This invention relates to a di-electric bandpass filter using a di-electric resonator for selecting a desired wave and removing an undesired wave. The di-electric resonator has one central conductive hole (10) for resonance and more than one non-metallized coupling bores (2, 2) which are provided at the open faces of plurality of resonators (1, 1, . . . 1) which are disposed so as to contact the respective earth faces of each other. Neighboring coupling bores (2, 2) are connected by coupling metal pieces (4), whith output and input matching pins (3) inserted into either coupling bores or central holes. In this invention, it is possible to dipose the resonators freely as constructed in a bandpass filter using the space effectively so that a compact installation can be realized.

FIELD OF THE INVENTION 
This invention relates to a di-electric bandpass filter using a di-electric 
resonator for selecting a desired wave and removing an undesired wave. 
BACKGROUND OF THE INVENTION 
Heretofore, in a multi-stage or section bandpass filter a plurality of 
di-electric resonators are integrally formed as shown in FIG. 17. The 
materials of the resonators are (ZnSn)TiO.sub.4 series ceramics, 
BaO--PbO--Nd.sub.2 O.sub.3 --TiO.sub.2 series ceramics etc. This filter is 
small but has the following defects. 
1. Frequency adjustment due to the disorder of sintering (calcination) is 
required and for this purpose, hot side or earth side electrodes 13 or 14 
(FIG. 17) of copper or silver are provided on the open face of the 
resonator. These hot side or earth side electrodes 13 or 14 are trimmed by 
scraping or shaving with a laser light, by sandblasting or a by cutting 
with diamond cutter. But laser trimming is expensive; sandblasting needs 
setting or adjusting of trimming time according to the thickness of the 
electrode and the work is not constant, and diamond cutter blades become 
clogged or choked with metal scraped from the electrode and needs 
troublesome maintenance. 
2. Adjustment of bandpass width by changing the coupling between resonators 
is proposed by the following methods: that is, distance P between 
resonators as shown in FIG. 18(a) is changed, a recess 15 on the open face 
between resonators as shown in FIG. 18(b) is provided, recesses 16, 16 on 
the side faces between resonators as shown in FIG. 18(c) are provided, or 
a non-metallized bore 17 between resonators as shown in FIG. 18(d) is 
provided. However, these methods require long times for changing and 
adjusting the mold in which the resonator is molded. 
3. For resolving the above problems, another method is proposed in which a 
plurality of resonators 18, 18 . . . 18 are coupled by base plate 19, as 
shown in FIG. 19. In this method, a certain amount of clearance between 
resonators 18 and base plate 19 is required to avoid frequency and 
coupling relation aberrations. But the presence of base plate 19 and the 
clearance required make the device bulky so it cannot be small like a 
small bandpass filter of the integral shaped type. 
BRIEF DESCRIPTION OF THE INVENTION 
This invention eliminates these drawbacks. One object of this invention is 
to provide a di-electric bandpass filter in which the period of 
development is short and it is not necessary to change the resonator mold 
so that a low cost device may be produced which can also be adapted to 
various types of small scale products. 
Another object of the invention is to provide a small di-electric bandpass 
filter like a bandpass filter of the integral shaped type. 
Another object of the invention is to provide a di-electric bandpass filter 
in which frequency trimming of a single resonator is possible and the 
number of retrimming times in constructing a bandpass filter is reduced so 
that trimming costs are low and mass production yield rate is improved. 
Another object of the invention is to provide a di-electric bandpass filter 
in which each resonator is freely disposed so that a compact installation 
can be realized. 
The above and other objects, advantages and novel features of this 
invention will be more fully understood from the following detailed 
description and the accompanying drawings, in which like reference numbers 
indicate like parts throughout wherein:

DETAILED DESCRIPTION OF THE INVENTION 
FIG. 1(a)(b) are a perspective view and a cross-sectional view respectively 
of the first embodiment of the invention. FIG. 2(a)(b) are a perspective 
view and a cross-sectional view respectively of a di-electric resonator 
used in the first embodiment of the invention. 
In the first embodiment, one central conductive hole or bore 10 for 
resonance and two non-metallized coupling bores 2, 2 are provided at the 
opened faces of resonator 1 for constructing a coaxial di-electric 
resonator (see FIG. 2). Three resonators 1, 1, 1 are disposed so that 
their earth faces contact each other and neighboring coupling bores 2, 2 
are connected by metal coupling pieces 4. Matching pins 3 are inserted 
into opposite ends of coupling bores 2, 2 respectively. 
FIG. 3(a)(b) are a perspective view and a cross-sectional view respectively 
of a second embodiment of this invention. 
In the second embodiment, one central conductive hole or bore 10 for 
resonance and one or more non-metallized coupling bores 2, 2 are provided 
at the opened faces of resonator 1 for constructing coaxial di-electric 
resonator (See FIG. 2). Three resonators 1, 1, 1 are disposed so their 
earth faces contact each other and neighboring coupling bores 2, 2 are 
connected by metal coupling pieces 4. Matching pins 3 are inserted into 
central conductive holes or bores 10, 10 respectively at opposite ends 
through insulating resin sleeves 7, 7. In this case, first and last 
resonators 1, 1 have only one coupling bore 2 and central resonator 1 has 
two coupling bores 2 (see FIG. 3). 
Coupling bore 2 may pass through to the bottom face of resonator 1 the same 
as central conductive hole 10. Coupling bore 2 may be formed when molding 
resonator 1 with central conductive hole 10, therefore cost does not 
increase. 
FIG. 4(a) is an equivalent circuit of the first and second embodiments and 
FIG. 4(b) is a general concentrated constant circuit of the first and 
second embodiments. 
In said first embodiment shown in FIG. 1 output and input matching pins 3 
and metal coupling pieces 4 are secured with a resin adhesive. 
Alternatively, output and input matching pins 3 and metal coupling pieces 
4 may be coated with synthetic resin 5 as shown in FIG. 5 and inserted by 
pressure into the respective holes or bores. 
To provide a di-electric bandpass filter of the invention according to 
various modes demanded, at first the required frequency of a single 
resonator is determined according to the specification demanded. The open 
face of resonator 1 is then ground to adjust the frequency. The dimension 
of output and input matching pins 3 and metal coupling pieces 4 to match 
the coupling amount is then determined. In prior bandpass filters, 
consisting of resonator 18, 18 and coupling base plate 19 shown in FIG. 
19, trimming the resonator is required to adjust for aberrations of 
frequency due to fringe capacitance, but in this invention, less trimming 
is required because there is no change in the resonators open face. 
This invention does not need the long time of development process as in the 
prior methods shown in FIG. 18, because changing and adjusting the mold in 
which the resonator is molded is not required. Moreover, since the height 
of the metal coupling pieces 4 from the open face is about 1 mm in a 10 mm 
cubic resonator, the device of this invention is as small as that of FIG. 
18. Thus, this invention provides a di-electric bandpass filter having a 
short period of development and small size. 
FIG. 6 shows the third embodiment of a bandpass filter of two resonators 
constructed according to the invention. In the third embodiment, a metal 
plate 4 and output and input matching pins 3 are integrally pressed in 
with metal plate 6 as shown in FIG. 8. Then metal plate 4 and matching 
pins 3 with metal plate 6 are inserted into both ends of coupling bores 2, 
2 and central coupling bores 2, 2 of the two resonators 1, 1 respectively. 
The hatched portion shown in FIG. 8 is then removed by a cutter. 
FIG. 7 shows a fourth embodiment of a bandpass filter having two resonators 
constructed according to the invention. In this embodiment metal plate 4 
and output and input matching pins 3 are integrally pressed in with metal 
plate 6 as shown in FIG. 8. Matching pins 3 and metal plate 4 with metal 
plate 6 are then inserted into insulator sleeve 7 and coupling bore 2, 2 
of resonators 1, 1 respectively. The hatched part shown in FIG. 8 is then 
removed by a cutter. 
In these third and fourth embodiments, the amount of coupling is stabilized 
making the cost low, therefore, these embodiments are suitable for mass 
production. 
FIG. 9 shows a perspective view of the fifth embodiment of a bandpass 
filter having three resonators constructed according to the invention. In 
the fifth embodiment, indirect coupling bores 9, 9 are provided at the 
open faces of first and last resonators 1, 1 and are coupled by indirect 
coupling metal piece 8 to polarize the bandpass filter. 
FIG. 10 is a perspective view of a sixth embodiment of the invention of a 
bandpass filter constructed according to the invention having three 
resonators. In this embodiment, indirect coupling bores 9, 9 are provided 
at the open faces of the first and last resonators 1, 1 connected by 
indirect coupling platinum metal piece 8 and insulator sleeve 10 is 
provided to polarize the bandpass filter. 
FIG. 11(a) is an equivalent circuit of the fifth and sixth embodiments. 
FIG. 11(b) is a graph of the frequency characteristic curve of the fifth 
and sixth embodiments. 
In the fifth and sixth embodiments, it is possible to set transmission zero 
point f at a lower frequency than resonant frequency fo and to obtain the 
necessary attenuation with less resonator. The value of the resonant 
frequency fo can be controlled by adjusting the length of indirect 
coupling metal piece 8 inserted into the indirect coupling bores 9, 9. 
FIG. 12(a)(b)(c) are a seventh embodiment of the invention using multiple 
resonators, for example five, with a variety of their disposition. Each 
resonator has four coupling bores 2, 2, . . . 2 around the vicinity of the 
center of each open face. 
FIG. 13(a)(b)(c) is an eighth embodiment of the invention using multiple 
resonators, for example five, with a variety of disposition. Matching pins 
3 are inserted into central conductive holes 10, 10 of the resonators at 
opposite ends respectively, through resin insulator sleeves 7, 7. As 
explained above, it is possible to dispose the multiple resonators freely 
in a bandpass filter constructed according to the invention to use space 
effectively so a compact installation can be realized. 
FIGS. 14 and 15 are perspective views of embodiments of the invention of a 
bandpass filter constructed according to the invention used as an antenna 
duplexer. In these embodiments, for example ten resonators 1 are 
associated. At the open faces of intermediate resonators 1, for example, 
fourth and fifth resonators 1, antenna coupling holes 11, 11 are provided 
and the antenna coupling holes 11, 11 are coupled by antenna coupling 
piece 12. FIG. 16 shows an equivalent circuit of the device shown in FIGS. 
14 and 15. 
In these embodiments, a small antenna duplexer having features of the 
seventh and eighth embodiment as shown in FIGS. 12 and 13 can be achieved. 
Moreover, when indirect coupling holes are provided at the open face of 
the first and last resonators, and these indirect coupling holes are 
coupled by a coupling metal piece, as shown in the fifth and sixth 
embodiment shown in FIGS. 9 and 10, a high efficiency antenna duplexer can 
be obtained. 
This invention is not to be limited by the embodiment shown in the drawings 
and described in the description which is given by way of example and not 
of limitation, but only in accordance with the scope of the appended 
claims.