JP2010088011A - Directional coupler - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a small-sized directional coupler passing high power therethrough. <P>SOLUTION: The directional coupler includes a master line 2 constituted of a microstrip line formed on a first dielectric substrate 1 and a sub line 4 constituted of a microstrip line formed on a second dielectric substrate 3 disposed while being spaced apart from the master line 2, the sub line 4 includes a projecting portion and the projecting portion makes it possible to adjust coupling due to an electric field and coupling due to a magnetic field, thereby a small-sized directional coupler having sufficient directivity is actualized. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a directional coupler for detecting microwave power, and more particularly to a directional coupler formed by a microstrip line.

  In the past, electronic circuits have become smaller and more integrated, and it has been desired to reduce the size of each component. Directional couplers are also known as one of the component components that are also desired to be reduced in size. ing.

  The directional coupler is used as a power detector such as a microwave, and is required to have sufficient directivity that can separately detect traveling wave power and reflected wave power.

  In general, a directional coupler using a microstrip line is well known to have a structure using a quarter wavelength coupled line as shown in FIG. Since it is defined, its size is limited by the frequency of the signal to be detected.

In addition, Patent Document 1 discloses a CM type directional coupler in which a main line and a sub line are covered with a glass base material for miniaturization. In the directional coupler of Patent Document 1, a CM type directional coupler is formed by glass as a dielectric, and the occupied area when mounted is smaller than that of a conventional quarter wavelength coupled line type directional coupler. The size can be reduced to 1/10.
JP-A-6-45811

  However, since the directional coupler having the configuration described in Patent Document 1 has an insertion loss, it is very difficult to reduce the size in order to pass a large power of, for example, several hundred watts. In this case, the loss increases exponentially, so that a factor for alienating the miniaturization occurs, such as requiring a dedicated heat dissipation structure. In addition, in the 1/4 wavelength coupled line type directional coupler, the structure is limited to the detection wavelength, and sufficient size reduction cannot be achieved. Also, since the main line and the sub line are arranged on the same dielectric substrate, the corner mode There is a problem that it is difficult to obtain sufficient directionality because the phase speeds of excitation and odd mode excitation are different.

  The present invention solves the above-described conventional problems, and provides a directional coupler capable of obtaining a large amount of passing power and reducing the size.

  In order to solve the conventional problem, a directional coupler according to the present invention includes a main line made of a microstrip line formed on a first dielectric substrate, and a second line disposed on the main line with a gap therebetween. A sub-line made of a microstrip line is formed on the dielectric substrate, and the sub-line has a U-shaped configuration.

  Thereby, since the coupling by the electric field and the coupling by the magnetic field can be adjusted by the U-shaped portion, it is possible to realize a small directional coupler having sufficient directivity.

Since the directional coupler of the present invention can adjust the coupling by the electric field and the coupling by the magnetic field by the U-shaped portion, it is possible to realize a small directional coupler having sufficient directionality.

  According to a first aspect of the present invention, there is provided a main line composed of a microstrip line formed on a first dielectric substrate, and a microstrip line formed on a second dielectric substrate disposed on the main line with a gap. A direction having sufficient directivity because the sub-line has a U-shaped configuration, and the coupling by the electric field and the coupling by the magnetic field can be adjusted by the U-shaped part. A sex coupler can be realized.

  According to the second invention, in particular, a part of the U-shaped portion of the sub-line of the first invention has an overlapping portion in the vertical direction of the main line and the substrate, so that the U-shaped portion depends on the electric field. Since the coupling and the coupling by the magnetic field can be adjusted, a directional coupler having sufficient directivity can be realized.

  In the third invention, the gap between the sub-line and the main line of the first and second inventions is set to be 2 mm or more, so that it is small and coupled by an electric field and a magnetic field by a U-shaped portion. Since the distance between the main line and the sub-line is 2 mm or more, a directional coupler that does not significantly affect the characteristic impedance of the main line can be realized.

  According to the fourth invention, in particular, the U-shaped portion of the third invention is configured to have a length of 5 mm or more and 8 mm or less, so that it is small and is coupled by an electric field and a magnetic field by the U-shaped portion. Can be adjusted, and the coupling can be in the best condition, so that a directional coupler having sufficient directivity can be realized.

  In the fifth aspect of the invention, the distance between the patterns of the U-shaped portion of the fourth invention is set to 0.5 mm or less, so that the coupling by the electric field and the coupling by the magnetic field is best by the U-shaped portion. Therefore, a directional coupler having sufficient directionality can be realized.

  According to the sixth aspect of the invention, in particular, the output of the directional coupler is configured by setting the width of the line so that the characteristic impedance of the sub-line consisting of the microstrip line of the first to fifth aspects is 50 ohms. When the detector circuit is connected to the directional coupler, the directionality and the degree of coupling of the directional coupler can be easily measured by the measuring instrument, and a directional coupler with stable performance can be realized.

  According to the seventh aspect of the invention, in particular, the line width of the sub line is set by setting the line width so that the characteristic impedance of the sub line composed of the microstrip line of the first to fifth aspects of the invention is larger than 50 ohms. Since the thickness can be reduced, a smaller directional coupler can be realized.

  According to the eighth aspect of the invention, in particular, by providing a metal shield member around the second dielectric substrate of the first to seventh aspects, the influence of an external electric field and magnetic field can be blocked. A directional coupler with high detection accuracy can be provided.

  According to the ninth aspect of the invention, the metal shield member is held by the metal shield member of the eighth aspect of the invention, and the distance from the first dielectric substrate is ensured. By holding the second dielectric substrate by the member and securing the distance from the first dielectric substrate, the influence of the electric field and magnetic field from the outside is cut off to improve the detection accuracy and between the substrates. Since the distance can be fixed by the shield member, it is possible to provide a directional coupler that suppresses variations during manufacturing.

  According to a tenth aspect of the invention, in particular, by providing a detection circuit at both output ends of the sub-line of the first to ninth aspects, and by configuring the input impedance of the detection circuit to match the characteristic impedance of the sub-line, It is possible to provide a directional coupler with high detection accuracy by preventing power reflection at the input end of the detection circuit.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the present invention is not limited to the embodiments.

(Embodiment 1)
1 and 2 are configuration diagrams of a directional coupler according to the first embodiment of the present invention. FIG. 1 is a plan view of the present embodiment, FIG. 2 (1) is a cross-sectional view taken along the line A1-A2 of FIG. 1, and FIG. 2 (2) is a cross-sectional view taken along the line B1-B2. In the present embodiment, it is configured to be used when passing power of several hundred W with a frequency of about 2 GHz to 3 GHz.

  1 and 2, the directional coupler is provided on a main line 2 configured on the first dielectric substrate 1 and on a second dielectric substrate 3 disposed to face the main line 2. The sub-line 4 is arranged, and a metal shield 5 is formed so as to cover the second dielectric substrate 3 including the sub-line 4. The metal shield 5 is formed with openings 5a in opposing side walls, and the main line 2 passes therethrough. The metal shield 5 is connected to the conductor surface 1a formed on the back surface of the first dielectric substrate 1 and has the same potential. The main line 2 has a back surface covered with a conductor surface 1a having a ground potential, and has a characteristic impedance with a line width of approximately 50Ω. The sub line 4 is arranged on the second dielectric substrate 3 and has a U-shaped projecting shape, and the projecting part has a part that overlaps the main line 2 in the vertical direction. Are arranged with gaps.

  About the directional coupler comprised as mentioned above, the operation | movement and an effect | action are demonstrated below.

  When the high frequency power passes through the main line 2, an electric field and a magnetic field corresponding to the high frequency power are generated around it. The generated electric field and magnetic field are combined with the sub-line 4 to generate signals at the end 4A and the end 4B of the sub-line 4. The electromotive force generated in the U-shaped sub-line 4 by the electric field is proportional to the electric field generated by the main line 2, and the electromotive force generated by this electric field is as shown in FIG. Thus, a voltage is generated at the end portions 4A and 4B of the sub line 4. When these voltages are VA1 and VB1, respectively, the relationship of VA1 = VB1 is established.

  Next, since a magnetic field current is generated between the end portions 4A and 4B of the sub-line 4 by the magnetic field interlinking the U-shaped sub-line 4, a load circuit having a predetermined impedance is provided at the end portions 4A and 4B. When connected, it can be observed as a voltage at the end portions 4A and 4B. FIG. 4 shows an equivalent circuit at this time, and assuming that the voltages at this time are VA2 and VB2, since the voltage VA2 and the voltage VB2 are voltages generated by the current flowing between the terminals, the relationship of VA2 = −VB2 is established.

  By superimposing the above relationship, when the voltage VA1 and the voltage VA2 are in the direction of adding, the voltage VB1 and the voltage VB2 are in the direction of subtraction, so By arranging the shape of the character and the distance between the first dielectric substrate 1 and the second dielectric substrate 3 in the best condition, a signal is output to one of the sub-lines 4 and no signal is output to the other. A directional coupler can be formed.

  FIG. 5 is a characteristic diagram illustrating an example of actual measurement of characteristics in the first embodiment.

  In the figure, the horizontal axis represents frequency, and the vertical axis represents traveling wave power Pf, reflected wave power Pr, and insertion loss in decibels. The frequency in the actual measurement is 2 GHz to 3 GHz. The insertion loss is approximately −0.2 dB or less over the measurement frequency band, and almost no loss occurs even when several hundreds of watts of power is passed. For example, even when 200 W of electric power is passed, only a loss of about 9 W or less is generated, and it is a value that can sufficiently dissipate heat and can be put to practical use.

  In the actual measurement, a Teflon (registered trademark) substrate having a relative dielectric constant of 2.7 and a substrate thickness of 0.8 mm was used as the first dielectric substrate 1, so that the characteristic impedance of the main line 2 was set to 50 ohms. The width is about 2 mm. By further increasing the thickness of the dielectric substrate of the first dielectric substrate 1 or by using a dielectric substrate material having a low relative dielectric constant and a low dielectric loss, the line width at which the characteristic impedance is 50 ohms is increased. This insertion loss can be further reduced.

  Further, the degree of coupling indicating the detection sensitivity for detecting the traveling wave power Pf and the degree of separation for detecting the reflected wave power Pr are approximately −30 dB and approximately −60 dB, respectively. As a result, the directionality is always 20 dB or more. Therefore, the traveling wave power and the reflected wave power can be sufficiently separated, and the directionality is good. The characteristics shown in FIG. 5 are as follows. The first dielectric substrate 1 is a Teflon (registered trademark) substrate, the second dielectric substrate 3 is a CEM3 substrate, the distance between the substrates is 2 mm, and the sub-line 4 has a U-shape. The interval between the parallel portions is 0.5 mm. Since the line width of the sub line 4 is 1.5 mm in order to make its characteristic impedance approximately 50 ohms, the width of the directional coupler can be configured to be 10 mm or less. Compared to a directional coupler using a filter, the size can be significantly reduced. Moreover, since it is not the structure which inserts and adds components to the main line 2, the heat_generation | fever by passing electric power does not become a problem, and a very small and directional coupler with good directivity can be obtained.

  FIG. 6 shows a change in impedance of the main line 2 when the distance between the first dielectric substrate 1 and the second dielectric substrate 3 is changed. From this figure, when the distance between the two substrates is close to less than 2 mm, the influence of the second dielectric substrate 3 appears to the main line 2 and the impedance changes greatly. When impedance mismatching occurs on the microwave line, power is reflected at the impedance mismatching point, and there is a possibility that surrounding power may be adversely affected by the reflected power.

  Further, in the directional coupler, the reflected wave generated at the input and output ends of the main line 2 is superimposed on the detection output, so that sufficient separation cannot be obtained, and the performance as a directional coupler is achieved. Will deteriorate. For this reason, in the directional coupler of the present invention, it is desirable that the distance between the substrates 1 and 3 is 2 mm or more in order to suppress the fluctuation of the characteristic impedance of the main line 2 to several ohms or less.

  FIG. 7 is a characteristic diagram showing an actually measured characteristic diagram of the directional coupler when the inter-pattern distance d of the U-shaped parallel portion 4a of the sub-line 4 shown in FIG. 1 is changed. This figure shows the difference between the degree of coupling indicating sensitivity for detecting traveling wave power Pf and the degree of separation for detecting reflected wave power Pr, and this figure can represent the directional characteristics of the directional coupler. . From this figure, it is shown that the directionality deteriorates when the inter-pattern distance d is increased. This is because by increasing the inter-pattern distance d, a phase difference occurs in the induced electromotive force due to the electric field generated in the U-shaped portion in this portion, and the equivalent circuit shown in FIGS. 3 and 4 is simply established. Since it disappears, it can be considered that the directionality has deteriorated.

For this reason, it is desirable that the distance between adjacent patterns in the U-shaped portion be as close as possible. Generally, in the pattern design of a printed circuit board, a good finished state can be obtained relatively easily when the distance between patterns is 0.25 mm or more. 0.25 mm to 0.5 mm is desirable.

  Moreover, in the directional coupler of this structure, since it has the structure which can add the subline 4 which detects the electric power which transmits the main line 2 later to the main line 2 which transmits electric power, The second dielectric substrate 3 including the sub line 4 can be disposed at an arbitrary position of the main line 2 having a length sufficient to detect transmission power, and the directional coupler can be installed at any position. It can be installed at a position, and the degree of freedom of mounting the substrate can be improved.

(Embodiment 2)
8 and 9 are configuration diagrams of a directional coupler according to the second embodiment of the present invention. 8 is a plan view of the present embodiment. FIG. 9A is a cross-sectional view taken along line A1-A2 of FIG. 8, and FIG. 9B is a cross-sectional view taken along line B1-B2. In the present embodiment, it is configured to be used when passing power of several hundreds of watts at a frequency of about 2 GHz to 3 GHz.

  8 and 9, the directional coupler is disposed on the main line 2 configured on the first dielectric substrate 1 and on the second dielectric substrate 3 disposed to face the main line 2. And a metal shield 5 which covers the second dielectric substrate 3 including the sub line 4. The main line 2 has a back surface covered with a conductor surface having a ground potential, and has a characteristic impedance with a line width of approximately 50Ω. The sub-line 4 is arranged on the second dielectric substrate 3 and protrudes in a U-shape, and the protruding part has a gap so that a part thereof overlaps the main line 2 in the vertical direction. It is arranged. The characteristic impedance Z of the sub line 4 is set to a value higher than 50 ohms, for example, 75 ohms or 100 ohms.

  About the directional coupler comprised as mentioned above, the operation | movement and an effect | action are demonstrated below.

  When the high frequency power passes through the main line 2, an electric field and a magnetic field corresponding to the high frequency power are generated around it. The generated electric field and magnetic field are combined with the sub line 4 to generate a signal at the end portions 4A and 4B of the sub line 4. The electromotive force generated in the U-shaped portion of the sub-line 4 by the electric field is proportional to the electric field generated by the main line 2, and the electromotive force generated by this electric field is the same as that of the above-described embodiment in terms of an equivalent circuit. Similarly, as shown in FIG. 3, a voltage is generated at the end portions 4 </ b> A and 4 </ b> B of the sub line 4. When these voltages are VA1 and VB1, respectively, the relationship of VA1 = VB1 is established.

  Next, since a magnetic field is generated between the end portions 4A and 4B by a magnetic field interlinking the U-shaped portions, when a predetermined impedance is connected to the end portions 4A and 4B, the end portion 4A, It can be observed as a voltage at 4B. The equivalent circuit at this time is similarly as shown in FIG. 4 as in the above-described embodiment. When the voltages at this time are VA2 and VB2, the relationship of VA2 = −VB2 is established. By superimposing the above relationship, when the voltages VA1 and VA2 are in the direction of adding up, the voltages VB1 and VB2 are in the direction of subtraction, so that the U-shaped shape so that VB1 = −VB2 By arranging the distance between the dielectric substrate 1 and the second dielectric substrate 3 in the best condition, a directional coupler that outputs a signal to one of the sub-lines 4 and does not output a signal to the other is formed. can do.

Further, since the characteristic impedance of the sub line 4 is designed to be larger than 50 ohms generally used in a high frequency circuit, the line width can be further reduced, and the second dielectric including the sub line 4 can be used. The shape of the substrate 3 itself can be further reduced, and the overall shape of the directional coupler can be reduced.

  Moreover, in the directional coupler of this structure, since it has the structure which can add the subline 4 which detects the electric power which transmits the main line 2 to the main line 2 which transmits electric power later, transmission power is transmitted by the subline 4. The second dielectric substrate 3 including the sub-line 4 can be disposed at an arbitrary position of the main line 2 having a length to be detected, and the directional coupler is disposed at an arbitrary position. The degree of freedom for mounting the board can be improved.

  As described above, since the directional coupler according to the present invention is small and can handle large passing electric power, a heating device, a garbage disposal machine, or a semiconductor using dielectric heating as represented by a microwave oven is used. The present invention can also be applied to a power detector of a power amplifier used for applications such as a microwave power source of a plasma power source as a manufacturing apparatus.

The top view of the directional coupler of the 1st Embodiment of this invention (A) Cross-sectional view of the directional coupler taken along line A1-A2 in FIG. 1 (b) Cross-sectional view of the directional coupler taken along line B1-B2 Equivalent circuit diagram of electric field coupling of the directional coupler Equivalent circuit diagram of magnetic coupling of directional coupler Characteristic diagram showing the measured characteristics of the directional coupler Characteristic diagram showing changes in distance between dielectric substrates and characteristic impedance of main line in co-directional coupler Characteristic diagram showing inter-pattern distance and directionality frequency characteristics of sub-line 4 of same direction coupler The top view of the directional coupler of the 2nd Embodiment of this invention (A) Cross-sectional view of the directional coupler taken along line A1-A2 in FIG. 1 (b) Cross-sectional view of the directional coupler taken along line B1-B2 (A) Plan view showing the configuration of a conventional quarter wavelength directional coupler (b) Cross-sectional view of the same directional coupler

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 1st dielectric substrate 2 Main line 3 2nd dielectric substrate 4 Subline 5 Metal shield

Claims (10)

A main line made of a microstrip line formed on a first dielectric substrate, and a sub-line made of a microstrip line formed on a second dielectric substrate disposed on the main line with a gap. The sub-line is a directional coupler having a U-shaped configuration. The directional coupler according to claim 1, wherein a part of the U-shape of the sub line has an overlapping portion in a direction perpendicular to the main line and the substrate. The directional coupler according to claim 1 or 2, wherein a gap between the sub line and the main line is 2 mm or more. The directional coupler according to claim 3, wherein the length of the U-shaped portion is configured to be 5 mm or more and 8 mm or less. The directional coupler according to claim 4, wherein a distance between patterns of the U-shaped portion is 0.5 mm or less. The directional coupler according to any one of claims 1 to 5, wherein the line width is set so that the characteristic impedance of the sub-line composed of a microstrip line is 50 ohms. The directional coupler according to any one of claims 1 to 5, wherein the line width is set so that the characteristic impedance of the sub-line composed of a microstrip line is greater than 50 ohms. The directional coupler according to claim 1, wherein a metal shield member is provided around the second dielectric substrate. The directional coupler according to claim 8, wherein the second dielectric substrate is held by a metal shield member to secure a distance from the first dielectric substrate. The directional coupler according to any one of claims 1 to 9, wherein a detector circuit is provided at both output ends of the sub line, and an input impedance of the detector circuit is matched with a characteristic impedance of the sub line.

Images