A Flexible Microstrip Low-Pass Filter Design Using Asymmetric Pi-Shaped DGS

This paper presents a flexible microstrip low-pass filter (LPF) fabricated on a polyimide film substrate. The proposed flexible microstrip LPF with ten cascaded asymmetrical Pi-shaped defected ground structure (DGS) resonators are designed, simulated, manufactured, and measured. The simulation and experiment results demonstrate that the designed flexible microstrip LPF has a very sharp transition band, an ultra-wide stop-band (SB) and high rejection in SB performance compared with the existed microstrip LPFs with symmetrical and asymmetrical DGS. The proposed flexible LPF with ten cascaded resonators is with a compact size of 100 mm × 2.6 mm × 0.254 mm, a very low insertion loss of less than 1.9 dB under 2.2 GHz, and a wide SB from 2.7 to 12 GHz with the rejection of larger than 50 dB. The proposed flexible LPF has the potential to be used in wireless terminals to replace the traditional RF coaxial cable because it is very thin and has good transmission and filtering functions.