JP3169820B2 - Directional coupler - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a directional coupler.

[0002]

2. Description of the Related Art Conventionally, there are various types of directional couplers for microwaves. Among them, there are various types of directional couplers which can find an application field in amplifiers of base stations of digital portable telephones, which have been remarkably developed in recent years. There are a microstrip directional coupler and a triplate directional coupler. As shown in a schematic perspective view in FIG. 19 of the accompanying drawings, the directional coupler of the microstrip type has a dielectric having a main line strip conductor 3 and a sub line strip conductor 4 on the upper surface and a ground surface on the rear surface. It comprises a body substrate 1. On the other hand, the triplate directional coupler has a main line strip conductor 3 and a sub line strip conductor 4 on the upper surface and a ground line on the rear surface, as shown in a schematic exploded perspective view of FIG. 14 includes a first dielectric substrate 1 having a surface, a second dielectric substrate 2 having a ground surface on the back surface superimposed on the upper surface of the first dielectric substrate 1, and FIG. As shown in a schematic exploded perspective view of a disassembled component arrangement, a first dielectric substrate 5 having a main line strip conductor 8 on an upper surface and a sub line strip conductor 9 on a rear surface, and the first dielectric substrate 5 , And a second dielectric substrate 6 and a third dielectric substrate 7 which are overlapped so as to sandwich them. The surfaces of the second dielectric substrate 6 and the third dielectric substrate 7 opposite to the first dielectric substrate 5 are ground surfaces.

[0003] In these types of directional couplers,
Normally, as schematically shown in FIG. 15, the main line strip conductor 3 and the sub-line strip conductor 4 are connected so that their coupling portion extends over a quarter of the wavelength of the center frequency (λ / 4). It is assumed to extend in close proximity. But,
In the directional coupler having such a structure, the coupling between the coupling portion of the main line strip conductor 3 and the coupling portion of the sub-line strip conductor 4 is changed while maintaining the coupling characteristic in a wide band, so that the coupling degree is improved. Can be adjusted, but it is very difficult to realize a directional coupler having a good directivity while maintaining the flatness of the degree of coupling.

Conventionally, various proposals have been made for a shape using such a multi-stage connection.
Directional couplers such as those disclosed in JP-A-23447 and JP-A-3-296304 have been proposed. Japanese Patent Application Laid-Open No. 54-23447 discloses a directional coupler of a coupling system using multiple stages of λ / 4 and a directional coupler of a system having an interdigital strip line. Japanese Patent Application Laid-Open No. 3-296304 discloses a coupling type directional coupler using a semi-reentrant coupling line.

[0005] Of these, the directional coupler of the coupling type using a multistage cascade of λ / 4 has, for example, three distributed couplings having a length of 1/4 wavelength as schematically shown in FIG. 16 of the accompanying drawings. Shape directional couplers 3A and 4A, 3B and 4B, 3
C and 4C are connected in cascade with couplers 3B and 4B having strong coupling therebetween.

[0006]

A conventional directional coupler using a λ / 4 multistage cascade coupling system can have a staggered frequency characteristic and a very wide band. However, there is a problem in that a large space is required on the pattern due to the strip line having a plurality of λ / 4, and the shape becomes large.
In addition, there are also things that need to be improved in various characteristics of the directional coupler such as isolation.

A conventional directional coupler having an interdigital strip line requires a wire bonding process, which complicates the manufacturing man-hours.
Only a tight coupling of about 3 dB or less can be supported, and it is difficult to obtain directionality.

Further, since a conventional directional coupler using a semi-reentrant coupling line has a floating conductor, a pattern having a floating conductor is required in addition to a pattern having a main line and a sub line.
There has been a problem that the number of manufacturing steps increases and the number of parts having accuracy increases. There is also a problem that the impedance of the main line and the sub line is disturbed, and the reflection loss is deteriorated.

An object of the present invention is to provide a directional coupler capable of solving the above-mentioned problems of the prior art.

[0010]

According to the present invention, in a directional coupler having an input port, an output port, a coupling port, and an isolation port, a main line strip between the input port and the output port is provided. The length of the joint of the sub-line strip conductor between the conductor and the coupling port and the isolation port,
One quarter of the wavelength of the center frequency, each coupling part is divided into three sections of substantially the same length, and the separation distance of at least one of the corresponding sections is set to another section. , And the length of each section is set to 1/12 of the wavelength of the center frequency.

According to one embodiment of the present invention, the at least one section is a center section.

According to another embodiment of the invention, the at least one section is a side section.

Further, the directional coupler of the present invention can be constituted by a microstrip system or a triplate system.

[0014]

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described in more detail with reference to the accompanying drawings, in particular with reference to FIGS. 1 to 12, FIG. 19 and FIGS. .

FIG. 1 is a plan view schematically showing the shapes of a main line strip conductor and a sub line strip conductor provided on a dielectric substrate of a directional coupler which is a loosely coupled coupler as one embodiment of the present invention. . The entire structure itself as a directional coupler is shown in FIGS. 19, 13 and 1 of the accompanying drawings.
4 is the same as the conventional directional coupler described above with respect to No. 4, and will not be described again here. The same applies to other embodiments described below.

In the embodiment shown in FIG. 1, one end of the main line strip conductor 10 constitutes an input port 11 and the other end constitutes an output port 12, and a coupling between the input port 11 and the output port 12 is provided. The length of the section is made equal to one quarter of the wavelength λ of the center frequency of the directional coupler, that is, λ / 4. This is the same as the prior art, but according to the invention, the coupling is divided into three sections of the same length λ / 12, namely a side section 13 and a center section 14. , And a side section 15. On the other hand, one end of the sub-line strip conductor 20 constitutes the coupling port 21 and the other end thereof forms the isolation port 2.
2, the length of the coupling portion between the coupling port 21 and the isolation port 22 is one quarter of the wavelength λ of the center frequency of the directional coupler, that is,
λ / 4. This is the same as the conventional one, but according to the invention, the couplings have the same length λ / 12
Is divided into three sections, that is, side section 2
3, a central section 24 and a side section 25. In this embodiment, the distance between the central section 14 of the coupling section of the main line strip conductor 10 and the central section 24 of the coupling section of the sub-line strip conductor 20 is:
The distance between the side section 13 and the side section 23 and the distance between the side section 15 and the side section 25 are narrower.

FIG. 2 is a plan view schematically showing the shapes of a main line strip conductor and a sub line strip conductor provided on a dielectric substrate of a directional coupler which is a tightly coupled coupler as another embodiment of the present invention. is there. In the embodiment of FIG. 2, one end of the main line strip conductor 10A constitutes the input port 11A and the other end constitutes the output port 12A, and the length of the coupling portion between the input port 11A and the output port 12A. The length is set equal to ４ of the wavelength λ of the center frequency of the directional coupler, that is, λ / 4. This is the same as the conventional one, but according to the invention, the coupling is divided into three sections of the same length λ / 12, namely a side section 13A and a central section 14A. , And a side section 15A. On the other hand, one end of the sub-line strip conductor 20A constitutes the coupling port 21A, and the other end constitutes the isolation port 22A, and the length of the coupling portion between the coupling port 21A and the isolation port 22A. Is ４ of the wavelength λ of the center frequency of the directional coupler, that is, λ / 4
Has been equal to. This is the same as in the prior art, but according to the invention the coupling is divided into three sections of the same length λ / 12, ie the side sections 23A
And a central section 24A and a side section 25A. In this embodiment, the distance between the central section 14A of the coupling section of the main line strip conductor 10A and the central section 24A of the coupling section of the sub-line strip conductor 20A is determined by the side section 13A and the side section 23A. And the distance between the side section 15A and the side section 25A. The center section 14A and the center section 24A are formed on surfaces opposite to each other with the dielectric substrate interposed therebetween, and are configured to overlap each other. Therefore, the separation distance S between the side sections 13A and 15A of the main line strip conductor 10A and the side sections 23A and 25A of the sub-line strip conductor 20A is very short.

FIG. 3 is a plan view schematically showing the shapes of a main line strip conductor and a sub line strip conductor provided on a dielectric substrate of a directional coupler which is a loosely coupled coupler as still another embodiment of the present invention. It is. In the embodiment of FIG. 3, one end of the main line strip conductor 10B constitutes the input port 11B and the other end constitutes the output port 12B, and the length of the coupling portion between the input port 11B and the output port 12B. The length is set equal to ４ of the wavelength λ of the center frequency of the directional coupler, that is, λ / 4. This is the same as the conventional one, but according to the invention, the coupling is divided into three sections of the same length λ / 12,
That is, it has a three-stage structure of the side section 13B, the center section 14B, and the side section 15B. On the other hand, the sub-line strip conductor 20B has one end connected to the coupling port 2.
1B, and the other end forms an isolation port 22B. The length of the coupling portion between the coupling port 21B and the isolation port 22B is equal to the wavelength λ of the center frequency of the directional coupler. Quarter, ie
λ / 4. This is the same as the conventional one, but according to the invention, the couplings have the same length λ / 12
Is divided into three sections, that is, side section 2
3B, a central section 24B, and a side section 25B. In this embodiment, the distance between the central section 14B of the coupling section of the main line strip conductor 10B and the central section 24B of the coupling section of the sub-line strip conductor 20B is determined by the side section 13B and the side section 23B. And the separation distance between the side section 15B and the side section 25B.

FIG. 4 is a plan view schematically showing the shapes of a main line strip conductor and a sub line strip conductor provided on a dielectric substrate of a directional coupler which is a loosely coupled coupler as still another embodiment of the present invention. It is. In the embodiment of FIG. 4, one end of the main line strip conductor 10C constitutes the input port 11C, the other end constitutes the output port 12C, and the length of the coupling portion between the input port 11C and the output port 12C. The length is set equal to ４ of the wavelength λ of the center frequency of the directional coupler, that is, λ / 4. This is the same as the prior art, but according to the invention, the coupling is divided into three sections of approximately the same length, namely a side section 13C, a central section 14C and a side section 13C. It has a three-stage structure with the section 15C. Central section 14C
Is slightly shorter than λ / 12, and the length of the side sections 13C and 15C is slightly longer than λ / 12. On the other hand, one end of the sub-line strip conductor 20C constitutes a coupling port 21C, and the other end constitutes an isolation port 22C, and the length of the coupling portion between the coupling port 21C and the isolation port 22C. Is the wavelength λ of the center frequency of this directional coupler.
, Ie, equal to λ / 4. This is the same as the prior art, but according to the invention, the coupling is divided into three sections of approximately the same length, namely a side section 23C, a central section 24C and a side section 24C. It has a three-stage structure with the section 25C. Central section 24
The length of C is slightly shorter than λ / 12, and the length of the side sections 23C and 25C is slightly longer than λ / 12. In this embodiment, the distance between the central section 14C of the coupling section of the main line strip conductor 10C and the central section 24C of the coupling section of the sub-line strip conductor 20C is determined by the side section 13C and the side section 23C. Is smaller than the distance between the side section 15C and the side section 25C.

Next, in order to confirm the operation and effect of the directional coupler according to the present invention, in comparison with a conventional structure, a result of a simulation or a result of a trial production and measurement of various characteristics will be described. I do. First,
FIG. 5 shows the result of simulating the microstrip directional coupler according to the present invention having the shapes of the main line strip conductor and the sub line strip conductor described with reference to FIG. Based on the simulation result of FIG. 1, the center frequency is set to 820 MHz.
FIG. 6 shows measurement data of a prototype product.
On the other hand, as a comparative example, the result of simulating the conventional example described with reference to FIG.
Is shown in In these graphs, the horizontal axis represents frequency, and the vertical axis represents coupling (Coup), insertion loss (Ins), reflection loss (RL), and isolation (ISO). The same applies to the following graphs.

As can be seen by comparing these graphs, according to the present invention, the isolation is improved by 20 dB or more. That is, while the conventional device shown in FIG. 17 has an isolation of 82 dB in a band of 800 to 1000 MHz, the device of the present invention shown in FIG.
05 dB. Comparing the simulation results of FIGS. 17 and 5, it can be seen that the reflection loss of the present invention is also improved by 15 dB or more over the conventional one. That is, in the conventional device shown in FIG.
B, in the case of the present invention shown in FIG.
It has become.

Next, FIG. 7 shows that the main line strip conductor and the sub-line strip conductor have a coupling portion of λ / 12 so that the center is dense and the outer side is loosely coupled as described with reference to FIG. 3 shows the results of simulating various characteristics of a directional coupler of the triplate type having three sections having the same length. As can be seen from FIG. 7, at a frequency center of 820 MHz, in a band of 810 to 830 MHz, the reflection loss is 62 dB and the isolation is 13 dB.
0 dB, the coupling degree is 41.00 dB, and 820 M
The isolation at Hz is 159 dB.

Next, FIG. 8 shows that, as described with reference to FIG. 3, the main line strip conductor and the sub-line strip conductor have a coupling portion of λ / 12 so that the center is sparse and the outside is tightly coupled. 3 shows the results of simulating various characteristics of a directional coupler of the triplate type having three sections having the same length. As can be seen from FIG. 8, in the frequency center of 820 MHz, in the band of 810 to 830 MHz, the reflection loss is 56 dB, and the isolation is 11
9 dB, coupling degree is 41.01 dB, and 820 M
The isolation at Hz is 159 dB.
7 that the performance is slightly reduced.

Next, FIG. 9 shows that the shape of the main line strip conductor and the sub line strip conductor as described with reference to FIG. The results of a simulation of various characteristics of a directional coupler of the triplate system in which the coupling portion is divided into three sections having a length slightly different from λ / 12 are shown. In this case, the section at the center is slightly shorter than λ / 12 and the section at the side is slightly longer than λ / 12. As can be seen from FIG. 9, the frequency center 820 MH
In z, in the band 810 to 830 MHz, the reflection loss is 59 dB, the isolation is 115 dB, and the coupling degree is 4
It is 1.05 dB, and the isolation at 820 MHz is 119 dB.

Next, FIG. 10 shows that the shape of the main line strip conductor and the auxiliary line strip conductor as described with reference to FIG. 19 is set to λ / 12 so that the center is dense and the outside is loosely coupled. 3 shows the results of simulating various characteristics of a microstrip directional coupler divided into three stages having the same length. As can be seen from FIG. 10, at a frequency center of 820 MHz, bands 810 to 8
At 30 MHz, the reflection loss is 40 dB, the isolation is 87 dB, the degree of coupling is 40.95 dB, and the isolation at 820 MHz is 140 dB.
dB.

FIG. 18 shows a microstrip type direction in which a conventional coupling portion as described with reference to FIG. 15 is formed in a one-stage shape having a length of λ / 4 for comparison with the one of the present invention shown in FIG. 3 shows the results of simulating various characteristics of a sex coupler. As can be seen from FIG. 18, at a frequency center of 820 MHz, in a band of 810 to 830 MHz, the reflection loss is 40 dB, and the isolation is 84 dB.
dB, coupling degree is 40.96 dB, 820 MH
The isolation at z is 97 dB. FIG.
As is clear from a comparison between FIG. 0 and FIG. 18, the peak value of the isolation is improved by 43 dB in the case of the present invention as compared with the conventional case.

Finally, the structure of the strip conductor of FIG.
Although it is suitable for a loosely-coupled directional coupler having a coupling degree of 10 dB or more, the structure of the strip conductor shown in FIG. 2 is suitable for a tightly-coupled directional coupler having a coupling degree of 3 dB or more to less than 10 dB. It is. In the tightly coupled coupler as shown in FIG. 2, it has also been confirmed that the following operational effects can be obtained by dividing the coupling portion into three stages of λ / 12 according to the present invention. That is, as schematically shown in FIG. 11, the deviation width ΔC between the output and the coupling degree has been greatly increased due to variations in processing accuracy and the like. However, according to the structure of the tightly coupled coupler as shown in FIG. 12, as shown in FIG.

[0028]

According to the present invention, the isolation and the reflection loss can be improved in the center of the frequency, and the flatness of the coupling degree can be obtained.

The total length of the joint is equal to the conventional λ / 4 (3
× λ / 12), so that it is not necessary to expand the space, and the same size as the conventional size can be maintained.

The directional coupler can be made highly isolated at the center of the coupling degree without disturbing the impedance and the return loss of the main line and the sub-line, so that the number of parts of the digital cellular phone base station and the system Simplification can be achieved.

Since the result of the simulation almost matches the actual result, it is effective in increasing the isolation.

It is possible to establish a design method for high isolation, which has been considered difficult in loosely coupled couplers.

[Brief description of the drawings]

FIG. 1 is a plan view schematically showing shapes of a main line strip conductor and a sub line strip conductor provided on a dielectric substrate of a directional coupler which is a loosely coupled coupler as one embodiment of the present invention.

FIG. 2 is a plan view schematically showing shapes of a main line strip conductor and a sub line strip conductor provided on a dielectric substrate of a directional coupler which is a tightly coupled coupler as another embodiment of the present invention.

FIG. 3 is a plan view schematically showing shapes of a main line strip conductor and a sub line strip conductor provided on a dielectric substrate of a directional coupler which is a loosely coupled coupler as still another embodiment of the present invention.

FIG. 4 is a plan view schematically showing shapes of a main line strip conductor and a sub line strip conductor provided on a dielectric substrate of a directional coupler which is a loosely coupled coupler as still another embodiment of the present invention.

FIG. 5 is a view showing a result of a simulation of a directional coupler of a triplate type according to the present invention at a center frequency of 900 MHz.

FIG. 6 shows measurement data of a prototype product with a center frequency of 820 MHz based on the simulation result of FIG.

FIG. 7 shows various characteristics of a tri-plate directional coupler according to the present invention having a main line strip conductor and a sub line strip conductor as shown in FIG.
It shows the result of simulating as Hz.

8 shows a result of simulating various characteristics of the directional coupler of the triplate type according to the present invention having the shapes of the main line strip conductor and the sub line strip conductor as shown in FIG.

9 shows a result of simulating various characteristics of the directional coupler of the triplate type according to the present invention having the shapes of the main line strip conductor and the sub line strip conductor as shown in FIG.

10 shows a result of simulating various characteristics of the microstrip directional coupler according to the present invention having the shapes of the main line strip conductor and the sub line strip conductor as shown in FIG.

FIG. 11 is a diagram illustrating an example in which a deviation width ΔC between an output and a coupling degree is greatly increased due to a variation in processing accuracy or the like in a directional coupler.

FIG. 12 is a diagram illustrating a deviation width between the output and the coupling degree due to the structure of the tightly coupled coupler according to the present invention.

FIG. 13 is a schematic exploded perspective view showing a structural example of a conventional triplate loosely-coupled directional coupler.

FIG. 14 is a schematic exploded perspective view showing an example of the structure of a conventional triplate type tightly coupled directional coupler.

FIG. 15 is a schematic view illustrating the shape of a main line strip conductor and a sub line strip conductor of a conventional directional coupler.

FIG. 16 is a schematic diagram showing another example of the shape of the main line strip conductor and the sub line strip conductor of the conventional directional coupler.

FIG. 17 shows a result of simulating various characteristics of a conventional triplate directional coupler in which a conventional coupling portion as described with reference to FIG. 15 is formed in a single-stage shape having a length of λ / 4.

FIG. 18 shows a result of simulating various characteristics of a microstrip directional coupler in which a conventional coupling unit as described with reference to FIG. 15 has a one-stage shape having a length of λ / 4, and .

FIG. 19 is a schematic perspective view showing a structural example of a conventional microstrip directional coupler.

DESCRIPTION OF SYMBOLS 10 Main line strip conductor 11 Input port 12 Output port 13 Side section 14 Center section 15 Side section 20 Subline strip conductor 21 Coupling port 22 Isolation port 23 Side section 24 Center section 25 Side division

Claims (5)

(57) [Claims] 1. A directional coupler having an input port, an output port, a coupling port, and an isolation port, wherein a main line strip conductor between the input port and the output port and a coupling port and an isolation port are provided. , The length of the coupling portion of the sub-line strip conductor between them is set to ４ of the wavelength of the center frequency, and each coupling portion is divided into three stages having substantially the same length. Wherein the distance between at least one of the sections is smaller than the distance between the other sections, and the length of each section is one-twelfth of the wavelength of the center frequency. . 2. The directional coupler according to claim 1, wherein the at least one section is a center section. 3. The directional coupler according to claim 1, wherein the at least one section is a side section. 4. The directional coupler according to claim 1, wherein the directional coupler is configured by a microstrip method. 5. The method according to claim 1, wherein the triplate system is used.
Or the directional coupler according to 2 or 3.