Electronically Tunable UWB Band Stop Filter Using Varactor Diode

Abstract

An electronically tunable Ultra-Wideband (UWB) Band Stop Filter (BSF) using the varactor diode is investigated. The open stubs and Step Impedance Resonator (SIR) topology are utilized to obtain UWB bandstop response. The concept of variable capacitive loading to get tuning, which is achieved by a varactor diode (SMV2019-079LF) and a biasing network is clearly elucidated. The validation of the |S| parameter of the proposed tunable BSF filter is carried out using the filter's transmission line model (TLM), consequently, even and odd mode impedances are calculated analytically, and a lumped equivalent circuit model of the proposed BSF filter is extracted. Moreover, the filter is fabricated, and corresponding |S| parameters are measured which offers a UWB response (2.44 GHz–9.65 GHz) with five Transmission Zeros (TZ) and has tuning of 1 GHz frequency range (8.65 GHz–9.65 GHz) at the upper edge. The proposed miniaturized BSF has a size of 0.23λg × 0.32λg. The simulation results of the electromagnetic (EM)/distributed model, and the measured results of the fabricated prototype are in good agreement. Additionally, a very high skirt factor (SF) of 380 dB/GHz is achieved.