Design of Equal-Ripple Dual-Wideband Bandpass Filter With Minimum Design Parameters Based on Cross-Shaped Resonator

A novel quarter-wavelength cross-shaped resonator (CSR) is presented in this brief for the design of equal-ripple dual-wideband bandpass filter (DWB BPF) with minimum design parameters. The proposed CSR is composed of a pair of parallel-coupled lines (PCLs) with short- and open-ended stubs. To extract the transmission poles and zeros, rigorous scattering-parameters and ABCD-matrix theories with even-odd-mode analysis method are used. After theoretical analysis, it is found that two passbands with equal-ripple responses can be realized on both sides of the operation frequency. In contrast to the reported DWB BPFs with complex structures, the proposed one is only formed by a quarter-wavelength CSR and featured as minimum design parameters. To verify this, a prototype is designed and fabricated. The measured results are in good agreement with the simulated ones, verifying a simple design approach of equal-ripple DWB BPFs.