance frequency may be adjusted by adjusting sizes and parameters of various parts in the multi-band antenna. By adjusting a length of the path from the point G to the point F, a length of the first resonant circuit may be adjusted, that is, a magnitude of the first resonance frequency is adjusted, and a magnitude of the second resonance frequency also changes. By adjusting a capacitance value of the capacitor component  143 , a resonance frequency may be adjusted for the first resonant circuit, where the capacitance value of the capacitor component  143  is inversely proportional to the first resonance frequency. By adjusting a width W of the grounding part  145 , the second resonance frequency may also be adjusted, where the width W of the grounding part  145  is inversely proportional to the second resonance frequency. Increasing the width W of the grounding part  145  is equivalent to increasing an equivalent inductance value of the inductor that is in parallel with the first resonant circuit. By adjusting a position, a length, and a width of the groove  149  on the radiation part  144 , the third resonance frequency may be adjusted. Generally, the length of the groove  149  is 0.25 times as great as a wavelength corresponding to the third resonance frequency. When the length or the width of the groove  149  increases, the third resonance frequency moves to a low frequency. 
     The multi-band antenna provided in this embodiment is disposed in a terminal device that needs to work in multiple wireless frequency bands. The feeding radio frequency circuit  147  is disposed in the terminal device, where the feeding radio frequency circuit  147  is configured to process a radio frequency signal received using the multi-band antenna or transmit a generated radio frequency signal using the multi-band antenna. The ground plane  148  for grounding is further disposed in the terminal device. The ground plane  148  is generally a copper cover on a circuit board in the terminal device, for example, a copper layer of the circuit board. 
     It can be learned from the principle of the CRLH antenna that, for the antenna based on the CRLH principle, a length of a resonant circuit that generates a fundamental frequency approximately ranges from 0.12 times to 0.18 times as great as a wavelength corresponding to the fundamental frequency. In contrast, for the antenna (for example, the antenna  11  shown in  FIG. 1 ) designed based on the IFA or PIFA principle, a length of a resonant circuit that generates a fundamental frequency is approximately 0.25 times as great as a wavelength corresponding to the fundamental frequency. Therefore, the wavelength corresponding to the fundamental frequency for the multi-band antenna provided in this embodiment is 0.09 times shorter than that for the antenna based on the IFA or PIFA principle, which is quite important to a terminal device of increasingly miniaturized design. For example, the fundamental frequency of the multi-band antenna in this embodiment is designed at a GPS frequency, and in an L1 frequency band of GPS, a center frequency of the fundamental frequency of the multi-band antenna is 1575 MHz, and a wavelength corresponding to 1575 MHz is approximately 190 mm. If the antenna designed based on the IFA or PIFA principle is used, a length of the antenna is approximately 47.6 mm. If the antenna provided in this embodiment is used, a length of the antenna approximately ranges from 30.5 mm to 34.3 mm. A length difference between the two antennas reaches 17.1 mm. Considering that an existing mainstream portable terminal device such as an IPHONE 4 smartphone of APPLE Incorporation has outline dimensions of only 115.2×58.6×9.3 mm 3 , it can be learned that, the difference of 17.1 mm is quite considerable for a current portable terminal device. Therefore, if a terminal device uses the multi-band antenna provided in this embodiment, space of the terminal device may be saved such that a size of the terminal device may be reduced or space may be reserved for another device for use, thereby enhancing a function of the terminal device. 
     In addition, for the multi-band antenna designed based on the CRLH principle in this embodiment, when the multi-band antenna works at a fundamental frequency, surface currents on the radiation part  144  of the multi-band antenna mainly concentrate near the grounding part  145 . For the antenna  11  that is designed based on the IFA or PIFA architecture and that is shown in  FIG. 1 , when the antenna  11  works at a fundamental frequency, surface current distribution on the antenna  11  at the fundamental frequency mainly concentrates on an end that is of the antenna  11  and that is close to a point B. If currents mainly concentrate near the point B on the antenna  11 , when there is a ground terminal near the point B, currents on the antenna  11  are affected by the ground terminal, consequently, a capacitance effect is generated, thereby severely affecting antenna performance. In contrast, in the multi-band antenna shown in  FIG. 14 , currents mainly concentrate near the grounding part  145 . In this case, if there is a ground terminal near the radiation part  144  or the grounding part  145 , because current distribution at a location that is of the radiation part  144  and that is away from the ground terminal is relatively small, a capacitance effect generated by the current distribution has relatively little impact on antenna performance. Current distribution is relatively large at the grounding part  145 , but the grounding part  145  is electrically connected to the ground plane. Therefore, a capacitance effect generated between the ground terminal near the grounding part  145  and the radiation part  144  also has relatively little impact on antenna performance. In this way, using the terminal device configured with the multi-band antenna provided in this embodiment, design of a metal back cover or another metal appearance part is used, and performance of the multi-band antenna is not affected greatly. 
       FIG. 15  is a schematic structural diagram of Embodiment 9 of a multi-band antenna according to an embodiment of the present disclosure. As shown in  FIG. 15 , a difference between the multi-band antenna in this embodiment and the multi-band antenna shown in  FIG. 14  lies in that the groove  149  in  FIG. 14  is in a “-” shape, while the groove  149  in  FIG. 15  is in an “L” shape. Setting the groove  149  to the “L” shape is mainly to increase the length of the groove  149  and to lower the third resonance frequency. For example, in the embodiment shown in  FIG. 15 , a center of the first resonance frequency is set to 1575 MHz, and a length of a path from a point G to a point F is approximately 30.5 mm. If a center of the third resonance frequency needs to be set to 2442 MHz (which is 2.4 GHz of a WI-FI frequency), the length of the groove  149  is approximately 30.7 mm. It can be learned that, if the groove  149  is set to the “-” shape, the length of the radiation part  144  may be insufficient. Therefore, the groove  149  may be set to the “L” shape such that the center of the third resonance frequency may be set to 2442 MHz. 
       FIG. 16  is a schematic structural diagram of Embodiment 2 of a terminal device according to an embodiment of the present disclosure. As shown in  FIG. 16 , the terminal device provided in this embodiment includes a housing  161 , a feeding radio frequency circuit  147 , a multi-band antenna  163 , a baseband processing circuit  164 , and a frequency mixing circuit  165 , where the feeding radio frequency circuit  147 , the multi-band antenna  163 , the baseband processing circuit  164 , and the frequency mixing circuit  165  are located inside the housing  161 . The housing  161  may further include another device  166 . 
     The feeding radio frequency circuit  147  is configured to process a radio frequency signal received using the multi-band antenna  163  and send a processed signal to the frequency mixing circuit  165  for down-conversion processing. The frequency mixing circuit  165  sends an intermediate frequency signal obtained by means of down-conversion to the baseband processing circuit  164  for baseband processing, or the baseband processing circuit  164  sends a baseband signal to the frequency mixing circuit  165  for up-conversion to obtain a radio frequency signal, and then the frequency mixing circuit  165  sends the radio frequency signal to the feeding radio frequency circuit  147  and the radio frequency signal is transmitted using the multi-band antenna  163 . 
     The terminal device shown in this embodiment may be any type of portable terminal device that needs to perform wireless communication, such as a mobile phone and a tablet computer. The multi-band antenna  163  may be any type of multi-band antenna in embodiments shown in  FIG. 14  or  FIG. 15 . For a specific structure and an implementation principle of the multi-band antenna  163 , reference may be made to the multi-band antenna in the embodiments shown in  FIG. 14  or  FIG. 15 , and details are not described herein again. 
     In the terminal device provided in this embodiment, overall dimensions of the terminal device are 140×70×7 mm 3 , but the multi-band antenna  133  occupies only 20×6×7 mm 3 . 
     In the terminal device shown in this embodiment, the multi-band antenna shown in  FIG. 14  or  FIG. 15  is used, and a size of the multi-band antenna is relatively small. Therefore, a size of an entire terminal device may be further reduced, which meets a miniaturized design trend of a current terminal device. On the premise of not changing outline dimensions of the terminal device, the saved space may be used for installing more functional devices for the terminal device. In addition, because the multi-band antenna complies with the CRLH principle, the housing  161  of the multi-band antenna may be produced using a metal appearance part, without affecting performance of the multi-band antenna. Generally, a back cover of the housing  161  of the terminal device may be made of a metal material, which can improve an appearance of the terminal device and enhance holding feeling of the terminal device, thereby attracting consumers to make a purchase. 
     Finally, it should be noted that the foregoing embodiments are merely intended to describe the technical solutions of the present disclosure, but not to limit the present disclosure. Although the present disclosure 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. Therefore, the protection scope of the present disclosure shall be subject to the protection scope of the claims.