JP2807003B2 - Interdigital filter - Google Patents

Description

The present invention relates to an interdigital filter mainly used in a VHF band, a UHF band, and a microwave band.

[Prior Art] Conventionally, there has been a filter of this type as shown in FIG. Fig. 3 (a) shows G. Matthaei et al., "MICR
OWAVE FILTERS, IMPEDANCE−MATCHING NETWORKS, AND COU
PLING STRUCTURES, "PP.614-626, 1964, McGraw-Hill. In the figure, (1) to (5) are inner conductors,
(6) is an outer conductor, (7) and (8) are coaxial terminals, (9) and
(10) is the center conductor of the coaxial terminals (7) and (8), respectively. FIG. 3 (b) is a cross section taken along line BB of FIG. 3 (a), and (1) to (6) are the same as FIG. 3 (a).
One end of the inner conductors (2), (3), and (4) is a short-circuited end, and the other end is an open end, and is supported on the short-circuited end side.

Here, as shown in FIG. 8.02-3 (a) on page 432 of the above-mentioned document, a general equivalent circuit of a high-frequency filter includes a reactance Xi representing a resonator and a coupling means between adjacent resonators. , And K01 and Kn, n + 1 representing input / output coupling means. On the other hand, as shown in FIG. 6.01-1 in p. 259 of the above document, the impedance step works as an inverter, and its value is variable according to the impedance ratio.

Further, a two-aperture resonator is considered for physical explanation. Generally, a two-aperture resonator is connected to an input / output terminal through a discontinuous portion such as a coupling hole, and reflects most of the radio waves from the input terminal due to the discontinuity at frequencies other than the resonance frequency, but at a resonance frequency, It has the property of strongly drawing radio waves from the input terminal into the resonator and storing electromagnetic energy. At this time, the energy that can be stored in the resonator is constant, and when the power of the radio wave incident from the input terminal and the power extracted from the output terminal are balanced, the radio wave from the input terminal is extracted to the output terminal without reflection. .
At this time, the passing power from the input terminal to the inside of the resonator increases as the reflection of the discontinuous portion alone decreases.

Assuming that the inner conductors (2), (3) and (4) resonate at the same frequency f ₀ in this interdigital filter, the inner conductors (1) and (5) resonate at the frequency f _0. Although not strongly coupled through the inner conductors (2), (3), and (4) in a resonance state, the incident wave to the coaxial terminal (7) is guided to the terminal (8). However, at frequencies other than f _0, the inner conductor (1) to (5) coupling is very weak, the coaxial terminal (7)
Most of the power of the incident wave is reflected. As described above, the interdigital filter shown in FIG. 3A has a function as a band-pass filter.

Note that the outer Q is the reciprocal of the strength of the coupling between the inner conductors (1) and (2) and the inner conductors (4) and (5).

[Problem to be Solved by the Invention] Since the conventional interdigital type filter is configured as described above, the inner conductors (1) and (5) are not resonators, so that the inner conductor (1) (2) and inner conductor (4)
The coupling between (5) and (5) is performed by arranging them close to each other, and the amount of coupling is limited by the processing limit of the gap, so that the external Q cannot be reduced to a specific value or less. Is difficult to obtain.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has as its object to obtain a compact, wideband interdigital filter which is easy to process.

[Means for Solving the Problems] An interdigital filter according to the present invention has a surface on each of two rectangular parallelepiped dielectric blocks, from one side surface to another side surface opposite to the side surface, in parallel with the surface. A plurality of grooves provided, an outer conductor formed by closely attaching a conductive film to the bottom surface of each of the two dielectric blocks and two side surfaces parallel to the grooves, and a conductive film formed on the entire inner wall of the groove. A plurality of inner conductors formed in close contact with each other, such that the two dielectric blocks are in close contact with their respective surfaces facing each other, and the dielectric blocks are symmetrical with respect to the adhered surfaces. A plurality of triplate line resonators, and an input / output terminal of the triplate line resonator. Is an open portion, the short-circuit portion is formed by connecting the inner conductor and the outer conductor on the bottom surface with a conductive film, and each of the triplate line resonators at both ends is electrically connected to the input / output terminal at the open portion. The triplate line at both ends is directly connected to the triplate line resonator at both ends, and the characteristic impedance of the triplate line is set lower than the characteristic impedance of the input / output terminal to be in an open state. The ratio of the characteristic impedance of the writing output terminal is set to be close to 1.

Further, the input / output terminals are electrically and mechanically connected to a conductor plate deformable by pressure, and the conductor plate is sandwiched between two sets of inner conductors constituting the triplate lines at both ends. , Electrically and mechanically directly connected to the inner conductor.

[Operation] In the present invention, two rectangular parallelepiped derivative blocks are brought into close contact with each other so as to be symmetrical with respect to the surfaces provided with the plurality of grooves, and one end is short-circuited. The other end forms a plurality of triplate lines having an open portion, at least the characteristic impedance of the triplate lines at both ends of the plurality of triplate lines is set to be lower than the characteristic impedance of the input / output terminal, and Since each of the plate lines is connected to the input / output terminal in the open portion and is in an open state, the input / output terminals at both ends can be configured with resonators. It can be downsized without waste. Furthermore, since the external Q is changed in accordance with the ratio of the characteristic impedance of the triplate line at both ends and the characteristic impedance of the input / output terminal, the process of narrowing the interval between the triplate lines as in the related art by bringing this ratio close to 1 is performed. Without doing so, the external Q can be easily reduced, and a broadband filter can be configured in a small size.

[Embodiment] FIG. 1 is a partially cut-away configuration diagram showing an embodiment of the present invention, and FIG. 2 is a diagram for explaining the details of FIG.
(1a) to (5a), (1b) to (5b) are inner conductors, (6a),
(6b) is an outer conductor, (7a) to (11a), (7b) to (11b) are grooves, (12a) and (12b) are derivative blocks, and (13) to (1)
7) is a short-circuit part, (18) is a conductor plate that can be deformed by pressure, (19) is an inner conductor (1a), (1b) and an outer conductor (6a),
(6b) and a triplate line composed of a conductor plate (18), (20) is an inner conductor (2a), (2b) and an outer conductor (6a),
A triplate line composed of (6b) and a conductor plate (18), (21) is an inner conductor (3a), (3b) and an outer conductor (6a),
(6b) and a triplate line composed of a conductor plate (18), (22) is an inner conductor (4a), (4b) and an outer conductor (6a),
(6b) a triplate line composed of a conductor plate (18), (23) an inner conductor (5a), (5b) and an outer conductor (6a),
A triplate line composed of (6b) and a conductor plate (18), (24) is a connector plate, (25) to (29) are open portions, P
1, P2 are input / output terminals.

In FIG. 1, the triplate lines (20), (2)
The conductor plate (18) of (1), (22) and (23) is not shown.

The inner conductors (1a) to (5a) and (1b) to (5b)
It is formed by closely attaching a conductive film to the entire inner walls of the substantially concave grooves (7a) to (11a) and (7a) to (11b) on the surfaces of the derivative blocks (12a) and (12b). Outer conductor (6a),
(6b) is formed by closely attaching a conductive film to the bottom surfaces of the derivative blocks (12a) and (12b) and the side surfaces parallel to the grooves (7a) to (11a) and (7b) to (11b).
The short-circuit portions (13) to (17) correspond to the corresponding inner conductors (1a) to (5
a), (1b) to (5b) A groove is formed by slightly cutting out the side surface of the dielectric block at one end, and a conductor film is formed in close contact with the groove. Inner conductors (1a) to (5a), (1b)
(5b) is short-circuited by being connected to the outer conductor (6a) or (6b) by the conductor film at the short-circuit portions (13) to (17), respectively. Also, opposing inner conductors (1a) and (1b), (2a)
And (2b), (3a) and (3b), (4a) and (4b), and (5a) and (5b), by sandwiching a conductor plate (18) that can be deformed by spring-shaped pressure. Electrically connected directly. The input / output terminals P1 and P2 are
8) It is electrically and mechanically directly connected to one end. The triplate lines (19) and (23) at both ends are the inner conductors (1a) and (1b) at the open portions (25) and (29), respectively.
Is the center conductor of the input terminal P1 via the conductor plate (18), the inner conductors (5a) and (5b) are the center conductor of the output terminal P2 via the conductor plate (18), and the outer conductor (6a) , (6b) are electrically connected directly to the outer conductors of the input / output terminals P1, P2 via the connector plate (24). The triplate lines (19) and (23) at both ends are the inner conductors (1a), (1b), (5a),
By adjusting the width of (5b) or the permittivity of the dielectric blocks (12a) and (12b), the characteristic impedance is set lower than the input / output terminals P1 and P2.

Here, the interdigital filter of the present invention is:
In the conventional filter of this type, an inverter at both ends is realized by an impedance step, and impedance matching is obtained by setting an impedance ratio corresponding to an inverter value obtained by design using an equivalent circuit. It is.

That is, by setting the triplate lines (19) and (23) at both ends to have a characteristic impedance lower than that of the input / output terminals P1 and P2 as described above, the triplate lines (19) and (23) are reduced to 1/4 wavelength. Since it is operated as a resonator, the magnitude of the impedance step between the input / output terminals P1 and P2 and the triplate lines (19) and (23), respectively, and the adjacent resonance with the triplate lines (19) and (23) By setting the distance between the units so that the passing power is balanced, impedance matching as a filter can be obtained.

Next, the operation will be described. In interdigital wave filter of the present invention shown in FIG. 1, if that triplate line (19) to (23) resonates at the same frequency f _0, and the output terminal the input terminal P1 at the frequency f ₀ P2 Are strongly coupled via the triplate lines (19) to (23) in a resonance state, and the incident wave to the input terminal P1 is guided to the output terminal P1. However, at frequencies other than f _0, triplate line (19) to
The coupling of (23) is very weak, and most of the power of the incident wave to the input terminal P1 is reflected. Thus, the interdigital filter shown in FIG. 1 has a function as a band-pass filter.

In the interdigital filter according to the present invention, a groove is formed in a substantially rectangular parallelepiped dielectric block, and a conductor film is formed in close contact with a predetermined portion of the dielectric block by, for example, baking or the like. And mechanically stable inner conductors (1a) to (5a) and (1b) to (5b) can be formed. Since the input / output terminals P1 and P2 are also sandwiched between the inner conductors (1a) and (1b) or (5a) and (5b), the processing is easy. Also, due to the effect of shortening the wavelength of the dielectric blocks (12a) and (12b), the inner conductors (1a) to (5a) and (1b) to
(5b) can be shortened.

Since the triplate lines (19) and (23) at both ends have lower characteristic impedance than the input / output terminals P1 and P2 connected to the open portions (25) and (29), the open portions (25) and (2)
9) open state is realized by, it acts as a quarter-wave resonator at the frequency f _0. At this time, the external Q of the filter of the present invention is determined according to the ratio of the characteristic impedance between the triplate lines (19) and (23) and the input / output terminals P1 and P2. By making the ratio of the characteristic impedance close to 1, the external Q can be reduced.

In the above embodiment, the case where the number of the inner conductors is five is shown. However, the number of the inner conductors may be two, three, four, or six or more.

In the above embodiment, the grooves (7a) to (11a), (7b)
Although the case where the cross-sectional shape of (11b) is substantially concave is shown, the shape may be semi-elliptical or semi-circular, and the same effects as those of the above embodiment can be obtained.

[Effects of the Invention] As described above, according to the present invention, a plurality of grooves provided on one surface of each of two rectangular parallelepiped dielectric blocks from one side to another side facing the side in parallel with the surface. And an outer conductor formed by closely attaching a conductive film to the bottom surface of each of the two dielectric blocks and two side surfaces parallel to the groove, and a conductive film formed by closely attaching the entire surface of the inner wall of the groove. A plurality of inner conductors, the two dielectric blocks being in close contact with their respective surfaces facing each other, and the plurality of dielectric blocks being combined such that the dielectric blocks are symmetrical with respect to the adhered surfaces. A triplate line resonator, and an input / output terminal of the triplate line resonator. The plurality of triplate line resonators alternately have one end on the opposite side short-circuited and the other end open. The part is above The inner conductor and the outer conductor on the bottom surface are connected by a conductive film, and each of the triplate line resonators at both ends is electrically connected directly to the input / output terminal at the open portion. The characteristic impedance of the triplate line constituting the plate line resonator is set lower than the characteristic impedance of the input / output terminal to be in an open state, and the ratio of the characteristic impedance of the triplate line to the characteristic impedance of the input / output terminal is determined. Since it is set to be close to 1, processing is easy, and there is an effect that a small and wide band interdigital filter can be obtained.

Further, the input / output terminals are electrically and mechanically connected to a conductor plate deformable by pressure, and the conductor plate is sandwiched between two sets of inner conductors constituting the triplate lines at both ends. By using an interdigital filter that is electrically and mechanically directly connected to the inner conductor, the connection between the input / output terminals and the inner conductors of the triplate lines at both ends can be further facilitated. There is also.

[Brief description of the drawings]

FIG. 1 is a partially cutaway view showing an embodiment of the present invention;
FIG. 2 is a diagram for explaining details of FIG. 1, and FIG. 3 is a schematic configuration diagram showing a conventional interdigital filter. In the figure, (1a) to (5a), (1b) to (5b) are inner conductors, (6a) and (6b) are outer conductors, and (7a) to (11a), (7
b) to (11b) are grooves, (12a) and (12b) are dielectric blocks, (13) to (17) are short-circuit portions, (18) is a conductor plate deformable by pressure, (19) to (23) ) Is a triplate line,
(24) is a connector plate, (25) to (29) are open parts, P1, P2
Is an input / output terminal. In the drawings, the same reference numerals indicate the same or corresponding parts.

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Osamu Ishida 5-1-1, Ofuna, Kamakura City, Kanagawa Prefecture Inside the Information and Electronics Laboratory, Mitsubishi Electric Corporation (56) References JP-A-60-62202 (JP, A) JP-A-61-156902 (JP, A) JP-A-8-78906 (JP, A) JP-A-60-30604 (JP, U) JP-A-63-1450 (JP, Y2) JP-A-4-25722 (JP, Y2)

Claims (2)

(57) [Claims] 1. A plurality of grooves provided on one surface of each of two rectangular parallelepiped dielectric blocks from one side surface to another side surface opposite to this side surface in parallel with the surface, and a plurality of grooves provided on each of the two dielectric blocks. An outer conductor formed by closely attaching a conductive film to the bottom surface and two side surfaces parallel to the groove; and a plurality of inner conductors formed by closely attaching the conductive film to the entire inner wall of the groove. A plurality of triplate line resonators which are formed by combining two dielectric blocks so that their respective surfaces face each other, and combining the dielectric blocks so as to be symmetrical with respect to the closely adhered surfaces; And the input / output terminals of the line resonator. The plurality of triplate line resonators alternately have one end on the opposite side short-circuited and the other end open, and the short-circuited portion is located outside the inner conductor and the bottom surface. Conductor and lead The triplate line resonators at both ends are electrically connected directly to the input / output terminals at the open portion to form the triplate line resonators at both ends. An impedance is set to be lower than the characteristic impedance of the input / output terminal to make it open, and the ratio of the characteristic impedance of the triplate line to the characteristic impedance of the input / output terminal is set to be close to 1. Digital filter. 2. The input / output terminal is electrically and mechanically connected to a conductor plate deformable by pressure, and the conductor plate is connected to each of two sets of inner conductors forming the triplate lines at both ends. 2. The interdigital filter according to claim 1, wherein the interdigital filter is sandwiched and directly connected electrically and mechanically to the inner conductor.