Dielectric Filter Having a Non-Conductive Region in Each Resonator Hole

1. Field of the Invention

The present invention relates to a dielectric filter of a type having first and second internally electroconductive holes defined therein in a juxtaposed fashion by depositing an electroconductive coating.

2. Description of the Prior Art

A prior art dielectric filter is shown in an exploded view in FIG. 6. The prior art dielectric filter shown in FIG. 6 comprises a generally parallelepiped block 61 of dielectric material, first and second coupling pins 62 and a metallic casing 63. The dielectric block 61 has first and second internally conductive holes 61a and 61b defined therein so as to extend parallel to each other and each having an internal surface lined with an electroconductive material, and also has a coupling hole 61c defined therein at a location intermediate between the first and second internally conductive holes 61a and 61b. In this dielectric filter, a coupling capacitance is defined between the coupling pins 62 and the internally conductive holes 61a and 61b.

Also, as shown in FIG. 7 in an exploded representation, in order to render the dielectric filter to have a polarity, internally conductive holes 71a and 71b have to be coupled with each other through a coupling hole 72a; internally conductive holes 71b and 71c have to be coupled with each other through a coupling hole 72b; internally conductive holes 71c and 71d have to be coupled with each other through a coupling hole 72c; and internally conductive holes 71d and 71e have to be coupled with each other through a coupling hole 72d. For the adjustment of each coupling degree, electroconductive patterns 73 are formed on a front surface of the dielectric block where the various holes 71a to 71e and 72a to 72d are opened towards the outside. The frequency of each resonator having the internally conductive holes 71a to 71e is adjusted by applying required electroconductive patterns 74 at the front surface of the dielectric block. The polarity of the dielectric filter can be obtained by forming a coupling capacitance exhibited by connecting the internally conductive holes 71b and 71d with each other through associated coupling pins 75 and an electrode conducting on a printed circuit board (PCB) 76. Alternatively, it is also known that, as is the case with the dielectric filter shown in FIGS. 8(a) and 8(b), internally conductive holes 81a and 81b, internally conductive holes 81b and 81c internally conductive holes 81c and 81d, and internally conductive holes 81d and 81e may be coupled with each other through respective coupling holes 82a, 82b, 82c and 82d, and individual resonators are designed to have a varying length defined by providing steps on a short-circuiting surface 84 so that each of the resonators can have a design resonance frequency.

In the prior art dielectric filters discussed above and shown in FIGS. 6, 7, 8(a), 8(b), since the coupling between each pair of neighboring resonators is determined by the coupling hole, the dielectric filter as a whole has a varying shape for each type, that is, each resonance frequency and/or each bandwidth and, therefore, the use of different molds is required for each type of the dielectric filters. In terms of manufacture, the presence of the coupling holes which are non-plated areas makes it difficult to mass-produce electrodes by the use of an electroless plating technique. Due to the problem associated with the mass-productivity, the prior art dielectric filter are disadvantageous in terms of cost. Also, due to the presence of the coupling holes, the dielectric block used in any of the prior art dielectric filters tends to become bulky and this is in contradiction to the demands for miniaturization of the dielectric filter.

The present invention has been devised to alleviate the above discussed problems inherent in the prior art dielectric filters and is intended to provide an improved dielectric filter of a type which is compact in size and which can be mass-produced at reduced costs while exhibiting an improved filtering characteristic and a favorable shield property.

To this end, the dielectric filter according to the present invention comprises a dielectric block having a plurality of through-holes defined therein so as to extend parallel to each other and spaced a predetermined distance from each other. Each through-holes has a peripheral wall lined with an electroconductive material to provide a respective hole electrode. This hole electrode has an isolation region dividing such hole electrode into two separate electrode components which are electrically connected with an electroconductive layer formed on an entire surface of the dielectric block. The dielectric filter also comprises at least one terminal member provided within one of the through-holes and coupled through a dielectric element separate from the dielectric block.

According to the present invention, due to the presence of a stray capacitance defined by each of the isolation regions in the hole electrodes, resonators having the respective through-holes can be coupled with each other. Moreover, the employment of the isolation regions eliminates the need to use coupling holes as required in the prior art dielectric filter, making it possible to manufacture the dielectric filter in a compact size and also to facilitate formation of both the internal and external conductors in the dielectric filter. Therefore, the present invention is effective to provide an inexpensive dielectric filter which can be mass-produced.

Also, any possible leakage of an electric field in the dielectric filter is considerably suppressed, allowing the dielectric filter of the present invention to exhibit an improved filtering characteristic.

This and other objects and features of the present invention will become clear from the following description of preferred embodiments thereof with reference to the accompanying drawings, in which like parts are designated by like reference numerals and in which:

FIG. 1 is an exploded view of a dielectric filter according to a first preferred embodiment of the present invention;

FIG. 2 is a transverse sectional view of a dielectric block used in the dielectric filter shown in FIG. 1;

FIG. 3 is an exploded view of the dielectric filter according to a second preferred embodiment of the present invention;

FIG. 4 is a transverse sectional view of a dielectric block used in the dielectric filter shown in FIG. 3;

FIG. 5 is an exploded view of the dielectric filter of a comb-line coupling type;

FIG. 6 is an exploded view of one type of the prior art dielectric filter;

FIG. 7 is an exploded view of another type of the prior art dielectric filter;

FIG. 8(a) is a perspective view of the dielectric block used in a further type of the prior art dielectric filter; and

FIG. 8(b) is an exploded view of the prior art dielectric filter of a type using the dielectric block shown in FIG. 8(a).

Referring first to FIGS. 1 and 2, a dielectric filter according to a first preferred embodiment of the present invention shown therein comprises a dielectric block 1 of a generally parallelepiped configuration having generally rectangular front and rear surfaces opposite to each other, a pair of coupling pins 2 and a metallic casing 3. The dielectric block 1 has first and second internally conductive through-holes 1a and 1b of a predetermined diameter defined therein so as to extend parallel to each other and spaced a required distance from each other, each of said through-holes 1a and 1b having its opposite ends opening on the front and rear surfaces of the dielectric block 1.

Each of the through-holes 1a and 1b has a peripheral wall surface lined with an electroconductive material such as, for example, gold, silver or copper to define a respective hole electrode. On the other hand, the illustrated dielectric block 1 has six surfaces including the front and rear surfaces referred to above, all of said six surfaces deposited with an electroconductive material such as, for example, gold, silver or copper to provide an external conductor or electrode 1c.

The hole electrodes inside the respective internally conductive through-holes 1a and 1b cooperate with the external conductor 1c to define two resonators. Accordingly, an electroless plating can easily be effected to the six surfaces of the dielectric body 1 and the peripheral wall surfaces defining the through-holes 1a and 1b to form the respective electrodes, i.e., the hole electrodes and the external electrode 1c, thereby making it possible to mass-produce the dielectric filters.

The hole electrode inside each of the through-holes 1a and 1b is partially removed at a location generally intermediate of the length of the respective through-hole to define a circumferentially extending isolation region 1ao or 1bo by which the respective hole electrode is divided into two electrode components. The resonators are coupled with each other by means of stray capacitances Cs exhibited by the respective isolation regions 1ao and 1bo.

The coupling pins 2a and 2b are coaxially inserted into the respective through-holes 1a and 1b through associated inserts 2ao and 2bo each made of synthetic resin, so that respective coupling capacitances can be formed between the coupling pins 2a and 2b and the hole electrodes inside the through-holes 1a and 1b.

The metallic casing 3 is mounted on the dielectric block 1 so as to fit over the front surface thereof with the coupling pins 2a and 2b exposed to the outside.

According to the first preferred embodiment of the present invention shown in and described with reference to FIGS. 1 and 2, the presence of the isolation regions 1ao and 1bo in the hole electrodes inside the through-holes 1a and 1b eliminates the need to use the coupling hole which has hitherto been required in the prior art dielectric filter, and therefore the dielectric filter of the present invention can be made compact in size by a volume corresponding to that occupied by the coupling hole in the prior art dielectric filter.

The details of each of the isolation regions 1ao and 1bo defined inside the respective through-holes 1a and 1b will now be described with particular reference to FIG. 2 which illustrates a transverse sectional view of the dielectric block 1. Formation of each isolation region 1ao or 1bo is effected after the respective through-hole 1a or 1b has been electrolessly plated to form the hole electrode. Each isolation region 1ao or 1bo can readily be formed in any suitable manner, for example, by cutting or grinding that portion of the hole electrode inside the respective through-hole 1a or 1b where the isolation region is desired.

The position and the width of the isolation region 1ao or 1bo inside the respective through-hole 1a or 1b are determinative of the associated stray capacitance Cs and hence determinative of the coefficient of coupling between the resonators. It is to be noted that, since in the dielectric filter of the present invention an electric field within the dielectric block 1 leaks only through the isolation regions 1ao and 1bo, the dielectric filter of the present invention exhibits an excellent shield property as compared with the prior art dielectric filter utilizing the coupling hole.

Where a suitable block of, for example, ceramics having the internally conductive through-holes 1a and 1b defined therein so as to have a predetermined diameter and a predetermined distance of spacing therebetween, both of which are determined in consideration of the bandwidth, is molded into the parallelepiped configuration by the use of a mold so as to have a substantial length from the front surface to the rear surface and is subsequently cut to provide the dielectric body 1 of a size required to permit it to exhibit a required resonance frequency, any change desired of the resonance frequency and/or the bandwidth can be accommodated by properly selecting the position and the width of one or both of the isolation regions 1ao and 1bo to adjust the respective stray capacitances Cs. Thus, it will readily be seen that one and the same mold can be employed to make dielectric filters of different filtering characteristics, making it possible to enhance the efficiency of manufacture and to reduce the cost of manufacture.

While the dielectric filter shown in and described with reference to FIGS. 1 and 2 is of a type utilizing two resonators, the number of the resonators may not be always limited to two such as shown, but may be more than two. Also, the size and the dielectric constant of the dielectric block 1 and those of any one of the coupling pins 2 are not limited to those shown and described.

A different embodiment of the dielectric filter of the present invention in which five resonators are employed is shown in FIGS. 3 and 4. Referring now to FIGS. 3 and 4, the dielectric filter shown therein comprises a dielectric block 11 of a generally parallelepiped configuration having generally rectangular front and rear surfaces opposite to each other, four coupling pins 2 and a metallic casing 3. The dielectric block 11 has first to fifth internally conductive through-holes 11a to 11e of a predetermined diameter defined therein so as to extend parallel to each other and spaced a required distance from each other, each of said through-holes 11a to 11e having its opposite ends opening on the front and rear surfaces of the dielectric block 11. Each of the through-holes 11a to 11e has a peripheral wall surface lined with an electroconductive material such as, for example, gold, silver or copper to define a respective hole electrode.

As is the case with the hole electrodes inside each of the internally conductive through-holes employed in the dielectric filter according to the foregoing embodiment of the present invention, the hole electrode inside each of the through-holes 11a to 11e is partially removed at a location generally intermediate of the length of the respective through-hole to define a circumferentially extending isolation region 11ao to 11eo by which the respective hole electrode is divided into two electrode components. The resonators are coupled with each other by means of stray capacitances Cs exhibited by the respective isolation regions 11ao to 11eo.

Again as is the case with the dielectric filter according to the foregoing embodiment, the coefficient of coupling between the resonators and the resonance frequency of each resonator can be adjusted by properly selecting the position and the width of the isolation regions 11ao to 11eo.

A printed circuit board 4 is used to connect coupling pins 2b and 2c together to define a capacitance coupling with which the dielectric filter can have a polarity.

It is to be noted that, although in any one of the foregoing preferred embodiments of the present invention, the resonators are oriented in the same direction, the present invention can be equally applied to the type utilizing an inter-digital coupling or a type employing a comb-line coupling that, as best shown in FIG. 5, utilizes a dielectric substrate for connection with the dielectric block.

Referring to FIG. 5, the dielectric filter having such a polarity as shown therein comprises a dielectric resonator 12 and a dielectric substrate 5 coupled with the dielectric resonator 12 to provide the dielectric filter. The dielectric resonator 12 has all surfaces, except for the surface thereof which confronts the dielectric substrate 5, lined with an electroconductive material and also has a plurality of, for example, three, internally conductive through-holes 12a, 12b and 12c defined therein, each of said through-holes 12a to 12c having a peripheral wall surface lined with an electroconductive material to provide a respective hole electrode. As is the case with any one of the foregoing embodiments of the present invention, each of the hole electrodes inside the through-holes 12a to 12c is formed with a circumferentially extending isolation region 12ao, 12bo or 12co through which the resonators are coupled while eliminating the need to use the coupling hole or holes hitherto required.

The dielectric substrate 5 has all surfaces, except for the surface thereof which confronts the dielectric resonator 12, lined with an electroconductive material. The surface of the dielectric substrate 5 facing the dielectric resonator 12 has patterned thereon capacitor electrodes 51 and inductor electrodes 52 each connecting the neighboring capacitor electrodes 51 together. In a condition in which the dielectric resonator 12 and the dielectric substrate 5 are coupled in face-to-face fashion with each other, the capacitor electrodes 51 are connected by capacitance coupling (comb line coupling) with the respective hole electrodes inside the through-holes 12a to 12c.

With the dielectric resonator 12 coupled with the dielectric substrate 5 in the manner described above, a pattern of the electrodes formed on that surface of the dielectric substrate 5 is conductive to an input/output electrode 53 which is formed by the use of, for example, a printing technique so as to extend therefrom to a portion of the surface of the dielectric substrate 5 which is opposite to that surface where the patterned electrodes are formed. This input/output electrode 53 is utilized for interfacing the patterned electrodes on the dielectric substrate 5 with an external electric circuit. Due to the presence of a part of the input/output electrode 53 on that opposite surface of the dielectric substrate 5, mounting of the dielectric filter according to the present invention onto the printed circuit board can be readily and assuredly accomplished.

Although the present invention has been described in connection with the preferred embodiments thereof with reference to the accompanying drawings, it is to be noted that various changes and modifications are apparent to those skilled in the art. Such changes and modifications are to be understood as included within the scope of the present invention as defined by the appended claims, unless they depart therefrom.