JPH0226801B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a small microwave band-stop filter that has a large attenuation amount in a microwave stop band and a small insertion loss in a pass band. Conventionally, as this type of filter, a method has been used in which a dielectric resonator tuned to a stopband frequency is inserted into a transmission line such as a waveguide. However, such a band rejection filter has the following drawbacks. That is, first of all, since there is no matching in the passband other than the stopband, the standing wave ratio in the passband is large, and secondly, the standing wave ratio between the dielectric resonator and the wall of the waveguide is large. Because the distance is small, the no-load Q value of the resonant system decreases,
This method has disadvantages in that it is not possible to sufficiently increase the amount of attenuation in the stopband, particularly at the attenuation center frequency that requires attenuation, and in addition, insertion loss in the passband increases. SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a small microwave band-stop filter that overcomes these drawbacks and has a large amount of attenuation in the stop band and a small insertion loss in the pass band. To achieve such an objective, the present invention
□ TE○ ₀₁ σ in ₁₀ mode or TE○ ₁₁ mode waveguide
In a microwave band-stop filter configured by coupling mode dielectric resonators, the dielectric resonators are arranged such that a plane of symmetry with respect to the odd mode electromagnetic field of the dielectric resonators is included in the cross section of the waveguide. At the same time, the wall of the waveguide adjacent to the dielectric resonator is made to have a symmetrical structure with respect to the plane of symmetry, with the H-plane portion protruding outward so that the resonant frequency of the waveguide is lower than the resonant frequency of the dielectric resonator. This is characterized by matching at high frequencies. The present invention will be explained in detail below with reference to the drawings. Figures 1A to 1C show an example of the configuration of a conventional microwave band-stop filter, in which a TE○ ₀₁ δ mode is inserted into a rectangular TE□ ₁₀ waveguide 1 with a width a and a height b. A dielectric resonator 2 (diameter D) is inserted. Figures B and C show the H plane 1H and E plane 1E of the waveguide 1.
This is a view of the blocking filters, and the dielectric resonator 2 is arranged at a distance d from one E surface 1E of the waveguide 1. Here, the TE○ ₀₁ δ dielectric resonator 2 has a high frequency magnetic field shown by a dotted line in FIG. 2A, and a high frequency electric field distributed along the circumference as shown by a solid line in FIG. 2B. When such a high-frequency magnetic field is coupled with a high-frequency magnetic field parallel to the H-plane 1H of the TE□ ₁₀ waveguide 1 as shown in FIG. 3, an operation according to an equivalent circuit as shown in FIG. 4 is achieved. . The resonant frequency of the parallel resonant circuit of the capacitance C _D and the inductance L _D forming this equivalent circuit matches the resonant frequency of the dielectric resonator 2, and the resonant frequency in the frequency attenuation characteristic shown in FIG.
Gives large attenuation in _R. Here, the solid line indicates the case where the interval d is small, and the dotted line indicates the case where the interval d is large (however, 0<d<a/2). As can be seen from the equivalent circuit in FIG. 4, the parallel circuit L _D C _D becomes capacitive at frequencies higher than the resonant frequency _R , and conversely becomes inductive at frequencies lower than the resonant frequency _R. Therefore, at any frequency, matching cannot be achieved unless the frequency is sufficiently far from the resonance frequency _R , resulting in the attenuation characteristic as shown in FIG. Furthermore, in order to increase the coupling between the dielectric resonator 2 and the waveguide 1 and increase the amount of attenuation at the resonant frequency _R , the distance d between the two should be increased,
It is necessary to bring the dielectric resonator 2 close to the center of the waveguide 1. In this case, as shown by the dotted line in FIG. 5, the amount of attenuation at the resonance frequency _R increases, but on the other hand, the matching at the pass frequency _P deteriorates, and the amount of attenuation at this frequency _P also increases. Furthermore, in the structure of FIG. 1A, the distance between the dielectric resonator 2 and the H-plane 1H of the waveguide 1 is at most (b
-D)/2 and cannot be made higher than that, so most of the magnetic flux from the resonator 2 crosses the H plane 1H of the waveguide 1, generating an induced current, and due to the conductor loss. The no-load Q value of the resonant system decreases, and sufficient attenuation cannot be obtained at the resonant frequency _R. Therefore, in order to solve the above-mentioned drawbacks, in the present invention, a band rejection filter is configured, for example, as shown in FIGS. 6A to 6D. That is, in the present invention, the H-plane portion 11H of the waveguide 11 that is close to the dielectric resonator 12 is oriented toward the outside of the waveguide by a length b' on the upper side and a length b'' on the lower side. Make it stand out,
As shown in FIG. 7, an inductance L is formed and inserted in series with the parallel resonant circuit of the capacitance C _D and the inductance L _D corresponding to the dielectric resonator 12 by the action of the magnetic energy in the above-mentioned protruding portion. . Furthermore, the surface 11 which is a discontinuous point of this protruding portion
As shown in Fig. 8, an E wave 13 having an electric field in the traveling component of the wave is generated in A to 11D, and this E wave 1
Since 3 is an evanescent wave (damped wave), a capacitance C is formed and acts as a parallel capacitance as shown in FIG. Now, in the case of _P > _R , as mentioned above, L _D
The C _D parallel circuit exhibits capacitance, and when its capacitance is expressed as C', the equivalent circuit of FIG. 7 becomes as shown in FIG. 9. In this case, the matching condition is ω _P L=ω _P CW ² /1+ω _P ² C ² W ² +1/2ω _P C′ (1) where W is the characteristic field impedance of the waveguide 11. _P = 2π _P. Here, by substituting the relationship ω _P C′=ω _P C _D −1/ω _P L _D (2), equation (1) becomes as follows. ω _P L=ω _P CW ² /1+ω _P ² C ² W ² +ω _P L _D /2(ω _P ² L _D
C _D −1) (3) Also, considering that L _D C _D is tuned at ω _R = 2π _R , equation (3) becomes ω _P L = ω _P CW ² /1 + ω _P ² C ² W ² +ω _R ² ω _P L _D /2(ω
_P ² −ω _R ² )(4), and considering the condition ω _P >ω _R (5), it always becomes ω _P L>0 (6), so the above-mentioned inductance L can always be realized. In other words, as shown in FIG. 6A, the waveguide 1
By forming a convex portion projecting vertically in 1, an inductance L and a capacitance _C are newly formed as shown in the equivalent circuit of FIG. Matching can be achieved for a high passing frequency _P.
The frequency-attenuation characteristic in this case is as shown in FIG. The actual measurement results of the specific example of the present invention are compared with the conventional example as follows.

[Table] Also, in this example, since matching can always be achieved with respect to the passband, as shown in Fig. 6A~
As shown in D, the dielectric resonator 12 is connected to the waveguide 11.
The waveguide 11 of the resonator 12 is placed near the center of the resonator 12.
Even if a sufficient degree of attenuation is provided at the resonant frequency _R , matching can be achieved at the pass frequency _P by increasing the coupling to the resonant frequency R. In the structure of this example, as can be seen from Figure 6C,
The maximum distance between the dielectric resonator 12 and the H plane 11H of the waveguide 11 is b + b' + b'' - D/2, so the high frequency magnetic field of the resonator 12 is There is sufficient attenuation in the vicinity of the plane 11H, so there is no deterioration of the no-load Q value of the resonant system due to conductor loss, which conventionally occurs in the _H plane. Next, another embodiment of the present invention is shown in FIGS. 11A to 11C. Here, the waveguide 11 has the same structure as in FIGS. The resonator 12 is arranged at an angle θ with respect to the horizontal plane.In this case, the high frequency magnetic field of the resonator 12 is coupled obliquely to the high frequency magnetic field of the waveguide 11, so the degree of coupling is proportional to sinθ. In other words, the stop band becomes narrower.In the case of θ=90°, the above-mentioned Fig. 6A
This corresponds to example ~D, and the degree of bonding is maximum. Since the parallel circuit L _D C _D in the equivalent circuit shown in FIG. 7 changes depending on the magnitude of this inclination angle θ, it is necessary to change the depths b' and b'' of the protruding portion accordingly. For example, , the smaller the angle θ, the smaller the depths b′ and b″ must be. Although we have only described the case where one dielectric resonator 12 is used above, it is also possible to use a waveguide with a plurality of band rejection filters having the structure shown in FIGS. 6A to D or 11A to C. They can also be arranged along the axial direction. For example, as shown in FIG.
The waveguide 21 formed with
and 22B, the distance between these protruding portions 21A, 21B and 22A, 22B is λg/4 (2n+1) (λg is TE□ ₁₀ in the waveguide). wavelength, n is a positive integer), and these protruding parts 21A and 21B
and 22A and 22B, by placing dielectric resonators 23 and 24 in waveguides 21 and 22, in any desired bandwidth.
A band-stop filter can be provided that can provide any desired amount of attenuation. As is clear from the above, the seventh
The equivalent circuit shown in the figure is not limited to the TE□ ₁₀ waveguide example, but can also be realized using general waveguides, such as TE○ ₁₁
It can also be applied to the case of circular waveguides of modes. In this case, as in the example shown in FIG. 13, in the TE○ ₁₁ circular waveguide 32, the outer periphery of the resonator 32 and _the guide The portions with the shortest distance from the wave tube 31 are made to protrude outward as shown in the figure to form protruding portions 31A and 31B. Thereby, the series inductance L in the equivalent circuit of FIG. 7 can be formed. Although specific embodiments of the present invention have been described above, the present invention is not limited to these embodiments. Parallel resonant circuit as shown
It may include any structure in which C _D L _D is inserted in series with the transmission line, an inductance L is inserted in series with this parallel resonant circuit, and a capacitance C is inserted in parallel. In order for the parallel resonant circuit C _D L _D to be inserted in series in the transmission line, a resonant current must flow when this equivalent circuit excites the input and output terminals with opposite signs. That is, since the input/output terminals of the filter are excited by an electromagnetic field in an odd mode, it is necessary to couple a dielectric resonator to such an electromagnetic field in an odd mode. Therefore, the plane of symmetry for the odd mode of the dielectric resonator must be included in the cross section of the waveguide. The electromagnetic field mode of the resonator is the second
In the case of the TE○ ₀₁ δ mode as shown in Figures A and B, the plane containing the axis of the disc-shaped resonator forms such a plane of symmetry, so for example, as shown in Figures 6B and C, By including the axis of the resonator 12 in the cross section SS of the waveguide 11, the above-mentioned plane of symmetry is included on the cross section SS. In this case, the dielectric resonator and the waveguide are
Magnetically couple as shown in the figure. The reason for this is that the waveguide is excited by an odd mode electromagnetic field whose plane of symmetry is the cross section of the waveguide, so the high frequency magnetic field is at its maximum and the electric field is at its minimum near the cross section of the waveguide. Therefore, the resonator is magnetically coupled to the waveguide, and in order to adjust the degree of coupling, it is necessary to adjust the angle between the direction of the high-frequency magnetic field in the plane of symmetry of the dielectric resonator and the high-frequency magnetic field in the cross section of the waveguide. Just change Ψ, Ψ=
The coupling is maximum when 0, and there is no coupling when Ψ=90°. In the example of FIGS. 11A to 11C, the magnetic field of the resonator is in the axial direction of the disk, and
Since the high frequency magnetic field of the waveguide is parallel to the H plane, Ψ
=90°-θ, and the degree of coupling can be adjusted according to θ. Regarding the insertion of the series inductance L and the parallel capacitance C described above, the tube wall of the portion of the waveguide that is close to the dielectric resonator that will become the H-plane is oriented outward so that it has a symmetrical structure with respect to the above-mentioned plane of symmetry. This can be achieved by making it stand out. It goes without saying that the technical concept of the present invention can also be applied to a sharp notch filter constructed by arranging a dielectric resonator in another shielding box coupled to a waveguide. As described above, according to the present invention, it is possible to construct a small band-stop filter with a length comparable to the diameter of a dielectric resonator, and its unloaded Q value is high and matching can be achieved in the pass band. Low insertion loss in the band.

[Brief explanation of drawings]

FIGS. 1A, B, and C are a perspective view, a plan view seen from the H plane, a front view seen from the E plane, and FIG. 2A, respectively, showing an example of a conventional band rejection filter.
and B are diagrams showing the electromagnetic field distribution of the dielectric resonator, Fig. 3 is an explanatory diagram of the state in which the dielectric resonator is magnetically coupled to the waveguide, and Fig. 4 is an equivalent circuit diagram of a conventional band rejection filter. , FIG. 5 is a frequency-attenuation characteristic diagram, and FIGS. 6A, B, C, and D are a perspective view, a plan view as seen from the H plane, and a plan view as seen from the E plane, respectively, showing an example of the band rejection filter of the present invention. 7 is an equivalent circuit diagram of the band rejection filter of the present invention, FIG. 8 is an explanatory diagram of the electric field distribution in FIG. 6C, and FIG. 9 is an illustration of the electric field distribution in FIG. 7. passing frequency
Fig. 10 is an equivalent circuit diagram for _P , and Fig. 10 is a characteristic curve diagram showing an example of frequency-attenuation characteristics in the present invention.
Figures A, B, and C show other examples of the present invention, respectively, a plan view as seen from the H plane, a front view as seen from the E plane, and a side view as seen from the input side. FIG. 13 is a perspective view showing still another example of the present invention. 1...TE□ ₁₀ waveguides, 1H...H plane, 1E...E plane,
2...TE○ ₀₁ δ dielectric resonator, C _D ...Capacity of parallel resonator, L _D ...Inductance of parallel resonator, 11...
TE□ ₁₀ waveguide, 11H...H plane, 11E...E plane, 1
1A, 11B, 11C, 11D... protruding surface, 12...
TE○ ₀₁ δ dielectric resonator, 13... E wave, L... series insertion inductance, C... parallel capacitance, C'... capacitance of L _D C _D parallel circuit when _P > _R , 21, 22... waveguide ,
21A, 21B, 22A, 22B...Protrusion, 2
3, 24...Dielectric resonator, 31...TE○ ₁₁ waveguide,
31A, 31B...protrusion, 32...TE○ ₀₁ δ dielectric resonator.

Claims (1)

[Claims] 1 In the waveguide of TE□ ₁₀ mode or TE○ ₁₁ mode
TE○ ₀₁ In a microwave band-stop filter configured by coupling σ-mode dielectric resonators, the dielectric resonator is arranged such that the plane of symmetry with respect to the odd-mode electromagnetic field of the dielectric resonator is the cross section of the waveguide. The dielectric resonator is arranged such that the wall of the waveguide adjacent to the dielectric resonator has a symmetrical structure with respect to the symmetry plane, with the H-plane portion protruding outward. A microwave band-stop filter characterized by matching at a frequency higher than the resonance frequency of the microwave band-stop filter. 2. In the microwave band-stop filter according to claim 1, a protruding portion of the tube wall is inserted into the waveguide in the tube axis direction by λg·(2n+1)/4 (where λg is the wavelength within the waveguide, n is a positive integer), and the dielectric resonator is arranged in each of the plurality of protruding parts.