Ultra wideband bandpass filters with specified relative bandwidth

Abstract

Algorithm for the realization of the broad range of values of wide relative bandwidth (RBW) bandpass filter is introduced. Algorithm is based on periodic ideal cells each with short-ended stub. Theory is developed for a symmetrical cell with proportional transmission lines, nonuniform or uniform, in term of characteristic impedance. The theory is applied for the uniform transmission lines. Simple equation of the ratio between characteristic impendence of the short-ended stub and the characteristic impendences of the main lines is given for the broad range of RBW. Realizable filters are for the very wide RBW up to over 1.5 (150%). Technology is chosen in microstrip with vias for the short ends. It is without coupling, without defected ground structure (DGS) and only with a single layer. The procedure is tested on the fabricated filters for very wide RBW of 1.5 (150%). Agreement between measurements and simulations is excellent.