Novel Compact Implementation of Rat-Race Hybrid Coupler Using Coaxial Cable For VHF Applications

This article presents a novel implementation of Rat-Race Hybrid Coupler (RRHC) using coaxial cable results in a very compact coupler for VHF applications. It shows good matching at all the ports and very good amplitude balance, desired relative phase difference, and isolation between the output ports. With proper choice of cables, the proposed method of implementation is capable of handling high power with low insertion loss. Besides, by merely trimming the length of the coaxial cable the fine frequency tuning and phase equalization can be easily accomplished, this is not easy with its microstrip line configuration once its fabrication process is carried out. The measured relative phase differences between two in-phase ports is 0.1
⁰
and that of for out-of-phase ports is 179.4
⁰
at the design frequency of 260 MHz. Furthermore, the fabricated RRHC occupies only 3.4 % of the conventional footprint, with potential for further miniaturization due to the use of the flexible coaxial cables. The measured and simulated results indicate good agreement.