A new compact, wide bandwidth dual‐passband microstrip filter based on dual‐mode stepped‐impedance‐resonators

Abstract

In this article, a new compact, wide bandwidth dual-band bandpass filter (DB-BPF) with four transmission zeros (TZs) is proposed. A dual-path configuration is realized by cascading different dual-mode resonators. The novel dual-mode resonators are based on stepped impedance resonators (SIRs) that generate the TZs owing to their intrinsic characteristics. The proposed DB-BPF can fulfill simultaneous independent control of the external and internal-resonator coupling. The design procedure based on the cascaded dual-mode resonators and frequency transformation is also introduced. The surface current distributions are simulated to verify the performance of the proposed filter. The measured results show 2.14/4.33 GHz DB-BPF with 3-dB fractional bandwidth (FBW) of 0.27/0.15, respectively, which is suitable for WLAN applications. The return and insertion losses of the passband are better than 15/15-dB and less than 0.8/1.3-dB, respectively. The overall physical size of the fabricated DB-BPF is 20.4 mm × 20.4 mm, equivalent to 0.23λg × 0.23λg, where λg is the guided wavelength at 2.14 GHz. The simulation results are in good agreement with the measurement results.