US Patent 7239221 Dual mode band-pass filter

A dual mode band-pass filter includes a metallic film for defining a resonator, disposed on the first main surface of a dielectric substrate having first and second main surfaces, or inside of the dielectric substrate. An opening is formed in the metallic film. At least one ground electrode is provided on the second main surface of the dielectric substrate or inside of the dielectric substrate, so as to be opposed to the metallic film through a dielectric layer. A pair of input-output coupling circuits is connected to the metallic film.