posted on 2013-06-03, 13:25authored byA. Hossainzadeh Bezminabady
Structures that include more than one layer of Frequency Selective Surfaces (FSS) are an
attractive feature in applications with stringent performance requirements. They provide
extra flexibility with regard to the adjustment of the transmission responses which can in
principle be insensitive to angle of incidence because of the increased bandwidth. This
thesis deals with computer simulation and experimental assessment of a variety of
multilayer FSS structures. The plane wave vector modal analysis technique is adapted for
analysing the scattering from these multilayer FSS structures. The novelty in the plane
wave modal analysis method lies in the fact that they can be applied to arbitrary lattice
and element geometries.
A novel super-resolution approach of analysing the scattering from FSS in cascade, with
arbitrary lattice geometries of the two arrays is outlined. These type of structures exhibit
multiresonant responses in a controlled manner. The problem of assigning different lattice
geometries to the structure is addressed here by assigning the periodic fields adjacent to
the arrays a common (or mutual) periodicity and by employing the convolution theorem to
the modal (Floquet) sets that expands the tangential fields in each array. As a result, the
spectral components of the Floquet mode coefficients from the various adjacent arrays are
related to those of the common periodicity by means of a correlation function. This
correlation function enables the spectral components of the Floquet mode sets expanding
the tangential fields from any two adjacent arrays to be super-resolved from those of their
common periodicity set. Once the convolution has been executed, application of
electromagnetic boundary conditions are utilised, thus obtaining the coupled electric field
integral equations. These integral equations relate the spectrums of the surface current
densities to the various Floquet mode coefficients. The integral equations are in turn
solved by the Method of Moment (MoM) technique for the unknown current coefficients
from which the unknown transmission and reflection coefficients from the entire structure
are obtained. A major assumption that is made in this technique for assigning a common
periodicity lattice is that the ratio of lattice periodicities of any two adjacent arrays must
be a rational number. The importance of the proposed technique lies in unlocking the complexities that exist
when the scattered Aoquet modal coefficients from the arrays are related to the spectral
components of the currents induced on the surfaces of the arrays, in the integral equation
formulation. Furthermore, the proposed approach offers a computational advantage when
applied to multilayer FSS structures, as it is invariant to the distance separating the arrays.
A computer model based on this technique is developed for obtaining the prediction
results. Various double layer FSS structures with arbitrary element types and lattice
geometries of the arrays and with variable separation distances between the two layers are
studied. The plane wave transmission coefficients of these multiresonant structures are
computed with a v1ew to predict their radiation parameters. Extensive measurements are
performed by using a purpose built experimental jig for mounting the structures, in an
indoor anechoic chamber. The validity of the theoretical model is assessed by comparison
with measurements from a variety of multilayer structures.
History
School
Mechanical, Electrical and Manufacturing Engineering