Design of Compact Cross-Fed Three-Dimensional Slot-Loaded Antenna and Its Application in Wideband Head Imaging System

Microwave head imaging systems require compact wideband antennas with directional radiation. To realize the antenna miniaturization, the halving technique based on image theory has been used. However, it causes a tilt in the main-beam direction. This letter demonstrates that the side feeding technique can be used to cross-feed the halved antennas with the potential to retain their beam direction. The performances of one-sided direct-feeding and cross-feeding methods are compared using a halved slot-loaded folded-dipole antenna. The underlying mechanism behind the beam correction is analyzed. The prototyped antenna achieves 97% fractional bandwidth (1.1-3.2 GHz) and an average gain of 3 dBi along its boresight direction. The overall dimensions of the designed antenna (with respect to the lowest operating wavelength) are 0.25 × 0.06 × 0.06λ03. The measured near- and far-field radiation patterns demonstrate the unidirectional radiation of the antenna with a stable boresight main beam. Moreover, considering the fundamental limit of antennas, the prototyped antenna is found to be near the edge of optimally attainable solutions. The antenna is applied in an automated microwave head imaging system. The reconstructed images illustrate the efficacy of increasing sensing elements, due to antenna compactness, to detect hemorrhagic strokes inside a realistic artificial human head.