JPH04401B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a bandpass filter that is used in the microwave band or millimeter wave band and utilizes the TE ₀₁₁ mode resonance of a cylindrical cavity resonator with a high no-load Q.

In order to simplify the explanation, here, we will limit the explanation to three frequency bands, and let the frequencies of these three frequency bands be f ₁ , f ₂ , and f ₃ , with the relationship of f ₁ < f ₂ < f ₃ . Explain it as something.

Here, explanation will be given assuming that the wave of f ₂ is filtered from the waves consisting of the above three frequency bands.

There is a polar filter as a bandpass filter with steep attenuation characteristics, but in this filter, cavity resonance is used to place the attenuation pole, which has an infinite amount of attenuation, near the passband. It is necessary to realize positive and negative connections with different polarities as connections between devices. There are two ways to achieve coupling with different polarities: a method that uses a combination of magnetic field coupling and electric field coupling, and a method that uses magnetic fields that have different polarities _.
Since it is difficult to obtain electric field coupling in bandpass filters that utilize mode resonance, the latter method has been adopted in conventional bandpass filters.

First, the conventional bandpass filter shown in FIG. 1 will be briefly explained.

In FIG. 1, FIG. 1a is a plan view with some parts missing, and FIG. 1b is a side view with some parts missing.
2 is an input/output waveguide, 3 to 6 are cylindrical cavity resonators, and 7 is an input/output waveguide.
-11 are coupling holes for magnetic field coupling.

The input/output waveguide 1, the cylindrical cavity resonators 3 to 6, and the input/output waveguide 2 are sequentially coupled through coupling holes 7 to 11,
Furthermore, the cavity resonators 3 and 6 are coupled through a coupling hole 12.

At this time, cavity resonators 4 and 5 are arranged so that their circular cross sections overlap, whereas cavity resonator 3
and 6 are arranged offset by the radius of the circular cross section. Therefore, as is clear from the electromagnetic field distribution in the cavity resonator 3 shown in FIG. 2, the polarity of the coupled magnetic field H is different between the coupling hole 9 and the coupling hole 12, and and negative coupling is realized.

Now, waves f ₁ , f ₂ , and f ₃ are introduced into input/output waveguide 1, and the axial length of resonators 3 to 6 is selected to be 1/2 of the wavelength in the tube of TE ₀₁ mode with frequency f ₂ . The waves of f ₂ coupled through the coupling holes 7 to 10 and 12 are transmitted to the cavity resonators 3 to 12.
It resonates at 6. The f ₂ wave is further extracted to the input/output waveguide 2 through the coupling hole 11 . Since the other waves f ₁ and f ₃ do not resonate in the resonators 3 to 6, most of the power is reflected to the input/output waveguide 1. At this time, due to the action of the negative coupling hole 12, the shearing characteristic becomes steep, and even if the frequencies f ₁ and f ₃ are close to the frequency f ₂ , the waves of f ₁ and f ₃ can provide a large amount of attenuation.

However, such a bandpass filter has a drawback that it cannot be accommodated in a low-height space because the cavity resonators are stacked in two stages.

In order to eliminate these drawbacks, this invention is constructed by combining a pair of semicircular cross-section cavity resonators with flat wall surfaces in contact with a cylindrical cavity resonator.The drawings will be explained in detail below. do.

FIG. 3 shows an embodiment of this invention, and shows 1, 2,
4, 5, 7-11 are the same as in Figure 1, 13,
14 is a cavity resonator with a semicircular cross section, 15 is a flat wall surface, and 16 is a coupling hole for electric field coupling. Figure a is a plan view, and figure b is a side view with some parts missing.

Input/output waveguide 1, cavity resonator 13, 4, 5, 1
4 and the input/output waveguide 2 are sequentially connected to a coupling hole 7 for magnetic field coupling.
.about.11, and the cavity resonators 13 and 14 are further coupled through a coupling hole 16 for electric field coupling. The coupling holes 7, 8, 10, 11 are 30 mm with respect to the flat wall surface 15.
It is located at an angle of ~45 degrees.

Since the flat wall surface 15 is provided in a plane perpendicular to the electric field E of the cylindrical cavity resonator shown in FIG. 2, the distribution of the electromagnetic field does not change by providing this wall surface 15. The electromagnetic field in the cavity resonators 13, 14 having a semicircular cross section is the same as the electromagnetic field distribution in the semicircular portion of FIG. The coupling hole 16 has an electric field E perpendicular to the wall surface.
By providing the coupling hole 9 at a position where it is maximum, it becomes a coupling hole for electric field coupling, and a negative coupling having a different polarity from the coupling hole 9 for magnetic field coupling can be realized.

Now, waves f ₁ , f ₂ , and f ₃ are introduced into the input/output waveguide 1, and the axial lengths of the resonators 4, 5, 13, and 14 are set to the frequency f ₂
If 1/2 of the tube wavelength of the TE ₀₁ mode is selected, the f ₂ wave coupled through the coupling holes 7 to 10 and 16 resonates in the cavity resonators 13, 4, 5, and 14. The f ₂ wave is further extracted to the input/output waveguide 2 through the coupling hole 11 . The other f ₁ and f ₃ waves are transmitted through resonators 4, 5,
13 and 14 do not resonate, most of the power is reflected to the input/output waveguide 1. At this time, the shearing characteristic becomes steep due to the function of the negative coupling hole 16, and even if the frequencies f ₁ and f ₃ are close to the frequency f ₂ , the waves of f ₁ and f ₃ It is possible to provide a large amount of attenuation.

Therefore, the band-pass filter of the present invention has the function of a band-pass filter with no steepness or cut-off characteristics similar to the conventional filter. Semicircular cross-section cavity resonator TE ₀₁₁
Mode is an IEEE Transaction published in July 1980.
on Microwave Theory and Techniques, Vol.
Paper published in MTT-28, No.7, pp.695-699 “TE ₀₁₁ Mode Sectral Circular Cylindrical
As shown in Figure 3 of ``Cavies Filters'', the no-load Q is higher than that of the TE ₁₁₁ mode of the cylindrical cavity resonator, so the loss is lower than that of the TE ₁₁₁ mode filter, similar to conventional filters.

As is clear from FIG. 3, in the bandpass filter of the present invention, the cavity resonators 4,
5, 13, and 14, it has the advantage that it can be accommodated in a low-height space. Further, in such a bandpass filter, many unnecessary resonance modes are suppressed by the flat wall surface 15. TE ₂₁₁
mode and TE ₃₁₁ mode remain unsuppressed and their resonant frequencies are close to the TE ₀₁₁ mode, but the axial magnetic fields of these modes are large at the flat wall surface 15 and 0 degrees, 90 degrees and 0 degrees, respectively. It is a position forming an angle of 60 degrees, and as shown in Fig. 3, the coupling hole 7,
This can be suppressed by positioning angles 8, 10, and 11 at 30 to 45 degrees.

FIG. 4 shows another embodiment of this invention, 1 to 6.
are the same as in Fig. 1, 13 and 14 are cavity resonators with a semicircular cross section, 15 is a flat wall surface, 7, 8, 10~
Coupling holes 12, 17 to 19 are for magnetic field coupling, and 16 is a coupling hole for electric field coupling.

Input/output waveguide 1, cavity resonator 3, 13, 4,
5, 14, 6 and the input/output waveguide 2 are sequentially connected to coupling holes 7, 8, 17, 18, 19, 10, 11 for magnetic field coupling.
Further, the cavity resonators 3 and 6 are coupled by a coupling hole 12 for magnetic field coupling, and the cavity resonators 13 and 14 are coupled by a coupling hole 16 for electric field coupling.

The function of the bandpass filter of this invention is basically the same as that of the bandpass filter of FIG. In addition to the effect of the coupling holes 13 for negative coupling, the number of cavity resonators is increased, so that the shear cutoff characteristic is even steeper than that of the bandpass filter of FIG.

Also in the filter of this invention, as is clear from FIG. 4, the cavity resonators 3 to 6, 13, 1
4, it has the advantage that it can be accommodated in a low-height space.

In addition, in the above, the number of cavity resonators having a semicircular cross section is 2, and the number of cylindrical cavity resonators is 2 or 4.
However, the present invention is not limited to this, and may be used in cases where the number of cavities with a semicircular cross section is four or more, and the number of cylindrical cavity resonators is six or more.

As described above, the bandpass filter according to the present invention combines a cylindrical cavity resonator that resonates in the TE ₀₁₁ mode and a cavity resonator with a semicircular cross section that is paired with flat wall surfaces in contact with each other. By providing coupling holes for electric field coupling in the flat wall surface, it is possible to create a thin filter with steep shearing characteristics, and it is said that it can be accommodated in a low-height space. There are advantages.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram showing a conventional bandpass filter, FIG. 2 is a diagram showing the electromagnetic field distribution in a cavity resonator, and FIG. 3 is a schematic configuration diagram showing an embodiment of the present invention. FIG. 4 is a schematic diagram showing another embodiment of the present invention. In the figure, 1 and 2 are input and output waveguides, 3 to 6 are cylindrical cavity resonators, 7 to 12 and 17 to 19 are coupling holes for magnetic field coupling, and 13 and 14 are cavity resonators with semicircular cross sections. , 15 is a flat wall surface, and 16 is a coupling hole for electric field coupling. In the drawings, the same or corresponding parts are denoted by the same reference numerals.

Claims (1)

[Claims] 1 In a bandpass filter in which cavity resonators are coupled through a coupling hole, a cylindrical cavity resonator that resonates in the TE ₀₁₁ mode is used as the cavity resonator, and a semicircular cross section that forms a pair by abutting a flat wall surface. The above-mentioned cavity resonators are arranged on the same plane, and the coupling between the pair of semicircular cross-section cavity resonators is an electric field coupling through the coupling hole provided in the flat wall surface, and the above-mentioned cylindrical cavity Coupling between the resonators and between the cylindrical cavity resonator and the cavity resonator having a semicircular cross section is a magnetic field coupling, and a coupling hole for magnetic field coupling provided in the cavity resonator having a semicircular cross section is provided. A band pass filter characterized in that it is provided at a position forming an angle of approximately 30 to 45 degrees with respect to the flat wall surface.