A wideband bandpass filter with wide upper stopband attenuation containing multiple resonators

A compact wideband bandpass filter with a wide passband and very‐wide out‐of‐band suppression is presented. The filter is constructed from a central rectangular‐ring resonator with two open stubs placed around it symmetrically. In addition, tri‐section stepped‐impedance resonators are symmetrically distributed on both sides of the two open stubs, and two symmetrical funnel‐shaped resonators are included to enhance out‐of‐band suppression. The out‐of‐band performance of filter is very good, with a suppression level greater than 20 dB up to 25.72 GHz. The center frequency of the filter is 5.84 GHz, with a fractional bandwidth of 115.8%. Good agreement between the simulations and measurements validates the design principle.