JP5111230B2 - Cavity resonator and high frequency filter - Google Patents

Description

  The present invention relates to a cavity resonator used in a microwave band and a millimeter wave band, and a high-frequency filter configured using the cavity resonator.

  Cavity resonators that resonate high-frequency electromagnetic fields in shielded cavities composed of conductors with high conductivity are used as low-loss, that is, high-performance resonators in various high-frequency circuits such as high-frequency filters and oscillators. ing. Typical examples of the cavity resonator include a rectangular waveguide resonator in which the shielding cavity has a rectangular parallelepiped shape and a circular waveguide resonator in which the shielding cavity has a cylindrical shape. . The high frequency electromagnetic field resonating with these cavity resonators has various electromagnetic field distribution forms, so-called resonance modes. An appropriate resonance mode is selected depending on the application of the cavity, and the shape of the shielding cavity is selected so that the resonance mode resonates at a required frequency.

  One parameter indicating the electrical performance of the resonator is a parameter called no-load Q value. This no-load Q value roughly indicates the amount of energy stored per unit time in the cavity resonator. It corresponds to the value divided by the amount of power loss, and the larger the value, the higher the performance of the cavity resonator. The amount of stored energy is basically proportional to the size of the space in which the electromagnetic field is distributed, that is, the volume of the cavity, while the amount of power loss is the total amount of heat loss generated by the high-frequency current flowing through the inner wall of the shielded cavity. Correspond. This heat loss is determined from the conductivity of the conductor that forms the cavity and the distribution of the high-frequency current that flows through the inner wall of the shielding cavity, assuming that the surface of the inner wall of the cavity is smooth. It is calculated by integrating the calculated product of the surface resistance value of the inner wall surface and the square of the current density over the entire inner wall surface.

  Therefore, the basic points for reducing heat loss are to produce a shielding cavity using a conductor having a high conductivity and to use a resonance mode with a uniform current density distribution and low density. The distribution of the high-frequency current on the inner wall surface is a distribution according to the electromagnetic field distribution in the shielding cavity. Therefore, in a cavity resonator with a typical shape such as a rectangular waveguide resonator or a circular waveguide resonator, Some low-loss resonance modes have already been recognized. In particular, the TE011 mode in a circular waveguide resonator (cylindrical cavity resonator) is known as one of the lowest-loss resonance modes (see, for example, Patent Document 1).

JP 2000-216602 A

  However, the cylindrical cavity resonator has a problem in principle that the TM111 mode also resonates at the same frequency as the TE011 mode. The electromagnetic field distribution in both modes is significantly different. Therefore, the degree of concentration of the high-frequency current on the inner wall surface is different, and there is a large difference in the no-load Q value. For these reasons, the use of the TE011 mode has been limited in a hollow cylindrical cavity resonator that does not include a dielectric.

  On the other hand, if the shape of the shielding cavity is approximately spherical, the resonance mode having an electromagnetic field distribution similar to the TE011 mode in the cylindrical cavity resonator can be resonated with the resonance frequency separated from the other resonance modes. Is possible. However, the spherical shielded cavity is not easy to manufacture, and there is a difficulty in limiting the application due to an increase in manufacturing cost. In that respect, the cylindrical cavity resonator has an advantage that it is relatively easy to manufacture.

  The present invention has been made to solve the above-described problems, and can be used without being mixed with an unnecessary resonance mode, and has a high unloaded Q value and an extremely high performance cavity resonator. And it aims at obtaining the high frequency filter comprised using a cavity resonator.

A cavity resonator according to the present invention includes a shield cavity made of a conductor having a rotationally symmetric shape with respect to a rotationally symmetric axis, and at least one input / output coupling means for electromagnetically coupling with an external circuit. In the resonator, the shielding cavity has a cylindrical shape having a constant radial dimension in a portion near one end side in the axial direction of the rotational symmetry axis, and the cylindrical portion and the hemispherical portion are rotated. It has a hemispherical cylindrical shape connected in the axial direction of the symmetry axis, most of the electric field components distributed in the shielding cavity are components in the circumferential direction with respect to the rotational symmetry axis, and the same radius with respect to the rotational symmetry axis Resonating in a resonance mode in which the amplitude of the electric field component in the circumferential direction is substantially constant on the circumference, and the diameter is approximately 1.4 times the wavelength at the resonance frequency of the resonance mode. Features.

  The high frequency filter according to the present invention is characterized by comprising a plurality of the cavity resonators.

  According to the present invention, resonance modes that can be expected to have low loss, such as the TE011 resonance mode, can resonate independently, and can be manufactured relatively easily and can be used without being mixed with unnecessary resonance modes. In addition, an extremely high performance cavity resonator having a large unloaded Q value can be obtained. Further, a band pass filter having a very narrow pass bandwidth or a band stop filter having a narrow stop bandwidth can be realized.

Embodiment 1 FIG.
1 is a perspective view showing a cavity resonator according to Embodiment 1 of the present invention, and FIG. 2 is a cross-sectional view taken along line AA ′ shown in FIG. The cavity resonator according to the first embodiment shown in these figures has an input for electromagnetic coupling with an external circuit in a shielding cavity 2 made of a conductor having a rotationally symmetric shape with respect to the rotational symmetry axis 3. Output shielding means 1a and 1b are provided, and the shielding cavity 2 has a constant portion in the vicinity of one end side in the axial direction of the rotationally symmetric axis 3 (an end 4a side portion of the shielding cavity that intersects the rotationally symmetric axis 3). Rotational symmetry in which the other part (the part on the side of the end 4b of the shielding cavity that intersects the rotational symmetry axis 3) has a diameter less than or equal to the diameter of the cylinder 5. A hemispherical portion 6 is formed.

  In this shielding cavity 2, the diameter dimension from the other end 4 b in the axial direction of the rotationally symmetric axis 3 of the hemispherical part 6 to the cylindrical part 5 continuously changes in the axial direction of the rotationally symmetric axis 3. Further, the inner wall surface of the shielding cavity 2 is formed so as not to have a portion protruding inside the cavity, and the cylindrical portion 5 and the hemispherical portion 6 are connected in the axial direction of the rotationally symmetric axis 3 to form a hemisphere A cylindrical shape is formed.

  As described above, the first member 7 and the second member 8 for constituting the shielding cavity 2 having a shape are both conductors having high conductivity, or conductors having high conductivity on members formed of metal or dielectric. Configured by plating. The first member 7 is formed by integrally forming a portion excluding the circular opening 10 on the side constituting the cylindrical portion 5 of the shielding cavity 2, and is a flat plate-like second member 8 so as to close the circular opening 10. Is in close contact with the first member 7 to form the shielding cavity 2. If the height dimension of the cylindrical part 5 is d and the diameter is 2a, it goes without saying that the radius of the hemispherical part 6 is a.

  FIG. 3 shows a schematic electromagnetic field distribution of a resonance mode resonated by this cavity resonator. (A) shows the distribution in the longitudinal section including the rotationally symmetric axis 3, and (b) shows the electromagnetic field distribution in the transverse section at z = d of the z axis shown in (a). Basically, the resonance mode has a distribution similar to that of the TE011 mode in the circular cavity resonator. Here, the TE011h mode is referred to to distinguish the resonance mode from the resonance mode of the circular cavity resonator or the like. In this resonance mode, most of the electric field components distributed in the shielding cavity 2 are components in the circumferential direction with respect to the rotational symmetry axis 3, and the electric field components in the circumferential direction are on the circumference of the same radius with respect to the rotational symmetry axis 3. In this mode, the amplitude is substantially constant. In the first embodiment, the input / output coupling means 1 is a circular waveguide having at least a part in contact with the shielding cavity 2 having a cross-sectional dimension in which the fundamental mode is cut off at the resonance frequency of the TE011h mode. The coupling means is extremely small.

  Next, FIG. 4 shows calculated values of the no-load Q value and the resonance frequency in the resonance mode in this structure. The calculation results shown in FIG. 4 are obtained by the finite element method. According to the result shown in FIG. 4, in the cavity resonator according to the first embodiment, the TE011h mode resonates independently, and other modes do not resonate at the same frequency as the circular cavity resonator. According to this calculation result, it can be seen that the unnecessary mode can be separated from the TE011h mode by a frequency of at least about 5%.

  Further, according to the comparison between the resonance mode no-load Q value and the resonance frequency calculation result in the conventional cylindrical cavity resonator shown in FIG. 5, regarding the value of the no-load Q value, the TE011 mode of the cylindrical cavity resonator It becomes equal or better. Note that the calculation results shown in FIG. 5 are obtained by the finite element method.

  In the cavity resonator according to the first embodiment, the TM111 system mode and the TE011 system mode can be separated in terms of frequency, as can be seen from the electromagnetic field distribution in the cylindrical cavity resonator of FIGS. 6 and 7. The mode has a distribution in which electromagnetic fields gather at both ends of the cavity (near z = 0, d), whereas the TE011 mode has electromagnetic fields gathered at the center of the cavity (near z = d / 2). Therefore, it can be understood that the frequency change method with respect to the shape change at the end of the cavity is different in both modes.

  Next, a comparison is made with the TE011 system mode in a spherical cavity resonator. FIG. 8 shows the calculation result of a spherical cavity resonator in which the TE011 system mode resonates at 10 GHz. In the case of a spherical cavity resonator, there are three structural symmetry planes orthogonal to each other, so that three TE011 system modes are degenerated, and three modes can resonate at the same frequency. The unloaded Q value of the TE011h mode resonance in the hemispherical cylindrical cavity resonator of the first embodiment is only about 10% lower than that of the TE011 system mode in the spherical cavity resonator.

  This is because the shielding cavity 2 has a hemispherical cylindrical shape, so that the radial dimension of the rotationally symmetric cavity continuously changes in the axial direction of the rotationally symmetric axis 3 and the inner wall surface protrudes inside the cavity. Since there is no portion, there is no bias in the electromagnetic field distribution of the TE011 system mode, and as a result, the density of the current in the circumferential direction flowing on the inner wall surface does not increase locally. In these calculation results, the influence of the input / output coupling means and the contact resistance at the contact surface between the members constituting the cavity are not considered at all.

  By the way, when manufacturing a cavity, for example, when manufacturing a member that forms a cavity by cutting a metal or the like, it is necessary to divide the member that forms the cavity into two or more in consideration of workability. Become. When two or more members are combined to form a cavity, there is always a contact surface between the members, and the presence of this contact surface increases power loss in the resonator, resulting in a decrease in unloaded Q value. . The power loss is caused by the fact that the contact resistance at the contact surface cannot be made zero. This problem is not as negligible as when a low-loss cavity resonator is constructed. When the current on the inner wall of the cavity flows across the contact surface, a potential difference occurs between the members due to contact resistance, and the loss increases, so that the contact surface is formed in parallel with the direction of the current on the inner wall of the cavity. It is better to select the position of the dividing plane. In the TE011 resonance mode, most of the high-frequency current on the inner wall surface of the cavity flows in the circumferential direction with respect to the rotationally symmetric axis.

  From the above viewpoint, in the first embodiment, the member that forms the cavity is divided into two on the surface of z = 0, and there is an advantage that there is little deterioration of the no-load Q value due to the contact resistance on the contact surface. In addition to this, since the second member 8 has a flat plate shape, there is an advantage that alignment of the first member 7 and the second member 8 is basically unnecessary. This is an advantage that can be realized because a part of the shielding cavity 2 has a cylindrical cavity shape.

  On the other hand, if the cavity is spherical, it is difficult to divide the cavity. Even if the cavity is divided at any cross section, the current corresponding to two of the three degenerate modes crosses the contact surface. Therefore, the unloaded Q value of two of the three resonance modes is It deteriorates and a difference occurs in performance between the three resonance modes. For this reason, in order to use a mode in which the Q value does not deteriorate due to contact resistance on the contact surface, in order to greatly shift the resonance frequency of the resonance mode in which the no-load Q value deterioration occurs from the resonance frequency in the resonance mode without deterioration, It is necessary to take measures such as modifying the shape. In addition, if the members are not precisely aligned, the shape of the cavity cannot be kept constant, and there is a problem that the resonance frequency varies.

  As described above, according to the cavity resonator according to the first embodiment, since the shape of the shielding cavity 2 is a hemispherical cylindrical shape, the TE011 system TE011h mode is separated from other resonance modes independently. It is possible to resonate, and the hemispherical part has no discontinuity in the diameter change from the central part to the end part of the shielding cavity 2, so there is almost no part where the current flows on the inner wall surface of the cavity. There is an effect that an extremely low-loss cavity resonator can be realized.

  In addition, the member forming the shielding cavity 2 is divided into the first member 7 and the second member 8, and the latter is used as a member constituting the cylindrical end of the hemispherical cylindrical cavity as a flat plate member. The gap (contact surface) generated between the members is parallel to the current direction of the TE011h mode flowing through the inner wall surface of the cavity, and there is an effect that the power loss caused by the contact resistance of the gap is small and the degradation of the no-load Q value is small.

  Further, alignment between the first member 7 and the second member 8 is not necessary, and assembly is easy. As a result, a low-cost and low-loss cavity resonator can be realized. Furthermore, since the input / output coupling means 1a and 1b are circular waveguides having a cross-sectional dimension in which the fundamental mode of the circular waveguide is cut off, the weakness required in many cases when utilizing a low-loss resonator. It is easy to realize an input / output coupling means having a simple coupling, and it is only necessary to make a cut hole from the side of the first member toward the cavity, and the manufacturing including the input / output coupling means 1a and 1b is facilitated. There is also an effect.

  In the cavity resonator according to the first embodiment, the shielding cavity 2 is configured by a combination of a cylindrical cavity and a hemispherical cavity. However, in order to resonate the TE011 system mode independently, as described above, the TE011 system Therefore, the shape of the hemispherical portion is not limited to this, and the radius of rotation from the center to the end of the cavity, such as a conical shape, may be used. It goes without saying that the same effect can be expected if the shape is a reduced shape and does not have a portion protruding inside the cavity.

The effects of the first embodiment described above are summarized as follows.
(1) Cavity resonance comprising at least one input / output coupling means 1a and 1b for electromagnetically coupling an external circuit to a shielding cavity 2 made of a conductor having a rotationally symmetric shape with respect to the rotationally symmetric axis 3 The shielding cavity 2 is a cylindrical portion 5 having a constant diameter in the vicinity of one end side in the axial direction of the rotationally symmetric axis, and has a diameter smaller than that of the cylindrical shape in the other portions. Since the rotationally symmetric hemispherical portion 6 has a resonance mode of the TE011 system (resonance mode having an electromagnetic field distribution similar to the TE011 mode in a cylindrical cavity resonator), a resonance mode that can be expected to have low loss is independent. A low-loss cavity resonator that resonates with can be obtained.

  (2) Most of the electric field component distributed in the shielding cavity 2 is a component in the circumferential direction with respect to the rotationally symmetric axis 3, and the amplitude of the electric field component in the circumferential direction is on the circumference of the same radius with respect to the rotationally symmetric axis 3. Since resonance occurs in a substantially constant resonance mode, the resonance mode of the TE011 system and the resonance mode of the TM111 system are separated in frequency, and a low-loss cavity resonator in which the former resonates alone can be obtained.

  (3) In the shielding cavity 2, the diameter dimension from the other end in the axial direction of the rotationally symmetric axis 3 of the other part to the cylindrical part 5 continuously changes in the axial direction of the rotationally symmetric axis 3. In addition, since the inner wall surface of the shielding cavity 2 does not have a portion protruding toward the inside of the cavity, there is almost no portion where the current flowing on the inner wall surface is concentrated, and a low-loss cavity resonator can be obtained.

  (4) The shielding cavity has a hemispherical cylindrical shape in which the cylindrical part 5 and the hemispherical part 6 are connected in the axial direction of the rotationally symmetric axis 3, so that the axial shape change of the inner wall surface in the cavity is changed. In addition to being continuous and having no portion where the inner wall surface protrudes toward the inside of the cavity, the change in the axial direction of the diameter of the cavity corresponds to the shape of the electromagnetic field distribution of the TE011 system mode. For this reason, a very low-loss cavity resonator can be obtained.

  (5) A portion excluding an end portion formed by a circular opening on the side constituting the cylindrical portion 5 is integrally formed with a first member 7 made of a conductor, and the conductor is formed so as to close the circular opening portion 10 of the first member 7. Since the shielded cavity 2 is formed by closely contacting the flat plate-like second member 8 made of the first member 7, a cavity resonator that can be easily manufactured and assembled can be obtained. As a result, a low-cost and low-loss cavity resonator can be obtained.

  (6) The input / output coupling means 1a and 1b are partly in contact with the shielding cavity 2 and are constituted by circular waveguides having a cross-sectional dimension in which the fundamental mode is cut off at the resonance frequency of the resonance mode. Manufacturing is easy, and there is an effect that a weak input / output coupling amount often required for a low-loss resonator can be easily realized.

Embodiment 2. FIG.
FIG. 9 is a perspective view of the cavity resonator showing the second embodiment of the present invention, and FIG. 10 is a longitudinal sectional view at the position AA ′ in FIG. In these drawings, the same parts as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted. As a new code, 9 indicates a cylindrical recess having a diameter of 2b provided on the main surface of the second member 8 made of a flat conductor on the first member 7 side. The dimension b of the recess 9 is set to a value smaller than the radius a of the cylindrical cavity portion formed in the first member 7.

  The operation of the cavity resonator of the second embodiment is basically the same as that of the cavity resonator of the first embodiment. However, in the second embodiment, the second member 8 is provided with a recess 9. Different. Since the recess 9 is provided and the diameter of the cylindrical recess 9 is smaller than the diameter of the cylindrical portion of the first member 7, the volume of the cavity is reduced not only below but also above the cavity. ing. For this reason, the shape of the spherical resonator is closer to that of the cavity resonator of the first embodiment, and as a result, the resonance frequency of the unnecessary mode generated in the vicinity of the TE011 system resonance mode is set to the cavity resonator of the first embodiment. Rather than the resonance frequency of the TE011 system mode. However, the first member 7 and the second member 8 need to be aligned. In addition, since a part of the inner wall of the shielding cavity protrudes toward the inside of the cavity by providing the recess, the no-load Q value in the TE011 resonance mode is lower than that in the case where the recess is not provided.

  As described above, according to the second embodiment, the main surface of the second member 8 on the shielding cavity 2 side has a rotationally symmetric shape with respect to the rotationally symmetric axis 3 and has a diameter smaller than the diameter of the cylindrical shape. Since the shape of the shielding cavity 2 is close to a sphere due to the provision of the recess 9, the frequency interval between the TE011 system resonance mode and nearby unnecessary modes is widened, and the low-loss cavity resonator is easy to use and is less susceptible to unnecessary modes. Is obtained.

  Note that a high-frequency filter can be configured by using a plurality of cavity resonators in the first and second embodiments, and a bandpass filter having a very narrow passband or a bandstop filter having a narrow stopband can be realized.

It is a perspective view which shows the cavity resonator which concerns on Embodiment 1 of this invention. It is A-A 'sectional drawing of the cavity resonator shown in FIG. It is a figure which shows the general electromagnetic field distribution of the resonance mode of the cavity resonator of FIG. It is a figure which shows the table | surface which put together the calculation result by the finite element method regarding the cavity resonator of FIG. It is a figure which shows the table | surface which put together the calculation result of the no-load Q value and resonance frequency of the resonance mode in the conventional cylindrical cavity resonator compared with FIG. FIG. 3 is a diagram showing an electromagnetic field distribution in the cavity resonator according to the first embodiment. FIG. 3 is a diagram showing an electromagnetic field distribution in the cavity resonator according to the first embodiment. It is a figure which shows the calculation result of the spherical cavity resonator in which a TE011 system mode resonates. It is a perspective view which shows the cavity resonator which concerns on Embodiment 2 of this invention. FIG. 10 is a cross-sectional view of the cavity resonator of FIG. 9 along AA ′.

Explanation of symbols

1a, 1b Input / output coupling means, 2 shielding cavity, 3 rotational symmetry axis, 4a, 4b end of shielding cavity 2 intersecting rotational symmetry axis 3, 5 cylindrical portion constituting part of shielding cavity 2, 6 shielding A hemispherical portion constituting a part of the cavity 2, 7 a first member, 8 a second member, 9 a recess provided in the second member, 10 a circular opening formed in the first member.

Claims (4)

A cavity resonator comprising at least one input / output coupling means for electromagnetically coupling an external circuit to a shielding cavity made of a conductor having a rotationally symmetric shape with respect to a rotationally symmetric axis,
The shielding cavity has a cylindrical shape having a constant diameter in the vicinity of one end side in the axial direction of the rotationally symmetric axis, and the cylindrically shaped portion and the hemispherical portion are in the axial direction of the rotationally symmetric axis. Having connected hemispherical cylindrical shapes,
Most of the electric field components distributed in the shielding cavity are components in the circumferential direction with respect to the rotational symmetry axis, and the amplitude of the electric field component in the circumferential direction is substantially constant on the circumference having the same radius with respect to the rotational symmetry axis. Resonates in the resonance mode
The cavity resonator is characterized in that the diameter is approximately 1.4 times the wavelength at the resonance frequency of the resonance mode . The cavity resonator according to claim 1 .
A portion excluding an end portion formed by a circular opening on the side constituting the cylindrical portion is integrally formed with a first member made of a conductor, and a flat plate shape made of a conductor is formed so as to close the circular opening of the first member. A cavity resonator is characterized in that the shielding member is formed by bringing a second member into close contact with the first member. The cavity resonator according to claim 1 or 2 ,
A part of the input / output coupling means in contact with the shielding cavity is formed of a circular waveguide having a cross-sectional dimension in which a fundamental mode is cut off at a resonance frequency of a resonance mode. A high frequency filter comprising a plurality of the cavity resonators according to any one of claims 1 to 3 .

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