JP2006005598A - Waveguide slot antenna system and aerial device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress spurious radiation of a waveguide slot antenna system used for a radar for ship etc. <P>SOLUTION: Radio waves of higher propagation mode generated at discontinuous parts A0 to A8 formed in a feed waveguide 1 are radiated from respective slots S0 to S9 formed on a wide wall surface H1 of the discontinous parts A0 to A8 along the length of the waveguide. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a waveguide slot antenna device that radiates a radio wave fed from a feed waveguide from a slot cut in a tube wall of the slot waveguide.

  In general, a magnetron is widely used as an output source of radio waves radiated from a waveguide slot antenna device used in marine radars. Since this magnetron is a self-excited oscillation type output tube, the oscillated pulse includes unnecessary radiation such as a second harmonic and a third harmonic in addition to the fundamental wave. However, it is desirable to suppress radio wave interference and the like due to unnecessary radiation.

JP 2001-136005 A

  An object of the present invention is to suppress radiation of unwanted radiation in a waveguide slot antenna device used for marine radars and the like.

  The waveguide slot antenna device according to the present invention includes a slot waveguide in which at least one radiation slot for radiating a desired radio wave is formed on a tube wall, and one end of the slot waveguide connected to the slot waveguide. In a waveguide slot antenna device comprising a feeding waveguide for supplying radio waves to a tube, a discontinuous portion that generates a higher-order propagation mode of radio waves propagating in the feeding waveguide, In order to cancel the reflection of the propagating fundamental wave, at least one of the discontinuous portions provided at predetermined intervals in the longitudinal direction of the waveguide and the wide wall surface corresponding to the long side of the rectangular cross section of the feed waveguide A slot cut in the longitudinal direction of the waveguide on the longitudinal central axis of the waveguide so as to emit radio waves in the even-order propagation mode of harmonics generated in the discontinuous portion to the outside of the feeding waveguide. The longitudinal direction of the waveguide of the discontinuous part Characterized in that it comprises at least one by one provided are discharge slots back and forth.

  According to the present invention, high-order propagation mode radio waves generated in the discontinuous portion formed in the feed waveguide are emitted from the emission slots formed on the wide wall surface of the discontinuous portion in the longitudinal direction of the waveguide. . Therefore, since the emission of higher harmonics from the slot waveguide can be suppressed, unnecessary radiation can be suppressed.

  According to one aspect of the waveguide slot antenna device according to the present invention, the interval between the discontinuous portion and the emission slot in the longitudinal direction of the waveguide is the high-order propagation mode of the fundamental wave generated in the discontinuous portion. It is determined based on the amount of radio wave attenuation.

  According to the present invention, the interval in the longitudinal direction of the waveguide between the discontinuous portion and the emission slot is determined based on the attenuation of the radio wave in the higher-order propagation mode of the fundamental wave generated in the discontinuous portion. The gap in the longitudinal direction of the waveguide between the discontinuous part and the emission slot can be determined so that the radio wave of the higher-order propagation mode of the fundamental wave generated at the part is not emitted from the emission slot, and the propagation efficiency of the fundamental wave is reduced. Can be prevented.

  According to one aspect of the waveguide slot antenna device according to the present invention, a radio wave absorber that absorbs radio waves emitted from the emission slot is provided on the emission slot of the external wide wall surface of the feed waveguide. And

  According to the present invention, since unnecessary radiation from the emission slot is absorbed by the radio wave absorber, it is possible to prevent diffusion of unwanted radiation.

  In addition, by using the waveguide slot antenna device configured as described above, an aerial device for a radar for navigation can be configured, for example, to make a major design change for incorporating a harmonic suppression filter in the pedestal. In addition, it is possible to provide a navigation radar that can cope with stricter spurious regulations.

  Currently, the problem of radio wave interference has been caused by the spread of radio astronomy fields using weak radio waves and communication / measurement systems using satellites. For this reason, spurious regulations are being strengthened internationally as a measure for suppressing unwanted radiation for the purpose of improving radio wave utilization efficiency.

  Under such a background, for example, in the Japanese Radio Law, the spurious regulation value for navigation radar is currently defined as -60 dBc. However, there is still a strong demand for spurious regulations, and there is a possibility that a stricter regulation of -70 dBc or more applied to land-based radars will be applied to navigational radars.

  By the way, as shown in FIG. 1, the antenna unit 100 constituting the navigation radar includes an antenna unit 10 that radiates radio waves and a pedestal unit 20 that controls driving of the antenna unit 10, and is incorporated in the pedestal unit 20. The antenna portion is rotationally driven by the rotary joint portion 21 thus formed. As shown in FIG. 2, the antenna unit 10 includes a feed waveguide 11, a slot waveguide 12, and a flare 13. Medium and large marine radars employ non-resonant waveguide arrays as slot waveguides to ensure band characteristics.

  Further, the pedestal unit 20 includes a magnetron 22 as a radio wave output source. The radio wave output from the magnetron 22 is propagated to the feed waveguide 11 via the rotary joint portion 21, and the radio wave is fed from the feed waveguide 11 to the slot waveguide 12. A radio wave fed from the feeding waveguide 11 to the slot waveguide 12 is radiated from the flare 13 to the outside through a slot formed in the tube wall of the slot waveguide 12. The flare 13 is a conductor such as a metal material for narrowing the vertical plane beam.

  In the navigation radar configured as described above, as a method for coping with the strengthening of the spurious regulation, there is a method of providing a filter for suppressing harmonics in the pedestal unit 20 as disclosed in Patent Document 1. However, in the apparatus that constitutes the conventional pedestal unit 20, there is often no space for a new built-in filter, and in order to provide such a filter in the apparatus, the apparatus that constitutes the pedestal part 20. The design must be changed to improve the device to a larger device.

  Therefore, in the embodiment of the present invention (hereinafter referred to as the embodiment), since the harmonic suppression filter is incorporated in the pedestal unit 20, it is possible to cope with the strengthening of spurious regulations without making a major design change. In order to provide a radar, the following filter is formed in the feed waveguide 11.

  Hereinafter, the present embodiment will be described in more detail with reference to the drawings, focusing on the configuration of the filter formed in the feed waveguide 11.

  In the present embodiment, the filter formed in the feed waveguide 11 is a filter for suppressing unnecessary radiation other than the fundamental wave among the radio waves output from the magnetron 22. In general, the magnetron 22 oscillates harmonics such as a second harmonic and a third harmonic in addition to the fundamental wave. However, since the harmonics to be normally considered are the second harmonic and the third harmonic, in this embodiment, An example of suppressing the second harmonic and the third harmonic as unnecessary radiation will be described.

  First, a radio wave propagating in a rectangular waveguide such as the feeding waveguide 11 in the present embodiment has a number of propagation modes depending on how an electric field or a magnetic field is generated, and the propagation mode varies depending on the frequency of the radio wave. For example, the fundamental wave has a propagation mode called a so-called TE10 mode. In addition, in the case of the second harmonic, in addition to the TE10 mode, the TE20 mode also has a propagation mode. Further, in the case of the third harmonic wave, there are TE10 mode, TE20 mode, and TE30 mode propagation modes. The ratio of the propagation modes of the second harmonic and the third harmonic varies greatly because mode conversion occurs due to the bending of the path in the tube and the unevenness of the wall surface.

  FIG. 3 is a perspective view showing the configuration of the feed waveguide 11 in the present embodiment. On the wide wall surface H1, which is the wall surface corresponding to the long side of the rectangular cross section of the feed waveguide 11, on the central axis T1 of the waveguide longitudinal direction Z1, the slots S0 to S0 are parallel to the waveguide longitudinal direction Z. S9 is formed.

  When a TE10 mode or TE30 mode radio wave propagates in the feed waveguide 11 thus configured, the electric field distribution of the TE10 mode or TE30 radio wave is symmetric with respect to the central axis T1, and crosses the slots S0 to S9. Since it has no component, it is not coupled in slots S0 to S9 and is not radiated from slots S0 to S9. On the other hand, since the TE20 mode radio wave has maximum coupling in the slots S0 to S9, the TE20 mode radio wave is emitted from the slots S0 to S9 to the outside of the feed waveguide 11.

  In consideration of this, the propagation mode of the fundamental wave is the only TE10 mode as described above, and is not emitted in principle from the slots S0 to S9. On the other hand, the second harmonic wave has a TE10 mode and a TE20 mode as propagation modes. Therefore, only in the TE20 mode, the second harmonic wave is emitted outside the feeding waveguide 11 through the slots S0 to S9. The Rukoto. That is, when the propagation mode is the TE10 mode, the second harmonic wave is not emitted outside the feeding waveguide 11 and is fed to the slot waveguide 12. Similarly, in the case of the third harmonic wave, when the propagation mode is the TE10 mode or the TE30 mode, the radio wave of the third harmonic wave is not emitted to the outside of the power supply waveguide 11, and only when the propagation mode is the TE20 mode, the power supply waveguide 11 is used. Released outside. Then, as described above, the ratio of each propagation mode fluctuates due to the bending of the path in the tube, unevenness of the wall surface, etc., and depending on the shape of the wall surface, it is unnecessary radiation simply by forming a slot on the wide wall surface. In some cases, the second and third harmonics cannot be sufficiently suppressed.

  Therefore, in the present embodiment, as shown in FIG. 3, discontinuous portions A0 to A8 for forcibly converting the TE10 mode or the TE30 mode to the TE20 mode are provided in addition to the slots S0 to S9.

  As shown in FIG. 4, the waveguide cross sections of the discontinuous portions A0 to A8 have an asymmetric shape with respect to the central axis T2 with respect to the long side of the rectangular cross section. Since the electric field distribution of the TE20 mode radio wave is point-symmetric with respect to the rectangular cross-section midpoint O1, the TE20 mode radio wave can be efficiently generated.

  FIG. 5 is a graph showing the conversion ratio of power from the TE10 mode to the TE20 mode of the second harmonic wave with respect to “long side width L of the discontinuous portion / long side width a of the waveguide”. From the graph shown in FIG. 5, it can be seen that when L / a ≧ 0.35, approximately half of the TE10 mode radio wave is converted to TE20 mode radio wave. Similarly, TE30 mode radio waves can also be efficiently generated by determining the long side width L of the discontinuous portion in consideration of the power conversion ratio with respect to L / a.

  Further, half of the TE20 mode radio waves generated at the discontinuous portions A0 to A8 are reflected by the discontinuous portions and propagate in the direction opposite to the waveguide propagation direction. The other half is directly propagated in the waveguide propagation direction. Therefore, by forming slots before and after the discontinuous portion, both TE20 mode radio wave reflected waves and transmitted waves can be emitted from the slots.

  However, if a discontinuous portion is formed in the feed waveguide 11, the propagation mode of the fundamental wave is also converted into a higher order mode such as the TE20 mode by the discontinuous portion. Therefore, depending on the distance between the discontinuous portion and the slot in the waveguide propagation direction (waveguide longitudinal direction), the fundamental wave is also emitted from the slot, and the propagation efficiency decreases.

  In order to prevent this reduction in propagation efficiency, it is necessary to form slots with sufficient intervals at which the higher-order modes of the fundamental wave generated at the discontinuous portions are sufficiently attenuated.

  FIG. 6 is a graph showing the amplitude ratio of the TE20 mode radio wave and the TE30 mode radio wave with respect to xxLg when the distance x in the longitudinal direction of the waveguide from the discontinuous portion to the slot and the wavelength Lg in the fundamental wave tube are set. It is. From this graph, by setting the interval in the longitudinal direction of the waveguide between the discontinuous portion and the slot to about 0.5 Lg, the fundamental wave generated in the discontinuous portion is sufficiently attenuated. It is possible to prevent the fundamental wave from being emitted from S0 to S9, and to prevent a decrease in propagation efficiency.

  Furthermore, since the fundamental wave is also reflected by the discontinuous portion, the propagation efficiency of the fundamental wave is reduced by forming the discontinuous portion in the waveguide. Therefore, the distance between the discontinuous part and the discontinuous part is adjusted so that the reflection at the discontinuous part of the fundamental wave is canceled, that is, the reflected wave to each discontinuous part has an opposite phase. Prevents wave propagation efficiency from decreasing. Specifically, the interval between the discontinuous portions in the longitudinal direction of the waveguide is set to an interval of (2n-1) / 4Lg [n is a positive integer], so that the fundamental wave is reflected at the discontinuous portions. Can be countered. In addition, the reflection can be canceled by setting an interval of (n / 2 + 1 / 2m) × Lg [n and m are positive integers].

FIG. 7 is a graph showing the attenuation characteristic of the second harmonic of the TE20 mode in the slot. In FIG. 7, the horizontal axis indicates the ratio of the fundamental wave of the slot length s to the free space wavelength λ ₀ , s / λ ₀ . The vertical axis represents the attenuation S21 of the second harmonic of the TE20 mode in the case of the slot length s. 7 that one-half of a free space wavelength lambda ₀ of the fundamental wave of slot length s, in other words, the free space wavelength lambda ₂ of the half wavelength of the second harmonic, and length approximately equal to twice the lambda _2/2 Thus, it can be seen that the TE20 mode radio wave is attenuated by about 30% in terms of power ratio of about -5 dB. Also, 1 of the length of half the free space wavelength lambda ₀ of the fundamental wave, the third harmonic of the free space wavelength lambda ₃ of the half-wavelength, lambda _3/2 of 3 times the same as the length, the slot length s By setting the length, it is possible to attenuate the third harmonic of the TE20 mode.

  As described above, by forming slots and discontinuous portions in the feed waveguide 11, for example, the TE10 mode double wave propagated to the feed waveguide 11 has a maximum of about 50% in the discontinuous portions. The second harmonic wave of the converted TE20 mode is attenuated to about 30% by the slots formed on the wide wall surface of the discontinuous portion in the longitudinal direction of the waveguide. That is, the second harmonic wave of the TE10 mode can be attenuated to about 65% (−1.8 dB) per one stage of the discontinuous portion. Therefore, when the discontinuous portion has a 10-stage configuration as shown in FIG. 3, for example, a TE10 mode second harmonic can be attenuated by a maximum of 18 dB.

  In the present embodiment, as shown in FIG. 3, the radiation outlet of each slot is covered with a radio wave absorber 14 to absorb unnecessary radiated radio waves emitted from each slot and prevent diffusion to the outside. Yes.

  Moreover, in the said embodiment, the discontinuous part formed in the feed waveguide 11 was formed in plate shape. However, as shown in FIG. 8, the discontinuous portions S'0 to S'9 may be formed in a rod shape instead of a plate shape. By adopting such a shape, the rod-like discontinuous portion can be easily formed with a bolt or the like, so that the production cost can be reduced.

  Furthermore, in the said embodiment, the example which arrange | positions a slot and a discontinuous part alternately by the waveguide longitudinal direction was shown. However, as shown in FIG. 9, at least one slot may be formed independently for each discontinuous part in the longitudinal direction of the waveguide.

  Also, a slot having a slot length with a large attenuation of the second harmonic of the TE20 mode and a slot with a large attenuation of the third harmonic of the TE30 mode may be separately formed on the wide wall surface of the feed waveguide 11. .

  In addition, in the above-described embodiment, an example in which the slot is formed on one wide wall surface H1 of the power supply waveguide 11 is shown, but the slot may be formed on each of the two wide wall surfaces H1 and H2.

  As described above, according to the present embodiment, slots and discontinuous portions are formed as harmonic suppression filters in the feed waveguide of the antenna for ship radar, and harmonics such as second harmonic and third harmonic are formed at the discontinuous portions. Among the wave propagation modes, the TE10 mode and the TE30 mode are forcibly converted to the TE20 mode, and harmonic waves such as a second harmonic and a third harmonic are efficiently emitted from the slot. As a result, it is possible to provide a nautical radar that can cope with strengthening of spurious regulations without requiring a major design change in order to incorporate a harmonic suppression filter in the pedestal.

It is a figure which shows the functional block of the antenna of the navigation radar in this embodiment. It is a figure which shows the perspective view of the antenna part in this embodiment. It is a perspective view of the feed waveguide in this embodiment. It is sectional drawing including the discontinuous part of the feed waveguide in this embodiment. It is a figure which shows the power conversion ratio from TE10 mode of the 2nd harmonic to TE20 mode with respect to discontinuous part long side width L / waveguide long side width a. It is a figure which shows the attenuation | damping characteristic of the higher order propagation mode of the fundamental wave produced by the discontinuous part. It is a figure which shows the attenuation characteristic of the 2nd harmonic of the TE20 mode in a slot. It is a perspective view of another aspect of the feed waveguide in this embodiment. It is a perspective view of another aspect of the feed waveguide in this embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Antenna part, 11 Feeding waveguide, 12 Slot waveguide, 13 Flares, 14 Wave absorber, 20 Pedestal part, 21 Rotary joint part, 22 Magnetron, 100 Aerial part.

Claims (7)

A slot waveguide in which at least one radiation slot from which a desired radio wave is radiated is formed in the tube wall;
A feeding waveguide connected to one end of the slot waveguide and supplying radio waves to the slot waveguide;
A waveguide slot antenna device comprising:
Discontinuous part that generates higher-order propagation modes of radio waves propagating in the feed waveguide, and is provided at predetermined intervals in the longitudinal direction of the waveguide so that reflection of the fundamental wave propagating in the feed waveguide is canceled out. Discontinuities that are made,
A slot formed by cutting in the longitudinal direction of the waveguide on the longitudinal central axis of the waveguide on at least one side of the wide wall surface corresponding to the long side of the rectangular cross section of the feed waveguide, the discontinuous portion An emission slot provided at least one each before and after the longitudinal direction of the waveguide of the discontinuity so as to emit the even-order propagation mode of the harmonics generated at the outside of the feed waveguide;
A waveguide slot antenna device comprising: The waveguide slot antenna apparatus according to claim 1, wherein
A waveguide slot characterized in that a predetermined interval between the discontinuous portions provided in the feed waveguide satisfies (2n-1) / 4 times [n is a positive integer] the guide wavelength Lg of the fundamental wave. Antenna device. The waveguide slot antenna apparatus according to claim 1, wherein
A waveguide slot antenna device characterized in that a predetermined interval between discontinuous portions provided in a feed waveguide satisfies (n / 2 + 1 / 2m) × Lg [n, m is a positive integer]. The waveguide slot antenna device according to any one of claims 1 to 3,
A waveguide slot antenna characterized in that the distance between the discontinuous portion and the emission slot in the longitudinal direction of the waveguide is determined based on the attenuation of radio waves in the higher-order propagation mode of the fundamental wave generated in the discontinuous portion. apparatus. The waveguide slot antenna apparatus according to claim 4, wherein
The waveguide slot antenna device characterized in that the gap in the longitudinal direction of the waveguide between the discontinuous portion and the emission slot is 0.5 × Lg or more. The waveguide slot antenna device according to any one of claims 1 to 5,
A waveguide slot antenna device comprising: a radio wave absorber that is provided on an emission slot of an external wide wall surface of a power supply waveguide and absorbs radio waves emitted from the emission slot. An antenna unit that emits a desired radio wave;
A pedestal section that controls the driving of the antenna section;
In the navigation radar antenna device comprising
An antenna unit comprising the waveguide slot antenna device according to any one of claims 1 to 6.

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