An NRD waveguide band-pass filter apparatus is provided which is simple in construction and which can be easily manufactured as well as being formed small in size and light in weight, and which operates in a single operating mode. An NRD waveguide band-pass filter apparatus includes a plurality of NRD waveguide resonators arrayed in such a way that two adjacent NRD waveguide resonators are electromagnetic coupled to each other. A plurality of arrayed rectangular dielectric waveguides are interposed between an upper surface portion and a lower surface portion which are parallel to each other. The upper surface portion and the lower surface portion, and the plurality of arrayed rectangular dielectric waveguides are formed integrally, thus forming a rectangular dielectric housing. A first superconducting electrode and a second superconducting electrode are formed on the outer surface of the upper surface portion and the lower surface portion, respectively. By setting the space between the first and second superconducting electrodes at one half or less of the wavelength of the resonance frequency in a vacuum of the present apparatus, the outer portion of each dielectric waveguide is formed to a cut-off region. IMAGE
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