A class of fully-reconfigurable planar multi-band bandstop filters

A new class of planar multi-band bandstop filters (BSFs) with spectrally-agile stopbands in terms of center frequency and bandwidth are presented. They are based on the in-series cascade of several frequency-reconfigurable multi-stopband filtering sections. Each of these sections is shaped by N tunable resonators-center-frequency control-that interact with the same non-resonating node (NRN) through independently-controlled impedance inverters-bandwidth reconfiguration-for an N-band BSF transfer function. Additional features of this adaptive multi-band BSF approach are: i) independent control of each rejection band with no influence on the remaining ones, ii) stopband-merging capability to effectively attain controllability in the number of generated stopbands along with increased bandwidth flexibility for them, and iii) concept scalability to any number of stopbands and poles. Its main operational principles are theoretically demonstrated through the coupling-matrix formalism for the engineered multi-band BSF configuration. Moreover, for experimental verification, a mechanically-reconfigurable three-band BSF prototype in the 0.9-1.2-GHz frequency range was manufactured in microstrip technology and characterized.