Two design methods of a filter in frequency-spatial frequency domain (f-k filter) have been developed for bistatic radar to suppress direct wave which causes significant artifacts in a radar image. One method is to reject a region in f-k domain, where the region is determined from a position information of a transmitter and a receiver. The other method uses time shift to eliminate a difference of arrival time of the direct wave. Then, f-k spectrum of the direct wave concentrates around frequency axis, and filter to reject DC component in spatial direction is designed. Both methods are verified with a laboratory measurement. They can suppress strong artifacts caused by the direct wave clearly, and give more reliable image to detect a buried object.