| Miniaturized-element frequency selective surface (MEFSS) is a class of sub-wavelength periodic structures that is entirely composed of non-resonant elements. This dissertation investigates the application of MEFSSs in designing various wavefront-manipulating structures including spatial filters, polarization converters, polarization selective surfaces, transmitarrays, and reflectarrays. These structures are presented in four parts of this dissertation. The focus of the first part is primarily on the design of low-profile spatial filters for reducing the radar signature of antennas mounted on military platforms. Broadband harmonic-free operations and narrowband highly-selective frequency responses are two important features of the presented spatial filters. These features are highly desired in low-observable antenna systems. In the second part, anisotropic versions of MEFSSs were employed in designing linear-to-circular polarization converters and circular-polarization selective surfaces (CPSS). Broad bandwidths and wide angular stability of the frequency responses are some of the key advantages of the proposed devices compared to the current state-of-the-art. The third part of this dissertation presents the design of wideband true-time-delay (TTD) transmitarrays and reflectarrays. The proposed transmitarrays and reflectarrays exploit the unit cells of appropriately designed MEFSSs as their spatial time-delay-units (TDUs), and are extremely suitable for broadband pulsed applications. Finally, in the last part, several mechanical tuning techniques are proposed as potential ways to make the presented wavefront-manipulating structures tunable. The proposed techniques do not require any electronic tunable devices and only rely on exploiting mechanical movements or deformations in the fabric of the structure to achieve tunability over a wide range. |
