JP5978180B2 - Millimeter wave filter and method for preventing leakage of electromagnetic wave - Google Patents

Description

  The present invention relates to a filter used in a millimeter wave band.

  In recent years, with the ubiquitous network society and the increasing need for radio waves, millimeter wave wireless systems such as WPAN (wireless personal area network) that realizes wireless broadband in the home and millimeter wave radar that supports safe and secure driving Has begun to be used. In addition, efforts to realize a 100 GHz super wireless system have been actively carried out.

  On the other hand, for the second harmonic evaluation of the radio system in the 60-70 GHz band and the evaluation of the radio signal in the frequency band exceeding 100 GHz, the noise level of the measuring instrument and the conversion loss of the mixer increase as the frequency increases. Since the frequency accuracy is lowered, a high-sensitivity and high-precision measurement technique for wireless signals exceeding 100 GHz has not been established. Moreover, the conventional measurement techniques cannot separate the local oscillation harmonics from the measurement results, making it difficult to accurately measure unwanted emissions.

  In order to overcome these technical issues and realize high-sensitivity and high-accuracy measurement of 100 GHz super-band radio signals, millimeter-wave narrow-band filter technology for suppressing image response and higher-order harmonic response Development is necessary, and it is particularly desirable to be adaptable to a variable frequency type (tunable).

  Up to now, the filters used as the variable frequency type in the millimeter wave band include (a) a filter using a YIG resonator, (b) a varactor diode added to the resonator, and (c) a Fabry-Perot resonator. It has been.

  A device using a YIG resonator of (a) is known that can be used up to about 80 GHz at present, and a device having a varactor diode of (b) added to the resonator can be used up to about 40 GHz. It is difficult to manufacture at a frequency exceeding 100 GHz.

  On the other hand, the Fabry-Perot resonator of (c) is often used in the field of light, and Non-Patent Document 1 discloses a technique of using this for millimeter waves. Non-Patent Document 1 discloses a confocal Fabry-Perot resonator in which a pair of spherical reflectors that reflect millimeter waves are opposed to each other at an interval equal to the radius of curvature to achieve a high Q.

  However, in the above-mentioned confocal Fabry-Perot resonator, when the distance between the mirror surfaces is moved to tune the pass band, the focal point is deviated in principle, so that a significant decrease in Q is expected. Therefore, it is necessary to selectively use reflector pairs having different curvatures for each frequency.

  On the other hand, a Fabry-Perot resonator often used in the field of light has a structure in which planar half mirrors are arranged opposite to each other. With this structure, the Q is lowered even if the distance between mirror surfaces is changed in principle. However, in order to realize a filter using the planar Fabry-Perot resonator in the millimeter wave band, there are the following problems to be solved.

(A) A plane wave needs to be incident on the half mirror in parallel. When the input to the filter is a waveguide, it may be possible to realize a plane wave by increasing its diameter like a horn antenna, but the size increases. Even in that case, it is difficult to realize a perfect plane wave, and the characteristics deteriorate.
(B) The half mirror needs to have a function of transmitting a certain amount of plane wave as it is. For this reason, the structure of the half mirror is limited, and the degree of freedom in design is low.
(C) Since it is an open type, there is a large loss due to radiation into space.

  As a technique for solving these problems, the present applicant arranges a pair of radio wave half mirrors facing each other with a space between them in a waveguide that propagates electromagnetic waves in a predetermined frequency range of the millimeter wave band in the TE10 mode. Thus, among the electromagnetic waves incident from one end side of the waveguide, the millimeter wave is configured to selectively output from the other end side a frequency component centered on the resonance frequency of the resonator formed between the pair of radio wave half mirrors. A waveband filter has been proposed (Patent Document 1).

JP 2013-138401

Teshirogi Satoshi, Yoneyama Tsutomu, "New Millimeter-wave Technology" Ohmsha, 1993, p71

  The millimeter-wave band filter disclosed in Patent Document 1 includes a pair of radio waves that are opposed to each other in a planar manner inside a waveguide that transmits a TE wave having an electric field only in a plane orthogonal to the traveling direction in a TE10 mode (single mode). Since it is a structure provided with a resonator formed of a half mirror, no special device for incident plane waves is required, and the radio wave half mirror does not need to transmit plane waves and can take any shape.

  Further, the filter as a whole is hermetically sealed, and there is no principle of loss due to radiation to the external space, and extremely high selection characteristics can be realized in the millimeter wave band.

  Further, by changing the distance between the pair of radio wave half mirrors, the resonance frequency of the resonator can be freely changed, and a filter with a variable resonance frequency can be realized with a small loss.

  An example of the structure for changing the resonance frequency is shown in FIG. 6A is a side view of the conventional millimeter wave band filter (viewed from the electric field plane), and FIG. 6B is a plan view of the conventional millimeter wave band filter (viewed from the magnetic field plane). Figure).

  The filter structure shown in FIG. 6 has a rectangular tube-shaped first waveguide 1 and an inner diameter on one end side that is sized to receive one end side of the first waveguide 1, and an inner diameter on the other end side. One radio wave half mirror is connected to a second waveguide 2 having a rectangular tube shape and a different diameter, which is formed substantially the same as the first waveguide 1, and closes one end side opening of the first waveguide 1. 3A is fixed, the other radio wave half mirror 3B is fixed to the boundary where the inner diameter of the second waveguide 2 changes, and the first waveguide 1 is guided in the waveguide direction with respect to the second waveguide 2 ( The resonance frequency can be easily changed by adopting a structure in which the distance L between the radio wave half mirrors 3A and 3B is varied by sliding relatively in the longitudinal direction. In the following description, the vertical and horizontal dimensions inside the rectangular tube-shaped waveguide are referred to as the inner diameter, and the outer and vertical dimensions are referred to as the outer diameter.

  In such a sliding structure of the waveguide, it is necessary to provide a gap G between the outer peripheral wall 1a of the first waveguide 1 and the inner peripheral wall 2a of the second waveguide 2. When electromagnetic waves leak, the loss as a resonator increases and the characteristics of the filter deteriorate.

  For this reason, in Patent Document 1, as shown in FIG. 6, electromagnetic wave leakage prevention is applied to the inner peripheral wall 2 a of the second waveguide 2 that faces the outer peripheral wall 1 a on one end side of the first waveguide 1. A groove (choke) 4 having a predetermined depth is formed around. The depth of the groove 4 is set to about ¼ of the in-tube wavelength of the electromagnetic wave to be prevented from leaking (for example, about 0.9 mm if the leakage prevention frequency is 110 GHz). The electromagnetic wave that has reached the entrance of the groove 4 through the gap G from the resonance circuit space formed therebetween is canceled by the electromagnetic wave that reciprocated in the depth direction in the groove 4 and returned to the entrance in the opposite phase. Suppresses leakage beyond 4.

  However, as a result of various experiments and measurements, a groove 4 formed around the inner peripheral wall 2a of the second waveguide 2 and the outer edge on the surface side of the radio wave half mirror 3A fixed to the tip of the first waveguide 1 It has been found that unnecessary resonance occurs due to reflection generated between the two portions, and the choke effect (electromagnetic wave leakage prevention effect) by the groove 4 is reduced by this unnecessary resonance, and the loss due to electromagnetic wave leakage is increased.

  A description will be given of a simulation result of filter characteristics in consideration of the influence of this unnecessary resonance. The simulation was performed with the dimensions shown in FIGS. 7 (a) and 7 (b).

  That is, the inner diameter a × b = 1.016 mm × 2.032 mm of the first waveguide 1, the outer diameter A × B = 1.976 mm × 2.992 mm, the thickness c of the outer peripheral wall 1a = 0.48 mm, One end side inner diameter a ′ × b ′ = 2.016 mm × 3.032 mm of the waveguide 2, the other end side inner diameter a ″ × b ″ = 1.016 mm × 2.032 mm, the distance p from the boundary to the groove 4 = 2.0 mm, width w of the groove 4 = 0.2 mm, depth d = 0.9 mm, gap G between the outer peripheral wall 1a of the first waveguide 1 and the inner peripheral wall 2a on the one end side of the second waveguide 2 = 0.02 mm.

  The radio wave half mirrors 3A and 3B are made of a metal that reflects electromagnetic waves and has a rectangular substrate 3a having a predetermined thickness, and extends so as to pass through the center of the substrate 3a along the long side, from one surface side to the opposite surface side. It is formed with a horizontally long electromagnetic wave passing slit 3b that penetrates, and the outer shape A × B = 1.976 mm × 2.922 mm of the substrate 3a, the thickness t = 0.5 mm, and the width u of the slit 3b = 2.032 mm. , Height s = 0.07 mm.

  FIG. 8 shows a simulation result of the pass characteristics of the filter when the first waveguide 1 is moved with respect to the second waveguide 2 under the above conditions. In the simulation, for simplicity, the material is a perfect conductor and there is no model of conductor loss.

  FIG. 8 shows the respective pass characteristics F1 to F10 when the mirror interval L is changed from 1.1 mm to 1.55 mm in 0.05 mm steps. As the pass center frequency of the filter increases, It can be seen that the loss is gradually increasing.

  This is because the distance from the outer edge portion on the surface side of the radio wave half mirror 3A fixed to the tip of the first waveguide 1 to the groove 4 (when the filter center frequency is the lowest (mirror interval L = 1.55 mm) ( (Hereinafter referred to as unnecessary resonance length) x is p−L = 0.45 mm, and the resonance frequency is sufficiently higher than the use band (110 to 140 GHz) of the filter, and the influence thereof is small, but the filter has a highest pass center frequency. (Mirror interval L = 1.1 mm), unnecessary resonance length x becomes p−L = 0.9 mm, the resonance frequency is close to the filter use band, and the electromagnetic wave leakage prevention effect decreases due to the influence of unnecessary resonance. It is recognized that the insertion loss has increased.

  As a method for solving this problem, it is considered that the groove 4 is formed away from the radio wave half mirror 3A, the unnecessary resonance length x is sufficiently increased with respect to the mirror interval L, and the resonance frequency is made smaller than the use band of the filter. However, since unnecessary resonance occurs at an integral multiple of half the wavelength of the electromagnetic wave, this effect cannot be suppressed. Moreover, in order to keep the formation position of the groove | channel 4 away from the electromagnetic wave half mirror 3A, it is necessary to lengthen the 2nd waveguide 2, and the whole filter will enlarge.

  Conversely, it is also conceivable to reduce the unnecessary resonance length x by bringing the formation position of the groove 4 as close as possible to the radio wave half mirror 3A. For example, if p = 1.55 mm, x = 0 mm when the mirror interval L = 1.55 mm, and x = 0.45 mm when the mirror interval L = 1.1 mm, it is formed between the mirrors. The resonator space and the groove 4 are too close to each other, and the characteristics of the filter itself may be deteriorated.

  The present invention solves this problem and effectively suppresses leakage of electromagnetic waves from the gaps between the waveguides necessary for changing the resonance frequency of the filter regardless of the relative positions of the waveguides. An object of the present invention is to provide a waveband filter and an electromagnetic wave leakage prevention method thereof.

In order to achieve the above object, the millimeter waveband filter according to claim 1 of the present invention comprises:
A waveguide for propagating electromagnetic waves in a predetermined frequency range in the millimeter wave band from one end to the other end in the TE10 mode is slightly larger than the outer diameter of the first waveguide (21) and one end side of the first waveguide. A second waveguide having an inner diameter and coupled in a state of being relatively movable in the waveguide direction with respect to the first waveguide, with one end of the first waveguide being received therein; 22), and
One (30A) of a pair of flat type radio wave half mirrors (30A, 30B) having a characteristic of transmitting a part of the electromagnetic wave in the predetermined frequency range and reflecting a part thereof is an opening on one end side of the first waveguide. The other (30B) is fixed inside the second waveguide in a state facing the one radio wave half mirror,
Of the electromagnetic wave incident from one end of the waveguide, a frequency component centered on the resonance frequency of the variable-length resonator formed between the pair of radio wave half mirrors is selectively added to the other of the waveguide. A millimeter wave band filter that outputs from the end side,
An outer peripheral portion of the one radio wave half mirror fixed so as to close an opening at one end of the first waveguide is formed at a predetermined depth inward, and an outer peripheral wall of the first waveguide A groove (50) for suppressing electromagnetic wave leakage from a gap with the inner peripheral wall of the second waveguide facing the outer peripheral wall is provided.

The millimeter waveband filter according to claim 2 of the present invention is the millimeter waveband filter according to claim 1,
The pair of radio wave half mirrors is
A substrate (30a) having an outer shape corresponding to the inner diameters of the first waveguide and the second waveguide, formed of a metal material that reflects electromagnetic waves to a predetermined thickness;
An electromagnetic wave transmitting slit (30b) extending through the center of the substrate along the long side direction of the substrate and penetrating from one surface side to the opposite surface side of the substrate;
The groove provided in the one radio wave half mirror fixed so as to close the opening on the one end side of the first waveguide is formed at the predetermined depth from the outer periphery of the long side of the substrate toward the slit. It is characterized by being.

Moreover, the electromagnetic wave leakage prevention method of the millimeter waveband filter according to claim 3 of the present invention includes:
A waveguide for propagating electromagnetic waves in a predetermined frequency range in the millimeter wave band from one end to the other end in the TE10 mode is slightly larger than the outer diameter of the first waveguide (21) and one end side of the first waveguide. A second waveguide having an inner diameter and coupled in a state of being relatively movable in the waveguide direction with respect to the first waveguide, with one end of the first waveguide being received therein; 22), and
One (30A) of a pair of flat type radio wave half mirrors (30A, 30B) having a characteristic of transmitting a part of the electromagnetic wave in the predetermined frequency range and reflecting a part thereof is an opening on one end side of the first waveguide. The other (30B) is fixed inside the second waveguide in a state facing the one radio wave half mirror,
Of the electromagnetic wave incident from one end of the waveguide, a frequency component centered on the resonance frequency of the variable-length resonator formed between the pair of radio wave half mirrors is selectively added to the other of the waveguide. An electromagnetic wave leakage prevention method for a millimeter-wave band filter output from the end side,
The first waveguide is provided with a groove (50) formed at a predetermined depth inward on one outer peripheral portion of the radio wave half mirror fixed so as to close the opening at one end of the first waveguide. Electromagnetic leakage from a gap between the outer peripheral wall of the tube and the inner peripheral wall of the second waveguide facing the outer peripheral wall is suppressed.

  Thus, in the present invention, the waveguide for propagating electromagnetic waves in a predetermined frequency range in the millimeter wave band in the TE10 mode is slightly larger than the outer diameter of the first waveguide and one end side of the first waveguide. Formed by a second waveguide having an inner diameter and connected in a state of being relatively movable in the waveguide direction with respect to the first waveguide, with one end side of the first waveguide being received therein In the millimeter wave band filter in which one of the radio wave half mirrors is fixed so as to close the opening on the one end side of the first waveguide, and the other is fixed inside the second waveguide, A groove for suppressing electromagnetic wave leakage from the gap between the outer peripheral wall of the first waveguide and the inner peripheral wall of the second waveguide is directed inward at the outer peripheral portion of the radio wave half mirror fixed to one end side. It is formed to a predetermined depth.

  For this reason, the distance (unnecessary resonance length) from the groove to the outer edge of the radio wave half mirror fixed to one end of the first waveguide can be made extremely small. Since it does not change even if it is moved relative to the two waveguides, the frequency of the above-described unnecessary resonance can be moved to a region sufficiently higher than the variable region of the resonance frequency of the filter. Thus, it is possible to obtain broadband characteristics with less loss due to electromagnetic wave leakage in a wide frequency band.

Structure diagram of embodiment of millimeter wave band filter of the present invention Enlarged view of the main part of the millimeter waveband filter of the embodiment The figure which shows the example of a dimension of each part of the millimeter wave band filter of embodiment Passage characteristics diagram of millimeter wave band filter in the dimension example of FIG. Diagram showing an example of structure using three waveguides Structure of conventional millimeter-wave band filter The figure which shows the example of a dimension of each part of the conventional millimeter wave band filter Passage characteristics diagram of millimeter-wave band filter in dimension example of FIG.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram showing a structure of a millimeter wave band filter 20 according to an embodiment of the present invention. 1A is a side view of the millimeter wave band filter 20 (viewed from the electric field surface), and FIG. 1B is a plan view of the millimeter wave band filter 20 (viewed from the magnetic field surface). It is. FIG. 2 is an enlarged view showing the structure of one radio wave half mirror 30A.

  As shown in these figures, the millimeter wave band filter 20 has a waveguide for propagating electromagnetic waves in a predetermined frequency range (for example, 110 to 140 GHz) in the millimeter wave band from one end to the other end in the TE10 mode. This is realized by a connection structure of the first waveguide 21 and the second waveguide 22.

  The first waveguide 21 is a rectangular tube-shaped waveguide (for example, WR-08) having a constant inner diameter from one end to the other end. One end side of the first waveguide 21 enters one end side of the second waveguide 22. Yes.

  The second waveguide 22 is a rectangular tube-shaped waveguide having different diameters on one end side and the other end side, and the inner diameter on one end side (left side in the drawing) is outside the first waveguide 21. It is formed slightly larger than the diameter, and the inner diameter of the other end side (the right side in the figure) is set equal to the inner diameter of the first waveguide 21, With one end side received concentrically, the first waveguide 21 is connected to the first waveguide 21 so as to be relatively movable in the waveguide direction (longitudinal direction).

  A gap G necessary for relative movement is provided between the outer peripheral wall 21 a of the first waveguide 21 and the inner peripheral wall 22 a on one end side of the second waveguide 22.

  One end of the first waveguide 21 transmits one part of the electromagnetic wave in the predetermined frequency range and reflects one of the pair of planar half-wave radio mirrors 30A and 30B. The half mirror 30A is fixed so as to close the opening on the one end side of the first waveguide 21, and the other radio wave half mirror 30B is provided at the boundary where the inner diameter changes inside the second waveguide 22. The radio wave half mirror 30A is fixed in a state of facing in parallel.

  With this structure, for example, among the electromagnetic waves incident on the first waveguide 21, the second frequency component centered on the resonance frequency of the resonator formed between the pair of radio wave half mirrors 30 </ b> A and 30 </ b> B is selectively second. The millimeter wave band filter 20 is output from the waveguide 22 side, and the first waveguide extends in the direction in which the distance L between the pair of radio wave half mirrors 30A and 30B (hereinafter referred to as mirror distance) L changes from the distance varying means 40. The center frequency of the filter can be varied by moving 21 relative to the second waveguide 22.

  The pair of radio wave half mirrors 30A and 30B is made of a metal having a predetermined thickness for reflecting electromagnetic waves, and has a rectangular substrate 30a having a size equal to the outer diameter of the first waveguide 21 and the center of the substrate 30a. It has a horizontally long electromagnetic wave passage slit 30b extending so as to pass along the long side and penetrating from one surface side to the opposite surface side. The length of the slit 30 b is equal to the lateral width of the inner diameter of the first waveguide 21.

  And in this millimeter wave band filter 20, the groove | channel 50 for preventing the electromagnetic wave leakage from the clearance gap G between the outer peripheral wall 21a of the 1st waveguide 21, and the inner peripheral wall 22a of the 2nd waveguide 22 facing it, 50 is a long side of the radio wave half mirror 30A provided at the tip of one end of the first waveguide 21 (in FIG. 1, (a), the upper and lower long sides in FIG. 2) from the outer periphery to the inside (center). It is formed with a predetermined depth toward the slit 30b. The length of the pair of upper and lower grooves 50, 50 sandwiching the slit 30b is equal to the upper and lower long sides of the radio wave half mirror 30A.

  As described above, the grooves 50 and 50 for preventing electromagnetic wave leakage are provided on the outer peripheral portion of the radio wave half mirror 30A provided so as to close the opening at the distal end portion of the inner first waveguide 21. The distance from 50 to the outer edge portion on the surface side of the radio wave half mirror 30A, that is, the above-described unnecessary resonance length x can be made extremely small, and the unnecessary waveguide length x can be reduced by the first waveguide 21 in the second waveguide. Even if it moves relative to 22, it does not change.

  Therefore, it is possible to eliminate the influence of the unnecessary resonance on the choke effect of the groove 50 by moving the frequency of the unnecessary resonance to a region sufficiently higher than the variable region of the resonance frequency of the filter, and there is little loss in a wide frequency band. Broadband characteristics can be obtained.

  Note that it is possible to provide the electromagnetic wave leakage preventing groove 50 not on the outer peripheral portion of the radio wave half mirror 30A but on the outer peripheral wall 21a of the first waveguide 21. In this case, the unnecessary resonance length x is set to the radio wave half mirror 30A. And the thickness of the outer peripheral wall 21a of the first waveguide 21 must be sufficiently larger than ¼ of the leakage prevention wavelength, whereby the outer diameter of the first waveguide 21 is increased. Accordingly, the inner diameter of the outer second waveguide 22 is increased accordingly.

  On the other hand, as in the above-described embodiment, the radio wave half mirror 30A having an outer shape large enough to close the opening of the first waveguide 21 has a depth necessary for preventing electromagnetic wave leakage from the outer periphery toward the inner side. Thus, the unnecessary resonance length x can be minimized without increasing the outer diameter of the first waveguide 21.

  Further, since it is not necessary to provide a groove on the inner periphery of the second waveguide 22, a thin and thin one can be used as the outer second waveguide 22, and the entire filter can be reduced in size.

  Next, a simulation result of the pass characteristic of the filter when the first waveguide 21 is moved relative to the second waveguide 22 in the millimeter waveband filter 20 of the above embodiment will be described.

This simulation was performed with the example dimensions shown in FIGS.
That is, the inner diameter a × b = 1.016 mm × 2.032 mm of the first waveguide 21, the outer diameter A × B = 1.976 mm × 2.992 mm, the thickness c of the outer peripheral wall 21a = 0.48 mm, the second One end inner diameter a ′ × b ′ = 2.016 mm × 3.032 mm of the waveguide 22, the other end inner diameter a ″ × b ″ = 1.016 mm × 2.032 mm, the outer peripheral wall 21 a of the first waveguide 21. And the gap G between the one end side inner peripheral wall 22a of the second waveguide 22 and G = 0.02 mm.

  For the radio wave half mirrors 30A and 30B, the outer shape A × B = 1.976 mm × 2.992 mm of the substrate 30a, the thickness t = 0.5 mm, the width u = 2.032 mm of the slit 30b, and the height s = 0. .07mm.

  The above conditions are the same as those of the millimeter-wave band filter having the conventional structure described above. The grooves 50 and 50 provided on the outer peripheral portion of the radio wave half mirror 30A have a length B = 2.922 mm, a width w = 0.2 mm, and a depth. The length d is set to 0.9 mm. Further, the distance (unnecessary resonance length) x from the upper and lower edges of the radio wave half mirror 30A to the grooves 50 and 50 is 0.15 mm.

  FIG. 4 shows a simulation result of the pass characteristics of the filter when the first waveguide 21 is moved relative to the second waveguide 22 under the above conditions. In the simulation, for simplicity, the material is a perfect conductor and there is no model of conductor loss.

  FIG. 4 shows the pass characteristics F1 to F10 when the mirror interval L is changed from 1.1 mm to 1.55 mm in 0.05 mm steps, as described above. The insertion loss is almost constant over a wide range of 146 GHz. As is clear from the comparison with FIG. 8, even when the resonance frequency of the filter becomes a high band, the increase in insertion loss hardly appears.

  The only difference in structure between FIG. 3 and FIG. 7 is the difference in the position of the electromagnetic wave leakage groove. Therefore, the characteristic improvement of FIG. 4 with respect to the characteristic of FIG. It can be seen that the effect is due to the provision at the outer periphery of the radio wave half mirror 30A provided at the tip.

  In the embodiment, the grooves 50 and 50 for preventing electromagnetic wave leakage are provided at a predetermined depth d so as to sandwich the slit 30b from the two opposing long sides of the radio wave half mirror 30A, and the conventional circular structure is not provided. However, from the above simulation results, it has been found that a sufficiently high electromagnetic wave leakage prevention effect can be obtained only by providing the outer periphery on the long side without providing the groove.

  Although not shown in the above description, a structure for supporting the first waveguide 21 and the second waveguide 22 is necessary. For example, in the case of a structure in which the first waveguide 21 is moved relative to the second waveguide 22, the second waveguide 22 is fixedly held on the base portion, and the first waveguide 21 is fixed to the second waveguide. The guide portion is guided so that it can move in the waveguide direction (longitudinal direction) in a concentric state with respect to 22, but this specific structure is arbitrary.

  The distance varying means 40 may be either manually operated or electrically operated as long as the first waveguide 21 can be moved relative to the second waveguide 22 so that the mirror distance L can be varied. The configuration is arbitrary. As an example, a mechanism that converts a rotational motion into a straight motion using a stepping motor that can be controlled from the outside, for example, a screw and a member having a screw hole screwed to the screw is used. A configuration in which the first waveguide 21 is moved relative to the second waveguide 22 via a conventional mechanism, rack and pinion, or the like is practical.

  In the above embodiment, a waveguide for propagating an electromagnetic wave in a millimeter wave band in a predetermined frequency range (for example, 110 to 140 GHz) in the TE10 mode, the first waveguide 21 and one end side of the first waveguide 21 inside However, in this structure, one of the waveguides is moved relative to the other in order to vary the resonance frequency, and the second waveguide 22 is moved. Inconvenience arises in connecting other circuits to the waveguide.

  In order to solve this, for example, as shown in FIG. 5, it is effective to provide a third waveguide 23 that receives the other end of the first waveguide 21 therein.

  As the third waveguide 23, for example, similarly to the second waveguide 22, different-diameter waveguides having different inner diameters on one end side and the other end side are used in the opposite direction. However, a tapered wall 23c whose inner diameter continuously changes is provided between the inner peripheral wall 23a on one end side and the inner peripheral wall 23b on the other end side so that reflection at the boundary portion where the inner diameter changes does not easily occur.

  In this way, the second waveguide 22 and the third waveguide 23 are connected to both sides of the first waveguide 21, respectively, and the fixed second waveguide 22 and third waveguide 23 are fixed. If the first waveguide 21 is structured to move in the waveguide direction (waveguide length direction) by the distance varying means 40, the external circuit is connected to the second waveguide 22 and the third waveguide on the fixed side. It is sufficient to connect to 23. In addition, as described above, the inner diameters of the small-diameter sides at the ends of the second waveguide 22 and the third waveguide 23 can be used with a standard diameter that propagates 110 to 140 GHz in the TE10 mode. A general-purpose waveguide can be used as it is for connection to the input / output circuit, and circuit construction including a filter becomes extremely easy.

  In the embodiment shown in FIGS. 1 and 5, the second waveguide 22 has a different-diameter structure with different inner diameters on one end side and the other end side. Similarly, an inner diameter of (a ′ × b ′) with a constant structure over the entire length may be used. In this case, the outer shape of the radio wave half mirror 30B may be made larger than the radio wave half mirror 30A by the gap G. In the case of the structure of FIG. 5, the third waveguide 23 may have a constant structure with an inner diameter of (a ′ × b ′) over the entire length, similarly to the first waveguide 21.

  20 …… Millimeter wave band filter, 21-23 …… Waveguide, 30A, 30B …… Radio wave half mirror, 40 …… Distance variable means, 50 …… Groove

Claims (3)

A waveguide for propagating electromagnetic waves in a predetermined frequency range in the millimeter wave band from one end to the other end in the TE10 mode is slightly larger than the outer diameter of the first waveguide (21) and one end side of the first waveguide. A second waveguide having an inner diameter and coupled in a state of being relatively movable in the waveguide direction with respect to the first waveguide, with one end of the first waveguide being received therein; 22), and
One (30A) of a pair of flat type radio wave half mirrors (30A, 30B) having a characteristic of transmitting a part of the electromagnetic wave in the predetermined frequency range and reflecting a part thereof is an opening on one end side of the first waveguide. The other (30B) is fixed inside the second waveguide in a state facing the one radio wave half mirror,
Of the electromagnetic wave incident from one end of the waveguide, a frequency component centered on the resonance frequency of the variable-length resonator formed between the pair of radio wave half mirrors is selectively added to the other of the waveguide. A millimeter wave band filter that outputs from the end side,
An outer peripheral portion of the one radio wave half mirror fixed so as to close an opening at one end of the first waveguide is formed at a predetermined depth inward, and an outer peripheral wall of the first waveguide A millimeter wave band filter provided with a groove (50) for suppressing electromagnetic wave leakage from a gap with an inner peripheral wall of the second waveguide facing the outer peripheral wall. The pair of radio wave half mirrors is
A substrate (30a) having an outer shape corresponding to the inner diameters of the first waveguide and the second waveguide, formed of a metal material that reflects electromagnetic waves to a predetermined thickness;
An electromagnetic wave transmitting slit (30b) extending through the center of the substrate along the long side direction of the substrate and penetrating from one surface side to the opposite surface side of the substrate;
The groove provided in the one radio wave half mirror fixed so as to close the opening on the one end side of the first waveguide is formed at the predetermined depth from the outer periphery of the long side of the substrate toward the slit. The millimeter waveband filter according to claim 1, wherein the millimeter waveband filter is provided. A waveguide for propagating electromagnetic waves in a predetermined frequency range in the millimeter wave band from one end to the other end in the TE10 mode is slightly larger than the outer diameter of the first waveguide (21) and one end side of the first waveguide. A second waveguide having an inner diameter and coupled in a state of being relatively movable in the waveguide direction with respect to the first waveguide, with one end of the first waveguide being received therein; 22), and
One (30A) of a pair of flat type radio wave half mirrors (30A, 30B) having a characteristic of transmitting a part of the electromagnetic wave in the predetermined frequency range and reflecting a part thereof is an opening on one end side of the first waveguide. The other (30B) is fixed inside the second waveguide in a state facing the one radio wave half mirror,
Of the electromagnetic wave incident from one end of the waveguide, a frequency component centered on the resonance frequency of the variable-length resonator formed between the pair of radio wave half mirrors is selectively added to the other of the waveguide. An electromagnetic wave leakage prevention method for a millimeter-wave band filter output from the end side,
The first waveguide is provided with a groove (50) formed at a predetermined depth inward on one outer peripheral portion of the radio wave half mirror fixed so as to close the opening at one end of the first waveguide. An electromagnetic wave leakage prevention method for a millimeter wave band filter, comprising suppressing electromagnetic wave leakage from a gap between an outer circumferential wall of a tube and an inner circumferential wall of the second waveguide facing the outer circumferential wall.

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