Parallel-Coupled-Line Filters for Inverted-Microstrip and Suspended-Substrate MIC´s

An improved design procedure is outlined for parallel-coupled-resonator filters in non-homogeneous media such as inverted microstrip and suspended stripline. A modified filter section is used, comprising a parallel-coupled o.c. section in cascade with short un-coupled line sections. Much improved characteristics, both in the pass-band and in the stop-band may be achieved, and the difficulties associated with the unequal even-and odd-mode velocities of the non-homogeneous coupled sections are largely overcome.