An approximate surface-current distribution of the rectangular dipole antennas, composed of two linear-currents along the antenna edges and a uniform surface-current within the antenna bodies, is proposed. It presents some new insights to planar dipole antennas, and could also be used for fast, explicit and Ultra-wideband predictions of their radiation patterns. The averaged errors between the calculated results based on the proposed distributions and the full-wave results are respectively 0.075 dB on the H-plane and 2.95° on the E-plane. From the explicit results, some design considerations for stable radiation patterns are presented.