JP2001060841A - Antenna device, method for adjusting circuit constant of its impedance matching circuit and portable communication apparatus using them - Google Patents

Abstract

PROBLEM TO BE SOLVED: To satisfactorily avoid an impedance mismatching state even if the impedance of an antenna changes in any state of transmission and reception. SOLUTION: Impedance matching circuits 104 and 106 are inserted between antennas 103 and 105 and a transmitting circuit 101 and a receiving circuit 102. A capacitance element 121 is arranged in the vicinity of the antennas 103 and 105. When a dielectric such as a human body and metallic material are present in the neighborhood of the antennas 103 and 105, the capacitance of the antennas 103 and 105 changes, and impedance matching collapses. However, the capacitance Cs of the element 121 also changes at the same time and in accordance with the change, the detection signal Vc of an impedance change detecting part 122 changes, the capacitance of variable capacitance diodes 104b and 106c of the circuits 104 and 106 changes and an impedance matching state is returned again.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an antenna device,
The present invention relates to a circuit constant adjusting method of the impedance matching circuit and a portable communication device using the same. In detail, by disposing an impedance element in the vicinity of the antenna and adjusting the circuit constant of the impedance matching circuit based on the change in the impedance of the impedance element, even if the impedance of the antenna changes in any state of transmission and reception, The present invention relates to an antenna device and the like that can favorably avoid a mismatch state.

[0002]

2. Description of the Related Art Conventionally, in a portable communication device such as a portable telephone, impedance matching between an antenna and a reception circuit or a transmission circuit is performed between an antenna and a reception circuit or a transmission circuit in order to reduce a loss due to reflection. Insertion of an impedance matching circuit has been performed.

In such a portable communication device, when used near a dielectric such as a human body or near a metal material, the antenna impedance changes. For example, if the human body is nearby,
The capacitance from the antenna to the ground via the human body relatively increases. If the antenna impedance changes in this way, impedance matching in the impedance matching circuit will not be performed well, and disadvantages such as an increase in return loss will occur.

Therefore, conventionally, a part of the reflected wave of the transmission wave is taken out by a coupler to detect the impedance mismatch of the antenna, and by switching the connection of the elements of the impedance matching circuit, a good result is obtained even if the impedance of the antenna changes. An antenna matching circuit in which impedance matching is performed has been proposed (JP-A-8-14).
No. 8960).

[0005]

However, as described above, there is a method for extracting a part of a reflected wave of a transmission wave by a coupler, detecting impedance mismatch of an antenna, and switching connection of elements of an impedance matching circuit. Since the direction of the change in the impedance of the antenna is not known, the connection of the elements of the impedance matching circuit may be inappropriate. Further, in this method, only the impedance mismatch state at the time of transmission can be avoided, and the impedance mismatch state at the time of reception cannot be avoided.

SUMMARY OF THE INVENTION In view of the foregoing, it is an object of the present invention to provide an antenna device and the like which can favorably avoid an impedance mismatching state even when the impedance of the antenna changes in any state of transmission and reception.

[0007]

An antenna device according to the present invention comprises: an antenna; an impedance matching circuit for impedance matching between the antenna and another circuit;
An impedance element disposed in the vicinity of the antenna, impedance change detecting means for detecting an impedance change of the impedance element, and a circuit constant adjustment for adjusting a circuit constant of the impedance matching circuit based on a detection result of the impedance change detecting means Means. For example, the impedance element arranged near the antenna is a capacitance element. Further, for example, the impedance change detecting means detects an impedance change as a frequency change.

In addition, a method of adjusting a circuit constant of an impedance matching circuit according to the present invention is a method of adjusting an impedance matching circuit inserted between an antenna and another circuit to perform impedance matching between the antenna and the other circuit. A method for adjusting a circuit constant, which detects an impedance change of an impedance element arranged near an antenna,
The circuit constant of the impedance matching circuit is adjusted based on the detection result.

In the portable communication device according to the present invention, an impedance matching circuit for impedance matching between the antenna and the reception circuit or the transmission circuit is inserted between the antenna and the reception circuit or the transmission circuit. A portable communication device, comprising: an impedance element disposed near an antenna; impedance change detection means for detecting an impedance change of the impedance element; and a detection result of the impedance change detection means.
Circuit constant adjusting means for adjusting the circuit constant of the impedance matching circuit.

In the present invention, if there is a dielectric substance such as a human body or a metal substance near the antenna, the antenna impedance changes, and accordingly, the impedance of the impedance element arranged near the antenna also changes. In this case, a change in the impedance of the impedance element is detected, and the circuit constant of the impedance matching circuit is adjusted based on the detection result. Therefore, even if the impedance of the antenna changes in any of the transmission and reception states, the circuit constant of the antenna matching circuit is adjusted in accordance with the change in the impedance, so that the impedance mismatch state is avoided.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a configuration of a portable communication device 100 as an embodiment. The portable communication device 100 includes a transmission circuit (TX circuit) 101,
A reception circuit (RX circuit) 102, a whip antenna 103 used for transmission and reception, an impedance matching circuit 104 for impedance matching between the whip antenna 103 and the transmission circuit 101 or the reception circuit 102 described above, Built-in antenna 105 used for reception, built-in antenna 105 and receiving circuit 10
2 and a changeover switch 107 for connecting the whip antenna 103 to the transmission circuit 101 at the time of transmission and connecting the whip antenna 103 or the built-in antenna 105 to the reception circuit 102 at the time of reception. , 108.

Here, the impedance matching circuit 104
Is a capacitor 104a, a variable capacitance diode 104b
And the coil 104c. The above-described whip antenna 103 is grounded via a series circuit of a capacitor 104a and a variable capacitance diode 104b, and the whip antenna 103 and the capacitor 104a
Is connected to the changeover switch 107 via the coil 104c.
Is connected to the movable terminal.

The impedance matching circuit 106 includes a coil 106a, a capacitor 106b, and a variable capacitance diode 106c. Then, the built-in antenna 10
5 is grounded via a series circuit of a coil 106a, a capacitor 106b and a variable capacitance diode 106c, and a connection point between the coil 106a and the capacitor 106b is connected to a fixed terminal on the b side of the changeover switch 108.

The fixed terminal on the a side of the changeover switch 107 is connected to the transmission circuit 101, and the fixed terminal on the b side is connected to the fixed terminal on the a side of the changeover switch 108. And
The movable terminal of the switch 108 is connected to the receiving circuit 102. The changeover switch 107 is connected to the a side during transmission, and is connected to the b side during reception. The changeover switch 108 is connected to the a side at the time of transmission, and is controlled by the control of the receiving circuit 102 at the time of reception so that the reception condition is optimized.
Side or b side.

The portable communication device 100 has a capacitance element 121 as an impedance element, and an impedance change detection unit 122 for detecting a change in capacitance of the capacitance element 121. The impedance change detection unit 122 includes a variable oscillator 123 that outputs a frequency signal Sv having a frequency fv,
a reference oscillator 124 that outputs the frequency signal So of the frequency o, and a phase comparator 125 that compares the phases of the frequency signals Sv and So.
And a low-pass filter 126 for extracting a low-frequency component Vc of the phase difference signal output from the phase comparator 125. The reference oscillator 124 is, for example, a temperature compensated crystal oscillator (TCXO).
oscilator).

In this case, the low-frequency component Vc output from the low-pass filter 126 is supplied to the variable oscillator 123 as a frequency control signal. Accordingly, the frequency fv of the frequency signal Sv output from the variable oscillator 123 is
It is controlled so as to match the frequency fo of the frequency signal So output from the reference oscillator 124, and the above-described low-frequency component Vc
Is a signal having a magnitude corresponding to the capacitance of the capacitance element 121. The above-described low-frequency component Vc is output from the impedance change detection unit 122 as a detection signal of the impedance change, and this detection signal is applied to the connection point between the capacitor 104a of the impedance matching circuit 104 and the variable capacitance diode 104b via the choke coil 127. At the same time, this detection signal is applied to the connection point between the capacitor 106b and the variable capacitance diode 106c of the impedance matching circuit 106 via the choke coil 128.

FIG. 2 shows a configuration example of the variable oscillator 123. That is, the variable oscillator 123 is configured using the NPN transistor 131. The low-frequency component Vc described above includes the choke coil 132 and the capacitor 1
It is connected to the base of the transistor 131 via 33 series circuits. The connection point between the choke coil 132 and the capacitor 133 is grounded via the above-described parallel circuit of the capacitance element 121, the variable capacitance diode 134 and the coil 135. The collector of transistor 131 is grounded via capacitor 136, and the collector is connected to the base of the transistor 131 via a series circuit of capacitors 137 and 138. The emitter of the transistor 131 is connected to a connection point between the capacitors 137 and 138, and a frequency signal Sv is obtained from the emitter.

In the variable oscillator 123 shown in FIG. 2, when the capacitance Cs of the capacitance element 121 increases, the frequency fv of the frequency signal Sv decreases. Also,
In the variable oscillator 123, when the low-frequency component Vc increases, the capacitance Cd of the variable capacitance diode 134 decreases, and the frequency fv of the frequency signal Sv increases.

FIG. 3 shows an arrangement example of the whip antenna 103, the built-in antenna 105, the impedance matching circuits 104 and 106, the impedance change detecting unit 122, and the capacitance element 121 on the circuit board 141. Here, the capacitance element 121 is composed of two conductor plates 142a and 142b. In this case, the portable communication device 100 is used near a dielectric such as a human body or near a metal material, and when the capacitance of the antenna changes, the capacitance Cs of the capacitance element 121 changes with the change. , The conductor plate 142a,
142b is arranged near the whip antenna 103 and the built-in antenna 105.

The operation of the portable communication device 100 will be described. At the time of transmission, the changeover switch 107 is connected to the a side. Therefore, the transmission signal from the transmission circuit 101 is transmitted to the whip antenna 10 via the impedance matching circuit 104.
3 and transmitted. During reception, the changeover switch 107 is connected to the b side and the changeover switch 108
Is selectively connected to the a-side or the b-side so that the reception condition becomes the best. Therefore, the reception signal received by the whip antenna 103 or the built-in antenna 105 is supplied to the reception circuit 102 via the impedance matching circuit 104 or 106, respectively.

Next, the operation when the portable communication device 100 is used near a dielectric such as a human body or near a metal material will be described. In this case, the capacitance of the antennas 103 and 105 increases, and the impedance matching circuit 10
The impedance matching at 4,106 is broken. However, at the same time, the capacitance Cs of the capacitance element 121 increases, and the frequency fv of the frequency signal Sv output from the variable oscillator 123 decreases. Therefore, the low-frequency component Vc output from the low-pass filter 126 of the impedance change detection unit 122 increases, and the variable capacitance diode 104 of the impedance matching circuits 104 and 106 increases.
The capacitances of b and 106c decrease and return to the state of impedance matching. In this case, as described above, the low-frequency component Vc increases, and the capacitance Cd of the variable capacitance diode 134 constituting the variable oscillator 123 (see FIG.
), The frequency fv of the frequency signal Sv increases, and this frequency fv becomes equal to the frequency fo of the frequency signal So output from the reference oscillator 124.

Thereafter, this state is maintained as long as the capacitance Cs of the capacitance element 121 does not change. Then, when the state near the antennas 103 and 105 changes again, the capacitance of the antennas 103 and 105 changes, and the impedance matching is broken. Accordingly, the capacitance Cs of the capacitance element 121 also changes, and the low-frequency component accordingly changes. Vc changes, and the variable capacitance diode 104 of the impedance matching circuits 104 and 106 changes.
The capacitances of b and 106c change and return to the state of impedance matching.

As described above, in the present embodiment, the capacitance element 121 is arranged near the whip antenna 103 and the built-in antenna 105, and based on the change in the capacitance Cs of the capacitance element 121, the impedance matching circuit 104, The capacitance of the variable capacitance diodes 104b and 106c of 106 is adjusted. Therefore, even if the capacitances of the antennas 103 and 105 change in any of the transmission and reception states, the impedance mismatch state can be satisfactorily avoided.

In the above-described embodiment, the capacitance element 121 is connected to the two conductor plates 142a and 142b.
4A and 4B, but as shown in FIGS.
The capacitance element 121 may be configured by one conductor plate 142 and the circuit board 141. For example, as shown in FIG.
, The change in capacitance of the built-in antenna 105 can be accurately detected.

Further, even if not described above, the capacitance element 1
21, the conductor plates 142a, 142b, 142
It must be installed outside a conductive shield such as a shield cover. Further, in the above-described embodiment, the capacitance element 121 is used as the impedance element. However, another impedance element whose impedance changes in response to a change in the impedance of the antenna may be used.

The present invention is not limited to the above embodiments, but includes a telescopic monopole antenna, a telescopic helical antenna, a telescopic helical-monopole composite antenna, a fixed monopole antenna, a fixed helical antenna. The present invention can be applied to adjustment of circuit constants of impedance matching circuits of all antennas such as antennas and fixed helical-monopole antennas.

[0027]

According to the present invention, an impedance element is arranged near an antenna, and the circuit constant of an impedance matching circuit is adjusted based on a change in impedance of the impedance element. , The impedance mismatch state can be satisfactorily avoided.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a portable communication device as an embodiment.

FIG. 2 is a circuit connection diagram showing a configuration example of a variable oscillator.

FIG. 3 is a diagram illustrating an arrangement example of an antenna and a circuit on a circuit board.

FIG. 4 is a diagram showing another arrangement example of the antenna and the circuit on the circuit board.

[Explanation of symbols]

100: portable communication device, 101: transmission circuit, 10
2 ... receiving circuit, 103 ... whip antenna, 1
04, 106 ... impedance matching circuit, 105
..Built-in antenna, 107,108... Changeover switch, 121... Capacitance element, 122... Impedance change detecting section, 123.
24 ... reference oscillator, 125 ... phase comparator, 12
6, low-pass filter, 127, 128, choke coil, 141, circuit board, 142, 142
a, 142b ... conductor plate

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Claims (7)

[Claims] 1. An antenna, an impedance matching circuit for matching impedance between the antenna and another circuit, an impedance element disposed near the antenna, and an impedance change detecting an impedance change of the impedance element. An antenna apparatus comprising: a detecting unit; and a circuit constant adjusting unit that adjusts a circuit constant of the impedance matching circuit based on a detection result of the impedance change detecting unit. 2. The antenna device according to claim 1, wherein the impedance element is a capacitance element. 3. The antenna device according to claim 1, wherein the impedance change detecting means detects the impedance change as a frequency change. 4. A method for adjusting a circuit constant of an impedance matching circuit inserted between an antenna and another circuit to perform impedance matching between the antenna and the other circuit, the method comprising: A method for adjusting a circuit constant of an impedance matching circuit, comprising: detecting a change in impedance of an impedance element disposed in the circuit; and adjusting a circuit constant of the impedance matching circuit based on the detection result. 5. A portable communication device comprising an antenna and a receiving circuit or a transmitting circuit, wherein an impedance matching circuit for performing impedance matching between the antenna and the receiving circuit or the transmitting circuit is inserted. An impedance element disposed in the vicinity of the antenna; impedance change detection means for detecting an impedance change of the impedance element; and a circuit constant for adjusting a circuit constant of the impedance matching circuit based on a detection result of the impedance change detection means. A portable communication device comprising an adjustment unit. 6. The portable communication device according to claim 5, wherein said impedance element is a capacitance element. 7. The portable communication device according to claim 5, wherein the impedance change detecting means detects the impedance change as a frequency change.