JPH0473641B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention applies to relatively high frequency bands, particularly VHF bands,
This article relates to high frequency filters that are often used in the UHF and microwave bands.

[Conventional technology]

First, a conventional high frequency filter shown in FIG. 7 will be explained. In Fig. 7, Fig. 7(a) is a partially cut out plan view, and Fig. 7(b) is a sectional view taken along the line A-A of Fig. 7(a).
a to 5a, 1b to 5b are strip conductors, 6a,
6b is a ground conductor, 7 and 8 are coaxial terminals, 9 is a center conductor of the coaxial terminal, and 10a and 10b are dielectric plates.

The strip conductors 1a to 5a and the ground conductor 6a are formed of a conductive film in close contact with the dielectric plate 10a, and the strip conductors 1b to 5b and the ground conductor 6b are formed of a conductive film in close contact with the dielectric plate 10b. or,
These strip conductors 1a-5a, 1b-5
b, ground conductors 6a, 6b, dielectric plates 10a, 10
b are superimposed so as to have a symmetrical structure with respect to the B-B plane of FIG. 7b.

The shape of the connecting portion of the coaxial terminal 8 is as shown in a detailed view in FIG. 8, and the coaxial terminal 8 is connected so that the center conductor 9 coincides with the position of the strip conductors 5a and 5b. Further, the method of connecting the coaxial terminal 7 is also the same.

In this high frequency filter, the strip conductor 2
If a, 2b, 3a, 3b and 4a, 4b resonate at the same frequency fo, then at the frequency fo, the strip conductors 1a, 1b and 5a, 5b resonate with the strip conductors 2a, 2b to 4a, 4b. The incident wave to the coaxial terminal 7 is strongly coupled to the terminal 8.
guided by. However, at frequencies other than fo, the coupling between the strip conductors 1a, 1b and 5a, 5b is very weak, and most of the power of the wave incident on the terminal 7 is reflected. In this way, the high frequency filter shown in FIG. 7 has a function as a bandpass filter.

[Problem that the invention seeks to solve]

However, in the conventional high frequency filter, the strip conductors 1a, 1b to 5a, 5b are connected to the dielectric plate 10a,
Since the structure is such that the strip conductors 1a, 1b to 5a, 5b are sandwiched between them, it is difficult to adjust the coupling amount and resonance frequency between the strip conductors 1a, 1b to 5a, 5b.

The present invention was made to eliminate the above-mentioned drawbacks of the conventional filter, and provides a high frequency filter in which the amount of coupling between strip conductors and the resonance frequency can be easily adjusted.

[Means for solving problems]

In the high frequency filter according to the present invention, a plurality of grooves are provided in a dielectric plate, and strip conductors are formed in each groove so that the open ends thereof are oriented in the same direction, and adjacent strip conductors are directly connected to each other. The strip conductors are connected to each other to perform interstage coupling of the strip conductors.

[Effect]

In the high frequency filter according to the present invention, since the strip conductor is formed on the exposed surface of the dielectric plate, it is easy to adjust the coupling amount and resonance frequency of the strip conductor, and since the strip conductor is formed in the groove, the dielectric The electric field leaking into the space outside the body is extremely small, and the wavelength shortening rate is greater than that of a normal microstrip line formed on a flat dielectric plate, making the strip conductor shorter and smaller.

Regarding the mutual coupling of the strip conductors, since the strip conductors are provided in the grooves, the condition is close to that of a homogeneous medium, and since the open ends are 1/4 wavelength resonators with the same direction, the mutual coupling is similar to that of a uniform medium. Although the coupling is small, in this filter, interstage coupling is performed by the conductor provided on the shorted end side, so a predetermined amount of coupling can be obtained between the strip conductors.

〔Example〕

FIG. 1 shows one embodiment of this invention.
1 to 13 are strip conductors, 14 is a ground conductor, 1
5 is a dielectric plate, 16 and 17 are external lead terminals, 18
20 are grooves provided in the dielectric plate, and 21 and 22 are interstage coupling conductors.

The strip conductors 11 to 13 are connected to a dielectric plate 15.
The upper edges of the grooves 18 to 20 provided in the grooves 18 to 20 are exposed and the lower bottom portions are covered with a conductive film, and one end is open and the other end is short-circuited with the ground conductor 14 to form a 1/4 wavelength resonator. These strip conductors 11 to 13 are arranged so that their open ends are oriented in the same direction. Further, external lead terminals 16 and 17 are directly connected to strip conductors 11 and 12, respectively.

Thus, the conductors 21 and 22 are provided at positions less than 1/2 of the total length of the strip conductors from the short-circuit ends between the strip conductors 11 and 12 and between the strip conductors 12 and 14, respectively. In addition, the strip conductors 11 to 1
3. The ground conductor 14, the external lead terminals 16 and 17, and the interstage coupling conductors 21 and 22 are integrally formed on the dielectric plate 15 with a conductor film.

Regarding the mutual coupling of the strip conductors 11 to 13, since the strip conductors 11 to 13 are provided in the groove, the state is close to that of a uniform medium, and the open ends become 1/4 wavelength resonators with the same direction. Therefore, the mutual coupling is small, but in the filter of this embodiment, this is compensated for by the conductors 21 and 22 to obtain the desired amount of coupling between the strip conductors 11-13.

In the filter having the above configuration, the strip conductor 1
1 to 13 resonate at the same frequency fo, the strip conductors 11 and 13 are strongly coupled at the frequency fo, and the wave incident on the external lead terminal 16 is guided to the external lead terminal 17. However, at frequencies other than fo, the coupling between the strip conductors 11 and 13 is very weak, and most of the power of the wave incident on the external lead terminal 16 is reflected. In this way, the high frequency filter shown in FIG. 1 has a function as a band pass filter.

In the high frequency filter of this embodiment, since the strip conductors 11 to 13 are formed on the exposed surface of the dielectric plate 15, the amount of coupling between the strip conductors 11 to 13 and the resonance frequency can be easily adjusted. The amount of coupling can be adjusted by changing the distance l ₁ from the short-circuited ends of the conductors 21 and 22. Further, the resonant frequency can be easily adjusted by changing the lengths of the strip conductors 11 to 13 or by bonding a dielectric material to the open ends. The amount of coupling between the external lead terminals 16, 17 and the strip conductors 11, 13 is determined by the amount of coupling between the short-circuited ends of the strip conductors 11, 13 and the external lead terminals 16, 13.
It can be adjusted by changing the distance l ₂ between the position where 17 is connected.

Furthermore, since the strip conductors 11 to 13 in FIG. 1 are formed in the grooves 18 to 20, the electric field leaking into the space outside the dielectric plate 15 is very small, and the electric field is formed on a flat dielectric plate. The wavelength shortening rate is greater than that of ordinary microstrip lines. Therefore, the strip conductors 11 to 13, whose lengths are selected to be approximately 1/4 wavelength, are shortened, resulting in miniaturization.

Further, the strip conductors 11 to 13 have a substantially semicircular arc shape, as shown in FIG. 2, which is a sectional view taken along the line C--C in FIG. For this reason, the current distribution on the surface facing the ground conductor 14 does not concentrate at the ends unlike in the case of a planar microstrip line, and the current distribution becomes more uniform, reducing line loss. Therefore, a filter with low loss can be obtained.

FIG. 3 shows another embodiment of this invention.
The same parts as in the figure are given the same reference numerals, and 23 and 24 indicate capacitors.

In the filter having the configuration shown in FIG. 3, the external lead terminal 16,
17 is connected to the open ends of the strip conductors 11 and 13 via capacitors 23 and 24, and the amount of coupling can be adjusted by changing the capacitance of the capacitors 23 and 24. The operation of this filter is similar to that of the filter of FIG.
Also, like the filter shown in FIG. 1, the strip conductor 11
It is easy to adjust the amount of coupling between .

4 and 5 show still another embodiment of the present invention, and the same parts as in FIG. 1 are given the same reference numerals. Note that FIG. 5 is a sectional view taken along the line DD in FIG. 4.

In the filter of FIG. 4, the strip conductors 11-1
3 is formed on the entire surface of the grooves 18 to 20, making it easy to work when integrally forming the conductor film with the ground conductor 14 and the external lead terminals 16 and 17. The operation of this filter is similar to that of the filter shown in FIGS. 1 and 3, and it has similar characteristics to the filter shown in FIGS. 1 and 3.

Furthermore, FIG. 6 is a composite of FIGS. 3 and 4 in still another embodiment of the present invention.
In the filter shown in the figure, the strip conductors 11 to 13 are formed over the entire surface of the grooves 18 to 20, similar to the filter shown in FIG. 4, so that the work is easy. The operation of this filter is similar to that of the filters shown in FIGS. have

In addition, although the case where the number of strip conductors is three is described above, it may be applied to the case where the number of strip conductors is four or more.

〔Effect of the invention〕

As described above, in the high frequency filter according to the present invention, grooves are provided in the dielectric plate, and strip conductors are formed in the grooves so that the open ends are oriented in the same direction, and adjacent strip conductors are By connecting the strip conductors directly and performing interstage coupling, it is easy to adjust the coupling amount and resonance frequency between the external terminal and the strip conductor, and the filter is small and has low loss. This has the effect of being able to obtain the following.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram of a high frequency filter of the present invention, FIG. 2 is a sectional view taken along the line CC in FIG. 1, and FIG. 4
The figure is a schematic configuration diagram showing still another embodiment of the present invention, FIG. 5 is a sectional view taken along the line DD in FIG. 4, and FIG. 6 is a schematic configuration diagram showing still another embodiment of the invention. , Fig. 7 is a schematic configuration diagram of a conventional high frequency filter, in which Fig. 7a is a plan view with some parts missing, Fig. 7b is a cross-sectional view taken along line A-A in Fig. 7a, and Fig. 8 is a cross-sectional view of the FIG. 3 is an enlarged view of the connecting portion between the strip conductors 5a and 5b and the coaxial terminal 8 shown in the figure. In the figure, 11 to 13 are strip conductors, 14 is a ground conductor, 15 is a dielectric plate, 16 and 17 are external lead terminals, 18 to 20 are grooves, 21 and 22 are conductors, and 2
3 and 24 are capacitors. In the drawings, the same or corresponding parts are denoted by the same reference numerals.

Claims (1)

[Scope of Claims] 1. In a high frequency filter in which a strip conductor and a ground conductor are integrally formed with a conductive film closely adhered to a dielectric plate, a plurality of grooves are provided on the dielectric plate, and one end is short-circuited in each groove. A high frequency filter characterized in that the strip conductors with the other ends open are formed so that the open ends thereof are oriented in the same direction, and the adjacent strip conductors are directly connected by a conductor to perform interstage coupling. . 2. Each of the grooves has a substantially semicircular arc shape, and the center portion of the strip conductor that is in close contact with the groove is close to the ground conductor, so that the current distribution on the surface facing the ground conductor is made uniform. A high frequency filter according to scope 1. 3. The high frequency filter according to claim 1 or 2, wherein each of the strip conductors is formed so that the upper edge of the groove is exposed and the lower bottom of the groove is covered. 4. The high frequency filter according to claim 1 or 2, wherein each of the strip conductors is formed on the entire surface of the groove. 5. Any one of claims 1 to 4, characterized in that a capacitor for adjusting the amount of coupling and resonance frequency is provided on the open end side of the strip conductor, and an external lead terminal is connected via this capacitor. A high frequency filter described in .