Quasi-elliptic compact high-power notch filters with selectivity both below and above the notched passband

Abstract

A quasi-elliptic notch filter response is defined as one in which the ultimate stopband depth is sacrificed in favor of a faster transition from the passband to a specified minimum equi-ripple stopband attenuation level (i.e. steeper attenuation slope) with no increase in filter order (as compared to a Chebychev or similar transfer function design). Such notch filter responses can be achieved if the topology synthesized includes arbitrary frequency variant impedances and line lengths in the main series line of filters, otherwise similar to those in [1], as was shown in [2]. The networks of [2] exhibit lowpass characteristics above the notched passband. In this paper, we substitute high pass sections for some of the lowpass series inverter sections of [2], thereby achieving selectivity both above and below the notched passband. This removes the frequent requirement to “window” the notched passband (add a bandpass filter) for harmonic and subharmonic suppression. The resulting filters exhibit lower loss than earlier “windowed” notch assemblies, provide selectivity above and below the system passband, without sacrificing notch characteristics required within the system passband.