Direct coupled waveguide filters with generalized Chebyshev response by resonating coupling structures

A novel compact solution is proposed to obtain a pseudo-elliptical response for bandpass waveguide filters with direct coupled resonators. It consists in substituting one or more inductive discontinuities by resonant ones, to have a corresponding number of transmission zeros in the frequency response. The resonant discontinuity is basically made of a partial-height post, either single or double (patent pending). A computational efficient design procedure is also presented, making use of accurate equivalent circuits. The resulting filters have both the same size and the same level of losses of conventional ones of equal order, as verified experimentally.