Compact and Unidirectional Resonance-Based Reflector Antenna for Wideband Electromagnetic Imaging

A unidirectional and wideband resonance-based reflector (RBR) antenna that can be used for biomedical applications, such as thorax imaging, is proposed. One of the main limitations in the design of biomedical systems, which utilize multiple densely spaced antennas, is the mutual coupling created by the radiating elements and the surface waves (SWs). The proposed RBR antenna is designed to achieve an in-phase reflection phase within a wide operating bandwidth. Moreover, it suppresses the SW propagation that reduces the overall mutual coupling by up to 12 dB across the whole operating bandwidth. It consists of a resonance-based loop reflector that is positioned in a perpendicular configuration to a wideband dipole antenna. To increase the electrical size of the loop reflector without physically altering the dimensions of the substrate, its structure is meandered, and a compact side size of 0.22λ × 0.22λ, which is more than 50% smaller than recent RBR antennas, is achieved. Unlike the majority of conventional double-layer high-impedance surfaces, the proposed RBR antenna consists of a single layer and a single unit cell and utilizes the actual dipole antenna element to achieve a measured wideband unidirectional radiation from 0.83 to 1.9 GHz (79%) with a peak gain of 3.8 dBi and a front-to-back ratio of 9 dB. Due to negligible electromagnetic coupling between RBR antennas, lateral SWs are suppressed, and thus multiple antennas can be located adjacent to each other without experiencing any frequency shift or impedance mismatch.