Fig 3 - uploaded by Francesco Monticone
Content may be subject to copyright.
Singularities on the two-sheeted complex plane of the longitudinal wavenumber k z = b - j a for a wave-guiding structure open on one side, as in Fig. 1(c), (d), and Fig. 2 (if the waveguide
Source publication
Leaky waves have been among the most active areas of research in microwave engineering over the second half of the 20th century. They have been shown to dominate the near-field of several open wave-guiding structures, of great interest to tailor their radiation, guidance and filtering properties. The elegant theoretical analyses and deep physical i...
Contexts in source publication
Context 1
... provided by the fundamental works of Marcuvitz [1] and Oliner [4], [5]. While in closed systems the eigenmodal spectrum is purely discrete, in open systems a continuous eigenmodal spectrum arises, determined by the branch cuts of (2) that emanate from the branch points k z ¼ AEk 0 . For a wave- guiding structure open on one side, the sketch in Fig. 3 shows the complex plane of the longitudinal wavenumber k z , with the typical choice of branch cuts. A proper spectral solution of the source-excited electromagnetic problem implies an integration over the top Riemann sheet associated with waves decaying at infinity, namely, Im½k x G 0, or x > 0, (radiation condition). However, as ...
Context 2
... shows the complex plane of the longitudinal wavenumber k z , with the typical choice of branch cuts. A proper spectral solution of the source-excited electromagnetic problem implies an integration over the top Riemann sheet associated with waves decaying at infinity, namely, Im½k x G 0, or x > 0, (radiation condition). However, as indicated in Fig. 3, pole singularities may also be present in the bottom Riemann sheet, and in this case they are denoted as nonmodal, or improper source-free solutions of the field equation. As shown by Marcuvitz [1], these complex poles can actually correspond to leaky modes. Although they do not directly contribute to the proper spectral solution, and ...
Similar publications
Recent demonstrations of metasurfaces show their great potential to realize flat and multifunctional optical elements, viable for many new device applications. Yet, a major frontier in this field is to develop active, tunable, and reconfigurable metasurface platforms. These are highly desirable in modern technologies that require dynamic modulation...
Citations
... The metasurface can be also designed to operate as a LWA in the forward-radiation and backward-radiation regimes [43], [44]. The former regime is also referred to as an anomalous (or fast-wave) radiation regime. ...
In this work, we show that propagating waves can be fully converted into surface waves and back using geometrically periodic arrays of simple electrically small metal elements loaded by adjustable reactive loads. The proposed approach allows the creation of all-angle scanning leaky-wave antennas with perfect or even superdirective aperture efficiency at all scan angles. Moreover, it is possible to co-design such leaky-wave antenna arrays with surface-wave waveguides that can guide the received power to the load or to another leaky-wave antenna section. That second section can either reradiate the received power into any direction or perform some other transformation of the reradiated wave front, for example, focusing the power at a point. These and other functionalities are realized by global optimization of the reactive loads of array elements. This global optimization, together with the use of arrays with a subwavelength geometrical period, allows proper control over both propagating and evanescent-field distributions, ensuring theoretically perfect performance at arbitrary scan angles. The proposed technique can be used in antenna engineering and in advanced designs of reconfigurable intelligent surfaces.
... This study represents an initial step in that direction. In the literature, many LWAs structures have been proposed, to address aspects such as miniaturisation, directivity, full scanning, and stop-band suppression [8], but they were not strictly relevant to the goal of this article. For this work, therefore, we chose a simple LWA-the Menzel antenna-due to its specific attenuation and phase vector properties [9]. ...
For this article, we approximated the field of a leaky-wave antenna (LWA) with the field produced by a uniform linear array (ULA). This article aims to provide an initial framework for applications where the generation of an inhomogeneous wave is wished, but, at the same time, a flexibility is required that is difficult to meet with the conventional LWA design. In particular, two different configurations were considered, one with a simple Menzel antenna operating at 12 GHz, and one, relevant for practical applications, with an antenna operating at 2.4 GHz. This study aimed, in both cases, to highlight the distance at which the field produced by the phased array with the chosen sampling method can approximate effectively the one produced by a leaky-wave antenna and to verify whether this could cause issues for the targeted application.
... = arccos ( ) , where and are the phase constant along the LWA and the propagation constant in free space [100]. Traditional LWA usually employs a metallic waveguide with a slit cut, namely uniform LWA, which is depicted in Fig. 9(a). ...
As a key enabling technology of the Internet of Things (IoT) and 5G communication networks, millimeter wave (mmWave) backscatter has undergone noteworthy advancements and brought significant improvement to prevailing sensing and communication systems. Past few years have witnessed growing efforts in innovating mmWave backscatter transmitters (e.g., tags and metasurfaces) and the corresponding techniques, which provide efficient information embedding and fine-grained signal manipulation for mmWave backscatter technologies. These efforts have greatly enabled a variety of appealing applications, such as long-range localization, roadside-to-vehicle communication, coverage optimization and large-scale identification. In this paper, we carry out a comprehensive survey to systematically summarize the works related to the topic of mmWave backscatter. Firstly, we introduce the scope of this survey and provide a taxonomy to distinguish two categories of mmWave backscatter research based on the operating principle of the backscatter transmitter: modulation-based and relay-based. Furthermore, existing works in each category are grouped and introduced in detail, with their common applications, platforms and technologies, respectively. Finally, we elaborate on potential directions and discuss related surveys in this area.
... After the first presentation of the leaky-wave antenna [1], it has attracted a lot of attention due to its simple feeding configuration, low profile, high gain, and inherent frequency beam-scanning characteristic [2,3]. Owing to these features, LWA has become increasingly popular in the past years, and many works have investigated based on its unique frequency beam-scanning property, such as periodic LWAs based on SIW [4,5], the low-loss Goubau Line [6,7], and many other transmission structures [8-10]. However, for some periodic LWAs, continuous backward-to-forward beam scanning cannot be generated if an open stopband (OSB) is not effectively suppressed. ...
... However, for some periodic LWAs, continuous backward-to-forward beam scanning cannot be generated if an open stopband (OSB) is not effectively suppressed. Furthermore, in some realistic applications, like radar detection, satellite communication, and mobile communication, where the beamscanning property within the specific operating frequency bands is more effective [4][5][6][7][8][9][10], an LWA with FFBS is much more preferred compared to frequency-dependent beam scanning. ...
A period-reconfigurable leaky-wave antenna (LWA) with circular polarization (CP) and fixed-frequency beam scanning (FFBS) is developed in this article. Operating in the Ka-band, this antenna consists of a low-loss groove gap waveguide (GGW) as the slow-wave transmission structure, a circular split-ring patch array on the top layer for radiation, and a slotted ground between them for energy coupling. Each slot is independently and electrically controlled by a pair of PIN diodes under the coupling slot. Thus, the period length of the patches can be manipulated and an LWA with CP and FFBS is achieved with −1th spatial harmonics radiated. The simulation results show that the bean-scanning range from 61° to 63° can be realized during the observation frequency band, with good circular polarization and a peak gain of 17.1 dBi, which is verified by the measurement.
... Leaky-wave antennas (LWAs) are radiating devices constituted by waveguiding structures which allow for continuous power radiation while propagating along their length [1][2][3]. Although the working principle is rather intuitive, the design of radiating devices by partially open waveguides found its mathematical and physical rigorous foundation only in the 1950s thanks to the famous work of N. Marcuvitz [4]. ...
... The main critical aspects of LWAs are typically related to the following trade-offs: pattern fractional bandwidth vs. directivity (leaky-wave antennas are usually highly directive but show a narrow bandwidth), reconfigurability vs. complexity (the higher the desired reconfigurability at a fixed frequency, the more complex the device architecture), and radiation efficiency vs. aperture size (a large radiating aperture is needed to achieve a highly directive antenna) [2]. Fortunately, various solutions have been proposed in recent years to address these challenges. ...
Two-dimensional leaky-wave antennas offer effective, compact, single-feeder, easy-to-fabricate solutions to the longstanding problem of realizing a simultaneously directive and low-profile radiating device. These traveling-wave antennas have been thus proposed as wideband, reconfigurable, or frequency-scanning radiating structures in different application contexts, spacing from the microwave to terahertz frequency range. These diverse contexts call for a comprehensive guide to characterizing and designing two-dimensional leaky-wave antennas. In this work, a review of numerical techniques for the analysis of either quasi-uniform or radially periodic leaky-wave antennas is proposed in order to provide the reader with straightforward yet effective design guidelines. Theoretical results are corroborated through full-wave simulations of realistic three-dimensional models of the considered devices, thus demonstrating the effectiveness of the proposed methods.
... The study of Bessel beams has attracted significant interest in many areas of engineering and physical sciences due to their diffraction-free nature and self-healing properties [1][2][3][4]. These properties make Bessel beams highly advantageous in integrated photonics, particularly within communication systems, where they contribute to extended propagation ranges, improved imaging capabilities, and efficient handling of optical signals [5]. ...
... where T (1,2),n is given as ...
... The primed version of the Hankel function H (1,2) indicates its derivative. By eliminating c n , the amplitudes of adjacent cladding pairs can be related by ...
In this study, we develop a photonics-based Bessel launcher characterized by a hollow-core cylindrical waveguide surrounded by Bragg gratings composed of concentric silicon rings, each 375 nm thick. The metasurface is constructed on a 5 µm high silicon cylindrical substrate. This configuration effectively generates a Bessel beam at the commonly used telecom infrared optical wavelength of 1.55 µm. We explore three variations of this optical antenna, featuring 3-, 6-, 16-, and 32-ring arrays, respectively. We compare the results with the geometrical optics approach as well as the Rayleigh hypothesis. The performance of the optical antenna configuration is assessed through simulated far-field polar plots and z-directed intensity distributions up to a non-diffracting range (NDR) of 1 mm using CST Microwave Studio and Lumerical FDTD INTERCONNECT. These simulations reveal that the optical antenna gain of the launcher in the far field varies from 20 to 26 dBi as the number of concentric rings increases from 6 to 32. We report the reflection coefficient of and the radiation efficiency of 0.01 dB. To independently verify the angular spectrum of the antenna, we employ dyadic Green’s functions, orthogonal vector wave functions, and Bloch’s theorem in MATLAB, demonstrating exceptional coupling of the Gaussian beam into the photonic device with a radiation efficiency of 99%.
... They originate from the physics of leaky waves, studied since the 1940s, which are guided modes that propagate along open wave-guiding structures [49,50]. Unlike conventional surface waves, leaky waves possess complex propagation constants, allowing energy radiation into free space as they travel [51][52][53]. Leaky wave antennas have utilised plasmonic metamaterials with Epsilon-Near-Zero (ENZ) dielectric constants to enhance directionality [54]. Anisotropic ENZ materials with tunable transverse dielectric responses and low magnetic permeability materials with strong tangential magnetic fields have also been employed to control emission and directivity [55]. ...
... To allow radiation leakage in an ATR setup, an air gap must be introduced to include the coupling of evanescent waves with the leaky wave. Leaky waves experience an exponential increase in air [52], which in the past has led them to be known as 'mathematically improper' [59], meaning that quite a large air gap (as used here) will be necessary to allow coupling. As leaky waves appear at low wavevectors, we only observe surface wave-like to be supported slightly beyond the critical angle, close to k x /k 0 = 1. ...
Manipulating hyperbolic polaritons at infrared frequencies has recently garnered interest as it promises to deliver new functionality for next-generation optical and photonic devices. This study investigates the impact of the crystal's anisotropy orientation on the Attenuated Total Reflection (ATR) spectra, more specifically, revealing the optical footprint of elliptical, ghost (GHP) and leaky (LHP) hyperbolic polaritons. Our findings reveal that the ATR spectra of GHPs exhibit a distinct hyperbolic behaviour which is similar to that recently observed using s-SNOM techniques. Similarly, the ATR spectra of LHPs show its clear lenticular behaviour; however, here we are able to discern the effects of large asymmetry due to cross-polarisation conversion when the crystal anisotropy is tilted away from the surface. Furthermore, we demonstrate that by controlling the anisotropy orientation of hyperbolic media it is possible to significantly alter the optical response of these polaritons. Thus, our results provide a foundation for the design of direction-dependent optical devices.
... Recent advancements in materials science have been crucial for the development of more efficient nanoantennas [9]. Although gold and silver have traditionally been utilized owing to their plasmonic properties [10], limitations such as the skin effect at higher frequencies reduce their efficiency. ...
The integration of infrared nanoantenna technology into architectural design presents a novel approach to enhancing buildings’ energy efficiency by converting ambient electromagnetic radiation, particularly in the infrared spectrum, into usable electrical power. This technology offers significant potential to reduce buildings’ reliance on external power sources, contributing to a more sustainable energy ecosystem. The development of advanced nanotechnology, metamaterials, and responsive coatings is essential for creating adaptive surfaces capable of capturing and utilizing radiant energy. Given the increasing global energy demand and the urgency to combat climate change, infrared nanoantennas represent a promising frontier in renewable energy harvesting. This paper provides a detailed examination of recent advancements in nanoantenna technology, fabrication methods, and integration strategies within building materials. Furthermore, it addresses the practical challenges of implementing these systems in architectural design, offering insights into how this emerging technology could contribute to the development of self-sustaining, energy-efficient structures.
... This leakage can occur via a uniform aperture along a waveguide, or through slots or arrays of shunts positioned at periodic intervals, thereby forming unit cells [16], [17]. Furthermore, the structure can be categorized as heterogeneous [18], [19], [8], [15] or designed based on acoustic metamaterials of the transmission line [11], [20]. The directivity of the radiated energy depends on the frequency of the propagating wave within the guide and the length of the antenna. ...
Acoustic signals, which have been utilized for decades in the spatial localization of objects, have found applications in fields as diverse as sonar for underwater navigation, communication, and object detection. Traditional methods often rely on arrays of transducers, which necessitate the use of expensive hardware and processing algorithms. An emerging alternative is the Acoustic Leaky Wave Antenna (ALWA), which is inspired by electromagnetic leaky wave antennas. ALWA technology employs a single transducer to emit directional beams that scan angular space by frequency manipulation. Conventional arrays offer cost-effectiveness and simplicity of design, but ALWAs have the advantage of operating on the principle of energy leakage, which is achieved by various mechanisms, such as uniform apertures or slits periodic along the waveguide. This technology, applicable to underwater and airborne communications, offers compact and energy-efficient solutions, which facilitate the development of the “Underwater Internet of Things” and autonomous communication systems for underwater vehicles. This work presents a parametric study of this type of antennas with axisymmetric geometry by means of a numerical solution based on the Finite Element Method. Together with analytical studies, the physical phenomenology underlying this technology will be described, including directivity, transmission and reflection parameters, beam scanning and dispersion curve. Finally, the design is validated through experiments.
... For the leaky-wave antenna, the radiation direction of the antenna can be expressed as [36,37]: ...
This letter proposes a compact air‐substrate single conductor endfire antenna, characterized by stable endfire radiation, high gain, high gain‐to‐length ratio and easy assembly. The proposed antenna is fed by air‐substrate double‐sided parallel strip lines (DSPSLs) in the TEM mode, ensuring stable endfire radiation pattern. Evolved from the periodic leaky‐wave antenna design, it also achieves high gain. Moreever, the radiating elements can couple energy through two paths, achieving an almost uniform electric field distribution, which contributes to a high gain‐to‐length ratio. Notably, a single‐conductor structure is achieved by terminating the short‐circuited DSPSLs, which simplifies the assembly process and minimizes manufacturing complexity. Finally, the proposed compact single‐conductor antenna is simulated, fabricated, and measured. The proposed endfire antenna features a compact size of 1.90λ0 × 0.42λ0 × 0.05λ0 operating at the center frequency of 5.00 GHz, where λ0 denotes the free‐space wavelength. According to the measurement results, the antenna also achieves a high gain of 11.37 dBi and a high gain‐to‐length ratio of 7.21, exhibiting a wide 1‐dB gain bandwidth of 4.00–5.30 GHz. These features make the antenna well‐suited for diverse long‐distance communication applications.
