BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a variable directional
antenna device that can switch directivity.
2. Description of the Related Art
A variable directional antenna device according to the
related art will be described with reference to Figs. 4 and 5. In Fig. 4, a first
antenna 10 is a dipole antenna that has two rod conductors and resonates at a frequency
to be used to have an electrical length of &lgr;/2. The first antenna 10 is connected
to a wireless device 12 via a feeding unit 11. The wireless device 12 has a transmitting
unit 16, a receiving unit 17, and an antenna duplexer 18 for sharing the antenna
at the time of transmitting and receiving signals. The first antenna 10 is connected
to the transmitting and receiving units 16 and 17 via the feeding unit 11 and the
antenna duplexer 18.
The receiving unit 17 outputs a voltage according to a
received field intensity and is connected to an A/D converter 19 provided in a control
circuit 15. An output of the A/D converter 19 is connected to a CPU 20. Similarly,
a second antenna 13 is a dipole antenna having two rod conductors. The second antenna
13 is disposed in parallel with the first antenna 10 at a small distance from the
first antenna 10 and is connected to a variable impedance circuit 14.
As shown in Fig. 5, the variable impedance circuit 14 has
a variable capacitance diode 21, a capacitor 22, a coil 23, and a high-frequency
choke coil 24. The second antenna 13 is connected in series to the coil 23, the
capacitor 22, and the variable capacitance diode 21, and is connected to an output
side of a D/A converter 25 in the control circuit 15 via the high-frequency choke
coil 24. An input side of the D/A converter 25 is connected to the CPU 20. Further,
the CPU is connected to a memory 26.
When a low voltage (output voltage V1 of the D/A converter
25) is applied to both ends of the variable capacitance diode 21, the electrical
length of the second antenna 13 is shorter than the original electrical length due
to the capacitance of the variable capacitance diode 21, such that the second antenna
13 functions as a wave director. At this time, a strong radiation field can be obtained
at the second antenna 13 side. Further, when the voltage applied to the variable
capacitance diode is high (V2), the capacitance of the variable capacitance diode
21 decreases, and thus the electrical length of the second antenna 13 is longer,
such that the second antenna 13 functions as a reflector. In this case, a strong
radiation field can be obtained at the first antenna 10 side. Data D1 and D2 corresponding
to the output voltages V1 and V2 of the D/A converter 25 when the second antenna
13 functions as the wave director and the reflector is stored in the memory 26 in
advance.
First, the CPU 20 selects data D1 of the memory 26 to cause
the second antenna 13 to function as the wave director, such that the output voltage
of the D/A converter 25 becomes V1. At this time, the voltage of a received electric
wave (first field intensity data) is inputted to the CPU 20 via the A/D converter
19 and then is stored in the memory 26. Next, the CPU 20 selects data D2 of the
memory 26 to cause the second antenna 13 to function as the reflector, such that
the output voltage of the D/A converter 25 becomes V2. At this time, the voltage
of a received electric wave (second field intensity data) is inputted to the CPU
20 via the A/D converter 19 and then is stored the memory 26. The CPU 20 compares
first field intensity data to second field intensity data and set the second antenna
13 to function as the wave director or the reflector based on the comparison result
(for example, see
Japanese Patent No. 3399545 B2
(Figs. 1 and 2)).
The related art variable directional antenna device has
directivity of two directions of the first antenna side and the second antenna side.
Accordingly, when the variable directional antenna device is mounted on a mobile
of which the traveling direction varies constantly, sufficient field intensity cannot
be obtained.
US 6 757 267
discloses a variable directional antenna device comprising a first antenna
having a capacitive unit located on the first antenna, and a second antenna disposed
away from the first antenna and a second capacitive unit, wherein, when the electrical
length of the second antenna is equal to that of the first antenna, a signal received
by the first antenna and a signal received by the second antenna are synthesized
and outputted.
JP 60 074801
discloses an antenna comprising a first loaded antenna and a second loaded
antenna.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a variable
directional antenna device that can switch directivity in four directions.
According to a first aspect of the invention, a variable
directional antenna device includes the features of claim 1.
Preferred embodiments are defined by the dependent claims.
According to a fifth aspect of the invention, at least
the first loaded antenna may resonate in a UHF band.
BRIEF DESCRIPTION OF THE DRAWINGS
- Fig. 1 is a circuit diagram showing a configuration of a variable directional
antenna device according to the invention;
- Fig. 2A is a diagram showing a radiation field directional property of the variable
directional antenna device according to the invention;
- Fig. 2B is a diagram showing a radiation field directional property of the variable
directional antenna device according to the invention;
- Fig. 2C is a diagram showing a radiation field directional property of the variable
directional antenna device according to the invention;
- Fig. 3 is a diagram showing a control circuit for controlling the variable directional
antenna device according to the invention;
- Fig. 4 is a circuit diagram showing a configuration of a variable directional
antenna device according to the related art; and
- Fig. 5 is a diagram showing a variable impedance circuit loaded on the variable
directional antenna device according to the related art.
DESCRIPTION OF THE PREFERRED EMBODIMENT
A variable directional antenna device of the invention
will now be described with reference to Figs. 1 and 2. A first loaded antenna 30
has a first antenna 31 and a first capacitive unit 32, which is loaded on the first
antenna 31. The first capacitive unit 32 is connected between one end of the first
antenna 31 and a ground, and has a first variable capacitance diode 32a of which
an anode is connected to one end of the first antenna 31 and a first capacitive
element 32b that is connected between a cathode of the first variable capacitance
diode 32a and the ground. The anode of the first variable capacitance diode 32a
is grounded in direct-current wise via a resistor 33.
Further, a second loaded antenna 40 has a second antenna
41 that is disposed away from the first antenna 31 and a second capacitive unit
42 that is loaded on the second antenna 41. The second capacitive unit 42 is connected
between one end of the second antenna 41 and the ground, and has a second variable
capacitance diode 42a of which an anode is connected to the one end of the second
antenna 41, a second capacitive element 42b that is connected between a cathode
of the second variable capacitance diode 42a and the ground, a third capacitive
element 42d that is connected in parallel to the second capacitive element 42b via
a first closing unit 42c, and a fourth capacitive element 42f that is connected
in parallel to the second capacitive element 42b via a second closing unit 42e.
The anode of the second variable capacitance diode 42a is grounded in direct-current
wise via a resistor 43.
The connection point between the cathode of the first variable
capacitance diode 32a and the first capacitive element 32b is connected to one input
terminal of a switching unit 50 and simultaneously is connected to one input terminal
of a synthesizing unit 52 via a third closing unit 51. Further, the connection point
between the cathode of the second variable capacitance diode 42a and the second
capacitive element 42b is connected to the other input terminal of the synthesizing
unit 52. An output terminal of the synthesizing unit 52 is connected to the other
input terminal of the switching unit 50. Further, an output terminal of the switching
unit 50 is connected to a receiving circuit 53. The receiving circuit 53 has, for
example, a UHF tuner and the like.
In the first loaded antenna 30 and the second loaded antenna
40, the first antenna 31 and the second antenna 41 have the same electrical length,
and the sum of the capacitance value of the second capacitive element 42b and the
capacitance value of the third capacitive element 42d is the same as the capacitance
value of the first capacitive element 32b. Further, the first and second variable
capacitance diodes 32a and 42a have the same characteristics. Further, the cathode
of the first variable capacitance diode 32a and the cathode of the second variable
capacitance diode 42a are applied with the same tuning voltage Vt. The tuning voltage
is variable.
Figs. 2A to 2C show directivity of radiation field intensity
by the first and the second loaded antennas 30 and 40 in a plane perpendicular to
the axis directions of the first and second antennas 31 and 41. In Fig. 2, M and
S indicate the positions of the first and second antennas 31 and 41, respectively.
Here, when the first and second closing units 42c and 42e
are turned off (opened) together, the resonant frequency of the second loaded antenna
40 is higher than that of the first loaded antenna 30, and the electrical length
of the second loaded antenna 40 is shorter than that of the first loaded antenna
30. Accordingly, the second loaded antenna 40 functions as a wave director, such
that the radiation field intensity is larger at the second antenna 41 side (S side),
as shown in Fig. 2C. In this case, the third closing unit 51 is turned off, such
that the output terminal of the switching unit 50 is switched to the one input terminal
(at the first loaded antenna 30 side).
Further, when the first closing unit 42c and the second
closing unit 42 are turned on (shorted) together, the resonant frequency of the
second loaded antenna 40 is lower than that of the first loaded antenna 30, and
the electrical length of the second loaded antenna 40 is longer than that of the
first loaded antenna 30. Accordingly, the second loaded antenna 40 functions as
a reflector, such that the radiation field intensity is larger at the first antenna
31 side (M side), as shown in Fig. 2B. In this case, the third closing unit 51 is
turned off, such that the output terminal of the switching unit 50 is switched to
the one input terminal (the first loaded antenna 30 side).
Further, when the first closing unit 42c is turned on and
the second closing unit 42e is turned off, the first loaded antenna 30 and the second
loaded antenna 40 have the same resonant frequency. Accordingly, the electrical
length of the second loaded antenna 40 is equal to that of the first loaded antenna
30. In this case, a signal received by the first loaded antenna 30 and a signal
received by the second loaded antenna 40 are synthesized to suppress a radiation
field at the first antenna 31 side and a radiation field at the second antenna 41
side, such that radiation field intensity is larger in a direction perpendicular
to a line connecting the position of the first antenna 31 to the position of the
second antenna 41, as shown in Fig. 2A. Accordingly, in this case, the third closing
unit 51 is turned on, and the output terminal of the switching unit 50 is switched
to the other input terminal (the synthesizing unit 52 side).
Therefore, the variable directional antenna device can
be switched to have directivity in four directions. According to the above-described
configuration, an antenna device suitable for receiving television signals when
being mounted on a mobile or the like can be realized.
Further, since the first loaded antenna 30 and the second
loaded antenna 40 have the first variable capacitance diode 32a and the second variable
capacitance diode 42a, respectively, the resonant frequencies of the loaded antennas
30 and 40 vary in conjunction with each other by changing the tuning voltage. Therefore,
even when a receiving frequency varies, the pattern of radiation field intensity
of Fig. 2 can be maintained.
Fig. 3 shows the configuration of a control circuit for
automatically controlling opening or closing of the first to third closing units
42c, 42e, and 51, and switching of the switching unit 50. As shown in Fig. 3, the
control circuit includes a detector circuit 61, an A/D converter 62, a temporary
register 63, a CPU 64, a MAX data register 65, a data switch 66, an antenna control
circuit 67, and the like. The CPU 64 has a comparing unit. Further, the antenna
control unit 67 controls the first to third closing units 42c, 42e, and 51 and the
switching unit 50 based on data from the CPU 64.
In the following description of a control method, a case
in which the resonant frequency of the second loaded antenna 40 is equal to that
of the first loaded antenna 30 is referred to as an A mode. Further, a case in which
the resonant frequency of the second loaded antenna 40 is lower than that of the
first loaded antenna 30 (a case in which the second loaded antenna 40 functions
as the reflector) is referred to as a B mode. In addition, a case in which the resonant
frequency of the second loaded antenna 40 is higher than that of the first loaded
antenna 30 (a case in which the second loaded antenna 40 functions as the wave director)
is referred to as a C mode.
First, the CPU 64 sets an AGC voltage applied to an amplifier
(not shown) in the receiving circuit 53 (see Fig. 1) to a constant value, and simultaneously
clears the temporary register 63 and the MAX data register 65. Then, the CPU 64
outputs data for the A mode to the antenna control circuit 67 to set the A mode
first, such that the first to third closing units 42c, 42e, and 51 are turned on
and the output terminal of the switching unit 50 is switched to the one input terminal
(the first loaded antenna 30 side).
A signal received in the A mode is detected by the detector
circuit 61 and then is converted into a digital signal by the A/D converter 62.
The converted digital signal is stored the temporary register 63 as receiving intensity
data. Then, receiving intensity data stored in the temporary register 63 is compared
to data of the MAX data register 65. At this time, since the MAX data register 65
has been cleared, receiving intensity data of the temporary register 63 is larger.
Subsequently, the CPU 64 turns on the data switch 66 so as to transfer receiving
intensity data of the temporary register 63 to the MAX data register 65.
Next, when the CPU 64 is switched to the B mode, the first
and second closing units 42c and 42e are tuned on, the third closing unit 51 is
turned off, and the output terminal of the switching unit 50 is switched to the
other input terminal (the synthesizing unit 52 side). Similarly, receiving intensity
data in the B mode is stored in the temporary register 63 and then is compared to
data of the MAX data register 65 (in which receiving intensity data in the A mode
is stored). As the comparison result, when receiving intensity data in the B mode
is larger than data of the MAX data register 65, receiving intensity data is stored
in the MAX data register 65.
Similarly, receiving intensity data in the C mode is compared
to data of the MAX data register 65, larger data of them is stored in the MAX data
register 65. Since data stored in the MAX data register 65 for the last time is
the maximum value, the CPU 64 outputs switching data of the mode corresponding to
data to the antenna control circuit 67, and the antenna control circuit 67 controls
opening or closing of the closing units 42c, 42e, and 51, and switching of the switching
unit 50 based on data. The variable directional antenna device can constantly maintain
the best receiving state by repeatedly performing the above-described sequences.
According to the first aspect of the invention, the variable
directional antenna device includes the first loaded antenna that has the first
antenna and the first capacitive unit loaded on the first antenna, and the second
loaded antenna that has the second antenna disposed away from the first antenna
and the second capacitive unit loaded on the second antenna. The electrical length
of the second loaded antenna is longer or shorter than, or equal to that of the
first loaded antenna by switching the capacitance value of the second capacitive
unit. When the electrical length of the second loaded antenna is equal to that of
the first loaded antenna, the signal received by the first loaded antenna and the
signal received by the second loaded antenna are synthesized. Therefore, when the
second loaded antenna is operated as a wave director or a reflector by causing the
electrical length of the second loaded antenna to be longer or shorter than that
of the first loaded antenna, a strong radiation field is obtained at the first or
second antenna side. Further, when the electrical length of the second loaded antenna
is equal to that of the first loaded antenna, a strong radiation field is obtained
in a direction perpendicular to a direction in which the first and second antennas
are arranged. Therefore, a radiation field in four directions is obtained, thereby
realizing an antenna device suitable for a mobile receiver.
Further, according to the second aspect of the invention,
in the first capacitive unit, the first variable capacitance diode is provided so
as to be interposed between the first antenna and the ground, and, in the second
capacitive unit, the second variable capacitance diode is provided so as to be interposed
the second antenna and the ground. Further, the first variable capacitance diode
and the second variable capacitance diode are applied with the same voltage for
switching the capacitance values of the first and second variable capacitance diodes.
Therefore, the variable directional antenna device can receive signals over a broad
band, such as television broadcasting signals, by continuously changing the resonant
frequency of each of the loaded antennas.
Further, according to the third aspect of the invention,
in the first capacitive unit, the first capacitive element is provided so as to
be interposed between the first variable capacitance diode and the ground. In the
second capacitive unit, the second capacitive element is provided so as to be interposed
between the second variable capacitance diode and the ground, the third capacitive
element is provided to be connected in parallel with the second capacitive element
via the first closing unit, and the fourth capacitive element is provided to be
connected in parallel with the second capacitive element via the second closing
unit. Further, the sum of the capacitance value of the second capacitive element
and the capacitance value of the third capacitive element is made to be equal to
the capacitance value of the first capacitive element. In addition, the first and
second closing units are turned on or off together, or the first closing unit is
turned on and simultaneously the second closing unit is turned off. Therefore, the
electrical length of the second loaded antenna can be made to be shorter or longer
than, or equal to that of the first loaded antenna.
Further, according to the fourth aspect of the invention,
the variable directional antenna device further includes the switching unit of which
the output terminal is connected to the receiving circuit, the synthesizing unit
that has the output terminal and the two input terminals, and the third closing
unit that is connected between the first loaded antenna and the one input terminal
of the synthesizing unit. Further, when the other input terminal of the synthesizing
unit is connected to the second loaded antenna, and the first and second closing
units are turned on or off together, the third closing unit is turned off and simultaneously
the output terminal of the switching unit is connected to the first loaded antenna.
Further, when the first closing unit is turned on and simultaneously the second
closing unit is turned off, the third closing unit is turned on and simultaneously
the output terminal of the switching unit is connected to the output terminal of
the synthesizing unit. Therefore, a signal having strong field intensity can be
constantly inputted to the receiving circuit.
According to the fifth aspect of the invention, at least
the first loaded antenna is resonated in a UHF band. Therefore, an antenna device
suitable for receiving of television signals can be obtained.
