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Glide-symmetric (G-S) waveguides made of metallic metasurfaces are a wideband, low-loss, low-cost, and conformable alternative to dielectric materials for the design of antenna lenses at millimeter waves. However, computing the effective refractive index of glide-symmetric waveguides with existing full-wave analysis techniques results in cumbersome parametric studies for each new design. This article presents a new analytic homogenization technique for glide-symmetric holey parallel-plate waveguides (PPWs). The dispersion equation of these structures, found by way of mode-matching, is simplified at low frequency using the properties of the modes resonating within the holes, independently of the hole shape. This simplified equation yields a closed-form expression of the effective refractive index, relying on the eigenmodes of the hole cross section. This formula avoids solving a 3-D full-wave problem and is fully analytic in the case of canonical hole shapes. Although derived in the quasi-static regime, it characterizes propagation over an ultrawide band, due to the low dispersive properties of glide symmetric structures. It is a function of the angle of propagation within the waveguide and can thus be used to study anisotropic properties. Its efficiency is demonstrated with the example of glide-symmetric PPWs with rectangular and circular holes. [ABSTRACT FROM AUTHOR]

A very efficient and accurate method is proposed to evaluate the lattice sums (LSs) for the analysis of leaky waves in 2-D periodic waveguides. The LSs are the series involving Hankel functions of arbitrary order, which are not convergent for complex wavenumbers. It is shown that by extending Ewald representations to higher order Hankel functions, the LSs can be expressed in terms of spatial and spectral series, granting Gaussian convergence even in the case of complex and leaky waves. The method allows for the appropriate choice of the spectral determination for each space harmonic of a given LS coefficient, thus permitting one to obtain modal solutions that may correspond to physical and nonphysical leaky-wave phenomena. First, the proposed LS calculation is exploited in the evaluation of the free-space 1-D periodic Green’s function for 2-D structures. Then, the same procedure for the LSs is implemented in a cylindrical harmonic expansion method, based on the transition-matrix and the generalized reflection-matrix approach, for the full-wave analysis of leaky modes in 2-D electromagnetic band-gap waveguides formed by layered arrays of cylindrical inclusions. The presented LS formalism is numerically slim, very fast, and thus well suited for the analysis of a significant class of lossy periodic waveguides and leaky-wave antennas. [ABSTRACT FROM AUTHOR]

Thin artificial surfaces that act as high frequency bandgap structures have been recently studied for the design of gap waveguides, hard surfaces, and planar lenses. Here, we propose a circuit-based method to analyze glide-symmetric corrugated metasurfaces that are embedded in a thin parallel plate waveguide. Our closed-form solution is based on rigorous analytical derivations. It achieves remarkable agreement with full-wave solvers, even when the waveguide thickness is extremely thin. In contrast, classical homogenization approaches are shown to be inaccurate for thin waveguides due to the interaction of higher order Floquet modes between the surfaces. Numerical results validate our theoretical analysis and show the utility of the proposed method. [ABSTRACT FROM PUBLISHER]

In this communication, it is shown that a nondiffracting vortex beam (i.e., a higher order Bessel beam with azimuthal phase variation) can be generated in the near field by synthesizing an inward cylindrical traveling-wave distribution over a finite aperture antenna. A radial line slot array (RLSA) is then designed to prove the concept. The collimated vortex beam is excited in the proximity of the RLSA, within a region properly defined by the nondiffracting range of the generated beam. The radial dependence of the longitudinal electric field of the vortex-beam magnitude follows a first-order Bessel function, and its phase presents a linear azimuthal variation. Full-wave results validate the generation of the nondiffractive higher order Bessel beam within the radiative near field of the launcher. [ABSTRACT FROM PUBLISHER]

We present a Bessel-beam launcher based on a leaky radial waveguide consisting of a capacitive sheet over a ground plane that supports higher-order leaky modes. A propagating Bessel beam is generated above the radiating waveguide. The Bessel beam is transverse-magnetic (TM) polarized with a vertical component of electric field that is a zeroth-order Bessel function of the first kind. A higher-order leaky-wave mode is used to reduce losses at millimeter waves and, at the same time, avoid the thin dielectric layers used in previously proposed lower order leaky-wave Bessel launchers. Closed-form design equations are provided for the proposed structure. In addition, the operating bandwidth of the launcher is defined using dispersion analysis. Near-field measurements of a prototype operating in the frequency range 38–39.5 GHz validate the concept. The measured launcher generates a Bessel beam with a stable spot size of about 4.3 mm ($0.57\,\lambda$) over a nondiffractive range of about 16.4 mm ($2.2\,\lambda$), within about a 4% fractional bandwidth. [ABSTRACT FROM PUBLISHER]

An efficient mixed-potential integral equation formulation is proposed for the analysis of one-dimensional (1-D) periodic leaky-wave antennas (LWAs) based on planar stratified configurations with inclusions of arbitrarily oriented metallic or dielectric perturbations. Both the transverse and vertical components of the mixed-potential Green’s functions due to a 1-D phased array of dipoles in a layered medium are accelerated using suitable homogeneous-medium asymptotic extractions from the standard spectral series of Floquet harmonics. A novel acceleration procedure is applied for the computation of the vertical potentials whose extracted terms can be expressed as potentials from a 1-D phased array of half-line sources in a homogeneous medium. Their numerical calculation requires a suitable modification of the Ewald method, thus resulting in new modified spectral and spatial series, having Gaussian convergence even in the case of complex modes and improper harmonics. Numerical comparisons for the 1-D periodic potentials, both in the case of bounded and unbounded (e.g., leaky) harmonics, validate the efficiency and accuracy of the proposed acceleration technique. The method is illustrated and verified by determining the dispersion behavior of both bound and leaky modes for several LWA test cases. [ABSTRACT FROM PUBLISHER]

We describe the design of a radial line slot array antenna with a shaped and focused near field. The antenna is designed in such a way to control the side lobe level and beamwidth of the normal component of the electric field with respect to the radiating aperture. The design procedure consists of two steps. In the first step, the requirements on the near-field pattern are provided over a focusing plane at a given distance from the radiating aperture. A set theoretic approach is then used to derive the aperture field distribution fitting the requirements over the near field. In the second step, the aperture field distribution is synthesized by accurately placing and sizing the slots of the antenna. The spillover efficiency is maximized during the design process. The antenna is centrally fed by a simple coaxial probe. The antenna design is validated by a prototype and measurements at 12.5 GHz. [ABSTRACT FROM PUBLISHER]

The effect of textiles on propagation along the body at 60 GHz is studied. A Green's function representation is used to investigate analytically the field excited by an infinitesimal dipole over a multilayer structure representing a flat skin model and clothing. The propagation between two rectangular open-ended waveguides is studied numerically and analytically in terms of path gain. Furthermore, the effect of an air gap between the textile and phantom is considered. Results show that the presence of a textile over a skin-equivalent phantom, as well as an air gap between them, induces a typical decrease of the path gain by 2–5 dB, but it doesn't significantly affect the path gain exponent. In all considered scenarios the power decay exponent is around 3.6. [ABSTRACT FROM PUBLISHER]

A novel spectral formulation is proposed here for the coupling integral between a cylindrical wave with arbitrary radial wavenumber and azimuthal dependence, and a slot placed on a plane orthogonal to the wavefront. Such a kind of integral is massively encountered in electromagnetic modeling of stratified structures comprising slots and vertical pins or vias. The twofold spatial integral defining the coupling is transformed into an equivalent onefold spectral integral, the integration path of which is selected to obtain Gaussian decay of the integrand. Both propagating and evanescent cylindrical modes are considered. An arbitrary stratification orthogonal to the slot plane can be considered, as well as an arbitrary current on the slot. Numerical comparisons against the standard spatial approach are shown to validate the new formulation, and its advantage in terms of computation cost is investigated in depth. [ABSTRACT FROM PUBLISHER]

We propose a fast and accurate full-wave code capable of analyzing electrically large substrate integrated waveguides consisting of stacked parallel-plate waveguides hosting dielectric or metallic posts and coupling and/or radiating slots. Boundary conditions enforced on posts yield scattering amplitudes, while slots are modeled by equivalent magnetic currents, solved by a method of moments. Substantial accelerations are proposed to exploit various symmetries of the structures and to select the optimal number of modes according to the relevant geometrical and physical parameters. The formulation is validated by full-wave simulations with a commercial software and measurement results. [ABSTRACT FROM PUBLISHER]

The on-body propagation at 60 GHz is studied analytically, numerically and experimentally using a skin-equivalent phantom. First, to provide analytical-based fundamental models of path gain, the theory of propagating waves near a flat phantom is studied by considering vertical and horizontal elementary dipoles. The analytical models are in excellent agreement with full-wave simulations. For a vertically polarized wave, a minimum power decay exponent of 3.5 is found. Then, propagation on the body is investigated experimentally in vertical and horizontal polarizations using two linearly-polarized open-ended waveguides. The analytical models fit very well with the measurements. Furthermore, the effect of polarization on the antenna performance is studied numerically and experimentally. [ABSTRACT FROM AUTHOR]

A new configuration of a self-polarizing Fabry–Perot (FP) antenna is presented to generate circular polarization with high gain levels using a simple linearly polarized feed. It consists of an FP resonator combined with a polarization-twisting ground plane. An analytical model is proposed to facilitate the antenna design, and the corresponding results are shown to be in very close agreement with full-wave simulations. The experimental prototype built in C-band exhibits a combined bandwidth (3 dB axial ratio, 3 dB gain drop, and -10 dB impedance matching) of 3% with a maximum realized gain of 18.0 dB. The antenna is completely shielded with an aperture size of 4.0\lambda0\times 4.0\lambda0 and a height of only \lambda0. Such antennas are attractive candidates for high-power space applications at low frequencies (L-to C-bands) where standard horns are very bulky. [ABSTRACT FROM PUBLISHER]

A simple and low-cost solution to reduce the height and weight of extended hemispherical lenses is proposed based on the introduction of a cylindrical air cavity above the primary feed. The presence of an additional air-dielectric interface enables one to shorten the focal length of the lens, which leads to antenna height and weight reductions of 13% and 27%, respectively. The communication describes the design principle and performance characteristics of the reduced-size integrated lens antenna, superimposed with a conventional synthesized elliptical one. Both prototypes are fabricated in Rexolite and measured in Ka band. A good agreement between the performance characteristics of the antennas is observed. The additional advantages of the proposed approach are explained, and its applicability for lens antennas made of high-k materials is discussed. [ABSTRACT FROM PUBLISHER]

An original acceleration procedure is proposed for the efficient calculation of the vertical components of the dyadic and scalar mixed-potential layered-media periodic Green's functions. The extraction of suitable asymptotic terms, i.e., quasi-static images, is performed in order to speed up the convergence of the relevant spectral series. This procedure, well known for planar Green's functions, is here generalized to treat the off-diagonal dyadic components and the corrective scalar potential arising from the vertical currents. The extracted terms are homogeneous-medium Green's functions due to a periodic phased array of half-plane currents, computed through a modified Ewald method, leading to a pair of Gaussian-convergent series. The highly improved convergence rate of the relevant series is shown, and the reduction of the computation time is numerically tested and discussed. The algorithm is implemented in EIGER, an open-source code based on the method of moments; several periodic structures are analyzed and fully validated through numerical comparisons. The proposed formulation has been proven very efficient, accurate, and stable. [ABSTRACT FROM PUBLISHER]

The problem of improving the computational efficiency in the numerical analysis of planar periodic structures is investigated here using the mixed-potential integral-equation (MPIE) approach. A new regularization of the periodic Green's functions (PGFs) that are involved in the analysis of multilayered structures is introduced, based on the effective-medium concept. This regularization involves extracting the singularities of the PGFs up to second-order terms. The resulting regularized PGF is very smooth and amenable to interpolation. Thus, optimized interpolation procedures for the PGFs can be applied, resulting in a considerable reduction of computation time without any significant effect on the accuracy. Another benefit of the regularization is that it significantly enhances the convergence of the series for both the vector- and scalar-potential PGFs. The theoretical formulation is fully validated with various numerical results for both two-dimensional (2-D) and one-dimensional (1-D) layered-media periodic structures. [ABSTRACT FROM AUTHOR]

The problem of accelerating the calculation of the periodic Green's function is addressed here for both 3-D and 2-D free-space configurations. In the 3-D case, periodicity is considered both along one axis and along two, generally skew, axes. A comprehensive review of the existing methods is first presented and some extensions are developed. The possibility of treating the case of complex phase shifts between unit cells, necessary for the study of complex modes in periodic structures, is also investigated. Comparisons among the various acceleration methods are performed, thus providing fundamental information on their actual efficiency in typical problems. [ABSTRACT FROM AUTHOR]