JP2004328458A - Composite band-pass filter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a narrow-band, low loss composite BPF (band-pass filter) for removing unwanted waves in low-pass bands and high-pass bands. <P>SOLUTION: BPFs 1 and 2, in the TE<SB>011</SB>mode and a BPF 3 in the TE<SB>101</SB>mode, are coupled in a concatenated fashion via connection waveguides 5 and 6 to make a composite BPF. The BPFs 1 and 2 in the TE<SB>011</SB>mode make a signal of predetermined passing frequency bands pass through, and the BPF 3 in the TE<SB>101</SB>mode suppresses unwanted mode resonance in low-pass bands and high-pass bands of the passing frequency bands. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a band-pass filter (hereinafter, abbreviated as "BPF") for attenuating unnecessary waves over a wide band by passing only in the vicinity of a center frequency (fo), for example, in a microwave band radar system or the like. About.
[0002]
[Prior art]
For example, as a BPF used in a microwave band radar system, there has been known a BPF in which a plurality of BPFs are cascade-coupled to thereby realize a narrow band property, that is, a characteristic of passing only an extremely narrow frequency band. Documents that disclose such a BPF include, for example, JP-A-5-335809 (first document) and U.S. Pat. No. 3,587,008 (second document).
[0003]
The BPF disclosed in the first document includes a BPF having a center frequency f01, a pass band width (hereinafter, referred to as a “pass band width”) ΔF1, an attenuation amount at the frequency f1 equal to or more than α1, a center frequency f02, and a pass band. Two BPFs whose attenuation at the band width ΔF2 and the frequency f2 are equal to or more than α2 (combined attenuation) are cascaded (three BPFs are cascaded in total) to obtain characteristics close to the characteristics of one BPF. Things. Further, in the BPF disclosed in the second document, two BPFs exhibiting mutually different characteristics are formed in a rectangular waveguide by providing a plurality of passing windows (irises) having different sizes on the inner wall of one rectangular waveguide. It was done. Each of the BPFs disclosed in these documents has the advantage that the passband width of each BPF can be widened, so that power durability can be ensured and the amount of attenuation for suppressing unnecessary waves can be ensured to some extent. is there.
[0004]
[Problems to be solved by the invention]
However, the BPF based on the structures disclosed in the first and second documents is still insufficient for narrow band in light of the recent policy of the International Telecommunication Union (ITU), which is a global standard. Not really. Further, in the BPF having such a structure, since the edge portion of the pass band width is used, the withstand power with respect to the peak power is reduced to half or less than when the BPF is used at the center frequency of the BPF alone. Further, as the number of cascade-coupled BPFs or the number of stages increases, the insertion loss rapidly deteriorates, which is not practical.
[0005]
As a measure to solve such a problem, attention is paid to the narrow band property and high power property (high withstand power against peak power) of the cylindrical cavity resonator, and a plurality of these are cascaded to form a multistage cylindrical cavity resonator. Constructing a BPF is also conceivable. However, in the cylindrical cavity resonator, unnecessary mode resonance always occurs in the low band and the high band of the center frequency of the pass band width. This will be specifically described with reference to FIG.
[0006]
FIG. 7 is a mode chart of a cylindrical cavity resonator, which is described in “MICROWAVE FILTERS, IMPEDANCE-MATCHING NETWORKS, AND COUPLING STRUCTURES, FIG. Is what it is. The horizontal axis is a function of the diameter D [inches] of the cylindrical cavity resonator and the resonator axis length L [inchs] (D / L) ² , and the vertical axis is the resonance frequency of the cylindrical cavity resonator (fD) ² which is a function of f [GHz] and the diameter D [inches] of the cylindrical cavity resonator. In FIG. 7, when (f · D) ² on the vertical axis is selected to be a certain value, the diameter D of the cylindrical cavity resonator and the axial length L of the cylindrical cavity resonator are determined. Also, the resonance frequency in each mode is determined from the dimensions of the cylindrical cavity resonator. For example, as shown in FIG. 7C, when (fD) ² on the vertical axis is selected to be “280”, the diameter D of the cylindrical cavity resonator in the TE ₀₁₁ mode and the diameter D of the cylindrical cavity resonator are determined. The axis length L is determined. Also, the resonance frequency in another mode, for example, the TE ₃₁₁ mode, is determined from the dimensions of the cylindrical cavity resonator.
[0007]
As shown in FIG. 7, the TE ₀₁₁ mode of the cylindrical cavity type resonator has a TE ₃₁₁ mode as a high-frequency heterogeneous resonance mode, and a TE ₂₁₁ mode and the like as a low-frequency hetero resonance mode. When a cylindrical cavity resonator is coupled in multiple stages to form a BPF, the heterogeneous resonance mode significantly degrades the attenuation characteristic in the TE ₀₁₁ mode. Therefore, if a spurious component occurs in the power amplification stage of the transmitter, the spurious component remains unchanged. It may be radiated from the antenna into the air and affect other external radar systems.
[0008]
It is an object of the present invention to provide a composite BPF that can solve the above-mentioned problems at once.
[0009]
[Means for Solving the Problems]
In the composite BPF of the present invention, one or a plurality of cascade-coupled TE _01n mode BPFs and a set or a plurality of cascade-coupled TE _10n mode BPFs are cascade-coupled via coupling components. The TE _01n mode BPF is characterized by passing a signal in a predetermined pass frequency band, and the TE _10n mode BPF is characterized by suppressing unnecessary mode resonance in high and low ranges of the pass frequency band.
[0010]
The TE _01n mode BPF is, for example, a cylindrical cavity filter formed by _cascading a plurality of cylindrical cavity resonators. The TE _10n mode BPF is, for example, an iris or a post having a predetermined susceptance. Is a rectangular waveguide type filter in which a plurality of resonators are formed in a tube by the above member.
[0011]
More specifically, the cylindrical cavity filter is formed by cascading a plurality of cylindrical cavity resonators in which the input direction and the output direction of the electromagnetic wave are at 90 degrees to the resonance axis of the cavity. Alternatively, a plurality of cylindrical cavity resonators in which the input direction and the output direction of the electromagnetic wave are at 180 degrees with respect to the resonance axis of the cavity are cascaded. Alternatively, a cylindrical cavity resonator in which the input direction and the output direction of the electromagnetic wave are 90 degrees with respect to the resonance axis of the cavity and a cylindrical cavity resonator in which the electromagnetic wave is 180 degrees are cascaded.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
<Structure of composite BPF>
FIG. 1 is a top external view of a composite BPF according to an embodiment of the present invention, and FIG. 2 is a side view thereof. This composite BPF is a cylindrical cavity resonator that is cascaded in three stages, that is, two cylindrical cavity resonators in which the input direction and the output direction of the electromagnetic wave are different from each other by 90 degrees with respect to the resonance axis of the cylindrical cavity. a vessel 11, and one cylindrical cavity type resonator 12 in which the direction is 180 degrees from each other are cascaded in this order (the number of stages N = _{3) TE 011} mode BPF1 the first stage BPF. In addition, the connection waveguide 4 is connected to the first stage of the first stage TE ₀₁₁ mode BPF 1, and the next stage TE ₀₁₁ mode BPF 2 having the same structure is connected to the second stage thereof via the connection waveguide 5. Further, a TE ₁₀₁ mode BPF 3 in which four rectangular waveguide type resonators (N = 4) are formed in the tube after the TE ₀₁₁ mode BPF 2 of the next stage via the connecting waveguide 6. Are connected.
Here, for example, the center frequency (fo) ± 2 MHz is set as the pass band width, and the frequency band of the center frequency (fo) ± 5 MHz or more is set as the attenuation band.
[0013]
In the input / output openings of the TE ₀₁₁ mode BPFs 1 and 2, a coupling plate C1 having a hole of a predetermined size is interposed, respectively, and between the cylindrical cavity resonators of the TE ₀₁₁ mode BPFs 1 and 2. Also, a coupling plate C2 having a hole of a predetermined size formed at the center thereof is interposed.
The size of the holes in the coupling plates C1 and C2 is determined according to the value of the susceptance by selecting the number of resonator stages, the pass band width, the ripple value, and the like.
[0014]
The TE ₁₀₁ mode BPF 3 has, for example, a structure as shown in FIG. 3 or FIG.
The TE ₁₀₁ mode BPF 3 having the structure shown in FIG. 3 is called a “side iris type rectangular waveguide BPF” and is shown in a top view of FIG. 3A, a side view of FIG. 3B, and a front view of FIG. As shown in the figure, four spaces are formed between the input side space and the output side space by the inductive side irises 31, 32, 33 extending from the inner wall of the rectangular waveguide toward the center. A TE ₁₀₁ mode BPF 3 in which four waveguide resonators are coupled is formed.
[0015]
The TE ₁₀₁ mode BPF 3 'having the structure shown in FIG. 4 is called a "double post type rectangular waveguide BPF" and has an inductive post 34 in place of the side irises 31, 32, and 33 shown in FIG. It is. The filter characteristics of the TE ₁₀₁ mode BPF 3 ′ are almost the same as those of the structure shown in FIG.
[0016]
<Operation principle of composite BPF>
Next, the operation principle of the composite BPF according to this embodiment will be described.
When the function value K of the free space wavelength λ [cm] and the guide wavelength λg [cm] is represented by “λg / λ {1− (λ / λg) ² }”, the individual components constituting the TE _01n mode BPF The withstand power P _01n due to the peak power of the cylindrical cavity resonator is a value determined by the equation (1), while the withstand power P _{10n with} respect to the peak power of the rectangular waveguide resonator constituting the TE _10n mode BPF is ( The value is determined by the expression 2). These formulas themselves are introduced in "MICROWAVE FILTERS, IMPEDANCE-MATCHING NETWORKS, AND COUPLING STRUCTURES table 15.03-1" and are well known.
[0017]
P _01n [MW] = K · 886 · n · w / (g _k · ω · f ² ) (1)
P _10n [MW] = K · 198 · n · bw / (a · g _k · ω · f ² ) (2)
[0018]
Here, f is the operating frequency (GHz), n is the resonance order of the resonator, the number of half wavelengths of the resonator, w is the ratio of the center frequency fo to the passband width Δf (± Δf / fo), g _k Is the g factor of the filter, a value determined by the number of stages, ripple, and passband width, a is the long side size of the rectangular waveguide, b is the short side size [cm] of the rectangular waveguide, and ω is a value defining the edge (Usually "1").
[0019]
As can be seen from the above equations (1) and (2), the withstand power P ₁₀₁ [MW] of the rectangular waveguide resonator is about 1 of the withstand power P ₀₁₁ [MW] of the cylindrical cavity resonator. / 8 (in the case where the resonance order is n = 1), it is difficult to obtain a narrow-band characteristic when the TE _101- mode BPF is combined in a plurality of stages. On the other hand, the TE ₀₁₁ mode BPF in which a plurality of cylindrical cavity resonators are coupled has a very high withstand power even when the bus band width is narrowed. This is shown in FIG. In FIG. 5, N (= i) is the number of resonator stages. As described above, the narrower the bandwidth of the TE ₁₀₁ mode BPF, the lower the withstand power becomes compared to the TE ₀₁₁ mode BPF.
[0020]
From the viewpoint of insertion loss, the TE ₀₁₁ mode BPF is such that the unloaded Q value of each cylindrical cavity resonator is about 3 to 4 times larger than that of the TE ₁₀₁ mode rectangular waveguide resonator, and the narrow band With such a configuration, sharp attenuation characteristics can be obtained even with a small number of stages, and the insertion loss is small. However, in the TE ₀₁₁ mode BPF, as described above, high-frequency different-mode resonance and low-frequency different-mode resonance always occur in individual cylindrical cavity resonators, and this is a major factor in deteriorating the attenuation characteristics.
[0021]
In _{contrast, TE 101} mode BPF is the insertion loss is relatively large in comparison with the _{TE 011} mode _{BPF, TE 011} high band different mode and a low heterologous mode resonance like mode BPF problems do not occur, If the passband width Δf is designed to be wide, the power durability can be improved in proportion thereto and the insertion loss can be reduced, as is apparent from the equation (2).
[0022]
Therefore, by combining the TE ₀₁₁ mode BPF and the TE ₁₀₁ mode BPF and cascading them, despite having a very narrow band, the insertion loss is small and high power (withstand power with respect to peak power) Is high), and furthermore, it is possible to realize a BPF in which the effects of the low-frequency heterogeneous mode resonance and the high-frequency heterogeneous mode resonance can be almost eliminated (that is, the attenuation characteristic becomes good over a wide band). Can be. The composite BPF of FIG. 1 is based on such a principle.
[0023]
FIG. 6A shows an actual measurement diagram of the filter attenuation characteristics in the S band of the TE ₀₁₁ mode BPF and the TE ₁₀₁ mode BPF in the composite BPF having such a structure. The solid line in FIG. 6A is a characteristic example when two sets of TE ₀₁₁ mode BPFs each having a three-stage coupled cylindrical cavity resonator are cascaded, and the broken line has a four-stage coupled rectangular waveguide resonator. 4 shows a characteristic example of a set of TE ₁₀₁ mode BPFs. In the drawing, TE ₂₁₁ , TE ₃₁₁ , TM ₂₁₀ , TE ₂₁₂ , and TM ₁₁₂ are unnecessary modes for the center frequency fo of the passband width.
On the other hand, FIG. 6B shows an actual measurement diagram of the filter attenuation characteristic of the composite BPF in which the TE ₀₁₁ mode BPF and the TE ₁₀₁ mode BPF shown in FIG. As can be seen from FIG. 6B, in the composite BPF of the present embodiment, it is possible to remove the different resonance modes on the low band side and the high band side with narrow band characteristics.
[0024]
As described above, the features of the present invention have been described with the embodiments. However, the scope of the present invention is not limited to the above-described embodiments, and various design changes can be made.
For example, in this embodiment, two sets of TE ₀₁₁ mode BPFs 1 and 2 having a three-stage coupled cylindrical cavity resonator and one set of TE ₁₀₁ mode BPF 3 having a four-stage coupled rectangular waveguide type resonator are provided. Although an example of a composite BPF in which the BPFs 1 and 2 are cascaded through coupling components has been described, the number of resonator stages in each of the BPFs 1, 2, and 3 and the number of sets of each of the BPFs 1, 2, and 3 may be arbitrary. According to the relationship between the withstand power and the number of resonator stages, as the number of resonator stages increases, the attenuation in a band other than the pass band (pass band) increases, but the withstand power decreases and the insertion loss tends to increase. Therefore, it is desirable to obtain the optimum filter characteristics by reducing the number of resonator stages as much as possible and increasing the number of BPF sets.
[0025]
In the present embodiment, in the TE ₀₁₁ mode BPFs 1 and 2 having the three-stage coupled cylindrical cavity resonator, the 90-degree coupled cylindrical cavity in which the input direction and the output direction of the electromagnetic wave differ from the resonance axis by 90 degrees. An example in which two cylindrical resonators 11 are cascade-coupled and a 180-degree coupling type cylindrical cavity resonator 12 is cascade-coupled to the subsequent stage is shown. Twelve combinations may be arbitrary. May constitute a _{TE 011} mode BPF only two cylindrical cavity shaped cavity 11 of the 90 ° coupling type, constituting the _{TE 011} mode BPF only a cylindrical cavity shaped resonator 12 of a plurality of 180-degree coupling type You can also. In comparison, it has been confirmed that the cylindrical cavity resonator 11 of the 90-degree coupling type has a reduced effect on unnecessary modes, especially the TE ₃₁₁ mode, and is superior in the symmetry of the attenuation characteristic with respect to the center frequency fo. I have.
[0026]
In the present embodiment, an example in which the TE ₀₁₁ mode BPF 1 is used as the input side BPF and the TE ₁₀₁ mode BPF 3 is used as the output side is shown. However, either of them may be the input side or the output side.
Further, in the present embodiment, an example in which the resonance order n of the resonator is 1 has been described, but the principle of the present invention can be similarly applied to the case where the resonance order n is other than 1.
[0027]
【The invention's effect】
As is clear from the above description, according to the present invention, despite having a very narrow band, insertion loss is small, and high power can be secured. It is possible to provide a composite BPF that also eliminates the influence of an unnecessary mode. In accordance with the policy of the International Telecommunication Union (ITU), the standards for spurious emissions of radars and the like are expected to become increasingly strict in the future, and filters that can conform to the standards are desired. The shape BPF is exactly one of the filters according to the policy.
[Brief description of the drawings]
FIG. 1 is a top external view of a composite BPF according to an embodiment of the present invention.
FIG. 2 is a side view of the composite BPF according to the embodiment.
3A and 3B show a structure of a side iris type rectangular waveguide BPF as an example of a TE ₁₀₁ mode BPF, wherein FIG. 3A is a top view, FIG. 3B is a side view, and FIG.
4A and 4B show a structure of a double post type rectangular waveguide BPF as an example of a TE ₁₀₁ mode BPF, wherein FIG. 4A is a top view, FIG. 4B is a side view, and FIG.
FIG. 5 is a diagram showing a relationship between power durability and pass bandwidth of a TE ₁₀₁ mode BPF and a TE ₀₁₁ mode BPF.
6A is an actual measurement diagram of the filter attenuation characteristics in the S band of the TE ₀₁₁ mode BPF and the TE ₁₀₁ mode BPF, and FIG. 6B is an actual measurement diagram of the filter attenuation characteristics of the composite BPF.
FIG. 7 is a mode chart of a cylindrical cavity resonator.
[Explanation of symbols]
1, 2 TE ₀₁₁ mode BPF
3, 3 'TE ₁₀₁ mode BPF
4, 5, 6 Connecting waveguide 11 90-degree coupling type cylindrical cavity resonator 12 180-degree coupling type cylindrical cavity resonator 31, 32, 33 Side iris 34 Inductive post C1, C2 Coupling plate

Claims (5)

One or more sets of cascaded TE _01n mode band-pass filters and one or more sets of cascaded TE _10n mode band-pass filters are cascaded through coupling components. ,
The TE _01n mode band pass filter passes a signal in a predetermined pass frequency band, and the TE _10n mode band pass filter causes unnecessary mode resonance in a high band and a low band of the pass frequency band. Characterized by suppression
Composite band pass filter. The TE _01n mode band pass filter is a cylindrical cavity filter formed by _cascading a plurality of cylindrical cavity resonators, and the TE _10n mode band pass filter has a predetermined susceptance. Characterized in that it is a rectangular waveguide filter in which a plurality of resonators are formed in a tube by a member having
A composite band pass filter according to claim 1. The cylindrical cavity filter, characterized in that a plurality of cylindrical cavity resonators in which the input direction and the output direction of the electromagnetic wave are at 90 degrees to the resonance axis of the cavity are cascaded,
A composite band pass filter according to claim 2. The cylindrical cavity filter is characterized in that a plurality of cylindrical cavity resonators in which an input direction and an output direction of an electromagnetic wave are at 180 degrees with respect to a resonance axis of the cavity are cascade-coupled,
A composite band pass filter according to claim 2. The cylindrical cavity filter includes a cylindrical cavity resonator in which an input direction and an output direction of an electromagnetic wave are at 90 degrees with respect to a resonance axis of the cavity, and a cylindrical cavity resonator having a 180 degrees direction. Characterized by being cascaded,
A composite band pass filter according to claim 2.

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