Compact dual-wideband bandstop filter using a stub-enclosed stepped-impedance resonator

A compact, wide dual-band bandstop filter (DBBSF) based on a stub-enclosed stepped-impedance resonator (SE-SIR) is proposed. The second order filter is employed to obtain two transmission zeros in each stopband for better selectivity. The proportional tuning of both center frequencies is achieved by proportionately varying the electrical length of the enclosing stub with that of the high impedance section of the stepped-impedance resonator. Additionally, the second center frequency is tuned independently only by varying the electrical length of the enclosing stub. Two center frequencies at 4.7 and 6.64 GHz are reported, corresponding to the rejection of 35.1 and 26.23 dB and the fractional bandwidth of 31.02 and 23.93%, respectively at −3 dB. The size of the proposed filter is achieved to be 0.38λg × 0.07λg. The experimental results demonstrate its potential application in C-band communication systems.