JP2003158401A - Waveguide type filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem that the filter length of a conventional waveguide filter depends upon a center frequency and the problem that it is difficult to miniaturize the waveguide filter as the filter has more stages, specially, when the center frequency is low. SOLUTION: A metallic case 11 is processed for molding five resonators and a susceptance coupling those resonators. The resonators are embodies by digging a length L obtained by correcting a length a half as large as the in-waveguide length by a susceptance quantity and lengths (depth) d1 to d3 of the long side of the in-waveguide aperture and the susceptance is embodied by a inductive window (coupling window). While the length of the resonators is held at a fixed value L, the length d0 of the long side of the waveguide aperture is varied to d1, d2, and d3 by the resonators and then the in-waveguide length in the waveguide is varied to vary the center frequency, thereby constituting a band-pass filter which has desired passing band width and a desired passing center frequency.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a waveguide filter, and more particularly to a TE101 mode N-stage waveguide filter.

[0002]

2. Description of the Related Art A waveguide type filter that constitutes a quarter-wave coupling type multi-stage band pass filter has an out-of-band attenuation characteristic and an in-band pass characteristic depending on the number of stages, the length of a resonator and the size of a coupling window. Is determined. That is, when the number of stages is increased, a steep out-of-band attenuation can be realized, when the length of the resonator is changed, the center frequency is changed, and when the coupling window is increased, the pass band is widened.

FIG. 3 is a top sectional view of an example of a conventional waveguide filter. In the figure, the waveguide filter 1 is
It is composed of a metal case 2 and a metal cover 3, and the two are combined to form a waveguide. The metal case 2 is processed to form five resonators and susceptances for coupling the resonators. This conventional waveguide filter 1 is designed by using a waveguide having a diameter d determined by the pass frequency band, and the center frequency is changed by changing the resonator lengths L1 to L3. ing.

As another conventional waveguide filter, in a band-stop filter having a resonator that resonates at one or more band-stop frequencies on the inner surface of a rectangular waveguide, a region where the resonator is provided. There is also known a waveguide filter having a configuration in which the inside dimension of the waveguide is smaller than the inside dimension of the input / output waveguide (Japanese Utility Model Laid-Open No. 1-169802).

[0005]

However, in the conventional waveguide filter shown in FIG. 3, the resonator length is shortened when the center frequency is increased, and the resonator length is reduced when the center frequency is decreased. There is a problem that the filter length depends on the center frequency because it needs to be long. Further, as the number of stages of filters increases, the filter length greatly changes depending on the center frequency. Therefore, it is difficult to reduce the size of the waveguide filter having a multistage structure, especially when the center frequency is low.

Further, in the conventional waveguide type filter disclosed in Japanese Utility Model Laid-Open No. 1-169802, the inner dimension of the waveguide in the region where the resonator is provided is made smaller than the inner dimension of the input / output waveguide. Thus, the band stop width can be expanded, but the center frequency cannot be changed. Therefore, when the center frequency is low, downsizing is still difficult.

By the way, as a method of reducing the cost of the waveguide filter, casting of mechanical parts is a general method. The conditions for maximizing the cost reduction effect by this casting are the large number of waveguide filters and the small amount of secondary processing. However, the shape of the waveguide filter depends on the frequency, and the frequency range covered by one filter is also limited. Therefore, if the cover band becomes wider, the types of filters increase. As a result, even if the total number of waveguide filters is the same, if the number of types increases, the number of filters per type will decrease, and the effect of cost reduction by casting will become less.

The present invention has been made in view of the above points,
It is an object of the present invention to provide a waveguide type filter which can have the same filter length without depending on the center frequency.

Another object of the present invention is to provide a waveguide filter capable of maximizing the effect of cost reduction due to casting by reducing secondary processing as much as possible.

[0010]

In order to achieve the above object, the present invention provides N (N is an integer of 2 or more) resonators and N resonators.
In an N-stage waveguide filter including a metal case that has been processed to form a coupling window that couples each of the resonators, and a metal cover that covers the metal case, In each of the resonators, the resonator length is a constant value, and the length of the long side of the waveguide diameter is one of M values (M is N or less and an integer of 2 or more) of different values. The configuration is set to.

In the present invention, the center frequency of the filter is changed by changing the length of the long side of the waveguide diameter for each resonator while the resonator lengths of the N resonators are constant. , The filter length can be made constant without depending on the center frequency, and in particular, in the case of a filter with a low center frequency that lengthens the long side of the waveguide diameter, the size of the entire filter can be further reduced compared to the conventional one. Can be noticeable.

Further, since the resonator length is constant regardless of the center frequency of the filter, the position of the coupling window does not change, and only the length of the long side of the waveguide aperture and the size of the coupling window are changed. It is possible to construct a waveguide filter having various center frequencies.

Here, the above resonator length is 1 of the guide wavelength.
It is a length obtained by correcting the susceptance amount to a length of / 2, and the length of the long side of the waveguide aperture is formed by the depth of the engraving of the metal case.

Further, the length of the long side of the waveguide aperture and the size of the coupling window are set according to the pass band width of the band pass filter and the center frequency of the pass band.

Further, in order to achieve the above object, the present invention provides (N1 + N2) (N1 and N2 are respectively N1 and N2 in the first and second waveguide filters which are connected by T-branch and constitute a duplexer. Same or different integer of 2 or more)
Metal case processed to form the resonator and the coupling window that couples each of the (N1 + N2) resonators, and an opening for T-branch is formed at the center in the longitudinal direction. And (N1 + N2) resonators provided on the one side in the longitudinal direction of the metal case from the opening of the (N1 + N2) resonators. And the coupling window that couples them together constitutes the first waveguide filter, and the N2 resonators provided on the other side in the longitudinal direction of the metal case from the opening and the coupling window that couples them. Constitutes a second waveguide filter,
In each of the (N1 + N2) resonators, the resonator length is set to a constant value, and the length of the long side of the waveguide aperture is different (M is (N1 + N2) / 2 or less and 2 or more). Integer) is set to any of the values.

In the present invention, the center frequency of the filter can be varied by changing the length of the long side of the waveguide aperture for each resonator while keeping the resonator length of the (N1 + N2) resonators constant. Therefore, the filter length can be made constant without depending on the center frequency.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 (a) is a perspective view of an embodiment of a waveguide filter according to the present invention, and FIG. 1 (b) is an upper sectional view (transverse sectional view) of FIG. 1 (a). The waveguide filter 10 according to the present embodiment shown in FIGS.
It is composed of a metal case 11 and a flat metal cover 12, and they are combined to form a TE101 mode five-stage waveguide filter.

As shown in FIG. 1B, the metal case 11 is processed to form five resonators and a susceptance for coupling the resonators. Further, the resonator has a length L obtained by correcting the susceptance amount to a length of 1/2 of the guide wavelength, and the length (depth) d of the long side of the waveguide diameter.
It is realized by excavating 1 to d3, and the susceptance is realized by an inductive window (coupling window) such as w1.

In this embodiment, as shown in FIG. 1B, the length d0 of the long side of the waveguide diameter is d1 for each resonator, while the length of the resonator is kept at a constant value L. By changing to d2 or d3, the in-wavelength in the waveguide can be changed and the center frequency can be changed, so that a bandpass filter having a desired pass center frequency and a desired pass center frequency can be configured.

As described above, in the waveguide filter, the out-of-band attenuation characteristic and the in-band pass characteristic are determined by the number of stages, the length of the resonator, and the size of the coupling window.
A steep out-of-band attenuation can be realized, the center frequency changes when the length of the resonator is changed, and the pass band becomes wider when the coupling window is increased. Therefore, the center frequency is changed by changing the length of the resonator in the conventional waveguide filter shown in FIG. 3, but in the present embodiment, as shown in FIG. The length d0 of the long side of the waveguide diameter is d for each resonator.
By changing the cutoff wavelength of the waveguide by changing the wavelength to 1, d2 or d3, the wavelength inside the waveguide is changed and the resonance frequency is changed.

That is, even with the same resonator length L, by shortening the length (depth) of the long side of the waveguide aperture, the center frequency of the filter can be increased and the long side of the waveguide aperture can be increased. The center frequency of the filter can be lowered by increasing the length (depth) of the filter.

As described above, in the present embodiment, the center frequency of the filter is changed by setting the length of the long side of the waveguide aperture, not the resonator length. In the case of the wave tube type filter, since the resonator length of each stage is a constant value L, the filter length can be made the same regardless of the center frequency. Therefore, in particular, if the length of the long side of the waveguide aperture is increased, the size can be reduced, which is very effective in the multi-stage waveguide filter.

Further, in the case of producing a waveguide type filter having various center frequencies, conventionally, it is necessary to carry out secondary processing according to the center frequency even if the filter is cast. That is, when cutting from the E surface of the waveguide, since the resonator length conventionally changes depending on the center frequency, the position of the coupling window also changes, and the waveguide section has the same secondary condition as when processing from the beginning. Processing is required.

On the other hand, in this embodiment, since the resonator length does not change at the constant value L even if the center frequency is changed, the position of the coupling window does not change and the long side of the waveguide aperture of the resonator is changed. Since only the length (depth) and the size of the coupling window need be changed, secondary processing is less and cost can be reduced.

The present invention is not limited to the above-mentioned embodiment, and it goes without saying that the present invention can be applied to, for example, a multi-stage waveguide type filter other than 5 stages. Further, as shown in the perspective view of FIG. 2A and the upper sectional view (transverse sectional view) of FIG. 2B, it is applied to the duplexer 20 in which two five-stage waveguide filters are connected by T-branches. You can also do it. This duplexer 20 has a metal case 2
1 and a cover 22 made of metal, the cover 22 made of metal
A rectangular opening 23 is formed in the central portion in the longitudinal direction.

Also in this case, the number of stages of the waveguide filter is 5.
It is not limited to steps. Further, in FIG. 2, two waveguide filters having the same number of stages (5 stages) are connected by a T-branch, but one waveguide filter has N1 stages and the other waveguide filter has N1 stages. May be N2 (≠ N1).

[0027]

As described above, according to the present invention,
By changing the center length of the filter by changing the length of the long side of the waveguide diameter for each resonator while keeping the resonator length of multiple resonators constant, the filter length does not depend on the center frequency. Therefore, in the case of a filter having a low center frequency in which the long side of the waveguide diameter is made long, the miniaturization of the entire filter can be made more remarkable as compared with the conventional case in which the resonator length is made longer.

Further, according to the present invention, since the resonator length is constant without depending on the center frequency of the filter,
The position of the coupling window does not change, and it is possible to construct a waveguide filter of various center frequencies by changing only the length of the long side of the waveguide aperture and the size of the coupling window. In this case, the secondary processing is small and the cost can be reduced.

Further, according to the present invention, a total of (N1 + N2) (N1 and N2) of the first and second waveguide filters which are connected by T-branch and constitute a duplexer are the same or different. (The above integer) depends on the center frequency by changing the center frequency of the filter by changing the length of the long side of the waveguide diameter for each resonator while keeping the resonator length constant. Since the filter length can be made constant without having to do so, the frequency dependence of the device shape of the duplexer can be reduced, and miniaturization can be expected.

[Brief description of drawings]

FIG. 1 is a perspective view and an upper sectional view of an embodiment of the present invention.

FIG. 2 is a perspective view and an upper sectional view of another embodiment of the present invention.

FIG. 3 is a top sectional view of a conventional example.

[Explanation of symbols]

10 Waveguide filter 11, 21 Metal case 12,22 Metal cover 20 Duplexer 23 opening d0, d1, d2, d3 Length of long side of waveguide diameter

Claims (6)

[Claims] 1. N (N is an integer of 2 or more) resonators,
N-stage waveguide filter including a metal case that has been processed to form a coupling window that couples each of the N resonators, and a metal cover that covers the metal case In, each of the N resonators has a constant resonator length,
In addition, the length M of the long side of the waveguide diameter is different (M is N
A waveguide type filter characterized in that it is set to any of the following values (integer of 2 or more). 2. The resonator length is a length obtained by correcting the susceptance amount to a length of 1/2 of the guide wavelength, and the length of the long side of the waveguide aperture is the digging of the metal case. 2. The waveguide type filter according to claim 1, wherein the waveguide type filter is formed by the depth of the recess. 3. The length of the long side of the waveguide aperture and the size of the coupling window are set according to the pass band width of the band pass filter and the center frequency of the pass band. Item 2. A waveguide filter according to item 1 or 2. 4. In the first and second waveguide filters connected by T-branch to form a duplexer, (N1 + N2) (N1 and N2 are each the same or different integers of 2 or more) resonators and A metal case that has been processed to form a coupling window that couples each of the (N1 + N2) resonators, and an opening for T-branching is formed in the center in the longitudinal direction. And a metal cover for covering the metal case, wherein (N1 + N
2) Among the resonators, the N1 resonators provided on the one side in the longitudinal direction of the metal case from the opening and the coupling window for coupling them are the first waveguide filter. And N2 resonators provided on the other side in the longitudinal direction of the metal case from the opening, and a coupling window for coupling the resonators constitute the second waveguide filter, In each of the (N1 + N2) resonators, the resonator length is set to a constant value, and the length of the long side of the waveguide aperture is different (M is (N1 + N2) / 2 or less and 2 or more). A waveguide filter characterized by being set to one of the values of (integer). 5. The resonator length is a length obtained by correcting the susceptance amount to a length of 1/2 of the guide wavelength, and the length of the long side of the waveguide aperture is the dug of the metal case. The waveguide filter according to claim 4, wherein the waveguide filter is formed by a depth of the recess. 6. The length of the long side of the waveguide aperture and the size of the coupling window are set according to the pass band width of the band pass filter and the center frequency of the pass band. Item 4. The waveguide filter according to Item 4 or 5.