JP2015056721A - Millimeter wave band filter and wide area attenuation method for millimeter wave band - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an easy-to-manufacture millimeter wave band filter which allows for sufficient wide area attenuation characteristics in a frequency band exceeding 100GHz.SOLUTION: First waveguide 21 and second waveguide 22 are arranged to pass each other in parallel while closing one ends 21a, 22a of a waveguide having a rectangular cross section and propagating electromagnetic waves of a predetermined frequency or more in the millimeter wave band, respectively, and facing the side faces (inner side face) 21b, 22b on the short side surrounding the one end side thereof each other. A manifold 23 couples the side faces on the short side of the first waveguide 21 and second waveguide 22 by a waveguide of a predetermined caliber, and regulates transmission ratio to the second waveguide 22 so as to decrease as the frequency of electromagnetic waves incident to the first waveguide 21 increases.

Description

  The present invention relates to a technique for attenuating the high band of the 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 problems and realize high-sensitivity and high-accuracy measurement of a 100 GHz super-band wireless signal, a filter that suppresses the input of an out-of-band signal to an amplifier or a mixer is required. Since a waveguide, which is a basic transmission line used in a band, basically functions as a high-pass filter, it is necessary to develop a low-pass type (high-cut type) filter that suppresses high-band out-of-band signals.

  To briefly explain this, the basic characteristic of a waveguide is a high-pass type in which the pass band extends from about 70 GHz to over 1000 GHz as shown in G1 of FIG. 14, for example. In order to selectively pass a signal in a band to be used, it is conceivable to provide a characteristic of a band pass filter having a resonance element in the waveguide and having a pass center frequency of, for example, 100 GHz. For the structural reason, the filter exhibits a selection characteristic not only in a desired band but also in an integral multiple band (passage centers 200 GHz, 300 GHz,...) As indicated by G2 in FIG.

  For this reason, if there is an unnecessary signal in a frequency band higher than the desired band, it cannot be removed. Therefore, as indicated by G3 in FIG. 14, for example, a filter having a high-frequency attenuation characteristic in a frequency region exceeding 120 GHz is required.

  As a filter that can be used for this purpose, a waffle iron type filter using a waveguide is known (Patent Documents 1 and 2).

JP 2007-194912 A JP 2007-088574 A

  However, the waffle iron type filter needs to be provided with a plurality of grooves with high accuracy inside the waveguide, and its difficulty increases as the frequency increases. Sufficient attenuation characteristics in a frequency band exceeding 100 GHz There was a problem that could not be obtained.

  An object of the present invention is to solve this problem and to provide a millimeter-wave band filter and a millimeter-wave band high-frequency attenuation method which can obtain sufficient high-frequency attenuation characteristics in a frequency band exceeding 100 GHz and are easy to manufacture. It is said.

In order to achieve the above object, the millimeter waveband filter according to claim 1 of the present invention comprises:
One end side of a rectangular waveguide that propagates electromagnetic waves of a predetermined frequency or higher in the millimeter wave band is closed, and the short sides surrounding each one end side waveguide are arranged so that they face each other. The first waveguide (21) and the second waveguide (22),
A guide having a predetermined diameter is provided between the waveguide of the first waveguide and the waveguide of the second waveguide between the side surfaces of the first waveguide and the second waveguide on the short side. A coupling tube (23) that is coupled by a waveguide and regulates so that a propagation rate to the second waveguide decreases as the frequency of the electromagnetic wave incident on the first waveguide increases. Yes.

The millimeter waveband filter according to claim 2 of the present invention is the millimeter waveband filter according to claim 1,
The connecting tube has a distance from the center of its aperture to the closed end of at least one of the first waveguide and the second waveguide of ¼ of the in-tube wavelength of the frequency to be passed. The waveguides of the first waveguide and the second waveguide are connected at a position that is an odd multiple of.

The millimeter wave band filter according to claim 3 of the present invention is the millimeter wave band filter according to claim 1 or 2,
Pins are erected at predetermined intervals inside the first waveguide or the second waveguide, and a band-pass filter that selectively passes a frequency band determined by the interval between the pins is formed.

Moreover, the millimeter waveband filter of Claim 4 of this invention is a millimeter waveband filter in any one of Claims 1-3,
A groove having a predetermined depth is provided on the inner wall of the first waveguide or the second waveguide, and a band rejection filter that blocks passage of a frequency band determined by the depth of the groove is formed.

Further, the high-frequency attenuation method of the millimeter wave band according to claim 5 of the present invention,
A first waveguide (21) and a second waveguide (22), each of which is closed at one end of a waveguide having a rectangular cross section for propagating an electromagnetic wave having a predetermined frequency or higher in the millimeter wave band, are respectively connected to the one end. Arranged so that the sides on the short side surrounding the waveguide face each other,
The waveguide of the first waveguide and the waveguide of the second waveguide are provided by a connecting tube (23) provided between the short-side surfaces of the first waveguide and the second waveguide. Are connected to each other by a waveguide having a predetermined diameter, and the rate of propagation to the second waveguide decreases as the frequency of the electromagnetic wave incident on the first waveguide increases. It is characterized by.

  As described above, according to the present invention, the short sides of the first waveguide and the second waveguide arranged so as to pass each other in a state where the short side surfaces on one end side where the waveguides are closed face each other. An electromagnetic wave incident on the first waveguide is formed by connecting the waveguides of the first waveguide and the second waveguide with a waveguide having a predetermined diameter by a coupling tube provided between the side surfaces on the side. The higher the frequency is, the lower the propagation ratio to the second waveguide is.

  For this reason, it is an extremely simple structure in which the short side surfaces of the waveguides of the two waveguides are connected by a waveguide having a predetermined aperture, and the electromagnetic wave in the millimeter wave band incident on one of the waveguides. The desired high frequency component can be attenuated.

A perspective view of an embodiment of the present invention Plan view and sectional view of millimeter wave band filter of embodiment Dimensional drawing of main part of millimeter-wave band filter of embodiment Passing characteristic diagram of millimeter waveband filter of embodiment The figure which shows another structural example of the millimeter wave band filter of this invention Passage characteristics diagram of millimeter-wave band filter with the structure of FIG. The figure which shows the structural example which incorporated another filter in the millimeter wave band filter of the structure of FIG. The figure which shows the cross-section of FIG. Passage characteristics diagram of millimeter-wave band filter with the structure of FIGS. An enlarged view of a part of FIG. Passage characteristic diagram when the diameter of the connecting pipe of the millimeter wave band filter of the present invention is changed Passage characteristic diagram when the length of the connecting pipe of the millimeter wave band filter of the present invention is changed Passage characteristics diagram when the aperture width of the connecting pipe of the millimeter wave band filter of the present invention is changed The figure which shows the relation between the passage characteristic of the waveguide and the characteristic of the filter

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a perspective view of a millimeter wave band filter 20 according to an embodiment of the present invention, FIG. 2A is a plan view thereof (viewed from a magnetic field surface), and FIGS. 2A is a cross-sectional view taken along line AA, a cross-sectional view taken along line BB, and a cross-sectional view taken along line CC.

  As shown in these drawings, the millimeter-wave band filter 20 includes a first waveguide 21, a second waveguide 22, and a connecting tube 23.

  The first waveguide 21 and the second waveguide 22 have the same diameter, and one end 21a and 22a of a rectangular waveguide that propagates an electromagnetic wave having a predetermined frequency or higher (for example, 90 GHz or higher) in the millimeter wave band is closed. The side surfaces (inner side surfaces) 21b and 22b on the short side surrounding the waveguide on one end side are arranged so as to pass in parallel with each other facing each other.

  And the front-end | tip part by the side of the side surfaces 21b and 22b of the 1st waveguide 21 and the 2nd waveguide 22 is opened over predetermined length, and the connection pipe 23 has connected the opening parts. The connecting tube 23 is connected to the short waveguide side surface of the first waveguide 21 and the second waveguide 22 with a waveguide having a predetermined aperture, and is incident on the first waveguide 21. The higher the frequency of the electromagnetic wave, the lower the propagation ratio to the second waveguide 22 is restricted.

  Here, the first waveguide 21 and the second waveguide 22 are standard waveguides (for example, WR-08) in which waveguides having a rectangular cross section, which are generally used in the millimeter wave band, are continuous. The inner dimension of the first waveguide 21 is a1 × b1, and the inner dimension of the waveguide of the second waveguide 22 is a2 × b2. Here, a1 = a2 and b1 = b2.

  Further, the connecting tube 23 is orthogonal to the first waveguide 21 and the second waveguide 22, and the entire filter is orthogonal to two waveguides arranged so that the tip side passes in parallel. A crank-type waveguide line connected by a waveguide (connecting tube 23) is obtained.

  In the case of such a crank-type waveguide line, among the electromagnetic waves incident on the first waveguide 21, the high-frequency electromagnetic waves are more straight ahead than the low-frequency electromagnetic waves. The ratio that can pass through 23 becomes small, and thereby, a high-frequency attenuation characteristic can be obtained.

Hereinafter, this principle will be described.
As shown in FIG. 2, assuming that the waveguide width a 1 of the first waveguide 21, the waveguide width a 2 of the second waveguide 22, and the waveguide length a 3 of the connection tube 23, the connection tube 23. The cut-off frequency fc of the electromagnetic wave that can pass through the connecting tube 23 is determined by the overall width of the portion sandwiching the light and the speed of light c ₀ .
fc = c ₀ / {2 (a1 + a2 + a3)}
Determined by.

  Further, as shown in FIG. 3, the larger the inclination θ with respect to the plane orthogonal to the traveling direction (longitudinal direction of the waveguide) of the wave front of the electromagnetic wave propagated to one end of the first waveguide 21, The greater the width d of the waveguide 23 (hereinafter referred to as the aperture width) d, the greater the proportion of electromagnetic waves entering the connecting tube 23.

Taking these into consideration, the penetration rate P of the wavefront of the inclination θ depending on the frequency f into the connecting pipe 23 is
P = (1/2) × (d / cos θ) × 2 sin θ ÷ a1 = (dtan θ) / a1
sin θ = fc / f
It becomes.

Considering the influence of resonance (Fabry-Perot resonance) due to the aperture width d of the connecting tube 23, the transmittance S21 from the first waveguide 21 to the second waveguide 22 is obtained.
^{S21 = P 2 / {1+ (} Fsin ψ) 2}
However, F = π√R / (1-R), ψ = 2πd / λg,
λg = λ / √ {1- [λ / 2 (a1 + a2 + a3)] ² },
R is the reflection coefficient at the entrance of the connecting tube 23, λ is the free space wavelength, and λg is the in-tube wavelength.

  From the above results, it can be seen that there is a high-frequency attenuation characteristic in which the transmittance S21 decreases as sin θ = fc / f decreases, that is, the frequency f increases.

  Next, a simulation result of the millimeter waveband filter 20 having the above basic structure will be described. In this simulation, the above-mentioned standard waveguide WR-08 is assumed, the inner diameter a1 × b1 = 2.032 mm × 1.016 mm of the first waveguide 21, and the inner diameter a2 × b2 = of the second waveguide 22. 2.032 mm × 1.016 mm, the aperture width d = 1.6 mm of the connecting tube 23, the length a3 = 0.2 mm, and the aperture height (height in the E plane direction) b3 = 1.016 mm.

  FIG. 4 shows the result (S21) obtained by simulation under the above conditions. In the simulation, for simplicity, the material is a perfect conductor and there is no model of conductor loss.

  As is apparent from FIG. 4, although there is a ripple, the transmittance S21 shows a remarkable high-frequency attenuation characteristic in which the attenuation becomes larger in a wide region from approximately 140 GHz to 1000 GHz as seen from the envelope. For example, it can be used as a high-frequency attenuation filter that is extremely effective in a system using 100 to 140 GHz.

  In the millimeter waveband filter 20 having the basic structure described above, the side surfaces at the distal ends of the waveguides of the first waveguide 21 and the second waveguide 22 are connected by the connection tube 23. As shown in (d), the side surfaces of the intermediate portions of the waveguides of the first waveguide 21 and the second waveguide 22 may be connected by a connecting tube 23.

  However, in this case, the distance H1 from the center of the diameter of the connecting tube 23 to the closed end 21a of the first waveguide 21 and the center of the diameter of the connecting tube 23 to the closed end 22a of the second waveguide 22 The distance H2 must be set to an odd multiple of 1/4 of the guide wavelength λg of the frequency to be passed. By setting in this way, the electromagnetic wave propagated to the connecting tube 23 and the return component reflected by the end face of the waveguide are in opposite phases and can be canceled, and adverse effects due to reflection can be prevented. In this example, H1 = H2, but H1 ≠ H2. Further, one of the first waveguide 21 and the second waveguide 22 is connected to one end of the connecting tube 23 on the side surface of the closed one end and the other waveguide is connected. The other end side of the connecting tube 23 may be connected to the side surface at a distance that is an odd multiple of 1/4 of the in-tube wavelength λg of the frequency that is desired to pass from the closed end.

  In the embodiment of FIG. 5, the aperture height b3 of the connecting tube 23 is shorter than the short sides b1 and b2 of the first waveguide 21 and the second waveguide. It has been confirmed that even the connecting pipe 23 having such a diameter can obtain the above-described high-frequency attenuation characteristics.

  In the embodiment of FIG. 5, the center of the pass band is 104 GHz, the inner diameter a1 × b1 of the first waveguide 21 is 2.032 mm × 1.016 mm, the inner diameter of the second waveguide 22 is a2 × b2 = 2. 032 mm × 1.016 mm, the aperture width d = 1.44 mm of the connecting tube 23, the length a3 = 0.3 mm, the aperture height b3 = 0.2 mm, the distance H1 from the tip of each waveguide to the connecting tube 23, The result of obtaining the transmittance S21 with H2 = 3.0 mm is shown in FIG. 6A shows characteristics up to a frequency of 90 to 1000 GHz, and FIG. 6B shows an enlarged view of the frequency range of 90 to 140 GHz in FIG. 6A. .

  As is clear from (a) of FIG. 6, although there is a ripple, in a wide band of 115 GHz to 1000 GHz, the high band attenuation characteristic is shown such that the attenuation amount increases in the high band, and the system has a pass band of 104 GHz. It can be used as a very effective high-frequency attenuation filter.

  The above embodiment is an example of a millimeter-wave band filter having only a high-frequency attenuation characteristic. However, other filters can be incorporated in the waveguide constituting the millimeter-wave band filter.

  FIG. 7 and FIG. 8 show an example thereof. The function of a BPF (band pass filter) 50 is provided in the first waveguide 21 of the millimeter waveband filter 20 having the above structure, and the second waveguide 22 is provided in the second waveguide 22. A function of a BRF (Band Rejection Filter) 60 is provided, and a high-pass attenuation characteristic is given by the connecting pipe 23 that connects between them. Although the BPF 50 is formed in the first waveguide 21 and the BRF 60 is formed in the second waveguide 22 here, the BPF 50 and the BRF 60 may be interchanged. Both the BPF 50 and the BRF 60 may be formed on either one of the second waveguides 22.

  The BPF 50 provided in the first waveguide 21 is erected in the waveguide at a predetermined interval u in the length direction thereof, as shown in the sectional view taken along the line GG in FIGS. In addition, a set of two pins 51A and 51B are continuously provided at intervals v (three sets in the figure).

  Further, the BRF 60 provided in the second waveguide 22 is provided on the upper and lower inner walls on the long side of the waveguide, as shown in the HH line cross-sectional views of FIGS. 7 and 8B. Grooves 61A and 61B provided with depths q1 and q2 and width w are continuously provided in a plurality of sets (two sets in the figure) at an interval r.

  In this case, the depths q1 and q2 of the grooves 61A and 61B are set to be ¼ of the guide wavelength of the blocking frequency, and the grooves 61A and 61B among the electromagnetic waves propagated through the waveguide to the grooves 61A and 61B. The electromagnetic wave component that has reciprocated in the depth direction and returned in the opposite phase is canceled and its passage is prevented.

  In the filter of this structure, the dimensions of the waveguides of the first waveguide 21 and the second waveguide 22 and the size of the connecting tube 23 are the same as those in the embodiment of FIG. 5, and the center frequency of the BPF 50 is 104 GHz. Therefore, the thickness of the pin is 0.15 mm, the pin interval u = 2.03 mm, the step interval v = 1.0 mm, the distance J1 from the third-stage pin 51B to the connecting tube 23 is 2.0 mm, and the connecting tube 23 is In order to set the distance J2 to the first-stage groove 61A to 3.0 mm and the blocking frequency of the BRF 60 to 150 GHz, the groove interval r = 0.3 mm, the groove width w0.2 mm, the groove depth q1 = 0.286 mm, q2 = The results of obtaining the transmittance S21 at 0.232 mm are shown in FIGS.

  FIG. 9 shows the entire characteristics up to a frequency of 70 to 1000 GHz, and FIG. 10 shows an enlarged view of the frequency range of 100 to 108 GHz in FIG.

  As is clear from FIG. 9, although there is a ripple, a high-frequency attenuation characteristic is obtained in which the attenuation amount increases as the frequency increases over a wide band of 150 GHz to 1000 GHz. This characteristic is an effect of the connecting pipe 23 described above.

  Further, from FIG. 10, a narrow band characteristic with an attenuation of 30 dB or more is obtained in the range of ± 1 GHz to ± 4 GHz on both sides of the design pass center frequency 104 GHz of the BPF 50, and the band of 150 GHz is attenuated by the BRF 60. It can be seen that extremely excellent characteristics are obtained as a filter.

  Next, simulation results for determining the transmittance S21 when the diameter and length of the connecting pipe 23 are varied in the millimeter waveband filter 20 having the basic structure shown in FIGS. 1 and 2 will be described.

  FIG. 11 shows the transmittance S21 when the length a3 of the connecting pipe 23 is 0.2 mm, the aperture width d is 1.6 m, and the aperture height b3 is changed to 1.016 mm, 0.5 mm, and 0.2 mm. The result shows that the smaller the aperture height b3, the larger the lip tends to be. However, it can be seen that there is no significant difference in the overall high-frequency attenuation characteristics (envelope).

  FIG. 12 shows the transmittance S21 when the connecting tube 23 has a diameter of 1.6 mm, a diameter of 1.016 mm, and the length a3 is changed to 0.2 mm, 0.5 mm, and 1.0 mm. As a result, the ripple tends to increase as the length a3 of the connecting pipe 23 becomes longer, but it can be seen that there is no significant difference in the overall high-frequency attenuation characteristics.

  On the other hand, FIG. 13 shows the transmittance S21 when the length a3 of the connecting pipe 23 is 0.2 mm, the aperture height is 1.016 mm, and the aperture width d is changed to 1.6 mm, 1.0 mm, and 0.5 mm. The result shows that the smaller the aperture width d, the greater the ripple, and the higher the high-frequency attenuation as a whole.

  The characteristic shown in FIG. 4 is an example of the aperture width of 1.6 mm in FIG. 13 in which priority is given to a characteristic with less ripple. However, when the required high frequency attenuation is larger, the aperture width d is set to 1.6 mm. It can be seen that it is only necessary to make it smaller, that is, the aperture width should be selected according to the required ripple and high-frequency attenuation.

  As shown in FIGS. 7 and 8, the structure in which the BPF 50 and the BRF 60 are provided in the millimeter wave band filter in which the intermediate portion of the waveguides of the first waveguide 21 and the second waveguide 22 is connected by the connecting tube 23. The basic structure shown in FIG.

  In each of the above embodiments, the outer shape of the first waveguide 21, the second waveguide 22, and the connection tube 23 is generally known as the waveguide shape so that the structure can be easily understood. Although it is shown in a cylindrical shape, the internal waveguide for propagating electromagnetic waves is the main part functionally, and the thickness of the metal wall forming the waveguide is arbitrary, and the whole as a millimeter wave band filter The outer shape is not limited to the above embodiment. For example, a millimeter-wave band filter having the above-described waveguide connection structure is configured by two plate-like metal blocks that are stacked and fixed one above the other, and the first waveguide is formed on the upper surface side of the lower metal block. Each waveguide of the tube 21, the second waveguide 22 and the connecting tube 23 is cut and formed with the upper surface side opened, and the upper metal block is overlapped and fixed to the waveguide, thereby opening each waveguide. Alternatively, the waveguide may have a waveguide whose upper surface is closed and whose outer periphery is closed. In this case, the outer shape of the two metal blocks is arbitrary as long as it is larger than the width necessary for forming each waveguide, and may be a rectangle, a circle, a polygon, or the like other than the crank shape.

  20... Millimeter wave filter, 21 and 22... Waveguide, 23... Connection tube, 50... BPF, 51 A, 51 B... Pin, 60 ... BRF, 61 A, 61 B.

Claims (5)

One end side of a rectangular waveguide that propagates electromagnetic waves of a predetermined frequency or higher in the millimeter wave band is closed, and the short sides surrounding each one end side waveguide are arranged so that they face each other. The first waveguide (21) and the second waveguide (22),
A guide having a predetermined diameter is provided between the waveguide of the first waveguide and the waveguide of the second waveguide between the side surfaces of the first waveguide and the second waveguide on the short side. A coupling tube (23) that is coupled by a waveguide and regulates so that a propagation rate to the second waveguide decreases as the frequency of the electromagnetic wave incident on the first waveguide increases. Millimeter wave filter.   The connecting tube has a distance from the center of its aperture to the closed end of at least one of the first waveguide and the second waveguide of ¼ of the in-tube wavelength of the frequency to be passed. The millimeter-wave band filter according to claim 1, wherein the side surfaces of the first waveguide and the second waveguide are connected to each other at an odd number multiple.   A band-pass filter is provided in which pins are erected at a predetermined interval inside the first waveguide or the second waveguide, and a frequency band determined by the interval between the pins is selectively passed. The millimeter wave band filter according to claim 1 or 2.   A groove of a predetermined depth is provided on the inner wall of the first waveguide or the second waveguide, and a band rejection filter that blocks passage of a frequency band determined by the depth of the groove is formed. Item 4. The millimeter waveband filter according to any one of Items 1 to 3. A first waveguide (21) and a second waveguide (22), each of which is closed at one end of a waveguide having a rectangular cross section for propagating an electromagnetic wave having a predetermined frequency or higher in the millimeter wave band, are respectively connected to the one end. Arranged so that the sides on the short side surrounding the waveguide face each other,
The waveguide of the first waveguide and the waveguide of the second waveguide are provided by a connecting tube (23) provided between the short-side surfaces of the first waveguide and the second waveguide. Are connected to each other by a waveguide having a predetermined diameter, and the higher the frequency of the electromagnetic wave incident on the first waveguide, the lower the propagation ratio to the second waveguide. Wave band high-frequency attenuation method.

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