LAUSR

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 tri-stopband 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 $\pi $ -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.