Transmission line filters with harmonic parallel foster sections

Abstract

Conventional wideband bandstop filters use Cauer prototypes, but become nonrealizable with Kuroda–Levy transforms for bandwidths of 150% or more. Transmission line filters with harmonic stubs have been shown to be realizable at these bandwidths, but have limited performance ranges due to the fixed positions of the transmission zeros. In this article, two structures that use shunt Foster resonators that enable the shift of the transmission zeros are described. Simulated and measured properties show that greatly improved performance can be realized while not adding to the complexity of the structure