In this paper, we introduce a novel and compact double-ridged horn (DRH) antenna for ultra-wide band microwave imaging. We first develop theoretical considerations useful to derive effective design guidelines and, thus, realizing the antenna model. Afterwards, an electromagnetic numerical solver is employed to study the conceived antenna both in free space and in the presence of a biological load; in both the simulation set-ups, excellent radiating performance are obtained, demonstrating the antenna robustness. Finally, a prototype is fabricated and experimentally measured to validate the final design. The proposed model presents overall dimensions that are 30% smaller with respect to traditional and commercially available DRH antennas (151 mm ×108 mm ×146.6 mm), retaining, at the same time, a significantly large operative band (VSWR <; 3 over the 1-9 GHz band). Among the broad class of possible applications, this frequency range is particularly suitable for biomedical devices, such as in microwave imaging, where reduced dimensions are fundamental in order to allow an easy integration within these systems. In addition, a safety assessment has been performed on the designed antenna, demonstrating that SAR is well below the regulating limits and it can be safely used in proximity of human operators.