Novel Compact Wideband Bandpass Filters with High Upper Stopband Rejection Featuring a Quadruple-Mode Resonator
Chuan Shao,
Rong Cai,
Xinnai Zhang and
Kai Xu
In this letter, a novel, compact bandpass filter architecture that leverages a quadruple-mode stepped impedance resonator (SIR) is introduced. This design is predicated on the principles of odd-even-mode analysis, which has been meticulously applied twice to elucidate the resonator's operational dynamics. The distinct boundary conditions inherent to the odd-odd and even-odd degenerate modes result in their splitting, a phenomenon that is pivotal to the filter's performance characteristics. The equivalent circuits representing the quadruple modes function as quarter-wavelength SIRs, a design choice that inherently confers a compact form factor upon the resonator. This is achieved without compromising the filter's functionality, as each mode contributes to the overall filtering response in a manner that is both efficient and space-saving. Furthermore, the filter is characterized by a 20-dB stopband rejection that extends up to 6.9 GHz, which corresponds to 3.8 times of the fundamental frequency (f0). This outstanding stopband performance is a testament to the design's effectiveness in attenuating unwanted signals while maintaining a compact footprint.
