Low-Pass, Quasi-Optical Filters for Oversized or Focused-Beam Waveguide Applications

摘要

A form of low-pass, quasi-optical filter for millimeter wave and possibly infrared applications is described which consists of thin layers of dielectric interspersed with arrays of thin metallic strips in a manner similar to an artificial dielectric. Equivalent circuits for filter half sections of the type used were developed, and formulas and graphs are presented from which image parameters for such half section can be obtained. A design procedure is given from which multisection filters of this type can be designed from low-pass, lumped-element prototypes in order to give prescribed transmission characteristics. Some trial designs were worked out and fabricated for use in oversized waveguide, and their responses were computed in detail with a digital computer. Except for some higher-order-mode effects believed to be due to the standard size to oversize waveguide tapers which were used, the measured responses were in good agreement with the theory. Stop band edge ratios between three- and four-to-one are possible. Filter structures of this type are amenable to fabrication by techniques similar to those used in integrated circuit technology. (Author)