Exact Solution for the Protected TEM edge mode in a PTD-Symmetric Parallel-Plate Waveguide

A Parity Time-reversal Dual (PTD) symmetric structure constituted by a Perfectly-Electric-Perfectly magnetic (PEC-PMC) parallel plate waveguide (PPW) is analyzed. This waveguide supports unimodal transverse electromagnetic (TEM) edge mode propagation protected against back-scattering from a certain class of deformations and defects. The TEM solution is found in analytical form by using three different methods, namely conformal mapping, mode-matching, and Fourier-transform methods. It is shown through numerical simulations that the mode propagation is robust with respect to deformations such as 90{\deg} bends and discontinuity such as transition to free-space. Implementation of the PMC boundary conditions via both a bed of nails and a mushroom structure is also successfully investigated

Generation of complex source point expansions from radiation integrals

This paper discusses methods for expanding fields radiated by arbitrary sources enclosed by a certain minimum sphere in terms of Complex Source Point (CSP) beams. Two different approaches are reviewed; the first one is based on a spectral radiation integral, where the Fourier-spectrum is obtained by far field matching. The second approach consists of two steps: first, the equivalence principle is applied to a sphere enclosing the real sources, and a continuous equivalent electric current distribution is obtained in terms of spherical waves; then, the continuous current is extended to complex space and its SW components are properly filtered and sampled to generate the discrete set of CSPs. In both cases, the final result is a compact finite series representation with a number of terms that matches the degrees of freedom of arbitrary radiated fields; it is particularly efficient when the fields are highly directional and the observation domain is limited to a given angular sector. The fact that the CSPs rigorously respect Maxwell's equations ensures the validity of the expansion from near to far zone and allows one to incorporate the CSP representation in a generalized admittance matrix formalism for the analysis of complex problems

Reduction of truncation errors in planar near-field aperture antenna measurements using the method of alternating orthogonal projections

A simple and effective procedure for the reduction of truncation error in planar near-field to far-field transformations is presented. The starting point is the consideration that the actual scan plane truncation implies a reliability of the reconstructed plane wave spectrum of the field radiated by the antenna only within a certain region inside the visible range. Then, the truncation error is reduced by a Maxwellian continuation of the reliable portion of the spectrum: after back propagating the measured field to the antenna plane, a condition of spatial concentration of the primary field is exploited to define a convergent iterative process which is also stable against moderately noisy data. Far-field patterns reconstructed from both simulated and measured near-field data demonstrate the effectiveness of the proposed procedure

A Metamaterial Surface for Compact Cavity Resonators

We suggest an idea for miniaturization of cavities by utilizing a properly designed metamaterial thin surface inserted inside the cavities. This metamaterial surface is constituted by a thin dielectric slab on both sides of which “gangbuster” dipoles are printed. Inserting the thin slab inside a parallel-plate one-dimensional (1-D) cavity resonator has the effect of decreasing the resonant frequency. Placing the metamaterial slab at the center of a rectangular waveguide also lowers the cut-off frequency of the dominant mode of the waveguide. The corresponding dispersion curve exhibits a smooth transition from a fast-wave to a slow-wave regime and then asymptotically tends to the dispersion curve of the first TE surface-wave mode of the metamaterial slab. This suggests a natural way to conceive a 3-D compact cavity resonator by placing two perfectly electric conducting walls, a half of the wavelength of the slow-wave mode apart, inside the above rectangular waveguide. The analysis, performed by a circuit network theory and validated by a full-wave numerical analysis, provides simple formulas to predict the resonant frequency and the dispersion diagrams of these structures

Complete Open-Stopband Suppression using Sinusoidally Modulated Anisotropic Metasurfaces

A novel and general approach is presented for the complete suppression of the open-stopband effects in circularly polarized one-dimensional periodic leaky-wave antennas using anisotropic modulated metasurfaces. A theoretical justification of this behaviour is found through the rigorous treatment of the canonical problem of an infinite homogenized impedance surface sinusoidally modulated along the propagation direction. By deriving a closed-form solution of this problem at broadside scan it is shown that, while the sinusoidally modulated isotropic impedance exhibits a null of the attenuation constant, the complex propagation constant for the proposed anisotropic modulation has a finite value and a regular behaviour. A closed-form formula for the leakage constant α is also derived, allowing for an accurate design of the aperture field amplitude. The full wave analysis of a patch-based implementation of the metasurface is in excellent agreement with the results based on the homogenized impedance model, thus, demonstrating the practical applicability of the theoretical results. The elimination of the open-stopband behaviour allows for the design of leaky-wave antennas able to scan the beam from backward to forward without any frequency regions of blindnes

Flexible Unidirectional PTD-Symmetric Waveguide

The transmission and reflection characteristics of a bent square transverse electromagnetic waveguide constituted by two opposite perfect electric conductor and perfect magnetic conductor walls are analyzed. This waveguide exhibits a parity, timereversal, duality (PTD) symmetry with respect to both the diagonal axes. It is found that this property is maintained even when the structure is bent in a plane orthogonal to one of the two PTD symmetry axes (PTDbend). As a consequence, the transverse electromagnetic mode propagation is protected against backscattering by this class of discontinuities. The preservation of the PTD symmetry in presence of a geometric flexibility of the bend is also analyzed, thus introducing a new class of bendable waveguides that are largely immune to backscattering by bend discontinuities

Spectral Filtering of the Spatial Green\u2019s Function

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