Performance of Directional and Omnidirectional Antennas in Wideband Head Imaging

Researchers have proposed numerous wideband antennas with directional or omnidirectional radiations to meet the requirements of microwave-based head imaging systems. This letter aims to study the effect of directionality on image quality of those systems. Hence, both directional and omnidirectional wideband antennas are designed and prototyped. Both antennas cover a wide bandwidth (1.25-2.4 GHz) that is typically used in microwave head imaging and attain a boresight average gain of 3.5 dBi. The antennas' near-field radiation patterns are measured and analyzed. The antennas' transient pulse performance in the near-field region along boresight direction is also studied. It is observed that without the effects of multipath inside the head, the directional antenna provides 20% higher impulse fidelity and 4 dB more peak transient response than the omnidirectional antenna. An experimental verification is examined by imaging a realistic artificial head phantom with an emulated brain injury. Quantitative analysis of the reconstructed images demonstrates that directional antenna yields more focused images with low artifacts than omnidirectional antenna.