Design of A Compact Dual-Band BPF for 5G Mobile Communications Using Folded $\lambda \mathrm{g}/2$ -Line Resonators

In this paper, a two-folded half guided wavelength resonators are used to propose dual-band bandpass filter with very simple structure, compact size, high selectivity, and isolated bands. This filter is intended to be used in 5G mobile communications. The two folded $\lambda \mathrm{g}/2$-line resonators resonating at 3.5 GHz and 5.45 GHz with fractional bandwidth of 4.8% and 8.9%, respectively. The frequencies at which the filter resonates are designed and arranged independently. The proposed filter achieves insertion loss of −0.8 dB and −0.5 dB, and return loss of −20 dB and −18.4 dB, respectively. In addition, four transmission zeros appeared. The proposed filter has a compact size of 0.26λg×0.15λg and built on RO4350B substrate with dielectric constant of 3.66, loss tangent of 0.0037, and 0.508 mm of thickness. The EM-simulation and LC equivalent circuits results appear to be in a good agreement with the theoretical response.