Theory, analysis and design of high order reflective, absorptive filters

Abstract

In this study, design methodology and equations necessary for low-loss high-order absorptive filters in the reflective-type configuration are introduced, derived and described in detail. Initially, a simple single, absorptive filter is described and its use in radio frequency front-ends is discussed. Based on this, improvements to the single, first-order absorptive filter are discussed and novel circuits that cater for lower loss higher-order absorptive filters are proposed. The necessary conditions for the achievement of the proposed higher-order absorptive filters from the proposed circuits are derived in order to establish the potential of the proposed circuits. As an experimental verification, first-, second- and third-order reflective-type absorptive filters are fabricated and their performances measured. In particular, in the case of a third-order absorptive filter, it is shown that the depth of the introduced attenuation is at least 27.4 dB across the frequency range of 2.17–2.27 GHz. Further, the use of the obtained absorptive filters was put to a test by inserting them in series with a commercially available band-pass filter.