A wide stopband, high selectivity microstrip low-pass filter for wireless communications

This article presents a compact microstrip low-pass filter (LPF) with a sharp roll-off rate (ROR) and an ultra-wide stopband for modern telecommunication applications. To achieve a relatively sharp transition band (−3 dB and −40 dB at the cut-off frequencies of 1.3 GHz and 1.57 GHz, respectively), a modified fifth-order circuit has been presented as the primary resonator. The frequency response of the primary filter is then enhanced by incorporating a few stubs in the primary resonator structure, which act as harmonic suppressors and help create a wide stopband. Simulation results show that the proposed LPF has a wide stopband width of approximately 28.43 GHz (from 1.57 to 30 GHz). The proposed LPF is fabricated on Rogers substrate with a total footprint of 35.3 mm × 15.9 mm. The measured values of ROR, suppression factor (SF), relative stopband band (RSB), and figure of merit (FOM) (137 dB/GHz, 2.2, 1.92, and 54,082, respectively) present the proposed LPF as a suitable choice for state-of-the-art communication circuits.