Beamformer

Abstract

The beamformer (10) is a beamformer that directs an incident electromagnetic wave and includes: a first conductive metamaterial cell (11A) configured to shift the phase of a first portion of the electromagnetic wave; a second conductive metamaterial cell (11B) arranged adjacent to the first conductive metamaterial cell and having a shape different from that of the first conductive metamaterial cell, and configured to shift the phase of a second portion of the electromagnetic wave; and a conductor (13) including at least a portion arranged between the first conductive metamaterial cell and the second conductive metamaterial cell. With the above configuration, capacitance fluctuations between adjacent metamaterial cells having different shapes (including dimensions) are reduced, thereby reducing side lobes.

Description

[Technical Field]

[0001] The present invention relates to a beamformer. [Background technology]

[0002] Beamforming achieves a clear radiation beam in a desired direction by aligning the phases of electromagnetic waves (signals) input from different parts of the array. As such beamforming, beamforming based on metamaterial structures has been studied (Non-Patent Document 1).

[0003] Metamaterials are artificial materials that derive their properties from subwavelength cells organized to mimic the atomic structure of natural materials. Metamaterials can manipulate electromagnetic waves by controlling various properties such as refractive index, permeability, and permittivity in desired frequency ranges. The unique properties of metamaterials result from the shape (including dimensions) and arrangement of the periodic metamaterials, as well as from the properties of the materials that comprise these structures. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] Iyemeh ​​Uchendu and James R. Kelly, "Survey of Beam Steering Techniques Available for Millimeter Wave Applications," Progress In Electromagnetics Research B, Vol. 68, 35-54, 2016. doi:10.2528 / PIERB16030703 Summary of the Invention [Problem to be solved by the invention]

[0005] Metamaterial-based beamforming is one of the leading options for controlling electromagnetic beams, but its design still poses many challenges, especially as the frequency of electromagnetic waves increases.

[0006] Typically, metamaterial cells exhibiting different phase values ​​are individually designed and then combined to form a beamformer. To achieve phase shift using metamaterial cells, the shape and size of the metamaterial cells are typically adjusted to exhibit the desired phase value while maintaining low transmission loss. For this reason, in beamformers, metamaterial cells with different phases are grouped together and arranged to meet the phase step change requirements. Because metamaterial cells are individually designed as an infinite array of identical cells, the arrangement of large and small cells can disrupt the capacitance between adjacent cells, resulting in phase shifts within the beamformer and the generation of sidelobes that differ from those obtained by simulation using separate cells.

[0007] The present invention has been made to reduce the capacitance disturbance between adjacent metamaterial cells with different shapes, thereby reducing side lobes. [Means for solving the problem]

[0008] In order to solve the above problem, the beamformer of the present invention is a beamformer that directs incident electromagnetic waves, and comprises: a first conductive metamaterial cell configured to shift the phase of a first portion of the electromagnetic wave; a second conductive metamaterial cell arranged adjacent to the first conductive metamaterial cell, having a shape different from that of the first conductive metamaterial cell, and configured to shift the phase of a second portion of the electromagnetic wave; and a conductor including at least a portion arranged between the first conductive metamaterial cell and the second conductive metamaterial cell.

[0009] According to the above configuration, the capacitance fluctuation between adjacent metamaterial cells having different shapes is reduced, thereby reducing side lobes. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic diagram of a beamformer according to an embodiment. [Figure 2] FIG. 2 is a schematic diagram of the AA cross section of FIG. [Figure 3] FIG. 3 shows variations in the shape of the metamaterial cell. [Figure 4] FIG. 4 is a schematic diagram showing the state of transmission of electromagnetic waves. [Figure 5] FIG. 5 is a schematic diagram of a cross section of a reflective beamformer. [Figure 6] FIG. 6 is a plan view for explaining various dimensional parameters of the metamaterial cell. [Figure 7] Figure 7 shows an equivalent circuit superimposed on a plan view of a metamaterial cell. [Figure 8] FIG. 8 is a diagram in which an equivalent circuit is superimposed on a plan view of a metamaterial cell. [Figure 9] FIG. 9 is a diagram in which an equivalent circuit is superimposed on a plan view of a metamaterial cell. [Figure 10] FIG. 10 is a schematic perspective view showing the metamaterial cell and the conductor used in the simulation. [Figure 11] Figure 11 is a graph of the total phase change when the size (radius R) of the metamaterial cell is changed. [Figure 12] FIG. 12 is a diagram showing the results of a simulation when electromagnetic waves are input to a beamformer that does not have a conductor. [Figure 13] FIG. 13 is a diagram showing the results of a simulation when an electromagnetic wave is input to a beamformer provided with a conductor. [Figure 14] FIG. 14 is a diagram in which an equivalent circuit is superimposed on a plan view of a metamaterial cell. DETAILED DESCRIPTION OF THE INVENTION

[0011] 1 and 2, a beamformer 10 according to this embodiment includes a plurality of conductive metamaterial cells 11A to 11E, a filled dielectric 12, and a conductor 13. The beamformer 10 is a transmission type that transmits incident electromagnetic waves. The beamformer 10 outputs the transmitted electromagnetic waves as electromagnetic waves with directionality in a desired direction.

[0012] Each of the plurality of conductive metamaterial cells 11A to 11E is a subwavelength metamaterial cell. The plurality of conductive metamaterial cells 11A to 11E are periodically arranged in an array and are designed to resonate at a millimeter wave band frequency (30 to 400 GHz). Hereinafter, the conductive metamaterial cells 11A to 11E are also simply referred to as cells 11A to 11E, respectively. The cells 11A to 11E are also collectively referred to as cells 11.

[0013] The cell 11 is made of a conductive material such as a metal, a highly conductive polymer, or a conductive oxide, or a highly conductive carbon-based material such as a carbon nanotube or graphene.

[0014] As shown in FIG. 1, the cells 11 are periodically arranged in an array, more specifically, in a matrix. The cells 11 as a whole form a passive array. Cells 11 of different shapes are periodically arranged in the X direction. For example, cell 11B is arranged next to cell 11A in the X direction, and cell 11C is arranged next to cell 11B. Cells 11 of the same shape are arranged in the Y direction. For example, cell 11A is arranged in a row along the Y direction. Here, two rows of each of the cells 11A to 11E are arranged. A plurality of cells 11 arranged in a row in the Y direction form a cell group.

[0015] 2, if a group of cells 11 arranged in a matrix, that is, in a plane, is considered to be one layer, the beamformer 10 has five layers. The number of layers may be one or more.

[0016] As described above, the shape of the cell 11 may be formed into a shape that resonates at millimeter-wave band frequencies (30 to 500 GHz). Examples of the shape of the cell 11 are shown in Figure 3. (A) is an electric resonator, (B) is a square Jerusalem cross, (C) is a round Jerusalem cross, (D) is a double split ring resonator, (E) is a square double loop, and (F) is a cross resonator. Here, the round Jerusalem cross of Figure 3(C) is used.

[0017] 1 and 2, cell 11A is formed to shift the phase of an incident electromagnetic wave incident on the region of beamformer 10 in which cell 11A is provided by a shift amount A. As will be described later, cell 11A shifts the phase in cooperation with a portion (frame 13A) of conductor 13 that surrounds cell 11A. Similarly, cells 11B to 11E are formed in shapes that shift the phase of an incident electromagnetic wave by shift amounts B to E, respectively. The shift amounts A to E are different from one another. Therefore, cells 11A to 11E have different shapes from one another, particularly different dimensions. The electromagnetic waves phase-shifted by each of cells 11A to 11E are combined and output from beamformer 10 as an output electromagnetic wave. Beamformer 10 is a passive type.

[0018] The filler dielectric 12 supports all of the cells 11 and the conductors 13. The filler dielectric 12 constitutes the majority of the volume of the beamformer 10. The filler dielectric 12 can be made of any type of non-conductive dielectric material, such as polyimide (PI), benzocyclobutene (BCB), parylene, polyethylene (PE), polytetrafluoroethylene (PTFE), etc. The filler dielectric 12 fills the gaps between the cells 11, the gaps between the cells 11 and the conductors 13, and the gaps within the cells 11.

[0019] The conductors 13 are provided on each layer where the array-shaped cells 11 are provided. That is, five conductors 13 are configured here. The conductors 13 are configured in a mesh shape, surrounding each cell 11 one by one. The function of the conductors will be described later.

[0020] In this embodiment, as shown in Fig. 4, a radiating element 101, for example an antenna, radiates millimeter waves of a certain frequency, which become incident electromagnetic waves on a beamformer 10. The electromagnetic waves incident on the beamformer 10 pass through the beamformer 10. The beamformer 10 gives directionality to the transmitted electromagnetic waves in a desired direction and then emits them. The emitted electromagnetic waves are received by a mobile terminal or the like of a user 103 via a reflective beamformer 102, in this case. As a result, electromagnetic waves that do not reach the user 103 directly due to obstacles 104, such as buildings, are supplied to the user 103.

[0021] 1 and 2 of this embodiment may be applied to a reflective beamformer 102. In this case, as shown in Fig. 5, the beamformer 102 includes a conductive reflective layer 102A in addition to the above-mentioned elements 11 to 13. The conductive reflective layer 102A is provided on the surface of the dielectric 12 opposite to the electromagnetic wave incident surface.

[0022] The amount of phase shift can be calculated using the following formula (1) for horizontal (azimuth) steering: For vertical (elevation) steering, it can be calculated using the following formula (2): where A is the azimuth angle, E is the elevation angle, p is the period or distance between cells, and λ is the wavelength of the incident wave (1 mm at 300 GHz).

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[0023] The selection criteria for the cells 11 were that the cell bodies be able to couple to an external electric field (E) generated by a radiative element such as an antenna, and induce current in the conductive structure of the metamaterial cells. In this embodiment, for use in the millimeter wave band, the cells, shape (including size), and period are optimized to achieve the desired frequency band. To achieve resonance excitation, the size of the cells 11 is typically λ / 2 or less of the operating frequency. In this embodiment, a conductor 11 is added to the cell 11 design to separate the coupling capacitance between adjacent cells 11 and reduce the effect on resonance generation in the cells 11.

[0024] The resonance frequency of the cell 11 can be calculated from the following formula (3).

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[0025] The equivalent inductance L is expressed as follows:

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[0026] The equivalent capacitance Ceq in this embodiment is made up of the gap capacitance Cg and the coupling capacitance Cc between adjacent cells 11, and can generally be expressed by the following equations (5) to (7).

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[0027] A schematic diagram of the cell 11 with the addition of the conductor 13 and superimposed geometric parameters is shown in Figure 6. The resonant cell RC in Figure 6 consists of the cell 11 and a frame 13A of the conductor 13 that surrounds the cell 11. The distance between cells (cell period) is p x , p in the Y direction yThe dimensions of cell 11 are a and b in the X and y directions, respectively. The width of the conductor portion of cell 11 is W, the size of the gap is g, and the width of conductor 13 is W2. Because conductor 13 is disposed between cells 11, a line of symmetry exists in each direction at the center of conductor 13. This means that an area of ​​conductor 13 with width W2 / 2, i.e., one frame 13A, contributes to one resonant cell RC, and an area with another width W2 / 2, i.e., another frame 13A, contributes to a different adjacent resonant cell RC. The shape of cell 11 in Figure 6 is different from that of cell 11 in Figure 1, but the concept is the same in both cases.

[0028] Figure 7 is a circuit diagram showing the superposition of the equivalent electrical circuits of two adjacent cells 11 without the conductor 13. The gap capacitance Cg and inter-cell coupling capacitance Cc of the designed cell 11 are shown. In a typical cell 11 design process, simulations using infinite boundaries are performed, and results such as the peak resonant frequency and the amount of phase shift at a certain operating frequency are obtained from the coupling effect and capacitance Cc between adjacent cells. The same phenomenon occurs when designing and simulating cells 11 of various sizes to obtain phase shifts. However, if the distance between the cells 11 differs, the capacitance Cc also changes. Therefore, as mentioned above, when cells 11 of different sizes (shapes) are used, the coupling capacitance between the cells 11 will be disturbed.

[0029] To alleviate this problem, when designing the shape of each cell 11, a conductor 13 is introduced to divide the coupling capacitance Cc between adjacent cells into two or more separate capacitances, as shown in Figure 8. When identically shaped cells 11 are surrounded by a mesh-shaped conductor frame 13A, the conductor 13 divides the total capacitance Cc between the two cells 11 into two separate capacitances: one cell-frame capacitance (C1) and the other cell-frame capacitance (C2). When the cells 11 are the same size, C1 = C2. When cells of different sizes are combined, C1 ≠ C2.

[0030] As shown in Figure 9, combining cells 11 of different shapes (sizes) generally results in a change in capacitance, C1 ≠ C2. In Figure 9, by separating individual cells 11 with conductors 13, changes in the shape of a cell 11 have only a negligible effect on neighboring cells 11, and the effect of size changes can be contained within the resonant cell RC. In Figures 8 and 9, the coupling capacitance Cc still exists, but because the conductors 13 introduce an isolation effect between cells 11, its effect is greatly reduced and the coupling capacitance Cc can be omitted.

[0031] FIG. 10 is a schematic diagram of a simulation in which the cell 11 used in this embodiment is tuned to a frequency band of 300 GHz. In this embodiment, a circular cell 11 is used. The material of the dielectric 12 used in the simulation is benzocyclobutene (BCB), with a dielectric constant ε r1 = 2.47, μ = 1, and loss tangent tanδ = 0.007 are typical values ​​for BCB material in the millimeter-wave band. Here, a total thickness of 0.72 mm was used. Cell 11 and conductor 13 were constructed of gold. In Figure 10, cell 11 was placed horizontally with conductor 13, perpendicular to the incident electromagnetic wave, and electromagnetic waves were emitted from port P1 and received at port P2. Cell 11 was oriented along the X-axis so that the electric field (E) component coupled to cell 11 and induced resonance. The BCB material properties are based on commercially available data and measurements in the millimeter-wave band.

[0032] In this simulation, a time-domain solver was used with periodic boundary conditions and normal incidence of the electric component of the electromagnetic wave along the X-axis. Assuming that the period of the cells 11 is constant, geometric parameters such as the gap size, cell size, and width of the cells 11 were optimized, and a high transmission coefficient of S21 < -3 dB or better was achieved over a wide range of cell sizes and phase shifts.

[0033] The circular Jerusalem cross cell 11 was fabricated by magnetron sputtering, electron beam evaporation, or other methods using a 500 μm-thick Au thin film, which can be fabricated directly on BCB. The parameters of the constant cell 11 are a gap size g = 25 μm and a metamaterial line width W = 20 μm. For the metamaterial cell without an additional conductive frame, the cell period size is Px = Py = 380 μm, the distance between each metamaterial layer is 170 μm, and the additional upper and lower dielectric layers are each 20 μm thick (total thickness 0.72 mm). For the metamaterial cell with a conductive frame, the cell period is Px = Py = 400 μm, the distance between each metamaterial layer is 160 μm, and the additional upper and lower dielectric layers are each 50 μm thick (total thickness 0.74 mm). The width of the conductor 13 is W2 = 4 μm.

[0034] The above parameters were obtained by changing the metamaterial cell size (radius R in this embodiment) and performing metamaterial cell optimization to obtain a high transmission coefficient S21 of -3 dB or more at 300 GHz. Note that the high transmission coefficient of -3 dB or more was maintained over a 360-degree phase variation region.

[0035] Figure 11 shows the total phase change when the size (radius R) of the cell 11 is changed, with and without the addition of a conductor 13. Individually designing and simulating cells 11 with different radii R—in this example, between 0.11 and 0.18 mm—results in different phase shift values. Metamaterial cells are typically optimized to exhibit a 360-degree (2π) phase shift in the high transmittance region of -3 dB or greater. Cells 11 with different sizes and phase values ​​are then combined in the beamformer 10 to achieve the desired beam steering angle for the incident electromagnetic wave.

[0036] In Figure 1, five types of cells 11A-11E were used with a phase difference Δφ between adjacent cells of 72 degrees to obtain a steering angle of 32 degrees for the designed periodic value. In this embodiment, the incident electromagnetic wave is steered in the XY plane. Therefore, the resonant metamaterial cells RC are arranged so that the gradual phase variation in the X direction is equal to Δφ. The incident wave is transmitted with a phase change, which steers the composite output wave. Since beamforming is only in a single plane, the elevation angle E = 0 and the azimuth angle A = θ, where θ is the steering angle of the composite output wave.

[0037] Figures 12 and 13 show simulations of signal (electromagnetic wave) propagation through the beamformer 10 without and with conductors 13, respectively. These simulations use a rectangular beamformer 10 with a multilayer cell element size of 11 × 5 to verify the designed metamaterial cell with conductors 13. Incident electromagnetic waves from a millimeter-wave radiation source are irradiated onto and transmitted through the beamformer 10. Due to the different phase shifts caused by cells 11 with different radii, the combined electromagnetic wave is steered at an angle θ. In Figure 12 (without conductors 13), two large side lobes (SL) are generated in addition to the main combined output wave lobe ML. In Figure 13 (with conductors 13), compared to Figure 12, it can be seen that the main combined output wave ML, i.e., the directional output electromagnetic wave, is wider and the side lobes SL are significantly reduced. Therefore, the passive beamformer 10 including the conductors 13 reduces the capacitance disturbance between cells 11 of different shapes, thereby reducing side lobes and increasing the directivity of the beamforming beam (emitted electromagnetic wave).

[0038] As shown in Figure 14, the mesh-shaped conductor 13 can be replaced with a linear conductor 19. Some applications, primarily reflective beamformers, require less millimeter-wave beamforming and only one direction of output combined waves is required. Therefore, to simplify the structure and provide design flexibility, some of the conductors 13 can be omitted. As shown in Figure 14, the conductors 19 extend along a direction perpendicular to the beam steering direction (SD). The conductors 19 may be placed between cells 11 of different shapes (especially sizes). The conductors 19 preferably extend along the direction in which the cells 11 of the same shape are aligned. For unidirectional beamforming, changing the size of each cell to achieve different phase values ​​results in only one-way changes in neighboring cells. Because the unidirectional conductors in Figure 14 are unnecessary, additional functions, such as linked cells or periodic gratings, can be added during metamaterial design. To further simplify the design, the continuous conductor 19 may be changed to a discontinuous conductor, the length of which is then smaller than the size of the periodic cell Px or Py, at the expense of a small decrease in the reliability of the beamforming device due to an increase in the coupling capacitive interaction between the cells.

[0039] Although the present invention has been described above with reference to the embodiments and modifications, the present invention is not limited to the above embodiments and modifications. For example, the present invention includes various modifications to the above embodiments and modifications that can be understood by a person skilled in the art within the scope of the technical concept of the present invention. The configurations listed in the above embodiments and modifications can be combined as appropriate within a range that does not cause inconsistencies. [Explanation of symbols]

[0040] 10...Beamformer, 11A to 11E...Conductive metamaterial cells, 11...Conductive metamaterial cells, 12...Filled dielectric, 13...Conductor 13, RC...Resonant cell.

Claims

1. A beamformer that directs incident electromagnetic waves, a first conducting metamaterial cell configured to shift the phase of a first portion of the electromagnetic wave; a second conductive metamaterial cell disposed adjacent to the first conductive metamaterial cell and having a different shape than the first conductive metamaterial cell, the second conductive metamaterial cell being electrically conductive and configured to shift the phase of a second portion of the electromagnetic wave; a conductor including at least a portion disposed between the first conductive metamaterial cell and the second conductive metamaterial cell; A beamformer comprising:

2. The conductor is formed in a mesh shape surrounding the first conductive metamaterial cell and surrounding the second conductive metamaterial cell. The beamformer of claim 1 .

3. The conductor is formed in a linear shape that does not surround both the first conductive metamaterial cell and the second conductive metamaterial cell. The beamformer of claim 1 .

4. a first cell group including a plurality of first cells arranged along a predetermined direction, each of the first conductive metamaterial cells; a second cell group adjacent to the first cell group, the second cell group including a plurality of second cells arranged along a predetermined direction, each of the second cells being made of the second conductive metamaterial cell; the portion of the conductor is disposed between the first cell group and the second cell group and extends along the predetermined direction; The beamformer of claim 1 .

5. further comprising a dielectric filled between the first conductive metamaterial cell and the second conductive metamaterial cell. The beamformer of claim 1 .

6. the conductor divides a coupling capacitance between the first conductive metamaterial cell and the second conductive metamaterial cell. The beamformer of claim 1 .

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