Directional coupler

Abstract

To provide a directional coupler with improved coupling.SOLUTION: A directional coupler according to an embodiment includes an insulating base material, a first microstrip line provided in parallel on one surface of the base material, a second microstrip line, a capacitive coupling pattern provided on the other surface of the base material, and a ground plane surrounding the capacitive coupling pattern and spaced apart from the capacitive coupling pattern. The capacitive coupling pattern is provided at a position overlapping the first microstrip line and the second microstrip line that are arranged in parallel when viewed from above.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The embodiment relates to a directional coupler. [Background technology]

[0002] Directional couplers are used in high-frequency circuits, and there is a demand for higher coupling efficiency.

[0003] In a directional coupler, in order to increase the degree of coupling, it is necessary to narrow the spacing between the parallel lines. However, due to constraints such as manufacturing precision, it is difficult to narrow the spacing beyond a certain point. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 63-286004 Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the embodiments of the present invention is to provide a directional coupler with an improved degree of coupling. [Means for solving the problem]

[0006] A directional coupler according to an embodiment includes an insulating substrate having a first surface and a second surface opposite to the first surface, a first microstrip line provided on the first surface, a second microstrip line provided on the first surface and arranged parallel to the first microstrip line and spaced a predetermined distance from the first microstrip line, a capacitive coupling pattern provided on the second surface at a position where the first microstrip line and the second microstrip line are arranged in parallel in a planar view and overlap the first microstrip line and the second microstrip line, and a ground plane provided on the second surface and spaced from the capacitive coupling pattern to surround the capacitive coupling pattern. [Brief description of the drawings]

[0007] [Figure 1] Fig. 1(a) is a schematic top view illustrating a directional coupler according to an embodiment, and Fig. 1(b) is a schematic bottom view illustrating the directional coupler according to the embodiment. [Diagram 2] 1 is a schematic perspective view illustrating a directional coupler according to an embodiment; [Diagram 3] Fig. 3(a) is a perspective view showing a model for simulating the directional coupler according to the embodiment, and Fig. 3(b) and Fig. 3(c) are perspective views showing a model for simulating the directional coupler of the comparative example. [Figure 4] FIG. 4 is a graph showing the results of calculating the degree of coupling by simulating the models of the directional couplers of FIGS. 3(a) to 3(c). [Diagram 5] Fig. 5(a) is a schematic equivalent circuit diagram showing a directional coupler according to an embodiment, and Fig. 5(b) is a schematic equivalent circuit diagram showing a directional coupler of a comparative example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. The drawings are schematic or conceptual, and the relationship between the thickness and width of each part, the size ratio between parts, etc. are not necessarily the same as in reality. Even when the same part is shown, the dimensions and ratios of each part may be different depending on the drawing. In this specification and each drawing, elements similar to those described above with reference to the previous drawings are given the same reference numerals and detailed description thereof will be omitted as appropriate.

[0009] Fig. 1(a) is a schematic top view illustrating a directional coupler according to an embodiment, and Fig. 1(b) is a schematic bottom view illustrating the directional coupler according to the embodiment. FIG. 2 is a schematic perspective see-through view illustrating a directional coupler according to the embodiment. As shown in FIGS. 1(a) to 2, a directional coupler 10 according to this embodiment includes a substrate 11, a first microstrip line 12, a second microstrip line 14, a ground plane 16, and a capacitive coupling pattern 18.

[0010] The substrate 11 has a first surface 11a and a second surface 11b. The second surface 11b is the surface opposite to the first surface 11a. Hereinafter, the surface on the first surface 11a side may be referred to as the upper surface, the space on the first surface 11a side may be referred to as the upper side, the surface on the second surface 11b side may be referred to as the lower surface, and the space on the second surface 11b side may be referred to as the lower side. In addition, the case where an object is viewed from the top surface and the case where an object is viewed from the bottom surface may be collectively referred to as a planar view.

[0011] The first microstrip line 12 and the second microstrip line 14 are provided on a first surface 11a of the substrate 11. The ground plane 16 and the capacitive coupling pattern 18 are provided on a second surface 11b of the substrate 11.

[0012] The substrate 11 is an insulating plate member. The material constituting the substrate 11 has a higher dielectric constant than air. By using a substrate having a high relative dielectric constant, the dimension of the microstrip line in the longitudinal direction of the substrate 11 can be shortened, and the directional coupler 10 can be made smaller. The substrate 11 contains, for example, an epoxy resin, and has a relative dielectric constant of about 3.6. From the viewpoint of broadening the bandwidth, it is preferable that the thickness of the substrate 11 is thin, and a thickness of about 0.4 mm is set as a sufficiently thin thickness while maintaining mechanical strength.

[0013] The first microstrip line 12 and the second microstrip line 14 are conductive foils arranged in parallel with a predetermined distance between them. The predetermined distance is a gap G1. The length over which the first microstrip line 12 and the second microstrip line 14 are arranged in parallel is represented by L1. L1 is set to be ¼ (λ / 4) of the wavelength of the signal handled by the directional coupler 10.

[0014] The first microstrip line 12 and the second microstrip line 14 both have the same width W1. The first microstrip line 12 and the second microstrip line 14 are, for example, foils of a conductor containing copper (Cu). The thickness of the first microstrip line 12 and the second microstrip line 14 can be any thickness, for example, about 35 μm. The widths of the first microstrip line 12 and the second microstrip line 14 are set to have a characteristic impedance of 50 Ω, but are not limited to the same width and may be different widths.

[0015] Terminals 12a and 12b are provided at both ends of the first microstrip line 12, and terminals 14a and 14b are provided at both ends of the second microstrip line 14. In the drawings, these terminals are indicated as "1," "2," "3," and "4," and may be referred to as terminals 1, 2, 3, and 4.

[0016] The first microstrip line 12 is a main line, and for example, a signal input from terminal 1 is output from terminal 2. The second microstrip line 14 is a coupled line, and couples a part of the signal transmitted through the first microstrip line 12, and the coupled part of the signal is output from terminal 3. In this case, the output from terminal 4 is sufficiently smaller than that from terminal 3.

[0017] The directional coupler 10 can also input a signal from terminal 2 and output it from terminal 1. In this case, a part of the coupled signal is output from terminal 4, and the output from terminal 3 is sufficiently smaller than that from terminal 4. Also, the reflected wave of the signal input from terminal 1 can be taken out from terminal 4. Furthermore, the main line and the coupled line may be interchanged. That is, a signal may be transmitted through the second microstrip line 14 having terminals 3 and 4, and the signal transmitted through the second microstrip line 14 may be branched to the first microstrip line 12 having terminals 1 and 2. Hereinafter, unless otherwise specified, the main signal is input from terminal 1 and output to terminal 2, and the coupled signal is output from terminal 3.

[0018] The capacitive coupling pattern 18 is provided so as to overlap a coupling portion between the first microstrip line 12 and the second microstrip line 14 in a plan view. The capacitive coupling pattern 18 has a length L2, which is approximately equal to the coupling length L1. The width W3 of the capacitive coupling pattern 18 is sufficiently wider than the gap G1 between the first microstrip line 12 and the second microstrip line 14. As will be described later in relation to Figures 3 and 4, the capacitive coupling pattern 18 is provided so as to overlap the coupling portion, thereby making it possible to increase the degree of coupling between the first microstrip line 12 and the second microstrip line 14.

[0019] The capacitive coupling pattern 18 may have any shape as long as it overlaps the coupling portion between the first microstrip line 12 and the second microstrip line 14 in a plan view. From the viewpoint of designing and manufacturing the directional coupler 10, the outer periphery of the capacitive coupling pattern 18 in a plan view is preferably formed by straight lines, for example, a rectangle. One side of the rectangle is preferably parallel to the direction in which the first microstrip line 12 and the second microstrip line 14 are arranged in parallel.

[0020] The coupling portion between the first microstrip line 12 and the second microstrip line 14 is a portion where they are arranged in parallel over a length L1, and where the first microstrip line 12 and the second microstrip line 14 are arranged opposite each other with a gap G1 between them.

[0021] The capacitive coupling pattern 18 is provided in the ground plane 16. The ground plane 16 is electrically connected to, for example, a ground potential. The ground plane 16 and the capacitive coupling pattern 18 are electrically isolated patterns, and the capacitive coupling pattern 18 is disposed away from the ground plane 16. The capacitive coupling pattern 18 is electrically not connected to anything and is floating. The length L4 of the ground plane 16 is longer than the length L3 of the capacitive coupling pattern 18, and the width W4 of the ground plane 16 is wider than the width W3 of the capacitive coupling pattern 18.

[0022] The operation and effects of the directional coupler 10 according to this embodiment will be described. Fig. 3(a) is a perspective view showing a model for simulating the directional coupler according to the embodiment, and Fig. 3(b) and Fig. 3(c) are perspective views showing a model for simulating the directional coupler of the comparative example.

[0023] In the directional coupler 10 of this embodiment shown in Fig. 3(a), a simulation of the degree of coupling is performed using the width W3 of the capacitive coupling pattern 18 shown in Fig. 2 as a parameter. The width W3 is 1.8 mm, 1.4 mm, and 1.0 mm.

[0024] For comparison, a model of directional coupler 10a shown in Fig. 3(b) is created without a capacitive coupling pattern 18, and a simulation of the degree of coupling is performed. Also, a model of directional coupler 10b shown in Fig. 3(c) is created without a capacitive coupling pattern, and a ground plane 16a is provided over the entire lower surface of the substrate 11, and a simulation of the degree of coupling is performed.

[0025] In the simulation, the target frequency is set to 10 GHz, and the dimensions of each element are set. Specifically, referring to FIG. 1, the width W1 of the first microstrip line 12 and the second microstrip line 14 is 0.8 mm. The gap G1 is 0.2 mm. The length L1 of the coupling portion is 4.5 mm. The directional couplers 10, 10a, and 10b are above the air, and the thickness of the air is 1 mm. The directional couplers and the air above and below are surrounded by a metal housing. The relative dielectric constant of the substrate 11 is 3.6, and the thickness of the substrate 11 is 0.4 mm.

[0026] FIG. 4 is a graph showing the results of calculating the degree of coupling by simulating the models of the directional couplers of FIGS. 3(a) to 3(c). In Fig. 4, A1 to A3 are calculation results of the degree of coupling of the directional coupler 10 shown in Fig. 3(a). A1 shows the calculation result of the degree of coupling when the width W3 of the capacitive coupling pattern 18 is 1.8 mm. A2 shows the calculation result of the degree of coupling when the width W3 of the capacitive coupling pattern 18 is 1.4 mm. A3 shows the calculation result of the degree of coupling when the width W3 of the capacitive coupling pattern 18 is 1.0 mm.

[0027] B is a calculation result of the degree of coupling of the directional coupler 10a shown in Fig. 3(b), and C is a calculation result of the degree of coupling of the directional coupler 10b shown in Fig. 3(c).

[0028] As shown in FIG. 4, at a frequency of 10 GHz, the coupling degrees of A1, A2, and A3 are −7.6 dB, −7.8 dB, and −8.4 dB, respectively, and all of them realize a coupling degree higher than −10 dB.

[0029] On the other hand, at a frequency of 10 GHz, the degree of coupling is −10.2 dB for B and −17.3 dB for C, both of which are lower than the degrees of coupling for A1, A2, and A3 and lower than −10 dB.

[0030] In this way, by providing a pattern for coupling two microstrip lines on the opposite surface of the substrate, the degree of coupling between the two microstrip lines can be increased. The capacitive coupling pattern 18 capacitively couples the first microstrip line 12 and the second microstrip line 14, so it is sufficient to provide the capacitive coupling pattern 18 so as to overlap the coupling portion of the two microstrip lines in a plan view.

[0031] A technique for increasing the degree of coupling of a directional coupler is disclosed in, for example, Patent Document 1. In the technique of Patent Document 1 and the like, two microstrip lines are provided on a ground plane, and another microstrip line is provided in a multi-layered manner. In such a technique, it is necessary to use a substrate having multi-layer wiring and to accurately set the thickness of the base material of each layer, which poses problems in terms of manufacturing and reliability and can be a factor in increasing costs.

[0032] In the directional coupler 10 according to this embodiment, a high degree of coupling can be easily achieved by forming a microstrip line and a capacitive coupling pattern on a double-sided substrate. Also, as shown in graphs A1 to A3 in Fig. 4, the dimensional accuracy of the capacitive coupling pattern can exhibit the desired performance even if it varies considerably (1.4 mm ± 0.4 mm in the example of Fig. 4), and the directional coupler 10 is easy to design and manufacture. This allows the manufacturing process to be shortened and costs to be reduced.

[0033] FIG. 5(a) is a schematic equivalent circuit diagram illustrating a directional coupler according to an embodiment. As shown in FIG. 5(a), in the directional coupler 10 according to the embodiment, the first microstrip line 12 and the second microstrip line 14 are mainly capacitively coupled via the capacitive coupling pattern 18. Therefore, as described above, the degree of coupling between the first microstrip line 12 and the second microstrip line 14 is improved, and a sufficiently large output can be taken out from "COUPLE OUT". As described in FIG. 4, by appropriately setting the shape of the capacitive coupling pattern 18, it is possible to obtain an optimal coupled output. In FIG. 5(a) and FIG. 5(b), RT denotes a termination resistor, and the resistance value is, for example, 50Ω.

[0034] FIG. 5(b) is a schematic equivalent circuit diagram showing a directional coupler of the comparative example. The directional coupler 110 in FIG. 5(b) is equivalent to the directional coupler 10b shown in FIG. 3(b), and as shown in FIG. 4C, the degree of coupling between the first microstrip line 12 and the second microstrip line 14 is restricted by the distance between the first microstrip line 12 and the second microstrip line 14.

[0035] Although some embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope and spirit of the invention, and are included in the scope of the invention and its equivalents described in the claims. [Explanation of symbols]

[0036] Reference Signs List 10, 10a, 10b...directional coupler, 11...substrate, 11a...first surface, 11b...second surface, 12...first microstrip line, 14...second microstrip line, 16...ground plane, 18...capacitive coupling pattern

Claims

1. an insulating substrate having a first surface and a second surface opposite to the first surface; a first microstrip line provided on the first surface; a second microstrip line provided on the first surface and arranged parallel to the first microstrip line at a predetermined distance from the first microstrip line; a capacitive coupling pattern provided on the second surface and overlapping the first microstrip line and the second microstrip line at a position where the first microstrip line and the second microstrip line are arranged in parallel in a plan view; a ground plane provided on the second surface and spaced apart from the capacitive coupling pattern so as to surround the capacitive coupling pattern; A directional coupler comprising:

2. 2. The directional coupler according to claim 1, wherein a first length over which the first microstrip line and the second microstrip line are arranged in parallel is equal to 1 / 4 of a wavelength of a signal passing through the first microstrip line or the second microstrip line.

3. 3. The directional coupler according to claim 2, wherein the capacitive coupling pattern has a side of a second length parallel to the direction of the first length.

4. The directional coupler according to claim 3 , wherein the capacitive coupling pattern has a shape in a plan view that is a rectangle including a side of the second length.

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