JP2001094315A - Directional coupler - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a directional coupler with a low pass filter function, which is suitable for miniaturization. SOLUTION: In a directional coupler where two strip lines are confronted each other or are made in parallel, first and second coils are connected to both ends of a main strip line. First and second capacitors are arranged between one end of a side that is not connected to the main strip line in each coil and ground. Thus, a low pass filter is constituted of the main strip line, the first and second coils and the first and second capacitors.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a directional coupler used in a wireless communication device such as a portable telephone.

[0002]

2. Description of the Related Art FIG. 5 shows a conventional directional coupler using a plurality of strip lines. This directional coupler is a coplanar directional coupler in which two strip lines constituting a main strip line and a sub-strip line are formed on the same substrate. Two strip lines 1 are formed on the surface of the formed dielectric substrate 11.
3 and 14 are arranged in parallel at a distance S from each other. The length of the parallel portions of these strip lines 13 and 14 is configured to be １ ／ of the wavelength of the electromagnetic wave propagating in the dielectric substrate.

[0003] The basic operation of this directional coupler will be described. The high frequency power input from the port P1 of the directional coupler passes through the main stripline line 13 and passes through the port P2.
To the main stripline line 13
A part of the power passing through the main strip line 13 flows to the sub strip line 14 due to the coupling between the sub strip line and the sub strip line 14, and is output to the port P3, but no output appears at the port P4. Next, in the opposite direction of the main stripline line 13, that is, from port P2 to port P
When power is supplied toward port 1, part of the power appears at port P4 and does not appear at port P3. In other words, by adopting such a configuration, a part of the forward power and the reverse power flowing through the main strip line 13 can be separately extracted to the output ports P3 and P4 of the sub strip line 14. it can.

The amount of coupling of the directional coupler from the main strip line 13 to the sub-strip line 14 can be achieved by adjusting the distance S between parallel portions of the two strip lines. In the description of the conventional example of FIG.
14, but as is apparent from the symmetrical structure of FIG.
Even if the roles of the main stripline line and the sub-stripline line are switched, the basic operation of the directional coupler can be realized in the same manner.

[0005] The directional coupler having a function of separating a part of the high-frequency power with directivity is used for controlling the transmission power of a transmitter of a cellular phone, for example. FIG. 6 shows a block diagram of the application example. Ports P1, P of main stripline line 22 of directional coupler 21
2 is arranged between the transmission power amplifier and the antenna 24, one port P3 of the sub strip line 23 is connected to the automatic gain control circuit, and the other port P4 is connected to the resistance element 25 for absorbing power. In this case, only a part of the output of the transmission power amplifier appears at the port P3 and is guided to the automatic gain control circuit. A part of the high-frequency power flowing backward from the antenna 24 appears at the port P4 and is absorbed by the resistance element 25. The signal output of the automatic gain control circuit is sent to a transmission power amplifier capable of controlling the gain, and the high-frequency output can be controlled according to the purpose. Since the transmission power output from the port P3 contains a harmonic component, a filter circuit (not shown) is connected to the next stage.

[0006] A wireless communication device such as a mobile phone is desired to be reduced in size and weight, and the number of components is required to be reduced accordingly. However, as described above, a mobile phone is composed of a combination of single-function components. In some cases, there is a limit.
Therefore, Japanese Patent Application Laid-Open No. H10-290108 (Conventional Example 2) proposes a directional coupler integrated with a low-pass filter. FIG. 7 shows an equivalent circuit diagram of the directional coupler. In this directional coupler, a capacitor is arranged between the main strip line and the ground, a capacitor is connected in parallel with the main strip line, and a low-pass filter is formed by utilizing the inductance of the main strip line. And a low-pass filter.

[0007]

However, in portable telephones and the like, which have been remarkably developed in the field of microwave communication, further miniaturization and lightening are desired, and components mounted on the portable telephone are required. Reduction in size and weight has become an important issue. In a method of forming a low-pass filter using the inductance of a main strip line as in the directional coupler with a low-pass filter of Conventional Example 2, a dielectric constant of 8
When the above material is used, the length of the main strip line needs to be about 0.1λ. This is 900MHz
In the case of (1), it corresponds to about 12 mm. However, in recent miniaturization of products (2012 size or the like), it has become difficult to accommodate such a strip line in a component.

An object of the present invention is to provide a directional coupler with a low-pass filter function suitable for miniaturization.

[0009]

According to a first aspect of the present invention, in a directional coupler having two strip lines opposing or parallel to each other, first and second coils are connected to both ends of a main strip line, First and second capacitors are arranged between one end of each of the coils not connected to the main stripline and the ground, and the main stripline, the first and second coils, and the first and second capacitors. This is a directional coupler that forms a low-pass filter with two capacitors.
According to a second invention, in a directional coupler in which two strip lines are opposed or parallel to each other, a first coil is connected to one end of a main strip line, and a side of the coil not connected to the main strip line. A first capacitor is disposed between one end of the main strip line and a ground, and a second capacitor is disposed between the other end of the main strip line and the ground. There is a directional coupler that forms a low-pass filter with two capacitors. In the first or second invention, it is preferable to include a capacitor connected in parallel to the main stripline and coils connected to both ends or one end thereof. It is preferable that the main and sub strip lines, the coil and the capacitor are printed and laminated on a dielectric green sheet, and then a plurality of external electrodes are formed on an end face of the laminated body. More preferably, a part of the two coils is formed on a different layer from the main stripline.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is an equivalent circuit diagram of one embodiment according to the present invention. 51 is a main strip line, 52 is a sub strip line, L1 and L2 are inductors, C1 and C
2, C3 denotes a capacitor. 53 is an input terminal,
54 is an output terminal, 55 is a monitor terminal, and 56 is connected to ground through a resistor.

FIG. 2 is an exploded view when the circuit diagram shown in FIG. 1 is configured as a laminate. A ground electrode 61 is formed on the lowermost dielectric layer 60, a capacitor electrode 63 is formed on the dielectric layer 62, a capacitor electrode 65 is formed on the dielectric layer 64, and a ground electrode 67 is formed on the dielectric layer 66. ing. Further, a coil electrode 69 is provided on the dielectric layer 68,
70 are formed, and the coil electrodes 72 and 73 are formed on the dielectric layer 71.
, A strip line 74 is formed, a strip line 76 is formed on the dielectric layer 75, a ground electrode 78 is formed on the dielectric layer 77, and a dielectric layer 79 is formed on the uppermost layer. The coil electrodes 69 and 72, and 70 and 73
1 are connected by through holes.

In the above laminated structure, the strip line 74 is composed of the main strip line 51 and the strip line 7 shown in FIG.
6 is the sub-strip line 52 of FIG.
2 is L1, the coil electrodes 70 and 73 are L2, the capacitance obtained when the capacitor electrode 65 and the ground electrode 67 face each other is C1, and the capacitor electrode 63 and the ground electrode 6 are C1.
1 The capacitance obtained by opposing is C3, and the capacitance obtained by opposing the capacitor electrodes 63 and 65 plays the role of C2. FIG. 3 is a perspective view of a laminated body obtained by laminating and firing the exploded view of FIG. 2 to form an external electrode on an end face.

With this configuration, the inductance of the main strip line is supplemented by the coils connected to both ends of the main strip line, so that a low-pass filter having a desired frequency can be obtained. The inductance can change the line width of the coil, the width of the winding frame, and the number of turns, and can easily cope with other frequencies. Further, the parallel resonator composed of the main strip line and the capacitor connected in parallel to the inductor connected to both ends thereof can increase the attenuation in the high frequency band.

FIG. 4 shows an equivalent circuit diagram according to another embodiment of the present invention. 51 indicates a main strip line, 52 indicates a sub strip line, L1 indicates an inductor, and C1, C2 and C3 indicate capacitors. 53 is an input terminal, 54 is an output terminal, 55 is a monitor terminal, and 56 is connected to ground through a resistor. Even in this case, the same result as in the above embodiment can be obtained.

[0015]

As is apparent from the above description, according to the present invention, the coils connected to both ends of the main strip line compensate for the inductance of the strip line which is reduced due to the miniaturization, thereby providing the directional characteristic with the low-pass filter function. The size of the coupler can be reduced.

[Brief description of the drawings]

FIG. 1 is an equivalent circuit diagram of one embodiment according to the present invention.

FIG. 2 is an internal pattern diagram of an embodiment according to the present invention.

FIG. 3 is a perspective view of one embodiment according to the present invention.

FIG. 4 is an equivalent circuit diagram of another embodiment according to the present invention.

FIG. 5 is a prior art perspective view of a directional coupler.

FIG. 6 is a circuit block diagram of a usage example of a directional coupler.

FIG. 7 is an equivalent circuit diagram of a conventional example.

[Brief Description of Symbols] 51 Main stripline 52 Substripline 53 Input terminal 54 Output terminal

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5J024 AA01 BA02 BA19 CA03 CA09 CA10 DA01 DA04 DA29 DA35 EA01

Claims (5)

[Claims] In a directional coupler comprising two strip lines facing or parallel to each other, first and second coils are connected to both ends of a main strip line and connected to the main strip lines of these coils. A first and a second capacitor are arranged between one end of each of the unexposed sides and the ground, and the main strip line, the first and the second coils, and the first and the second capacitors constitute a low-pass filter. A directional coupler, comprising: 2. A directional coupler comprising two strip lines opposing or parallel to each other, wherein a first coil is connected to one end of a main strip line, and a side of the coil not connected to the main strip line is connected to the first coil. A first capacitor is arranged between one end and ground, a second capacitor is arranged between the other end of the main stripline and ground, and the main stripline, the first coil, the first and second A directional coupler, comprising a low-pass filter with the capacitor of (1). 3. The directional coupler according to claim 1, further comprising a capacitor connected in parallel to the main strip line and a coil connected to both ends or one end thereof. 4. The main and sub strip lines, the coil and the capacitor are printed on a dielectric green sheet.
4. The directional coupler according to claim 1, wherein a plurality of external electrodes are formed on an end face of the laminated body after the lamination. 5. The directional coupler according to claim 4, wherein a part of the first and / or second coil is formed on a different layer from the main strip line.