JPS6243901A - Filter - Google Patents

Abstract

PURPOSE:To miniaturize a filter by connecting an end of a resonance electrode to an earth electrode via a through hole provided to a dielectric base while being folded to the opposite face of the base so as to prolong substantially the length of the resonance electrode thereby lowering the resonance frequency. CONSTITUTION:The rear face of the dielectric base 1 is provided with a folded electrode 8 corresponding to each resonance electrode on the surface and connected to the earth electrode 9, and the end of each folded electrode 8 and the resonance electrode corresponding thereto is connected by an electrode 10 formed in the through hole 7. Since the length of the resonance electrode 6 is the length of itself L2 added by the length L3 of the folded electrode 8 and results in being longer substantially, the resonance frequency is lowered. Thus, the length L2 of the resonance electrode 6 is shortened far more than lambda/4 by adjusting the length L3 of the folded electrode 8. Thus, the entire filter is miniaturized easily.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a comb-type or interdigital-type filter, and particularly to means for miniaturizing the filter.

[Conventional technology]

Conventionally, a comb-type or interdigital type filter has been used in a so-called microstrip line band-pass filter.

For example, FIG. 3 shows an example of a comb-shaped filter, in which a ground electrode 5 is formed on the entire back surface of a rectangular plate-shaped dielectric substrate 1, and the ground electrode 5 extends from the side surface of the dielectric substrate 1 to the surface of the dielectric substrate 1. It has been extended to the periphery. Further, on the surface of the dielectric substrate 1, there are formed a plurality of elongated resonant electrodes 2 extending in a comb shape from the ground electrode 5, and two input/output electrodes 3 along the resonant electrodes 2 at both ends. .

[Problem that the invention seeks to solve]

In the above-mentioned filter, a line with a length Ll of λ/4 is used as the resonant electrode 2, so the length Ll becomes considerably long for a filter with a low frequency, for example, a MHz band.
There is a problem that the overall shape becomes larger and the cost also becomes higher.

Furthermore, since the ground electrode 5 must also be formed on the side surface of the dielectric substrate 1, the assembly process is time-consuming.
This will further increase the cost.

Exactly the same problem exists in the case of the interdigital type.

Therefore, the main object of the present invention is to reduce the size of the filter as described above.

[Means for solving problems]

The filter of the present invention is characterized in that the end of the resonant electrode is connected to the ground electrode by being folded back on the opposite side of the substrate via a through hole provided in the dielectric substrate.

[Effect]

By folding back the ends of the resonant electrode, the length of the resonant electrode is substantially increased and the resonant frequency is lowered.

Therefore, the filter can be made smaller.

〔Example〕

FIG. 1(A) is a plan view showing a comb filter according to an embodiment of the present invention, FIG. 1(B) is a back view thereof, and FIG. 1(C) is a line C-C of the comb filter. FIG.

Components equivalent to those in FIG. 3 are given the same reference numerals and their explanations will be omitted.

In this embodiment, each end of the four stages of resonant electrodes 6 is connected to a ground electrode 9 by being folded back on the back side of the substrate 1 via a through hole 7 provided in the dielectric substrate 1. That is, a folded electrode 8 connected to a ground electrode 9 and corresponding to each resonance electrode 6 on the front surface is provided on the back surface of the dielectric substrate 1, and the ends of each folded electrode 8 and the corresponding resonance electrode 6 are connected to a through hole 7. Connect with the electrode 10 formed inside °ζ
There is.

In the above filter, the length of the resonant electrode 6 is substantially
Since the length becomes the sum of the length of the folded electrode 8 and the length of the folded electrode 8, the resonant frequency decreases. An equivalent circuit of a portion corresponding to FIG. 1(C) in this case is shown in FIG. In other words, in the resonant electrode 6, the part where the electric field is strong is the part on the opposite side of the through hole 7 (that is, the part near the open end), so the capacitance C hardly changes even if the folded electrode 8 is provided. On the other hand, since the part where the magnetic field is strong is on the side where the through hole 7 is (i.e. the part near the short-circuit end),
The inductance increases approximately in proportion to the length, lowering the resonant frequency. Therefore, the length L of the resonant electrode 6
2 can be made considerably shorter than λ/4 by adjusting the length of the folded electrode 8, thereby easily downsizing the entire filter. Moreover, since the materials used are also reduced, the cost of the filter can also be reduced.

Further, as a method of forming the electrodes 10 etc. in the through holes 7, for example, a dielectric substrate 1 with holes is plated with an electrode material on the entire surface, etched to form a predetermined electrode pattern, and then the dielectric substrate 1 is plated with an electrode material. All you have to do is cut the dielectric substrate 1, and there is no need for the conventional process of canting the dielectric substrate 1 and then applying an electrode (earth electrode) to its side again.This improves mass productivity and improves productivity. Cost reduction becomes possible.

Although the above description has been made using a comb type as an example, the present invention can also be applied to an interdigital type, and it goes without saying that the same effects as in the case of a comb type can be obtained in that case as well.

(Effects of the Invention) As described above, according to the present invention, it is possible to reduce the size of the filter, and it is also possible to reduce costs in terms of both materials and manufacturing processes.

[Brief explanation of the drawing]

FIG. 1(A) is a plan view showing a comb filter according to an embodiment of the present invention, FIG. 1(B) is a back view thereof, and FIG. 1(C) is a line C-c of the comb filter. FIG. FIG. 2 is an equivalent circuit diagram of the portion shown in FIG. 1(C). FIG. 3(A) is a plan view showing an example of a conventional comb filter, and FIG. 3(B) is a sectional view taken along the line BB.

Claims (1)

[Claims] (1) In a comb-shaped or interdigital type filter in which a resonant electrode is formed on one main surface of a dielectric substrate and a ground electrode is formed on the other main surface, the end of the resonant electrode is formed through a through hole in the dielectric substrate. A filter characterized in that it is folded back on the opposite side of the substrate and connected to a ground electrode via the board.