A miniaturized wideband 180° hybrid ring coupler

In this letter, a compact 3 dB 180°· hybrid coupler was proposed, designed, fabricated and measured. This device was derived from the classical hybrid ring coupler whose 3λ/4 section was replaced with inverting suspended microstrip line (SML). The proposed structure has a reduced size compared with the conventional and enhanced variants of the 3 dB 180° hybrid coupler topologies. Moreover, the new architecture has a greatly improved bandwidth. The measured 0.5 dB insertion loss bandwidth is over the 2-5 GHz band. Because of its symmetrical architecture, the proposed hybrid shows frequency independent balance performance. The maximum of 0.5 dB amplitude imbalance and 5° phase imbalance measured over frequency band of 2-5 GHz. Measured port isolation is also about 40 dB at the center frequency. Compared with other available coupler structures, this coupler has 20% wider bandwidth and 40% smaller sizes without any significant performance degradation.