Contactless Air–Filled Substrate Integrated Waveguide on Low–Cost PCB for D–Band Applications

D-band radar systems offer significant advantages for automotive applications, including large bandwidth for high-precision object detection in crowded environments and compact solutions. However, their widespread adoption is hindered by significant transmission losses and high manufacturing costs in conventional transmission line technologies. This paper addresses these challenges by introducing a novel, cost-effective contactless air-filed substrate integrated waveguide (CLAFSIW) design for the 134-148.5 GHz frequency range. It features an E-bend vertical transition allowing for compact integration with next generation monolithic microwave integrated circuit radars. Fabricated using a standard FR4 printed circuit board, the design is suitable for mass production. The prototype board demonstrate an excellent performance close to simulation predictions despite manufacturing discrepancies. Measurements confirm an average insertion loss of 0.037 dB/mm with a back-to-back transition matching below -10 dB across the desired band. The design also exhibits high isolation, with crosstalk between adjacent CLAFSIW lines remaining below -26 dB.