A design of band-pass filter with steep stopband attenuation based on transmission zeros

To improve the stopband attenuation performance, a modified Chebyshev filter based on transmission zeros is proposed. In the improved design process, several transmission zero-points out of passband is introduced to make stopband steeper, meanwhile, the network transformation is used to eliminate parasitic parameters in actual project realization, thus enhancing the performance of suppression outside passband. In order to verify the improved design process, a center frequency of 115MHz with over -45 dB stopband attenuation at the outer edge of the stopband (10 MHz) is designed. Compared with the Chebyshev prototype filter, which has only -27 dB stopband attenuation, the stopband attenuation of the modified filter is 12-19 dB lower. The results of the measurement fit well with the simulation ones and confirm the method is feasible and effective.