Second-order reflective-type, absorptive notch filter with lumped elements

In this article, a design methodology and equations necessary for a second-order absorptive, reflective-type, transmission zero notch filter are introduced, derived, and described in detail. Initially, a single (first order), absorptive, reflective-type transmission zero notch filter is described. Based on this, improvements to the first-order reflective-type notch filter are discussed and a novel circuit that achieves a second-order absorptive, reflective-type, transmission zero notch response is proposed. The necessary conditions for the achievement of the second-order absorptive, reflective-type, transmission zero from the proposed circuit are derived. As an experimental verification, first- and second-order absorptive, reflective-type, transmission zero circuits are fabricated and their performance measured. It is shown that the first-order notch circuit introduces a zero into the response of a main filter with a depth of over 12 dB in the frequency range 2.19-2.27 GHz, while the second-order notch circuit introduces a transmission zero with a depth of over 20 dB GHz, in the same frequency range as its first-order counterpart.