JP3340621B2 - Planar antenna - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a planar antenna used for a portable radio device or the like, and more particularly to a planar antenna adapted to a plurality of frequency bands.

[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 they are low-profile, they can be easily mounted on a thin housing, and are often used for diversity antennas of mobile phones.

For example, as shown in FIG. 18, an inverted F antenna includes a flat antenna element 101, a feeder line 102 for guiding a signal received by the antenna element 101 to a radio, and
And a short stub 103 for grounding the antenna element 101 to the ground plane 104.

[0004] The inverted F antenna has an antenna element 101.
The center frequency is determined by the peripheral length of the antenna element 101, and the sum of the vertical length (W) and the horizontal length (L) of the antenna element 101 is λ /
4 (that is, the circumference of the antenna element 101 is λ
/ 2). The bandwidth is determined by the height (H) of the element, and the larger the H, the wider the bandwidth.
Since the inverted-F antenna is a resonance antenna, it has a narrower band than a linear antenna such as a whip antenna.

[0005]

Since the planar antenna is a resonance type antenna, it has a narrow band essentially, and has a drawback that a wide band characteristic cannot be obtained.

[0006] The present invention is intended to solve such conventional problems, and its object is to provide an operable planar antenna without gain falls in a band of several.

[0007]

Therefore, in the planar antenna according to the present invention, a stripe is formed on the periphery of the planar antenna element .
A load impedance that is selectively electrically connected by the switch means is provided.
The loading impedance is electrically connected to the antenna element.
Between the first resonance frequency and the loading impedance
Second resonance frequency when not electrically connected to antenna element
Switchable to wave number and electric load impedance
The effective circumference of the antenna element when connected
The loading noise is set so as to be half the wavelength of the first resonance frequency.
Impedance impedance value and loading position
ing. Thereby, it is possible to use a plurality of bandwidth.

Further, a means for compensating for the temperature characteristic of the loaded impedance is provided to suppress temperature fluctuation of the resonance frequency of the antenna.

[0009]

The invention according to claim 1 of the present invention comprises a planar antenna element, and the antenna comprises:
In a planar antenna whose resonance frequency is determined based on the perimeter of the antenna element ,
A load impedance selectively electrically connected by the switch means is provided, and the resonance frequency is selected by selecting the switch means.
The loading impedance is electrically connected to the antenna element.
The first resonance frequency and the loading impedance
Is not electrically connected to the antenna element.
The frequency can be switched to the loading impedance
Of the antenna element when the
So that the circumference is １ ／ of the wavelength of the first resonance frequency
In addition, the impedance value of loading impedance and loading position
The same effect as changing the perimeter of the antenna element can be obtained by connecting the loading impedance, the resonance frequency of the antenna can be changed, and two resonances can be made by turning on / off the switch means. frequency
You can take numbers.

[0010]

[0011]

[0012]

The invention according to claim 2 is provided with a temperature compensating means for compensating for the temperature characteristic of the loaded impedance, and can suppress the fluctuation of the resonance frequency of the antenna due to the fluctuation of the ambient temperature.

According to a third aspect of the present invention, the temperature compensating means includes a detecting means for detecting the ambient temperature and a correcting means for correcting the temperature characteristic of the load impedance based on the temperature detected by the detecting means. Therefore, it is possible to accurately compensate for a change in the load impedance due to a change in the ambient temperature.

According to a fourth aspect of the present invention, in order to constitute the temperature compensating means, an element having a temperature characteristic having a tendency opposite to the loaded impedance is electrically connected in series or parallel to the loaded impedance. The temperature compensation can be realized without increasing the circuit scale.

[0016]

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(First Embodiment) As shown in FIG. 1, the planar antenna according to the first embodiment has a loading impedance switch for selecting loading of an impedance element at an edge of an antenna element 101 of an inverted-F antenna. A circuit 200 is connected, the loaded impedance switching circuit 200 includes a capacitive impedance element 202, an inductive impedance element 203, a switch circuit 201 for selecting connection between those elements and the antenna element 101, and a switch Circuit 2
01 is provided with a control terminal 204 for giving an operation signal.
Other configurations are the same as the conventional inverted F antenna (FIG. 18).

The switch circuit 201 is constituted by an FET, a PIN diode, or another component having an equivalent function.

FIG. 2 shows that the switch circuit 201 of the loaded impedance switching circuit 200 is controlled to be in the open state, the antenna element 101 is connected to the capacitive impedance element 202, or the inductive impedance element 203 is connected to the antenna element 101. It shows how the electric field distribution at the edge of the antenna element 101 changes when connected.

In FIG. 2, A and G are the connection positions between the antenna element 101 and both sides of the short stub 103;
Is the connection position between the antenna element 101 and the feed line 102, F
Is the connection position between the antenna element 101 and the loading impedance switching circuit 200, and C, D, and E are the antenna element 1
01, respectively.

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 phase of the electric field at the edge of the antenna element 101 is delayed. Therefore, the same effect is obtained as when the perimeter of the antenna element 101 is increased, the resonance wavelength λ1 is λ1> λ0, and the resonance frequency f1 is f1 <
f0. Note that λ1 is the capacitive impedance element 20
It can be adjusted by the impedance value of 2 or the loading position F.

When the switch circuit 201 selects the inductive impedance element 203, the phase of the electric field at the edge of the antenna element 101 advances. Therefore, the same effect as the reduction of the perimeter of the antenna element 101 is obtained, the resonance wavelength λ2 becomes λ2 <λ0, and the resonance frequency f2
Is f2> f0. λ2 is an inductive impedance element
It can be adjusted by the impedance value of 203 and the loading position F.

As described above, by switching the type of the loaded impedance element connected to the antenna element, the center frequency of the resonance frequency of the antenna can be changed.

(Second Embodiment) A planar antenna according to a second embodiment uses a capacitive element as a loaded impedance element to enable switching between two frequencies.

This antenna has an inverted F, as shown in FIG.
At the edge of the antenna element 101 of the antenna, a capacitor 301 as a loading impedance element and a switch circuit 201 for selecting loading of the capacitor 301 on the antenna element 101 are connected.
Is a control terminal for controlling ON / OFF of the switch
204, an RFC (high-frequency coil) 302, and a PIN diode 303 as a switch element.

When no current flows through the control terminal 204, since the PIN diode 303 is in the OFF state, the inverted-F antenna has a center frequency at the resonance frequency f0 determined by the perimeter of the antenna element 101. On the other hand, control terminal 20
When a current flows through 4, the PIN diode 303 is turned on, and the loading capacitor 301 is loaded on the antenna element 101. Therefore, the center frequency f1 is f1 <f0.

FIG. 4 shows the VSWR characteristics of the antenna of FIG. VSWR is an abbreviation of voltage standing wave ratio, and the smaller this value is, the more efficiently power can be transmitted to the next stage circuit. Here, the impedance of the next stage is set to 50Ω. Note that the minimum value of VSWR is 1.

In FIG. 4, the horizontal axis represents the reception frequency, and the vertical axis represents VS.
The relationship between the reception frequency and the VSWR when WR is taken and a current flows from the control terminal 204 and when no current flows is shown by a curve. As can be seen from FIG. 4, when the current flows from the control terminal 204, the minimum center frequency of the VSWR changes from f0 = 878 MHz to f1 = 825 MHz. As described above, by selecting whether to electrically connect / disconnect the loading capacitor 301 to / from the antenna element 101, the planar antenna can be used in a plurality of frequency bands.

FIG. 5 shows the directivity characteristics of the antenna of FIG. This is the XY, Y
It indicates how many radio waves are radiated at which angles in the Z and ZX planes, and is one of the important characteristics of the antenna. In FIG. 5, the case where the loading capacitor 301 is connected to the antenna element 101 (f0 = 810 MHz)
And X when not connected (f0 = 885 MHz)
The directivity characteristics of the Y, YZ, and ZX planes are shown in comparison. From FIG. 5, when the loading element is connected to the antenna,
It can be seen that the directivity characteristics do not change when not connected, and that the directivity characteristics are not affected even when the center frequency is switched.

FIG. 6 shows a wireless device equipped with the planar antenna according to the second embodiment. This radio is
A whip antenna 501, a planar antenna 502 according to the second embodiment, and a shared radio circuit 400 that handles two different bands are provided. The shared radio circuit 400 includes a transmission circuit 402, a reception circuit 404, and a transmission circuit 402. An oscillation circuit 403 that supplies a signal of a local oscillation frequency to the circuit 402 and the reception circuit 404, an antenna changeover switch 401 that switches the connection between the whip antenna 501 and the planar antenna 502, and the connection between the transmission circuit 402 and the reception circuit 404,
A control circuit 405 for controlling each part of the shared radio circuit 400 and switching the frequency band of the planar antenna 502 is provided.

In this radio, the center frequency of planar antenna 502 can be changed by the control signal from control circuit 405, and good reception characteristics can be obtained in two bands.

As described above, the planar antenna according to the second embodiment is a planar antenna having a narrow band characteristic, but can be used in a plurality of bands that cannot be achieved by the conventional technique. In the band, it has sufficient characteristics required as a receiving antenna of a portable wireless device.

(Third Embodiment) The planar antenna according to the third embodiment prevents the center frequency of the antenna from fluctuating with a change in the ambient temperature.

In this antenna, as shown in FIG. 7, a loaded impedance switching circuit 200 is connected to an antenna element 101 via a temperature compensation circuit 600, and the temperature compensation circuit 600 includes a variable impedance element 601 and It includes a temperature sensor 603 for measuring the ambient temperature, and a control circuit 602 for controlling the impedance value of the variable impedance element 601 according to the temperature measured by the temperature sensor 603. Other configurations are the same as those of the first embodiment (FIG. 1).

FIG. 8 shows the loading impedance switching circuit 20.
7 is a graph showing temperature versus impedance characteristics in 0, a temperature compensating circuit 600, and a combined circuit of both.

When the ambient temperature fluctuates, the control circuit 602
Temperature fluctuation is detected by the temperature sensor 603, and the loading impedance of the antenna element 101, that is, the temperature compensation circuit 6
The variable impedance element 601 is controlled so that the fluctuation of the impedance in the combined circuit of 00 and the loaded impedance switching circuit 200 is reduced.

As a result, the fluctuation of the loading impedance of the antenna element 101 due to the fluctuation of the ambient temperature is compensated, and the fluctuation of the antenna center frequency due to the fluctuation of the ambient temperature is suppressed.

Although FIG. 7 shows a configuration in which the loaded impedance switching circuit 200 and the temperature compensation circuit 600 are connected in series, the same function can be realized by connecting them in parallel.

(Fourth Embodiment) A planar antenna according to a fourth embodiment has a temperature compensation function in the configuration of the second embodiment (FIG. 3).

In this antenna, as shown in FIG.
A loading capacitor 701 having a temperature gradient opposite to that of the IN diode 303 is loaded on the antenna element 101. Other configurations are the same as those of the second embodiment.

FIG. 10 is a graph showing the temperature versus impedance characteristics of the PIN diode 303, the loaded capacitor 701, and the combined circuit of both.

As described above, by using the loading capacitor 701 having the temperature characteristic opposite to that of the PIN diode 303, the fluctuation of the loading impedance of the antenna element 101 due to the fluctuation of the ambient temperature is canceled out. Fluctuation due to temperature can be suppressed.

With this antenna, temperature compensation can be realized without increasing the circuit scale.

Although FIG. 9 shows a configuration in which the PIN diode 303 and the loading capacitor 701 are connected in series, the same function can be realized by connecting them in parallel.

(Fifth Embodiment) In the planar antenna according to the fifth embodiment, the center frequency can be continuously varied.

As shown in FIG. 11, the antenna includes a variable impedance circuit 800 that continuously varies the impedance with a signal from a control terminal 801.
Loading at 01.

With such a configuration, by changing the capacitive or inductive impedance value of the variable impedance circuit 800, the same effect as changing the perimeter of the antenna element 101 can be obtained. Can be changed.

In this planar antenna, the center frequency can be continuously changed by the continuous control of the loading impedance, and control with a greater degree of freedom is possible.

(Sixth Embodiment) A planar antenna according to a sixth embodiment includes a variable impedance circuit 800 according to the fifth embodiment (FIG. 11), as shown in FIG. DC blocking capacitor 803, RF
This is realized with C804. In this circuit, the capacitive impedance of the variable capacitance diode 802 can be continuously varied depending on the level of the voltage applied to the control terminal 801.

(Seventh Embodiment) A planar antenna according to a seventh embodiment is obtained by adding a temperature compensation function to the configuration of the fifth embodiment (FIG. 11).

As shown in FIG. 13, this antenna realizes a control terminal 903 for specifying a center frequency, a temperature sensor 901 for measuring an ambient temperature, and a center frequency specified under the measured ambient temperature. And a comparator 902 that outputs a control signal to the variable impedance circuit 800 for performing the control.

The comparator 902 compares the frequency designation information given from the control terminal 903 with the temperature information given from the temperature sensor 901 and outputs an output which can obtain a desired impedance at the current temperature.
0 is given to the control terminal 801. Thereby, the impedance fluctuation 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, in the planar antenna, the center frequency can be continuously changed, and the fluctuation of the center frequency of the antenna due to the fluctuation of the ambient temperature can be suppressed.

(Eighth Embodiment) A planar antenna according to an eighth embodiment has a configuration in which the temperature compensation function is added to the configuration of the sixth embodiment (FIG. 12).

As shown in FIG. 14, in this antenna, a temperature compensating capacitor 1001 having a temperature gradient of the opposite sign to that of the variable capacitance diode 802 is added in parallel with the variable capacitance diode 802 of the variable impedance circuit 800. Other configurations are the same as in the sixth embodiment.

FIG. 15 shows the temperature versus impedance characteristics of the variable capacitance diode 802, the temperature compensating capacitor 1001, and the combined circuit of both. As is clear from this figure, the temperature fluctuation of the combined impedance can be reduced by combining the temperature compensating capacitor 1001. Note that the DC blocking capacitor 803 has a sufficiently large capacity due to its DC blocking function, and impedance fluctuations caused by capacitance fluctuations due to temperature fluctuations can be ignored.

With such a configuration, the fluctuation of the loading impedance of the antenna element 101 due to the fluctuation of the ambient temperature is suppressed, and as a result, the fluctuation of the center frequency of the antenna due to the fluctuation of the ambient temperature is suppressed.

In this antenna, continuous change of the center frequency and suppression of the fluctuation due to the ambient temperature can be realized by a small-scale circuit.

In FIG. 14, the variable capacitance diode 80
2 and the temperature compensating capacitor 1001 are connected in parallel, but even if they are connected in series, the DC blocking capacitor 803 has a small capacity, and the function of the temperature compensating capacitor 1001 is added to this. Even if it is provided, the same effect can be obtained.

(Ninth Embodiment) A planar antenna according to a ninth embodiment has a configuration in which a compensation circuit for compensating for the variation in the impedance of the variable impedance circuit 800 is added to the configuration of the fifth embodiment (FIG. 11). Things.

As shown in FIG. 16, the impedance variation compensating circuit 1100 used in this antenna has a variable impedance circuit 1 having the same characteristics as the variable impedance circuit 800.
101, an impedance detection circuit 1102 for detecting the impedance of the variable impedance circuit 1101, a control terminal 1104 to which a predetermined impedance is given, and an impedance detected by the impedance detection circuit 1102 and an impedance given from the control terminal 1104. A comparator 902 for comparing and outputting a control signal for eliminating the difference.

In this antenna, when the impedance of the variable impedance circuit 800 fluctuates due to fluctuations in the surrounding environment such as temperature, the amount of the fluctuation is determined by the variable impedance circuit 800
It appears equally in the variable impedance circuit 1101 having the same characteristics as 800. The impedance detection circuit 1102 detects the impedance of the variable impedance circuit 1101 and outputs it to the comparator 1103.The comparator 1103 compares the detected value with a desired impedance value given from the control terminal 1104. A control signal corresponding to the difference is output. This control signal is input to both the variable impedance circuit 1101 and the variable impedance circuit 800, and these circuits output the desired impedance value given from the control terminal 1104 with high accuracy based on the control signal.

With such a configuration, the impedance fluctuation compensating circuit 1100 can compensate not only the fluctuation of the surrounding environment such as the temperature but also the fluctuation of the impedance value of the variable impedance circuit 800 with high accuracy. , The center frequency of the antenna can be controlled with high accuracy.

FIG. 17 shows a configuration diagram of a radio device equipped with the planar antenna of the ninth embodiment. This is substantially the same as that shown in FIG.
The only difference is that the planar antenna of the ninth embodiment is used as 07.

With such a configuration, the wireless device can continuously change the center frequency of antenna 1207 by transmitting a control signal from control circuit 1205, and can obtain stable reception characteristics over a wide band. .

As described above, the planar antenna of the present invention can be used in a wide band, which cannot be achieved by the conventional technology.

In each of the embodiments, the present invention is mainly described by the inverse F
Although the case where the present invention is applied to an antenna has been described, it is needless to say that the present invention can be applied to other planar antennas.

[0070]

As apparent from the above description, the planar antenna of the present invention is operable in a plurality of bandwidth.
In addition, since this antenna can be configured to be small, it has excellent suitability as an antenna for a compatible portable wireless device that supports a plurality of bands and systems.

[Brief description of the drawings]

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

FIG. 2 is a view showing an electric field distribution at an element edge of the planar antenna according to the first embodiment;

FIG. 3 is a configuration diagram of a planar antenna according to a second embodiment of the present invention;

FIG. 4 shows VSWR characteristics of the planar antenna according to the second embodiment;

FIG. 5 shows the directivity characteristics of the planar antenna according to the second embodiment,

FIG. 6 is a configuration diagram of a wireless device equipped with the antenna according to the second embodiment;

FIG. 7 is a configuration diagram of a planar antenna according to a third embodiment of the present invention,

FIG. 8 shows temperature versus impedance characteristics of the planar antenna according to the third embodiment;

FIG. 9 is a configuration diagram of a planar antenna according to a fourth embodiment of the present invention;

FIG. 10 shows temperature versus impedance characteristics of the planar antenna according to the fourth embodiment;

FIG. 11 is a configuration diagram of a planar antenna according to a fifth embodiment of the present invention;

FIG. 12 is a configuration diagram of a planar antenna according to a sixth embodiment of the present invention;

FIG. 13 is a configuration diagram of a planar antenna according to a seventh embodiment of the present invention;

FIG. 14 is a configuration diagram of a planar antenna according to an eighth embodiment of the present invention;

FIG. 15 shows temperature versus impedance characteristics of the planar antenna according to the eighth embodiment;

FIG. 16 is a configuration diagram of a planar antenna according to a ninth embodiment of the present invention;

FIG. 17 is a configuration diagram of a wireless device equipped with the antenna according to the ninth embodiment;

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

[Explanation of symbols]

 101 Antenna element 102 Feed line 103 Short stub 104 Ground plane 200 Load impedance switching circuit 201 Switch circuit 202 Capacitive impedance element 203 Inductive impedance element 204 Control terminal 301, 701 Loading capacitor 302, 804 RFC 303 PIN diode 400, 1200 Shared radio Circuits 401, 1201 Antenna changeover switches 402, 1202 Transmission circuits 403, 1203 Oscillation circuits 404, 1204 Receiving circuits 405, 1205 Control circuits 501, 1206 Whip antennas 502 Antennas 600, 900 of the second embodiment Temperature compensation circuits 601 Variable impedance elements 602 Control circuit 603, 901 Temperature sensor 800, 1101 Variable impedance circuit 801, 903, 1104 Control terminal 802 Variable capacitance diode 803 DC blocking capacitor 902, 1103 Comparator 1001 Temperature compensation capacitor 1100 Impedance fluctuation compensation circuit 1102 Impedance detection circuit 1207 A of Embodiment 9 Antenna

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-6-224618 (JP, A) JP-A-7-297627 (JP, A) JP-A-2-124605 (JP, A) JP-A 8- 186427 (JP, A) JP-A-8-186428 (JP, A) JP-A-9-93030 (JP, A) JP-A-5-291818 (JP, A) JP-A-61-196603 (JP, A) JP-A-52-106661 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01Q 13/08

Claims (4)

(57) [Claims] 1. It has a planar antenna element ,
Resonance frequency based on the perimeter of the antenna element
In the planar antenna is determined by the switch means in the peripheral portion of the antenna element
Comprising a loading impedance that is selectively electrically connected, by the selection of said switch means, a resonance frequency, said instrumentation
Load impedance is electrically connected to the antenna element
The first resonance frequency when the
The antenna is not electrically connected to the antenna element.
2 and can be switched to the resonance frequency of 2 when the load impedance is electrically connected.
The effective peripheral length of the tena element is equal to the first resonance frequency.
The loading impedance so that it is half the number of wavelengths.
A flat antenna , wherein an impedance value and a loading position are set . 2. The temperature characteristic of the loading impedance is supplemented.
2. A temperature compensation means for compensating temperature.
A planar antenna according to claim 1. 3. The temperature compensating means detects an ambient temperature.
Detecting means based on the temperature detected by the detecting means.
Correction means for correcting the temperature characteristic of the loading impedance
The planar antenna according to claim 2 , comprising: 4. A method for constructing said temperature compensating means,
It has a temperature characteristic that tends to be opposite to the loading impedance
The element is connected in series or parallel to the loading impedance.
The planar antenna according to claim 2 , wherein the planar antenna is connected by air .