Ultrathin flexible BI-directional leaky-wave antennas for use in the WI-FI band

Abstract

Two novel designs for ultrathin flexible bi-directional leaky-wave antennas (LWA) are proposed and experimentally verified. Both designs are based on microstrip technology and use a periodic antipodal Vivaldi array to emit side-fire radiation beams. The first design utilizes a single feed to achieve bi-directional radiation, while the second uses two feed lines. Each design was tested for two broadside frequencies, 5.5 GHz and 6 GHz, for a total of four antennas. The designs are verified in full-wave simulations using HESS before being fabricated using a thin polyethylene terephthalate (PET) sheet substrate and kapton sheets. The fabricated antennas show high gain, high directivity, and acceptable reflection characteristics. The antennas can be engineered to point high-gain beams in multiple desired directions and can be further adapted to allow for precision control of the beams in various frequency bands.

Description

ULTRATHIN FLEXIBLE BI-DIRECTIONAL LEAKY- WAVE ANTENNAS FOR USE IN THE WI-FI BANDTECHNICAL FIELD

[0001] One technical field of the present disclosure is flexible and conformal antennas for receiving electromagnetic radiation. Another technical field is antennas for transceivers for wireless networking signals.BACKGROUND

[0002] The approaches described in this section are approaches that could be pursued but not necessarily approaches that have been previously conceived or pursued. Therefore, unless otherwise indicated, it should not he assumed that any of the approaches described in this section qualify as prior art merely by virtue of their inclusion in this section.

[0003] Flexible and conformal antennas have received widespread attention in recent years for use in various applications, including wearable technologies, loT, and medical testing

[0001] — [3]. In these technologies, the ability of the antenna to conform to fit on non-uniform, curved surfaces or adapt to variable changes in their mounted positions while maintaining their gain and reflection characteristics is essential.

[0004] To achieve significant levels of flexibility, antennas of this type must be made of a suitably flexible material, which makes typical substrates such as PCB materials unsuitable for these applications [4]. This has led to the widespread adoption of polyethylene terephthalate (PET) sheets as replacements due to their low cost, high flexibility, and variable available thicknesses [5]-[7]. However, even a suitably flexible material can be made more malleable by decreasing the thickness of the dielectric and overall stack-up layers. This has the benefit of decreasing power loss by preventing unwanted surface waves but has the side effect of narrowing the antenna bandwidth, which is already an issue for flexible antennas, whose properties typically prevent them from possessing both wide bandwidths and high beam directivity [4], [8].

[0005] The previously cited flexible examples are typically based on S1W technology, but ultrathin antennas are too thin for waveguide elements such as via walls to be implemented. An alternative design is to use microstrip-based antennas, which only require a ground plane and microstrip line to function [9],

[0010] . These designs are typically lighter weight, lower cost, and more easily integrated into circuits than their SIW counterparts, which makes them idealfor radar, satellite, navigation, and general wireless communication fields

[0011] —

[0013] . These traits have also made them especially desirable for flexible designs in the literature, many of which implement Kapton polyimide sheets that were manually bonded to the substrate for improved loss performance [4],

[0013] —

[0016] .

[0006] One subset of microstrip-based antennas that have been used sparingly in the literature is leaky-wave antennas (LWA), whose low cost, simple feeding networks, and high gain have seen them used in a multitude of applications, ranging from satellite communications to spectrum analyzers

[0017] -

[0019] . Periodic LWAs possess frequency scanning capabilities, allowing the angle of their radiated beam to be altered depending on the frequency of the input, which has made them very popular for beam-forming and direction-finding applications

[0020] . LWAs also suffer from a stopband at their broadside frequency, which must be suppressed through various means for the antenna to achieve full-space scanning

[0021] ,

[0022] ,

[0007] The examples of flexible microstrip LWAs in the literature have focused on conformal and wearable applications, using LWA designs such as line source antennas to achieve high gain and high directivity as well as full-space beam scanning capability over two- phase quadrants

[0023] ,

[0024] . One design seen in the literature is capable of omnidirectional radiation, but its gain is limited to 2.5 dBi

[0025] . To date, no flexible LWAs with symmetric high-gain beam control in opposite phase quadrants have been reported to the knowledge of the inventors as of the priority date.

[0008] A flexible microstrip LWA design capable of beamforming in multiple directions simultaneously with high gain and precision control would open a number of possibilities for loT, wireless communication, and direction-finding applications while retaining their low-cost fabrication and simple feeding networks.SUMMARY

[0009] The appended claims may serve as a summary of the invention.BRIEF DESCRIPTION OF THE DRAWINGS

[0010] In the drawings:

[0011] FIG. 1A illustrates a flexible bi-directional side- fire Vivaldi leaky- wave antenna with double microstrip feed lines.

[0012] FIG. IB illustrates a flexible bi-directional side-fire Vivaldi leaky-wave antenna with a single microstrip feed line.

[0013] FIG. 2A illustrates an example of a slot-line Vivaldi antenna.

[0014] FIG. 2B illustrates an example antipodal Vivaldi antenna.

[0015] FIG. 3A illustrates flexible side-fire Vivaldi matching stub parameters.

[0016] FIG. 3B illustrates two-port flexible side-fire Vivaldi S-parameters.

[0017] FIG. 4A, FIG. 4B, and FIG. 4C illustrate flexible bi-directional side-fire Vivaldi leaky-wave antenna designs, according to at least two embodiments, and their radiation patterns.DETAILED DESCRIPTION

[0018] I. INTRODUCTION

[0019] In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent, however, that the present invention may be practiced without these specific details. In other instances, well- known structures and devices are shown in block diagram form in order to avoid unnecessarily obscuring the present invention.

[0020] The text of this disclosure, in combination with the drawing figures, is intended to state in prose the algorithms that are necessary to program the computer to implement the claimed inventions at the same level of detail that is used by people of skill in the arts to which this disclosure pertains to communicate with one another concerning functions to be programmed, inputs, transformations, outputs and other aspects of programming. That is, the level of detail set forth in this disclosure is the same level of detail that persons of skill in the art normally use to communicate with one another to express algorithms to be programmed or the structure and function of programs to implement the inventions claimed herein.

[0021] This disclosure may describe one or more different inventions, with alternative embodiments to illustrate examples. Other embodiments may be utilized, and structural, logical, software, electrical, and other changes may be made without departing from the scope of the particular inventions. Various modifications and alterations are possible and expected. Some features of one or more of the inventions may be described with reference to one or more particular embodiments or drawing figures, but such features are not limited to usage in the one or more particular embodiments or figures with reference to which they are described. Thus, the present disclosure is neither a literal description of all embodiments of one or more inventions nor a listing of features of one or more inventions that must be present in all embodiments.

[0022] Headings of sections and the title are provided for convenience but are not intended to limit the disclosure in any way or as a basis for interpreting the claims. Devices described as in communication with each other need not be in continuous communication with each other unless expressly specified otherwise. In addition, devices that communicate with each other may communicate directly or indirectly through one or more intermediaries, logical or physical.

[0023] A description of an embodiment with several components in communication with one other does not imply that all such components are required. Optional components may be described to illustrate a variety of possible embodiments and to illustrate one or more aspects of the inventions fully. Similarly, although process steps, method steps, algorithms, or the like may be described in sequential order, such processes, methods, and algorithms may generally be configured to work in different orders unless specifically stated to the contrary. Any sequence or order of steps described in this disclosure is not a required sequence or order. The steps of the described processes may be performed in any order practical. Further, some steps may be performed simultaneously. The illustration of a process in a drawing does not exclude variations and modifications, does not imply that the process or any of its steps are necessary to one or more of the invention(s), and does not imply that the illustrated process is preferred. The steps may be described once per embodiment but need not occur only once. Some steps may be omitted in some embodiments or occurrences, or some steps may be executed more than once in a given embodiment or occurrence. When a single device or article is described, more than one device or article may be used in place of a single device or article. Where more than one device or article is described, a single device or article may be used instead of more than one device or article.

[0024] The functionality or features of a device may be alternatively embodied by one or more other devices that are not explicitly described as having such functionality or features. Thus, other embodiments of one or more inventions need not include the device itself. Techniques and mechanisms described or referenced herein will sometimes be described in singular form for clarity. However, it should be noted that particular embodiments include multiple iterations of a technique or manifestations of a mechanism unless noted otherwise. Process descriptions or blocks in figures should be understood as representing modules, segments, or portions of code, including one or more executable instructions for implementing specific logical functions or steps in the process. Alternate implementations are included within the scope of embodiments of the present invention in which, for example, functions may beexecuted out of order from that shown or discussed, including substantially concurrently or in reverse order, depending on the functionality involved.

[0025] The drawing figures and all the descriptions and claims in this disclosure are intended to present, disclose and claim a technical system and technical methods. The disclosure is directed exclusively to technical solutions to technical problems, and any interpretation of the disclosure or claims to cover any judicial exception to patent eligibility, such as an abstract idea, mental process, method of organizing human activity, or mathematical algorithm, has no support in this disclosure and is erroneous.

[0026] Embodiments comprise a flexible bi-directional LWA capable of symmetric radiation beam angles featuring full-space scanning with suppressed stopbands at the broadside. The disclosure experimentally demonstrates two novel antenna architectures suitable for the Wi-fi band. These architectures were designed to operate with two unique broadside frequencies, making for a total of four fabricated antennas that are experimentally verified. Both antenna architectures are based on broadside differential microstrip lines and provide beam-scanning capabilities along the left and right side of the transmission lines simultaneously, i.e. a side-fire configuration.

[0027] Section II details the process of designing the two antenna architectures, discussing both chosen radiative elements and the limitations that a flexible design imposes on fulfilling the general principles of LWA design. Section III involves the decisions made during the fabrication process. Section IV discusses the results obtained from the four antennas that were ultimately produced and how they will affect future work in this field of study. Section V concludes with an overview of embodiments.

[0028] II. LEAKY- WAVE ANTENNA DESIGNS

[0029] A. GENERAL PRINCIPLES AND OVERALL DESIGN

[0030] There are three types of LWA - uniform, quasi-uniform, and periodic. Uniform and quasi-uniform LWAs are limited in their ability to scan the forward quadrant space, while periodic LWAs have a non-radiating fundamental mode and instead radiate with the n=- 1 first harmonic mode, which gives them full-space frequency scanning capabilities

[0026] —

[0028] . For the purposes of the design, a periodic LWA was chosen, as well as an operating frequency range of 5-7 GHz.

[0031] The broadside frequency of an LWA is decided through the beam-scanning law of periodic LWAs, which defines the relationship between the period of the LWA’s radiating elements and the broadside frequency

[0029] ,

[0030] . Since the period is the main control over thebeam angle, having a perfectly symmetrical design, with the periodic elements on either side sharing the same period, will ensure that the radiated beams will also be symmetrical.

[0032] In an embodiment, a thin PET sheet with a thickness of 250pm comprises the substrate, as used in several flexible antenna designs [5]-[7],

[0031] . Due to the antenna’s thinness, via walls would be difficult to implement, meaning the LWA would need to use a microstrip line to propagate the wave modes. In an embodiment, a variant of broadside-coupled differential strip lines provides the main transmission line along the antenna. Various examples of differential designs have been used in the literature to replace the need for electrical shorts. Differential antennas have also been noted to have improved efficiency but tend to have lower gains and must be matched to their differential impedance

[0032] —

[0034] .

[0033] Typical broadside-coupled strip lines have additional conducting layers above and below them, but they usually show tight coupling between the middle lines with minimal coupling between these additional layers, allowing the 1-D microstrip design seen in the embodiments of FIG. 1A and FIG. IB. Certain elements can minimize potential losses in addition to their physical footprint

[0032] ,

[0035] .

[0034] B. FLEXIBLE SIDE-FIRE VIVALDI DESIGN AND CLOSING THE BROADSIDE STOPBAND

[0035] For achieving side-fire radiation, antipodal Vivaldi antennas were chosen as the LWA’s radiating element. FIG. 2A and FIG. 2B provide a comparison between two exponentially tapered slot antennas (ETSAs), commonly termed Vivaldi antennas. The typical Vivaldi antenna, seen in FIG. 2A, was an aperiodic antenna structure prized for its high gain and wide instantaneous bandwidth

[0036] . This design typically requires a ground plane, a balun and drill hole to feed it, or another complex feeding network, which is unviable for this disclosure. The antipodal Vivaldi antenna, seen in FIG. 2B, was designed with a differential microstrip feed, and thus it offers significantly simpler integration at the expense of increased cross-polarization

[0037] ,

[0038] . The feeding network is equivalent to a broadside-coupled differential microstrip line. Based on the thin substrate of embodiments of this disclosure, cross-polarization levels for the designed flexible antennas are expected to be minimal.

[0036] Embodiments use a matching element to close the stopband. Previous examples of antipodal Vivaldi LWAs in the literature

[0039] —

[0042] have used matching sections where the via walls varied in width, which was not an option for this design. The typical Vivaldi design could be matched by altering the location of the feed line, which theoretically could be incorporated by extending the antipodal Vivaldi feed as a stub, but this would interfere with the symmetricdesign of Vivaldi LWAs

[0043] ,

[0044] . Other examples of individual antipodal Vivaldi antennas have been matched by making cuts in the ground plane structure of the antenna

[0045] .

[0037] In an embodiment, a differential open stub is introduced to the microstrip line. With a suitably long feed line, the antipodal Vivaldi antenna could be viewed as a load at the end of a microstrip line, which would allow it to be impedance matched with an open stub as in a typical microstrip design. The length, width, and relative position of the stub compared to the antipodal Vivaldi feed are all relevant parameters for antenna matching. The effects of the matching stub on reflection characteristics can be seen in detail in FIG. 3 A and FIG. 3B.

[0038] FIG. 3A shows flexible side-fire Vivaldi matching stub parameters, thus unit-cell parameters, where I stub corresponds to the sub length, wstub corresponds to the stub width, and d corresponds to its relative position along the differential microstrip line. FIG. 3B shows S- parameters for a two-port flexible side-fire Vivaldi structure and the result of varying the relevant parameters and removing the stub altogether vs. keeping it in its optimized position. The individual graphs show, at the Top-Left, optimized matching stub reflection characteristics compared with no matching stub reflection characteristics. Top-Right: Compares the effect of increasing or decreasing lstUb on the reflection characteristics to the optimized matching stub reflection characteristics. Bottom-Left: Compares the effect of increasing or decreasing wstub on the reflection characteristics to the optimized matching stub reflection characteristics. Bottom-Right: Compares the effect of increasing or decreasing d on the reflection characteristics to the optimized matching stub reflection characteristics.

[0039] The disclosure encompasses two antenna architectures. The first antenna architecture uses a single feed for both left and right radiation, with a single broadside-coupled differential microstrip line connected to symmetrical antipodal Vivaldi structures and differential open stubs. The second is a double-feed design, with two separate differential microstrip lines providing left and right radiation, respectively. This second design could allow for independent control over the frequency scanning (and hence direction) of each beam if desired.

[0040] The feed network tapering for both architectures and the separation between the two differential microstrip lines in the double feed design were both optimized in full-wave simulations with HFSS to minimize reflection and crosstalk. The antipodal Vivaldi parameters were varied until they achieved upwards of 10 dB of gain. The stub sizes and offsets used in the final designs were also optimized. While initial testing was done with multiple ports, thefinal designs omit an output port due to negligible power remaining after the wave travels the antenna length.

[0041] The final designs of example embodiments can be seen in FIG. 1A and FIG. IB, with FIG. 1A showing the double-feed architecture while FIG. IB shows the single-feed architecture. FIG. 1 A illustrates a flexible bi-directional side- fire Vivaldi leaky- wave antenna with double microstrip feed lines, using PET sheet substrate with er=3.0 and land =0.01 ; the value of sep was optimized alongside the feed network. FIG. IB illustrates a flexible bidirectional side-fire Vivaldi leaky-wave antenna with a single microstrip feed line and stack- up layers, from top to bottom, of coverlay-copper-PLPET-PI-copper-coverlay.

[0042] In one embodiment, the disclosure provides the subject matter of the following numbered clauses:

[0043] 1A. A flexible leaky-wave antenna (LWA) for conducting energy in the Wi-Fi radiofrequency spectrum comprises, in an ordered stack: a top copper layer; a first flexible mostly inelastic layer; a flexible sheet; a second flexible mostly inelastic layer; and a bottom copper layer.

[0044] In one embodiment of clause 1A, the first flexible, mostly inelastic layer and the second flexible, mostly inelastic layer comprise polyimide. However, other materials providing an inelastic layer of known thickness to receive the copper-printed layer can be used. Examples include polyimide flex printed circuit boards (PCBs) with copper ink printing on top of polyimide, polyester film, fluorinated ethylene propylene (FEP), fluoropolymers (PTFE), or LCP. Other materials can be used that do not stretch. Thus, in this context, the term “flexible mostly inelastic” means that the material is capable of flexing or twisting, without stretching, so the copper layer on the flexible mostly inelastic layer does not rip, whether that layer is copper foil, printed ink, or deposited ink.

[0045] In an embodiment of clause 1A, the flexible sheet comprises PET, polyimide, polyester film, FEP, PTFE, LCP, foams or rubbers like EDPM, silicone, or PVC foam, capable of serving as a filler to create spacing between the top and bottom layers. The flexible sheet need not be elastic as it is sandwiched between two inelastic sheets. Thus, embodiments typically provide two faces kept mostly in alignment without stretching as the antenna experiences cycles of flexing. It will be seen that the bottom layers act as the reverse of the top with a negative image of the Vivaldi antennas.

[0046] IB. A flexible leaky-wave antenna (LWA) for conducting energy in the Wi-fi radiofrequency spectrum, comprising, in an ordered stack: a first coverlay; a top copper layer;a first polyimide layer; a polyethylene terephthalate (PET) sheet; a second polyimide layer; a bottom copper layer; a second coverlay.

[0047] Embodiments of clause 1A or clause IBcan include, in one or more other embodiments, the subject matter of the following numbered clauses:

[0048] 2. The flexible leaky- wave antenna of clause 1 A or IB comprising a bi-directional side-fire Vivaldi LWA with double microstrip feed lines.

[0049] 3. The flexible leaky-wave antenna of clause 2 further comprising a plurality of differential open stubs coupled to each microstrip feed line of the double microstrip feed lines.

[0050] 4. The flexible leaky- wave antenna of clause 1 A or IB, comprising a bi-directional side-fire Vivaldi LWA with a single microstrip feed line.

[0051] 5. The flexible leaky-wave antenna of clause 2, further comprising a plurality of differential open stubs coupled to the single microstrip feed line.

[0052] 6. The flexible leaky- wave antenna of clause 1A or IB, having a broadside frequency of 5.5 GHz.

[0053] 7. The flexible leaky- wave antenna of clause 1A or IB, having a broadside frequency of 6 GHz.

[0054] 8. A method of manufacturing a flexible leaky-wave antenna for conducting energy in the Wi-fi radiofrequency spectrum, the method comprising fabricating a top copper layer on a first Kapton sheet; separately fabricating a bottom copper layer on a second Kapton sheet; each of the first Kapton sheet and the second Kapton sheet comprising a stack-up from a bottom-up of a flexible elastic sheet, two flexible mostly inelastic layers, copper, and coverlay; cutting the first Kapton sheet and the second Kapton sheet into a first antenna and a second antenna respectively; aligning and attaching the first antenna and the second antenna.

[0055] 9. The method of clause 8 further comprising attaching the first antenna and the second antenna with a single sheet of double-sided tape having a first thickness in the stack- up with a second thickness of the flexible elastic sheet being 250 pm.

[0056] 10. A method of manufacturing a flexible leaky- wave antenna for conducting energy in the Wi-fi radiofrequency spectrum, the method comprising fabricating a top copper layer on a first Kapton sheet; separately fabricating a bottom copper layer on a second Kapton sheet; each of the first Kapton sheet and the second Kapton sheet comprising a stack-up from a bottom-up of PET, polyimide, copper, and coverlay; cutting the first Kapton sheet and the second Kapton sheet into a first antenna and a second antenna respectively; aligning and attaching the first antenna and the second antenna.

[0057] 11. The method of clause 10 further comprising attaching the first antenna and the second antenna with a single sheet of double-sided tape having a first thickness in the stack-up with a second thickness of the PET being 250 pm.

[0058] III. FABRICATION AND EXPERIMENTAL VERIFICATION

[0059] Embodiments can be fabricated as follows. To fully prove the architectures’ viability, separate antennas were designed for each architecture with different broadside frequencies, namely 5.5 GHz and 6 GHz. These designs were completed and simulated via fullwave simulation in HFSS.

[0060] Attaching any material or stack-up to a flexible material is more difficult than for a rigid material, as keeping the material straight is a difficult proposition. Multiple methods of attaching conducting layers to a flexible substrate have been proposed, including the use of silver ink. However, such printing methods have low conductivity and, thus, higher dissipation losses, which made them unsuitable for these designs

[0031] . Instead, in an embodiment, the top and bottom copper layers were fabricated separately on Kapton sheets, each with a stack-up consisting, from the bottom-up, of PET-Polyimide-copper-coverlay. The two sheets were then cut into separate antennas, aligned using the holes added during the original design, and attached using a single sheet of double-sided tape. The thickness of the PET attached to each Kapton sheet was halved, and the thickness of the tape chosen was such that when the full stack-up was complete, the PET thickness was equal to 250, um. The simulations were redone with new relative permittivity values and loss tangents to account for these differences. Hand or machine assembly is possible. The four fabricated antennas were then experimentally tested and verified.

[0061] IV. DISCUSSION

[0062] FIG. 4A, FIG. 4B, and FIG. 4C show flexible bi-directional side-fire Vivaldi LWA designs and their radiation patterns, Gv(<p, 9 = 90°), from / = 5 GHz to = 7 GHz using FEM- HFSS. The single feed designs used a PET sheet substrate with= 2.60 and land = 0.0155, while the double feed designs used a PET sheet substrate with &r- 2.60 and tan 5 = 0.0255. All designs used the following dimensions: h = 0.25 mm, t = 17 pm, hn= 25 pm, ta,ver= 33 pm, a = 2.584 mm, r = 4.6 mm, / = 2.9 mm, sep = 1.39 mm. The 6 GHz designs both used the following dimensions: d - 0.275 mm, L = 12.8 mm, s = 10.47 mm, wjesd = 0.34 mm, p = 29.48625 mm, wstub = 1.1 mm, lstUb = 1.525 mm. The 5.5 GHz designs both used the following dimensions: d = 0.585 mm, L = 14.8 mm, s = 12.32 mm, wfeed = 0.4 mm, p = 32.1425 mm, Wstub — 1.04 mm, lstub= 1.3 mm. Individual views include:

[0063] FIG. 4A, left and right sides: (a) Fabricated Single-Feed Flexible Bi-Directional side-fire Vivaldi Antennas; (b) Fabricated Double-Feed Flexible Bi-Directional side-fire Vivaldi Antennas. 6 GHz Broadside Single-Feed Flexible Bi-Directional Vivaldi LWA radiation for design with 14 side-fire Vivaldi pairs with W = 30.74 mm.

[0064] FIG. 4B, top three graphs: (c) 6 GHz Single Vivaldi S-Parameters; (d) 6 GHz Single Vivaldi Gain; (e) 6 GHz Single Vivaldi Peak Gain. 6 GHz Broadside Double-Feed Flexible Bi- Directional Vivaldi LWA radiation for design with 14 side- fire Vivaldi pairs with W = 34.71 mm.

[0065] FIG 4B, bottom three graphs: (f) 6 GHz Double Vivaldi S-Parameters; (g) 6 GHz Double Vivaldi Gain; (h) 6 GHz Double Vivaldi Peak Gain. 5.5 GHz Broadside Single-Feed Flexible Bi-Directional Vivaldi LWA radiation for design with 13 side-fire Vivaldi pairs with W= 30.74 mm.

[0066] FIG. 4C, top three graphs: (i) 5.5 GHz Single Vivaldi S-Parameters; (j) 5.5 GHz Single Vivaldi Gain; (k) 5.5 GHz Single Vivaldi Peak Gain. 5.5 GHz Broadside Double-Feed Flexible Bi-Directional Vivaldi LWA radiation for design with 13 side-fire Vivaldi pairs with W= 30.74 mm.

[0067] FIG. 4C, bottom three graphs: (1) 5.5 GHz Double Vivaldi S-Parameters; (m) 5.5 GHz Double Vivaldi Gain; (n) 5.5 GHz Double Vivaldi Peak Gain.

[0068] Thus, measured and simulated results for all four fabricated antennas are visible in FIG. 4B and FIG. 4C. FIG. 4A, left side, shows the fabricated Single Feed antenna architecture, while FIG. 4A, right side, shows the fabricated Double Feed architecture. FIG. 4B, top three graphs, show the Single Feed 6 GHz Broadside frequency antenna’s reflection, gain, and peak gain measurements, respectively. While the reflection characteristics do not perfectly match, they are consistently below -lOdB while still exhibiting a noticeable stopband. The gain pattern is almost perfectly matched, however, with at most a minor phase shift of 5°, keeping it from being exact. The peak gains are also very closely matched throughout the frequency range. It should be noted, however, that there has been a noticeable frequency shift due to the addition of the tape to the stack-up, with the broadside frequency here actually being closer to 6.5 GHz. This frequency shift would also explain the difference between the simulated and measured S- parameters.

[0069] FIG. 4B, bottom three graphs, show the same results for the Double Feed 6 GHz design. This design has much the same result as the Single Feed; the reflection characteristics are acceptable but exhibit more of a stopband than the simulated results, while the gain patternsare much more closely matched and exhibit a frequency shift for a broadside around 6.5 GHz. The peak gains, by contrast, do not match the simulations as closely as in the previous design, though they do follow the same general trend.

[0070] This then repeats for the Single and Double feed 5.5 GHz Broadside designs, seen in FIG. 4C, top three graphs, and FIG. 4C, bottom three graphs, respectively. The reflection characteristics are below - 1 OdB but do not match their simulated values, while the gain patterns are matched but show broadsides closer to 6 GHz than 5.5 GHz. The peak gains are also rather poorly matched while generally following the same trend.

[0071] For all the antennas, their Si l parameters were safely below -lOdB across the frequency range. The measured gains were consistently at or around lOdB for the single-feed designs, while the double-feed designs were lower at 8-9 dB. While this aspect was not investigated in-depth, it was also noted that the S-parameters remained fairly consistent regardless of the amount of bending that occurred.

[0072] These results clearly show that the antennas are working mostly as intended, successfully proving that high-gain symmetrical bidirectional radiation is possible using a flexible LWA.

[0073] V. CONCLUSION

[0074] Two flexible bi-directional periodic LWA architectures were proposed and experimentally verified based on microstrip technology for use in the Wi-fi band. Both architectures used broadside-coupled differential microstrip lines to guide the wave along the antenna length. Antipodal Vivaldi antennas were used as periodic radiating elements to emit symmetric bi-directional radiation beams at specified angles simultaneously, which was confirmed both through simulations in HFSS and experimental measurements. Designs were made to achieve these results with both single and double-feed networks, each with separate broadsides of 5.5 GHz and 6 GHz, for a total of four fabricated and tested antennas. Since the antennas are periodic in nature, their beam angles can be altered by changing the frequency of the signal or the period of the antenna. Any changes to the design will result in a stopband developing around the broadside, which can here be suppressed through the use of a differential matching stub. Properly balancing these design parameters gives the antennas great utility in multiple fields. Further work can be done by testing whether the architectures can be modified to fire two high-gain beams at independent angles simultaneously, which would achieve near- omni-directional directive beam scanning.

[0075] In the foregoing specification, embodiments of the invention have been described with reference to numerous specific details that may vary from implementation to implementation. Accordingly, the specification and drawings are to be regarded in an illustrative rather than a restrictive sense. The sole and exclusive indicator of the scope of the invention, and what is intended by the applicants to be the scope of the invention, is the literal and equivalent scope of the set of claims issued from this application in the specific form in which such claims issue, including any subsequent correction.

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Claims

CLAIMSWhat is claimed is:

1. A flexible leaky-wave antenna (LWA) for conducting energy in the Wi-Fi radiofrequency spectrum comprising, in an ordered stack: a top copper layer; a first flexible mostly inelastic layer; a flexible sheet; a second flexible mostly inelastic layer; and a bottom copper layer.

2. The flexible leaky- wave antenna of claim 1, comprising a bi-directional sidefire Vivaldi LWA with double microstrip feed lines.

3. The flexible leaky-wave antenna of claim 2, further comprising a plurality of differential open stubs coupled to each microstrip feed line of the double microstrip feed lines.

4. The flexible leaky- wave antenna of claim 1 , comprising a bi-directional sidefire Vivaldi LWA with a single microstrip feed line.

5. The flexible leaky-wave antenna of claim 2, further comprising a plurality of differential open stubs coupled to the single microstrip feed line.

6. The flexible leaky-wave antenna of claim 1, having a broadside frequency of 5.5 GHz.

7. The flexible leaky-wave antenna of claim 1, having a broadside frequency of 6 GHz.

8. A flexible leaky-wave antenna (LWA) for conducting energy in the Wi-fi radiofrequency spectrum, comprising, in an ordered stack: a first coverlay; a top copper layer;a first polyimide layer; a polyethylene terephthalate (PET) sheet; a second polyimide layer; a bottom copper layer; a second coverlay.

9. The flexible leaky-wave antenna of claim 8, comprising a bi-directional sidefire Vivaldi LWA with double microstrip feed lines.

10. The flexible leaky-wave antenna of claim 9, further comprising a plurality of differential open stubs coupled to each microstrip feed line of the double microstrip feed lines.

11. The flexible leaky- wave antenna of claim 8, comprising a bi-directional sidefire Vivaldi LWA with a single microstrip feed line.

12. The flexible leaky-wave antenna of claim 9, further comprising a plurality of differential open stubs coupled to the single microstrip feed line.

13. The flexible leaky-wave antenna of claim 8, having a broadside frequency of 5.5 GHz.

14. The flexible leaky-wave antenna of claim 8, having a broadside frequency of 6 GHz.

15. A method of manufacturing a flexible leaky- wave antenna for conducting energy in the Wi-fi radiofrequency spectrum, the method comprising: fabricating a top copper layer on a first Kapton sheet; separately fabricating a bottom copper layer on a second Kapton sheet; each of the first Kapton sheet and the second Kapton sheet comprising a stack-up from a bottom -up of PET, polyimide, copper, and coverlay; cutting the first Kapton sheet and the second Kapton sheet into a first antenna and a second antenna respectively; aligning and attaching the first antenna and the second antenna.

16. The method of claim 15, further comprising attaching the first antenna and the second antenna with a single sheet of double-sided tape having a first thickness in the stack-up with a second thickness of the PET being 250 pm.l. A flexible leaky-wave antenna (LWA) for conducting energy in the Wi-fi radiofrequency spectrum, comprising, in an ordered stack: a first coverlay; a top copper layer; a first polyimide layer; a polyethylene terephthalate (PET) sheet; a second polyimide layer; a bottom copper layer; a second coverlay.

17. A method of manufacturing a flexible leaky- wave antenna for conducting energy in the Wi-fi radiofrequency spectrum, the method comprising: fabricating a top copper layer on a first Kapton sheet; separately fabricating a bottom copper layer on a second Kapton sheet; each of the first Kapton sheet and the second Kapton sheet comprising a stack-up from a bottom-up of a flexible elastic sheet, flexible mostly inelastic layers, copper, and coverlay; cutting the first Kapton sheet and the second Kapton sheet into a first antenna and a second antenna respectively; aligning and attaching the first antenna and the second antenna.

18. The method of claim 17, further comprising attaching the first antenna and the second antenna with a single sheet of double-sided tape having a first thickness in the stack-up with a second thickness of the PET being 250 pm.

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