Investigating Single- to Dual-Band Bandpass Filter Transformation for Wireless Communication Systems

Abstract

A simple technique for transforming a single-band bandpass filter (BPF) into a dual-band BPF is presented in this chapter. The method starts with a 2nd-order single-band BPF design, giving rise to a 4th-order dual-band BPF after the proposed transformation. Both filters are implemented using compact U-shaped microstrip resonator for improved device miniaturization. The proposed work features a centre frequency of 1.4 GHz for the single-band BPF, with a 3.4% fractional bandwidth. The dual-band BPF operates at 1.35 and 1.45 GHz for the first and second bands, respectively. The design implementation employs the commercially available Rogers RT/Duroid 6010LM substrate, having a dissipation factor of 0.0023, dielectric constant of 10.7, and thickness of 1.27 mm. The practical responses of the prototype dual-band BPF indicate a good return loss of better than 18 dB across both bands, and an insertion loss of better than 0.1 dB. The design prototype achieved physical size of 0.23 x 0.18 λg. λg is the guided wavelength for the microstrip line impedance at the centre frequency of the filter.