Herein, a new source location estimation method the iterative shrinkage-thresholding algorithm (ISTA), which is a compressed sensing method, and unmanned aerial vehicles (UAVs) is presented. By using the source location information of the primary system, secondary use of the unused vacant frequencies is possible. The proposed source location estimation method utilizes a virtual array using UAVs; however the estimation took considerable time. Therefore, we evaluate the effect of the source location estimation method using a small number of antennas by ISTA and clarify this effect.