JP2012060614A - Directional coupler - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a directional coupler capable of achieving size reduction of a circuit configuration and improvement in directivity.SOLUTION: The directional coupler includes: a main line 11 provided on a dielectric substrate; a loop-shaped sub line 12 which is patterned on the dielectric substrate and a part of which is spaced from the main line; and a pair of correction pattern 13 disposed on both ends of a coupled portion of the main line to the sub line.

Description

  Embodiments described herein relate generally to a directional coupler.

  Conventionally, as a general structure, a microstrip line structure in which the entire back surface of a dielectric substrate is a conductor ground and a main line and sub-line (directional coupler) pattern is constructed on the surface is used as a general structure. A coupled line (sub line) having a line pattern of an appropriate length is configured with an appropriate interval from the main line according to the degree of coupling.

  Generally, it is known that the directionality is best when the length of the coupled line is λ / 4. However, in the UHF band, the line length of λ / 4 wavelength is long and the circuit becomes large. Therefore, a loop coupling line having an appropriate length shorter than λ / 4 is often used. However, in this structure, the directionality as a directional coupler is lowered, and improvement is required.

Japanese Patent Laid-Open No. 2-116201 JP-A-4-2203

  By the way, in a device that transmits high power, such as a transmitter, since the level of output power of the transmission line is large, the directionality (isolation characteristic) of this directional coupler is regarded as important when detecting high power. ing. Therefore, realization of a small directional coupler having high directivity is required.

  An object of the present embodiment is to provide a directional coupler capable of realizing a reduction in circuit configuration and improvement in directionality.

  The directional coupler according to the present embodiment includes a main line provided on a dielectric substrate, a pattern formed on the dielectric substrate, and a loop-shaped sub-portion part of which is arranged with a certain gap from the main line. A line, and a pair of correction patterns disposed at both ends of a coupling portion between the main line and the sub line.

The figure which shows the directional coupler which concerns on this embodiment. The enlarged view of the coupling line part of the directional coupler of FIG. The figure which shows the frequency characteristic of the directional coupler of FIG. The figure which shows the conventional directional coupler. The figure which shows the frequency characteristic of the directional coupler of FIG.

  Hereinafter, the directional coupler according to the present embodiment will be described with reference to the drawings.

  FIG. 1 is a diagram illustrating a directional coupler according to the present embodiment. In FIG. 1, the directional coupler includes a main transmission line 11, a sub line 12, and a correction pattern 13. The main transmission line 11 is composed of a strip line using a copper plate, for example. The sub line 12 is composed of a microstrip line formed on a dielectric substrate, and has a loop antenna shape. A part of the sub line 12 is arranged along the main transmission line 11 with a certain gap. In FIG. 1, the upper and lower conductor grounds of the strip line of the main transmission line 11 are omitted. The main transmission line 11 is theoretically the same whether it is formed of a microstrip line on a dielectric substrate as in the case of the sub line 12 or a copper plate as shown in FIG.

  FIG. 2 is an enlarged view of a coupled line portion of the directional coupler of FIG. In the present embodiment, in order to improve the directivity of the directional coupler, as shown in FIG. 2, a pair of correction patterns 13 are provided so as to be symmetrical at both ends of the coupling portion between the main transmission line 11 and the sub line 12. Provide.

When attention is paid to the port P4, the directionality D of the directional coupler is expressed by the following equation (1): the coupling degree I with respect to the traveling direction from the port P1 and the coupling degree C with respect to the reflection direction from the port P2. It shall be expressed as a difference.
Directionality D = | I−C | [dB] Formula (1)
It is effective to improve the characteristics that the correction pattern 13 is arranged symmetrically at both ends of the coupled line. The directionality increases as the area of the correction pattern 13 increases. The shape of the width and length of the correction pattern 13 is optimized using electromagnetic field simulation. With this pattern shape, the directionality of traveling wave power and reflected wave power can be improved. As an example, the result is shown in FIG. Based on the simulation result, it can be seen that the directionality of 32 dB or more can be obtained according to the equation (1).

  Here, for comparison, a configuration example of a conventional directional coupler is shown in FIG. FIG. 4 shows a structure in the case where a directional coupler having a microstrip structure is used as a sub-line for a main transmission line such as a high-power transmitter having a stripline structure as in FIG. It is. 4 differs from the configuration of FIG. 1 in that the correction pattern 13 is not provided.

  The coupling line portion of the directional coupler has a structure in which it is wired like a loop antenna. However, this structure has a drawback that the directivity of the directional coupler deteriorates if the degree of coupling is weak. An example of the simulation result in this case is shown in FIG. From the above formula (1), it can be seen that the directivity is about 24 dB in the conventional structure.

  Comparing FIG. 3 and FIG. 5, in the directional coupler of this embodiment, the directivity is improved by 8 dB compared to the conventional one, and the coupled line portion of the sub line 12 has a length of λ / 4 wavelength. Even if it does not do, sufficient directionality can be obtained.

  As described above, in the above embodiment, a pair of line patterns for correcting the directivity are provided at both ends of the coupling portion between the main transmission line using the copper plate and the loop-shaped coupling line using the dielectric substrate. I am trying to provide it. By comprising in this way, the directional coupler which can implement | achieve size reduction and high directionality of a circuit structure can be provided.

  Furthermore, as an application example of the directional coupler of the present embodiment, for example, it can be provided in an output transmission path of a power amplifier for a high power transmitter in a UHF (Ultra-High Frequency) band. The directional coupler of the present embodiment is provided in a place where the main transmission line is not affected on the side surface of the strip transmission line of the copper plate which is the main line. Since the coupling line portion of the directional coupler is electromagnetically coupled to the main line, the power level of the traveling wave at the input port can be detected.

  In addition, although some embodiment of this invention was described, these embodiment is shown as an example and is not intending limiting the range of invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

  11: Main transmission line, 12: Sub line, 13: Correction pattern.

Claims (1)

A microstrip main line using a dielectric substrate or a strip main line using a copper plate;
A loop-shaped sub-line that is patterned on a dielectric substrate, a part of which is arranged with a certain gap from the main line;
A directional coupler comprising a pair of correction patterns disposed at both ends of a coupling portion between the main line and the sub line.

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