JPH07226609A - Directional coupler - Google Patents

Abstract

PURPOSE:To provide a directional coupler capable of being used in a relatively high frequency band and obtaining satisfactory directivity. CONSTITUTION:This directional coupler is constituted by providing a microstrip line 2 composed of 1/2 wavelength coupling line parts L2 whose length is 1/2 of a wavelength inside a tube and port parts P1-P4 connected to the 1/2 wavelength coupline line parts L2 and used as input/output parts on a dielectric substrate 1. In this case, the port part Pi is used for input, the port part P2 is used for a main line, the port part P3 is used for coupling, the port part P4 is used for isolation and the respective port parts P1-P4 are provided with notches respectively formed so as to vary a line width by notching the microstrip line 2. The notches function as impedance matching parts Ip1-Ip4 in the respective port parts P1-P4. Thus, the direction coupler secures the directivity and isolation characteristics well even when it is used in the high frequency band.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a directional coupler provided mainly in a waveguide such as an attenuation circuit element, and more particularly, it is used in a relatively high frequency band such as microwaves, especially millimeter waves. The present invention also relates to a directional coupler provided with a microstrip line including a coupling line portion having a length determined by a predetermined multiple of the guide wavelength.

[0002]

2. Description of the Related Art Conventionally, in this type of directional coupler, for example, as shown in FIG. 2, a quarter-wavelength coupling line portion L1 having a length determined by a quarter wavelength of a guide wavelength, and this one. There is a structure in which a microstrip line 2 that is coupled to the / 4 wavelength coupling line portion L1 and that is used as an input / output portion and that includes port portions P1 to P4 is formed on a dielectric substrate 1.

In this directional coupler, the port portion P1 is used for input, the port portion P2 is used for main line, the port portion P3 is used for isolation (passive attenuation), and the port portion P4 is used for coupling. From port P2 for use
A weak electric power of 20 [dB] or less can be taken out.

By the way, when the directional coupler is configured to be usable at a relatively high frequency such as a millimeter wave band, it is 50
The central conductor portion of the microstrip line 2 having an impedance characteristic of Ω cannot be regarded as a line sufficiently thin with respect to the guide wavelength. That is, in the case of this directional coupler, the length of the quarter-wavelength coupling line portion L1 approaches the line width of the microstrip line 2, and thus the shape of the quarter-wavelength coupling line portion L1 is as shown in FIG. It is reduced. This makes it difficult to distinguish between the quarter-wavelength coupled line portion L1 and the port portions P1 to P4.

When the directional coupler including the 1/4 wavelength coupling line portion L1 is configured for high frequencies as described above, not only the circuit design becomes difficult, but also the corner C portion in each of the port portions P1 to P4 and The electromagnetic fields in the quarter-wavelength coupled line portion L1 are coupled to each other, and the directivity is impaired, so that the basic characteristics of the directional coupler cannot be obtained.

[0006]

Generally, in a distributed constant line, since a 1/2 wavelength line does not cause impedance change, a circuit using a 3/4 wavelength line is used in place of the 1/4 wavelength line at high frequencies. However, even with this configuration, electric power is often coupled to the isolation port portion P3 and the coupling port portion P4, and as a result, the directivity is impaired and the basic characteristics of the directional coupler are reduced. It has the drawback of being damaged.

That is, in the case of the conventional directional coupler, basically, it is difficult to obtain the directivity in a high frequency band and it is difficult to apply the present invention at present.

The present invention has been made to solve the above problems, and its technical problem is to provide a directional coupler which can be used in a relatively high frequency band and which can obtain a good directivity. To do.

[0009]

According to the present invention, there is provided a microstrip line including a coupling line portion having a length defined by a predetermined multiple of the guide wavelength and an input / output portion coupled to the coupling line portion. In this directional coupler, the length of the coupling line portion is 1/2 to 1 times the guide wavelength, and a directional coupler having an impedance matching portion at the input / output portion can be obtained.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A directional coupler according to the present invention will be described in detail below with reference to the drawings by referring to embodiments.

First, referring to the conventional directional coupler shown in FIG. 2, a technical outline relating to the configuration of the directional coupler of the present invention will be described.

FIG. 4 shows the port P when the wavelength in the tube is variable and the length L of the quarter wavelength coupling line L1 is constant.
1 shows the transmission characteristics between P1 and P4 by the relationship of the coupling amount S ₄₁ [dB] with respect to the frequency F. In FIG. 4, f ₁ is the frequency when the guide wavelength is 4L, f ₂ is the frequency when the guide wavelength is 2L, f ₃ is the frequency when the guide wavelength is 4L / 3, and f ₄ is the guide The frequency when the wavelength becomes L is shown. From Figure 4, when the guide wavelength with respect to the length L of the coupling line part is the frequency f ₃ as a frequency f _1, and 4L / 3 becomes 4L, in other words,
It can be seen that the coupling amount S ₄₁ with respect to the coupling port P4 is maximized when the length L of the coupling line portion is 1/4 times or 3/4 times the guide wavelength.

Further, FIG. 5 shows that the wavelength inside the tube is constant and
The transmission characteristics between the ports P1 and P3 when the length of the / 4 wavelength coupled line portion L1 is varied are shown by the relationship of the coupling amount S ₃₁ [dB] with respect to the frequency F. However, in FIG. 5, f ₁ ′ is the frequency when the length of the ¼ wavelength coupling line portion L1 becomes ¼ times the guide wavelength, and f ₂ ′ is the length of the ¼ wavelength coupling line portion L1. F ₃ ′ is a frequency at which the wavelength becomes 1/2 of the guide wavelength, the quarter wavelength coupled line portion L
Frequency when the length of 1 becomes 3/4 times the guide wavelength, f
₄ 'length of one quarter-wavelength coupling line portion L1 is the guide wavelength
The frequency at which the frequency doubles is shown.

It can be seen from FIG. 5 that the power leakage (transmission amount) to the isolation port P3 gradually increases as the frequency F increases.

Specifically, at the frequency f ₁ ', the port portion P is compared with the coupling amount S ₄₁ between the port portions P1 and P4.
Since the leakage of the electric power of the coupling amount S ₃₁ between 1 and P3 is small, the electric power input from the port portion P1 is coupled to the port portion P4, but it is difficult to couple to the port portion P3, and as a result, the directionality is increased. Will be shown. This is nothing but the operating principle of the directional coupler of the normal frequency type including the coupled line portion. Further, at the frequency f ₃ ′, the coupling to the port portion P4 becomes maximum, but the leakage of electric power also increases to the port portion P3, so that the directivity cannot be obtained. Further, at frequencies f ₂ ′ and f ₄ ′, the leakage of power to the port portion P3 is large, but the coupling to the port portion P4 is minimal, so that it shows directionality.

Therefore, by replacing the port portion P3 for coupling and the port portion P4 for isolation, the basic operation of the directional coupler can be ensured.

Therefore, in the directional coupler of the present invention, the length of the 1/4 wavelength coupling line portion L1 is 1 / the wavelength of the guide tube.
Keeping in mind that the directional coupler operates even if it is defined by 2 to 1 times, and by improving the basic configuration of the directional coupler, the length of the quarter-wavelength coupling line portion L1 is reduced to the length of the microstrip line 2. It can be used even in a high frequency band close to the line width of (each port P1 to P4). However,
If corners or bends are used when extracting an input / output port from the microstrip line 2 using the quarter wavelength coupling line portion L1 having a length of 1/2 to 1 times the guide wavelength, reflection characteristics of the input port Regarding the 1/4 wavelength coupling line section L
In itself, the reflection coefficient becomes small regardless of its length,
Reflection from corners and bends (pattern deviation portions in the microstrip line 2) is superimposed at intervals of ½ to 1 wavelength, and the reflection characteristics are deteriorated.

For this reason, when the directional coupler is constructed using the quarter-wavelength coupling line portion L1 having a length of 1/2 to 1 times the guide wavelength, impedance is matched to the input / output port. Action is required.

FIG. 1 shows the basic structure of a directional coupler according to an embodiment of the present invention. This directional coupler is coupled to the ½ wavelength coupling line section L2 having a length ½ times the guide wavelength and the ½ wavelength coupling line section L2, and is a port used as an input / output section. Parts P1 to P4
The microstrip line 2 is formed on the dielectric substrate 1.

In this directional coupler, the port P1 is used for input, the port P2 is used for main line, the port P3 is used for coupling, and the port P4 is used for isolation. Further, each of the port portions P1 to P4 is provided with a cutout formed by cutting out the microstrip line 2 so that the line width can be varied. These notches function as impedance matching sections I _p 1 to I _p 4 in the respective port sections P1 to P4.

That is, comparing this directional coupler with the directional coupler shown in FIG. 2, the point that the ½ wavelength coupling line section L2 is used instead of the ¼ wavelength coupling line section L1 and the port The point that the functions of the parts P3 and P4 are exchanged, and each port part P
A point of providing the impedance matching part I _p 1 to I _p 4 to 1~P4 is different.

In the case of this directional coupler, as described above, the leakage of power to the coupling port portion P3 becomes large and the coupling to the isolation port portion P4 becomes minimal to show the directivity. The reflection characteristic is the impedance matching portion I provided in each of the port portions P1 to P4.
_{for p} 1 to I _p 4 is matched impedance, superposition is suppressed deterioration of characteristics reflected from the corner portion C is avoided. As a result, the directional coupler has good directivity and isolation characteristics even when used in a relatively high frequency band.

By the way, in the impedance matching parts I _p 1 to I _p 4 in the directional coupler of the above-mentioned embodiment, by providing notches for varying the line width of the microstrip line 2 in each of the port parts P1 to P4. Although different impedance characteristics are obtained, other configurations of the impedance matching units I _p 1 to I _p 4 may include parallel stubs (pseudo modules), microstrip lines 2 having different impedance characteristics and a plurality of impedance matching units I _p 1 to I _p 4. The case where a stub is used in combination is included.

[0024]

As described above, according to the present invention, the directional coupler can be used even in a relatively high frequency band, which is difficult to use with the conventional directional coupler. A combiner can be obtained. In the case of this directional coupler, since the length of the coupled line portion can be particularly lengthened,
The decrease in the coupling force of the electromagnetic field between the corners and bends in the microstrip line is suppressed, and the deterioration of the reflection characteristics is avoided, so good directionality and isolation characteristics are secured even when used in the high frequency band. Will be done. As a result, even when an equivalent circuit is designed using this directional coupler, there is an advantage that the design value and the circuit characteristics are likely to match.

[Brief description of drawings]

FIG. 1 shows a basic configuration of a directional coupler according to an embodiment of the present invention.

FIG. 2 shows a basic configuration of a conventional frequency-compatible directional coupler including a conventional quarter-wavelength coupling line section.

FIG. 3 is a diagram showing a configuration example when the directional coupler shown in FIG. 2 is of a high frequency type.

4 is a basic configuration of the directional coupler shown in FIG.
6 shows the transmission characteristics between the port portions P1 and P4 when the wavelength in the tube is variable and the length of the coupling line portion is constant.

5 is a diagram showing a basic configuration of the directional coupler shown in FIG.
6 shows the transmission characteristics between the port parts P1 and P3 when the wavelength in the tube is fixed and the length of the coupling line part is varied.

[Explanation of symbols]

First dielectric substrate 2 microstrip line C corner I _p 1 to I _p 4 impedance matching unit L1 1/4 wavelength coupling line portion L2 1/2 wavelength coupling line portion P1~P4 ports

Claims (1)

[Claims] 1. A directional coupler comprising a microstrip line including a coupling line portion having a length defined by a predetermined multiple of the guide wavelength and an input / output portion coupled to the coupling line portion, wherein the coupling line is provided. The directional coupler according to claim 1, wherein the length of the portion is 1/2 to 1 times the guide wavelength, and the input / output portion is provided with an impedance matching portion.