JP2008131488A - Bandpass filter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable a bandpass filter to be small-sized in simple configuration, to individually set a high-pass side and a low-pass side of a cutoff frequency and further to reduce unwanted emission that is generated at a lower frequency side than an oscillation frequency. <P>SOLUTION: In order to cut off a high-pass side frequency band, a corrugated filter is used with which three stages of slots 14 are formed on a first surface S1 (surface of a longer side of a rectangle) within a rectangular waveguide 12, and a second surface S2 (surface of a shorter side of the rectangle) perpendicular to the first surface S1 within the waveguide 12 between the slots 14 of the corrugated filter is protruded toward a transmission line center just by ta, namely, a width between confronted second surface S2 is shortened, thereby cutting of a low-pass side frequency band. Furthermore, a waffle iron filter is used, a part of the second surface S2 within the rectangular waveguide of the waffle iron filter is protruded toward a stab, and an interval between a part of the second surface and the stab is shortened to cut off the low-pass side frequency band. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a configuration for suppressing unnecessary components of radio waves radiated from a radar device, particularly in a band-pass filter having a waveguide structure for transmitting microwaves.

  Conventionally, radar devices have been used to search for targets mainly using microwaves in frequency bands such as S band, C band, and X band, but this type of radar device uses a high frequency. In addition, a waveguide circuit is often used to transmit large power without loss, and a filter is used to transmit only a specific frequency for various reasons and prevent transmission of other frequency components. It is done. For example, when a magnetron is used as an oscillation source, a π-1 mode wave or a harmonic wave having an oscillation frequency other than the fundamental wave is oscillated, but oscillation of an unnecessary frequency wave band other than these fundamental waves, so-called spurious is suppressed. At the same time, a waveguide and a filter capable of narrowing the occupied bandwidth are required.

  FIG. 8 shows an example of a wideband spectrum observed by a conventional X-band radar device. As shown in the figure, in the X-band radar device, in addition to the fundamental wave P, a π-1 mode wave SP1 is shown. A second harmonic SP2 that is one of the harmonics is observed. These spurious levels are already considerably lower than the fundamental wave, but further reduction is desired from the viewpoint of effective use of radio waves.

  And in order to suppress and reduce the said spurious, the filter shown by the patent documents etc. which are shown below is used. That is, Japanese Patent Laid-Open No. 2001-136005 (Patent Document 1) combines two types of filters having different frequency cutoff characteristics by a resonance window, and Japanese Patent Laid-Open No. 2004-117132 (Patent Document 2) is a basic one. A low-pass filter that cuts off frequencies higher than the wave and a high-pass filter that cuts off frequencies lower than the fundamental wave are arranged, and a band-pass filter is configured with two types of filters. Japanese Patent Laying-Open No. 2005-005930 (Patent Document 3) forms an asymmetric inductive resonance window portion integrally with a waveguide transmission path and folds the waveguide transmission path halfway. .

JP 2001-136005 A JP 2004-117132 A JP 2005-005930 A “MICROWAVE FILTERS, IMPEDANCE-MATCHING NETWARKS, AND COUPLING STRUCTRES”, published by McGRAW-HILL BOOK COMPANY, GEORGE L. MATTHAEI et al., Columns 425, pages 14 and 15.

  However, in the above-mentioned patent document 1, since two types of filters are coupled by a resonance window, the configuration and design become complicated. In the above-mentioned patent document 2, two independent filters, a low-pass filter and a high-pass filter, are used. Therefore, in order to secure the attenuation, there is a problem that the total length becomes long and the filter cannot be downsized.

  Further, in Patent Document 3, there is an advantage that a large attenuation amount can be ensured although the total length is short. However, when the waveguide transmission line is folded, the configuration becomes complicated, and an attempt is made to increase the inclination of the attenuation amount. The passband is narrowed. That is, in this case, the reactance of the cavity of the filter is single and becomes a single resonance. Therefore, if the attenuation amount is increased, the pass band becomes narrower. Therefore, in order to widen the bandwidth while increasing the slope of the attenuation, it is necessary to overlap the number of filter stages. In this case, since the filters with shifted resonance frequencies are overlapped by the stagger method, A filter having a frequency shift is used, and as a result, there is an inconvenience that the insertion loss of the passing frequency increases. There is also a problem that the high frequency side and the low frequency side of the cutoff frequency cannot be adjusted individually.

  Further, the bandpass lid described in Non-Patent Document 1 in which the basic design example of the bandpass filter is disclosed has a single reactance of the filter cavity and a single resonance. When trying to increase the value, the passband width becomes narrower.

Further, the conventional radar apparatus has a problem that spurious emission within the fundamental wave lobe (hereinafter referred to as unnecessary emission) occurs when the magnetron is used as an oscillation source, and the influence of the unnecessary emission cannot be removed.
FIG. 9 shows an example of a spectrum around the fundamental wave observed by a conventional X-band radar device. As shown in FIG. 9, the X-band radar device has a peak oscillation frequency (P) − At a level of about 60 dBc to −80 dBc, unnecessary emission LE is observed in the lobe on the frequency side lower than the peak oscillation frequency. This unnecessary emission LE is a phenomenon generally observed when the magnetron is oscillated with a pulse. When the oscillation of the fundamental wave is established, the unnecessary emission LE oscillates on the lower frequency side when the anode voltage at the rising edge of the pulse is low. Is what happens.

  The unnecessary emission LE generated on the frequency side lower than the oscillation frequency cannot be removed conventionally, and spurious due to this is radiated from the antenna, but the bandwidth occupied from the viewpoint of effective use of radio waves. It is desirable to suppress spurious due to this unnecessary emission LE even in a region of about −60 dBc which is extremely small compared to the output level of the fundamental oscillation frequency.

  The present invention has been made in view of the above-mentioned problems, and its object is to maintain a characteristic of keeping insertion loss low in a wide band, and to achieve downsizing with a simple configuration and to achieve a high cutoff frequency. An object of the present invention is to provide a band-pass filter that can set the side and the low-frequency side separately, further reduce unnecessary emission generated on the frequency side lower than the oscillation frequency, and enable effective use of radio waves.

In order to achieve the above object, a bandpass filter according to claim 1 is provided on a first surface in a rectangular waveguide (transmission path) in order to cut off a predetermined frequency band higher than the passing frequency band. A corrugated filter having two or more slots is used, and a second surface perpendicular to the first surface in which the slot is formed in the rectangular waveguide between the slots of the corrugated filter (for example, the first surface has a rectangular length). If the side surface is the second surface, the rectangular short side surface) protrudes toward the center of the waveguide, that is, by shortening the width between the second surfaces, so that the lower frequency side than the pass frequency band. It is characterized by being configured to cut off the frequency band.
The band-pass filter according to claim 2 is formed with a concave portion on the first surface in the rectangular waveguide in order to cut off a predetermined frequency band higher than the passing frequency band, and a waffle iron type protrusion in the concave portion. The waffle iron type filter is used, and a part of the second surface perpendicular to the first surface on which the waffle iron type protrusion (stub) is formed in the rectangular waveguide of the waffle iron type filter is formed into the waffle iron type. By projecting toward the protrusion (toward the side surface of the stub), that is, by shortening the interval between a part of the second surface and the waffle iron type protrusion, the frequency band on the lower frequency side than the passing frequency band is set. It is characterized by being configured to shut off.

According to the configuration of claim 1, the cutoff frequency on the high frequency side in the pass frequency band is set by adjusting the slot width (W ₂ ), depth (D), or length (La) of the corrugated filter. Further, by adjusting the protrusion amount of the second surface between the two slots, that is, the width between the second surfaces, the cutoff frequency on the low frequency side in the pass frequency band is set, and the cutoff frequency The high frequency side and the low frequency side can be set individually.

  According to the configuration of claim 2, by adjusting the width (W), height (H), or length (Lb) of the waffle iron projection (stub), the cutoff frequency on the high frequency side in the pass frequency band is By adjusting the amount of projection of a part of the second surface, that is, the interval between the second surface and the waffle iron type protrusion, the cutoff frequency on the low frequency side in the pass frequency band is set. Also in this case, the high frequency side and the low frequency side of the cutoff frequency can be set individually.

  That is, according to the present invention, a conventional corrugated type or waffle iron type low-pass filter is added with a configuration for blocking the low frequency side of the passing frequency so as to function as a band-pass filter. Then, the cutoff frequency of the low-pass filter is matched with the π-1 mode frequency or harmonic of the magnetron, and the cutoff frequency on the low frequency side is matched with a frequency lower by about 300 to 1000 MHz than the fundamental frequency, thereby providing a bandpass with good characteristics. A filter can be obtained.

  According to the present invention, it is only necessary to adjust the protrusion amount of the second surface or the protrusion amount of a part of the second surface between the slots in the waveguide of the conventional corrugated type or waffle iron type low-pass filter. In addition, while maintaining the characteristic of keeping the insertion loss low, it is possible to reduce the size with a simple configuration, and it is possible to individually set the high frequency side and the low frequency side of the cutoff frequency. Further, the protrusion of the second surface in the waveguide of the corrugated type or waffle iron type low-pass filter has little influence on the reactance of the corrugated type or waffle iron type low-pass filter, so that the original characteristic is maintained as it is. Modes and double wave spurious can be cut off. Further, it is possible to newly obtain an effect of blocking unnecessary emission generated in the lobe on the frequency side lower than the fundamental wave. As a result, the occupied frequency band can be narrowed, and the radio wave can be effectively used.

  1 and 2 show the configuration of a band-pass filter according to a first embodiment of the present invention, and this band-pass filter uses a corrugated filter (low-pass filter). In the figure, the band-pass filter 10 is provided with a waveguide 12 whose entire transmission path (cross section) including the shape of the input port 12i to the output port 12o is rectangular, and this rectangular waveguide (transmission path) 12 In the two first surfaces S1 [the left and right inner surfaces in FIG. 1A, the H surface] which are the long-side surfaces of the rectangle, a recess is formed from the first surface S1 to the inside of the wall surface (direction perpendicular to the transmission direction). Three slots (grooves) 14 are formed in the transmission direction 70. By providing such a slot 14 in the rectangular waveguide 12, a corrugated low-pass filter is configured.

That is, by adjusting the width W ₁ (same as the width of the long side of the rectangular waveguide 12), the depth D, and the length La of the slot 14, a high-frequency side higher than a predetermined frequency band can be obtained. At a frequency lower than the cut-off frequency, the insertion loss becomes relatively small and can be suppressed to 0.2 dB or less in the X band. Further, the slot 14 can increase the amount of attenuation in the cut-off frequency region by increasing the number of stages. In the first embodiment, a large amount of cut-off frequency can be ensured as three stages. The number of stages is increased or decreased according to the required attenuation.

In the first embodiment, the inner surface of the waveguide 12 between the three slots 14 is a surface perpendicular to the first surface S1, that is, a surface located on the short side of the rectangle. A projecting portion (projecting wall) 16 is formed on the second surface (E surface) S2 so as to project from the second surface S2 toward the center of the waveguide 12 by a width ta. That is, the protruding portion 16 is provided, by narrowing the width W ₂ a rectangular cross-section of the longer of the rectangular waveguide 12, set the cut-off frequency of the lower of the pass band set by the corrugated low-pass filter And a predetermined low frequency can be cut off. Further, since the effect of this narrowing operates as another reactance, unlike the conventional cavity-type bandpass filter, the high frequency side and the low frequency side can be calculated and set separately.

In the first embodiment, for example, the width W _{1 of the} slot 14 (which is also the width of the long side of the rectangular waveguide 12) is 22.2 mm, the depth D is 9.3 mm, and the length La is 3.2 mm. sets the protruding amount ta of the second surface S2 and 2.5 mm, the width _{W 2} between opposing S2 is 17.2 mm. Then, with respect to the basic frequency of 9400 MHz, the high frequency side cutoff (blocking) frequency is set to the π-1 mode or the harmonic frequency, and the low frequency side cutoff frequency is set to a frequency lower by about 300 to 1000 MHz than the basic frequency. ing.

FIG. 3 shows the characteristics of the insertion loss 101 and the reflection loss 201 of the bandpass filter of the first embodiment. As shown in FIG. 3, the insertion loss 101 has a corrugated structure in which the slot 14 is formed. the type filter, cutoff characteristics HR ₁ of high range shown can be obtained and will be cutoff characteristics LR ₁ of the low-pass illustrated by the projection of the second surface S2 is obtained. These cutoff characteristics HR ₁ and LR ₁ can be adjusted independently. Further, the periphery of the desired fundamental frequency f _0, the insertion loss over a wide band is kept low.

  According to the first embodiment, the configuration is simple because only the amount of protrusion of the waveguide second surface S2 between the slots is adjusted with respect to the conventional corrugated low-pass filter. It is possible to reduce the size of the bandpass filter without joining two different types of filters in series.

  The three slots 14 in the first embodiment are provided on the left and right of the waveguide 12 in the state shown in FIG. 1A, but may be on either the left or right, and the protrusion 16 may be You may make it form in any one.

  4 and 5 show the configuration of the bandpass filter according to the second embodiment. This bandpass filter uses a waffle iron type filter (lowpass filter). In the figure, similarly to the first embodiment, the bandpass filter 20 is provided with a waveguide 22 having a rectangular cross section of the entire transmission path including the shape of the input port 22i to the output port 22o. Concave portions 23 are provided in two first surfaces S1 [the left and right inner surfaces in FIG. 4A and the H surface] which are the long-side surfaces of the wave tube 22. Three waffle iron type protrusions, that is, three stubs 24 are formed so as to protrude toward the center (direction perpendicular to the transmission direction 70). The stubs 14 are arranged in one stage with respect to the transmission direction 70. However, the number of stubs 14 arranged in the direction perpendicular to the transmission direction 70 is not limited to three but may be two. By providing such a stub 24 in the rectangular waveguide 22, a waffle iron type low-pass filter is configured.

  That is, by adjusting the width W, height H, and length Lb of the stub 24, a high-frequency side higher than a predetermined frequency band can be blocked over a wide band, and a frequency lower than the cutoff frequency. In FIG. 5, the insertion loss is relatively small and can be suppressed to 0.2 dB or less in the X band. The stub 24 can increase the attenuation in the cut-off frequency region by increasing the number of stages in the transmission direction 70, and may be two stages, three stages, or the like.

  In the second embodiment, the inner surface of the waveguide 22 is perpendicular to the first surface S1, that is, two second surfaces (E surfaces) S2 that are surfaces on the short side of the rectangle. Then, a protruding portion (projecting wall portion) 26 is formed by projecting a part of the second surface S2 toward the side surface of the stub 24 (toward the center of the waveguide 22) by a width tb. That is, by narrowing the width of the protrusion 26 and the stub 24, a lower cut-off frequency of the pass frequency band set by the waffle iron type low-pass filter is set, and a predetermined low-frequency is cut off. Can do. Also, since the effect of this narrowing operates as another reactance, unlike the conventional cavity-type bandpass filter, the high frequency side and the low frequency side are calculated and set separately.

  In the second embodiment, for example, the width W of the stub 24 is 4.1 mm, the height H is 3.9 mm, the length Lb is 4.1 mm, and the protruding amount tb of the second surface S2 is set to 2.6 mm. To do. Then, with respect to the fundamental frequency of 9400 MHz, the high frequency side cutoff (blocking) frequency is set to a π-1 mode or a harmonic frequency, and the low frequency side cutoff frequency is set to a frequency lower by about 300 to 1000 MHz than the basic frequency. be able to.

FIG. 6 shows the characteristics of the insertion loss 102 and the reflection loss 202 of the band-pass filter of the second embodiment. As shown in FIG. 6, the insertion loss 102 is a waffle in which the stub 24 is formed. the iron-type filter, cutoff characteristics HR ₂ in high range shown can be obtained and barrier properties LR ₂ of the low-range shown by the projection of the second surface S2 is obtained. These cutoff characteristics HR ₂ and LR ₂ can be adjusted independently. Further, in the vicinity of the desired fundamental frequency f ₀ , the insertion loss is suppressed low over a wide band, and a good attenuation is ensured over the frequency 2f ₀ of the second harmonic of the fundamental frequency f _0. It was.

  According to the second embodiment, since the protrusion amount of the waveguide second surface S2 between the slots is only adjusted with respect to the conventional waffle iron type low-pass filter, the configuration is simple, and the transmission direction It is possible to reduce the size of the band-pass filter without joining two different types of filters in series with 70.

  FIG. 7 shows a spectrum observed by an X-band radar apparatus incorporating the bandpass filters of the first and second embodiments. This is because the cutoff frequency on the high frequency side is the π-1 mode frequency of the magnetron. Or, it is a spectrum radiated from the antenna when the cutoff frequency on the low frequency side is adjusted to a frequency lower by 300 to 1000 MHz than the fundamental frequency in accordance with the harmonics. In this case, the band-pass filter includes a magnetron oscillator and an antenna. Between the circulator, TR tube, rotary joint and the like.

  As shown in FIG. 7, when the bandpass filters of the first and second embodiments are employed, the frequency is 9.2 GHz or less in the conventional FIG. 9 at a level that is −60 dBc to −80 dBc smaller than the peak frequency P. Observed unnecessary emission LE was suppressed, and a good spectrum was obtained. In addition, the frequency of the second harmonic SP2 observed in FIG. 8 is also suppressed.

The first stub 24 of the second embodiment is provided on the left and right sides of the waveguide 12 in the state shown in FIG. 4A. You may form in either one.
In the second embodiment, the protrusions 26 are formed on the one-stage stub 24. However, when the stubs 24 are provided in a plurality of stages, the protrusions 26 are provided for the stubs 24 in the plurality of stages. A plurality of protrusions may be arranged, or one (wide) protrusion may be arranged over the entire stub 24 in a plurality of stages.

The structure of the band pass filter concerning 1st Example of this invention is shown, A figure (A) is the figure seen from the input port side, A figure (B) is a side view, A figure (C) is I-- of figure (B). It is I line sectional drawing. It is a perspective view which shows the band pass filter of 1st Example. It is a figure which shows the characteristic of the insertion loss and reflection loss of the band pass filter of 1st Example. The structure of the band pass filter which concerns on 2nd Example of this invention is shown, A figure (A) is the figure seen from the input port side, A figure (B) is a side view, A figure (C) is II- of figure (B). It is II sectional view. It is a perspective view which shows the band pass filter of 2nd Example. It is a figure which shows the characteristic of the insertion loss and reflection loss of the band pass filter of 2nd Example. It is a figure which shows the spectrum observed with the radar apparatus using the band pass filter of 1st Example and 2nd Example. It is a figure which shows the wideband spectrum observed with the conventional radar apparatus. It is a figure which shows the spectrum around the fundamental wave observed with the conventional radar apparatus.

Explanation of symbols

10, 20 ... band pass filter,
12, 22 ... Waveguide (rectangular transmission line),
14 ... slot,
16, 26 ... protrusions,
23 ... recess,
24 ... Stub (waffle iron type protrusion).

Claims (2)

In order to cut off a predetermined frequency band higher than the pass frequency band, a corrugated filter having two or more slots formed on the first surface in the rectangular waveguide is used.
By projecting a second surface perpendicular to the first surface in which the slots are formed in the rectangular waveguide between the slots of the corrugated filter to the center side of the waveguide, a lower frequency side than the pass frequency band is obtained. Bandpass filter configured to cut off the frequency band. In order to cut off a predetermined frequency band higher than the pass frequency band, a concave portion is formed on the first surface in the rectangular waveguide, and a waffle iron type filter having a waffle iron type protrusion formed in the concave portion is used.
By projecting a part of the second surface perpendicular to the first surface on which the waffle iron type protrusion is formed in the rectangular waveguide of the waffle iron type filter toward the waffle iron type protrusion, the passing frequency band A band-pass filter configured to cut off the lower frequency band.

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