A novel directional coupler loaded with feedback capacitances on the coupled lines is presented. Its effect of enhancing the coupling is qualitatively shown by deriving an equation for the coupling. Besides, a method to compensate for the phase difference between the even and odd modes of the coupler is presented. To demonstrate, a novel tandem 3-dB coupler consisting of the proposed coupled lines is designed and described. In addition, a waveguide (rectangular coaxial line) 8×8 HYB matrix using planar double-layer structure that is composed of the proposed tandem 3-dB couplers and branch-line couplers, which is operated in S-band, is designed and fabricated showing excellent performance.

A hexagonal waveguide branch line coupler suitable for additive manufacturing is proposed in this study, and its design method is elucidated. The additive manufactured Ka-band coupler exhibits characteristics similar to those of a machined coupler, but its weight and cost are reduced by 40% and 60%, respectively. Its effectiveness is also confirmed in this study.

We propose a T-junction OMT consisting of an offset stepped post. The offset stepped post contributes to the matching of two rectangular ports at the short circuit, situated at the opposite side walls. The structure without conventional ridges is simple and makes it possible to achieve robust performance. We fabricated a proposed T-junction OMT in a single piece of an aluminum alloy, using a commercial metal 3D-printer. The simple and compact structure with robust performance is proposed to overcome the disadvantages of a 3D-printer, such as fabrication tolerance and surface roughness. The measured results demonstrated a return loss of 22dB and an insertion loss of 0.3dB, with a bandwidth of 8% in the K-band.

A novel waveguide power divider based on a coaxial-to-waveguide transition using a H-plane probe is presented. The waveguide consists of split metal blocks and substrates which are alternately stacked. The power divider is realized by arranging identical transitions using coaxial probes short-circuited with metal patterns on the substrate. The parasitic reactance of probes can be canceled out with the metal patterns on the substrate, so it is ease to design the power divider. The advantages of this structure are small footprint, low insertion loss, simple fabrication, and ease of design. A design method of the proposed power divider is described. The fabricated eight-way power divider shows excellent performances at 10 GHz-band.