A new design approach for lumped band-pass filters with improved frequency response symmetry and stop-band rejection

In this paper a new design approach is introduced to significantly improve the filter selectivity of lumped band-pass filters, BPF. The filter design is based on an admittance inverter circuit that employs a parallel resonant circuit. The admittance inverter proposed in this paper is used to introduce finite frequency zeros at selected frequencies whether below or above pass-band. The design technique introduced not only controls and improves the selectivity of the filter with only few added elements, it also serves to improve the symmetry of the magnitude and group delay response of the filter of interest. To illustrate the design procedure, a top-C coupled filter based on a 5th order low pass Chebyshev prototype is used as reference. The filter is then modified to employ the proposed admittance inverter circuit. The simulation results verify the significant improvement in magnitude and group delay response compared to the standard top-C coupled design.