The problems of analysis and design of the broadband groove guide directional couplers are investigated by the microwave network method. Using the transverse equiva- lent network for partially dielectric-filled asymmetrical double-groove guide, a related program for solving the problems is developed. The calculations show that the relative bandwidths of the couplers given in this paper are all larger than 24%, which is five times as many as the bandwidth of the conventionally designed groove guide couplers; whereas the lengths of the present couplers are much shorter than those designed in the references.