Patent Publication Number: US-7589673-B2

Title: Antenna and mobile wireless equipment using the same

Description:
This nonprovisional application claims priority under 35 U.S.C. § 119(a) on Patent Application No. 2004-118067 filed in Japan on Apr. 13, 2004, the entire contents of which are hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an antenna capable of transmitting or receiving signal waves in not less than two frequency bands and capable of good transmission and reception when used for mobile wireless equipment, regardless of usage form. 
     2. Background Art 
     An inverted F antenna is used for mobile phones, for example, as it has a small shape relative to the wavelengths of radio waves and is readily adapted to a wide band. For example,  FIG. 15  shows the configuration of a conventional inverted F antenna. As shown in  FIG. 15 , a conventional inverted F antenna  210  comprises a solid conductor plate  211  disposed on a ground conductor  215 , the solid conductor plate  211  having a radiation conductor plate  212  and a connection conductor plate  213  formed via a punching process or a folding process, such that a first conductor strip  212   a  and a second conductor strip  212   b  of the radiation conductor plate  212  and the connection conductor plate  213 , respectively, can each resonate with different frequencies. A feed pin  216  is soldered at a predetermined location on the radiation conductor plate  212 . The feed pin  216  is connected to an antenna circuit that is not shown in the drawings without contacting the ground conductor  215 . The inverted F antenna  210  configured in the above feeds two kinds, namely high and low, of high-frequency currents to the radiation conductor plate  212  via the feed pin  216  thereby causing the first conductor strip  212   a  to resonate with a signal wave in a first resonant frequency band and the second conductor strip  212   b  to resonate with a signal waves in a second resonant frequency band. Thus, the antenna is capable of operation as an antenna for two-band sharing (see Patent Document 1). 
     Patent Document 1: JP Utility Model Registration No. 3094677 
     SUMMARY OF THE INVENTION 
     The characteristics of the antenna of a mobile phone tend to change depending on the conditions of surrounding areas, usage forms, or the like. For example, clamshell type (folding type) mobile phones may perform transmission or reception in either a folded state or an open state, which poses a problem in that it is difficult to obtain good antenna characteristics in various different usage conditions. 
     It is an object of the present invention to reduce changes in antenna characteristics resulting from circumstances or usage forms, and to obtain good characteristics under any conditions. 
     In accordance with an antenna of the invention, a feed portion and a short-circuit portion in a tabular antenna are spaced apart from one another by a distance not less than ⅙ of the circumference of the antenna so as not to resonate in a desired frequency band. Further, adjusting means for adjusting the resonant frequency of the antenna is separately provided. In this way, improved reflection characteristics of the antenna can be obtained in not less than two desired frequency bands. 
     In one aspect of the present invention, there is provided an antenna comprising a ground conductor plate, a radiation conductor plate disposed at a certain distance from the ground conductor plate in a facing manner, a short-circuit portion for connecting the radiation conductor plate and the ground conductor plate, and a feed portion for exciting the radiation conductor plate, wherein the short-circuit portion and the feed portion are spaced apart from one another by a distance not less than ⅙ of the circumference of the radiation conductor plate. The antenna further comprises a matching circuit connected to the feed portion for adjusting the impedance of the antenna. Also, there is provided an antenna comprising a ground conductor plate, a radiation conductor plate disposed at a certain distance from the ground conductor plate in a facing manner, a short-circuit portion for connecting the radiation conductor plate and the ground conductor plate, and a feed portion for exciting the radiation conductor plate, wherein the short-circuit portion and the feed portion are disposed such that the antenna does not resonate with a desired frequency, the antenna further comprising a matching circuit connected to the feed portion for adjusting the impedance of the antenna. 
     The feed portion and the short-circuit portion are thus disposed such that the resonant frequency determined by the feed portion and the short-circuit portion differs from the resonant frequency of the antenna. Further, the frequency is adjusted through impedance matching via the matching circuit. In this way, stable reflection characteristics can be available in a plurality of frequencies and the influences of circumstances on antenna characteristics can be reduced, for example. In other words, the matching circuit board is used for performing an impedance matching such that the reflection characteristics in a desired frequency can be improved. For example, by performing an impedance matching in one or more frequencies using the matching circuit, antenna characteristics at desired frequencies can be improved. 
     In our embodiment, a notch cutting is provided in the radiation conductor between the feed portion and the short-circuit portion. Also, by providing the notch cutting in the radiation conductor between the feed portion and the short-circuit portion, a length L is adjusted to be the distance that corresponds with the edge of the notch cutting. By thus providing the notch cutting between the feed portion and the short-circuit portion, the range of frequencies in which matching can be achieved can be increased, so that an antenna band can be widened, especially in low frequencies. 
     A variable inductor may be provided between the short-circuit portion and a grounded portion of the ground conductor plate. In this way, the adjustment of the resonant frequency becomes possible. In particular, this makes it possible for the antenna to easily take a band in lower frequencies. Also, a parasitic element that is connected to the short-circuit portion may be provided between the feed portion and the short-circuit portion, which makes it possible to increase antenna band. Preferably, the short-circuit portion is disposed in the vicinity of an end of the ground conductor plate. In this way, the antenna becomes less likely to be affected by any change in the condition of the surrounding areas. 
     In another aspect of the present invention, there is provided mobile wireless equipment comprising a first casing including a display unit and a first circuit board and a second casing including an operation portion, a second circuit board, and any one of the above-described antennas. The first casing and the second casing are disposed so as to face each other, and the first casing is slidable in at least one direction. The antenna is disposed on the end portion towards the aforementioned one direction of the second casing. The short-circuit portion is disposed on the end portion of the board. These features allow the equipment to be less susceptible to the influences of the head of a human body when in use. Also, they reduce the impedance fluctuation of mobile wireless equipment even when the casings slide or the casings open or close. 
     Since the antenna characteristics are adjusted by impedance matching via a matching circuit rather than by resonance of an antenna per se, the antenna characteristics are less susceptible to the influences of condition changes. Thus, it is not necessary to consider a tradeoff of characteristics among a plurality of usage conditions, so that the antenna characteristics can be improved. Since the antenna characteristics are less susceptible to influences of circumstances, they are not subject to influences of change of resonant frequency resulting from the influences of circumstances, such as when the user&#39;s head is near, when the antenna is applied to a folding type mobile phone, for example. Thus, the antenna is advantageous in that it causes less deterioration of antenna characteristics. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows an example of the configuration of an antenna apparatus according to a first embodiment of the present invention.  FIG. 1(A)  shows a perspective view and  FIG. 1(B)  shows a side view. 
         FIG. 2  shows a circuit diagram of an example of a matching circuit that is connected to the antenna apparatus. 
         FIG. 3  schematically shows an example of the configuration of an antenna apparatus that is a variation of the antenna apparatus according to the first embodiment.  FIG. 3(A)  shows a first positional relationship among a ground conductor, a radiation conductor, a feed portion, and a short-circuit portion.  FIG. 3(B)  shows a second positional relationship. 
         FIG. 4  shows the positional relationships as shown in  FIG. 3  in greater detail. 
         FIG. 5(A)  and  FIG. 5(B)  show an example of the antenna apparatus according to the variation. 
         FIG. 6  schematically shows the appearance of a mobile phone according to a second embodiment of the present invention. 
         FIG. 7  shows an example of the internal structure of the mobile phone according to the embodiment. 
         FIG. 8  shows a perspective view ( FIG. 8(A) ) of a mobile phone according to a third embodiment of the present invention, showing the appearance of the sliding mobile phone when it is closed; a side view ( FIG. 8(B) ) indicating the corresponding positional relationships of the antenna; and a plan view ( FIG. 8(C) ) of the antenna apparatus. 
         FIG. 9  shows a perspective view ( FIG. 9(A) ) when the slide mobile phone of  FIG. 8  is open, and a side view ( FIG. 9(B) ) indicating the corresponding positional relationships. 
         FIG. 10  shows a mobile phone according to the variation of the present invention, illustrating the case where the antenna apparatus according to the first embodiment of the present invention is used for a rotary mobile phone.  FIG. 10(A)  shows a mode of used when the device is in operation, indicating the state where a first casing and a second casing are disposed in a substantially parallel manner while having a rotation axis therebetween.  FIG. 10(B)  shows a mode during stand by, indicating the state where the first casing almost covers the second casing.  FIG. 10(C)  shows a transitional state. 
         FIGS. 11(A) and 11(B)  show examples the configuration of an antenna apparatus according to a fourth embodiment of the present invention, where a notch cutting is provided in a radiation conductor. 
         FIG. 12  shows a side view of a mobile phone using an antenna apparatus according to a fifth embodiment of the present invention and also shows the internal configuration thereof. 
         FIG. 13  shows an example of the configuration of an antenna apparatus according to a sixth embodiment of the present invention. 
         FIG. 14  shows a main portion of an antenna apparatus according to a seventh embodiment of the present embodiment. 
         FIG. 15  shows the configuration of a conventional inverted F antenna. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the following, an antenna apparatus according to a first embodiment of the present invention is described with reference to the drawings.  FIG. 1  shows an example of the configuration of the antenna apparatus according to the present embodiment.  FIG. 1(A)  shows a perspective view and  FIG. 1(B)  shows a side view. As shown in  FIG. 1(A)  and  FIG. 1(B) , an antenna apparatus A according to the present embodiment comprises a tabular ground conductor  1 , a radiation conductor  3  disposed in a location facing the ground conductor  1 , a short-circuit portion  7  for shod-circuiting the ground conductor  1  and the radiation conductor  3 , an opening  11  disposed on the ground conductor  1  where the location is positioned at a distance of d from the short-circuit portion  7  in the in-plane direction of the tabular ground conductor  1 , and a feed portion  5  extending from the radiation conductor  3  and passing through the opening  11  so as to not be in contact with the ground conductor  1 . These members are disposed in the vicinity of the lower end of a casing. The feed portion  5  is connected to a matching circuit  150  shown in  FIG. 2 . In the antenna apparatus A according to the present embodiment, the distance d between the short-circuit portion  7  and the feed portion  5  is not less than ⅙ and preferably not less than ¼, of the length of the circumference (the total circumference) of the radiation conductor  3 . This enables an increase of the distance d between the short-circuit portion  7  and the feed portion  5 , and an adjustment of the resonant frequency of the antenna via the matching circuit, whereby the antenna is made less susceptible to influences of circumstances or influences of changes of usage forms. It is assumed that the antenna apparatus AT according to the present embodiment is disposed in the vicinity of the lower end inside a casing that is not shown in the drawings, in which the antenna apparatus AT is accommodated. 
       FIG. 2  shows a circuit diagram of an example of a matching circuit that is connected to the antenna apparatus AT (denoted by reference A in  FIG. 1 ). As shown in  FIG. 2 , the matching circuit  150  according to the present embodiment is connected to the antenna AT, and comprises a first coil L 1  disposed on a first wiring LD 1  connecting the antenna AT to a first ground point GND 1 , a second wiring LD 2  extending from a nodal point between the antenna AT and the first coil L 1 , a first capacitor C 1  and a second coil L 2  individually disposed on the second wiring LD 2  from the first nodal point side, a third wiring LD 3  extending from a nodal point disposed between the first capacitor C 1  and the second coil L 2  and leading to a second ground point GND 2 , and a capacitor C 2  disposed on the third wiring LD 3 . An RF circuit that is not shown in the drawings is disposed on the opposite side of the first nodal point on the second wiring LD  2 . 
     In the aforementioned configuration, good reflection characteristics can be obtained in two types of frequency bands using the first combination of the coil L 1  and the capacitor C 1  on the antenna AT side and the second combination of the coil L 2  and the capacitor C 2  on the RF circuit side. 
     The matching circuit  150  performs impedance matching for the antenna AT, adjusts the impedance of the antenna as shown in  FIG. 1 , and tunes it to a desired frequency that is used for transmission or reception. According to the antenna provided with the matching circuit according to the present embodiment, by using the antenna apparatus AT that is impedance-matched via connection to the aforementioned matching circuit  150 , an antenna having good reflection characteristics in desired frequency bands, such as two frequency bands of the GSM band and the DCS band or three frequency bands further including the PCS band, is provided. In this case, contrary to the configuration of an antenna apparatus where the first conductor strip  212   a  and the second conductor strip  212   b  of the radiation conductor plate  212  and the connection conductor plate  213  are disposed such that they resonate with different frequencies as shown in  FIG. 15 , the feed portion  5  and the short-circuit portion  7  are disposed such that they resonate with frequencies that are not in a desired frequency band and the adjustment of frequencies is carried out via the matching circuit. Thus, it is advantageous in that influences of circumstances on the antenna characteristics can be reduced. One example of such an advantage is that when a conductor, for example comes close to the periphery of the antenna, the characteristics can be maintained such that they do not differ from those of the conductor in a remote state, so that the antenna characteristics are made less susceptible to influences of a change of circumstances. 
     A variation of the antenna apparatus according to the first embodiment of the present invention is described with reference to the drawings.  FIG. 3  schematically shows an example of the configuration of the antenna apparatus that is the variation of the present embodiment.  FIG. 3(A)  shows an example of the configuration of the antenna apparatus according to the present embodiment, indicating the planar positional relationship among the ground conductor  1 , the radiation conductor  3 , the feed portion  5 , and the short-circuit portion  7 . A line connecting the feed portion  5  with the short-circuit portion  7  is disposed substantially parallel with one side of the substantially rectangular radiation conductor  3 . By contrast,  FIG. 3(B)  shows an example of the configuration of an antenna apparatus according to the variation of the present embodiment. As can be seen by comparing  FIG. 3(A)  with  FIG. 3(B) , they differ in that in  FIG. 3(A) , the feed portion  5  and the short-circuit portion  7  are disposed such that they are disposed along one side of the rectangle relative to the substantially rectangular radiation conductor  3 , while in the antenna apparatus according to the variation, the feed portion  5  and the short-circuit portion  7  are disposed along a diagonal line relative to the substantially rectangular radiation conductor  3 . In this manner, the positions of the feed portion  5  and the short-circuit portion  7  can be disposed on the radiation conductor  3  at any position with a distance of d (that has a length not less than ⅙ of the circumference of the radiation conductor  3 ). 
     The positional relationship between  FIGS. 3(A) and 3(B)  are described in detail with reference to  FIG. 4 . In  FIG. 4 , in the case where the feed portion  5  and the short-circuit portion  7  are disposed along one side of the rectangle, it is assumed that the distance between the feed portion  5  and the short-circuit portion  7  is L, the distance between the other side of the rectangle extending substantially perpendicularly from an end point of the aforementioned one side of the rectangle and the short-circuit portion  7  is d 1 , and the distance between one side in the opposite side and the feed portion  5  is d 2 , for example. When the circumference of the aforementioned radiation conductor  3  is N, L/N&gt;⅙. Meanwhile, in the case of the positional relationship as shown in  FIG. 3(B) , L′/N&gt;⅙, as well. Further, in the former case, L&gt;d 1  and L&gt;d 2  are preferred, and in the latter case, L′&gt;d 1 ′ and L′&gt;d 2 ′ are preferred. In accordance with the aforementioned configuration, antenna characteristics that are less susceptible to influences of usage forms or circumstances can be obtained. 
     The antenna apparatus according to the variation of the first embodiment of the present invention is described with reference to the drawings.  FIG. 5(A)  and  FIG. 5(B)  show an example of the antenna apparatus according to the variation. Basically, the antenna apparatus comprises the same configuration members as those of the first embodiment. However, the antenna apparatus differs in that individual members that constitute the antenna apparatus are disposed in the vicinity of the upper end of a casing that accommodates the antenna apparatus. Although the individual members are disposed in the upper end portion of the casing, conditions described in  FIGS. 3 and 4  are applied in the same manner. 
     As stated above, in the antenna apparatus according to the present embodiment, the same effects as in the first embodiment can be obtained even if the positions of the feed portion or the short-circuit portion in the radiation conductor is changed. 
     A second embodiment according to the present invention is described with reference to the drawings. The present embodiment is an example where the antenna apparatus according to the first embodiment is applied to a radio communication device. Although radio communication devices include PDAs having communication functions and personal computers, an example where the antenna apparatus is applied to general mobile phones is described. 
       FIG. 6  schematically shows the appearance of a mobile phone according to the present embodiment. As shown in  FIG. 6 , a mobile phone B according to the present embodiment comprises an upper casing  11   a , a lower casing  11   b , and a hinge  25  for rotatably connecting these members. The upper casing  11   a  comprises a built-in antenna  23 , a speaker  21 , and an LCD display screen  27 . The lower casing  11   b  comprises a microphone  17  and a button operation portion  15 . 
       FIG. 7  shows an example of the internal structure of the mobile phone B according to the present embodiment. As shown in  FIG. 7 , the mobile phone B according to the present embodiment comprises a control unit  231 , the antenna  23  (AT), a key input portion (button operation portion)  15 , the speaker  21 , the LCD display screen (display unit)  27 , the microphone  17 , a storage memory  232 , and a radio unit  238 . The control unit  231  unifies and controls the aforementioned individual members. The radio unit  238  comprises the matching circuit  150  as shown in  FIG. 2  and the RF circuit connected thereto that is not shown in the drawings. As stated above, by using the antenna apparatus to which the matching circuit  150  disposed for impedance matching is connected, return loss (R L ) can be reduced via the matching circuit  150  in two frequency bands, such as in the 800 MHz band and the 1700 to 1900 MHz band, thereby realizing antenna characteristics capable of use in a desired plurality of frequency bands. 
     Further, when the positional relationship among the ground conductor  1 , the radiation conductor  3 , and the short-circuit portion  7  of the antenna apparatus as shown in  FIG. 5(B)  is assumed, it is assumed that a user&#39;s face (or head) approaches the LCD display side (denoted by broken line of reference  11   a  in  FIG. 5(B) ) of the upper casing  1  as during a telephone call. In this case, by disposing the feed portion  5  and the short-circuit portion  7  such that resonant frequency differs due thereto and by adjusting the frequency via the matching circuit  150 , antenna characteristics are made less susceptible to influences of circumstances changing in accordance with usage forms. In this respect, the mobile phone B according to the present embodiment is different from a mobile phone having a conventional configuration ( FIG. 15 ) where the first conductor strip  212   a  and the second conductor strip  212   b  of the radiation conductor plate  212  and the connection conductor plate  213  are disposed, so that they resonate with different frequencies. 
     A mobile phone according to a third embodiment of the present invention is described with reference to the drawings.  FIGS. 8 and 9  show perspective views ( FIGS. 8(A) and 9(A) ) of a mobile phone according to the third embodiment of the present invention, showing the appearances of the slide mobile phone when it is open and closed; side views ( FIGS. 8(B) and 9(B) ) indicating the positional relationships of the antenna corresponding to each perspective view; and a plan view ( FIG. 8(C) ) of the antenna apparatus. As shown in  FIGS. 8(A) and 9(A) , the slide mobile phone according to the present embodiment comprises a first casing  51  and a second casing  53 . The slide mobile phone comprises an LCD display portion  57  disposed on the first casing  51 , a first operation portion (input portion)  55 , and a second operation portion  62  disposed on the second casing  53 . The first casing  51  and the second casing  53  can be used with a slide as indicated by an arrow shown by reference AR 5  ( FIG. 9 ). In the closed state as shown in  FIG. 8(A) , the first casing  51  and the second casing  53  are in a state where the front and the back thereof are joined together, including during telephone call standby mode or an input operation using the first operation portion  55 , for example. In the opened state as shown in  FIG. 9(A) , the area of contact surface regarding the first casing  51  and the second casing  53  is reduced, and a telephone call is generally made in this state. As shown in  FIG. 8(C) , a feed portion  72  of a radiation conductor  65  ( FIG. 8  (B)) is connected to the RF circuit through a microstrip line and the matching circuit  150 , and a short-circuit portion  71  is connected to a ground GND through a microstrip line. 
     In the closed state as shown in  FIG. 8(B) , even when the positions of a first circuit board  61  disposed inside the first casing  51  and a radiation conductor  65  are changed as in  FIG. 9(B) , the radiation conductor  65  being disposed via the short-circuit portion  71  that is disposed on the opposite side of the LCD display portion  57  and that extends from a second circuit board  63  (ground conductor) that is disposed inside the second casing  53  to the back of the normal direction of the display surface of the LCD display portion  57 , the short-circuit portion  71  is disposed on the end portion direction of the second circuit board indicated by the arrow AR 5  in the second casing  53  and comprises a configuration where frequencies are adjusted via the matching circuit. Thus, in both states as shown in  FIG. 8(B)  and  FIG. 9(B) , the reflection characteristics of the antenna apparatus (the radiation conductor  65 ) are not significantly changed. Also, because the short-circuit portion  71  is disposed in the vicinity of the open-end portion of the ground conductor plate (second circuit board)  63 , even if metal exists nearby, for example, the short-circuit portion  71  is less susceptible to the influences thereof. Thus, even in the case where the antenna apparatus is applied to the slide mobile phone according to the present embodiment, the antenna characteristics are not liable to change between standby and telephone calls, providing an advantage that enables stable telephone calls and communication. 
       FIG. 10  shows a mobile phone according to the variation of the present invention, illustrating the case where the antenna apparatus according to the first embodiment of the present invention is applied to a rotary mobile phone.  FIG. 10(A)  shows a mode of use when the device is in operation, indicating the state where a first casing  10   a  and a second casing  10   b  are disposed in a substantially parallel manner having a rotation axis  20  therebetween.  FIG. 10(C)  shows a mode when standing by, indicating the state where the first casing  10   a  almost covers the second casing  10   b.    
       FIG. 10(B)  shows a transitional state of rotation. Even in such a case, by disposing the antenna apparatus according to the first embodiment of the present invention inside the first casing  10   a , the antenna characteristics are made less susceptible to influences of circumstances, so that an advantage is provided by which good antenna characteristics can be obtained in any of the states of  FIGS. 10(A) to 10(C) . 
     An antenna apparatus according to a fourth embodiment of the present invention is described with reference to the drawings. As shown in  FIG. 11(A) , in the present embodiment, a notch cutting is provided in the radiation conductor between the feed portion and the short-circuit portion, thereby adjusting the distance between a feed portion  87  and a short-circuit portion  85 . The antenna apparatus according to the present embodiment comprising a ground conductor  81  and a radiation conductor  83  has a notch cutting portion  91  formed in an L-shaped manner from the top side of the radiation conductor  83  as shown in the drawings, which is formed in an area including a straight line that connects the feed portion  87  with the short-circuit portion  85 . In such a configuration, the electrical length between the feed portion  87  and the short-circuit portion  85  is based on the length of reference L 11  circling the notch cutting portion  91  rather than the length of the top side as shown in the drawings (reference L 15 ). Also, in  FIG. 11(B) , a large notch cutting portion  91 ′ is provided on the top side of a radiation conductor  83 ′. Also in this configuration, a substantial antenna length is determined on the basis of reference L 11 ′ rather than in accordance with a length L 15 ′ indicated by reference  91 ′. In this manner, by providing a notch cutting on an area including a straight line that connects the feed portion  87  with the short-circuit portion  85  in the radiation conductors  83  and  83 ′, adjustment to an effective antenna length can be achieved and the frequency range in which impedance matching can be achieved is widened. This is advantageous in that it effectively works especially when securing antenna characteristics for low frequency bands. 
     A mobile phone according to a fifth embodiment of the present invention in which the antenna apparatus according to each of the aforementioned embodiments is used is described.  FIG. 12  shows a side view of the mobile phone according to the present embodiment and also shows the internal configuration thereof. As shown in  FIG. 12 , a mobile phone  100  according to the present embodiment shows an example of the configuration of a folding type mobile phone where a first casing  101  and a second casing  103  are capable of folding such that the LCD display portion and the input operation portion are disposed face-to-face with a rotation axis  105  as an axis. A radiation conductor  101   b  or  103   b  is disposed on either a first circuit board  101   a  or a second circuit board  102   b  disposed on both the first casing  101  and the second casing  103 , the radiation conductor extending from the vicinity of one end of the rotation axis  105  to the other end that comes away from the rotation axis  105  (in the drawing, the radiation conductor  101   b  is disposed and the radiation conductor  103   b  is shown with broken lines, as it is not disposed). The circuit board  101   a  and the circuit board  102   b  are connected. In the so-called clamshell type mobile phone as shown in  FIG. 12 , the difference between the dispositions of the radiation conductor  101   b  and the metal circuit board (ground conductor)  102   b  during folding can be adjusted via the aforementioned matching circuit, so that an advantage is provided by which suitable antenna characteristics can be obtained in any usage form. Further, such characteristics are less susceptible to influences of circumstances, since the short-circuit portion is disposed in the vicinity of the open end portion of either the circuit board  101   a  or the circuit board  102   b  when the radiation conductor is disposed on the position of either  101   b  or  103   b.    
     An antenna apparatus according to a sixth embodiment of the present invention is described with reference to the drawings.  FIG. 13  shows an example of the configuration of the antenna apparatus according to the present embodiment. As shown in  FIG. 13 , an antenna apparatus  160  according to the present embodiment comprises a ground conductor  161 , a radiation conductor  163 , a GND ground point  173  disposed on the ground conductor  161 , and a variable inductor  174  for adjusting frequencies disposed between a short-circuit portion  165  that short-circuits the ground conductor  161  and the radiation conductor  163  and the GND ground point  173 . An inductance L′ between the short-circuit portion  165  and the GND ground point  173  is represented by the following formula.
 
 L′=L+α 
 
     In this case, L represents the inductance between the short-circuit portion  165  and the GND ground point  173  without the variable inductor  174 , and α represents the volume of adjustment by variable inductance. Frequencies f′ depends on L′, namely, L+α. Thus, an advantage is provided by which frequency adjustment becomes possible via the volume of α. 
     An antenna apparatus according to a seventh embodiment of the present invention is described with reference to the drawings.  FIG. 14  shows a main portion of the antenna apparatus according to the present embodiment of the present invention. As shown in  FIG. 14 , an antenna apparatus  180  according to the present embodiment of the present invention comprises a ground conductor  181 , a radiation conductor  183 , and a parasitic element  193  extending from a short-circuit portion  185  to the internal area of a notch cutting  191  provided in the radiation conductor  183 . By disposing the parasitic element  193  in this manner, an advantage is provided by which the band of the antenna is widened. By appropriately adjusting the length of the parasitic element  193  to about λ/4 of a desired frequency, for example, antenna characteristics can be improved. 
     As stated above, the embodiments of the present invention are described with reference to the drawings. However, the present invention is not limited to these embodiments, and it is obvious that various modifications are possible. 
     The present invention can be applied to various antenna apparatuses and a communication apparatus using an antenna apparatus. For example, the present invention also improves antenna characteristics when used for straight type mobile phones, and the antenna can be applied to both slide types and folding types.