An optimized wideband biconical antenna is presented for EMC measurement which potentially can be used as a standard-reference antenna. The antenna is "direct-fed" (no Balun is needed) with optimized dimension to match with 50 Ω coaxial cable from 200 MHz to 2 GHz. Radiation pattern of the antenna indicates that the common mode current existing on the coaxial cable is negligible. Meanwhile, the biconical antenna has a fixed phase-center for the various frequencies and the related uncertainties can be improved. The antenna factors (AF) of the antenna have been evaluated using analytical and numerical methods. Experimental "Standard Antenna Method SAM" has been used to verify the theoretical results and good agreements were observed.