Abstract: This paper presents a novel design of miniaturized dual-band branch-line coupler. The port extensions are introduced for the dual-band operation of the coupler. The microstrip via transition is connected to two microstrip lines in different layers to configure a sandwich structure to reduce the passive component circuit size. By transmission line theory, a T-type transmission line structure is equivalent to traditional λ/4 transmission line, additionally, the part of extensions are folded to further reduce the structure size. In the paper, a novel dual-band branch-line coupler is designed at 0. 97/1. 8GHz,simulated results can verify the coupler has a good performance. In physical processing, measured results agree well with simulated results.