A superconducting microstrip filter capable of achieving an improvement of power resistance without enlarging the overall size and while maintaining steep cut characteristics. LEDs are mounted on a plane in the enclosure and are operable to emit light through the lens when energized through an electrical path. The high frequency antenna has a sloped segment that produces a relatively large capacitive coupling with the reaction tube. The cylinder bore is consequently provided with the coating, which at least partially overlaps the chamfered window edge. The third layer which abuts against the surface of the concave face plate is in the form of a plurality of pins which extend through the cells of the other two layers.