A Tunable Microstrip Bandstop Filter Using Compact Spiral Folded Spurline For RF Microwave Systems

This paper briefly describes the design principle of a tunable compact spurline bandstop filter using a spiral folded resonator. A compact rejection bandstop filter (BSF) is designed by using a conventional microstrip coupled line methodology at 2.4 GHz. The physical length has been reduced up to 75% with a good tunability results in comparing with a traditional spurline filter. Spurline section is loaded with a p-n junction varactor diode to make tunability from 1.8 GHz to 2.2GHz by applying a DC control voltage from 0V to 10V. The tunable design provides a satisfactory result for simulation and fabrication filter circuits. The modeling of the proposed filter is simulated and fabricated by Advanced Design System (ADS).