A Lowpass Filter with Sharp Roll - off and High Relative Stopband Bandwidth Using Asymmetric High - Low Impedance Patches

In this letter, a microstrip lowpass filter with -3 dB cut-off frequency at 1.286 GHz is proposed. By using two main resonators which are placed symmetrically around Y axis a sharp roll-off rate (250 dB/GHz) is obtained. The proposed resonators are consisted of two asymmetric high-low impedance patches. To achieve a high relative stopband bandwidth (1.82) four high - low impedance resonators and four radial stubs as suppressing cells are employed. Furthermore, a flat insertion loss in the passband and a low return loss in the stopband can prove desired in-band and out-band frequency response. The proposed LPF has a high FOM about 63483

A Compact Microstrip Lowpass Filter with Ultra-Wide Rejection Band and Sharp Transition Band Utilizing Combined Resonators with Triangular Patches

In this paper, a microstrip lowpass filter with -3 dB cut-off frequency of 1.8 GHz consisting of two resonators with different triangular patches and four high-low impedance resonators as suppressing cells has been designed. To design this filter, the influence of each transmission line on the frequency response of the utilized resonators has been clarified by calculating the equations of S21 and S11 based on the lumped circuit of them separately. The designed filter has been constructed and tested, and an good agreement between the simulation and measurement results has been achieved. The stopband covers an ultra-wide frequency range from 1.94 to 34.556 GHz with a suppression level of -21.2 dB. Furthermore, the insertion loss in the passband region is close to zero from DC to 1.68 GHz and an acceptable return loss (17.44 dB) in this band can prove desired in-band character. Moreover, the proposed filter provides a sharp transition band equal to 228 (dB/GHz). The designed lowpass filter has a high figure of merit equal to 26583.4

A Design of Microstrip Lowpass Filter with Wide Rejection Band and Sharp Transition Band Utilizing Semi-Circle Resonators

In this paper, a microstrip lowpass filter with -3 dB cut-off frequency of 2.1 GHz consisting of three cascaded resonators with different semi-circle patches and four suppressors employing radial stubs has been proposed. To indicate the role of each employed microstrip transmission line in the structure of its resonance cell, the equations of the transfer function and transition zero of the resonator have been calculated, separately. The designed filter has been constructed and tested, and a good agreement between the results of simulation and measurement has been achieved. In the whole rejection region, a return loss better than +0.28 dB and a 19.656 GHz stopband bandwidth with high rejection level of 32 dB have been obtained. Moreover, a flat insertion loss close to zero in the passband and sharp cutoff slope (203.57 dB/GHz) can verify desired frequency response. The proposed filter has a high figure of merit equal to 24241.69