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.