Parallel-Coupled Coplanar-Waveguide Bandpass Filter With Multiple Transmission Zeros

A compact parallel-coupled coplanar-waveguide bandpass filter with good selectivity and stopband response is proposed. By using the quarter-wavelength resonators in implementation, the filter size can be reduced and no spurious passband is observed at twice the center frequency (2f₀). In addition, by suitably introducing the capacitive and inductive cross-coupling effects, four transmission zeros around the passband edges may be created for improving the filter selectivity. For design purpose, the equivalent-circuit models are also established. In this study, the compact fourth-order filter with multiple transmission zeros for improving the selectivity is implemented, and its stopband is extended up to 3.43f₀ with a rejection better than -30dB