Compact Design of an S-Band Rat Race Hybrid Coupler with Enhanced Phase Balance Using Parallel Coupled-Lines

This paper presents the design and implementation of an S-band Rat Race Hybrid Coupler operating at 2.2-2.3 GHz, integrated with parallel coupled-line phase shifters to reduce circuit size for satellite communication systems. The proposed design improves critical performance parameters, including phase balance, insertion loss, isolation, and bandwidth. The design achieves enhanced isolation and bandwidth by incorporating the coupled-line phase shifter into the traditional rat-race structure, making it suitable for applications in signal processing, antenna-feeding networks, and radar systems. Simulations using a 70.7-Ω microstrip line at 2.25 GHz demonstrate significant improvements in phase shift accuracy and return loss. Measurement results validate the simulations, confirming the compact and efficient nature of the design, which offers promising potential for modern microwave communication technologies.