JP6598727B2 - Reflect array antenna - Google Patents

Description

    The present invention relates to a reflectarray antenna composed of a primary radiator and a reflector, for example, used for an antenna mounted on a satellite.

Conventionally, as a satellite-mounted antenna, a parabolic antenna is used in which a primary radiator composed of a horn antenna or the like and a parabolic curved reflector are opposed to each other. A reflector of a general parabolic antenna mounted on a satellite is launched into space in a folded state, and the reflector is deployed in outer space. Therefore, there is a problem that the structure for deploying the reflector is complicated and the reliability during operation is low.
Thus, a reflectarray antenna using a flat reflector instead of a parabolic curved reflector has been developed (see Non-Patent Document 1, for example). Since the reflectarray antenna uses a flat reflector, the structure is simplified, and the cost can be reduced and the reliability can be improved.

  The reflector of the reflectarray antenna is composed of a plurality of resonant elements, and the electromagnetic wave having a spherical wavefront radiated from the primary radiator is corrected in phase by the reflector and reflected as a plane wave in a predetermined direction. . In order to realize such a reflected wave, the reflector of the reflectarray antenna has resonant elements having different shapes and sizes depending on the position. The phase amount to be corrected is expressed as the sum of the phase correction amount for converting the electromagnetic wave incident as a spherical wave into a plane wave and the phase correction amount for directing the reflection direction of the electromagnetic wave in a desired direction, and is relative to the design frequency. Thus, the shape and size of the resonant element are determined so as to realize the phase correction amount.

M. R. Chaharmir, J. Shaker, M. Cuhaci, and A. Ittipiboon, “Broadband reflectarray antenna with double cross loops,” Electron. Lett., Vol. 42, no. 2, pp. 65-66, Jan. 2006.

However, the phase correction amount determined by the above-described conventional method is optimal for the design frequency, but not optimal for other frequencies. Therefore, the correction amount is excessive or insufficient, and the reflected wave There is a problem that the direction is deviated from a desired direction, and as a result, the reflect array antenna becomes narrow band.
In general, a reflectarray antenna has a problem that it has a narrow band. Conventionally, as shown in Non-Patent Document 1, a method for increasing the bandwidth by devising the shape of a resonant element has been devised. However, focusing on the correction of the optical path length, a technique for determining the position of the reflector and the primary radiator has not been realized.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to obtain a reflectarray antenna capable of widening the bandwidth by determining the positions of the reflector and the primary radiator.

The reflectarray antenna according to the present invention is arranged so as to face a reflecting plate in a positional relationship to form an offset antenna and a flat reflecting plate having a plurality of resonant elements, and a mirror image of the reflecting plate surface reflects electromagnetic waves. The center of the reflector is positioned so that the distance from the straight line passing through the center of the reflector as seen from the reflection direction of the electromagnetic wave and the distance from the straight line is within half a wavelength. A primary radiator that radiates electromagnetic waves in the direction, and a point serving as a reference when determining the reflection phase of the plurality of resonant elements is set to a position different from the opening center of the reflector .

In the reflectarray antenna of the present invention, the position of the primary radiator is such that the mirror image of the primary radiator with respect to the surface of the reflecting plate faces the reflection direction of the electromagnetic wave and is parallel to the reflection direction of the electromagnetic wave and viewed from the reflection direction of the electromagnetic wave. When determining the reflection phase of a plurality of resonant elements , arranged so that the distance from the straight line passing through the center of the plate is within half a wavelength, radiating electromagnetic waves toward the center of the reflector Since the reference point is set at a position different from the aperture center of the reflector, the influence of secondary aberration at a frequency different from the design frequency can be reduced , and the bandwidth of the reflectarray antenna can be increased.

It is explanatory drawing which shows the reflectarray antenna by Embodiment 1 of this invention. It is explanatory drawing which shows the mirror image of reflection of a primary radiator. It is explanatory drawing which shows the aberration correct | amended with a reflecting plate. It is explanatory drawing which shows two types of aberrations. FIG. 5A, FIG. 5B, and FIG. 5C are explanatory views showing wavefronts at frequencies lower than the design frequency. 6A, 6B, and 6C are explanatory diagrams showing wavefronts at a frequency higher than the design frequency. It is explanatory drawing which shows the other example of the parameter which determines the positional relationship of the primary radiator and reflector of the reflectarray antenna by Embodiment 1 of this invention. It is explanatory drawing which shows the reflection phase of a general resonant element (rectangular element). It is explanatory drawing which shows the wave front and aberration at the time of taking the reference | standard of a reflection phase in the opening center of a reflecting plate. FIG. 10 is an explanatory diagram showing the relationship between the distance from the center of the opening and the desired reflection phase of the resonant element in the configuration of FIG. 9. It is explanatory drawing which shows the wave front and aberration at the time of taking the reference | standard of the reflection phase of the reflectarray antenna by Embodiment 1 of this invention in the position different from the opening center of a reflecting plate. It is explanatory drawing which shows the relationship between the distance from the opening center in the structure of FIG. 11, and the desired reflection phase of a resonant element. It is explanatory drawing which shows the gain fall amount with respect to the design frequency of the reflectarray antenna by Embodiment 1 of this invention compared with the past.

Embodiment 1 FIG.
FIG. 1 is an explanatory diagram showing a reflectarray antenna according to Embodiment 1 of the present invention.
The reflectarray antenna shown in FIG. 1 includes a primary radiator 1 and a reflector 2, and the reflector 2 is a flat reflector having a plurality of resonant elements. The primary radiator 1 is disposed opposite to the reflector 2 in a positional relationship forming an offset antenna, the mirror image 3 of the primary radiator with respect to the surface of the reflector 2 is directed in the electromagnetic wave reflection direction 4, and the electromagnetic wave is reflected. It is arranged so as to be positioned on a straight line passing through the center of the reflection plate 2 as viewed from the reflection direction 4 of the electromagnetic wave parallel to the direction 4 and to radiate the electromagnetic wave toward the center of the reflection plate 2. The wavefront 5 represents a wavefront related to a first-order aberration described later. Hereinafter, the positional relationship between the primary radiator 1 and the reflecting plate 2 will be described.

First, a case where phase correction is not performed will be described. FIG. 2 is an explanatory diagram thereof.
When the reflector 2 that does not perform phase correction as shown in FIG. 2 is considered, the electromagnetic wave 6 radiated from the primary radiator 1 is reflected by the reflector 2 and propagates in space as a reflected wave 7. The reflected wave 7 at this time can be regarded as equivalent to the electromagnetic wave radiated from the mirror image 3 of the primary radiator with respect to the reflector surface. The wavefront of the electromagnetic wave radiated from the mirror image 3 of the primary radiator becomes a wavefront 8 as shown in FIG. In order to make the wavefront 8 a desired wavefront 9, it is necessary to correct the aberration 10 shown in FIG. The aberration 10 includes a first-order aberration 11 generated when the wavefront is inclined with respect to the desired wavefront 9 and a second-order aberration 12 generated when the electromagnetic wave radiated from the primary radiator 1 is a spherical wave. It can be divided into two parts. The aberration is corrected based on the following equation (1).

Here, φ ₀ represents the amount of phase correction, and is represented by the sum of a term for correcting the primary aberration 11 represented by Δ ₁ and a term for correcting the secondary aberration 12 represented by Δ _2. . λ ₀ represents the wavelength at the design frequency f ₀ . The designing the phase correction amount phi ₀ reflector 2 as given.
On the other hand, let us consider a case where an electromagnetic wave having a frequency f ₁ different from the design frequency is reflected by the reflector 2 designed with the phase correction amount φ ₀ . Considering the aberration correction amount Δ ′ when corrected with the phase correction amount φ ₀ , the value is expressed by the following equation (2).

Here, λ represents the wavelength at the frequency f ₁ , φ ₀₁ is the phase correction amount for the first-order aberration expressed by the first term on the right side of Equation (1), and φ ₀₂ is the right side of Equation (1). This represents the phase correction amount for the second-order aberration expressed by the second term. The terms related to φ ₀₁ and φ ₀₂ on the right side of Equation (2) indicate the correction amount of the aberration with respect to each aberration. From this equation, it can be seen that the corrected aberration is proportional to λ. That is, when correction is performed with the phase correction amount φ ₀ , the phase correction amount is optimal for an electromagnetic wave with λ = λ ₀ , but is excessively corrected for an electromagnetic wave with λ> λ ₀ , and λ <λ ₀ . For electromagnetic waves, the amount of correction is insufficient.

As an example, FIG. 5 shows a wavefront after phase correction of an electromagnetic wave having a wavelength of λ> λ ₀ when a reflector designed with a phase correction amount φ ₀ is used. FIG. 5A is an explanatory diagram when the aberration is corrected for the primary aberration. Wavefront 13 caused by the primary aberrations by the aberration correction amount 14 of the formula (2), because for the electromagnetic waves of lambda> lambda _0, which is excessively corrected wavefront as the wavefront 15 Thus, the wavefront is inclined from the desired wavefront 16. This means that the reflection direction of electromagnetic waves is inclined from a desired direction. FIG. 5B is a schematic diagram when the aberration is corrected for the secondary aberration. Since wavefront 17 caused by second order aberrations by the aberration correction amount 18 which is represented by first-order aberrations as well as the formula (2), which is excessively corrected for the electromagnetic waves of lambda> lambda _0, the wavefront 19 Therefore, the desired wavefront 20 cannot be obtained. By combining the two types of aberrations as described above, the reflected wave in the electromagnetic wave of λ> λ ₀ becomes a wavefront having a curvature and a curvature from the desired wavefront 21 as indicated by the wavefront 22 in FIG. 5C.

Also shows the wavefront corrected of an electromagnetic wave lambda <lambda ₀ in FIG. FIG. 6A is a schematic diagram when the aberration is corrected for the primary aberration. Wavefront 13 caused by the primary aberrations, but is corrected by the aberration correction amount 14 of the formula (2) Δ determined ', insufficient correction amount with respect to the electromagnetic waves of lambda <lambda ₀ Therefore, the wave front becomes a wave front 15 and tilts from the desired wave front 16. FIG. 6B is an explanatory diagram schematically showing a wavefront when the aberration is corrected for the secondary aberration. The wavefront 17 caused by the secondary aberration is corrected by the aberration correction amount 18, but the correction amount is insufficient for the electromagnetic wave of λ <λ ₀ , and the wavefront has a curvature like the wavefront 19, and is desired. The wavefront 20 cannot be obtained. By combining the above two types of aberrations, the reflected wave in the electromagnetic wave of λ <λ ₀ becomes a wavefront having a curvature and a tilt from the desired wavefront 21 as shown by the wavefront 22 in FIG. 6C.

As described above, there is a problem that the reflect array antenna becomes narrow band due to the fact that the reflection direction differs depending on the frequency and the plane wave is not generated. Therefore, by arranging the primary radiator 1 and the reflector 2 as shown in FIG. 1, the primary aberration among the two types of aberrations can be reduced to zero. That is, the position of the primary radiator 1 is located on the straight line of the reflection direction 4 of the electromagnetic wave passing through the center of the reflector as seen from the reflection direction 4 of the electromagnetic wave, with the mirror image 3 of the primary radiator facing the reflection direction 4 of the electromagnetic wave. To be determined. Thus, the wavefront 5 becomes equal to the desired wavefront 16 in FIGS. 5 and 6, since the correction amount delta ₁ to the primary aberration can be 0, the front regardless radial direction of the electromagnetic wave frequency It will turn in the direction, and broadband characteristics can be obtained.

  The primary radiator 1 is positioned such that the mirror image 3 of the primary radiator is positioned on a straight line in the reflection direction 4 of the electromagnetic wave, but the separation distance from the straight line passing through the center of the reflector 2 is within half a wavelength. If it is arranged so as to be positioned, a wide band characteristic can be obtained practically as a reflectarray antenna.

このような構成とすることで、１次の収差に対する補正量Δ_１を０とすることができるため、電磁波の放射方向が周波数にかかわらずに正面方向を向くことになり、広帯域な特性を得ることができる。なお、ｘ軸からの反射板面の傾きθは、０゜＜θ＜９０゜の範囲であるとする。 Moreover, you may determine the positional relationship of the primary radiator 1 and the reflecting plate 2 as follows.
As shown in FIG. 7, the center of the surface of the reflecting plate 2 when viewed from the reflection direction of the electromagnetic wave is the origin 23, the reflection direction of the electromagnetic wave is the positive direction of the z axis, and the z axis satisfies z> 0 from the origin. A line drawn from an arbitrary point to a point where a perpendicular line dropped on the reflecting plate surface and a plane satisfying z = 0 intersect is defined as a positive direction of the x axis. The coordinate of the phase center of the primary radiator 1 is (z _f , x _f ), the distance from the origin to the primary radiator 1 is r, the inclination of the reflector surface from the x axis is θ, and the wavelength of the design frequency is λ _0. When the arbitrary number satisfying 0 ≦ α <2π is α, the position of the primary radiator is determined in an arrangement satisfying the following expression (3). The ideal position of the primary radiator is (rcos 2θ, −rsin 2θ) indicated by a point 24 in FIG. 7, but the primary radiator is arranged so that the separation distance from the straight line connecting the origin and the point 24 is within a half wavelength. If so, a wide band characteristic can be obtained practically as a reflectarray antenna.

With such a configuration, since the correction amount delta ₁ to the primary aberration can be 0, the radiation direction of the electromagnetic wave is to face the front direction regardless of the frequency, to obtain a wide band characteristic be able to. The inclination θ of the reflecting plate surface from the x-axis is assumed to be in the range of 0 ° <θ <90 °.

On the other hand, the secondary aberration cannot be completely reduced to 0, but can be reduced by determining the reflection phase of each resonance element as follows.
FIG. 8 shows a reflection phase of a general resonant element. As is apparent from FIG. 8, the reflection phase of the resonant element tends to be delayed as the frequency increases.
On the other hand, the frequency characteristic of the desired reflection phase of each resonant element may be delayed or delayed as the frequency increases depending on the method of determining the reflection phase at the design frequency. Consider the case where the reference 25 of the reflection phase is set at the center of the aperture as shown in FIG. In order to make the wavefront 26 of the electromagnetic wave reflected by the reflector 2 assumed to have no phase correction to be a desired wavefront 27, all elements other than the center of the aperture must be corrected so as to advance the phase. The magnitude of the desired reflection phase of each resonant element at this time is expressed by the second term on the right side of Equation (1). FIG. 10 shows a desired reflection phase of the resonant element located at a certain distance from the center of the opening. Here, Δf indicates a frequency difference with reference to the design frequency f ₀ and is a positive value. It can be seen that as the frequency increases, the desired reflection phase must be corrected in a more advanced direction. That is, considering that the reflection phase of the resonance element is delayed as the frequency increases as described above, the difference between the desired reflection phase and the phase of the electromagnetic wave actually reflected from the resonance element increases as the frequency increases. I understand that

  Next, consider a case where the reference 25 of the reflection phase is set at a position different from the center of the aperture as shown in FIG. In order to make the wavefront 26 the desired wavefront 27, the desired reflection phase of the resonance element closer to the center of the opening than the reference resonance element when determining the reflection phase of each resonance element must be corrected so as to be delayed. I must. FIG. 12 shows a desired reflection phase of each resonance element. It can be seen that as the frequency increases, the desired reflection phase must be corrected in a more delayed manner. Therefore, the frequency characteristic of the phase of the electromagnetic wave actually reflected from the resonant element follows the desired frequency characteristic, and the influence of secondary aberration at a frequency different from the design frequency can be reduced.

  Thus, by taking the reference of the reflection phase at a position away from the center of the aperture and determining the reflection phase of each resonant element, the frequency characteristics of the reflectarray antenna can be improved. FIG. 13 shows the frequency characteristics of the amount of decrease in gain when the directivity gain at the design frequency is used as a reference. The solid line shows the characteristic when the reflection phase is determined with reference to the resonant element at a position away from the center of the aperture, and the broken line shows the characteristic of the conventional reflectarray antenna. As shown in the figure, it is understood that the reflection array antenna can be widened by determining the reflection phase with reference to the resonant element located away from the center of the aperture.

  As described above, according to the reflectarray antenna of the first embodiment, the flat reflector having a plurality of resonance elements and the reflector formed in a positional relationship to form the offset antenna are arranged and reflected. The mirror image on the surface of the plate faces the reflection direction of the electromagnetic wave, and is parallel to the reflection direction of the electromagnetic wave, and the distance from the straight line passing through the center of the reflection plate viewed from the reflection direction of the electromagnetic wave is within half a wavelength. Since the primary radiator that radiates electromagnetic waves in the center direction of the reflector is provided, the bandwidth of the reflect array antenna can be increased.

を満たす配置としたので、リフレクトアレーアンテナの広帯域化を図ることができる。 Further, according to the reflectarray antenna of the first embodiment, a flat reflector having a plurality of resonant elements, and a primary radiator disposed to face the reflector in a positional relationship to form an offset antenna. The primary radiator and the reflector are arranged such that the center of the surface of the reflector when viewed from the reflection direction of the electromagnetic wave is the origin, the reflection direction of the electromagnetic wave is the positive direction of the z axis, and z> 0 from the origin. A line drawn from an arbitrary point on the z-axis to a point where a perpendicular line dropped on the surface of the reflector and a plane satisfying z = 0 intersect is defined as the positive direction of the x-axis, and the coordinates of the primary radiator are (z _f , x _f), the distance from the origin to the primary radiator r, the inclination of the surface of the reflector from the x-axis theta, the wavelength of the design frequency and lambda _0, any number and alpha that satisfies 0 ≦ α <2π When the following formula

Since the arrangement satisfies the above, it is possible to increase the bandwidth of the reflect array antenna.

  In addition, according to the reflectarray antenna of the first embodiment, since the inclination θ of the surface of the reflector satisfies 0 ° <θ <90 °, the formula (3) can be satisfied, and the reflectarray antenna Can be widened.

  Further, according to the reflectarray antenna of the first embodiment, the reference point for determining the reflection phase of the plurality of resonant elements is set at a position different from the opening center of the reflector, and therefore a frequency different from the design frequency. 2 can be reduced, and the bandwidth of the reflectarray antenna can be increased.

  In the present invention, any constituent element of the embodiment can be modified or any constituent element of the embodiment can be omitted within the scope of the invention.

  1 primary radiator, 2 reflector, 3 mirror image of primary radiator, 4 electromagnetic wave reflection direction, 5 wavefront, 23 origin, 24 phase center of primary radiator, 25 reference of reflection phase, 26 assumed no phase correction The wavefront of the electromagnetic wave reflected by the reflector, 27 the desired wavefront.

Claims (3)

A flat reflector having a plurality of resonant elements;
An offset antenna is disposed so as to be opposed to the reflecting plate, and a mirror image on the surface of the reflecting plate faces the reflection direction of the electromagnetic wave and is parallel to the reflection direction of the electromagnetic wave and viewed from the reflection direction of the electromagnetic wave. And a primary radiator that radiates electromagnetic waves in the direction of the center of the reflector, arranged so as to be located on a straight line passing through the center of the reflector or within a half-wave distance from the straight line ,
A reflectarray antenna in which a reference point for determining a reflection phase of the plurality of resonance elements is set at a position different from an opening center of the reflection plate . A flat reflector having a plurality of resonant elements;
A primary radiator disposed facing the reflector in a positional relationship to form an offset antenna;
The primary radiator and the reflector are arranged such that the center of the surface of the reflector when viewed from the reflection direction of the electromagnetic wave is the origin, the reflection direction of the electromagnetic wave is the positive direction of the z axis, and z> 0 from the origin. A line drawn from an arbitrary point on the z-axis satisfying a perpendicular line drawn on the surface of the reflector to a point where a plane satisfying z = 0 intersects is defined as the positive direction of the x-axis, and the coordinates of the primary radiator are ( zf, xf), r is the distance from the origin to the primary radiator, θ is the inclination of the surface of the reflector from the x-axis, θ is the wavelength of the design frequency, and any number satisfying 0 ≦ α <2π. where α is

Arrangement der to meet the is,
A reflectarray antenna in which a reference point for determining a reflection phase of the plurality of resonance elements is set at a position different from an opening center of the reflection plate .   3. The reflectarray antenna according to claim 2, wherein the inclination [theta] of the surface of the reflector satisfies 0 [deg.] <[Theta] <90 [deg.].

Images