A novel miniaturized planar ultra-wideband antenna is proposed. The antenna design comprises an electromagnetically coupled structure and a tapered radiating slot, while a triangular slot is etched on the ground plane. The antenna miniaturization is realized by adopting an electromagnetically coupled structure formed by the notched half-ellipse patch and the strip attached to the ground. The proposed antenna can yield a large 10-dB impedance bandwidth ranging from 1.5 to 10.4 GHz with satisfactory radiation properties. It also features a physical size of 37.4 mm $\times64$ mm, equivalent to a compact electrical size of $0.19\lambda \times 0.32 \lambda $ at 1.5 GHz. The important design parameters are analyzed to comprehend the operating principle of the antenna. A good agreement between the simulated and measured results is achieved.