SYSTEM AND METHOD FOR USING PASSIVE REFLECTORS TO ENHANCE NON-LINEAR-LINE (NLOS) SIGNALS - Patent application

Abstract

A system and method is provided that uses passive reflectors or reflectarrays to enhance non-line-of-sight (NLOS) wireless signals. Multiple reflectarrays are combined and positioned to cover a wide range of user positions / beam angles. The passive reflectarrays include at least one of a first reflectarray configured to split an incident beam and a second reflectarray configured to steer the incident beam out of the plane of incidence.

Description

[Background technology]

[0001] The fifth generation technology standard (5G) for broadband cellular networks uses high-frequency radio waves in the 6 GHz to 300 GHz spectrum range, previously referred to as microwave or millimeter wave, or mmWave. The higher the frequency radio waves, the shorter the useful physical range and the smaller the geographical cells required. Line-of-sight (LOS) links, using high-gain, highly directional antennas, provide focused beams directly to mobile users. Using this LOS connection, the high path loss and signal degradation at mmWave frequencies are compensated for. Beam steering of radio frequency (RF) waves for LOS connections is now becoming an integral part of modern wireless communications with mobile network providers' frequencies entering the mmWave regime. At higher frequencies, propagation losses typically increase, while path components generated by reflections (e.g., from building walls, window glass, metal surfaces) become inefficient (e.g., due to loss, diffuse scattering, or multipath interference), resulting in various dead zones. This problem is usually solved by introducing a much denser network of base stations and repeaters. However, the enterprise costs, including multiple active phased array antennas (which become even more complex in the mmWave spectrum as they require active beamforming and multiple-input multiple-output (MIMO) capability), repeaters, and the associated installation and licensing, are enormous. Summary of the Invention

[0002] It is desirable to provide a cost-effective solution for beam steering of radio frequency (RF) waves in wireless communications. In one aspect, the present disclosure provides a method for enhancing non-line-of-sight (NLOS) signals for wireless communications. The method includes providing a plurality of passive reflectarrays including a first reflectarray and a second reflectarray, at least one of the reflectarrays comprising a pattern of repeating unit cells of resonant elements configured to reflect incident radio frequency (RF) electromagnetic waves having a wavelength λ in a range of about 1.0 mm to about 10.0 cm, the first reflectarray having a first phase gradient along a first longitudinal direction thereof and the second reflectarray having a second phase gradient along a second longitudinal direction thereof; and positioning at least one of the first passive reflectarray and the second passive reflectarray to face the incident RF electromagnetic wave such that the incident RF electromagnetic wave is reflected by the first passive reflectarray and the second passive reflectarray with a signal improvement of at least 3 dB, the signal improvement being defined as an increase in signal strength in at least one NLOS direction relative to a baseline signal strength measured without the benefit of the plurality of passive reflectarrays.

[0003] In another aspect, the present disclosure provides a system for enhancing non-line-of-sight (NLOS) signals for wireless communications. The system includes one or more passive reflectarrays, at least one of which includes a pattern of repeating unit cells of resonant elements configured to reflect incident radio frequency (RF) electromagnetic waves with a wavelength λ in a range of about 1.0 mm to about 10.0 cm. The one or more passive reflectarrays include at least one of a first reflectarray configured to split an incident beam and a second reflectarray configured to steer the incident beam out of the plane of incidence. [Brief description of the drawings]

[0004] [Figure 1] FIG. 2 is a schematic top view of a geometric pattern of a reflectarray according to some embodiments. [Figure 1A] 1 is a schematic diagram of the reflection behavior of a reflectarray. [Figure 2A] 1A and 1B are schematic cross-sectional and top views of an exemplary reflect array. [Figure 2B] 2B is a plot of the reflectance curves of the reflectarray of FIG. 2A at various phase gradients ∇φ; [Figure 2C] FIG. 2 is a schematic diagram of the reflective behavior of a specular reflector. [Figure 2D] FIG. 1 is a schematic diagram of the reflection behavior for a constant phase gradient structure. [Figure 3A] FIG. 1 is a schematic diagram of an indoor application with a basic set of reflectarrays at an L-junction according to one embodiment. [Figure 3B] FIG. 1 is a schematic diagram of an indoor application with a basic set of reflectarrays at an L-junction according to one embodiment. [Figure 3C] FIG. 1 is a schematic diagram of an indoor application with a basic set of reflectarrays at an L-junction according to one embodiment. [Figure 3D] FIG. 1 is a schematic diagram of an indoor application with a basic set of reflectarrays at an L-junction according to one embodiment. [Figure 3E] FIG. 1 is a schematic diagram of an indoor application with a basic set of reflectarrays at an L-junction according to one embodiment. [Figure 4A] FIG. 1 is a schematic diagram of an indoor application with a basic set of reflectarrays at a T-junction according to one embodiment. [Figure 4B] FIG. 1 is a schematic diagram of an indoor application with a basic set of reflectarrays at a T-junction according to one embodiment. [Figure 4C] FIG. 1 is a schematic diagram of an indoor application with a basic set of reflectarrays at a T-junction according to one embodiment. [Figure 4D] FIG. 1 is a schematic diagram of an indoor application with a basic set of reflectarrays at a T-junction according to one embodiment. [Figure 5A] FIG. 1 is a schematic diagram of an indoor application with a basic set of reflectarrays at a four-way junction according to one embodiment. [Figure 5B]FIG. 1 is a schematic diagram of an indoor application with a basic set of reflectarrays at a four-way junction according to one embodiment. [Figure 6A] FIG. 1 is a schematic diagram of beam splitting reflection behavior. [Figure 6B] FIG. 13 is a schematic diagram of the reflection behavior for out-of-plane steering. [Figure 6C] FIG. 1 is a schematic diagram of an indoor application with a combination of reflectarrays on the ceiling and floor according to one embodiment. [Figure 7A] FIG. 1 is a schematic diagram of an indoor application with a combination of reflectarrays at an L-junction according to one embodiment. [Figure 7B] FIG. 1 is a schematic diagram of an indoor application with a combination of reflectarrays at a T-junction according to one embodiment. [Figure 7C] FIG. 1 is a schematic diagram of an indoor application with a combination of reflectarrays at an L-junction according to one embodiment. [Figure 7D] FIG. 1 is a schematic diagram of an indoor application with a combination of reflectarrays at a T-junction according to one embodiment. [Figure 7E] FIG. 1 is a schematic diagram of an indoor application with a combination of reflectarrays at an L-junction according to one embodiment. [Figure 7F] FIG. 1 is a schematic diagram of an indoor application with a combination of reflectarrays at an L-junction according to one embodiment. [Figure 7G] FIG. 1 is a schematic diagram of an indoor application with a combination of reflectarrays at an L-junction according to one embodiment. [Figure 7H] FIG. 1 is a schematic diagram of an indoor application with a combination of reflectarrays at a T-junction according to one embodiment. [Figure 7I] FIG. 1 is a schematic diagram of an indoor application with a combination of reflectarrays at a T-junction according to one embodiment. [Figure 7J] FIG. 1 is a schematic diagram of an indoor application with a combination of reflectarrays at a four-way junction according to one embodiment. [Figure 8A] FIG. 1 is a schematic diagram of a characterization setup. [Figure 8B] FIG. 2 is a top plan view of Examples 0, 1, and 2. [Figure 8C] 1 is a plot of the reflection versus frequency curves for Examples 0, 1, and 2. [Figure 8D] 13 is a plot of scattering curves at frequencies corresponding to best performance for selected 0 degrees→θ1 geometries for Examples 0, 1, and 2. [Figure 8E] 8D is a plot of the angle of reflection θr versus the angle of incidence θi for the frequencies selected in FIG. 8C. [Figure 8F] 1 is a plot of signal intensity versus angle of incidence for Examples 0, 1, and 2. [Figure 8G] FIG. 1 is a schematic cross-sectional view of the reflect array film of Example 1. [Figure 8H] FIG. 1 is a schematic cross-sectional view of the reflect array film of Example 2. [Figure 9A] FIG. 11 is a top plan view of the third embodiment. [Figure 9B] FIG. 13 is a top plan view of the fourth embodiment. [Figure 9C] FIG. 13 is a top plan view of the fifth embodiment. [Figure 9D] FIG. 1 is a schematic diagram of the characterization setup for Example 4. [Figure 9E] FIG. 1 is a schematic diagram of the characterization setup for Example 5. [Figure 9F] 1 is a plot of the reflectance spectra of Examples 0, 3, 4, and 5. [Figure 9G] 1 is a plot of the scattering curves for Examples 0, 3, and 4. [Figure 9H] 1 is a schematic cross-sectional view of the reflect array films of Examples 3 to 5. [Figure 10A] FIG. 13 is a schematic diagram of the test environment for the L-joint of Example 6. [Figure 10B] 13 is a plot of output angle versus incidence angle for the reflectarray combination of Array 1 and Array 2 of Example 6. [Figure 10C] 13 is a plot of output angle versus frequency for Example 6. [Figure 10D] 1 is a plot of measured total reflectance versus frequency for Example 6. [Figure 10E] FIG. 13 is a schematic diagram of the test setup for Example 6 at an L-junction. [Figure 10F] 1 is a plot of total reflection versus total path length for a reflectarray at 31.1 GHz.

[0005] In the following description of the exemplary embodiments, reference is made to the accompanying drawings, which illustrate, by way of example, various embodiments in which the present disclosure may be practiced. It should be understood that the embodiments may be utilized and structural changes may be made without departing from the scope of the present disclosure. The figures are not necessarily drawn to scale. Like numbers used in the figures indicate like components. However, it will be understood that the use of numbers to indicate components in a given figure is not intended to limit the components in another figure that are indicated with the same number. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0006] The present disclosure provides for enhancement of non-line-of-sight (NLOS) signals at T-junctions, L-junctions, and 4-way junctions, etc. In some embodiments, passive reflectors or reflectarrays and combinations thereof, such as metalized or conductive films, passive repeater antennas, reflectarrays, etc., are provided to connect one part of a communication network to another, where each part of the network can be an end user, a repeater, a base station, or another active component that redistributes the communication signal, and each component or single component of this network is capable of active beam steering. Here, non-line-of-sight ("NLOS") refers to a zone where a user of a device may have no wireless access, have significantly reduced coverage, or have some kind of impaired coverage. The embodiments described herein provide a general solution that can be adapted to various scenarios, for example, indoors, such as airways, hallways, corridors or basements of office spaces, warehouses, distribution centers, factory floors, and outdoors, such as street intersections, building obstructions, and urban canyons.

[0007] As used herein, the term "reflectarray" refers to a planar array of phase-shifting elements supported by a ground plane that, when illuminated by a feeding antenna (which may be nearby or distant, stationary or moving), reflects that RF radiation in a particular direction (or redistributes it in multiple directions).

[0008] As used herein, the term "resonating elements" or "phase shifting elements" refers to the basic building blocks of a reflectarray that resonate in the presence of radio frequency (RF) radiation and their phase characteristics depend on their dimensions (geometry). The resonating elements can be made of metallic materials or high permittivity or high-k dielectric materials, or can be open spaces within a conductive plane or mesh.

[0009] As used herein, the term "beam steering" refers to the static property of a reflectarray to redirect incident RF radiation by a specific desired amount (i.e., without dynamic tunability).

[0010] In various embodiments, one or more reflectarray articles are provided for beam steering of radio frequency (RF) waves. The reflectarray articles may each include a frequency selective surface (FSS) layer including a pattern of resonant elements configured to reflect incident radio frequency (RF) electromagnetic waves with a free space wavelength λ in the range of about 1.0 mm to about 10.0 cm. In some embodiments, each resonant element may include a wire-like, patch-like structure, or an empty space in a conductive mesh. The reflectarray article may further include a ground plane layer including patterned conductors formed by metal traces defining cells of a continuous metal mesh disposed on a major surface thereof. One or more dielectric layers may be sandwiched between the resonant elements and the ground plane layer, or on either side of the patterned layer or the ground plane layer.

[0011] 1 is a schematic top view of various reflectarray geometric patterns, according to some embodiments. The reflectarrays each include a pattern of resonating elements, which may be metastructures that include a two-dimensional array of repeating unit cells as shown in the respective dashed rectangular boxes. The geometric patterns of the metastructures can be designed to provide various reflectarray angles, where the reflectarray angle θ array (For multiple reflectarrays, θ array,n Or θ n The reflectarray response (also denoted as θ ) refers to the intrinsic (frequency-dependent) property of a reflectarray that describes its response to normally incident RF waves, i.e., the corresponding reflection angle with respect to the surface normal. Figure 1A shows the angle of incidence θ , which is the angle of incidence with respect to the surface normal along the z-axis, for a particular incidence vector. i , and the projection angle φ with respect to the x-axis i ) is expressed by a specific exit vector (reflection angle θ r , and the projection angle φ with respect to the x-axis r 1 shows a representation of a metastructure or metasurface configured to selectively reflect light toward a light source (having an incident angle θ). The incident and exit vectors have a generalized geometric relationship to each other. i If = 0, the reflection angle θ r is the reflectarray angle θ array Corresponds to.

[0012] As a benchmark, a metallic mirror film provides specular steering performance at a reflectarray angle θ array is approximately 0 degrees. The negative reflectarray angle (θ array <0) is the positive reflectarray angle |θ array | is rotated 180 degrees in its film plane (for example, the XY plane in FIG. 1A). In the embodiment of FIG. 1, the passive reflectarray 110 has a reflectarray angle θ of about 5 degrees to about 20 degrees. array The passive reflect array 120 has a reflect array angle θ of about 30 degrees to about 60 degrees. array The passive reflect array 130 has a reflect array angle θ of about 60 degrees to about 90 degrees. arrayThe passive reflectarrays 142 and 144 each have a reflectarray angle θ of about 30 degrees to about 60 degrees or about −30 degrees to about −60 degrees. array The passive reflectarrays 152 and 154 each have a reflectarray angle θ of about 60 degrees to about 90 degrees or about −60 degrees to about −90 degrees. array The passive reflectarrays 162 and 164 each have a reflectarray angle θ of about 15 degrees to about 90 degrees. array has.

[0013] Structures 110, 120, and 130 (SKUs 1-3) represent typical reflectarrays that substantially satisfy the constant phase gradient condition. Structure 110 (SKU1) is a reflectarray that is suitable for small reflectarray angles (5 degrees < θ array Structure 120 (SKU2) can be used when slight redirection of the beam is preferred (compared to the mirror response) in a beam path that includes two or more reflectarray panels (e.g., doublets or pairs of reflectarrays) arranged in, for example, L junctions (see, e.g., FIG. 3B), T junctions (see, e.g., FIG. 4B), and 4-way junctions (see, e.g., FIG. 5B), as well as auxiliary structures for L junctions (e.g., combined with a 120 structure as in FIG. 3C) and T junctions (e.g., combined with a 142 / 144 structure as in FIG. 4D). Structure 120 (SKU2) has an intermediate value reflectarray angle θ (30 degrees <θ array <60 degrees) and can be used to complement the auxiliary structures described above (see, e.g., FIG. 3C) or as a stand-alone doublet (see, e.g., FIG. 3D). In the latter case, optimal performance is achieved when both arrays have an θ array = 45 degrees, or the sum of the reflectarray angles is approximately 90 degrees, i.e., 80 degrees < |θ array,1 |+|θ array,2 |<100 degrees. Structure 130 (SKU3) is provided for large reflectarray angles (60 degrees < θ array<90 degrees), which represents the most commonly applied scenario and is typically applied as a stand-alone. In one embodiment, structure 130 can be applied as a doublet, resulting in two separate signal path components as shown in FIG. 3E.

[0014] The structures 142 and 144 have a reflectarray angle median of 30 degrees <|θ array It exhibits beam-splitting behavior for |θ<60 degrees and can be used as a supporting structure for T-junctions (see, for example, FIG. 4D). One way to implement this behavior is to fabricate a twice-larger unit cell (142) with top and bottom rows stacked in the opposite order, as visualized in FIG. 6A. Alternatively, a stack of oppositely oriented patches (144) can be fabricated. Structures 152, 154 are equivalent to 142, 144, but for larger reflectarray angles 30 degrees <|θ array |<60 degrees, which can be used for unitary structures at T-junctions (see, for example, Figure 4C).

[0015] Structure 162 can take advantage of the floor and ceiling of an L-junction by performing incident out-of-plane beam redirection (see, for example, FIG. 6C). Its unit cell has a square n×n shape, where n is the number of components. All columns have the same gradient direction (15 degrees <θ for a regular constant phase gradient structure). array <90 degree performance). The corresponding structure has a beam redirecting performance (θ i =θ array * ,φ i =0 degrees, θ r =θ array * ,φ r = 90 degrees) in Figure 6B. Structure 164 represents a stack of opposing patches (162) and can be applied to the floor and ceiling of a T-junction (Figure 6C). Structures 162 and 164 can each be used in combination with a specular reflector (32) and a low angle reflectarray (110) and a mid angle reflectarray (120) to guide signals across the floor and ceiling of a hallway.

[0016] The repeating unit cell of the structure etc. shown within the dashed box of FIG. 1 may include any suitable number of alternating phase shift elements. The repeating unit cell may include, for example, one, two, three, four, five, six, seven, eight, or more phase shift elements. The unit cell has dimension dx in the x-axis and dimension dy in the y-axis, and the elements are arranged as an array in the x-y plane. The resonant elements may be arranged to be periodic along at least one axis such as the x-axis. When the number of phase shift elements in the unit cell is 1, the performance of the reflect array may degrade to the performance like a mirror (specular reflection). When the number of phase shift elements in the unit cell is two or three, it may be difficult for the reflect array to properly steer the incident RF beam, and instead of obtaining one reflected beam, the pattern of the phase shift elements may generate a lot of scattering in different directions. The RF reflection performance of the reflect array may depend on dx / m and dy / n, where m is the number of phase shift elements in the unit cell along the x-axis and n is the number of phase shift elements in the unit cell along the y-axis. In the present disclosure, suitable dimensions dx / m and dy / n may be selected such that λ / 10 < dy / m < λ and λ / 10 < dx / n < λ, where λ is the free space wavelength of the operating frequency, that is, the free space wavelength of the wave incident on the reflect array film.

[0017] To act as a phase shift element, the resonant element may include an array of periodic meta-structures of suitable shapes. In the embodiment shown in FIG. 1, each of the phase shift elements has a "cross" shape. It should be understood that the phase shift element may include other shape structures such as a ring shape, a "cross" or a "plus sign" shape structure, a "cross" structure arranged in the central region of the ring, a triangular shape, etc.

[0018] Each resonant element may have a wire-like or patch-like structure, which may be formed by providing one or more metallic or high-k dielectric materials on the first major surface 132 of the dielectric layer 130. The resonant elements may each have a two-dimensional geometric structure with a lateral dimension of less than or equal to λ, where λ is the free space wavelength of the operating frequency, i.e., the free space wavelength of the wave incident on the reflectarray film. The resonant elements may each have a lateral dimension, for example, in the range of about 10 to about 50,000 micrometers. The wire-like resonant elements may each have a linewidth, for example, in the range of about 1.0 to about 50,000 micrometers, and a thickness of at least 5% of the skin depth of the selected metal in the operating frequency range. The thickness of the metallic resonant elements may, for example, be in the range of about 0.02 to about 100 micrometers. The aspect ratio of the linewidth to thickness of the wire-like resonant elements may, for example, be in the range of 0.1 to 2500. The high-k dielectric resonator element may have a thickness in the range of, for example, about 1.0 to about 100,000 micrometers.

[0019] Each of the passive reflectarrays 142, 144, 152, 154 performs beam splitting. A schematic diagram of the beam splitting behavior is shown in Figure 6A. For example, a normal incidence beam is reflected in two directions θ r = ±θ1. As shown in Figures 4C-4D, the incident beam from the station is deflected to the user at the opposing arm of the T-junction. A passive reflectarray performing beam splitting can include a column of resonating elements with alternating column directions. As shown in Figure 1, the resonating elements of the reflectarrays 142, 144, 152, 154 are arranged by alternating the column directions of the reflectarrays. For example, if the resonating elements are arranged to be periodic in the x-axis, the largest element(s) of a unit cell will be located directly adjacent to the smallest element(s) of an adjacent unit cell in the y-axis.

[0020] Each of the passive reflectarrays 162, 164 performs beam steering out of the plane of incidence. A schematic of out of the plane of incidence beam steering is shown in FIG. 6B. The structure 162 features an n×n lattice unit cell of n separate elements, each column of which is shifted one element to the right (left) relative to the column below it. This structure has an intrinsic property θ array * can be characterized by (θi = θarray * ,φi=0 degrees) and (θr=θarray * ,φr=90 degrees) results in maximum signal transmission (see, for example, FIG. 6A). A typical reflectarray (i.e., structures 110, 120, 130) composed of identical elements has a θarray=θarray * Note that this results in a reflectarray angle of 162. Structure 164, which adds to the beamsplitting performance of 162, consists of multiple patches featuring structure 162, stacked together forming a "checkerboard" pattern such that the phase gradient of any two neighbors are oppositely oriented.

[0021] FIG. 2A shows a schematic cross-sectional view and a top view of the reflectarray 120 of FIG. 1 with the beam angle rule introduced. The reflectarray 120 includes a pattern of resonant metallic (or high-k dielectric) elements 122 arranged on a dielectric layer 124. FIG. 2B shows a plot of the reflection curves of the reflectarray 120 with different phase gradients ∇φ. Here, phase gradient refers to an inherent property of a constant phase gradient reflectarray that represents the maximum difference in phase advance that a normally incident electromagnetic wave exhibits upon reflection from two adjacent resonant elements (along the direction of maximum phase change, i.e., along the x direction in FIG. 2, but in general it can be along any direction), divided by the distance between their centers (px in FIG. 2). The phase gradient is expressed by the relationship θ cr =sin -1The phase gradient is related to the reflectarray angle by (|λ∇φ / 2π|). In some structures, such as structure 120, the phase gradient along the y direction is zero, and the phase gradient parameter can be referred to interchangeably as the notation ∇φ and dφ / dx. According to the reflectarray angle, the phase gradient can be either positive or negative, depending on the direction of maximum phase increase (e.g., increasing or decreasing the size of the elements along the x-axis). Figures 2C and 2D show the reflection behavior of a typical specular reflector (e.g., phase gradient dφ / dx=0) and a constant phase gradient structure (e.g., phase gradient dφ / dx=constant). Schematic diagrams (c1), (c2), and (c3) in Figure 2C correspond to points (c1), (c2), and (c3) in Figure 2B, respectively. Schematic diagrams (d1), (d2), and (d3) in Figure 2D correspond to points (d1), (d2), and (d3) in Figure 2B, respectively. The schematic diagrams of (c1) of FIG. 2C and (d1) of FIG. 2D show the critical angle θ back =sin -1 (sinθ array ) / 2)=sin -1 The backscattering condition (θ i =θ r =θ back ) in which θ array is the reflectarray angle, ∇φ is the phase gradient of the reflectarray, and λ is the free-space wavelength of the incident radio frequency (RF) electromagnetic wave. i =0 degrees, θ r =θ array ) for the reflectarray scenario, i.e., the reflection angle θ away from the surface normal array The schematic diagram (d3) in FIG. 2D shows that the critical condition is θ cr =sin -1 (1-sinθ array )=sin -1 The shallow angle (θ i =θ cr , θ r This shows the scenario of a reflected beam approaching an angle of 0.05° (=90°).

[0022] FIG. 2B shows a higher reflection angle θr It has been shown that a reflectarray with a sufficiently large phase gradient can significantly extend the range of beam sweeping (i.e., when the nonlinear regime takes over, θ cr For angles of incidence approaching dθ r / dθ i >>1) For example, the phase gradient ∇φ=312 degrees / cm (θ at a frequency of 30 GHz) array = 60 degrees), the incidence angle dθ i A small change in the reflection angle dθ r For a specular reflector (i.e., with a phase gradient ∇φ=0 deg / cm), dθ r = dθ i ).

[0023] In some embodiments, various basic sets of mutual beam propagation solutions are provided to enhance signals in non-line-of-sight ("NLOS") zones such as indoor L-junctions, T-junctions, and 4-way junctions. These solutions are based on metalized films (with mirror performance) and various reflectarrays such as 110, 120, 130, 142, and 144 in FIG. 1. Various mirror films and reflectarrays can be placed on the walls of the junctions. Optimized performance can be achieved by selecting appropriate reflectarrays with optimized characteristics for a given situation and active network deployment. Such set configurations can bring several technical advantages compared to their typical single point-to-point use cases. One such advantage is better overall NLOS coverage. Another advantage of sets is increased generality, i.e., the ability to serve various angles of interest, so that various user requirements can be met with a finite number of stock-keeping units (SKUs), which simplifies installation and minimizes the need for user-dependent customization. Such combinations of reflectarrays are also characterized by improved reciprocity (i.e., mobile users and fixed base stations can swap locations without compromising signal quality) and an increased number of available multipath signal components (hence less chance of connection drops when physical barriers are present). However, combining multiple reflectarrays can also generate additional losses, such as destructive self-interference (known as multipath distortion), increased free-space path loss, and substrate loss.

[0024] 3A-3E, 4A-4D, 5A, 5B, and 6C are schematic diagrams of various indoor applications using a basic set of reflectarray films or panels at an L junction, a T junction, and a four-way junction, respectively. Reverse data reception (RX) and data transmission (TX) scenarios are also shown for some solutions. The positions of the base station 2 and the user 4 depicted in the schematic correspond to the focal positions of the TX side or the RX side, respectively. As shown in FIG. 3A, a metal mirror film 32 is provided to reflect the signal from the base station 2 at the L junction toward the user 4. As shown in FIG. 3B, two passive reflectarrays 110 of FIG. 1 are provided to reflect the signal from the base station 2 at the L junction toward the user 4. As shown in FIG. 3C, the passive reflectarrays 110 and the passive reflectarrays 120 of FIG. 1 are provided to reflect the signal from the base station 2 at the L junction toward the user 4 for the RX and TX scenarios. As shown in FIG. 3D, two passive reflect arrays 120 of FIG. 1 are provided to reflect signals from the base station 2 to the user 4 at the L junction. As shown in FIG. 3E, two passive reflect arrays 130 of FIG. 1 are provided to reflect signals from the base station 2 to the user 4 at the L junction. As shown in FIG. 4A, a metal mirror film 32 is provided to reflect signals from the base station 2 to the user 4 at the T junction. As shown in FIG. 4B, four passive reflect arrays 110 of FIG. 1 are provided to reflect signals from the base station 2 to the user 4 at the T junction. As shown in FIG. 4C, a passive reflect array 152 of FIG. 1 is provided to reflect signals from the base station 2 to the user 4 at the T junction for RX and TX scenarios. As shown in Figure 4D, the passive reflect arrays 110 and 142 of Figure 1 are provided to reflect signals from the base station 2 towards the user 4 at the T-junction for RX and TX scenarios. As shown in Figure 5A, a metallic mirror film 32 is provided to reflect signals from the base station 2 towards the user 4 at the 4-way junction.As shown in FIG. 5B, four passive reflect arrays 110 of FIG. 1 are provided to reflect signals from the base station 2 towards the users 4 at a four-way junction.

[0025] In some embodiments, various metallized films, reflectarrays, and combinations thereof can be applied to ceilings, floors, as well as walls, at L-joints, T-joints, and 4-way junctions. The reflectarrays can be of any suitable shape with any desired size. For example, in indoor applications, the reflectarrays can be in the form of panels with lengths / widths of 1 cm to 500 cm and thicknesses of 0.01 mm to 50 mm. The reflectarrays described herein can also be applied to other functional films or devices, such as graphic films, adhesive films, flexible circuit films, etc.

[0026] As shown in FIG. 6, the metallized film, the reflectarray (such as 110, 120 in FIG. 1), and the off-plane reflectarray are placed on the ceiling 3 and the floor 5. The off-plane reflectarray 162 in FIG. 1 may be more suitable for an L-junction since it redirects the beam only in one direction (e.g., to the right in FIG. 6C). The off-plane reflectarray 164 in FIG. 1 may be more suitable for a four-way junction and a T-junction since it has an additional beam splitting behavior and can therefore redirect the beam in both directions (e.g., in the opposite left and right directions in FIG. 6C). The structure 164 has an added beam splitter that can serve both the left and right directions (both are present in the T-junction and the four-way junction). In contrast, the structure 162 can only reflect in one direction (only has a single turn in any direction, like the L-junction).

[0027] Various basic sets of reflectarrays shown in Figures 3A-3D, 4A-4D, 5A, 5B, and 6 can be combined to form complementary passive signal enhancers that generate additional multipath components. Figures 7A-7J show various combinations of functional elements from the basic sets described in Figures 3A-3D, 4A-4D, 5A, 5B, and 6. The systems in Figures 7A-7E include non-overlapping combinations of reflectarrays. The systems in Figures 7F-7J further include combinations with metallized films. It should be understood that the system can be further combined with ceiling and floor solutions such as the embodiment shown in Figure 6C.

[0028] Various embodiments are provided, such as a reflectarray film, a portion of a reflectarray film, a method of making at least a portion of a reflectarray film, and a method of using a reflectarray film.

[0029] In some embodiments, the passive signal enhancement system may include a first reflectarray and a second reflectarray, which may be selected from the reflectarrays shown herein, such as, for example, in Figures 1, 3A-3E, 4A-4D, 5A, 5B, and 7A-7J. At least one of the reflectarrays includes a pattern of repeating unit cells of resonating elements configured to reflect incident radio frequency (RF) electromagnetic waves of wavelength λ in a range of about 1.0 mm to about 10.0 cm. Each resonating element includes a wire-like or patch-like structure. The first reflectarray has a first phase gradient along its first longitudinal direction. The second reflectarray has a second phase gradient along its second longitudinal direction. The respective phase gradients may be in a range suitable for a desired application. For example, the first phase gradient may be in a range of 5 degrees / cm to 5000 degrees / cm. The second phase gradient may be in a range of 5 degrees / cm to 5000 degrees / cm. The first and second passive reflectarrays may be positioned to orient the incident RF electromagnetic wave at a first and second angle of incidence, respectively.

[0030] In some embodiments, at least one of the first reflectarray and the second reflectarray provides nonlinear steering performance. The reflectarray based on the constant phase gradient metasurface has a reflection angle of a limit angle θ cr (defined above), it may exhibit nonlinear behavior as its derivative ranges from 1<|dθr / dθi|<infinity.

[0031] In some embodiments, the combination of at least two reflectarrays provides linear steering performance. Linearity can be achieved through the opposing net compensating effect of the nonlinearities present in each of the underlying reflectarrays. The embodiment shown in FIG. 3D includes two reflectarrays at an L-junction, with the sum of their reflectarray angles being 80 degrees <|θ array,1 |+|θ array,2 Illustrative structures in the range |<100 degrees.

[0032] In some embodiments, at least one of the first and second reflectarrays provides specular steering capabilities, which can be achieved, for example, through a metallic mirror film where the unit cell is composed of a single resonating element, or any reflectarray or metasurface with uniformly arranged identical resonating elements.

[0033] In some embodiments, at least one of the first and second reflectarrays provides beam-splitting performance. Beam-splitting performance can be achieved when the reflectarray has a unit cell with a phase gradient and includes two oppositely oriented sublattices (either in terms of the dimensions of the resonating elements or in terms of their underlying phase advance). The desired performance can be achieved when the element of the first sublattice that produces the smallest phase advance is located immediately next to the element of the second sublattice that produces the largest phase advance (see, for example, structures 142, 152 in FIG. 1). An alternative approach to reach beam-splitting behavior is to combine regular reflectarray patches (see, for example, structures 144, 154 in FIG. 1).

[0034] In some embodiments, at least one of the plurality of passive reflectarrays is disposed on a vertical wall of a T-junction, an L-junction, or a 4-way junction. At least one of the plurality of passive reflectarrays is disposed on a ceiling or floor at a T-junction, an L-junction, or a 4-way junction.

[0035] In some embodiments, at least one of the passive reflectarrays provides out-of-plane steering. Out-of-plane steering (more specifically, a 90-degree rotation of the plane of incidence) can be achieved when a unit cell of the reflectarray (e.g., based on a constant phase gradient structure) includes a row of resonant elements shifted left (right) relative to the next closest row (either relative to the element dimensions or relative to the underlying phase advance). For example, a second reflectarray can be designed to steer the incident beam out-of-plane, in which case the resonant elements of the second reflectarray can be positioned such that every subsequent row of the pattern is shifted left (right) by a fixed number of elements relative to the underlying row. The structures 162, 164 of FIG. 1 are exemplary structures for performing out-of-plane beam redirection.

[0036] In some embodiments, the incident RF electromagnetic waves are from a network featuring adaptive beamforming at the transmitting and / or receiving ends (in a "single-input single-output" or SISO, "multiple-input single-output" or MISO, "single-input multiple-output" or SIMO, "multiple-input multiple-output" or MIMO, "multiple-user multiple-input multiple-output" or MU-MIMO communication network). At least one of the nodes of the network is capable of adaptive beamforming (i.e., spatial filtering). All previously proposed reflectarray schemes can function similarly to a normal broadcast type network.

[0037] In some embodiments, a system for enhancing non-line-of-sight (NLOS) signals for wireless communications may include one or more passive reflectarrays. At least one of the reflectarrays includes a pattern of repeating unit cells of resonating elements configured to reflect incident radio frequency (RF) electromagnetic waves with a wavelength λ in a range of about 1.0 mm to about 10.0 cm, each resonating element including a wire-like or patch-like structure. The one or more passive reflectarrays include at least one of a first reflectarray configured to split an incident beam and a second reflectarray configured to steer the incident beam out of the plane of incidence. The first reflectarray and the second reflectarray may be selected from any suitable reflectarrays shown herein, for example, in Figures 1, 3A-3E, 4A-4D, 5A, 5B, and 7A-7J. In some embodiments, the resonating elements of the first reflectarray row are arranged in alternating row directions. In some embodiments, the resonating elements of the first reflectarray row are arranged in a checkerboard pattern, hi some embodiments, the resonating elements of the second reflectarray are arranged such that every subsequent row in the pattern is shifted by a fixed number of elements relative to the row below. EXAMPLES

[0038] These examples are for illustrative purposes only and are not meant to limit the scope of the appended claims.

[0039] Modeling Process The reflectarray article was modeled using a modeling process that included: (i) performing preliminary electromagnetic simulations using CST Studio Suite Software (commercially available from Dassault Systemes Company, WALTHAM, MA, USA); (ii) ray optics approximation theory (see Ozgecan et al., IEEE Wireless Communications Letters 9.5, (2019)); and (iii) verifying long-range performance using reflectarray theory (see J. Huang, "Reflectarray Antennas," IEEE (2007)).

[0040] Characterization The beam steering performance of various reflectarray films of various embodiments was characterized using a custom arc setup as shown in FIG. 8A. The RF mirror is a 38 micrometer thick aluminum foil glued onto a 5 micrometer thick foam. As shown in FIG. 8A, the arc 92 consists of a semicircle with a radius of 0.8 meters. To record the reflected beam intensity as a function of frequency, the transmitter horn antenna 94 and the receiver horn antenna 96 were independently positioned at various angles along the arc 92. The transmitter horn 94 and the receiver horn 96 were ERAVANT WR-28 standard gain horn antennas. They were connected to two ports of a vector network analyzer (Agilent Technologies E836C).

[0041] Examples 0, 1, and 2 Examples were prepared including a specular reflector (Example 0 as a benchmark) and a reflectarray (Examples 1 and 2). The reference Example 0 is a flat aluminum mirror measuring 12.7 cm x 12.7 cm and 38 micrometers thick. Examples 1 and 2 are reflectarrays based on a constant phase gradient metasurface with a phase gradient of dφ / dx=237 degrees / cm in Example 1 (312 degrees / cm in Example 2) and a grating period of 1.90 mm in Example 1 (1.93 mm in Example 2). Table 1 below summarizes the description of Examples 0, 1, and 2.

[0042] Top views of Examples 0, 1, and 2 are shown in FIG. 8B. Example 0 was adhered onto a 5 micrometer thick foam. The laminated film cross section of Example 1 ("0-39 degree array") is shown in FIG. 8G. The laminated film cross section of Example 2 ("0-60 degree array") is shown in FIG. 8H. Example 1 has a total thickness of 0.68 mm and consists of a ground layer and FSS layer patterned on a 125 micrometer thick PET layer, which are oriented inward and separated by a dielectric laminate made from one 128 micrometer thick PET layer and two optically clear adhesive (OCA) layers. For outer protection of the ground and patterns, additional 50 micrometer thick PET and 50 micrometer thick OCA layers are added on both sides of the stack. Example 2 has a total thickness of 0.76 mm and consists of a ground layer and an FSS layer patterned on a 125 micrometer thick PET layer (which also serves as an outer protective layer) separated by a dielectric stack made from two 129 micrometer thick PET films and one 50 μm PET film, all of which are separated by four layers of 50 micrometer thick OCA.

[0043] [Table 1]

[0044] manufacturing process The following manufacturing steps were used to fabricate Examples 1 and 2. It should be understood that similar steps can be used to fabricate various reflectarrays such as the reflectarray shown in FIG. 1. Each sample had two copper pattern layers: a resonator structure in the form of a ring pattern and a ground plane in the form of a uniform grid pattern. The film substrate was prepared by sputter coating a tie layer and a copper seed layer onto an optical grade heat stabilized PET film. The patterned resonator structure and ground plane grid pattern were prepared by electroplating the sputtered / seeded film substrate with 5 microns of copper. A photoresist layer was then vacuum laminated onto the exposed copper. The photoresist was exposed by laser direct imaging and then the unexposed areas were developed. The patterned photoresist served as a mask in a copper etching step using cupric chloride etchant, followed by electroless tin finish plating.

[0045] Functional reflectarray films were prepared by roll lamination of a film layer between the patterned resonator film and the ground plane film using an optically clear adhesive (OCA). The ground plane mesh patterns for the 60 degree and 39 degree samples were identical. The mesh layers had square repeating units with a period of 192 microns and a trace width of 40 microns. The dimensions of the resonant rings (labeled "a" through "f") of Example 2 ("0-60 degree array") and the resonant rings (labeled "a" through "h") of Example 1 ("0-39 degree array") are shown in Table 2 below. In both samples, all rings have a trace width of 40 microns. The polyester terephthalate (PET) film is commercially available from Tekra (New Berlin, WI) under the trade name MELINEX ST-504. The optically clear adhesive (OCA) is commercially available from 3M Display Materials and Systems (Oakdale, Minn.) under the optically clear adhesive trade name 3M8212.

[0046] [Table 2]

[0047] Each ring in the reflectarray unit cell is assigned a specific diameter (listed in Table 2 for Examples 1 and 2) to produce a phase response that increases incrementally (as defined up to any additive constant) from 360 / n degrees for the first ring of the unit cell (360 / 6=60 degrees for sample 2 and 360 / 8=45 degrees for sample 1) to 360 degrees for the last ring of the unit cell, where n is the number of rings in each row in the unit cell. This corresponds to a phase gradient of 311.7 degrees / cm for sample 2 and 237.1 degrees / cm for sample 1 (this corresponds to a grating period of dx=6dy, dy=1.925 mm for sample 2 and dx=8dy, dy=1.898 mm for sample 1). Finally, the generalized Snell's law sin(θr)=sin(θi)+grad(φ) * For operating frequencies of 30 GHz (Example 2) and 31.1 GHz (Example 1) using λ / 2π, where grad(φ) is the phase gradient, this results in beam steering performances of 0-60 degrees (Example 2) and 0-39 degrees (Example 1).

[0048] Characterization The beam steering performance of the various reflectarray films of Examples 1 and 2, as well as the 12.7 cm RF mirror, was characterized using a custom arc setup as shown in FIG. 8A. FIG. 8C shows plots of reflection vs. frequency curves for Examples 0, 1, and 2. The sample was placed at the center of the arc. The distance between the center and the horn was 0.8 m, which corresponds to the far-field measurements used to measure Ka-band horns. Such a distance also results in a sufficiently flat wavefront as long as the sample is 12.7 cm or less. The solid lines correspond to 0°→θ1, where θ1 was chosen in the vicinity of the pre-modeled parameters that produced a maximum signal at about 30 GHz. The dashed lines correspond to combinations of endfire angles, which were selected by extending the generalized Snell's law from the corresponding 0°→θ1 points (at the frequencies where they reached a maximum) to shallower reflection angles. FIG. 8D shows the scattering curves plotted at frequencies corresponding to the best performance of the selected 0°→θ1 geometry. FIG. 8E shows the scattering curves plotted at frequencies corresponding to the best performance of the selected 0°→θ1 geometry at reflection angles θ1. r Incident angle θ i The plot of θ i , θ r The combination of (for the frequency selected in FIG. 8C) results in the maximum reflected signal. The corresponding signal strength versus the plotted incidence angle is plotted in FIG. 8F. In FIG. 8C-F, six common data points are highlighted, with ("i"n)- representing the normal incidence case (i.e., 0 degrees → θ1) and ("i"s)- representing the shallow reflection angle case of Example i.

[0049] The plots in Figures 8D-8F are further explained below. First, the optimal characteristics of the reflectarrays of Examples 1 and 2 were determined. Pre-fabrication modeling results were obtained by CST, which resulted in 0 degrees → 45 degrees @ 27.9 GHz and 0 degrees → 60 degrees @ 30 GHz for Examples 1 and 2, respectively. After performing a 0 degrees → θ scan, the optimal θ1 that resulted in the maximum reflectivity near the frequency of interest was determined. This procedure resulted in optimal values ​​of 0 degrees → 40 degrees @ 30.9 GHz and 0 degrees → 60 degrees @ 30 GHz for Examples 1 and 2, respectively, with the corresponding curves plotted as solid lines in Figure 8C. The best performance of about -16 dB was achieved by the Al mirror of Example 0 with mirror geometry, while Examples 1 and 2 resulted in about -17 dB and about -18 dB, respectively. Also, unlike Example 0, which has a relatively flat spectrum, Examples 1 and 2 have finite (about 3 dB) bandwidths of 12.3% and 9%, respectively. These values ​​are within the specifications of current 5G standards, such as the n261 and n260 bands (which have 3% and 7.8% bandwidth at the respective frequencies).

[0050] Next, the amount of signal lost to other diffraction orders was determined for the selected 0°→θ1 reflectarray geometry. For this, a scan of the reflection angle was performed in the range of 0° to 80° with the angle of the incident beam fixed relative to the normal orientation. The resulting scattering curves are plotted in FIG. 8D with points representing the experimental data and dashed lines for better visibility. A maximum signal leakage of -9 dB (Example 2) and -17 dB (Example 1) occurs in the specular reflection direction (0°→0°), followed by a leakage of -17 dB in the 0°→-θ1 direction (for both samples). Indeed, for subwavelength reflectarrays such as Examples 1 and 2 (e.g., the grating period is less than λ / 5), the only possible scattering options are either 0°→θ1 specular reflection (0°→0°) or -1° non-specular reflection (0°→-θ1). For Examples 1 and 2, such losses were found to be relatively small, so the selected 0°→θ1 geometry is indeed close to optimal.

[0051] Once the optimal 0°→θ1 configuration was established, the fabricated embodiment was verified to follow the so-called generalized Snell's law for a wide range of incidence angles. To do this, it is necessary to determine the reflection angle at which maximum reflection is achieved if the frequency is held constant for all selected angles of incidence. The resulting data points plotted as dots in FIG. 8E match very closely with the theoretical Snell's law plotted as a solid line (assuming that the frequency and phase slope values ​​are given by the fabricated sample specifications). The corresponding S as a function of incidence angle 21 As is evident from FIG. 8F, which plots the parameters (the reflection angle is chosen according to Snell's law in FIG. 8E), different parts of the curve in FIG. 8E result in different amounts of transmitted power. The maximum amount of power is always achieved in the backscattering direction (see, for example, (c1) and (d1) in FIG. 2C), and drops steadily as the reflection angle becomes shallower, θ r It can be seen that the degradation reaches about 10 dB at about 80 degrees. The bandwidth at shallower reflection angles also degrades somewhat, as shown by the dashed line in Figure 8C, with increasing θ r At about 80 degrees it drops to about 8%.

[0052] The fabricated reflectarrays (e.g., Examples 1 and 2) operate efficiently and are in full agreement with the generalized Snell's law, and therefore can be considered as useful building blocks for building more complex designs, such as those proposed in Figures 3A-3D, 4A-4D, 5A, 5B, and 6.

[0053] Examples 3, 4, and 5 Examples 3-5 were fabricated to demonstrate reflectarrays that perform beam splitting (such as reflectarrays 142, 144, 152, and 154 in FIG. 1) and beam steering outside the plane of incidence (such as reflectarrays 162 and 164 in FIG. 1). One simple method for adding beam splitting functionality to a normal reflectarray (i.e., θ 2 with normal beam deflection in two directions) is shown. r= ±θ1) is to stack the reflectarray in multiple sheets, so that all adjacent sheets have opposite orientations. This approach requires that each sheet is appropriately sized, neither too small (leading to signal degradation due to destructive interference from adjacent sheets) nor too large (leading to dominance of single reflections rather than beam splitting).

[0054] From numerical reflectarray theory (Huang & Encinar, 2008), we know that in order to eliminate destructive interference effects, the columns must be oriented so that all the largest elements are located just below the smallest elements, as shown in reflectarrays 142, 144, 152, and 154 in FIG. 1. Example 4 is an example of a beamsplitter with θ:0→±60° functionality (see FIG. 9B and FIG. 9D), the characteristics of which are shown in yellow in FIG. 9F and FIG. 9G. For reference, the performance of Example 4 is compared to that of Example 3, which has a typical 0°→+60° structure constructed from the same unit cell elements (see FIG. 9A, and the purple lines in FIG. 9F and FIG. 9G). Note that the beamsplitter is about 2-3 dB worse than a typical reflectarray. This is consistent with the fact that the beamsplitter is effectively a power divider.

[0055] To achieve out-of-plane steering at the junction floor / ceiling (indicated by the green arrow in Figure 6), the more general reflectarray formula can be used (Huang & Encinar, 2008), φ i =0 degrees, φ r After applying the condition: = 90 degrees, this results in the following phase distribution:

number

[0056] The cross-sections of the laminated films of Examples 3-5 are shown in Figure 9H. Each sample has a layer thickness of 0.77 mm and consists of a 38 micrometer thick Cu undercoat and FSS layer patterned on a 127 micrometer thick PET layer (also serving as an outer protective layer) separated by a 508 micrometer thick polycarbonate (PC) film sandwiched between two 50 micrometer thick OCA layers. The results of Examples 3, 4, and 5 are shown in Table 3 below. The PC film is commercially available from CS Hyde Company (Lake Villa, IL) under the trade name #38-20F-GG.

[0057] [Table 3]

[0058] manufacturing process The following fabrication steps were the same for Examples 3 to 5. Each example had a thin Al patterned layer with a resonator structure in the form of a square patch, and a ground plane in the form of 38 micrometer thick copper.

[0059] The film substrate was prepared by evaporation coating a Ti (5 nm) seed layer onto an optical grade heat stabilized PET film. The patterned resonator structures were prepared by depositing 150 nm of aluminum onto the evaporation / seed film substrate. The patterning process is based on a proprietary technology with a feature resolution of less than about 0.1 mm.

[0060] Functional reflectarray films were prepared using OCA by roll lamination with a film layer interposed between the patterned resonator film and the ground plane film. The ground plane mesh pattern for all samples was identical and based on 1 oz copper (from a single layer FR-4 substrate). The dimensions of the resonant square patches (labeled "a" through "d") for Examples 3-5 are listed in Table 4 below.

[0061] [Table 4]

[0062] Each square in the reflectarray unit cell is assigned a specific size (listed in Table 4) to produce a phase response that increases incrementally (defined up to any additive constant) from 360 / n degrees (where 360 / 4=90 degrees) for the first ring of the unit cell to 360 degrees for the last ring of the unit cell. This translates to a phase gradient of 311.7 degrees / cm (which in turn translates to a grating period of dx=4dy, dy=2.887 mm). Finally, the generalized Snell's law sin(θr)=sin(θi)+grad(φ) * For an operating frequency of 30 GHz using λ / 2π, this results in a beam steering performance of 0 to 60 degrees. Examples 3, 4 and 5 have respective patterns that correspond to the grating patterns 120, 142 and 162 of Figure 1. The only difference between Examples 3 to 5 is the grating arrangement along the y direction, as shown in Figures 9A-9C.

[0063] Example 6: Basic set of reflectarrays at L-junction In Example 6, multiple reflectarrays are placed at an L-junction according to the configuration shown in FIG. 3D. The performance of multiple reflectarrays was tested when they were combined into a beam steering configuration. Here, an L-corner inside a building was selected as the test environment shown in FIG. 10A. Multiple reflectarrays from Example 1 were combined into two large 76.8 cm x 40.1 cm stacks (Assay 1 and Assay 2), which were then placed on both walls of the L-junction. Although such a rolled-up structure is optimal at 0 degrees → 40 degrees rather than 0 degrees → 45 degrees beam redirection performance, the structure still performs well overall and within the previous reflectarray angle range defined for 80 degrees < |θ1| + |θ2| < 100 degrees (see the inset of FIG. 3D for θ1, θ2 angle definition). The performance of these arrays is compared to the specular performance of a flat aluminum sheet (ie, Reference Example 0) having dimensions of 96.8 cm x 96.8 cm (45 degree projection is comparable to the dimensions of Arrays 1 or 2).

[0064] First, we determined the expected beam steering performance for an idealized configuration / system as shown in Figure 3D. Using basic ray optics theory, we find that the output angle δ of this system depends on the off-normal input angle θ (as visualized in the inset of Figure 10B) in the following equation (2):

number

[0065] Since the optimum angle of the reflectarray in array 1 or 2 is 40 degrees instead of 45 degrees (and does not sum to 90 degrees as shown in FIG. 3D), the actual output angle of Example 6 was evaluated as a function of frequency when the input beam is vertically incident (considering the case of x=0, i.e., θ1=θ2=45 degrees, as visualized in FIG. 3D). To this end, ray optics and reflectarray theory were used to arrive at the curve plotted in FIG. 10C, which shows a plot of output angle vs. frequency for Example 6, which is composed of multiples of Example 1, with the incident beam strictly vertical. The extra x-axis (green) is the θ1=θ2=θ 1、28C shows the effective reflectarray parameters for the ((0→θ1),(0→θ2)) system obtained by the formula: The reflectarray of Example 6 was originally designed for 27.9 GHz, at which frequency the output angle is δ=0 degrees. As shown by the single reflectarray spectrum in FIG. 8C, the amount of signal that can actually be transferred at this frequency is very small. In contrast, at the optimum performance frequency of about 31 GHz, the expected steering angle was observed to shift to δ=-8 degrees. This simulation result is in close agreement with the actual data point δ=-6.5 degrees in (a), which was found when the two horn antennas (connected to the network analyzer) were placed about 10 feet (3.05 m) away from the reflectarray, so that the incidence angle was fixed at θ=0 degrees, but the receiver was moved off-center until the signal maximum was achieved (at 31.1 GHz).

[0066] Figure 10D shows the total reflection spectrum of the reflectarray recorded using a network analyzer. Notably, the band center of the system of Example 6 is shifted to the right by about 0.5 GHz compared to the band center of the single reflectarray of Example 1 (see solid blue line in Figure 8C). The 3 dB bandwidth also drops from 12.3% reached by the single reflectarray to about 5.4%, which is likely a result of the larger reflectarray area (Huang & Encinar, 2008) as well as their mutual near-field interactions. It was observed that removing the sample results in a signal drop of about 50 dB (as shown in yellow), i.e., the L-junction is nearly impenetrable for mm-wave signals. In contrast, the arrangement of aluminum mirrors in a mirror geometry results in a signal (shown in green) that is comparable to the direct line-of-sight (DLOS) case (as measured when the two horns are facing each other, shown in red). Overall, at the optimum 31.1 GHz frequency, the reflectarray is about 9 dB worse than the mirror, with about 4 dB of that coming from the larger cumulative optical path. The remaining ~5 dB loss amounts to about 2.5 dB per sample, which is comparable to the value obtained in Figure 8C. Small extra losses may arise from destructive interference due to lattice mismatch of the elements that make up the stacked reflectarray, as well as non-flatness of the samples we mounted.

[0067] Finally, complementary measurements were made at longer distances by placing the transmitter and receiver horns 25 ft and 35 ft away from the reflectarray (Figure 10E). In this case, a different setup was used consisting of a signal generator on the TX side and an amplifier with a voltmeter on the RX side. Measurements taken at optimal performance at 31.1 GHz are shown in blue for the reflectarray and in green for the specular Al mirror. For the Al mirror, the total distance path loss model P (equivalent to free space) was used. r ~(d1+d2) -2The corresponding theoretical curves are plotted, where d1 (d2) is the distance from the transmitter (receiver) (Wu, 2021). Overall, it was observed that at longer distances, Example 6 is about 17 dB worse than the Al mirror. The two-fold larger value compared to the previous figure of about 9 dB is likely the result of poor sample and horn alignment at longer distances.

[0068] The results of Example 6 show that the reflectarrays perform very well even after being combined together (even though their reflectarray angles are slightly out of spec). The resulting performance is somewhat worse than that of the Al mirror, but is at least about 50 dB better than the absence of any wall at the L junction. It can be expected that the reflectarrays, once properly pre-modeled and placed together, can substantially improve mmWave signal propagation in problematic NLOS areas such as hallway junctions.

Claims

1. 1. A method for enhancing a non-line-of-sight (NLOS) signal for wireless communication, comprising: providing a plurality of passive reflectarrays including a first reflectarray and a second reflectarray, at least one of the reflectarrays comprising a pattern of repeating unit cells of resonating elements configured to reflect incident radio frequency (RF) electromagnetic waves of a wavelength λ in a range from about 1.0 mm to about 10.0 cm, the first reflectarray having a first phase gradient along its first longitudinal direction and the second reflectarray having a second phase gradient along its second longitudinal direction; and positioning at least one of the first and second passive reflective arrays to face the incident RF electromagnetic wave such that the incident RF electromagnetic wave is reflected by the first and second passive reflective arrays with a signal improvement of at least 3 dB.

2. The method of claim 1 , wherein at least one of the first reflectarray and the second reflectarray provides non-linear steering performance.

3. The method of claim 1 , wherein at least one of the first reflectarray and the second reflectarray provides angular-spatial separation.

4. The method of claim 1 , wherein the at least one of the first reflectarray and the second reflectarray provides beamsplitting capabilities.

5. The method of claim 1 , wherein at least one of the plurality of passive reflectarrays is disposed on a ceiling or a floor at a T-junction, an L-junction, or a four-way junction.

6. The method of claim 5 , wherein the at least one of the plurality of passive reflectarrays provides out-of-plane steering.

7. The method of claim 1 , wherein the incident RF electromagnetic waves are from a network featuring adaptive beamforming on the transmitting or receiving end.

8. 1. A system for enhancing a non-line-of-sight (NLOS) signal for wireless communications, comprising: one or more passive reflectarrays, at least one of the reflectarrays comprising a pattern of repeating unit cells of resonating elements configured to reflect incident radio frequency (RF) electromagnetic waves having a wavelength λ in a range from about 1.0 mm to about 10.0 cm; the one or more passive reflectarrays comprising at least one of a first reflectarray configured to split an incident beam and a second reflectarray configured to steer the incident beam out of a plane of incidence.

9. 10. The system of claim 8, wherein the resonating elements of a first reflectarray row are arranged in alternating row directions.

10. 10. The system of claim 8, wherein the resonating elements of the first reflectarray row are arranged in a checkerboard pattern.

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