Patent Publication Number: US-8981997-B2

Title: Antenna and wireless communication device

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation of International Application No. PCT/JP2009/055099 filed Mar. 17, 2009, which claims priority to Japanese Patent Application No. 2008-149650 filed Jun. 6, 2008, the entire contents of each of these applications being incorporated herein by reference in their entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to an antenna for use in a wireless communication device, such as a cellular phone terminal, and to a wireless communication device that includes the same. 
     BACKGROUND 
     Examples of a single antenna that supports a plurality of frequency bands are disclosed in Patent Document 1 (International Publication No. WO 2006/073034) and International Publication No. WO 2006/077714 (Patent Document 2). 
     Here, the configuration of the antenna illustrated in Patent Document 1 is described on the basis of  FIG. 1 . In the example of  FIG. 1 , a feed radiation electrode  7  is provided on a rectangular columnar dielectric base member  6 . This feed radiation electrode  7  resonates in a fundamental mode and a higher mode. The feed radiation electrode  7  has a first end formed as a feed end  7 A for use in connection to a circuit for wireless communication. The feed radiation electrode  7  has a second end formed as an open end  7 B. The position of a capacitance-loading portion α is set in advance between the feed end  7 A and the open end  7 B of the feed radiation electrode  7 . The capacitance-loading portion α is connected to a capacitance-loading conductor  12 . The capacitance-loading conductor  12  produces a capacitance for use in adjusting the resonant frequency in the fundamental mode between the feed end  7 A and the capacitance-loading portion α. 
     In the antenna illustrated in Patent Document 2, a dielectric base member on which a feed radiation electrode and a non-feed radiation electrode are disposed is arranged in an ungrounded area of a substrate, each of the feed and non-feed electrodes having a spiral slit, and capacitance is formed in the spiral slit. 
     With the antenna illustrated in Patent Document 1, the magnitude of the capacitance connected between the feed end  7 A and the capacitance-loading portion α is specified by the capacitance-loading conductor  12 . The use of this can adjust the resonant frequency in the fundamental mode. Setting the position of the capacitance-loading portion α in advance enables the adjustment of the resonant frequency in the fundamental mode while the resonant frequency in a harmonic mode remains substantially constant. 
     However, in order to adjust or change the load capacitance, it is necessary to alter the shape of the electrode pattern on the rectangular columnar dielectric base member. The same applies to the antenna illustrated in Patent Document 2. For example, when it operates as a double-channel antenna for the 2 GHz band and the 900 MHz band, the resonant frequency in the fundamental mode is set as the 900 MHz band and the resonant frequency in the harmonic mode is set as the 2 GHz band. In order to change the resonant frequency in the fundamental mode by using the load capacitance, as well as in order to change the resonant frequency in the harmonic mode, it is necessary to alter the electrode pattern. Because of this, development and design time is required, and a problem also exists in an increase in cost. 
     SUMMARY 
     The invention is directed to an antenna that can allow frequency characteristics to be adjusted and set without altering the shape of an antenna element in which an electrode pattern is disposed on a dielectric base member, and also to a wireless communication device including the antenna. 
     An antenna consistent with the claimed invention includes an antenna element in which a feed radiation electrode and a non-feed radiation electrode are provided on a dielectric base member. The antenna includes a substrate including an ungrounded area having no ground electrode provided at an end of the substrate, and the antenna element is provided in the ungrounded area of the substrate. 
     Each of the feed radiation electrode and the non-feed radiation electrode includes a radiation electrode that resonates at a fundamental frequency and a harmonic frequency. 
     A feed terminal is provided at a feed end of the feed radiation electrode. The feed radiation electrode has a helical or loop shape that develops along a surface of the dielectric base member so as to once extend distant from the feed terminal and then return to a position close to the feed terminal. A first external terminal is provided at an external-terminal leading portion close to the feed terminal. 
     A ground terminal is provided at a ground end of the non-feed radiation electrode. The non-feed radiation electrode has a helical or loop shape that develops along the surface of the dielectric base member so as to once extend distant from the ground terminal and then return to a position close to the ground terminal. A second external terminal is provided at a position close to the ground terminal. 
     A feed-terminal connecting electrode to which the feed terminal is connected, first and second external-terminal connecting electrodes to which the first and second external terminals are connected, respectively, and a ground-terminal connecting electrode to which the ground terminal is connected are provided on the substrate. A first inductance element is connected between the first external-terminal connecting electrode and the feed-terminal connecting electrode. A second inductance element is connected between the second external-terminal connecting electrode and the ground-terminal connecting electrode. 
     According to a more specific embodiment consistent with the claimed invention, the first and second external electrodes may be provided at a position where an electric field distribution of the harmonic radiation electrode exhibits an approximate node in the vicinity of the external-terminal leading portion of the dielectric base member. A capacitance-forming electrode may be provided on the substrate and electrically connected to the external-terminal connecting electrode and cause a capacitance resulting from a base of the substrate to be formed between the feed-terminal connecting electrode and the capacitance-forming electrode. 
     According to another more specific embodiment consistent with the claimed invention, the capacitance-forming electrode may include a plurality of discrete electrodes. The plurality of electrodes may be connected by at least one chip capacitor. 
     According to yet another more specific embodiment consistent with the claimed invention, the plurality of discrete electrodes may have different lengths, and the at least one chip capacitor may include a plurality of chip capacitors mounted at a plurality of respective positions. 
     In another more specific embodiment, a wireless communication device may be configured such that an antenna having a configuration specific to any one of the above embodiments is provided in a casing. 
     Other features, elements, characteristics and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments of the present invention with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  illustrates a configuration of an antenna disclosed in Patent Document 1. 
         FIG. 2  is a partially exploded perspective view that illustrates a configuration of an antenna to be incorporated in a casing of a wireless communication device, such as a cellular phone terminal, according to a first exemplary embodiment. 
         FIGS. 3A to 3F  show six-views of the antenna element illustrated in  FIG. 2 . 
         FIG. 4  is a top view showing a pattern of electrodes provided on a substrate illustrated in  FIG. 2 . 
         FIG. 5  is an equivalent circuit diagram of an antenna illustrated in  FIGS. 2 to 4 . 
         FIGS. 6A and 6B  are graphs illustrating return-loss characteristics of an antenna when changing the inductance value of the chip inductor illustrated in  FIGS. 4 and 5 . 
         FIGS. 7A and 7B  illustrate a pattern of electrodes provided on a substrate for use in an antenna according to a second exemplary embodiment, where  FIG. 7A  is a top view and  FIG. 7B  is a bottom view. 
         FIG. 8  is an equivalent circuit diagram of the antenna using the substrate illustrated in  FIGS. 7A and 7B  according to the second exemplary embodiment. 
         FIGS. 9A and 9B  illustrate relationships between a loading position of a capacitance with respect to a radiation electrode and an electric field distribution, where  FIG. 9A  illustrates an electric field distribution of fundamentals caused by a fundamental radiation electrode, and  FIG. 9B  illustrates an electric field distribution of harmonics caused by a harmonic radiation electrode. 
         FIG. 10  is a bottom view of a substrate for use in an antenna according to a third exemplary embodiment. 
         FIG. 11  is an equivalent circuit diagram of the antenna according to the third exemplary embodiment. 
         FIG. 12  is a bottom view of a substrate for use in an antenna according to a fourth exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     A configuration of an antenna and a wireless communication device including the antenna according to a first exemplary embodiment is described with reference to  FIGS. 2 to 6B . 
       FIG. 2  is a partially exploded perspective view that illustrates the configuration of an antenna to be incorporated in the casing of a wireless communication device, such as a cellular phone terminal. An antenna  101  includes an antenna element  1  in which a predetermined electrode is disposed (provided) on a dielectric base member  10  having a shape extending the shape of the casing of the wireless communication device and a substrate  2  in which a predetermined electrode is disposed, or provided on a base  20 . 
     The substrate  2  has a grounded area GA where a ground electrode  23  is provided and an ungrounded area UA where no ground electrode  23  is disposed. The ungrounded area UA extends along one side of the substrate  2 . The antenna element  1  can be implemented by surface mounting in a position existing in the ungrounded area UA and being remote from the grounded area GA as far as possible. 
     To incorporate antenna  101  into a folding-type cellular phone terminal, it can be arranged in a position adjacent to a hinge portion. 
       FIGS. 3A to 3F  constitute a six-view drawing of the antenna element  1  illustrated in  FIG. 2 .  FIG. 3A  is a top view,  FIG. 3B  is a front view,  FIG. 3C  is a bottom view,  FIG. 3D  is a rear view,  FIG. 3E  is a left side view, and  FIG. 3F  is a right side view. 
     The dielectric base member  10  and an electrode pattern disposed thereon are symmetrical with respect to alternate long and short dashed line in each of  FIGS. 3A to 3D . In this example, the single dielectric base member  10  is used and the antenna element  1  is configured such that a feeding-side (feed side) antenna element is at the left side to the alternate long and short dashed lines and a non-feeding side (non-feed side) antenna element is at the right side thereto. 
     First, the feeding side will be described. With reference to  FIG. 3B , a first external terminal  11   i , a feed terminal  11   a , and electrodes  11   b  and  11   d  are disposed on the bottom surface of the dielectric base member  10 .  FIG. 3B  shows electrodes  11   c ,  11   e ,  11   g ,  11   j , and  11   k  disposed on the front surface of the dielectric base member  10 , and an external-terminal leading portion  11   h  extending from the front surface to the bottom surface. 
     As shown in  FIG. 3A , an electrode  11   f  is disposed on the upper surface of the dielectric base member  10 . 
     The above terminals and electrodes are contiguous as follows: the feed terminal  11   a  to the electrode  11   b  to the electrodes  11   c  to  11   d  to  11   e  to  11   f  to  11   g  to  11   j  to  11   k . The external-terminal leading portion  11   h  is electrically connected to the first external terminal  11   i  on the bottom surface. The electrode  11   k  is disposed so as to be contiguous with the electrode  11   j . In such a manner, the feed radiation electrode having a helical or loop shape is configured. 
     The non-feeding side will now be described below. As shown in  FIG. 3C , a second external terminal  12   i , a ground terminal  12   a , and electrodes  12   b  and  12   d  are disposed, or provided on the bottom surface of the dielectric base member  10 .  FIG. 3B  shows electrodes  12   c ,  12   e ,  12   g ,  12   j , and  12   k  are disposed, or provided on the front surface of the dielectric base member  10 , and an external-terminal leading portion  12   h  extending from the front surface to the bottom surface. 
     As shown in  FIG. 3A , an electrode  12   f  is disposed, or provided on the upper surface of the dielectric base member  10 . 
     The above terminals and electrodes are contiguous as follows: the ground terminal  12   a  to the electrode  12   b  to the electrodes  12   c  to  12   d  to  12   e  to  12   f  to  12   g  to  12   j  to  12   k . The external-terminal leading portion  12   h  is electrically connected to the second external terminal  12   i  on the bottom surface. The electrode  12   k  is disposed, or provided so as to be contiguous with the electrode  12   j . In such a manner, the non-feed radiation electrode having a helical or loop shape is configured. 
       FIG. 4  is a top view that illustrates a pattern of electrodes disposed on the substrate  2  illustrated in  FIG. 2 . A configuration at the feeding side is now described. As shown in  FIG. 4 , a first external-terminal connecting electrode  21   i , a feed-terminal connecting electrode  21   a , and electrodes  21   b  and  21   d  are disposed on the upper surface in the ungrounded area (UA) of the substrate  2 . An electrode  21   m  extends from the feed-terminal connecting electrode  21   a , and discrete electrodes  21   n  and  21   p  are disposed apart from an end of the electrode  21   m.    
     A chip inductor CL is mounted between the first external-terminal connecting electrode  21   i  and the feed-terminal connecting electrode  21   a.    
     The above first external-terminal connecting electrode  21   i  is connected to the first external terminal  11   i  illustrated in  FIG. 3C . The feed-terminal connecting electrode  21   a  is connected to the feed terminal  11   a  of the antenna element  1 . Similarly, the electrodes  21   b  and  21   d  on the substrate are connected to the electrodes  11   b  and  11   d  of the antenna element  1 , respectively. 
     A feeder circuit (transmitter/receiver circuit) (not shown) is connected between the electrode  21   m  extending from the above feed-terminal connecting electrode  21   a  and the ground electrode  23 . A chip capacitor or chip inductor (not shown) for a matching circuit is mounted between each of the discrete electrodes  21   n  and  21   p  and each of the ground electrode  23  and the electrode  21   m.    
     A configuration at the non-feeding side is now described. As shown in  FIG. 4 , second external-terminal connecting electrode  22   i , a ground-terminal connecting electrode  22   a , and electrodes  22   b  and  22   d  are disposed on the upper surface in the ungrounded area (UA) of the substrate  2 . 
     The above second external-terminal connecting electrode  22   i  is connected to the second external terminal  12   i  illustrated in  FIG. 3C . The ground-terminal connecting electrode  22   a  is connected to the ground terminal  12   a  of the antenna element  1 . Similarly, the electrodes  22   b  and  22   d  on the substrate are connected to the electrodes  12   b  and  12   d  of the antenna element  1 , respectively. 
     A chip inductor CL is connected, for example mounted, between the second external-terminal connecting electrode  22   i  and the ground-terminal connecting electrode  22   a.    
       FIG. 5  is an equivalent circuit diagram of the antenna  101  illustrated in  FIGS. 2 to 4 . First, the feeding side is described with reference to the left-hand side of  FIG. 5 . 
     The loop from the feed terminal  11   a  to the electrode  11   k  through the electrodes  11   b  to  11   g  and  11   j  forms a fundamental radiation electrode that resonates with a substantially ¼ wavelength and a harmonic radiation electrode that resonates with a substantially ¾ wavelength. 
     The first external terminal  11   i  is electrically connected to the first external-terminal connecting electrode  21   i  on the upper surface of the substrate  2 . 
     Similarly, the non-feeding side shown on the right-hand side of  FIG. 5  is configured such that the loop from the ground terminal  12   a  to the electrode  12   k  through the electrodes  12   b  to  12   g  and  12   j  forms a fundamental radiation electrode that resonates with a ¼ wavelength and a harmonic radiation electrode that resonates with a ¾ wavelength. 
     The second external terminal  12   i  is electrically connected to the second external-terminal connecting electrode  22   i  on the upper surface of the substrate  2 . 
     As illustrated in  FIG. 5 , the fundamental radiation electrode and the harmonic radiation electrode made up of the feed terminal  11   a  and the electrodes  11   b  to  11   k  are fed directly from the feed terminal  11   a.    
     If each of the chip inductors CL is not present in  FIG. 5 , in the radiation electrode  11  ( 11   a ,  11   b  to  11   f ,  11   g ,  11   j ) at the feeding side, a current passes around the loop from the feed end to the open end. When the chip inductor CL is connected between the first external-terminal connecting electrode  21   i  and the feed-terminal connecting electrode  21   a , a shortcut route passing through the chip inductor is present between a point within the above radiation electrode  11  and the feed end. Therefore, the route passing around the above loop and the route passing through the chip inductor are present, so the equivalent electrical length of the radiation electrode  11  is shortened and the resonant frequency in the fundamental mode is increased. 
     The proportion of the amount of current flowing through the route passing through the chip inductor of the above two current routes increases with a reduction in inductance of the above chip inductor. This leads to a further reduction in the equivalent electrical length of the radiation electrode and a further increase in the resonant frequency in the fundamental mode. 
     Because the resonant frequency in the harmonic mode is higher than that in the fundamental mode, the proportion of the amount of current flowing through the above chip inductor is small. Therefore, in the range of an inductance value of a chip inductor used in order to control the resonant frequency in the fundamental mode, the resonant frequency in the harmonic mode remains substantially unchanged. 
       FIGS. 6A and 6B  illustrate return-loss characteristics of the antenna when the inductance value of the chip inductor CL illustrated in  FIG. 4  is changed. In  FIG. 6A , a smaller return-loss characteristic indicated by RLf appearing in lower frequencies results from resonance in the fundamental mode, whereas a smaller return-loss characteristic indicated by RLh appearing in higher frequencies results from resonance in the harmonic mode. 
     From the above-described reason, the amount of current allowed to flow through the shortcut route increases with a reduction in inductance value of the chip inductor CL, so the resonant frequency in the fundamental mode is increased. The characteristic of the return loss RLf in lower frequencies varies with a change in inductance value of the chip inductor CL, whereas that of the return loss RLh in higher frequencies remains substantially unchanged. 
       FIG. 6B  illustrates how the return loss RLf in the fundamental mode illustrated in  FIG. 6A  is changed. When the inductance value of the chip inductor CL illustrated in  FIGS. 4 and 5  is open, the return loss exhibits the characteristic indicated by RL 0  in the drawing; when the inductance value of the chip inductor is 120n, the return loss is the one indicated by RL 1 ; when the inductance value of the chip inductor is 100n, 68n, 33n, and 15n, the return loss varies as indicated by RL 2 , RL 3 , RL 4 , and RL 5 , respectively. That is, the resonant frequency in the fundamental mode increases with a reduction in inductance value of the chip inductor. 
     It is assumed that the reason why the resonant frequency in the fundamental mode when the chip inductor of 120nH is used is lower than that when the chip inductor being open is used is that the chip inductor acts as a capacitance in an equivalent manner by its capacitance component. 
     Setting the inductance value of the chip inductor CL in such a way enables the frequency in lower frequencies to be set without any alterations to the antenna element  1 . 
       FIGS. 7A and 7B  illustrate a pattern of electrodes disposed, or provided on the substrate  2  of an antenna according to a second exemplary embodiment.  FIG. 7A  is a top view and  FIG. 7B  is a bottom view. The configuration of the antenna element  1  to be implemented on the substrate  2  is substantially the same as that illustrated in  FIG. 3  in the first exemplary embodiment. The pattern of electrodes on the upper surface of the substrate  2  is substantially the same as that illustrated in  FIG. 4  in the first exemplary embodiment. 
     A feature of the antenna according to the second exemplary embodiment is that a capacitance is formed by electrodes on the upper and lower surfaces of the substrate  2  and it is loaded on the antenna. 
     A configuration at the feeding side will now be described. The first external-terminal connecting electrode  21   i , the feed-terminal connecting electrode  21   a , and the electrodes  21   b  and  21   d  are disposed on the upper surface in the ungrounded area of the substrate  2 . The electrode  21   m  extends from the feed-terminal connecting electrode  21   a , and the discrete electrodes  21   n  and  21   p  are disposed apart from the end of the electrode  21   m.    
     The above first external-terminal connecting electrode  21   i  is connected to the first external terminal  11   i  illustrated in  FIG. 3C . The feed-terminal connecting electrode  21   a  is connected to the feed terminal  11   a  of the antenna element  1 . Similarly, the electrodes  21   b  and  21   d  on the substrate are connected to the electrodes  11   b  and  11   d  of the antenna element  1 , respectively. 
     A configuration at the non-feeding side is now described. As shown in  FIG. 7A , the second external-terminal connecting electrode  22   i , the ground-terminal connecting electrode  22   a , and the electrodes  22   b  and  22   d  are disposed on the upper surface in the ungrounded area (UA) of the substrate  2 . A discrete electrode  22   n  is disposed between the ground-terminal connecting electrode  22   a  and the ground electrode  23 . 
     The above second external-terminal connecting electrode  22   i  is connected to the second external terminal  12   i  illustrated in  FIG. 3C . The ground-terminal connecting electrode  22   a  is connected to the ground terminal  12   a  of the antenna element  1 . Similarly, the electrodes  22   b  and  22   d  on the substrate are connected to the electrodes  12   b  and  12   d  of the antenna element  1 , respectively. 
     As illustrated in  FIG. 7B , at the feeding side of the lower surface of the substrate  2 , an electrode  24   i  is disposed at a position that faces the first external-terminal connecting electrode  21   i  on the upper surface, and an electrode  24   a  is disposed at a position that faces the feed-terminal connecting electrode  21   a  on the upper surface. The above first external-terminal connecting electrode  21   i  and its facing electrode  24   i  are electrically connected to each other through a through hole (not shown in  FIG. 7B ). Because the electrodes  24   i  and  24   a  are contiguous with to each other, a capacitance is formed in a portion where the electrode  24   a  faces the feed-terminal connecting electrode  21   a  such that the base of the substrate  2  (i.e., the base  20  illustrated in  FIG. 2 ) is disposed therebetween. 
     As illustrated in  FIG. 7B , at the non-feeding side of the lower surface of the substrate  2 , an electrode  25   i  is disposed at a position that faces the second external-terminal connecting electrode  22   i  on the upper surface, and an electrode  25   a  is disposed at a position that faces the ground-terminal connecting electrode  22   a  on the upper surface. The above second external-terminal connecting electrode  22   i  and its facing electrode  25   i  are electrically connected to each other through a through hole (not shown in  FIG. 7B ). Because the electrodes  25   i  and  25   a  are contiguous with each other, a capacitance is formed in a portion where the electrode  25   a  faces the ground-terminal connecting electrode  22   a  such that the base of the substrate  2  (the base  20  illustrated in  FIG. 2 ) is disposed therebetween. 
       FIG. 8  is an equivalent circuit diagram of the antenna using the substrate  2  illustrated in  FIGS. 7A and 7B  according to the second exemplary embodiment. The configuration of the antenna element to be implemented on the substrate is substantially the same as that illustrated in the first exemplary embodiment. 
     First, with reference to the left-hand side of  FIG. 8 , the feeding side is described. The loop from the feed terminal  11   a  to the electrode  11   k  through the electrodes  11   b  to  11   g  and  11   j  forms a fundamental radiation electrode that resonates with a substantially ¼ wavelength and a harmonic radiation electrode that resonates with a substantially ¾ wavelength. 
     The first external terminal  11   i  is electrically connected to the first external-terminal connecting electrode  21   i  on the upper surface of the substrate  2 . This first external-terminal connecting electrode  21   i  is electrically connected to the electrodes  24   i  on the lower surface of the substrate  2  through a through hole. As indicated by broken lines representing the symbol of a capacitor in the drawing, a capacitance is formed between the capacitance-forming electrode  24   a , which extends from the electrode  24   i , and the feed-terminal connecting electrode  21   a  on the upper surface of the substrate  2 . 
     Similarly, the non-feeding side shown in the right-hand side of  FIG. 8  is configured such that the loop from the ground terminal  12   a  to the electrode  12   k  through the electrodes  12   b  to  12   g  and  12   j  forms a fundamental radiation electrode that resonates with a ¼ wavelength and a harmonic radiation electrode that resonates with a ¾ wavelength. 
     The second external terminal  12   i  is electrically connected to the second external-terminal connecting electrode  22   i  on the upper surface of the substrate  2 . This second external-terminal connecting electrode  22   i  is electrically connected to the electrodes  25   i  on the lower surface of the substrate  2  through a through hole. As indicated by dashed lines representing the symbol of a capacitor in the drawing, a capacitance is formed between the capacitance-forming electrode  25   a , which extends from the electrode  25   i , and the ground-terminal connecting electrode  22   a  on the upper surface of the substrate  2 . 
       FIG. 9A  illustrates an electric field distribution of fundamentals caused by the fundamental radiation electrode described above, and  FIG. 9B  illustrates an electric field distribution of harmonics caused by the harmonic radiation electrode. As is clear from reference to  FIG. 8 , the fundamental radiation electrode resonates with a ¼ wavelength, and a capacitance is loaded between the external-terminal leading portion  11   h  of the fundamental radiation electrode and the feed end. This loaded capacitance changes the resonant frequency in the fundamental mode. 
     For the harmonic radiation electrode resonating with a ¾ wavelength, the external-terminal leading portion  11   h  is set such that a node of the electric field distribution of harmonics is in the vicinity of the external-terminal leading portion  11   h . Therefore, the resonant frequency of harmonics is not substantially affected by the load capacitance. 
     In such a manner, the resonant frequency in the fundamental mode can be adjusted independently of the resonant frequency in the harmonic mode. 
       FIG. 10  is a bottom view of the substrate  2  of an antenna according to a third exemplary embodiment. It is different from the configuration illustrated in  FIG. 7B  in the second exemplary embodiment in that a capacitance-forming electrode is made up of a plurality of electrodes being discrete. In the example illustrated in  FIG. 10 , the capacitance-forming electrode  24   i  illustrated in  FIG. 7B  is separated into a capacitance-forming electrode  24   q  contiguous with the capacitance-forming electrode  24   a  and a capacitance-forming electrode  24   i , and a chip capacitor CC is mounted between these capacitance-forming electrode  24   q  and capacitance-forming electrode  24   i.    
     Similarly, also at the non-feeding side, the capacitance-forming electrode  25   i  illustrated in  FIG. 7B  is separated into a capacitance-forming electrode  25   q  liked to the capacitance-forming electrode  25   a  and a capacitance-forming electrode  25   i , and a chip capacitor CC is mounted between these capacitance-forming electrode  25   q  and capacitance-forming electrode  25   i.    
       FIG. 11  is an equivalent circuit diagram of the antenna using the substrate  2  illustrated in  FIG. 10  according to the third exemplary embodiment. The configuration of the antenna element to be implemented on the substrate is substantially the same as that illustrated in the first exemplary embodiment. As illustrated in the left-hand side of  FIG. 11 , at the feeding side, the chip capacitor CC is connected between the capacitance-forming electrodes  24   i  and  24   q , and a capacitance resulting from the substrate is formed between the capacitance-forming electrode  24   a  and the feed-terminal connecting electrode  21   a . Accordingly, both the chip inductor CL and a series circuit made up of the capacitance resulting from the substrate and the capacitance of the chip capacitor CC are connected between the feed terminal  11   a  and the external-terminal leading portion  11   h . Therefore, the proportion of the shortcut is specified by the chip inductor CL, and the load capacitance with respect to the radiation electrode is set by the capacitance of the substrate and the capacitance of the chip capacitor CC. 
     Similarly, at the non-feeding side illustrated in the right-hand side of  FIG. 11 , the chip capacitor CC is connected between the capacitance-forming electrodes  25   i  and  25   q , and a capacitance resulting from the substrate is formed between the capacitance-forming electrode  25   a  and the ground-terminal connecting electrode  22   a . Accordingly, both the chip inductor CL and a series circuit made up of the capacitance resulting from the substrate  2  and the capacitance of the chip capacitor CC are connected between the ground terminal  12   a  and the external-terminal leading portion  12   h . Therefore, the proportion of the shortcut is specified by the chip inductor CL, and the load capacitance with respect to the radiation electrode is set by the capacitance of the substrate and the capacitance of the chip capacitor CC. 
     In such a way, mounting not only a chip inductor having a predetermined inductance but also a chip capacitor having a predetermined capacitance enables the load capacitance between the feed end and the external-terminal leading portion or between the ground point and the external-terminal leading portion to be specified. Hence, the resonant frequency in the fundamental mode of the electrodes on the substrate  2  can also be set and adjusted without altering the pattern of the electrodes. 
       FIG. 12  is a bottom view of a substrate portion of an antenna according to a fourth exemplary embodiment. In this example, as a capacitance-forming electrode, discrete capacitance-forming electrodes  24   r  and  24   s  are disposed at the feeding side, and discrete capacitance-forming electrodes  25   r  and  25   s  are disposed at the non-feeding side. The capacitance-forming electrodes  24   r  and  24   s  face an electrode that extends from the feed-terminal connecting electrode on the upper surface of the substrate  2 , whereas the capacitance-forming electrodes  25   r  and  25   s  face an electrode that extends from the ground-terminal connecting electrode on the upper surface of the substrate  2 . The electrode pattern on the upper surface of the substrate  2  is substantially the same as that illustrated as the first exemplary embodiment in  FIG. 4 . 
     At the feeding side, a chip capacitor CC 2  is mounted between the capacitance-forming electrodes  24   q  and  24   r , and a chip capacitor CC 3  is mounted between the capacitance-forming electrodes  24   i  and  24   s . The use of capacitance of these chip capacitors CC 1  to CC 3  enables the load capacitance between the external-terminal leading portion ( 11   h ) and the feed terminal ( 11   a ) of the antenna element to be specified with high accuracy. 
     Similarly, at the non-feeding side, a chip capacitor CC 2  is mounted between capacitance-forming electrodes  25   q  and  25   r , and a chip capacitor CC 3  is mounted between the capacitance-forming electrodes  25   i  and  25   s . The use of capacitance of these chip capacitors CC 1  to CC 3  enables the load capacitance between the external-terminal leading portion ( 12   h ) and the ground terminal ( 12   a ) of the antenna element to be specified with high accuracy. 
     Embodiments consistent with the claimed invention can allow for adjusting the resonant frequency in the fundamental mode merely by alteration in the electrode pattern on the substrate while the electrode pattern on the antenna element remains unchanged. 
     Also, the resonant frequency in the fundamental mode can be controlled solely and independently while the resonant frequency in the harmonic mode remains substantially constant. 
     Additionally, it is not necessary to alter the antenna element to make an adjustment of the resonant frequency in the fundamental mode, so the lead time can be shortened and cost reduction can be achieved. 
     While exemplary embodiments of the invention have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing from the scope and spirit of the invention. 
     The scope of the invention, therefore, is to be determined solely by the following claims and their equivalents.