Wideband chebyshev-response bandpass filter by cascading of cascadable180° hybrid rings

A novel wideband bandpass filter using two cascadable 180deg hybrid rings is proposed and analyzed. The synthesis mathematics shows that the filter should be a Chebyshev response of order three. Design equations and design curves of this filter are provided. Using these equations and curves, a wideband bandpass filter can be readily realized. A filter with 85% bandwidth and 15-dB passband return loss is designed as an example. This filter is implemented by finite-ground coplanar waveguide on a 15-mil Al₂O₃ substrate. The experimental results show excellent agreements with the calculated results.