A novel waveguide directional coupler with high directivity and broad bandwidth

In this paper, an waveguide directional coupler with broad bandwidth, high directivity and high flatness using an efficient and rapid design procedure is proposed. This waveguide directional coupler achieve a weak coupling of - 20 dB by using one circular aperture at the broad wall sharing by the main waveguide and the branch waveguide. A metal insert in the coupling hole is the key of the design which can significantly enlarge the isolation. The simulation results show that in 92.2~140 GHz(full bandwidth of waveguide WR8) the return loss of the input port is better than - 20 dB and the flatness of the coupling is ± 0.255 dB. The isolation of the structure is beyond -50 dB thus guaranteeing a high directivity of 30 dB.