Design of an Ultra-wideband Multiple-Mode Resonator (MMR)-Based High Selectivity Bandpass Filter

The growing need for high-quality signal transmission in radio communication systems has made ultra-wideband bandpass filters indispensable. Recent research shows a variety of bandpass filter circuit configurations aiming at improving the bandwidth, selectivity, return loss, stopband, insertion loss, etc. However, the performance of each filter is different from all the rest. Therefore, this paper proposes a new ultra-wide bandpass filter configuration consisting of different combinations of series, shunt, and coupled transmission lines. Due to the symmetry, an even and odd mode analysis is carried out to determine closed-form expressions for S parameters and transmission zeros. The ADS software is utilized to determine the impedances and electrical lengths for achieving an ultra-wide passband. For validation, full-wave simulations were performed at a center frequency of 2.49 GHz. The simulations show a fractional bandwidth of 125% and a selectivity factor of 0.87, showing significant improvement over the state-of-the-art designs.