Technical Field
The present invention relates to antennas used for wireless
communications and to wireless communication devices.
Background Art
Recently, in the field of wireless communication devices,
such as cellular phones, development for achieving multiple resonances or multiple
bands is in progress in order to achieve wide bandwidths. Researches are being carried
out for antennas in which a plurality of resonant frequencies are controlled to
allow transmission and reception with a wide bandwidth. Also, antennas in which
a frequency can be changed to achieve a wide bandwidth are being considered.
Examples of such antennas that have hitherto been proposed
include antennas disclosed in Patent Documents 1 to 3.
An antenna disclosed in Patent Document 1 is an inverted-F-shaped
antenna device. More specifically, an antenna element is disposed in parallel above
a ground conductor, and at least one coupling element is provided in parallel between
the ground conductor and the antenna element. The antenna element is electrically
connected to the ground conductor via a short-circuiting conductor, and is connected
to a feeding point of a feeding coaxial cable. By providing the coupling element
in addition to the antenna element as described above, two resonant frequencies
are obtained.
In an antenna disclosed in Patent Document 2, an antenna
element and a variable capacitor are provided, the variable capacitor being connected
in series or parallel with the antenna element to form a resonant circuit, and the
control voltage is applied to the variable capacitor to change a resonant frequency.
In an antenna disclosed in Patent Document 3, a radiating
element and a tuning circuit are connected in series. In the tuning circuit, a first
inductor is connected in series with a parallel circuit including a variable capacitor.
A first resonance frequency is obtained by a first antenna element and a second
antenna element connected in series, and a second resonant frequency is obtained
by the first antenna element alone. Furthermore, a third resonant frequency is obtained
by a third antenna element provided from a feeding element.
- Patent Document 1:
Japanese Unexamined Patent Application Publication No. 2003-51712
- Patent Document 2:
Japanese Unexamined Patent Application Publication No. 2002-232313
- Patent Document 3:
Japanese Unexamined Patent Application Publication No. 2004-320611
Disclosure of Invention
However, the antennas according to the related art described
above have the following problems.
Regarding the antenna disclosed in Patent Document 1, since
the antenna is an inverted-F-shaped antenna device, when the antenna is mounted
on a small and thin wireless communication device such as a cellular phone, the
position of attachment of the coupling element is restricted to a low position because
the height from the ground conductor to the antenna element must be small. Thus,
restriction is imposed on the control of resonant frequencies of multiple resonances,
so that the bandwidth can be increased only to approximately 1.5 times the bandwidth
of an inverted-F antenna element. Also, the bandwidth ratio is approximately several
percents at best.
Regarding the antenna disclosed in Patent Document 2, it
is possible to control the resonant frequency according to the control voltage.
However, since a frequency-changing resonance circuit implemented using a variable
capacitor is provided in the proximity of a feeding section of the antenna element,
the condition of matching between the feeding section and the antenna element changes.
Thus, a complex matching circuit is needed. As contrasted with the above, an example
where a frequency-changing resonance circuit is provided at a distal-end portion
of an antenna element is disclosed. In this example, although a complex circuit
configuration is not required, since the resonance circuit is provided at the distal-end
portion of the antenna element, where the electric field is most intense (current
density is smallest), it is not possible to change the resonant frequency greatly.
Furthermore, a large control voltage is needed in order to change the resonant frequency
of the antenna by a desired range by controlling a single variable capacitor. This
does not allow satisfying the demand for low-voltage operation required for a wireless
communication device such as a cellular phone.
Regarding the antenna disclosed in Patent Document 3, it
is possible to achieve multiple resonances and to change resonant frequencies. However,
since the third antenna element is connected in parallel to the feeding element
without an intervening tuning circuit, it is not possible to change the third resonant
frequency greatly. Furthermore, since the parallel circuit is disposed in the proximity
of a feeding section of the radiating element, the problems of the antenna disclosed
in Patent Document 2 also exist.
The present invention has been made in order to overcome
the problems described above, and it is an object thereof to provide an antenna
and a wireless communication device in which a plurality of resonant frequencies
can be changed simultaneously by a desired range at a low voltage.
In order to overcome the problems described above, the
invention according to Claim 1 is an antenna including a first antenna section in
which a radiating electrode having an open distal end is connected to a feeding
electrode via a frequency-changing circuit, and a second antenna section formed
of an additional radiating electrode and the feeding electrode, the additional radiating
electrode having an open distal end and being connected to a middle portion of the
frequency-changing circuit, wherein the frequency-changing circuit is formed by
connecting a first reactance circuit with a second reactance circuit, the first
reactance circuit being connected to the feeding electrode and having a reactance
that is variable according to a direct-current control voltage, and the second reactance
circuit being connected to the radiating electrode of the first antenna section,
and wherein the additional radiating electrode of the second antenna section branches
from a node between the first and second reactance circuits.
With the configuration described above, the first antenna
section is formed of the feeding electrode, the frequency-changing circuit, and
the radiating electrode, and the second antenna section is formed of the feeding
electrode, the first reactance circuit of the frequency-changing circuit, and the
additional radiating electrode. Thus, it is possible to achieve multiple resonances
with a resonant frequency associated with the first antenna section and a resonant
frequency associated with the second antenna section. By changing the reactance
of the first reactance circuit of the frequency-changing circuit, the resonant frequency
of the first antenna section and the resonant frequency of the second antenna section
change simultaneously. That is, with the frequency-changing circuit, it is possible
to simultaneously change a plurality of resonant frequencies by a desired range.
When a wide bandwidth is to be achieved using a single-resonance antenna, it is
needed to apply a large control voltage to a frequency changing circuit so that
a resonant frequency can be changed over a wide range. In contrast, with the antenna
according to this invention, it is possible to simultaneously change a plurality
of resonant frequencies with different frequencies using a low control voltage.
Thus, it is possible to achieve a wide bandwidth using a low control voltage.
The invention according to Claim 2 is the antenna according
to Claim 1, wherein the second reactance circuit has a reactance that is variable
according to the control voltage.
With the configuration described above, the reactance of
the second reactance circuit can be changed according to the control voltage by
a desired range, so that the resonant frequency of the first antenna section can
be changed to various values.
The invention according to Claim 3 is the antenna according
to Claim 1, wherein the second reactance circuit has a reactance that is fixed.
With the configuration described above, the reactance of
the frequency-changing circuit is the sum of the variable reactance of the first
reactance circuit and the fixed reactance of the second reactance circuit. Thus,
when the reactance of the first reactance circuit is changed, the resonant frequencies
of the first and second antenna sections change simultaneously.
The invention according to Claim 4 is the antenna according
to Claim 2, wherein the first reactance circuit is a series circuit including a
variable capacitor or a parallel circuit including a variable capacitor, wherein
the second reactance circuit is a series circuit including a variable capacitor
or a parallel circuit including a variable capacitor, and wherein terminals of the
variable capacitors of the first and second reactance circuits, the terminals having
the same polarity, are connected to each other to form a node between the first
and second reactance circuits, and the control voltage is applied to the node to
control capacitances of the variable capacitors.
The invention according to Claim 5 is the antenna according
to Claim 3, wherein the first reactance circuit is a series circuit including a
variable capacitor or a parallel circuit including a variable capacitor, wherein
the second reactance circuit is a series circuit including a fixed capacitor or
a parallel circuit including a fixed capacitor, and wherein the variable capacitor
of the first reactance circuit is connected to the second reactance circuit to form
a node between the first and second reactance circuits, and the control voltage
is applied to the node to control a capacitance of the variable capacitor.
The invention according to Claim 6 is the antenna according
to one of Claims 1 to 5, wherein an inductor is connected in parallel to the first
reactance circuit and the second reactance circuit across the first and second reactance
circuits.
With the configuration described above, by using the inductor,
a third antenna section is formed, which resonates in a frequency band lower than
the frequencies covered by the first antenna section and the second antenna section.
The invention according to Claim 7 is the antenna according
to one of Claims 1 to 6, wherein the additional radiating electrode branches from
the node via an inductor for controlling a resonant frequency.
The invention according to Claim 8 is the antenna according
to one of Claims 1 to 7, wherein one or more additional radiating electrodes that
are separate from the earlier mentioned additional radiating electrode branch from
the node.
With the configuration described above, it is possible
to achieve further multiple resonances.
The invention according to Claim 9 is the antenna according
to Claim 8, wherein each of the one or more separate additional radiating electrodes
branches from the node via another reactance circuit configured the same as the
first reactance circuit, and another control voltage for controlling a capacitance
of a variable capacitor of the another reactance circuit is applied to the another
reactance circuit.
With the configuration described above, the resonant frequencies
of antenna sections associated with individual additional radiating electrodes can
be freely changed independently among the antenna sections.
The invention according to Claim 10 is the antenna according
to one of Claims 1 to 9, wherein an additional radiating electrode that is separate
from the earlier mentioned additional radiating electrode is connected to a middle
portion of the radiating electrode.
The invention according to Claim 11 is the antenna according
to Claim 10, wherein the separate additional radiating electrode is connected to
the radiating electrode via an inductor.
The invention according to Claim 12 is the antenna according
to one of Claims 1 to 11, wherein the first antenna section has a shape of a loop
in which the feeding electrode and the open distal end of the radiating electrode
are opposed via a gap.
With the configuration described above, the reactance of
the first antenna section can be changed by changing the gap between the feeding
electrode and the open distal end of the radiating electrode.
The invention according to Claim 13 is the antenna according
to one of Claims 1 to 12, wherein all or one or more of antenna elements including
the feeding electrode, the frequency-changing circuit, the radiating electrode,
and the additional radiating electrode are formed on a dielectric base.
With the configuration described above, the reactances
of the first and second antenna sections can be changed by changing the dielectric
constant of the dielectric base.
The invention according to Claim 14 is the antenna according
to one of Claims 1 to 13, wherein in one or more or all of the radiating electrode
of the first antenna section, the additional radiating electrode of the second antenna
section, and the one or more separate additional radiating electrodes, a middle
portion or an open distal end of the electrode is connected to a ground via a discrete
inductor or a reactance circuit.
With the configuration described above; a new resonance
based on the discrete inductor or the reactance circuit can be obtained.
The invention according to Claim 15 is the antenna according
to Claim 14, wherein the reactance circuit is a series resonance circuit or a parallel
resonance circuit, or a composite circuit including a series resonance circuit and
a parallel resonance circuit.
The invention according to Claim 16 is the antenna according
to Claim 14 or 15, wherein the antenna is configured to allow reception of FM electromagnetic
waves, electromagnetic waves in the VHF band, and electromagnetic waves in the UHF
band.
A wireless communication device according to Claim 17 includes
the antenna according to one of Claims 1 to 16.
As described above in detail, with the antennas of the
inventions according to Claims 1 to 16, it is possible to achieve multiple resonances.
Furthermore, advantageously, it is possible to achieve a wide bandwidth at a low
control voltage. Thus, application to a wireless communication device or the like
for which a low power-supply voltage is required, such as a cellular phone, is allowed.
Particularly, with the antenna of the invention according
to Claim 2, since the second reactance circuit of the frequency-changing circuit
is also of the variable type, the resonant frequency of the first antenna section
can be changed to even more various values.
With the antenna of the invention according to Claim 3,
since the second reactance circuit of the frequency-changing circuit is of the fixed
type, it is possible to change the resonant frequencies of the first and antenna
sections by different amounts at a low cost.
With the antenna of the invention according to Claim 6,
by using an additional inductance, a third antenna is formed of the feeding electrode,
the inductor, and the radiating electrode. Thus, a band of a low resonant frequency
is newly obtained.
With the antenna of the invention according to Claim 8,
it is possible to achieve further multiple resonances. Thus, a multi-band antenna
compatible with multimedia can be provided.
Particularly, with the antenna of the invention according
to Claim 9, each of the resonant frequencies can be changed to various values.
With the antennas of the inventions according to Claims
14 to 16, it is possible to add a new resonance while maintaining a small cubic
size of antenna.
Particularly, in the antenna of the invention according
to Claim 15, when the reactance circuit is implemented by a series resonance circuit,
the effect on the resonant frequency of the electrode connected to the series resonance
circuit can be reduced. When the reactance circuit is implemented by a parallel
resonance circuit, the constant of a load inductor can be reduced, so that the problem
of a chip component regarding the self-resonant frequency can be solved. When the
reactance circuit is implemented by a composite circuit including a series resonance
circuit and a parallel resonance circuit, it is possible to achieve both the advantage
of the series resonance circuit and the advantage of the parallel resonance circuit.
With the invention according to Claim 17, a wireless communication
device that allows transmission and reception in a wide band at a low voltage can
be provided.
Brief Description of the Drawings
- [Fig. 1] Schematic plan view showing an antenna according to a first embodiment
of the present invention.
- [Fig. 2] Diagram for explaining the variable states of multiple resonances.
- [Fig. 3] Diagram for explaining that a wide bandwidth can be achieved at a low
voltage.
- [Fig. 4] Schematic plan view showing an antenna according to a second embodiment
of the present invention.
- [Fig. 5] Circuit diagrams showing examples of a first reactance circuit formed
of a series circuit.
- [Fig. 6] Circuit diagrams showing examples of a second reactance circuit of
the variable type.
- [Fig. 7] Schematic plan view showing an antenna according to a third embodiment
of the present invention.
- [Fig. 8] Circuit diagrams showing examples of the second reactance circuit of
the fixed type.
- [Fig. 9] Schematic plan view showing a modification of the third embodiment.
- [Fig. 10] Schematic plan view showing an antenna according to a fourth embodiment
of the present invention.
- [Fig. 11] Circuit diagrams showing examples of the first reactance circuit formed
of a parallel circuit.
- [Fig. 12] Schematic plan views showing modifications of the fourth embodiment,
and part (a) of Fig. 12 shows a first modification, part (b) of Fig. 12 shows a
second modification, and part (c) of Fig. 12 shows a third modification.
- [Fig. 13] Schematic plan view showing an antenna according to a fifth embodiment
of the present invention.
- [Fig. 14] Diagrams showing curves representing return loss that is caused due
to the characteristics of an added inductor, and part (a) of Fig. 14 shows a case
where the inductor is provided as a choke coil, and part (b) of Fig. 14 shows a
case where the inductor is provided to allow adjustment of a resonant frequency.
- [Fig. 15] Schematic plan views showing modifications of the fifth embodiment,
and part (a) of Fig. 15 shows a first modification, and part (b) of Fig. 15 shows
a second modification.
- [Fig. 16] Schematic plan view showing an antenna according to a sixth embodiment
of the present invention.
- [Fig. 17] Perspective view showing an antenna according to a seventh embodiment
of the present invention.
- [Fig. 18] Schematic plan view showing an antenna according to an eighth embodiment
of the present invention.
- [Fig. 19] Diagram showing a curve representing return loss that is caused due
to the characteristics of an added inductor.
- [Fig. 20] Schematic plan view showing an antenna according to a ninth embodiment
of the present invention.
- [Fig. 21] Diagram showing a curve representing return loss that is caused due
to the characteristics of two added inductors.
- [Fig. 22] Schematic plan view showing an antenna according to a tenth embodiment
of the present invention.
- [Fig. 23] Diagram showing a curve representing return loss that is caused due
to the characteristics of three added inductors.
- [Fig. 24] Schematic plan view showing an antenna according to an eleventh embodiment
of the present invention.
- [Fig. 25] Diagram showing a curve representing return loss that is caused due
to the characteristics of an added series resonance circuit.
- [Fig. 26] Diagram showing comparison between the reactance of a discrete inductor
and the reactance of a series resonance circuit.
- [Fig. 27] Schematic plan view showing an antenna according to a twelfth embodiment
of the present invention.
- [Fig. 28] Diagram showing a curve representing return loss that is caused due
to the characteristics of an added series resonance circuit.
- [Fig. 29] Schematic plan view showing an antenna according to a thirteenth embodiment
of the present invention.
- [Fig. 30] Diagram showing a curve representing return loss that is caused due
to the characteristics of an added series resonance circuit.
- [Fig. 31] Schematic plan view showing a modification in which a radiating electrode
is directly formed on an additional radiating electrode.
Reference Numerals
1: antenna; 2: first antenna section; 3: second antenna
section; 4: frequency-changing circuit; 4a: first reactance circuit; 4b: second
reactance circuit; 5: feeding electrode; 6: radiating electrode; 6', 7, 7': additional
radiating electrodes; 9: series resonance circuit; 9': parallel resonance circuit;
10: composite circuit; 40, 41, 43, 46, 47, 90 to 94, 94', 111, 112: inductors; 42,
44: variable-capacitance diodes; 45, 48, 95, 95': capacitors; 60: open distal end;
61, 70, 71: resonant-frequency adjusting inductors; 100: circuit board; 101: non-ground
region; 102: ground region; 110: transceiver; 120: reception-frequency controller;
121, DC: high-frequency-cut resistor; 122: pass capacitor; G: gap; M, M1, M: amounts
of change; P: node; Vc: control voltage; f0, fa, fb, fc, f1 f2: resonant frequencies
Best Mode for Carrying Out the Invention
Now, the best mode of the present invention will be described
with reference to the drawings.
First Embodiment
Fig. 1 is a schematic plan view showing an antenna according
to a first embodiment of the present invention.
An antenna 1 according to this embodiment is provided on
a wireless communication device, such as a cellular phone.
As shown in Fig. 1, an antenna 1 is formed in a non-ground
region 101 of a circuit board 100 of the wireless communication device, and the
antenna 1 exchanges high-frequency signals with a transceiver 110 mounted on a ground
region 102. Furthermore, a DC control voltage Vc is input to the antenna 1 from
a reception-frequency controller 120 provided in the transceiver 110.
The antenna 1 includes a first antenna section 2 and a
second antenna section 3, and the first and second antenna sections 2 and 3 share
a frequency-changing circuit 4.
In the first antenna section 2, a radiating electrode 6
is connected to a feeding electrode 5 via the frequency-changing circuit 4. More
specifically, a matching circuit constituted by inductors 111 and 112 is formed
on the non-ground region 101, and the feeding electrode 5 formed of a conductor
pattern is connected to the transceiver 110 via the matching circuit. That is, the
feeding electrode 5 constitutes a feeding section of the first antenna section 2.
The radiating electrode 6 is formed of a conductor pattern connected to the feeding
electrode 5 via the frequency-changing circuit 4, with an open distal end 60 thereof
opposing the feeding electrode 5 via a certain gap G. Thus, the first antenna section
2 forms a loop as a whole. Since the gap G causes a capacitance between the feeding
electrode 5 and the radiating electrode 6, the reactance of the first antenna section
2 can be changed to a desired value by changing the size of the gap G.
The frequency-changing circuit 4 is disposed between the
feeding electrode 5 and the radiating electrode 6 of the first antenna section 2.
The frequency-changing circuit 4 allows changing the resonant frequency of the first
antenna section 2 by changing its reactance value and thereby changing the electrical
length of the first antenna section 2.
The frequency-changing circuit 4 has a circuit configuration
in which a first reactance circuit 4a (denoted as "jX1" in Fig. 1), which is connected
to the feeding electrode 5, is connected to a second reactance circuit 4b (denoted
as "jX2" in Fig. 1) connected to the radiating electrode 6. A reactance of the first
reactance circuit 4a can be changed according to the control voltage Vc.
The first reactance circuit 4a is a series circuit including
a variable capacitor or a parallel circuit including a variable capacitor.
The second reactance circuit 4b is a circuit whose reactance
can be controlled according to the control voltage Vc, i.e., a series circuit including
a variable capacitor or a parallel circuit including a variable capacitor, or a
circuit whose reactance is fixed, i.e., a series circuit including a fixed capacitor
or a parallel circuit including a fixed capacitor.
A node P between the first reactance circuit 4a and the
second reactance circuit 4b is connected to the reception-frequency controller 120
via a high-frequency-cut resistor 121 and a DC-pass capacitor 122.
Thus, when the control voltage Vc from the reception-frequency
controller 120 is applied to the node P, the reactances of the first and second
reactance circuits 4a and 4b change according to the magnitude of the control voltage
Vc.
The second antenna section 3 is formed of an additional
radiating electrode 7 and the feeding electrode 5. The additional radiating electrode
7 having an open distal end is connected in the middle of the frequency-changing
circuit 4.
More specifically, the additional radiating electrode 7
of the conductor pattern is connected to the node P between the first and second
reactance circuits 4a and 4b via a resonant-frequency adjusting inductor 70. Thus,
the second antenna section 3 is formed of the feeding electrode 5, the first reactance
circuit 4a of the frequency-changing circuit 4, and the additional radiating electrode
7. When the reactance of the first reactance circuit 4a of the frequency-changing
circuit 4 changes by applying the control voltage Vc to the node P, the electrical
length of the second antenna section 3 changes, whereby the resonant frequency of
the second antenna section 3 changes.
Next, the operation and advantage exhibited by the antenna
according to this embodiment will be described.
Fig. 2 is a diagram for explaining the variable states
of multiple resonances, and Fig. 3 is a diagram for explaining that a wide bandwidth
can be achieved at a low voltage.
Since the first antenna section 2 is formed of the feeding
electrode 5, the frequency-changing circuit 4, and the radiating electrode 6, and
the second antenna section 3 is formed of the feeding electrode 5, the first reactance
circuit 4a of the frequency-changing circuit 4, and the additional radiating electrode
7 as described above, two resonant states of a resonant frequency f1 associated
with the first antenna section 2 and a resonant frequency f2 associated with the
second antenna section 3 can be achieved. With a design in which the length of the
radiating electrode 6 is longer than the length of the additional radiating electrode
7, the resonant frequency f1 associated with the first antenna section 2 becomes
lower than the resonant frequency f2 associated with the second antenna section
3, so that a return-loss curve S1 represented by a solid line in Fig. 2 is obtained.
Thus, when the second reactance circuit 4b is a variable circuit that can be controlled
according to the control voltage Vc as described earlier, by applying the control
voltage Vc from the reception-frequency controller 120 to the node P of the frequency-changing
circuit 4, the reactances of the first and second reactance circuits 4a and 4b change,
so that the electrical length of the first antenna section 2 changes. As a result,
as indicated by a return-loss curve S2 represented by a broken line in Fig. 2, the
resonant frequency f1 of the first antenna section 2 is shifted to a frequency f1'
by an amount of change M1 corresponding to the magnitude of the control voltage
Vc. At the same time, the resonant frequency f2 of the second antenna section 3
is shifted to a frequency f2' by an amount of change M2 corresponding to change
in the reactance of a variable-capacitance diode 42. Thus, through the design of
parts of the first and second reactance circuits 4a and 4b, it is possible to make
the amount of change M1 of the resonant frequency f1 and the amount of change M2
of the resonant frequency f2 equal or different and to change the resonant frequencies
f1 and f2 within desired ranges. Since the reactance of the second reactance circuit
4b is also variable, it is possible to change the resonant frequency f1 of the first
antenna section 2 to various values.
Furthermore, with the antenna 1 according to this embodiment,
it is possible to achieve a wide bandwidth with the control voltage Vc at a low
voltage. More specifically, as shown in part (a) of Fig. 3, when it is attempted
to achieve a wide bandwidth so as to allow transmission and reception at frequencies
f1 to f3 using a single-resonance antenna with the resonant frequency f1 alone,
it is needed to apply a large control voltage Vc to a frequency-changing circuit
to change the resonant frequency f1 by an amount of change M so that the resonant
frequency f1 ranges from the frequency f1 to the frequency f3. Thus, this type of
antenna is not suitable for a wireless communication device such as a cellular phone,
for which low-voltage operation is required.
In contrast, in the antenna 1 according to this embodiment,
the resonant frequencies f1 and f2 of two resonant states can be changed simultaneously
according to the control voltage Vc. Thus, as shown in part (b) of Fig. 3, transmission
and reception with a wide bandwidth corresponding to the frequencies f1 to f3 are
allowed by changing the resonant frequency f2 up to a desired frequency f2' (= f3)
and changing the resonant frequency f1 up to a frequency f1' that is higher than
or equal to a lowest frequency f2 of the resonant frequency f2. At this time, the
amounts of change of the resonant frequencies f1 and f2 are M1 and M2, respectively,
and each of the amounts of change is much smaller than the amount of change M in
the case of single resonance. That is, in the antenna 1, transmission and reception
with a wide bandwidth corresponding to the frequencies f1 to f3 are allowed since
the resonant frequencies f1 and f2 can be changed within the range of the frequencies
f1 to f3 according to a low control voltage Vc that causes changes by the slight
amounts of change M1 and M2. Accordingly, using the antenna 1, transmission and
reception with a wide bandwidth are allowed even in a wireless communication device
or the like, for which low-voltage operation is required.
Furthermore, in the antenna 1, when a control voltage Vc
having the same magnitude as in the case of single resonance is applied to the frequency-changing
circuit 4, transmission and reception in a wide range far exceeding the frequencies
f1 to f3 are allowed. Depending on the design of parts of the frequency-changing
circuit 4, it is possible to achieve a bandwidth that is double or even wider than
the bandwidth in the case of single resonance.
Second Embodiment
Fig. 4 is a schematic plan view showing an antenna according
to a second embodiment of the present invention. Fig. 5 is circuit diagrams showing
specific examples of the first reactance circuit 4a formed of a series circuit,
and Fig. 6 is circuit diagrams showing specific examples of the second reactance
circuit 4b of the variable type.
In an antenna 1 according to this embodiment, specific
variable series circuits are used as the first reactance circuit 4a and the second
reactance circuit 4b in the first embodiment.
The first reactance circuit 4a is a series circuit including
a variable capacitor or a parallel circuit including a variable capacitor. In this
embodiment, a series circuit including a variable capacitor is used. The series
circuit including a variable capacitor may be a series circuit shown in part (a)
or (b) of Fig. 5. In this example, the series circuit shown in part (a) of Fig.
5 is used.
The second reactance circuit 4b is a series circuit including
a variable capacitor or a parallel circuit including a variable capacitor, or a
series circuit including a fixed capacitor or a parallel circuit including a fixed
capacitor. In this embodiment, a series circuit including a variable capacitor or
a parallel circuit including a variable capacitor is used. The series circuit including
a variable capacitor or a parallel circuit including a variable capacitor may be
any of circuits shown in parts (a) to (d) of Fig. 6. In this example, the series
circuit shown in part (a) of Fig. 6, which is a variable circuit, is used.
More specifically, as shown in Fig. 4, the first reactance
circuit 4a is formed of a series circuit in which an inductor 41 connected to the
feeding electrode 5 is connected to the anode side of a variable-capacitance diode
42 as a variable capacitor, and the second reactance circuit 4b is formed of a series
circuit in which an inductor 43 connected to the radiating electrode 6 is connected
to the anode side of a variable-capacitance diode 44 as a variable capacitor. The
terminals of the variable-capacitance diodes 42 and 44 with the same polarity (the
cathodes thereof) are connected to each other, and a node P therebetween is connected
to the reception-frequency controller 120 via the high-frequency-cut resistor 121
and the DC-pass capacitor 122. Since the potentials at the anode sides of the variable-capacitance
diodes 42 and 44 must be both zero, an inductor 4c is connected between an end of
the inductor 41 on the side of the feeding electrode 5 and an end of the inductor
43 on the side of the radiating electrode 6.
Thus, when the control voltage Vc is applied from the reception-frequency
controller 120 to the node P of the frequency-changing circuit 4, the capacitances
of the variable-capacitance diodes 42 and 44 change and therefore the electrical
length of the first antenna section 2 changes, so that the resonant frequency of
the first antenna section 2 is shifted to a resonant frequency corresponding to
the magnitude of the control voltage Vc. At the same time, the resonant frequency
of the second antenna section 3 is shifted in accordance with change in the reactance
of the variable-capacitance diode 42.
In this embodiment, as the second reactance circuit 4b
connected to the first reactance circuit 4a formed of a series-connection circuit,
the circuit shown in part (a) of Fig. 6, in which the inductor 43 and the variable-capacitance
diode 44 are connected in series, is used. However, without limitation thereto,
any series circuit or parallel circuit including the variable-capacitance diode
44 may be used. Thus, any of the parallel circuits shown in part (d) of Fig. 6 may
be used as the second reactance circuit 4b.
Third Embodiment
Next, a third embodiment of the present invention will
be described.
Fig. 7 is a schematic plan view showing an antenna according
to the third embodiment of the present invention. Fig. 8 is circuit diagrams showing
specific examples of the second reactance circuit 4b of the fixed type.
In the second embodiment described above, a series circuit
including a variable capacitor is used as the first reactance circuit 4a, and a
series circuit including a variable capacitor or a parallel circuit including a
variable capacitor is used as the second reactance circuit 4b. In this embodiment,
as the second reactance circuit 4b, a series circuit including a fixed capacitor
or a parallel circuit including a fixed capacitor is used.
The series circuit including a fixed capacitor or the parallel
circuit including a fixed capacitor may be any of circuits shown in parts (a) to
(e) of Fig. 8. In this example, the series circuit shown in part (a) of Fig. 8,
which is a fixed circuit, is used.
More specifically, as shown in Fig. 7, similarly to the
first embodiment described earlier, the first reactance circuit 4a of the frequency-changing
circuit 4 is formed of a series circuit of the inductor 41 and the variable-capacitance
diode 42, and the second reactance circuit 4b is formed of a series circuit of a
capacitor 45 as a fixed capacitor and the inductor 43. Furthermore, the variable-capacitance
diode 42 of the first reactance circuit 4a is connected to the capacitor 45 of the
second reactance circuit 4b, and a control voltage Vc for controlling the capacitance
of the variable-capacitance diode 42 is applied to a node P therebetween.
With the configuration described above, since the reactance
of the second reactance circuit 4b is fixed, the variable-capacitance diode 44 or
the like, which is expensive, is not needed, so that manufacturing cost is reduced
accordingly.
The configuration, operation, and advantage are otherwise
similar to those of the second embodiment described earlier, so that description
thereof will be omitted.
In this embodiment, the circuit shown in part (a) of Fig.
8, in which the inductor 43 and the capacitor 45 are connected in series, is used
as the second reactance circuit 4b connected in series with the first reactance
circuit 4a formed of a series-connection circuit. However, without limitation thereto,
any series circuit or parallel circuit including the capacitor 45 may be used. Thus,
the parallel circuit shown in part (e) of Fig. 8 may be used. That is, by forming
the second reactance circuit 4b of a parallel circuit in which the inductor 43 and
the capacitor 45 are connected in parallel and connecting the cathode side of the
variable-capacitance diode 42 to the second reactance circuit 4b as shown in Fig.
9, it is possible to achieve operation and advantage similar to those in this embodiment.
Fourth Embodiment
Next, a fourth embodiment of the present invention will
be described.
Fig. 10 is a schematic plan view showing an antenna according
to the fourth embodiment of the present invention, and Fig. 11 is circuit diagrams
showing specific examples of the first reactance circuit 4a formed of a parallel
circuit.
In the second and third embodiments described above, a
series circuit including a variable capacitor is used as the first reactance circuit
4a. In this embodiment, a parallel circuit including a variable capacitor is used
as the first reactance circuit 4a.
The parallel circuit including a variable capacitor may
be any of circuits shown in parts (a) and (b) of Fig. 11. In this example, the parallel
circuit shown in part (a) of Fig. 11 is used.
More specifically, as shown in Fig. 10, the first reactance
circuit 4a formed of a parallel circuit is formed by connecting a series circuit
formed of an inductor 47 and a shared capacitor 48 in parallel to a series circuit
formed of the inductor 41 and the variable-capacitance diode 42. Furthermore, regarding
the second reactance circuit 4b, similarly, the second reactance circuit 4b formed
of a parallel circuit is formed by connecting a series circuit formed of an inductor
46 and the shared capacitor 48 in parallel to a series circuit formed of the inductor
43 and the variable-capacitance diode 44.
Furthermore, the terminals of the variable-capacitance
diodes 42 and 44 with the same polarity are connected to each other, a control voltage
Vc for controlling the capacitances of the variable-capacitance diodes 42 and 44
is applied to a node P therebetween.
With the configuration described above, since the first
reactance circuit 4a of the frequency-changing circuit 4 is formed of a parallel
circuit, compared with the case where a series circuit is used, the reactance of
the first reactance circuit 4a can be changed more greatly.
Furthermore, by using one of the inductors 46 and 47 as
a choke coil, it is possible to configure one of the first and second reactance
circuits 4a and 4b as a reactance circuit formed of a series circuit to configure
the other as a reactance circuit formed of a parallel circuit. Thus, for example,
by using the inductor 46 as a choke coil, the second antenna section 3 is formed
of the feeding electrode 5, the series circuit of the inductor 41 and the variable-capacitance
diode 42, and the additional radiating electrode 7, and the setting and variable
range of the resonant frequency f2 are determined under this condition. The capacitor
48 functions as a DC-cut capacitor.
The configuration, operation, and advantage are otherwise
similar to those of the second and third embodiments described earlier, so that
description thereof will be omitted.
In this embodiment, as an example, the parallel circuit
shown in part (c) of Fig. 8 is connected as the second reactance circuit 4b connected
to the first reactance circuit 4a formed of a parallel circuit. However, without
limitation thereto, obviously, any of the circuits shown in Figs. 6 and 8 may be
used as the second reactance circuit 4b. Thus, modifications shown in Fig. 12 are
possible. That is, as a combination of connection of the first reactance circuit
4a and the second reactance circuit 4b, for example, a combination of the parallel
circuit shown in Fig. 11(a) and the variable parallel circuit shown in part (d)
of Fig. 6, shown in part (a) of Fig. 12, a combination of the parallel circuit shown
in part (b) of Fig. 11 and the fixed series circuit shown in part (a) of Fig. 8,
shown in part (b) of Fig. 12, or a combination of the parallel circuit shown in
part (a) of Fig. 11 and the fixed parallel circuit shown in part (d) of Fig. 8,
may be used.
Fifth Embodiment
Next, a fifth embodiment of the present invention will
be described.
Fig. 13 is a schematic plan view showing an antenna according
to the fifth embodiment of the present invention. Fig. 14 is diagrams showing curves
representing return loss that is caused due to the characteristics of an added inductor.
Part (a) of Fig. 14 shows a case where the inductor is provided as a choke coil,
and part (b) of Fig. 14 shows a case where the inductor is provided to allow adjustment
of the resonant frequency.
This embodiment differs from the first to fourth embodiments
in that an inductor 40 is added in parallel across the first and second reactance
circuits 4a and 4b of the frequency-changing circuit 4, as shown in Fig. 13.
In an example described below, the inductor 40 is connected
to the frequency-changing circuit 4 in which the variable series circuit shown in
part (a) of Fig. 5 is used as the first reactance circuit 4a and in which the variable
circuit shown in part (b) of Fig. 6 is used as the second reactance circuit 4b.
That is, the inductor 40 is disposed between the feeding
electrode 5 and the radiating electrode 6, and the ends of the inductor 40 are connected
respectively to the cathode sides of the variable-capacitance diodes 42 and 44.
Thus, with the inductor 40 provided as a choke coil, noise
can be removed from the band, and it is possible to greatly shift only an arbitrary
resonant frequency. Thus, as indicated by a return-loss curve S1 represented by
a solid line and a return-loss curve S2 represented by a broken line in part (a)
of Fig. 14, it is possible to shift only the resonant frequency f1 so that the amount
of change M1 of the resonant frequency f1 is larger than the amount of change M2
of the resonant frequency f2.
Also, when the inductor 40 is provided to allow adjustment
of the resonant frequency, it is possible to configure a third antenna section formed
of the feeding electrode 5, the inductor 40, and the radiating electrode 6. As a
result, as indicated by a return-loss curve S1 represented by the solid line in
part (b) of Fig. 14, a new resonant frequency f0 associated with the third antenna
section is generated in a frequency range lower than the resonant frequency f1 of
the first antenna section 2, so that the low band is obtained. Also, as indicated
by a return-loss curve S2 represented by a broken line, the resonant frequency f0
of the third antenna section can be changed arbitrarily by adjusting the inductance
of the inductor 40.
The configuration, operation, and advantage are otherwise
similar to those of the first to fourth embodiments described earlier, so that description
thereof will be omitted.
In this embodiment, the frequency-changing circuit 4 is
formed by using the variable series circuit shown in part (a) of Fig. 5 as the first
reactance circuit 4a and using the variable circuit shown in part (b) of Fig. 6
as the second reactance circuit 4b. However, it suffices that the inductor 40 is
added in parallel to and across the first and second reactance circuits 4a and 4b,
and otherwise there is no limitation to the configuration of the frequency-changing
circuit 4. Thus, an antenna shown in Fig. 15 can be proposed.
That is, it is possible to achieve operation and advantage
similar to those of this embodiment by connecting the inductor 40 in parallel to
the frequency-changing circuit 4 having the configuration according to the second
embodiment, as shown in part (a) of Fig. 15. Also, it is possible to achieve operation
and advantage similar to those of this embodiment by using a series circuit formed
of the inductor 43 and the capacitor 45 as the second reactance circuit 4b, as shown
in part (b) of Fig. 15. Sixth Embodiment
Next, a sixth embodiment of the present invention will
be described.
Fig. 16 is a schematic plan view showing an antenna according
to the sixth embodiment of the present invention.
In this embodiment, in addition to the configuration of
the fourth embodiment described earlier, an additional radiating electrode 7' separate
from the additional radiating electrode 7 of the second antenna section 3 is connected
to the node P via a resonant-frequency adjusting inductor 71, and an additional
radiating electrode 6' is connected to the radiating electrode 6 via a resonant-frequency
adjusting inductor 61. The control voltage Vc is applied to the node P.
Thus, a third antenna section is formed of the feeding
electrode 5, the first reactance circuit 4a, the resonant-frequency adjusting inductor
71, and the additional radiating electrode 7', and a fourth antenna section is formed
of the feeding electrode 5, the frequency-changing circuit 4, and the additional
radiating electrode 6', so that a four-resonance antenna is formed. That is, it
is possible to further increase the number of resonances, so that a multi-band antenna
compatible with multimedia can be provided.
The configuration, operation, and advantage are otherwise
the same as those of the embodiments described earlier, so that description thereof
will be omitted. Seventh Embodiment
Next, a seventh embodiment of the present invention will
be described.
Fig. 17 is a perspective view showing an antenna according
to the seventh embodiment of the present invention.
In this embodiment, antenna elements, such as the feeding
electrode 5, the frequency-changing circuit 4, the radiating electrode 6, and the
additional radiating electrode 7, are formed on a predetermined dielectric base.
This embodiment will be described in the context of an
example where the antenna shown in part (a) of Fig. 15 is formed on a surface of
a dielectric base 8, as shown in Fig. 17.
More specifically, the dielectric base 8 has a rectangular-parallelepiped
shape having a front surface 80, side surfaces 81 and 82, a top surface 83, a bottom
surface 84, and a rear surface 85, and is mounted on the non-ground region 101 of
the circuit board 100.
The feeding electrode 5 is formed so as to have a pattern
extending from the front surface 80 to the top surface 83 on the left side of the
dielectric base 8. On the non-ground region 101, a pattern 113 is formed, and the
pattern 113 is connected to the transceiver 110 via the inductor 112. One end 5a
of the feeding electrode 5 is connected to the pattern 113, and the other end 5b
is connected to the frequency-changing circuit 4. In the frequency-changing circuit
4, the inductor 41 and the variable-capacitance diode 42 of the first reactance
circuit 4a and the inductor 43 and the variable-capacitance diode 44 of the second
reactance circuit 4b are implemented individually by chip components, and the chip
components are connected via a pattern 48 formed on the top surface 83.
The inductor 40 is formed on the top surface 83 across
the first reactance circuit 4a and the second reactance circuit 4b. More specifically,
a pattern 49 that is parallel to the pattern 48 is formed, and the inductor 40 is
disposed in the middle of the pattern 49.
The radiating electrode 6 has an electrode section 6a extending
rightward from a connecting portion of the patterns 48 and 49 along the upper end
of the top surface 83 and then extending downward on the side surface 81. An electrode
section 6b, which is continuous with the electrode section 6a, extends leftward
on the bottom surface 84 and then extends upward on the side surface 82. A top end
of the electrode section 6b is joined with an electrode section 6c formed at a corner
on the top surface 83. That is, the radiating electrode 6 is constituted by the
electrode sections 6a to 6c, and forms a loop as a whole.
Furthermore, a pattern 72 extends from a connecting portion
of the variable-capacitance diodes 42 and 44 of the frequency-changing circuit 4.
The pattern 72 extends on the top surface 83 and the front surface 80 and is connected
to a pattern 123 formed on the non-ground region 101 and extending to the reception-frequency
controller 120. The high-frequency-cut capacitor 121 is disposed in the middle of
the pattern 72.
The additional radiating electrode 7 is formed so as to
have a pattern extending perpendicularly to the pattern 72 described above, and
is connected to the pattern 72 via the resonant-frequency adjusting inductor 70.
With the configuration described above, it is possible
to adjust the reactances of the first and second antenna sections 2 and 3 by changing
the dielectric constant of the dielectric base 8.
The configuration, operation, and advantage are otherwise
the same as those of the first to sixth embodiments described above, so that description
thereof will be omitted.
Although substantially all the antenna elements, such as
the feeding electrode 5, are formed on the dielectric base 8 in this embodiment,
it is possible to form only some of the antenna elements on the dielectric base
8. Also, although the antenna shown in part (a) of Fig. 15 is formed on a surface
of the dielectric base 8 in this embodiment, without limitation thereto, obviously,
any of the antennas according to all the embodiments described above may be formed
on a surface of the dielectric base 8. Eighth Embodiment
Next, an eighth embodiment of the present invention will
be described.
Fig. 18 is a schematic plan view showing an antenna according
to the eighth embodiment of the present invention, and Fig. 19 is a diagram showing
a curve representing return loss that is caused due to the characteristics of an
added inductor.
This embodiment differs from the embodiments described
above in that a discrete inductor 90 is connected in the middle of the additional
radiating electrode 7 of the second antenna section 3, as shown in Fig. 18.
More specifically, one end 90a of the inductor 90 is connected
to the distal-end side of the additional radiating electrode 7, and the other end
90b is connected to the ground region 102 (see Fig. 1).
With the configuration described above, as indicated by
a return-loss curve S1 in Fig. 19, assuming that the resonant frequency associated
with the inductor 111, the feeding electrode 5, and a frequency-changing-circuit
portion 4' is f0, the resonant frequency associated with the inductor 111, the feeding
electrode 5, the frequency-changing circuit 4, and the radiating electrode 6 is
f1, and the resonant frequency associated with the inductor 111, the feeding electrode
5, the frequency-changing circuit 4, the resonant-frequency adjusting inductor 70,
and the additional radiating electrode 7 is f2, a resonant frequency fa associated
with the inductor 111, the feeding electrode 5, the frequency-changing circuit 4,
the resonant-frequency adjusting inductor 70, the additional radiating electrode
7, and the inductor 90 is newly generated.
As the inductor 90, an inductor that exhibits a high impedance
when it is connected to the additional radiating electrode 7 and the ground region
102 is chosen, so that degradation of antenna gain is prevented. By using the inductor
90 with a high impedance, without significantly affecting the resonant frequency
f2 associated with the inductor 111, the feeding electrode 5, the frequency-changing
circuit 4, the resonant-frequency adjusting inductor 70, and the additional radiating
electrode 7, the new resonant frequency fa, which is lower than the frequency of
the additional radiating electrode 7 at the source of branching, is generated. When
the low resonant frequency is obtained using only an electrode, a considerably long
electrode must be used, so that the cubic size of the antenna increases. However,
by generating the new resonant frequency fa using the inductor 90 as in this embodiment
instead of using an electrode, the cubic size of the antenna can be reduced.
Furthermore, since the frequency-changing circuit 4 including
the variable-capacitance diodes 42 and 44 is disposed between the feeding electrode
5 and the radiating electrode 6 and between the feeding electrode 5 and the additional
radiating electrode 7, by applying the control voltage Vc to the frequency-changing
circuit 4, the resonant frequencies f0, fa, f1, and f2 can be changed as a whole,
as indicated by a return-loss curve S2 represented by a broken line in Fig. 19.
By setting the resonant frequencies f0, fa, f1, and f2
appropriately, FM electromagnetic waves, electromagnetic waves in the VHF band,
and electromagnetic waves in the UHF band can be received.
The configuration, operation, and advantage are otherwise
the same as those of the embodiments described above, so that description thereof
will be omitted.
Although the inductor 90 is connected in the middle of
the additional radiating electrode 7 of the second antenna section in this embodiment,
the inductor 90 may be provided on the side of the open distal end 7a of the additional
radiating electrode 7. However, antenna gain could be degraded when the inductor
90 is disposed too close to the side of the open distal end 7a, so that it is preferable
that the inductor 90 be connected to the additional radiating electrode 7 with consideration
of this point.
Furthermore, although the inductor 90 is connected only
to the additional radiating electrode 7 of the second antenna section in this embodiment,
it is possible to connect the inductor 90 only to the middle of the radiating electrode
6 of the first antenna section 2 instead of connecting to the additional radiating
electrode 7.
Furthermore, although one inductor 90 is connected as the
inductor 90, without limitation thereto, a plurality of inductors 90 may be connected
in parallel.
Ninth Embodiment
Next, a ninth embodiment of the present invention will
be described.
Fig. 20 is a schematic plan view showing an antenna according
to the ninth embodiment of the present invention, and Fig. 21 is a diagram showing
a curve representing return loss that is caused due to the characteristics of two
added inductors.
This embodiment differs from the eighths embodiment described
above in that a discrete inductor 91 is connected also in the middle of the radiating
electrode 6 of the first antenna section 2, as shown in Fig. 20.
More specifically, one end 91a of the inductor 91 is connected
to a bent portion 6d of the radiating electrode 6, and the other end 91b is connected
to the ground region 102.
Thus, as indicated by a return-loss curve S1 in Fig. 21,
in addition to the resonant frequency f0 associated with the inductor 111, the feeding
electrode 5, and the frequency-changing-circuit portion 4', the resonant frequency
fa associated with the inductor 111, the feeding electrode 5, the frequency-changing
circuit 4, the resonant-frequency adjusting inductor 70, the additional radiating
electrode 7, and the inductor 90, the resonant frequency f1 associated with the
inductor 111, the feeding electrode 5, the frequency-changing circuit 4, and the
radiating electrode 6, and the resonant frequency f2 associated with the inductor
111, the feeding electrode 5, the frequency-changing circuit 4, the resonant-frequency
adjusting inductor 70, and the additional radiating electrode 7, a new resonant
frequency fb, which is lower than the frequency of the radiating electrode 6 at
the source of branching, is newly generated by the inductor 111, the feeding electrode
5, the frequency-changing circuit 4, the radiating electrode 6, and the inductor
91.
The inductor 91 is also an inductor with a high impedance,
similarly to the inductor 90, and the resonant frequency fb is a low frequency located
between the resonant frequencies fa and f1.
By applying the control voltage Vc to the frequency-changing
circuit 4, the resonant frequencies f0, fa, fb, f1, and f2 can be changed as a whole,
as indicated by a return-loss curve S2 represented by a broken line in Fig. 21.
The configuration, operation, and advantage are otherwise
the same as those of the eighth embodiment described earlier, so that description
thereof will be omitted.
Tenth Embodiment
Next, a tenth embodiment of the present invention will
be described.
Fig. 22 is a schematic plan view showing an antenna according
to the tenth embodiments of the present invention, and Fig. 23 is a diagram showing
a curve representing return loss that is caused due to the characteristics of three
added inductors.
This embodiment differs from the eighth and ninth embodiments
described above in that, in an antenna in which additional radiating electrodes
6' and 7' separate from the additional radiating electrode 7 of the second antenna
section 3 are provided, discrete inductors 92 and 93 are also connected to the additional
radiating electrodes 6' and 7', respectively, as shown in Fig. 22.
More specifically, one end 92a of the inductor 92 is connected
to a bent portion 6e of the radiating electrode 6, and the other end 92b is connected
to the ground region 102. Also, one end 93a of the inductor 93 is connected to an
open distal end of the additional radiating electrode 7', and the other end 93b
is connected to the ground region 102.
Thus, as indicated by a return-loss curve S1 in Fig. 23,
in addition to the resonant frequencies f0, fa, f1, and f2, a new resonant frequency
fb, which is lower than the frequency of the additional radiating electrode 6' at
the source of branching, is newly generated by the inductor 111, the feeding electrode
5, the frequency-changing circuit 4, the radiating electrode 6, the resonant-frequency
adjusting inductor 61, the additional radiating electrode 6', and the inductor 92,
and a new resonant frequency fc, which is lower than the frequency of the additional
radiating electrode 7' at the source of branching, is newly generated by the inductor
111, the feeding electrode 5, the frequency-changing circuit 4, the resonant-frequency
adjusting inductor 71, the additional radiating electrode 7' and the inductor 93.
These inductors 92 and 93 are inductors with high impedances,
similarly to the inductors 90 and 91. The resonant frequency fb is a low frequency
located between the resonant frequencies fa and f1, and the resonant frequency fc
is a low frequency located between the resonant frequencies f0 and fa.
By applying the control voltage Vc to the frequency-changing
circuit 4, the resonant frequencies f0, fc, fa, fb, f1, and f2 can be changed as
a whole, as indicated by a return-loss curve S2 represented by a broken line in
Fig. 23.
The configuration, operation, and advantage are otherwise
the same as those of the eighth and ninth embodiments described earlier, so that
description thereof will be omitted.
Eleventh Embodiment
Next, an eleventh embodiment of the present invention will
be described.
Fig. 24 is a schematic plan view showing an antenna according
to the eleventh embodiment of the present invention. Fig. 25 is a diagram showing
a curve representing return loss that is caused due to the characteristics of an
added series resonance circuit. Fig. 26 is a diagram showing comparison between
the reactance of a discrete inductor and the reactance of the series resonance circuit.
This embodiment differs from the eighths to tenth embodiments
described above in that a series resonance circuit 9 as a reactance circuit is connected
to the additional radiating electrode 7 of the second antenna section 3, as shown
in Fig. 24.
More specifically, the series resonance circuit 9 is formed
of an inductor 94 and a capacitor 95 connected in series. One end 94a of the inductor
94 is connected to the distal-end side of the additional radiating electrode 7,
and one end 95a of the capacitor 95 is connected to the ground region 102.
Thus, as indicated by a return-loss curve S1 in Fig. 25,
in addition to the resonant frequencies f0, f1, and f2, a new frequency fa associated
with the inductor 111, the feeding electrode 5, the frequency-changing circuit 4,
the resonant-frequency adjusting inductor 70, the additional radiating electrode
7, and the series resonance circuit 9 is newly generated.
By applying the control voltage Vc to the frequency-changing
circuit 4, the resonant frequencies f0, fa, f1, and f2 can be changed as a whole,
as indicated by a return-loss curve S2 represented by a broken line in Fig. 25.
In a series resonance circuit such as the series resonance
circuit 9, as indicated by a reactance curve R1 in Fig. 26, the slope of change
of reactance in relation to frequency is large compared with cases of discrete inductors
90 to 93 indicated by a reactance curve R2. Thus, when the reactance of a discrete
inductor and the reactance of a series resonance circuit needed for an additional
resonance are equal, the reactance at the resonant frequency of an electrode at
the source of branching (the additional radiating electrode 7 in this embodiment)
is larger in the case of the series resonance circuit compared with the case of
the discrete inductor. That is, in this embodiment, by connecting the series resonance
circuit 9 to the additional radiating electrode 7 instead of the inductor 90, a
new resonant frequency fa is obtained without significantly affecting the resonant
frequency f2 associated with the inductor 111, the feeding electrode 5, the frequency-changing
circuit 4, the resonant-frequency adjusting inductor 70, and the additional radiating
electrode 7. Thus, an antenna having favorable operation characteristics can be
provided.
The configuration, operation, and advantage are otherwise
the same as the eighth to tenth embodiments described earlier, so that description
thereof will be omitted.
Twelfth Embodiment
Next, a twelfth embodiment of the present invention will
be described.
Fig. 27 is a schematic plan view showing an antenna according
to the twelfth embodiment of the present invention, and Fig. 28 is a diagram showing
a curve representing return loss that is caused due to the characteristics of an
added series resonance circuit.
This embodiment differs from the eleventh embodiment described
above in that a parallel resonance circuit 9' as a reactance circuit is connected
to the additional radiating electrode 7 of the second antenna section 3, as shown
in Fig. 27.
More specifically, the parallel resonance circuit 9' is
formed of an inductor 94' and a capacitor 95' connected in parallel. One end 9a'
of the parallel resonance circuit 9' is connected to the distal end of the additional
radiating electrode 7, and one end 9b' of the other ends is connected to the ground
region 102.
Thus, as indicated by a return-loss curve S1 in Fig. 28,
in addition to the resonant frequencies f0, f1, and f2, a resonant frequency fa
associated with the inductor 111, the feeding electrode 5, the frequency-changing
circuit 4, the resonant-frequency adjusting inductor 70, the additional radiating
electrode 7, and the parallel resonance circuit 9' is newly generated.
By applying the control voltage Vc to the frequency-changing
circuit 4, the resonant frequencies f0, fa, f1, and f2 can be changed as a whole,
as indicated by a return-loss curve S2 represented by a broken line in Fig. 28.
In order to obtain a large reactance using the series resonance
circuit 9 in the eleventh embodiment described earlier, the inductor 94 that is
used must have a large constant (nH). Usually, a chip component is used as the inductor
94. When a chip component having a large constant is used, the self-resonant frequency
decreases, so that the inductivity is degraded. In contrast, by using the parallel
resonance circuit 9' as in this embodiment, it is possible to obtain a large reactance
using the inductor 94' having a small constant. Thus, by using the parallel resonance
circuit 9', the problem of a chip component regarding the self-resonant frequency
can be solved.
The configuration, operation, and advantage are otherwise
the same as the eleventh embodiment described earlier, so that description thereof
will be omitted. Thirteenth Embodiment
Next, a thirteenth embodiment of the present invention
will be described.
Fig. 29 is a schematic plan view showing an antenna according
to the thirteenth embodiment of the present invention, and Fig. 30 is a diagram
showing a curve representing return loss that is caused due to the characteristics
of an added series resonance circuit.
This embodiment differs from the eleventh and twelfth embodiments
described above in that a composite circuit 10 formed of the series resonance circuit
9 and the parallel resonance circuit 9' is connected as a reactance circuit to the
additional radiating electrode 7 of the second antenna section 3, as shown in Fig.
29.
More specifically, the composite circuit 10 is formed of
the series resonance circuit 9 and the parallel resonance circuit 9' connected in
series. One end 94a of the inductor 94 of the series resonance circuit 9 is connected
to the distal-end side of the additional radiating electrode 7, and one end 9b'
of the parallel resonance circuit 9' is connected to the ground region 102.
Thus, as indicated by a return-loss curve S1 in Fig. 30,
in addition to the resonant frequencies f0, f1, and f2, a resonant frequency fa
associated with the inductor 111, the feeding electrode 5, the frequency-changing
circuit 4, the resonant-frequency adjusting inductor 70, the additional radiating
electrode 7, and the composite circuit 10 is newly generated.
By applying the control voltage Vc to the frequency-changing
circuit 4, the resonant frequencies f0, fa, f1, and f2 can be changed as a whole,
as indicated by a return-loss curve S2 represented by a broken line in Fig. 30.
With the configuration described above, it is possible
to achieve both the advantage of the series resonance circuit 9 that the new resonant
frequency fa can be obtained without significantly affecting the resonant frequency
f2 associated with the additional radiating electrode 7 and the advantage of the
parallel resonance circuit 9' that the problem of an inductor chip component regarding
the self-resonant frequency can be solved.
The configuration, operation, and advantage are otherwise
the same as those of the eleventh and twelfth embodiments described earlier, so
that descriptions thereof will be omitted.
The present invention is not limited to the embodiments
described above, and various alternatives or modifications are possible without
departing from the spirit of the present invention.
For example, although the above embodiments have been described
in the context of examples where an additional radiating electrode is connected
to the node P of the frequency-changing circuit 4 or the middle of the radiating
electrode 6 via a resonant-frequency adjusting inductor, an additional radiating
electrode 6' that is separate from the additional radiating electrode 7 constituting
the second antenna section 3 may be formed directly in the middle of the radiating
electrode 6.
