A High-Isolation S-Band Ring Hybrid Combiner

Through careful dimensioning, avoidance of line transition discontinuities and by using special blocking elements to reduce stray couplings across the internal airgap together with inductive fine-tuning posts, a conventional ring hybrid can be an attractive RF power combiner for L- or S-band transceiver applications, where a high isolation is desired between the transmitter output arrangement and the receiving front-end, or for antenna arrays. When typical commercial units hardly exceed 40 dB, an improved narrow-band isolation up to 90 dB and more is demonstrated here while keeping the residual attenuation for desired coupling below 0.15 dB. The required milling and mounting uncertainty for a successful and repeatable result in a combined metallic / PTFE stripline form was found to be 0.01 mm.