KR102127201B1 - Nonlinear metasurface for compensating scan loss at designed angle - Google Patents

Abstract

A non-linear meta surface according to an embodiment of the present invention is composed of a plurality of unit cells arranged in two dimensions, and some of the plurality of unit cells are configured to reduce gain loss generated at a specific angle by beam steering of the array antenna. It is characterized by being arranged in a non-linear structure to compensate. According to an embodiment, by arranging the unit cells non-linearly at the edge portion of the meta surface where loss due to beam steering of the array antenna is relatively large, beam steering loss at a specific angle can be compensated to improve the overall antenna gain. have.

Description

Non-linear metasurface to compensate for beam steering loss at a specific angle{NONLINEAR METASURFACE FOR COMPENSATING SCAN LOSS AT DESIGNED ANGLE}

The present invention relates to a meta-surface, and more particularly, to a technique for preventing deterioration of antenna gain occurring at a specific angle by non-linearly arranging some of the plurality of unit cells constituting the meta-surface. It is about.

An array antenna is an antenna configured to form a main beam by arranging a plurality of antenna elements to adjust the phase of the excitation current of each element and make the antenna the same phase as a specific direction. When the antenna elements are configured in an array as described above, it is possible to adjust the maximum radiation in a specific direction or the minimum radiation in an unnecessary direction. The maximum gain that can be obtained by the antenna is determined by the performance and arrangement of the device, and the technology that can improve the gain beyond this is the meta surface.

The meta-surface generally means a planar structure made to perform an optical function using a pattern of a two-dimensional thin film. The meta surface used in the antenna technology field is composed of a plurality of unit cells arranged in two dimensions, and each unit cell is composed of a metal layer and a dielectric layer of 3 to 5 layers. These unit cells act as a resonant circuit and serve as a spatial filter capable of passing a desired phase of a beam emitted from an antenna. The square wave passing through the meta surface is transformed into a plane wave by compensating the phase at each point, and as a result, the gain can be improved.

1A is a graph showing the gain of an antenna according to the presence or absence of a meta surface in the prior art. Referring to FIG. 1A, it can be seen that the gain when the meta surface is provided on the antenna is improved by about 3.8 dB compared to the gain when the meta surface is not provided based on when the phase shift is 0 degrees.

However, in the case of an array antenna with meta-surfaces, when the beam is steered, a phenomenon in which a gain deteriorates due to interference of a beam at a specific angle occurs. 1B is a simulation/measurement graph showing the gain of an antenna having a meta surface of the prior art according to phases (0 Hz, 45 Hz, 90 Hz, and 135 Hz). Referring to the graph (P = 90 　) in which the phase offset (Phase Offset) is 90 degrees in FIG. 1B, it can be seen that the antenna gain is relatively largely reduced at the point where the gain is maximized (the point where the steering angle Theta is about 26deg). .

In the array antenna, when the beam is steered, the gain deteriorates at a specific angle. Since the beam steer is one of the very important parts in the millimeter wave, a technique capable of solving the above problem is required.

Republic of Korea Patent Publication No. 10-2018-0030213 Republic of Korea Registered Patent Publication No. 10-1202339

T. Hongnara, S. Chaimool, P. Akkaraekthalin and Y. Zhao, "Design of Compact Beam-Steering Antennas Using a Metasurface Formed by Uniform Square Rings," in IEEE Access, vol. 6, pp. 9420-9429, 2018 J. Oh, "Millimeter-Wave Thin Lens Employing Mixed-Order Elliptic Filter Arrays," in IEEE Transactions on Antennas and Propagation, vol. 64, no. 7, pp. 3222-3227, July 2016.

As described above, the conventional millimeter wave linear meta-surface has a problem in that a sufficient gain cannot be obtained during beam steering due to a problem in that the gain is significantly lowered at a specific angle.

The present invention has been devised to solve this problem, and a meta-surface of a non-linear structure that is different from a meta-surface of a conventional linear structure to compensate for gain loss at a specific angle that occurs when beam steering of the array antenna is compensated. It aims to provide.

A non-linear meta surface according to an embodiment of the present invention is composed of a plurality of unit cells arranged in two dimensions, and some of the plurality of unit cells are configured to reduce gain loss generated at a specific angle by beam steering of the array antenna. It is arranged in a non-linear structure to compensate.

In one embodiment, the non-linear structure may be a structure in which the unit cells are arranged in a sinusoidal form that repeats with a predetermined amplitude and period.

In one embodiment, a dispersion relation on the surface is defined based on the surface impedance and modulation rate of the meta surface, and a predetermined amplitude and period in the sinusoidal wave may be determined based on the dispersion relation.

In one embodiment, the unit cells may be arranged in a non-linear structure at the edge portion of the meta surface, and the unit cells may be arranged in a linear structure except for the edge portion.

In one embodiment, each unit cell includes a metal layer and an insulating layer, and operates as a low-pass filter or band-pass filter for modulating the phase of radio waves output from the antenna.

A non-linear meta surface according to an embodiment of the present invention, and an array antenna arranged at a predetermined distance from the non-linear meta surface; And a receiving antenna for receiving radio waves output from the array antenna and passing through the non-linear meta-surface. An antenna transmission/reception system using a non-linear meta-surface may be provided.

The meta surface according to an embodiment of the present invention is characterized in that unit cells in an edge portion in which gain loss due to beam steering of the array antenna is relatively large are arranged non-linearly. According to this, it is possible to improve the overall antenna gain by compensating for beam steering loss at a specific angle. The non-linear meta-surface of the structure proposed in the present invention can be widely used in base stations, repeater antennas and radar fields where beam steering is important.

1A is a graph showing the gain of an antenna according to the presence or absence of a meta surface in the prior art.
1B is a simulation/measurement graph showing the gain of an antenna having a meta surface of the prior art according to a phase shift.
2 illustrates an arrangement structure of an array antenna and a meta surface according to an embodiment.
3 shows various structures of a unit cell constituting a meta surface according to an embodiment.
4A and 4B are graphs showing insertion loss and phase change according to the size of the grid and the metal patch constituting the unit cell of FIG. 3, respectively.
5 is a diagram illustrating the structure of an array antenna according to an embodiment.
6A and 6B show a linear metasurface according to the prior art.
7A and 7B show a nonlinear metasurface according to one embodiment.
8 illustrates a configuration of an antenna transmission/reception system having a nonlinear meta surface according to an embodiment.

Hereinafter, embodiments will be described in detail with reference to the accompanying drawings and contents described in the accompanying drawings, but the scope to be claimed is not limited or limited by the embodiments.

The terminology used in the present specification has been selected as a general terminology that is currently widely used while considering functions, but this may be changed according to intentions or customs of technicians in the field or the appearance of new technologies. In addition, in certain cases, some terms are arbitrarily selected by the applicant, and in this case, the meaning will be described in the description of the corresponding specification. Therefore, the terms used in the present specification are intended to clarify that the terms should be interpreted based on the actual meaning of the terms and the contents of the present specification rather than simply the names of the terms.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

2 illustrates an arrangement structure of an array antenna and a meta surface according to an embodiment. As shown in FIG. 2, the meta surface 30 is disposed at an upper end spaced a certain distance from the array antenna 10. An array antenna is an antenna configured to form a main beam by arranging a plurality of antenna elements to adjust the phase of the excitation current of each element and make the antenna the same phase as a specific direction, and thus the antenna elements are arrayed. If configured, it can be adjusted so that the maximum radiation in any particular direction, or the minimum radiation in the unnecessary direction.

A meta-surface is a planar structure made to perform an optical function by using a pattern of a two-dimensional thin film, and passes through the meta-surface using phase shifts of a plurality of unit cells arranged in two dimensions. The square wave can be converted to a plane wave, and as a result, the antenna gain can be improved. As described with reference to FIG. 1A, it can be seen that the gain when the meta surface is provided on the antenna is improved by about 3.8 dB, compared to the gain when the meta surface is not provided, based on when the phase shift is 0 degrees.

However, as described above with reference to FIG. 1B, at a certain angle, for example, when the phase shift is 90 degrees (PO=90　), the antenna gain is relatively large at the point where the gain is maximized (the point where the actual steering angle Theta is about 26deg). It can be seen that it decreases. As described above, when the beam is steered in the array antenna, a phenomenon in which the gain is deteriorated at a specific angle may occur. Since the beam steer is one of the very important parts in the millimeter wave, a technique capable of solving the above problem is required.

In this specification, as an embodiment for solving the problems of the prior art, a meta-surface of a nonlinear structure capable of compensating for a loss of gain at a specific angle that occurs during beam steering of an array antenna is proposed.

3 shows various structures of a unit cell constituting a meta surface according to an embodiment. As illustrated in FIG. 3, each unit cell 21 may be formed of a multi-layered structure in which a metal layer and an insulating layer are stacked, and is composed of a metal patch and an insulating layer as shown in (a) and (b) of FIG. 3. It can be operated as a low-pass filter, or configured to include a metal patch, an insulating layer and a metal grid as shown in (c) and (d) of FIG. 3 to operate as a band-pass filter.

4A and 4B are graphs respectively showing insertion loss and phase according to the size of the grid and the metal patch constituting the unit cell of FIG. 3. The insertion loss of the unit cell is related to the loss tangent of the dielectric, and an appropriate phase shift range within 1.5 dB of insertion loss can be realized by appropriately using a low-pass filter and an efficient band-pass filter.

5 is a diagram illustrating the structure of an array antenna according to an embodiment. As shown in FIG. 5, the array antenna 10 has a form in which a plurality of antenna elements 11 are arranged in two dimensions, and adjusts the phase of each antenna element 11 to steer the direction of the output beam.

6A and 6B show a linear meta surface according to the prior art. According to the prior art, the unit cells constituting the meta surface are arranged in a linear structure to compensate for the beam incident from the antenna to have a constant phase value at each point. That is, a plurality of unit cells are arranged at regular intervals up, down, left, and right as shown in FIG. 6B. According to such a structure, a phenomenon in which antenna gain is deteriorated at a specific angle during beam steering occurs.

7A and 7B show a non-linear meta surface according to an embodiment of the present invention. As shown, the unit cells are arranged in a non-linear structure at the corner portions A, B, C, and D of the metasurface 30, and the unit cells may be arranged in a linear structure except for the corner portions. .

Here, the non-linear structure may be, for example, a structure in which unit cells are arranged in a sinusoidal form that is repeated with a constant amplitude and period. At this time, the amplitude and period of the sinusoidal wave can be determined according to the dispersion relation at the surface of the meta surface, and the dispersion relation can be calculated based on the surface impedance and the modulation rate of the meta surface.

In general, surface impedance in a SMRS (Sinusoidally-Modulated Reactance Surface) structure can be calculated by the following equation.

은 표면 임피던스의 평균값이고, M은 변조율(modulation factor), a는 사인(sine) 곡선의 주기이다. 설계자는

와 a를 조절하여 특정 방향에 대한 안테나 이득을 향상시킬 수 있다. 안테나로부터 출력되는 웨이브의 파수

와 자유공간의 파수

를 알면 표면에서의 분산관계를 계산할 수 있고, 이에 따라 SMRS 구조의 메타표면을 설계할 수 있다. 표면에서 분산관계는 다음의 식에 따라 표현될 수 있다.here,

Is the average value of the surface impedance, M is the modulation factor, and a is the period of the sine curve. The designer

By adjusting and a, antenna gain for a specific direction can be improved. The number of waves of the wave output from the antenna

And free wave number

By knowing, the dispersion relationship on the surface can be calculated, and accordingly, the metasurface of the SMRS structure can be designed. The dispersion relationship on the surface can be expressed according to the following equation.

From Equation 2, a period of a sinusoidal structure suitable for a specific angle in which gain is deteriorated when steering a beam on a conventional meta surface can be calculated and applied to the arrangement of unit cells. When the unit cells are non-linearly arranged at the edge portion of the meta surface, the overall antenna gain can be improved by compensating for the gain loss occurring at a specific angle.

In the above, a non-linear structure of a sinusoidal shape having a constant period has been described, but the arrangement structure of the unit cells is not limited thereto, and may have an aperiodic non-linear structure that has been experimentally proven to improve gain at a specific angle.

8A and 8B show a configuration of an antenna transmission/reception system having a linear meta surface according to the prior art and a non-linear meta surface according to the embodiment, respectively, in order to investigate effects according to an embodiment of the present invention. As shown, the system includes an array antenna 10, meta-surfaces 20 and 30 disposed at a certain distance from the transmitting antenna, and reception for receiving radio waves output from the array antenna and passing through the non-linear meta-surface. An antenna 40, a vector network analyzer 50 for analyzing antenna gain due to the metasurface 30.

Hereinafter, it is examined whether the antenna gain at a specific angle is improved by using the meta-surface 30 of the nonlinear structure through the experimental example.

In this experimental example, FR4 insulating layer substrates having a dielectric constant of 3.8 and a loss tangent of 0.03 were used for each unit cell constituting the meta surfaces 20 and 30. The performance of the array antenna used in the experimental example of the present invention, that is, the gain due to the phase shift when the meta surface is not applied is as follows.

Phase shift (deg) Gain (dB) Steering angle (deg) 0 19.5 0 -45 19.3 14 -90 18.5 28 -135 17.4 45

In FIGS. 8A and 8B, the array antenna 10 and the reception antenna 40 are separated at a distance of 3 m, and each meta surface 20 and 30 is disposed at a distance of 3 cm from the array antenna 10. The result values for the linear meta-surface 20 according to the prior art are shown in Table 2, and the result values for the non-linear meta-surface 30 according to the embodiment are shown in Table 3.

Phase shift (deg) Gain (dB) Steering angle (deg) 0 23.4 0 -45 23.3 13.5 -90 20.1 26 -135 20.2 45

Phase shift (deg) Gain (dB) Steering angle (deg) Simu Measure Simu Measure 0 23.2 23.4 0 0 -45 23.2 22.6 13.5 13 -90 21.8 21.3 27 25 -135 20.2 19.5 45 45

Referring to Tables 1 to 3, when applying the meta-surface according to the prior art, it is possible to obtain an improvement in antenna gain for all phases, but for a phase shift of -90 degrees, it can be seen that the gain increase is low compared to other angles. have. Specifically, referring to Table 2, it can be seen that for phase shifts of 0 degrees, -45 degrees, and -135 degrees, the gain increased by at least 2 dB to a maximum of 3.9 dB, while it increased by 1.6 dB for -90 degrees.

Referring to Table 3, when applying a non-linear meta surface according to an embodiment, the gain of the antenna for a phase shift of -90 degrees is a total of 3.3 dB, which is improved by 1.7 dB compared to a linear meta surface of the prior art to a specific angle It can be seen that the beam steering loss for is greatly reduced.

According to the embodiments described above, in the meta surface for improving the gain of the array antenna, by disposing unit cells non-linearly at the edge portion of the meta surface where loss due to beam steering is relatively large, at a specific angle It is possible to improve the gain of the overall antenna by compensating for beam steering loss.

The non-linear meta-surface of the structure proposed in the present invention can be widely used in the field of base stations, repeaters, antennas, and radars where beam steering is important, and can be easily applied to a vehicle radar field due to its easy miniaturization.

Although described above with reference to embodiments, those skilled in the art can variously modify and change the present invention without departing from the spirit and scope of the present invention as set forth in the claims below. You will understand.

Claims (6)

A non-linear meta surface for compensating beam steering loss of an array antenna,
The meta surface is composed of a plurality of unit cells arranged in two dimensions,
Some of the plurality of unit cells, the sinusoidal (sinusoidal) of the unit cells are repeated with a predetermined amplitude and period, in order to compensate for the gain loss occurring at a specific angle by the beam steering of the array antenna non-linear sinusoidal (sinusoidal) form Non-linear meta-surface characterized by being arranged in a structure.
delete According to claim 1,
The dispersion relation on the surface is defined based on the surface impedance and modulation rate of the meta surface,
In the sinusoidal wave, a predetermined amplitude and period are determined based on the dispersion relation.
According to claim 1,
In the edge portion of the meta surface, the unit cells are arranged in a non-linear structure,
Non-linear metasurface, characterized in that the unit cells are arranged in a linear structure except for the edge portion.
According to claim 1,
Each unit cell includes a metal layer and an insulating layer, and is characterized by operating as a low-pass filter or a band-pass filter for modulating the phase of the radio wave output from the antenna.
The non-linear meta surface according to any one of claims 1 and 3 to 5;
An array antenna disposed at a predetermined distance from the non-linear meta surface; And
And a receiving antenna for receiving radio waves output from the array antenna and passing through the non-linear meta-surface.

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