JPH02113602A - Inter-digital filter - Google Patents

Abstract

PURPOSE:To secure an external band attenuation quantity at a higher range than an interruption frequency by forming a step part along the length-wise direction of the resonator of a metallic resonance plate at the inner wall of a metallic case and reducing in a step way the width dimension of a cavity delimited in a metal by the step part. CONSTITUTION:Metallic cases 4 and 5 are fitted so that a metallic resonator 1 can be sandwiched and an electromagnetic wave cannot be leaked, a step part 4a is formed along the lengthwise direction of a resonator 2 at the inner wall of a metallic case 4 at the side to screw a coupling screw 6 for band variable and the width dimension between step parts 4a, namely, the width dimension of the cavity of the metallic case is narrowed in the step way. Consequently, by the resonance in the resonator 2 of the metallic resonating plate 1, a band attenuation effect at a central frequency f0 is obtained, here, the inner wall width of the metallic case 4 to be easiest to give an influence to a coupling adjusting screw 6 for band variable is made small, and therefore, especially, the external band attenuation at the high frequency side can be increased. Thus, even when the same metallic resonance plate is used, the attenuation quantity at the external band in the high frequency side can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to the structure of an ink digital filter used in the microwave band or millimeter wave band.

[Conventional technology]

Conventionally, interdigital filters used in high frequency bands such as microwave bands and millimeter wave bands consist of a metal resonator plate with resonators each having a length of about 174 wavelengths and cantilevered in an alternating manner, and It consists of a metal case with a U-shaped cross section sandwiching a resonant plate, and achieves the desired bandpass filter characteristics in coaxial mode.

For example, FIGS. 2(a) and 2(b) show configuration examples of conventional interdigital filters.

FIG. 2(a) is a longitudinal sectional view, and FIG. 2(b) is a sectional view taken along line CC. In the figure, ■ is a metal resonator plate equipped with resonators 2 and antennas 3 each having a cantilever structure alternately having a length of about 174 wavelengths.

Reference numerals 4 and 5 denote metal cases having a U-shaped cross section that sandwich the metal resonant plate 1, and the two metal cases 4 and 5 constitute a rectangular waveguide. A coupling adjustment screw 6 for varying the band is screwed into one of the metal cases 4, and the screw 6 is located in the middle of the resonator 2.

In addition, metal cases 4, 5. The metal resonant plate 1 is tightened with mounting screws or the like to prevent electromagnetic waves from leaking.

(Problems to be Solved by the Invention) In the conventional ink digital filter described above, the dimension I!2 in FIG. Since the cutoff frequency is determined by the width dimension, it is not possible to obtain out-of-band attenuation of a bandpass filter in a region higher than the cutoff frequency.To deal with this problem, metal resonant plates or Although it is necessary to make the metal case 45 smaller, this makes it impossible to obtain the required 2! spread wave number.

In particular, when the amount of insertion of the band variable coupling Lf bus for loading capacitance increases, the cutoff frequency of the rectangular waveguide becomes even lower, making it even more difficult to obtain out-of-band attenuation of the hand pass waveform and f filter. There is a problem with becoming.

An object of the present invention is to provide an ink digital filter that can secure out-of-band attenuation in a region higher than the cutoff frequency.

[Means for Solving the Problem] The ink digital filter of the present invention has a stepped portion formed on the inner wall of the metal resonator plate along the longitudinal direction of the resonator of the metal resonator plate. The width of the cavity defined within the case is reduced in a stepped manner.

1 Effect] 1- In the configuration described in 7, the width dimension inside the metal case is reduced by the stepped portion, thereby improving the amount of attenuation outside the high frequency band even when the same metal resonant plate is used.

(Example〕 Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a diagram for explaining the present invention in detail; FIG. 1(a) is a sectional view in the plane direction, FIG. is a cross-sectional view taken along the line B-[3. In these figures, ■ is a resonator 2. with a cantilever structure alternately having a length of about 174 wavelengths. The metal resonant plates 4 and 5 provided with the metal resonator plate 1 and the antenna 3 are metal cases having a U-shaped cross section that sandwich the metal resonator plate 1, and the metal cases 4 and 5 constitute a rectangular waveguide.

Further, a coupling adjustment screw 6 for varying the band is screwed into one metal case 4, and the screw 6 is located in the middle of the resonator 2.

Then, the metal cases 4 and 5 are assembled with screws or the like to sandwich the metal resonant plate 1 to prevent electromagnetic waves from leaking, and the metal cases 4 and 5 are assembled using screws or the like to prevent electromagnetic waves from leaking. Steps 4a are formed on the inner wall along the longitudinal direction of the resonator 2, and the width between the steps 4a, in other words, the width of the cavity of the metal case is narrowed stepwise. That is, this width dimension 11 is i! with respect to the original width dimension 12 of the metal case 4. 1<p,2.

According to this configuration, not only can a band attenuation effect at the center frequency r0 be obtained due to the resonance in the resonator 2 of the metal resonant plate 1, but also the metal case, which is most likely to affect the band variable coupling adjustment screw 6, can be obtained. Since the inner wall width of 4 is made small, it is possible to increase out-of-band attenuation, especially on the high frequency side. As a result, as shown by the solid line in FIG. 3, it is possible to improve the amount of attenuation outside the band on the high frequency side and obtain an out-of-band attenuation of -1-. As a result, a filter with high out-of-band attenuation can be constructed even when the metal resonator plate 2 having the same quarter-wavelength resonator as the conventional one is used.

Incidentally, the attenuation characteristic shown by the broken line in FIG. 3 shows the ink digital filter of the conventional structure shown in FIG.

Here, in this embodiment, a part of the width of the cavity in the portion of one metal case 4 sandwiching the band variable coupling adjustment screw 4 is narrowed in a stepwise manner, but the width of the cavity in the other metal case 5 is all narrowed in a stepwise manner. Needless to say, the same effect can be obtained even if the width is narrowed.

Further, even if the band variable coupling adjustment screw 6 is not present, the same effect can be obtained by making the width of the cavity of the metal case step-like.

Furthermore, although the ink digital filter in the above embodiment has a two-stage structure, the present invention can of course be applied to filters with various numbers of stages other than that.

[Effects of the Invention] As explained above, the present invention forms a stepped portion on the inner wall of the metal case along the longitudinal direction of the resonator of the metal resonant plate, and creates a cavity defined in the metal case by the stepped portion. Since the width dimension is reduced in a stepwise manner, it is possible to improve the amount of attenuation outside the high frequency band even when the same metal resonant plate is used.

[Brief explanation of the drawing]

FIG. 1(a) is a cross-sectional view of the ink digital filter of the present invention in the planar direction, and FIG. 1(b) is a cross-sectional view of the ink digital filter of the present invention.
A sectional view, FIG. 1(c) is a BB sectional view of FIG. 1(b), FIG. 2(a) is a vertical sectional view of a conventional ink digital filter, and FIG. FIG. 2(a) is a sectional view taken along the line CC, and FIG. 3 is a diagram showing the attenuation characteristics of the ink digital filter. DESCRIPTION OF SYMBOLS 1...Metal resonator plate, 2...Resonator, ;shi...Antenna, 4.5...Metal case, 4a...Step part, 6...
・Coupling adjustment for variable band. (a) (b)

Claims (1)

[Claims] 1. In an interdigital filter consisting of a metal resonant plate having resonators of alternating cantilever structure with a length of about 1/4 wavelength, and a metal case defining a cavity inside with the metal resonator plate in between. An interdigital filter characterized in that a stepped portion is formed on the inner wall of the metal case along the longitudinal direction of the resonator, and the width dimension inside the metal case is reduced in a stepwise manner by the stepped portion.