A miniaturized 3-dB branch-line coupler based on substrate integrated coaxial line technology

A miniaturized 3-dB branch-line coupler based on substrate integrated coaxial line (SICL) technology is presented. The proposed SICL coupler is nearly shielded and takes the merits of low insertion loss, extremely low radiation loss, and insensitive to outside interference, etc. By using an equivalent π-type topology to replace the quarter-wavelength SICLs, the miniaturized SICL coupler achieves 72.2% size reduction compared to the conventional SICL coupler with comparable performances. The proposed SICL coupler can be realized under the multilayer PCB process, and therefore can easily be integrated with other planar circuits.