JP2016119531A - Tunable evanescent mode band pass filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a tunable evanescent mode band pass filter which is reduced in size, reduces a change of a bandwidth even if a frequency is changed, and reduces a passage loss.SOLUTION: A plurality of capacitive fins 4 each formed from a thin metal plate 3 are held between cutoff waveguides 1 and 2 which are bisected on an H plane and a dielectric plate 7 that is disposed along the metal plates 3 on at least one side of the cutoff waveguides 1 and 2, is installed so as to be movable in a direction of H plane. Further, series capacitive fins 5 are provided which are formed towards a neighboring capacitive fin 4 in any height direction of at least one capacitive fin 4 on the metal plate 3 and on at least one side of the cutoff waveguides 1 and 2, a projection 12 in the direction of H plane is provided oppositely to the metal plates 3 and at a position between neighboring capacitive fins 4. Thus, by making the dielectric plate 7 movable, a resonant frequency can be changed and even if the resonant frequency is changed, a bandwidth of the filter can be prevented from being changed.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a tunable evanescent mode band-pass filter, and in particular, among tunable waveguide band-pass filters that are used in microwaves and millimeter waves and have a characteristic that a change in bandwidth is small even when the frequency is changed. The present invention relates to a tunable evanescent mode bandpass filter using a waveguide size that is cut off in the passband.

  As a microwave and millimeter wave band filter whose resonance frequency can be arbitrarily changed, there is a technique described in, for example, Japanese Patent No. 5187766 “Tunable Band Pass Filter” of Patent Document 1.

  The technique described in Patent Document 1 includes a filter element made of a thin metal plate that is sandwiched by a rectangular waveguide divided into two at the center of the H plane (wide surface) and designed to resonate at a predetermined frequency; A structure that is arranged either above or below the metal plate so as to extend in the longitudinally extending direction of the metal plate, and the connecting portion is movable with respect to the rectangular waveguide protruding outside the rectangular waveguide. And a dielectric plate. Thus, by changing the relative positional relationship, that is, the distance between the dielectric plate and the metal plate from the outside, the length of the wide surface of the waveguide can be improved by utilizing the wavelength shortening effect due to the dielectric constant. Is a technique for realizing a change in the center frequency, that is, a frequency shift.

  According to such a technique, the resonance frequency of the filter can be changed by changing the distance between the dielectric plate and the filter element made of a thin metal plate, and the dielectric plate is used as the filter element. As the frequency approaches (resonance frequency decreases), the coupling coefficient between the filter elements changes in the direction of increasing. That is, the filter described in Patent Document 1 has a feature that the change in bandwidth is very small even if the resonance frequency is varied over a wide range by the dielectric plate. In general, such a filter is referred to as a “tunable bandpass filter” as a filter that changes the frequency.

  Other conventional techniques of a tunable evanescent mode bandpass filter include, for example, “High-Q RF-MEMS Tunable Evanescent-Mode Cavity Filter” (Microwave Symposium Digest. 2009. MTT'09. IEEE MTT). -S International Digital Object Identifier), Non-Patent Document 2, “High Q RF-MEMS 4-6 GHz Tunable Evanescent-Mode Cavity Filter” (IEEE Trans. MTT-Vol. 58, NO.2, FEBRUARY 2010) There is technology.

  In Non-Patent Document 1 and Non-Patent Document 2, in a waveguide evanescent mode band-pass filter, a capacitive post provided in the waveguide is combined with a cantilever switch capacitance network, and connected to the capacitive post by operation of the cantilever. By switching the capacitance, the resonance frequency variable element of the filter is made to function. In the case of the technique described in Non-Patent Document 1, the no-load Q is about 270 to 510 with respect to the variable frequency range from 4.4 GHz to 5.5 GHz. In the case of the technique described in Non-Patent Document 2, the configuration is the same as that in Non-Patent Document 1. However, for a variable frequency range from 4.1 GHz to 5.6 GHz, no load Q is It is about 350 to 400.

Japanese Patent No. 5187766 (page 3-4)

“High-Q RF-MEMS Tunable Evanescent-Mode Cavity Filter”, Microwave Symposium Digest. 2009. MTT '09. IEEE MTT-S International Digital Object Identifier: 10.1109 / MWSYM. 2009. 5165904 Publication Year: 2009, Page (s): 1145-1148 “High Q RF-MEMS 4-6 GHz Tunable Evanescent-Mode Cavity Filter”, IEEE Trans. MTT-Vol. 58, NO.2, FEBRUARY 2010

  In the case of the technique described in Patent Document 1, a waveguide having a size that allows a passband frequency to pass through without loss is divided into two on the H plane as a filter, and a metal plate for forming a filter element is sandwiched therebetween. It has a configuration. Therefore, there is a problem that the shape becomes very large depending on the frequency. In order to reduce the size of the waveguide, a measure is taken to construct a so-called ridge waveguide in which a protrusion is provided at the center of the H surface of the waveguide of the filter element formed of a metal plate. It is also possible. However, although the ridge structure as described above can reduce the waveguide size to some extent, if the ridge part becomes large, the part constituting the filter becomes very low, which is not a realistic dimension. come.

  The techniques described in Non-Patent Document 1 and Non-Patent Document 2 are based on the same configuration, and both are capacitive posts provided in the waveguide in the waveguide evanescent mode bandpass filter. In addition, by combining the cantilever switch capacitance network and switching the capacitance directly connected to the capacitive post by the operation of the cantilever, it is operated as a resonant frequency variable element of the filter. For this reason, there is a problem that the configuration related to frequency variation is complicated due to the configuration of the tunable method, and an increase in passage loss cannot be avoided.

(Object of the present invention)
The present invention has been made in view of such circumstances, and provides a tunable evanescent mode band-pass filter that is significantly reduced in size, has little bandwidth change even when the frequency is changed, and has low pass loss. The purpose is to do.

  In order to solve the above-described problems, the tunable evanescent mode bandpass filter according to the present invention mainly adopts the following characteristic configuration.

  A tunable evanescent mode bandpass filter according to the present invention is a tunable evanescent mode bandpass filter having a characteristic that a change in bandwidth is small even when a frequency is changed, and an H plane in which a cutoff waveguide is a wide surface. And is divided into two parts by sandwiching a plurality of capacitive fins formed of a thin metal plate in the longitudinal direction of the cut-off waveguide. A dielectric plate is disposed along at least one side of the cut-off waveguide along the metal plate, and the position of the dielectric plate is set to move in the H-plane direction of the cut-off waveguide. It is characterized by that.

  According to the tunable evanescent mode bandpass filter of the present invention, the following effects can be obtained.

  A tunable evanescent mode bandpass filter according to the present invention has a configuration in which a plurality of capacitive fins formed of a thin metal plate are sandwiched between cut-off waveguides divided into two on the H plane, and adjacent capacitive fins. Because it has a structure that forms series capacitive fins that give more electrical capacitance between them, even if the frequency is low using a small waveguide, there is little passing loss and the frequency Even if the frequency is changed over a wide range, a tunable evanescent mode bandpass filter with a small change in coupling coefficient can be provided, so that the bandwidth can be changed even if the size is greatly reduced and the frequency is changed. It is possible to realize a filter with a small amount of passage loss.

It is a perspective view which shows one structural example of the tunable evanescent mode bandpass filter by this invention. FIG. 2 is an exploded perspective view illustrating an example of an internal structure of a tunable evanescent mode bandpass filter illustrated in FIG. 1. FIG. 2 is an exploded perspective view for explaining an example of a structure of a series capacitive fin provided in the tunable evanescent mode bandpass filter illustrated in FIG. 1. FIG. 3 is a perspective plan view illustrating an example of an arrangement structure of capacitive fins and series capacitive fins when the tunable evanescent mode bandpass filter illustrated in FIG. 1 includes series capacitive fins. It is a perspective view which shows the other structural example different from FIG. 1 of the tunable evanescent mode bandpass filter by this invention. It is a circuit diagram for demonstrating the equivalent circuit of the tunable evanescent mode bandpass filter shown in FIGS. 1-3 as one Embodiment of this invention. FIG. 2 is a characteristic graph showing a change in coupling coefficient between resonators with and without capacitive fins when the frequency is changed in the tunable evanescent mode bandpass filter shown in FIG. 1.

  Preferred embodiments of a tunable evanescent mode bandpass filter according to the present invention will be described below with reference to the accompanying drawings. In addition, it is needless to say that the drawing reference numerals attached to the following drawings are added for convenience to each element as an example for facilitating understanding, and are not intended to limit the present invention to the illustrated embodiment. Yes.

(Features of the present invention)
Prior to the description of the embodiments of the present invention, an outline of the features of the present invention will be described first. The present invention is configured by sandwiching a plurality of capacitive fins formed of a thin metal plate between cut-off waveguides divided into two by an H-plane which is a wide surface, and the cut-off waveguide divided into two. The main feature is that a dielectric plate is disposed along at least one side of the tube along the metal plate, and the position of the dielectric plate is arranged so as to be movable in the H-plane direction of the waveguide. With such a configuration, the tunable evanescent mode bandpass filter according to the present invention can change the resonance frequency by moving the dielectric plate in the H-plane direction.

  Further, as a means of reducing the change in the filter bandwidth even when the frequency is changed, at least one capacitive fin on the metal plate is formed from any height direction toward the adjacent capacitive fin. Providing a fin (ie, a “series capacitive fin”) that further provides electrical capacitance between adjacent capacitive fins, and at least one side of the cut-off waveguide divided in two Is characterized in that a protrusion in the H-plane direction of the waveguide is provided at a position between the capacitive fins facing the metal plate.

  With the configuration as described above, the resonance of the filter is achieved by moving the metal fin in which the capacitive fin and the series capacitive fin are formed and the dielectric plate disposed in parallel with the metal plate in the waveguide in the H plane direction. By changing the frequency and changing the coupling coefficient in the opposite direction to the resonant frequency change, a tunable evanescent mode bandpass filter with little bandwidth change can be obtained even if there is a wide range of resonant frequency changes. It is possible to realize.

  Here, the change in the resonance frequency of the filter is realized simply by spatially electrically coupling a dielectric plate having a small dielectric loss tangent (tan δ) to the filter element constituting the tunable evanescent mode bandpass filter. Therefore, there is no big impact on the passage loss.

(Embodiment)
Next, an example of an embodiment of a tunable evanescent mode bandpass filter according to the present invention will be described in detail with reference to FIGS.

  FIG. 1 is a perspective view showing a structural example of a tunable evanescent mode bandpass filter according to the present invention. As an example using the present invention, a case where a seven-stage tunable evanescent mode bandpass filter is configured is illustrated. ing.

  2A is an exploded perspective view showing an example of the internal structure of the tunable evanescent mode bandpass filter illustrated in FIG. 2B is an exploded perspective view for explaining an example of a structure of a series capacitive fin included in the tunable evanescent mode bandpass filter illustrated in FIG. 1. 2C is a perspective plan view illustrating an example of an arrangement structure of capacitive fins and series capacitive fins when the tunable evanescent mode bandpass filter illustrated in FIG. 1 includes series capacitive fins.

  FIG. 3 is a perspective view showing another example of the structure of the tunable evanescent mode bandpass filter according to the present invention, which is different from that shown in FIG. 1. Unlike FIG. 2B, each of the adjacent capacitive fins on the metal fin is shown. 3 shows a structure formed so that series capacitive fins face each other from any of a plurality of height directions (two height directions in the case of FIG. 3).

  Hereinafter, embodiments of the tunable evanescent mode band-pass filter according to the present invention will be described in more detail with reference to the structural diagrams of FIGS. As shown in FIGS. 1 to 3, a tunable evanescent mode bandpass filter according to an embodiment of the present invention includes a cutoff waveguide 1, a cutoff waveguide 2, a metal plate 3, a capacitive fin 4, It has a structure including at least a series capacitive fin 5, an input / output terminal 6, a dielectric plate 7, a support bar 8, a metal top plate 9, a metal guide 10, a motor unit 11, and a protrusion 12.

  That is, the tunable evanescent mode bandpass filter shown in FIGS. 1 to 3 includes a cut-off waveguide 1 and a cut-off guide divided into two vertically on the H plane (horizontal plane: magnetic field plane) that is the wide plane of the waveguide. A thin metal plate 3 is sandwiched between the wave tube 2 and a capacitive shape having a capacity between the cut-off waveguide 1 and the cut-off waveguide 2 on the metal plate 3. A plurality of fins 4 are formed in the longitudinal direction of the cut-off waveguide 1 and the cut-off waveguide 2, and from at least one arbitrary height direction of each capacitive fin 4 toward the adjacent capacitive fin 4. In this structure, fins that impart electrical capacitance between adjacent capacitive fins 4, that is, series capacitive fins 5 are formed. Moreover, the coaxial line which short-circuited one end was provided along the capacitive fin 4 of both ends among each capacitive fin 4 as the input / output terminal 6, and has become an interface with the exterior.

  Here, either one of the cut-off waveguide 1 and the cut-off waveguide 2 divided into two (in FIG. 1 to FIG. 3, the upper cut-off waveguide 1) Inside, a dielectric plate 7 is disposed along the metal plate 3, and the position of the dielectric plate 7 is movable in the H-plane direction of the cutoff waveguide 1 and the cutoff waveguide 2. It is installed as a structure.

  As an example of a method for moving the dielectric plate 7, in the embodiment shown in FIGS. 1 to 3, the support plate 8 attached to the dielectric plate 7 (the material of the support rod 8 is a dielectric or metal) is used to form a metal ceiling. As a structure in which the dielectric plate 7 is attached to the motor unit 11 through the plate 9 and further through the metal guide 10, the motor of the motor unit 11 is moved in the H-plane direction so that the dielectric plate 7 is moved to H. It can be moved in the surface direction.

  Further, as shown in FIG. 2B and FIG. 3, with the adjacent capacitive fins 4 toward the adjacent capacitive fins 4 from at least one arbitrary height direction of each capacitive fin 4 on the metal plate 3. Series capacitive fins 5 are formed to provide more capacity between them. As for the series capacitive fin 5, in FIGS. 2B and 3, all the capacitive fins 4 on the metal plate 3 are adjacent to each other from the two capacitive fins 4 facing each other. Although the case where the series capacitive fins 5 are respectively formed toward the capacitive fins 4 is shown, at least one capacitance on the metal plate 3 instead of all the capacitive fins 4 on the metal plate 3 is shown. The series capacitive fin 5 may be formed on the conductive fin 4.

  Furthermore, at least one side of the cut-off waveguide 1 and the cut-off waveguide 2 divided into two (the lower cut-off waveguide 2 in FIGS. 1 to 3) faces the metal plate 3. In addition, a protrusion 12 protruding in the H-plane direction of the cutoff waveguide 1 and the cutoff waveguide 2 is provided at a position between the adjacent capacitive fins 4.

  FIG. 4 shows an equivalent circuit of the tunable evanescent mode bandpass filter shown in FIGS. 1 to 3 as an embodiment of the present invention. As shown in the equivalent circuit of FIG. 4, the waveguides (cut-off waveguide 1 and cut-off waveguide 2) of the tunable evanescent mode band-pass filter shown in FIGS. Capacitive fins 4 that are represented by inductances L1 to L5 and that form a resonance frequency with the waveguides (cutoff waveguide 1 and cutoff waveguide 2) are represented by conductances C1 to C2.

  Here, by moving the dielectric plate 7 attached to the motor unit 11 in the H-plane direction, the capacitances of the conductances C1 to C2 can be varied to adjust the resonance frequency of the tunable evanescent mode bandpass filter. it can. That is, the evanescent mode bandpass filter according to the present invention affects the filter depending on the position of the dielectric plate 7, and as a result, the resonance frequency of the filter can be changed.

  In general, when the resonance frequency of the filter changes, the coupling coefficient between the resonators constituting the filter is also affected, and the bandwidth of the filter is changed. In the conventional evanescent mode bandpass filter described in Patent Document 1 and the like, when the resonance frequency is lowered, the amount of coupling between the resonators of the filter is reduced, and as a result, the bandwidth of the filter is reduced. Conversely, when the resonant frequency increases, the amount of coupling between the resonators of the filter increases, and as a result, the bandwidth of the filter increases.

  Therefore, in the evanescent mode bandpass filter according to the present invention, the metal plate 3 is provided on the series capacitive fin 5 and at least one side of the cutoff waveguide 1 and the cutoff waveguide 2, for example, inside the cutoff waveguide 2. And a projecting portion 12 provided so as to project in the H-plane direction of the cutoff waveguide 2 (or the cutoff waveguide 1) at a position between the adjacent capacitive fins 4 By changing the coupling coefficient in the direction opposite to the change in the resonance frequency, it is possible to perform an operation that reduces the influence between the resonators on the change in the resonance frequency. This makes it possible to suppress changes in the bandwidth of the filter as much as possible.

  FIG. 5 is a characteristic graph showing a change in the coupling coefficient between the resonators with and without the capacitive fin 4 when the frequency is changed in the tunable evanescent mode bandpass filter shown in FIG. The result of calculating the coupling coefficient between adjacent resonators when the resonance frequency is changed by the movement of the position of is shown. In addition, in the case where the capacitive fin 4 is present in FIG. 5, the capacitive fin 4 is formed from at least one arbitrary height direction of the at least one capacitive fin 4 on the metal plate 3 toward the adjacent capacitive fin 4. The case where the series capacitive fin 5 which gives a capacity | capacitance further between the capacitive fin 4 to provide is shown. Further, in FIG. 5, even in the case where the tunable operation is performed, the calculation coupling coefficient necessary for maintaining the bandwidth constant is simultaneously indicated by a dotted line.

  As in the conventional tunable evanescent mode bandpass filter, there is no problem in the tunable operation in the case where the capacitive fin 4 is not provided. However, as shown by the broken line in the graph of FIG. Along with the change, there is a drawback that the coupling coefficient changes greatly and the bandwidth also changes accordingly. On the other hand, in the configuration including the capacitive fin 4 and the series capacitive fin 5 as in the tunable evanescent mode bandpass filter shown in FIG. 1 as an example of the present invention, the series capacitive fin 5 and the capacitive fin 4 By optimizing the dimensions of the projection 12 and the projection 12, as shown by the solid line in FIG. 5, even if the resonance frequency changes, it is possible to control the change of the coupling coefficient between the resonators. It is. That is, the series capacitive fin 5, the capacitive fin 4, and the protrusion 12 can be set so as to correct a change in the coupling coefficient of the filter in a configuration that does not include the capacitive fin 4. This means that the amount of change in the pass band width of the filter is greatly increased even when the resonance frequency is changed, as compared with the case where the capacitive fin 4 is not provided as in the conventional tunable evanescent mode band pass filter. It means that it can be improved.

  Therefore, in the tunable evanescent mode bandpass filter shown in FIG. 1 to FIG. 3 as one embodiment of the present invention, when the pass frequency is changed according to the use situation, the operation of the change of the respective bandwidths Can be set to an optimum state.

  The configuration of the preferred embodiment of the present invention has been described above. However, it should be noted that such embodiments are merely examples of the present invention and do not limit the present invention in any way. Those skilled in the art will readily understand that various modifications and changes can be made according to a specific application without departing from the gist of the present invention.

DESCRIPTION OF SYMBOLS 1 Cut-off waveguide 2 Cut-off waveguide 3 Metal plate 4 Capacitive fin 5 Series capacitive fin 6 Input / output terminal 7 Dielectric plate 8 Support bar 9 Metal top plate 10 Metal guide 11 Motor unit 12 Protrusion part

Claims (7)

  A tunable evanescent mode bandpass filter having a characteristic that a change in bandwidth is small even when a frequency is changed, and the cut-off waveguide is divided into two by an H plane which is a wide surface, and the cut-off is divided into two A plurality of capacitive fins formed of a thin metal plate is sandwiched between the waveguides in the longitudinal direction of the cutoff waveguide, and at least one side of the cutoff waveguide divided into two A tunable evanescent mode bandpass characterized in that a dielectric plate is disposed along the metal plate and the position of the dielectric plate is arranged so as to be movable in the H-plane direction of the cutoff waveguide. filter.   A series formed from at least one arbitrary height direction of at least one of the capacitive fins toward the adjacent capacitive fin to provide electrical capacitance between the adjacent capacitive fins. 2. A tunable evanescent mode bandpass filter according to claim 1, wherein capacitive fins are arranged.   The tunable evanescent mode bandpass filter according to claim 2, wherein a plurality of the series capacitive fins are formed on the at least one capacitive fin in the metal plate.   The said metal plate WHEREIN: The said series capacitive fin is formed toward the said opposing capacitive fin from each of the said two capacitive fins which mutually adjoin mutually. Or a tunable evanescent mode bandpass filter according to 3;   The tunable evanescent mode bandpass filter according to any one of claims 2 to 4, wherein the series capacitive fins are arranged in each of all the capacitive fins formed on the metal plate.   At least one side of the cut-off waveguide divided into two is provided with a protrusion in the H-plane direction of the cut-off waveguide at a position between the capacitive fins that are opposed to the metal plate and adjacent to each other. The tunable evanescent mode bandpass filter according to any one of claims 1 to 5, wherein the tunable evanescent mode bandpass filter is provided.   A support rod is attached to the dielectric plate and connected to the motor unit via the support rod, and the motor of the motor unit is moved in the H-plane direction of the cutoff waveguide, thereby the dielectric plate The tunable evanescent mode bandpass filter according to claim 1, wherein the tunable evanescent mode bandpass filter is movable in the H-plane direction of the cut-off waveguide.

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