Reflection cancellation plate

Abstract

A reflection cancellation plate, wherein a plurality of transmission reflection layers (1)-(3) are laminated, and each of the plurality of transmission reflection layers (1)-(3) reflects an incident wave having a different frequency, and transmits an incident wave having a frequency higher than the reflection frequency.

Description

Reflection canceling plate

[0001] The present disclosure relates to a reflection cancellation plate that reduces reflected waves due to incident waves incident on an object.

[0002] Reducing radio wave reflection and reducing radar cross section have been widely studied in order to make devices less detectable by radar or to suppress unintended interference waves that cause communication failures. Patent Document 1 also discloses an electromagnetic wave absorber that blocks electromagnetic waves from passing through or leaking, although this is different from reducing radio wave reflection and radar cross section. The electromagnetic wave absorber disclosed in Patent Document 1 is a see-through electromagnetic wave absorber that includes two layers laminated on one side of a transparent substrate: a reflective layer made of a fine-wire mesh pattern that has the function of reflecting all electromagnetic waves that reach it; and a frequency-selective shielding layer on the reflective layer that attenuates electromagnetic waves of a predetermined frequency that is set to resonate with a fine-wire pattern made of an FSS element.

[0003] JP 2009-170887 A

[0004] The electromagnetic wave absorber disclosed in Patent Document 1 is intended to control the frequency of absorption, and is difficult to apply to reducing or canceling reflected waves due to incident waves incident on a target. Moreover, since the electromagnetic wave absorber disclosed in Patent Document 1 is directly applied to electronic devices that generate electromagnetic waves, it may impair the original functions of the target electronic devices.

[0005] The present disclosure has been made in consideration of the above points, and aims to provide a reflection cancellation plate that reduces reflected waves caused by incident waves incident on an object from which it is desired to cancel or reduce reflected waves.

[0006] The reflection cancellation plate according to the present disclosure has a plurality of transmissive-reflective layers stacked one on top of the other, each of which reflects incident waves of different frequencies and transmits incident waves of frequencies higher than the reflected frequencies.

[0007] According to the present disclosure, it is possible to reduce reflected waves due to incident waves that are incident on a target.

[0008] FIG. 1 is a diagram showing an example of the configuration of a reflection cancellation plate according to embodiment 1. FIG. 2 is a diagram for explaining the relationship between the frequency and reflection amplitude of the first transmission-reflection layer and the second transmission-reflection layer when setting the sizes of the first transmission-reflection layer and the second transmission-reflection layer in the reflection cancellation plate according to embodiment 1. FIG. 3 is a diagram showing the relationship between frequency and reflection amplitude during operation in the first transmission-reflection layer to the third transmission-reflection layer in the reflection cancellation plate according to embodiment 1. FIG. 4 is a schematic diagram showing the relationship between frequency and reflection reduction in the reflection cancellation plate according to embodiment 1. FIG. 5 is a diagram showing setting values ​​of the transmission-reflection layer in the reflection cancellation plate according to embodiment 1. FIG. 6 is a diagram showing an example of the configuration of a reflection cancellation plate according to embodiment 2. FIG. 7 is a diagram showing an example of the configuration of a reflection cancellation plate according to embodiment 3.

[0009] Embodiment 1. A reflection cancellation plate according to embodiment 1 will be described using Figures 1 to 5. The reflection cancellation plate according to embodiment 1 is a reflection cancellation plate for making it difficult for a radar to detect a cancellation target (hereinafter referred to as target) 100 whose reflected waves are to be canceled or reduced, or for suppressing unintended interference waves that cause communication failures in communications. The reflection cancellation plate according to embodiment 1 reduces radio wave reflection from target 100 and reduces the radar cross-section (RCS).

[0010] As shown in Fig. 1, the reflection cancellation plate according to the first embodiment comprises a first transmission-reflection layer 1, a second transmission-reflection layer 2, and a third transmission-reflection layer 3, which are located on different planes in this order from the surface side on which the incident wave is incident. The reflection cancellation plate according to the first embodiment has a layered structure in which the third transmission-reflection layer 3, the second transmission-reflection layer 2, and the first transmission-reflection layer 1 are layered in this order with respect to a reflection position reference including the main scattering point of the object 100. The reflection cancellation plate according to the first embodiment, which comprises the first transmission-reflection layer 1 to the third transmission-reflection layer 3, is installed on or around the object 100. In Fig. 1, the object 100 is schematically shown as an isotropic reflector (a sphere made of a perfect conductor).

[0011] The first to third transmission-reflection layers 1 to 3 each reflect incident waves of a different frequency and transmit incident waves of a higher frequency than the reflected frequencies. Note that although the reflection cancellation plate according to embodiment 1 is a laminate of three transmission-reflection layers, namely the first to third transmission-reflection layers 1 to 3, it may also be a laminate of two transmission-reflection layers. In short, it is sufficient that the reflection cancellation plate has at least two transmission-reflection layers that reflect incident waves of different frequencies and transmit incident waves of a higher frequency than the reflected frequencies.

[0012] Below, we will explain a reflection cancellation plate comprising a laminate of three layers, first transmission-reflection layer 1 to third transmission-reflection layer 3. The first transmission-reflection layer 1 reflects incident waves of frequencies equal to or less than F1 and transmits incident waves of frequencies higher than F1. The second transmission-reflection layer 2 reflects incident waves of frequencies equal to or less than F2, which are higher than F1, and transmits incident waves of frequencies higher than F2. The third transmission-reflection layer 3 reflects incident waves of frequencies equal to or less than F3, which are higher than F2, and transmits incident waves of frequencies higher than F3.

[0013] The frequencies of the first transmission-reflection layer 1 to the third transmission-reflection layer 3 have a relationship of F1<F2<F3. That is, the frequencies at which the incident wave is reflected increase in the order of the first transmission-reflection layer 1 located on the surface side where the incident wave is incident, to the second transmission-reflection layer 2, and to the third transmission-reflection layer 3. In the first embodiment, as an example, the frequency F1 is set to 4.7 GHz, the frequency F2 is set to 7 GHz, and the frequency F3 is set to 11 GHz.

[0014] The first to third transflective layers 1 to 3 are composed of a metal grid or a periodic structure. Because the metal grid and the periodic structure basically have the same function, the following description will focus on the metal grid. The first to third transflective layers 1 to 3 each have a different grid period or period of the periodic structure.

[0015] The first to third transflective layers 1 to 3 each have a square planar shape, and their central axes perpendicular to a plane passing through the center of the plane coincide with each other. The second transflective layer 2 is disposed in a positional relationship so as to completely cover the third transflective layer 3, and the first transflective layer 1 is disposed in a positional relationship so as to completely cover the second transflective layer 2.

[0016] The planar area S1 of the first transmission-reflection layer 1 is larger than the planar area S2 of the second transmission-reflection layer 2. The planar area S2 of the second transmission-reflection layer 2 is larger than the planar area S3 of the third transmission-reflection layer 3. The planar areas of the first transmission-reflection layer 1 to the third transmission-reflection layer 3 have the relationship S1>S2>S3. That is, the planar areas of the first transmission-reflection layer 1 to the third transmission-reflection layer 3 decrease in the order of the first transmission-reflection layer 1 located on the surface side onto which the incident wave is incident, to the second transmission-reflection layer 2, and to the third transmission-reflection layer 3.

[0017] In the first transflective layer 1, the grid period D １ , and in the case of a periodic structure, the period D of the periodic structure １ 1, the reflected wave from the first transflective layer 1 is indicated as R1. The size of the first transflective layer 1, i.e., the length of one side a １ 2, is set so that the amplitude of the reflection by the first transmissive reflective layer 1, which reflects the incident wave of frequency F1, is the same as the amplitude of the reflected wave reflected by the object 100. In FIG. 1, the reflected wave from the object 100 is indicated as R.

[0018] In FIG. 2, the horizontal axis indicates frequency, the vertical axis indicates reflection amplitude, a straight line S0 indicates the reflection amplitude of the wave R reflected by the object 100, a curve A1 indicates the reflection amplitude of the wave R1 reflected by the first transmission-reflection layer 1, a curve A2 indicates the reflection amplitude of the wave R2 reflected by the second transmission-reflection layer 2, and a dashed line B1 has a side of a １ The reflected amplitude of the wave reflected by the metal plane plate is shown by the dashed line B2, which has a side length of a ２ At frequency F1, if the reflection amplitude of the reflected wave R1 by the first transmission-reflection layer 1 is made the same as the reflection amplitude of the reflected wave R by the object 100, the size of the first transmission-reflection layer 1, that is, the length a of one side, １ is the length calculated by the following formula (1).

[0019]

[0020] In the above formula (1), λ Ｆ１ is the wavelength of the incident wave of frequency F1 reflected by the first transflective layer 1, σ Ｆ１ is the radar cross section of the target 100 for an incident wave of frequency F1. In the first embodiment, when frequency F1 is 4.7 GHz, for example, length a1 is 150 mm, and grid period D １ The diameter of the grid is 30 mm, and the number of grids is 5 x 5. The reflection amplitude with respect to frequency in the first transflective layer 1 was calculated by numerical calculation, and the result is shown as curve A1 in FIG.

[0021] In the second transflective layer 2, the grid period D ２ , and in the case of a periodic structure, the period D of the periodic structure ２ 1, the reflected wave from the second transflective layer 2 is indicated as R2. The size of the second transflective layer 2, i.e., the length of one side a ２ As shown in FIG. 2, the amplitude of the reflection by the second transmissive reflective layer 2 that reflects the incident wave of frequency F2 is set to be the same as the amplitude of the reflected wave reflected by the object 100.

[0022] At frequency F2, when the reflection amplitude of the wave R2 reflected by the second transmission-reflection layer 2 is set to be the same as the reflection amplitude of the wave R reflected by the object 100, the size of the second transmission-reflection layer 2, that is, the length a of one side, ２ is the length calculated by the following equation (2).

[0023]

[0024] In the above equation (2), λ Ｆ２ is the wavelength of the incident wave of frequency F2 reflected by the second transflective layer 2, σ Ｆ２ is the radar cross section of the target 100 for an incident wave of frequency F2. In the first embodiment, when frequency F2 is 7 GHz, for example, length a2 is 120 mm, and grid period D ２The diameter of the grid is 20 mm, and the number of grids is 6 x 6. The reflection amplitude with respect to frequency in the second transflective layer 2 was calculated by numerical calculation, and the result is shown as curve A2 in FIG.

[0025] In the third transflective layer 3, the grid period D ３ , and in the case of a periodic structure, the period D of the periodic structure ３ 1, the reflected wave from the third transflective layer 3 is indicated as R3. The size of the third transflective layer 3, i.e., the length of one side a ３ is set so that the amplitude of the reflection by the third transmissive reflective layer 3 that reflects the incident wave of frequency F3 is the same as the amplitude of the reflected wave reflected by the object 100.

[0026] At frequency F3, when the reflection amplitude of the wave R3 reflected by the third transmission-reflection layer 3 is set to be the same as the reflection amplitude of the wave reflected by the object 100, the size of the third transmission-reflection layer 3, that is, the length a of one side, ３ is the length calculated by the following equation (3).

[0027]

[0028] In the above equation (3), λ Ｆ３ is the wavelength of the incident wave of frequency F3 reflected by the third transflective layer 3, σ Ｆ３ is the radar cross section of the target 100 for an incident wave of frequency F3. In the first embodiment, when the frequency F2 is 11 GHz, for example, the length a3 is 91 mm and the grid period D ３ The diameter of the grid is 13 mm, and the number of grids is 7 x 7. The reflection amplitude with respect to the frequency in the third transflective layer 3 was calculated by numerical calculation, and the result is shown as curve A3 in FIG.

[0029] In addition, when a laminate of N transflective layers is used instead of a laminate of three layers, such as when a fourth transflective layer is disposed under the third transflective layer 3, the size of the nth transflective layer, that is, the length of one side a ｎ is the length calculated by the following equation (4).

[0030]

[0031] In the above formula (4), n is an integer from 1 to N, N is an integer of 2 or more, and λ Ｆｎ is the wavelength of the incident wave reflected by the nth transmissive-reflective layer, σ Ｆｎ is the radar cross section of the object 100 for an incident wave of frequency Fn.

[0032] The length a of one side of the first transflective layer 1 １ is the length a of one side of the second transflective layer 2 ２ The grid period D of the first transflective layer 1 is longer. １ is the grid period D of the second transflective layer 2 ２ The length a of one side of the second transflective layer 2 is longer than ２ is the length a of one side of the third transflective layer 3 ３ The grid period D of the second transflective layer 2 is longer. ２ is the grid period D of the third transflective layer 3 ３ Longer.

[0033] The length of one side of the first transflective layer 1 to the third transflective layer 3 is a １ >a ２ >a ３ The grid periods of the first to third transflective layers 1 to 3 are D １ >D ２ >D ３ The first to third transmission-reflection layers 1 to 3 have shorter sides and shorter grid periods in the order of the first transmission-reflection layer 1 located on the surface side onto which the incident wave is incident, to the second transmission-reflection layer 2, and to the third transmission-reflection layer 3.

[0034] The first transflective layer 1 is positioned relative to the target 100 at a distance d from the main scattering point of the target 100, as shown in the following equation (5): １ , i.e., the distance d from the reflection phase reference containing the main scattering point １ d １ = λ Ｆ１ / 4 (5)

[0035] The distance d shown in the above formula (5) １ is the wavelength λ of the incident wave reflected by the first transflective layer 1 at frequency F1. Ｆ１Therefore, the reflected wave R1 of frequency F1 reflected by the first transmissive reflective layer 1 has the same amplitude as the reflected wave R of frequency F1 reflected by the target 100 but is in opposite phase.

[0036] As a result, the reflected wave R1 of frequency F1 reflected by the first transmissive reflective layer 1 is superimposed on the reflected wave R of frequency F1 reflected by the object 100, canceling out the reflected wave R of frequency F1 reflected by the object 100. That is, due to the action of the first transmissive reflective layer 1, the superimposed wave S of the reflected wave R and the reflected wave R1 is reflected and reduced with respect to the incident wave of frequency F1, as shown in Fig. 4. Therefore, the reflected wave R of frequency F1 from the object 100 is reduced, and the radar cross section (RCS) for frequency F1 is reduced.

[0037] The second transflective layer 2 is positioned relative to the target 100 at a distance d from the main scattering point of the target 100, as shown in the following equation (6): ２ , i.e., the distance d from the reflection phase reference containing the main scattering point ２ d ２ = λ Ｆ２ / 4 (6)

[0038] The distance d shown in the above equation (6) ２ is the wavelength λ of the incident wave reflected by the second transflective layer 2 at frequency F2. Ｆ２ Therefore, the reflected wave R2 of frequency F2 reflected by the second transmissive reflective layer 2 has the same amplitude as the reflected wave R of frequency F2 reflected by the target 100 but is in opposite phase.

[0039] As a result, the reflected wave R2 of frequency F2 reflected by the second transmissive reflective layer 2 is superimposed on the reflected wave R of frequency F2 reflected by the object 100, canceling out the reflected wave R of frequency F2 reflected by the object 100. That is, due to the action of the second transmissive reflective layer 2, the superimposed wave S of the reflected wave R and the reflected wave R2 is reflected and reduced with respect to the incident wave of frequency F2, as shown in Fig. 4. Therefore, the reflected wave R of frequency F2 from the object 100 is reduced, and the radar cross section (RCS) for frequency F2 is reduced.

[0040] The third transflective layer 3 is positioned relative to the target 100 at a distance d from the main scattering point of the target 100, as shown in the following equation (7):３ , i.e., the distance d from the reflection phase reference containing the main scattering point ３ d ３ = λ Ｆ３ / 4 (7)

[0041] The distance d shown in the above equation (7) ３ is the wavelength λ of the incident wave reflected by the third transflective layer 3 at frequency F3. Ｆ３ Therefore, the reflected wave R3 of frequency F3 reflected by the third transmissive reflective layer 3 has the same amplitude as the reflected wave R of frequency F3 reflected by the target 100 but is in opposite phase.

[0042] As a result, the reflected wave R3 of frequency F3 reflected by the third transmissive reflective layer 3 is superimposed on the reflected wave R of frequency F3 reflected by the object 100, canceling out the reflected wave R of frequency F3 reflected by the object 100. Therefore, the reflected wave R of frequency F3 from the object 100 is reduced, and the radar cross section (RCS) for frequency F3 is reduced.

[0043] In addition, when a laminate of N transmissive-reflective layers is used instead of a laminate of three layers, such as when a fourth transmissive-reflective layer is placed under the third transmissive-reflective layer 3, the installation position of the nth transmissive-reflective layer with respect to the target 100 is determined by the distance d ｎ , i.e., the distance d from the reflection phase reference containing the main scattering point ｎ d ｎ = λ Ｆｎ / 4 (8)

[0044] The distance d shown in the above equation (8) ｎ is the wavelength λ of the incident wave at frequency Fn reflected by the nth transmissive-reflective layer Ｆｎ Therefore, the reflected wave of frequency Fn reflected by the nth transmissive reflective layer n has the same amplitude but an opposite phase to the reflected wave R of frequency Fn reflected by the target 100. Therefore, the reflected wave R of frequency Fn from the target 100 is reduced, and the radar cross section (RCS) for frequency Fn is reduced.

[0045] The distance d from the main scattering point of the object 100 where the first transflective layer 1 is placed １is the distance d from the main scattering point of the object 100 where the second transflective layer 2 is placed. ２ The distance d from the main scattering point of the object 100 at which the second transflective layer 2 is disposed is longer. ２ is the distance d from the main scattering point of the object 100 where the third transflective layer 3 is disposed. ３ The distance from the main scattering point of the object 100 where the first transflective layer 1 to the third transflective layer 3 are arranged is d １ >d ２ >d ３ This is the relationship.

[0046] In the reflection canceling plate according to the first embodiment, the first transmission-reflection layer 1 to the third transmission-reflection layer 3 have the same central axis perpendicular to the plane passing through the center of the plane, and the distance from the main scattering point is d １ >d ２ >d ３ The length of one side is a １ >a ２ >a ３ Therefore, a three-layer laminate is formed in which the first transmissive reflective layer 1 located on the surface side onto which the incident wave is incident completely covers the second transmissive reflective layer 2 and the third transmissive reflective layer 3 located below, and the second transmissive reflective layer 2 completely covers the third transmissive reflective layer 3 located below.

[0047] Therefore, of the incident waves that are incident on the first transmission-reflection layer 1, those with frequencies equal to or less than F1 are reflected by the first transmission-reflection layer 1, and those with frequencies exceeding F1 transmit through the first transmission-reflection layer 1 to reach the second transmission-reflection layer 2. Of the incident waves with frequencies exceeding F1, those with frequencies equal to or less than F2 are reflected by the second transmission-reflection layer 2, and those with frequencies exceeding F2 transmit through the second transmission-reflection layer 2 to reach the third transmission-reflection layer 3. Of the incident waves with frequencies exceeding F2, those with frequencies equal to or less than F3 are reflected by the third transmission-reflection layer 3, and those with frequencies exceeding F3 transmit through the third transmission-reflection layer 3 to reach the third transmission-reflection layer 3.

[0048] That is, the first transmissive reflective layer 1 reflects incident waves of frequencies equal to or less than frequency F1, canceling out the reflected wave R of frequency F1 reflected by the object 100; the second transmissive reflective layer 2 reflects incident waves of frequencies greater than frequency F1 and equal to or less than frequency F2, canceling out the reflected wave R of frequency F2 reflected by the object 100; and the third transmissive reflective layer 3 reflects incident waves of frequencies greater than frequency F2 and equal to or less than frequency F3, canceling out the reflected wave R of frequency F3 reflected by the object 100.

[0049] In this way, the transmissive-reflective layers are stacked in order from the surface side where the incident wave is incident, with the size of the transmissive-reflective layers decreasing, and the lower transmissive-reflective layers are hidden by the upper transmissive-reflective layers, so that the lower the transmissive-reflective layer, the higher the frequency of the incident wave that is reflected. By stacking multiple transmissive-reflective layers so as to satisfy the above formulas (4) and (8), the reflected waves of the frequency reflected by each transmissive-reflective layer have the same amplitude but opposite phase to the reflected waves of the corresponding frequency reflected by the object 100, so that the reflected waves of the corresponding frequency from the object 100 are canceled out, the reflected waves from the object 100 are reduced over a wide band, and the radar cross section (RCS) of the object 100 is reduced over a wide band.

[0050] 5 shows an example of calculation of the grid period and the length of one side with respect to the reflected frequency for each of the first transmissive-reflective layer 1 to the third transmissive-reflective layer 3. By setting a reflected wave that is reflected with respect to the incident wave and stacking multiple transmissive-reflective layers that satisfy the above formulas (4) and (8) with respect to the frequency of the set reflected wave, it is possible to cancel out the desired reflected wave from the target 100.

[0051] In the reflection cancellation plate of embodiment 1, the first transmission-reflection layer 1 to the third transmission-reflection layer 3 each reflect incident waves of different frequencies and transmit incident waves of higher frequencies than the reflected frequencies, and are installed at positions that are 1 / 4 wavelength of the wavelength at the frequency of the reflected incident wave from the reflection phase reference.Therefore, the reflected waves R1 to R3 reflected from each of the first transmission-reflection layer 1 to the third transmission-reflection layer 3 are superimposed in opposite phase on the reflected wave R from the object at the reflected frequency, so the reflected wave R from the object 100 is reduced and the radar cross section (RCS) is reduced over a wide band.

[0052] The reflection cancellation plate of embodiment 1 acts to cancel out the reflected wave R from the object 100 by using the reflected waves R1 to R3 reflected from the first transmissive reflective layer 1 to the third transmissive reflective layer 3, respectively, and therefore the radar cross section (RCS) is reduced over a wide band without making any direct changes to the object 100.

[0053] Embodiment 2 A reflection-canceling plate according to embodiment 2 will be described with reference to Fig. 6. In the reflection-canceling plate according to embodiment 1, the transmissive-reflective layers are stacked in order from the surface side to which the incident wave is incident, with the size of the transmissive-reflective layers decreasing in size, so that the lower transmissive-reflective layers are hidden by the upper transmissive-reflective layers.

[0054] In contrast, the reflection-cancelling plate according to embodiment 2 differs from the reflection-cancelling plate according to embodiment 1 in that multiple transmission-reflection layers are stacked in order without overlapping when viewed from the surface side where the incident wave is incident, but is otherwise the same as the reflection-cancelling plate according to embodiment 1. The reflection-cancelling plate according to embodiment 2 is suitable when the frequencies of the reflected waves from the multiple transmission-reflection layers are close and the spacing between the multiple transmission-reflection layers is narrow. Below, we will mainly explain the differences from the reflection-cancelling plate according to embodiment 1.

[0055] There are three means for stacking multiple transmissive-reflective layers in sequence without overlapping: First, each of the multiple transmissive-reflective layers has a cutout at one corner of a quadrangle, and, in order from the surface side where the incident wave is incident, the lower transmissive-reflective layer fits into the cutout of the upper transmissive-reflective layer as viewed from the surface side where the incident wave is incident; Second, each of the multiple transmissive-reflective layers has a cutout, and, in order from the surface side where the incident wave is incident, the lower transmissive-reflective layer fits into the cutout of the upper transmissive-reflective layer as viewed from the surface side where the incident wave is incident; Third, a configuration in which the multiple transmissive-reflective layers are shifted laterally so as not to overlap as viewed from the surface side where the incident wave is incident.

[0056] The following description will focus on the first configuration. As shown in Fig. 1, the reflection cancellation plate according to the second embodiment includes a first transmission-reflection layer 10, a second transmission-reflection layer 20, a third transmission-reflection layer 30, and a fourth transmission-reflection layer 40, which are located on different planes in this order from the surface side on which the incident wave is incident. The reflection cancellation plate according to the second embodiment has a layered structure in which the fourth transmission-reflection layer 40, the third transmission-reflection layer 30, the second transmission-reflection layer 20, and the first transmission-reflection layer 10 are layered in this order with respect to a reflection position reference including the main scattering point of the object 100.

[0057] The first transflective layer 10 reflects incident waves of frequencies equal to or less than F10 and transmits incident waves of frequencies higher than F10. The second transflective layer 20 reflects incident waves of frequencies equal to or less than F20 but higher than F10 and transmits incident waves of frequencies higher than F20. The third transflective layer 30 reflects incident waves of frequencies equal to or less than F30 but higher than F20 and transmits incident waves of frequencies higher than F30. The fourth transflective layer 40 reflects incident waves of frequencies equal to or less than F40 but higher than F30 and transmits incident waves of frequencies higher than F40. The frequencies of the first transflective layer 10 to the fourth transflective layer 40 have a relationship of F1<F2<F3<F4.

[0058] The first to fourth transflective layers 10 to 40 are made of a metal grid or periodic structure, and each of the first to fourth transflective layers 10 to 40 has a different grid period or period of the periodic structure.

[0059] Each of the first to fourth transmissive-reflective layers 10 to 40 has a notch at one corner of a quadrangle, and in order from the surface side onto which the incident wave is incident, the lower transmissive-reflective layer fits into the notch of the upper transmissive-reflective layer as seen from the surface side onto which the incident wave is incident. The cutouts of each of the first to fourth transmissive-reflective layers 10 to 40 are square. The fourth transmissive-reflective layer 40 has a square planar shape without a cutout.

[0060] The view from the surface side where the incident wave is incident is hereinafter referred to as the surface view. The second transmissive reflective layer 20 is accommodated in the cutout portion of the first transmissive reflective layer 10, the third transmissive reflective layer 30 is accommodated in the cutout portion of the second transmissive reflective layer 20, and the fourth transmissive reflective layer 40 is accommodated in the cutout portion of the third transmissive reflective layer 30.

[0061] The laminate of four transmissive-reflective layers, the first transmissive-reflective layer 10 to the fourth transmissive-reflective layer 40, is arranged in a square, one side of which is the long side of the first transmissive-reflective layer 10, as viewed from the surface onto which the incident wave is incident. When viewed from the surface side onto which the incident wave is incident, the lowest transmissive-reflective layer, that is, the fourth transmissive-reflective layer 40 in the second embodiment, has a square planar shape without a cutout, and the remaining transmissive-reflective layers, that is, the first transmissive-reflective layer 10 to the third transmissive-reflective layer 30 in the second embodiment, have an L-shape with a cutout.

[0062] The planar area S10 and outer periphery L10 of the first transflective layer 10 are larger than the planar area S20 and outer periphery L20 of the second transflective layer 20. The planar area S20 and outer periphery L20 of the second transflective layer 20 are larger than the planar area S30 and outer periphery L30 of the third transflective layer 30. The planar area S30 and outer periphery L30 of the third transflective layer 30 are larger than the planar area S40 and outer periphery L40 of the fourth transflective layer 40.

[0063] The plane areas and peripheries of the first to fourth transmission-reflection layers 10 to 40 have the relationships S10 > S20 > S30 (> S40) and L10 > L20 > L30 (> L40). That is, the plane areas and peripheries of the first to fourth transmission-reflection layers 10 to 40 decrease in order from the first transmission-reflection layer 10 located on the surface side onto which the incident wave is incident to the second transmission-reflection layer 20, the third transmission-reflection layer 30, and the fourth transmission-reflection layer 40.

[0064] In the first transflective layer 10, the grid period D １０ , and in the case of a periodic structure, the period D of the periodic structure １０ In the second transflective layer 20, the grid period D ２０ , and in the case of a periodic structure, the period D of the periodic structure ２０In the third transflective layer 30, the grid period D ３０ , and in the case of a periodic structure, the period D of the periodic structure ３０ In the fourth transflective layer 40, the grid period D ４０ , and in the case of a periodic structure, the period D of the periodic structure ４０ By configuring it as follows, an incident wave of frequency F40 is reflected.

[0065] The period of the elements of the first transflective layer 10 to the fourth transflective layer 40 is D １０ >D ２０ >D ３０ >D ４０ That is, the element periods of the first to fourth transmission-reflection layers 10 to 40 decrease in the order of the first transmission-reflection layer 10 located on the surface side where the incident wave is incident, to the second transmission-reflection layer 20, the third transmission-reflection layer 30, and the fourth transmission-reflection layer 40.

[0066] The size of the first transflective layer 10, i.e., the length of one side a １０ is set so that the amplitude of the reflection by the first transmissive-reflective layer 10 of the incident wave of frequency F10 is the same as the amplitude of the reflection by the object 100. The size of the second transmissive-reflective layer 20, i.e., the length a of one side, ２０ is set so that the amplitude of the reflection by the second transmissive reflective layer 20 that reflects the incident wave of frequency F20 is the same as the amplitude of the reflected wave reflected by the object 100.

[0067] The size of the third transflective layer 30, i.e., the length of one side a ３０ is set so that the amplitude of the reflection by the third transmissive-reflective layer 30, which reflects the incident wave of frequency F30, is the same as the amplitude of the reflected wave reflected by the object 100. The size of the fourth transmissive-reflective layer 40, i.e., the length a of one side ４０ is set so that the amplitude of the reflection by the fourth transmissive reflective layer 40 that reflects the incident wave of frequency F40 is the same as the amplitude of the reflected wave reflected by the object 100.

[0068] The length a of one side of the first transflective layer 10 to the third transflective layer 30 １０~a ３０ is the length calculated by the following equation (9).

[0069]

[0070] In the above formula (9), n is an integer from 1 to N-1, N is an integer of 3 or more, and λ Ｆｎ is the wavelength of the incident wave reflected by the nth transmissive-reflective layer, σ Ｆｎ is the radar cross section of the target 100 for an incident wave of frequency Fn. The length a of one side of the lowest transmissive reflective layer, the fourth transmissive reflective layer 40 in the second embodiment, as seen from the surface side where the incident wave is incident is ４０ is the length calculated by the above formula (4).

[0071] First, the length a of one side of the bottommost transflective layer, the fourth transflective layer 40 in the second embodiment, is ４０ is determined by the above formula (4), and the length a of one side of the upper transmissive-reflective layer, i.e., the third transmissive-reflective layer 30 in the second embodiment, is determined. ３０ , the length a of one side of the second transflective layer 20 ２０ , the length a of one side of the first transflective layer 10 １０ is determined by the above equation (9).

[0072] The length of one side of each of the first to fourth transflective layers 10 to 40 is a １０ >a ２０ >a ３０ >a ４０ The first to fourth transmission-reflection layers 10 to 40 have shorter sides and shorter grid periods in the order of the first transmission-reflection layer 10 located on the surface side onto which the incident wave is incident, to the second transmission-reflection layer 20, the third transmission-reflection layer 30, and the fourth transmission-reflection layer 40.

[0073] The installation positions of the first to fourth transflective layers 10 to 40 relative to the target 100 are determined by the distance d １０ ~d ４０ , i.e., the distance d from the reflection phase reference containing the main scattering point １０ ~d ４０ That is, the distance d between the first transflective layer 10 and the fourth transflective layer 40 is １０ ~d１０ is 1 / 4 wavelength of the wavelength at the frequency of the incident wave reflected by each of the transmissive reflective layers 10 to 40, and the reflected waves of the frequency reflected by each of the transmissive reflective layers 10 to 40 have the same amplitude but opposite phase as the reflected waves of the corresponding frequency reflected by the target 100.

[0074] As a result, even when the spacing between the first to fourth transmissive reflective layers 10 to 40 is narrow, interference between the layers can be avoided, and the reflected waves from the object 100 are reduced, thereby achieving broadband reflection cancellation in a narrow space and reducing the radar cross section (RCS) of the object 100 over a wide band.

[0075] In the reflection canceling plate according to the second embodiment, the first to fourth transmission-reflection layers 10 to 40 each reflect incident waves of different frequencies and transmit incident waves of frequencies higher than the reflected frequencies. When viewed from the surface side where the incident waves are incident, the lowest transmission-reflection layer 40 has a flat shape with no cutouts, and the remaining transmission-reflection layers 10 to 30 other than the lowest layer have L-shapes with cutouts. When viewed from the surface, the lower transmission-reflection layers fit into the cutouts of the upper transmission-reflection layers, and the first to fourth transmission-reflection layers 10 to 30 Since each of the four transmissive reflective layers 40 is placed at a position that is 1 / 4 wavelength of the wavelength at the frequency of the incident wave reflected from the reflection phase reference, even if the frequencies of the waves reflected by the first transmissive reflective layer 10 to the fourth transmissive reflective layer 40 are close to each other and the spacing between the first transmissive reflective layer 10 to the fourth transmissive reflective layer 40 is narrow, interference between the incident wave and the reflected wave between the layers can be avoided, wideband reflection cancellation can be achieved in a narrow space, and the radar cross section (RCS) of the target 100 can be reduced over a wide band.

[0076] The reflection cancellation plate of embodiment 2 acts to cancel out reflected waves from the object 100 using reflected waves reflected from each of the first transmissive reflective layer 10 to the fourth transmissive reflective layer 40, thereby reducing the radar cross section (RCS) over a wide band without making any direct changes to the object 100.

[0077] When a cutout portion is provided in each of the plurality of transmissive-reflective layers instead of a notch portion, the size of one side of the plurality of transmissive-reflective layers and their installation positions are determined as follows: the outer diameter shape of each of the plurality of transmissive-reflective layers is square, the central axes of the plurality of transmissive-reflective layers that are perpendicular to a plane passing through the center of the plane coincide with each other, and the remaining transmissive-reflective layers other than the lowest transmissive-reflective layer have a cutout portion in their centers.

[0078] First, the length a of one side of the bottommost transflective layer, the fourth transflective layer 40 in the second embodiment, is ４０ is determined by the above formula (4). Next, the length a of one side of the third transflective layer 30 located above the fourth transflective layer 40 is determined as ３０ is determined by the above formula (4), and the center is ４０ Similarly, the length a of one side of the second transflective layer 20 is ２０ and the length of one side of the cutout part a ３０ , the length a of one side of the first transflective layer 10 １０ and the length of one side of the cutout part a ２０ The positions of the transmissive-reflective layers are determined relative to the main scattering points of the object 100 by the above formula (8).

[0079] When the transflective layers do not overlap, the size of one side and the installation positions are determined in the same manner as in the reflection canceling plate according to the first embodiment.

[0080] Embodiment 3. A reflection-cancelling plate according to embodiment 3 will be described using Figure 7. The reflection-cancelling plate according to embodiment 3 differs from the reflection-cancelling plate according to embodiment 1 in that a radio wave absorber 5 is provided below the lowest transmission-reflective layer as seen from the surface side onto which the incident wave is incident, that is, below the third transmission-reflective layer 3 in embodiment 1, and is arranged in parallel with the plurality of transmission-reflective layers 1 to 3, but is otherwise the same. In Figure 7, the same reference numerals as those in Figure 1 indicate the same or corresponding parts.

[0081] 7, the reflection-canceling plate according to the third embodiment comprises, in order from the surface side onto which the incident wave is incident, a first transmission-reflection layer 1, a second transmission-reflection layer 2, and a third transmission-reflection layer 3, which are located on different planes, and a radio wave absorber 5 disposed below the third transmission-reflection layer 3 and parallel to the third transmission-reflection layer 3. The three-layer stack of the first transmission-reflection layer 1 to the third transmission-reflection layer 3 is the same as the three-layer stack of the first transmission-reflection layer 1 to the third transmission-reflection layer 3 in the reflection-canceling plate according to the first embodiment, and therefore a description thereof will be omitted.

[0082] The wave absorber 5 has a flat metal base plate 5a and a wave absorbing layer 5b on the surface of the base plate 5a where the incident wave is incident. The length of one side of the wave absorber 5, that is, the length of one side of the base plate 5a and the length of one side of the wave absorbing layer 5b, is 1 / 2 the length of one side of the first transflective layer 1. １ In addition, the length of at least one side of the radio wave absorption layer 5b is equal to the length a of one side of the first transmission-reflection layer 1. １ The length of one side of the base plate 5a should be equal to the length a of one side of the first transflective layer 1. １ Longer is fine.

[0083] Next, the role of the radio wave absorber 5 will be described. An incident wave that has passed through the periphery of the first transmission-reflection layer 1 located on the periphery of the second transmission-reflection layer 2 is absorbed by the radio wave absorbing layer 5b of the radio wave absorber 5. An incident wave that has passed through the periphery of the second transmission-reflection layer 2 located on the periphery of the third transmission-reflection layer 3 is absorbed by the radio wave absorbing layer 5b of the radio wave absorber 5. An incident wave that has passed through the third transmission-reflection layer 3 is absorbed by the radio wave absorbing layer 5b of the radio wave absorber 5.

[0084] In this way, the incident wave that has passed through the three-layer laminate of the first transmission-reflection layer 1 to the third transmission-reflection layer 3 is absorbed by the radio wave absorbing layer 5b of the radio wave absorber 5. As a result, the radio wave absorber 5 blocks the incident wave that has passed through the three-layer laminate below the radio wave absorber 5, making it possible to avoid interference of unnecessary radio waves below the reflection-cancelling plate.

[0085] The reflection cancellation plate of embodiment 3 has the same effect as the reflection cancellation plate of embodiment 1, in particular, it acts to cancel out the reflected wave R from the object 100 by the reflected waves R1 to R3 reflected from the first transmissive reflective layer 1 to the third transmissive reflective layer 3, respectively, so that the radar cross section (RCS) is reduced over a wide band without making any direct changes to the object 100, and furthermore, by providing the radio wave absorber 5, it is possible to avoid interference of unnecessary radio waves below the reflection cancellation plate.

[0086] In the reflection canceling plate according to the second embodiment, a radio wave absorber 5 may be provided below the lowest transmission-reflection layer seen from the surface side where the incident wave is incident, that is, the fourth transmission-reflection layer 40 in the second embodiment, so as to be parallel to the plurality of transmission-reflection layers 10 to 40. In this case as well, the length of one side of the radio wave absorber 5 is the length a of one side of the first transmission-reflection layer 10. １０ is the same as

[0087] With this configuration, incident waves that have passed through the first transmission-reflection layer 10 to the fourth transmission-reflection layer 40 are absorbed by the radio wave absorbing layer 5b of the radio wave absorber 5. As a result, the radio wave absorber 5 blocks incident waves that have passed through the four-layer stack below the radio wave absorber 5, making it possible to avoid interference of unnecessary radio waves below the reflection-cancelling plate.

[0088] Therefore, similar to the reflection cancellation plate of embodiment 2, the reflected waves reflected from each of the first to fourth transmission-reflection layers 10 to 40 act to cancel out the reflected waves from the target 100, so that the radar cross section (RCS) is reduced over a wide band without making any direct changes to the target 100, and furthermore, by providing the radio wave absorber 5, it is possible to avoid interference of unnecessary radio waves below the reflection cancellation plate.

[0089] It should be noted that the embodiments may be freely combined, or any of the components in each embodiment may be modified, or any of the components in each embodiment may be omitted.

[0090] The reflection cancellation plate of the present disclosure is suitable as a reflection cancellation plate used to make it difficult for radar to detect an object whose reflected waves you want to cancel or reduce, or to suppress unintended interference waves that cause communication failures in communications.

[0091] 1, 10 First transflective layer, 2, 20 Second transflective layer, 3, 30 Third transflective layer, 40 Fourth transflective layer, 5 Radio wave absorber, 5 Ground plate, 5b Radio wave absorbing layer, 100 Target.

Claims

1. A reflection-canceling plate having a plurality of laminated transmissive-reflective layers, each of which reflects incident waves of a different frequency and transmits incident waves of a higher frequency than the frequency that it reflects.

2. A reflection cancellation plate as described in claim 1, wherein the frequency at which the incident wave is reflected increases from the transmissive reflective layer located on the surface side where the incident wave is incident.

3. A reflection canceling plate as described in claim 1, wherein the plane areas of the plurality of transmissive reflective layers decrease in order from the transmissive reflective layer located on the surface side to which the incident wave is incident.

4. A reflection cancellation plate as described in claim 3, wherein each of the plurality of transmissive reflective layers is constituted by either a metal grid or a periodic structure, and the period of the elements constituting either the metal grid or the periodic structure decreases in order from the transmissive reflective layer located on the surface side where the incident wave is incident.

5. The reflection canceling plate according to any one of claims 1 to 4, wherein each of the plurality of transmissive reflective layers is disposed at a distance from a scattering reference point for which the reflected wave is to be reduced, the distance being expressed by the following formula (8). ｎ = λ Ｆｎ / 4 (8) where n is an integer from 1 to N, N is an integer of 2 or more, and λFn is the wavelength of the incident wave reflected by the transmissive reflective layer.

6. The length of one side of each of the plurality of transmissive and reflective layers is a given by the following formula (4): ｎ 5. The reflection canceling plate according to claim 1, wherein In the above formula (4), n is an integer from 1 to N, N is an integer of 2 or more, and λ Ｆｎ is the wavelength of the incident wave reflected by the nth transmissive-reflective layer, σ Ｆｎ is the radar cross section of the target for which it is desired to reduce the reflected wave with respect to the incident wave of frequency Fn.

7. The length of one side of each of the plurality of transmissive and reflective layers is a given by the following formula (4): ｎ 6. The reflection cancelling plate according to claim 5, In the above formula (4), n is an integer from 1 to N, N is an integer of 2 or more, and λ Ｆｎ is the wavelength of the incident wave reflected by the nth transmissive-reflective layer, σ Ｆｎ is the radar cross section of the target for which it is desired to reduce the reflected wave with respect to the incident wave of frequency Fn.

8. The reflection canceling plate according to claim 1, wherein the plurality of transmissive reflective layers are stacked in order without overlapping when viewed from the surface side on which the incident wave is incident.

9. The reflection canceling plate according to claim 8, wherein the plurality of transmissive reflective layers have successively smaller planar areas and peripheries from the transmissive reflective layer located on the surface side to which the incident wave is incident.

10. A reflection cancellation plate as described in claim 9, wherein each of the plurality of transmissive reflective layers is constituted by either a metal grid or a periodic structure, and the period of the elements constituting either the metal grid or the periodic structure decreases in order from the transmissive reflective layer located on the surface side where the incident wave is incident.

11. The reflection canceling plate according to any one of claims 8 to 10, wherein each of the plurality of transmissive reflective layers is disposed at a distance from a scattering reference point for which reflected waves are to be reduced, the distance being expressed by the following formula (8). ｎ = λ Ｆｎ / 4 (8) where n is an integer from 1 to N, N is an integer of 2 or more, and λFn is the wavelength of the incident wave reflected by the transmissive reflective layer.

12. Each of the plurality of transmissive reflective layers, except for the lowermost transmissive reflective layer, has a notch at one corner of a quadrangle, and in order from the surface side where the incident wave is incident, the lower transmissive reflective layer fits into the notch of the upper transmissive reflective layer when viewed from the surface side where the incident wave is incident, and the length of one side of each of the plurality of transmissive reflective layers is a length a given by the following formula (4): ｎ 11. The reflection canceling plate according to claim 8, wherein: In the above formula (4), n is an integer from 1 to N, N is an integer of 2 or more, and λ Ｆｎ is the wavelength of the incident wave reflected by the nth transmissive-reflective layer, σ Ｆｎ is the radar cross section of the target for which it is desired to reduce the reflected wave with respect to the incident wave of frequency Fn.

13. Each of the plurality of transmissive reflective layers has a notch at one corner of a quadrangle, and in order from the surface side where the incident wave is incident, the lower transmissive reflective layer fits into the notch of the upper transmissive reflective layer when viewed from the surface side where the incident wave is incident, and the length of one side of each of the plurality of transmissive reflective layers is a length a given by the following formula (4): ｎ 12. The reflection cancelling plate of claim 11, In the above formula (4), n is an integer from 1 to N, N is an integer of 2 or more, and λ Ｆｎ is the wavelength of the incident wave reflected by the nth transmissive-reflective layer, σ Ｆｎ is the radar cross section of the target for which it is desired to reduce the reflected wave with respect to the incident wave of frequency Fn.

14. Each of the plurality of transmissive reflective layers has a cutout portion, and in order from the surface side where the incident wave is incident, the lower transmissive reflective layer fits into the cutout portion of the upper transmissive reflective layer when viewed from the surface side where the incident wave is incident, and the length of one side of each of the plurality of transmissive reflective layers is a length a given by the following formula (4): ｎ 11. The reflection canceling plate according to claim 8, wherein: In the above formula (4), n is an integer from 1 to N, N is an integer of 2 or more, and λ Ｆｎ is the wavelength of the incident wave reflected by the nth transmissive-reflective layer, σ Ｆｎ is the radar cross section of the target for which it is desired to reduce the reflected wave with respect to the incident wave of frequency Fn.

15. Each of the plurality of transmissive reflective layers has a cutout portion, and in order from the surface side where the incident wave is incident, the lower transmissive reflective layer fits into the cutout portion of the upper transmissive reflective layer when viewed from the surface side where the incident wave is incident, and the length of one side of each of the plurality of transmissive reflective layers is a length a given by the following formula (4): ｎ 12. The reflection cancelling plate of claim 11, In the above formula (4), n is an integer from 1 to N, N is an integer of 2 or more, and λ Ｆｎ is the wavelength of the incident wave reflected by the nth transmissive-reflective layer, σ Ｆｎ is the radar cross section of the target for which it is desired to reduce the reflected wave with respect to the incident wave of frequency Fn.

16. A reflection cancellation plate as described in any one of claims 1 to 4 or claims 8 to 10, comprising a radio wave absorber arranged below the lowest transmissive reflective layer as viewed from the surface side where the incident wave is incident, parallel to the multiple transmissive reflective layers, and having a base plate and a radio wave absorbing layer on the surface of the base plate where the incident wave is incident.

17. A reflection cancellation plate as described in claim 16, wherein the length of one side of the radio wave absorbing layer in said radio wave absorber is the same as the length of one side of the transmissive reflective layer located on the surface side onto which the incident wave is incident.

18. The reflection canceling plate according to claim 17, in which the radio wave absorbing layer of the radio wave absorber is disposed as the lowest transmissive reflective layer as viewed from the surface side on which the incident wave is incident.

Images