DIRECTIONAL COUPLER

Abstract: There is disclosed a directional coupler (1) which is compact, thin and ready to manufacture. The directional coupler (1) has a high isolation characteristics. The directional coupler (1) comprises a first dielectric layer (3) having one surface formed with a first coupling line (2), a second dielectric layer (5) having one surface formed with a second coupling line (4), and an intermediate dielectric layer (6) disposed between the first and second dielectric layers. Outside the first dielectric layer, there is a third dielectric layer (14) having a grounding electrode (16) covering substantial portion of the surface thereof. Outside the second dielectric layer, there is a fourth dielectric layer (15) having a grounding electrode (17) covering substantial portion of the surface thereof. The dielectric layers are laminated together so that a dielectric layer is interposed between the grounding electrode and adjacent one of the coupling lines and the first and second coupling lines are aligned with each other in the direction of laminate. Each of the first and second coupling lines are of a spiral configuration including a first portion substantially parallel with an edge of the dielectric layer on which the line is formed, a second portion having one end connected with one end of the first portion and extending substantially perpendicularly to the first portion, a third portion having one end connected with the other end of the second portion and extending substantially perpendicularly to the second portion, a fourth portion having one end connected with the other end of the third portion and extending substantially perpendicularly to the third portion, and a fifth portion having one end connected with the other end of the fourth portion and located inside the first portion to extend substantially perpendicularly to the fourth portion.

Description: The present invention relates to a directional coupler for electromagnetically coupling a signal input primary line with an auxiliary line. More specifically, the present invention pertains to a directional coupler having conductors provided on a layer of a dielectric material to thereby provide paired lines to be coupled. German patent application DE 42 39 990 discloses a chip-shaped directional coupler with a laminate structure comprising two dielectric substrates each having a coupling line and two dielectric substrates with a grounding electrode, between which the dielectric substrates with the coupling lines are sandwiched. A plurality of electrodes is arranged at side edges of the laminate structure and provides electrical contact with corresponding end portions of the coupling lines or of the grounding electrodes. The coupling lines generally have a meander shape comprising curved and piecewise polygonal (linear) shapes or a U-shape. The grounding electrodes extend in a direction perpendicular to the laminate direction over the coupling lines. A protective substrate is provided at least on one side of the laminate structure. The United States patent 5,329,263 issued on July 12, 1994 to Kazuaki Minami discloses a directional coupler having a dielectric substrate provided on one side surface with a conductive grounding electrode which extends throughout the surface and on the other side surface with paired signal transmitting coupling lines of a conductive material. These lines are formed on the surface of the substrate by parallel extending portions, each of the parallel extending portions or the coupling lines having opposite ends provided with leads which extend perpendicular to the parallel extending portions. One of the coupling lines is connected through the lead at one end thereof with an input port and through the lead at the other end with an output port. The other coupling line is connected through the lead at one end with a second output port and through the lead at the other end with an isolation port. The coupling lines and the leads are connected together through a deposition of a conductive metal such as gold. In this type of coupler, the isolation port is connected normally to the ground. As a signal is applied to the input port of the one coupling line, a corresponding signal is produced at the output of the one coupling line. A signal is also produced through electromagnetic coupling between the paired coupling lines at the second output port of the other coupling line. When an input signal is applied to the output port of the one coupling line, an output is produced at the input port of the one coupling line, and at the same time an output is produced at the second output port of the other coupling line with a level which is different from the level when the input signal is applied to the input port. The difference in the signal level at the second output port of the other coupling line between the case when the input signal is applied to the input port of the one coupling line and the case when the input signal is applied to the output port is defined as the directionality or isolation of the coupler. It has been recognized that the coupler shows a large directionality in response to an input signal wherein the length of the parallelly extending coupling lines is equal to 1/4 of the wavelength. It is noted further that the coupling power of the coupler is dependent on the distance between the coupling lines whereby a tight coupling is produced with a small distance whereas a weak coupling is produced with a large distance. In the coupler of the type disclosed by the aforementioned U.S. patent, the coupling lines are formed on a surface of the dielectric substrate. It should however be noted that the coupling lines may be embedded in the body of a dielectric body. In that case, the effective line wavelength is decreased to λ/4 ε r , where ε r designates a specific dielectric constant and λ the wavelength of the input signal. Thus, the coupler size can be decreased by using a material of higher specific dielectric constant. It should therefore be understood that a dielectric material of an appropriate specific dielectric constant may be used for decreasing the size of a directional coupler. In the case where the dielectric body is of a laminated structure wherein a plurality of dielectric layers are laid one over the other, the coupling lines can be provided between adjacent dielectric layers. In this structure, the paired coupling lines may be arranged on the opposite sides of a dielectric layer. In a directional coupler having coupling lines embedded in a dielectric body as described, the dielectric layers are generally formed of a material of a high dielectric constant. However, using a dielectric material of high dielectric constant is likely to cause a decrease in the impedance of the signal line conductor, so that it is required to increase the distance between the signal line conductor and the ground electrode or to decrease the width of the signal line conductor. Dielectric layers are formed of sintered ceramics. It should therefore be noted that to increase the distance between the signal line conductors and the ground electrode will cause a corresponding increase in the thickness of the dielectric layer. Thus, an increased time will be required for a sintering process to remove binder and an increased processing time will therefore be required for the manufacture. Particularly, in a structure wherein paired signal lines are provided at the opposite sides of a dielectric layer, the thickness of the dielectric substrate is undesirably increased so that the structure is disadvantageous in making the device compact. It should further be noted that the structure having a decreased signal line conductor width involves another problem, namely that the transmission loss in the signal line conductor is increased. The present invention is therefore aimed to solve some of the aforementioned problems in conventional directional coupler and has a general objective to provide a directional coupler which is compact and thin in structure and easy to manufacture, in particular providing a directional coupler having the advantages of embedding the coupling lines in a dielectric body having a high dielectric constant like decrease of the effective line wavelength, while avoiding the related disadvantages like the increase of the distance between the signal line conductor and the grounding electrode related to compensating for the decrease in line impedance. In order to accomplish these objectives, a directional coupler comprises a first dielectric layer provided at least on one surface with a first coupling line, a second dielectric layer provided at least on one surface with a second coupling line, and a first outer dielectric layer and a second outer dielectric layer each having a grounding electrode extending to cover substantially throughout the surface thereof. The first and second dielectric layers are laid one over the other so that the first and second coupling lines are aligned with each other and are located by a predetermined distance in a direction of laminate with dielectric material interposed therebetween. The outer dielectric layers are laid over outer surfaces of the first and the second dielectric layers respectively, with dielectric material interposed between the coupling lines and the grounding electrodes. Each of the first and second coupling line are of a convoluted configuration comprising at least one turn. According to the invention, the directional coupler further comprises a first intermediate layer laid over the first dielectric layer so that the first coupling line is embedded between the first dielectric layer and the first intermediate layer, a second intermediate layer laid over the second dielectric layer so that the second coupling line is embedded between the second dielectric layer and the second intermediate layer. Another dielectric layer is disposed between the first dielectric layer and the second intermediate layer. Further according to the invention, the first dielectric layer, the first intermediate layer, the second dielectric layer and the second intermediate layer are formed of a material having a high specific dielectric constant; and the other dielectric layers are made of a material having a relatively low specific dielectric constant. This structure provides advantages in that the signal wavelength can be decreased due to the dielectric layers of a high specific dielectric constant at the opposite sides of each coupling line, and it is not necessary to increase the substrate thickness because the line impedance will not be substantially increased by forming the other dielectric layers from a material of relatively low specific dielectric constant. At least a third intermediate dielectric layer of a material having said relatively low specific dielectric constant may be laid over the first outer dielectric layer so that the grounding electrode is embedded between the third intermediate dielectric layer and the first outer dielectric layer. The directional coupler may further comprise at least a fourth intermediate dielectric layer of a material having said relatively low specific dielectric constant and laid over the second outer dielectric layer so that the grounding electrode is embedded between the fourth intermediate dielectric layer and the second outer dielectric layer. Each of the first and second coupling lines may be of a spiral configuration including a first portion which extends in parallel with one edge of the dielectric layer on which the coupling line is formed, a second portion having one end connected with one end of the first portion and extending substantially perpendicularly to the first portion, a third portion having one end connected with the other end of the second portion and extending substantially perpendicularly to the second portion, a fourth portion having one end connected with the other end of the third portion and extending substantially perpendicularly to the third portion, and a fifth portion having one end connected with the other end of the fourth portion and located inside the first portion to extend substantially perpendicularly to the fourth portion. Outside the grounding electrode, there is formed at least one dielectric layer to provide a protective layer. For the purpose, either one or both of the third and fourth dielectric layers may be disposed so that the grounding electrodes formed thereon are located inside the respective layers, or alternatively, a further dielectric layer may be laid over the third or fourth dielectric layer. In the structure of this aspect, each of the first and second coupling lines are connected at the other end of the first portion and the other end of the fifth portion with leads which are extending to an edge portion of the laminated structure to form external connecting ports. For the purpose, the other end of the first portion may be connected through a lead to a port on the edge portion of the laminated structure. The other end of the fifth portion may be connected through the dielectric layer adjacent to the coupling line with a lead formed on a surface of another dielectric layer which is in turn connected with the port on the edge portion of the laminated structure. In the directional coupler of the present invention, each of the first and second coupling lines may be formed in two or more dielectric layers. Each of the coupling lines preferably has an outermost edge which is located in a projection in the direction of laminate thickness inside by a predetermined distance from the edge of the grounding electrode. It is possible to accomplish an extremely excellent isolation characteristics by choosing the predetermined distance at least 0.3 mm, preferably 0.45 mm. Thus, a high isolation characteristics is achieved. The present invention is described with reference to embodiments shown in the enclosed figures, in which: Figure 1 is an exploded perspective view of a directional coupler of a laminated structure in accordance with the present invention; Figure 2 is a perspective view showing an external appearance of the directional coupler shown in Figure 1; Figure 3 is a sectional view taken along the line III-III in Figure 2; Figure 4 is a sectional view similar to Figure 3 but showing another embodiment of the present invention; Figure 5 is an exploded perspective view of a directional coupler similar to Figure 1 but showing a further embodiment of the present invention; and, Figure 6 is a diagram showing influences of the distance between edges of the coupling line and the grounding electrode on the isolation characteristics in the directional coupler in accordance with the present invention, wherein (a) is a sectional view of the coupler for showing the manner of measuring the distance, (b) a plan view showing projections in the direction of laminate thickness of the coupling line and the grounding electrode, (c) a diagram showing the isolation characteristics under the distance of 0.2 mm, and (d) a diagram showing the isolation characteristics under the distance of 0.45 mm. Referring to Figure 1, there is shown a directional coupler 1 which is formed by sintering a plurality of laminated green sheets of dielectric material. The coupler 1 includes a first dielectric layer 3 having a first coupling line 2 formed thereon, a second dielectric layer 5 having a second coupling line 4 formed thereon, and a second intermediate dielectric layer 6 disposed between the dielectric layers 3 and 5. The first coupling line 2 is formed on the top surface of the first dielectric layer 3. The coupling line 2 is of a spiral configuration including a first portion 2a extending substantially in parallel with an edge 3a of the first dielectric layer 3, a second portion 2b having one end connected with one end of the first portion 2a and extending substantially perpendicularly to the first portion 2a, a third portion 2c having one end connected with the other end of the second portion 2b and extending substantially perpendicularly to the second portion, a fourth portion 2d having one end connected with the other end of the third portion and extending substantially perpendicularly to the third portion 2c, and a fifth portion 2e having one end connected with the other end of the fourth portion 2d and located inside the first portion 1a to extend substantially perpendicularly to the fourth portion 2d. The second coupling line 4 is formed on the top surface of the second dielectric layer 5. The second coupling line 4 includes a first portion 4a, a second portion 4b, a third portion 4c, a fourth portion 4d and a fifth portion 4e which are aligned in the direction of laminate thickness to the first portion 2a, the second portion 2b, the third portion 2c, the fourth portion 2d and the fifth portion 2e, respectively. In accordance with the present invention, a satisfactory result can be obtained with the coupling lines 2 and 4 each having the first to third portions. In this instance, the coupling line comprised of the first to third portions constitute a part of a spiral configuration. The term "convoluted configuration" is herein used to include this configuration as well as a spiral configuration. A first intermediate dielectric layer 7 is laid over the first dielectric layer 3. The first portion 2a of the first coupling line 2 formed on the first dielectric layer 3 has an end connected with a lead 8 which is in turn connected with a first port 8a provided on an edge 3a of the first dielectric layer 3. The first intermediate dielectric layer 7 is provided on the top surface with a lead 9. The lead 9 has one end connected through the dielectric layer 7 with an end of the fifth portion 2e of the first coupling line 3. The lead 9 extends to an edge portion of the dielectric layer 7 to be connected with a second port 9a formed thereon. A fourth intermediate dielectric layer 10 is provided beneath the second dielectric layer 5. The first portion 4a of the second coupling line 4 formed on the second dielectric layer 5 has an end connected with a lead 11 which is in turn connected with a third port 12 formed on an edge 5a of the second dielectric layer 5, the edge 5a being at a side opposite to the side where the edge 3a is located on the first dielectric layer 3. The fourth intermediate dielectric layer 10 is formed on the top surface with a lead 13. The lead 13 has one end which is connected through the dielectric layer 5 with an end of the fifth portion 4e of the second coupling line 4. The other end of the lead 13 is connected with a fourth port 13a which is provided on an edge 10a of the dielectric layer 10, the edge 10a being vertically aligned with the edge 5a of the second dielectric layer 5. Above the first intermediate dielectric layer 7, there is laminated a third dielectric layer (or first outer dielectric layer) 14 for a grounding electrode 16. Similarly, a fourth dielectric layer (or second outer dielectric layer) 15 is laminated beneath the fourth intermediate dielectric layer 10 for another grounding electrode. A grounding electrode 16 is formed on the top surface of the third dielectric layer 14 to cover substantial part of the surface. Similarly, a grounding electrode 17 is formed on the top surface of the fourth dielectric layer 14. The grounding electrodes 16 and 17 are connected with grounding ports 18 and 19 provided at the opposite side edges of the dielectric layers. A dielectric layer 20 is laminated on the top surface of the third dielectric layer 14 to provide a protective layer. The directional coupler 1 of the aforementioned laminated structure is shown in Figure 2. The coupler 1 has port electrodes for providing ports 8a, 9a, 12, 13a, 18 and 19 at edge portions thereof. Figure 3 shows a section of the coupler 1. In this embodiment, the dielectric layers in the laminate are of the same specific dielectric constant. Figure 4 is a sectional view similar to Figure 3 but shows an embodiment according to the invention. Corresponding parts are designated by the same reference characters as in the directional coupler shown in Figures 1 to 3, and detailed description will be omitted. According to the invention, another dielectric layer 21 is disposed between the first dielectric layer 3 and the second intermediate dielectric layer 6. The first dielectric layer 3 and the first intermediate dielectric layer 7 which is located above the first dielectric layer 3 with the first coupling line 2 interposed therebetween, and the second dielectric layer 5 and the second intermediate dielectric layer 6 which is located above the second dielectric layer 5 with the second coupling line 4 interposed therebetween are formed of a material having a high specific dielectric constant. The other dielectric layers are made of a material having a low specific dielectric constant. According to the invention, it is possible to decrease the signal wavelength by providing the dielectric layers having a coupling line interposed therebetween with a high specific dielectric constant. Since the other dielectric layers are of a material having a low specific dielectric constant, the line impedance is not significantly decreased. Figure 5 shows another directional coupler in which the first and the second coupling lines 2 and 4 are of a two layer structure. the laminated structure is substantially the same as in the embodiment of Figure 1, however, the second intermediate dielectric layer 7 is formed with a spiral. pattern 7a which provides a portion of the first coupling line and the spiral pattern 7a has an outer end connected with the lead 9. The inner end of the spiral pattern 7a is connected through the dielectric layer 7 with an end of the fifth portion 2e of the coupling line 2 on the first dielectric layer 3. Similarly, the dielectric layer 10 is formed with a conductor providing a spiral pattern 10a having an outer end connected with the lead 13. The inner end of the spiral pattern 10a is connected through the dielectric layer 5 with an end of the fifth portion 4e of the coupling line 4 on the second dielectric layer 5. In other respects, the structures are the same as in the directional coupler of Figure 1. According to the invention, as shown in Figure 4, another dielectric layer like the further dielectric layer 21 is disposed between the first dielectric layer (3) and the second intermediate layer (6). The first dielectric layer (3), the first intermediate layer (7), the second dielectric layer (5) and the second intermediate layer (6) are formed of a material having a high specific dielectric constant. The other dielectric layers are made of a material having a relatively low specific dielectric constant. Referring now to Figure 6, there is shown in (a) and (b) the relationship between the coupling line E and the grounding electrode G in the form of projections in the direction of the laminate thickness. As shown therein, the coupling line E has an outer edge which is located inside the edge of the grounding electrode by a distance d. In Figure 6(c), there is shown an isolation characteristics obtained with the distance d of 0.2 mm. Figure 6(d) shows an isolation characteristics obtained with the distance of 0.45 mm. In these drawings, it will be understood that a better isolation characteristics can be obtained with a larger distance d. A significant isolation characteristics can be obtained with the distance d of 0.3 mm or larger.

Claims: A directional coupler (1) comprising a first dielectric layer (3) provided at least on one surface with a first coupling line (2), a second dielectric layer (5) provided at least on one surface with a second coupling line (4) and a first outer dielectric layer (14) and a second outer dielectric layer (15) each having a grounding electrode (16 and 17, respectively) extending to cover substantially throughout the surface thereof, the first and second dielectric layers (3, 5) being laid one over the other so that the first and second coupling lines (2, 4) are aligned with each other and are located by a predetermined distance in a direction of laminate with dielectric material interposed therebetween, the outer dielectric layers (14, 15) being laid over outer surfaces of the first and the second dielectric layers (3, 5), respectively, with dielectric material interposed between the coupling lines (2, 4) and the grounding electrodes (16,17), and each of the first and second coupling line (2, 4) being of a convoluted configuration comprising at least one turn; characterised in that the directional coupler further comprises a first intermediate layer (7) laid over the first dielectric layer (3) so that the first coupling line (2) is embedded between the first dielectric layer (3) and the first intermediate layer (7), a second intermediate layer (6) laid over the second dielectric layer (5) so that the second coupling line (4) is embedded between the second dielectric layer (5) and the second intermediate layer (6) and another dielectric layer (21) disposed between the first dielectric layer (3) and the second intermediate layer (6); in that the first dielectric layer (3), the first intermediate layer (7), the second dielectric layer (5) and the second intermediate layer (6) are formed of a material having a high specific dielectric constant; and in that the other dielectric layers are made of a material having a relatively low specific dielectric constant . The directional coupler in accordance with claim 1, further comprising at least a third intermediate dielectric layer (20) of a material having said relatively low specific dielectric constant laid over the first outer dielectric layer (14) so that the grounding electrode (16) is embedded between the third intermediate dielectric layer (20) and the first outer dielectric layer (14). The directional coupler in accordance with claims 1 or 2, further comprising at least a fourth intermediate dielectric layer (10) of a material having said relatively low specific dielectric constant laid over the second outer dielectric layer (15) so that the grounding electrode (17) is embedded between the fourth intermediate dielectric layer (10) and the second outer dielectric layer (15). The directional coupler in accordance with anyone of the claims 1 to 3, wherein at least one of said outer dielectric layer (14, 15) having the grounding electrode (16, 17) formed thereon is disposed so that the grounding electrode formed thereon is located inside the respective outer dielectric layer. The directional coupler in accordance with anyone of the claims 1 to 4, wherein at least one of said third or fourth intermediate dielectric layer (20, 10) is disposed outside the corresponding grounding electrode (16, 17) so as to be a protective layer. The directional coupler in accordance with anyone of the claims 1 to 5, wherein at least one of the first and second coupling line (2, 4) comprises a first portion (2a, 4a) extending in parallel with one edge of the dielectric layer on which the coupling line is formed, a second portion (2b, 4b) having one end connected with one end of the first portion and extending substantially perpendicular to the first portion, a third portion (2c, 4c) having one end connected with one end of the second portion and extending substantially perpendicular to the second portion, a fourth portion (2d, 4d) having one end connected with one end of the third portion and extending substantially perpendicular to the third portion, and a fifth portion (2e, 4e) having one end connected with one end of the fourth portion and located inside the first portion (2a, 4a) to extend substantially perpendicular to the fourth portion (2d, 4d). The directional coupler in accordance with anyone of the claims 1 to 6, wherein each of the coupling lines (2, 4, respectively) is connected at one end with leads (8, 11, respectively) to form a first external connecting port (8a, 12, respectively) and at another end with leads (9, 13, respectively) to form a second external connecting port (9a, 13a, respectively) on an edge portion of the laminated structure. The directional coupler in accordance with claim 6 or 7, wherein the other end of the fifth portion (2e) is connected through the dielectric layer (7) adjacent to the coupling line (2) with a lead (9) formed on a surface of another dielectric layer (7) which lead (9) is in turn connected with the port (9a) on the edge of the laminated structure. The directional coupler in accordance with anyone of the preceding claims, wherein each of the first and second coupling line (2, 4) is formed on two or more dielectric layers formed of a material having said high specific dielectric constant. The directional coupler in accordance with anyone of the preceding claims, wherein each of the first and second coupling line (2, 4) has an edge which is located in a projection in the direction of the laminate inside by a predetermined distance d from an edge of the grounding electrode, the distance d being defined so that an excellent isolation characteristics can be obtained. The directional coupler in accordance with claim 10, wherein the distance d is at least 0.3 mm, preferably 0.45 mm.

Inventors: HAYASHI KATUHIKO, HAYASHI, KATUHIKO, HAYASHI, Katuhiko, TDK Corporation
Applicants: TDK CORP, TDK CORPORATION
Application year: 1995
Main classification: H01P5
IPC codes: H01P5