Patent Publication Number: US-6700543-B2

Title: Antenna element with conductors formed on outer surfaces of device substrate

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an antenna element for use in reception or transmission of radio waves, and more particularly, to an antenna element which has conductors formed on outer surfaces of a device substrate. 
     2. Description of the Related Art 
     At present, radio communication apparatuses called a mobile telephone and the like are pervasive in general users, and a reduction in size and weight is required for the radio communication apparatuses. The radio communication apparatus receives and transmits radio waves through an antenna element, where the total length of a conductive line is closely related to the wavelength of a radio wave transmitted or received thereby. 
     For this reason, since a simple reduction in the length of the conductive line causes a rise in the resonant frequency, difficulties are encountered in efficiently radio communicating a radio wave at a predetermined frequency. To address this problem, a variety of techniques have been devised for reducing the shape of an overall antenna element while maintaining a required resonant frequency. 
     For example, an antenna element called a helical antenna has a conductive line formed in a spiral shape, while an antenna element called a meander antenna has a conductive line in a meandering shape. While these antennas do not achieve a reduction in the total length of the conductive line, the overall shape can be substantially reduced. 
     There is also an antenna element called a dielectric antenna which has a conductive line formed on the surface of a dielectric material to reduce the length of the conductive line. Since the wavelength of a radio wave is reduced within a member having a high dielectric constant or permeability, the formation of the conductive line on or within a dielectric material or a magnetic material results in a reduction in the total length thereof. 
     Moreover, there is an antenna element called a loaded antenna which adds a reactance element, an inductance element or a capacitance element to a conductive line to reduce the length of the conductive line. It should be understood that a variety of foregoing techniques may be combined to create, for example, an antenna element which has a conductive line formed in a helical shape or in a meander shape on the surface of a dielectric material. 
     In another technique, a ground electrode is connected to a conductive line of an antenna element by a short pin to generate a current through the short pin in opposite phase to that in the conductive line in an opposite direction. Since the opposite phase current generated in the opposite direction in this manner can be regarded as an in-phase current generated in the same direction, a radiation resistance of the antenna element can be increased as a result. 
     A variety of techniques as described above permit an improvement in the performance of antenna elements without uselessly increasing the size thereof. However, in the helical antenna and meander antenna, a long conductive line is bent to reduce the area occupied thereby, so that adjacent portions of the conductive line are electromagnetically coupled to cause an increase in surface current and high frequency loss. 
     To solve the problem as mentioned, the present inventor invented an antenna element which has a conductive line formed in a shape different from the helical shape or meander shape on the surface of a dielectric material, and filed the invention as Japanese Patent Application No. 2001-026002. This application discloses an antenna element which has a first conductor and a second conductor, parallel to each other, connected by a short-circuit conductor to form a loaded inductance. 
     Referring now to FIGS. 1 and 2, the antenna element disclosed in the above-cited application will be described below in brief, as a related art which precedes the present invention and is not known. The antenna element described below was filed in Japan on Feb. 1, 2001 as Japanese Patent Application No. 2001-026002, and filed in the United States of America on Jan. 31, 2002 as U.S. Ser. No. 10/059423 by the present inventor. However, this application has not been opened in any country, so that this is not a prior art but merely a related art of the present invention. 
     Antenna element  100  in the aforementioned application has device substrate  101  made of a dielectric material, and conductive line  102  formed of a printed wire on a front surface and a bottom surface of device substrate  101 . Conductive line  102  is comprised of power supply conductor  103 , first conductor  104 , short-circuit conductor  105 , and second conductor  106 , each of which is linearly formed in succession. 
     More specifically, power supply conductor  103  of conductive line  102  comprises a linear portion formed from the bottom surface to the front surface of device substrate  101 , while first conductor  104  comprises a linear portion formed from an upper end which is a terminate end of power supply conductor  103  and bent at a right angle to the right in the figure. Short-circuit conductor  105  comprises a linear portion formed from a right end which is a terminate end of first conductor  104  and bent upward at a right angle in the figure, i.e., in the opposite direction to power supply conductor  103 , while second conductor  106  comprises a linear portion formed from an upper end which is a terminate end of short-circuit conductor  105  and bent at a right angle to the left in the figure, and positioned in parallel to first conductor  104 . 
     Then, antenna apparatus  200  using antenna element  100  as described above comprises a circuit board  201  made of glass epoxy resin, ethylene tetrafluoride or the like, as illustrated in FIG. 2. A copper foil is adhered in a lower half and the like of a front surface of circuit board  201  to form a ground electrode  202 . 
     Ground electrode  202  is partially formed with a recess in which power supply electrode  204  is formed for power supply circuit  203  (for example, a coaxial cable) which serves as a power supply means. Then, antenna element  100  is mounted on an upper half of the front surface of circuit board  201  on which ground electrode  202  is not formed. Power supply conductor  103  is connected to power supply electrode  204 . 
     In antenna element  100  of the structure as described above, conductive line  102  can be reduced in length since first conductor  104  and second conductor  106 , positioned in parallel to each other, act as a loaded inductance. In addition, since conductive line  102  is generally bent in an inverted C-shape, the overall shape can be reduced in size. 
     Unlike the meander antenna, helical antenna and the like, in spite of the reduction in size, first conductor  104  and second conductor  106 , positioned in parallel to each other, are sufficiently spaced away from each other, so that their electromagnetic coupling is reduced, thereby making it possible to realize radio communications with a high gain, high efficiency and wide band. 
     In antenna element  100 , since short-circuit conductor  105  mainly transmits and receives radio waves, the transmission/reception have a directivity in the horizontal direction in the figure orthogonal to the longitudinal direction of the short-circuit conductor  105 . For this reason, if a conductor such as ground electrode  202  is positioned in a direction orthogonal to short-circuit conductor  105 , the conductor will impede the transmission/reception of radio waves through short-circuit conductor  105 . 
     To solve the foregoing problem, it is contemplated to avoid forming ground electrode  202  and the like in the direction orthogonal to short-circuit conductor  105 . However, this solution would cause a reduction in the area of ground electrode  202  available for mounting circuit parts (not shown). In other words, it is necessary to minimize an antenna mounting area on which ground electrode  202  is not formed in order to maximize an area available for mounting circuit parts. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a highly efficient antenna element which is capable of minimizing an antenna mounting area in a structure which has a first conductor and a second conductor positioned in parallel to each other and connected through a short-circuit conductor. 
     Similarly to the aforementioned related art, an antenna element of the present invention includes a device substrate and a conductive line which is comprised of at least a power supply conductor, a first conductor, a short-circuit conductor, and a second conductor. The device substrate is made of at least one of a dielectric material and a magnetic material, and is formed with the power supply conductor, first conductor, short-circuit conductor, and second conductor. The power supply conductor is made of a linear conductor, and supplied with electric power at a leading end thereof. The first conductor is connected to a terminate end of the power supply conductor at a right angle, while the short-circuit conductor is connected to a terminate end of the first conductor at a right angle on the opposite side of the power supply conductor. The second conductor is connected to a terminate end of the short-circuit conductor at a right angle, and positioned in parallel to the first conductor. 
     In the antenna element of the present invention as described above, the device substrate is also formed with a ground conductor which has a terminate end connected to the conductive line, and a leading end applied with a ground potential. 
     Since this structure allows the ground conductor to function in a manner similar to a conventional short-pin, the antenna element can have an increased radiation resistance. Also, impedance matching can be adjusted by changing reactance and/or resistance of input impedance of the conductive line. The resonance frequency can also be adjusted by a position at which the ground conductor is connected to the conductive line. Further, the performance can be improved in the antenna element which includes a loaded inductance formed of the parallel first and second conductors. 
     In another implementation of the antenna element as described above, a capacitive conductor having a given capacitance is formed as part of the conductive line, and connected to a terminate end of the second conductor. Thus, the conductive line can be reduced in length by a loaded capacitance of the capacitive conductor, so that the antenna element can be reduced in size. 
     The ground conductor has a terminate end electromagnetically coupled to the conductive line in non-contact manner. Since the electromagnetic coupling eliminates the need for directly connecting the ground conductor to the conductive line, the ground conductor can be readily formed. 
     A first antenna apparatus according to the present invention includes an antenna element, a circuit board, a ground electrode, and a ground wire. The antenna element includes the antenna element according to the present invention, and the circuit board has the antenna element mounted on a front surface thereof. The ground electrode is formed at a position spaced apart from the antenna element on the front surface of the circuit board for generating a ground potential. The ground wire is formed on the front surface of the circuit board, and has a leading end connected to the ground electrode, and a terminate end connected to a leading end of the ground conductor. 
     A second antenna apparatus according to the present invention includes a device substrate, a conductor line, a circuit board, a ground electrode, and a ground wire. The conductive line is comprised of a power supply conductor, a first conductor, a short-circuit conductor, and a second conductor. The device substrate is made of at least one of a dielectric material and a magnetic material, and is formed with the power supply conductor, first conductor, short-circuit conductor, and second conductor. The power supply conductor is made of a linear conductor, and is supplied with electric power with a leading end thereof. The first conductor is connected at a right angle to a terminate end of the power supply conductor, while the short-circuit conductor is connected at a right angle to a terminate end of the first conductor on the opposite side of the power supply conductor. The second conductor is connected at a right angle to a terminate end of the short-circuit conductor, and positioned in parallel to the first conductor. The circuit board is mounted with the device substrate on a front surface thereof. The ground electrode is formed at a position spaced apart from the device substrate on the front surface of the circuit board for generating a ground potential. The ground wire is formed on the front surface of the circuit board, and has a leading end connected to the ground electrode, and a terminate end connected to a leading end of the ground conductor. 
     In the antenna apparatus of the present invention configured as described above, since the ground potential at the ground electrode is applied to the ground conductor of the antenna element through the ground wire, the ground conductor of the antenna element can function in a manner similar to a conventional short pin. 
     In another implementation of the antenna apparatus as described above, a capacitive conductor having a given capacitance is connected to a terminate end of the second conductor and additionally formed as part of the conductive line. Thus, the conductive line can be reduced in length by a loaded capacitance of the capacitive conductor, making it possible to reduce the antenna apparatus as well as the antenna element in size. 
     Also, since the ground conductor has a terminate end electromagnetically coupled to the conductive line in non-contact manner, the ground conductor need not be directly connected to the conductive line. Consequently, the ground conductor, for example, may be formed only on the front surface of he circuit board without extending to the antenna element, thereby facilitating the formation of the ground conductor. 
     A third antenna apparatus according to the present invention includes a conductive line, a device substrate, a circuit board, a ground electrode, a power supply electrode, and a ground wire. The device substrate is made of at least one of a dielectric material and a magnetic material, and is formed with the conductive line. The circuit board is mounted with the device substrate on a front surface thereof. The ground electrode is formed at a position spaced apart from the device substrate on a front surface of the circuit board for generating a ground potential. On the front surface of the circuit board, the power supply electrode has a terminate end connected to the conductive line on the device substrate, and is supplied with electric power at a leading end. The ground wire, which is formed on the front surface of the circuit board, has a leading end connected to the ground electrode, and a terminate end connected to the power supply electrode. 
     As appreciated from the foregoing, since the ground potential at the ground electrode is applied to the power supply electrode through the ground wire in the antenna apparatus according to the present invention, the ground wire functions in a manner similar to a conventional short pin. In addition, the present invention can provide a reduction in the entire size of the antenna apparatus, as well as a wider bandwidth and a higher efficiency for the same. 
     The above and other objects, features and advantages of the present invention will become apparent from the following description with reference to the accompanying drawings which illustrate examples of the present invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view illustrating an antenna element according to an unknown related art, invented by the present inventor; 
     FIG. 2 is a perspective view illustrating an antenna apparatus according to an unknown related art, invented by the present inventor; 
     FIG. 3 is a perspective view illustrating an antenna apparatus according to one embodiment of the present invention; 
     FIGS. 4 a - 4   c  are perspective views illustrating several exemplary modifications to the antenna element; 
     FIG. 5 is a perspective view illustrating a first exemplary modification to the antenna apparatus; 
     FIG. 6 is a perspective view illustrating a second exemplary modification; 
     FIG. 7 is a perspective view illustrating a third exemplary modification; 
     FIG. 8 is an exploded perspective view illustrating a fourth exemplary modification; 
     FIG. 9 is an exploded perspective view illustrating a fifth exemplary modification; and 
     FIG. 10 is an exploded perspective view illustrating a sixth exemplary modification; 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     One embodiment of the present invention will hereinafter be described with reference to FIGS. 3 and 4. It should be first noted however that with respect to the following embodiment, parts identical to those of antenna element  100  and antenna apparatus  200  described above are designated by the same names, and detailed description thereon is omitted. 
     Also, while in the following embodiments, directions such as front and back, right and left, and up and down are referred to in correspondence to the drawings, these directions are used for convenience of simplifying the description and do not at all limit the directions in actual manufacturing and use of associated products. 
     Referring to FIG. 3, like the aforementioned antenna element  100 , antenna element  300  in this embodiment comprises device substrate  101  made of a dielectric material, and conductive line  102  on front and bottom surfaces of device substrate  101 . Conductive line  102  is comprised of a power supply conductor  103 , first conductor  104 , short-circuit conductor  105 , and second conductor  106 . 
     Similarly, like the aforementioned antenna apparatus  200 , antenna apparatus  400  in this embodiment has ground electrode  202  in a lower half and the like of a front surface of circuit board  201 , and power supply electrode  204  of power supply circuit  203 , serving as a power supply means, formed in a recess of ground electrode  202 . 
     Antenna element  300  is mounted in an upper half of the front surface of circuit board  201  on which ground electrode  202  is not formed. Power supply conductor  103  of antenna element  300  is connected to power supply electrode  204 . 
     However, unlike the aforementioned antenna element  100 , antenna element  300  in this embodiment additionally has ground conductor  301  formed on a side surface of device substrate  101 . Ground conductor  301  is connected to conductive line  102 . 
     More specifically, ground conductor  301  has a terminate end connected near a leading end of short-circuit conductor  105 , and a leading end positioned on the boundary of a side surface and a rear surface of device substrate  101 . 
     Then, unlike the aforementioned antenna apparatus  200 , antenna apparatus  400  in this embodiment has ground wire  401  on the front surface of circuit board  201 . Ground wire  401  has a leading end connected to ground electrode  202 . 
     Since ground wire  401  has a terminate end connected to a leading end of ground conductor  301  of antenna element  300 , a ground potential at ground electrode  202  is applied to ground conductor  301  of antenna element  300  through ground wire  401 . 
     In the foregoing structure, antenna element  300  in this embodiment is similar to the aforementioned antenna element  100  in that first conductor  104  and second conductor  106  positioned in parallel to each other act as a loaded inductance, so that the length of conductive line  102  is reduced to make the overall shape smaller, while ensuring a desired resonant frequency. 
     Unlike the meander antenna, helical antenna and the like, in spite of the reduction in shape, first conductor  104  and second conductor  106  positioned in parallel to each other are sufficiently spaced apart from each other, so that their electromagnetic coupling is reduced, making it possible to realize radio communications with a high gain, high efficiency, and wide band. 
     In antenna apparatus  400  in this embodiment, however, ground conductor  301  is connected at a predetermined position of conductive line  102  of antenna element  300 , so that ground conductor  301  is applied with the ground potential at ground electrode  202  through ground wire  401 . 
     Thus, ground conductor  301  can function as a conventional short pin to increase a radiation resistance of antenna element  300 , so that impedance matching can be adjusted by changing reactance and/or resistance of input impedance of conductive line  102 . 
     In other words, since improved performance can be achieved for antenna element  300  which uses parallel first conductor  104  and second conductor  106  as a loaded inductance, antenna element  300  can transmit and receive radio waves relatively satisfactorily even if a conductor such as ground electrode  202  is positioned in a direction orthogonal to short-circuit conductor  105 . 
     For this reason, since ground electrode  202  can be placed relatively close to antenna element  300  even if ground electrode  202  is positioned in the direction orthogonal to short-circuit conductor  105 , antenna apparatus  400  can be reduced in size without the need for reducing ground electrode  202  in a downward or a lateral direction in the figure. 
     The present invention is not limited to the foregoing embodiment, but a variety of alterations are permitted without departing from the spirit and scope of the invention. For example, in antenna element  300  illustrated in the foregoing embodiment, conductive line  102  is comprised of power supply conductor  103 , first conductor  104 , short-circuit conductor  105  and second conductor  106 . Alternatively, as antenna elements  501 - 503  illustrated in FIGS. 4 a - 4   c , capacitive conductors  507 - 509  having given capacitances may be added as parts of conductive lines  504 - 506 . 
     In this event, as antenna element  501  illustrated in FIG. 4 a , connection conductor  510  formed on the top surface of device substrate  101  may have a leading end connected to a terminate end of second conductor  106  on the front surface, and capacitive conductor  507  likewise formed on the top surface of device substrate  101  may be connected to a terminate end of connection conductor  510 . 
     Also, as antenna element  502  illustrated in FIG. 4 b , capacitive conductor  508  formed over the entire top surface of device substrate  101  may be connected directly to second conductor  106 . Further, as antenna element  503  illustrated in FIG. 4 c , capacitive conductor  509  formed over the entire top surface of device substrate  101  may be used as second conductor  106 . 
     As noted, the capacitances of capacitive conductors  507 - 509  as mentioned above are generated between capacitive conductors  507 - 509  and ground electrode  202 , so that the capacitances of capacitive conductors  507 - 509  vary depending on their sizes and shapes, relationships with ground electrode  202  in distance and shape, and the like. 
     For actually forming capacitive conductors  507 - 509 , the capacitances are adjusted corresponding to the resonant frequencies of conductive lines  504 - 506  by a computer simulation or the like. 
     Since antenna elements  501 - 503  as described above provide a reduction in resonant frequency by virtue of loaded capacitances of capacitive conductors  507 - 509 , antenna elements  501 - 503  can be reduced in overall shape, with reduced conductive lines  504 - 506 , without relatively increasing the resonant frequency. 
     Also, since illustrative antenna apparatus  400  in the foregoing embodiment adjusts impedance matching by changing reactance and resistance of input impedance of conductive line  102 , ground conductor  301  of antenna element  300 , to which ground wire  401  is connected, is connected near a leading end of short-circuit conductor  105 . 
     However, as antenna apparatus  600  illustrated in FIG. 5, ground conductor  603  of antenna element  602 , to which ground conductor  601  is connected, may be connected to first conductor  104 . Further alternatively, as antenna apparatus  700  illustrated in FIG. 6, ground conductor  702  of antenna element  701  may be connected near a terminate end of short-circuit conductor  105 . 
     Since antenna apparatus  600 ,  700  as described above has a pass of current defined by a path extending from a leading end of power supply electrode  204  to a terminate end of conductive line  102  and turning back to a leading end of ground wire  601 ,  401 , the resonant frequency can be adjusted by changing the position of conductive line  102  at which ground conductor  603 ,  702  is connected, and the lengths of ground wire/conductor  601 ,  603 ,  401 ,  702 . 
     While antenna apparatus  400  in the foregoing embodiment illustrates ground conductor  301  of antenna element  300  directly connected to conductive line  102 , ground conductor  802  of antenna element  801  may be electromagnetically coupled to conductive line  102  in non-contact manner, as antenna apparatus  800  illustrated in FIG.  7 . 
     Further, while antenna apparatus  400  in the foregoing embodiment illustrates that ground conductor  301  connected to conductive line  102  is also formed in antenna element  300 , ground wire  901  formed only on the front surface of circuit board  201  may be connected to conductive line  504  of antenna element  902 , as antenna apparatus  900  illustrated in FIG.  8 . 
     Particularly, since this antenna apparatus  900  has capacitive conductor  507  formed on the top surface of antenna element  902 , ground wire  901  is readily connected to capacitive conductor  507 . In addition, when ground wire  901  is connected to a terminate end of conductive line  504  in this manner, conductive line  504  and ground wire  901  can function as a folded antenna. 
     Connection  903  is formed integrally with terminate ends of power supply electrode  204  and ground wire  901 , and connection  904  in the same shape is also formed integrally with power supply conductor  103  and capacitive conductor  507  on a back surface of antenna element  902 . 
     These connections  903 ,  904  are connected by soldering to electrically connect power supply conductor  103  to power supply electrode  204 , electrically connect capacitive conductor  507  to ground wire  901 , and secure antenna element  902  integrally with circuit board  201 . 
     As antenna apparatus  1000  illustrated in FIG. 9, ground wire  1001  formed only on the front surface of circuit board  201  may be electromagnetically coupled to conductive line  504  of antenna element  902  in non-contact manner. 
     In this configuration, antenna apparatus  1000  can be readily manufactured because ground wire  1001  formed on circuit board  201  need not be directly connected to conductive line  504  formed on device substrate  101 . 
     While power supply conductor  103  is not illustrated in FIGS. 8 and 9, it is actually formed on the bottom surface of device substrate  101  and connected to power supply electrode  204 , as is the case with FIG.  3  and other figures. 
     In addition, since power supply electrode  204  connected to conductive line  102  of antenna element  100  also functions as an antenna line, ground wire  1101  formed on the surface of circuit board  201  may be connected to power supply electrode  204  formed on the surface of circuit board  201 , as antenna apparatus  1100  illustrated in FIG.  10 . 
     In this configuration, such antenna apparatus  1100  readily provides a reduction in resonant frequency, an increase in bandwidth and radiation efficiency, and the like by forming longer ground wire  1101 , and defining a position at which ground wire  1101  is connected in close proximity to a leading end of power supply electrode  204 . 
     Further, since the formation of ground wire  1101  longer than power supply electrode  204  results in an increased antenna length and resulting reduction in resonant frequency, as described above, the whole apparatus can be relatively reduced in size. Provided that antenna apparatus  1100  has a lower resonant frequency in this manner, conductive line  102  may be made wider to increase the bandwidth. 
     Moreover, since no ground conductor need be formed in antenna element  1100  and power supply electrode  204  can be formed integrally with ground wire  1101 , antenna apparatus  1100  can be simplified in structure. 
     The foregoing structure in which ground wire  1101  is connected to power supply electrode  204  on the surface of circuit board  201  may be applied to a conventional dielectric antenna which does not comprise parallel first conductor  104  and second conductor  106 . 
     While one each of ground conductor  301  and ground wire  401  are provided in antenna element  300  and the like in the foregoing illustrative embodiment, a plurality of these elements may be provided. Since antenna element  300  functions similarly to a folded antenna by the action of ground conductor  301  and ground wire  401 , an increase in the number of ground conductor  301  and ground wire  401  can result in an increased radiation resistance and an improved radiation efficiency. Alternatively, the radiation resistance can be increased to improve the radiation efficiency by increasing line widths of ground conductor  301  and ground wire  401 . 
     While preferred embodiment(s) of the present invention has (have) been described using specific terms, such description is for illustrative purposes only, and it is to be understood that changes and variations may be made without departing from the spirit or scope of the following claims.