Patent Publication Number: US-6670862-B2

Title: Nonreciprocal circuit device and communication apparatus

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a nonreciprocal circuit device, such as an isolator used in a high frequency band such as microwave band, and further to a communication apparatus using the same. 
     2. Description of the Related Art 
     Hitherto, a lumped-constant type circulator has been constructed by accommodating, within a case, a plurality of center conductors which intersect each other and which are disposed adjacent to a ferrite plate, and a magnet which applies a DC magnetic field to the ferrite plate. Also, an isolator is formed by terminating one predetermined port of the three ports thereof by a resistor. 
     FIG. 4 is an exploded perspective view illustrating a conventional isolator. Herein, reference numeral  2  designates a box-shaped upper yoke formed of a magnetic metal, and  3  designates a rectangular plate-shaped permanent magnet which is to be disposed on the inner surface of the upper yoke  2 . Reference numeral  5  designates a magnetic assembly. The magnetic assembly  5  has a construction wherein a ferrite  54  is disposed on the coupling portion of center conductors, the coupling portion having the same shape as that of the bottom surface of the disk-shaped ferrite  54 , wherein three center conductors extending from the coupling portion are folded so as to wrap the ferrite  54  in a state of intersecting one another at an angle of 120°, and wherein the port portions P 1 , P 2 , and P 3  on the tip sides of the center conductors are projected outward, respectively. Reference numeral  4  denotes a spacer for keeping the gap between the magnetic assembly  5  and the permanent magnet  3  at a predetermined spacing, and  7  denotes a resin case. Matching capacitors C 1 , C 2 , and C 3  are connected between the respective port portions P 1 , P 2 , and P 3 , and a ground electrode in the resin case  7 . A terminating resistor R is connected between the electrode conducting to the port portion P 3  and the ground electrode. Reference numeral  8  denotes a lower yoke formed of a magnetic metal, which forms a closed magnetic circuit by being combined with the upper yoke  2 . 
     The conventional isolator shown in FIG. 4 uses a disk-shaped ferrite, and has the structure as shown in FIGS. 5A and 5B in order to dispose the three center conductors adjacent to the ferrite so as to intersect one another with a cross angle of 120°. FIG. 5A is a view showing the center conductors before being folded, that is, a development view thereof. FIG. 5B shows the center conductors which are being folded. Here, the portion indicated by reference numeral  50  is the center conductor coupling portion. From this center conductor coupling portion, the three center conductors  51 ,  52 , and  53  are led out in three directions, and the tip portions thereof define the port portions P 1 , P 2 , and P 3 , respectively. The magnetic assembly  5  shown in FIG. 4 is formed by placing the ferrite  54  on the top surface of the center conductor coupling portion  50 , in the configuration shown in FIG. 5A, and by then folding the three center conductors  51 ,  52  and  53  so as to wrap the ferrite  54 , as shown in FIG.  5 B. 
     As a method for bending the center conductor, a method can be adopted wherein the ferrite is abutted against the center conductor coupling portion, and while utilizing this push force, each of the center conductors extending from the center conductor coupling portion in the radial directions is once raised at an angle of about 30 to 70°. This is an effective method when the center conductors are bent by means of an automatic machine. 
     Meanwhile, the port portions provided at the tips of the center conductors are connected to the input/output terminals or the capacitors. In order to enhance the quality of the bonding portions with the input/output terminals and the capacitors, it is necessary to ensure sufficiently large bonding areas. For this purpose, it is desirable to form the port portion at the tip part of each of the center conductors into a size as large as possible. 
     In the resin case having a rectangular shape in a plan view as a whole, in order to make the volume of the magnetic body coupled with the center conductors as large as possible, as well as to facilitate the molding of the magnetic body, it is effective to use a magnetic body having a rectangular shape in a plan view (i.e., a magnetic body of a rectangular parallelepiped). FIG. 6 shows the shapes of the center conductors when a magnetic body having a rectangular shape in a plan view is used. In the configuration shown in FIG. 6A, the ferrite  54  is placed on the top surface of the center conductor coupling portion  50 , and firstly the center conductor  51  is folded. Then, when attempting to fold the center conductor  52 , the port portion P 1  at the tip part of the first center conductor  51  can interfere with the second center conductor  52 , as indicated by a mark ◯ in FIG. 6B, thereby not allowing the second center conductor  52  to be bent. One solution to this problem is to form the port portion at the tip part of one center conductor into a smaller size so as not to interfere with the other center conductor. However, this raises a problem that the bonding areas between the port portions and the capacitors or the input/output terminals cannot be sufficiently ensured, resulting in a reduced reliability of the bonding portions. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to solve the above-described problem, and to provide a nonreciprocal circuit device which prevents the center conductors thereof from interfering with each other when folded toward a magnetic body even when the magnetic body has a rectangular shape in a plan view, and which thereby increases the reliability of the bonding portions between the port portions at the tip parts of the center conductors and the capacitors or the input/output terminals, and further to provide a communication device using this nonreciprocal circuit device. 
     In accordance with a first aspect of the present invention, there is provided a nonreciprocal circuit device comprising a plurality of center conductor, a magnetic body placed on the coupling portion of the center conductors, and a magnetic assembly in which the center conductors extending from the coupling portion outward are folded so as to wrap the magnetic body. In this nonreciprocal circuit device, the magnetic body is formed as a rectangular shape, and the port portions of the center conductors which are to be connected to the capacitors or the input/output terminals are formed asymmetrically with each other so as not to mutually interfere when the center conductors are folded toward the magnetic body. 
     By these structures, the center conductors can be prevented from an interference when they are folded, without the need to reduce the size of the port portion at the tip part of each of the center conductors. 
     In the first aspect of the present invention, preferably, the port portion of one of the two center conductors which extend from the coupling portion outward substantially line-symmetrically, is formed smaller than the port portion of the other center conductor. In virtue of this structure, when folding the two center conductors so as to wrap the magnetic body, by folding the center conductor having a smaller port portion earlier and folding the other center conductor later, the port portion of the center conductor which has been already bent can be prevented from interfering with the other center portion, and the port portion of the center conductor to be folded later can be provided with a sufficiently large size. 
     Also, in the first aspect of the present invention, it is preferable that at least one of a notch or a hole be formed in the port portions. This structure increases the area of the solder fillets when the port portions are soldered to the capacitors or the input/output terminals, thereby enhancing the reliability of the bonding portions. 
     A second aspect of the present invention provides a communication apparatus using the above-described nonreciprocal circuit device. 
     The above and other objects, features, and advantages of the present invention will be clear from the following detailed description of the preferred embodiments of the invention in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an exploded perspective view illustrating an isolator in accordance with an embodiment of the present invention; 
     FIG. 2 is a top view illustrating the isolator shown in FIG. 1, the isolator being rid of the upper yoke thereof; 
     FIG. 3 is a diagram showing center conductors before being folded; 
     FIG. 4 is an exploded perspective view illustrating a conventional isolator; 
     FIGS. 5A and 5B are diagrams illustrating the center conductors used in the conventional isolator, wherein FIG. 5A shows the center conductors before being folded, and FIG. 5B shows the center conductors which are being folded; and 
     FIG. 6A is a diagram illustrating the shapes of the center conductors in accordance with the conventional art, the center conductors corresponding to a rectangular ferrite, and FIG. 6B is a diagram illustrating these center conductors which are being folded. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The construction of the isolator in accordance with a first embodiment of the present invention will be described with reference to FIGS. 1 through 3. 
     FIG. 1 is an exploded perspective view illustrating the isolator. FIG. 2 is a top view illustrating the isolator shown in FIG. 1, the isolator being rid of the upper yoke  2  thereof. The upper yoke  2  is a box-shaped one formed of a magnetic metal. A rectangular plate-shaped permanent magnet  3  is to be disposed on the inner surface of the upper yoke  2 . A magnetic assembly  5  has a construction wherein a ferrite  54  is disposed on the coupling portion of center conductors, the coupling portion having substantially the same shape as that of the bottom surface of the disk-shaped ferrite  54 , wherein three center conductors  51 ,  52 , and  53  extending from the coupling portion are folded so as to wrap the ferrite  54  with insulating sheets (not shown) interposed therebetween, in a state of intersecting one another at an angle of 120°, and wherein the port portions P 1 , P 2 , and P 3  on the tip sides of the center conductors  51 ,  52 , and  53  are projected outward, respectively. A spacer  4  is provided for keeping the gap between the magnetic assembly  5  and the permanent magnet  3  at a predetermined spacing. Reference numeral  7  denotes a resin case. A ground electrode, of which one portion is exposed to the top surface of the case, and an input/output terminal  72 , a ground terminal  73 , etc., which are exposed from the bottom to a side surface of the case, are insert-molded to this resin case  7 . Matching capacitors C 1 , C 2 , and C 3  are connected between the port portions P 1 , P 2 , and P 3 , and the ground electrode in the resin case  7 . A terminating resistor R is connected between the electrode conducting to the port portion P 3  and the ground electrode. A lower yoke  8  formed of a magnetic metal, which forms a closed magnetic circuit by being combined with the upper yoke  2 . The magnetic field by the permanent magnet  3  is applied to the ferrite  54  in the thickness direction thereof. 
     FIG. 3 is a diagram showing the center conductors before being folded. In FIG. 3, the portion indicated by reference numeral  50  is the coupling portion of the center conductors. On this coupling portion  50 , the ferrite  54  is placed. The center conductors  51 ,  52 , and  53  extend from the coupling portion  50  into three directions, and the tip parts of the center conductors  51 ,  52 , and  53  are formed as port portions P 1 , P 2 , and P 3 , respectively. The center conductor  53  among these three center conductors  51 ,  52 , and  53  is led out from the coupling portion  50  along the straight line through the center portion of the coupling portion  50 . The other two center conductors  51  and  52  are led out so as to be symmetrical with each other with respect to the line along which the center conductor  53  extends, each forming an angle of 60° with respect to the direction in which the center conductor  53  extends. When the center conductors  51  and  52  which have a line-symmetrical relationship with each other, among the center conductors thus led out in the three directions, are folded, the port of one of these center conductors  51  and  52  can interfere with the other center conductor. However, like this embodiment, by forming the port portion P 1  of the center conductor  51  smaller than the port portion P 2  of the other center conductor  52 , and by folding the center conductor  51  firstly and the center conductor  52  thereafter, the interference of the port portion P 1  with respect to the conductor  52  is prevented. The center conductor  53  extending along the symmetry axis with respect to the center conductors  51  and  52  which have a line-symmetrical relationship with each other, does not interfere with the center conductor  51  or  52 , irrespective of the point in time when the center conductor  53  is folded, that is, irrespective of its turn to be folded. 
     As shown in FIGS. 2 and 3, by providing each of the port portions P 1 , P 2 , and P 3  with at least one notch A and/or a hole H, it is possible to increase the areas of the solder fillets when soldering the port portions to the electrodes of the top surfaces of the matching capacitors, and to the one electrode of the terminating resistor and the input/output terminals  71  and  72 . Thereby, the reliability of the soldered portions can be ensured. 
     By providing the center portion of the coupling portion  50  of the center conductors with a hole H, a displacement of the ferrite can be prevented by sucking the ferrite from the bottom surface of the hole at the center portion, while the magnetic assembly is performed. This can enhance the assembling accuracy of the magnetic assembly. 
     In the above-described embodiments, an isolator has been constructed by firstly forming a three-port circulator using the center conductors extended in the three directions, and by then terminating a predetermined port among these three ports by a resistor. However, the present invention can also be applied to the case where a three-port circulator is constructed without terminating one of the ports by a resistor. 
     Furthermore, the present invention can also be applied to a two-port type isolator wherein two center conductors are led out from the coupling portion of the center conductors in two directions, and wherein the center conductors are folded so as to wrap a magnetic body in a state of intersecting each other. For example, in the embodiment shown in FIG. 3, a two-port type isolator can be achieved by setting the angle formed between the two center conductors to a predetermined angle, and by leading out only the center conductors  51  and  52  from the coupling portion  50 . 
     In the above-described embodiments, the cross angles among the center conductors was set to 120°, but the cross angles in the present invention are not limited to 120°. The cross angles may be changed within the range in which the center conductors do not contact one another, that is, the center conductors are not short-circuited. 
     Also, the number or positions of the holes and notches formed in the port portions of the center conductors are not restricted to the above-described embodiments, but may be changed as required. Similar effects will be thereby obtained. 
     As is evident from the foregoing, in accordance with the first aspect of the present invention, the port portions at the tip parts of the center conductors can be prevented from an interference when the center conductors are folded, without the need to reduce the size of the port portion. 
     Furthermore, in accordance with the first aspect of the present invention, when folding the above-described two center conductors so as to wrap the magnetic body, by folding the one center conductor having a smaller port portion earlier, and folding the other center conductor later, the port portion of the center conductor which has been already bent can be prevented from interfering with the other center conductor, and the port portion of the center conductor to be folded later can be provided with a sufficiently large size. 
     Moreover, in accordance with the first aspect of the present invention, the area of solder fillets can be increased when the port portions are soldered to the capacitors or the input/output terminals, thereby increasing the reliability of the bonding portions. 
     In accordance with the second aspect of the present invention, by using the above-described small-sized and high-reliability nonreciprocal circuit device having predetermined nonreciprocal characteristics, a high reliability communication apparatus which has a small size as a whole can be achieved. 
     While the present invention has been described with reference to what are at present considered to be the preferred embodiments, it is to be understood that various changes and modifications may be made thereto without departing from the invention in its broader aspects and therefore, it is intended that the appended claims cover all such changes and modifications as fall within the true spirit and scope of the invention.