Compact 3-D Slot-Loaded Folded Dipole Antenna With Unidirectional Radiation and Low Impulse Distortion for Head Imaging Applications

A compact 3-D antenna for microwave-based head imaging systems is presented. The antenna, which is fed by a coplanar waveguide, consists of a slot-loaded folded dipole structure with four furled sides. Because of the presence of stronger currents on the top layer and reflections from the slightly extended bottom layer, the antenna exhibits directional radiation in the frequency domain in both near and far fields. The transient response of the antenna is also analyzed. Despite the existence of multiple slot loading and folding in the proposed antenna, the investigation of the time domain responses reveals a directional low-distorted radiation (impulse fidelity factor of more than 80%) toward the boresight direction in both near and far fields. The antenna has the compact size and low profile, with respect to the lowest operating wavelength, of 0.29 x 0.08, and 0.04, respectively, and 67% fractional bandwidth over 1.1-2.2 GHz. Since the antenna is designed to operate within an array for head imaging, a 16-element array of the antenna is tested in a realistic simulation environment to confirm a safe radiation exposure level. Finally, the array is employed on a realistic human head model to successfully detect and locate a hemorrhagic brain injury.