Novel Dual-Band SIW-To-Metal Waveguide Transition with Integrated Filtering for Diplexing 77GHz and 130GHz Frequency Bands

This paper presents a novel dual-band transition from a substrate-integrated waveguide (SIW) to two air-filled waveguides (WGs) operating at 77 GHz and 130 GHz, targeting applications such as automotive radar systems. The proposed structure incorporates a diplexing mechanism to effectively combine/separate the two frequency bands, allowing them to share a common WG environment while keeping their signals distinct. The diplexer consists of a filter in the 77 GHz WG, blocking the 130 GHz signals, and a below cut-off SIW and WG in the 130 GHz signal path, providing inherent filtering for the 77 GHz signal. This inherit filtering helps minimize the size compared to that of classical filter-type diplexers. The reduced size comes at the cost of a lower isolation between the two WG outputs. The proposed structure overcomes the limitations of existing single-band transition designs by reducing the insertion loss to below 1 dB in each band, achieving a wide bandwidth, and ensuring good matching performance. Furthermore, the predicted isolation is at least 15 dB at 77 GHz and at least 40 dB at 130 GHz, and an insertion loss of 0.6 dB at 77 GHz and 0.4 dB at 130 GHz is achieved. The insertion loss is increased by the inclusion of surface roughness in the metal mainly at 77 GHz due to the presence of the filter.