JPH0744364B2 - Polarized low pass filter - Google Patents

Description

TECHNICAL FIELD The present invention relates to a low pass filter mainly used in the microwave band. More specifically, according to the present invention, a plurality of grooves are provided on one surface of the dielectric block, and a conductor film is formed on the surface on the opposite side, the inner surface of the groove, and the surface facing the groove. A polar low-pass filter in which conductor films in the groove are connected by a coil.

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

[Prior Art] A stripline structure is generally used as a low-pass filter used in the microwave band. 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, an entire ground electrode is formed on the back surface, and the front surface electrodes are connected by strip lines. Ground capacitance (C component) between the electrodes on both the front and back of the board
And the strip line connecting the surface 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. When a substrate having a high dielectric constant is used, the areas of both the ground capacitance and the inductance are small, but the variation in capacitance is large and the characteristics are greatly changed. Since the electrodes and the like are formed by screen printing, variations in characteristics are determined by the printing accuracy, and it is difficult to adjust the electrode area.

Further, in order to perform polarized feedback with the above filter, it is necessary to provide an additional electrode, which results in a disadvantage that the man-hours increase in design and manufacturing, the cost becomes high, and the board size also becomes large.

An object of the present invention is to solve the above-mentioned drawbacks of the prior art, to provide a low-pass filter having a polar feedback circuit, which can be miniaturized, can reduce assembly man-hours.

[Means for Solving the Problems] According to the present invention which can achieve the above object, a plurality of grooves are provided in parallel on one of the surfaces of the dielectric block facing each other in a comb shape, and a conductor is provided on the wall surface and the bottom surface of each groove. A film is formed and a ground electrode is provided on the other surface to form a ground capacitance between the conductor film at the bottom of the groove and the ground electrode, and an opposing capacitance between the wall surface conductor films of adjacent grooves to form a gap between the conductor films of the grooves. This is a polarized low-pass filter in which is connected by a coil.

Here, it is also possible to mount the coil by providing a notch in the convex portion between the grooves.

In the present specification, the term "groove" refers to an elongated recessed portion, which has a wall surface on both sides in the usual sense, and has no wall surface on one side when positioned at the end of the dielectric block. (See Figure 10) is also used in a broad sense.

[Operation] A ground capacitance is formed between the conductor film at the bottom of the groove and the ground electrode, and an inductance is generated in the coil connecting between the conductor films of the groove. A basic low-pass filter characteristic can be obtained by a four-terminal LC network in which a plurality of coils are connected in series and grounding capacitors are connected in parallel between interconnection points of the coils. Further, a facing capacitance is generated between the wall surface conductor films of the adjacent grooves, and a parallel resonance circuit is formed by the capacitance and the inductance of the coil, thereby forming an attenuation pole for blocking passage. The attenuation pole can be formed near the pass band by selecting the inductance and the opposing capacitance to appropriate values, so that the pass band becomes steep and the filter characteristic is improved.

Further, when the coil is mounted by forming a notch in the convex portion between the grooves, the fixing of the coil is stabilized and the entire size is reduced.

[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 front view thereof, and FIG. 3 is an equivalent circuit diagram thereof. A dielectric block 10 made of a high dielectric constant material such as barium titanate is one in which five grooves 12 are provided in parallel on one of a pair of opposed surfaces (upper surface in the drawing) of a rectangular parallelepiped. As you can see, it looks like a comb, as shown in Figure 2. Conductor films 14a and 14b are provided on the inner surface of each groove 12, that is, both the wall surfaces and the bottom surface, and the ground electrode 16 is formed on the entire other surface (lower surface in the drawing) of the dielectric block 10. A coil 20 connects between the input / output terminal 18 and the conductor films of the grooves located at both ends and between the conductor films of the grooves.

In FIG. 1, in order to make the drawing easy to understand, portions where there is no conductor film and the base material of the dielectric is exposed as it are are indicated by fine dots. The dielectric block can be manufactured by pressing the powder into a predetermined shape and firing the powder. The conductor film may be formed by baking silver paste, for example.

Between the conductor film 14a at the bottom of the groove and the ground electrode 16, the ground capacitance C ₁ ,
C ₂ is formed, and the opposing capacitance C is formed between the wall surface conductor films 14b of the adjacent grooves.
₃ and C ₄ are formed. L ₁ , ..., L ₃ represent the inductance due to the coil. As shown in FIG. 4, when the width w of the dielectric block is constant, the ground capacitances C ₁ and C ₂ are groove widths l ₁ and l ₂ ,
Adjustable by the distance h ₁ between the ground electrode and the bottom of the groove,
C _3, C ₄ width l ₃ of the convex portion between the grooves, l _4, can be adjusted by the groove depth h _2.
Ground capacitance C _1, C ₂ and the inductance L _1, ..., to achieve basic low-pass filter characteristic in the L _3, counter capacity C _3, C ₄ and the inductance L _1, ..., parallel resonance with the L ₃ Next, create an attenuation pole that blocks passage.

An example of filter characteristics obtained by such a low-pass filter is shown in FIG. In the figure, the solid line A shows the characteristics of the product of the present invention with a pole, and the broken line B shows the characteristics without a pole (low-pass characteristics due to only L ₁ , ..., L ₃ and C ₁ , C ₂ ). ing. In the product of the present invention, when the opposing capacitances C ₃ and C ₄ are increased at a constant ratio, the pass band does not change and the attenuation pole P moves in the direction of arrow a.

6 to 10 show another embodiment of the present invention. Fifth
In the example shown in the figure, the bottom of the groove 30 has a semicircular shape.
Such a groove shape may be used.

In the example shown in FIG. 7, the depths of the five grooves 32 and 34 are the same, but the groove widths are changed. The two grooves 34 near the center are wide, and C ₂ is larger than C ₁ by that amount. In order to achieve the desired low-pass filter characteristics, C ₂ is
Make it about twice that of C ₁ . Therefore, the groove width l ₂ near the center is designed to be about double the groove width l ₁ at both ends.

Instead of changing the groove width, the groove depth may be changed as shown in FIG. Two grooves 38 near the center with respect to the grooves 36 at both ends
Is deeper, so C ₂ is larger than C ₁ . Also
C ₄ is larger than C ₃ .

In the example shown in FIG. 9, a notch 44 is provided in the central upper portion of the protrusion 42 between the grooves 40, and a coil is mounted in the notch 44. In this way, if the coil can be stably fixed and reliability is improved, there is an advantage that the entire size can be reduced.

Since the outer wall of the groove at both ends may be omitted,
It can be deleted as shown. This allows for size reduction and material cost savings.

Next, the experimental results will be described. FIG. 11 is an explanatory diagram of the dielectric filter used in the experiment, and FIG. 12 is a filter characteristic diagram obtained. The dielectric block is made of a material having a permittivity of ε = 39, and each dimension is as described in FIG. Width is
It is 6.2 mm. Coil L ₁ has a wire diameter of 0.32 mmφ
It is a coil L that has been turned two times to become 1.4 mmφ.
₂ and L ₃ are 3 turns. As can be seen from FIG. 12, an attenuation pole was generated near the pass band, and a steep filter characteristic was obtained.

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 grooves is arbitrary, and the groove shape and the like may be changed appropriately.

[Effects of the Invention] According to the present invention, a plurality of grooves are arranged in parallel in a dielectric block as described above, and a conductor film is formed on the inner surface of the dielectric block to provide a ground capacitance between the bottom of the groove and an opposing ground electrode. Since the conductor films of the groove are sequentially connected by the coil, the LC circuit network as described above can be equivalently realized by them, and desired low-pass filter characteristics can be realized. Also, a polar feedback circuit can be formed by the opposing capacitance generated between the wall surfaces of adjacent grooves and the inductance of the coil.By selecting the value of the opposing capacitance, the attenuation pole for blocking the passage can be formed near the passband, so the passband becomes steep. The filter characteristics are improved.

Further, since the filter of the present invention has the capacitance portion integrated, the insertion loss in the pass band is improved. Since the present invention is an integrated type, the capacities of C ₁ , ..., C ₄ are made uniform, and it is possible to suppress the dispersion of the capacities by forming an accurate groove shape.
The formation of the conductor film does not require high-precision screen printing technology, which reduces the manufacturing cost. Moreover, the filter characteristics can be freely changed by changing the inductance and the width.

Further, unlike the conventional flat plate type, the capacitance is formed three-dimensionally, so the occupied mounting area is reduced and the board mounting density is improved.

[Brief description of drawings]

FIG. 1 is a perspective view showing an embodiment of a polarized low-pass filter according to the present invention, FIG. 2 is a front view thereof, FIG. 3 is an equivalent circuit diagram thereof, and FIG. 5 and 5 are graphs showing characteristic examples of the filter of the present invention, and FIGS. 6, 7, 8, 9, and 10 are explanatory views showing other embodiments of the present invention. FIG. 11 is an explanatory diagram of the dielectric filter used in the experiment, and FIG. 12 is its filter characteristic diagram. 10 ... Dielectric block, 12 ... Groove, 14a, 14b ... Conductor film, 16 ... Ground electrode, 18 ... Input / output terminal, 20 ... Coil.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Nobuhiro Togami 5 36-11 Shinbashi, Minato-ku, Tokyo Fuji Electric Chemical Co., Ltd. (56) Reference JP-A-3-205902 (JP, A) JP Flat 3-205903 (JP, A) JP-A-61-161805 (JP, A)

Claims (2)

[Claims] 1. A plurality of grooves are provided in parallel on one of opposite surfaces of a dielectric block to form a comb shape, a conductor film is formed on the wall surface and the bottom surface of each groove, and an earth electrode is provided on the other surface. Ground capacitance between the conductor film at the bottom of the groove and the ground electrode,
A polar low-pass filter in which an opposing capacitance is formed between the wall conductor films of adjacent grooves, and the conductor films of the grooves are connected by a coil. 2. The filter according to claim 1, wherein the coil is mounted by providing a notch in the convex portion between the grooves.