Patent Publication Number: US-9905904-B2

Title: Artificial dielectric resonator and artificial dielectric filter using the same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 14/460,120, filed on Aug. 14, 2014, which is a continuation of International Patent Application No. PCT/JP2013/053440, filed on Feb. 13, 2013, which claims priority to Japanese Patent Application No. JP2012-029991, filed on Feb. 14, 2012. All of the afore-mentioned patent applications are hereby incorporated by reference in their entireties. 
    
    
     TECHNICAL FIELD 
     The embodiments of the present invention relate to an artificial dielectric resonator and an artificial dielectric filter using the same. 
     BACKGROUND 
     In recent years, there have not been many cases in which high-frequency filters that are used in a microwave band and the like are made up of dielectric resonators using dielectric substances with high relative dielectric constants for the purpose of downsizing and enhancement in performance by downsizing. By forming a dielectric substance into a block in a specific size and shape, a dielectric resonator can be resonated at a desired frequency that is fixed by the size and shape of the dielectric substance and the relative dielectric constant. 
     A dielectric resonator using ceramics with a high relative dielectric constant (dielectric ceramics) as the material of the dielectric substance is widely known. When an electric field is applied to the molecules that configure the dielectric ceramics, the bound electrons in the molecules migrate and are polarized, and thereby the dielectric ceramics shows a high relative dielectric constant. As the relative dielectric constant of dielectric ceramics, the dielectric ceramics having relative dielectric constants of 20 to 100 can be generally put to practical use when smallness of loss at a high frequency and temperature stability are taken into consideration. 
     As a dielectric resonator, the dielectric resonator using an artificial dielectric substance (an artificial dielectric resonator) has been also proposed (For example, Patent Literature 1). An artificial dielectric substance is formed from assembly of a number of metallic pieces. The artificial dielectric substance behaves as a dielectric substance as a result that free electrons that are present in the metallic pieces migrate and are polarized when an electric field is applied thereto, and can obtain a high equivalent relative dielectric constant in accordance with the size and the shape of the metallic pieces, depending on the number of free electrons and the length of the migration distance. Note that artificial dielectric substances are disposed in a certain base material in order to retain the respective metallic pieces. 
     Further, an artificial dielectric substance has such anisotropy that the relative dielectric constant changes depending on which direction of the metallic pieces an electric field is applied as described in Patent Literature 1. Due to the anisotropy, the metallic pieces are disposed so that in resonance (a basic mode) at a desired frequency, the relative dielectric constant becomes high, and at other resonances (spurious mode) at frequencies relatively close to the desired frequency, the relative dielectric constant becomes low, whereby the artificial dielectric resonator can separate these frequencies, and thereby can suppress the spurious mode. 
     CITATION LIST 
     Patent Literature 
     [Patent Literature 1] Japanese Patent Laid-Open No. 2003-133820 
     SUMMARY 
     Technical Problem 
     As above, an artificial dielectric resonator can obtain an excellent characteristic which ordinary resonators of dielectric ceramics do not have, in accordance with the sizes, shapes and disposition of metallic pieces. However, an artificial dielectric resonator still has a room for improvement, in order to respond to the request of customers of today for high-frequency filters (artificial dielectric filters) using the artificial dielectric resonators. In particular, in order to respond to the request for downsizing, an artificial dielectric resonator needs to further enhance the relative dielectric constant in a basic mode. 
     In the artificial dielectric filter using artificial dielectric resonators, a plurality of artificial dielectric resonators are usually disposed therein, and input/output terminals that are coupled to the artificial dielectric resonators to exchange signals with an outside are disposed. By properly controlling the degree of coupling between the input/output terminals and the artificial dielectric resonators (input/output coupling degree) and an inter-stage coupling degree between two artificial dielectric resonators, a filter characteristic (for example, a Chebyshev type or the like) of a desired band width is implemented with respect to a predetermined basic mode. With respect to an artificial dielectric filter, the degree of input/output coupling is small, and the band width of the filter characteristic tends to be narrow, and it is sometimes difficult to obtain the desired filter characteristic. 
     Further, an artificial dielectric filter is also desired to implement accurate positioning of a plurality of artificial dielectric resonators while restraining a lot of time and effort from being taken by the manufacture process, for the purpose of control of the inter-stage coupling degree between two artificial dielectric resonators. 
     The embodiments of the present invention are provided in the light of the foregoing circumstances, and an objective of the embodiments of the present invention is to provide an artificial dielectric resonator that can further enhance a relative dielectric constant in a basic mode, and to provide an artificial dielectric filter that has a large input/output coupling degree, and can implement accurate positioning of the artificial dielectric resonators. 
     Solution to Problem 
     In order to attain the foregoing described objective, an artificial dielectric resonator according to a preferable embodiment of the present invention has a first series metal strip group including a plurality of metal strips each in a thin sheet shape arranged with microscopic gaps provided in a longitudinal direction, and a second series metal strip group including a plurality of metal strips each in a thin sheet shape arranged with microscopic gaps provided in a longitudinal direction, where the first series metal strip group and the second series metal strip group are disposed close to each other in a thickness direction of the metal strips, and the metal strip of one of the metal strip groups is disposed to face and cross the gap of the other metal strip group. 
     It is preferable that in the artificial dielectric resonator, the first series metal strip group and the second series metal strip group separately form annular shapes. More preferably, the artificial dielectric resonator further has a third series metal strip group including a plurality of metal strips each in a thin sheet shape annularly arranged with microscopic gaps provided in a longitudinal direction, the third series metal strip group being disposed coaxially with the first series metal strip group and close to the first series metal strip group in width directions of the metal strips, and a fourth series metal strip group including a plurality of metal strips each in a thin sheet shape annularly arranged with microscopic gaps provided in a longitudinal direction, the fourth series metal strip group being disposed coaxially with the second series metal strip group and close to the second series metal strip group in width directions of the metal strips. 
     It is preferable that an artificial dielectric filter includes a plurality of the artificial dielectric resonators, and two input/output terminals, where the artificial dielectric resonators which are adjacent to each other are coupled to each other, and the input/output terminals are coupled to the artificial dielectric resonators which are adjacent to the input/output terminals. 
     It is preferable that in the artificial dielectric filter, the respective input/output terminals are directly connected to the metal strips of the artificial dielectric resonators which are adjacent to the input/output terminals. 
     It is preferable that in the artificial dielectric filter, the plurality of artificial dielectric resonators are formed in an integral multilayer substrate so that a relative position of the plurality of artificial dielectric resonators is fastened to achieve a predetermined inter-stage coupling degree. 
     It is preferable that in the artificial dielectric filter, the artificial dielectric resonator resonates with a basic mode set as a TE01δ mode. 
     Advantageous Effect of the Embodiments of the Invention 
     According to the embodiments of the present invention, the first series metal strip group and the second series metal strip group are disposed close to each other in the thickness directions of the metal strips, and the metal strip of one of the metal strip groups is disposed to face and cross the gap of the other metal strip group. Therefore, by a large capacitance there between, the artificial dielectric resonator showing an extremely high relative dielectric constant can be provided. Further, the input/output terminal is directly connected to the metal strip by using the artificial dielectric resonator, and a plurality of artificial dielectric resonators are formed in the integral multilayer substrate, whereby the artificial dielectric filter which has a large input/output coupling degree, and implements accurate positioning of the artificial dielectric resonators can be provided. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view of an artificial dielectric resonator according to an embodiment of the present invention. 
         FIG. 2  is a plan view showing a first series metal strip group of the artificial dielectric resonator of an embodiment of the present invention. 
         FIG. 3  is a plan view showing a second series metal strip group of the artificial dielectric resonator of an embodiment of the present invention. 
         FIG. 4  is a view explaining electric charges that are generated in the first series metal strip group and the second series metal strip group of the artificial dielectric resonator of an embodiment of the present invention. 
         FIG. 5  is a perspective view of a modification of the artificial dielectric resonator of an embodiment of the present invention. 
         FIG. 6  is a plan view showing a first series metal strip group and a third series metal strip group of the modification of the artificial dielectric resonator of an embodiment of the present invention. 
         FIG. 7  is a plan view showing a second series metal strip group and a fourth series metal strip group of the modification of the artificial dielectric resonator of an embodiment of the present invention. 
         FIG. 8  is a perspective view of an artificial dielectric filter of an embodiment of the present invention. 
         FIG. 9  is a plan view of an inside of the artificial dielectric filter of an embodiment of the present invention. 
         FIG. 10  is a characteristic diagram of an inter-stage coupling degree of the artificial dielectric filter of an embodiment of the present invention. 
         FIG. 11  is a characteristic diagram of an input/output coupling degree of the artificial dielectric filter of an embodiment of the present invention. 
         FIG. 12  is a plan view of an inside of an artificial dielectric filter in which an input/output method of the artificial dielectric filter of an embodiment of the present invention is changed. 
         FIG. 13  is a characteristic diagram of an input/output coupling degree of the artificial dielectric filter in which the input/output method of the artificial dielectric filter of an embodiment of the present invention is changed. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, an embodiment of the present invention will be described with reference to the drawings. As shown in  FIGS. 1, 2, and 3 , an artificial dielectric resonator  1  according to the embodiment of the present invention has a first series metal strip group  2  including a plurality of metal strips  20 ,  20 , . . . each in a thin sheet shape annularly arranged with microscopic gaps  20 G,  20 G, . . . provided in a longitudinal direction, and a second series metal strip group  3  including a plurality of metal strips  30 ,  30 , . . . each in a thin sheet shape annularly arranged with microscopic gaps  30 G,  30 G, . . . provided in a longitudinal direction. The first series metal strip group  2  and the second series metal strip group  3  are disposed close to each other in a thickness direction of the metal strips  20  and  30 , and the metal strip  20  or  30  of either one of the metal strip group  2  or  3  is disposed to face and cross the gap  30 G or  20 G of the other metal strip group  3  or  2 . 
     The metal strips  20  and  30  each in a thin sheet shape are metal pieces with large aspect ratios (widths are short, and lengths are long). Further, in the artificial dielectric resonator  1 , the first series metal strip group  2  and the second series metal strip group  3  are disposed in a base material for retaining them (for example, a multilayer substrate which will be described later such as a resin multilayer substrate and an LTCC (low temperature co-fire ceramics) substrate). 
     In the artificial dielectric resonator  1 , metal strip groups similar to the first series metal strip group  2  or the second series metal strip group  3  are properly provided by being stacked in sequence similarly to the positional relation of the first series metal strip group  2  and the second series metal strip group  3 .  FIG. 1  shows the artificial dielectric resonator in which three layers of the metal strip groups similar to the first series metal strip group  2 , and two layers of the metal strip groups similar to the second series metal strip group  3 , that is, five layers in total are provided in layer. 
     In the artificial dielectric resonator  1  as above, free electrons in the metal strips  20  and  30  migrate by an applied electric field, and positive charges or negative charges are present at one end sides of the metal strips  20  and  30 , and negative charges or positive charges are present at the other end sides. This state is a state in which the metal strips  20  and  30  cause polarization, and the positive charges and the negative charges which are present configure an electric dipole. As a dipole moment which is obtained by multiplying the amount of charges in the electric dipole and a polarization distance is larger, a higher relative dielectric constant can be obtained. 
     Therefore, the first series metal strip group  2  and the second series metal strip group  3  each forming an annular shape show a high relative dielectric constant to an annular electric field which is applied. Thereby, the artificial dielectric resonator  1  having the first series metal strip group  2  and the second series metal strip group  3  can have a TE01δ mode in which the direction of the electric field of resonance forms an annular shape as an object basic mode. A TE01δ mode is willingly used as a basic mode, because of small loss. 
     Further, the positional relation of the metal strip  20  of the first series metal strip group  2  and the metal strip  30  of the second series metal strip group  3  generates a large capacitance between the metal strip  20  and the metal strip  30 . Thereby, as shown in  FIG. 4 , a larger number of electric charges (positive charges or the negative charges at one end side and the negative charges or the positive charges at the other end side) are stored, whereby the dipolar moment becomes large, and a very high relative dielectric constant can be obtained in the annular direction. Note that the electric fields between the adjacent metal strips  20  and  20  and between the adjacent metal strips  30  and  30  are strong. Further, an electric field occurs between the metal strip  20  and the metal strip  30 . 
     Note that the relative dielectric coefficient can be also adjusted by changing a width of the metal strip  20  and a distance of the gap  20 G in the first series metal strip group  2 , and a width of the metal strip  30  and a distance of the gap  30 G in the second series metal strip group  3 , and the like. 
     If the basic mode is set as the TE01δ mode of a predetermined resonance frequency, the artificial dielectric resonator  1  is downsized. When a spurious mode (for example, a TM11δ mode or the like) having a resonance frequency relatively close to the resonance frequency of the TE01δ mode is present, the size of the artificial dielectric resonator  1  changes, whereby the resonance frequency of the spurious mode changes in accordance with the size thereof, and as a result, the resonance frequencies of the basic mode and the spurious mode can be separated. 
     Next, an example of modifying the artificial dielectric resonator  1  will be described. An artificial dielectric resonator  1 ′ further has a third series metal strip group  4  and a fourth series metal strip group  5 , in addition to the configuration of the artificial dielectric resonator  1 , as shown in  FIGS. 5, 6 and 7 . Namely, the third series metal strip group  4  includes a plurality of metal strips  40  each in a thin sheet shape annularly arranged with microscopic gaps  40 G provided in a longitudinal direction, and is disposed coaxially with the first series metal strip group  2  and close to the first series metal strip group  2  in the width direction of the metal strip  20 . The fourth series metal strip group  5  includes a plurality of metal strips  50  each in a thin sheet shape annularly arranged with microscopic gaps  50 G provided in a longitudinal direction, and is disposed coaxially with the second series metal strip group  3 , and in a close vicinity to the second series metal strip group  3  in the width direction of the metal strip  30 . 
     The artificial dielectric resonator  1 ′ as above also generates capacitances between the metal strip  20  and the metal strip  40 , and between the metal strip  30  and the metal strip  50 , separately. These capacitances are not so large as the capacitance between the metal strip  20  and the metal strip  30 , but contributes to storing a larger number of charges (positive charges or negative charges at one end side, and negative charges or positive charges at the other end side). Thereby, the relative dielectric constant can be enhanced more. 
     Next, an artificial dielectric filter  10  will be described. As shown in  FIGS. 8 and 9 , the artificial dielectric filter  10  includes a plurality of artificial dielectric resonators  1 ′ and  1 ′ and two input/output terminals  11  and  11 . The respective artificial dielectric resonators  1 ′ and  1 ′ are retained by being disposed in a base material  13  in a case  12 , and the adjacent artificial dielectric resonators  1 ′ and  1 ′ are coupled to each other by an electromagnetic field. The respective input/output terminals  11  and  11  are fastened to the case  12 , the input/output terminals  11  are coupled to the artificial dielectric resonators  1 ′ adjacent to the input/output terminals  11 . Note that reference sign  14  in  FIG. 8  designates a support member that supports the base material  13 . 
     Note that the number of artificial dielectric resonators  1 ′ and  1 ′ is not limited, and may be two, or three, or more. Further, while in the present embodiment, the aforementioned artificial dielectric resonators  1 ′ and  1 ′ are used as shown in  FIGS. 8 and 9 , the aforementioned artificial dielectric resonators  1  and  1  may be used. 
     For the purpose of coupling of the artificial dielectric resonator  1 ′ and the input/output terminal  11 , the input/output terminal  11  of the artificial dielectric filter  10  is directly connected to the metal strip  20  of the artificial dielectric resonator P. The direct connection is enabled because the artificial dielectric resonator  1 ′ has the separate metal strips  20 ,  20 , . . . . In more detail, a probe section  11   a  that is a section which directly connects the input/output terminal  11  to the metal strip  20  is provided, and a probe section  11   a ′ that is a section which directly connects the metal strips  20  other than the metal strip  20  which is connected to the probe section  11   a  to a ground section G is provided. The probe sections  11   a  and  11   a ′ are formed in layers (metal layers) which are the same as the first series metal strip group  2  and the third series metal strip group  4 . 
     By the direction connection, an input/output connection degree between the input/output terminal  11  and the artificial dielectric resonator  1 ′ is increased, and can be brought close to the inter-stage coupling degree of the artificial dielectric resonators  1 ′ and  1 ′. If the input/output coupling degree is brought close to the inter-stage coupling degree, the band width of the filter characteristic of the entire artificial dielectric filter  10  is restrained from becoming narrower than a relative band of the filter characteristic between the artificial dielectric resonators  1 ′ and  1 ′. Further, by the direct connection, wiring for coupling of the input/output terminal  11  and the artificial dielectric resonator  1 ′ is fastened, and the input/output coupling degree is stabilized. Further, an additional layer as shown in a reference example described later is not required or a large area for coupling is not required, for the purpose of coupling the input/output terminal  11  and the artificial dielectric resonator  1 ′, and therefore, the direct connection also contributes to downsizing. 
     Further, the plurality of artificial dielectric resonators  1 ′ and  1 ′ of the artificial dielectric filter  10  are both formed in an integral multilayer substrate which is the base material  13 . Thereby, relative position of the plurality of artificial dielectric resonators  1 ′ and  1 ′ is fastened, and a predetermined inter-stage coupling degree is obtained. As the multilayer substrate, a resin multilayer substrate, an LTCC (low temperature co-fire ceramics) substrate and the like can be used. 
     A simulation analysis result of the artificial dielectric filter  10  will be shown as follows. In the analysis, three-dimensional electromagnetic simulation software HFSS is used. The thickness of the metal layer is 18 μm, and five layers are stacked. As for the base material, a relative dielectric constant is set at 2.4 and dielectric loss is set at 0.00114. In the artificial dielectric resonator  1 ′, the width of the metal strip is set at 0.8 mm, and all the gaps each between the two metal strips in the same layer are all set at 0.2 mm. An outside diameter of the first series metal strip group  2  which forms an annular shape is set at 8.4 mm. Widths of the probe sections  11   a  and  11   a ′ were set at 0.5 mm. Note that although explanation will be omitted because it is not the gist of the invention, the numeric value showing the input/output coupling degree in the characteristic diagram in the analysis is a value which is a so-called external k, and the numeric value showing the inter-stage coupling degree is a value which is a so-called a coupling constant. 
       FIG. 10  shows a characteristic of the inter-stage coupling degree of the artificial dielectric filter  10 . The axis of abscissa of  FIG. 10  represents a distance X between the two artificial dielectric resonators  1 ′ and  1 ′. Where the distance X between the artificial dielectric resonators  1 ′ and  1 ′ is short, the inter-stage coupling degree is in the order of 10 −2 . Further, if the distance between the artificial dielectric resonators  1 ′ and  1 ′ becomes short within the range, the inter-stage coupling degree increases relatively abruptly. Thereby, it proves to be effective to form the two artificial dielectric resonators  1 ′ and  1 ′ in the integral multilayer substrate and fix the relative position thereof. 
       FIG. 11  shows a characteristic of the input/output coupling degree of the artificial dielectric filter  10 . The axis of abscissa of  FIG. 11  represents a distance Y between the probe section  11   a  and the probe section  11   a ′ of the input/output terminal  11 . Where the distance Y of the probe section  11   a  and the probe section  11   a ′ is short, the input/output degree can be achieved in the order of 10 −2 , and is a value close to the inter-stage coupling degree. Thereby, it is found out that if the input/output terminal  11  is directly connected to the artificial dielectric resonator  1 ′, the band width of the filter characteristic of the entire artificial dielectric filter  10  can be restrained from being narrowed. 
     Note that  FIG. 12  shows an artificial dielectric filter  10 A as a reference example. The artificial dielectric filter  10 A is such that a loop-shaped section  11   aa  is provided at the probe section  11   a  of the input/output terminal  11  and is coupled to the artificial dielectric resonator  1 ′ via a gap, without directly connecting the input/output terminal  11  to the metal strip  20  of the artificial dielectric resonator P. This is such that when the basic mode is a TE01δ mode, a lot of magnetic field energy is present around the artificial dielectric resonator  1 ′, and the artificial dielectric resonator  1 ′ and the loop-shaped section  11   aa  mutually capture the magnetic field energy, and thereby are coupled (magnetic coupling) to each other. 
       FIG. 13  shows a characteristic of the input/output coupling degree of the artificial dielectric filter  10 A. It is found out that the input/output coupling degree cannot be achieved in the order of 10 −2 . This is because however close the artificial dielectric resonator  1 ′ and the loop-shaped section  11   aa  are brought to each other, the magnetic energy which the artificial dielectric resonator  1 ′ and the loop-shaped section  11   aa  can mutually capture is limited. Note that the axis of abscissa of  FIG. 13  is a ratio of a radius r of the loop-shaped section  11   aa  and a radius R of an outer circumference of the first series metal strip group  2 . 
     While the artificial dielectric resonator and the artificial dielectric filter using the same according to the embodiment of the present invention are described thus far, the present invention is not limited to what is described in the aforementioned embodiment, and various design changes within the range of the matters described in claims can be made. For example, in addition to the configuration of the aforementioned artificial dielectric resonator  1 ′, the metal strip group which is similar to the first series metal strip group  2  and the third series metal strip group  4  and is close to them in the width direction can be properly increased. Further, while the one in which the input/output terminal  11  of the artificial dielectric filter  10  and the metal strip  20  of the first series metal strip group  2  are directly connected is described, the art of the direct connection is applicable without being limited to the detailed configuration of the artificial dielectric resonator  1 ′ (or  1 ) if only the artificial dielectric resonator has the aforementioned first series metal strip group  2 . 
     REFERENCE SIGNS LIST 
     
         
         
           
               1  Artificial dielectric resonator 
               10  Artificial dielectric filter 
               11  Input/output terminal 
               2  First series metal strip group 
               20  Metal strip of first series metal strip group 
               20 G Gap of metal strips of first series metal strip group 
               3  Second series metal strip group 
               30  Metal strip of second series metal strip group 
               30 G Gap of metal strips of second series metal strip group 
               4  Third series metal strip group 
               40  Metal strip of third series metal strip group 
               40 G Gap of metal strips of third series metal strip group 
               5  Fourth series metal strip group 
               50  Metal strip of fourth series metal strip group 
               50 G Gap of metal strips of fourth series metal strip group