E-band CPW ring hybrid using an overlapped coupling structure

A novel E-band coplanar waveguide (CPW) 180° ring hybrid coupler is presented. The proposed ring hybrid adopts a vertically overlapped coupling structure (OCS) having the length of 0.25λ_g to replace the conventional 0.75λ_g line or previous short-ended coupling section on the same plane. The OCS is realized by placing two metal layers to face them with each other up and down three-dimensionally. The OCS permits the ring hybrid to have a small size and wideband operation due to the broadside coupling. The proposed 180° ring hybrid coupler is fabricated using MMIC technology. The predicted and measured performances show that the operating frequency of the ring hybrid covers E- to W-band (60 ∼ 110GHz) with a good agreement preserved.