Wave transmission lines and networks – Plural channel systems – Having branched circuits
Reexamination Certificate
1998-03-31
2001-05-22
Lee, Benny (Department: 2817)
Wave transmission lines and networks
Plural channel systems
Having branched circuits
C333S206000, C333S222000
Reexamination Certificate
active
06236288
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
The present invention relates to a dielectric filter, a dielectric duplexer, and a communication apparatus using the same.
2. Related Art of the Invention
There has been known a dielectric filter used for a mobile communication unit, which has a single dielectric block in which a plurality of resonator holes are provided. The resonator holes have large-diameter hole sections and small-diameter hole sections mechanically connected to each other, and also have step portions between the large-diameter hole sections and the small-diameter hole sections. Inner conductors are formed on the inner surfaces of the resonator holes, and an outer conductor is formed on almost all outer surfaces of the block except for one opening end face among both end faces where the resonator holes have openings. The inner conductors are electrically disconnected (open) at one opening end face (open-circuited end face) and electrically short-circuited (connected) at the other opening end face (short-circuited end face). A pair of input and output electrodes are formed on outer surfaces of the dielectric block without being connected to the outer conductor.
The center frequency of such a dielectric filter depends on the conductive-path length of the inner conductors from the open-circuited end face to the short-circuited end face. The length of the inner conductors is set to &lgr;/4, where &lgr; indicates the wavelength at the center frequency. The center frequency of the dielectric filter becomes lower as the conductive-path length increases, and the center frequency becomes higher as the conductive-path decreases. Therefore, to make the dielectric filter compact by reducing the size in the axial direction (the direction from the open-circuited end face to the short-circuited end face) of the resonator holes without changing the center frequency, it is necessary to increase the ratio of the diameter of the large-diameter hole sections to that of the small-diameter hole sections to make the conductive-path length of the inner conductors equal to that in the filter before being made compact.
Since the distance between the axes of adjacent resonator holes, which specifies the degree of coupling in the dielectric filter, is set to a certain length, however, the diameter of the large-diameter hole sections is limited. On the other hand, it is difficult to extremely reduce the diameter of the small-diameter hole sections in terms of the forming technologies of the dielectric filter.
In addition, since the conventional dielectric filter has a low impedance when viewed from the input and output electrodes, the filter needs to be connected to an external circuit through a capacitor or other elements. Therefore, a space required for installing a capacitor needs to be held and the capacitor needs to be soldered to the dielectric filter, which is complicated.
SUMMERY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a dielectric filter and a dielectric duplexer which can be easily made compact and which can be connected to an external circuit without using a capacitor or other elements, and a communication apparatus provided with the dielectric filter or the dielectric duplexer.
The invention provides dielectric filter or a dielectric duplexer, comprising: a dielectric block having two opposite end surfaces and an outer surface; resonator holes in said dielectric block extending between said end surfaces; inner conductors on inner surfaces of said resonator holes; an outer conductor on said an outer surface of said dielectric block; input and output electrodes on the outer surfaces of said dielectric block; at least one of said resonator holes comprising a large-sectional area portion and a small-sectional area portion connected to each other and providing a step portion therebetween; and at least one of a recessed portion and a protruding portion being provided at said step portion.
With the above configuration, since the recessed portions or the protruding portions are provided on the step portions, the conductive paths of the inner conductors at the step portions pass along the surfaces of the recessed portions or the protruding portions and become longer by that length. Therefore, when the dielectric filter and the dielectric duplexer are reduced in size in the axial direction of the resonator holes, the conductive-path lengths of the inner conductors do not change.
Another advantage of the above dielectric filter or dielectric duplexer is that the inner conductors on inner surfaces of said resonator holes may be directly connected to said input and output electrodes.
When an inner conductor is directly connected to an input and output electrode, external coupling Qe usually becomes too strong. However, due to large capacitances generated between the inner conductors and the outer conductor, and between the input and output electrodes and the outer conductor by providing the recessed portions or the protruding portions on the step portions, the impedance viewed from the input and output electrodes becomes low, external coupling Qe becomes weak, and it becomes unnecessary to use a capacitor or other elements, which are conventionally required for connection to an external circuit. Thus, it becomes unnecessary to keep a space required for installing a capacitor and to perform complicated soldering between the capacitor and the dielectric filter or the dielectric duplexer.
In the above dielectric duplexer, another advantage is that the shape of at least one first resonator hole constituting the transmission filter may differ from that of at least one second resonator hole constituting the receiving filter. Or, at least the transmission filter may comprise at least two first resonator holes having different shapes from each other, or at least the receiving filter comprise at least two second resonator holes having different shapes from each other.
With the above configuration, the degree of freedom in designing the dielectric duplexer is increased.
The present invention further provides a communication apparatus comprising the above described dielectric filter or dielectric duplexer.
The apparatus can be made compact by the use of the above dielectric filter or the above dielectric duplexer having a short axial length of resonator holes. In addition, a capacitor or other elements which are conventionally required for connection to a dielectric filter or a dielectric duplexer can be omitted.
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Lee Benny
Murata Manufacturing Co. Ltd.
Ostrolenk Faber Gerb & Soffen, LLP
Summons Barbara
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