The scientific motivation of this thesis is to surpass some limitations in the state-of-the-art radiometers and spectropolarimeters used in Cosmic Microwave Background observations. The document follows the Three Papers Format of PhD theses. The first article, entitled A High Sensitivity Fourier Transform Spectrometer for Cosmic Microwave Background Observations, presents an innovative ultra-wide band and high-sensitivity spectropolarimeter to be used in Cosmic Microwave Background experiments, with remarkable stability and simplicity. In this manuscript, a proof-of-concept detection unit is fabricated and measured in the laboratory, demonstrating the theory. The second publication, entitled Fundamentals of Horn Antennas with Low Cross-polarization Levels for Radioastronomy and Satellite Communications, reviews the theoretical framework on cross-polarization in feedhorns, and solves from a theoretical-experimental point of view an open problem in radio astronomy due to the limited bandwidth of the corrugated horns used in polarization experiments, proposing metamaterial-Science to broadly overcome these limits, in a well justified and repeatable way. The third article, entitled Manufacturing of 3D-metallic electromagnetic metamaterials for feedhorns used in radioastronomy and satellite communications, explores the manufacturability of these meta-horns by mechanical techniques and additive printing, fabricating a novel meta-ring which can be used in feedhorns with excellent results. These efforts have been funded through the Tenerife Microwave Spectrometer project, but the results are generic.
Beyond these three publications, three chapters had been included to present the research carried out during three stays at the Universidad Carlos III de Madrid, the Riken Center of Advanced Photonics and the Università degli Studi di Milano Statale. In these chapters the work carried out on novel radiometers based on whispering gallery mode resonators, an antenna for the kinetic inductance detectors of the GroundBIRD experiment and the experimental demonstration of the meta-horn prototype presented in the articles are respectively included.
A final chapter presents a global assessment of the contributions to Science of this thesis, and points towards some future lines of work which may be of interest for the Community.