A Novel Design of Wide Stopband Filter with High Selectivity

In this paper, a wide stopband bandpass filter with high selectivity is designed, which uses three stepped impedance resonators to form the main body of the filter, which improves the stopband width of the filter, and has a wide stopband to 3f
0
. The parasitic passband of the filter is suppressed by etching the double T-shaped defected ground structure that changes the current distribution on the floor, generate a band gap with band-stop characteristics, the stopband width is over 4f
0
. Transmission zero is introduced by cross coupling resonance. There are two coupling paths for the signal from the input to output, one transmission zero is obtained on the upper stopband, then the selectivity of the filter is improved obviously. The simulation results show that the return loss of the filter can reach 46 dB and the insertion loss is less than 0.5 dB in the passband of 4.8 GHz-5.0 GHz. The stopband attenuation of 5.8 GHz-20 GHz is better than 20 dB. The rectangular coefficient of 30 dB/3dB is 3.72, and the size is 12 * 45.9 mm
²
.