1,721,092 research outputs found
Generation of complex source point expansions from radiation integrals
Full text linkThis 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
Modulated Metasurfaces for Microwave Field Manipulation: Models, Applications, and Design Procedures
Full text linkMetasurfaces (MTSs) have emerged in the last years as a promising platform for next generation planar devices in a broad range of frequencies, thanks to their unique field manipulation capability. In particular, in the microwave range this solution is characterized by low-cost, lightweight, and simple integration with electronic circuits, since MTSs can be realized in PCB technology by printing electrically small patches over a dielectric slab. The MTS behavior can then be conveniently described in terms of homogenized boundary conditions of impedance type. Spatial modulation of these boundary conditions allows one to implement a broad class of functionalities, involving space wave or surface wave control, as well as conversion from surface waves to leaky waves. This paper reviews numerical and analytical models, design procedures and microwave applications of modulated MTSs, with particular emphasis on surface wave manipulation, and it discusses expected future developments of this technology
Transformation optics applied to metasurfaces
No full textThis work presents a theory of metasurface transformation which extends Transformation Optics to control the wavefront of surface waves (SW) through the use of modulated metasurfaces. As the outputs of the conventional TO approach are the metamaterial constitutive parameters able to perform a certain modification of the ray-field path, here the outcomes are the components of the metasurface reactance tensor. This approach, combined with the use of tunable metasurfaces, may lead to the realization of a large number of unconventional adaptive devices. © 2013 EurAAP
Line integral representation of physical optics scattering from a perfectly conducting plate illuminated by a Gaussian beam modeled as a complex point source
No full textAn exact line integral representation of the physical optics fields scattered by a perfectly conducting plate illuminated by a vector complex point source is derived. Complex point sources provide, in the paraxial region, an accurate model of Gaussian beams, and can thus be used to efficiently represent the pattern of directive sources. Numerical results are shown to illustrate the exactness of the procedure and the computation time saving is investigated by comparison with surface integration. Moreover, by analyzing the scattering from a plate illuminated by a corrugated circular horn, the feasibility and accuracy of the proposed approach for modeling scattering due to real sources are demonstrated
Spherical near field measurements with truncated scan area
No full textThis paper presents a technique for the determination of the full sphere pattern of an antenna from truncated spherical near field measurements. The approach is based on an iterative procedure which exploits the band-limitedness properties of the radiated field to correctly reconstruct the full sphere data. Tests performed on synthetic as well as measured near-field data demonstrate the effectiveness of the procedure and its stability against measurement errors. © 2011 EurAAP
A hybrid finite-element-modal-expansion method with a new type of curvilinear mapping for the analysis of microwave passive devices
No full textA hybrid finite-element-modal-expansion procedure for the three-dimensional analysis of passive microwave devices exploiting higher order vector basis functions and an innovative class of curved elements is presented. If modal expansions on ports are not analytically known, they can be numerically obtained via a preliminary two-and-one-dimensional finite-element analysis; curved triangular and tetrahedrical elements are defined by a rational Bézier mapping, which provides a remarkable increase in accuracy and flexibility over the conventional polynomial mapping without a significant increase in computational burden. Numerical results are provided to illustrate the efficiency and feasibility of the proposed technique
Surface wave dispersion for anisotropic metasurfaces constituted by elliptical patches
No full textThis paper presents an effective approach for the derivation of the two-dimensional (2-D) frequency-wavenumber dispersion surface of anisotropic metasurfaces (MTSs) consisting of elliptical patches printed over a grounded slab. These MTSs are important in the design of leaky-wave antennas and transformation optics (TO) surface-wave based devices. The formulation resorts to an analytical expression of the currents excited on the element of the periodic texture to define a reduced spectral method of moments (MoM) procedure with only three basis functions. An exact compact formula, which links the MoM matrix to the homogenized equivalent anisotropic impedance of the MTS, is derived. The formulation presented here has been found accurate and useful for designing MTS antennas and TO devices
Reduction of Truncation Errors in Planar Near-Field Aperture Antenna Measurements Using the Gerchberg-Papoulis Algorithm
No full textA simple and effective procedure for the reduction of truncation errors in planar near-field measurements of aperture antennas is presented. The procedure relies on the consideration that, due to the scan plane truncation, the calculated plane wave spectrum of the field radiated by the antenna is reliable only within a certain portion of the visible region. Accordingly, the truncation error is reduced by extrapolating the remaining portion of the visible region by the Gerchberg-Papoulis iterative algorithm, exploiting a condition of spatial concentration of the fields on the antenna aperture plane. The proposed procedure is simple and computationally efficient; it does not require any modification of the measurement procedure and it allows for the usual probe correction. Far-field patterns reconstructed from both simulated and measured truncated near-field data demonstrate its effectiveness and stability against measurement inaccuracies
Exact solution for the protected TEM edge mode in a PTD-Symmetric parallel-plate waveguide
No full textA parity time-reversal duality symmetric structure constituted by a perfect electric conductor and perfect magnetic conductor (PMC) parallel plate waveguide is analyzed. This waveguide supports unimodal transverse electromagnetic (TEM) edge mode propagation protected against backscattering 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° bends and discontinuities 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
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