Near-field time-domain characterisation of wideband antennas

Time-domain characterisation is vital in verifying the suitability of wideband antennas for near-field applications such as microwave medical imaging and sensing. To that end, a near-field time-domain characterisation method to calculate the near-field transient response and the distortion of wideband antennas is proposed. The method uses a pulse merit factor, which consists of the near-field time-domain signal amplitude and a fidelity factor, both normalised to the highest values attained from the antennas. To verify the method, the transient responses of unidirectional and omnidirectional antennas designed for near-field imaging are analysed. The analyses show that even though the investigated antennas cover the same band with the same average far-field gain along the boresight direction, the unidirectional antenna exhibits 35% more pulse merit factor with less impulse distortion along the intended direction, which suggests better suitability for wideband near-field imaging systems.