Abstract: Two microwave circuits are interconnected through a plurality of juxtaposed but physically separated modular units each consisting of a substantially cylindrical grounded conductive shell and a central conductor extending axially within that shell, the latter being open at one or both ends. The central conductor, which may be straight or helically coiled, has a length equal to one or more quarter wavelengths, with points separated by odd numbers of quarter wavelengths alternately grounded to the shell and ungrounded. The central conductors of adjoining modular units confront each other through the open shell ends, the confronting extremities of each juxtaposed pair being either both grounded or both ungrounded for inductive or capacitive coupling. To tune the resulting microwave filter, the juxtaposed units can be relatively shifted or rotated.