Design of compact multilevel folded-line RF couplers

A new design methodology for compact multilevel multiconductor folded-line couplers is presented in this paper. The approach is based on a general net work representation of folded-line structures as interconnected coupled lin es in a multilayered environment. Simple design equations are presented for compact directional couplers using two-level C-sections, and branch-line h ybrids with single and cascaded C-sections, The new folded-line couplers ex hibit a significant reduction in foot print compared to the conventional de signs. The directional and hybrid folded-line coupler designs are validated by full-wave electromagnetic simulation. Also, a 3-dB branch-line hybrid u sing three folded-line sections is fabricated. The measured response is fou nd to be in good agreement with the proposed theory.