Robust Filter Design Built in a Contactless Metallic Multilayer Waveguide at W-Band

This article presents the design and experimental validation of a W-band waveguide cavity filter operating around 91 GHz, using a periodic electromagnetic bandgap (EBG) structure with glide symmetry to implement the filter in a stack of multiple thin metallic sheets without electric contact between them. The filter is based on vertically stacked cavities that use the TE<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">103</sub> mode, which offers increased robustness to manufacturing and assembly errors due to the large dimensions of the cavity. The glide-symmetric circular hole EBG structure is analyzed and integrated to suppress unwanted field leakage between the metallic layers with a broad stopband. The proposed filter maintains effective operation in the 88–94-GHz frequency range, even with gap variations between layers of up to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$20~\mu $</tex-math> </inline-formula>m. The filter is fabricated using laser cutting, achieving a low surface roughness and high dimensional accuracy. Experimental measurements show excellent agreement with the simulations, with a return loss greater than 20 dB and an insertion loss below 0.5 dB. These results demonstrate the possibility to achieve high performance filters at millimeter-wave frequencies while maintaining low fabrication complexity and cost using the multilayer waveguide technology.