JPS6340484B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a novel distributed constant filter used, for example, in the several 100 MHz range.

Conventionally, filters in the several 100 MHz range have used LC resonant circuits or coaxial resonators, but these were structurally unstable or complex, had unsatisfactory characteristics, and were difficult to adjust. There were problems such as the high cost and the inability to reduce costs.

Therefore, a distributed constant type filter with a simple structure, satisfactory characteristics, and low cost was invented by the inventor of the present invention, and the application was filed (Japanese Patent Application No. 56-107548 (Japanese Unexamined Patent Publication No. 58-9401)). )) was done. The gist of this prior invention is that at least two through holes are provided in a dielectric block in a line at a constant interval, a conductive film is provided on the inner surface of the through holes, and a conductive film is provided on at least four sides of the dielectric block. The conductive film provided on the inner surface of the through hole, the conductive film provided on at least four sides of the dielectric block, and the intervening dielectric constitute a resonant unit, and a cavity is formed in the dielectric block between at least a pair of adjacent resonant units. In addition, the external circuit and the resonant unit are electrostatically coupled. The cavity is provided for setting the degree of coupling between a pair of resonant units.

According to this prior invention, the coupling coefficient is 2%.
A relatively wide band with a coupling coefficient of about 10% is possible, but a narrow band with a coupling coefficient of less than 1 to 2% has not been put to practical use. That is, in FIG.
When a increases from 0.5 mm to 10 mm, the first
As shown in Figure 2, the coupling coefficient decreases from 10% to 1%, but it does not easily decrease below that level, while the insertion loss of the filter decreases from 1dB to 40dB.
If the value of a becomes more than about 3 mm, it cannot be practically used as a filter. In this case, if the value c in FIG. 11 is increased, the Q value will increase, and the drop in insertion loss can be suppressed, but there is a drawback that the shape becomes larger.

Therefore, an object of the present invention is to provide a distributed constant type filter that has low insertion loss, is small, and can further reduce the coupling coefficient.

That is, the gist of the present invention is to provide a rectangular parallelepiped-shaped dielectric block having four side faces and two end faces with at least two through holes opening at the two end faces arranged in a line at a constant interval. An inner conductive film is provided on the inner surface of the hole, and an outer conductive film is provided on the four sides, and the inner and outer conductive films and the dielectric interposed between these constitute a resonant unit, and the dielectric block A groove for adjusting the degree of coupling is formed across the entire width of the dielectric block in the area between a pair of adjacent resonant units on one end face, and a through cavity is formed that penetrates from the bottom of the groove to the other end face. An electrode film is formed on the side surface and a portion of the groove other than the through-hole at the bottom, and the degree of coupling between the pair of resonant units is set by the groove and the through-hole. be.

Embodiments of the invention will be described below with reference to the drawings.

FIG. 1 is an equivalent circuit diagram of an embodiment of the present invention.

In the figure, 1 is an input terminal, 2 is an output terminal, and 3 is an input terminal.
is the input coupling capacitance, 4 is the output coupling capacitance,
5 and 6 show 1/4 wavelength resonant circuits as lumped constant circuits. Therefore, the example is 1/4
The wavelength resonant circuits are inductively coupled to each other, and the external circuit and
The filter is capacitively coupled to a 1/4 wavelength resonant circuit. FIGS. 2 to 7 show an example of its specific structure. In the figure, 10 is a cubic dielectric block made of a titanium oxide based ceramic dielectric, and 11 and 12 are through holes, which are arranged in the dielectric block 10 at regular intervals. 1
3 and 14 are conductive films (inner conductive films) provided on the inner surfaces of the through holes 11 and 12, respectively, and 15 is a conductive film (outer conductive film) provided on at least four sides of the dielectric block 10. A conductive film 16 is provided on the bottom surface of the dielectric block 10, and is used to short-circuit one end side of the conductive films 13 and 14 and the conductive film 15 to generate 1/4 wavelength resonance. Reference numeral 17 denotes an input coupling capacitor connected to the other end of the conductive film 13, which has a cylindrical dielectric 18 and opposing electrodes 19 and 20. To be more specific, a mounting member 21 made of a conductor such as a metal cylinder or a conductive paste is electrically and mechanically connected and fixed to the other end of the conductive film 13, and the counter electrode 20 is connected to the mounting member 21. It is electrically and mechanically connected and fixed. Reference numeral 22 denotes an output coupling capacitor connected to the other end of the conductive film 14, which has opposing electrodes 24 and 25 on a cylindrical dielectric 23. To be more specific, a mounting member 26 made of a conductor such as a metal cylinder or a conductive paste is electrically and mechanically connected and fixed to the other end of the conductive film 14, and the counter electrode 25 is connected to this mounting member 26. Connected and fixed electrically and mechanically. The resonant frequency is determined by the electrical length of the conductive film 13 or 14, which is shortened by the dielectric constant of the dielectric 10. The electrical length may be 1/4 wavelength or 1/2 wavelength as in the illustrated embodiment. When the wavelength is 1/2, the conductive film 16 is not necessary.
Note that the conductive films and electrodes in each figure are drawn with exaggerated film thicknesses for better understanding. In any case, two resonant units are constructed in this embodiment.
Each resonant unit is coupled by odd mode and even mode. Reference numeral 27 denotes a through cavity, which has a rectangular cross section, for example. 27a is a recess or groove provided on the bottom side in FIG. 2, and the through cavity 27 penetrates from the bottom of the groove 27a to the upper end surface of the dielectric block 10 in the drawing. Also,
An electrode film 1 formed by extending the conductive film 16 provided on the lower end surface of the dielectric block 10 is provided on the bottom surface of the groove 27a except for the through cavity 27 and on the side surface.
6a is formed. In this way, the groove 2
The degree of coupling is set to a target value at depth Δt of 7a. Now, in FIG. 11, a=2 mm, and FIG. 13 shows the state when Δt/t in FIG. 7 is changed. As is clear from the graph, by increasing the depth Δt, the coupling coefficient can be reduced without increasing the insertion loss. This tendency is a
This also applies to items with different dimensions.

FIG. 8 shows another embodiment in which the input coupling capacitor 17 and the output coupling capacitor 22 in the above embodiment are omitted. 28 is an input terminal pin, and 29 is an output terminal pin. The pin 28 is embedded in a portion of the dielectric block 10 on the opposite side of the cavity 27 when viewed from the conductive film 13, in close proximity to the conductive film 13. Similarly, the pin 29 is placed close to the conductive film 14 so that the cavity 2
It is embedded in the dielectric block 10 portion on the opposite side from 7. Therefore, a certain amount of capacitance exists between the input terminal pin 28 and the conductive film 13, and a certain amount of capacitance also exists between the output terminal pin 29 and the conductive film 14. In the structure shown in FIG. 8, two capacitors are omitted compared to the structures shown in FIGS. 2 to 7, and the structure becomes simpler and costs can be reduced. FIG. 9 shows yet another embodiment.

In the distributed constant type filter shown in FIG. 9, a groove 27a is formed in the upper end surface of the dielectric block 10 as shown in the drawing, and a conductive film 15 is extended on the bottom surface of the groove 27a except for the through cavity 27 and on the side surfaces. An electrode film 15a is formed. In addition, in this filter, a 10th
Dielectric units 41, 41 as shown in the figure are press-fitted, respectively.

As shown in FIG. 10, the dielectric unit 41 includes a part of a conductive wire 42 having a diameter of, for example, 0.5 mmφ.
The dielectric unit 41 is coated with a dielectric material such as plastic or titanium oxide and formed into a columnar shape so that the conductive wire 42 passes through the axial center. body block 1
In order to facilitate press-fitting into the holes 11 and 12 of the dielectric unit 4, a tapered portion 43 is provided.
The hole 1 of the dielectric block 10 is provided at the rear end of the dielectric block 10.
A flange portion 44 is provided that is abutted against the opening periphery of the non-forming side of the conductive films 15 of Nos. 1 and 12.

As shown in FIG. 9, the dielectric units 41, 41 are formed from a dielectric block 1 having conductive films 13, 14 formed on the inner surface thereof, from the tapered portions 43, 43 side.
Dielectric units 41 and 4 are inserted into the holes 11 and 12 of 0.
The flange portions 44, 44 of 1 are the dielectric block 10
It is press-fitted until it makes contact with the

By doing as described above, the conductive films 13 and 14 formed on the conductive wires 42 and the inner surfaces of the holes 11 and 12 of the dielectric block 10 are connected to the dielectric units 41 and 41.
will be electrostatically coupled by the dielectric part of
The input coupling capacitor 17 and the output coupling capacitor 22 as shown in FIG. 2 become unnecessary.

Therefore, there is no need for troublesome installation work as in the case of the input coupling capacitor 17 and the output coupling capacitor 22.

As is clear from the above embodiments, the distributed constant filter of the present invention includes at least two through holes arranged in a dielectric block at regular intervals, a conductive film provided on the inner surface of the through holes, and a conductive film provided on the inner surface of the through holes. A conductive film is provided on at least four sides of the dielectric block, the conductive film provided on the inner surface of the through hole, the conductive film provided on at least the four sides of the dielectric block, and the intervening dielectric constitute a resonant unit, and the dielectric A groove having a depth in the axial direction of the through hole is provided across the entire width of the dielectric block in a portion between a pair of adjacent resonant units on one end face of the dielectric block,
Since a through cavity is formed that penetrates from the bottom of the groove to the other end of the block, and an electrode film is formed on the bottom and side surfaces of the groove, the degree of coupling as designed can be obtained with good reproducibility. Moreover, there is an effect that a small, narrow-band filter can be obtained without increasing insertion loss.

Note that the number of stages of resonance units is not limited to two stages, but any number of stages can be provided, and the resonance units can also be arranged in an interdigital configuration.

[Brief explanation of the drawing]

Fig. 1 is an equivalent circuit diagram of an embodiment of the present invention, Fig. 2 is a front view of the same, Fig. 3 is a left side view of the same,
Figure 4 is a right side view, Figure 5 is a top view, Figure 6 is a back view, Figure 7 is a sectional view, and Figure 8 is another embodiment. 9 is a sectional view of another embodiment, FIG. 10 is a front view of the dielectric unit, FIG. 11 is a dimensional diagram of the conventional example, FIG. 12 is a characteristic diagram of the conventional example, and FIG. FIG. 13 is a characteristic diagram of an embodiment of the present invention. 10 is a dielectric block, 11 and 12 are through holes,
13, 14 are inner conductive films, 15 are outer conductive films, 15
a, 16a are electrode films, 27 is a through cavity, and 27a is a groove.

Claims (1)

[Claims] 1. A rectangular parallelepiped dielectric block having four side faces and two end faces is provided with at least two through holes opening at the two end faces arranged at a constant interval, and an inner conductive film is provided on the inner surface of each through hole. and outer conductive films are provided on the four sides, and the inner and outer conductive films and the dielectric interposed between these constitute a resonant unit, and on either end face of the dielectric block, A groove for adjusting the degree of coupling over the entire width of the dielectric block is formed between a pair of adjacent resonant units, and a through cavity passing through from the bottom surface of the groove to the other end surface is formed. 1. A distributed constant filter characterized in that an electrode film is formed on the side surface and a portion excluding the through cavity, and the degree of coupling between the pair of resonant units is set by the groove and the through cavity.