JPH0736482B2 - Polarized low-pass filter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to a low-pass filter used in a microwave band or the like. More specifically, the present invention provides a grounding capacitance between a conductor film in a through hole and a side surface ground electrode arranged side by side in a dielectric block, an opposing capacitance between conductor films in adjacent through holes, and
It is a polar low-pass filter that has an attenuation pole that blocks a signal of a specific frequency due to the inductance of the coil.

This filter is useful, for example, in mobile communication in the microwave band, satellite communication, and the like.

[Prior Art] As a conventional low-pass filter used in the microwave band, a stripline structure is generally used. This is a structure in which a plurality of electrodes are formed on the front surface of a substrate made of alumina or the like, a ground electrode is formed on the entire back surface, and the front surface electrodes are connected by strip lines. A ground capacitance (C component) is formed between the electrodes on both the front and back sides of the substrate, and the strip line connecting the front electrodes serves as an inductance (L component), and the LC circuit network by them realizes a low-pass filter characteristic. .

The ground capacitance changes depending on the dielectric constant and thickness of the substrate and the electrode area, and the inductance changes depending on the width and length of the conductor pattern.

[Problems to be Solved by the Invention] In order to miniaturize the above low-pass filter, it is conceivable to use a material having a high dielectric constant as the substrate. If a substrate having a high dielectric constant is used, both the ground capacitance and the inductance can be reduced in area, but since these are produced by screen printing, variations in characteristics are determined by the printing accuracy, and a laborious work of adjusting the electrode area is required.
If the strip line of inductance becomes thin, Q
However, this problem can be ameliorated by a coil wound with copper wire.

Furthermore, it is necessary to separately provide an electrode in order to carry out polar return with the above-mentioned filter, which results in a drawback that the number of steps in designing and manufacturing is large, the cost is high, and the size of the substrate is large.

An object of the present invention is to solve the above-mentioned drawbacks of the prior art and to provide a low-pass filter having a polar feedback circuit which can be downsized.

[Means for Solving the Problems] According to the present invention that can achieve the above object, a dielectric block is provided.
By arranging more than one through-holes side by side, forming a conductor film on the inner surface of each through-hole, and forming a conductor film on the side surface of the dielectric block where the through-holes are not open to form an earth electrode, This is a polar type low-pass filter in which conductor films 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 an inductance is generated by the coil coupling between the conductor films in the through holes. Basic low-pass characteristics can be obtained with a 4-terminal LC network in which a plurality of these inductance elements are connected in series and grounding capacitance elements are connected in parallel between interconnection points of the inductance elements. Further, an opposing capacitance is generated between the conductor films on the inner surfaces of the adjacent through holes, and a parallel resonance circuit is formed by the capacitance and the inductance of the coil to form an attenuation pole for blocking passage. Since this attenuation pole is formed near the pass band, the pass band becomes steep 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 diagram thereof.

The dielectric block 10 made of a high dielectric constant material such as barium titanate has a convex shape in which both ends of a rectangular parallelepiped are lowered. This dielectric block 10 has three through holes 12a,
…, 12c is formed. The three through holes 12a, ..., 12c all have the same hole diameter, but the through hole 12b at the center is long and the through holes 12a, 12c at both ends are short corresponding to the shape of the dielectric block 10. A conductor film 14 is formed on the inner surface of each through hole 12a, ..., 12c, and a conductor film is formed on the side surface of the dielectric block 10 (the surface where the through holes 12a, ... 16 (see Figure 2). There is no conductor film on the bottom surface of the dielectric block. Then, the conductor films 14 in the through holes are sequentially connected by the coil 18. The conductor films 14 in the through holes 12a and 12c at both ends are connected to the input / output connector 22 by the lead wire 20.

In order to make the drawing easy to understand, the portions where there is no conductor film and the dielectric body is exposed as it are are indicated by fine dots. The dielectric block is manufactured by press molding powder and firing it. The conductor film may be formed by baking silver paste, for example.

In FIG. 3, L ₁ and L ₂ indicate the inductance of the coil 18. C ₁ , C ₂ and C ₃ are conductor films on the inner surface of the through holes 12a, ..., 12c
It represents the ground capacitance formed by 14 and the ground electrode 16, and C ₂ is larger than C ₁ and C ₃ by the length of the central through hole 12b. Here, C ₂ is about twice as large as C ₁ and C ₃ in order to realize the preferable low-pass filter characteristic. Therefore, the height of the dielectric block is designed so that the central portion is approximately twice as high as both ends. C ₄ and C ₅ are adjacent through holes 12a and 12b and 12
It represents the opposing capacitance formed between the conductor films b and 12c.
The opposing capacitances C ₄ and C ₅ and the inductances L ₁ and L _{2 of the} coil 18 cause parallel resonance to form an attenuation pole for blocking passage.

FIG. 4 shows an example of filter characteristics obtained by such a low-pass filter. A in the figure shows a characteristic with a strong pole, FIG. B shows a characteristic with a weak pole, and FIG. C shows a characteristic with a moderate polarization. These are opposite capacities
It can be adjusted by selecting C ₄ and C ₅ and inductances L ₁ and L ₂ , and the mutual inductance M between both coils 18.

5 to 7 show another embodiment of the present invention. In the example shown in FIG. 5, the dielectric block 30 is a simple rectangular parallelepiped, the central through hole 32b is larger than the through holes 32a and 32c at both ends, and the distance between the conductor film in the central through hole and the ground electrode 36 is large. And the grounding capacitance is increased by bringing them close to each other.

In the example shown in FIG. 6, the three through holes 42a, ..., 42c have the same hole diameter, but constricted portions (narrow width portions) 43 are provided on both sides of the central portion of the dielectric block 40, and the central through holes are formed. The ground capacitance is increased by shortening the distance between the conductor film of the hole 42b and the earth electrode 46 in the vicinity thereof.

Instead of changing the hole diameter of the through hole or changing the shape of the dielectric block, the shape of the side ground electrode may be changed as shown in FIG. By reducing the size of the ground electrode 56 near the through holes 52a and 52c located at both ends, the ground capacitance of that portion is reduced, and the ground capacitance of the central through hole 56b portion is relatively increased. In this case, the dielectric block 50 may be a simple rectangular parallelepiped.

Although the preferred embodiment of the present invention has been described in detail above, the present invention is not limited to such a configuration. The number of through holes may be four or more, and the conductor films may be connected by a coil.

[Effects of the Invention] According to the present invention, as described above, three or more through-holes are arranged in parallel in the dielectric block, and a conductor film is formed on the inner surface of the dielectric block to provide a ground capacitance with the outer ground electrode. Since the conductor films of the through-holes are sequentially connected by the coils, they can equivalently form the LC network as described above and realize desired low-pass filter characteristics. In addition, a polar feedback circuit is added by 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, so the pass band becomes steep and the filter characteristics are improved. It

Further, the filter of the present invention is a coaxial type, unlike the conventional flat plate type, and can use a material having a high dielectric constant, so that it can be miniaturized. Therefore, the mounting area is reduced and the mounting density on a circuit board or the like is improved.

[Brief description of drawings]

FIG. 1 is a perspective view showing an embodiment of a polar 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. 4A, B, C are the present invention. FIG. 5, FIG. 6, FIG. 7 and FIG. 7 are graphs showing characteristic examples of the low-pass filter of FIG. 10 ... Dielectric block, 12a, 12b, 12c ... Through hole, 14 ...
… Conductive film, 16 …… Earth electrode, 18 …… Coil.

Claims (1)

[Claims] 1. A dielectric block is provided with three or more through holes in parallel, a conductor film is formed on an inner surface of each through hole, and a conductor film is formed on a side surface of the dielectric block where the through hole is not opened. A polar low-pass filter in which the conductor film of each through hole is sequentially connected by a coil as a ground electrode.