Design of High-Selective Wideband Bandpass Filter with a Notched-Band and Harmonic Suppression

A high-selective wideband bandpass filter (BPF) with a notched-band and harmonic suppression is proposed in this paper. Firstly, a uniform impedance resonator with an embedded open-circuited stub square loop is applied in the filter design. By adopting parallel-coupling structure at I/O ports, such a resonator can generate a notched-band within the passband due to the counter-phase cancellation of two dissimilar signal paths. The width of the square loop can be adjusted to select the location of the notched-band. Secondly, by introducing an L-shaped open-circuited stub to one input feed line, a transmission zero (TZ) is created. It can be used to suppress higher harmonic passband. The filter is designed and fabricated with the notched-band centered at 8.1 GHz, and two TZs are implemented at the both sides of the passband. Simulated and measured results show that the filter has a good selectivity and a wider stopband characteristic.