Patent Publication Number: US-6700541-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 its 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 path 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 path 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 path formed in a spiral shape, while an antenna element called a meander antenna has a conductive path in a meandering shape. While these antennas do not achieve a reduction in the total length of the conductive path, the overall shape can be substantially reduced. 
     There is also an antenna element called a dielectric antenna which has a conductive path formed on the surface of a dielectric material to reduce the length of the conductive path. Since the wavelength of a radio wave is reduced within a member having a high dielectric constant or permeability, the formation of the conductive path 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 path to reduce the length of the conductive path. It should be understood that a variety of foregoing techniques may be combined, for example, to create an antenna element which has a conductive path formed in a helical shape or in a meander shape on the surface of a dielectric material. 
     An antenna element can be made compact by a variety of techniques as described above. However, in the helical antenna and meander antenna, a long conductive path is bent to reduce the area occupied thereby, so that adjacent portions of the conductive path 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 path 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 FIG. 1, the antenna element disclosed in the 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 in rectangular solid, and conductive path  102  formed of a printed wire on the front surface of device substrate  101  to implement a dielectric antenna as described above. Conductive path  102  is comprised of power supply conductor  103 , first conductor  104 , short-circuit conductor  105 , and second conductor  106 . 
     More specifically, power supply conductor  103  of conductive path  102  comprises a linear portion formed from the bottom surface to front surface of device substrate  101 , while first conductor  104  comprises a linear portion formed from an upper end or 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 or 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 or terminate end of short-circuit conductor  105  and bent at a right angle to the left in the figure, and positioned in parallel with first conductor  104 . 
     In antenna element  100  of the structure as described, conductive path  102  can be reduced in length since first conductor  104  and second conductor  106 , positioned in parallel with each other, act as a loaded inductance. In addition, since conductive path  102  is generally bent in a U-shape (which has three straight lines forming two right angles), the overall shape can be made compact. 
     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 with 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 high gain, high efficiency and wide band. 
     Antenna element  100  of the structure described above presents a rise in the resonant frequency as the overall shape is simply reduced in shape, whereas the resonant frequency is reduced as the loaded inductance is increased. In other words, when the resonant frequency is maintained constant, an increase in the loaded inductance can result in a relative reduction in the size of the overall shape. 
     The loaded inductance of conductive path  102  in the aforementioned antenna element  100  may be increased by spacing first conductor  104  and second conductor  106  away from each other, reducing the width of conductive path  102 , extending the length of conductive path  102  such as first/second conductors  104 ,  106 , and the like. 
     However, for spacing first conductor  104  and second conductor  106  away from each other, device substrate  101  must be extended, resulting in an increased size of the overall shape. The width of conductive path  102  has a lower limit determined by a thermal condition, and a reduction in the width of the conductive path  102  will cause a reduced bandwidth and an increased high frequency loss, so that the width of conductive path  102  cannot be reduced without prudence. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a antenna element which is made compact, and has a first conductor and a second conductor positioned in parallel with each other and connected through a short-circuit conductor. 
     The antenna element according to the present invention has a first conductor, a short-circuit conductor, a second conductor, and a device substrate. The device substrate is made of at least one of a dielectric material and a magnetic material, and is formed with the first conductor, short-circuit conductor and second conductor on its outer surface. The first conductor is made of a linear conductor supplied with electric power at a leading end thereof, while the short-circuit conductor is connected perpendicularly to a terminate end of the first conductor. The second conductor is connected at a right angle to a terminate end of the short-circuit conductor and positioned in parallel with the first conductor. 
     In a first aspect of the antenna element described above, an extended portion bent in a U-shape is formed in at least one of the first conductor and the second conductor. In a second aspect, the first conductor and second conductor are formed continuously on a plurality of outer surfaces of the device substrate. In a third aspect, the first conductor and second conductor are formed continuously on a plurality of outer surfaces of the device substrate, and an extended portion bent in a U-shape is formed in at least one of the first conductor and second conductor. 
     Thus, the antenna element of the present invention can extend the conductive path without increasing the size of the device substrate even though the parallel first conductor and second conductor are connected through the short-circuit conductor on the outer surface of the device substrate. It is therefore possible to reduce the size of the device substrate without relatively extending the conductive path, and reduce the size of the overall shape while ensuring a desired resonant frequency. 
     In another implementation of the antenna element as described above, a power supply conductor is also formed as part of the conductive path. The power supply conductor has a terminate end connected at a right angle to the leading end of the first conductor, and positioned on the opposite side to the short-circuit conductor. By supplying electric power to a leading end of the power supply conductor, the electric power can be supplied to the first conductor from the power supply conductor. 
     Since the first conductor and second conductor are formed from the front surface to the back surface across one side surface of the device substrate formed in rectangular solid, the conductive path can be extended, effectively making use of a plurality of outer surfaces of the solid device substrate. 
     Since the first conductor is formed at different positions on the front surface and rear surface of the device substrate, a portion of the first conductor positioned on the front surface of the device substrate can be spaced apart from a portion of the first conductor positioned on the back surface to reduce a distributed capacitance, thereby making it possible to prevent a reduction in the bandwidth of communication frequencies due to accumulation of unwanted electromagnetic energy. 
     Since the second conductor is formed at different positions on the front surface and rear surface of the device substrate, a portion of the second conductor positioned on the front surface of the device substrate can be spaced apart from a portion of the second conductor positioned on the back surface to reduce a distributed capacitance, thereby making it possible to prevent a reduction in the bandwidth of communication frequencies due to accumulation of unwanted electromagnetic energy. 
     Also, by virtue of: 
     a conductive pathar connection of a leading end of the extended portion formed and connected to the leading end of the first conductor to a terminate end of the power supply conductor; 
     a linear connection of a terminate end of the extended portion formed and connected to the terminate end of the first conductor to a leading end of the short-circuit conductor; 
     a linear connection of the leading end of the extended portion formed and connected to the leading end of the second conductor to a terminate end of the short-circuit conductor; and 
     a linear connection of the terminate end of the extended portion formed and connected to the terminate end of the second conductor to a leading end of a connection conductor, 
     the shape can be simplified, even though the conductive path is extended, thus making it possible to improve the productivity of the antenna element. 
     Since a capacitive conductor having a given capacitance is connected to the terminate end of the second conductor, the conductive path can be reduced in length due to a capacitance load of the capacitive conductor. 
     Since the second conductor is formed integrally with a capacitive conductor of a given capacitance, the conductive path is reduced in length due to a capacitance load of the capacitive conductor. Since the capacitive conductor and second conductor need not be separately formed and connected to each other through a connection conductor, it is possible to simplify the structure to improve the productivity, and reduce the size of the overall shape. 
     Since a resonant circuit is formed of a resonant conductor formed at a predetermined position of at least one of the first conductor and second conductor to the vicinity of the other one, the resonant circuit permits the antenna element to support radio communications at a plurality of frequencies, making it possible to improve the performance of the antenna element. 
     Since a plurality of resonant conductors are connected respectively to at least one of the first conductor and second conductor, a plurality of resonant circuits resonate at different frequencies from one another, permitting the antenna element to support radio communications at a plurality of frequencies and at frequencies in a wide band. 
     A radio communication apparatus according to the present invention, with the provision of the antenna element of the present invention, can radio communicate a radio wave at a desired frequency through the small antenna element. 
     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 element according to a first embodiment of the present invention; 
     FIG. 3 is a perspective view illustrating a main portion of a radio communication apparatus according to one embodiment of the present invention; 
     FIG. 4 is a vertical cross-sectional view illustrating a main portion of the radio communication apparatus; 
     FIG. 5 a  is a schematic diagram illustrating a circuit function of the antenna element; 
     FIG. 5 b  is a circuit diagram illustrating an equivalent circuit of the antenna element; 
     FIG. 6 is a perspective view illustrating a first exemplary modification to the antenna element of the first embodiment; 
     FIG. 7 is perspective view illustrating a second exemplary modification; 
     FIG. 8 is a perspective view illustrating an antenna element according to a second embodiment; 
     FIG. 9 is a perspective view illustrating a first exemplary modification to the antenna element of the second embodiment; 
     FIG. 10 is a perspective view illustrating a second exemplary modification; 
     FIG. 11 is a perspective view illustrating a third exemplary modification; 
     FIG. 12 is a perspective view illustrating a fourth exemplary modification; and 
     FIG. 13 is a perspective view illustrating a fifth exemplary modification. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A first embodiment of the present invention will hereinafter be described with reference to FIGS. 2 through 5. 
     It should be first noted however that with respect to the following embodiments, parts identical to those of antenna element  100  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. 
     Like the aforementioned antenna element  100 , antenna element  200  in this embodiment comprises device substrate  201  made of a dielectric material in rectangular solid, and conductive path  202  formed of a printed wire or the like on the front surface of device substrate  201 , as illustrated in FIG.  2 . Conductive path  202  is comprised of a power supply conductor  203 , first conductor  204 , short-circuit conductor  205 , and second conductor  206 . 
     Unlike antenna element  100 , connection conductor  207  is connected at a right angle to a terminate end of second conductor  206 , and capacitive conductor  208  is connected to a terminate end of connection conductor  207 . Capacitive conductor  208  is made of a conductor formed on a top surface of device substrate  201 , and generates a given capacitance between ground electrode  302 , later described, and itself. Antenna element  200  of this embodiment is also formed with extended portion  209  bent in a U-shape at a leading end of first conductor  204 . A leading end of extended portion  209  is continuous to the terminate end of power supply conductor  203 . 
     As illustrated in FIG. 3, radio communication apparatus  300  in this embodiment has circuit board  301 . In a lower half of the front surface of the circuit board  301 , a copper foil is applied to form ground electrode  302 . Ground electrode  302  has a portion thereof formed in recess, where power supply electrode  304  is formed for power supply circuit  303  which functions as a power supply means. 
     In radio communication apparatus  300  in this embodiment, antenna element  200  is mounted on an upper half of the front surface of circuit board  301  on which ground electrode  302  is not formed. As illustrated in FIGS. 3 and 4, conductive path  202  of antenna element  200  has a leading end connected to a terminate end of power supply electrode  304 . 
     In the foregoing structure, antenna element  200  in this embodiment is similar to the aforementioned antenna element  100  in that first conductor  204  and second conductor  206 , positioned in parallel with each other, act as a loaded inductance, as illustrated in FIG. 5 a , so that the length of conductive path  202  is reduced to make the overall shape smaller, while ensuring a desired resonant frequency. 
     Unlike the meander antenna, helical antenna and the like, however, since first conductor  204  and second conductor  206  positioned in parallel to each other are sufficiently spaced away from each other, their electromagnetic coupling is reduced, making it possible to realize radio communications with high gain, high efficiency, and wide band. 
     Further, since capacitive conductor  208  is connected to a terminate end of conductive path  202 , this capacitive conductor  208  has a large capacitance between ground electrode  302  and itself. For this reason, as illustrated in FIG. 5 b , an equivalent circuit of antenna element  200  in this embodiment is represented by an LC series circuit, with a reduced resonant frequency, so that conductive path  202  can be relatively reduced further in length. 
     Moreover, since antenna element  200  in this embodiment has extended portion  209  formed in first conductor  204 , conductive path  202  is extended without increasing the size of device substrate  201 . In other words, device substrate  201  is made compact without relatively extending conductive path  202 ,  50  that the overall shape is made compact while ensuring a desired resonant frequency. 
     As described above, since first conductor  204  and second conductor  206  are sufficiently spaced away from each other, the formation of extended portion  209  in first conductor  204  will not cause strong electromagnetic coupling with second conductor  206 , so that antenna element  200  in this embodiment can provide good radio communications. 
     Further, in antenna element  200  in this embodiment, extended portion  209  formed in first conductor  204  is connected in linear fashion to power supply conductor  203 , so that the shape of antenna element  200  can be simplified while extending conductive path  202 , thereby making antenna element  200  highly productive. 
     As appreciated, the present invention is not limited to the foregoing embodiment, and permits a variety of alterations without departing from the spirit and scope of the invention. For example, while antenna element  200  in the foregoing embodiment illustrates that extended portion  209  formed at the leading end of first conductor  204  is connected in a linear fashion to power supply conductor  203 , the foregoing structure can be recognized as well in such a manner that an extended portion formed at the terminate end of first conductor  204  is connected in a linear fashion to short-circuit conductor  205 . 
     Alternatively, as antenna element  210  illustrated in FIG. 6, extended portion  211  may be formed at the terminate end of second conductor  206  and connected in a linear fashion to connection conductor  207 , and this structure can be recognized as well in such a manner that an extended portion formed at the leading end of second conductor  206  is connected in a linear fashion to short-circuit conductor  205 . 
     Further, while antenna element  200  in the foregoing embodiment illustrates that capacitive conductor  208  is formed on second conductor  206  by connection conductor  207 , second conductor  221  can be formed integral with a capacitive conductor, as antenna element  220  illustrated in FIG.  7 . Alternatively, antenna element  200  may not be formed either with capacitive conductor  208  or with connection conductor  207 . 
     Further, while antenna element  200  in the foregoing embodiment illustrates that conductive path  202  is formed on its outer surface of device substrate  201 , some antenna element (not shown) has a dielectric material integrally laminated on the outer surface of device substrate  201 , on which conductive path  202  is thus formed, to form an element member. In this structure, even though conductive path  202  is positioned inside the element member made of the dielectric material, device substrate  201  is still positioned inside the element member, with conductive path  202  positioned on the outer surface of device substrate  201 , as is the case with antenna element  200 . 
     Next, a second embodiment of the present invention will be described below with reference to FIG.  8 . In antenna element  400  in the second embodiment, though device substrate  201  is formed in rectangular solid just like the aforementioned antenna element  200  and the like, antenna element  400  differs from the aforementioned antenna element  200  and the like in that first conductor  402  and second conductor  403  of conductive path  401  are formed continuously from the front surface to one side surface of device substrate  201 . 
     In the foregoing structure, antenna element  400  in the second embodiment can extend first conductor  402  and second conductor  403  without increasing the size of device substrate  201 , so that the overall shape can be made compact while maintaining a desired resonant frequency. Particularly, since a plurality of outer surfaces of solid device substrate  201  are effectively utilized to extend first/second conductors  402 ,  403 , first/second conductors  402 ,  403  can be extended as appropriate while they are sufficiently spaced away from each other. 
     As appreciated, the present invention is not limited to the foregoing second embodiment, and permits a variety of alterations without departing from the spirit and scope of the invention. For example, while antenna element  400  in the second embodiment illustrates that first/second conductors  402 ,  403  are formed continuously on a plurality of outer surfaces of device substrate  201 , the aforementioned extended portions  209 ,  211  may be formed in first/second conductors  402 ,  403  which are continuously formed on a plurality of outer surfaces of device substrate  201  in the foregoing manner. 
     Also, while antenna element  400  in the second embodiment illustrates that first conductor  402  and second conductor  403  are formed continuously from the front surface to the side surface of device substrate  201 , first conductor  411  and second conductor  412  may be continuously formed from the front surface to the back surface across one side surface of device substrate  201 , for example, as antenna element  410  illustrated in FIG. 9, to further extend first/second conductors  411 ,  412  to relatively reduce the size of the overall shape. 
     It should be noted however that in the foregoing antenna element  410 , portions of first/second conductors  411 ,  412  positioned on the front surface and the back surface of device substrate  201  are in close proximity to and in parallel with each other, giving rise to a concern of an increased distributed capacitance to reduce the bandwidth of radio communications. Thus, if the reduction in bandwidth is unacceptable, first and second conductors  421 ,  422  are preferably inclined in opposite directions on one side surface of device substrate  201  to form first and second conductors  421 ,  422  at different positions on the front surface and rear surface of device substrate  201 , as antenna element  420  illustrated in FIG.  10 . 
     In this structure, since the portions of first/second conductors  421 ,  422  positioned on the front surface and the back surface of device substrate  201  are spaced away from each other, the distributed capacitance can be reduced to extend the bandwidth of radio communication. Alternatively, even when first/second conductors  421 ,  422  are inclined in the same direction on the side surface of device substrate  201  (not shown), first/second conductors  421 ,  422  can be formed at different positions on the front surface and the back surface of device substrate  201  to reduce the distributed capacitance. 
     Further, while antenna element  400  in the second embodiment illustrates that power supply conductor  203  is also formed integrally with conductive path  401  drawn on a plurality of outer surfaces of device substrate  201 , no power supply conductor may be formed together with conductive path  431  drawn continuously on a plurality of outer surfaces of device substrate  201 , as antenna element  430  illustrated in FIG.  11 . 
     Antenna element  430  is formed with first/second conductors  432 ,  433  of conductive path  431  from the front surface to the back surface of device substrate  201 , and connections  434  are formed at a leading end of first conductor  432  and at a terminate end of second conductor  433 , positioned on the back surface of device substrate  201 . 
     Then, in radio communication apparatus  500  utilizing antenna element  430 , a pair of connections  501  are formed for connection with respective connections  434  on the front surface of circuit board  301  opposite to the back surface of device substrate  201 , and power supply electrode  304  is connected to one of connections  501  connected to first conductor  432 . 
     Because of the elimination of the need for forming a power supply conductor in conductive path  431 , antenna element  430  as described above is simple in structure and highly productive. Moreover, since first/second conductors  432 ,  433  can be disposed at both ends of device substrate  201 , the whole element can be further made compact. 
     Alternatively, as antenna element  440  illustrated in FIG. 12, resonant conductor  441  may be formed at a predetermined position of at least one of first/second conductors  432 ,  433  to the vicinity of the other one, such that a resonant circuit is formed of this resonant conductor  441  to support radio communications at a plurality of frequencies. 
     While in antenna element  440 , a terminate end of resonant conductor  441  having a leading end connected to second conductor  433  is positioned near first conductor  432 , a sufficient inductance can be generated because resonant conductor  441  is linear near the leading end and meandering near the terminate end. In addition, since resonant conductor  441  has a terminate end formed in parallel with first conductor  432 , a sufficient capacitance can be generated as well, thereby providing a satisfactory resonant circuit formed of resonant conductor  441  and first conductor  432 . 
     Also, while resonant conductor  441  has a leading end connected to second conductor  433  and a terminate end positioned near first conductor  432  in FIG. 12, resonant conductor  441  may have the leading end connected to first conductor  432  and the terminate end positioned near second conductor  433  (not shown), in which case the terminate ends of a pair of resonant conductors, which have the leading ends connected to first/second conductors  432 ,  433 , respectively, can be placed in close proximity (not shown). 
     Further, while antenna element  440  in FIG. 12 illustrates resonant conductor  441  which is meandering near the terminate end and parallel with first conductor  432  near the leading end, the present invention can be implemented as well in an antenna element which has a resonant conductor (not shown) not formed in a meander shape, a resonant conductor (not shown) with a terminate end portion not in parallel with first conductor  432 , and the like. 
     Alternatively, as antenna element  450  illustrated in FIG. 13, a plurality of resonant conductors  411  can be connected one by one at a plurality of positions on second conductor  433 . In such antenna element  450 , since a plurality of resonant circuits formed of the plurality of resonant conductors  441  differ in resonant frequency from one another, antenna element  450  can support radio communications at a plurality of frequencies. Further, when the plurality of frequencies are close to one another, communication frequencies can be virtually provided in a wide band. 
     While preferred embodiments) 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.