Patent Publication Number: US-2013229320-A1

Title: Small antenna apparatus operable in multiple bands including low-band frequency and high-band frequency and shifting low-band frequency to lower frequency

Description:
TECHNICAL FIELD 
     The present disclosure relates to an antenna apparatus mainly for use in mobile communication such as mobile phones, and relates to a wireless communication apparatus provided with the antenna apparatus. 
     BACKGROUND ART 
     The size and thickness of portable wireless communication apparatuses, such as mobile phones, have been rapidly reduced. In addition, the portable wireless communication apparatuses have been transformed from apparatuses to be used only as conventional telephones, to data terminals for transmitting and receiving electronic mails and for browsing web pages of WWW (World Wide Web), etc. Further, since the amount of information to be handled has increased from that of conventional audio and text information to that of pictures and videos, a further improvement in communication quality is required. In such circumstances, there are proposed a multiband antenna apparatus and a compact antenna apparatus, supporting a plurality of wireless communication schemes. Further, there is proposed an array antenna apparatus capable of reducing electromagnetic coupling among antenna apparatuses each corresponding to the above mentioned one, and thus, performing high-speed wireless communication. 
     According to an invention of Patent Literature 1, a two-frequency antenna is characterized by having: a feeder, an inner radiation element connected to the feeder, and an outer radiation element, all of which are printed on a first surface of a dielectric board; an inductor formed in a gap between the inner radiation element and the outer radiation element printed on the first surface of the dielectric board to connect the two radiation elements; a feeder, an inner radiation element connected to the feeder, and an outer radiation element, all of which are printed on a second surface of the dielectric board; and an inductor formed in a gap between the inner radiation element and the outer radiation element printed on the second surface of the dielectric board to connect the two radiation elements. The two-frequency antenna of Patent Literature 1 is operable in multiple bands by forming a parallel resonant circuit from the inductor provided between the radiation elements and a capacitance between the radiation elements. 
     An invention of Patent Literature 2 is characterized by forming a looped radiation element, and bringing its open end close to a feeding portion to form a capacitance, thus a fundamental mode and its harmonic modes occur. By integrally forming a looped radiation element on a dielectric or magnetic block, it is possible to operate in multiple bands, while having a small size. 
     CITATION LIST 
     Patent Literature 
     
         
         PATENT LITERATURE 1: Japanese Patent Laid-open Publication No. 2001-185938 
         PATENT LITERATURE 2: Japanese Patent No. 4432254 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     In recent years, there has been an increasing need to increase the data transmission rate on mobile phones, and thus, a next generation mobile phone standard, 3G-LTE (3rd Generation Partnership Project Long Term Evolution) has been studied. According to 3G-LTE, as a new technology for an increased the wireless transmission rate, it is determined to use a MIMO (Multiple Input Multiple Output) antenna apparatus using a plurality of antennas to simultaneously transmit or receive radio signals of a plurality of channels by spatial division multiplexing. The MIMO antenna apparatus uses a plurality of antennas at each of a transmitter and a receiver, and spatially multiplexes data streams, thus increasing a transmission rate. Since the MIMO antenna apparatus uses the plurality of antennas so as to simultaneously operate at the same frequency, electromagnetic coupling among the antennas becomes very strong under circumstances where the antennas are disposed close to each other within a small-sized mobile phone. When the electromagnetic coupling among the antennas becomes strong, the radiation efficiency of the antennas degrades. Therefore, received radio waves are weakened, resulting in a reduced transmission rate. Hence, it is necessary to provide a technique for reducing electromagnetic coupling among the antennas, by reducing the antennas&#39; size to substantially increase the distance among the antennas. In addition, in order to implement spatial division multiplexing, it is necessary for the MIMO antenna apparatus to simultaneously transmit or receive a plurality of radio signals having a low correlation therebetween, by using different radiation patterns, polarization characteristics, or the like. 
     According to the two-frequency antenna of Patent Literature 1, if decreasing the low-band operating frequency, the size of the radiation elements should be increased. In addition, no contribution to radiation is made by slits between the inner radiation elements and the outer radiation elements. 
     The multiband antenna of Patent Literature 2 achieves the reduction of the antenna&#39;s size by providing a loop element on a dielectric or magnetic block. However, since the antenna&#39;s impedance decreases due to the dielectric or magnetic block, the radiation characteristics degrades in resonance frequency bands for the fundamental mode and its harmonic modes. 
     In addition, according to the configuration of the multiband antenna of Patent Literature 2, it is not possible to adjust only the low-band operating frequency. Therefore, it is desired to provide an antenna apparatus capable of easily adjusting its resonance frequency, and capable of achieving both multiband operation and size reduction. 
     In addition, according to the configuration of the multiband antenna of Patent Literature 2, it is not possible to increase the bandwidth of only the high operating frequency band. Therefore, it is desired to provide an antenna apparatus capable of easily increasing the bandwidth, and capable of achieving both multiband operation and size reduction. 
     The present disclosure solves the above-described problems, and provides an antenna apparatus capable of achieving both multiband operation and size reduction, and also provides a wireless communication apparatus provided with such an antenna apparatus. 
     Solution to Problem 
     According to an aspect of the present disclosure, an antenna apparatus is provided with at least one radiator. Each radiator is provided with: a looped radiation conductor having an inner perimeter and an outer perimeter; at least one capacitor inserted at a position along a loop of the radiation conductor; at least one inductor inserted at a position along the loop of the radiation conductor, the position of the inductor being different from the position of the capacitor; a feed point provided on the radiation conductor; and a magnetic block provided at at least a part of an inside of the loop of the radiation conductor. Each radiator is excited at a first frequency and at a second frequency higher than the first frequency. When each radiator is excited at the first frequency, a first current flows along a first path, the first path extending along the inner perimeter of the loop of the radiation conductor and including the inductor and the capacitor, and magnetic flux produced by the first current passes through the magnetic block, thus increasing an inductance of the radiation conductor. When each radiator is excited at the second frequency, a second current flows through a second path including a section, the section extending along the outer perimeter of the loop of the radiation conductor, and the section including the capacitor but not including the inductor, and the section extending between the feed point and the inductor. Each radiator is configured such that the loop of the radiation conductor, the inductor, and the capacitor resonate at the first frequency, and a portion of the loop of the radiation conductor included in the second path, and the capacitor resonate at the second frequency. 
     Advantageous Effects of Invention 
     According to the antenna apparatus of the present disclosure, it is possible to provide an antenna apparatus operable in multiple bands, while having a simple and small configuration. 
     In addition, according to the antenna apparatus of the present disclosure, it is possible to adjust only the low-band operating frequency so as to shift to a lower frequency. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic diagram showing an antenna apparatus according to a first embodiment. 
         FIG. 2  is a schematic diagram showing an antenna apparatus according to a comparison example of the first embodiment. 
         FIG. 3  is a diagram showing a current path for the case where the antenna apparatus of  FIG. 1  operates at a low-band resonance frequency f 1 . 
         FIG. 4  is a diagram showing a current path for the case where the antenna apparatus of  FIG. 1  operates at a high-band resonance frequency f 2 . 
         FIG. 5  is a schematic diagram showing an antenna apparatus according to a first modified embodiment of the first embodiment. 
         FIG. 6  is a schematic diagram showing an antenna apparatus according to a second modified embodiment of the first embodiment. 
         FIG. 7  is a schematic diagram showing an antenna apparatus according to a third modified embodiment of the first embodiment. 
         FIG. 8  is a schematic diagram showing a radiator  44  of an antenna apparatus according to a fourth modified embodiment of the first embodiment. 
         FIG. 9  is a schematic diagram showing a radiator  45  of an antenna apparatus according to a fifth modified embodiment of the first embodiment. 
         FIG. 10  is a schematic diagram showing a radiator  46  of an antenna apparatus according to a sixth modified embodiment of the first embodiment. 
         FIG. 11  is a schematic diagram showing a radiator  47  of an antenna apparatus according to a seventh modified embodiment of the first embodiment. 
         FIG. 12  is a schematic diagram showing an antenna apparatus according to a second embodiment. 
         FIG. 13  is a diagram showing a current path for the case where the antenna apparatus of  FIG. 12  operates at the low-band resonance frequency f 1 . 
         FIG. 14  is a diagram showing a current path for the case where the antenna apparatus of  FIG. 12  operates at the high-band resonance frequency f 2 . 
         FIG. 15  is a perspective view showing a charge distribution for the case where the antenna apparatus of  FIG. 2  operates at the high-band resonance frequency f 2 . 
         FIG. 16  is a perspective view showing a charge distribution for the case where the antenna apparatus of  FIG. 12  operates at the high-band resonance frequency f 2 . 
         FIG. 17  is a diagram showing an equivalent circuit for the case where the antenna apparatus of  FIG. 12  operates at the high-band resonance frequency f 2 . 
         FIG. 18  is a perspective view showing an antenna apparatus according to a first modified embodiment of the second embodiment, and showing a charge distribution for the case where the antenna apparatus operates at the high-band resonance frequency f 2 . 
         FIG. 19  is a side view showing a charge distribution for the case where the antenna apparatus of  FIG. 18  operates at the high-band resonance frequency f 2 . 
         FIG. 20  is a perspective view showing an antenna apparatus according to a second modified embodiment of the second embodiment. 
         FIG. 21  is a perspective view showing an antenna apparatus according to a third modified embodiment of the second embodiment. 
         FIG. 22  is a perspective view showing an antenna apparatus according to a fourth modified embodiment of the second embodiment. 
         FIG. 23  is a perspective view showing an antenna apparatus according to a fifth modified embodiment of the second embodiment. 
         FIG. 24  is a perspective view showing an antenna apparatus according to a sixth modified embodiment of the second embodiment. 
         FIG. 25  is a side cross-sectional view showing an antenna apparatus according to a comparison example of the second embodiment. 
         FIG. 26  is a side cross-sectional view showing an antenna apparatus according to a seventh modified embodiment of the second embodiment. 
         FIG. 27  is a side cross-sectional view showing an antenna apparatus according to an eighth modified embodiment of the second embodiment. 
         FIG. 28  is a schematic diagram showing an antenna apparatus according to a third embodiment. 
         FIG. 29  is a schematic diagram showing an antenna apparatus according to a first modified embodiment of the third embodiment. 
         FIG. 30  is a schematic diagram showing an antenna apparatus according to a second modified embodiment of the third embodiment. 
         FIG. 31  is a schematic diagram showing an antenna apparatus according to a third modified embodiment of the third embodiment. 
         FIG. 32  is a schematic diagram showing an antenna apparatus according to a fourth modified embodiment of the third embodiment. 
         FIG. 33  is a schematic diagram showing an antenna apparatus according to a fifth modified embodiment of the third embodiment. 
         FIG. 34  is a schematic diagram showing an antenna apparatus according to a sixth modified embodiment of the third embodiment. 
         FIG. 35  is a schematic diagram showing an antenna apparatus according to a seventh modified embodiment of the third embodiment. 
         FIG. 36  is a schematic diagram showing an antenna apparatus according to an eighth modified embodiment of the third embodiment. 
         FIG. 37  is a schematic diagram showing an antenna apparatus according to a ninth modified embodiment of the third embodiment. 
         FIG. 38  is a schematic diagram showing an antenna apparatus according to a tenth modified embodiment of the third embodiment. 
         FIG. 39  is a schematic diagram showing an antenna apparatus according to a fourth embodiment. 
         FIG. 40  is a side view showing an antenna apparatus according to a first modified embodiment of the fourth embodiment. 
         FIG. 41  is a schematic diagram showing an antenna apparatus according to a second modified embodiment of the fourth embodiment. 
         FIG. 42  is a schematic diagram showing an antenna apparatus according to a comparison example of the fourth embodiment. 
         FIG. 43  is a schematic diagram showing an antenna apparatus according to a third modified embodiment of the fourth embodiment. 
         FIG. 44  is a perspective view showing an antenna apparatus according to a first comparison example used in a simulation. 
         FIG. 45  is a top view showing a detailed configuration of a radiator  51  of the antenna apparatus of  FIG. 44 . 
         FIG. 46  is a graph showing a frequency characteristic of a reflection coefficient S 11  of the antenna apparatus of  FIG. 44 . 
         FIG. 47  is a perspective view showing an antenna apparatus according to a second comparison example used in a simulation. 
         FIG. 48  is a graph showing a frequency characteristic of a reflection coefficient S 11  of the antenna apparatus of  FIG. 47 . 
         FIG. 49  is a perspective view showing an antenna apparatus according to a third comparison example used in a simulation. 
         FIG. 50  is a graph showing a frequency characteristic of a reflection coefficient S 11  of the antenna apparatus of  FIG. 49 . 
         FIG. 51  is a perspective view showing an antenna apparatus according to an implementation example of the first embodiment used in a simulation. 
         FIG. 52  is a graph showing a frequency characteristic of a reflection coefficient S 11  of the antenna apparatus of  FIG. 51 . 
         FIG. 53  is a perspective view showing an antenna apparatus according to a fourth comparison example used in a simulation. 
         FIG. 54  is a graph showing a frequency characteristic of a reflection coefficient S 11  of the antenna apparatus of  FIG. 52 . 
         FIG. 55  is a perspective view showing an antenna apparatus according to a first implementation example of the second embodiment used in a simulation. 
         FIG. 56  is a graph showing a frequency characteristic of a reflection coefficient S 11  of the antenna apparatus of  FIG. 55 . 
         FIG. 57  is a perspective view showing an antenna apparatus according to a second implementation example of the second embodiment used in a simulation. 
         FIG. 58  is a graph showing the influence of the width of a dielectric block D 8  of the antenna apparatus of  FIG. 57 , over the bandwidth. 
         FIG. 59  is a perspective view showing an antenna apparatus according to an implementation example of the third embodiment used in a simulation. 
         FIG. 60  is a graph showing a frequency characteristic of a reflection coefficient S 11  of the antenna apparatus of  FIG. 59 . 
         FIG. 61  is a block diagram showing a configuration of a wireless communication apparatus according to a fifth embodiment, provided with the antenna apparatus of  FIG. 28 . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Antenna apparatuses and wireless communication apparatuses according to embodiments will be described below with reference to the drawings. Like components are denoted by the same reference signs. 
     First Embodiment 
       FIG. 1  is a schematic diagram showing an antenna apparatus according to a first embodiment. The antenna apparatus of the present embodiment is characterized in that the antenna apparatus operates at dual bands, including a low-band resonance frequency f 1  and a high-band resonance frequency f 2 , using a single radiator  40 , and that the low-band resonance frequency f 1  is being shifted to a lower frequency due to a magnetic block M 1 . 
     Referring to  FIG. 1 , the radiator  40  is provided with: a first radiation conductor  1  having a certain width and a certain electrical length; a second radiation conductor  2  having a certain width and a certain electrical length; a capacitor C 1  connecting the radiation conductors  1  and  2  to each other at a position; and an inductor L 1  connecting the radiation conductors  1  and  2  to each other at another position different from that of the capacitor C 1 . In the radiator  40 , the radiation conductors  1  and  2 , the capacitor C 1 , and the inductor L 1  form a loop surrounding a central portion. In other words, the capacitor C 1  is inserted at a position along the looped radiation conductor, and the inductor L 1  is inserted at another position different from the position where the capacitor C 1  is inserted. In addition, the radiator  40  is provided with the magnetic block M 1  at at least a part of the inside of the looped radiation conductor. The looped radiation conductor has a width, and thus, has an inner perimeter close to the magnetic block M 1 , and an outer perimeter remote from the magnetic block M 1 . A signal source Q 1  generates a radio frequency signal of the low-band resonance frequency f 1  and a radio frequency signal of the high-band resonance frequency f 2 . The signal source Q 1  is connected to a feed point P 1  on the radiation conductor  1 , and is connected to a connecting point P 2  on a ground conductor G 1  provided close to the radiator  40 . The signal source Q 1  schematically shows a wireless communication circuit connected to the antenna apparatus of  FIG. 1 , and excites the radiator  40  at one of the low-band resonance frequency f 1  and the high-band resonance frequency f 2 . If necessary, a matching circuit (not shown) may be further connected between the antenna apparatus and the wireless communication circuit. In the radiator  40 , a current path for the case where the radiator  40  is excited at the low-band resonance frequency f 1  is different from a current path for the case where the radiator  40  is excited at the high-band resonance frequency f 2 , and thus, it is possible to effectively achieve dual-band operation. 
     As the magnetic block M 1 , it is possible to use a block made of material such as ferrite, nickel, or manganese suitable for radio frequencies, and having a relative permeability of, for example, about 5 to 60, but the magnetic block M 1  is not limited to this example. In addition, as the magnetic block M 1 , it is possible to use a block having a thickness of about 0.5 to 2 mm. The frequency characteristics of the antenna apparatus are not much affected by the differences in size of the magnetic block M 1 , but mainly affected by the relative permeability of the magnetic block M 1 , as will be described later. 
       FIG. 2  is a schematic diagram showing an antenna apparatus according to a comparison example of the first embodiment. The applicant of the present application proposed, in the International Application No. PCT/JP2012/000500, an antenna apparatus characterized by a single radiator operable in dual bands, and  FIG. 2  shows that antenna apparatus. A radiator  50  of  FIG. 2  has the same configuration as that of the radiator  40  of  FIG. 1 , except that the magnetic block M 1  is removed. In the radiator  50 , a current path for the case where the radiator  50  is excited at the low-band resonance frequency f 1  is different from a current path for the case where the radiator  50  is excited at the high-band resonance frequency f 2 , and thus, it is possible to effectively achieve dual-band operation. 
       FIG. 3  is a diagram showing a current path for the case where the antenna apparatus of  FIG. 1  operates at the low-band resonance frequency f 1 . By nature, a current having a low frequency component can pass through an inductor (low impedance), but is difficult to pass through a capacitor (high impedance). Hence, a current I 1 , for the case where the antenna apparatus operates at the low-band resonance frequency f 1 , flows along a path extending along the inner perimeter of the looped radiation conductor and including the inductor L 1 . Specifically, the current I 1  flows through a portion of the radiation conductor  1  from the feed point P 1  to a point connected to the inductor L 1 , passes through the inductor L 1 , and flows through a portion of the radiation conductor  2  from a point connected to the inductor L 1 , to a point connected to the capacitor C 1 . Further, due to the voltage difference across both ends of the capacitor, a current flows through a portion of the radiation conductor  1  from a point connected to the capacitor C 1 , to the feed point P 1 , and is connected to the current I 1 . Hence, it can be considered that the current I 1  substantially also passes through the capacitor C 1 . The current I 1  flows strongly along an edge of the inner perimeter of the looped radiation conductor, close to the magnetic block M 1 . Magnetic flux F 1  produced by the current I 1  passes through the magnetic block M 1 , and thus, the inductance of the looped radiation conductor increases. As a result, there is an effect that when the antenna apparatus operates at the low-band resonance frequency f 1 , an electrical length of the looped radiation conductor increases, and thus, the low-band resonance frequency f 1  is shifted to the lower frequency, compared to the case without the magnetic block M 1  ( FIG. 2 ). In other words, it is substantially equivalent to the size reduction of the antenna apparatus. The larger the relative permeability of the magnetic block M 1  is, the stronger the magnetic flux F 1  is. Therefore, the larger the relative permeability of the magnetic block M 1  is, the longer the electrical length of the looped radiation conductor is, and the more the low-band resonance frequency is shifted to the lower frequency. 
     In addition, when the antenna apparatus operates at the low-band resonance frequency f 1 , a current I 3  flows along a portion of the ground conductor G 1 , the portion being close to the radiator  40 , and flows toward the connecting point P 2 . 
     The radiator  40  is configured such that when the antenna apparatus operates at the low-band resonance frequency f 1 , the current I 1  flows along the current path as shown in  FIG. 3 , and the looped radiation conductor, the inductor L 1 , and the capacitor C 1  resonate at the low-band resonance frequency f 1 . Specifically, the radiator  40  is configured such that, taking into account the increased electrical length of the looped radiation conductor due to the magnetic block M 1 , the sum of the electrical length of the portion of the radiation conductor  1  from the feed point P 1  to the point connected to the inductor L 1 , an electrical length of the portion of the radiation conductor  1  from the feed point P 1  to the point connected to the capacitor C 1 , an electrical length of the inductor L 1 , an electrical length of the capacitor C 1 , and an electrical length of the portion of the radiation conductor  2  from the point connected to the inductor L 1  to the point connected to the capacitor C 1  is equal to an electrical length at which the antenna apparatus resonates at the low-band resonance frequency f 1 . The electrical length at which the antenna apparatus resonates is, for example, 0.2 to 0.25 times of an operating wavelength λ 1  of the low-band resonance frequency f 1 . When the antenna apparatus operates at the low-band resonance frequency f 1 , the current I 1  flows along the current path as shown in  FIG. 3 , and accordingly, the radiator  40  operates in a loop antenna mode, i.e., a magnetic current mode. Since the radiator  40  operates in the loop antenna mode, it is possible to achieve a long resonant length while maintaining a small size, thus achieving good characteristics even when the antenna apparatus operates at the low-band resonance frequency f 1 . In addition, when the radiator  40  operates in the loop antenna mode, the radiator  40  has a high Q value. The larger the diameter of the looped radiation conductor is, the more the radiation efficiency of the antenna apparatus improves. 
       FIG. 4  is a diagram showing a current path for the case where the antenna apparatus of  FIG. 1  operates at the high-band resonance frequency f 2 . By nature, a current having a high frequency component can pass through a capacitor (low impedance), but is difficult to pass through an inductor (high impedance). Hence, a current I 2 , for the case where the antenna apparatus operates at the high-band resonance frequency f 2 , flows along a path including a section, the section extending along the outer perimeter of the looped radiation conductor, and the section including the capacitor C 1  but not including the inductor L 1 , and the section extending between the feed point P 1  and the inductor L 1 . Specifically, the current I 2  flows through a portion of the radiation conductor  1  from the feed point P 1  to a point connected to the capacitor C 1 , passes through the capacitor C 1 , and flows through a portion of the radiation conductor  2  from a point connected to the capacitor C 1 , to a certain position (e.g., a point connected to the inductor L 1 ). At this time, the current I 2  strongly flows through the outer perimeter of the looped radiation conductor, and thus, is not strongly affected by the magnetic block M 1 . In general, magnetic materials such as ferrite cause losses in a high-frequency range. However, according to the antenna apparatus of the present embodiment, since the magnetic block M 1  is provided only the inside of the looped radiation conductor, there is an effect that when the antenna apparatus operates at the high-band resonance frequency f 2 , it is possible to minimize the influence on the antenna characteristics. 
     In addition, when the antenna apparatus operates at the high-band resonance frequency f 2 , a current I 3  flows along a portion of the ground conductor G 1 , the portion being close to the radiator  40 , and flows toward the connecting point P 2  (i.e., in the opposite direction to that of the current I 2 ). 
     The radiator  40  is configured such that when the antenna apparatus operates at the high-band resonance frequency f 2 , the current I 2  flows along the current path as shown in  FIG. 4 , and the portion of the looped radiation conductor, through which the current I 2  flows, and the capacitor C 1  resonate at the high-band resonance frequency f 2 . Specifically, the radiator  40  is configured such that the sum of an electrical length of the portion of the radiation conductor  1  from the feed point P 1  to the point connected to the capacitor C 1 , an electrical length of the capacitor C 1 , and an electrical length of the portion of the radiation conductor  2  through which the current I 2  flows (e.g., an electrical length of the portion of the radiation conductor  2  from the point connected to the capacitor C 1  to the point connected to the inductor L 1 ) is equal to an electrical length at which the antenna apparatus resonates at the high-band resonance frequency f 2 . The electrical length at which the antenna apparatus resonates is, for example, 0.25 times of an operating wavelength λ 2  of the high-band resonance frequency f 2 . When the antenna apparatus operates at the high-band resonance frequency f 2 , the current I 2  flows along the current path as shown in  FIG. 4 , and accordingly, the radiator  40  operates in a monopole antenna mode, i.e., an electric current mode. 
     As described above, the antenna apparatus of the present embodiment forms a current path passing through the inductor L 1 , when operating at the low-band resonance frequency f 1 , and forms a current path passing through the capacitor C 1 , when operating at the high-band resonance frequency f 2 , and thus, the antenna apparatus effectively achieves dual-band operation. The radiator  40  forms a looped current path, and thus, operates in a magnetic current mode, and resonates at the low-band resonance frequency f 1 . On the other hand, the radiator  40  forms a non-looped current path (monopole antenna mode), and thus, operates in an electric current mode, and resonates at the high-band resonance frequency f 2 . Further, since the antenna apparatus of the present embodiment is provided with the magnetic block M 1 , it is possible to easily adjust only the low-band resonance frequency so as to be shifted to the lower frequency. Since the low-band resonance frequency is being shifted to the lower frequency, it is possible to achieve substantial size reduction. 
     According to the prior art, when an antenna apparatus operates at the low-band resonance frequency f 1  (operating wavelength λ 1 ), an antenna element length of about (λ 1 )/4 is required. On the other hand, the antenna apparatus of  FIG. 2  forms the looped current path, and accordingly, the lengths in the horizontal and vertical directions of the radiator  40  can be reduced to about (λ 1 )/15, and under ideal conditions, the lengths can be reduced to about (λ 1 )/25. Since the antenna apparatus of the present embodiment is provided with the magnetic block M 1 , it is possible to achieve further size reduction than that of the antenna apparatus of  FIG. 2 . 
     Now, a matching effect brought about by the inductor L 1  and the capacitor C 1  of the antenna apparatus of  FIG. 1  will be described. The low-band resonance frequency f 1  and the high-band resonance frequency f 2  can be adjusted using a matching effect brought about by the inductor L 1  and the capacitor C 1  (particularly, a matching effect brought about by the capacitor C 1 ). When the antenna apparatus operates at the low-band resonance frequency f 1 , the current flowing through the portion of the radiation conductor  2  from the point connected to the inductor L 1  to the point connected to the capacitor C 1 , and the current flowing through the portion of the radiation conductor  1  from the point connected to the capacitor C 1  to the feed point P 1  are connected to the current flowing through the portion of the radiation conductor  1  from the feed point P 1  to the point connected to the inductor L 1 , and accordingly, the looped current path is formed. Since the voltage difference appears across both ends of the capacitor C 1  (on the side of the radiation conductor  1  and the side of the radiation conductor  2 ), there is an effect of controlling the reactance component of the input impedance of the antenna apparatus by the capacitance of the capacitor C 1 . The larger the capacitance of the capacitor C 1 , the lower the resonance frequency of the radiator  40 . On the other hand, when the antenna apparatus operates at the high-band resonance frequency f 2 , the current flows through the portion of the radiation conductor  1  from the feed point P 1  to the point connected to the capacitor C 1 , passes through the capacitor C 1 , and flows through the portion of the radiation conductor  2  from the point connected to the capacitor C 1  to the point connected to the inductor L 1 . Since the capacitor C 1  passes a high frequency component, reduction in the capacitance of the capacitor C 1  results in a shortened electrical length, and thus, the resonance frequency of the radiator  40  shifts to a higher frequency. Since the voltage at the feed point P 1  is the minimum in the radiator  40 , the resonance frequency of the radiator  40  can be decreased by increasing a distance of the capacitor C 1  from the feed point P 1 . 
     The antenna apparatus of the present embodiment can use 800 MHz band frequencies as the low-band resonance frequency f 1 , and use 2000 MHz band frequencies as the high-band resonance frequency f 2 , as will be described in implementation examples which will be described later. However, the frequencies are not limited thereto. 
     Each of the radiation conductors  1  and  2  is not limited to be shaped in a strip as shown in  FIG. 1 , etc., and may have any shape, as long as a certain electrical length can be obtained between the capacitor C 1  and the inductor L 1 . 
     The radiation efficiency of the antenna apparatus is improved by forming a large loop in the radiator  40 . 
     Since the antenna apparatus of the present embodiment is provided with the radiator  40  operable in one of the loop antenna mode and the monopole antenna mode according to the operating frequency, it is possible to effectively achieve dual-band operation, and achieve the size reduction of the antenna apparatus. Further, since the antenna apparatus of the present embodiment is provided with the magnetic block M 1 , it is possible to easily adjust only the low-band resonance frequency so as to be shifted to the lower frequency. 
       FIG. 5  is a schematic diagram showing an antenna apparatus according to a first modified embodiment of the first embodiment.  FIG. 6  is a schematic diagram showing an antenna apparatus according to a second modified embodiment of the first embodiment. A method for adjusting the resonance frequency of the antenna apparatus can be summarized as follows. In order to reduce the low-band resonance frequency f 1 , for example, it is effective to increase the capacitance of the capacitor C 1 , increase the inductance of the inductor L 1 , increase the electrical length of the radiation conductor  1 , increase the electrical length of the radiation conductor  2 , etc. In order to reduce the high-band resonance frequency f 2 , for example, it is effective to increase the electrical length of the radiation conductor  2 , provide the capacitor C 1  at a position remote from the feed point P 1 , etc.  FIG. 5  shows an antenna apparatus configured to reduce the low-band resonance frequency f 1 . The antenna apparatus of  FIG. 5  has a reduced low-band resonance frequency f 1  due to an increased electrical length of a radiation conductor  2 .  FIG. 6  shows an antenna apparatus configured to reduce the high-band resonance frequency f 2 . The antenna apparatus of  FIG. 6  has a reduced high-band resonance frequency f 2  due to an increased distance between a capacitor C 1  and a feed point P 1 . 
     In order to surely change the operation of the antenna apparatus between the magnetic current mode and the electric current mode, it is necessary to provide a clear difference between the respective electrical lengths of the current paths for the cases where the antenna apparatus operates at the low-band resonance frequency f 1  and the high-band resonance frequency f 2 . To this end, it is preferred that the electrical length of the radiation conductor  2  be longer than that of the radiation conductor  1 . In addition, by reducing the electrical lengths on the radiation conductor  1  from the feed point P 1  to the inductor L 1  and from the feed point P 1  to the capacitor C 1 , a current tends to flow from the feed point P 1  to the inductor L 1  when the antenna apparatus operates at the low-band resonance frequency f 1 , and a current tends to flow from the feed point P 1  to the capacitor C 1  when the antenna apparatus operates at the high-band resonance frequency f 2 , and thus, any current is less like to flow in unwanted directions. 
       FIG. 7  is a schematic diagram showing an antenna apparatus according to a third modified embodiment of the first embodiment. According to the antenna apparatus of  FIG. 1 , the capacitor C 1  is closer to the feed point P 1  than the inductor L 1 . On the other hand, according to the antenna apparatus of  FIG. 7 , an inductor L 1  is provided closer to a feed point P 1  than a capacitor C 1 . Since the antenna apparatus of  FIG. 7  is also provided with the radiator  40  operable in one of the loop antenna mode and the monopole antenna mode according to the operating frequency, it is possible to effectively achieve dual-band operation, and achieve the size reduction of the antenna apparatus. Further, since the antenna apparatus of  FIG. 7  is also provided with the magnetic block M 1 , it is possible to easily adjust only the low-band resonance frequency so as to be shifted to the lower frequency. 
       FIG. 8  is a schematic diagram showing a radiator  44  of an antenna apparatus according to a fourth modified embodiment of the first embodiment. The upper part of  FIG. 8  shows a plan view of the radiator  44 , and the lower part shows a cross-sectional view along line B 1 -B 1 ′ of the upper-part drawing. The antenna apparatus of  FIG. 1  is provided with the magnetic block M 1  in the entire inside of the looped radiation conductor. On the other hand, the radiator  44  of the antenna apparatus of  FIG. 8  is provided with a magnetic block M 2  only in a part of the inside of a looped radiation conductor. The magnetic block is not necessarily in contact with the inner perimeter of the looped radiation conductor, and may be provided only in a part of the inside of the looped radiation conductor, as long as the magnetic flux F 1  shown in  FIG. 3  passes through the magnetic block. Thus, it is possible to reduce the usage of magnetic material. 
       FIG. 9  is a schematic diagram showing a radiator  45  of an antenna apparatus according to a fifth modified embodiment of the first embodiment. The upper part of  FIG. 9  shows a plan view of the radiator  45 , and the lower part shows a cross-sectional view along line B 2 -B 2 ′ of the upper-part drawing. The radiator  45  of the antenna apparatus of  FIG. 9  is provided with a magnetic block M 3  having a central hollow portion. As described above, when the antenna apparatus operates at the low-band resonance frequency f 1 , the current strongly flows along the edge of the inner perimeter of the looped radiation conductor. By providing the magnetic block M 3  so as to be close to the edge portion, magnetic flux is concentrated, and thus, the inductance of the looped radiation conductor is effectively increased. Therefore, according to the antenna apparatus of  FIG. 9 , while reducing the usage of magnetic material, when the antenna apparatus operates at the low-band resonance frequency f 1 , the electrical length of the looped radiation conductor effectively increases, and thus, the low-band resonance frequency is effectively shifted to the lower frequency. 
       FIG. 10  is a schematic diagram showing a radiator  46  of an antenna apparatus according to a sixth modified embodiment of the first embodiment. The upper part of  FIG. 10  shows a plan view of the radiator  46 , and the lower part shows a cross-sectional view along line B 3 -B 3 ′ of the upper-part drawing. The radiator  46  of the antenna apparatus of  FIG. 10  is provided with a magnetic block M 4  made of a ferrite sheet. When a path of a current I 2  for the case where the antenna apparatus operates at the high-band resonance frequency f 2  is known in advance from an electromagnetic field analysis or the like, the magnetic block M 4  can be provided so as to avoid the path of the current I 2 . The magnetic block M 4  may overlap radiation conductors  1  and  2  as long as the magnetic block M 4  does not overlap the path of the current I 2 . For example, a sheet magnetic block M 4  may be attached on planar radiation conductors  1  and  2 . Such a configuration provides a special advantageous effect of easy manufacturing. Further, even when the antenna apparatus operates at the high-band resonance frequency f 2 , the current I 2  is not strongly affected by the magnetic block M 1 . 
       FIG. 11  is a schematic diagram showing a radiator  47  of an antenna apparatus according to a seventh modified embodiment of the first embodiment. The upper part of  FIG. 11  shows a plan view of the radiator  47  integrally formed with a housing  10  of the antenna apparatus, and the lower part shows a cross-sectional view along line B 4 -B 4 ′ of the upper-part drawing. In the upper-part drawing of  FIG. 11 , radiation conductors  1  and  2 , a capacitor C 1 , and an inductor L 1  are shown in phantom seen from the top of the housing  10 . In the radiator  47  of the antenna apparatus of  FIG. 11 , a magnetic block is formed by embedding magnetic material (e.g., magnetic powder M 5 ) in a portion of the housing  10  close to the inner portion of a looped radiation conductor. A wireless terminal apparatus such as a mobile phone or a tablet terminal is usually provided with a housing made of resin such as ABS, within which an antenna apparatus is provided. In that case, by mixing the magnetic powder M 5  into the material of the housing  10 , it is possible to obtain the same effects as those obtained when using the magnetic block M 1  of  FIG. 1 , etc. In this case, there is an advantageous effect of easily adjusting effective relative permeability by adjusting the concentration of magnetic powder upon manufacturing. 
     Instead of mixing the magnetic powder M 5  into the material of the housing  10  as shown in  FIG. 11 , the magnetic powder M 5  may be sprayed onto the housing  10 , or a sheet magnetic material may be attached on the housing  10 . 
     Second Embodiment 
       FIG. 12  is a schematic diagram showing an antenna apparatus according to a second embodiment. The antenna apparatus of the present embodiment is characterized in that the antenna apparatus operates at dual bands, including low-band resonance frequency f 1  and high-band resonance frequency f 2 , using a single radiator  40 , and that the bandwidth of a high frequency operating band including the high-band resonance frequency f 2  is increased due to a dielectric block D 1 . 
     Referring to  FIG. 12 , the radiator  60  is provided with radiation conductors  1  and  2 , a capacitor C 1 , and an inductor L 1 , which are the same as those of a radiator  40  of  FIG. 1 . A looped radiation conductor has a width, and thus, has an inner perimeter close to a central hollow portion, and an outer perimeter remote from the central hollow portion. Further, the looped radiation conductor is provided with respect to a ground conductor G 1  such that a part of the looped radiation conductor is close to and electromagnetically coupled to the ground conductor G 1 . A signal source Q 1  generates a radio frequency signal of the low-band resonance frequency f 1  and a radio frequency signal of the high-band resonance frequency f 2 , in a manner similar to that of the antenna apparatus of  FIG. 1 . The signal source Q 1  is connected to a feed point P 1  on the radiation conductor  1 , and is connected to a connecting point P 2  on the ground conductor G 1  provided close to the radiator  60 . The feed point P 1  is provided at a position of the radiation conductor  1  close to the ground conductor G 1 . The radiator  60  is further provided with the dielectric block D 1  between the radiation conductor  1  and the ground conductor G 1 , the dielectric block D 1  being provided in a portion where the looped radiation conductor and the ground conductor G 1  are close to each other, and the dielectric block D 1  provided along at least a part of a portion of the radiation conductor  1  between the feed point P 1  and the capacitor C 1 . In the radiator  60 , a current path for the case where the radiator  60  is excited at the low-band resonance frequency f 1  is different from a current path for the case where the radiator  60  is excited at the high-band resonance frequency f 2 , and thus, it is possible to effectively achieve dual-band operation. 
       FIG. 13  is a diagram showing a current path for the case where the antenna apparatus of  FIG. 12  operates at the low-band resonance frequency f 1 . As described with reference to  FIG. 3 , a current I 1 , for the case where the antenna apparatus operates at the low-band resonance frequency f 1 , flows along a path including the inductor L 1  and extending along the inner perimeter of the looped radiation conductor. The radiator  60  is configured such that when the antenna apparatus operates at the low-band resonance frequency f 1 , the current I 1  flows along a current path as shown in  FIG. 13 , and the looped radiation conductor, the inductor L 1 , and the capacitor C 1  resonate at the low-band resonance frequency f 1 . Specifically, the radiator  60  is configured such that the sum of an electrical length of a portion of the radiation conductor  1  from the feed point P 1  to a point connected to the inductor L 1 , an electrical length of a portion of the radiation conductor  1  from the feed point P 1  to a point connected to the capacitor C 1 , an electrical length of the inductor L 1 , an electrical length of the capacitor C 1 , and an electrical length of a portion of the radiation conductor  2  from a point connected to the inductor L 1 , to a point connected to the capacitor C 1  is equal to an electrical length at which the antenna apparatus resonates at the low-band resonance frequency f 1 . The electrical length at which the antenna apparatus resonates is, for example, 0.2 to 0.25 times of the operating wavelength λ 1  of the low-band resonance frequency f 1 . When the antenna apparatus operates at the low-band resonance frequency f 1 , the current I 1  flows along a current path as shown in  FIG. 3 , and accordingly, the radiator  60  operates in a loop antenna mode, i.e., a magnetic current mode. 
       FIG. 14  is a diagram showing a current path for the case where the antenna apparatus of  FIG. 12  operates at the high-band resonance frequency f 2 . As described with reference to  FIG. 4 , a current I 2 , for the case where the antenna apparatus operates at the high-band resonance frequency f 2 , flows along a path including a section, the section including the capacitor C 1  but not including the inductor L 1 , and the section extending along the outer perimeter of the looped radiation conductor, and extending between the feed point P 1  and the inductor L 1 . At this time, a current I 3  flows through a portion of the ground conductor G 1 , the portion close to the radiator  60 , and flows toward the connecting point P 2  (i.e., in the opposite direction to that of the current I 2 ). Therefore, the currents I 2  and I 3  of opposite phases flow through the portion where the looped radiation conductor and the ground conductor G 1  are close to each other.  FIG. 15  is a perspective view showing a charge distribution for the case where the antenna apparatus of  FIG. 2  operates at the high-band resonance frequency f 2 . The antenna apparatus of  FIG. 2  corresponds to one obtained by removing the dielectric block D 1  from the antenna apparatus of  FIG. 12 . As the currents I 2  and I 3  flow, positive and negative charges are distributed over a portion where a looped radiation conductor and a ground conductor G 1  are close to each other, as shown in  FIG. 15 , and electric flux is produced between the looped radiation conductor and the ground conductor G 1 . Thus, parallel capacitors is equivalently configured so as to be continuously distributed between the looped radiation conductor and the ground conductor G 1 .  FIG. 16  is a perspective view showing a charge distribution for the case where the antenna apparatus of  FIG. 12  operates at the high-band resonance frequency f 2 . As described above, the dielectric block D 1  is provided between the radiation conductor  1  and the ground conductor G 1 , in a portion where the looped radiation conductor and the ground conductor G 1  are close to each other, along at least a part of the portion of the radiation conductor  1  between the feed point P 1  and the capacitor C 1 . The density of electric flux near the feed point P 1  increases due to the dielectric block D 1 , and thus, the capacitance of capacitors between the looped radiation conductor and the ground conductor G 1  substantially increases. A parallel resonant circuit is formed from: the capacitance between the radiation conductor  1  and the ground conductor G 1  which are close to each other and between which the dielectric block D 1  is provided; and the inductances of the radiation conductors  1  and  2 . The radiator  60  is matched by the parallel resonant circuit. 
       FIG. 17  is a diagram showing an equivalent circuit for the case where the antenna apparatus of  FIG. 12  operates at the high-band resonance frequency f 2 . When the antenna apparatus operates at the high-band resonance frequency f 2 , the current I 2  flows as shown in  FIG. 14 . Therefore, the input impedance of the antenna apparatus can be represented by a radiation resistance Rr and an inductance La connected in series, and an equivalent capacitance Ce connected in parallel to the radiation resistance Rr and the inductance La. Consequently, the parallel resonant circuit is formed by the inductance La and the equivalent capacitance Ce, and thus, it is possible to increase the bandwidth of the high frequency operating band including the high-band resonance frequency f 2 . 
     The radiator  60  is configured such that when the antenna apparatus operates at the high-band resonance frequency f 2 , the current I 2  flows along the current path as shown in  FIG. 14 , and a portion of the looped radiation conductor through which the current I 2  flows, the capacitor C 1 , and the parallel resonant circuit resonate at the high-band resonance frequency f 2 . Specifically, the radiator  60  is configured such that, taking into account the above-described matching due to the parallel resonant circuit, the sum of an electrical length of a portion of the radiation conductor  1  from the feed point P 1  to a point connected to the capacitor C 1 , an electrical length of the capacitor C 1 , and an electrical length of a portion of the radiation conductor  2  through which the current I 2  flows (e.g., an electrical length of a portion of the radiation conductor  2  from a point connected to the capacitor C 1 , to a point connected to the inductor L 1 ) is equal to an electrical length at which the antenna apparatus resonates at the high-band resonance frequency f 2 . The electrical length at which the antenna apparatus resonates is, for example, 0.25 times of the operating wavelength λ 2  of the high-band resonance frequency f 2 . When the antenna apparatus operates at the high-band resonance frequency f 2 , the current I 2  flows along the current path as shown in  FIG. 14 , and accordingly, the radiator  60  operates in a monopole antenna mode, i.e., an electric current mode. 
     In the antenna apparatus of  FIG. 12 , the dielectric block D 1  is provided only along at least a part of the portion of the radiation conductor  1  between the feed point P 1  and the capacitor C 1 , and is not provided at a portion remote from the feed point P 1 . It is possible to avoid reduction in radiation resistance, because the dielectric block is not provided at a portion close to an open end for the case where the radiator  60  operates in a monopole antenna mode. 
     It is possible to adjust the bandwidth of the antenna apparatus by changing the thickness and dielectric constant of the dielectric block D 1  provided between the radiation conductor  1  and the ground conductor G 1  of the antenna apparatus of  FIG. 12 , in a stepwise manner, according to its position. 
     As described above, the antenna apparatus of the present embodiment forms a current path passing through the inductor L 1 , when operating at the low-band resonance frequency f 1 , and forms a current path passing through the capacitor C 1 , when operating at the high-band resonance frequency f 2 , and thus, the antenna apparatus effectively achieves dual-band operation. The radiator  60  forms a looped current path, and thus, the radiator  60  operates in a magnetic current mode, and resonates at the low-band resonance frequency f 1 . On the other hand, the radiator  60  forms a non-looped current path (monopole antenna mode), and thus, the radiator  60  operates in an electric current mode, and resonates at the high-band resonance frequency f 2 . Further, since the antenna apparatus of the present embodiment is provided with the dielectric block D 1 , it is possible to increase the bandwidth of only the high frequency operating band including the high-band resonance frequency f 2 . 
       FIG. 18  is a perspective view showing an antenna apparatus according to a first modified embodiment of the second embodiment, and showing a charge distribution for the case where the antenna apparatus operates at the high-band resonance frequency f 2 .  FIG. 19  is a side view showing a charge distribution for the case where the antenna apparatus of  FIG. 18  operates at the high-band resonance frequency f 2 . According to the antenna apparatus of  FIG. 12 , the dielectric block D 1  is provided over the entire portion of the radiation conductor  1  between the feed point P 1  and the capacitor C 1 . However, a dielectric block may be provided between the radiation conductor  1  and the ground conductor G 1 , in a portion where the looped radiation conductor and the ground conductor G 1  are close to each other, and along at least a part of a portion of the radiation conductor  1  between the feed point P 1  and the capacitor C 1 . A radiator  61  of the antenna apparatus of  FIGS. 18 and 19  is provided with a dielectric block D 2 , which is provided along only a small portion of a radiation conductor  1  between a feed point P 1  and a capacitor C 1 . The antenna apparatus of  FIGS. 18 and 19  can also increase the bandwidth of only the high frequency operating band including the high-band resonance frequency f 2 , by forming a parallel resonant circuit from: the capacitance between the radiation conductor  1  and a ground conductor G 1  which are close to each other and between which the dielectric block D 2  is provided; and the inductances of the radiation conductors  1  and  2 , in a manner similar to that of the antenna apparatus of  FIG. 12 . 
       FIGS. 20 to 22  are perspective views showing antenna apparatuses according to second to fourth modified embodiments of the second embodiment. A radiator  62  of the antenna apparatus of  FIG. 20  is provided with a dielectric block D 3 , a radiator  63  of the antenna apparatus of  FIG. 21  is provided with a dielectric block D 4 , and a radiator  64  of the antenna apparatus of  FIG. 22  is provided with a dielectric block D 5 . The dielectric block only needs to be provided between the radiation conductor  1  and the ground conductor G 1 , in a portion where the looped radiation conductor and the ground conductor G 1  are close to each other, and along at least a part of a portion of the radiation conductor  1  between the feed point P 1  and the capacitor C 1 . It is possible to use a dielectric block having a desired size according to capacitance between the radiation conductor  1  and the ground conductor G 1  which are close to each other and between which the dielectric block D 2  is provided, etc. The antenna apparatuses of  FIGS. 20 to 22  can also increase the bandwidth of only the high frequency operating band including the high-band resonance frequency f 2 , by forming a parallel resonant circuit from: the capacitance between the radiation conductor  1  and the ground conductor G 1  which are close to each other and between which the dielectric block D 3 , D 4 , or D 5  is provided; and the inductances of the radiation conductors  1  and  2 , in a manner similar to that of the antenna apparatus of  FIG. 12 . 
       FIG. 23  is a perspective view showing an antenna apparatus according to a fifth modified embodiment of the second embodiment.  FIG. 24  is a perspective view showing an antenna apparatus according to a sixth modified embodiment of the second embodiment. A radiator  63  of the antenna apparatus of  FIG. 23  is provided with a dielectric block D 1 , and a radiator  64  of the antenna apparatus of  FIG. 24  is provided with a dielectric block D 2 . According to the antenna apparatus of  FIG. 12 , the capacitor C 1  is closer to the feed point P 1  than the inductor L 1 . On the other hand, according to the antenna apparatuses of  FIGS. 23 and 24 , an inductor L 1  is provided closer to a feed point P 1  than a capacitor C 1 . Since the antenna apparatuses of  FIGS. 23 and 24  is also provided with the radiators  65  and  66  operable in one of a loop antenna mode and a monopole antenna mode according to the operating frequency, it is possible to effectively achieve dual-band operation, and achieve the size reduction of the antenna apparatus. Further, since the antenna apparatuses of  FIGS. 23 and 24  is provided with the dielectric blocks D 1  and D 2 , it is possible to increase the bandwidth of only the high frequency operating band including the high-band resonance frequency f 2 . 
     The dielectric block only needs to be provided between the radiation conductor  1  and the ground conductor G 1 , in a portion where the looped radiation conductor and the ground conductor G 1  are close to each other, and along at least a part of a portion of the radiation conductor  1  between the feed point P 1  and the capacitor C 1 . Thus, there is an advantageous effect of reducing the usage of dielectric. In addition, the dielectric block may be partially provided along a portion of the radiation conductor  1  between the feed point P 1  and the inductor L 1 , as long as the dielectric block is provided along at least a part of a portion of the radiation conductor  1  between the feed point P 1  and the capacitor C 1 . 
     Next, with reference to  FIGS. 25 to 27 , modified embodiments will be described in which a radiator and a ground conductor G 1  are provided on the same plane.  FIG. 25  is a side cross-sectional view showing an antenna apparatus according to a comparison example of the second embodiment. In the antenna apparatus of  FIG. 25 , a radiation conductor of a radiator  50  (only a radiation conductor  1  is shown) and a ground conductor G 1  of an antenna apparatus of  FIG. 2  are provided on the same plane, and further, the antenna apparatus is provided within a housing  20 . As shown in  FIG. 25 , positive and negative charges are distributed at a portion where the radiation conductor of the radiator  50  and the ground conductor G 1  are close to each other, and electric flux is produced between the radiation conductor of the radiator  50  and the ground conductor G 1 . 
       FIG. 26  is a side cross-sectional view showing an antenna apparatus according to a seventh modified embodiment of the second embodiment. A radiation conductor of a radiator  67  (only a radiation conductor  1  is shown) and a ground conductor G 1  of the antenna apparatus of  FIG. 26  are provided on the same plane. The radiator  67  is provided with a dielectric block D 6  on one side of the plane, in a portion where the radiation conductor  1  and the ground conductor G 1  are close to each other, and along at least a part of a portion of the radiation conductor  1  between a feed point P 1  and a capacitor C 1  (not shown). According to the antenna apparatus of  FIG. 26 , the density of electric flux near the feed point P 1  increases due to the dielectric block D 6 , and thus, the capacitance of a capacitor between the radiation conductor  1  and the ground conductor G 1  substantially increases, in a manner similar to that of the antenna apparatus of  FIG. 12 . A parallel resonant circuit is formed from: the capacitance between the radiation conductor  1  and the ground conductor G 1  which are close to each other and between which the dielectric block D 6  is provided; and the inductances of the radiation conductors  1  and  2 . 
       FIG. 27  is a side cross-sectional view showing an antenna apparatus according to an eighth modified embodiment of the second embodiment. A radiation conductor of a radiator  68  (only a radiation conductor  1  is shown) and a ground conductor G 1  of the antenna apparatus of  FIG. 27  are provided on the same plane. The radiator  68  is provided with a dielectric block D 6  on one side of the plane and a dielectric block D 7  provided on the other side of the plane, in a portion where the radiation conductor  1  and the ground conductor G 1  are close to each other, and along at least a part of a portion of the radiation conductor  1  between a feed point P 1  and a capacitor C 1  (not shown). By using the two dielectric blocks D 6  and D 7 , it is possible to more effectively increase the bandwidth of the high frequency operating band including the high-band resonance frequency f 2 , compared to the case of using one dielectric block D 6 . The dielectric constants of the dielectric blocks D 6  and D 7  may be the same, or may be different from each other. By using the dielectric blocks D 6  and D 7  with different dielectric constants, it is possible to improve flexibility in design. 
     A wireless terminal apparatus such as a mobile phone or a tablet terminal usually has a housing made of resin such as ABS. In the antenna apparatuses of  FIGS. 26 and 27 , a housing  20  made of dielectric with a certain dielectric constant may be used such that the housing  20  contributes to increased bandwidth in combination with a dielectric block(s). 
     In the antenna apparatuses of  FIGS. 26 and 27 , the dielectric blocks D 6  and D 7  may be attached to the housing  20 . In this case, by attaching sheet dielectric blocks D 6  and D 7  to the housing  20 , there is an advantageous effect of simplifying the assembly process of the antenna apparatus. 
     Third Embodiment 
       FIG. 28  is a schematic diagram showing an antenna apparatus according to a third embodiment. A radiator  70  of the antenna apparatus of the present embodiment is characterized by both a magnetic block M 1  of the first embodiment and a dielectric block D 1  of the second embodiment. Since the antenna apparatus of the present embodiment is provided with the radiator  70  operable in one of a loop antenna mode and a monopole antenna mode according to the operating frequency, it is possible to effectively achieve dual-band operation, and achieve the size reduction of the antenna apparatus. Further, since the antenna apparatus of the present embodiment is provided the magnetic block M 1 , it is possible to easily adjust only the low-band resonance frequency so as to be shifted to the lower frequency. Further, since the antenna apparatus of the present embodiment is provided with the dielectric block D 1 , it is possible to increase the bandwidth of only the high frequency operating band including a high-band resonance frequency f 2 . 
     As to a capacitor C 1  and an inductor L 1 , for example, it is possible to use discrete circuit elements, but the capacitor C 1  and the inductor L 1  are not limited thereto. With reference to  FIGS. 29 to 35 , modified embodiments of the capacitor C 1  and the inductor L 1  will be described below. 
       FIG. 29  is a schematic diagram showing an antenna apparatus according to a first modified embodiment of the third embodiment. A radiator  71  of the antenna apparatus of  FIG. 29  includes pa capacitor C 2  formed by portions of radiation conductors  1  and  2  close to each other. As shown in  FIG. 29 , a virtual capacitor C 2  may be formed between the radiation conductors  1  and  2 , by arranging the radiation conductors  1  and  2  close to each other to produce a certain capacitance between the radiation conductors  1  and  2 . The closer the radiation conductors  1  and  2  approach to each other, or the wider the area where the radiation conductors  1  and  2  are close to each other increases, the more the capacitance of the virtual capacitor C 2  increases. Further,  FIG. 30  is a schematic diagram showing an antenna apparatus according to a second modified embodiment of the third embodiment. A radiator  72  of the antenna apparatus of  FIG. 30  includes a capacitor C 3  formed at portions of radiation conductors  1  and  2  close to each other. As shown in  FIG. 30 , when forming a virtual capacitor C 3  by a capacitance between the radiation conductors  1  and  2 , an interdigital conductive portion (a configuration in which fingered conductors are engaged alternately) may be formed. The capacitor C 3  of  FIG. 30  can have an increased capacitance than the capacitor C 2  of  FIG. 29 . A capacitor formed by portions of the radiation conductors  1  and  2  close to each other is not limited to a linear conductive portion as shown in  FIG. 29 , or an interdigital conductive portion as shown in  FIG. 30 , and may be formed by conductive portions of other shapes. For example, the distance between the radiation conductors  1  and  2  of the antenna apparatus of  FIG. 29  may be changed according to their positions, such that the capacitance between the radiation conductors  1  and  2  varies depending on the positions on the radiation conductors  1  and  2 . 
       FIG. 31  is a schematic diagram showing an antenna apparatus according to a third modified embodiment of the third embodiment. A radiator  73  of the antenna apparatus of  FIG. 31  includes an inductor L 2  formed as a strip conductor.  FIG. 32  is a schematic diagram showing an antenna apparatus according to a fourth modified embodiment of the third embodiment. A radiator  74  of the antenna apparatus of  FIG. 32  includes an inductor L 3  formed as a meander conductor. The thinner the widths of conductors forming the inductors L 2  and L 3  are, and the longer the lengths of the conductors are, the more the inductances of the inductors L 2  and L 3  increase. 
     The capacitors C 2  and C 3  and the inductors L 2  and L 3  shown in  FIGS. 29 to 32  may be combined with each other. For example, a radiator may be configured to include the capacitor C 2  of  FIG. 29  and the inductor L 2  of  FIG. 31 , instead of the capacitor C 1  and the inductor L  1  of  FIG. 28 . 
       FIG. 33  is a schematic diagram showing an antenna apparatus according to a fifth modified embodiment of the third embodiment. A radiator  75  of the antenna apparatus of  FIG. 33  includes a capacitor C 3  formed at portions of radiation conductors  1  and  2  close to each other, and an inductor L 3  formed as a meander conductor. According to the antenna apparatus of  FIG. 33 , since both the capacitor and the inductor can be formed as conductive patterns on a dielectric substrate, there are advantageous effects such as cost reduction and reduction in manufacturing variations. 
       FIG. 34  is a schematic diagram showing an antenna apparatus according to a sixth modified embodiment of the third embodiment. A radiator  76  of the antenna apparatus of  FIG. 34  includes a plurality of capacitors C 4  and C 5 . An antenna apparatus of the present embodiment is not limited to one provided with a single capacitor and a single inductor, and may be provided with concatenated capacitors, including two or more capacitors, and/or provided with concatenated inductors, including two or more inductors. Referring to  FIG. 34 , the capacitors C 4  and C 5  connected to each other by a third radiation conductor  3  having a certain electrical length are inserted, instead of the capacitor C 1  of  FIG. 28 . In other words, the capacitors C 4  and C 5  are inserted at different positions along a looped radiation conductor. Also in the case of including a plurality of inductors, the antenna apparatus is configured in a manner similar to that of the modified embodiment shown in  FIG. 34 .  FIG. 35  is a schematic diagram showing an antenna apparatus according to a seventh modified embodiment of the third embodiment. A radiator  77  of the antenna apparatus of  FIG. 35  includes a plurality of inductors L 4  and L 5 . Referring to  FIG. 35 , the inductors L 4  and L 5  connected to each other by a third radiation conductor  3  having a certain electrical length are inserted, instead of the inductor L 1  of  FIG. 28 . In other words, the inductors L 4  and L 5  are inserted at different positions along a looped radiation conductor. In a manner similar to that of the antenna apparatuses of  FIGS. 34 and 35 , a plurality of capacitors and a plurality of inductors may be inserted at different positions along the looped radiation conductor. According to the antenna apparatuses of  FIGS. 34 and 35 , since capacitors and inductors can be inserted at three or more different positions in consideration of the current distribution on the radiator, there is an advantageous effect that when designing the antenna apparatus, it is possible to easily achieve fine adjustments of the low-band resonance frequency f 1  and the high-band resonance frequency f 2 . 
       FIG. 36  is a schematic diagram showing an antenna apparatus according to an eighth modified embodiment of the third embodiment.  FIG. 36  shows an antenna apparatus provided with a feed line as a microstrip line. The antenna apparatus of the present modified embodiment is provided with a feed line as a microstrip line, including a ground conductor G 1 , and a strip conductor S 1  provided on the ground conductor G 1  with a dielectric substrate  90  therebetween. The antenna apparatus of the present modified embodiment may have a planar configuration for reducing the profile of the antenna apparatus, in other words, the ground conductor G 1  may be formed on the back side of a printed circuit board, and the strip conductor S 1  and a radiator  70  may be integrally formed on the front side of the printed circuit board. The feed line is not limited to a microstrip line, and may be a coplanar line, a coaxial line, etc. 
       FIG. 37  is a schematic diagram showing an antenna apparatus according to a ninth modified embodiment of the third embodiment.  FIG. 37  shows an antenna apparatus configured as a dipole antenna. A left radiator  70 A of  FIG. 37  is configured in the similar manner as that of the radiator  70  of  FIG. 28 , except for the dielectric block D 1 . A right radiator  70 B of  FIG. 37  is also configured in the similar manner as that of the radiator  70  of  FIG. 28 , except for the dielectric block D 1 , and the radiator  70 B is provided with a first radiation conductor  11 , a second radiation conductor  12 , a capacitor C 11 , and an inductor L 11 . The radiators  70 A and  70 B are provided adjacent to each other so as to have portions close to each other and electromagnetically coupled to each other. A feed point P 1  of the radiator  70 A and a feed point P 11  of the radiator  70 B are provided close to each other. A signal source Q 1  is connected to the feed point P 1  of the radiator  70 A and to the feed point P 11  of the radiator  70 B, respectively. The antenna apparatus is further provide with a dielectric block D 11  provided between a radiation conductor  1  of the radiator  70 A and the radiation conductor  11  of the radiator  70 B, in a portion where the radiation conductor  1  of the radiator  70 A and the radiation conductor  11  of the radiator  70 B are close to each other, and along at least a part of a portion of the radiation conductor  1  between the feed point P 1  and a capacitor C 1 , and along at least a part of a portion of the radiation conductor  11  between the feed point P 11  and the capacitor C 11 . When the antenna apparatus operates at the high-band resonance frequency f 2 , a parallel resonant circuit is formed from: the capacitance between the radiation conductors  1  and  11  which are close to each other and between which the dielectric block D 11  is provided; and the inductances of the radiation conductors  1 ,  2 ,  11 , and  12 , in a manner similar to that of the antenna apparatus of  FIG. 12 . Therefore, the antenna apparatus of  FIG. 37  is substantially configured to include the radiator  70 B instead of the ground conductor G 1  of  FIG. 28 . The antenna apparatus of the present modified embodiment has a dipole configuration, and accordingly, is operable in a balance mode, thus suppressing unwanted radiation. 
       FIG. 38  is a schematic diagram showing an antenna apparatus according to a tenth modified embodiment of the third embodiment.  FIG. 38  shows a multiband antenna apparatus operable in four bands. A left radiator  70 A of  FIG. 38  is configured in the similar manner as that of the radiator  70  of  FIG. 28 . A right radiator  70 D of  FIG. 38  is also configured in the similar manner as that of the radiator  70  of  FIG. 28 , and the radiator  70 D is provided with a first radiation conductor  21 , a second radiation conductor  22 , a capacitor C 21 , and an inductor L 21 , and further is provided with a magnetic block M 21  and a dielectric block D 21 . However, an electrical length of a loop formed by the radiation conductors  21  and  22 , the capacitor C 21 , and the inductor L 21  of the radiator  70 D is different from an electrical length of a loop formed by radiation conductors  1  and  2 , a capacitor C 1 , and an inductor L 1  of the radiator  70 C. A signal source Q 21  is connected to a feed point P 1  on the radiation conductor  1 , a feed point P 21  on the radiation conductor  21 , and a connecting point P 2  on a ground conductor G 1 . The signal source Q 21  generates a radio frequency signal of the low-band resonance frequency f 1  and a radio frequency signal of the high-band resonance frequency f 2 , and generates another low-band resonance frequency f 21  different from the low-band resonance frequency f 1 , and another high-band resonance frequency f 22  different from the high-band resonance frequency f 2 . The radiator  70 C operates in a loop antenna mode at the low-band resonance frequency f 1 , and operates in a monopole antenna mode at the high-band resonance frequency f 2 . On the other hand, the radiator  70 D operates in a loop antenna mode at the low-band resonance frequency f 21 , and operates in a monopole antenna mode at the high-band resonance frequency f 22 . Thus, the antenna apparatus of the present modified embodiment is capable of multiband operation in four bands. The antenna apparatus of the present modified embodiment can achieve further multiband operation by further providing a radiator. 
     Further, as another modified embodiment, an antenna apparatus according to the present embodiment can be configured as an inverted-F antenna apparatus, for example, by providing a radiator including planar or linear radiation conductors in parallel with a ground conductor, and short-circuiting a part of the radiator to the ground conductor (not shown). Short-circuiting a part of the radiator to the ground conductor results in an increased radiation resistance, and it does not impair the basic operating principle of the antenna apparatus according to the present embodiment. 
     The antenna apparatuses according to the modified embodiments of the third embodiment described with reference to  FIGS. 29 to 38  may be provided with only one of a magnetic block and a dielectric block. In the case of having only a magnetic block, it is possible to easily adjust only the low-band resonance frequency so as to be shifted to the lower frequency, in a manner similar to that of the first embodiment. In the case of having only one of the dielectric blocks, it is possible to increase the bandwidth of only the high frequency operating band including the high-band resonance frequency f 2 , in a manner similar to that of the second embodiment. 
     Fourth Embodiment 
       FIG. 39  is a schematic diagram showing an antenna apparatus according to a fourth embodiment. The antenna apparatus of the present embodiment is characterized in that the antenna apparatus includes two radiators  78 A and  78 B configured according to the similar principle as that of a radiator  70  of  FIG. 28 , and the radiators  78 A and  78 B are independently excited by different signal sources Q 31  and Q 32 . 
     Referring to  FIG. 39 , the radiator  78 A is provided with: a first radiation conductor  31  having a certain electrical length; a second radiation conductor  32  having a certain electrical length; a capacitor C 31  connecting the radiation conductors  31  and  32  to each other at a certain position; and an inductor L 31  connecting the radiation conductors  31  and  32  to each other at a position different from that of the capacitor C 31 . In the radiator  78 A, the radiation conductors  31  and  32 , the capacitor C 31 , and the inductor L 31  form a loop surrounding a central portion. In other words, the capacitor C 31  is inserted at a position along the looped radiation conductor, and the inductor L 31  is inserted at another position along the looped radiation conductor different from the position where the capacitor C 31  is inserted. The signal source Q 1  is connected to a feed point P 31  on the radiation conductor  31 , and is connected to a connecting point P 32  on a ground conductor G 1  provided close to the radiator  78 A. In the antenna apparatus of  FIG. 39 , the capacitor C 31  is provided closer to the feed point P 31  than the inductor L 31 . The radiator  78 A is further provided with a magnetic block M 31  and a dielectric block D 31 , in a manner similar to that of a magnetic block M 1  and a dielectric block D 1  of an antenna apparatus of  FIG. 28 . The radiator  78 B is configured in the similar manner as that of the radiator  78 A, and is provided with a first radiation conductor  33 , a second radiation conductor  34 , a capacitor C 32 , and an inductor L 32 . In the radiator  78 B, the radiation conductors  33  and  34 , the capacitor C 32 , and the inductor L 32  form a loop surrounding a central portion. The signal source Q 2  is connected to a feed point P 33  on the radiation conductor  33 , and is connected to a connecting point P 34  on the ground conductor G 1  provided close to the radiator  78 B. In the antenna apparatus of  FIG. 20 , the capacitor C 32  is provided closer to the feed point P 33  than the inductor L 32 . The radiator  78 B is further provided with a magnetic block M 32  and a dielectric block D 32 , in a manner similar to that of the radiator  78 A. The signal sources Q 31  and Q 32  generate, for example, radio frequency signals as transmitting signals of MIMO communication scheme, and generate radio frequency signals of the same low-band resonance frequency f 1 , and generate radio frequency signals of the same high-band resonance frequency f 2 . 
     The looped radiation conductors of the radiators  78 A and  78 B are formed, for example, symmetrically with respect to a reference axis B  15 . The radiation conductors  31  and  33  and feed portions (the feed points P 31  and P 33  and the connecting points P 32  and P 33 ) are provided close to the reference axis B 15 , and the radiation conductors  32  and  34  are provided remote from the reference axis B 15 . The feed points P 31  and P 33  are provided at positions symmetrical with respect to the reference axis B  15 . It is possible to reduce the electromagnetic coupling between the radiators  78 A and  78 B by shaping radiators  78 A and  78 B such that a distance between the radiators  78 A and  78 B gradually increases as a distance from the feed points P 31  and P 32  along the reference axis B  15  increases. Further, since the distance between the two feed points P 31  and P 33  is small, it is possible to minimize an area for placing traces of feed lines from a wireless communication circuit (not shown). 
       FIG. 40  is a side view showing an antenna apparatus according to a first modified embodiment of the fourth embodiment. In order to reduce the size of the antenna apparatus, any of the radiation conductors  31  to  34  may be bent at at least one position. For example, as shown in  FIG. 40 , the radiation conductors  31  and  32  may be bent at the positions of dashed lines B  11  to B  14  on the radiation conductors  31  and  32  of  FIG. 39 . The positions and numbers of bends of the radiation conductors are not limited to those shown in  FIG. 40 , and the size of the antenna apparatus can be reduced by bending the radiation conductors at at least one position. In addition, when the antenna apparatus operates at the high-band resonance frequency f 2 , a current may flow to the tip (top end) of the radiation conductor  32  or to a certain position on the radiation conductor  32 , e.g., a position at which the radiation conductor is bent, depending on the frequency, instead of flowing to the position of the inductor L 31 . 
       FIG. 41  is a schematic diagram showing an antenna apparatus according to a second modified embodiment of the fourth embodiment. In the antenna apparatus of the present modified embodiment, radiators  78 A and  78 B are not disposed symmetrically, but disposed in the same direction (i.e., asymmetrically). Asymmetric disposition of the radiators  78 A and  78 B results in their asymmetric radiation patterns, thus providing the advantageous effect of reduced correlation between signals transmitted or received through the radiators  78 A and  78 B. However, However, since a difference occurs between powers of transmitting signals and powers of received signals, it is not possible to maximize the transmitting or receiving performance for a MIMO communication scheme. Further, three or more radiators may be disposed in a manner similar to that of the antenna apparatus of this modified embodiment. 
       FIG. 42  is a schematic diagram showing an antenna apparatus according to a comparison example of the fourth embodiment. In the antenna apparatus of  FIG. 42 , radiation conductors  32  and  34  not having a feed point are disposed close to each other. By separating feed points P 31  and P 33  from each other, it is possible to reduce the correlation between signals transmitted or received through radiators  78 A and  78 B. However, since the open ends of the respective radiators  78 A and  78 B (i.e., the edges of the radiation conductors  32  and  34 ) are opposed to each other, the electromagnetic coupling between the radiators  78 A and  78 B is large. 
       FIG. 43  is a schematic diagram showing an antenna apparatus according to a third modified embodiment of the fourth embodiment. The antenna apparatus of the present modified embodiment is characterized by a radiator  78 C, instead of the radiator  78 B of  FIG. 39 , and the radiator  78 C is configured such that the positions of a capacitor C 32  and an inductor L 32  are asymmetrical with respect to the positions of a capacitor C 31  and an inductor L 31  of a radiator  78 A, in order to reduce electromagnetic coupling between the two radiators for the case where the antenna apparatus operates at the low-band resonance frequency f 1 . 
     For comparison, at first, the case is considered in which when the antenna apparatus of  FIG. 39  operates at the low-band resonance frequency f 1 , for example, only one signal source Q 31  operates. When the radiator  78 A operates in a loop antenna mode due to a current inputted from the signal source Q 31 , a magnetic field produced by the radiator  78 A induces a current in the radiator  78 B of  FIG. 39 , the current flowing in the same direction as a current on the radiator  78 A, and flowing to the signal source Q 32 . Since the large induced current flows through the radiator  78 B, large electromagnetic coupling between the radiators  78 A and  78 B occurs. On the other hand, when the antenna apparatus of  FIG. 39  operates at the high-band resonance frequency f 2 , in the radiator  78 A, a current inputted from the signal source Q 31  flows in a direction remote from the radiator  78 B. Therefore, electromagnetic coupling between the radiators  78 A and  78 B is small, and an induced current flowing through the radiator  78 B and the signal source Q 32  is also small. 
     Referring to the antenna apparatus of the present modified embodiment of  FIG. 43  again, when proceeding along the symmetric loops of the radiation conductors of the radiators  78 A and  78 C in corresponding directions starting from respective feed points P 31  and P 33  (e.g., when proceeding counterclockwise in the radiator  78 A and proceeding clockwise in the radiator  78 C), the radiator  78 A is configured such that the feed point P 31 , the inductor L 31 , and the capacitor C 31  are located in this order, and the radiator  78 C is configured such that the feed point P 33 , the capacitor C 32 , and the inductor L 32  are located in this order. In addition, while the radiator  78 A is configured such that the capacitor C 31  is provided closer to the feed point P 31  than the inductor L 31 , the radiator  78 C is configured such that the inductor L 32  is provided closer to the feed point P 33  than the capacitor C 32 . Thus, the capacitors and the inductors are asymmetrically arranged between the radiators  78 A and  78 C, electromagnetic coupling between the radiators  78 A and  78 C is reduced. 
     As described above, by nature, a current having a low frequency component can pass through an inductor, but is difficult to pass through a capacitor. Therefore, when the antenna apparatus of  FIG. 43  operates at the low-band resonance frequency f 1 , even if the radiator  78 A operates in a loop antenna mode due to a current inputted from a signal source Q 31 , an induced current on the radiator  78 C is small, and a current flowing from the radiator  78 C to a signal source Q 32  is also small. Thus, electromagnetic coupling between the radiators  78 A and  78 C for the case where the antenna apparatus of  FIG. 43  operates at the low-band resonance frequency f 1  is small. When the antenna apparatus of  FIG. 43  operates at the high-band resonance frequency f 2 , electromagnetic coupling between the radiators  78 A and  78 C is small. 
     The above-described antenna apparatus according to the fourth embodiment may be provided with only one of a magnetic block and a dielectric block. In the case of having only a magnetic block, it is possible to easily adjust only the low-band resonance frequency so as to be shifted to the lower frequency, in a manner similar to that of the first embodiment. In the case of having only one of the dielectric blocks, it is possible to increase the bandwidth of only the high frequency operating band including the high-band resonance frequency f 2 , in a manner similar to that of the second embodiment. 
     Fifth Embodiment 
       FIG. 61  is a block diagram showing a configuration of a wireless communication apparatus according to a fifth embodiment, provided with an antenna apparatus of  FIG. 28 . A wireless communication apparatus according to the present embodiment may be configured as, for example, a mobile phone as shown in  FIG. 61 . The wireless communication apparatus of  FIG. 61  is provided with an antenna apparatus of  FIG. 28 , a wireless transmitter and receiver circuit  81 , a baseband signal processing circuit  82  connected to the wireless transmitter and receiver circuit  81 , and a speaker  83  and a microphone  84  which are connected to the baseband signal processing circuit  82 . A feed point P 1  of a radiator  70  and a connecting point P 2  of a ground conductor G 1  of the antenna apparatus are connected to the wireless transmitter and receiver circuit  81 , instead of a signal source Q 1  of  FIG. 28 . When a wireless broadband router apparatus, a high-speed wireless communication apparatus for M2M (Machine-to-Machine), or the like, is implemented as the wireless communication apparatus, it is not necessary to have a speaker, a microphone, etc., and alternatively, an LED (Light-Emitting Diode), etc., may be used to check the communication status of the wireless communication apparatus. Wireless communication apparatuses to which the antenna apparatuses of  FIG. 28 , etc., are applicable are not limited to those exemplified above. 
     Since the wireless communication apparatus of the present embodiment is provided with the radiator  70  operable in one of a loop antenna mode and a monopole antenna mode according to the operating frequency, it is possible to effectively achieve dual-band operation, and achieve the size reduction of the antenna apparatus. Further, since the wireless communication apparatus of the present embodiment is provided with a magnetic block M 1 , it is possible to easily adjust only the low-band resonance frequency so as to be shifted to the lower frequency. Further, since the wireless communication apparatus of the present embodiment is provided with the dielectric block D 1 , it is possible to increase the bandwidth of only the high frequency operating band including the high-band resonance frequency f 2 . 
     The wireless communication apparatus of  FIG. 61  can use any of the other antenna apparatuses disclosed here or its modifications, instead of the antenna apparatus of  FIG. 28 . 
     The embodiments and modified embodiments described above may be combined with each other. 
     Implementation Example 1 
     Simulation results for an antenna apparatus according to the first embodiment will be described below. In the simulations, a transient analysis was performed using the software, “CST Microwave Studio”. A point at which reflection energy at the feed point is −40 dB or less with respect to input energy was used as a threshold value for determining convergence. A portion where a current flows strongly was finely modeled using the sub-mesh method. 
       FIG. 44  is a perspective view showing an antenna apparatus according to a first comparison example used in a simulation.  FIG. 45  is a top view showing a detailed configuration of a radiator  51  of the antenna apparatus of  FIG. 44 . The antenna apparatus of the comparison example of  FIGS. 44 and 45  does not have either a magnetic block or a dielectric block. A capacitor having a capacitance of 1 pF was used for a capacitor C 1 . An inductor having an inductance of 3 nH was used for an inductor L 1 . The same capacitance of the capacitor C 1  and the same inductance of the inductor L 1  were used for the other simulations.  FIG. 46  is a graph showing a frequency characteristic of a reflection coefficient S 11  of the antenna apparatus of  FIG. 44 . When the low-band resonance frequency f 1 =1035 MHz, the reflection coefficient S 11 =−13.1 dB, and when the high-band resonance frequency f 2 =1835 MHz, the reflection coefficient S 11 =−10.7 dB. Thus, it can be seen that dual-band operation was effectively achieved at two frequencies. 
       FIG. 47  is a perspective view showing an antenna apparatus according to a second comparison example used in a simulation. A radiator  52  of  FIG. 47  was configured such that a magnetic block M 41  was provided on the entire underside (−X side) of the radiator  51  of  FIG. 44 . The magnetic block M 41  had a relative permeability of 5.  FIG. 48  is a graph showing a frequency characteristic of a reflection coefficient S 11  of the antenna apparatus of  FIG. 47 . When the low-band resonance frequency f 1 =780 MHz, the reflection coefficient S 11 =−8.4 dB, and when the high-band resonance frequency f 2 =1440 MHz, the reflection coefficient S 11 =−8.1 dB. Comparing  FIG. 48  with  FIG. 46 , it can be seen that the antenna apparatus of  FIG. 47  achieved dual-band operation, and further reduced the low-band resonance frequency f 1  to 780 MHz, but also reduced the high-band resonance frequency f 2 . Normally, the loss in magnetic material increases when frequency exceeds 1 GHz. Therefore, it is expected that the antenna characteristics degrades when the high-band resonance frequency f 2  is affected by the magnetic material. 
       FIG. 49  is a perspective view showing an antenna apparatus according to a third comparison example used in a simulation. A radiator  53  of  FIG. 49  was configured such that a dielectric block D 41  is provided on the entire underside (−X side) of the radiator  51  of  FIG. 44 . The dielectric block D 41  had a relative dielectric constant of 5.  FIG. 50  is a graph showing a frequency characteristic of a reflection coefficient S 11  of the antenna apparatus of  FIG. 49 . When the low-band resonance frequency f 1 =896 MHz, the reflection coefficient S 11 =−4.3 dB, and when the high-band resonance frequency f 2 =1604 MHz, the reflection coefficient S 11 =−4.1 dB. Comparing  FIG. 50  with  FIG. 46 , although the antenna apparatus of  FIG. 49  achieved dual-band operation, the antenna radiation resistance decreased, since an electric field was concentrated between a radiation conductor and a ground conductor G 1  due to the influence of the dielectric block D 41 . As a result, it can be seen that the reflection coefficient S 11  degraded, compared to the antenna characteristics of  FIG. 46 . 
     According to  FIGS. 48 and 50 , it can be seen that it is not possible to achieve size reduction while maintaining antenna characteristics, using a magnetic block or a dielectric block provided on the entire underside of a radiator (see Patent Literature 2). 
       FIG. 51  is a perspective view showing an antenna apparatus according to an implementation example of the first embodiment used in a simulation. A radiator  48  of  FIG. 51  was configured such that a magnetic block M 1  was provided in the entire inside of a looped radiation conductor of the radiator  51  of  FIG. 44 . The magnetic block M 1  had a relative permeability of 5. The thickness in the X direction of the magnetic block M 1  was 0.5 mm.  FIG. 52  is a graph showing a frequency characteristic of a reflection coefficient S 11  of the antenna apparatus of  FIG. 51 . When the low-band resonance frequency f 1 =850 MHz, the reflection coefficient S 11 =−10.1 dB, and when the high-band resonance frequency f 2 =1785 MHz, the reflection coefficient S 11 =−9.5 dB. According to  FIG. 52 , it can be seen that dual-band operation was effectively achieved at two frequencies. Comparing with  FIG. 46  as to the antenna apparatus of  FIG. 44 , it can be seen that when the antenna apparatus of  FIG. 51  operated at the high-band resonance frequency f 2 , the high-band resonance frequency f 2  was not shifted since the high-band resonance frequency f 2  was not affected by the magnetic block M 1 , and on the other hand, only the low-band resonance frequency f 1  was effectively shifted to the lower frequency. As a result, it was numerically shown that there is a special advantageous effect of substantially reducing the size of the antenna apparatus without impairing antenna characteristics. 
       FIG. 53  is a perspective view showing an antenna apparatus according to a fourth comparison example used in a simulation. A radiator  54  of  FIG. 53  corresponds to a configuration in which a dielectric block D 42  is provided in the entire inside of a looped radiation conductor of the radiator  51  of  FIG. 44 . The dielectric block D 42  had a relative dielectric constant of 5. The thickness in the X direction of the dielectric block D 42  was 0.5 mm.  FIG. 54  is a graph showing a frequency characteristic of a reflection coefficient S 11  of the antenna apparatus of  FIG. 52 . When the low-band resonance frequency f 1 =1025 MHz, the reflection coefficient S 11 =−12.9 dB, and when the high-band resonance frequency f 2 =1823 MHz, the reflection coefficient S 11 =−10.5 dB. According to  FIG. 54 , it can be seen that dual-band operation was achieved. However, comparing with the results of  FIG. 46 , there is no significant difference. This is because the antenna apparatus has a characteristic that when the antenna apparatus operates at the low-band resonance frequency f 1 , the antenna apparatus is less likely to be affected by the dielectric block D 42 , since the antenna apparatus operates in a loop antenna mode, i.e., a magnetic current mode. 
     Implementation Example 2 
     Simulation results for an antenna apparatus according to the second embodiment will be described below.  FIG. 55  is a perspective view showing an antenna apparatus according to a first implementation example of the second embodiment used in a simulation. A radiator  69  of  FIG. 55  was configured such that a dielectric block D 8  was provided on the entire underside (−X side) of a radiation conductor  1  of a radiator  51  of  FIG. 44 . The dielectric block D 8  had a relative dielectric constant of 10.  FIG. 56  is a graph showing a frequency characteristic of a reflection coefficient S 11  of the antenna apparatus of  FIG. 55 . When the low-band resonance frequency f 1 =1013 MHz, the reflection coefficient S 11 =−12.4 dB, and when the high-band resonance frequency f 2 =1845 MHz, the reflection coefficient S 11 =−9.9 dB. Comparing with the results of  FIG. 46  (no dielectric block), it can be seen that the bandwidth of the operating band including the high-band resonance frequency f 2  was increased. Specifically, when a dielectric block was not provided, Bw=895 MHz, and when the dielectric block D 8  was provided, Bw=1045 MHz, where Bw denotes the frequency bandwidth where the reflection coefficient S 11  is −6 dB or less. Thus, it can be seen that that the bandwidth was increased by about 150 MHz. 
       FIG. 57  is a perspective view showing an antenna apparatus according to a second implementation example of the second embodiment used in a simulation.  FIG. 58  is a graph showing the influence of the width of a dielectric block D 8  of the antenna apparatus of  FIG. 57 , over the bandwidth. “W 1 ” denotes the width in the Y direction of a radiation conductor  1 , and “W 2 ” denotes the width in the Y direction of the dielectric block D 8 .  FIG. 58  shows computation results of variations of the bandwidth where the reflection coefficient S 11  was −6 dB or less in the operating band including the high-band resonance frequency f 2 , when changing the width W 2  of the dielectric block D 8 . According to the computation results, it can be seen that the maximum bandwidth is obtained when the dielectric block D 8  was provided on the entire underside of the radiation conductor  1 . Meanwhile, it can be seen that when the dielectric block D 8  was also provided on the underside of a radiation conductor  2 , the bandwidth decreased steeply. This is because the radiation conductor  2  is a portion that strongly contributes to radiation as an open end of the antenna apparatus. It can be seen that this portion should be configured to easily radiate energy into space as much as possible, without providing the dielectric block D 8  to concentrate the density of electric flux and accumulate energy. 
     Implementation Example 3 
     Simulation results for an antenna apparatus according to the third embodiment will be described below.  FIG. 59  is a perspective view showing an antenna apparatus according to an implementation example of the third embodiment used in a simulation. A radiator  79  of  FIG. 59  was configured to be provided with both a magnetic block M 1  of  FIG. 51  and a dielectric block D 8  of  FIG. 55 . The magnetic block M 1  had a relative permeability of 5, and the dielectric block D 8  had a relative dielectric constant of 10.  FIG. 60  is a graph showing a frequency characteristic of a reflection coefficient S 11  of the antenna apparatus of  FIG. 59 . When the low-band resonance frequency f 1 =868 MHz, the reflection coefficient S 11 =−10.6 dB, and when the high-band resonance frequency f 2 =1833 MHz, the reflection coefficient S 11 =−9.1 dB. It can be seen that the low-band resonance frequency f 1  was shifted to the lower frequency in the similar manner as that of the antenna apparatus of  FIG. 51 , and further, the bandwidth the operating band including the high-band resonance frequency f 2  was increased without impairing the characteristics of the low-band resonance frequency f 1 . 
     According to the above results, it is verified that it is possible to obtain a special advantageous effect of increasing the bandwidth of the operating band including the high-band resonance frequency f 2  without impairing the characteristics of the low-band resonance frequency f 1 , by providing a dielectric block only on the underside of the radiation conductor  1 , instead of filling the entire antenna apparatus with a dielectric block. 
     CONCLUSION 
     The antenna apparatuses and wireless communication apparatuses disclosed here are characterized by the following configurations. 
     According to an antenna apparatus of a first aspect of the present disclosure, the antenna apparatus is provided with at least one radiator. Each radiator is provided with: a looped radiation conductor having an inner perimeter and an outer perimeter; at least one capacitor inserted at a position along a loop of the radiation conductor; at least one inductor inserted at a position along the loop of the radiation conductor, the position of the inductor being different from the position of the capacitor; a feed point provided on the radiation conductor; and a magnetic block provided at at least a part of an inside of the loop of the radiation conductor. Each radiator is excited at a first frequency and at a second frequency higher than the first frequency. When each radiator is excited at the first frequency, a first current flows along a first path, the first path extending along the inner perimeter of the loop of the radiation conductor and including the inductor and the capacitor, and magnetic flux produced by the first current passes through the magnetic block, thus increasing an inductance of the radiation conductor. When each radiator is excited at the second frequency, a second current flows through a second path including a section, the section extending along the outer perimeter of the loop of the radiation conductor, and the section including the capacitor but not including the inductor, and the section extending between the feed point and the inductor. Each radiator is configured such that the loop of the radiation conductor, the inductor, and the capacitor resonate at the first frequency, and a portion of the loop of the radiation conductor included in the second path, and the capacitor resonate at the second frequency. 
     According to an antenna apparatus of a second aspect of the present disclosure, in the antenna apparatus of the first aspect of the present disclosure, the antenna apparatus is further provided with a housing. The magnetic block is formed by embedding magnetic material in a portion of the housing close to an inner portion of the loop of the radiation conductor. 
     According to an antenna apparatus of a third aspect of the present disclosure, in the antenna apparatus of the first or second aspect of the present disclosure, the radiation conductor includes a first radiation conductor and a second radiation conductor. The capacitor is formed by capacitance between the first and second radiation conductors. 
     According to an antenna apparatus of a fourth aspect of the present disclosure, in the antenna apparatus of one of the first to third aspects of the present disclosure, the inductor is formed as a strip conductor. 
     According to an antenna apparatus of a fifth aspect of the present disclosure, in the antenna apparatus of one of the first to third aspects of the present disclosure, the inductor is formed as a meander conductor. 
     According to an antenna apparatus of a sixth aspect of the present disclosure, in the antenna apparatus of one of the first to fifth aspects of the present disclosure, the antenna apparatus is further provided with a ground conductor. 
     According to an antenna apparatus of a seventh aspect of the present disclosure, in the antenna apparatus of the sixth aspect of the present disclosure, the antenna apparatus is provided with a printed circuit board provided with the ground conductor, and a feed line connected to the feed point. The radiator is formed on the printed circuit board. 
     According to an antenna apparatus of an eighth aspect of the present disclosure, in the antenna apparatus of one of the first to fifth aspects of the present disclosure, the antenna apparatus is a dipole antenna including at least a pair of radiators. 
     According to an antenna apparatus of a ninth aspect of the present disclosure, in the antenna apparatus of one of the first to eighth aspects of the present disclosure, the antenna apparatus is provided with a plurality of radiators. The plurality of radiators have a plurality of different first frequencies and a plurality of different second frequencies. 
     According to an antenna apparatus of a tenth aspect of the present disclosure, in the antenna apparatus of one of the first to ninth aspects of the present disclosure, the radiation conductor is bent at at least one position. 
     According to an antenna apparatus of an eleventh aspect of the present disclosure, in the antenna apparatus of one of the first to tenth aspects of the present disclosure, the antenna apparatus is provided with a plurality of radiators connected to different signal sources. 
     According to an antenna apparatus of a twelfth aspect of the present disclosure, in the antenna apparatus of the eleventh aspect of the present disclosure, the antenna apparatus is provided with a first radiator and a second radiator, the first and second radiators having respective radiation conductors formed symmetrically with respect to a reference axis. Respective feed points of the first and second radiators are provided at positions symmetrical with respect to the reference axis. The radiation conductors of the first and second radiators are shaped such that a distance between the first and second radiators gradually increases as a distance from the feed points of the first and second radiators along the reference axis increases. 
     According to an antenna apparatus of a thirteenth aspect of the present disclosure, in the antenna apparatus of the eleventh or twelfth aspect of the present disclosure, the antenna apparatus is provided with a first radiator and a second radiator. Respective loops of radiation conductors of the first and second radiators are formed substantially symmetrically with respect to a reference axis. When proceeding along the respective symmetric loops of the radiation conductors of the first and second radiators in corresponding directions starting from the respective feed points, the first radiator is configured such that the feed point, the inductor, and the capacitor are located in this order, and the second radiator is configured such that the feed point, the capacitor, and the inductor are located in this order. 
     According to a wireless communication apparatus of a fourteenth aspect of the present disclosure, the wireless communication apparatus provided with such an antenna apparatus. 
     According to the antenna apparatus of the present disclosure, it is possible to provide an antenna apparatus operable in multiple bands, while having a simple and small configuration. 
     In addition, when the antenna apparatus of the present disclosure is provided with a plurality of radiators, the antenna apparatus has low coupling between antenna elements, and thus, is operable to simultaneously transmit or receive a plurality of radio signals. 
     In addition, according to the antenna apparatus of the present disclosure, it is possible to adjust only the low-band operating frequency so as to shift to a lower frequency. 
     In addition, according to the wireless communication apparatus of the present disclosure, it is possible to provide a wireless communication apparatus provided with such antenna apparatuses. 
     INDUSTRIAL APPLICABILITY 
     As described above, an antenna apparatus of the present disclosure is operable in multiple bands, while having a simple and small configuration. In addition, when including a plurality of radiators, the antenna apparatus of the present disclosure has low coupling between antenna elements, and is operable to simultaneously transmit or receive a plurality of radio signals. 
     According to the antenna apparatus of the present disclosure and the wireless communication apparatus using the antenna apparatus, they can be implemented as, for example, mobile phones or can also be implemented as apparatuses for wireless LANs, PDAs, etc. The antenna apparatus can be mounted on, for example, wireless communication apparatuses for MIMO communication. In addition to MIMO, the antenna apparatus can also be mounted on (multi-application) array antenna apparatus capable of simultaneously performing communications for a plurality of applications, such as an adaptive array antenna, a maximal-ratio combining diversity antenna, and a phased-array antenna. 
     REFERENCE SIGNS LIST 
     
         
         
           
               1 ,  2 ,  3 ,  11 ,  12 ,  21 ,  22 ,  31  to  34 , and  51  to  54 : RADIATION CONDUCTOR, 
               10  and  20 : HOUSING, 
               40  to  48 ,  50 ,  60  to  69 ,  70  to  78 ,  70 A to  70 D,  78 A to  78 C, and  79 : RADIATOR, 
               81 : WIRELESS TRANSMITTER AND RECEIVER CIRCUIT, 
               82 : BASEBAND SIGNAL PROCESSING CIRCUIT, 
               83 : SPEAKER, 
               84 : MICROPHONE, 
               90 : DIELECTRIC SUBSTRATE, 
             C 1  to C 5 , C 11 , C 21 , C 31 , and C 32 : CAPACITOR, 
             Ce: EQUIVALENT CAPACITANCE, 
             D 1  to D 8 , D 11 , D 21 , D 31 , D 32 , D 41 , and D 42 : DIELECTRIC BLOCK, 
             G 1 : GROUND CONDUCTOR, 
             L 1  to L 5 , L 11 , L 21 , L 31 , and L 32 : INDUCTOR, 
             La: INDUCTANCE, 
             M 1  to M 4 , M 11 , M 21 , M 31 , M 32 , and M 41 : MAGNETIC BLOCK, 
             M 5 : MAGNETIC POWDER, 
             P 1 , P 11 , P 21 , P 31 , and P 33 : FEED POINT, 
             P 2 , P 32 , and P 34 : CONNECTING POINT, 
             Q 1 , Q 21 , Q 31 , and Q 32 : SIGNAL SOURCE, 
             Rr: RADIATION RESISTANCE, 
             S 1 : STRIP CONDUCTOR.