A novel transversal filter using triple-coupled-line directional couplers is proposed. Simple design method which uses sinc function for computing coupling coefficients of the proposed transversal filter are also introduced. The frequency characteristics of the proposed filter are seldom degraded by the connecting sections between the cascaded directional couplers while those of the conventional transversal filter are aggravated. Moreover, the less number of the connecting sections and the directional couplers is required in the proposed filter than fer the case of the conventional transversal filter having the same bandwidth. The performance of the proposed transversal filter is verified by measurement and the measured results are compared with the calculated results.