In this paper , the transient radiation in space of a trilateral dipole antenna is mainly analyzed. It starts with the scalar and vector potential calculation of the Hertz dipole. The superposition theorem is employed in obtaining the radiation fields and power of this trilateral dipole antenna , which then are compared with the results of Hertz dipoles and fan - shaped dipoles. It has proved in the practical test and use that this antenna is a good ultra wide - band one.