1. Field of the Invention
The present invention relates to a dielectric filter and a dielectric duplexer using a dielectric block, a communication apparatus using the same, and a method of designing a dielectric resonator apparatus.
2. Description of the Related Art
There is provided a dielectric filter using a dielectric block which adopts a structure that a plurality of resonator holes are provided for the dielectric block, inner diameters of the resonator holes are made different partly, and the line impedance on an opening end side is different from the line impedance on a short-circuited end side. In particular, according to a dielectric filter as disclosed in Japanese unexamined Patent Application Publication No. 8-250904, sectional forms of portions whose inner diameters of resonator holes are different are non-similar and the central axis of small inner diameter is decentered from the central axis of a large inner diameter. According to a dielectric filter as disclosed in Japanese Unexamined Patent Application Publication No. 10-308604, the sectional form of a large inner diameter of the resonator hole is oval or elliptic and the long diameter direction is inclined to the alignment direction of the resonator hole.
According to the dielectric filters disclosed in Japanese Unexamined Patent Application Publications No. 8-250904 and No. 10-308604, it is possible to largely improve the free degree to design a resonance frequency, a coupling degree, and an attenuation frequency. If forming an input/output electrode, which causes an external coupling through the input/output electrode between the large inner diameter portion and an external part, to the dielectric block, it is also possible to largely improve the free degree of designing the external coupling.
However, in order to arbitrarily decide forms of large and small-diameter portions of the resonator hole and positions therebetween and obtain a desired characteristic of the dielectric filter, this causes a problem that the coupling between the resonators and the external coupling must be set simultaneously, and the designing method becomes a remarkably high level. If inclining the long diameter of the large-diameter portion to the alignment direction of the resonator holes, this also causes a problem that the size of the dielectric block is wholly large.
To overcome the above described problems, preferred embodiments of the present invention provide a dielectric filter, a dielectric duplexer, a communication apparatus, and a method of designing a dielectric resonator apparatus, capable of arbitrarily deciding the intensity of the external coupling without changing the coupling degree between the resonators and miniaturization.
One preferred embodiment of the present invention provides a dielectric filter, comprising: a dielectric block; a plurality of resonator holes aligned substantially in parallel in the dielectric block; an input/output means in association with the dielectric block; the resonator holes comprising a large-sectional area hole and a small-sectional area hole whose sectional area is smaller than that of the large-sectional area hole, the section of the large-sectional area hole being extended in the directions substantially vertical to an alignment direction and a central axis direction of the resonator holes; and the small-sectional area hole being electro-magnetically coupled to the input/output means.
According to the above described structure and arrangement, it is possible to narrow a pitch between central axes of large-diameter portions of adjacent resonator holes and miniaturize a dielectric filter. It is also possible to determine a coupling degree between resonators and intensity of an external coupling, almost independently, the design is simple, and a dielectric resonator apparatus such as a dielectric filter having a predetermined characteristic is obtained easily.
In the above described dielectric filter, the input/output means may be an excitation hole which is provided in the dielectric block. According to the above described structure and arrangement, an intensity of an external coupling can be decided by a position of a small-diameter portion in a resonator hole and a forming position of an excitation hole, so that the dielectric block formation enables a stable characteristic to be obtained easily.
Or, the input/output means may be an electrode which is disposed on an outer surface of the dielectric block. In this case, an intensity of an external coupling can be decided by a position of a small diameter in a resonator hole and a position of input/output electrodes on an outer surface of a dielectric block, so that the adjustment of a forming position of the input/output electrodes enables a predetermined external coupling intensity to be obtained easily.
Another preferred embodiment of the present invention provides a dielectric duplexer constituted by two sets of above described dielectric filters provided in the dielectric block.
Yet another preferred embodiment of the present invention provides a communication apparatus including the above described dielectric filter or the above described dielectric duplexer.
Yet another preferred embodiment of the present invention provides a method of designing a dielectric resonator apparatus, comprising: aligning a plurality of resonator holes substantially in parallel in a dielectric block, the resonator holes comprising a large-sectional area hole and a small-sectional area hole whose sectional area is smaller than that of the large-sectional area hole, the section of the large-sectional area hole being extended in the directions substantially vertical to an alignment direction and a central axis direction of the resonator holes; and determining an external coupling by a distance between input/output means and the small-sectional area hole by decentering a central axis of the small-sectional area hole from a central axis of said large-sectional area hole.