Compact dual‐band BPF with SR and SMR for wideband and WLAN applications

Abstract

A compact dual-band bandpass filter (BPF) with a slotline resonator (SR) and a short stub centre-loaded microstrip resonator (SMR) is proposed for wideband and wireless local area network (WLAN) applications. The high-impedance microstrip feedlines for the filter with the SMR can function as the quarter-wavelength resonators for the filter with the SR to realise a wideband passband. Owing to the source-load coupling, the loaded short stub and the intrinsic characteristics of the SMR, three transmission zeros can be created to improve selectivity and isolation. Compact size can be obtained by adopting the folded SR and folded SMR inserted between the arms of the SR. A compact dual-band BPF for wideband and WLAN applications is simulated and measured, and good agreement can be obtained between the measured and simulated results.

Design of compact size and tunable band pass filter for WLAN applications

“…To miniaturise the resonator size and tune its resonance frequency, Variable lumped capacitors are used [7,8]. WLAN applications which are operated at frequency band from 5.15 to 5.825 GHz need to be filtered out [9].…”

Dual‐wideband BPF with wide upper stopband using shorted stepped‐impedance stub‐loaded lowpass filter

“…To realise wideband characteristic, multimode resonators (MMRs) [1][2][3][4] have been extensively investigated to address these requirements. The MMR uses configuration of the stepped-impedance resonator (SIR) [1][2][3][4][5] or the short-/open-circuited stubs loaded SIR [2][3][4][5]. Although the BPFs with a single resonator are compact in size, their bandwidths (BWs) controlled by the coupling strength [1,2] are finite.…”

“…The MMR uses configuration of the stepped-impedance resonator (SIR) [1][2][3][4][5] or the short-/open-circuited stubs loaded SIR [2][3][4][5]. Although the BPFs with a single resonator are compact in size, their bandwidths (BWs) controlled by the coupling strength [1,2] are finite. Besides shorted stub centre-loaded microstrip resonator, the BPF in [2] also uses a slot-line resonator to realise the first wideband passband, but the slot-line structure causes difficulty when integrated on chips.…”

“…Although the BPFs with a single resonator are compact in size, their bandwidths (BWs) controlled by the coupling strength [1,2] are finite. Besides shorted stub centre-loaded microstrip resonator, the BPF in [2] also uses a slot-line resonator to realise the first wideband passband, but the slot-line structure causes difficulty when integrated on chips. For filters in [3], a two-end-shorted three-section SIR with two identical open stubs was used to introduce transmission zeros (TZs), and then to divide multiple resonant modes, forming multi-passband.…”

“…Dual-band bandpass transversal filtering sections based on directional couplers with double loading stubs in [4] were investigated to design widely spaced broad passbands. However, BPF based on MMR has unnecessary higher-order harmonic to produce spurious response [1][2][3][4]. To have good out-of-band performance, harmonic suppression is realised by tuning the impedance ratio and the physical length ratio of shorted SIR [5].…”