Herbert Jaag: Multisection bandpass filter from small signal circuits. SABA Schwarzwalder Apparate Bau Anstalt August Schwer, Michael S Striker, October 31, 1972: US3701958 (21 worldwide citation)

Individual sections of the filter are printed on separate circuit boards, e rear faces of which are covered with a shielding layer. The boards are sandwiched together, separated by insulating plates, resulting pile forming the multisection filter.