Wide Stopband Bandpass Filter with High Selectivity Using I/O Coupling

A bandpass filter (BPF) with high selectivity and wide stopband is proposed in this paper. I/O coupling is employed to introduce zeros in both sides of the passband and thus selectivity is improved. Out-of-band rejection is deepened due to I/O coupling as well while broadened by extra low pass units at feeding ports. Simulation and measurement results show the proposed BPF centers at 2.4GHz with 3dB bandwidth of 24.6% and has a wide stopband to over 6f
₀
. The size of the proposed BPF is 0.33λ
_g
×0.12λ
_g
.