Low-Insertion-Loss Fin-Line Filters for Millimetre-Wave Applications

A design theory is described for low-insertion-loss fin-line filters with fin-line gap widths over the total height of the waveguide housing. The theory includes both higher order mode propagation and the finite thicknesses of the dielectric and the metallic fins. An evolution strategy synthesis method yields optimum design data for three- and five resonator-type fin-line filters with several substrate thicknesses. The midband frequencies chosen are about 13, 34, 66, and 75 GHz. Measured minimum insertion-losses in the passband are about 0.2 dB (13 GHz), 0.5 dB (34 GHz), and 1.9 dB (65 GHz) for three-resonator-type filters as an example.