Design and analysis of a decade bandwidth 180° hybrid coupler

Abstract

The design and analysis of a decade bandwidth 3 dB 180° hybrid coupler using tandem connection of two similar wideband 8.34 dB hybrids is presented. The designed coupler has return loss better than 12 dB over a decade bandwidth, insertion loss below 6 dB, amplitude balance within ± 1 dB, phase balance of ± 20° and isolation above 18 dB. Gap and overlap ground patterns at the junction of the tightly coupled to uncoupled region are introduced to improve isolation by preventing odd-mode field coupling and preserving equal even- and odd-mode phase velocities across the junction.