High-selective wideband bandpass filter with adjustable notched-band using stub-loaded resonator

A high-selective microstrip wideband bandpass filter (BPF) with an adjustable notched-band is proposed. First, a pair of open-ended stubs is tap-connected to a λ/2 uniform impedance resonator at two symmetrical locations with respect to its centre, and they are further electrically connected by a microstrip line section. Such an arrangement leads to the emergence of a notched-band owing to the out-ofphase cancellation of two dissimilar signal paths in a wide passband. Secondly, the electrical path connecting the two open-ended stubs is gradually tuned so as to adjust the notched-band to the desired frequency location. Finally, a prototype filter is designed and fabricated, and its measured results are provided to verify the predicted frequency response.