Wideband antenna such as biconical is preferable for EMC measurement. Therefore, deep study on biconical antenna is required to ensure the accuracy of the measurement. This paper introduce a direct fed biconical antenna without connect to the balun. The dimension is adjusted to match with the 50 ohm coaxial cable. In this paper, the direct feeding biconical antenna is studied from frequency 100MHz to 2GHz.therefore, the uncertainty can be reduced. The preliminary results are reported. The simulation results indicate that the S11 is below -10 db. It shows good wideband behaviour. The radiation pattern for various frequencies also present as a references.