Multi-functional low-pass filters with dynamically-controlled in-band rejection notches

A new class of multi-functional low-pass filters (LPFs) with multiple dynamically-controlled rejection bands in their passband is reported. They are based on series-cascaded RF modules that functionalize a low-pass (LP) transfer function with/without an embedded absorptive notch (AN). In this manner, multiple rejection bands that exhibit theoretically-infinite attenuation and do not affect the passband insertion loss (IL) are incorporated within the passband of a highly-selective LPF that features smaller size and lower IL than a conventional cascade of individual filter blocks. Further advantages include: i) scalability to an arbitrary number of rejection bands, ii) independent control of the ANs in terms of frequency and isolation (IS), and iii) the ability to control the number of active notches in the passband. The concept is experimentally validated through a manufactured lumped-element prototype with two frequency-tunable ANs. They are located within a low-IL (<0.8 dB) LPF with cut-off frequency of 765 MHz and wide out-of-band IS (<30 dB between 0.9-11 GHz). Moreover, they can be independently controlled or merged into a wider rejection band for frequencies between 275-491 MHz (1.8?1). Independent control of AN IS (15-58 dB) is also shown.