Surface-mount-type antenna and communication equipment using same

A current-inducing-type surface-mount-type antenna which is short in length and thin in thickness and which can be formed into a small size and communication equipment having the same mounted therein. A radiation electrode substantially in the shape of a letter L or a sideways U and a power supply electrode are formed on the surface of a base made of a dielectric or a magnetic substance with a gap therebetween. A short-circuit end of the radiation electrode and the power supply electrode are connected to a grounding terminal and a power supply terminal, respectively, which are formed on an end surface of the base.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a current-inducing-type surface-mount-type 
antenna for use in mobile communication equipment, such as portable 
telephones, and a radio LAN (Local Area Network), and communication 
equipment using the same. 
2. Description of the Related Art 
A conventional surface-mount-type antenna is shown in FIG. 8. A radiation 
electrode 72 and a power supply electrode 73 are formed on the surface of 
a base 71 of this surface-mount-type antenna 70 with a gap g therebetween. 
A grounding terminal 72a and a power supply electrode 73a, which are 
connected to one end of the radiation electrode 72 and to one end of the 
power supply electrode 73, are formed on one end surface 71a of the base 
71. A capacity loaded electrode 74 is formed on the other end surface 71b 
of the base 71, which capacity loaded electrode 74 is connected to the 
other end of the radiation electrode 72. 
In the conventional surface-mount-type antenna 70, the capacity loaded 
electrode 74 is provided for shortening the wavelength. However, the 
capacitance formed by this capacity loaded electrode 74 can be increased 
only by the specific inductive capacity er of the base 71 and the 
thickness of the base 71. Also, even if the radiation electrode 72 is 
formed into a meandering shape in order to increase the length of the 
radiation electrode 72 which resonates at a predetermined wavelength, 
there are limitations in terms of dimensions and shape, and the length of 
the base 71 cannot be made short. Therefore, it is difficult to achieve a 
small size with the conventional surface-mount-type antenna 70. Further, 
communication equipment having the conventional surface-mount-type antenna 
70 incorporated therein has the drawback of the housing of the 
communication equipment being incapable of being formed to be small in 
size. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of the present invention to provide a 
surface-mount-type antenna which is short in length and thin in thickness 
and which can be formed into a small size, and communication equipment 
having the same mounted therein. 
To achieve the above and other objects, according to one aspect of the 
present invention, there is provided a current-inducing-type 
surface-mount-type antenna, comprising a radiation electrode arranged 
substantially in the shape of a letter L or a sideways U, in which one end 
is open and the other end is short-circuited and a power supply electrode 
for exciting the radiation electrode, the radiation electrode and power 
supply electrode formed with a gap therebetween on one main surface of a 
base made of a dielectric or a magnetic substance, the radiation electrode 
and the power supply electrode being connected to a grounding terminal and 
a power supply terminal, respectively, formed on an end surface of the 
base. 
According to another aspect of the present invention, there is provided a 
current-inducing-type surface-mount-type antenna, comprising a radiation 
electrode arranged substantially in the shape of a letter L or a sideways 
U, in which one end is open and the other end is short-circuited, the 
radiation electrode being formed extending over one main surface and at 
least one end surface of a base made of a dielectric or a magnetic 
substance, a power supply electrode formed on one main surface of the base 
with a gap being provided between the radiation electrode and the power 
supply electrode, the radiation electrode and the power supply electrode 
being connected to a grounding terminal and a power supply terminal, 
respectively, formed on another end surface of the base. 
According to a further aspect of the present invention, there is provided 
communication equipment having the surface-mount-type antenna mounted 
therein 
In the present invention, as described above, since a radiation electrode 
substantially in the shape of a letter L or a sideways U is provided on at 
least one main surface from among the main surfaces and the end surfaces 
of a base, it is possible to increase the resonance wavelength with 
respect to the chip (base) size, and since a capacitance similar to a 
loading capacity is formed between the open end portion of the radiation 
electrode and the grounding electrode, it is possible to increase the 
resonance wavelength even further. This fact means that when the frequency 
is made fixed, it is possible to decrease the chip (base) size. Therefore, 
a small-sized surface-mount-type antenna can be realized, and thus 
communication equipment having the same mounted therein can be formed into 
a small size.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION 
The preferred embodiments of the present invention will be described below 
with reference to the accompanying drawings. FIG. 1 shows a 
surface-mount-type antenna 10 according to a first embodiment of the 
present invention. A radiation electrode 2 in the shape of a letter L is 
formed on the surface of a rectangular base 1, made of a dielectric or a 
magnetic substance, of the surface-mount-type antenna 10. In the L-shaped 
radiation electrode 2, a short-circuit end 2a thereof is positioned on one 
short edge of the surface of the base 1, a main body 2b thereof extends 
straight to the other short edge opposite said one short edge and bends at 
right angles towards a long edge and extends in that direction, and an 
open end 2c is positioned at one corner of the surface of the base 1. The 
short-circuit end 2a of the radiation electrode 2 is connected to a 
grounding terminal 4 formed on one end surface of the base 1 and extends 
onto a rear surface thereof. 
Further, a power supply electrode 3 is formed on the surface of the base 1 
separated by a gap g from the short-circuit end portion 2a of the 
radiation electrode 2. This power supply electrode 3 is connected to a 
power supply terminal 5 which is formed on one end surface of the base 1 
and extends to the rear surface thereof. 
This power supply electrode 3 and the open end 2c of the radiation 
electrode 2 are equivalently spaced by a distance d and are 
electric-field-coupled with a capacitance Cd formed within this distance 
d. The power supply electrode 3 and the radiation electrode 2 are closest 
to each other at a gap g; however, since the short-circuit end portion 2a 
of the radiation electrode 2 is inductive, the degree of coupling is 
small. Meanwhile, even if the power supply electrode 3 and the open end 2c 
are apart from each other, since the surface-mount-type antenna 10 itself 
is small, the degree of coupling is large. 
An equivalent electrical circuit diagram of this embodiment is shown in 
FIG. 2. In FIG. 2, reference letter L denotes the radiation inductance of 
the radiation electrode 2. Reference letter R denotes radiation 
resistance. Reference letter Cd denotes capacitance which is formed mainly 
between the open end portion 2c of the radiation electrode 2 and the power 
supply electrode 3. Reference letter Cg denotes capacitance which is 
formed in the gap g. Reference letter C denotes capacitance between the 
radiation electrode and ground. 
In this embodiment, since the radiation electrode 2 bends substantially in 
the shape of a letter L which increases its length, the radiation 
inductance L is increased. Therefore, as described above, a small chip 
(base) size can be achieved by itself, and the above-described capacitance 
Cd is increased by the capacitance loading effect of the open end portion 
2c, thus achieving an-even smaller size. 
Next, a second embodiment of the present invention will be described below 
with reference to FIG. 3. A radiation electrode 22 substantially shaped 
like a sideways U and a power supply electrode 23 are formed on the 
surface of a rectangular base 21, made of a dielectric or a magnetic 
substance, of a surface-mount-type antenna 20 with a gap g therebetween. A 
short-circuit end 22a of the radiation electrode 22 is positioned on one 
short edge of the surface of the base 21, and a main body 22b thereof 
extends straight to the other short edge facing said one short edge and 
bends at right angles there, extending to one corner of a long edge along 
said other short edge and further bends at right angles there and extends 
along this long edge, and an open end 22c thereof is positioned 
approximately in the middle of this long edge. As a result, the radiation 
electrode 22 is formed substantially in the shape of a sideways U. 
The short-circuit end 22a of the radiation electrode 22 and the power 
supply electrode 23 are respectively connected to a grounding terminal 24 
and a power supply terminal 25 formed on one end surface of the base 21. 
The power supply electrode 23 and the open end 22c of the radiation 
electrode 22 are equivalently spaced by a distance d in the same way as in 
the first embodiment and are electric-field-coupled with a capacitance Cd 
formed within this distance d. The power supply electrode 23 and the 
radiation electrode 22 are closest to each other at a gap g; however, 
since the short-circuit end portion 22a is inductive, the degree of 
coupling is small. Meanwhile, even if the power supply electrode 23 and 
the open end 22c are apart from each other, since the surface-mount-type 
antenna 10 itself is small, the degree of coupling is large. 
This embodiment is structured as described above, and its equivalent 
electrical circuit diagram is similar to FIG. 2 which is referred to in 
the first embodiment. 
In this embodiment, as compared with the radiation electrode 2 
substantially shaped like a letter L shown in FIG. 1, there is provided 
the radiation electrode 22 substantially shaped like a sideways U, and the 
effective length of the radiation electrode 22 is longer and the loading 
capacity effect is large as the power supply electrode 23 and the open end 
22c of the radiation electrode 22 are close to each other. Thus, an even 
smaller size can be achieved. 
Next, a third embodiment of the present invention will be described below 
with reference to FIG. 4. A part of a radiation electrode 32 in the shape 
of a letter L and a power supply electrode 33 are formed on the surface of 
a rectangular base 31, made of a dielectric or a magnetic substance, of a 
surface-mount-type antenna 30 with a gap g therebetween. A short-circuit 
end 32a of the radiation electrode 32 is positioned on one edge side of 
the surface of the base 31. A main body 32b thereof extends straight to 
the other short edge facing said one short edge and bends from said other 
short edge to an adjacent end surface 31b, and extends in one direction on 
the adjacent end surface 31b. An open end 32c thereof is positioned at an 
edge of the adjacent end surface 31b. As a result, the radiation electrode 
32 is formed substantially in the shape of a letter L extending over the 
surface and the end surface of the base 31. 
The short-circuit end 32a of the radiation electrode 32 and the power 
supply electrode 33 are respectively connected to a grounding terminal 34 
and a power supply terminal 35 formed on one end surface of the base 31. 
The power supply electrode 33 and the open end 32c of the radiation 
electrode are equivalently spaced by a distance d in the same way as in 
the first embodiment and are electric-field-coupled with a capacitance Cd 
formed within this distance d. 
This embodiment is structured as described above and is expressed by the 
equivalent electrical circuit diagram shown in FIG. 2. The same effects 
and advantages as those of the first embodiment described with reference 
to FIG. 1 can be realized. In particular, an even smaller size can be 
achieved due to a large capacitance loading effect. 
Next, a fourth embodiment of the present invention will be described below 
with reference to FIG. 5. A part of a radiation electrode 42 substantially 
in the shape of a sideways U and a power supply electrode 43 are formed on 
the surface of a rectangular base 41, made of a dielectric or a magnetic 
substance, of a surface-mount-type antenna 40 with a gap g therebetween. A 
short-circuit end 42a of the radiation electrode 42 is positioned on one 
short edge of the surface of the base 41, a main body 42b thereof extends 
straight to the other short edge facing said one short edge, bends from 
said other short edge to an end surface 41b adjacent thereto, extends in 
one direction on this adjacent end surface 41b, bends to the 
above-mentioned surface again at the end of the adjacent end surface 41b, 
and extends on this surface along a long edge thereof. An open end 42c 
thereof is positioned in the middle of this long edge. As a result, the 
radiation electrode 42 is formed substantially in the shape of a sideways 
U such that it extends from the surface of the base 41 along the end 
surface thereof and returns to the surface and extends in parallel. 
A short-circuit end 42a of the radiation electrode 42 and the power supply 
electrode 43 are respectively connected to a grounding terminal 44 and a 
power supply terminal 45 formed on one end surface of the base 41. 
The power supply electrode 43 and the open end 42c of the radiation 
electrode 42 are equivalently spaced by a distance d in the same way as in 
the first embodiment and are electric-field-coupled with a capacitance Cd 
formed within this distance d. 
This embodiment is structured as described above and is expressed by the 
equivalent electrical circuit diagram shown in FIG. 2. The same effects 
and advantages as those of the second embodiment described with reference 
to FIG. 3 can be realized. In particular, the capacitance loading effect 
is large, and an even smaller size can be achieved. 
Next, a fifth embodiment of the present invention will be described below 
with reference to FIG. 6. In a surface-mount-type antenna 50 of this 
embodiment, there is provided a radiation electrode 42d formed by changing 
the shape of the base 41 of the radiation electrode 42 in the fourth 
embodiment shown in FIG. 5 from a line shape to a meandering shape. 
This embodiment is expressed by the equivalent electrical circuit shown in 
FIG. 2, and the same effects and advantages as those of the fourth 
embodiment described with reference to FIG. 5 can be realized. Since, in 
particular, the radiation electrode 42d has a meandering shape, an even 
smaller size can be achieved. 
Next, FIG. 7 shows a state in which the surface-mount-type antennas 10 to 
50 of the above-described embodiments are mounted into communication 
equipment. The surface-mount-type antennas 10 to 50 are mounted by 
soldering grounding terminals and power supply terminals to predetermined 
terminals (not shown) on a set board (or a subboard thereof) 61 in 
communication equipment 60. 
In the present invention, a radiation electrode in the shape of a letter L 
or a sideways U is provided on at least one main surface from among the 
main surfaces and end surfaces of a base, and a small thin base can 
respond to a long wavelength, i.e., a low frequency. Therefore, when the 
frequency is made fixed, it is possible to realize a small-sized 
current-inducing-type surface-mount-type antenna. 
Since a surface-mount-type antenna can be made very small, the space 
occupied by communication equipment having a surface-mount-type antenna 
mounted therein is small, thus achieving a small size. 
Many different embodiments of the present invention may be constructed 
without departing from the spirit and scope of the present invention. It 
should be understood that the present invention is not limited to the 
specific embodiments described in this specification. To the contrary, the 
present invention is intended to cover various modifications and 
equivalent arrangements included within the spirit and scope of the 
invention as hereafter claimed. The scope of the following claims is to be 
accorded the broadest interpretation so as to encompass all such 
modifications, equivalent structures and functions.