JPH1028013A - Planar antenna - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform an operation without lowering the gain even in a wide band or plural bands by adding a load impedance to an antenna element and discretely or continuously controlling the value. SOLUTION: A load impedance switch circuit 200 for switching and connecting the mutually different plural load impedances is provided in the antenna element 101. The load impedance switch circuit 200 is composed of a switch circuit 202, a capacitive impedance element 202, an inductive impedance element 203 and a control terminal 204. In this case, when a resonance frequency in the open circuit of the switch circuit 201 is defined as f0 and the wavelength is defined as λ0, in the case that the switch circuit 201 selects the capacitive impedance element 202 for instance, the electric field phase of the edge part of the antenna element 101 is delayed and a resonance wavelength λ1 becomes >λ0. The resonance wavelength λ1 is adjusted by the impedance value of the capacitive impedance element 202 and a loading position.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a planar antenna corresponding to a plurality of frequencies suitable for an antenna of a portable radio apparatus.

[0002]

2. Description of the Related Art Conventionally, planar antennas such as an inverted F antenna and a microstrip antenna have been known as antennas mounted on portable radio apparatuses. Since these antennas have a low attitude, they can be easily mounted on a thin housing, and are often used for diversity antennas of mobile phones. FIG. 18 is a conceptual diagram showing the configuration of this inverted-F antenna, where 101 is an antenna element, 102 is a feeder,
103 is a short stub and 104 is a main plate. The center frequency of the inverted F antenna is determined by the peripheral length of the antenna element 101, resonates when the sum of W and L shown is λ / 4, and the bandwidth is determined by the height of the antenna element 101, and H shown is large. The wider the bandwidth.

[0003]

However, since these conventional planar antennas are resonance type antennas, they have an essentially narrow band as compared with a linear antenna such as a whip antenna, and cannot provide a wide band characteristic. was there.

An object of the present invention is to solve the above-mentioned conventional problems, and an object of the present invention is to provide a planar antenna which operates without a decrease in gain even in a wide band or a plurality of bands.

[0005]

A planar antenna according to the present invention has a loading impedance added to an antenna element and its value is controlled discretely or continuously.

According to the present invention, it is possible to obtain a planar antenna whose gain does not decrease even in a wide band or a plurality of bands.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. It is to be noted that the same reference numerals are used for the same parts as those of the conventional one.

(Embodiment 1) FIGS. 1 to 6 show Embodiment 1 of a planar antenna according to the present invention. FIG. 1 is a conceptual diagram showing the configuration thereof, and FIG. 2 is a plan view of the planar antenna shown in FIG. FIG. 3 is a conceptual diagram showing a configuration in which the planar antenna shown in FIG. 1 is applied to a receiving antenna of a portable wireless device, and FIG. 4 is a VSWR of the planar antenna shown in FIG.
FIG. 5 is a characteristic diagram showing characteristics, FIG. 5 is a characteristic diagram showing directional characteristics of the planar antenna shown in FIG. 3, and FIG. 6 is a block diagram showing a configuration of a portable wireless device equipped with the receiving antenna of FIG. First,
In FIG. 1, 101 is an antenna element, 102 is a feed line, 103 is a short stub, 104 is a ground plane, 200 is a loaded impedance switching circuit, and includes a switch circuit 201, a capacitive impedance element 202, an inductive impedance element 203, and the switch circuit 201. And a control terminal 204 for supplying an operation signal to the control terminal. Here, the switch circuit 201 can be configured by an FET, a PIN diode, or another component having an equivalent function.

Next, the operation will be described. FIG. 2 is a diagram showing an electric field distribution at an edge of the antenna element 101, and portions corresponding to FIG. 1 are denoted by the same reference numerals. Here, assuming that the resonance frequency in the open state of the switch circuit 201 is f0 and its wavelength is λ0, when the switch circuit 201 selects the capacitive impedance element 202, the antenna element 1
The phase of the electric field at the edge of 01 is delayed, and as a result, the same effect as when the peripheral length of the antenna element 101 is increased is obtained. Since the resonance wavelength λ1> λ0, the resonance frequency f1 <f0. Note that the resonance wavelength λ1 can be adjusted by the impedance value of the capacitive impedance element 202 and the loading position.

Similarly, when the switch circuit 201 selects the inductive impedance element 203, the electric field phase at the edge of the antenna element 101 advances, and as a result, the same effect as when the peripheral length of the antenna element 101 is shortened is obtained. Since the resonance wavelength λ2 <λ0, the resonance frequency f2> f0
Becomes The resonance wavelength λ2 can be adjusted by the impedance value of the inductive impedance element 203 and the loading position as in the case described above.

By changing the impedance of the loaded impedance element as described above, the center frequency of the antenna can be changed. FIGS. 3 to 6 show a case where the antenna is applied to a portable wireless device. This example realizes a two-frequency switching antenna using an inverted-F antenna as an antenna, a PIN diode as a switch circuit, and a capacitive impedance element as a loaded impedance element. FIG. 3 is a conceptual diagram showing the configuration. . In FIG. 3, reference numeral 301 denotes a loading capacitor, 302 denotes an RFC, 303 denotes a PIN diode, and other components are the same as those described in FIG.

Here, when no current flows through the control terminal 204, since the PIN diode 303 is in the off state, the reverse F
The center frequency of the antenna is equal to the resonance frequency f0 determined by the perimeter of the antenna element 101. When a current flows through the control terminal 204, the PIN diode 303 is turned on, so that the loading capacitor 301 is loaded on the antenna element 101. As a result, the center frequency becomes f1 <f0 with respect to the center frequency f0. The frequency f1 has the following relationship. The specific numerical values, as is apparent from the VSWR characteristic diagram of FIG. 4, it will vary from f0 = 878MH _Z to f1 = 825MH _Z. On the other hand, the directivity characteristics is as shown in FIG. 5, the center frequency f0 = 878MH _Z from f1 = 825 m
Be varied to H _Z, directional characteristic itself is seen that does not change.

FIG. 6 shows a configuration of a portable radio equipped with the planar antenna shown in FIG. 3. In the drawing, 400 is a shared radio circuit that handles two different bands, 401 is an antenna changeover switch, 402 is a transmission circuit, 403 is an oscillation circuit, 404 is a reception circuit, 4
05 is a control circuit, 501 is a whip antenna for transmission, and 502 is a planar antenna for reception shown in FIG. 3. In this configuration, the center frequency of the planar antenna 502 is changed by a control signal from the control circuit 405. And good reception characteristics can be obtained in two bands.

As described above, according to the present embodiment, since the center frequency of the antenna can be discretely changed by switching the impedance of the loaded impedance element connected to the antenna element, at least two different bands are provided. The antenna which does not decrease the gain and handles the above can be easily realized.

(Embodiment 2) FIGS. 7 and 8 show Embodiment 2 of the planar antenna of the present invention. FIG. 7 is a conceptual diagram showing the configuration, and FIG. 8 is a graph showing its temperature characteristics. is there. The second embodiment is obtained by adding a temperature compensation circuit to the first embodiment. In FIG. 7, 600 is a temperature compensation circuit, 601 is a variable impedance element, 602 is a control circuit, 60
3 is a temperature sensor and other components are shown in Fig. 1.
Since they are the same as those described above, the same reference numerals are given.

Next, the operation will be described. FIG. 8 shows the temperature-impedance characteristics of the loading impedance switching circuit 200, the temperature compensation circuit 600, and the combined circuit of the two, and the loading impedance switching circuit varies depending on the ambient temperature (horizontal axis).
It can be seen that the impedance characteristics of 200 and the temperature compensation circuit 600 change significantly. In order to compensate for this change, the control circuit 602 detects a temperature change by the temperature sensor 603, and reduces the load impedance of the antenna element 101, that is, the impedance change of the combined circuit of the load impedance switching circuit 200 and the temperature compensation circuit 600. To control the variable impedance element 601. Although the loading impedance switching circuit 200 and the temperature compensating circuit 600 are configured as a series circuit in the illustrated configuration, the same operation can be obtained by using a parallel circuit.

As described above, according to the present embodiment, the fluctuation of the loading impedance due to the change of the ambient temperature is suppressed,
A change in the center frequency of the antenna can be prevented.

(Embodiment 3) FIGS. 9 and 10 show Embodiment 3 of the planar antenna of the present invention. FIG. 9 is a conceptual diagram showing the configuration, and FIG. 10 is a graph showing its temperature characteristics. is there. In the third embodiment, the present invention is applied to an inverted-F antenna, and a temperature compensation circuit is added to the inverted-F antenna. The load having a temperature gradient opposite to that of the PIN diode 303 in the first embodiment shown in FIG. A capacitor 701 is loaded on the antenna element 101. The other components are the same as those described in FIG.
The same reference numerals are given to them.

The operation is as follows. As apparent from the temperature-impedance characteristics of the PIN diode 303, the loaded capacitor 701, and the combined circuit of both, as shown in FIG.
PIN diode 30 changes significantly with changes in (horizontal axis)
By the complementarity of the impedance characteristics of 3 and the loading capacitor 701, the variation of the temperature-impedance characteristics of the two combined circuits is reduced.

As described above, according to the present embodiment, it is possible to suppress a change in the load impedance due to a change in the ambient temperature without increasing the circuit scale, and to effectively prevent a change in the center frequency of the antenna. .

(Embodiment 4) FIGS. 11 and 12 show Embodiment 4 of the planar antenna of the present invention. FIG. 11 is a conceptual diagram showing the configuration, and FIG. FIG. In the third embodiment, the present invention is applied to an inverted-F antenna, and a variable impedance circuit is loaded as a loading impedance. In the figure, 800 is a variable impedance circuit, and 801 is its control terminal. The other components are the same as those described with reference to FIG. 3, and thus are denoted by the same reference numerals.

In operation, the variable impedance circuit 800 is controlled by a signal from the control terminal 801, and the capacitance or inductive impedance value of the variable impedance circuit 800 is changed. By changing the perimeter, the center frequency is changed. Further, the circuit shown in FIG. 12 is realized by the variable impedance circuit 800 shown in FIG.
Since the capacitive impedance can be varied depending on the level of the voltage applied to 01, the same result as that shown in FIG. 11 can be obtained.

As described above, according to the present embodiment, since the center frequency of the antenna can be changed continuously instead of discretely, control with a greater degree of freedom is possible.

(Embodiment 5) FIG. 13 is a conceptual diagram showing a configuration of a planar antenna according to Embodiment 5 of the present invention. In the fifth embodiment, a temperature compensation circuit is added to the fourth embodiment. In FIG. 13, 900 is a temperature compensation circuit, 901 is a temperature sensor, 902 is a comparator, 903 is a control terminal, and other components are the same as those described in FIG. is there.

First, the operation of the comparator 902 will be described.
Compares the temperature information given from the temperature sensor 901 with the control terminal 903 and gives an output to the control terminal 801 of the variable impedance circuit 800 such that a desired impedance can be obtained at the current temperature. Thereby, the fluctuation of the impedance of the variable impedance circuit 800 due to the fluctuation of the ambient temperature is suppressed, and the fluctuation of the center frequency of the antenna is also suppressed.

As described above, according to the present embodiment, the center frequency of the antenna can be changed not discretely but continuously, and the fluctuation of the load impedance due to the change of the ambient temperature is suppressed. Can be prevented from changing.

(Embodiment 6) FIGS. 14 and 15 show Embodiment 6 of the planar antenna of the present invention. FIG. 14 is a conceptual diagram showing the configuration, and FIG. 15 is a graph showing its temperature characteristics. is there. In the sixth embodiment, the present invention is applied to an inverted-F antenna, and a temperature compensation circuit is added to the inverted-F antenna. The variable capacitance diode 802 in the fourth embodiment shown in FIG. Temperature compensating capacitor 10 with
01 is added. Other components are diagrams
Since they are the same as those described in 12, the same reference numerals are given.

As apparent from the temperature-impedance characteristics of the variable capacitance diode 802 and the temperature compensating capacitor 1001 shown in FIG. 15 and the combined circuit of the two, as shown in FIG. By the complementarity of the impedance characteristics of the variable capacitance diode 802 and the temperature compensating capacitor 1001, the variation of the temperature-impedance characteristic of the combined circuit is reduced.

As described above, according to the present embodiment, the center frequency of the antenna can be changed continuously instead of discretely, and the variation of the load impedance due to the change of the ambient temperature can be reduced without increasing the circuit scale. Thus, it is possible to effectively prevent the center frequency of the antenna from fluctuating.

(Embodiment 7) FIGS. 16 and 17 show Embodiment 7 of the planar antenna of the present invention. FIG. 16 is a conceptual diagram showing the configuration thereof, and FIG. 17 is equipped with the planar antenna of FIG. FIG. 2 is a block diagram illustrating a configuration of a portable wireless device. In the seventh embodiment, the present invention is applied to an inverted-F antenna, and a circuit for compensating the variation of the loaded impedance is added to the inverted-F antenna. A compensation circuit 1100 is added. This impedance variation compensation circuit 11
00 is a variable impedance circuit 1101 having the same characteristics as the variable impedance circuit 800, an impedance detection circuit 11
02, a comparator 1103, and a control terminal 1104. Also,
The other components are the same as those described with reference to FIG. 11, and thus are denoted by the same reference numerals.

First, when the impedance of the variable impedance circuit 800 fluctuates due to a change in the surrounding environment such as a temperature change, the amount of the fluctuation is equally generated in the variable impedance circuit 1101 having the same characteristics as the variable impedance circuit 800. However, since the variable impedance circuit 1101 is controlled by a control loop including the impedance detection circuit 1102 and the comparator 1103 so that the desired impedance value given from the control terminal 1104 is maintained with high accuracy, When such an impedance variation occurs, a control signal for immediately correcting the impedance variation is applied to the variable impedance circuit 1101, and an operation is performed to return the impedance to a normal value. At the same time, the same control signal is also input to the control terminal 801 of the variable impedance circuit 800, so that the impedance value is returned to a normal value and is maintained with high accuracy.

FIG. 17 shows the configuration of a portable radio equipped with the receiving antenna shown in FIG. 16, in which 1200 is a common radio circuit for handling a wide band, 1201 is an antenna changeover switch, 1202 is a transmission circuit, and 1203 is an oscillation circuit. Circuit, 1204 is a reception circuit, 1205 is a control circuit, 1206 is a whip antenna for transmission, 1207 is a planar antenna for reception shown in FIG. 16, and in this configuration, the planar antenna 12 is controlled by a control signal from the control circuit 1205.
The center frequency of 07 can be changed continuously, and good reception characteristics can be obtained in a wide band.

As described above, according to the present embodiment, the variation of the impedance value of the variable impedance circuit loaded on the antenna element can be controlled with high accuracy regardless of the cause of the variation. The center frequency of the antenna can be controlled with high accuracy.

[0034]

As described above, according to the present invention, a planar antenna having a narrow band characteristic can operate in a plurality of bands or a wide band without a decrease in gain. An advantageous effect that an antenna suitable for a compatible portable wireless device or the like can be realized in a small size can be obtained.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing a configuration of a planar antenna according to a first embodiment of the present invention.

FIG. 2 is a distribution characteristic diagram showing an electric field distribution of the planar antenna shown in FIG.

FIG. 3 is a conceptual diagram showing a configuration when the planar antenna according to the first embodiment of the present invention is applied to a receiving antenna of a portable wireless device.

FIG. 4 is a characteristic diagram showing VSWR characteristics of the planar antenna shown in FIG.

5 is a characteristic diagram showing the directional characteristics of the planar antenna shown in FIG.

FIG. 6 is a block diagram showing a configuration of a portable wireless device equipped with the planar antenna shown in FIG.

FIG. 7 is a conceptual diagram showing a configuration of a planar antenna according to a second embodiment of the present invention.

8 is a graph showing a temperature characteristic of the planar antenna shown in FIG.

FIG. 9 is a conceptual diagram showing a configuration of a planar antenna according to a third embodiment of the present invention.

FIG. 10 is a graph showing temperature characteristics of the planar antenna shown in FIG.

FIG. 11 is a conceptual diagram showing a configuration of a planar antenna according to a fourth embodiment of the present invention.

FIG. 12 is a conceptual diagram in a case where the configuration of the planar antenna shown in FIG. 11 is further embodied.

FIG. 13 is a conceptual diagram showing a configuration of a planar antenna according to a fifth embodiment of the present invention.

FIG. 14 is a conceptual diagram showing a configuration of a planar antenna according to a sixth embodiment of the present invention.

15 is a graph showing a temperature characteristic of the planar antenna shown in FIG.

FIG. 16 is a conceptual diagram showing a configuration of a planar antenna according to a seventh embodiment of the present invention.

FIG. 17 is a block diagram showing a configuration of a portable wireless device equipped with the planar antenna shown in FIG.

FIG. 18 is a conceptual diagram showing a configuration of a conventional planar antenna.

[Explanation of symbols]

101: antenna element, 102: feed line, 103: short stub, 104: ground plane, 200: loaded impedance switching circuit, 201: switch circuit, 202: capacitive impedance element, 203: inductive impedance element,
204, 801, 903, 1104: control terminal, 301, 701: loading capacitor, 302: RFC, 303: PIN diode, 400, 1200: shared radio circuit, 401, 1201: antenna switch, 402, 1202: transmission circuit , 403, 12
03… Oscillation circuit, 404, 1204… Reception circuit, 405, 1205…
Control circuit, 501, 1206 ... whip antenna, 502, 12
07… Planar antenna, 600, 900… Temperature compensation circuit, 601
... variable impedance element, 602 ... control circuit, 603, 90
1… Temperature sensor, 800, 1101… Variable impedance circuit, 902, 1103… Comparator, 1001… Capacitor for temperature compensation, 1100… Impedance fluctuation compensation circuit, 1102…
Impedance detection circuit.

Claims (7)

[Claims] 1. A planar antenna, comprising a loading impedance switching circuit for switching and connecting a plurality of different loading impedances to an antenna element. 2. The planar antenna according to claim 1, further comprising a temperature compensation circuit for compensating for a change in center frequency due to a change in ambient temperature. 3. The planar antenna according to claim 1, wherein the loaded impedance switching circuit further has a temperature compensation function for compensating for a change in center frequency due to a change in ambient temperature. 4. A planar antenna, wherein a loaded variable impedance circuit whose impedance changes continuously is connected to the antenna element. 5. The planar antenna according to claim 4, further comprising a temperature compensating circuit for compensating for a change in center frequency due to a change in ambient temperature. 6. The planar antenna according to claim 4, wherein the loaded variable impedance circuit further has a temperature compensation function for compensating for a change in center frequency due to a change in ambient temperature. 7. The planar antenna according to claim 4, further comprising a fluctuation compensation circuit for detecting an impedance fluctuation of the loaded variable impedance circuit and compensating for the fluctuation.