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Second‐order topological insulators can be characterized by their bulk polarization, which is believed to be intrinsically connected to the center of the Wannier function. In this study, the existence of second‐order topological insulators is demonstrated that feature a pair of partially degenerate photonic bands. These arise from the nonsymmorphic glide symmetry in an all‐dielectric photonic crystal. The center of the maximally localized Wannier function (MLWF) is consistently located at the origin but is not equivalent with respect to the sum of constituent polarizations. As a result, topological corner modes can be identified by the distinctly hybridized MLWFs that truncate at the sample boundary. Through full‐wave numerical simulations paired with microwave experiments, the second‐order topology is clearly confirmed and characterized. These topological corner states exhibit notably unique modal symmetries, which are made possible by the inversion of the Wannier bands. These results provide an alternative approach to explore higher‐order topological physics with significant potential for applications in integrated and quantum photonics. [ABSTRACT FROM AUTHOR]

Recently, plasmonic metasurfaces have emerged as a platform for topological photonics, exhibiting both advantages of plasmon‐induced tight confinement of local field and topological robustness. Most previous works regarding plasmonic systems are limited to the first‐order topologies and only a few studies dealt with higher‐order topological states in honeycomb lattices. Moreover, second‐order topologies of square lattice plasmonic systems have not yet been studied. This work presents second‐order topological corner states in the square lattices of metallic nanoparticles (NPs) with various symmetries, taking two different C4 and glide symmetries as examples. Their unit cells are obtained from nonprimitive cells, consisting of four equal spheroidal NPs, by expanding (or shrinking), rotating, and resizing. Bulk bands and spectral functions of the unit cells calculated by using the coupled dipole method well agree with COMSOL simulation results, revealing the accuracy of the numerical calculations as well as the experimental realizability of the systems. Second‐order topological corner states and their robustness against structural disorder are numerically shown for three different square lattices. This work will trigger extensive investigations to open a new realm of topological metasurfaces with promising applications. [ABSTRACT FROM AUTHOR]

The electrical response of low-frequency band-pass filters based on periodic substrate integrated waveguide (SIW) technology typically shows permitted and forbidden frequency bands. Therefore, this type of filters can be designed using a conceptually very simple and efficient procedure based exclusively on the study of the dispersion properties of the periodic structure. In this paper, we go a step further with the design of a periodically air-filled SIW band-pass filter in which part of the dielectric substrate is removed to reduce insertion losses, and whose unit cell parameters, which are directly related to the center frequency ( $f_{c}$ ) and bandwidth (BW) of the first passband, and also to the first stopband or bandgap (BG) of the structure, have been appropriately selected for filtering purposes, thus providing some useful design rules. Furthermore, we apply the concept of glide symmetry for achieving a much larger fractional bandwidth (FBW) than that obtained in conventional air-filled SIW filters found in the technical literature. Finite implementations of both periodic structures with and without glide symmetry have been analyzed, showing their filtering response for validation purposes. Additionally, to overcome the matching level restrictions in the resulting air-filled periodic SIWs, a microstrip-to-SIW transition including a novel coupling iris is proposed. A prototype of the proposed air-filled glide-symmetric periodic SIW filter has been manufactured and experimentally validated, illustrating the potential of this technique to obtain large FBWs that can not be achieved in conventional air-filled SIW filters. The proposed filter proves to be a good candidate for millimeter wave applications.

In this paper, a mode-matching procedure is used to prove for the first time the dispersionless behavior of glide symmetry (GS) in corrugated metasurface waveguides. Depending on their field symmetry, the Floquet harmonics have a different impact onto the frequency dispersion, which is reduced with GS when the gap between the surfaces is small. Indeed, the glide-symmetric waveguide is shown to have the same effective propagation features as a scaled mirror-symmetric waveguide with half the period and a doubled gap. We propose closed-form formulas for the effective refractive index of the glide-symmetric waveguide in the first Brillouin zone, having a small groove compared to the period. The closed-form expressions analytically prove the dispersionless behavior of GS. [ABSTRACT FROM AUTHOR]

This article suggests a new waveguide design that utilizes a "walled" architecture. Instead of relying on conventional gap waveguide structures to create electronic bandgaps and prevent field leakage, the proposed design introduces a "walled" guiding mechanism. This technique preserves transmission while maintaining the multilayer approach and eliminates the need for nails or chemical bonds to attach the layers. Simulations were carried out in the W-band (75–110 GHz) and D-band (110–170 GHz) using several metals, and measurements were performed in the W-band using aluminum. The simulation results show that the reflection coefficient was less than −40 dB over the entire D-band. At the same time, the average insertion loss was around 0.0054 dB/mm and around 0.0065 dB/mm for silver and gold, respectively. Similarly, the reflection coefficient was less than −45 dB over the 75–110 GHz range, with an average insertion loss of 0.0018 dB/mm for silver and 0.003 dB/mm for gold, respectively. The aluminum model's reflection coefficient was less than −35 dB, and the average insertion loss was 0.0035 dB/mm. The experimental results achieved a reflection coefficient of less than –30 dB and the average transmission coefficient was −0.2 dB, with an insertion loss of 0.002 dB/mm. The simple stacking ability of the weightless walled metal plates and easy fabrication makes the proposed transmission line a promising technology in mmWave and Terahertz applications. [ABSTRACT FROM AUTHOR]

This article investigates the dispersion properties of metasurfaces with hexagonal lattices, including potential higher symmetric configurations. We explore the relationships between the periodicity of hexagonal lattices and their dispersion properties, paying special attention to how hexagonal periodic structures can be analyzed with either a hexagonal primitive unit cell or a rectangular supercell. We also study the possibility of introducing higher symmetries into hexagonal periodic structures, including glide symmetry and mirrored half-turn symmetry. To complement and validate the analysis, we designed a graded-index Luneburg lens antenna with a dielectric-filled hexagonal holey structure working in the K$_{\mathrm{a}}$-band. The antenna generates steerable highly directive beams from 26 GHz to 30 GHz, which corroborates our analysis. Our findings provide valuable insight into the dispersion properties of hexagonal-lattice metasurfaces and demonstrate the feasibility of using such structures in practical applications.

In this paper, a novel dielectric metasurface-inspired multi-beam directional Luneburg lens is proposed as a wireless power transfer medium at 5G mm-wave band. The lens is constructed using dielectric-based unit cells made up of a glide symmetric approach. It is connected with a set of microwave detector integrated multi-port tapered rectangular feeds to convert the received RF energy from different directions to DC power across a combined load. The proposed structure can be a potential candidate to harvest ambient energy from a wide coverage range of around 160° and produce a power conversion efficiency of about 76% for an input power of 14.9 dBm at 24 GHz.

In this letter, we present a planar half-Luneburg lens antenna based on a glide-symmetric dielectric structure. The proposed half-Luneburg lens antenna provides a compact alternative to planar beamformers such as conventional Luneburg and Rotman lenses, as well as pillbox antennas. Importantly, we demonstrate that the peak gain of the half-Luneburg lens antenna is less than 1 dB lower than the peak gain of a conventional Luneburg lens antenna, despite being almost half the size. The proposed antenna can steer its beam in a 50 $^{\circ }$ range with scan losses lower than 2 dB and side lobe levels below $-$ 10 dB. The proposed design is validated experimentally with a robust and cost-effective implementation using additive manufacturing. [ABSTRACT FROM AUTHOR]

In this paper, a concept of a reconfigurable chipless radio frequency identification (RFID) sensor tag for detecting solvent vapors/gas in IoT applications was presented. The concept was based on the authors' previously published rectangular loop structure equipped with a U-folded dipole loaded with a glide-symmetrical interdigital capacitor coated with a thin layer of tetrasulfonated copper phthalocyanine deposited as a sensing layer to improve the sensing capability in the presence of acetone vapor. In order to further maximize the sensitivity of the designed structure to the desired solvent, a circuit for a central frequency adjustment using a radio frequency varactor diode biased with a wireless power transfer (WPT) was designed. By varying the DC bias of the diode, a continuous tunable range of approximately 200 MHz was achieved. The proposed reconfigurable wireless sensor tag was manufactured and the frequency shift was verified by measurement. The proposed external frequency control can be applied to a wide class of electrical resonators. [ABSTRACT FROM AUTHOR]

A fully metallic leaky-wave antenna (LWA) with enhanced scanning rate is presented. The leaky waveguide is implemented in groove gap waveguide technology and is periodically loaded to produce backward radiation. Furthermore, glide-symmetric pins are placed inside the leaky waveguide to increase the dispersion. A parallel-plate waveguide metasurface prism lens is used to disperse the backward radiation and increase the scanning rate of the LWA. The designed antenna can steer the radiation from −26° to 26° from 27 to 35 GHz, and an average total efficiency of 74% is achieved. A prototype of the designed antenna is manufactured, and measurements corroborate the simulated results. The proposed concept is applicable to other frequency-scanning antennas and can be used to increase the scanning rate in radar and imaging systems. [ABSTRACT FROM AUTHOR]

In this work, the degeneracy of the two lowest-order modes of spoof surface plasmon polariton (SSPP) is realized by the surface plasmonic waveguide (SPW), which takes the form of a slotline with glide symmetric dumbbell grooves. It is found that the non-zero group velocity can be observed on the two lowest-order modes at the Brillouin zone boundary of such glide symmetric SPW, which exhibits higher propagation constant of the dispersion relation than conventional non-glide SPW. The dispersion relation of SSPP unit cells when glide symmetric conditions are broken is also calculated and analyzed by the finite difference time domain (FDTD) method. Finally, a wideband bandpass filter (BPF) based on this glide symmetric waveguide scheme is designed for validating its broadband essential attribute and circuitry function. The experimental and simulation results show good consistency. The proposed glide symmetric SPW may be potential applications in plasmonic devices and wideband leaky-wave antenna at the microwave or THz frequency. [ABSTRACT FROM AUTHOR]

In this paper, a novel dielectric metasurface-inspired multi-beam directional Luneburg lens is proposed as a wireless power transfer medium at 5G mm-wave band. The lens is constructed using dielectric-based unit cells made up of a glide symmetric approach. It is connected with a set of microwave detector integrated multi-port tapered rectangular feeds to convert the received RF energy from different directions to DC power across a combined load. The proposed structure can be a potential candidate to harvest ambient energy from a wide coverage range of around 160° and produce a power conversion efficiency of about 76% for an input power of 14.9 dBm at 24 GHz. [ABSTRACT FROM AUTHOR]

• A topological metamaterial plate perforated with unique glide-symmetric holes is developed. • Dual-band helical interface states of flexural waves are demonstrated both numerically and experimentally. • Second-order topological corner state with asymmetric localization is observed. This study investigates the topological localization and propagation of flexural waves in metamaterial plates with perforated holes exhibiting glide symmetry. The dispersion relations of flexural waves in this mechanical system exhibit four-fold Dirac degeneracies at the M point of the Brillouin zone. By properly adjusting the rotation angles of the perforated holes, these degeneracies can be lifted up to create omnidirectional bandgaps, enabling nontrivial topological phases. Both numerical and experimental results demonstrate multiple topological states of flexural waves in the developed elastic metaplates, including dual-band helical interface states and anisotropic interface/corner states. The simple perforated metaplates with glide-symmetric holes provide novel, manufacturable platforms for the flexible manipulation of topological flexural waves, greatly facilitating potential applications such as energy harvesting and signal enhancement. [Display omitted] [ABSTRACT FROM AUTHOR]

In this article, we propose a hybrid glide-symmetric metasurface which presents an electromagnetic bandgap (EBG) behavior at the $Ka$ -band. The innovative part of this work is the hybrid nature of the periodic structure, which is implemented with holes on two different technologies: printed circuit board (PCB) and metallic waveguide. These holes avoid propagation in an undesired parallel plate created between a PCB and a metallic waveguide. To demonstrate the potential of this concept, a hybrid glide-symmetric configuration was placed surrounding a PCB–waveguide transition at the $Ka$ -band to reduce the leakage created by undesired air gaps. A prototype was manufactured and measured to corroborate the effectiveness of this technique to reduce losses and crosstalk. [ABSTRACT FROM AUTHOR]

In recent years, metasurfaces have become a rapidly growing domain of research in several fields of engineering and applied physics due to their ability to manipulate both phase and amplitude of electromagnetic fields. These artificial 2D-materials, usually composed of metallic elements printed on dielectric substrates, have the advantages of being low profile, lightweight as well as easy to fabricate and integrate with standard circuit technologies. In this context, this paper reviews the latest progress in metasurface antenna design, where metasurfaces are used to miniaturize the profile, increase the bandwidth, and control the radiation pattern in the near- and far-field regions.

In this paper, a rectifier integrated Luneburg lens is designed at K band for wireless power transfer (WPT) applications. The lens consists of two metallic layers with a gap of 0.3 mm between them and has been made by employing the glide symmetry technique. A flare is tailored to match the outer impedance of the lens to the free space impedance. Five microstrip tapers are used at intervals of $18^{0}$ at the periphery of the lens to collect the energy from it. The rectifying circuits are co-designed and are integrated with these five tapered launchers so as to make the entire structure suitable for capturing the transmitted power from the solar power satellite wirelessly, and to convert it to the equivalent voltage. Finally, all the ports are connected with a common load for DC power combining, and the overall performance of the lens integrated rectifier as an energy harvesting system is reported in terms of its power conversion efficiency (PCE).

The presence of glide symmetries in periodic structures can introduce beneficial modifications in their electromagnetic properties. The difference between glide and non-glide periodic structures is due to the distinctive coupling between their constituent sub-unit cells. In this paper, we describe the recent discoveries on the remarkable properties of glide-symmetric periodic structures, which include widened stopbands, reduced dispersion, as well as enhanced anisotropy and magnetic response. These properties are explained through canonical structures simulated with two methods: mode matching and multimode transfer-matrix analysis. We also review the recent use of these distinctive properties for solving technological problems in practical devices such as filters, gap waveguide components, low-leakage flanges, compressed lenses, low-reflected material transitions and leaky-wave antennas with applications in 5G terrestrial communication systems, millimetre-wave satellite systems and automated contactless measurement techniques.

In this article, we present a novel application of glide symmetry to differential lines with common-mode (CM) rejection filter properties. Two different topologies are investigated. First, glide symmetry is applied to a pair of differential lines where ground-connected mushrooms are employed as a CM rejection structure. The same idea is also used in a pair of differential lines where defective ground structures are introduced to stop the CM propagation. It is demonstrated that the CM rejection bandwidth is drastically increased when glide symmetry is exploited in both topologies when compared with their corresponding structures without glide symmetry. Furthermore, we show that the differential-mode propagation is hardly affected by the use of glide symmetry, ensuring the good integrity of the transmitted information. Experimental demonstration for both mushroom and defected ground structure is provided. Good agreement between simulations and measurements results is observed. [ABSTRACT FROM AUTHOR]

A Huygens’ metasurface with unit cells of glide symmetric I-shape metal strips is proposed for a high-efficiency metalens antenna. The proposed unit cell achieves more than 98.6% transmission amplitude with 360° phase shift coverage for dual polarization. The mechanism is presented by analyzing a unit cell with two dislocated I-shape metal strips, where the electric dipole and magnetic dipole resonances are tuned by the dislocation. The analysis implies that glide symmetric I-shape metal strips are preferable for high transmittance Huygens’ unit cell design. With the proposed Huygens’ unit cell, a high-efficiency metalens antenna is realized. The simulated and measured results show that the proposed metalens antenna of a 14-wavelength diameter achieves a maximum gain of 30.7 dBi at 27.2 GHz, which is only 1.1 dB lower than its theoretical limit. The maximum antenna efficiency is 61.5%. The 3-dB bandwidth of achieved gain ranges from 25.9 to 29 GHz, covering the fifth generation (5G) millimeter-wave bands. The proposed metalens remarkably enhances the radiation performance of the metalens antennas. [ABSTRACT FROM AUTHOR]

In this letter, we propose and study a 2-D glide-symmetric dielectric periodic structure. We demonstrate that glide symmetry broadens the bandwidth of operation and achieves lower effective refractive indices when compared to non-glide configurations. These two properties are beneficial for producing graded-index lens antennas. To demonstrate the potential of the proposed unit cell, we designed a Luneburg lens operating in the K- and K $_\text {a}\!$ -bands. The lens was manufactured with conventional additive manufacturing and it has a potential use for future wireless communications given its low-cost and low-profile. [ABSTRACT FROM AUTHOR]

Many frequency-selective surface (FSS) structures are based on the use of a single periodic array of slot/apertures in a conducting sheet embedded in a layered medium. However, it is well known that stacking several conducting sheets and breaking the alignment of the stack can bring multiple benefits to the structure. In this article, the analysis and design of stacks of 2-D aperture arrays are carried out by exploiting as much as possible all the potential of a rigorous and systematic formulation based on the multimodal equivalent circuit approach (ECA). A key feature of the formulation is that linear transformations between the apertures of adjacent plates (rotation, translation, and scaling) can be dealt with from a purely analytical perspective. This fact is of potential interest for many practical applications, such as the design of polarization converters, absorbers, filters, and thin matching layers. When the apertures have an arbitrary geometry, it can be applied a hybrid approach that combines the ability of commercial simulators to handle arbitrary geometries with the fast computation times and physical insight of the ECA. In general, either the purely analytical or the hybrid approach can be applied in those many practical scenarios where the spatial profile of the electric field on the considered apertures hardly changes with frequency. As an additional feature of the approach, the dispersion properties (phase/attenuation constants and Bloch impedance) of infinite periodic stacks can be derived, and in particular, analytical expressions for the mirror- and glide-symmetric configurations are provided. [ABSTRACT FROM AUTHOR]

In this paper, a concept of a reconfigurable chipless radio frequency identification (RFID) sensor tag for detecting solvent vapors/gas in IoT applications was presented. The concept was based on the authors’ previously published rectangular loop structure equipped with a U-folded dipole loaded with a glide-symmetrical interdigital capacitor coated with a thin layer of tetrasulfonated copper phthalocyanine deposited as a sensing layer to improve the sensing capability in the presence of acetone vapor. In order to further maximize the sensitivity of the designed structure to the desired solvent, a circuit for a central frequency adjustment using a radio frequency varactor diode biased with a wireless power transfer (WPT) was designed. By varying the DC bias of the diode, a continuous tunable range of approximately 200 MHz was achieved. The proposed reconfigurable wireless sensor tag was manufactured and the frequency shift was verified by measurement. The proposed external frequency control can be applied to a wide class of electrical resonators.

Lenses are used for multiple applications, including communications, surveillance and security, and medical instruments. In homogeneous lenses, the contour is used to control the electromagnetic propagation. Differently, graded-index lenses make use of inhomogeneous materials, which is an extra degree of freedom. This extra degree of freedom enables the design of devices with a high performance. For instance, rotationally symmetric lenses without spherical aberrations, e.g., the Luneburg lens, can be designed. However, the manufacturing of such lenses is more complex. One possible approach to implement these lenses is using metamaterials, which are able to produce equivalent refractive indices. Here, we propose a new type of three-dimensional metamaterial formed with two independent sets of wires. The double-mesh twin-wire structure permits the propagation of a first mode without cut-off frequency and with low dispersion and high isotropy. These properties are similar to periodic structures with higher symmetries, such as glide symmetry. The variations of the equivalent refractive index are achieved with the dimension of the meandered wires. The potential of this new metamaterial is demonstrated with simulated results of a Luneburg meta-lens. [ABSTRACT FROM AUTHOR]

Leaky-wave antenna (LWA) is known as a type of traveling antenna with dispersive frequency responses, which has found important applications in modern communication, imaging, and radar systems. The beam scanning rate is a key consideration in some applications since it can minimize the bandwidth requirement of the system, during the scanning in broad angular regions. However, the sweeping linearity, namely the scanning angular range per unit frequency, is seldom considered at the same time in the published literature. In this article, we propose a waveguide-type LWA working from 11.1 to 12 GHz. By loading periodical pins with glide symmetry in the waveguide, it is possible to manipulate the dispersion properties of the fast wave mode, hereby giving rise to a good balance between the scanning rate and the sweeping linearity. This scenario has been validated by numerical simulation and experiment with excellent agreement. The measurement results reveal that the scanning angles have been increased to a range from 16.7°~67.5° varying the frequency from 11.1 to 12.1 GHz. The relative average scanning rate is enhanced up to 589.3°, with high sweeping linearity. [ABSTRACT FROM AUTHOR]

In this paper, a rectifier integrated Luneburg lens is designed at K band for wireless power transfer (WPT) applications. The lens consists of two metallic layers with a gap of 0.3 mm between them and has been made by employing the glide symmetry technique. A flare is tailored to match the outer impedance of the lens to the free space impedance. Five microstrip tapers are used at intervals of 180 at the periphery of the lens to collect the energy from it. The rectifying circuits are co-designed and are integrated with these five tapered launchers so as to make the entire structure suitable for capturing the transmitted power from the solar power satellite wirelessly, and to convert it to the equivalent voltage. Finally, all the ports are connected with a common load for DC power combining, and the overall performance of the lens integrated rectifier as an energy harvesting system is reported in terms of its power conversion efficiency (PCE). [ABSTRACT FROM AUTHOR]

This document presents different phase shifter designs implemented in contactless air-filled substrate-integrated waveguide (CLAF-SIW) technology. The phase shifters are based on unit cells that avoid leakage losses in the assembled layers and produce the desired phase shift along the waveguide. The unit cells are represented by waveguides whose lateral walls have double-mushroom structures, and phase-shifting elements are in their propagation zone. The proposed phase-shifting elements are integrated cavities, integrated cavities with patches, and integrated cavities with mushroom-like patches. Transitions are needed to match impedances between the waveguides loaded with phase-shifting elements and a reference CLAF-SIW. Other transitions are designed to measure the prototypes, from coplanar waveguide to SIW and SIW to CLAF-SIW. Finally, some prototypes are manufactured to provide an experimental validation of the proposed phase-shifting elements. Good agreement is obtained between the simulated and measured results for all the CLAF-SIW phase shifters in the frequency range between 30 and 50 GHz. • We propose a method to achieve phase shifters in CLAF-SIW technology at mmWaves. • Different phase shift behaviors are obtained through different SIH unit cells. • The proof of concept is demonstrated using several phase shifter prototypes. • Good agreement is obtained between measurements and simulations. [ABSTRACT FROM AUTHOR]

Acoustic topological insulators (ATIs) with topological states that are insensitive to defects and impurities offer a robust way to steer acoustic waves. However, current ATIs in square lattice only host topological interface states within one bulk bandgap, restricting their multiband applications. Here, we design the ATI, made of glide-symmetric sonic crystals (SCs), hosting multiband topological interface states within multiple bulk bandgaps. First, SCs restricted with glide and mirror symmetries are inversely designed to host multiple bulk bandgaps. Then, the ATI with multiband helical interface states is constructed by selecting two kinds of unit cells (UCs) from the inverse-designed SC and arranging them to form an interface. Both dual-band and triple-band ATIs are designed and experimentally validated. The total size of interface states hosted by the triple-band ATI is about 8.5 times of the record. Besides, by exploiting the mismatch of frequency windows of interface states at the horizontal and vertical interfaces, we realize acoustic demultiplexers for routing interface states. Our work suggests a route to engineering multiband ATIs, having promising applications in designing novel acoustic devices for multiband information processing and communication. [ABSTRACT FROM AUTHOR]

This paper presents a compact and low-loss V-band waveguide phase shifter based on glide-symmetric pin configuration. This kind of higher symmetry permits the control and improvement of the electromagnetic behavior or radiofrequency devices, as it is the case of the proposed phase shifter. The study of the dispersion diagram of the phase shifter unitary cell demonstrates that the pin configuration is a proper option for introducing a phase shift in a waveguide-based system. There is a significant increase in terms of phase shift when using a glide-symmetric pin distribution compared to its corresponding non-glide-symmetric configuration. Through this paper, the key geometrical parameters are also determined. The complete phase shifter is composed of an optimized cascade of tailored unitary cells so that the desired final phase shift value is achieved. A prototype has been manufactured in order to validate the theoretical approach through the comparison of phased shifters with both non-glide-symmetric and glide-symmetric configurations. The measurement results demonstrate the higher performance and compactness of the glide-symmetric phase shifter. For the same distance, the glide-symmetric version of the phase shifter provides more than 60% of phase shifting compared to the non-glide-symmetric phase shifter. Both phase shifters have a good impedance matching between 46 and 60 GHz and an insertion loss lower than 1 dB, thus clearly enabled as a 5G technology.

In this letter, we present the experimental validation of a $K_{a}$ -band Luneburg lens antenna based on a novel cost-effective metasurface. The metasurface is composed of a parallel plate waveguide (PPW) loaded with quasi-periodic inclusions in both conductors. The inclusions are square holes printed on a substrate, with vias placed around the holes. The vias connect the printed layer of the substrate to the ground. This configuration is named substrate-integrated hole (SIH). It is demonstrated that the SIH metasurface can obtain a higher effective refractive index, compared to the conventional holey metasurface. To further increase the effective refractive index, the SIHs in the two conductors of the PPW are glide-symmetrically arranged. The refractive index distribution of the Luneburg lens is realized by locally tuning the dimensions of the SIHs. The lens is fed with 11 waveguide feeds with an angular separation of 10°. Thus, the antenna can steer its radiation in a 100° angular range. A flare is integrated with the PPW to match the antenna to the free-space impedance. Since the wave propagates mainly in the PPW air gap, the dielectric losses are low. The measured radiation efficiency of the antenna is roughly 80%. [ABSTRACT FROM AUTHOR]

The dispersion characteristics of a glide-symmetric holey periodic surface are investigated, with special emphasis on a detailed study of its stopbands. The unit cell is modeled as a multiport network associated with multiple modes at each of the lattice boundaries. Enforcing the periodic conditions, the real and imaginary parts of the wavenumbers of the Floquet modes are calculated through an eigenproblem posed in terms of the generalized multimodal transfer matrix, which is computed from the scattering parameters obtained with a full-wave simulator. This procedure allows us to take into account the higher order modal couplings between adjacent unit cells that are crucial for accurate dispersion analysis. The resulting simulation-assisted approach provides both a convenient computational tool and a very fruitful physical insight that reveals the existence of complex modes, the convergence of opposite-parity modes, and the anisotropy in both passband and stopband. This approach enables a precise calculation of the attenuation constant, which is not possible with conventional techniques as the eigenmode solvers of commercial software. Based on this approach, an extensive parametric study is carried out, rigorously establishing a set of critical criteria for the use of such a periodic surface as an electromagnetic bandgap structure in gap waveguide technology. Moreover, the analysis of the directional properties of the structure is applied to further suppress the leakage. [ABSTRACT FROM AUTHOR]

This article analyzes thoroughly the dispersion and filtering features of periodic holey waveguides in the millimeter-wave frequency range. Two structures are mainly studied depending on the glide and mirror symmetries of the holes. A parametric study of the dispersion characteristics of their unit cells is carried out. Glide-symmetric holey waveguides provide a higher propagation constant and a low dispersion over a wide frequency range regarding hollow waveguides. This property is particularly useful for the design of low-loss and low-dispersive phase shifters. We also demonstrate that glide-symmetric holey waveguides are less dispersive than waveguides loaded with glide-symmetric pins. Furthermore, we perform a Bloch analysis to compute the attenuation constants in holey waveguides with mirror and broken glide symmetries. Both configurations are demonstrated to be suitable for filter design. Finally, the simulation results are validated with two prototypes in gap-waveguide technology. The first one is a 180° phase shifter based on a glide-symmetric holey configuration that achieves a flat phase shift response over a wide frequency range (27.5% frequency bandwidth). The second one is a filter based on a mirror-symmetric holey structure with a 20-dB rejection from 63 to 75 GHz. [ABSTRACT FROM AUTHOR]

This paper presents the design and fabrication of a mechanically reconfigurable filter at W band based on the concept of glide symmetry. The tunability is achieved by breaking and regenerating the glide symmetry. The filters are made of two glide-symmetric pieces that can be displaced in a certain direction, and therefore, break the symmetry. The high filtering capacity of these designs is demonstrated by simulation and measurement and can also be adjusted mechanically. The transmission level in the manufactured filter varies from a value between −1 and −2 dB when the filter is in the glide symmetry position to values close to −40 dB in the stop-band when it is in the broken symmetry position. The transmission band obtained in the symmetrical mode is around 20%, but, after breaking the symmetry, it is split into two passbands of 6.5% and 11% separated by a stop-band of 6%. The position, bandwidth, filtering level and filter roll-off can be adjusted for both modes of operation by appropriately selecting the unit cell design parameters and the number of unit cells.

In this paper, we present a general mode matching formulation to analyze the wave propagation in glide-symmetric metallic surfaces drilled with periodic holes with an arbitrary cross section. A generalized Floquet theorem is applied to reduce the computational cost by imposing boundary conditions only on one of the two surfaces. With a small modification, the formulation can be used also for dispersion analysis of a holey metallic surface with or without a metal plane above it. The method is fast and efficient, and it provides physical insight on the specific symmetry properties of Floquet harmonics in glide-symmetric structures. The formulation is applied to obtain dispersion diagrams of glide-symmetric structures with circular holes as this kind of hole is usually used in practical applications to realize gap waveguides or wideband planar lenses. The results agree well with the reference results from commercial software CST Microwave Studio.

In recent years, metasurfaces have become a rapidly growing domain of research in several fields of engineering and applied physics due to their ability to manipulate both phase and amplitude of electromagnetic fields. These artificial 2D-materials, usually composed of metallic elements printed on dielectric substrates, have the advantages of being low profile, lightweight as well as easy to fabricate and integrate with standard circuit technologies. In this context, this paper reviews the latest progress in metasurface antenna design, where metasurfaces are used to miniaturize the profile, increase the bandwidth, and control the radiation pattern in the near- and far-field regions. [ABSTRACT FROM AUTHOR]

In this article, we study the wave propagation in a metallic parallel-plate structure with glide-symmetric elliptical holes. To perform this study, we derived a mode-matching technique based on the generalized Floquet theorem for glide-symmetric structures. This mode-matching technique benefits from a lower computational cost since it takes advantage of the glide symmetry in the structure. It also provides physical insight into the specific properties of Floquet modes propagating in these specific structures. With our analysis, we demonstrate that glide-symmetric structures with periodic elliptical holes exhibit an anisotropic refractive index over a wide range of frequencies. The equivalent refractive index can be controlled by tuning the dimensions of the holes. Finally, by combining the anisotropy related to the elliptical holes and transformation optics, a Maxwell fish-eye (MFL) lens with a 33.33% size compression is designed. This lens operates in a wideband frequency range from 2.5 to 10 GHz. [ABSTRACT FROM AUTHOR]

We demonstrate the beneficial effects of introducing glide symmetry in a two-dimensional periodic structure. Specifically, we investigate dielectric parallel plate waveguides periodically loaded with Jerusalem cross slots in three configurations: conventional, mirror- and glide-symmetric. Out of these three configurations, it is demonstrated that the glide-symmetric structure is the least dispersive and has the most isotropic response. Furthermore, the glide-symmetric structure provides the highest effective refractive index, which enables the realization of a broader range of electromagnetic devices. To illustrate the potential of this glide-symmetric unit cell, a Maxwell fish-eye lens is designed to operate at 5 GHz. The lens is manufactured in printed circuit board technology. Simulations and measurements are in good agreement and a measured peak transmission coefficient of −0.5 dB is achieved. [ABSTRACT FROM AUTHOR]

In this article, we propose a wideband fully metallic impedance-matching horn lens antenna based on glide symmetry realized in the gap waveguide technology. A multiple iterative method is adopted, which overcomes the limitation of large phase deviations at the interface of traditional lens antennas, thus increases the directivity as a result. Moreover, the glide-symmetric configurations of inner metallic pins within the gap waveguide are employed to construct the artificial dielectric lens, with the advantage of the ultralow dispersion, which is especially helpful to broaden the working bandwidth and improve the lens performance. The antenna is fed by a stepped double-ridged gap waveguide which can easily excite the antenna working in a wideband. To reduce the undesired reflections at the antenna aperture, the antenna is ended with a tapered structure as an impedance transition. A prototype of the horn lens antenna is manufactured and measured, showing a broad operation bandwidth from 12 to 18.5 GHz with S11 less than −10 dB. The antenna can be further extended to the millimeter band due to the low losses of the gap waveguide at high frequencies and the iterative method can also be applied to other types of lens antenna designs. [ABSTRACT FROM AUTHOR]

A glide-symmetry Goubau line leaky-wave antenna for achieving both high scanning rate and wide scanning angle range is introduced. The novelty of the design is its combination of glide symmetry and a single-layer Goubau line. This combination leads to performance enhancement in both scanning rate and scanning angle range. Utilizing a corrugated Goubau line in a glide-symmetry fashion closes its stopband at the cutoff frequency while slowing down its group velocity. As the dispersion around the closed stopband is shifted to the fast-wave region by periodic profile modulation, the space harmonics exhibit high-scanning-rate radiation. In conjunction with this, the single-layer nature of the Goubau line allows the beam to scan from nearly endfire to backfire directions, leading to a wide scanning angle range. Numerical examples and experimental validation are provided to validate the proposed design. These show that the proposed antenna exhibits dual-band operation, where one band scans 152° within 2.2 GHz (corresponding to scanning rate of 69°/GHz) with 67% efficiency, while the second band scans 145° within 0.7 GHz (corresponding to scanning rate of 207°/GHz) with 26% efficiency. A tradeoff between scanning rate and efficiency always exists in high-scanning-rate leaky-wave antennas. One is able to freely choose the preferred scanning rate in this single antenna. A comparison with other related works shows that the proposed antenna exhibits the best performance. [ABSTRACT FROM AUTHOR]

Mushroom-type electromagnetic bandgap (EBG) structures are known to operate as high-impedance surfaces at low-frequency bands. They are broadly used in the microwave regime. However, one of the main drawbacks of mushroom-type EBG structures is their narrow bandwidth. In this article, we propose a mushroom-type EBG structure with glide-symmetric edge vias to increase the operational bandwidth. This bandwidth increment is explained by the physical insight provided by an equivalent circuit model of the structure as well as the description of the field behavior. Simulation and measurement results show an improvement of approximately 67% over the case without glide symmetry in the structure. We conclude that applying glide symmetry to the mushroom-type EBG structures can improve their bandwidth without adding additional manufacturing costs. [ABSTRACT FROM AUTHOR]

In this article, two novel efficient leaky-wave antennas (LWAs) with stable radiation patterns operating in the 60 GHz band are proposed. The LWAs are implemented in groove-gap waveguide (GGW) technology. To mitigate the beam squint due to the dispersive nature of LWAs, complementary-dispersive prisms are coupled to the LWA radiation aperture. The antennas are implemented in fully metallic purely holey periodic structures, resulting in a more cost-effective and robust manufacturing process compared to previously reported pin-based structures. Two prisms are proposed, one with mirror symmetry and one with glide symmetry. When the prism possesses a glide symmetry, much fewer holes are required while maintaining a similar performance, which even further decreases the fabrication costs. The complex propagation constant is optimized for low sidelobe levels (SLLs) with tailored hole diameters and waveguide dimensions, thus for the first time demonstrating the capability of using glide-symmetric holes to control the leakage rate. Two prototypes with mirror- and glide-symmetric prisms are theoretically synthesized and validated by the simulated and experimental results. A frequency bandwidth of 11% is achieved for both prototypes with the beam squint within ±0.9° (mirror) and ±1.7° (glide), SLLs below −15 dB (mirror) and −13 dB (glide), total efficiency almost 90%, and realized gain of 17 ± 0.5 dB at a fixed observing angle. The developed antennas are intended for mm-wave point-to-point communications. [ABSTRACT FROM AUTHOR]

This paper studies wave propagation in a periodic parallel-plate waveguide with equilateral triangular holes. A mode-matching method is implemented to analyze the dispersion diagram of the structure possessing glide and mirror symmetries. Both structures present an unexpected high degree of isotropy, despite the triangle not being symmetric with respect to rotations of 90°. We give some physical insight on the matter by carrying out a modal decomposition of the total field on the hole and identifying the most significant modes. Additionally, we demonstrate that the electrical size of the triangular hole plays a fundamental role in the physical mechanism that causes that isotropic behavior. Finally, we characterize the influence of the different geometrical parameters that conform the unit cell (period, triangle size, hole depth, separation between metallic plates). The glide-symmetric configuration offers higher equivalent refractive indexes and widens the stopband compared to the mirror-symmetric configuration. We show that the stopband is wider as the triangle size is bigger, unlike holey structures composed of circular and elliptical holes where an optimal hole size exists. [ABSTRACT FROM AUTHOR]

This letter demonstrates that glide symmetry can be used to match the impedance of highly dense dielectric profiles in wide angle and broad bandwidth. Using glide-symmetric metasurfaces permits tuning the magnetic properties of materials, so high values of permittivity can be matched to free space in wideband. This matching is achieved without disturbing the performance of the device, since the refractive index remains fixed. The performance of the proposed matching method is validated through measurements for normal incidence. For oblique incidence, a hyperbolic dielectric lens is matched with glide-symmetric structures in simulations. These simulations demonstrate a smooth transmission of the fields, manifesting a well-matched profile of the lens. [ABSTRACT FROM AUTHOR]

A fully metallic glide-symmetric waveguide filter with transmission in $Ka$ -band and attenuation at its second harmonic is proposed. The filter is low-loss and cost-effective for high frequencies, and it can be easily integrated with an antenna. Glide symmetry and the possibility of breaking this symmetry provide an additional degree of freedom for passband and stopband control. A new kind of 2-D glide symmetry, referred to as braided glide symmetry, is presented, showing an increased attenuation per unit cell. [ABSTRACT FROM AUTHOR]