Leaky Wave Research Articles

Compact Leaky-Wave SIW Antenna With Broadside Radiation and Dual-Band Operation for CubeSats

This letter presents a substrate-integrated waveguide (SIW) antenna for CubeSat applications. The compact structure utilizes middle-point feeding and shorting walls to achieve broadside radiation in the far-field at two distinct frequencies. In particular, this dual-frequency behavior is related to the transition from a dominant leaky wave (LW) on the aperture at lower frequencies to more hybrid radiation (at higher frequencies) due to LW fields and structure resonance due to truncation. This response is generated by the shorting vias at the lateral ends of the SIW antenna. Given these conditions, the developed leaky-wave antenna (LWA) prototype is well matched ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$|S_{11}|$</tex-math></inline-formula> <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\leq$</tex-math></inline-formula> −10 dB) from 23.2 to 23.5 GHz and 24.8 to 25.2 GHz with realized gains of 8 and 6 dBi, respectively. Maximum efficiency (including the connector) is around 87%. Such dual-frequency operation could enable up-link and down-link operation in the K-band. Overall dimensions of the antenna are 2 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\lambda _0$</tex-math></inline-formula> × 2.6 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\lambda _0$</tex-math></inline-formula> (at the lower frequency). Possible placement on CubeSats can be underneath solar panels, thus increasing the available surface area for solar power harvesting. Also, to the best knowledge of the authors, no similar dual-frequency SIW-LWA has been previously reported.

Optimization of leaky-wave surface coil current using an analytical approach

In this work, we investigate the optimal coefficients of the exponential current excited on a leaky wave surface coil. The respective functional is first derived analytically and later computed numerically using Python. The results are compared to the same problem modeled in Comsol Multiphysics.

Leaky-Wave Radiation From 2-D Dielectric Lattices Excited by an Embedded Electric Line Source

This article presents an analytical and numerical investigation of the radiation features of an interesting class of electromagnetic bandgap (EBG) structures excited by an electric line source. The radiation from 2-D lattices made with lossless dielectric cylinders, typically optimized by using the Bloch analysis of the corresponding 2-D photonic crystals, is originally investigated in terms of leaky waves. A thorough modal analysis of open waveguides, composed of a finite number of periodic chains of circular dielectric rods, is presented, which shows a multiplicity of bound and leaky modes. Two radiation windows are identified and the relevant directive features are described in terms of properly excited dominant leaky modes. The possible excitation of higher order leaky modes and guided modes has been carefully considered, by also capturing the relevant residue contributions in a nonspectral representation of the excited fields. The final results on radiated fields by realistic truncated structures, obtained by <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ad hoc</i> software as well as full-wave EM simulators, are in excellent agreement with those predicted by the proposed leaky-wave approach.

Design of Reconfigurable Antenna for 5G Applications

Abstract: With rapid evolution of wireless communication and mobile networking techniques, one of the major advancements is that fifth generation (5G) is envisioned in-order to meet the perpetual demand for greater network speed and capacity. This paper provides an overview of the design of five reconfigurable antennas for 5G wireless application is introduced by varying the substrate material used. Teflon, Taconic TLY, Rogers Ultralam 1217, Rogers RT/Duroid 5880, FR4 are the substrate materials used in designing the respective antennas. The proposed antenna designs employ a leaky-wave antenna based on half-mode substrate integrated waveguide. Since this antenna is used in 5G communication systems, the centre frequency is taken as 28.5 GHz. The length width and height of each of the antennas are designed using design procedures of rectangular patch antenna for all five substrates respectively. Each antennas are compared based on their return loss, VSWR, gain, directivity and radiation pattern respectively and an inference regarding performance of each substrate is obtained. On comparing the results of all the five antennas in the ON and OFF condition of switch, the results are found to be best in case of Rogers RT/duroid 5880 with return loss of -15.2719dB, VSWR of 1.4165, gain of 4.6dB, directivity of 4.31dB in the ON condition and with a return loss of - 13.0779dB, VSWR of 1.6893, gain of 3.4dB and directivity of 3.7dB in the OFF condition. Further by changing the switches and replaced it by conducting sheet switches for reduction of loss and were able to achieve improved results with return loss of24.5026dB, gain of 5.1dB in the ON condition and return loss of -12.6608dB and gain of 3.8dB in the OFF condition which contributed to the novelty of the project. In the proposed antennas, beam steering is obtained due to the disturbances in surface current under the influence of changing voltage bias of the switches. The technologies used make the antenna design compact provides configurability, which makes this antenna a suitable candidate for 5G applications. Keywords: 5G, reconfigurable antenna, leaky wave antenna, half mode substrate integrated waveguide, millimeter wave, beam steering

Parallel‐plates‐based Dirac Leaky Wave Antennas

In this work, the authors experimentally show Dirac Leaky Wave Antennas (DLWAs) at upper microwave frequencies. For the first time, DLWAs are implemented using simple Parallel plate waveguide (PPW) technology, while yielding desirable radiation features and continuous beam scanning through broadside, as well as extremely low profile, with significant ease of fabrication, making them well suited for Ku band applications such as satellite communication, radar and emerging fifth-generation (5G). A planar Dirac photonic crystal in PPW is shown with a closed bandgap and linear dispersion around broadside. In this work, 1D and 2D PPDLWAs are designed that provide scannable fan and pencil beams, respectively, with a symmetric beamwidth. Phase and attenuation constants are controlled with unit cell dimensions to obtain a directive beam and scanning in a wide range of angles. For the 2D design, an appropriate wideband feeding network is designed that excites the antenna appropriately. The presented PPDLWAs operate with a peak gain of about 13 dB for the fan beam and 22 dB for the pencil beam, in the frequency range from 12 to 16 GHz.

Surface acoustic waves and Mach stem formation produced by lithotripter shock wave-stone interaction

Lithotripter shock wave (LSW)-stone interaction may vary significantly due to respiratory motion of the patient. In this work, we have investigated the variations of the LSW-stone interaction and associated stone fracture pattern using photoelastic imaging, phantom experiments, and three-dimensional fluid-solid interaction modeling at different lateral locations in a lithotripter field. In contrast to the T-shaped fracture pattern observed in a disk-shaped stone under symmetric loading, we have observed a gradual transition of the fracture pattern to a tilted L-shape under asymmetric loading. Importantly, our model simulations reveal the generation of surface acoustic waves (SAWs)—a leaky Rayleigh wave on the anterior and a Scholte wave on the posterior surface of the stone. The propagation of SAWs on the stone boundary is accompanied by a progressive transition of the LSW reflection pattern from regular to von Neumann and to weak von Neumann reflection near the glancing incidence and, concomitantly, the development of a Mach stem, swirling around the stone boundary. The maximum tensile stress and stress integral are produced by SAWs on the stone boundary under asymmetric loading, which drive the initiation and extension of surface cracks into the bulk of the stone that has been confirmed by microCT analysis.

A finite element formulation to determine the complex wavenumber spectrum of an underwater leaky wave antenna

Underwater acoustic imaging traditionally utilizes phased arrays of electro-acoustic transducers to steer acoustic energy in specific directions. An alternative approach to steer acoustic beams is to use an acoustic leaky wave antenna (LWA). Acoustic LWAs consists of a single transducer attached to a dispersive antenna that enables frequency-dependent directionality of acoustic radiation and reception. Finite element analysis of an underwater LWA presents a unique computational challenge due to the presence of fluid loading from the surrounding water domain. Previous unit cell analyses performed on the underwater LWA approximated the surrounding fluid as a lumped mass on the surface of the LWA [Broadman et al., J. Appl. Phys., 129(19), 194902 (2021)]. In this work, we investigate LWA unit cell analysis that includes fluid-solid coupling and an exact absorbing boundary condition to enforce outgoing waves from the LWA. We solve for the complex wavenumbers of the propagating and leaky modes of the LWA given a real-valued frequency via a nonlinear eigenvalue problem, providing insight into the propagation and attenuation of elastic waves in the LWA. Finally, we compare the present approach with the lumped mass approximation and numerical results from a finite LWA. [Work supported by ONR.]

An EH₀-Mode Microstrip Leaky Wave Antenna on Differentially Excited Coupled Line for Transversal Single-Beam Radiation

This communication presents a method to make the EH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> -mode microstrip leaky wave antenna (MLWA) radiate single beam in its transversal plane based on the differentially excited coupled microstrip line structure with low cross-polarization. The conventional EH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> -mode MLWA is constructed by periodically loading a series of shorting pins along the center line of the uniform line, but it mainly radiates dual beams in its transversal plane. If a ground plane approaches to one of its edges with rotation of the whole structure, only one radiation aperture will be left to radiate single beam in the broadside direction. Herein, a planar differentially excited coupled line configuration is implemented to validate the proposed method and simultaneously inherits the original outstanding characteristic of freely designed narrow strip width. In design, a unified equivalent model is first established to provide insight into its radiation principle through propagation characteristics. Then, the dispersion and radiation properties are further investigated under mixed geometrical parameters. Finally, a prototype MLWA with transversal single-beam radiation is designed and fabricated with good agreement between the simulated and measured results, which validates the proposed method for designing a single-beam EH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> mode MLWA.

A Multilayered SIW-Based Circularly Polarized CRLH Leaky Wave Antenna

In this article, a multilayered circularly polarized (CP) leaky-wave antenna (LWA) is proposed, based on the composite right/left-handed (CRLH) transmission line concept. The proposed design is composed of a substrate integrated waveguide (SIW) structure and its multilayered unit cell consists of H-shaped interdigital (ID) slots on the top with a truncated patch, sandwiched between the two substrates. Circular slots are introduced periodically on the ground plane to achieve wideband circular polarization. Proposed CRLH SIW-based LWA shows the capability of continuous beam scanning from −38° to +71° within the frequency range of 7.6–10.6 GHz while maintaining good circular polarization in the frequency range of 8.3–10.6 GHz. The peak gain of the proposed LWA is 10 dB and the average radiation efficiency is 86.1% over the complete impedance bandwidth. The measured results of the fabricated prototype are in good agreement with the simulated ones. The proposed antenna can be used for <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$X$ </tex-math></inline-formula> -band radar and satellite applications.

Substrate integrated waveguide leaky wave antenna with circular polarization and improvement of the scan angle

AbstractIn this paper, a leaky wave antenna is presented based on the substrate integrated waveguide structure. The proposed antenna has a periodic structure with a combination of rectangular and H‐shaped slots on the top of the antenna. By providing this new design for slots, a better angular scanning achieved rather than the previous designs from broadside to end‐fire, so that with this design, the leaky wave antenna can scan from 2.5 to 87° by changing the feeding frequency, which is the highest scanning angle relative to the design of uniform rectangular slots, the butterfly shaped slots and the H‐shaped slots. The proposed antenna was designed to have circular polarization in the entire operating frequency range.

Machine learning-based leaky momentum prediction of plasmonic random nanosubstrate.

In this work, we explore the use of machine learning for constructing the leakage radiation characteristics of the bright-field images of nanoislands from surface plasmon polariton based on the plasmonic random nanosubstrate. The leakage radiation refers to a leaky wave of surface plasmon polariton (SPP) modes through a dielectric substrate which has drawn interest due to its possibility of direct visualization and analysis of SPP propagation. A fast-learning two-layer neural network has been deployed to learn and predict the relationship between the leakage radiation characteristics and the bright-field images of nanoislands utilizing a limited number of training samples. The proposed learning framework is expected to significantly simplify the process of leaky radiation image construction without the need of sophisticated equipment. Moreover, a wide range of application extensions can be anticipated for the proposed image-to-image prediction.

Near-Resonances of Superinertial and Tidal Fluctuations at Islands

AbstractA linear numerical model of an island or a tall seamount is used to explore superinertial leaky resonances forced by ambient vertically and horizontally uniform current fluctuations. The model assumes a circularly symmetric topography (including a shallow reef) and allows realistic stratification and bottom friction. As long as there is substantial stratification, a number of leaky resonances are found, and when the island’s flanks are narrow relative to the internal Rossby radius, some of the near-resonant modes resemble leaky internal Kelvin waves. Other “resonances” resemble higher radial mode long gravity waves as explored by Chambers. The near-resonances amplify the cross-reef velocities that help fuel biological activity. Results for cases with the central island replaced by a lagoon do not differ greatly from the island case which has land at the center. As an aside, insight is provided on the question of offshore boundary conditions for superinertial nearly trapped waves along a straight coast.

Plasmonic leaky wave antenna based on modulated radius of cylindrical graphene waveguide

In this paper, the concept, analysis, and synthesis of a novel plasmonic leaky wave antenna (LWA) based on the modulated radius of a cylindrical graphene waveguide (CGW) at the terahertz band are presented. Devices based on the planar graphene waveguide (PGW) suffer from high attenuations, which significantly limit the radiation efficiency and beam width of LWAs. It is shown here that the LWA based on CGW compared to PGW can decrease the beam width from 55° to 12° and increase the radiation efficiency from 20% to 50%. A sinusoidally modulated graphene surface is employed to excite the leaky wave antenna. A sinusoidally modulated reactance surface is realized by the modulation of the radius of the cylindrical waveguide. In comparison to other structures, the proposed antenna can be implemented by applying a single voltage to graphene sheets. As a result, the antenna beam direction can be readily changed by varying the applied voltage.

Gain enhancement of optical leaky wave antenna excited by parabolic reflector with photonic crystal

Gain enhancement of optical leaky wave antenna excited by parabolic reflector with photonic crystal

Dual-polarized Fixed-frequency Beam Scanning Leaky-wave Antenna for 5G Communication

A low profile and dual-polarized fixed-frequency beam scanning leaky wave antenna for 5G communication is presented, which is based on a corrugated microstrip line (CML) called spoof surface plasmons transmission line. The antenna radiates horizontally polarized electromagnetic wave and vertically polarized electromagnetic wave using two different periodic antennas elements. The fabricated antenna is measured and the results show that the operating frequency of the antenna is 3.4-3.7 GHz. The measured main beam angle scans from -9° to -30°. The measured gain is from 8.3 dB to 9.7 dB over the working band.

Verification of the electromagnetic deep-penetration effect in the real world

The deep penetration of electromagnetic waves into lossy media can be obtained by properly generating inhomogeneous waves. In this work, for the very first time, we demonstrate the physical implementation and the practical relevance of this phenomenon. A thorough numerical investigation of the deep-penetration effects has been performed by designing and comparing three distinct practical radiators, emitting either homogeneous or inhomogeneous waves. As concerns the latter kind, a typical Menzel microstrip antenna is first used to radiate improper leaky waves. Then, a completely new approach based on an optimized 3-D horn TEM antenna applied to a lossy prism is described, which may find applications even at optical frequencies. The effectiveness of the proposed radiators is measured using different algorithms to consider distinct aspects of the propagation in lossy media. We finally demonstrate that the deep penetration is possible, by extending the ideal and theoretical evidence to practical relevance, and discuss both achievements and limits obtained through numerical simulations on the designed antennas.

Variations of stress field and stone fracture produced at different lateral locations in a shockwave lithotripter field

During clinical procedures, the lithotripter shock wave (LSW) that is incident on the stone and resultant stress field is often asymmetric due to the respiratory motion of the patient. The variations of the LSW-stone interaction and associated fracture pattern were investigated by photoelastic imaging, phantom experiments, and three-dimensional fluid-solid interaction modeling at different lateral locations in a lithotripter field. In contrast to a T-shaped fracture pattern often observed in the posterior region of the disk-shaped stone under symmetric loading, the fracture pattern gradually transitioned to a tilted L-shape under asymmetric loading conditions. Moreover, the model simulations revealed the generation of surface acoustic waves (SAWs), i.e., a leaky Rayleigh wave on the anterior boundary and Scholte wave on the posterior boundary of the stone. The propagation of SAWs on the stone boundary is accompanied by a progressive transition of the LSW reflection pattern from regular to von Neumann and to weak von Neumann reflection near the glancing incidence and, concomitantly, the development and growth of a Mach stem, swirling around the stone boundary. The maximum tensile stress and stress integral were produced by SAWs on the stone boundary under asymmetric loading conditions, which drove the initiation and extension of surface cracks into the bulk of the stone that is confirmed by micro-computed tomography analysis.

Numerical Study of Propagation of Nonlinear Coupled Surface and Leaky Electromagnetic Waves in a Circular Cylindrical Metal–Dielectric Waveguide

Numerical Study of Propagation of Nonlinear Coupled Surface and Leaky Electromagnetic Waves in a Circular Cylindrical Metal–Dielectric Waveguide

NONLINEAR PROPAGATION OF LEAKY TE-POLARIZED ELECTROMAGNETIC WAVES IN A METAMATERIAL GOUBAU LINE

Propagation of leaky TE-polarized electromagnetic waves in the Goubau line (a perfectly conducting cylinder covered by a concentric dielectric layer) filled with nonlinear metamaterial medium is studied. The problem is reduced to the analysis of a nonlinear integral equation with a kernel in the form of the Green function of an auxiliary boundary value problem on an interval. The existence of propagating nonlinear leaky TE waves for the chosen nonlinearity (Kerr law) is proved using the method of contraction. For the numerical solution, a method based on solving an auxiliary Cauchy problem (a version of the shooting method) is proposed. New propagation regimes are discovered.

Anomalous reflection and transmission of surface acoustic waves at a crystal edge via coupling to leaky wedge waves

Surface acoustic waves are propagated toward the edge of an anisotropic elastic medium (a silicon crystal), which supports leaky waves with a high degree of localization at the tip of the edge. At an angle of incidence corresponding to phase matching with this leaky wedge wave, a sharp peak in the reflection coefficient of the surface wave was found. This anomalous reflection is associated with efficient excitation of the leaky wedge wave. In laser ultrasound experiments, surface acoustic wave pulses were excited and their reflection from the edge of the sample and their partial conversion into leaky wedge wave pulses was observed by optical probe-beam deflection. The reflection scenario and the pulse shapes of the surface and wedge-localized guided waves, including the evolution of the acoustic pulse traveling along the edge, have been confirmed in detail by numerical simulations.