JP2014017694A - Millimeter wave band filter and method for varying resonance frequency therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a millimeter wave band filter having no characteristic deterioration due to wavefront conversion, applying a high degree of freedom in design of a radio wave half mirror, having little loss due to space radiation, and being capable of varying a frequency with a compact structure, and highly maintaining its characteristics of a filter.SOLUTION: A millimeter wave band filter comprises: a waveguide tube 21 including a waveguide rectangular in cross section for propagating electromagnetic waves in a prescribed frequency range within a millimeter wave band from its one end to the other end in a TE10 mode; and a pair of radio wave half mirrors 40A and 40B fixed in the waveguide tube at a prescribed interval so as to close the waveguide. The millimeter wave band filter selectively allows frequency components having a resonance frequency of a resonator provided between the radio wave half mirrors 40A and 40B, as the center thereof, to pass therethrough. The waveguide tube 21 varies a distance W between wall faces 23c and 23d, which are along short sides of four wall faces enclosing a waveguide 22b rectangular in cross section formed between the radio wave half mirrors 40A and 40B, in order to vary the resonance frequency.

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 wave use, WPAN (wireless personal area network) that realizes wireless broadband in the home and millimeter wave radio systems such as 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.

Teshirogi, Satoshi Yoneyama, “New Millimeter-Wave Technology” Ohmsha, 1993, p70

  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 millimeter wave band filter that solves the above problem, as shown in FIG. 6, the inside of a waveguide 1a formed by a waveguide 1 that propagates electromagnetic waves in a predetermined frequency range of the millimeter wave band from one end to the other end in a TE10 mode. In addition, a pair of flat radio wave half mirrors 2 and 3 having a characteristic of transmitting a part of the electromagnetic wave in the predetermined frequency range and reflecting a part thereof are arranged to face each other with a space therebetween, and the pair of radio wave half mirrors A structure in which a frequency component centered on the resonance frequency of the resonator formed between the electrodes is selectively passed is conceivable.

  With the above structure, there is no characteristic deterioration due to wavefront conversion, a high degree of freedom can be given to the design of the radio wave half mirror, and loss due to spatial radiation can be reduced.

  The resonance frequency of the resonator can be varied by changing the electrical length between the pair of radio wave half mirrors 2, 3. For this purpose, a mechanism for varying the distance between the pair of radio wave half mirrors may be used.

  However, when the frequency variable millimeter wave band filter based on the principle of changing the distance between the pair of radio wave half mirrors as described above is actually manufactured, there is a further problem to be solved.

  That is, when realizing a mechanism for changing the distance between the pair of radio wave half mirrors 2 and 3, as shown in FIG. 7, the first waveguide 11 for propagating electromagnetic waves in a predetermined frequency range in the TE10 mode, and the first waveguide. The first waveguide 12a that receives one end side of the tube 11 with a gap between the first waveguide 12a and the outer periphery of the tube 11 and the waveguide 11a of the first waveguide 11 are concentrically continuous with the first waveguide 12a with the same inner diameter. The second waveguide 12 having the second waveguide 12b can be relatively moved along the length direction of the waveguide, and one of the radio wave half mirrors 2 is guided by the first waveguide 11. The other radio wave half mirror 3 is fixed to the end of the second waveguide 12 near the first waveguide 12a and fixed to the tip of the waveguide 11a.

  In other words, in order to change the resonance frequency of the filter, it is necessary to move the waveguide in the propagation direction of the electromagnetic wave, and that direction inevitably becomes a connection part with the external circuit with the waveguide, so the frequency can be changed. The external circuit that does not contribute to the structure is also movable.

  In order to prevent this, for example, as shown in FIG. 8, the other end of the first waveguide 11 that is movable for variable frequency is received inside (or outside) the fixed third waveguide 15. By adopting the filter structure, even if the first waveguide 11 slides to change the frequency, the length of the entire filter remains unchanged, and the fixed second waveguide 12 and third waveguide 15 are fixed. An external circuit can be fixedly connected.

  However, the structure using three waveguides as described above increases the size of the filter, and causes deterioration of characteristics due to leakage of electromagnetic waves and the like as the number of sliding portions increases.

  The present invention solves these problems, does not deteriorate characteristics due to wavefront conversion, can provide a high degree of freedom in the design of a radio wave half mirror, requires little loss due to spatial radiation, and has a small structure and frequency. An object of the present invention is to provide a millimeter-wave band filter that can be varied and maintain high characteristics as a filter, and a method for varying the resonance frequency thereof.

In order to achieve the above object, the millimeter waveband filter according to claim 1 of the present invention comprises:
A waveguide (21) having a waveguide having a rectangular cross section for propagating electromagnetic waves in a predetermined frequency range of the millimeter wave band from one end side to the other end side in a TE10 mode;
A pair of radio wave half mirrors (40A, 40A, 40a, 40b, having a characteristic of transmitting a part of the electromagnetic wave in the predetermined frequency range and reflecting a part thereof, and being fixed at a predetermined distance so as to close the waveguide in the waveguide 40B)
Among the electromagnetic waves in the predetermined frequency range, a millimeter wave band filter that selectively passes electromagnetic waves having a resonance frequency of a resonator formed between the pair of radio wave half mirrors,
The waveguide has a structure capable of varying the interval of the wall surfaces along the short side of the rectangular cross section among the four wall surfaces surrounding the rectangular waveguide formed between the pair of radio wave half mirrors. And
The resonance frequency can be varied by varying the interval between the wall surfaces along the short side.

The millimeter waveband filter according to claim 2 of the present invention is the millimeter waveband filter according to claim 1,
An air duct (60) continuous from the wall surface along the short side of the rectangular cross section to the outer peripheral surface of the waveguide among the four wall surfaces surrounding the waveguide having a rectangular cross section formed between the pair of radio wave half mirrors. It is provided.

Further, the resonance frequency varying method of the millimeter waveband filter according to claim 3 of the present invention is:
A waveguide (21) having a waveguide having a rectangular cross section for propagating electromagnetic waves in a predetermined frequency range of the millimeter wave band from one end side to the other end side in a TE10 mode;
A pair of radio wave half mirrors (40A, 40A, 40a, 40b, having a characteristic of transmitting a part of the electromagnetic wave in the predetermined frequency range and reflecting a part thereof, and being fixed at a predetermined distance so as to close the waveguide in the waveguide 40B)
Among the electromagnetic waves in the predetermined frequency range, a resonant frequency variable method for a millimeter-wave band filter that selectively passes electromagnetic waves having a resonance frequency of a resonator formed between the pair of radio wave half mirrors,
Among the four wall surfaces surrounding the waveguide having a rectangular cross section formed between the pair of radio wave half mirrors of the waveguide, the resonance is achieved by varying the interval between the wall surfaces along the short side of the rectangular cross section. The frequency is variable.

  As described above, the millimeter waveband filter of the present invention has a structure in which a resonator formed of a pair of planar radio wave half mirrors is provided inside a waveguide of a waveguide that transmits only the TE10 mode. No special device is required for incident plane waves, 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.

  In addition, the waveguide has a structure in which the interval between the wall surfaces along the short side of the rectangular cross section among the four wall surfaces surrounding the rectangular waveguide formed between the pair of radio wave half mirrors can be varied. Since the resonance frequency can be changed by changing the interval between the wall surfaces along the short side, the size can be reduced.

  In addition, in the case where the air duct is provided, it is possible to prevent the distortion of the radio wave half mirror due to the air pressure generated when the frequency is varied, and the frequency can be varied stably.

The figure which shows the basic structure of the millimeter wave band filter of this invention The figure which shows the structure example of an electric wave half mirror, and the relation of arrangement of a movable block Simulation results showing changes in filter characteristics when the wall spacing along the short side of the waveguide between radio wave half mirrors is varied Structure of filter that moves only one wall surface The figure which shows the example which provided the air duct in the movable block Principle structure diagram of millimeter wave band filter which is the basis of the present invention First structure example for realizing a millimeter-wave band filter Second structural example for realizing millimeter-wave band filter

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows a basic structure of a millimeter wave band filter 20 of the present invention.

  As shown in FIG. 1A, the millimeter wave band filter 20 includes a waveguide 21, a pair of radio wave half mirrors 40 </ b> A and 40 </ b> B, and a resonance frequency variable mechanism 50.

  The waveguide 21 is formed of a metal material in a rectangular tube shape having a rectangular cross section, and has a diameter (for example, width) for propagating electromagnetic waves in a millimeter wave band in a predetermined frequency range (for example, 110 to 140 GHz) in a TE10 mode (single mode). A waveguide 22 of a × height b = 2.032 mm × 1.016 mm) is continuously formed in a straight line from one end side to the other end side.

  A pair of radio wave half mirrors 40 </ b> A and 40 </ b> B having a characteristic of transmitting a part of the electromagnetic wave in the predetermined frequency range and reflecting a part of the electromagnetic wave in the predetermined frequency range is separated from the central part of the waveguide 21 by a certain distance. Are fixed so that they face each other.

  For example, as shown in FIG. 2, the pair of radio wave half mirrors 40A and 40B includes a rectangular dielectric substrate 41 having a size corresponding to the diameter of the waveguide 22 to be fixed, and a metal film 42 covering the surface thereof. The slit 43 for transmitting electromagnetic waves provided in the metal film 42 is fixed so that the outer periphery of the metal film 42 is in contact with the inner wall of the waveguide 22, and corresponds to the shape and area of the slit 43. Transmit electromagnetic waves with transmittance.

  The waveguide 22 surrounded by the inner wall of the waveguide 21 is partitioned into a first waveguide 22a, a second waveguide 22b, and a third waveguide 22c by two radio wave half mirrors 40A and 40B.

  Of the four wall surfaces 23a to 23d surrounding the rectangular waveguide second waveguide 22b formed between the radio wave half mirrors 40A and 40B, the interval W between the wall surfaces 23c and 23d along the short side of the rectangle is The resonance frequency variable mechanism 50 can be varied.

  That is, the waveguide 21 has guide holes 51 and 52 that are continuous from both side surfaces along the short side of the second waveguide 22b to both side surfaces 21a and 21b of the waveguide 21 along the long side direction. It is formed through.

  The height of the guide holes 51 and 52 substantially matches the height b (short side = 1.016 mm) of the second waveguide 22b, and the width of the guide holes 51 and 52 is the propagation direction of the second waveguide 22b. (Here, equal to the interval D between the radio wave half mirrors 40A and 40B).

  The guide holes 51 and 52 are inscribed and accommodated so that the four side surfaces are in contact with the inner circumferences of the guide holes 51 and 52, and are slidable in the long side direction of the second waveguide 22b having a rectangular cross section. Metal movable blocks 53 and 54 are arranged.

  Accordingly, the inner surfaces of the two movable blocks 53 and 54 facing each other form wall surfaces 23c and 23d along the short side of the second waveguide 22b.

  The two movable blocks 53 and 54 are connected to driving devices 55 and 56 fixed to the side surfaces 21a and 21b of the waveguide 21, and the driving devices 55 and 56 allow the distance between them, that is, the second guide. The interval W between the wall surfaces 23c and 23d on the short side of the waveguide 22b is changed. Here, the driving devices 55 and 56 may be any device that can increase the distance W from about 2.032 mm to 2 m from the long side length of the first waveguide 22a and the third waveguide 22c. The solenoid can be used as a drive source.

  As described above, by changing the wall surface distance W along the short side of the second waveguide 22b between the pair of radio wave half mirrors 40A and 40B, the resonator formed between the radio wave half mirrors 40A and 40B can be changed. The resonance frequency can be varied.

That is, it is known that the guide wavelength λg of the waveguide is expressed by the following equation.
λg = λ / [1- (λ / λ _C10 ) ² ] ^1/2
= Λ / [1- (λ / 2a ′) ² ] ^1/2
λ: free space wavelength λ _C10 : cutoff frequency of TE01 mode a ′: long side of waveguide opening

  Since the resonance wavelength (center wavelength of the pass band) of the filter having the structure in which the radio wave half mirrors 40A and 40B are opposed to each other is ½ of the guide wavelength λg, the long side a ′ of the second waveguide 22b, that is, The resonance frequency of the filter can be varied by varying the interval W between the wall surfaces along the short side of the second waveguide 22b.

  In FIG. 3, the half mirror interval D = 1.28 mm, and the wall surface interval W along the short side of the second waveguide 22b is changed in steps of 0.2 mm from 2.032 mm (= a) to 4.032 mm (waveguide). This is a result of simulating a change in resonance frequency when both movable blocks 53 and 54 are changed symmetrically with respect to the center.

  As is apparent from this figure, it can be seen that the resonance frequency can be varied in a range of approximately 125 GHz to 140 GHz.

  In the millimeter waveband filter 20 having the above-described structure, a planar Fabry-Perot resonator that resonates at half the guide wavelength of the second waveguide 22b formed between the pair of radio half mirrors 40A and 40B facing each other. Is formed, and only a frequency component centered on the resonance frequency can be selectively passed.

  In addition, the waveguide 22 is formed of a waveguide structure as a closed transmission line with extremely low loss in the millimeter wave band, and uses a TE wave having an electric field only in a plane orthogonal to the traveling direction. Such a process is unnecessary, and only the signal component extracted by the resonator can be output in the TE10 mode with extremely low loss.

  Further, the filter as a whole is almost hermetically sealed so that there is little loss due to radiation to the external space, and extremely high selection characteristics can be realized in the millimeter wave band.

  And in this millimeter wave band filter 20, by changing the interval W between the wall surfaces along the short side of the second waveguide 22b formed between the pair of radio wave half mirrors 40A, 40B, the radio wave half mirror 40A, Since the resonance frequency of the resonator formed between 40B is varied, an external circuit can be fixedly connected to both ends (both ends of the waveguide 21) of this filter, and other guides for movable absorption can be obtained. A wave tube is also unnecessary, and the entire filter can be made compact.

  Here, both the wall surfaces along the short side of the second waveguide 22b formed between the pair of radio wave half mirrors 40A and 40B are moved to change the interval, but as shown in FIG. In addition, the resonance frequency can be varied by varying only one wall surface.

  In the above embodiment, the basic structures of the waveguide 21 and the resonance frequency variable mechanism are schematically shown. However, the actual structure can be arbitrarily modified.

  In addition, when the movable blocks 53 and 54 are moved at a relatively high speed with the above structure, the volume of the space between the pair of radio wave half mirrors 40A and 40B increases or decreases, but the air present therein has a narrow gap. The internal pressure changes without being removed, and the pressure causes distortion in the thin radio wave half mirrors 40A and 40B, which may cause problems such as the resonance frequency of the filter deviating from a desired value and loss.

  When the influence on the filter characteristics due to the pressure change cannot be ignored, an air duct that continues from the wall surface along the short side of the second waveguide 22b to the outer peripheral surface of the waveguide 21 is provided, and the radio wave half mirrors 40A and 40B What is necessary is just to make air easy to pass between the space between and the waveguide exterior. FIG. 5 shows an example of this. An air duct 60 is formed on the side of the movable block 53 that forms the wall surface along the short side of the second waveguide 22b, and the inside of the waveguide and the outside of the waveguide 21 are shown. Air is easy to pass between.

  Although there is a concern about the effect on the filter characteristics due to the formation of a cavity between the second waveguide 22b and the outside of the waveguide as described above, the shape change on the short side compared to the long side of the rectangular waveguide It is known that there are few adverse effects, and it has been confirmed that there is no problem if the air is removed. Here, the air duct 60 is provided in the movable block 53. However, an air duct is provided on the guide hole 51 side, or an air duct penetrating from the non-movable wall surface 23d to the side surface 21b of the waveguide 21 as shown in FIG. May be.

  20... Millimeter wave filter, 21... Waveguide, 22... Waveguide, 22 a... First waveguide, 22 b... Second waveguide, 22 c. Radio wave half mirror, 50 ... Resonance frequency variable mechanism, 60 ... Air duct

Claims (3)

A waveguide (21) having a waveguide having a rectangular cross section for propagating electromagnetic waves in a predetermined frequency range of the millimeter wave band from one end side to the other end side in a TE10 mode;
A pair of radio wave half mirrors (40A, 40A, 40a, 40b, having a characteristic of transmitting a part of the electromagnetic wave in the predetermined frequency range and reflecting a part thereof, and being fixed at a predetermined distance so as to close the waveguide in the waveguide 40B)
Among the electromagnetic waves in the predetermined frequency range, a millimeter wave band filter that selectively passes electromagnetic waves having a resonance frequency of a resonator formed between the pair of radio wave half mirrors,
The waveguide has a structure capable of varying the interval of the wall surfaces along the short side of the rectangular cross section among the four wall surfaces surrounding the rectangular waveguide formed between the pair of radio wave half mirrors. And
A millimeter-wave band filter characterized in that the resonance frequency can be varied by varying the interval between the wall surfaces along the short side.   An air duct (60) continuous from the wall surface along the short side of the rectangular cross section to the outer peripheral surface of the waveguide among the four wall surfaces surrounding the waveguide having a rectangular cross section formed between the pair of radio wave half mirrors. The millimeter waveband filter according to claim 1, wherein the millimeter waveband filter is provided. A waveguide (21) having a waveguide having a rectangular cross section for propagating electromagnetic waves in a predetermined frequency range of the millimeter wave band from one end side to the other end side in a TE10 mode;
A pair of radio wave half mirrors (40A, 40A, 40a, 40b, having a characteristic of transmitting a part of the electromagnetic wave in the predetermined frequency range and reflecting a part thereof, and being fixed at a predetermined distance so as to close the waveguide in the waveguide 40B)
Among the electromagnetic waves in the predetermined frequency range, a resonant frequency variable method for a millimeter-wave band filter that selectively passes electromagnetic waves having a resonance frequency of a resonator formed between the pair of radio wave half mirrors,
Among the four wall surfaces surrounding the waveguide having a rectangular cross section formed between the pair of radio wave half mirrors of the waveguide, the resonance is achieved by varying the interval between the wall surfaces along the short side of the rectangular cross section. A method for varying the resonant frequency of a millimeter-wave band filter, wherein the frequency is varied.

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