This work presents the concept and development of the so called Tridimensional Yagi Antenna, which is a novel type of Yagi antenna operating in P band. It was idealized from two other types of Yagi antennas: Quasi-Yagi and Yagi-Uda. The resultant antenna is based on a microstrip balun, as in Quasi-Yagi, and its driver and directors are made from metal tubes, as in Yagi-Uda, both integrated to a reflecting plane. The key point of this new antenna model is its asymmetric and reconfigurable radiation pattern and therefore the possibility of a high rejection between bands in a plane. This feature was accomplished with the new concept of progressive rotation of directors around driver. We present a design methodology to adjust return loss and radiation pattern characteristics. The final prototype presents 9.4 dB gain at 450 MHz and 47% bandwidth centered at 425 MHz. ©2009IEEE.