A wideband coaxial filtering branch-line coupler

A wideband coaxial branch-line coupler with filtering function working at Q-band is proposed, which consists of a quadrature coupler and four bandpass filters. By cascading a coaxial quadrature coupler with bandpass filters, the branch-line coupler has a self-supporting structure and achieves both a wide operating bandwidth and bandpass filtering characteristics. Simulation results show that the filtering branch-line coupler centered at 37 GHz has a wide bandwidth of 37.84% (30 GHz to 44 GHz) and an output power imbalance better than 0.5 dB, while the return loss and isolation are better than 13.5 dB. Compared with conventional branch-line couplers, the filtering branch-line coupler in this paper has a wide operating bandwidth and is easy to process.