DGS embedded transformed radial stub for ultra-wide stopband lowpass filter

A novel lowpass filter (LPF) with a wide stopband by using defected ground structures (DGSs) and a transformed radial stub (TRS) in combination is proposed. The characteristics of DGS cells are investigated and the DGS embedded TRS LPFs are designed and verified by experiment. The designed DGS embedded TRS LPF demonstrates a passband insertion loss of less than 1dB, a cutoff frequency (f(c)) of 2.5GHz, a wide stopband with more than 16dB rejection up to 14f(c), a passband return loss of better than 18dB and a compact size of 0.26 lambda(g) x 0.167 lambda(g) (lambda(g) is the guided wavelength at the cutoff frequency).