60 GHz low-loss branch-line hybrid coupler on nanoporous alumina interposer

This paper presents the design, fabrication and characterization of a low loss branch-line hybrid coupler that operates at 60 GHz. The coupler is fabricated using the Metallic-nanowire-filled-Membrane platform, where the nanoporous alumina substrate is selectively filled with metal, forming nanowires that interconnect the metallic layers, using a simple fabrication procedure. The couplers presented return loss and isolation better than 10 dB for a 20-GHz bandwidth and a maximum power unbalance of 0.4 dB for a 10-GHz bandwidth.