Design, analysis, and development of UWB antennas for microwave brain imaging systems

This thesis addresses broadband antenna design methods used in microwave radar imaging within the context of breast cancer and stroke diagnosis applications. The analysis and characterization of the antennas were conducted around tissue environments and validated through laboratory testing. First, a broadband slot antenna was designed for breast cancer diagnosis and tested within a "matching medium." The matching medium was prepared by considering the average dielectric constant of breast tissues; the antenna parameters were analyzed in a simulation environment, and the S11 parameter was measured in the laboratory. Second, a realistic head phantom was developed to analyze the antenna designed for brain imaging. The phantom was constructed to include different tissue types such as skin, skull, gray matter, white matter, and cerebrospinal fluid (CSF), and its electrical properties were measured in a laboratory setting. The phantom model contains four cavities of varying sizes and positions, allowing the simulation of various stroke scenarios by placing healthy or unhealthy cores in these cavities. Additionally, a broadband, miniaturized sinuous antenna was designed for microwave brain imaging. The bandwidth was enhanced by adding three strip rings to the back of the substrate and connecting them to the radiator arms through vias. The antenna was optimized, fabricated, and tested within a matching medium. A broadband, low-profile metasurface antenna was also designed for operation in the low-frequency band (2.3–3.6 GHz), achieving reconfigurable radiation properties using a three-arm slotted antenna with PIN diodes. The antenna dynamically controls a wide beam steering range of -35° to 35° across three different scenarios. Finally, a three-layer active phase gradient metasurface (PGM) design was presented. In this design, the phases of electromagnetic waves were controlled by adjusting the states of the PIN diodes, enabling dynamic beam steering directions of 0°, ±11°, ±18°, ±26°, and ±35° within the 3.6–3.9 GHz frequency range.