Compact LPF with pair of coupling slots for wide stopband suppression

A compact and small lowpass filter (LPF) with a pair of coupling slots for wide stopband suppression is presented. Based on a classic dumbbell DGS cell, a pair of coupled parasitic slots has a good mutual coupling effect with it, which can be used to improve the stopband characteristic significantly. We extended the stopband to six times the cutoff frequency of 3 GHz with a smaller size, about 15×15 mm, which is superior to the conventionally cascaded dumbbell DGS-LPF in reduction of the harmonic passbands and the size. In addition, a good skirt response can be also achieved by controlling the dimensions of a pair of coupling slots.