Abstract:
A nonreciprocal circuit device includes a magnet and a center electrode. The center electrode includes a nonmagnetic substrate having a first surface having a groove, a magnetic body provided on a second surface of the nonmagnetic substrate, and a center electrode conductor, with a portion of the center electrode conductor being arranged in the groove. The magnet applies a direct-current magnetic field to the magnetic body and is disposed in proximity to the magnetic body.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a nonreciprocal circuit device such as a circulator and an isolator for use in a microwave band.  
           [0003]    2. Description of the Related Art  
           [0004]    Generally, lumped element isolators used in portable communication apparatuses such as cellular phones allow signals to pass only in the transmission direction, and inhibit transmission in the opposite direction. The recent trend toward lighter and smaller portable communication apparatuses has increased the demand for lighter and smaller isolators.  
           [0005]    In order to meet such demands, Japanese Unexamined Utility Model Application Publication No. 5-80009 discloses a nonreciprocal circuit device including wound-wire center electrodes formed by winding center electrode conductors around a magnetic body to reduce the size and weight of the device. The center electrodes of this nonreciprocal circuit device have greater effective lengths to improve the inductance of the center electrodes and to reduce the diameter of the magnetic body.  
           [0006]    However, the center electrodes are formed by winding the center electrode conductors around the magnetic body with the nonmagnetic substrate that is left at the bottom of the magnetic body for reinforcement when the thickness of the magnetic body is thin. Since the portions of the wound center electrode conductors at the bottom of the magnetic body are separated from the corresponding portion of the magnetic body by the nonmagnetic substrate, the insertion loss of the resulting isolator is not sufficiently low as required for isolators.  
         SUMMARY OF THE INVENTION  
         [0007]    To overcome the above-described problems, preferred embodiments of the present invention provide a nonreciprocal circuit device including a magnetic body provided with a nonmagnetic substrate, that achieves miniaturization, weight reduction, and low insertion loss.  
           [0008]    A preferred embodiment of the present invention provides a nonreciprocal circuit device including a center electrode including a nonmagnetic substrate including a first surface having a groove, a magnetic body provided on a second surface of the nonmagnetic substrate, and a center electrode conductor, a portion of the center electrode conductor being arranged in the groove, and a magnet for applying a direct-current magnetic field to the magnetic body, the magnet being disposed in proximity to the magnetic body.  
           [0009]    Since the nonmagnetic substrate is provided with the groove and has a reduced thickness at the groove, the distance between the center electrode conductor and the magnetic body is greatly reduced as compared with the case where no groove is provided. Thus, the insertion loss greatly decreased. Moreover, since the depth of the groove in the nonmagnetic substrate can be controlled, the insertion loss is easily controlled. Furthermore, since a portion of the center electrode conductor is provided in the groove, displacement of the center electrode is effectively prevented.  
           [0010]    Preferably, the magnetic body includes a side of the groove, and the nonmagnetic substrate includes a base of the groove.  
           [0011]    The depth of the groove is arranged to reach an interface between the nonmagnetic substrate and the magnetic body. Also, the magnetic body defines a base of the groove. Moreover, sides of the nonmagnetic substrate define sides of the groove.  
           [0012]    According to this preferred embodiment of the present invention, the nonmagnetic substrate is not provided between the center electrode conductor and the magnetic body, and the thickness of the magnetic body is sufficiently maintained. Therefore, the insertion loss of structure described above is greatly reduced.  
           [0013]    Preferably, the center electrode conductor includes a wire having an insulating coat, and the center electrode conductor is either wound around the nonmagnetic substrate and the magnetic body or only wound around the magnetic body.  
           [0014]    When the center electrode conductor is wound around the nonmagnetic substrate and the magnetic body, the windings of the conductor are not in direct contact with one another at the intersections of the windings since the conductor is provided with an insulating coat.  
           [0015]    The magnetic body preferably includes a magnetic garnet single crystal so as to further reduce the insertion loss.  
           [0016]    The magnetic body is preferably grown by liquid phase epitaxy. In this manner, the magnetic body has the same crystal structure as that of the substrate and has high crystallinity. Thus, a high-quality nonreciprocal circuit device having a low insertion loss is manufactured using this magnetic body.  
           [0017]    The nonmagnetic substrate preferably includes a garnet single crystal. When both the nonmagnetic substrate and the magnetic body have the same garnet single crystal structure, a nonreciprocal circuit device having stable characteristics and low insertion loss is manufactured therefrom.  
           [0018]    Further elements, characteristics, features and advantages of the present invention will become apparent from the following description of the preferred embodiments with reference to the attached drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]    [0019]FIG. 1 is an assembly view of a two-terminal isolator according to a preferred embodiment of the present invention.  
         [0020]    [0020]FIG. 2A is a perspective view of a single crystal composite provided with coated copper wires so as to provide center electrodes which define the two-terminal isolator shown in FIG. 1.  
         [0021]    [0021]FIG. 2B is a cross-sectional view of the single crystal composite taken along line A-A′ in FIG. 2A.  
         [0022]    [0022]FIG. 3 is a perspective view of another single crystal composite which defines the two-terminal isolator shown in FIG. 1. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0023]    [0023]FIG. 1 is an assembly view of a two-terminal isolator including a nonreciprocal circuit device according to a preferred embodiment of the present invention.  
         [0024]    In the present preferred embodiment, the two-terminal isolator preferably has the following exemplary dimensions, approximately 3.2 mm×2.5 mm×2.0 mm.  
         [0025]    Referring to FIG. 1, an isolator  10  includes an upper yoke  12 , a lower yoke  14 , a permanent magnet  16 , a resin substrate  18 , four capacitors  20 , a resistor  22 , and a single crystal composite  23 . The permanent magnet  16  and the substrate  18  are arranged between the upper yoke  12  and the lower yoke  14 . The capacitors  20 , the resistor  22 , and the single crystal composite  23  are provided on the substrate  18 .  
         [0026]    The single crystal composite  23  is preferably defined by a nonmagnetic garnet single crystal substrate  26  and a magnetic garnet single crystal  24  grown on the garnet single crystal substrate  26  by liquid phase epitaxy (LPE method). The surface of the garnet single crystal substrate  26  opposite to the surface provided with the magnetic garnet single crystal  24  includes two grooves  28   a  and  28   b . The grooves  28   a  and  28   b  extend substantially parallel to the main surfaces of the magnetic garnet single crystal  24  and intersect each other at the approximate center of the surface of the garnet single crystal substrate  26 .  
         [0027]    Center electrodes are provided on the surface of the single crystal composite  23  defined by two coated copper wires  30   a  and  30   b . The configuration of the center electrodes is described below with reference to FIGS. 2A and 2B.  
         [0028]    [0028]FIG. 2A is a perspective view of the single crystal composite  23  provided with the center electrodes defined by the coated copper wires  30   a  and  30   b . FIG. 2B is a cross-sectional view taken along a two-dot chain line A-A′ in FIG. 2A.  
         [0029]    As shown in FIGS. 2A and 2B, center portions of the coated copper wires  30   a  and  30   b  are respectively arranged in the grooves  28   a  and  28   b  provided on the garnet single crystal substrate  26  of the single crystal composite  23 . The end portions of the coated copper wires  30   a  and  30   b  are wound around the single crystal composite  23 . The coated copper wires  30   a  and  30   b  overlap each other at the approximate centers of the top and bottom surfaces of the single crystal composite  23 .  
         [0030]    One end of each of the coated copper wires  30   a  and  30   b  defining the center electrodes is grounded to the substrate  18  shown in FIG. 1. The other end of the coated copper wire  30   a  is connected in series to an input terminal via one of the capacitors  20  and is also connected in parallel to another one of the capacitors  20 . The other end of the coated copper wire  20   b  is connected in series to an output terminal via another one of the capacitors  20  and is also connected in parallel to another one of the capacitors  20 . The resistor  22  is connected in series between the two series capacitors  20 .  
         [0031]    The present invention will now be described by way of examples of preferred embodiments thereof.  
         [0032]    A magnetic garnet single crystal (Y 3 Fe 5 O 12 ) layer was grown on a nonmagnetic garnet single-crystal substrate (Gd 3 Ga 5 O 12 ) by the LPE method to prepare a single crystal composite.  
         [0033]    A plurality of sample pieces was cut from the resulting single crystal composite. Each sample piece had a planar dimension of about 0.5 mm×about 0.5 mm, a thickness of the magnetic garnet single crystal layer of about 0.1 mm, and a thickness of the nonmagnetic garnet single crystal substrate of about 0.2 mm.  
         [0034]    For each of the prepared sample pieces, the two grooves  28   a  and  28   b  were provided on the surface of the nonmagnetic garnet single crystal substrate opposite to the surface provided with the magnetic garnet single crystal layer using a dicing saw. The grooves  28   a  and  28   b  of which each width is about 0.07 mm intersect each other at the approximate center of the surface and had a depth shown in Table 1.  
                                             TABLE 1                               Location of the bottom of the                   groove/Distance between the bottom                   of the groove and the interface               Depth of   between the magnetic garnet single           Sample   the groove   crystal layer and the nonmagnetic   Insertion loss       No.   (mm)   garnet single crystal substrate (mm)   (dB)                                1   0   In the substrate/0.20   2.8       2   0.05   In the substrate/0.15   1.9       3   0.15   In the substrate/0.05   1.4       4   0.20   At the interface/0   0.9       5   0.25   In the magnetic garnet single   1.2               crystal/0.05       6   0.27   In the magnetic garnet single   1.8               crystal/0.07                  
 
         [0035]    As shown in FIGS. 2A and 2B, the center portions of the two coated copper wires  30   a  and  30   b  were respectively arranged in the grooves  28   a  and  28   b  of each of the resulting single crystal composites. The end portions of the coated copper wires  30   a  and  30   b  were wound around the single crystal composite  23  so as to form the center electrodes. Subsequently, the center electrodes and other components shown in FIG. 1 were assembled to form the two-terminal isolator  10 . In this example, the grooves  28   a  and  28   b  were provided in the single crystal composite after the composite was cut into a size of a nonreciprocal circuit device. Alternatively, the grooves  28   a  and  28   b  may be provided before the cutting.  
         [0036]    Next, the relationship between the insertion loss and depth of the grooves  30   a  and  30   b  provided in the single crystal composite was determined for each prepared two-terminal isolator  10 . The results are shown in Table 1. In Table 1, the expression “in the substrate” means in the nonmagnetic garnet single crystal substrate.  
         [0037]    Referring to Table 1, the two-terminal isolator of Sample 2 including having a depth of about 0.05 mm formed in the nonmagnetic garnet single crystal substrate has an improved insertion loss as compared with Sample 1 having no grooves.  
         [0038]    As shown in Samples 3 and 4, as the bottom of the groove get closer to the interface between the magnetic garnet single crystal and the nonmagnetic garnet single crystal substrate, the distance between the coated copper wire arranged in the groove and the magnetic garnet single crystal decreases and the insertion loss decreases.  
         [0039]    Samples 5 and 6 which include grooves extending past the interface between the magnetic garnet single crystal and the nonmagnetic garnet single crystal substrate also have improved insertion loss as compared with Sample 1 having no grooves. However, since the effective thickness of the magnetic garnet single crystal layer decreases, the insertion loss increases after the depth of the grooves reaches the interface.  
         [0040]    Accordingly, when the smallest insertion loss is needed, the groove is arranged so as to reach the interface between the magnetic garnet single crystal  24  and the nonmagnetic garnet single crystal substrate  26 , and the magnetic garnet single crystal  24  defines the base of the grooves  28   a′  and  28   b′  which are provided on the single crystal having the substrate shown in FIG. 3, and the nonmagnetic garnet single crystal  26  defines the sides of the grooves  28   a′  and  28   b′.    
         [0041]    With this structure, when a center electrode is defined by coated copper wires provided on a surface of a single crystal, the nonmagnetic substrate is not interposed between the center electrode conductor and the magnetic body, and the thickness of the magnetic body is sufficiently maintained. Therefore, the insertion loss of the above-described structure is reduced to the greatest extent in sample 4 as shown in Table 1.  
         [0042]    Although the present invention is described with reference to two-terminal isolators for use in a 1 GHz band in the above examples, the present invention can be effectively used in other frequency bands and can be applied to nonreciprocal circuit devices such as lumped element isolators and circulators other than the two-terminal isolators. The overall structure of the present invention is not limited to that shown in FIG. 1.  
         [0043]    While preferred embodiments of the present invention have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing the scope and spirit of the invention. The scope of the invention, therefore, is to be determined solely by the following claims.