A Fourth-Order Lumped-Element Bandpass Filter Constructed on Multilayer Substrates

A fourth-order bandpass filter scheme and its implementation with multilayer substrates are proposed in this letter. The filter is composed of two second-order filters and an impedance matching network between them, which provides one additional controllable transmission zero. By using two different feedback capacitors, two additional transmission zeros are introduced. The physical layout is fully interpreted and an experimental prototype is fabricated and measured. Good agreement between measured results and simulated results is observed. The results show the high out-of-band suppression.