Miniaturized Frequency Controllable Band-Stop Filter Using Coupled-Line Stub-Loaded Shorted SIR for Tri-Band Application

Based on the coupled-line stub-loaded shorted stepped-impedance resonator (CLSLSSIR), a compact microstrip tri-band band-stop filter (TB-BSF) with controllable frequencies, stopband attenuations (SAs), and sharp transition band roll-off skirts has been presented. The proposed CLSLSSIR exhibits multimode resonant behavior and is employed to achieve tristopband application by applying the virtual ground effect at the attaching position. Due to the infinite input impedance effect of CLSLSSIR, as well as the resonance of π-type network combined with two loaded CLSLSSIRs and transmission line, multiple transmission poles can be yielded to obtain high selectivity of transition band. Finally, an example TB-BSF operating at 1.57, 2.4, and 3.5 GHz with respective SAs of 18, 26.5, and 33.2 dB has been designed and fabricated.