JPH03205903A - Polar type low-pass filter - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a low-pass filter used in the microwave band, etc. More specifically, the present invention provides a grounding capacitance between a conductor film and a side earth electrode in through holes arranged in parallel in a dielectric block, an opposing capacitance between conductor films in adjacent through holes,
This is a polarized low-pass filter that has an attenuation pole that blocks signals at specific frequencies using the inductance of the coil. This filter is useful, for example, in microwave band mobile communications, satellite communications, and the like.

[Prior Art] Conventional low-pass filters used in the microwave band generally have a stripline structure. This is a structure in which multiple electrodes are formed on the surface of a substrate made of alumina, etc., a ground electrode is formed on the entire surface of the substrate, and the electrodes on the surface are connected with strip lines. A grounded capacitance (C-Kibun) is formed between the electrodes on both the front and back sides of the board, and the strip line that connects the surface electrodes becomes an inductance (L-Kibun), and the LC circuit network created by them achieves low-pass filter characteristics. ing. Grounding capacitance changes depending on the dielectric constant and thickness of the substrate and electrode area, and inductance changes depending on the width and length of the conductor pattern. [Problem to be solved by the invention] In order to miniaturize the above-mentioned low-pass filter, it is conceivable to use a material with a high dielectric constant as the substrate. Using a substrate with a high dielectric constant can reduce the area of both ground capacitance and inductance, but since these are manufactured by screen printing, variations in characteristics are determined by printing accuracy, and tedious work is required to adjust the electrode area.

Note that when the inductance strip line becomes thinner, Q
However, this problem can be improved by using a coil wound with copper wire.

Furthermore, in order to provide polarized feedback with the above-mentioned filter, it is necessary to provide a separate electrode, which increases the number of man-hours and costs in design and manufacturing, and also has the drawback of increasing the size of the substrate. SUMMARY OF THE INVENTION An object of the present invention is to eliminate the drawbacks of the prior art as described above, and to provide a low-pass filter that can be made smaller and has a polarized feedback circuit. [A Thousand Steps to Solve the Problems] The present invention, which can achieve the above object, comprises arranging three or more through holes in parallel in a dielectric plate and forming a conductive film on the inner surface of each through hole. It is also a polarized low-pass filter in which a conductive film is formed on the side surface of a dielectric block that does not have through-holes to serve as a ground electrode, and the conductive films in each through-hole are sequentially connected by coils. [Operation] A ground capacitance is formed between the conductor film in the through hole and the ground electrode on the side surface of the dielectric block, and inductance is generated by the coil coupling between the conductor films in the through hole. Basic low-pass characteristics can be obtained with a four-terminal LC network in which a plurality of these inductance elements are connected in series and each grounded capacitance element is connected in parallel between the interconnection points of the inductance elements. In addition, opposing capacitance occurs between the conductor films on the inner surfaces of adjacent through holes, and this and the inductance of the coil create a parallel resonant circuit, creating an attenuation pole that blocks passage.
Since this attenuation pole is formed close to the passband, the passband becomes steeper and the filter characteristics are improved. [Embodiment] Fig. 1 is a perspective view showing an embodiment of a polarized low-pass filter according to the present invention, Fig. 2 is a sectional view thereof, and Fig. 3 is an equivalent circuit IIIi diagram thereof. The dielectric block lO made of a high dielectric constant material such as barium titanate has a convex shape with both ends of a rectangular parallelepiped being lowered one step. Three through holes 12a. ..., 12C is formed. The three through holes 12a, . . . 12C all have the same hole diameter, but the central through hole 12b is long, corresponding to the shape of the dielectric prosock 10, and the through holes 12a at both ends are long.
．． 12c is short. Each through hole 12a. ..., 12C, a conductor film l4 is formed on the inner surface, and a dielectric bronch 10
A conductive film is formed on the side surface (the surface where the through holes 12a, . . . , 12c are not opened) to form the ground electrode 16 (
(See Figure 2). There is no conductive film on the bottom of the dielectric block. Then, the coil l8 is sequentially inserted between the conductor films 14 in each through hole.
Connect with . Conductor film 14 in through holes 12a and 12c at both ends
is connected to the input/output connector 22 by a lead wire 20. In order to make the drawing easier to understand, parts where there is no conductor film and the dielectric base is exposed are shown as small dots. Dielectric blocks are manufactured by pressing and burning powder. The conductive film may be formed by baking silver paste, for example. In FIG. 3, L+, Lx indicate the inductance of the coil 18, Ct, Cs . Cs represents the grounding capacity formed by the conductor film 14 and the earth electrode 16 on the inner surface of the through holes 12a, .
Greater than s. Here, in order to achieve desirable low-pass filter characteristics, Cz is made approximately twice as large as CI and C. Therefore, the height of the dielectric block is designed so that the center part is approximately twice as high as the both ends. It represents the capacity. This opposing capacitance Ca
．． Cs and the inductances L+ and Lx of coil 1B create parallel resonance, creating an attenuation pole that blocks passage. Figure 4 shows an example of filter characteristics obtained by such a low-pass filter. Figure A shows a characteristic with a strong polarity, B shows a characteristic with a weak polarity, and C shows a characteristic with a moderate amount of polarity. These are the opposing capacitance C
a, Cs and inductance Ll. L. selection of,
It can be adjusted by mutual inductance M between both coils 18, etc.

5 to 7 show other embodiments of the present invention. In the example shown in FIG. 5, the dielectric block 30 is a simple rectangular parallelepiped, and the central through hole 32b is replaced by through holes 32a and 32c at both ends.
, and the distance between the conductor film in the center through-hole and the ground electrode 36 is made closer to increase the grounding capacity. The example shown in FIG. 6 has three through holes 42a,...42c.
Although the hole diameters are the same, constrictions (narrow width portions) 43 are provided on both sides of the central portion of the dielectric block 40 to shorten the distance between the conductor film of the central through hole 42b and the ground electrode 46 in its vicinity. This increases the grounding capacity. Instead of changing the hole diameter of the through hole or changing the shape of the dielectric block, the shape of the side earth electrode may be changed as shown in FIG. By reducing the size of the ground electrodes 56 near the through holes 52a and 52c located at both ends, the ground capacity of those areas is reduced, and the ground capacity of the central through hole 56b is relatively increased. In this case, the dielectric bronc 50 may be a simple rectangular parallelepiped. Although the preferred embodiments of the present invention have been described in detail above, the present invention is not limited to such a structure. The number of through holes may be four or more, and the conductor films may be connected by a coil. [Effects of the Invention] As described above, the present invention includes three or more through holes arranged in parallel in a dielectric block, a conductive film formed on the inner surface of the through holes, and a grounding capacitance between the outer ground electrode and the outer ground electrode. Since the conductor films in the through holes are successively connected by coils, they can equivalently form an LC network similar to the one described above, and achieve the desired low-pass filter characteristics. In addition, a polarized feedback circuit is added due to the opposing capacitance generated between the conductor films of adjacent through holes and the inductance of the coil, and the attenuation pole for pass blocking can be formed near the pass band, resulting in a steep pass band and improved filter characteristics. Ru. Furthermore, the filter of the present invention is a coaxial type, unlike the conventional flat plate type, and can be made smaller because it can use materials with a high dielectric constant. This reduces the mounting area and improves the mounting density on circuit boards, etc.

[Brief explanation of drawings]

FIG. I is a perspective view showing one embodiment of a polarized low-pass filter according to the present invention, FIG. 2 is a sectional view thereof, FIG. 3 is an equivalent circuit diagram thereof, and FIGS. C is a graph showing an example of the characteristics of the low-pass filter of the present invention, and FIGS. 5, 6, and 7 are perspective views showing other embodiments of the present invention, respectively. 1 0
...Dielectric board 07, 12a, 12b, 12c...
・Through hole, 14... Conductor film, 16... Earth electrode,
18...Coil.

Claims (1)

[Claims] 1. Three or more through holes are arranged in parallel in a dielectric block, and a conductive film is formed on the inner surface of each through hole, and a conductive film is formed on the side surface of the dielectric block where no through holes are open to serve as a ground electrode. , a polarized low-pass filter in which the conductor membranes of each through hole are sequentially connected by coils.