JPS6291001A - Strip line filter - Google Patents

Abstract

PURPOSE:To obtain a strip line filter with excellent attenuation characteristic by forming parts near the opening end of resonance electrodes opposed at an interval larger than other parts of the resonance electrodes. CONSTITUTION:In the resonance electrodes opposed at an interval among resonance electrodes 51-53, that is, the resonance electrodes 51, 53 of both ends, electrode parts 91, 93 at the opening end are formed to be of step type projected to both sides in the prolonged direction and have larger area than those of other parts of the resonance electrodes 51, 53. In this case, a coupling capacitor C13 produced between the resonance electrodes 51, 53 at an interval of an electrode is sufficiently smaller than coupling capacitors C12, C23 produced among the adjacent resonance electrodes 51, 52, 52, 53. Thus, the attenuation characteristic of the filter is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to an ink digital type or combline type stripline filter.

<Prior Art> FIG. 4 is a perspective view of a conventional ink digital type stripline filter, and FIG. 5 is a cross-sectional view taken along the cutting line ``---'' in FIG. 4. The filter shown in these figures has three stages of resonators provided on one dielectric substrate and functions as a bandpass filter.

A ground electrode I3 is formed over the entire surface of one main surface 12 of the dielectric substrate 11. Also, the other main surface 12. has a pair of guard electrodes 14. ．． A plurality of (three in the figure) resonant electrodes 151 to 153 each consisting of 14t and strip lines are formed. Each guard electrode 141.1
4t is formed by extending the ground electrode 13 from one main surface LL of the dielectric substrate 11 to the other main surface 122 via both side surfaces of the substrate 11, and the one main surface LL. are placed on both sides of the Each resonance electrode 151~
153 are guard electrodes 141 or 14.1, respectively. from,
Resonant electrode 15. which consists of a rectangular pattern of substantially the same size and shape extended toward the opposite side, and which extends from one guard electrode 14+. ．． 153 and the other guard electrode 1
Resonant electrodes 152 extending from 42 are alternately arranged in parallel. Each resonant electrode 15. ~153 resonant electrodes at the ends of the array 15. ．． External lead electrodes 181 and 182 are formed at 153 as input and output electrodes. Note that the dielectric substrate 11
These electrode patterns formed on the other main surface 122 of the dielectric substrate 11 are generally created by printing or ink photo-etching on the dielectric substrate 11.

<Problems to be Solved by the Invention> In a filter having such a configuration, as shown in FIG. 5, each of the resonant electrodes 15. 153 and the ground electrode 13, there is a capacitance C1o' + Cto' + C3
0' are formed, and adjacent resonant electrodes L51. L52
．． 15. .

A coupling capacitance CI 2' + 023' is formed between the input stage resonance electrode 15□ and the output stage resonance electrode 153 due to the miniaturization of the filter. A capacitance C13' may also occur between the two.

However, in this case, as in the conventional example, each resonant electrode 15
．． .about.153 are formed to have approximately the same size and shape, the coupling field ffl C+ 3' of every adjacent resonant electrode 1
51.152.1' Coupling capacitance Ca2' between 52 and 153
.

In view of these conventional problems, it is an object of the present invention to provide a stripline filter with excellent attenuation characteristics by reducing the coupling capacitance generated between resonant electrodes.

Means for Solving the Problems In the present invention, in order to achieve the above-mentioned object, out of a plurality of resonant electrodes formed on a dielectric substrate and consisting of strip lines, one resonant electrode facing the other is The resonant electrode is characterized by a structure in which a portion closer to the open end side is formed to have a larger area than other portions of the resonant electrode.

<Example> Hereinafter, the present invention will be described in detail based on an example shown in the drawings.

FIG. 1 is a perspective view of an ink digital stripline filter according to this embodiment. The filter shown in this figure is a bandpass filter having three stages of resonators, and includes a dielectric substrate 1. On one main surface 21 of this dielectric substrate 1, a ground electrode 3 made of silver or the like is formed over the entire surface. From this ground electrode 3, the other main surface 2. The electrodes are formed to extend to both sides of the guard electrodes 4, 4, . 42 is formed continuously with the ground electrode 3. Each guard electrode4. ,4. From there, a plurality of (three in the figure) resonant electrodes 51 to 53 are formed extending in parallel and alternately at predetermined intervals toward the guard electrodes 41 or 42 facing each other. Therefore, each of the resonant electrodes 5I to 53 has one end connected to the ground electrode 3 via the guard electrode 4I or 42 at the short-circuited end 6. ~63, and
It is composed of a strip line with the other end being open ends 71 to 73. Among these, one guard electrode 4. From the resonant electrodes 51.53 at both ends extending from the external lead electrodes 8.53 as input/output electrodes. ．． 82 are these resonant electrodes 5I,
It is formed to extend perpendicularly to 53.

Among the resonance electrodes 51 to 53, the resonance electrodes 5. ．． 5° open end electrode section 9. ．． 93 is formed in a step shape projecting on both sides in its extending direction, and is set to have a larger area than other parts of the resonant electrodes 51 and 53.

In this case, one resonant electrode 5. ．． The coupling capacitance C,3 generated between adjacent resonant electrodes 5. ．． 52.52
．． This value is sufficiently small compared to the coupling capacitance CI 2 + 023 generated between 53 and 53.

That is, in the stripline filter having the above configuration, the odd mode resonance frequency is generally higher than the even mode resonance frequency, so every resonance electrode 5. ．． When the coupling capacitance of each jump is changed by making the area on the open end side of 53 larger than the other parts, the resonance frequency of the odd mode will decrease more than the resonance frequency of the even mode. growing.

FIG. 2 is a diagram showing the resonance frequency-attenuation characteristic in this case in comparison with a conventional example. In this figure, the solid line A is the characteristic line of this embodiment, and the broken line B is the characteristic line of the conventional example. As is clear from this figure, in the case of this embodiment, the difference (f, -f2) between the odd mode resonance frequency C3 and the even mode resonance frequency ft is different from that of the conventional example (f, '
-f,').

This also means that every single resonant electrode 5. ．． The coupling capacitance CI3 between adjacent resonant electrodes 5. ．． 5. ．． 52.5
This indicates that the coupling capacitance between CI2 and C21 is sufficiently smaller than that between CI2 and C21.

Moreover, the resonant electrode 5. ．． Since the large area portion 53 is located on the open end side of the resonator, it has almost no effect on the no-load Q and can prevent deterioration of insertion loss.

In addition to the ink digital strip line filter as shown in the above embodiment, the present invention is also applicable to, for example, as shown in FIG. A plurality of (three in the figure) resonant electrodes made of strip lines are formed extending from the
It can also be applied to a so-called combline type stripline filter. In this case as well, 1
Jumping resonant electrode 5. ．． Open end portion 9 of 53. ．． 93 is formed to have a larger area than other electrode portions.

Further, in each of the embodiments described above, the resonant electrodes 5, . 5
．． Large area part9. ．． 93 is set to the open end,
The present invention is not limited to this, and the resonant electrode 5. , 53 closer to the open ends will produce the same effect. And the large area part 9. ．． 9. In addition to the stepped shape, any shape such as a circular shape can be selected.

Furthermore, the guard electrodes in each of the above embodiments are provided as necessary, and may be omitted. Furthermore, the manner of input/output coupling is not limited to the embodiments described above.

Further, in each of the above embodiments, a filter having three stages of resonators has been described, but the present invention can also be applied to a multistage filter having four or more stages.

In this case, for example, in an ink digital strip line filter, it is conceivable to set the open end side portions of both resonance electrodes extending on opposite sides to have a large area.

<Effects of the Invention> As described above, according to the present invention, one of the plurality of resonant electrodes made of strip lines formed on a dielectric substrate
Since the portions closer to the open ends of the resonant electrodes facing each other at intervals are formed to have a larger area than the other portions of the resonant electrodes, the coupling capacitance between the adjacent resonant electrodes is This can be made sufficiently smaller than the coupling capacitance between the filters, thereby improving the attenuation characteristics of the filter.

In addition, in this case, the shape change of the resonant electrode is performed closer to the open end where the current is less concentrated than the short-circuited end, so the shape change has almost no effect on the no-load Q. Deterioration of insertion loss can also be prevented.

[Brief explanation of drawings]

1 and 2 show an embodiment of the present invention, FIG. 1 is a perspective view of an ink digital strip line filter according to this embodiment, and FIG. 2 is a resonant frequency-attenuation diagram of this embodiment and a conventional example. FIG. 3 is a diagram showing quantitative characteristics. FIG. 3 is a perspective view of a combline type stripline filter according to another embodiment of the present invention. Fig. 4 is a perspective view of a conventional ink digital type strip line filter, and Fig. 5 is a perspective view of a conventional ink digital strip line filter.
It is a sectional view taken along the cutting line ■-■ in the figure. ■... Dielectric substrate, 21... One main surface of the dielectric substrate, 22... Other main surface of the dielectric substrate, 3... Earth electrode, 51-53... Resonant electrode, 6, ~63... Short-circuited end of the resonant electrode, 7, ~73... Open end of the resonant electrode, 91.93... Portion closer to the open end side.

Claims (1)

[Claims] (1) A dielectric substrate is provided, a ground electrode is formed on one main surface of the dielectric substrate, a plurality of resonant electrodes consisting of strip lines are formed in parallel on the other main surface of the dielectric substrate, and , in a strip line filter in which one end of each resonant electrode is connected to the ground electrode to form a short-circuit end, and the other end of the resonant electrode is an open end, among the resonant electrodes, one resonant electrode is opposed to the other resonant electrode; A strip line filter characterized in that a portion of the resonant electrode near the open end is formed to have a larger area than other portions of the resonant electrode.