A simple-geometry hybrid branchline microstrip coupler for wireless communication systems

Abstract

This work presents a hybrid branch-line microstrip coupler with a simple geometry operating at 2.68 GHz. The design is intended for low-cost implementation on an FR-4 substrate and takes fabrication limitations into account. A fully symmetric layout based only on rectangular branches is used, and the structure is analyzed with full-wave electromagnetic simulations in Sonnet Suites. To verify the design, a prototype is fabricated and measured. The measured results indicate that the coupling and insertion loss are close to −3.07 dB at the center frequency, while the input return loss and isolation remain better than −25 dB. The proposed coupler exhibits a fractional bandwidth from 2.14 GHz to 2.95 GHz, where the main S-parameters remain within acceptable limits. A parametric study is also carried out to evaluate the impact of dimensional variations, substrate properties, and dielectric thickness on the scattering parameters, demonstrating the robustness of the proposed geometry. Owing to its simple layout, measured performance, and use of an inexpensive substrate, the presented coupler is suitable for practical microwave front-end and signal-splitting applications.