LAUSR

An extremely compact 900-MHz microstrip branch-line coupler with a novel fold structure was proposed. A novel profile of the fold structure prevented the overlapping of stub lines to minimize the branch-line coupler dimensions. The measured insertion, isolation, and return losses of the proposed coupler were 3.94, 38.2, and 23.9 dB, respectively, and the measured phase difference between the two output ports was 90° ± 0.1°. Compared with the optimized area of a conventional branch-line coupler, the optimized area of the proposed coupler was reduced to 14.9%. Notably, the proposed coupler can be easily integrated with wireless communication systems because it can be implemented using standard printed circuit board etching processes without any lumped elements, bonding wires, or via holes.