Millimeter waveband filter

Abstract

In an end surface 32b of the second transmission line forming body 32 forming a second waveguide 30, the height of a central region 33 which includes an opening of the second transmission line 30b is a reference plane. A depressed portion 32e that is depressed to a depth greater than the length of a thread portion of a screw 205 from the reference plane is provided in a region outside the central region 33 and includes a screw hole forming position. A screw hole 32d for fixing an external circuit 200 to be connected is provided at the screw hole forming position in the depressed portion 32e. The height of a region, which is excluding the depressed portion 32e and is further away from the central region 33 than the screw hole forming position, is equal to the reference plane.

Claims

1. A millimeter waveband filter comprising: a first waveguide including a transmission line with a size that is capable of transmitting electromagnetic waves in a predetermined frequency range of a millimeter-wave band in a TE10 mode; a second waveguide that includes a first transmission line which has a size that is greater than an outside size of the first waveguide and is capable of transmitting the electromagnetic waves in the predetermined frequency range in the TE10 mode and into which one end of the first waveguide is inserted, with a gap between the outside of the first waveguide and the first transmission line, and a second transmission line which has a size less than that of the first transmission line and is formed such that the first transmission line and the second transmission line are concentrically continuous; a pair of radio wave half mirrors which transmit some of the electromagnetic waves in the predetermined frequency range and reflect some of the electromagnetic waves, one of the pair of radio wave half mirrors being fixed to the transmission line at the one end of the first waveguide, the other radio wave half mirror being fixed to a boundary between the first transmission line and the second transmission line of the second waveguide; and a moving device that moves the first waveguide in a length direction of the transmission line such that a gap between the pair of radio wave half mirrors is changed, thereby selectively transmitting an electromagnetic wave with a resonance frequency which is determined by the gap between the pair of radio wave half mirrors among the electromagnetic waves in the predetermined frequency range, wherein the second waveguide further includes: a first transmission line forming body in which a rectangular hole forming the first transmission line is formed in a plate portion with a predetermined thickness to a thickness direction so as to pass through the plate portion; and a second transmission line forming body in which a rectangular hole forming the second transmission line is formed in a plate portion with a predetermined thickness in a thickness direction so as to pass through the plate portion, the first transmission line forming body and the second transmission line forming body are formed so as to be connected to and separated from each other, with the plate portions overlapping each other such that the rectangular holes are concentrically continuous, a central region that includes an opening of the second transmission line, and a depressed portion, are provided in one surface of the second transmission line forming body which is opposite to the other surface connected to the first transmission line forming body, a reference plane is at a height of the central region, and the depressed portion is depressed from the reference plane and is provided in a region which is outside the central region and includes screw hole forming positions, screw holes, into which screws for fixing an external circuit to be connected to the second transmission line forming body are inserted, are provided at the screw hole forming positions in the depressed portion, the depressed portion has a depth greater than the length of a thread portion of the screw, and a height of a region that is excluding the depressed portion and is further away from the central region than the screw hole forming positions is equal to the height of the reference plane.

2. The millimeter waveband filter according to claim 1, wherein the first transmission line forming body is fixed to a base portion, and the second transmission line forming body is fixed to the first transmission line forming body at a predetermined position and is screwed to the base portion at a position that is further away from the opening of the second transmission line than the screw hole forming positions.

3. The millimeter waveband filter according to claim 1, wherein the central region has the same size as a protruding portion that is defined by a flange structure based on a predetermined standard depending on the size of the second transmission line, the screw hole forming positions are defined by the flange structure, and the length of the thread portion is defined by the flange structure.

4. The millimeter waveband filter according to claim 2, wherein the central region has the same size as a protruding portion that is defined by a flange structure based on a predetermined standard depending on the size of the second transmission line, the screw hole forming positions are defined by the flange structure, and the length of the thread portion is defined by the flange structure.

5. The millimeter waveband filter according to claim 3, wherein the second transmission line has a rectangular shape in a cross-sectional view, a number of the screw holes is four, the four screw holes are defined by the flange structure of the second waveguide, and the four screw holes are formed at positions that are a predetermined distance away from the center of the second transmission line and are arranged on a center line extending in a width direction of the transmission line and a center line extending in a height direction of the transmission line.

6. The millimeter waveband filter according to claim 4, wherein the second transmission line has a rectangular shape in a cross-sectional view, a number of the screw holes is four, the four screw holes are defined by the flange structure of the second waveguide, and the four screw holes are formed at positions that are a predetermined distance away from the center of the second transmission line and are sited on a center line extending to a width direction of the transmission line and on a center line extending to a height direction of the transmission line.

7. The millimeter waveband filter according to claim 5, wherein the length of a shaft portion of the screws are greater than the thickness of a flange portion of the external circuit, the depth of the depressed portion is greater than the length of the thread portion having a thread groove formed therein in the screws, and the sum of the depth of the depressed portion and the thickness of the flange portion of the external circuit is less than the sum of the lengths of the shaft portion and the thread portion of the screw.

8. The millimeter waveband filter according to claim 6, wherein the length of a shaft portion of the screws are greater than the thickness of a flange portion of the external circuit, the depth of the depressed portion is greater than the length of the thread portion having a thread groove formed therein in the screws, and the sum of the depth of the depressed portion and the thickness of the flange portion of the external circuit is less than the sum of the lengths of the shaft portion and the thread portion of the screw.

9. The millimeter waveband filter according to claim 7, wherein the predetermined standard is a MIL standard.

10. The millimeter waveband filter according to claim 8, wherein the predetermined standard is a MIL standard.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a plan view illustrating an embodiment of the invention.

(2) FIG. 2 is a cross-sectional view taken along the line A-A of FIG. 1.

(3) FIG. 3 is an exploded view illustrating a main portion of the embodiment of the invention.

(4) FIG. 4 is a diagram illustrating an operation of connecting an external circuit to a filter according to the embodiment of the invention.

(5) FIG. 5 is a diagram illustrating the operation of connecting the external circuit to the filter according to the embodiment of the invention.

(6) FIG. 6 is a diagram illustrating the operation of connecting the external circuit to the filter according to the embodiment of the invention.

(7) FIG. 7 is a diagram illustrating the operation of connecting the external circuit to the filter according to the embodiment of the invention.

(8) FIG. 8 is a diagram illustrating the operation of connecting the external circuit to the filter according to the embodiment of the invention.

(9) FIGS. 9A and 9B are diagrams illustrating another example of the structure of an end surface of a second transmission line forming body.

(10) FIG. 10 is a diagram illustrating an example of a structure in which the second transmission line forming body is screwed to a base portion.

(11) FIG. 11 is an exploded perspective view illustrating the structure shown in FIG. 10.

(12) FIGS. 12A and 12B are diagrams illustrating a flange structure based on a MIL standard.

(13) FIG. 13 is a diagram of the related art illustrating an example of a structure when external circuits are connected to a first waveguide and a second waveguide on the basis of a flange structure based on a predetermined standard.

(14) FIG. 14 is a diagram of the related art illustrating the transmission of force when the external circuit is connected to.

(15) FIG. 15 is a diagram of the related art illustrating a change in a resonance frequency due to the strength of a screw tightening force.

(16) FIG. 16 is a diagram of the related art illustrating a structure and an operation when an external circuit with a flat flange structure is screwed.

(17) FIG. 17 is a diagram of the related art illustrating the structure and the operation when the external circuit with the flat flange structure is screwed.

BEST MODE FOR CARRYING OUT THE INVENTION

(18) Hereinafter, an embodiment of the invention will be described with reference to the drawings. In the following description, a flange structure is based on a MIL standard, specifically, MIL-F-3922/67B.

(19) FIG. 1 is a plan view illustrating a millimeter waveband filter 100 according to the invention, FIG. 2 is a cross-sectional view taken along the line A-A of FIG. 1, and FIG. 3 is an exploded view illustrating a main portion.

(20) In FIGS. 1 to 3, the millimeter waveband filter 100 includes a first waveguide 21, a second waveguide 30, radio wave half mirrors 50A and 50B, a base portion 60, and a moving device 70.

(21) The first waveguide 21 includes a transmission line 22 which has a size of about 2 mm×1 mm and transmits electromagnetic waves in a predetermined frequency range (for example, 110 GHz to 140 GHz) of a millimeter-wave band in a TE10 mode. One end 21a of the first waveguide 21 is inserted into the second waveguide 30 and a flange portion 21b with a large width is formed at the other end of the first waveguide 21. The other end of the first waveguide 21 can have the following structures: the above-mentioned structure in which a prescribed protruding portion is provided in a flange structure based on a predetermined standard and an external circuit is screwed to the flange structure; a structure in which a flange structure is not provided at one end, similarly to the one end 21a, the one end is inserted into a fixed waveguide that is symmetrical to the second waveguide 30, which will be described below, and an external circuit is connected to a flange portion of the fixed waveguide; and various other structures. Therefore, the shape of the other end of the first waveguide 21 will not be described in detail in this embodiment.

(22) The second waveguide 30 has a size that is larger than the outside size of the first waveguide 21 and is capable of transmitting electromagnetic waves in a predetermined frequency range in the TE10 mode, and is formed such that a first transmission line 30a into which the one end 21a (the right end in the drawings) of the first waveguide 21 is inserted, with a gap between the first transmission line and the outside of the first waveguide, and a second transmission line 30b having a size less than that of the first transmission line 30a (here, the second transmission line 30b has the same size as the first waveguide 21) are concentrically continuous.

(23) A first transmission line forming body 31 and a second transmission line forming body 32 overlap each other to form the second waveguide 30. The second waveguide 30 is positioned such that a slight gap (several tens of micrometers) between the outside of the first waveguide 21 and the second waveguide 30 is uniform.

(24) That is, as shown in FIG. 3, in the first transmission line forming body 31, a rectangular hole forming the first transmission line 30a is formed in a plate portion with a predetermined thickness so as to pass through the plate portion to a thickness direction (from one surface 31a to a surface 31b opposite to the one surface 31a). In the second transmission line forming body 32, a rectangular hole forming the second transmission line 30b is formed in a plate portion with a predetermined thickness so as to pass through the plate portion to a thickness direction (from one surface 32a to a surface 32b opposite to the one surface 32a). The two transmission line forming bodies are connected to each other, with the plate portions overlapping each other such that the rectangular holes are concentrically continuous. Here, connection screw holes 31c are provided at four corners of the opposite surface 31b of the first transmission line forming body 31. In the second transmission line forming body 32, holes 32c for connection screws 35 are provided at positions corresponding to the screw holes 31c. The screws 35 inserted into the holes 32c are tightened to connect the two transmission line forming bodies, with the transmission lines being concentrically continuous. The head of the screw 35 is inserted into the middle of the hole 32c so as not to protrude from the surface.

(25) Since the second waveguide 30 can be connected and separated in this way, the second waveguide 30 is positioned with respect to the first waveguide 21 such that the gap between the outside of the first waveguide 21 and the inside of the first transmission line 30a is uniform, while being observed by, for example, a microscope from the opposite surface 31b of the first transmission line forming body 31 at the beginning. Then, the second transmission line forming body 32 which is formed in advance so as to be concentrically connected to the first transmission line forming body 31 is screwed to the first transmission line forming body 31. In this way, the positioning between the first waveguide 21 and the second waveguide 30 is completed.

(26) The radio wave half mirror 50A is fixed to one end of the first waveguide 21 so as to close the transmission line 22. The radio wave half mirror 50B is fixed so as to close a boundary portion between the first transmission line 30a and the second transmission line 30b of the second waveguide 30, practically, the leading end of the second transmission line 30b of the second transmission line forming body 32.

(27) The radio wave half mirrors 50A and 50B have a structure in which a slit for transmitting some of electromagnetic waves is provided in a metal substrate that reflects electromagnetic waves. The resonance of a frequency that is determined by the gap between the two radio wave half mirrors 50A and 50B occurs between the radio wave half mirrors 50A and 50B and the operation of a Fabry-Perot filter is obtained.

(28) The first waveguide 21 can be moved in the length direction of the transmission line 20 by the moving device 70 provided in the base portion 60. In this way, a variable-frequency filter with a variable resonance frequency is formed.

(29) An end surface (the above-mentioned opposite surface) 32b opposite to the surface of the second transmission line forming body 32 to which the first transmission line forming body 31 is connected has a structure that can be screwed to an external circuit 200 with a flat connection surface while coming into close contact with the external circuit 200.

(30) That is, in the end surface, a reference plane is at the height of a central region 33 which includes an opening of the second transmission line 30b and has the same size as the protruding portion that is defined by the flange structure based on the predetermined standard with respect to the size of the second transmission line 30b. A depressed portion 32e that is depressed to a depth greater than the length of a thread portion of a screw 205 used in the flange structure from the reference plane is provided in a region which is sited outside the central region 33 and includes a screw hole forming position defined by the flange structure. A screw hole 32d for screwing the external circuit 200 is provided at the screw hole forming position in the depressed portion 32e.

(31) The height of a region, which is excluding the depressed portion 32e and is further away from the central region 33 than the screw hole forming position, is equal to the reference plane.

(32) In this example, in the end surface 32b of the second transmission line forming body 32, the depressed portion 32e is limited to a narrow region surrounding the position where the screw hole 32d is formed and the height of the other region including the central region 33 is equal to the reference plane. However, the range of the depressed portion 32e may expand to the outer edge of the central region 33 and the depressed portion 32e may have any outward shape.

(33) Next, an operation when the external circuit 200 having a flange structure with a flat connection surface is connected to the second transmission line forming body 32 having the above-mentioned end surface structure will be described.

(34) First, as shown in FIG. 4, the prescribed screw 205 is inserted into a screw hole 200c with a thread groove which is provided in a flange portion 200b of the external circuit 200. Here, the screw 205 includes a head 205a, a shaft portion 205b, and a thread portion 205c. According to the above-mentioned standard, the length L1 of the shaft portion 205b is greater than the thickness t of the flange portion 200b. In addition, the depth D of the depressed portion 32e is slightly greater than the length L2 of the thread portion 205c having the thread groove provided therein and the sum t+D of the depth D of the depressed portion 32e and the thickness t of the flange portion 200b is set to be less than the sum L1+L2 of the length of the shaft portion 205b and the length of the thread portion 205c. A preferred condition for inserting the entire thread portion 205c into the screw hole 32d of the second transmission line forming body 32 is that the sum of the depth D of the depressed portion 32e and the thickness t of the flange portion 200b is equal to the length L1 of the shaft portion 205b. In FIG. 4, reference numeral 200d is a transmission line of the external circuit 200.

(35) When the screw 205 is tightened on the basis of this condition, the thread portion 205c passes through the screw hole 200c and the screw 205 is not taken off the flange portion 200b and can turn freely, as shown in FIG. 5.

(36) In this state, the external circuit 200 is placed close to the second transmission line forming body 32 and the leading end of the thread portion 205c is inserted into the screw hole 32d through the depressed portion 32e and is then tightened. Then, the flange portion 200b is close to the second transmission line forming body 32. Finally, as shown in FIG. 6, the flange portion 200b and the second transmission line forming body 32 come into close contact with each other and the screw 205 is tightened.

(37) FIG. 7 shows the insertion of another screw 205 into the flange portion 200b in the above-mentioned state. In this state, the screw 205 can turn freely, similarly to the above. When the leading end of the screw 205 is inserted into the screw hole 32d of the second transmission line forming body 32 and is then turned, the thread portion 205c is threadably engaged with the screw hole 32d, regardless of continuity between the screw hole 200c of the flange portion 200b and the thread groove of the screw hole 32d of the second transmission line forming body 32. As a result, the screw 205 is tightened as shown in FIG. 8.

(38) When the same operation as described above is performed on the other screws, the tightening of four screws around the transmission line ends. In the end surface 32b of the second transmission line forming body 32, a region including the central region 33 which includes at least the opening of the transmission line excluding the depressed portion 32e and has a height equal to the reference plane and a region outside the screw hole forming position is connected to the flat connection surface of the external circuit 200 while coming into close contact with the flat connection surface.

(39) As such, the second transmission line forming body 32 is screwed to the external circuit while the central region 33 which is arranged inside the screwing position and the region which is away from the screwing position come into close contact with the external circuit. Therefore, a force to curve an outer circumferential portion of the second transmission line forming body 32 is not generated and a change in the position of the radio wave half mirror 50B is suppressed.

(40) Therefore, when control data indicating the relationship between the resonance frequency and the position of the first waveguide 21 relative to the second waveguide 30 is calculated in advance, accurate variable frequency control is performed on the basis of the control data even in the state in which the external circuit is connected.

(41) In the above-described embodiment, in the end surface 32b of the second transmission line forming body 32, the depressed portion 32e is limited to a possible narrow region which surrounds the position where screw hole 32d is formed and the other region including central region 33 has a height equal to the reference plane. However, the depressed portion may have any size or shape as far as the height of central region 33 which has the same size as the protruding portion defined by the flange structure based on the predetermined standard is the reference plane and the depressed portion that is depressed to a depth greater than the length of the thread portion of screw 205 used in flange structure from the reference plane is provided in the region which is arranged outside the central region 33 and includes the screw hole forming position defined by flange structure, as described above. For example, as shown in FIGS. 9A and 9B, the range of depressed portion 32e may expand to the outer edge of the central region 33.

(42) In the above-described embodiment, the first transmission line forming body 31 of the second waveguide 30 is fixed and supported by the base portion 60 and the second transmission line forming body 32 is screwed to the first transmission line forming body 31 at the predetermined position. However, when the second transmission line forming body 32 is fixed to the first transmission line forming body 31, the second transmission line forming body 32 may be screwed to the base portion 60 at a position that is further away from the transmission line 30b than a screwing position for connecting the external circuit. In this case, it is possible to further suppress deformation when the external circuit is connected.

(43) FIGS. 10 and 11 show an example of the structure of the above-mentioned modification. The first transmission line forming body 31 is fixed such that an end surface 31b thereof is continuously flush with an end surface 60b of the base portion 60. The periphery of the transmission line 30b of the second transmission line forming body 32 having an extended lower part is fixed to the end surface 31b of the first transmission line forming body 31 by screws 35, similarly to the above. Screws 65 pass through holes (without a thread groove) 32f which are provided in the extended lower part and are then inserted into screw holes (with a thread groove) 60c provided in the end surface 60b of the base portion 60. However, the hole 32f has a tolerance with respect to the diameter of the screw 65, considering the slight positional deviation of the second transmission line forming body 32.

(44) As such, the second transmission line forming body 32 is screwed to the base portion 60 at the position that is further away from the transmission line 30b than a standard external circuit screwing position. Therefore, it is possible to further suppress deformation when the external circuit is connected and the concern that the relationship between the resonance frequency and the position of a waveguide in a single filter (the gap between the radio wave half mirrors) will vary depending on the connection of the external circuit is further reduced.

DESCRIPTION OF REFERENCE NUMERALS AND SIGNS

(45) 21: FIRST WAVEGUIDE 22: TRANSMISSION LINE 30: SECOND WAVEGUIDE 30a: FIRST TRANSMISSION LINE 30b: SECOND TRANSMISSION LINE 31: FIRST TRANSMISSION LINE FORMING BODY 32: SECOND TRANSMISSION LINE FORMING BODY 32e: DEPRESSED PORTION 33: CENTRAL REGION 50A, 50B: RADIO WAVE HALF MIRROR 60: BASE PORTION 70: MOVING DEVICE 200: EXTERNAL CIRCUIT