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 TE103 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 20 µm. 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.