Dual mode band-pass filter having coupled modes

A dual mode band-pass filter comprising:

• a dielectric substrate having first and second main surfaces;
• a metallic film having an opening disposed on the first main surface of the dielectric substrate or inside of the dielectric substrate;
• at least one ground electrode disposed 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;
• and
• a pair of input-output coupling circuits connected to different portions of the metallic film;
• wherein
• the metallic film has a first resonance mode and a second resonance mode;
• the first resonance mode is propagated substantially parallel to an imaginary straight line passing through connection points of the pair of input-output coupling circuits;
• the second resonance mode is propagated substantially perpendicular to an imaginary straight line passing through connection points of the pair of input-output coupling circuits;
• the first resonance mode has a {fraction (λ/2)} resonance in which the resonator length is defined by the length of the metallic film extending in the substantially parallel direction to the imaginary straight line;
• the second resonance mode has a {fraction (λ/2)} resonance in which the resonator length is defined by the length of the metallic film extending in the substantially perpendicular direction to the imaginary straight line;
• and
• the first and second resonance modes are coupled by the opening of the metallic film.