JPS6112402B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a directional coupler, particularly for VHF band, UHF band,
This invention relates to a directional coupler with a microstrip circuit structure used in high frequency bands such as microwave bands and millimeter wave bands.

FIG. 1 shows a plan view of an example of a conventional directional coupler. In the figure, 1 is an insulating substrate, 2 is a main line,
3 represents a sub-line, and 4, 5, 6, and 7 represent input/output ends.
The purpose of a directional coupler is to extract part of the signal transmitted through a line separately depending on the signal transmission direction. For example, a part of the signal input from the input/output terminal 4 in Fig. Transmit to end 6, input/output end 7
It is desirable to have characteristics that do not transmit This transmits a part of the signal input from the input/output terminal 4 to the input/output terminal 6, transmits a part of the signal input from the input/output terminal 5 to the input/output terminal 7, and separates each signal. The purpose is to do. However, the directional coupler with the structure shown in Figure 1 is inferior to other directional couplers, such as those with a stripline structure, in its signal separation characteristics (hereinafter referred to as directionality). . This is considered to be because the phase speeds of propagation of even mode and odd mode signals in the directional coupler are different.

Conventionally, as shown in Figure 2, the method of improving the directionality of a directional coupler is to change the shape of the line in the coupling part as shown in the figure to increase the phase velocity of even mode and odd mode signal propagation. I found something that made it match. However, this method is effective when the degree of decoupling of the directional coupler is close to about 10 dB, but it is not effective when the degree of decoupling is 30 dB or more. The example shown in Fig. 3 is also a method of improving this, in which an insulator 8 having a dielectric constant similar to that of the insulating substrate material is placed at the coupling part, which also reduces even mode and odd mode signals. The phase velocity of propagation is made to match. However, this method has disadvantages in that it requires work to bond the insulating material and that the value of improved directionality varies depending on the thickness of the adhesive during bonding.

The present invention eliminates such drawbacks of the conventional method and provides two parallel lines arranged on one surface of an insulating substrate and connected to each other, or a substantially parallel line and the other surface of the insulating substrate. It is characterized by comprising a grounded conductor plate placed between the two lines, and a grounded conductor placed along the line between the two lines.

FIGS. 4a and 4b are cross-sectional views of a conventional directional coupler taken in a plane perpendicular to the direction of the line. In the figure, 9 is a back ground conductor. Further, the distribution state of the electric lines of force is schematically shown using chain lines and arrows. FIG. 4a shows the electric field distribution during odd mode propagation, and FIG. 4b shows the electric field distribution during even mode propagation. As is clear from this figure, the ratio of the number of electric lines of force distributed in the insulating substrate to the number of lines of electric force distributed in the air is significantly different depending on the electric field distribution in odd mode and even mode. .

FIGS. 5a and 5b show an embodiment of the directional coupler of the present invention, and are sectional views taken in a plane perpendicular to the direction of the line, similar to FIG. 4. In the figure, 10 is the two conductors 2 and 3
A ground conductor placed between the Figure 5 a, b
Similarly to FIG. 4, the distribution state of the electric field in the propagation of odd mode and even mode is shown by chain lines and arrows, respectively.

As is clear from FIG. 5, the ratio of the number of electric lines of force distributed in the insulating substrate and the number of lines of electric force distributed in the air is almost the same.

Now, if the ratio of the number of electric lines of force in the insulating substrate to the number of all lines of electric force is Q, then the effective relative dielectric constant ε in the propagation of electromagnetic waves is expressed as ε=Q(ε _r −1)+1. Here, ε _r is the dielectric constant of the insulating substrate material. At this time, the phase velocity V of the electromagnetic wave is becomes. Here, C represents the speed of light in vacuum.

In the conventional device shown in FIG. 4, the Q values of the even mode and the odd mode are significantly different, so the phase velocities of the propagation of the even mode and the odd mode have different values. In the embodiment of FIG. 5, the Q of even mode and odd mode is
Since the values of are almost equal, the values of the phase velocities of each propagation are almost the same. Therefore, it is considered that the directional coupler according to the present invention exhibits good directional characteristics.

FIG. 6 is a perspective view of the embodiment shown in FIG. 5.
In FIG. 6, a through hole is provided in the insulated conductor 10, and the ground conductor 10 and the back ground conductor 9 are electrically connected.

FIG. 7 is a perspective view of another embodiment of the present invention, showing an example in which the intervals between the lines of the coupling portion of the directional coupler are not uniform.

As is clear from the above description, according to the present invention, a directional coupler with good electrical characteristics and good reproducibility can be obtained.

[Brief explanation of the drawing]

Figures 1, 2, and 3 are top views of conventional directional couplers, Figures 4 a and b are diagrams of electric field distribution in the cross section of the conventional directional coupler, and Figures 5 a and b 6 is a diagram showing the electric field distribution in a cross section of an embodiment of the directional coupler of the present invention, and FIGS. 6 and 7 are perspective views of the embodiment of the present invention. In the figure, 1 is an insulating substrate, 2 and 3 are coupled lines, 4, 5, 6, and 7 are input and output ends of the lines, 8 is an insulator, 9 is a back ground conductor, and 10 is a ground conductor.

Claims (1)

[Claims] 1. Two parallel or nearly parallel lines disposed on one surface of the insulating substrate and connected to each other; a ground conductor plate disposed on the other surface of the insulating substrate; A directional coupler comprising a conductor placed between two lines along the line and grounded.