A compact wide bandwidth bandpass filter with SIR and S‐shaped coupled spiral resonator

Abstract

ABSTRACTThis article proposes a compact wide bandwidth band pass filter (BPF) with a stepped impedance resonator (SIR) and an S‐shaped coupled spiral resonator. The SIR has a wide bandwidth while the S‐shaped coupled line has a compact structure due to the spiral type resonator. The BPF used the S‐shaped folded structure instead of the λg/4 transmission line to reduce the size and to enhance the performance of the BPF. The via‐hole was not used in order to keep the design simple. Due to the narrow coupling gap, the bandwidth of conventional BPFs can barely exceed 40%. However, in this work, the proposed BPF achieved a bandwidth of 68%, which is larger than the conventional filter. The experimental results in terms of insertion loss (S21) and return loss (S11) are 0.61 dB and 15.7 dB at 5.3 GHz. The smaller size of the BPF is suitable for microwave communication systems. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:2334–2336, 2016