High-directivity single- and dual-band directional couplers based on substrate integrated coaxial line technology

The high-directivity single- and dual-band directional couplers based on substrate integrated coaxial line (SICL) are first proposed in this paper. As the SICL features the propagation of TEM mode, the SICL directional coupler can keep its high-directivity compared with the microstrip one. The SICL coupler also characterizes a vias-shielded structure keeping it away from lateral leakage, cross-talk or unwanted parallel-plate mode. The design approaches of the single- and dual-band SICL couplers with proper width-spacing are given. Experiments are carried on a SICL 2.35 GHz coupler and a SICL 0.8/2.35 GHz coupler. Compared with microstrip couplers, the SICL ones show a great enhancement in directivity.