A small planar antenna with an enhanced bandwidth and a small rectenna for RFID (Radio Frequency Identification) and wireless sensor transponder are provided. The small planar antenna includes a dielectric substrate, a metal layer formed on an upper part of the dielectric substrate, a main slot formed in pattern on the metal layer, and a plurality of sub-slots connected to the main slot and winding in a specified direction, and the plurality of sub-slots form a pair of symmetric sub-slot groups around the main slot. According to the small planar antenna, the antenna region that substantially takes part in the radiation is substantially increased, and thus an enhanced bandwidth can be obtained without affecting the radiation pattern, radiation efficiency, polarization purity, etc., of the antenna.