Design of microstrip lowpass filter with very good return loss using stepped impedance resonators

In this letter, a symmetrical microstrip lowpass filter (LPF) with many excellent specifications such as a compact size, sharp roll-off, outstanding return loss and high rejection in the stopband is presented. This structure is composed of a straight transmission line loaded by several stepped impedance, radial stubs and T-shaped resonators. The transition band is from 2.110 up to 2.337 GHz with -3 and -40 dB attenuation points, respectively, which is represented a narrow transition band. In order to achieve an ultra-wide bandwidth and 26 dB attenuation level in the stopband, multiple open stub and T-shaped patches are added to the proposed main resonator. This filter with cut-off frequency equal to 2.110 GHz is designed and simulated. The proposed lowpass filter can accomplish a low insertion loss less than 0.4 dB in the passband and an excellent return loss better than 18.3 dB. The results show that a roll-off rate of 138.5 dB/GHz, relative stopband bandwidth of 145% and a high figure-of-merit (FOM) of 20179 have been achieved

کلیدواژه ها:

T-shape resonator ، Microwave filters ، Lowpass filters ، Stepped impedance resonator