Design of a small modified microstrip lowpass filter with folded U-shaped defected ground structure

A new technique to reduce the size and improve the rejection in the stopband of a lowpass filter using folded U-shaped defected ground structure (DGS) is proposed. The proposed DGS by using higher order harmonics of the main attenuation pole provides several attenuation poles (depending on the slot length). Five folded U-shaped DGS cells are applied to form a miniaturized lowpass filter, which has a smaller area, wider stopband and also better passband characteristic in comparison to previous works. The size of the fabricated filter is as small as 43.5 mm × 14 mm.