Near-field Microwave Antenna for Brain Screening

This thesis presents the selection and optimization of a compact on-body wideband microwave antenna for brain screening, adaptable to sensing and imaging tasks exploited for diagnosis and monitoring. Specifically, the proposal antenna is projected to be integrated with the stroke monitoring system developed by the Wavison Research Group at Politecnico di Torino, extending its physical and electromagnetic performance requirements. Building on the requirement definitions, the first part of the work conducts a scoping review of state-of-the-art microwave bio-imaging antennas, resulting in the selection of five candidates — circular patch antenna with parasitic element, double substrate bowtie antenna, double ridge filled horn waveguide antenna, edge feed planar log periodic antenna and central feed planar log periodic antenna—which are studied in depth via full-wave simulations. Their performance was evaluated on both simplified and anatomically realistic head phantoms, focusing on reflection and transmission coefficients, near-field radiation patterns, and wave penetration. Among the selected designs, the filled-horn double-ridged waveguide antenna demonstrates superior performance, minimizing surface waves, reducing back radiation, and achieving deeper penetration —critical parameters. The second part covers the optimization of the latter by adjusting its geometry and including dielectric filling. The final optimized antenna operates in the -10 dB band from 0.84 to 1.34 GHz while maintaining a compact footprint of 31 × 23 mm2, suitable for a helmet-antenna-array with up to twenty-four elements. The filling material has a relative permittivity of 30, obtainable through rubber-graphite mixtures. The optimized horn antenna represents a significant advancement, overcoming critical problem-specific system design requirements.