In contrast to phased-array radar, frequency-diverse-array (FDA) radar transmits signals of linearly increasing frequencies across the array. As a consequence, the beampattern of an FDA radar becomes range, angle, and time dependent, which is different from only angle dependent beampattern of phased-array radar. The main limitation of FDA is its shorter dwell time. In this work, a novel algorithm with low complexity is proposed to focus the transmitted power of an FDA radar in the desired region-of-interest for longer dwell time. The proposed algorithm exploits the discrete-Fourier-transform and provides closed-form solution to find the weights of individual antenna elements of the array. The proposed algorithm is validated through simulation on both continuous-wave (CW) and pulsed FDA radars. Moreover, in contrast to the "S" shaped beampattern of the conventional CW-FDA radar, which is more difficult to deal with at the receiver, the beampattern of our proposed CW-FDA radar changes linearly with respect to the range.