An improved dual-band design method is presented for the 180coupler. It uses the non-uniform impedance ring structure for the arbitrary power division and a π-shaped branch for the dual-band operation The increased design freedom offered by the proposed structure helps to extend the useful dual-band operation range.

A new dual-band operation scheme is proposed for the Wilkinson power divider. The proposed structure has an open stub at the input and its two output ports are extended through a transmission line section. It offers improved bandwidth performance in the dual-band operation along with some structural advantages.

Non-equal length, three section coupled transmission line couplers are proposed. The proposed structure offers increased design flexibility and the compact circuit design capability over the conventional quarterwave coupled lines. The detailed analysis results and design method are presented along with the numerical and the experimental verification.