In block transmission systems, performance degrades due to inter-block interference (IBI) when there are multipaths with delays exceeding cyclic prefix (CP) length. An interesting technique to overcome this problem is an array antenna proposed by Hori et al., which restores the CP property by minimizing a cost function. However, its performance has not been theoretically cleared. In this letter, the performance of a method which minimizes the cost function under a unit norm constraint is analyzed. It is shown that the method can suppress IBI and its interference suppression capability depends on a certain parameter. The analytical result is verified through computer simulation.