Tri-band bandpass filter with wide stop-band using stub-loaded triple-mode resonator

Abstract

A novel microstrip tri-band bandpass filter (BPF) based on stub-loaded triple-mode resonator is proposed. The open- and short-circuited stubs are asymmetrically loaded to a uniform impedance open-loop resonator, constructing a triple-mode resonator. Benefiting from the proposed asymmetrical loading scheme, the designed tri-band BPF not only possesses the controllable bandwidths of the three passbands, but also shows very wide stopband. Finally, a tri-band microstrip BPF with good performance is designed at 1.5, 2.57, and 3.83 GHz. Three transmission zeros near the passbands are obtained to improve the selectivity of the tri-band BPF. Meanwhile, the other transmission zeros produced in the stopband enhance the harmonic suppression level. The rejection level from 4.3 to 13.7 GHz is better than 20 dB. The measured results are in good agreement with the simulated data.