Multi-band reconfigurable intelligent surface (RIS)

Abstract

An assembly is provided including a first layer defining a two-dimensional plane. The first layer includes one or more first unit cells configured to operate at a first frequency. Each of the first unit cell(s) defines a first surface coverage area in the two-dimensional plane. The first layer also includes a plurality of second unit cells configured to operate at a second frequency. Each of the second unit cells defines a second surface coverage area in the two-dimensional plane. The second surface coverage area is less than the first surface coverage area. A first unit cell of the first unit cell(s) defines at least two openings within a footprint correponding to an outer perimeter of the first unit cell. At least a portion of two or more second unit cells of the second unit cells is positioned inside of the openings defined in the first unit cell, respectively.

Description

MULTI-BAND RECONFIGURABLE INTELLIGENT SURFACE (RIS)CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of priority under 35 U.S.C. § 119 of U.S. Provisional Application Serial No. 63 / 638676 filed on April 25, 2024, the content of which is relied upon and incorporated herein by reference in its entirety.FIELD

[0002] Embodiments relate generally to reconfigurable intelligent surfaces (RIS) including a dual band region comprising small unit cells and large unit cells within a single layer.BACKGROUND

[0003] 5G, 6G, and satellite communications use higher frequency bands relative to previous 2G, 3G, and 4G communications. Thus, these 5G, 6G, and satellite communications suffer from high propagation losses relative to previous 2G, 3G, and 4G communications. To help address this issue for 5G, 6G, and satellite communications, reconfigurable intelligent surfaces (RIS) have been used to optimize propagation paths by steering radiation waves from a base station and a user device. These new wireless communications operate across two or more bands that are distributed in a wide frequency spectrum.

[0004] Frequency bands occupied for 5G and 6G communications might be differently distributed from 3 GHz to 300 GHz according to the requirements of certain telecommunication companies and countries. Generally, the 5G frequency spectrum is largely divided into the sub- 6 GHz band or the millimeter wave (mmWave) band. Most of today’s 5G network systems adopt the sub-6GHz band due to its lower propagation loss, which creates wider coverage than that of the mmWave band. On the other hand, the mmWave band can be used for securing much higher data rates at limited cases, even though it is expected to have a smaller coverage area.

[0005] In an attempt to accommodate both the mmWave band and the sub-6GHz band, some have attempted to use multi-layer RIS to provide multi-band RISs. However, multiple layers lead to increases in the fabrication cost and thickness of a product. Additionally, the use of multiple layers often causes interference between elements of the different layers, with one layer blocking signals for elements in another layer. This interference degrades the overall performance of a multi-layer RIS. Others have also attempted to position a frequency selective surface (FSS) in a separate layer that is spaced from unit cells in another layer, but this leadsto a relatively complicated and bulky structure. This also leads to a high fabrication cost and blockage of signals for the RIS.

[0006] Other attempts to form a dual band RIS with a single layer structure also have had shortcomings. Others have attempted to interlace two different unit cells of RIS patterns on the same substrate with the same periodicity but with each unit cell operating at a different frequency. This approach often causes a bigger grating lobe at an upper frequency if the frequency ratio (the upper frequency divided by the lower frequency) increases more because it means a wavelength distance between unit cells for the upper frequency should be considerably increased. Therefore, the frequency ratios in most preceding attempts at forming dual band RISs were set from 1.5 to less than 3. Additionally, forming dual -band RIS using existing approaches is very difficult because dual band RIS require unit cells with significantly different sizes, making it difficult to arrange the unit cells on the same surface without conflicts and also making it difficult to suppress high grating lobes due to sparsely deployed unit cells. Additionally, mutual interference between unit cells for both frequency bands has to be reduced to secure a stable designated phase (regardless of positions) for unit cells even though the unit cells are located very closely to each other.

[0007] Additionally, attempts to position unit cells of different sizes in a single layer has led to mutual interference between small unit cells and large unit cells in the same layer, with electromagnetic coupling occuring to cause an electrical signal to jump a gap from one unit cell to the other. Dual-band, single layer RISs have also led to issues with abnormal differences in periodicity between unit cells. To limit this mutual interference, the unit cells may be spaced farther apart from each other, but space limitations are already a pressing concern when attempting to deploy a dual band region in a single layer.

[0008] To compensate for propagation loss, high gain phased array antennas have been employed. However, if many radiation elements are used, then the gain of any array antenna often becomes over saturated. This happens due to the high loss of long feeding networks, shown in cases like base stations using many radiators. Some network operators deploy repeaters using amplifiers with semiconductors to solve these high loss problems. However, using repeaters tends to increase costs because expensive repeaters for 5G and 6G communications are often densely installed to compensate for high propagation loss resulting from the use of high frequency bands. Additionally, repeaters typically have to be installed in specific locations that are capable of reaching electrical power sockets because they need considerable power to amplify the RF signal. Continuous power consumption to the repeater is also a drawback from a carbon neutrality perspective.BRIEF SUMMARY

[0009] Various embodiments described herein help realize the benefits of a multi-layer RIS by providing a dual -band region on a single layer of an RIS. A dual -band region may be accomplished even where the frequency ratio (the upper frequency divided by the lower frequency) between the different bands is two or more. The multi-layer RIS may be utilized in 5G, 6G, and satellite communications, with lower frequencies set to sub-6GHz band levels and with higher frequencies set to mmWave band levels. However, the multi-layer RIS may be utilized for other purposes as well. In various embodiments, RISs are provided with small unit cells and large unit cells within a single layer, with the small unit cells and large unit cells having various beam widths and reflection (or transmission) angles, and these properties may be independent to the operating frequency and other properties of other unit cells.

[0010] RISs may be provided with a single layer, with both large unit cells and small unit cells positioned in this single layer. The large unit cells cover a larger surface coverage area relative to the small unit cells, and the large unit cells may have a lower frequency relative to the small unit cells. The large unit cells may have one or more openings defined within their surface coverage area, and a small unit cell or a portion thereof may be positioned within each of these openings. Doing so may allow for the large unit cells and the small unit cell to fit within a single layer, and doing so may also allow the large unit cells to have a high surface coverage area and a low frequency relative to the small unit cells. In some embodiments, the frequency ratio for an RIS may be at least about two, but this frequency ratio may be significantly higher.

[0011] Additionally, large unit cells may be provided with one or more stubs and a body, with the stubs extending outwardly from the body. The stub may extend on an RIS so that the stub does not interfere with any small unit cells positioned on the RIS. During the design of an RIS, the size and / or length of a stub may be easily adjusted without requiring significant changes to the body of the large unit cells. Adjustments to the stub may also keep the overall geometry and distance between adjacent cells the same. Thus, the stubs may enable fine-tuning of properties such as surface coverage area, frequency, frequency ratio, phase, inductance, capacitance, and / or resistance.

[0012] Small unit cells may comprise a boundary structure that encircles portions of the small unit cell for a higher frequency to block the electromagnetic field for adjacent unit cells. This boundary structure may be provided in the form of a closed loop structure. The boundary structure may be part of a large unit cell for some small unit cells, but the boundary structuremay not be part of the large unit cell for other small unit cells. The boundary structure serves as a guard structure that reduces mutual interference from adjacent small and large unit cells.

[0013] In an example embodiment, an assembly is provided. The assembly comprises a first layer defining a two-dimensional plane. The first layer comprises one or more first unit cells configured to operate at a first frequency, and each of the one or more first unit cells defines a first surface coverage area in the two-dimensional plane. The first layer also comprises a plurality of second unit cells configured to operate at a second frequency, where a frequency ratio may be equal to the second frequency divided by the first frequency, and each of the plurality of second unit cells defines a second surface coverage area in the two- dimensional plane, and the second surface coverage area is less than the first surface coverage area. A first unit cell of the one or more first unit cells defines at least two openings within a footprint correponding to an outer perimeter of the first unit cell, and at least a portion of two or more second unit cells of the plurality of second unit cells are positioned inside of the at least two openings defined in the first unit cell, respectively.

[0014] In some embodiments, the frequency ratio may be at least about two. In some embodiments, the assembly may be a reconfigurable intelligent surface assembly.

[0015] In some embodiments, each first unit cell of the one or more first unit cells may comprise a stub extending in the two-dimensional plane without coming in contact with any of the plurality of second unit cells. Additionally, in some embodiments, each first unit cell of the one or more first unit cells may comprise a body, and the stub may extend a first length in the two-dimensional plane from the body. Furthermore, in some embodiments, the first frequency and the frequency ratio may be dependent upon a size of the stub. In some embodiments, the first frequency and the frequency ratio may be dependent upon the first length. In some embodiments, a phase of each first unit cell of the one or more first unit cells may be dependent upon a size of the stub. Additionally, in some embodiments, the stub may define a width in the two-dimensional plane. The plurality of second unit cells may be spaced apart from each other in a grid pattern, adjacent second unit cells may be spaced apart by a minimum distance from each other, and the width of the stub may be less than the minimum distance such that the stub is capable of extending through a space between the adjacent second unit cells.

[0016] In some embodiments, each second unit cell of the plurality of second unit cells may have an associated boundary structure configured to reduce interference from other second unit cells. A first boundary structure for a first set of one or more second unit cells may be part of a respective first unit cell of the one or more first unit cells, and a second boundary structurefor a second set of one or more second unit cells may be provided that is is not part of the one or more first unit cells.

[0017] In some embodiments, each second unit cell of the plurality of second unit cells may possess an identical boundary shape. Furthermore, in some embodiments, the boundary shape may be at least one of a square shape, a rectangular shape, a triangular shape, a polygonal shape, a circular shape, an oval shape, or an asymmetrical shape. In some embodiments, each second unit cell of the plurality of second unit cells may comprise a boundary structure configured to reduce interference from other second unit cells of the plurality of second unit cells.

[0018] In some embodiments, each second unit cell may define a central portion and an outer portion in the two-dimensional plane, the outer portion may surround the central portion, and the outer portion may be separated from the central portion by a gap. Furthermore, in some embodiments, at least one of a resistance, a capacitance, or an inductance generated by each second unit cell of the plurality of second unit cells may depend at least partially on a size of the gap and a size of the central portion.

[0019] In some embodiments, each first unit cell of the one or more first unit cells may define a first length, each second unit cell of the plurality of second unit cells may define a second length that extends parallel to the first length, and a length ratio may be equal to the first length divided by the second length. Increasing the length ratio may result in an increase in the frequency ratio.

[0020] In some embodiments, each first unit cell of the one or more first unit cells may define four openings within the first surface coverage area, and a second unit cell of the plurality of second unit cells may be positioned inside each of the four openings, respectively. In some embodiments, a first thickness of each first unit cell of the one or more first unit cells may be about the same as a second thickness of each second unit cell of the plurality of second unit cells.

[0021] In another example embodiment, an assembly is provided. The assembly comprises a first layer defining a two-dimensional plane. The first layer comprises one or more first unit cells configured to operate at a first frequency. Each of the one or more first unit cells defines a first surface coverage area in the two-dimensional plane. The first layer also comprises a plurality of second unit cells configured to operate at a second frequency. Each second unit cell of the plurality of second unit cells defines a second surface coverage area in the two- dimensional plane, and the second surface coverage area is less than the first surface coverage area. A frequency ratio is equal to the second frequency divided by the first frequency, and thefrequency ratio is at least about two. In some embodiments, the frequency ratio may be at least about eight or at least about thirty -two.

[0022] In another example embodiment, an assembly is provided. The assembly comprises a first layer defining a two-dimensional plane. The first layer comprises one or more first unit cells configured to operate at a first frequency, and each of the one or more first unit cells defines a first surface coverage area in the two-dimensional plane. The first layer also comprises a plurality of second unit cells configured to operate at a second frequency. Each second unit cell of the plurality of second unit cells defines a second surface coverage area in the two-dimensional plane, and the second surface coverage area is less than the first surface coverage area. A first unit cell of the one or more first unit cells defines an opening within a footprint correponding to an outer perimeter of the first unit cell. At least a portion of a second unit cell of the plurality of second unit cells is positioned inside of the opening defined in the first unit cell. The first unit cell comprises a stub extending in the two-dimensional plane without coming in contact with any of the plurality of second unit cells. A frequency ratio is equal to the second frequency divided by the first frequency, and the first frequency and the frequency ratio are dependent upon a size of the stub.

[0023] In some embodiments, the first frequency, the frequency ratio, and the phase may be dependent upon the size of the stub. Additionally, in some embodiments, the stub may define a width in the two-dimensional plane, the plurality of second unit cells may be spaced apart from each other in a grid pattern, adjacent second unit cells may be spaced apart by a minimum distance from each other, and the width of the stub may be less than the minimum distance such that the stub is capable of extending through a space between the adjacent second unit cells. In some embodiments, each second unit cell of the plurality of second unit cells may have an associated boundary structure configured to reduce interference from other second unit cells.BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and wherein:

[0025] FIG. l is a graphic illustrating various frequency bands that may be utilized in 5G, advanced 5G (5G-A), and 6G wireless communications, in accordance with some embodiments discussed herein;

[0026] FIG. 2 is a schematic view illustrating an RIS being used to tilt incident waves from a small unit cell and a mobile device to pave new and effective communication channel signals, in accordance with some embodiments discussed herein;

[0027] FIG. 3 is a top view illustrating an example RIS assembly with small unit cells and large unit cells, in accordance with some embodiments discussed herein;

[0028] FIG. 4 is a top view illustrating an example RIS assembly with small unit cells and large unit cells, in accordance with some embodiments discussed herein;

[0029] FIG. 5 is a top view illustrating an example small unit cell, in accordance with some embodiments discussed herein;

[0030] FIG. 6 is a schematic view illustrating various designs that may be used for small unit cells, in accordance with some embodiments discussed herein;

[0031] FIG. 7 illustrates various metal structures that may be used to form small and large unit cells, in accordance with some embodiments discussed herein;

[0032] FIG. 8A is a top view illustrating an example RIS with a cross-dipole style unit cell positioned on a substrate, in accordance with some embodiments discussed herein;

[0033] FIG. 8B is a line graph illustrating phase change as a function of distance, with the distance being the distance from one side of the cross-dipole style unit cell of FIG. 8A to the opposite side, in accordance with some embodiments discussed herein;

[0034] FIG. 8C is a line graph illustrating the reflection magnitude as a function of distance, with the distance being the distance from one side of the cross-dipole style unit cell of FIG. 8 A to the opposite side, in accordance with some embodiments discussed herein;

[0035] FIG. 9A is a top view illustrating an example RIS having a dual-band region with both small unit cells and a large unit cell, with the large unit cell having openings therein and with small unit cells being positioned within the openings, in accordance with some embodiments discussed herein;

[0036] FIG. 9B is an enhanced, top view illustrating the RIS of FIG. 9A, in accordance with some embodiments discussed herein;

[0037] FIG. 9C is a line graph illustrating the phase change as a function of distance, with the distance being the stub length used on the large unit cell of FIG. 9A, in accordance with some embodiments discussed herein;

[0038] FIG. 9D is a line graph illustrating reflection magnitude as a function of distance, with the distance being the stub length used on the large unit cell of FIG. 9A, in accordance with some embodiments discussed herein;

[0039] FIG. 10A is a top view illustrating an example small unit cell having a double ring structure with a central circle patch, in accordance with some embodiments discussed herein;

[0040] FIG. 10B is a line graph illustrating the phase change as a function of distance from a center of the circle patch to the outer perimeter of the inner ring of the small unit cell of FIG. 10A, in accordance with some embodiments discussed herein;

[0041] FIG. 10C is a line graph illustrating the reflection magnitude as a function of distance from a center of the circle patch to the outer perimeter of the inner ring of the small unit cell of FIG. 10A, in accordance with some embodiments discussed herein;

[0042] FIG. 11 A is a top view illustrating an example small unit cell with a single ring and a circle patch, in accordance with some embodiments discussed herein;

[0043] FIG. 1 IB is a line graph illustrating the phase change as a function of distance from a center of the circle patch to the outer perimeter of the ring, in accordance with some embodiments discussed herein;

[0044] FIG. 11C is a line graph illustrating the reflection magnitude as a function of distance from a center of the circle patch to the outer perimeter of the ring, in accordance with some embodiments discussed herein; and

[0045] FIG. 12 is a cross-sectional view illustrating an example RIS with both a small unit cell and a large unit cell, with the large unit cell having an opening therein and with the small unit cell being positioned within the opening, in accordance with some embodiments discussed herein.DETAILED DESCRIPTION

[0046] Example embodiments now will be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all embodiments are shown. Like reference numerals generally refer to like elements throughout. For example, reference numbers 322A-322E, 422A-422B, and 522 each refer to small unit cells. Additionally, any connections or attachments may be direct or indirect connections or attachments unless specifically noted otherwise.

[0047] 5G and 6G wireless communications may adopt frequency bands over around 3 gigahertz (GHz) to secure a wide bandwidth while avoiding 2G / 3G / 4G legacy bands. Frequencies over around 3 GHz (e.g., around 3.5GHz and around 30GHz) are notably considered for 5G wireless communications, and frequencies over around 7.125 GHz (around 10 GHz and around 100 GHz) have also been considered for 6G wireless communications. Additionally, a satellite spectrum between around 2 GHz and around 50 GHz may be used in advanced 5G and 6G communications for non-terrestrial networks (NTN), which may use airborne or spaceborne vehicles or devices for communication.

[0048] As noted previously, the 5G frequency spectrum is largely divided into the sub-6 GHz band or the mmWave band. To accommodate both the sub-6GHz band and the mmWave band, a dual-band RIS might operate around 3.5 GHz (sub-6GHz) and 28 GHz (mmWave) bands, so 5G dual band RIS may be designed while considering a very high frequency ratio of about 8. However, other frequency ratios may be utilized.

[0049] FIG. 1 is a graphic 100 illustrating various frequency bands that may be utilized with 5G and 6G wireless communications. 5G and 5G-A wireless communications often occur at frequency bands of between around 450 MHz and around 7.125 MHz as well as a frequency band of between 24 GHz and about 52 GHz. 6G wireless communications may occur in these bands as well, but 6G wireless communications may be configured to operate in a new spectrum spanning from about 7.125 GHz to about 15.35 GHz.

[0050] Frequency bands that may be utilized for satellite communications may include a S band, a C band, an X band, a Ku band, a Ka band, and a Q / V band. The S band may span from about 1.97 GHz to about 2.69 GHz. The C band may span from about 3.4 GHz to about 7.025 GHz. The X band may span from about 7.25 GHz to about 8.44 GHz. The Ku band may span from about 10.7 GHz to about 14.5 GHz. The Ka band may span from about 17.3 GHz to about 30 GHz. The Q / V band may span from about 37.5 GHz to about 51.4 GHz.

[0051] However, there are challenges in transmitting and receiving wireless signals of very high frequencies. When these high frequency wireless signals are used, they may experience significantly higher propagation loss and reflection loss due to obstacles. As a result, the wireless signal quality of high frequency wireless signals may be severely degraded as the communication distance increases.

[0052] In order to improve propagation channel conditions between base stations and mobile devices, RIS may be used. These RISs have been used to tilt incident waves from a small cell and a mobile device to pave new and effective communication channel signals, and an example of this is illustrated in the schematic view of FIG. 2. In FIG. 2, a typical deployment environment 202 for an RIS 205 is illustrated. Within this environment 202, a base station 204, and a mobile device 208 are included. The mobile device 208 may take a variety of forms (e.g., a smart phone, a tablet, etc.). The base station 204 and the mobile device 208 generate multiple radiation beams in different directions in order to find the best possible communication channel. Communication channels extending close to a straight line between the mobile device 208 and the base station 204 may be the best possible communication channel in some instances, but these communication channels may not be effective in some environments because of a blockage 206. The blockage 206 may cause issues even when the distance betweena base station 204 and a mobile device 208 is very short. For example, in FIG. 2, the arrows Al extend in a straight line between the base station 204 and the mobile device 208. However, a blockage 206 interferes with the communication channel represented by arrows Al. 5G communications often suffer from high propagation losses and are often more susceptible to physical blockages such as blockage 206.

[0053] RISs may be used to help address these issues. In FIG. 2, the RIS 205 tilts incident waves from the base station 204 and the mobile device 208 along arrows A2 to pave a new and effective communication channel. RISs may result in a concentration of incident signals at a desired reflection angle with a shaped beam. The RIS 205 may consist of sub -wavelength resonators, which may adaptively reflect, transmit, absorb, and convert the polarizations of an incident wave with low power consumption. The RIS may be either a passive or active RIS in some embodiments, with active RIS devices consuming electric power and with passive RISs not consuming any electric power. By providing passive RISs that do not consume any electric power, the passive RISs may be more environmentally friendly. The RIS 205 and other RISs described herein are passive RISs, but active RISs may also be used.

[0054] RISs may be fabricated at a low cost, particularly where passive RIS devices are used. Where active RISs are used, additional materials such as substrates, conductive materials, and impedance control components may be used to help control a signal reflection direction. To fabricate an active RIS, additional active components such as pin diodes, varactors, liquid crystal (LC), transistors, micro electro-mechanical systems (MEMS), ferroelectric films, and graphene may also be used.

[0055] An example RIS assembly 310 with small unit cells and large unit cells is illustrated in the top view of FIG. 3. All of the small unit cells and large unit cells are positioned in a single layer rather than spreading these unit cells across two or more layers. The RIS assembly 310 comprises two large unit cells, including first large unit cell 312A and second large unit cell 312B. Each of the large unit cells 312A, 312B may be configured to operate at a first frequency, and each of the large unit cells 312 A, 312B may define a first surface coverage area in a two-dimensional plane that is visible in FIG. 3.

[0056] The RIS assembly 310 also comprises several small unit cells, including a first small unit cell 322, a second small unit cell 322B, a third small unit cell 322C, a fourth small unit cell 322D, and a fifth small unit cell 322E. Each of the small unit cells possess an identical boundary shape, with this boundary shape being a square shape in FIG. 3. However, as discussed in reference to FIG. 6 and in reference to other figures, other boundary shapes may be utilized in other embodiments. By keeping the boundary shape of small unit cells the samewithin an RIS assembly, consistent phases may be obtained at the upper frequency band. While all of the small unit cells possess the same boundary shape in FIG. 3, some small unit cells may have different boundary shapes in other embodiments.

[0057] The small unit cells are configured to operate at a second frequency. The second frequency of the small unit cells is larger than the first frequency of the large unit cells 312A, 312B so that a frequency ratio for the RIS assembly 310 is greater than one. The frequency ratio for the RIS assembly 310 may be calculated by dividing the second frequency of the small unit cells by the first frequency of the large unit cells 312A, 312B. In some embodiments, this frequency ratio may be at least about two. Where the frequency ratio is less than two, the large unit cells and small unit cells may have much more similar surface coverage areas, and this may make it more difficult to fit the large unit cells and small unit cells in a single layer with small unit cells positioned within openings of the large unit cells.

[0058] In some embodiments, a unit cell may cover a fundamental frequency and harmonic frequencies based on that fundamental frequency. Generally, the unit cells described herein may be configured to operate at a fundamental frequency (fo), and the frequencies described herein are generally a fundamental frequency rather than a harmonic frequency unless explicitly noted otherwise. In addition to the fundamental frequencies at which the unit cells are configured to operate, the unit cells may also be configured to operate at harmonic frequencies (fo x n, where n= 2, 3, 4, ... .).

[0059] However, frequency ratios may be even higher in some embodiments, with frequency ratios of at least about two, at least about three, at least about four, at least about five, at least about six, at least about eight, at least about twelve, at least about twenty four, or at least about thirty two. Theoretically, the frequency ratios may increase to infinity as the small unit cells may be made infinitesimally smaller to cause the frequency ratios to significantly increase. However, other practical considerations such as the ability to effectively make small unit cells and / or other considerations may create an upper limit on the frequency ratio.

[0060] Each of the small unit cells defines a second surface coverage area in a two- dimensional plane that is visible in FIG. 3. The second surface coverage area for each of the small unit cells is less than the first surface coverage area for each of the large unit cells. In FIG. 3, each large unit cell defines a length Cl in directions parallel to the X-axis, and each small unit cell defines a length C2 in directions parallel to the X-axis. The length Cl may be the length of the body for each large unit cell without including the additional length added by any stubs. For example, the length Cl is the length of the body 375 without including the additional length provided by stubs 314A-314D. A length ratio is defined as the length Cl ofthe large unit cells divided by the length C2 of the small unit cells. In some embodiments, the frequency ratio may increase as the length ratio increases. In some embodiments, this length ratio may be equal to the frequency ratio.

[0061] The RIS assembly 310 comprises single band regions 365A and dual band regions 365B. The single band regions 365A are areas where only small unit cells are present, and the dual band regions 365B are areas where both small unit cells and large unit cells are present. The single band regions 365 A are each positioned outside of a footprint correponding to an outer perimeter of the large unit cells 312A, 312B, and the dual band regions 365B are each positioned inside of the footprint correponding to the outer perimeter of the large unit cells 312A, 312B.

[0062] To enable dual band regions 365B to be used, the large unit cells 312A, 312B each define openings within the footprint correponding to an outer perimeter of the large unit cells 312A, 312B. For example, openings 316A, 316B are defined in the large unit cell 312A, and openings 316C, 316D are defined in the large unit cell 312B. Each of the openings defined within the large unit cells 312A, 312B may be configured to receive a small unit cell. For example, the opening 316A receives the first small unit cell 322A, the opening 316B receives the second small unit cell 322B, the opening 316C receives the third small unit cell 322C, and the opening 316D receives the fourth small unit cell 322D. The fifth small unit cell is positioned in a single band region 365 A.

[0063] Each of the small unit cells are identical to each other in FIG. 3. For example, the small unit cell 322D comprises a center patch 324D having a square shape, a ring 326D having a square shape, and a gap positioned between the center patch 324D and the ring 326D. The small unit cell 322E also comprises a center patch 324E having a square shape, a ring 326E having a square shape, and a gap positioned between the center patch 324E and the ring 326E. However, small unit cells having different shapes may be utilized in a single layer in other embodiments. For example, small unit cells and / or large unit cells may be provided with some geometry variation to cause the unit cells to operate at different phases.

[0064] The large unit cell 312A and the large unit cell 312B may each comprise a body and stubs that extend outwardly from the body. For example, the large unit cell 312A comprises a body 375 and stubs 314A, 314B, 314C, 314D extending outwardly from the body 375. The stubs 314A-314D extend outwardly from the body 375 without coming in contact with any of the small unit cells or other large unit cells. The stubs 314A-314D may each possess an identical shape and size in some embodiments, but these stubs 314A-314D may differ in shape and / or size in other embodiments to distinguish the phase, a frequency, or other properties of alarge unit cell from other unit cells. For example, changing the length of one or more of the stubs 314A-314D may impact various properties of the large unit cell 312B. The stubs 314A- 314D may also be used to adjust the frequency ratio for an RIS.

[0065] The small unit cells and the large unit cells 312A, 312B of FIG. 3 and other unit cells described herein may each comprise transparent metal structures such as meshed patterns, silver nano wire, carbon nano tubes, or graphene structures. These transparent metal structures are each illustrated in FIG. 7, with a meshed pattern structure 750 A, a silver nano wire structure 750B, a carbon nano tube structure 750C, and a graphene structure 750D being illustrated in FIG. 7. Unit cells may also include a metallic material such as copper. However, other solid metal patterns or other structures may be utilized to form unit cells described herein.

[0066] Looking now at FIG. 4, an example RIS assembly 410 with small unit cells and large unit cells is illustrated, with the small unit cells being spaced apart from each other evenly within a grid pattern. The small unit cells of FIG. 4 are identical to the small unit cells of FIG. 3, but small unit cells of FIG. 4 are spaced apart in both rows and columns.

[0067] Four different large unit cells are visible in the RIS assembly 410, including a first large unit cell 412A, a second large unit cell 412B, a third large unit cell 412C, and a fourth large unit cell 412D. However, other large unit cells may also be included in the RIS assembly 410. The single band regions 465 A are each positioned outside of a footprint correponding to an outer perimeter of the large unit cells 412A-412D, and the dual band regions 465B are each positioned inside of a footprint correponding to an outer perimeter of a respective large unit cell. While the large unit cells of FIG. 3 included only two openings, the large unit cells 412A- 412D illustrated in FIG. 4 each have four openings, and a small unit cell is positioned inside each of the openings. For example, the large unit cell 412C includes openings 416A, 416B, and a small unit cell 422 A is positioned in the opening 416B. Small unit cells 422B are also positioned in the single band regions 465A. The small unit cells 422A positioned in dual band regions 465B and the small unit cells 422B positioned in the single band regions 465A are identical in FIG. 4, but these small unit cells 422A, 422B may possess different geometries in other embodiments.

[0068] The large unit cells 412A-412D each comprise four stubs extending outwardly from a body of the large unit cells 412A-412D. An example of this is illustrated in the third large unit cell 412C where a stub 414 extends outwardly from the body. The stubs may operate in a similar fashion to the stubs described in reference to FIG. 3.

[0069] In FIG. 4, each large unit cell defines a length C3 in directions parallel to the X- axis, and each small unit cell defines a length C4 in directions parallel to the X-axis. The lengthC3 may be the length of the body for each large unit cell without including the additional length added by any stubs. A length ratio is defined as the length C3 of the large unit cells divided by the length C4 of the small unit cells. In some embodiments, the frequency ratio may increase as the length ratio increases. In some embodiments, this length ratio may be equal to the frequency ratio.

[0070] An example small unit cell 522 is illustrated in FIG. 5. The small unit cell 522 is similar to the ones illustrated in FIGS. 3 and 4. The small unit cell 522 includes a central patch 524, and the small unit cell 522 includes a boundary structure in the form of outer ring 526. The outer ring is positioned outwardly from the central patch 524. The outer ring 526 is configured to reduce interference from other small unit cells when the small unit cell 522 is utilized in an RIS. The outer ring 526 and other boundary structures described herein may decrease the total capacitance between small unit cells so that electric coupling between these small unit cells is reduced. Both the outer ring 526 and the central patch 524 have a square shape, but these components may have different shapes in other embodiments.

[0071] The central patch 524 has a minimum width DI, and a gap width D2 is defined between the boundary of the central patch 524 and the inner boundary of the outer ring 526. The minimum width DI and gap width D2 may be adjusted during the design process to obtain a small unit cell with the desired properties. For example, changing these values may impact the surface coverage area and the frequency for the small unit cell 522. Changing these values may also impact other parameters such as the resistance, inductance, and / or the capacitance for the small unit cell 522.

[0072] In some embodiments, small unit cells may each have a consistent boundary shape, and this may help to reduce the effects of adjacent unit cells. The boundary shape of the small unit cells may ensure that a gap is present between a large unit cell and inner parts of small unit cells. Also, the outer ring or another boundary structure of a small unit cell may act as a barrier, reducing electromagnetic coupling between the inner parts of the small cells. However, other features of the small unit cells’ geometries may be altered slightly to alter the phase and / or other properties of the small unit cells. For example, the small unit cell 522 has an outer ring 526 and a central patch 524. In some embodiments, an adjacent small unit cell may have an outer ring that is identical to the outer ring of small unit cell 522, but the size and / or shape of the central patch for the adjacent small unit cell may be different from the size and / or shape of the small unit cell 524. In other embodiments, the shape and / or size of an inner boundary of the outer ring 526 may vary between small unit cells. While only one ring is included in the small unit cell 522 of FIG. 5, additional rings may be included.

[0073] Various designs may be used for small unit cells within an RIS, and various examples are illustrated in FIG. 6. The boundary shapes for the small unit cells may be provided in a square shape, a rectangular shape, a triangular shape, a polygonal shape, a circular shape, an oval shape, or an asymmetrical shape. However, other boundary shapes may be used for the small unit cells.

[0074] A triangular shaped small unit cell 630 is illustrated in FIG. 6. This triangular shaped small unit cell 630 comprises an outer ring 630 A, with the outer ring 630 A defining an outer boundary and an inner boundary, with both boundaries having a triangular boundary shape. An inner ring 630B is positioned inwardly from the outer ring 630A. This inner ring 630B defines an outer boundary and an inner boundary, with both boundaries having a triangular boundary shape. A first gap 632A is positioned between the inner boundary of the outer ring 630A and the outer boundary of the inner ring 630B. A central patch 630C is positioned inwardly from the inner ring 630B, with this central patch 630C also defining a boundary with a triangular shape. A second gap 632B is positioned between the inner boundary of the inner ring 630B and the boundary of the central patch 630C.

[0075] Other alternative shapes for small unit cells are also included in FIG. 6. For example, a square shaped small unit cell 634 is illustrated. This square shaped small unit cell 634 includes a square shaped outer ring 634A, a square shaped inner ring 634B, and a square shaped central patch 634C. A first gap 636A is positioned between the outer ring 634A and the inner ring 634B, and a second gap 636B is positioned between the inner ring 634B and the central patch 634C. Other rectangular shaped small unit cells may be used instead of the square shaped small unit cell 634 in some embodiments.

[0076] As another example, an oval shaped small unit cell 638 is illustrated in FIG. 6. This oval shaped small unit cell 638 includes an oval shaped outer ring 638 A, an oval shaped inner ring 638B, and an oval shaped central patch 638C. A first gap 640A is positioned between the outer ring 638 A and the inner ring 638B, and a second gap 640B is positioned between the inner ring 638B and the central patch 638C.

[0077] A hexagonal shaped small unit cell 642 is also provided as another example in FIG. 6. The hexagonal shaped small unit cell 642 includes a hexagonal shaped outer ring 642A, a hexagonal shaped inner ring 642B, and a hexagonal shaped central patch 642C. A first gap 644A is positioned between the outer ring 642A and the inner ring 642B, and a second gap 644B is positioned between the inner ring 642B and the central patch 642C. While various polygonal shaped small unit cells are described herein and illustrated in FIG. 6, other polygonal shapes may be used for small unit cells.

[0078] An asymmetrical shaped small unit cell 646 is also provided as another example in FIG. 6. The asymmetrical shaped small unit cell 646 includes an asymmetrical shaped outer ring 646A, an asymmetrical shaped inner ring 646B, and an asymmetrical shaped central patch 646C. A gap 648A is positioned between the outer ring 646A and the inner ring 646B, and a gap 648B is positioned between the inner ring 646B and the central patch 646C.

[0079] While many of the small unit cells within FIG. 6 include both an outer ring and an inner ring, small unit cells may also be provided with just one ring alongside the central patch. However, three or more rings may also be used within small unit cells. Additionally, while each of the small unit cells within FIG. 6 comprise a central patch, no central patch may be provided in other embodiments. The shape, size, and design of small unit cells may be optimized to obtain the desired resistance, inductance, and capacitance values for the small unit cells.

[0080] An example RIS 852 is illustrated in the top view of FIG. 8A with a cross-dipole style unit cell 856 positioned on a substrate 854. The substrate 854 and other substrates described herein may have various compositions and geometries to meet the design requirements. The first dipole 855A of the unit cell 856 extends a length Bl, and the second dipole 855B extends a length B2. The lengths Bl, B2 are equal to each other, but these lengths Bl, B2 may be different from each other in some embodiments. The first dipole 855A also extends across a width B3, and the second dipole 855B extends across a width B4 that is equal to the width B3. The widths B3, B4 are both equal to about 13 millimeters in the illustrated embodiment of FIG. 8 A, but other width values may be used.

[0081] The properties of the RIS 852 of FIG. 8 A may be adjusted by adjusting the lengthsBl, B2 during the design process. For example, FIG. 8B illustrates the phase change that occurs based on changes in the lengths Bl, B2 of the unit cell 856. The phase change may be around 105.6880 degrees when the lengths Bl, B2 are around 0.5000 millimeters. The phase change may continue to decrease to lower values as the lengths Bl, B2 are increased, with the phase change being around -294.1907 degrees when the lengths Bl, B2 are around 1.4500 millimeters. Thus, by varying the lengths Bl, B2 from about 0.50 millimeters to about 1.4500 millimeters, the unit cell 852 may have a reflection phase range of around 400 degrees, which is greater than one full phase cycle of 360 degrees.

[0082] Additionally, changing the lengths Bl, B2 may also impact a reflection magnitude of the unit cell 856. FIG. 8C illustrates the intensity or the reflection magnitude that occurs based on changes in the lengths Bl, B2 of the unit cell 856. The reflection magnitude reaches a peak of around -0.17 decibels at lengths Bl, B2 of around 0.5000 millimeters and reachesanother peak of around -0.18 decibels at lengths Bl, B2 of around 1.25 millimeters. The reflection magnitude reaches a minimum value of around -0.64 decibels at lengths Bl, B2 of around 0.95 millimeters, and the reflection magnitude reaches another minimum value of around -0.66 decibels at lengths Bl, B2 of around 1.45 millimeters. The reflection magnitude values for the line graph 858 of FIG. 8B and the phase change values for the line graph 860 of FIG. 8C were obtained by maintaining the values for the widths B3, B4 at a set value of 13 millimeters. The phase change values for the line graph 858 of FIG. 8B and the reflection magnitude values for the line graph 860 of FIG. 8C were obtained by adjusting the lengths Bl, B2 of both dipoles 855A, 855B of the cross-dipole unit cell 856 rather than just one dipole.

[0083] Turning now to FIG. 9A, another example RIS is illustrated having both single band regions 965A and dual band regions 965B positioned within a single layer, and FIG. 9B is an enhanced, top view illustrating the RIS of FIG. 9A. This structure for the RIS 962 is configured to consider different radiation beam widths according to the operation bands. The single band regions 965A include only small unit cells configured to operate at a higher frequency of around 28 GHz. The dual band region 965B includes both small unit cells and a large unit cell 966, with the large unit cell 966 being configured to operate at a frequency of around 3.5 GHz (which may be in the sub-6 GHz band) and with the small unit cells being configured to operate at a higher frequency of around 28 GHz (which may be in the mmWave band). The large unit cell 966 incubates the small unit cells within the dual band region 965B, resulting in a reduction of grating lobes. The large unit cell 966 may radiate a wider beam than the small unit cells. The large unit cell 966 and small unit cells may both be positioned in a dual band region 965B without forcibly increasing the periodicity of any unit cell.

[0084] The RIS 962 comprises a substrate 964 as well as a large unit cell 966, and the large unit cell 966 comprises a perimeter 967. The substrate 964 has a square shape with sides extending a distance D5. This distance D5 is about 27 millimeters in some embodiments, but the distance D5 may possess different values in other embodiments. The single band regions 965 A are each positioned outside of a footprint correponding to an outer perimeter 967 of the large unit cell 966, and the dual band region 965B is positioned inside of a footprint correponding to an outer perimeter of the large unit cell 966.

[0085] By using single band regions 965A and a dual band region 965B, small unit cells may be more easily maintained in a grid pattern. In the grid pattern, small unit cells are spaced apart from each other by a minimum distance. For small unit cells positioned outside of the large unit cell, this minimum distance is the smallest distance between outer rings of adjacent small unit cells.

[0086] The large unit cell 966 defines twelve openings within the footprint correponding to the outer perimeter of the large unit cell 966, and a portion of a second unit cell is positioned in each of the openings. The large unit cell 966 comprises a body 975 having a cross-dipole shape including a first dipole 955 A and a second dipole 955B. Each dipole 955 A, 955B has a length that extends the distance D4. This distance D4 is about 18.5 millimeters in the illustrated embodiment. Additionally, each dipole 955 A, 955B has a width that extends the distance D3. This distance D3 is about 9.5 millimeters in the illustrated embodiment. However, the distances D3, D4 may possess other values.

[0087] The large unit cell 966 also includes eight stubs extending outwardly from the body 975. For example, a stub 980 A extends outward (upward from the perspective shown in FIG. 9A) from the body 975, and the stub 980A extends in a gap between two adjacent small unit cells without coming in contact with either of the small unit cells. The stub 980A defines a width W that is smaller than the minimum distance between small unit cells. The shape of the body 975 of large unit cell 966 is generally similar to the shape of the cross-dipole style unit cell 856 of FIG. 8A, but the body 975 includes stubs and a plurality of openings 974 within the footprint correponding to the perimeter of the body 975.

[0088] In some embodiments, a larger RIS may be created that generally maintains the spacing and periodicity of small unit cells while also adding additional large unit cells positioned in two or more rows and / or columns. Where additional large unit cells are added, the center of each large unit cell may be spaced apart by a distance of about 27.9 millimeters so that the periodicity for these large unit cells is about 27.9 millimeters. However, other periodicity values may be used.

[0089] In order to reduce interference between small unit cells and the large unit cell 966, a pair of phase delay stub lines may be attached at one or more locations around the perimeter of the large unit cell 966. For example, a series of phase delay stub lines may be positioned around the perimeter of the body 975 in some embodiments, but the series of phase delay stub lines may be positioned around the entire perimeter of the large unit cell 966 in some embodiments. The length of phase delay stub lines may be varied to generate phase variation in the 3.5 GHz band for the large unit cell 966. The use of phase delay stub lines may also help to avoid physical collisions between small unit cells and large unit cells.

[0090] Similarly, a stub 980B extends outwardly (towards the right from the perspective shown in FIG. 9A) from the body 975, and the stub 980B extends in a gap between two adjacent small unit cells without coming in contact with either of the small unit cells. Each of the stubs define a width and a length. The length of the stub extends in an outward direction from thebody 975, and the width of the stubs extend perpendicularly from the length of the stubs within the two-dimensional plane that is shown in FIG. 9A. The length, width, and / or the overall size of the stubs may impact the surface coverage area and frequency of the large unit cell 966. The length, width, and / or the overall size of the stubs may also impact the frequency ratio of the RIS 962. The length, width, and / or the overall size of the stubs may also impact the phase of the large unit cell 966. During the design of a large unit cell 966, the shape and / or size of stubs may be changed without requiring changes to the shape and / or size of the body 975. This may help allow reflection phases to be easily controlled and this may also be helpful to deploy 28 GHz unit cells periodically. The use of the stubs allows the stub design to be changed without altering the design of the body 975, so adjustment of the stub design may avoid impacting the small unit cells within either the single band regions 965A or the dual band region 965B.

[0091] As can be seen in FIG. 9B, the small unit cells of the RIS 962 are different from each other, with a different small unit cell being used within single band regions 965 A than the type of small unit cell used within dual band regions 965B.

[0092] In the RIS 962, each small unit cell has an associated boundary structure configured to reduce interference from other small unit cells and any other large unit cells. The boundary structures may decrease the total capacitance between small unit cells so that electric coupling between unit cells is reduced. Small unit cells positioned in the single band regions 965A comprise a boundary structure in the form of an outer ring. For example, small unit cell 968B is positioned outside of the footprint correponding to the outer perimeter of the large unit cell 966, and the small unit cell 968B comprises an outer ring 970A that acts as a boundary structure. The outer ring 970A for each small unit cell positioned in the single band regions 965A may maintain a consistent shape and size for the outer boundary, which may lead to a reduction of interference between small unit cells with other small unit cells and large unit cells. The small unit cell 968B also comprises an inner ring 970B having a circular shape, a gap 972A positioned between the outer ring 970A and the inner ring 970B, a central patch 970C having a circular shape, and a gap 972B positioned between the central patch 970C and the inner ring 970B.

[0093] For small unit cells positioned inside of the footprint correponding to the outer perimeter of the large unit cell 966, the boundary structure for the small unit cells is also part of the large unit cell 966. For example, for small unit cell 974A, the boundary structure is the wall 977 of the large unit cell 966 surrounding the gap 978A. The small unit cell 974A comprises a central patch 976B comprising a circular shape, the central patch 976B is surrounded by a ring 976A having a circular shape, and a gap 978B is positioned between thering 976A and the central patch 976B. A gap 978 A is also positioned between the ring 976A and the wall 977. The diameter of the wall 977 and the inner diameter of the outer ring 970A of the small unit cell 968B are identical, which may lead to a reduction of interference between small unit cells with other small unit cells and large unit cells.

[0094] Each of the small unit cells may be positioned within a grid pattern, with small unit cells positioned in rows and columns. The center of each small unit cell may be spaced a distance D6 from the center of adjacent small unit cells in each row and column. This distance D6 may be adjusted to accomplish the desired properties for a given design. The distance D6 is about 4.65 millimeters in FIG. 9B, but other values may be used for the distance D6 in other embodiments.

[0095] As illustrated in FIG. 9A, the stubs may each define a width W. The small unit cells are spaced apart from each other in a grid pattern, with adjacent small unit cells are spaced apart by a minimum distance from each other. The width of the stubs is less than the minimum distance such that the stubs are capable of extending through space between adjacent second unit cells. For example, in FIG. 9B, the stub 980C has a sufficiently small width to enable the stub 980C to extend through the space 982A between the small unit cell 968A and the small unit cell 968B. As another example, the stub 980D has a sufficiently small width to enable the stub 980D to extend through the space 982B between the small unit cell 968C and the small unit cell 968D.

[0096] Changing the stub length LI may impact various properties of the RIS 962, including the reflection magnitude and phase of the large unit cell 966. FIG. 9C illustrates the phase change as a function of the stub length LI. The phase change is about 140.8049 decibels when the stub length LI is about 0.1000 millimeters in length. This phase change may continue to drop until the phase change reaches a value of about -168.3342 at a stub length LI of around 4.4000 millimeters in length. Thus, by varying the stub length LI from around 0.1000 millimeters to around 4.4000 millimeters, the unit cell may have a reflection phase range of around 309 degrees. FIG. 9D illustrates the intensity or the reflection magnitude for the large unit cell 966 as a function of the stub length LI. The reflection magnitude is about -0.18 decibels at a stub length LI of around 0.1000 millimeters. The reflection magnitude for the large unit cell 966 decreases to a minimum value of around -2.48 decibels at a stub length of around 2.3000 millimeters. The reflection magnitude for the large unit cell 966 increases as the stub length increases to values above around 2.3000 millimeters, with the reflection magnitude reaching a maximum value of around -0.10 at a stub length of about 4.4000 millimeters.

[0097] FIG. 10A is a top view illustrating an example small unit cell 1068B positioned in a single band region of an RIS. The small unit cell 1068B includes a double ring structure with a center patch 1070C. The small unit cell 1068B may operate at a frequency of about 28 GHz, but other small unit cells may have different operating frequencies. The small unit cell 1068B includes an outer ring 1070A and an inner ring 1070B in addition to the center patch 1070C. The outer ring 1070A, the inner ring 1070B, and the center patch 1070C each have a circular shape. A gap 1072A is positioned between the outer ring 1070A and the inner ring 1070B, and a gap 1072B is positioned between the inner ring 1070B and the center patch 1070C. The small unit cell 1068B may have a multi-resonance behavior, operating at a fundamental frequency and harmonic frequencies.

[0098] The center patch 1070C has a radius equal to the distance D7. The distance D7 is equal to the distance D9 subtracted by the thickness of the inner ring 1070B (e.g., about 0.2 millimeters in FIG. 10A) and also subtracted by the thickness of the gap 1072B (e.g., about 0.2 millimeters in FIG. 10A). The distance D8 is the distance from a center point of the center patch 1070C to the inner boundary of the inner ring 1070B. The distance D8 is equal to the distance D9 subtracted by the thickness of the inner ring 1070B (e.g., about 0.2 millimeters in FIG. 10A). The distance D9 is the distance from a center point of the center patch 1070C to an outer boundary of the inner ring 1070B. The distance D9 may range from about 0.50 millimeters to about 1.50 millimeters in some embodiments. However, distance D9 may possess other values in other embodiments.

[0099] The distance D10 is the distance from a center point of the center patch 1070C to an inner boundary of the outer ring 1070A. The distance D10 may range from about 0.4 millimeters to about 2.25 millimeters in some embodiments, and the distance D10 may be about 1.55 or 1.60 millimeters in some embodiments. The distance Dl l is the distance from a center point of the center patch 1070C to an outer boundary of the outer ring 1070A. The distance Dl l may range from about 0.5 millimeters to about 2.3 millimeters in some embodiments, and the distance Dl l may be about 1.75 millimeters or about 1.8 millimeters in some embodiments. All small unit cells within the single band regions 965A may possess the same distance Dl l fortheir respective outer rings, and this may help to minimize mutual interference between the small unit cells with other unit cells. The thickness of the outer ring 1070A (e.g., distance Dl l minus distance D10) may range from about 0.05 millimeters to about 0.40 millimeters in some embodiments, and this thickness may be about 0.2 millimeters in some embodiments.

[0100] The distance D9 (which is the radius of inner ring 1070B) may be adjusted to tune the reflection phase. FIG. 10B is a line graph 1092 illustrating the phase change as a functionof distance D9 from a center of the circle patch 1070C to the outer perimeter of the inner ring 1070B. The phase change is about 158.8101 degrees at a distance D9 of about 15.0000 millimeters. The phase change drops as the distance D9 increases above about 15.0000 millimeters, with the phase change dropping to about -170.0567 when the distance D9 is about 25.0000 millimeters. Thus, by varying the distance D9 from about 15.0000 millimeters to about 25.0000 millimeters, the unit cell may have a reflection phase range of around 328.87 degrees.

[0101] FIG. 10C is a line graph 1094 illustrating the intensity or the reflection magnitude as a function of distance D9 from a center of the circle patch 1070C to the outer perimeter of the inner ring 1070B. The reflection magnitude is about -0.04 decibels when the distance D9 is about 15.00 millimeters. The reflection magnitude drops to a minimum value of about -2.05 decibels when the distance D9 is about 20.6 millimeters. The reflection magnitude rises to a maximum value of about -0.04 decibels when the distance D9 is about 25.00 millimeters.

[0102] The values obtained in the line graph 1092 of FIG. 10B and in the line graph 1094 of FIG. 10C were obtained by keeping the distance Dl l constant, by maintaining a gap size between the inner ring 1070B and the center patch 1070C at around 0.2 millimeters, and by maintaining thicknesses of the outer ring 1070A and the inner ring 1070B at around 0.2 millimeters. Also, as the distance D9 was increased or decreased, the distance D7 (which is the radius of the center patch 1070C) was also increased or decreased in equal amounts.

[0103] FIG. 11 A is a top view illustrating an example small unit cell 1174A within a dual band region of an RIS. Similar to small unit cell 974A of FIG. 9B, the small unit cell 1174A includes a ring 1176A in addition to the center patch 1176B. The small unit cell 1174A is positioned within an opening 1178 A of a large unit cell 1166, and a wall 1177 formed by the large unit cell 1166 envelops the opening 1178 A. The ring 1176 A and the center patch 1176B each have a circular shape. A gap 1178A is positioned between the ring 1176A and the wall 1177, and a gap 1178B is positioned between the ring 1176A and the center patch 1176B.

[0104] The small unit cell 1174 A may be provided with various geometries in order to accomplish the desired properties. The outer boundary of the ring 1176A extends a distance D12 from the center of the center patch 1176B. This distance D12 may range from about 0.50 millimeters to about 1.40 millimeters in some embodiments. The outer boundary of the ring 1176A extends a distance D13 from the center patch 1176B. This distance D13 is about 0.40 millimeters in the small unit cell 1174A. Additionally, the wall 1177 at the perimeter of the opening 1178A of the large unit cell 1166 extends a distance D14 from the center of the center patch 1176B. This distance D14 is about 1.60 millimeters. However, the distances D12, D13, D14 may possess other values for other small unit cells.

[0105] A line graph 1196 illustrating the phase change as a function of the distance D12 from a center of the circle patch to the outer perimeter of the ring is illustrated in FIG. 11B. When the distance D12 is about 0.50 millimeters, the phase change is about 134.4022 degrees. As the distance D12 increases, the phase change decreases. At a distance D12 of about 1.4000 millimeters, the phase change is about -249.2164 decibels. Thus, by varying the distance D12 from around 0.50 millimeters to around 1.4000 millimeters, the unit cell may have a reflection phase range of around 383.62 degrees, which is greater than one full phase cycle of 360 degrees.

[0106] A line graph 1198 illustrating the intensity or the reflection magnitude as a function of the distance D12 from a center of the circle patch to the outer perimeter of the ring is illustrated in FIG. 11C. The reflection magnitude is about -0.15 decibels when the distance D12 is about 0.50 millimeters. The reflection magnitude then decreases as the distance D12 is increased, with the reflection magnitude being about -1.09 decibels when the distance D12 is about 0.96 millimeters. The reflection magnitude then increases as the distance D12 is increased, with the reflection magnitude being about -0.12 decibels at a distance D12 of about 1.22 millimeters. The reflection magnitude then decreases again as the distance is increased above 1.22 millimeters, with the reflection magnitude being about -0.56 decibels when the distance D 12 is about 1.40 millimeters. The reflection magnitude values for the line graph 1196 of FIG. 11B and the phase change values for the line graph 1198 of FIG. 11C were obtained by maintaining the values for the distance D13 and the distance D14 at set values of 0.4 millimeters and 1.6 millimeters respectively.

[0107] The unit cells described herein may be formed on substrates, and FIG. 12 is a cross- sectional view illustrating an example RIS 1201 with both a small unit cell 1222 and a large unit cell 1212. The RIS 1201 comprises a substrate 1264 comprising a surface 1215. A large unit cell 1212 is formed on the surface 1215 of the substrate 1264, with the large unit cell 1212 having a surface 1213 extending parallel to the surface 1215 of the substrate 1264. The surface 1213 of the large unit cell 1212 is separated by a distance A from the surface 1215 of the substrate 1264. The large unit cell 1212 also includes an opening 1227, and a small unit cell 1222 is formed on the surface 1215 of the substrate 1264 within the opening 1227 of the large unit cell 1212. The small unit cell 1222 has a surface 1223 that extends parallel to the surface 1215 of the substrate 1264, with the surface 1223 separated by a distance A from the surface 1215 of the substrate 1264. The surfaces 1213, 1215, 1223 are each the top surfaces of the large unit cell 1212, the substrate 1264, and the small unit cell 1222 in FIG. 12, but these surfaces1213, 1215, 1223 may not be the top surfaces in other embodiments depending on the orientation of the RIS 1201.

[0108] While the distance A may possess a wide variety of values, the distance A may be between about 0.001 millimeters and about 0.1 millimeters, between about 0.002 millimeters and about 0.075 millimeters, or between about 0.003 millimeters and about 0.050 millimeters. While the thicknesses of the large unit cell 1212 and the small unit cell 1222 are both equal to the distance A in FIG. 12, the thicknesses of the large unit cell 1212 and the small unit cell 1222 may be different in other embodiments. Where the distance A is made larger, RIS 1201 may generally operate with a higher performance. However, a larger distance A also results in higher cost and higher difficulty for fabrication. Additionally, maintaining identical thicknesses for the unit cells 1212, 1222 may allow for fabrication to be less difficult and less costly.

[0109] Various embodiments described herein describe small unit cells having an operating frequency of around 28 GHz, large unit cells having an operating frequency of around 3.5 GHz, and dual band regions having a frequency ratio of around 8. However, the operating frequencies of the unit cells and the frequency ratio may be adjusted significantly in other embodiments. For example, the small unit cells may be configured to have another operating frequency in the mmWave range (e.g., above 24 GHz), and the large unit cells may be configured to have another operating frequency in the sub-6 GHz range (e.g., below 6 GHz). While various embodiments described herein discuss an RIS having a single layer including a dual band region, other RISs may include multiple layers, with one or more of these layers including a dual band region.

[0110] Various embodiments are described herein where an RIS is provided with small unit cells and large unit cells positioned in a single layer. However, in other embodiments, an RIS may be provided with unit cells of three or more distinct sizes. For example, an RIS may be provided with one or more first unit cells, one or more second unit cells, and one or more third unit cells, with the first unit cell(s) being the larger than second unit cell(s) and third unit cell(s) and with second unit cell(s) being larger than the third unit cell(s). Providing an RIS with unit cells having three or more distinct sizes may be beneficial to target three or more different frequency bands.CONCLUSION

[0111] Many modifications and other embodiments set forth herein will come to mind to one skilled in the art to which these embodiments pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to beunderstood that the embodiments are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the invention. Moreover, although the foregoing descriptions and the associated drawings describe example embodiments in the context of certain example combinations of elements and / or functions, it should be appreciated that different combinations of elements and / or functions may be provided by alternative embodiments without departing from the scope of the invention. In this regard, for example, different combinations of elements and / or functions than those explicitly described above are also contemplated within the scope of the invention. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

Claims

THAT WHICH IS CLAIMED:

1. An assembly comprising: a first layer defining a two-dimensional plane, the first layer comprising: one or more first unit cells configured to operate at a first frequency, wherein each of the one or more first unit cells defines a first surface coverage area in the two- dimensional plane; and a plurality of second unit cells configured to operate at a second frequency, a frequency ratio may be equal to the second frequency divided by the first frequency, and wherein each of the plurality of second unit cells defines a second surface coverage area in the two-dimensional plane, wherein the second surface coverage area is less than the first surface coverage area, wherein a first unit cell of the one or more first unit cells defines at least two openings within a footprint correponding to an outer perimeter of the first unit cell, wherein at least a portion of two or more second unit cells of the plurality of second unit cells are positioned inside of the at least two openings defined in the first unit cell, respectively.

2. The assembly of claim 1, wherein the frequency ratio is at least about two.

3. The assembly of claim 1, wherein the assembly is a reconfigurable intelligent surface assembly.

4. The assembly of claim 1, wherein each first unit cell of the one or more first unit cells comprise a stub extending in the two-dimensional plane without coming in contact with any of the plurality of second unit cells.

5. The assembly of claim 4, wherein the each first unit cell of the one or more first unit cells comprise a body, wherein the stub extends a first length in the two-dimensional plane from the body.

6. The assembly of claim 5, wherein the first frequency and the frequency ratio are dependent upon a size of the stub.

7. The assembly of claim 6, wherein the first frequency and the frequency ratio are dependent upon the first length.

8. The assembly of any of claims 4-7, wherein a phase of the each first unit cell of the one or more first unit cells is dependent upon a size of the stub.

9. The assembly of any of claims 4-8, wherein the stub defines a width in the two- dimensional plane, wherein the plurality of second unit cells are spaced apart from each other in a grid pattern, wherein adjacent second unit cells are spaced apart by a minimum distance from each other, wherein the width of the stub is less than the minimum distance such that the stub is capable of extending through a space between the adjacent second unit cells.

10. The assembly of any of claims 1-9, wherein each second unit cell of the plurality of second unit cells has an associated boundary structure configured to reduce interference from other second unit cells, wherein a first boundary structure for a first set of one or more second unit cells is part of a respective first unit cell of the one or more first unit cells, wherein a second boundary structure for a second set of one or more second unit cells is not part of the one or more first unit cells.

11. The assembly of any of claims 1-9, wherein each second unit cell of the plurality of second unit cells possesses an identical boundary shape.

12. The assembly of claim 11, wherein the boundary shape is at least one of a square shape, a rectangular shape, a triangular shape, a polygonal shape, a circular shape, an oval shape, or an asymmetrical shape.

13. The assembly of any of claims 1-9, wherein each second unit cell of the plurality of second unit cells comprises a boundary structure configured to reduce interference from other second unit cells of the plurality of second unit cells.

14. The assembly of any of claims 11-13, wherein each second unit cell of the plurality of second unit cells defines a central portion and an outer portion in the two-dimensional plane, the outer portion surrounds the central portion, and the outer portion is separated from the central portion by a gap.

15. The assembly of claim 14, wherein at least one of a resistance, a capacitance, or an inductance generated by each second unit cell of the plurality of second unit cells depends at least partially on a size of the gap and a size of the central portion.

16. The assembly of claim 1, wherein each first unit cell of the one or more first unit cells defines a first length, wherein each second unit cell of the plurality of second unit cells defines a second length that extends parallel to the first length, wherein a length ratio is equal to the first length divided by the second length, and wherein increasing the length ratio results in an increase in the frequency ratio.

17. The assembly of any of claims 1-16, wherein each first unit cell of the one or more first unit cells defines four openings within the first surface coverage area, and wherein a second unit cell of the plurality of second unit cells is positioned inside each of the four openings, respectively.

18. The assembly of any of claims 1-17, wherein a first thickness of each first unit cell of the one or more first unit cells is about the same as a second thickness of each second unit cell of the plurality of second unit cells.

19. An assembly comprising: a first layer defining a two-dimensional plane, the first layer comprising: one or more first unit cells configured to operate at a first frequency, wherein each of the one or more first unit cells defines a first surface coverage area in the two- dimensional plane; and a plurality of second unit cells configured to operate at a second frequency, wherein each second unit cell of the plurality of second unit cells defines a second surface coverage area in the two-dimensional plane, wherein the second surface coverage area is less than the first surface coverage area, wherein a frequency ratio is equal to the second frequency divided by the first frequency, and wherein the frequency ratio is at least about three.

20. The assembly of claim 19, wherein the frequency ratio is at least about eight.

21. The assembly of claim 19, wherein the frequency ratio is at least about thirty -two.

22. An assembly comprising: a first layer defining a two-dimensional plane, the first layer comprising: one or more first unit cells configured to operate at a first frequency, wherein each of the one or more first unit cells defines a first surface coverage area in the two- dimensional plane; and a plurality of second unit cells configured to operate at a second frequency, wherein each second unit cell of the plurality of second unit cells defines a second surface coverage area in the two-dimensional plane, wherein the second surface coverage area is less than the first surface coverage area, wherein a first unit cell of the one or more first unit cells defines an opening within a footprint correponding to an outer perimeter of the first unit cell, wherein at least a portion of a second unit cell of the plurality of second unit cells is positioned inside of the opening defined in the first unit cell, and wherein the first unit cell comprises a stub extending in the two-dimensional plane without coming in contact with any of the plurality of second unit cells, wherein a frequency ratio is equal to the second frequency divided by the first frequency, and wherein the first frequency and the frequency ratio are dependent upon a size of the stub.

23. The assembly of claim 22, wherein the first frequency, the frequency ratio, and the phase are dependent upon the size of the stub.

24. The assembly of any of claims 22-23, wherein the stub defines a width in the two- dimensional plane, wherein the plurality of second unit cells are spaced apart from each other in a grid pattern, wherein adjacent second unit cells are spaced apart by a minimum distance from each other, wherein the width of the stub is less than the minimum distance such that the stub is capable of extending through a space between the adjacent second unit cells.

25. The assembly of any of claims 22-24, wherein each second unit cell of the plurality of second unit cells has an associated boundary structure configured to reduce interference from other second unit cells.

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