A design of cascaded CPW low-pass filter with broad stopband

A coplanar waveguide low-pass filter (LPF) using two different LPF unit cells (LUCs) and a small defected ground structure (DGS) unit cell (DUC) is presented. By cascading two LUCs, which are different in structure and harmonic passbands, and combining a dumbbell-like-shaped DUC to the cascaded LPF, we extended the stopband to seven times the cutoff frequency. The proposed LPF is superior to the conventionally cascaded LPF, in which the same LUCs are used, in reduction of the harmonic passbands and the size. The fabricated LPF shows a compact size of 18.2 mm x 11 mm, the cutoff frequency of 3 GHz, and the sharp skirt response like a fifth-order LPF with two notch frequencies. The measured frequency responses agree well with the simulated ones.