Quad-band bandstop filter modeled by comprising quad-section stepped-impedance resonator Rajendra Dhakal 1 • Seongsoo Cho 2 • Bhanu Shrestha 3 • Changho Seo 4 Received: 27 February 2018 / Revised: 8 June 2018 / Accepted: 22 June 2018 Ó Springer Science+Business Media, LLC, part of Springer Nature 2018 Abstract This paper presents the implementation of symmetric folded meandered-line structure that includes a quad-section stepped impedance resonator (QSIR). The existence of four stop bands at 1.81/5.16/8.08/10.90 GHz was successfully synthesized by the incorporation of QSIR comprising an electrical length of 0.84kg–0.19kg–0.15kg–0.22kg. The throughput of the filter was further improved by the inclusion of five attenuation poles at 340 MHz, 3.24, 6.38, 9.45, and 11.92 GHz with the rejection levels of - 32.19, - 25.19, - 28.68, - 21.57, - 32.63 dB, respectively. The concept achieves a wide fractional bandwidth of 59/18.23/13.86/10.46% at 1.81/5.16/8.08/10.90 GHz, respectively. Noticeable attenuation of - 25 dB at the respective stop bands in the frequency range of 2.34–1.28, 5.60–4.66, 8.56–7.44, and 11.35–10.21 GHz, with a spurious- free response up to 13 GHz was confirmed. Furthermore, a sharp response is demonstrated by a simulation and shows strong agreement with the measurement results. Keywords Bandstop filter (BSF)  Symmetric meandered-line  Quad-band  Quad-section  Stepped-impedance resonator (SIR) 1 Introduction With the evolution of more sophisticated wireless com- munication system, the multifunctional performance of the device is desirable and typically adopted in the transmitter and receiver system, where quad-band bandstop filter (QBBSF) is a vital and an obvious candidate for the con- current suppression of unwanted signals at several fre- quencies at air interference [1]. The bandstop filters (BSFs) are the crucial and key components for the extraction of the desired signal from the bunch of unwanted signals. Although the performance of the BSF is more prominent and crucial, researchers had paid much less attention in the design and the development of the BSF with respect to bandpass filters. Obtaining a pure and a noiseless signal in every mode of communication by removing unwanted noise in an air interface is important [2]. The assembling of two or more BSFs in a confined area, that independently provide the passband is the challenging task as both the filters are packed in a compact area, where we can expe- rience a strong inductive coupling between the elements, which ultimately leads to the performance degradation. To date, many researchers have proposed microstrip structural categories to develop the single-to multiband BSFs [3]. These include the dual mode resonator [4], stepped-impedance resonator [5], cross-coupling [6], Hil- bert fork resonator [7], split ring resonator [8], defected ground structure (DGS) [9, 10], and defected microstrip & Seongsoo Cho css3617@gmail.com & Changho Seo chseo@kongju.ac.kr Rajendra Dhakal aperioraj@gmail.com Bhanu Shrestha bnu@kw.ac.kr 1 Department of Computer Science and Engineering, Sejong University, Seoul 05006, Republic of Korea 2 Department of Culture Contents and Convergence ICT, Songho University, 210, Hoengseon, Gangwon-do, Republic of Korea 3 Department of Electronic Engineering, Kwangwoon University, Seoul 01897, Republic of Korea 4 Department of Applied Mathematics, Kongju National University, Kongju 32588, Republic of Korea 123 Analog Integrated Circuits and Signal Processing https://doi.org/10.1007/s10470-018-1260-z