Microwave and Optical Technology Letters · 2017 · 12 citations · 8 references
EngineeringElectrical EngineeringMicroelectronicsMicrowave EngineeringSemiconductor DevicesIntegrated Circuit DesignMicrowave FiltersMicrowave Integrated CircuitsMicrowave Semiconductor DevicesMicrowave Transmission LinesRadio-frequency Integrated CircuitsCutoff FrequencyEquivalent Circuit AnalysisEquivalent Circuit ModelingInsertion LossInsertion Loss ReductionLow-pass FiltersStepped-impedance FiltersVaractor Diodes
Abstract A novel continuously tunable lowpass filter (LPF) with compact size, sharp roll‐off and low insertion loss is presented in this paper. The filter employs two varactor diodes, a pair of open‐ended coupled lines and a U‐shape step impedance line (SIL) with an open‐ended stub loaded at the center of the SIL to form a very compact layout. The odd‐ and even‐mode analysis and equivalent circuit model are demonstrated for estimation of the transmission characteristics. Tuning the DC voltage applied on the varactor diodes, the varactor capacitance accordingly changes leading to a varying cutoff frequency f c . The measured results show that the achieved 3‐dB f c tuning range is 60.6% (1.15–2.15 GHz). The measured insertion loss (IL) and roll‐off rate are 0.2‐0.4 dB and 50–73 dB/GHz, respectively. The overall size of the LPF is only 0.005λ g 2 , which shows a competitive advantage comparing with the state‐of‐the‐art work.
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