Dual-band hybrid patch coupler with embedded spiral open stubs

In this paper, we propose a compact dual-band planar 3-dB hybrid patch coupler with embedded spiral open stubs. In order to install stubs on the hybrid for dual-band application, four equally circular holes are firstly etched on the cross-slotted patch, where the performance of the single-band hybrid coupler is almost maintained because of the slightly influence on the current distribution along the patch. Next, four spiral open stubs are embedded into the circular holes without increasing the whole size of the coupler and the dual-band operation are simultaneously achieved. Finally, a prototype of proposed dual-band hybrid patch coupler is designed and verified experimentally.