New MM-wave filter uses screened waveguide

A new, experimentally demonstrated, modification of the quasi-optical space filter allows the filtering phenomena to take place in a circular waveguide instead of in free space, permitting the filter to be small enough to be usable in millimeter wave systems, yet large enough to allow convenient fabrication. The filter uses multiple layers of parallel-strip gratings ofiented in a specific fashion to provide bandpass filtering. It is a three-pole Chebyshev filter with 0.01-dB ripple and one percent fractional bandwidth. It contains five screens oriented at different angles and is designed to allow adjustment of their orientations but not of the cavity length. Although the loss is high, the validity of using multiple screens in a circular waveguide to design a bandpass filter at millimeter wavelengths is clearly demonstrated.