On the Synthesis of Lossy Analog Filter Networks With Lossless-Like Passband Shape

An original class of lossy analog filter networks with lossless-like passband shape is reported. They are based on the inseries cascade connection of input-perfectly-matched/input-fully-absorptive first-order filtering cells with frequency-contiguous transmission bands. In this manner, despite their lossy resonators, an ideal-i.e., lossless-like-transfer-function shape and perfectinput-reflectionless behavior can be obtained in the overall filter network at the expense of a constant-frequency attenuation factor. The theoretical foundations of the proposed filter approach and synthesis examples for Butterworth- and Chebyshev-type responses are detailed. An optimization-based design example for a quasi-elliptic-type response with transmission zeros (TZs) is also illustrated. Moreover, a fully-lumped-element circuit equivalent that allows the direct synthesis of fully-input-reflectionless lossy bandpass filters with lossless-like passband shape is presented.