Abstract: A dielectric line having a sufficient ensured strength and being suitable for mass production and a production method therefor are provided. The production method is a method for manufacturing a dielectric line having a dielectric strip which is provided between two conductive plates approximately parallel to each other and which has a width smaller than that of the conductive plates, and dielectric medium layers which are filled between the conductive plates other than the dielectric strip and which is composed of a porous material having a dielectric constant smaller than that of the dielectric strip.

Abstract: A pluri-tubular aerator includes a vertical central tube member, at least one outer tube member disposed concentrically around said central tube member, and at least one of an diffuser and an air tank disposed on an lower end of the aerator for delivering externally supplied air into the central tube member or a space between the central and outer tube members. The diffuser produces a continuous stream of fine air bubbles while the air tank intermittently produces a bulky air bubble of either a spherical shape or a ring-shape. Preferably, the diffuser and the air tank are used concurrently.