A Flexible Ultra-Wideband Bandpass Filter Based on Stepped Impedance Multi-Mode Resonator

Microwave filters play an important role in the RF telecommunication system. With the wide application of UWB wireless communication technology, the demand for flexible UWB microwave filters is increasing rapidly. In this paper, a flexible ultra-wideband bandpass filter is proposed based on the step- impedance multi-mode resonance structure, with a pair of parallel open-circuit stubs loaded to suppress the high-order harmonic and a set of U-shaped gaps etched to improve the in-band return loss. By comparing the simulation results in the flat and bend state, the proposed filter is demonstrated that it has an ultra-wide passband from 2.93 to 10.86 GHz, with the insertion loss less than 0.89 dB and the reflection loss better than 12 dB, and good suppression of parasitic passband is obtained. Good filtering performance and out-of-band suppression can still be maintained in the case of bending deformation.