Higher order lumped element absorptive lowpass and bandpass filter structures

Here, the authors present a class of lumped-element low-pass and bandpass absorptive filter circuits. To begin with, the authors discuss a new type of absorptive low-pass filter (LPF) structure that has an excellent impedance matching performance in both passband and stopband. This work provides low-pass prototype values for the proposed absorptive LPFs in terms of those for the conventional reflective filters, namely g-parameters, so that the new type of absorptive LPF can be designed in a straightforward manner. In addition, it is shown that traditional low-pass-to-bandpass frequency transformations can be applied to the absorptive low-pass prototype cases in the design of absorptive bandpass filters (BPFs). Second- and third-order LPF and BPFs are designed and measured to verify the new type of absorptive filter and its design method.