A simple design methodology for compact multilevel multiconductor folded-li
ne bandpass filters is presented in this paper. Several new compact folded-
line filter topologies in single, as well as multilevel environments are pr
oposed. Simple closed-form design equations are presented for the extractio
n of an equivalent coupled transmission line representing the folded-line f
ilter section. The folded-line filter designs are validated by full-wave el
ectromagnetic simulation, as well as by measurement for a four-section maxi
mally flat four-coupled-line bandpass filter. The new folded-line filters e
xhibit a significant reduction in footprint compared to the conventional de
signs.