Design of metamaterial-inspired electrically small active radiating elements

In this thesis, we present a detailed description of the work and the results achieved on the research for the study of innovative active electromagnetic components and radiating microwave components metamaterial-inspired, which can be easily integrated in practically realizable systems for industrial application. First, we analyze the use of non-Foster active circuits to obtain a widening of the operating bandwidth of devices based on metamaterials (MTMs); in particular we present study and realization of a demonstrator NIC (Negative Impedance Converter) compact, high integration and low cost, made of printed circuit with discrete components in SMD (Surface Mount Technology). The non-Foster circuit is designed by using only real components and the stability of the entire system is properly evaluated. Then we explore the possibility to generate an electromagnetic field with a non-zero orbital angular momentum (OAM) using a single patch antenna. In particular, we report an analytical study of a circular patch antenna in order to show that a circular polarized TMnm mode generates an OAM of order n-1. Then, we design an elliptical patch antenna that radiates a circular polarized electromagnetic field with OAM of the first order. Third, we propose a new class of horn antennas with integrated MTM-inspired filtering modules. In particular, we present some horn antennas that, depending on the used resonant inclusion, show a band-pass or band-stop filtering and polarization transformer behavior. Afterward, we present some radiating elements based on the use of MTM-inspired resonant inclusions. As an example, we propose a compact antenna for Wi-Fi application consisting of two orthogonal parasitic meandered monopoles and a driven bow-tie. Finally, we show that properly designed mantle cloaks, consisting of patterned metallic sheets placed around cylindrical monopoles, allow tightly packing the same antennas together in a highly dense telecommunication platform. Our experimental demonstration is applied to the relevant example of two cylindrical monopole radiators operating for 3G and 4G mobile communications.