JPH0779218B2 - Comb band stop filter - Google Patents

Description

The present invention relates to a comb-type band stop filter mainly used in a microwave band. More specifically, by arranging a plurality of grooves in parallel on one surface of the dielectric block and forming a conductor film on the surface on the opposite side and the inner surface of the groove, a plurality of capacitance sections are formed, and a coil between the conductor films in the groove is formed. The present invention relates to a band elimination filter in which the input and output terminals are connected by a capacitor capacitance.

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

[Prior Art] A dielectric resonator structure is generally used as a band elimination filter used in the microwave band. This is a structure in which a plurality of dielectric resonators made of a high dielectric constant ceramic material for microwaves are arranged side by side and coupled by an appropriate lumped element. In a dielectric resonator, a through hole is provided in the center of a prism, a conductor film is attached to the inner wall surface of the through hole, and a conductor is formed on the outer surface except one surface (open surface) where the through hole is open. A film is attached to form an inner conductor and an outer conductor, respectively. A capacitor is connected to each open end of the inner conductor, and a coil is connected between the capacitors to form a filter.

Each dielectric resonator has a resonance frequency determined by the prism height, relative permittivity, capacitor capacity, etc.
A coaxial resonance type band stop filter is obtained.

[Problems to be Solved by the Invention] In the band elimination filter described above, since a plurality of single resonators are arranged in an array, the number of parts is large, the number of assembling steps is increased, and positioning between resonators and outer conductor surface accuracy are required. Get tougher. Further, there is a problem such as deterioration of mechanical strength and environmental resistance due to the necessity of joining the resonators to each other.

An object of the present invention is to solve the above-mentioned drawbacks of the conventional technique, to reduce the number of assembly and adjustment steps, and to provide a band elimination filter which is easy to manufacture.

[Means for Solving the Problems] In the present invention that can achieve the above object, a plurality of grooves are provided in parallel on one of opposing surfaces of a dielectric block to form a comb shape, and a conductor film is formed on at least the bottom surface of each groove. And a ground electrode is provided on the other surface, the conductor films of adjacent grooves are connected by a coil, and the input and output are coupled via a capacitor capacitance.

Here, the input and the output may be coupled by connecting a capacitor and a coil in series. In addition to the bottom surface of the groove, a conductor film may be formed on the wall surface.

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. Is used in a broad sense, including.

[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 low-pass filter characteristic can be obtained by a four-terminal LC network in which a plurality of these coils are connected in series and grounding capacitors are connected in parallel between the interconnection points of the coils. Then, by coupling the input and output with a capacitor capacitance, a high-pass filter characteristic can be obtained. A desired band stop filter is obtained by combining the two.

If the input and output are connected in series with a capacitor and a coil, series resonance will occur and the passband on the high frequency side will become steep.
Good filter characteristics can be obtained.

Further, when a conductor film is formed on the wall surface of the groove, an opposing capacitance is generated between the wall surface conductor films of the adjacent grooves, and a parallel resonance circuit is formed by it and the inductance of the coil. And the filter characteristics are improved.

[Embodiment] FIG. 1 is a perspective view showing an embodiment of a comb band stop filter according to the present invention, and FIG. 2 is an explanatory view showing an equivalent circuit thereof.

A dielectric block 10 made of a high dielectric constant material for microwaves such as barium titanate is one in which four grooves 12 are provided in parallel on one side (upper surface in the drawing) of a pair of opposed faces of a rectangular parallelepiped. , It has a comb shape as shown in FIG. And each groove
Conductor films 14a and 14b are provided on the bottom surface and both wall surfaces of 12 and a ground electrode 16 is formed on the entire other surface (lower surface in the drawing) of the dielectric block 10. The coil 20 is provided 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.
Maintain at.

Further, the input / output terminals 18 are connected via a chip capacitor 22.

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, for example, by press-molding powder into a predetermined shape and firing. Alternatively, the groove may be formed by cutting a rectangular parallelepiped sintered product. The conductor film may be formed by baking silver paste, for example.

As shown in FIG. 2, the conductor film 14a at the bottom of the groove and the ground electrode 1
The grounding capacitances C ₁ and C ₂ are formed between them and the opposing capacitances C ₃ and C ₄ are formed between the wall surface conductor films 14b of the adjacent grooves. L ₁ ..., L ₃ represent the inductance due to the coil 20. Ground capacity
A low-pass filter characteristic is generated by C ₁ , C ₂ and the inductances L ₁ , ..., L ₃ . Further, the input / output terminals 18 are coupled by the capacitance C of the capacitor 22. As a result, high pass filter characteristics are obtained.

A band rejection filter is obtained by combining circuits having the above low-pass filter characteristics and high-pass filter characteristics in parallel. In this filter, the capacitance of the chip capacitor 22,
By appropriately selecting the values of the ground capacitances C ₁ and C ₂ and the inductances L ₁ , ..., L ₃ , it is possible to adjust to desired characteristics.

In this embodiment, since the conductor film is also formed on the wall surface of the groove, the opposing capacitances C ₃ and C ₄ are generated, and the inductances L ₁ , ..., L
_{At 3} and, parallel resonance occurs and the passband on the low frequency side becomes steep. Further, although not shown, it is preferable to couple the input and output with a series connection of a capacitor and a coil since series resonance occurs and the pass band on the high frequency side becomes steep.

When the width of the dielectric block is fixed, the ground capacitance
C ₁ and C ₂ can be adjusted by the groove width and the distance between the ground electrode and the groove bottom, and the opposing capacitances C ₃ and C ₄ can be adjusted by the width of the convex portion between the grooves and the groove depth.

Next, the experimental results will be described. FIG. 3 is an explanatory diagram of the dielectric filter used in the experiment, and FIG. 5 is a filter characteristic diagram obtained. The dielectric block is made of a material having a dielectric constant ε = 39, and the respective dimensions are as described in FIG. The unit is mm. The width of the dielectric block is 6.3 mm.
The input / output coil has 2 turns, the coil between the grooves has 3 turns, and a wire having a wire diameter of 0.4 mmφ was used. Two tin-plated wires 32 (core wire diameter 0.8 mmφ, insulation coating diameter) on the I / O connector 30
1.2 mmφ) cores were each soldered, and the other ends were twisted four times to give a capacitor coupling capacity. Fifth
As can be seen, this configuration yields a bandstop filter characteristic. The characteristic indicated by the broken line is the characteristic when the tin-plated coated wire between the input and output connectors is removed, and it can be seen that the low-pass filter characteristic occurs. That is, a band stop filter characteristic is generated by adding a capacitor coupling between the input and the output by the tin-plated wire.

If a coil is further added to the coupling between the input and output in addition to the capacitor to cause series resonance, the passband portion on the high frequency side (the portion shown in a in the figure) becomes steep, and better filter characteristics are obtained. can get.

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.
For example, a groove having a rectangular cross section may be used. It is also possible to adjust the capacity in each groove portion by changing the groove width and the groove depth. Further, the outer wall portions of the grooves at both ends may be omitted because they may be omitted. This allows for size reduction and material cost savings.

[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 bottom surface of the dielectric block to provide a ground capacitance between the groove bottom and an opposing ground electrode. Since the conductor films of the groove are sequentially connected by the coil and the input and output are coupled by the capacitor capacitance, the LC circuit network as described above can be equivalently realized and a desired band stop filter characteristic can be realized. If a coil other than a capacitor is provided in series for coupling between the input and output to cause series resonance, the pass band on the high frequency side becomes steep and the filter characteristic is improved.

When a conductor film is formed on the wall surface of the groove, a parallel resonance circuit is formed by the inductance of the coil and the opposing capacitance generated between the wall surfaces of the adjacent grooves, and the pass band on the low frequency side becomes steep.

Since the filter of the present invention is an integrated type, the capacity is made uniform, and it is possible to suppress the capacity variation by forming an accurate groove shape, and it is not necessary to use a high-precision screen printing technique for forming the conductor film, and therefore, the manufacturing is possible. Cost is reduced. Further, since the capacitors are three-dimensionally formed, 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 comb band elimination filter according to the present invention, FIG. 2 is an explanatory view showing its equivalent circuit, FIG. 3 is an explanatory view of a filter used in an experiment, and FIG. FIG. 5 is a graph showing the dimensions of the groove and the like, and FIG. 5 is a graph showing a characteristic example of the filter. 10 ... Dielectric block, 12 ... Groove, 14a, 14b ... Conductor film, 16 ... Ground electrode, 18 ... Input / output terminal, 20 ... Coil, 22 ... Chip capacitor.

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. A comb band stop filter in which the conductor films of adjacent grooves are connected by a coil, the conductor films of the grooves located at both ends are connected to the input / output ends, and the input / output ends are coupled via a capacitor capacitance. 2. The filter according to claim 1, wherein the input and output ends are connected by a series connection of a capacitor and a coil.