Frequency-Selective Transition From Substrate-Integrated-Waveguide to Rectangular Waveguides for 77/130-GHz Automotive Radar Using Metal-Only Additive Manufacturing

This paper presents a compact dual-band substrate integrated waveguide-to-rectangular waveguide frequency-selective transition (FST). This FST is a key enabler of future dual-band systems, such as automotive radar operating at 77 GHz and 130 GHz. The proposed structure enables efficient signal routing from a single beamforming integrated circuit to two separate antenna arrays, leveraging waveguide-based filtering for high-frequency integration. A vertical transition topology is adopted to enhance mechanical robustness and to simplify assembly. This robustness is validated by performing a sensitivity analysis on the assembly. The structure is fabricated using aluminum-based laser powder-bed fusion, enabling monolithic integration of complex millimeter-wave features. Experimental results demonstrate insertion loss around 2.5 dB for the low and high bands of the FST, with measured isolation exceeding 30 dB in the high band. The results validate the feasibility of the proposed FST and highlight the impact of manufacturing tolerances on millimeter-wave performance. This work contributes a scalable, low-loss packaging solution for dual-band radar front ends in next-generation automotive and 6G sensing applications.