A Group Delay Equalization Method for Filters Based on DGS NGD Structure

This paper presents an innovative group delay (GD) equalization method for bandpass filter (BPF) based on defected ground structure (DGS) negative GD (NGD) structure. This equalization method works by adding DGS units on the microstrip circuit ground plane. A third-order BPF prototype with NGD equalization is designed. After equalization, the GD fluctuation is reduced from 0.55 ns to 0.25 ns, a decrease of $54.5 \%$. This significantly reduces the intra band GD fluctuation of the filter and improves its phase linearity.