This paper presents a new spectrum sensing scheme using an energy detector and multiple antennas. This scheme helps us finding the low level signals to realize a spectrum sharing in a primary and secondary system. The spectrum sensing by using multiple antennas has a problem that the channel state information of the primary signal is required for obtaining the diversity gain. However, the primary signal level is very low so that it is difficult to obtain the accurate channel status (accurately estimate the channel status). In this paper we propose a signal processing scheme for spectrum sensing to utilize multiple antennas without requiring the knowledge about the channel state information. We adapt the conventional energy detector to the proposed scheme, so we can use it in our simulation. We show the simulation results, to evaluate the performance of the proposed system. The results show the improvement of the sensing performance by the proposed scheme.