Miniaturized Branch-Line Coupler Using Delta Stubs

A miniaturized branch-line coupler using delta stubs is proposed and implemented. The length of quarter-wavelength branch-line is reduced and a size reduction of 55% is achieved due to using the delta stubs. Measured S-11, S-21, S-31 and S-41 of the proposed coupler are better than -24, -3.2, -3.4 and -28 dB from 2.8- 3.2 GHz, respectively. And the phase difference between through and coupling ports of the coupler is within 90 degrees +/- 1 degrees at operating bandwidth. Performance and size comparisons are also implemented.