Simultaneous flattening of amplitude and group delay responses in narrowband bandpass filters using a novel systematic design method

Abstract

In this article, a novel systematic method for compensation of the simultaneous amplitude and group delay (GD) flatness in the narrowband bandpass filters is proposed. The proposed technique can be used systematically in any type of filters with the possibility of resonator quality factor adjustment. This technique is presented using an RLC resonator equalizer in two steps. First, the compensation of the GD response is accomplished by tuning the external Q-factor, then the amplitude response is compensated by adjusting the resonator Q-factor. To verify this technique, design and fabrication of a TM dualmode equalizer for joint compensation of the amplitude and GD responses in a narrowband waveguide filter is presented. The simulation results for a novel TE dual mode equalizer is also presented. The passband response of an unequalized narrowband filter with passband flatness of 1.5 dB amplitude and 55 ns GD at the center frequency of 10.970 GHz is improved to 0.5 dB amplitude flatness and 30 ns GD flatness. This improvement is achieved at the cost of passband insertion loss. The designed equalizer is fabricated and tested and the measurement results, after and before equalization, prove the design technique capability.

Self‐equalized linear‐phase microstrip bandpass filter based on negative group delay parallel‐coupled three‐line units

“…As an essential device in the system, the bandpass filter (BPF) is required to have a linear phase response (flat group delay) within the passband in addition to good out‐of‐band suppression performances 4 . One way to realize linear phase response is to design an external group delay (GD) equalizer with complementary GD characteristics to the BPF and cascade it with the BPF through a coupler or a circulator 5 . One disadvantage of this external equalization approach is that the absolute time delay and circuit size are increased significantly 6–8 .…”