OLIVEIRA, M. A.; http://lattes.cnpq.br/4314604376564074; OLIVEIRA, Maciel Alves de.
Resumo:
In this thesis work, a cascade bioinspired frequency selective surface (FSS) is presented, with
a tri-band frequency response, with closely spaced resonances, angular stability and
polarization independence. The element geometry of the proposed FSS is a segmented
Fibonacci spiral. The ratios between the resonance frequencies are very close, 1.5 from the first
to the second resonance and 1.4 from the third to the second resonance. FSS simulation is
performed using the HFSS software. Simulations of the proposed structures were carried out,
for a better understanding of the frequency response behavior of the FSSs. The initial parametric
analysis allowed obtaining the physical dimensions, which allowed the application of the
proposed structure in modern communication systems. In simulations varying the parameter w,
width of the spiral strip, it was observed that as the metallic area in the unit cell increases, a
displacement to higher resonant frequencies is caused and, simultaneously, an increase in the
width of band. This increase in the width of the spiral strip can be used as a parameter for
adjusting the resonant frequencies or even the bandwidths. Initially, a simulation of the
bioinspired FSS with one layer was performed. One resonance was observed for horizontal
polarization and two resonances for vertical polarization. Structures with only one layer did not
show polarization independence or angular stability. Thus, it was proposed to cascade the two
structures, one FSS with the normal spiral and another FSS with the spiral rotated to the right
by 90°, with an air gap of 18mm between them. This gap influences the electromagnetic
behavior of the FSS and can be used to improve polarization independence, for example. A
multiband frequency response was obtained with three resonant frequencies, operating in
commercial bands such as ISM and 5G.