JPH11122037A - Antenna for portable radio terminal equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To unite the changeover control signals of a matching circuit for providing equal antenna characteristics in any band, into a single signal when the addition of an allocation frequency band is allocated separately from a band in use at present. SOLUTION: A changeover matching circuit 8 is provided between a power feeding pin 5, connected to the power feeding point (a) of a radiation flat plate 1 and a power feeding cable 3. A power supply voltage Vcc is applied to the serial arm composed of a switching diode CR1 and a parallel capacitor C6 of the changeover matching circuit 8, and a bias control voltage Vcont is supplied to a parallel arm composed of a switching diode CR2 and a serial capacitor C5. When a control voltage is turned off, the CR1 is turned on, when the CR2 is turned off, the power feeding point (a) of this antenna and receiver input are directly connected and matching with a first band is performed. When it is turned on, the CR1 is turned off, the CR2 is turned on, the matching circuit constituted of the C5 and C6 is inserted, and matching with a separated second band is performed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverted-F antenna mounted on a portable radio terminal, and more particularly, to a switching matching circuit for matching impedance with a receiver input in response to selection of two antenna tuning frequencies. It is about an antenna.

[0002]

2. Description of the Related Art FIG. 6 is a perspective view showing an outline of an inverted F-type built-in antenna used in a conventional portable radio terminal.
FIG. 7 is an example of the reflection characteristics. In the figure, 1 is a radiation plate, 2 is a ground plate, 3 is a feed cable, 4 is a short-circuit pin, 5 is a feed pin, and a is a feed point. Conventionally, a low-profile planar antenna as shown in FIG. 6 is used, and the tuning frequency bandwidth (fractional band) is such that the return loss is a predetermined voltage standing wave ratio (VSWR) < −10 dB that satisfies 2.0
It is about a few% below. In FIG. 7, the bandwidth (f2-
f1) / f0 is about 2%.

[0003] In recent years, portable wireless terminals have been rapidly spread with the expansion of service areas for cellular phones and the like, lower prices of terminals, and lowering of call costs.
Along with this, the necessary radio channels are insufficient, and for example, as shown in the A band and the B band shown in the frequency band allocation example diagram of FIG.
The channel of the currently used frequency band A becomes full, and a radio channel may be additionally allocated to a frequency band B distant from the band A.

[0004] If the additional allocation of such a radio channel is a frequency band that is continuous with the currently used frequency band,
If the band of the antenna is realized, the antenna characteristics can be dealt with without deteriorating the antenna characteristics. However, as shown in the band B in FIG. However, there is a problem that the antenna gain is deteriorated only by widening the band, and it is impossible to obtain good antenna characteristics. Further, even when the two bands are switched without widening the antenna, there is a problem in that good impedance conversion characteristics cannot be obtained, a mismatch loss (mismatch loss) occurs, and the antenna gain is impaired.

[0005] In order to solve the problems of the prior art, the present applicant has previously proposed an antenna for a portable radio terminal capable of providing good antenna characteristics in any frequency band apart from each other ( Japanese Patent Application 8-2739
No. 39).

FIG. 9 is a perspective view showing the structure of the previously proposed antenna, in which a series variable capacitance circuit 7 comprising a variable capacitance diode and a bias control circuit for changing the capacitance is supplied to a power supply pin 5 and a receiver input. 3 is a structural example of a portable wireless terminal antenna connected in series with a cable 3;

FIG. 10 is a detailed circuit example of the series variable capacitance circuit 7 of FIG. This series variable capacitance circuit 7 includes a variable capacitance diode CR10 and its bias control circuit.
Changing the series capacitance value by applying a control voltage Vcont to the variable capacitance diode CR10, to arbitrarily control the resonant frequency f ₀ of the antenna (matching) are configured to be able.

FIG. 11 is a diagram showing an example of reflection characteristics of an antenna circuit when the capacitance value is changed by controlling the bias voltage of the variable capacitance diode CR10, and the vertical axis indicates the return loss. The control voltage Vcont is high in the curve g resonating at the highest frequency, and the control voltage Vcont is low in the curve c resonating at the low frequency. However, in the configuration proposed earlier, as shown in FIG. 11, there is a problem that when the frequency is changed to a low frequency, the adjustment combined bandwidth becomes narrow, or the frequency variable width cannot be sufficiently widened. In addition, since the varicap (variable capacitance diode) has a variation in performance, there is a problem that a frequency control amount varies.

The inventor of the present invention has solved the problems of the above-mentioned proposed structure, namely, the fact that the antenna alone has a narrow band, and that when the frequency is changed, the adjustment combined bandwidth becomes narrower. However, an antenna for a portable wireless terminal capable of providing good antenna characteristics in any of frequency bands separated from each other has been proposed (Japanese Patent Application No. Hei 8-8).
No. 327987). This is called the second proposal.

FIG. 12 is a perspective view of an antenna according to the second proposal, and FIG. 13 is a circuit diagram of a main part thereof. This second proposal is based on the feeding pin 5 of the antenna and the feeding cable 3.
And a switching matching circuit 6 is provided between them. The switching matching circuit 6 includes an inverted L-shaped capacitive reactance matching circuit including a series capacitor C6 for impedance matching and a parallel capacitor C5 between the ground and a first switching diode CR1 connected in parallel with the series capacitor C6. , A second switching diode CR2 connected in series with the parallel capacitor C5, and a bias control circuit for the two switching diodes. By alternately turning on / off the two switching diodes, the reverse L of the capacitors C5 and C6 is obtained. By switching the matching impedance by inserting or short-circuiting a capacitive matching circuit, antenna tuning can be achieved well in any of two distant frequency bands.

In FIG. 13, R1 to R3 are bias resistors and have high resistance (several kΩ or more) so as not to affect high frequency characteristics. The capacitors C1 to C4 are high frequency pass capacitors and have large capacitance values. Capacitors C5 and C6 are matching capacitors and constitute an inverted L-shaped capacitive reactance matching circuit. For example, C6 = 10p
F, C5 = 5 pF. Switching diode CR1
By applying the control voltages Vcont1 and Vcont2 to CR2 and CR2, when one is turned on, the other is turned off and the insertion / removal of the matching circuit of the capacitors C5 and C6 is switched.

FIG. 14 is an example of the characteristic, and is a graph showing an example of the reflection characteristic of the antenna circuit when the switching matching circuit 6 is turned on and off by switching. Even if the resonance characteristic changes from a to b or from b to a, and the resonance frequency changes by several tens of MHz, the bandwidth is almost the same.

[0013]

However, the switching matching circuit of FIG. 13 requires two control signals Vcont1 and Vcont2, and either supplies two control signals from the logic circuit side, or To Vcont
1, and an inverter is connected to the terminal thereof to generate the other control signal Vcont2. However, there is a problem that the circuit becomes complicated.

An object of the present invention is to enable the switching of the matching frequency with a single control signal without using a paricap (variable capacitance diode) when a frequency band is additionally allocated at intervals. An object of the present invention is to provide an antenna for a portable wireless terminal having a switching matching circuit.

[0015]

According to the present invention, there is provided an antenna for a portable radio terminal, comprising: a ground plate; a radiating plate disposed in parallel with and facing the ground plate; one end of the radiating plate; An inverted-F antenna consisting of a short-circuit pin for short-circuiting the flat plate and a feed pin attached to a feed point on the side edge of the radiating flat plate, and connected to and separated from the feed pin and a feed cable to a receiver input; In a portable wireless terminal antenna comprising a switching matching circuit that performs impedance matching in any of the assigned first frequency band and the second frequency band, the switching matching circuit is provided between the power supply pin and the power supply cable. L-shaped capacitive reactor having a high frequency composed of a series capacitor connected to the power supply cable side of the series capacitor and a parallel capacitor connected between the ground and the ground. Impedance matching circuit, a first switching diode connected in parallel to the series capacitor so that an anode is on the power supply pin side, and the series capacitor side is a cathode between the parallel capacitor and the series capacitor. A second switching diode connected in series as described above, a first resistor connected between the anode of the first switching diode and ground, and a second switching diode connected between the cathode of the first switching diode and ground. A second resistor connected between the anode of the first switching diode and a constant-voltage DC power supply;
A fourth resistor connected between the anode of the second switching diode and a control power supply, and turning on / off the control voltage of the control power supply to directly connect the impedance matching circuit at a high frequency. Alternatively, it is characterized by being inserted so that impedance matching can be achieved in both the first frequency band and the second frequency band.

[0016]

FIG. 1 is a perspective view showing an embodiment of the present invention, and 8 is a switching matching circuit which is a main part of the present invention. FIG. 2 is a circuit diagram of the switching matching circuit 8. The difference from the previously proposed circuit of FIG. 13 is that the control voltage Vcont for the first switching diode CR1 is
1 is a constant DC voltage Vcc, and a point that a bias resistor R4 is provided between the anode terminal of the first switching diode CR1 and the ground.

By turning on / off (for example, 3V / 0V) one control voltage Vcont applied to the anode side of the second switching diode CR2, the capacitor C
An inverted L-shaped matching circuit composed of 6 and C5 is inserted or short-circuited.

The operation of the present invention shown in FIG. 2 will be described. For example, the voltage when Vcont is on is changed to the power supply voltage Vcc.
(For example, Vcont = Vcc = 3V). First
The potential of the anode side of the connection point of the switching diode CR1 and V _1, V ₂ the potential of the cathode side of the connection point of the first and second switching diodes CR1 and CR2, the anode of the second switching diode CR2 of the potential and V _3. And the bias resistor R1
The values of R4 are set so as to satisfy the following conditions. When the (condition 1) Vcont is on (3V), Vcont> V ₃
> V ₂ > V ₁ , CR1 is off (1 pF), CR2
Is turned on (0.5 to 1Ω). (Condition 2) When Vcont is off (0 V), V ₁ > V ₂ >
Become a V _3> Vcont, CR1 is on (0.5 to 1
Ω), CR2 is turned off (1 pF).

The points for selecting the bias resistors R1 to R4 are such that R1, R2, and R4 are set to substantially equal values, and R3 is small in a range where the influence is small in terms of high frequency, and is not too small in terms of current consumption. Set to. For example, R1
= R2 = R4 = 9 kΩ to 12 kΩ, R3 ≒ 1 kΩ, the above conditions were satisfied, and good results were obtained as described below.

FIG. 3 shows a high-frequency equivalent circuit when Vcont = 0 V. The feeding point a of the antenna and the input terminal of the receiver are directly connected to match the lower frequency band.

FIG. 4 shows a high-frequency equivalent circuit when Vcont = 3 V. An impedance matching circuit composed of capacitors C5 and C6 is inserted between the feeding point a of the antenna and the input terminal of the receiver to match the higher frequency band. I do. The series resistance Rs of the switching diode during conduction is 0.5 to 1.0Ω. Under this condition, the frequency band is switched on the low impedance side of the antenna, so that the loss is low.

FIG. 5 is a diagram showing an example of reflection characteristics when the switching matching circuit 8 of the present invention is switched on and off by switching, and is almost the same as the characteristic in FIG. 14 when there are two control voltages.

Although two diodes are separately shown in the circuit diagram, the diode is actually small because two diodes in one package can be used.

[0024]

As described above, by implementing the present invention, a matching circuit can be switched and controlled by one control signal so as to tune in any of two different frequency bands, so that an additional circuit such as an inverter can be provided. This is unnecessary, the circuit is simplified, and sufficient antenna characteristics can be maintained even in radio channels with distant frequencies.

[Brief description of the drawings]

FIG. 1 is a perspective view showing the structure of an embodiment of the present invention.

FIG. 2 is a circuit diagram showing an embodiment of the present invention.

FIG. 3 is a high-frequency equivalent circuit diagram of the circuit of FIG. 2 when Vcont = 0V.

4 is a high-frequency equivalent circuit diagram of the circuit of FIG. 2 when Vcont = 3V.

FIG. 5 is a characteristic example diagram of the embodiment of the present invention.

FIG. 6 is a perspective view of a conventional inverted-F antenna.

FIG. 7 is a characteristic example diagram of a conventional example.

FIG. 8 is a diagram illustrating an example of frequency band allocation.

FIG. 9 is a perspective view showing the structure of the antenna proposed earlier.

FIG. 10 is a partial detailed circuit example of FIG. 9;

FIG. 11 is a characteristic example diagram of the antenna having the structure of FIGS.

FIG. 12 is a perspective view of the previously proposed antenna.

FIG. 13 is a circuit diagram of the previously proposed antenna.

FIG. 14 is a diagram illustrating an example of characteristics of the antenna proposed earlier.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Radiation plate 2 Ground plate 3 Power supply cable 4 Short-circuit pin 5 Power supply pin 6 Switching matching circuit, 7 Series variable capacitance circuit 8 Switching matching circuit

Claims (1)

[Claims] 1. A grounding plate, a radiating plate disposed in parallel with and opposed to the grounding plate, a short-circuit pin for short-circuiting one end of the radiating plate and the grounding plate, and a side edge of the radiating plate. An inverted-F antenna comprising a feed pin attached to a feed point; and a first and second frequency band connected between the feed pin and a feed cable to a receiver input and allocated apart from each other. In any case, the switching matching circuit includes a series capacitor connected between the power supply pin and the power supply cable, and a power supply cable side of the series capacitor. An impedance matching circuit based on an inverted L-shaped capacitive reactance formed at a high frequency with a parallel capacitor connected to the ground; A first switching diode connected in parallel to the series capacitor so as to be connected to the power pin, and a second switching diode connected in series between the parallel capacitor and the series capacitor such that the series capacitor side is the cathode. A diode, a first resistor connected between the anode of the first switching diode and ground,
A second resistor connected between the cathode of the first switching diode and ground, and a third resistor connected between the anode of the first switching diode and a constant voltage DC power supply And a fourth resistor connected between the anode of the second switching diode and a control power supply, and turning on / off the control voltage of the control power supply to change the impedance matching circuit to a high frequency. An antenna for a portable wireless terminal, wherein the antenna is directly connected to or inserted into the antenna so that impedance matching can be achieved in either the first frequency band or the second frequency band.