JP2015050491A - High frequency cutoff filter, microwave output device, transmission circuit and radar device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high frequency cutoff filter suppressing higher harmonic wave transmitted in a TM11 mode.SOLUTION: A waveguide having a rectangular cross section includes a convex 201A (and convex 201B) on the short-length cross section direction side of the inner wall face of the waveguide. An electric field in the TM11 mode is strongest at the center of the inner wall face on the short-length cross section side. Therefore, with the provision of the convex 201A and the convex 201B on the short-length cross section direction side of the inner wall face, a transmittable frequency in the TM11 mode varies, so that the transmission of a secondary higher harmonic wave in the TM11 mode can be suppressed in the waveguide transmitting a fundamental wave in a TE10 mode.

Description

  The present invention relates to a high-frequency cutoff filter that suppresses transmission of harmonic components other than the fundamental frequency.

  Magnetrons are used as microwave generators for marine radars. The magnetron outputs a second harmonic in addition to a microwave having a fundamental frequency (hereinafter referred to as a fundamental wave).

  Therefore, conventionally, in order to suppress the transmission of the second harmonic, a harmonic cutoff filter provided with a convex portion inside the waveguide has been proposed (see, for example, Patent Documents 1 and 2).

Japanese Patent Laid-Open No. 61-60501 JP 2010-252182 A

  In a rectangular waveguide that transmits a fundamental wave in the TE10 mode, there are mainly a TE10 mode, a TE20 mode, and a TM11 mode as propagation modes of the second harmonic. However, the conventional harmonic cutoff filter only suppresses the second harmonic transmitted in the TE10 mode or the TE20 mode, and cannot suppress the second harmonic transmitted in the TM11 mode.

  Accordingly, an object of the present invention is to provide a high-frequency cutoff filter that suppresses harmonics transmitted in the TM11 mode.

  The present invention is a high-frequency cutoff filter including a waveguide having a rectangular cross section, wherein at least one of the inner wall surfaces on the short-side direction of the cross-section of the waveguide, and the inner wall surface on the long-side section It has a recessed part in at least one of these.

  As described above, by providing the first convex portion on at least one of the inner wall surfaces on the short side direction of the cross section of the waveguide, the electromagnetic field in the TM11 mode of the second harmonic is changed, and transmission is performed in the TM11 mode. The possible frequency changes. Further, by providing a recess on at least one of the inner wall surfaces on the long cross section side, second harmonics transmitted in the TE10 mode or the TE20 mode can be suppressed. Therefore, transmission of the second harmonic can be suppressed.

  Further, in the TE10 mode, the strength of the electromagnetic field is low near the inner wall surface in the direction of the short cross section, and therefore the first convex portion is hardly affected even when the fundamental wave is transmitted in the TE10 mode.

  In addition, it is desirable that the first convex portion is provided to face both of the inner wall surfaces on the short cross section side.

  Moreover, it is preferable that the 1st convex part is provided in the center of the inner wall surface by the side of a short cross section with the highest electric field strength.

  According to the present invention, harmonics transmitted in the TM11 mode can be suppressed.

It is a block diagram which shows the structure of the radar apparatus provided with the high frequency cutoff filter of this invention. It is a figure which shows the structure of the high frequency cutoff filter which concerns on 1st Embodiment. It is simulation data which shows the passage characteristic (S21 characteristic) of TM11 mode. It is a figure which shows the structure of the high frequency cutoff filter which concerns on 2nd Embodiment. It is a figure which shows the structure of the high frequency cutoff filter which concerns on 3rd Embodiment. It is a figure which shows the structure of the high frequency cutoff filter which concerns on 4th Embodiment. It is a figure which shows the structure of the high frequency cutoff filter which concerns on 5th Embodiment. It is a figure which shows the structure of the high frequency cutoff filter which concerns on 6th Embodiment.

  FIG. 1 is a block diagram showing a configuration of a radar apparatus 71 provided with a high-frequency cutoff filter according to the present invention. The radar device 71 includes a microwave output device 72, a rotary joint 56, an antenna 57, a limiter 58, and a receiving circuit 59. The microwave output device 72 includes a magnetron 51, a drive circuit 52, a circulator 53, a terminator 54, a band pass filter 2, a circulator 55, and a high frequency cutoff filter 1.

  The magnetron 51 is a microwave generator that generates, for example, a 9.4 GHz microwave as a fundamental wave. The drive circuit 52 drives the magnetron 51 at a predetermined cycle. Microwaves generated by the magnetron 51 are transmitted to various components through the waveguide.

  The circulator 53 guides the microwave output from the magnetron 51 to the band pass filter 2. The bandpass filter 2 removes unnecessary waves in the low and high frequencies of the fundamental wave. The circulator 53 guides the unnecessary wave reflected by the band pass filter 2 to the terminator 54. The terminator 54 absorbs the input unnecessary wave.

  The circulator 55 guides the microwave output from the high frequency cutoff filter 1 to the rotary joint 56 via the high frequency cutoff filter 1. The rotary joint 56 outputs the microwave input from the fixed-side circulator 55 to the rotating-side antenna 57.

  The high frequency cutoff filter 1 is a filter that suppresses transmission of harmonics generated by the magnetron 51. That is, the high frequency cutoff filter 1 passes the fundamental wave and reflects the harmonic.

  The antenna 57 transmits the microwave output from the rotary joint 56 in the air, receives the microwave reflected by the object, and outputs the microwave to the rotary joint 56. The received microwave is output to the limiter 58 through the rotary joint 56 and the circulator 55.

  The limiter 58 reflects the microwave when a microwave of a predetermined level or higher is input, and protects the receiving circuit 59 in the subsequent stage.

  FIG. 2 is a diagram illustrating a configuration of the high-frequency cutoff filter 1 according to the first embodiment. FIG. 2A is an exploded perspective view, and FIG. 2B and FIG. 2C are diagrams showing an electric field distribution in a cross section of a partial waveguide.

  The high-frequency cutoff filter 1 is made of a conductive metal such as aluminum, and in this example, is made up of a waveguide 11A, a waveguide 11B, and a waveguide 11C. The waveguide 11A corresponds to the high frequency cutoff filter 1 of the present invention, and the waveguide 11B and the waveguide 11C correspond to an external transmission circuit. The waveguide 11A is connected to the waveguide 11B and the waveguide 11C on both sides in the tube axis direction.

  The waveguide 11A, the waveguide 11B, and the waveguide 11C include a waveguide 201, a waveguide 202, and a waveguide 301, each having a rectangular cross section.

  The waveguide 201, the waveguide 202, and the waveguide 301 all have a width W1 in the cross-sectional long direction and a short cross-sectional direction so that a 9.4 GHz microwave that is a fundamental wave is transmitted in the TE10 mode in the tube axis direction. Height D1 is set.

  11 A of waveguides have the convex part 201A and the convex part 201B in the inner wall surface of the cross-sectional short direction side of the waveguide 301. As shown in FIG. The convex portion 201A and the convex portion 201B correspond to the first convex portion of the present invention. In this example, the convex portion 201A and the convex portion 201B are each provided at the center of the inner wall surface on the short cross section side. The convex portion 201A and the convex portion 201B have a protruding length W2 and a protruding width D2, respectively.

  As shown in the electric field distribution in FIG. 2C, the electric field in the TM11 mode is strongest at the center of the inner wall surface on the short cross section side. Therefore, when the convex portion 201A and the convex portion 201B are provided on the inner wall surface on the short cross-section direction side, the frequency that can be transmitted in the TM11 mode changes. Thereby, in the waveguide that transmits the fundamental wave in the TE10 mode, the transmission of the second harmonic in the TM11 mode can be suppressed. If the protrusion length W2 or the protrusion width D2 is increased, the frequency that can be transmitted in the TM11 mode is greatly changed, and the suppression amount of the second harmonic is increased.

  On the other hand, since the dimension L in the tube axis direction of the waveguide 11A is shorter than the in-tube wavelength of the fundamental wave, the influence of the convex portion 201A and the convex portion 201B on the fundamental wave is small. In particular, if the dimension L is 1/8 or less of the fundamental wave guide wavelength, there is almost no influence on the fundamental wave.

  As shown in FIG. 2B, the electric field strength in the TE10 mode is highest at the central portion in the cross-sectional long direction, decreases toward the short cross-section side, and becomes lowest on the inner wall surface on the short cross-section side. Therefore, when the fundamental wave is transmitted in the TE10 mode, the convex portion 201A and the convex portion 201B hardly affect the fundamental wave.

  FIG. 3 shows the TM11 mode when the fundamental wave frequency is 9.4 GHz (in-tube wavelength 44.4 mm), the width W1 is 11.5 mm, the height D1 is 4.6 mm, and the dimension L is 2.0 mm. It is the simulation data which shows the passage characteristic (S21 characteristic). As shown in FIG. 3, by providing the convex portion 201A and the convex portion 201B, a large attenuation (attenuation of about −50 dB) is obtained at a frequency near 18.8 GHz which is the second harmonic.

  In addition, in FIG. 2, although the example which provides the convex part 201A and the convex part 201B in the center of the inner wall surface on the short cross section side is shown, it is not limited to this example and is provided at a position near one of the long cross section side. May be.

  Moreover, in FIG. 2, although the example which provided the convex part 201A and the convex part 201B facing both the inner wall surfaces by the side of a short cross section of the waveguide 11A was shown, even if it provides only at least one, it is a 2nd harmonic. Transmission in the TM11 mode can be suppressed.

  As described above, in the first embodiment, a simple high-frequency cutoff filter having a simple shape can be configured by merely forming a convex portion in the middle of the waveguide 301. Therefore, manufacturing costs and component costs are reduced. In addition, since the electromagnetic field of the fundamental wave is not disturbed, insertion loss in the fundamental wave is also suppressed.

  Next, FIG. 4 is a diagram illustrating a configuration of the high-frequency cutoff filter 1 according to the second embodiment. 4A is an exploded perspective view, FIG. 4B is a cross-sectional view of a partial waveguide, and FIG. 4C is simulation data showing pass characteristics (S21 characteristics).

  The high-frequency cutoff filter according to the second embodiment includes a waveguide 101A instead of the waveguide 11A of the first embodiment. Similarly to the waveguide 11A, the waveguide 101A is connected to the waveguide 11B and the waveguide 11C on both sides in the tube axis direction, respectively. The waveguide 101A has a waveguide 301A having a rectangular cross section.

  The waveguide 301A has a convex portion 201A and a convex portion 201B on the inner wall surface on the side of the short cross section. The waveguide 301 </ b> A has a recess 401 and a recess 402 in which a part of the inner wall surface on the long cross section side is recessed. The concave portion 401 and the concave portion 402 are spaces each having a rectangular cross section. The recess 401 and the recess 402 have a width W3 and a height D3, respectively.

  Here, if the width W3 and the height D3 of the concave portion 401 and the concave portion 402 correspond to the frequency of the second harmonic, the second harmonic propagating in the TE10 mode can be suppressed. Specifically, if the height D3 is set to about ¼ of the in-tube wavelength of the second harmonic, and the width W3 is set to ½ or more of the in-tube wavelength of the second harmonic, the second harmonic is The recess 401 and the recess 402 are entered, and reflected from the bottom surfaces of the recess 401 and the recess 402. Since this reflected wave has an antiphase with respect to the input wave, the second harmonic wave cancels out in the waveguide 301A and the propagation is suppressed.

  By providing the concave portion 401 and the concave portion 402 as described above, a large attenuation characteristic can be obtained at a frequency near 18.8 GHz which is the second harmonic, as shown in FIG.

  On the other hand, if the dimension L in the tube axis direction of the waveguide 101A and the width W3 of the recess are set shorter than the in-tube wavelength of the fundamental wave, the influence of the recess 401 and the recess 402 on the fundamental wave is reduced. In particular, if the dimension L is 1/8 or less of the fundamental wave guide wavelength and the width W3 is 1/2 or less of the fundamental wave guide wavelength, the fundamental wave is hardly affected.

  As described above, in the second embodiment, a simple band-rejecting filter having a simple shape can be configured only by forming a recess in the middle of the waveguide 301A. Therefore, also in this example, the manufacturing cost and the part cost are reduced.

  In this example, the concave portions are provided on the inner wall surfaces on both sides on the long side of the cross section. However, the transmission of the second harmonic in the TE10 mode can be suppressed only by providing it on at least one inner wall surface.

  Next, FIG. 5 is a diagram for explaining the configuration of the third embodiment of the high-frequency cutoff filter 1. 5A is an exploded perspective view, FIG. 5B is a cross-sectional view of a partial waveguide, and FIG. 5C is simulation data showing pass characteristics (S21 characteristics).

  The high-frequency cutoff filter according to the third embodiment includes a waveguide 102A instead of the waveguide 101A of the second embodiment. The waveguide 102A is connected to the waveguide 11B and the waveguide 11C on both sides in the tube axis direction. The waveguide 102A has a waveguide 302A having a rectangular cross section.

  The waveguide 302A has a convex portion 201A and a convex portion 201B on the inner wall surface on the short side direction. Further, the waveguide 302A is different from the waveguide 301A of the second embodiment in that two concave portions are provided on each inner wall surface on the long side of the cross section. Each inner wall surface on the long side of the cross section of the waveguide 302A has a recess 401A, a recess 401B, a recess 402A, and a recess 402B. The recess 401A, the recess 401B, the recess 402A, and the recess 402B have a width W4 and a height D3. In addition, the recess 401A, the recess 401B, the recess 402A, and the recess 402B are spaced apart from each other by a distance W5 from the center position in the longitudinal direction of the cross section.

  The electric field strength in the TE20 mode is lowest at the center and both ends in the longitudinal direction of the cross section, and is highest at positions 1/4 and 3/4 from one end in the longitudinal direction of the cross section. Therefore, the concave portion 401A, the concave portion 401B, the concave portion 402A, and the concave portion 402B are formed around the position of ¼ and the position of ¾ from one end in the longitudinal direction of the cross section, respectively.

  By providing the recesses 401A, the recesses 401B, the recesses 402A, and the recesses 402B as described above, as shown in FIG. Attenuation characteristics can be obtained.

  In this example, the recesses are provided on the inner wall surfaces on both sides on the long side of the cross section. However, the transmission of the second harmonic in the TE20 mode can be suppressed only by providing the recesses on at least one inner wall surface.

  Next, FIG. 6 is a diagram for explaining the configuration of the fourth embodiment of the high-frequency cutoff filter 1. 6A is an exploded perspective view, FIG. 6B is a cross-sectional view of a partial waveguide, and FIG. 5C is simulation data showing S11 characteristics and S21 characteristics.

  The high-frequency cutoff filter according to the fourth embodiment includes a waveguide 103A instead of the waveguide 102A of the third embodiment. The waveguide 103A has the same structure as that of the waveguide 102A of the second embodiment. However, in the vicinity of the center of the inner wall surface in the longitudinal direction of the cross section, the convex portion 501A and convex Part 501B.

  As described above, the dimension L and the width W3 of the recess are shorter than the in-tube wavelength of the fundamental wave, so the influence of the recess on the fundamental wave is small. However, the second harmonic is a desired attenuation at a desired frequency. When the dimension L and the width W3 of the recess are increased in order to suppress them, the fundamental wave slightly enters the recess. In the concave portion, the electric field of the fundamental wave becomes weak, and thus corresponds to the -C component (L component) on the equivalent circuit.

  Therefore, in the fourth embodiment, the convex portion 501A and the convex portion 501B are provided on the inner wall surface of the waveguide 301A on the long side. In these convex portions, the electric field of the fundamental wave becomes strong, and thus corresponds to the C component on the equivalent circuit. Therefore, the L component in the concave portion is canceled by the C component in the convex portion.

  Thereby, as shown in FIG.6 (C), the reflection loss of 9.4 GHz which is a fundamental wave can be suppressed, suppressing the transmission in 18.8 GHz which is a 2nd harmonic.

  In the example of FIG. 6, the two convex portions 501 </ b> A and 501 </ b> B are provided to face each other, but may be provided on at least one of them.

  Next, FIG. 7 is a cross-sectional view showing the configuration of the fifth embodiment of the high-frequency cutoff filter 1. In this example, instead of the convex portion 501A and the convex portion 501B shown in the fourth embodiment, a screw hole is made in the long side surface (upper and lower surfaces) of the waveguide, and the screw 502A and screw 502B is inserted. Also in this example, similarly to the convex portions 501A and 501B shown in the fourth embodiment, the L component in the concave portion can be canceled and the fundamental wave reflection loss can be suppressed. Furthermore, in this example, the resonance frequency can be easily changed by changing the insertion length of the screw 502A and the screw 502B.

  Next, FIG. 8 is a cross-sectional view showing the configuration of the sixth embodiment of the high-frequency cutoff filter 1. FIG. 8A is an exploded perspective view, and FIG. 8B is a cross-sectional view of a partial waveguide. In this example, a waveguide 105 and an iris plate 106 are further sandwiched between the waveguide 102A and the waveguide 12B of the fourth embodiment shown in FIG.

  The waveguide 105 has a long cross-sectional width W1 and a short cross-sectional height D1 so that a fundamental wave of 9.4 GHz microwaves is transmitted in the TE10 mode in the tube axis direction. Yes. The iris plate 106 has a waveguide having a width W6 that is slightly narrower than the width W1. For this reason, the magnetic field of the fundamental wave is stronger in the iris plate 106 than in other waveguides, and corresponds to the L component on the equivalent circuit.

  Here, the dimension L2 of the waveguide 105 in the tube axis direction is set to about ¼ of the in-tube wavelength of the fundamental wave. That is, the iris plate 106 and the waveguide 102A are present at a position separated by about ¼ of the in-tube wavelength of the fundamental wave. As a result, the L component in the iris plate 106 is equivalent to the −L component (C component) because the impedance is inverted. Therefore, also in this example, like the convex portions 501A and 501B shown in the fourth embodiment, the L component in the concave portions can be canceled and the fundamental wave reflection loss can be suppressed.

DESCRIPTION OF SYMBOLS 1 ... High frequency cutoff filter 11A, 11B, 11C ... Waveguide 51 ... Magnetron 52 ... Drive circuit 53 ... Circulator 54 ... Terminator 55 ... Circulator 56 ... Rotary joint 57 ... Antenna 58 ... Limiter 59 ... Reception circuit 71 ... Radar apparatus 72 ... Microwave output devices 201A, 201B ... Projections

Claims (12)

A high-frequency cutoff filter including a waveguide having a rectangular cross section,
A high-frequency cutoff filter having a first convex portion on at least one of the inner wall surfaces on the short cross section side of the waveguide and a concave portion on at least one of the inner wall surfaces on the long cross section side. The high-frequency cutoff filter according to claim 1,
A high-frequency cutoff filter characterized in that a dimension of the waveguide in the tube axis direction is shorter than an in-tube wavelength of a fundamental wave. The high-frequency cutoff filter according to claim 2,
A dimension of the waveguide in the tube axis direction is 1/8 or less of the in-tube wavelength. A high-frequency cutoff filter according to any one of claims 1 to 3,
The high-frequency cutoff filter, wherein the first convex portion is provided to face both of the inner wall surface on the short cross section side. A high-frequency cutoff filter according to any one of claims 1 to 4,
The high frequency cutoff filter is characterized in that the first convex portion is provided at the center of the inner wall surface on the short side in section. A high-frequency cutoff filter according to any one of claims 1 to 5,
A high-frequency cutoff filter comprising a second convex portion extending to the inside of the waveguide having a rectangular cross section on at least one of the inner wall surfaces on the long side of the cross section of the waveguide. The high frequency cutoff filter according to claim 6,
The high frequency cutoff filter, wherein the second convex portion is provided to face both of the inner wall surface on the long side of the cross section. The high-frequency cutoff filter according to claim 6 or 7,
The second convex portion is provided at the center of the inner wall surface on the long side of the cross section,
The high frequency cutoff filter, wherein the concave portion is provided on both the left and right sides of the second convex portion. A high-frequency cutoff filter according to any one of claims 1 to 8,
The high-frequency cutoff filter is characterized in that the convex portion and the concave portion are extended in a direction perpendicular to the tube axis direction, and the size in the tube axis direction is shorter than the in-tube wavelength of the fundamental wave. Harmonic cutoff filter according to any one of claims 1 to 8,
A plurality of waveguides respectively connected to both sides of the tube axis direction with respect to the harmonic cutoff filter;
A transmission circuit comprising:
The plurality of waveguides have a rectangular cross section, and have the same width in the long cross section and the same height in the short cross section as the harmonic blocking filter. A high-frequency cutoff filter according to any one of claims 1 to 9,
A microwave generator for generating microwaves;
A microwave output device comprising:
The microwave output device, wherein the high frequency cutoff filter blocks passage of a second harmonic of the microwave generated from the microwave generator. A microwave output device according to claim 11;
An antenna for launching the microwave into the air;
A radar apparatus comprising:

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