Design of compact multilevel folded-line bandpass filters

A simple design methodology for compact multilevel multiconductor folded-line bandpass filters is presented in this paper. Several new compact folded-line filter topologies in single, as well as multilevel environments are proposed. Simple closed-form design equations are presented for the extraction of an equivalent coupled transmission line representing the folded-line filter section. The folded-line filter designs are validated by full-wave electromagnetic simulation, as well as by measurement for a four-section maximally flat four-coupled-line bandpass filter. The new folded-line filters exhibit a significant reduction in footprint compared to the conventional designs.