(Received: 7-Jul.-2023, Revised: 12-Aug.-2023 , Accepted: 2-Sep.-2023)
In this paper, a microstrip bandpass filter for dual-band sub-6 GHz 5G mobile communications is designed. The two first resonance frequencies of the stepped-impedance resonator are used as the operating frequencies of the two passbands. Furthermore, the stepped-impedance resonator is folded to form an open-loop stepped-impedance resonator for compactness. This form of the resonator generates a second transmission zero in the upper stopband, which improves the out-of-band rejection. A 50 Ω tapped-line input/output is used to feed the filter. The proposed structure is designed, analyzed and manufactured and the measured results are found to be in good agreement with the simulation results. From the measured results, it is found that the proposed filter achieved a return loss of 21.5 dB and 28.3 dB, an insertion loss of 0.4 dB and 1.7 dB and a bandwidth of 12.5% and 10.81% at 3.61 GHz and 5.55 GHz, respectively. In addition, the proposed filter has a compact size, which makes it suitable for sub-6 GHz 5G mobile communications.

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