Investigations into nonuniform photonic-bandgap microstripline low-pass filters

With the advent of planar photonic bandgap (PBG) materials, different PBG topologies have been proposed to improve bandgap performances of microwave signals. Conventional circular-patterned PBGs have constraints in the wide stopband performance due to high passband ripples. In this paper, we suggest two novel configurations with nonuniform dimensions of circular-patterned PBGs to improve the stop bandwidth and passband ripples. The dimensions of PBG units are varied proportionally to the coefficients of binomial and Chebyshev polynomials. The simulated and measured responses of the proposed PBG units are presented. It is seen that Chebyshev distribution produces excellent performance by suppressing passband ripples and producing distinct stopband. These performances of passband ripples and stop bandwidth are further improved with Chebyshev distributed annular-ring PBG units with their unique feature of aspect ratio control.