Dual block ceramic resonator filter having common electrode defining coupling/tuning capacitors

A re-entrant dielectric ceramic resonator and filters incorporating a plurality thereof are suitable for use in mobile and portable radio transmitting and receiving devices. The inventive re-entrant dielectric ceramic resonator comprises a dielectric means comprised of a dielectric ceramic material having a top surface, a bottom surface and outer side surfaces, the top and bottom surfaces being flat and parallel to each other, the dielectric means further having a cylindrical hole extending partially from the top surface toward the bottom surface thereby forming an inner side surface and an inner bottom surface, the inner bottom surface being flat and parallel to the bottom surface. Furthermore, the top and outer side surfaces of the dielectric means and the inner side and inner bottom surfaces of the cylindrical hole are covered completely with a first conductive material, and the bottom surface of the dielectric means is partially covered with a second conductive material, to thereby form a coupling/tuning capacitor between the first conductive material covering the inner bottom surface and the second conductive material partially covering the bottom surface, whereby the re-entrant dielectric ceramic resonator is constructed.

FIELD OF THE INVENTION 
The present invention relates to dielectric ceramic filters; and, more 
particularly, to an improved dielectric ceramic resonator and filter that 
is particularly well adapted for use in mobile and portable radio 
transmitting and receiving devices. 
BACKGROUND OF THE INVENTION 
Conventional dielectric ceramic filters offer high performance with 
scalability which make them ideally suited for use in mobile and portable 
radio transceivers. They are usually comprised of a plurality of 
dielectric ceramic resonators that are typically foreshortened, 
short-circuited quarter-wavelength coaxial. 
In FIG. 1, there is illustrated a prior art dielectrically loaded bandpass 
filter 100 employing a conventional input connector 101 and a conventional 
output connector 103. Such a filter is more fully descirbed in U.S. Pat. 
No. 4,431,977, entitled "Ceramic Bandpass Filter" and is incorporated by 
reference herein. The filter 100 comprises a block 105 which is generally 
made of a dielectric ceramic material with a conductive material 
selectively plated thereon, having a low loss, a high dielectric constant, 
and a low temperature coefficient of the dielectric constant, e.g., a 
ceramic compound comprising barium oxide, titanium oxide and zirconium 
oxide. 
A dielectric filter such as that of the block 105 of the filter 100 is 
generally covered or plated, except for areas 107, with an electrically 
conductive material, for example, silver or copper. The dielectric filter 
such as the block 105 includes a multiplicity of holes 109, wherein each 
of the holes extends from the top surface to the bottom surface thereof 
and is likewise plated with the electrically conductive material. The 
plating of the holes is electrically connected with the conductive plating 
covering the block 105 at one end side of the holes 109 and is isolated 
from the plating covering the block 105 at the opposite end side of the 
holes 109. Further, the plating of the holes 109 at the isolated one end 
side may extend onto the top surface of the block 105. Thus, each of the 
plated holes 109 is essentially a foreshortened coaxial resonator 
comprised of a short coaxial transmission line having a length selected 
for desired filter response characteristics. Although the block 105 is 
shown in FIG. 1 with six plated holes, any number of plated holes may be 
utilized depending upon the filter response characteristics desired. 
The plating of the holes 109 in the filter block 105 is illustrated more 
clearly in a cross sectional view cut through any one of the holes 109. As 
shown in FIG. 2, the conductive plating 204 on the dielectric material 202 
extends through the hole 201 to the top surface with the exception of a 
circular portion 240 around the hole 201. Other conductive plating 
arrangements may also be utilized. In FIG. 3, the conductive plating 304 
on the dielectric material 302 extends through the hole 301 to the bottom 
surface with the exception of the portion 340. The plating arrangement in 
FIG. 3 is substantially identical to that in FIG. 2, the difference being 
that the unplated portion 340 is on the bottom surface instead of on the 
top surface. In FIG. 4, the conductive plating 404 on the dielectric 
material 402 extends partially through the hole 401 leaving a portion of 
the hole 401 unplated. The plating arrangement in FIG. 4 can also be 
reversed as in FIG. 3 so that the unplated portion 440 is on the bottom 
surface. 
Coupling between the plated hole resonators is accomplished through the 
dielectric material and may be adjusted or controlled by varying the width 
of the dielectric material and the distance between adjacent coaxial 
resonators. The width of the dielectric material between adjacent holes 
109 (see FIG. 1) can be adjusted in any suitable regular or irregular 
manner, e.g., by using slots, cylindrical holes, square or retactangular 
holes, or irregularly shaped holes. 
As shown in FIG. 1, RF signals are capacitively coupled to and from the 
dielectric filter 100 by means of input and output electrodes, 111, 113, 
respectively, which in turn, are coupled to input and output connectors 
101, 103, respectively. 
The resonant frequency of the coaxial resonators provided by the plated 
holes 109 is determined primarily by the depth of each hole, the thickness 
of the dielectric block, and the amount of plating removed from the top of 
the filter near the hole. Tuning of the filter 100 may be accomplished by 
the removal of additional ground plating or resonator plating extending 
upon the top of each plated hole. The removal of plating for tuning the 
filter can easily be automated, and can be accomplished by means of a 
laser, sandblast trimmer, or other suitable trimming devices while 
monitoring the return loss angle of the filter. 
SUMMARY OF THE INVENTION 
It is a primary object of the present invention to provide a dielectric 
ceramic resonator having a novel structure capable of storing equal 
amounts of electric and magnetic energies at its resonant frequency. 
It is another object of the present invention to provide a dielectric 
ceramic filter comprising a plurality of the dielectric ceramic resonators 
having the novel structure. 
It is a further object of the present invention to provide a dielectric 
ceramic resonator and filter having an improved capacitive coupling/tuning 
capability. 
It is still another object of the present invention to provide a dielectric 
ceramic resonator and filter whose response characteristics can be easily 
modified. 
In accordance with one aspect of the present invention, there is provided a 
re-entrant dielectric ceramic resonator comprising a dielectric means made 
of a dielectric ceramic material having a top surface, a bottom surface 
and outer side surfaces, the top and bottom surfaces being flat and 
parallel to each other, said dielectric means further having a cylindrical 
hole extending partially from the top surface toward the bottom surface to 
thereby form an inner side surface and an inner bottom surface, wherein 
the inner bottom surface being flat and parallel to the bottom surface, 
and the top and outer side surfaces of said dielectric means and the inner 
side and inner bottom surfaces of the cylindrical hole being covered 
completely with a first conductive material, and the bottom surface of 
said dielectric means being partially covered with a second-conductive 
material to thereby form a coupling/tuning capacitor between the first 
conductive material covering the inner bottom surface and the second 
conductive material partially covering the bottom surface, whereby the 
re-entrant dielectric ceramic resonator is constructed. 
In accordance with another aspect of the present invention, there is 
provided a single-block dielectric ceramic filter, made of a plurality of 
re-entrant dieletric ceramic resonators, comprising: 
a dielectric means made of a dielectric ceramic material having a top 
surface, a bottom surface and four outer side surfaces, the top and bottom 
surfaces being flat and parallel to each other, said dielectric means 
further having at least two cylindrical holes, each of the cylindrical 
holes partially extending from the top surface toward the bottom surface, 
each of the cylindrical holes having an inner side surface and an inner 
bottom surface, the inner bottom surface being flat and parallel to the 
bottom surface, and each of the cylindrical holes being disposed at a 
predetermined distance from one another; 
a first electrode means comprised of a first conductive material disposed 
on the bottom surface of the dielectric means, the first electrode means 
being located below one of the cylindrical holes; and 
a second electrode means comprised of a second conductive material disposed 
on the bottom surface of said dielectric means, the second electrode means 
being located below a cylindrical hole other than the cylindrical hole 
located above the first electrode means; and 
a third conductive material completely covering said dielectric means, 
except the portions surrounding the first and second electrode means, 
thereby forming a pair of coupling/tuning capacitors between the first 
electrode means and the third conductive material covering the inner 
bottom surface of the cylindrical hole located above the first electrode 
means and between the second electrode means and the inner bottom surface 
of the cylindrical hole located above the second electrode means, whereby 
a re-entrant resonator is produced for each of the cylindrical holes. 
In accordance with yet another aspect of the present invention, there is 
provided a dual-block dielectric ceramic filter made of a plurality of 
re-entrant dielectric ceramic resonators, comprising: 
a dielectric means consisting of a pair of dielectric bodies, each of the 
dielectric bodies made of a dielectric ceramic material having a top 
surface, a bottom surface and four outer side surfaces, the top and bottom 
surfaces being flat and parallel to each other, each of the dielectric 
bodies further having at least two cylindrical holes, each of the 
cylindrical holes partially extending from the top surface toward the 
bottom surface, each of the cylindrical holes having an inner side surface 
and an inner bottom surface, the inner bottom surface being flat and 
parallel to the bottom surface, each of the cylindrical holes being 
disposed at a predetermined distance from one another, the bottom surfaces 
of the dielectric bodies being joined together such that each of the 
cylindrical holes in one of the dielectric bodies is aligned with each of 
the cylindrical holes in the other dielectric body; 
a first common electrode means comprised of a first conductive material 
disposed between a pair of aligned cylindrical holes; 
a second common electrode means comprised of a second conductive material 
disposed between a pair of aligned holes other than the pair of aligned 
cylindrical holes with the first common electrode means disposed 
therebetween; and 
a third conductive material completely covering said dielectric means 
including the bottom surface of the dielectric bodies except the portions 
surrounding the first and second common electrode means to thereby form a 
pair coupling/tuning capacitors between the first common electrode means 
and the third conductive material covering the inner bottom surface of the 
aligned cylindrical holes with the first common electrode means disposed 
therebetween and another pair of coupling capacitors between the second 
common electrode means and the third conductive material covering the 
inner bottom surface of the aligned cylindrical holes with the second 
common electrode means disposed therebetween.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Wherever appropriate, the same reference numbers will be used throughout 
the drawings to refer to the same or like parts. 
There is illustrated in FIG. 5 a cross sectional view of the inventive 
re-entrant dielectric ceramic resonator 10 for use in mobile and portable 
radio transmitting and receiving devices, capable of storing equal amounts 
of electric and magnetic energies at its resonant frequency, comprising a 
dielectric means 11 made of a dielectric ceramic material having a top 
surface 12, a bottom surface 13, and outer side surfaces 14, wherein the 
top and bottom surfaces 12, 13 are flat and parallel to each other. The 
dielectric ceramic material making up the dielectric means 11 must have a 
high dielectric constant, a low loss and a low temperature coefficient of 
the dielectric constant as exemplified by a ceramic compound comprising a 
barium oxide, rare-earth oxide and titanium oxide. The dielectric means 11 
further has a cylindrical hole 15 formed thereon, extending partially from 
the top surface 12 toward the bottom surface 13 thereby forming an inner 
side surface 16 and an inner bottom surface 17, wherein the inner bottom 
surface 17 is flat and parallel to the bottom surface 13. Furthermore, the 
top surface 12 and the outer side surfaces 14 of the dielectric means 11 
and the inner side surface 16 and the inner bottom surface 17 of the 
cylindrical hole 15 are covered completely with a first conductive 
material 18 and the bottom surface 13 of the dielectric means 11 is 
covered partially with a second conductive material 19 thereby forming a 
coupling/tuning capacitor between the first conductive material 18 
covering the inner bottom surface 17 and the second conductive material 19 
partially covering the bottom surface 13, whereby the re-entrant 
dielectric resonator is constructed. The first and second conductive 
materials 18, 19 on the inner bottom surface 17 and the bottom surface 13 
are respectively electrically isolated in principle and can therefore 
function as a pair of electrodes. One of these electrodes will be 
connected to ground and the other, to the input signal source(not shown). 
The first and second conductive materials 18, 19 can be made of the same 
material, e.g., silver(Ag) or copper(Cu); and the dielectric means 11 can 
be, as shown in FIGS. 6 and 7, either orthorhombic or cylindric. 
The resonator response characteristics of the inventive re-entrant 
dielectric ceramic resonator 10 are determined by: 
##EQU1## 
wherein fr=the resonant frequency, 
C=the speed of light, 
.epsilon..sub.r =the dielectric constant of the dielectric ceramic 
material, 
A=the inner diameter of the cylindrical hole 15, 
B=the outer diameter when the dielectric means 11 is cylindric (FIGS. 5 and 
7) or the width when the dielectric means 11 is orthorhombic (see FIGS. 5 
and 6), 
L=the height of the dielectric means 11, and 
D=the distance between the inner bottom surface 17 of the cylindrical hole 
15 and the bottom surface 13 of the dielectric means 11. 
The above equation has been derived by using the procedure described in, 
for example, Kazuo Fujisawa, "General Treatment of Klystron Resonant 
Cavities", IRE Transactions on Microwave Theory and Techniques, Vol. 
MTT-6, No. 4, October 1958, Pages 344-357. 
There is listed in Table 1 a set of exemplary dimensions of the inventive 
re-entrant dielectric ceramic resonators with the corresponding resonant 
frequency(f.sub.r) values calculated in accordance with Eq.(1), with the 
assumption that the dielectric constant (.epsilon..sub.r) of the ceramic 
material is 50. 
TABLE 1 
______________________________________ 
Resonant frequency of re-entrant dielectric ceramic 
resonators 
B(cm) L(cm) A(cm) D(cm) f.sub.r (GHz) 
______________________________________ 
0.5 0.5 0.2 0.05 2.3337 
0.5 0.75 0.2 0.05 1.2437 
0.5 1.00 0.2 0.05 0.9741 
0.5 1.25 0.2 0.05 0.8385 
0.5 1.5 0.2 0.05 0.7531 
0.5 2.0 0.2 0.05 0.6469 
______________________________________ 
The resonator response characteristics of the inventive re-entrant 
dielectric ceramic resonators are mainly determined by the dimension of 
the dielectric means and the cylindrical hole formed thereon. 
The resonator response characteristics, especially the resonant frequency, 
can further be fine-tuned by controlling the capacitance of the 
coupling/tuning capacitor formed between the first conductive material 18 
covering the inner bottom surface 17 and the second conductive material 19 
partially covering the bottom surface 13 of the dielectric means 11 by 
controlling the dimension and the shape of the second conductive material 
19 deposited on the bottom surface 13 of the dielectric means 11. There 
are shown in FIGS. 8A to 8C a number of different electroding patterns, 
e.g., 19, 19', 19", that may be formed on the bottom surface 13 of the 
dielectric means 11. 
It is possible to construct dielectric ceramic filters comprising a 
plurality of the above-described re-entrant dielectric ceramic resonators 
depending upon the filter response characteristics desired, two of which 
are described below. 
As a first exemplary embodiment, there are illustrated in FIGS. 9 and 10 a 
cross-sectional view and a three-dimensional view of an inventive 
single-block dielectric ceramic filter 200, made of a plurality of the 
above-described re-entrant dielectric ceramic resonators, comprising a 
dielectric means 20 made of a dielectric ceramic material in the shape of 
a parallelepiped having a top surface 21, a bottom surface 22, and four 
outer side surfaces 23, (see FIG. 10) 24', (see FIG. 10) 25, 26, wherein 
the top and bottom surfaces 21, 22 are flat and parallel to each other. 
The dielectric means 20 is further provided with at least two cylindrical 
holes, e.g., 27, 28, each of the holes partially extending from the top 
surface 21 toward the bottom surface 22 thereof, each of the holes having 
an inner side surface 29 and an inner bottom surface 30, the inner bottom 
surface 30 being flat and parallel to the bottom surface 22 and each of 
the holes being disposed at a predetermined distance from one another. The 
dielectric ceramic material comprising the dielectric means 20 is 
characterized by a high dielectric constant, a low loss and a low 
temperature coefficient of the dielectric constant. The dielectric means 
20 is further provided with a first electrode means 32 comprised of a 
first conductive material, e.g., Ag or Cu, and a second electrode means 33 
comprised of a second conductive material, e.g., Ag or Cu, on the bottom 
surface 22 thereof, wherein the first electrode means 32 is located below 
one of the cylindrical holes thereof, e.g., 27, and the second electrode 
means 33 is located below a cylindrical hole, e.g., 28, other than the one 
under which the first electrode means 32 is located. 
Furthermore, the dielectric means 20 is completely covered, including the 
inner side surfaces 29 and the inner bottom surface 30, with a third 
conductive material 80' (see FIG. 9), e.g., Ag or Cu, with the exception 
of the portions surrounding the first and second electrode means 32, 33 to 
thereby form a pair of coupling/tuning capacitors between the first and 
second electrode means 32, 33 and the third conductive material 80 
covering the inner bottom surfaces 30 of the cylindrical holes located 
above the respective electrode means 32, 33, whereby a re-entrant 
resonator is produced for each cylindrical hole. 
Each of the re-entrant resonators 40, 41, 42, 43 has a different resonant 
frequency and when more than two such resonators are combined, it can be 
made into a filter. The filter response characteristics of the 
single-block dielectric ceramic filter 200 can be controlled and fine 
tuned by controlling the dimension of the dielectric means 20, the 
dimension and location of the cylindrical holes formed thereon and/or the 
capacitance of the coupling/tuning capacitors. 
In the single-block dielectric ceramic filter 200 the input and output 
signals are coupled to the first and second electrode means 32, 33, 
respectively, and the third conductive material 80 covering the dielectric 
means 20 is coupled to signal ground. 
Although the single-block dielectric ceramic filter 200 shown in FIGS. 9 
and 10 is comprised of four re-entrant dielectric ceramic resonators and a 
pair of coupling/tuning capacitors 32, 33 coupled to the input and output 
signals, any number of re-entrant dielectric ceramic resonators and 
coupling/tuning capacitors may be utilized, as shown in FIGS. 11 and 12, 
depending upon the filter response characteristics desired, with a 
condition that the number of coupling/tuning capacitors does not exceed 
the number of re-entrant dielectric ceramic resonators. FIGS. 11 and 12 
illustrate a cross-sectional view and a three-dimensional view of the 
inventive single-block dielectric ceramic filter shown in FIGS. 9 and 10 
with more than a pair of coupling/tuning capacitors. In FIGS. 11 and 12, 
the additional coupling/tuning capacitors are formed between the third 
conductive material 80 covering the inner bottom surface 30 of the 
cylindrical hole in the re-entrant dielectric ceramic resonator 41 and a 
fourth electrode material 91 partially covering the corresponding bottom 
surface 22, and between the third conductive material 80 covering the 
inner bottom surface 30 of the cylindrical hole in the re-entrant 
dielectric ceramic resonator 42 and a fifth electrode material 92 
partially covering the corresponding bottom surface 22. By controlling the 
dimension of the fourth and fifth electrode materials 91, 92, the filter 
response characteristics can be further fine-tuned. The first, second, 
third, fourth and fifth conductive materials 32, 33, 80, 91, 92 can all be 
made of the same material, e.g., Ag or Cu. 
As a second preferred embodiment, there are illustrated in FIGS. 13 and 14 
a cross sectional view and a three-dimensional view of an inventive 
dual-block dielectric ceramic filter 300, made of a multiplicity of the 
above-described re-entrant dielectric ceramic resonators, comprising a 
dielectric means 50 including a pair of dielectric bodies 51, 52, wherein 
each dielectric body is made of a dielectric ceramic material in the shape 
of a parallelepiped, having a top surface 53, a bottom surface 54 and four 
side surfaces 55, 56, 57, 58, the top and bottom surfaces 53, 54 being 
flat and parallel to each other. 
The dielectric ceramic material constituting the dielectric bodies 51, 52 
is characterized by a high dielectric constant, a low loss and a low 
temperature coefficient of the dielectric constant. Each of the dielectric 
bodies, e.g., 51, is further provided with at least two cylindrical holes, 
e.g., 59, 60, wherein each of the cylindrical holes, e.g., 59, partially 
extends from the top surface 53 toward the bottom surface 54 thereof 
thereby generating a corresponding inner side surface 70 and an inner 
bottom surface 61, the inner bottom surface 61 being flat and parallel to 
the bottom surface 54, each of the cylindrical holes being disposed at a 
predetermined distance from one another. Furthermore, the bottom surfaces 
54 of the dielectric bodies 51, 52 are joined together such that each of 
the-cylindrical holes, e.g., 59, in one of the dielectric bodies, e.g., 
51, is aligned with each of the cylindrical holes, e.g., 63, in the other 
dielectric body 52. In addition, the dielectric means 50 is provided with 
a first common electrode means 65, comprised of a first conductive 
material, e.g., Ag or Cu, disposed between a pair of aligned cylindrical 
holes, e.g., 59, 63, and a second common electrode means 66, comprised of 
a second conductive material, e.g., Ag or Cu, disposed between a pair of 
aligned cylindrical holes, e.g., 63, 64, other than the pair of aligned 
cylindrical holes with the first common electrode means 65 disposed 
therebetween. 
Furthermore, the dielectric means 50 is completely covered with a third 
conductive material 68 made of, e.g., Ag or Cu, including the bottom 
surface 54 of the dielectric bodies 51, 52 except the portions surrounding 
the first and second common electrode means 65, 66 to thereby form a 
plurality of coupling/tuning capacitors between the first common electrode 
means 65 and the third conductive material 68 covering the inner bottom 
surfaces 61, 61 of the pair of aligned cylindrical holes 59, 63 and the 
second common electrode means 66 and the third conductive material 68 
covering the inner bottom surfaces 61", 61"' of the pair of aligned 
cylindrical holes 60, 64, whereby a re-entrant resonator is produced for 
each cylindrical hole. In constructing a filter having the same number of 
poles, i.e., resonators, the dielectric ceramic filter constructed in the 
above described manner will have a width(B') which will be half the width 
of the single-block dielectric ceramic filter having the same number of 
poles. 
Each of the re-entrant dielectric resonators 81 82, 83, 84 has a different 
resonant frequency and when more than two such resonators are combined, it 
can be made into a filter. The filter response characteristics of the 
dual-block dielectric ceramic filter can be controlled and fine tuned by 
controlling the dimension of the dielectric bodies, hence the dielectric 
means, the dimension and location of the cylindrical holes formed thereon, 
and/or the capacitance of the coupling/tuning capacitors. 
In the dual-block dielectric ceramic filter the input and output signals 
are coupled to the first and second common electrode means 65, 66, 
respectively, and the third conductive material 68 covering the dielectric 
means 50 is coupled to signal ground. 
Although the dual-block dielectric ceramic filter 300 shown in FIGS. 13 and 
14 is comprised of four re-entrant dielectric ceramic resonators and the 
corresponding number of coupling/tuning capacitors, any number of 
re-entrant dielectric ceramic resonators may be utilized depending upon 
the filter response characteristics desired with a condition that the 
number of coupling/tuning capacitors does not exceed the number of 
re-entrant dielectric ceramic resonators. As an exemplary embodiment of 
another dual-block dielectric ceramic filter incorporating the present 
invention, there is illustrated in FIG. 15 a cross sectional view of a 
dual-block dielectric ceramic filter 500 comprising six re-entrant 
dielectric ceramic resonators 85, 86, 87, 88, 89, 90 and four 
coupling/tuning capacitors. 
As another exemplary embodiment of another dual-block dielectric ceramic 
filter incorporating the present invention, there is illustrated in FIG. 
16 a cross sectional view of the dual block ceramic filter 500 shown in 
FIG. 15 with an additional pair of coupling/tuning capacitors formed 
between the third conductive material 68 covering the inner bottom surface 
69 of the cylindrical hole 71 of the re-entrant dielectric ceramic 
resonator 86 and a third common electrode means 93 partially covering the 
corresponding bottom surface 54, and between the third conductive material 
68 covering the inner bottom surface 69' of the cylindrical hole 72 of the 
re-entrant dielectric ceramic resonator 89 and the third common electrode 
means 93 partially covering the corresponding bottom surface 54. The 
filter response characteristics can be further fine-tuned by controlling 
the dimension of the third common electrode means 93. The first common 
electrode means 65, the second common electrode means 66, the third 
conductive material 68 and third common electrode means 93 can be made of 
the same material. 
While the present invention has been shown and described with reference to 
the particular embodiments, it will be apparent to those skilled in the 
art that many changes and modifications may be made without departing from 
the spirit and scope of the invention defined in the appended claims.