A wide bandstop filter using negative permeability achieved by complementary electrical L-C resonators

This paper proposes an improved approach for designing a compact microstrip line-based band stop filter (BSF) using a new Z-shaped complementary electrical LC (CELC) resonator with negative permeability. The design offers advantages in terms of compactness and large stopband. The measured insertion loss exhibits a 3 dB bandwidth from 6.7 to 9 GHz, resulting in a relative stopband bandwidth of 28.75% with rejection exceeding 20 dB between 7.5 and 8.2 GHz. Both the simulation and the measurements reveal a high level of selectivity in both the lower and upper transition bands. The final filter has 0.33λ_g×1.32λ_g circuit size and is very effective in rejecting unwanted frequency in terms of its selectivity and size.