A Stub Tapped Branch-Line Coupler for Dual-Band Operations

Abstract

This letter presents a stub tapped branch-line coupler for dual-band applications. In the new design, a tapped stub is used to realize 90deg phase change at two frequencies. Both the characteristic impedance and the length of the proposed branch lines are adjusted accordingly compared with the conventional structure. Explicit design equations are derived using the ABCD-matrix. To verify the design concept, a microstrip coupler operating at 0.9 and 2GHz is fabricated and measured on a Rogers' RO4003 board