A Wideband Transition Design Technique from RWG to SIW Technologies

Efficient wide-band transitions play a critical role in integrating substrate-integrated waveguide (SIW) and air-filled substrate-integrated waveguide (AFSIW) systems with conventional rectangular waveguide (RWG) systems in millimeter wave communication. However, existing techniques lack a systematic design approach, overlook mode purity, encounter performance issues, involve tedious optimizations, and feature complex structures. This paper presents a first-of-its-kind design technique that addresses these limitations, enabling seamless transitions from RWG to both SIW and AFSIW. For the first time, a clear and systematic design flow is introduced, covering both transition scenarios. The proposed technique eliminates the need for separate design procedures, simplifying the process, reducing complexity, and offering a cost-effective solution with state-of-the-art performance. The key innovation lies in the analytical expression for the shortest transition length, derived for both SIW and AFSIW cases, facilitating the design process and optimizing transition performance. The effectiveness of the design flow is extensively validated through four design examples, evaluating mode purity, reflection coefficient, and insertion loss. The results demonstrate excellent performances, confirming the accuracy of the approach. Furthermore, a fabricated prototype achieves remarkable results with an insertion loss of 0.35 dB and a relative bandwidth of 40%, exhibiting state-of-the-art performances when compared to reported works in the literature. In summary, the novel design technique enables seamless wide-band transitions from RWG to both SIW and AFSIW, offering a unified approach with state-of-the-art performance.