A Super-Wideband Bandpass Filter Using Quarter Wavelength Parallel Microstrip Lines and Capacitors

A super-wideband bandpass filter (SWBPF) using quarter wavelength parallel microstrip lines and lumped capacitors is designed in this brief. The proposed BPF comprises a couple of quarter-wavelength coupled lines, two open stubs and two short stubs. To promote the performance of the BPF and minimize its size, four capacitors are connected in parallel/series of the circuit. Because of its symmetric topological configuration, the odd- and even-mode analysis method is utilized for formula derivation. The filter design centered at 0.23GHz is realized by ADS and EM simulation, the 3-dB fractional bandwidth (FBW) is close to 130% with the size of only $0.002 \lambda_{\mathrm{g}}^{2} (\lambda\mathrm{g}$: guided wavelength at center frequency). The final comparison results indicate a high degree of consistency between theoretical calculations and electromagnetic simulations.