Three-wire-line interdigital filters of Chebyshev and elliptic-function characteristic for broad bandwidths

Two new forms of interdigital filters suitable for broadpass bandwidths are presented. Each type of filter is composed of a number of basic 3-wire-line sections in cascade. The Cheby¿shev filter gives superior stopband performance in comparison with the conventional interdigital filter and is synthetised directly from closed formulas. The elliptic filter is also directly derived from a lumped-element prototype and is convenient for printed-circuit applications.