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 open-loop stepped-impedance resonator for compactness. This form of the resonator generates a second transmission zero in the upper stopband which improve 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 their 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 return loss of 21 dB and 28.3 dB, insertion loss of 0.4 dB and
1.7 dB and 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 make it suitable for sub-6 GHz 5G mobile communications.
Key words: 5G, bandpass filter, dual-band, stepped-impedance resonators, sub-6 GHz.
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