Novel Ultralow Profile Waveguide Terminal With Spiral-Type High-Loss SIW Cavity for Integrated Microwave Systems

A novel ultralow profile waveguide terminal (WT) based on spiral-type high-loss substrate integrated waveguide (SIW) cavity is presented in this letter. The circuit is fabricated via standard printed circuit board (PCB) processes, ensuring low cost and extremely simple architecture without metal cavities or assembly steps. An innovative vertical transition structure from WR-28 waveguide (WG) to SIW is developed, using a semi-H-shaped coupling window and three metallized vias to efficiently couple energy into the FR4 dielectric substrate, which is fully absorbed in the form of traveling standing wave by the spiral-type high-loss SIW cavity. Meanwhile, the progressive loss mechanism avoids local overheating, enabling it to exhibit high-power capacity characteristics. For the fabricated WT, simulated and measured results show a −20-dB return loss bandwidth of 32.1–38.03 and 31.5–37.18 GHz, respectively. With a compact size of$31\times 31\times 1.2$mm3($1.86\lambda _{0}^{3}$), it features miniaturization, ultralow profile, low cost, one-piece processing capability, high-power capacity, easy to assemble, and integrate with other microwave devices.