Lowpass filters using series stubs

A number of short circuited series stubs have been measured. Based on parameters derived from these measurements, a range of lowpass filters have been constructed which show excellent agreement in cut-off frequencies but unexpected behaviour in their stopbands. Simulated results for filters with ideal stubs are presented with no observance of these peculiarities. It is proposed that these peculiarities are due to resonant coupling between the stubs and evidence to support this theory is presented.