Nonreciprocal circuit device

Abstract: A nonreciprocal circuit device is provided which is capable of preventing a problem with electrode peeling in a case in which a single-board-type capacitor (C1, C2, C3) is employed. A single-board-type capacitor (C1, C2, C3) (nonreciprocal circuit device) having characteristics such that attenuation is small in the direction of signal transmission and attenuation is large in the reverse direction and having matching capacitors disposed in signal input/output ports (P1, P2, P3) is constructed in such a way that the matching capacitors are formed of single-board-type capacitors (C1, C2, C3) including capacitor electrodes (18) formed so as to be opposed each other on the entire surface of both main surfaces of a dielectric substrate (17) with the substrate in between, and an outer peripheral edge (8a) of a grounding electrode (8) (connected electrode), to which a capacitor electrode (18) of the single-board-type capacitor (C1, C2, C3) is connected, is positioned inwardly from the outer peripheral edge (18a) of the capacitor electrode (18).

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nonreciprocal circuit device, such as an isolator, a circulator, etc., used in a microwave band. 2. Description of the Related Art In general, concentrated-constant-type isolators for use in mobile communication apparatuses, such as portable telephones, have functions of allowing a transmission signal to pass only in the transmission direction and preventing transmission thereof in the reverse direction. Also, in recent mobile communication apparatuses, there has been a strong demand for a lower cost as well as a smaller size and a lighter weight from the viewpoint of its use, and in response to this, similarly a smaller size, a lighter weight, and a lower cost are in demand also in the isolator. As such concentrated-constant-type isolators, conventionally, there is a concentrated-constant-type isolator of a construction in which, as shown in Fig. 20, a permanent magnet 52, a center electrode body 53, a matching circuit board 54, and a grounding plate 55 are disposed in sequence from the top between upper and lower yokes 50 and 51. This center electrode body 53 is constructed in such a way that three center electrodes 57 are placed so as to intersect each other in a circular-plate ferrite 56 in an electrically insulated state. The matching circuit board 54 has a circular hole 54b through which the center electrode body 53 is inserted and placed is formed in the central portion of a dielectric substrate 54a in the form of a rectangular thin plate. Around the edge of the circular hole 54b of the dielectric substrate 54a capacitor electrodes 58 are formed to be connected to input/output ports P1 to P3 of each of the center electrodes 57. A termination resistance film 59 is connected to the port P3. However, in the conventional matching circuit board 54, the circular hole 54b must be formed and each capacitor electrode 58 must be pattern-formed in the dielectric substrate 54a of a thin plate. Therefore, processing during manufacture and handling during assembly take time and effort, presenting the problem that the costs are increased. Also, in the conventional matching circuit board 54, portions other than the capacitor electrode 58 cause an increase in area and an increase in weight, presenting the problem that the above-described demand for a smaller size and a lighter weight cannot be met. In this regard, in recent isolators, there has been a demand for reduction in weight in units of milligrams. As a matching capacitor in place of such a matching circuit board, there is a case in which a single-board-type capacitor is employed such that capacitor electrodes are formed on the entire surface of both sides of a dielectric substrate with the board in between. This single-board-type capacitor can be manufactured merely by forming electrodes on both main surfaces of a motherboard made of a large flat plate and by cutting the motherboard to predetermined dimensions, and mass production thereof is possible. For this reason, compared to a conventional case in which circular holes and a plurality of capacitor electrodes are formed on a dielectric substrate, processing and handling are easy, and costs can be reduced. Also, since electrodes are formed on the entire surface of the board, a wasteful increase in area and in weight can be eliminated, and a smaller size and a lighter weight can be achieved by an amount corresponding to the elimination. Figs. 16 to 18 show an example of an isolator employing the single-board-type capacitor. In the figures, the reference numerals which are the same as those of Fig. 20 indicate the same or corresponding components. This isolator is constructed such that a circular hole 61 through which a center electrode body 53 is inserted and placed is formed on a bottom wall 60a of a grounding member 60 made of a resin, each of single-board-type capacitors C1 to C3 is disposed in such a manner as to surround the center electrode body 53 around the edge of the circular hole 61, and a single-board-type resistor R is disposed. A grounding electrode 63 formed in the grounding member 60 is connected to a capacitor electrode 62 on the cold end side (bottom surface) of each of the single-board-type capacitors C1 to C3, and the input/output ports P1 to P3 of each center electrode 57 are connected to the capacitor electrode 62 on the hot end side (top surface.) Here the cold end side means one side of a capacitor electrode to be connected to a grounding electrode and hot end side means another side of the capacitor electrode to be connected to a port electrode (i.e. signal line.) In the single-board-type capacitors C1 to C3, as shown in Figs. 19A and 19B, the capacitor electrode 62 is positioned up to an edge 64a of a dielectric substrate 64, stress is likely to concentrate in the capacitor electrode 62 at this edge 64a portion, very small cracks are prone to be generated when the motherboard is cut, and the capacitor electrode 62 may be peeled from the dielectric substrate 64. Also, as shown in Fig. 19C, when the entire surface of the capacitor electrode 62 is soldered and connected to the grounding electrode 63, thermal stress due to a difference in the thermal expansion coefficients between the dielectric substrate 64 and the grounding electrode 63 causes the capacitor electrode 62 to be easily peeled. When, in particular, the capacitor is employed in an isolator, during transmission, heat is generated as a result of insertion loss and consumption of reflection power at the termination resistor. During reception, on the other hand, since the capacitor is subjected to a thermal cycle, such as being cooled again, the problem with electrode peeling is likely to occur. JP 07263917 A relates to a irreversible circuit element having three input/output ports and three single plate capacitors connected between the input/output ports and ground. EP-A-0 779 673 relates to a non-reciprocal circuit element comprising a first central electrode and a second central electrode, which are disposed on a main surface of a ferret member, so that they intersect with each other in an electrically-insulating state. A first input/output port and a second input/output port, which are connected to the ends on one side of both central electrodes and a third input/output port, which is connected to the ends on the other side of the central electrodes are provided and two matching capacitors are connected between the first and second input/output ports and the third input/output port. The central conductors are connected to an upper electrode of the matching capacitors. EP 0 618 636 A2 relates to a multi-layer circulator including a circulator element and a plurality of terminal electrodes formed on side surfaces of the circulator element. Resonating capacitors are connected to the terminal electrodes formed on the side surfaces of the circulator. It is the object of the present invention to provide a non-reciprocal circuit device having a connection structure of a single-board-type capacitor, which is capable of avoiding the problem of electrode peeling. This object is achieved by a non-reciprocal circuit device according to claim 1. Particular embodiments of the invention are set out in the dependent claims. The above and further objects, aspects and novel features of the invention will become more apparent from the following detailed description when read in connection with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is an exploded, perspective view illustrating a concentrated constant-type isolator according to preferred embodiments of the present invention. Figs. 2A, 2B, and 2C are views showing a grounding member of the isolator. Fig. 3 is a view showing a connected state of the grounding member on the cold end side of a single-board-type capacitor. Fig. 4 is a plan view showing a connected state on the hot end side of the single-board-type capacitor. Fig. 5 is a view showing a method of manufacturing the single-board-type capacitor. Fig. 6 is an exploded, plan view showing an isolator according to an exemplary embodiment of the present invention. Fig. 7 is an exploded, plan view showing an isolator according to an exemplary embodiment of the present invention. Fig. 8 is an exploded, plan view showing an isolator according to preferred embodiments of the present invention. Fig. 9 is a view showing a connected state of a single-board-type capacitor of the isolator. Fig. 10 is a view showing an isolator according to an exemplary embodiment of the present invention. Fig. 11 is a perspective view showing an isolator according to an exemplary embodiment of the present invention. Fig. 12 is an exploded, plan view of the isolator. Fig. 13 is a view showing a connected state of the isolator. Fig. 14 is an exploded, plan view of the isolator according to preferred embodiments of the present invention. Fig. 15 is a view showing a connection state of the isolator. Fig. 16 is an exploded, perspective view illustrating a forming process of the present invention. Fig. 17 is a plan view showing an exploded construction of a single-board-type capacitor in the forming process. Fig. 18 is a view showing the connection state. Figs. 19A, 19B, and 19C are views showing electrode peeling of the single-board-type capacitor. Fig. 20 is an exploded, perspective view showing a conventional isolator. Fig. 21 is a view illustrating test 1 carried out to confirm the advantages of a single-board-type capacitor of an embodiment of the present invention. Figs. 22A and 22B are views illustrating test 2 carried out to confirm the advantages of the embodiment. Fig. 23 is a characteristic view showing the relationship between the number of heat cycles of test 1 and the electrostatic capacity change rate. Fig. 24 is a characteristic view showing the relationship between the electrostatic capacity change rate of test 1 and the thickness of the dielectric board. Fig. 25 is a characteristic view showing the relationship between the number of heat cycles of test 2 and the electrostatic capacity change rate. Fig. 26 is a characteristic view showing the relationship between the electrostatic capacity change rate of test 2 and the thickness of the dielectric board. DESCRIPTION OF THE PREFERRED EMBODIMENTS The embodiments of the present invention will be described below with reference to the accompanying drawings. Figs. 1 to 5 are views illustrating a concentrated-constant-type isolator according to embodiments of the present invention. Fig. 1 is an exploded, perspective view showing a single-board-type capacitor. Figs. 2A to 2C are respectively a top plan view and a bottom plan view of a grounding member, and a see-through view of an electrode pattern. Figs. 3 and 4 are respectively a sectional view and a plan view showing a state in which a single-board-type capacitor is connected. Fig. 5 is a view showing a method of manufacturing a single-board-type capacitor. A concentrated-constant-type isolator 1 of this embodiment is constructed in such a way that a resin grounding member 3 is disposed in a magnetic metal lower yoke 2 having right and left side walls 2a and 2a, and a bottom wall 2b; a center electrode assembly 4 is placed in the grounding member 3; and a box-shaped upper yoke 5 similarly made of a magnetic metal is mounted in the lower yoke 2, forming a magnetic closed circuit. Also, a circular-shaped permanent magnet 6 is attached onto the inner surface of the upper yoke 5, so that a DC magnetic field is applied to the center electrode assembly 4 by the permanent magnet 6. The isolator 1 is a rectangular-parallelepiped, the outer shape of which has the plane dimensions 7.5 x 7.5 mm or less and a height of 2.5 mm or less, and is surface-mounted onto a line of a circuit board (not shown). The center electrode assembly 4 is of a construction in which three center electrodes 13 to 15 are placed on the top surface of a circular-plate-shaped ferrite 12 in such a manner as to intersect each other with an angle of 120 degrees in an electrically insulated state, the input/output ports P1 to P3 on one end side of each of the center electrodes 13 to 15 are made to project outwards, and a shield section 16 common to each of the center electrodes 13 to 15 on the other end side is brought into abutment with the bottom surface of the ferrite 12, this shield section 16 being connected to the bottom wall 2b of the lower yoke 2. The grounding member 3 has a construction in which a bottom wall 3b is integrally formed with side walls 3a in the shape of a rectangular frame, with a circular hole 7 through which the center electrode assembly 4 is inserted and placed being formed in the central portion of the bottom wall 3b. Capacitor positioning recesses 3c are each provided around the edge of the circular hole 7 of this bottom wall 3b, and a grounding electrode 8 is formed in the bottom surface of each recess 3c. Each of these grounding electrodes 8 is connected to grounding terminals 9 and 9 formed on the outer surfaces of the right and left side walls 3a. Input/output port electrodes 10 and 10 are respectively formed on the right and left upper end portions of the bottom wall 3b, and each of the port electrodes 10 is connected to input/output terminals 11 and 11 formed on the outer surfaces of the right and left side walls 3a. Each of the grounding terminals 9 and the input/output terminals 11 is surface-mounted onto a line of a circuit board (not shown). The single-board-type matching capacitors C1 to C3 are housed and disposed inside each of the positioning recesses 3c. Also, a termination resistor R is placed in parallel with the single-board-type matching capacitor C3 inside the lower-edge positioning recess 3c, and the termination resistor R is connected to the grounding terminal 9. As shown in Fig. 3, each of the single-board-type matching capacitors C1 to C3 is of a construction in which capacitor electrodes 18 and 18 are formed on the entire surface of both main surfaces of a rectangular thin-plate-shaped dielectric substrate 17 in such a manner as to be opposed each other with the substrate 17 in between. Also, as shown in Fig. 5, each of the single-board-type matching capacitors C1 to C3 is manufactured by pattern-forming a silver thick-film electrode 20 on both surfaces of a motherboard 19 made of a large flat plate by a method, such as printing, plating, contact bonding, or vapor deposition, and by cutting the motherboard 19 into predetermined dimensions. Each of the grounding electrodes 8 is formed smaller than the capacitor electrode 18 in such a manner as to be positioned inwardly from an outer peripheral edge 18a of the capacitor electrode 18 around the entire outer peripheral edge 8a of the grounding electrode 8. Thus the outer peripheral section of the grounding electrode 8 forms a non-connected section 21 to which the capacitor electrode 18 is not connected. The capacitor electrode 18 on the cold end side of each of the single-board-type matching capacitors C1 to C3 is soldered and connected to each of the grounding electrodes 8. Each of the input/output ports P1 to P3 of each of the center electrodes 13 to 15 is formed so as to be positioned inwardly from an outer peripheral edge 18a of the capacitor electrode 18 of the single-board-type matching capacitors C1 to C3. Each of the input/output ports P1 to P3 is soldered and connected to the capacitor electrode 18 on the hot end side. Fig. 4 shows an exemplary magnified diagram that input/output port P3 is connected to capacitor electrode 18 on hot end side of capacitor C3 and capacitor electrode 18 of capacitor C3 on cold end side is connected to grounding electrode 8. The tip portions of the two ports P1 and P2 of the input/output ports P1 to P3 are connected to the input/output port electrodes 10, and the tip portion of the remaining port P3 is connected to the termination resistor R. Next, the operational effect of this embodiment will be described. According to the concentrated-constant-type isolator 1 of this embodiment, since the outer peripheral edge 8a of the grounding electrode 8 to which the capacitor electrode 18 of each of the single-board-type matching capacitors C1 to C3 is connected, and the input/output ports P1 to P3 are formed small so as to be positioned inwardly from the outer peripheral edge 18a of the capacitor electrode 18, electrode peeling in the edge portion of the capacitor electrode 18, in which cracks are likely to occur during stress concentration and manufacture, can be prevented, and reliability with respect to quality can be improved. Since the edge portion of the capacitor electrode 18 is not connected even if thermal stress due to the difference in the thermal expansion coefficients among the dielectric substrate 17 of each of the single-board-type matching capacitors C1 to C3, the grounding electrode 8, and the center electrodes 13 to 15 is generated, electrode peeling does not occur. As a result, even if repeated thermal cycling occurs during transmission and reception of the isolator 1, the problem with electrode peeling can be solved, and also from this point, reliability with respect to quality can be improved. In this embodiment, since the single-board-type matching capacitors C1 to C3 are employed, as described above, manufacturing becomes easy and mass production is possible, making it possible to reduce the costs of parts. Also, compared to a conventional case in which circular holes and capacitor electrodes are formed, processing and handling are easy, and a wasteful increase in area and in weight can be eliminated, contributing to a smaller size and a lighter weight. Figs. 6 to 15 are views illustrating a concentrated-constant-type isolator according to each embodiment of the present invention. In the figures, the reference numerals which are the same as those of Figs. 2 to 4 indicate the same or corresponding components. Fig. 6 shows an embodiment of the present invention. This embodiment is constructed such that only both long-side edges 8b of the grounding electrode 8 which are formed rectangular are formed in such a manner as to be positioned inwardly from both long-side edges of the capacitor electrode 18. In th..s embodiment, since the long-side edges 8b of the grounding electrode 8 are positioned inwardly from the capacitor electrode 18, electrode peeling in the transverse direction in which electrode peeling is likely to occur can be prevented, and an electrode area in the longitudinal direction can be increased. Also, since the long side of the grounding electrode 3 can be lengthened, it is possible to deal with a single-board-type capacitor of a different length. Fig. 7 shows an embodiment of the present invention. This embodiment is constructed such that both long-side edges 8b of a capacitcr electrode 8 are positioned inwardly from both long-side edges of a grounding electrode 18, and a central portion 8c along the longitudinal direction of the long-side edge 8b is extended and formed up to the edge of the capacitor electrode 18. Also in this embodiment, while preventing electrode peeling in the transverse direction in which electrode peeling is likely to occur, the electrode area can be increased. Figs. 8 and 9 show an embodiment of the present invention. This embodiment is constructed such that an insulating film 25 is coated and formed on a non-connected section 21 of each grounding electrode 8 by printing an insulating resin, and an outer peripheral edge 18a of a capacitor electrode 18 of each of the single-board-type matching capacitors C1 to C3 is brought into contact with this insulating film 25. In this embodiment, since the insulating film 25 formed by a resin is coated onto the non-connected section 21, insulation of the outer peripheral edge 18a of the capacitor electrode 18 can be reliably ensured, making it possible to further prevent electrode peeling. This makes it possible to decrease grounding impedance of the isolator 1, to reduce unwanted radiation by an amount corresponding to the decrease in insertion loss, to improve harmonic wave elimination capability, leading to higher performance when the isolator is employed in a communication apparatus, and a stable operation can be obtained. The insulating film 25 is not limited to a resin, and other insulating materials can be coated. Fig. 10 shows a concentrated-constant-type isolator according to an embodiment of the present invention. This isolator is constructed such that an insulating film 26 is coated and formed on the entire bottom surface of the housing recess 3c, and a grounding electrode 8 is formed over the insulating film 26. Stainless steel is employed for this insulating film 26, and gold plating is employed for the grounding electrode 8. In this embodiment, since the grounding electrode 8 is formed over the insulating film 26 coated as a base, portions other than the grounding electrode 8 become the insulating film 26. Therefore, the formation of the insulating film 26 is easy in a case in which the shape or the like of the grounding electrode 8 becomes complex, and, similarly to that described above, electrode peeling can be reliably prevented, unwanted radiation can be reduced, and harmonic wave elimination performance can be improved. Figs. 11 to 13 show a concentrated-constant-type isolator according to an embodiment of the present invention. This isolator is constructed such that a step-down section 3d is formed in a portion corresponding to the non-connected section 21 of the recess 3c of the grounding member 3 in such a manner as to be away from an outer peripheral edge 18a of a capacitor electrode 18. In this embodiment, since the step-down section 3d is formed in a portion corresponding to the non-connected section 21, the outer peripheral edge 18a of the capacitor electrode 18 does not come into contact, making it possible to prevent electrode peeling in a case in which the grounding electrode 8 is formed on the entire surface inside the recess 3c. Figs. 14 and 15 show a concentrated-constant-type isolator according to an embodiment of the present invention. This isolator is constructed such that a non-connected section 30 defines a portion of the dielectric substrate 17 is exposed and a capacitor electrode is not formed thereon, the non-connected section 30 is formed around the outer peripheral edge of the dielectric substrate 17 of each of the single-board-type matching capacitors C1 to C3, and as a result, the outer peripheral edge 18b of the capacitor electrode 18 is positioned inwardly from the outer peripheral edge 8c of the grounding electrode 8. The formation of this non-connected section 30 can be realized by forming the capacitor electrode 18 in a portion excluding the non-connected section 30 of the dielectric substrate 17 by printing, or by removing the outer peripheral edge of the electrode formed on the entire surface of the dielectric substrate 17 by etching. In this embodiment, since the non-connected section 30 is formed around the outer peripheral edge of the dielectric substrate 17 of each of the single-board-type matching capacitors C1 to C3, and since no electrodes are disposed in the edge portion of the dielectric substrate 17 where cracks are likely to occur during stress concentration and manufacture, it is possible to prevent electrode peeling in the edge portion and to improve reliability with respect to quality. Next, a description will be given of an isolator according to an embodiment of the present invention. A feature of the isolator of this embodiment is that the thickness of a dielectric substrate 17 of each of the above-described single-board-type capacitors C1, C2, and C3 is 0.5 mm or less, and that the film thickness of a capacitor electrode 18 is 0.05 mm or less (see Figs. 3, 9, 10, 13, and 15). Since the thickness of the dielectric substrate 17 of the single-board-type capacitors C1, C2, and C3 is 0.5 mm or less, it is possible to form the single-board-type capacitors C1, C2, and C3 into a smaller size and a thinner plate without causing electrode peeling, thereby contributing to an even smaller size of the isolator. In this regard, in a conventional case in which the entire surface of the electrode is soldered, in order to obtain a required capacitance value while preventing electrode peeling, the thickness of the dielectric substrate must be, for example, 1 mm or more, presenting the problem that the capacitor becomes larger. Furthermore, as a result of the film thickness of the capacitor electrode 18 of each of the single-board-type capacitors C1, C2, and C3 being set to 0.05 mm or less, the problem with electrode peeling when the thickness of the dielectric substrate 17 is 0.5 mm or less can be prevented more reliably. The heat cycle tests carried out to confirm the advantages of the above-described embodiments will be described below with reference to Figs. 21 to 26. Test 1 In this test 1, as shown in Fig. 21, a single-board-type capacitor was used, in which the thickness td of the dielectric substrate D was varied, the entire surface of a capacitor electrode E on one side of each single-board-type capacitor was soldered and connected to a Cu board 70 as a connected electrode, and a heat cycle test was carried out in this state. Then, the change rate of the electrostatic capacity value between the capacitor electrode E on the non-soldered side and the Cu board 70 was checked (see the → marks in Fig. 21). The thicknesses td of the respective dielectric substrate D were 0.1, 0.2, 0.5, and 1.0 mm. For the capacitor electrode E, an Ag thick film electrode was used, and the film thickness of the electrode E was 0.02 mm. The solder thickness ta for connecting was 0.01 to 0.02 mm, and the thickness of the Cu board 70 was 0.2 mm. Test 2 In this test 2, as shown in Figs. 22A and 22B, a single-board-type capacitor as a product of the present invention was used, in which the film thickness te of the capacitor electrode E was varied, Cu boards 71 and 71 were soldered and connected to both sides of the capacitor electrode E of each single-board-type capacitor in such a manner as to be positioned inwardly from the outer peripheral edge of the capacitor electrode E, and a heat cycle test was carried out in this state, so that the change rate of the electrostatic capacity value was checked in the same way as in test 1 described above. Single-board-type capacitors each having a size of length 3 mm x width 1 mm were used (see the plan view of Fig. 22B). The film thicknesses te of the respective capacitor electrodes E were 0.005, 0.01, 0.02, 0.05, and 0.1 mm. The thickness td of the dielectric board D was 0.2 mm. The solder thickness ta for connecting, and the thickness tb of the Cu board 71 were of the same thickness as that of test 1 described above. Figs. 23 and 24, and Figs. 25 and 26 are characteristic views showing the test results of tests 1 and 2, respectively. In the figures, the O mark indicates the maximum or minimum value, and the • mark indicates the average value thereof. Figs. 24 and 26 are characteristic views in which the change rate of the electrostatic capacity value in 2,000 cycles of tests 1 and 2 is summarized, respectively. As shown in Figs. 23 and 24, the results of test 1 reveal that, when the substrate thickness td is 0.1 or 0.2 mm, the electrostatic capacity change rate is as large as -1.4% and -1.2% (see the • marks in the figure) in terms of average value, and also indicate the occurrence of electrode peeling. Also, when the substrate thickness td is 0.5 or 1.0 mm, the change rate during 2,000 heat cycles is as low as -0.3% and -0.05% in terms of average value, and the larger the substrate thickness td becomes, the more unlikely it is for electrode peeling to occur. However, the capacitor becomes larger by an amount corresponding to an increase in the thickness td of the dielectric substrate D, thus making it impossible to achieve a smaller size of the isolator. In comparison, in the results of test 2, as is clear from Figs. 25 and 26, in spite of the fact that the thickness td of the dielectric substrate D was as small as 0.2 mm, there is hardly a change in the electrostatic capacity in the range in which the film thickness te of the capacitor electrode E is 0.005 to 0.05 mm, and electrode peeling has not occurred. As a result, by soldering and connecting the connected electrode (here e.g. Cu board) on the inside of the outer peripheral edge of the capacitor electrode of the single-board-type capacitor, the dielectric substrate can be formed much thinner than in the conventional case. Meanwhile, when the film thickness te of the capacitor electrode E is 0.1 mm, the electrostatic capacity during 2,000 heat cycles changes greatly to -1.0% (see the • marks in the figure). This becomes nearly the same as that in which the entire surface of the capacitor electrode is soldered to a thick Cu board, and this is considered to cause electrode peeling to easily occur because of the thermal stress resulting from the difference in the thermal expansion coefficients. However, the setting of the film thickness te of the capacitor electrode E at 0.1 mm is difficult in practice in consideration of cost and manufacturing time and labor, because this results in a thickness that is half the thickness td of the dielectric substrate D. In the manner described above, the results of tests 1 and 2 show that as a result of the thickness td of the dielectric substrate D of the single-board-type capacitor being set to 0.5 mm or less and the film thickness te of the capacitor electrode E being set to 0.05 mm or less, the capacitor can be formed into a smaller size and a thinner plate without causing a problem with electrode peeling, contributing to an even smaller size of the isolator. Specifically, it is preferable that the thickness td of the dielectric substrate D be in a range of 0.1 to 0.5 mm and the film thickness te of the capacitor electrode E be in a range of 0.005 to 0.05 mm. Although in the above-described embodiments a description is given by using a concentrated-constant-type isolator as an example, it is a matter of course that the present invention can be applied to a nonreciprocal circuit device, such as a circulator. According to the nonreciprocal circuit device of the present invention, since at least a part of the outer peripheral edge of a connected electrode, to which the cold end side of the capacitor electrode of the single-board-type capacitor is connected, is positioned inwardly from the outer peripheral edge of the capacitor electrode, there is the advantages that electrode peeling in the edge portion of a capacitor electrode, in which cracks are likely to occur during stress concentration and manufacture, can be prevented, and reliability with respect to quality can be improved. Furthermore, since the edge portion of a capacitor electrode is not connected even if thermal stress due to a difference in the thermal expansion coefficients occurs, there is the advantage that, also from this point, electrode peeling can be prevented. In the present invention, since a part of the outer peripheral edge of a connected electrode to be connected to hot end side of the capacitor electrode is positioned inwardly from the outer peripheral edge of the capacitor electrode, there is the advantage that electrode peeling can be prevented in the same way as that described above. In the present invention, since the outer peripheral edge of the connected electrode is positioned inwardly from the outer peripheral edge of the capacitor electrode around the entire periphery of the connected electrode, there is the advantage that electrode peeling can be reliably prevented. In the present invention, since the capacitor electrode and the connected electrode are formed rectangular, and the long-side edge of the connected electrode is positioned inwardly from the long-side edge of the capacitor electrode, there is the advantage that electrode peeling in the transverse direction in which electrode peeling is likely to occur can be prevented, and an electrode area in the longitudinal direction can be increased. Also, there is the advantage that it is possible to deal with a capacitor of a different length. In the present invention, since a part of the long-side edge of the connected electrode is extended and formed up to the long-side edge of the capacitor electrode, there is the advantage that the electrode area along the transverse direction can be increased while preventing electrode peeling similarly to that described above. In the present invention, since an insulating film formed from an insulating material is coated onto the non-connected section on the outside of the connected electrode, there is the advantage that electrode peeling can be prevented more reliably. In the present invention, since the insulating film is formed by printing a resin, there is the advantage that the insulating film can easily be formed with high accuracy. In the present invention, since a connected electrode is formed over an insulating film coated as a base, portions other than the connected electrode become an insulating film. Therefore, there is the advantage that the formation of the insulating film is easy in a case in which a grounding electrode having a complex shape is formed. In the present invention, since a non-connected section on the outside of a connected electrode is step-down-formed so as to be away from the outer peripheral edge of the capacitor electrode, the outer peripheral edge of the capacitor electrode can be placed in a non-contact state, yielding the advantage that electrode peeling can be prevented more reliably. In the present invention, since at least a part of the outer peripheral edge of the capacitor electrode is positioned inwardly from the outer peripheral edge of the dielectric substrate, an electrode in the edge portion of the dielectric substrate, in which cracks are likely to occur during stress concentration and manufacture, can be eliminated, yielding the advantage that electrode peeling can be prevented. In the present invention, since the capacitor electrode is formed by printing, there is the advantage that a non-connected section around the edge of the dielectric substrate can be easily formed. In the present invention, since the outer peripheral edge of the capacitor electrode is removed by etching, there is the advantage that a non-connected section can be easily formed. In the present invention, since a single-board-type capacitor is manufactured in such a way that electrodes are pattern-formed on both main surfaces of a dielectric motherboard in such a manner as to be opposed each other with the motherboard in between and the motherboard is cut to predetermined dimensions, manufacturing becomes easy and mass production is possible, yielding the advantage that the costs of parts can be reduced, and a wasteful increase in area and in weight can be eliminated, contributing to a smaller size and a lighter weight. In the present invention, since a single-board-type capacitor and a grounding member with the connected electrode formed thereon, are assembled integrally, there is the advantage that electrode peeling can be prevented to improve reliability with respect to quality, and unwanted radiation can be reduced, and harmonic wave elimination performance can be improved. In the present invention, since the thickness of the dielectric substrate of the single-board-type capacitor is 0.5 mm or less, the entire capacitor can be formed smaller and thinner without causing a problem with electrode peeling, thereby contributing to an even smaller size of the isolator. In the present invention, since the film thickness of the capacitor electrode of the single-board-type capacitor is 0.05 mm, there is the advantage that the problem with electrode peeling when the thickness of the dielectric substrate is 0.5 mm or less can be prevented more reliably.

Claims: A nonreciprocal circuit device having characteristics such that attenuation is small in the direction of signal transmission and attenuation is large in the reverse direction and having matching capacitors disposed in signal input/output ports (P1, P2, P3), wherein said matching capacitors are formed of single-board-type capacitors (C1, C2, C3) including capacitor electrodes (18) formed so as to be opposed each other on the entire surface of both main surfaces of a dielectric substrate (17) with the substrate in between, characterized in that at least a part of the outer peripheral edge (8a; 8b; 8b, 8c) of a grounding electrode (8) of the nonreciprocal circuit device, to which the ground side electrode of the capacitor electrodes (18) of the single-board-type capacitor (C1, C2, C3) is connected, is positioned inwardly from the outer peripheral edge (18a) of said capacitor electrode (18). A nonreciprocal circuit device according to ctaim 1, wherein at least a part of the outer peripheral edge of a port electrode (P1,P2,P3) of the nonreciprocal circuit device, to which the port line side electrode of the capacitor electrodes (18) of the single-board-type capacitor (C1, C2, C3) is connected, is positioned inwardly from the outer peripheral edge (18a) of said capacitor electrode (18). A nonreciprocal circuit device according to one of claims 1 and 2, wherein the outer peripheral edge (8a) of said grounding electrode (8) is positioned inwardly from the outer peripheral edge (18a) of the ground side capacitor electrode (18) around the entire periphery of said grounding electrode (8). A nonreciprocal circuit device according to one of ciaims 1 and 2, wherein said capacitor electrode (18) and said grounding electrode (8) are formed rectangular, and the long-side edge (8b) of the grounding electrode (8) is positioned inwardly from the long-side edge of the capacitor electrode (18). A nonreciprocal circuit device according to ctaim 4, wherein a part (8c) of the long-side edge (8b) of said grounding electrode (8) is extended and formed up to the long-side edge of the capacitor electrode (18). A nonreciprocal circuit device according to one of claims 1 and 2, wherein a non-connected section (21) on the outside of said grounding electrode (8) is covered with an insulating film (25) made from an insulating material. A nonreciprocal circuit device according to claim 6, wherein said insulating film (25) made from a resin is covered. A nonreciprocal circuit device according to claim 7, wherein said insulating film (25) is formed by printing a resin. A nonreciprocal circuit device according to claim 6, wherein said grounding electrode (8) is formed over an insulating film (26) coated as a base. A nonreciprocal circuit device according to one of claims 1 and 2, wherein a non-connected section (21) on the outside of said grounding electrode (8) is step-down-formed in such a manner as to be away from the outer peripheral edge (18a) of the ground side capacitor electrode (18). A nonreciprocal circuit device according to one of claims 1 to 10, wherein a single-board-type capacitor (C1, C2, C3) is manufactured in such a way that electrodes are pattem-formed on both main surfaces of a dielectric motherboard in such a manner as to be opposed each other with the motherboard in between and the motherboard is cut to predetermined dimensions. A nonreciprocal circuit device according to one of claims 1 to 10, whereina single-board-type capacitor (C1, C2, C3) and a grounding member with said grounding electrode (8) formed thereon are assembled integrally in a state in which they are connected with each other. A nonreciprocal circuit device according to one of claims 1 to 12, wherein the thickness of the dielectric substrate (17) of said single-board-type capacitor (C1, C2, C3) is 0.5 mm or less. A nonreciprocal circuit device according to one of claims 1 to 13, wherein the film thickness of the capacitor electrode (18) of said single-board-type capacitor (C1, C2, C3) is 0.05 mm or less.

Inventors: KAWANAMI TAKASHI, MAKINO TOSHIHIRO, MASUDA AKIHITO, KAWANAMI, TAKASHI, MAKINO, TOSHIHIRO, MASUDA, AKIHITO
Applicants: MURATA MANUFACTURING CO, MURATA MANUFACTURING CO., LTD.
Application year: 1998
Main classification: H01P1
IPC codes: H01P1