High-Q Tunable Filter with a Novel Tuning Structure

This paper presents a novel structure for realizing high-Q tunable combline filters using RF MEMS switches. The design employs planar circuits loaded with RF MEMS switches integrated strategically inside the combline filter structure. The advantage of the proposed structure is that the MEMS switches do not need to be connected to lumped element capacitors which are known to degrade the loaded Q of the tunable filters over the tuning range. Simulation and measurement results are presented illustrating a reasonably wide tuning range. The concept was experimentally demonstrated using a 2-pole tunable combline filter designed at 7 GHz.