A double split-ring resonator based tunable filter for frequency detection and monitoring system
DOI:
https://doi.org/10.54939/1859-1043.j.mst.IITE.2025.54-61Keywords:
Tunable filters; Double split-ring resonator; Frequency detection.Abstract
This paper presents a compact, continuously tunable bandpass filter based on a double split-ring resonator (DSRR) loaded with two varactor diodes for modern wireless communication systems. The proposed design achieves a wide tuning range of 8 - 12 GHz (40% fractional bandwidth) through precise capacitance adjustment, addressing critical limitations of conventional tunable filters in bandwidth, reliability, and control complexity. By leveraging the DSRR's coupled resonance characteristics and independent varactor tuning, the filter maintains stable performance with return loss exceeding 10 dB across a 250-MHz passband. The architecture eliminates mechanical switches, offering improved reliability compared to MEMS/p-i-n diode alternatives while greatly reducing component count compared to traditional multi-bank filters. This work provides a foundation for developing reconfigurable RF front-ends that balance wide tunability, miniaturization, and power efficiency for 5G/6G and cognitive radio applications.
References
[1]. Yang, Y.; Zhu, X.; Xue, Q. “Design of an ultracompact on-chip bandpass filter using mutual coupling technique,” IEEE Trans. Electron Devices, 65, 1087–1093, (2018).
[2]. Liu, B.-G.; Zhou, Y.-J.; Cheng, C.-H. “Miniaturized ultra-wideband bandpass filter with ultra-wide stopband using π-type unit with inductive loading on integrated passive device,” IEEE Trans. Circuits Syst. II Exp. Briefs, 68, 3406–3410, (2021).
[3]. Pradhan, N.C.; Koziel, S.; Barik, R.K.; Pietrenko-Dabrowska, A.; Karthikeyan, S.S. “Miniaturized dual-band SIW-based bandpass filters using open-loop ring resonators,” Electronics, 12, 3974, (2023).
[4]. Huang, X. “Design of miniaturized SIW filter loaded with improved CSRR structures,” Electronics, 12, 3789, (2023).
[5]. Sekar, V.; Entesari, K. “A half-mode substrate-integrated waveguide tunable filter using packaged RF MEMS switches,” IEEE Microw. Wirel. Compon. Lett., 7, 336–338, (2012).
[6]. Lee, G.; Jung, J.; Song, J.-I. “A SiGe BiCMOS power amplifier using a lumped element-based impedance tuner,” IEEE Microw. Wirel. Compon. Lett., 26, 58–60, (2016).
[7]. Lin, F.; Rais-Zadeh, M. “Continuously tunable 0.55–1.9-GHz bandpass filter with a constant bandwidth using switchable varactor-tuned resonators,” IEEE Trans. Microw. Theory Tech., 65, 792–803, (2017).
[8]. El-Tanani, M.A.; Rebeiz, G.M. “High-performance 1.5–2.5-GHz RF-MEMS tunable filters for wireless applications,” IEEE Trans. Microw. Theory Tech., 58, 1629–1637, (2010).
[9]. Zhang, N.; Deng, Z.; Sen, F. “CPW tunable band-stop filter using hybrid resonator and employing RF MEMS capacitors,” IEEE Trans. Electron Devices, 60, 2648–2655, (2013).
[10]. Chen, J.-X.; Zhang, Y.-J.; Cai, J.; Li, Y.-L.; Yang, Y.-J. “Overall study of frequency-agile mechanism of varactor-loaded λ/4 resonator for designing tunable filter with stable wide stopband,” IEEE Trans. Ind. Electron., 66, 6302–6310, (2019).
[11]. Li, Q.; Chen, X.; Chi, P.-L.; Yang, T. “Tunable bandstop filter using distributed coupling microstrip resonators with capacitive terminal,” IEEE Microw. Wirel. Compon. Lett., 30, 35–38, (2020).
[12]. Kenney, R.H.; Walker, C.J.; Sigmarsson, H.H.; McDaniel, J.W. “A varactor-based tunable combline bandpass filter using suspended integrated stripline (SISL),” IEEE J. Miniaturization Air Space Syst., 2, 112–116, (2021).
[13]. Chen, Z.-H.; Chu, Q.-X. “Wideband fully tunable bandpass filter based on flexibly multi-mode tuning,” IEEE Microw. Wirel. Compon. Lett., 26, 789–791, (2016).
[14]. Xiang, Q et al. “A 5th-order constant bandwidth tunable bandpass filter with two cascaded trisection structures,” IEEE Trans. Circuits Syst. II Express Briefs, 70, 126–130, (2022).
[15]. Wu, H.; You, B.; Gao, K.-K.; Li, X.-G. “A 4th-order LTCC bandpass filter with both tunable center frequency and bandwidth,” Electronics, 11, 4119, (2022).
[16]. Li, S.; Li, S.; Yuan, J. “A compact fourth-order tunable bandpass filter based on varactor-loaded step-impedance resonators,” Electronics, 12, 2539, (2023).
[17]. Yang, G.-M.; Wu, J.; Lou, J.; Liu, M.; Sun, N.X. “Low-loss magnetically tunable bandpass filters with YIG films,” IEEE Trans. Magn., 49, 5063–5068, (2013).
[18]. Du, S.; Yang, Q.; Fan, X.; Wang, M.; Zhang, H. “A compact and low-loss tunable bandpass filter using YIG/GGG film structures,” IEEE Microw. Wirel. Technol. Lett., 33, 259–262, (2023).
[19]. Zheng, S.Y. “Simultaneous phase- and frequency-tunable hybrid coupler,” IEEE Trans. Ind. Electron., 64, 8088–8097, (2017).
[20]. Khanjar, K.; Djeraf, T. “Highly reconfigurable patch coupler with frequency and power-dividing ratio control for millimeter-wave applications,” IEEE Trans. Microw. Theory Tech., 71, 2118–2128, (2023).
[21]. Tan, X.; Zhang, Y. “A compact rat-race coupler with widely tunable frequency and power-dividing ratio,” IEEE Microw. Wirel. Technol. Lett., (2023).
[22]. Liu, B.; Qiu, J.; Chen, L.; Li, G. “Dual band-notched rectangular dielectric resonator antenna with tunable characteristic,” Electronics, 8, 472, (2019).
[23]. D. M. Pozar. “Microwave Engineering.” John Wiley & Sons, Inc., (2012).
