Non-uniform Chebyshev distributed chirped dumbbell-shaped photonic bandgap structure (PBGs) low-pass filter

Purpose: The purpose of this paper is to introduce a non-uniform Chebyshev distributed low-pass filter (LPF) with dumbbell-shaped photonic bandgap structure (PBGs), implemented in the 50Ω microstrip line, with improved defected ground structure. Design/methodology/approach: The non-uniform distribution of PBGs and dumbbell-shaped DGS of PBGs have been discussed in open literatures. In this study, the influence of FF of PBGs in dumbbell-shaped PBG is represented. Findings: By varying filling factor (FF) of the periodic structure from 0.25 to 0.8 of the dumbbell squares can generate better rejection band than uniform dumbbell LPF. Different FF of each square can produce different band rejection range and then yields the LPF with different cutoff. By using chirp adjustment of distance between PBGs, the band rejection performance can be optimized. Originality/value: It can be seen that the chirped and non-uniform dumbbell-shaped PBGs generate excellent bandgap performances in linearly varying period (chirped devices) than those of structures with constant period (non-chirped or uniform devices).