A filter with equal-ripple negative group delay

A new design method is proposed for filters with equal-ripple negative group delay (NGD). By combining the coupling matrix of bandstop filter with the nonuniform-ß technique, the equal-ripple NGD characteristic is achieved. The ripple is mainly determined by the minimum dissipation factor of resonators, while the NGD is controlled by the maximum insertion loss and dissipation factors. A prototype is developed at 2.0 GHz, with the measured NGD of -3.1 ns and NGD ripple of -0.5 ns within the bandwidth of 85 MHz.