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 Art

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

[0003] A metamaterial is an artificial material that obtains its properties from sub-wavelength cells organized by mimicking the structure of atoms in natural substances. A metamaterial can manipulate electromagnetic waves by controlling various properties such as refractive index, permeability, and permittivity in a desired frequency range. The unique properties of a metamaterial are due to the periodic shape (including dimensions) and arrangement of the metamaterial, and also due to the properties of the materials constituting these structures.

Prior Art Documents

Non-Patent Documents

[0004]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

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

[0006] Generally, metamaterial cells exhibiting different phase values ​​are designed individually and then combined to form a beamformer. To achieve phase shift using metamaterial cells, the shape and size of the metamaterial cells are usually adjusted to exhibit the desired phase value while maintaining low transmission loss. For this reason, beamformers group metamaterial cells with different phases and arrange them to satisfy the requirements for phase step changes. Since metamaterial cells are designed separately as infinite arrays of identical cells, the arrangement of large and small cells causes disturbances in the capacitance between adjacent cells, resulting in phase shifts within the beamformer and generating waves (sidelobes) that differ from those obtained in simulations of individual cells.

[0007] This invention aims to reduce capacitance disturbances between adjacent metamaterial cells of different shapes, thereby reducing side lobes. [Means for solving the problem]

[0008] To solve the above problems, the beamformer according to the present invention is a beamformer for directing incident electromagnetic waves, comprising: a first conductive metamaterial cell configured to shift the phase of a first portion of the electromagnetic waves; a conductive second conductive metamaterial cell disposed next to the first conductive metamaterial cell and having a different shape from the first conductive metamaterial cell, configured to shift the phase of a second portion of the electromagnetic waves; and a conductor including at least a portion disposed between the first conductive metamaterial cell and the second conductive metamaterial cell.

[0009] According to the above configuration, capacitance disturbances between adjacent metamaterial cells with different shapes are reduced, thereby reducing side lobes. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1 is a schematic diagram of a beamformer according to an embodiment. [Figure 2] Figure 2 is a schematic diagram of the AA section in Figure 1. [Figure 3] Figure 3 shows variations in the shape of metamaterial cells. [Figure 4] Figure 4 is a schematic diagram illustrating the transmission of electromagnetic waves. [Figure 5] Figure 5 is a schematic diagram of a cross-section of a reflective beamformer. [Figure 6] Figure 6 is a plan view illustrating the 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] Figure 8 shows an equivalent circuit superimposed on a plan view of a metamaterial cell. [Figure 9] Figure 9 shows an equivalent circuit superimposed on a plan view of a metamaterial cell. [Figure 10] Figure 10 is a schematic perspective view showing the metamaterial cell and 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] Figure 12 shows the simulation results when electromagnetic waves are input to a beamformer without a conductor. [Figure 13] Figure 13 shows the simulation results when electromagnetic waves are input to a beamformer equipped with a conductor. [Figure 14] Figure 14 shows an equivalent circuit superimposed on a plan view of a metamaterial cell. [Modes for carrying out the invention]

[0011] As shown in FIGS. 1 and 2, the beamformer 10 according to this embodiment includes a plurality of conductive metamaterial cells 11A to 11E, a filling dielectric 12, and a conductor 13. The beamformer 10 is a transmission type that transmits incident electromagnetic waves. The beamformer 10 emits the transmitted electromagnetic waves as electromagnetic waves having directivity in a desired direction.

[0012] Each of the plurality of conductive metamaterial cells 11A to 11E is a sub-wavelength metamaterial cell. The plurality of conductive metamaterial cells 11A to 11E are periodically arranged in an array and designed to resonate at a frequency in the millimeter-wave band (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 metal, highly conductive polymer, or conductive oxide, or a highly conductive carbon-based material such as 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 constitute a passive array as a whole. In the X direction, cells 11 having different shapes are periodically arranged. For example, cell 11B is arranged next to cell 11A in the X direction, and cell 11C is arranged next to cell 11B. In the Y direction, cells 11 having the same shape are arranged. For example, cell 11A is arranged in a row along the Y direction. Here, each array of cells 11A to 11E is arranged in two rows. The plurality of cells 11 formed in a row in the Y direction constitute a cell group.

[0015] As shown in FIG. 2, if a set of cells 11 arranged in a matrix, that is, in a plane, is regarded as one layer, the beamformer 10 includes five layers. The number of layers may be one or more.

[0016] As mentioned above, the shape of cell 11 only needs to be formed to resonate at millimeter-wave frequencies (30-500 GHz). Examples of cell 11 shapes 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 shown in Figure 3(C) is used.

[0017] Returning to Figures 1 and 2, cell 11A is formed to shift the phase of the incident electromagnetic wave incident on the region of the beamformer 10 where cell 11A is provided by a shift amount A. As will be described later, cell 11A works in cooperation with the portion of the conductor 13 surrounding cell 11A (frame 13A) to shift the phase. Similarly, cells 11B to 11E are formed to shift the phase of the incident electromagnetic wave by shift amounts B to E, respectively. Each of the shift amounts A to E is different from the other. For this reason, cells 11A to 11E have different shapes, in particular, different dimensions. The electromagnetic waves that have been phase-shifted by each of cells 11A to 11E are combined and emitted from the beamformer 10 as an emitted electromagnetic wave. The beamformer 10 is a passive type.

[0018] The packing dielectric 12 supports all the cells 11 and the conductors 13. The packing dielectric 12 constitutes the majority of the volume of the beamformer 10. The packing dielectric 12 can be made from any type of nonconductive dielectric material such as polyimide (PI), benzocyclobutene (BCB), parylene, polyethylene (PE), and polytetrafluoroethylene (PTFE). The packing 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 conductor 13 is provided in each layer where the array of cells 11 is located. In other words, five conductors 13 are configured here. The conductor 13 is configured in a mesh-like manner, surrounding each cell 11 one by one. The function of the conductor will be described later.

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

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

[0022] The phase shift amount can be calculated from equation (1) below in the case of horizontal (azimuth) steering. For perpendicular (elevation) steering, it can be calculated from equation (2) below. Here, 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).

number

number

[0023] The selection criteria for cell 11 was that the cell body could couple to an external electric field (E) generated from a radiating element such as an antenna, and that it could induce a current in the conductive structure of the metamaterial cell. In this embodiment, the cell, shape (including size), and period are optimized to achieve the desired frequency band for use in the millimeter-wave band. To achieve resonance excitation, the size of cell 11 is typically less than or equal to λ / 2 of the operating frequency. In this embodiment, an additional conductor 11 is introduced into the design of cell 11 to isolate the coupling capacitance between adjacent cells 11 and reduce the influence on resonance generation in cell 11.

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

number

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

number

[0026] In this embodiment, the equivalent capacitance Ceq consists of the gap capacitance Cg and the coupled capacitance Cc between adjacent cells 11, and can generally be expressed as shown in the following equations (5) to (7).

number

[0027] Figure 6 shows a schematic diagram of cell 11 with added conductor 13 and superimposed geometric parameters. The resonant cell RC in Figure 6 consists of cell 11 and a frame 13A of conductor 13 surrounding this cell 11. The distance between cells (cell period) is p in the X direction. x , in the Y direction p 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. Since conductor 13 is positioned between cells 11, lines of symmetry exist in the center of conductor 13 in each direction. This means that a region of conductor 13 with a width W2 / 2, i.e., one frame 13A, contributes to one resonant cell RC, and a region 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 the shape of cell 11 in Figure 1, but the concept is the same in both.

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

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

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

[0031] Figure 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 dielectric material 12 used in the simulation is benzocyclobutene (BCB), with dielectric constant ε r1 The values ​​of =2.47, μ=1, and tangent loss tanδ=0.007 are typical values ​​for BCB material in the millimeter-wave band. A total thickness of 0.72 mm was used here. Cell 11 and conductor 13 were made of gold. In Figure 10, cell 11 was placed horizontally with conductor 13, perpendicular to the incident electromagnetic wave, and electromagnetic waves were radiated from port P1 and received at port P2. Cell 11 was oriented in the X-axis direction so that the electric field (E) component would couple to cell 11 and induce resonance. The properties of the BCB material are based on commercially available data and measurements in the millimeter-wave band.

[0032] In this simulation, a time-domain solver was used with the electrical component of the electromagnetic wave being perpendicularly incident along the X-axis and with periodic boundary conditions. Assuming that the period of cell 11 is constant, the geometric parameters of cell 11, such as the gap size, cell size, and width, were optimized to achieve a high transmission coefficient of S21 < -3 dB or higher for a wide range of cell size and phase shift amounts.

[0033] The circular Jerusalem cross cell 11 was constructed by directly fabricating a 500 μm thick Au thin film on the BCB using methods such as magnetron sputtering and electron beam deposition. The parameters of the constant cell 11 are a gap size g = 25 μm and a metamaterial line width W = 20 μm. In the metamaterial cell without an additional conductive frame, the cell period size is Px = Py = 380 μm, the inter-layer distance of each metamaterial is 170 μm, and the additional upper and lower dielectric layers are each 20 μm thick (total thickness 0.72 mm). In the metamaterial cell using a conductive frame, the cell period is Px = Py = 400 μm, the inter-layer distance of each metamaterial is 160 μm, and the 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 parameters described above were obtained by optimizing the metamaterial cell to achieve a high transmission coefficient S21 of -3dB or higher at 300GHz by varying the value of the metamaterial cell size (radius R in this embodiment). Furthermore, the high transmission coefficient of -3dB or higher was maintained throughout the 360-degree phase variation region.

[0035] Figure 11 shows the total phase shift when the size (radius R) of cell 11 is varied, both with and without the addition of conductor 13. In this example, individually designing and simulating cells 11 with different radii R, between 0.11 and 0.18 mm, yields different phase shift values. Generally, metamaterial cells are optimized to exhibit a 360-degree (2π) phase shift in the high transmittance region above -3 dB. Cells 11 with different sizes and phase values ​​are then combined in the beamformer 10 to achieve the desired beam steering angle of the incident electromagnetic wave.

[0036] In Figure 1, five types of cells 11A to 11E were used with a phase difference Δφ = 72 degrees between adjacent cells to obtain a steering angle of 32 degrees relative to the designed period value. In this embodiment, the incident electromagnetic wave is steered in the XY plane. Therefore, the resonant metamaterial cell RC is arranged such that the gradual phase fluctuation 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 in only one 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 a beamformer 10 with and without the conductor 13. These simulations use a rectangular beamformer 10 with 11×5 multilayer cell elements to verify the designed metamaterial cell with conductor 13. The incident electromagnetic wave from the millimeter-wave source is irradiated onto and transmitted through the beamformer 10. Due to different phase shifts caused by cells 11 of different radii, the combined electromagnetic wave is directed at an angle θ. In Figure 12 (without conductor 13), it can be seen that in addition to the main combined output wave lobe ML, two large side lobes (SL) are generated. In Figure 13 (with conductor 13), compared to Figure 12, the main combined output wave ML, i.e., the directional emitted electromagnetic wave, is wider, and the side lobes SL are significantly reduced. Therefore, the passive beamformer 10 equipped with the conductor 13 reduces capacitance disturbances between cells 11 of different shapes, thereby reducing side lobes and improving the directivity of the beamforming beam (emitted electromagnetic wave).

[0038] As shown in Figure 14, the mesh-like conductor 13 may be changed to a linear conductor 19. In some applications, mainly in reflective beamformers, the requirements for millimeter-wave beamforming are low, and only one direction of output multiplexing is needed. Therefore, to simplify the structure and provide design flexibility, some of the conductor 13 can be omitted. As shown in Figure 14, the conductor 19 extends along a direction perpendicular to the beam steering direction (direction) SD. The conductor 19 can be placed between cells 11 of different shapes (especially size). The conductor 19 may extend along the direction in which cells 11 of the same shape are lined up. In unidirectional beamforming, if the size of individual cells is changed to achieve different phase values, the result is that neighboring cells only change in one direction. In Figure 14, since a unidirectional conductor is not needed, further functions such as connected cells or periodic gratings can be added during metamaterial design. To further simplify the design, the continuous conductor 19 may be replaced with a discontinuous conductor, at the expense of a small decrease in the reliability of the beamforming device due to increased coupling capacitance interactions between cells. In this case, the length of the conductor will be smaller than the size of the periodic cell Px or Py.

[0039] Although the present invention has been described above with reference to 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 those 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 to the extent that they do not contradict each other. [Explanation of Symbols]

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

Claims

1. A beamformer that directs incident electromagnetic waves, A first conductive metamaterial cell configured to shift the phase of the first portion of the electromagnetic wave, A conductive second conductive metamaterial cell is disposed next to the first conductive metamaterial cell, has a different shape from the first conductive metamaterial cell, and is configured to shift the phase of the 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 equipped with this feature.

2. The conductor is formed in a mesh shape that surrounds the first conductive metamaterial cell and the second conductive metamaterial cell. The beamformer according to 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 according to claim 1.

4. A first cell group comprising a plurality of first cells arranged along a predetermined direction, each consisting of the first conductive metamaterial cell, The first cell group and the adjacent second cell group include a plurality of second cells arranged along a predetermined direction, each consisting of the second conductive metamaterial cell, The portion of the conductor is positioned between the first cell group and the second cell group and extends along the predetermined direction. The beamformer according to claim 1.

5. The dielectric further comprises a dielectric filled between the first conductive metamaterial cell and the second conductive metamaterial cell. The beamformer according to claim 1.

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

Images