Compact Single-/Dual-Wideband BPF Using Stubs Loaded SIR (SsLSIR)

Abstract

This letter presents a new stubs loaded stepped impedance resonator (SsLSIR) to design single-/dual-wideband bandpass filter (BPF). The proposed SsLSIR exhibits multiple tunable transmission zeros (TZs) and transmission poles (TPs), which can be arranged to build up single/dual-wideband BPF. The proposed single-band BPF has a central frequency of 1.91 GHz with <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${-}3$</tex></formula> dB fractional bandwidth (FBW) of 52.4% and the dual-band BPF has a central frequency of 1.92/5.44 GHz with <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${-}3$</tex> </formula> dB FBW of 66.7%/28.3%. The higher-order spurious frequencies of the single-band BPF are tuned and canceled by the TZs, resulting in a wide stopband with <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${-}20$</tex> </formula> dB spurious suppression from 2.19 to 9.19 GHz. The TZs between two passbands of the dual-band BPF provide a wideband and high band-to-band isolation. Two filters have the merits of low insertion loss, simple physical topology and compact size.