JPH09232854A - Small planar antenna system for mobile radio equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a small planar antenna device for mobile radio equipment which is capable of having a wide band frequency characteristic in a single planar antenna. SOLUTION: An end face short-circuited 1/4 wavelength microstrip antenna is composed by electrically connecting a first conductive plate 1 and a second conductive plate 2 by a connection part 3. On the first conductive plate 1, a power feeding part 4 is placed at the point of the distance of c1 from the connection part 3. The power feeding part 4 is connected with the one end of a serial resonance circuit 5 whose resonance frequency is adjusted to the vicinity of a use frequency and the other end is connected with a power feeding terminal 8.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an antenna mainly used in a mobile radio device, and more particularly to a small planar antenna device incorporated in the housing of a radio device.

[0002]

2. Description of the Related Art In recent years, demand for mobile communication fields such as mobile phones and personal handyphone systems has been rapidly increasing. The portable terminal radios of these systems include
Small antennas of various structures are used. Among them, there are two typical types, a whip antenna having a structure protruding to the outside of the casing and a small and thin planar antenna having a structure to be incorporated inside the casing.
In these mobile radios, a whip antenna is generally used as a main antenna for both transmission and reception, and a flat antenna is often used as an antenna for diversity reception.

FIG. 5 shows the structure of a conventional small planar antenna for mobile radio equipment. In FIG. 5, 34 is a first conductive plate, 35 is a second conductive plate, 34 and 35 are respectively arranged with a distance of t, and are electrically connected by a connecting portion of 36 to short-circuit the end face. Configure a quarter wave microstrip antenna (MSA). The power supply to the radio side circuit is performed by the power supply unit 3 provided at a specific location 34.
This is done by connecting a power supply line to the wireless device side circuit to 7. Generally, in the planar antenna having this structure, a method is used in which the conductive plates 34 and 35 are formed by a double-sided copper foil pattern on a dielectric substrate having a thickness t, and the connecting portion 37 is realized by a through hole. Alternatively, as another implementation method, the first conductive plate 34
Is formed of a metal plate such as a copper plate, and the ground plane on the circuit board of the radio device is used as the second conductive plate 35. The circuit board (second conductive plate 35) and the copper plate (first conductive plate 34) are connected to each other. A method of mechanically supporting the space with an insulating material such as a molding material is used. The resonance frequency of this planar antenna is a frequency at which the length a5 of the first conductive plate 34 becomes λg / 4 (λg is a wavelength on the first conductive plate), and therefore it is extremely small and is the casing of the mobile wireless device. It is suitable as a small built-in antenna incorporated inside. An example of such an antenna can be found in "Radio Antenna" of Japanese Patent Laid-Open No. 4-129302.

[0004]

Most mobile communication systems employ a diversity system in order to secure the line quality and expand the communication area. Conventionally, in mobile radios such as mobile phones, generally, the antenna reception type diversity reception system is adopted, and the whip antenna as the main antenna and the built-in antenna as the sub antenna are electrically switched, and the reception signal level is changed. I was working to select the higher one.

Further, the diversification of mobile communication systems has progressed, and a time division duplex (TDD) system and a frequency division duplex (FDD) system have been adopted for each duplex system.

Against this background, in recent years, in the diversity system of mobile radios, a system has been proposed in which antenna switching is performed not only for reception but also for transmission. Further, since the system is a frequency division duplex system, the transmission frequency and the reception frequency are, for example, several tens MHz to one hundred and several tens M.
Systems have been proposed that are as far apart as Hz. Therefore, the built-in small planar antenna as a sub-antenna is not a narrow band characteristic of only the receiving band as in the conventional case,
It is desired to have a very wide band frequency characteristic such as several tens of MHz to one hundred and several tens of MHz (for example, a specific bandwidth of 5% to 10%).

However, the small planar antenna having the structure shown in FIG. 5 has a narrow band characteristic as compared with a whip antenna or the like, for example, 40 to 55 M in the 1.9 GHz band.
Generally, it has a bandwidth of about Hz (the bandwidth is a frequency bandwidth at which the input VSWR is 2 or less) and the relative bandwidth is about 2 to 3%. Therefore, for example, 1.9
In a system in which the transmission / reception frequencies are 80 MHz apart in the GHz band and the total frequency band reaches 125 MHz, the small planar antenna in FIG. 5 cannot cover both the transmission and reception bands, and a plurality of planar antennas are arranged. There is a problem in that it is necessary to switch the resonance frequency by some means or to switch the resonance frequency by some means.

According to the present invention, a single plane antenna can have a wide band frequency characteristic of, for example, 5% to 10% of a specific band without using a plurality of plane antennas or resonance frequency switching means. An object is to provide a small planar antenna device for a wireless device.

[0009]

In order to achieve the above object, the present invention provides a first conductive plate having a rectangular shape, a second conductive plate arranged to face the first conductive plate, and the first conductive plate. A planar antenna part made of at least one conductor connecting the end face of the conductive plate and the second conductive plate, and a fixed distance from the connection part of the first conductive plate and the second conductive plate of the planar antenna part. A small planar antenna device for a mobile radio device, characterized in that one end of a series resonant circuit is connected to a power feeding portion on a first conductive plate provided separately and the other end of the series resonant circuit is used as a power feeding terminal. It was done.

In the small planar antenna device for a mobile radio device, the first conductive plate and the second conductive plate may be formed on and supported by a dielectric substrate. Further, in the small planar antenna device for mobile radio device, the inductance of the series resonance circuit can be formed by a transmission line element formed on a dielectric substrate. Further, the series resonance circuit can be configured by a transmission line element formed on the dielectric substrate and an interlayer capacitance between the transmission line element and the inner layer pattern of the dielectric substrate.

Therefore, according to the present invention, a single plane antenna has a wide band frequency characteristic of, for example, 5% to 10% of the specific band without using a plurality of plane antennas or resonance frequency switching means. It is possible to provide a small-sized planar antenna device for a mobile wireless device that can perform

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The invention according to claim 1 of the present invention includes a first conductive plate having a rectangular shape, a second conductive plate arranged to face the first conductive plate, and the first conductive plate. A planar antenna part formed of at least one conductor connecting the end face of the plate and the second conductive plate; and a first planar antenna part of the planar antenna part.
One end of the series resonant circuit is connected to a power feeding portion on the first conductive plate provided at a constant distance from the connecting portion between the conductive plate and the second conductive plate, and the other end of the series resonant circuit is used as a power feeding terminal. A small planar antenna device for a mobile radio device, which is characterized in that it has an action of obtaining wideband frequency characteristics.

The invention according to claim 2 is characterized in that the first conductive plate and the second conductive plate are formed and supported on a dielectric substrate to support the small planar antenna for a mobile radio device. The device is configured and has an action of obtaining a wide band frequency characteristic.

According to a third aspect of the present invention, there is provided a small planar antenna device for a mobile radio device according to the first aspect, wherein the inductance of the series resonance circuit is formed by a transmission line element formed on a dielectric substrate. It has a function of obtaining a wide band frequency characteristic.

According to a fourth aspect of the present invention, the series resonant circuit includes a transmission line element formed on a dielectric substrate and an interlayer capacitance between the transmission line element and an inner layer pattern of the dielectric substrate. According to another aspect of the present invention, there is provided a compact planar antenna device for a mobile radio device as set forth in claim 1, which has an effect of obtaining a wide band frequency characteristic.

Hereinafter, an embodiment of the present invention will be described with reference to FIG.
This will be described with reference to FIG. (Embodiment 1) FIG. 1 is a diagram showing an antenna device according to Embodiment 1 of the present invention. In FIG. 1, 1 is the first
A conductive plate is formed of a metal plate such as a copper plate, and 2 is a second conductive plate that utilizes a ground plane pattern on the circuit board of the wireless device. Copper plate (first conductive plate 1) and circuit board (second
By mechanically supporting the conductive plate 2) with an insulating material such as a molding material, each of 1 and 2 is arranged with a distance of t. Generally, t is selected to be about 2 mm to 5 mm. Further, 1 and 2 are electrically connected by a connecting portion 3 formed of a metal plate such as a copper plate, and end face short circuit 1
Configure a / 4 wavelength microstrip antenna (MSA). The above shows the same structure as the small planar antenna for mobile radio in the prior art of FIG. In the first embodiment, the feeding portion 4 is placed on the first conductive plate 1 at a point separated from the connecting portion 3 by the distance c1, and the feeding portion 4 has series resonance in which its resonance frequency is adjusted to the vicinity of the working frequency. One end of the circuit 5 is connected, and the other end is connected to the power supply terminal 8. In the first embodiment, the series resonance circuit 5 is composed of the inductance 6 and the capacitor 7 mounted on the circuit board of the wireless device. The power supply terminal 8 is connected to the antenna switching circuit on the radio side.

The resonance frequency of this planar antenna is a frequency at which the length a1 of the first conductive plate 1 becomes λg / 4 (where λg is the wavelength on the first conductive plate). Therefore, for example, 1.9G.
In the case of a small planar antenna for a Hz band mobile wireless device, the length of a1 is about 40 mm. Width b1 of the first conductive plate 1
Can be selected almost independently of the resonance frequency, but the bandwidth of the planar antenna of this structure is almost proportional to the area S1 of the first conductive plate 1, that is, S1 = a1 x b1. However, a wide bandwidth can be obtained. Generally, b1 is selected to be almost the same as a1, and the bandwidth at that time is about 5 in the 1.9 GHz band, for example.
It is about 0 MHz.

The feeding portion 4 of the small planar antenna described above is arranged at a predetermined location on the first conductive plate 1. At this time, between the input impedance between the power feeding unit 4 and the second conductive plate 2 and the distance c1 between the power feeding unit 4 and the connection unit 3, the input impedance is high when c1 is large and is small when c1 is small. There is a relationship that the input impedance becomes low. Reference numeral 38 in FIG. 6 shows a frequency characteristic of the input VSWR as seen from the power feeding unit 4, and shows a state in which c1 is selected to have an appropriate length (for example, about 5 mm) so that the input impedance is closest to 50Ω. From the frequency characteristic of 38 in FIG. 6, the bandwidth is about 50 MHz.

In FIG. 1, the series resonance circuit 5 is inserted between the power supply section 4 and the power supply terminal 8, the resonance frequency of the series resonance circuit 5 is selected near the resonance frequency of the plane antenna, and the inductance L of the inductance 6 is set. And the capacity C of the capacitor 7, that is, by selecting L / C to an optimum value,
A two-resonance impedance matching characteristic as shown by 39 in FIG. 6 can be obtained. At this time, there exists an optimum value of L / C that maximizes the frequency range (bandwidth) where the input VSWR is 2 or less, and the optimum value is the longer the length of c1 (that is, the impedance of the power feeding unit 4). Is smaller), L is smaller, and C is larger. Here, for example, when c1 is selected to be about 10 mm, 39 in FIG.
As shown in, the bandwidth is about 95 MHz, which is 1.9 times as wide as 38. Also, good radiation efficiency can be obtained over the entire bandwidth of 95 MHz.

In the first embodiment, the first conductive plate 1 is a metal plate such as a copper plate having a substantially square shape, but it is not limited to this shape and material, and operates as a similar antenna. The same effect can be obtained by using a shape or material. The second conductive plate 2 uses the ground plane pattern on the circuit board of the wireless device, but the present invention is not limited to this. For example, a shield plate for shielding the circuit of the wireless device may be used. Similar effects can be obtained. Also, the connecting portion 3 can be obtained by integrally molding the same material as that of the first conductive plate 1 and even if it has a bent structure, the same effect can be obtained. In addition, the series resonance circuit 5 is
Although it is composed of the inductance 6 and the capacitor 7 mounted on the circuit board of the wireless device, the invention is not limited to this, and the same effect can be obtained by using a dielectric resonant element or a resonant element having another structure. You can

(Second Embodiment) FIG. 2 is a diagram showing an antenna device according to a second embodiment of the present invention. In FIG. 2, 9 is a first conductive plate, 10 is a second conductive plate,
It is composed of a copper foil pattern formed on the dielectric substrate 11 having a thickness t. Generally, the thickness t of the dielectric substrate 11 is 2 mm.
To about 5 mm, and the relative permittivity of the dielectric substrate 11 is selected to about 2 to 4. By arranging a plurality of through holes 12 formed in the dielectric substrate 11 in the vicinity of the end surface of the dielectric substrate, the conductive plates 9 and 10 are electrically connected to each other to short-circuit the end surface 1/4 wavelength microstrip antenna (MSA). ). In many cases, the second conductive plate 10 is soldered to a ground plane pattern or a shield plate on the circuit board of the wireless device and forms the second conductive plate together with them. In the second embodiment, the power feeding unit 13 is placed on the first conductive plate 9 at a point spaced a distance c2 from the end face, and the power feeding unit 13 has a series resonance circuit 14 in which its resonance frequency is adjusted to the vicinity of the working frequency. Is connected to one end and the other end is connected to the power supply terminal 17. In the second embodiment, the series resonance circuit 14 includes the inductance 15 and the capacitor 1 mounted on the circuit board of the wireless device.
6. The power supply terminal 17 is connected to the antenna switching circuit on the radio side.

The operation of the planar antenna of the second embodiment shown in FIG. 2 is almost the same as that of the planar antenna of the first embodiment shown in FIG. 1, but the wavelength on the dielectric substrate is approximately the square root of the relative permittivity. Since it is inversely proportional, the length a of the first conductive plate 9
2 is shorter than that in the case of FIG. 1. For example, in the case of a small planar antenna for a 1.9 GHz band mobile wireless device using a material having a relative permittivity of about 3.6, a2 is about 19 mm. For this reason, although the bandwidth is slightly narrower than that of the planar antenna of the first embodiment shown in FIG. 1, there is a tendency of the bandwidth expansion rate due to the addition of the series resonance circuit 14 and the relationship between the L / C value and c2. Have almost the same characteristics.

(Third Embodiment) FIG. 3 is a diagram showing an antenna device according to a third embodiment of the present invention. In FIG. 3, 18 is a first conductive plate, 19 is a second conductive plate, and is composed of a copper foil pattern formed on a dielectric substrate 20 having a thickness t. Generally, the thickness t of the dielectric substrate 20 is 2
The dielectric constant of the dielectric substrate 20 is selected to be about 2 to 4 mm. By arranging a plurality of through holes 21 formed in the dielectric substrate 20 in the vicinity of the end face of the dielectric substrate, the conductive plates 18 and 19 are electrically connected to each other to short-circuit the end face 1/4 wavelength microstrip antenna (MSA). ). In addition, the second conductive plate 19
Is often soldered to a ground plane pattern or a shield plate on the circuit board of the wireless device and forms the second conductive plate together with them. The above planar antenna section is shown in FIG.
The same operation as the planar antenna according to the second embodiment in In the third embodiment, the power feeding section 22 is placed on the first conductive plate 18 at a point separated from the end surface by a distance of c3 (for example, about 10 mm), and the high impedance transmission line 23 (for example, width 1 to 2 mm, length 1
0 mm) and connect the other end to capacitor 2
4 is connected to one end and the other end is connected to the power supply terminal 25. In the third embodiment, the same operation and the same characteristics as those in the second embodiment shown in FIG. 2 can be obtained except that the inductance of the series resonance circuit is realized by the high impedance transmission line 23.

(Fourth Embodiment) FIG. 4 is a diagram showing an antenna device according to a fourth embodiment of the present invention. In FIG. 4, reference numeral 26 is a first conductive plate, 27 is a second conductive plate, and is composed of a copper foil pattern formed on a dielectric substrate 28 having a thickness t. Generally, the thickness t of the dielectric substrate 28 is 2
The dielectric constant of the dielectric substrate 28 is selected to be about 2 to 4 mm. By arranging a plurality of through holes 29 formed in the dielectric substrate 28 in the vicinity of the end face of the dielectric substrate, the conductive plates 26 and 27 are electrically connected to each other, and the end face is short-circuited 1/4 wavelength microstrip antenna (MSA). ). In addition, the second conductive plate 27
Is often soldered to a ground plane pattern or a shield plate on the circuit board of the wireless device and forms the second conductive plate together with them. In the fourth embodiment, the length a4 of the first conductive plate 26 has, for example, a relative dielectric constant of 3.6.
In the case of a small planar antenna for a 1.9 GHz band mobile wireless device using a material of approximately the same size as about 19 mm as in FIGS. 2 and 3, the width b4 is selected to be about twice as large as a4 (about 40 mm). I'm out. Therefore, the input VSW in the power supply unit 30
The frequency characteristic of R is as shown by 40 in FIG.
The bandwidth at which SWR is 2 or less is about 90 MHz. However, the length of c4 at this time indicates a state in which an appropriate length (for example, about 5 mm) is selected so that the input impedance in the power feeding unit 30 is closest to 50Ω.

In the fourth embodiment, the power feeding portion 30 is arranged at a distance c4 (for example, about 12 mm) from the end face of the substrate approximately at the center of the first conductive plate 26, and the high impedance line 31 is provided in the power feeding portion 30. One end of (width of about 1 to 2 mm, length of about 10 mm) is connected, and the other end is overlapped with, for example, about 2 mm by the power supply pattern 32 formed on the inner layer of the dielectric substrate, for example, 100 to 200 μm.
The inner layer thickness is about m. The tip 33 of the power feeding pattern 32 is connected to the radio device side circuit as a power feeding terminal. The high-impedance line 31 operates as an inductance of the series resonance circuit, and the overlapping portion of the high-impedance line 31 and the feeding part pattern 32 operates as a capacitor, so that the feeding part of the planar antenna of FIGS. It operates similarly to the series resonant circuit inserted in. By changing the length d of the high impedance line 31, the inductance of the series resonance circuit is changed, and at the same time, the capacitance of the series resonance circuit is changed by changing the area of the portion that overlaps with the power feeding pattern 32. It is possible to adjust so that the frequency characteristic of the input impedance at the power supply terminal 33 is optimized. The frequency characteristic of the input VSWR at this time is as shown by 41 in FIG. 7, and the bandwidth in which the input VSWR is 2 or less is about 180 MHz.

In the fourth embodiment, the feeding portion 30 and the high impedance transmission line 31 are the first conductive plate 2 and the high impedance transmission line 31.
Although it is arranged substantially at the center of 6, it is not limited to this position, and the same effect can be obtained if the structure is such that the power feeding unit 30 is arranged at a position spaced a distance c4 from the end face of the substrate. Further, the capacitive element of the series resonant circuit uses the interlayer coupling capacitance between the high impedance transmission line 31 and the feeding portion pattern 32, but the invention is not limited to this.
Similar effects can be obtained by using a capacitive element having another structure.

[0027]

As described above, according to the present invention,
By inserting a series resonant circuit in the feeding part of the planar antenna,
It is possible to provide a small planar antenna device for a mobile wireless device that can have a wide band frequency characteristic.

[Brief description of drawings]

FIG. 1 is a diagram showing an antenna device according to a first embodiment of the present invention.

FIG. 2 is a diagram showing an antenna device according to a second embodiment of the present invention.

FIG. 3 is a diagram showing an antenna device according to a third embodiment of the present invention.

FIG. 4A is a diagram showing an antenna device according to a fourth embodiment of the present invention. FIG. 4B is a diagram showing a cross section taken along the line ee ′ of the antenna device.

FIG. 5 is a diagram showing an antenna device according to a conventional technique.

6 is a diagram showing measured values of frequency characteristics of the antenna device of FIG.

7 is a diagram showing measured values of frequency characteristics of the antenna device of FIG.

[Explanation of symbols]

1 1st conductive plate 2 2nd conductive plate 3 Connection part 4 Feed part 5 Series resonance circuit 6 Inductance 7 Capacitor 8 Feed terminal 9 1st conductive plate 10 2nd conductive plate 11 Dielectric substrate 12 Through hole 13 Feed part 14 Series resonance Circuit 15 Inductance 16 Capacitor 17 Feed terminal 18 First conductive plate 19 Second conductive plate 20 Dielectric substrate 21 Through hole 22 Feed part 23 High impedance transmission line 24 Capacitor 25 Feed terminal 26 First conductive plate 27 Second conductive plate 28 Dielectric Body board 29 Through hole 30 Feeding part 31 High impedance transmission line 32 Feeding part pattern 33 Feeding terminal 34 First conductive plate 35 Second conductive plate 36 Connection plate 37 Feeding part 38, 39, 40, 41 Measured value of input VSWR characteristic a1 , A2, a3, a4, a5 First conductive plate length b1, b2 3, b4, b5 first conductive plate width c1, c2, c3, c4, c5 length t first conductive plate distance d high impedance line of the short-circuit point and the feed portion and the distance between the second conductive plate (thickness)

Claims (4)

[Claims] 1. A square-shaped first conductive plate, a second conductive plate arranged to face the first conductive plate, an end surface of the first conductive plate and the second conductive plate are connected to each other. A planar antenna part made of at least one conductor and a power feeding part on the first conductive plate provided at a constant distance from a connection part of the first conductive plate and the second conductive plate of the planar antenna part. A small planar antenna device for a mobile radio, wherein one end of a resonance circuit is connected and the other end of the series resonance circuit is used as a power supply terminal. 2. The small planar antenna device for a mobile radio device according to claim 1, wherein the first conductive plate and the second conductive plate are formed on and supported by a dielectric substrate. 3. The small planar antenna device for a mobile radio device according to claim 1, wherein the inductance of the series resonance circuit is constituted by a transmission line element formed on a dielectric substrate. 4. A series resonance circuit is constituted by a transmission line element formed on a dielectric substrate and an interlayer capacitance between the transmission line element and an inner layer pattern of the dielectric substrate. A small planar antenna device for a mobile wireless device as described above.