3-D frequency selective structures
Creators: name: AZEMI, SAIDATUL NORL YANA BINTI
Publisher: name: RMIT University
Year: 2024
Subjects: classificationCode: 400899
subject: Electrical engineering not elsewhere classified

description: The purpose of this thesis is to investigate novel designs of 3-D FSSs extending the potential functionality of the structure beyond that of its 2D analogue. First, a novel 3-D FSS architecture based on a circular ring unit element is presented. The length of the cylinder is shown to have a significant effect on the frequency characteristics of the FSS, providing tuning and reconfiguration from a band-stop to a band-pass filter response. Dielectric materials can also be introduced in the center of the cylindrical unit cell elements to simultaneously obtain a stop and pass band with a sharp transition. A similar close band response can be obtained using dual cylinder 3-D FSS. Alteration to this length adjusts the frequency characteristics of the FSS, enabling a close band response to be achieved.<br><br>3-D FSSs have displayed the ability to set resonant frequency and shift operational filter states with a change in the length of a cylindrical resonator. A new tuning technique using spring resonator element is also proposed in this thesis. The FSS frequency response can be adjusted by changing the spring height, h, with applied pressure. The functional characteristic of the FSS can also be altered between a band-stop and band-pass filter response<br><br>It is often required that an FSS provides stable performance for various incidence angles. Hence, 3-D FSS with a response that is essentially independent of incident angle is presented. The FSS is a periodic array of 3-D hollow tapered resonators. The TE and TM angular stable is obtained by tapering the width of a cylinder with a square cross-section from upper opening to the lower opening. Impressive frequency stability and transmission characteristics have been achieved up to 80 degrees for both TE and TM incidence angles. A novel 3-D Frequency Selective Surface (FSS) with horn shaped resonators is also proposed which exhibits a very wide stop band. Simulation results prove that the FSS can realize selectivity of waves with a bandwidth more than 57%, and is very stable under oblique TM incidence angles from 0 to 80 degrees.<br><br>FSSs with high selectivity and compact size are of increasing demand in wireless and mobile communication systems. The FSS with miniaturized resonator elements structure is shown to have a unit cell dimension that is miniaturized to 0.067 λ0, achieved by coupling two meandered wire resonators separated by single thin substrate layer. The FSS produces a stable angular response up to 80 degrees for TE and TM incident angles. The meandered wire resonator structure is also utilized to enable transmission through a subwavelength aperture. The structure exhibits effectively 100% transmission at approximately 1.94 GHz through a square aperture of only 0.035 λ0 0.035 λ0 in size. A complementary subwavelength resonator is also proposed which exhibits a narrow band filter response operating at 1.92 GHz with a fractional bandwidth of 0.04%. The subwavelength structures are sensitive to fabrication tolerances, but are realizable with modern printed circuit fabrication techniques.<br>