A new half-annular bull-eye leaky-wave antenna (LWA) design with suppressed open stopband (OSB) and integrated feeding is presented. The 2-D aperture offers a pencil beam with scanning through ...broadside and with stable gain values as a function of frequency. To achieve directional radiation, a TM<inline-formula><tex-math notation="LaTeX">_{0}</tex-math></inline-formula> surface wave supported by a grounded dielectric slab is properly perturbed by means of a suitable planar-periodic double-strip aperture. In addition, the proposed structure offers improved performance and reduced design complexity with respect to previous LWAs having a nonsuppressed OSB. Dispersion analyses based on a well-established method-of-moments approach are also performed to characterize the fast spatial harmonic supported by the structure and to determine the size, position, and periodicity of the strips needed for optimal OSB suppression. Simulations and experiments have been carried out to validate the antenna performance against the optimized unit cell. The fabricated planar-periodic LWA also provides continuous beam scanning from <inline-formula><tex-math notation="LaTeX">-35^{\circ }</tex-math></inline-formula> to <inline-formula><tex-math notation="LaTeX">40^{\circ }</tex-math></inline-formula>, with a peak realized gain of 21 dBi.
A low-cost leaky-wave antenna using cylindrical surface waves propagating on a grounded dielectric slab is proposed. The excited surface waves are then perturbed into a leaky-wave regime, by the ...addition of annular microstrip-based ("bull-eye") gratings. Various surface-wave modes may be considered, however, we desire to achieve radiation from the fundamental TM0 mode due to its zero cutoff frequency and possibility for efficient excitation. A comprehensive design strategy is detailed in the paper. It is based on both an accurate knowledge of the modal spectrum, obtained with the method of moments, and an analysis of the resonant modes supported by the constituent microstrip rings. To further support our methodology, numerical calculations, full-wave simulations, and antenna measurements are reported for the basic structure. Also, additional designs for enhanced gain at broadside, reduced cross-polarization levels, and improved wide-angle frequency beam scanning are presented.
An annular periodic leaky-wave antenna (LWA) fed by a simple azimuth-symmetric source is designed to generate a high-gain omnidirectional conical-beam pattern, which scans with frequency over a wide ...angular range. The proposed structure is defined by a finite metallic radial strip grating printed on a grounded dielectric slab, which supports an <inline-formula><tex-math notation="LaTeX">n=0</tex-math></inline-formula> cylindrical leaky wave (CLW). The distinctive features of CLWs supported by such a truncated structure are also highlighted and discussed. The directional far-field pattern generated by the proposed LWA, in conjunction with its nondiffracting and wideband behavior in the near field (as previously reported by the authors), defines an original dual-operational LWA. Possible applications include next-generation wireless power transfer systems that provide functionality in both the near and far field, vehicle roof-mounted antennas for base-station data connectivity as well as future short-range near-field communications, and object tracking by ceiling-mounting devices for indoor localization.
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.
A novel terahertz (THz) Fabry-Perot cavity (FPC) antenna is proposed, based on a multistack of alternating layers of highly birefringent nematic liquid crystal (NLC) and high-permittivity dielectric, ...which comprehensively acts as a Bragg reflector. This layout is able to provide enhanced reconfigurability and improved directivity with respect to standard FPC leaky-wave antenna (LWA) designs. The application of a low driving voltage to the NLC layers allows for the dynamic control of the radiating properties of the LWA, at a fixed frequency in the low-THz range. The attractive features and performance of two different configurations are rigorously discussed in a theoretical context, taking into account the realistic implementation of the proposed device.
In this work, the transition at backward endfire between bound (nonleaky) and leaky modes on one‐dimensional periodic structures printed on a grounded dielectric substrate is examined. This mode ...evolution has been characterized for a class of structures with a finite‐width cross section. Such structures support leakage into surface waves as well as into space due to the presence of the substrate. The solutions in this transition region are calculated using an accurate full‐wave moment‐method approach that allows for the determination of both physical and nonphysical solutions, both of which play an important role in the transition region.
Bessel, Bessel-Gauss, and Gaussian beams have widely been investigated in optics in the paraxial approximation, under the frame of a scalar wave theory. Such approximations can hardly be applied in ...the microwave/millimeter-wave range, where the vectorial nature of the electromagnetic fields cannot be neglected, and experimental realizations for some of these beams appeared only recently. In this work, we discuss the generation of Bessel, Bessel-Gauss, and Gaussian beams through a fully vectorial electromagnetic approach. The field derivation of all these beams is first illustrated and numerical evaluations are then reported to compare their different propagation and diffractive behaviors. Finally, an innovative approach for realizing such solutions with planar microwave devices exploiting leaky waves is demonstrated through accurate numerical simulations.
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.
An efficient method-of-moments formulation is proposed for the analysis of planar structures in the presence of azimuthally symmetric fields. Boundary integral equations are derived for TM and TE ...polarizations, assuming as a reference structure a metal plate with a finite number of concentric annular slots placed above a stratified medium. The equations are discretized with a Galerkin testing scheme in the Fourier-Bessel domain, adopting suitable sub-domain basis functions that ensure a very rapid convergence of the involved spectral integrals. Numerical validation is provided by comparison with state-of-art simulation software, considering planar antennas with omnidirectional radiation patterns, in order to show the accuracy of the proposed formulation.
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