Five-order Equal Ripple Wideband Bandpass Filter with Minimized Variation in Group Delay

A wideband bandpass filter, consisting of two shunt short-circuited stubs and a two-staged cascading coupled line section, is presented. The analytical study reveals that an equal-ripple response in magnitude and the flattest group delay can be achieved simultaneously in passband when choosing the impedances of the lines properly. In addition, those impedances can be determined exactly by solving a set of equations describing the matching between the transfer function of the filter topology and a target function with equal-ripple response. For verification, two filter samples with different design specifications are designed, simulated and discussed.