Novel tunable lowpass filters using folded slots etched in the ground plane

This paper presents a concept to implement tunable lowpass filters by employing slot resonators etched in the ground plane. The tunability is achieved with the use of switches to change the effective length of the slots on the ground. A tuning range of more than 60% has been obtained. The concept is demonstrated by considering 4-slots and 10-slots lowpass filters. RF MEMS switches are integrated on the ground plane to short circuit the slots. The measured results are in good agreement with simulations confirming the validity of the proposed concept. The experimental filter exhibits a superior RF performance demonstrating a low insertion-loss, good rejection and a large tuning range.